EPA/600/R-99/029
Innovative Urban Wet-Weather
Flow Management Systems
By
James P. Heaney
Department of Civil, Environmental, and Architectural Engineering
University of Colorado
Boulder, CO 80309
Robert Pitt
Department of Civil and Environmental Engineering
The University of Alabama at Birmingham
Birmingham, AL 35294
and
Richard Field
Water Supply and Water Resources Division
National Risk Management Research Laboratory
Edison, NJ 08837
Cooperative Agreement Nos. CX824932 & CX 824933
Project Officer
Chi-Yuan Fan
Water Supply and Water Resources Division
National Risk Management Research Laboratory
Edison, NJ 08837
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
-------
Notice
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under cooperative agreements no. CX824932 for the
American Society of Civil Engineers and no. CX 824933-01 -0 for the University of
Alabama at Birmingham. Although it has been subjected to the Agency's peer and
administrative review and has been approved for publication as an EPA document, it
does not necessarily reflect the views of the Agency and no official endorsement should
be inferred. Also, the mention of trade names or commercial products does not imply
endorsement by the United States government.
-------
Foreword
The U.S. Environmental Protection Agency is charged by Congress with
protecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to
support and nurture life. To meet this mandate, EPA's research program is providing
data and technical support for solving environmental problems today and building a
science knowledge base necessary to manage our ecological resources wisely,
understand how pollutants affect our health, and prevent or reduce environmental risks
in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks from
threats to human health and the environment. The focus of the Laboratory's research
program is on methods for the prevention and control of pollution to air, land, water and
subsurface resources; protection of water quality in public water systems; remediation
of contaminated sites and ground water; and prevention and control of indoor air
pollution. The goal of this research effort is to catalyze development and
implementation of innovative, cost-effective environmental technologies; develop
scientific and engineering information needed by EPA to support regulatory and policy
decisions; and provide technical support and information transfer to ensure effective
implementation of environmental regulations and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Research
and Development to assist the user community and to link researchers with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
-------
Abstract
This research project describes innovative methods to develop improved wet weather
flow (WWF) management systems for urban developments of the 21st century. This
document addresses the competing objectives of providing drainage services at the
same time as decreasing stormwater pollutant discharges. Water quality aspects of
WWF discharges and associated receiving water problems have only been studied for a
relatively short period (a few decades), compared to conventional drainage designs (a
few centuries), and few large-scale drainage systems adequately address both of these
suitable objectives.
General principles of urban water management are presented that might permit the
development of more sustainable systems by integrating the traditionally separate
functions of providing water supply, collecting, treating, and disposing of wastewater,
and handling urban WWF. Integration can be achieved by designing
neighborhood scale, integrated infrastructure systems wherein treated wastewater
and stormwater are reused for nonpotable purposes such as lawn watering and toilet
flushing. The automobile is seen to have caused major changes in urban land use in
the 20th century. For the average urban family, the area devoted to streets and parking
in their neighborhood exceeds the area devoted to living. Similarly, more area is devoted
to parking than to office and commercial space in urban areas. The net result of the
large scale changes to accommodate the automobile in cities is about a two to three
fold increase in impervious area per family and business activity.
The physical, chemical, and biological water quality characteristics of urban runoff are
evaluated and summarized. Then, the impacts of urban WWF on receiving
waters are evaluated. These impacts on surface and groundwater are complex and
difficult to evaluate. Physical changes in smaller urban streams can be detected in
terms of degraded channels from higher peak flows. Also, sediment transport
characteristics change with urbanization. Toxic effects on aquatic organisms
have been detected.
Traditionally, wet-weather collection systems were designed to move stormwater from
the urban area as quickly as possible. This design approach often simply transferred
the problem from upstream to downstream areas. More recently, restrictions on the
allowable maximum rate of runoff have forced developing areas to include onsite
storage in detention ponds to control these peak rates of runoff. On-site detention also
allows smaller pipe sizes downstream. In the early part of the 20th century, communities
relied on combined sewers. Later, separate storm and sanitary sewers became
accepted practice. However, as the need to treat more contaminated storm water
becomes more apparent, it is necessary to take a fresh look at combined sewers.
However, because of the strong trend to lower density urban development to
accommodate the automobile, the quantity of urban runoff per family is two to three
times what it was with higher density developments. Most of the traffic flow in cities
occurs on a relatively small percentage of streets, about 10-20%. Also, most parking
areas are underutilized. Thus, it may be possible to focus WWF treatment on these
-------
more intensively used areas including commercial and industrial areas. This finding
suggests that hybrid collection systems may be attractive alternatives for 21st century
collection systems. Another innovative option is to oversize sewer systems and utilize
storage in the sewers as part of a real-time control system.
Extensive discussions regarding the effectiveness of a wide variety of WWF controls are
presented in two chapters. These descriptions include design guidelines. Source
controls as well as downstream controls are included. Source area controls, especially
biofiltration practices that can be easily implemented with simple grading, may be
appropriate in newly developing areas. In addition, critical source areas (such as
vehicle service facilities) may require more extensive onsite treatment strategies. An
innovative approach is to reuse stormwater within the same service areas for irrigation,
toilet flushing, and other nonpotable purposes. More aggressive stormwater reuse
systems would capture roof runoff in cisterns, treat this water, and use it for potable
purposes. Monthly water budgets for cities throughout the United States indicates that
sufficient quantities of precipitation are generated, except in the arid southwestern
United States, to make such systems technically feasible. The cost of providing for
water infrastructure is summarized. The traditional problem of finding the optimal size
of service area for water supply is addressed by finding the minimum sum of the costs
of source acquisition, treatment, and distribution. For wastewater and stormwater, the
minimum total cost is the sum of collection, treatment, and disposal. These costs per
residence have grown substantially as development densities have decreased. Also, if
wastewater and stormwater reuse are included, then the optimal size of infrastructure
system may be at the neighborhood scale since piping costs remain the largest single
cost in urban water infrastructure.
Lastly, institutional arrangements need to change in order to successfully implement
changes in how urban water infrastructure is managed. Privatization, moving from large
centralizes systems to neighborhood based systems, and other projected changes
required innovative changes in the governing institutions.
This report was submitted in fulfillment of Cooperative Agreement Nos. CX824932 and
CX824933 by American Society of Civil Engineers (University of Colorado and the
Urban Water Resources Research Council) and the University of Alabama at
Birmingham, respectively under the sponsorship of the U.S. Environmental Protection
Agency. This report covers a period from May 1996 to August 1998, and work was
completed as of August 1998.
-------
Contents
Notice ii
Forward iii
Abstract iv
Tables xviii
Figures xxii
Abbreviations and Symbols xxvi
Acknowledgments xxix
Chapter 1 Introduction 1-1
James P. Heaney, Robert Pitt, and Richard Field
Introduction .1-1
Chapter 2: Principles of Integrated Urban Water Management .1-1
Chapter 3: Sustainable Urban Water Management .1-1
Chapter4: Source Characterization .1 -2
Chapter 5: Receiving Water and Other Impacts .1-2
ChapterS: Collect ion System s .1. -3
Chapter 7: Assessment of Stormwater Best Management
Practice Technology 1-3
Chapter 8: Stormwater Storage-Treatment-Reuse Systems. .1 -3
Chapter 9: Urban Stormwater and Watershed Management:
A Case Study .1-4
Chapter 10: Cost Analysis and Financing of Urban Water
Infrastructure .1-4
Chapter 11: Institutional Arrangements. .1 -5
Chapter 2 Principles of Integrated Urban Water Management 2-1
James P. Heaney
Introduction 2-1
The Neighborhood Spatial Scale 2-1
Trends in Urbanization 2-1
Historical Patterns 2-1
Impact of the Automobile 2-2
Impact of Subdivision Regulations 2-5
Contemporary Neighborhoods and Urban Sprawl 2-5
Historical Infrastructure Development Patterns 2-7
Interceptor Sewers and Urban Sprawl 2-8
Federal Housing and Urban Development Programs 2-9
Federal Transportation Programs. 2-10
Summary of the Impacts of Federal Urban Programs. 2-10
VI
-------
Possible New Approaches 2-11
Neo-traditional Neighborhoods. 2-11
Related EPA Activities Dealing with Urban Growth Patterns. 2-13
Green Development 2-13
Studies of Chesapeake Bay. 2-14
Brownfield Redevelopment 2-15
Sustainability Principles for Urban Infrastructure 2-16
Sustainability and Optimal Size of Infrastructure Systems. 2-18
Models for Evaluating Future Infrastructure. 2-19
Research Initiatives Related to Urban Infrastructure 2-20
Transportation/Land Use Strategies to Alleviate Congestion 2-21
Projected Future Trends 2-21
Origins of Stormwater in Urban Areas. 2-22
Introduction 2-22
Rainfall-Runoff Relationships at the Neighborhood Scale 2-22
Previous Studies of Imperviousness 2-25
Sources of Urban Runoff 2-28
Categories ofUrbanCatchments 2-28
How Imperviousness Varies for Different Types of Urban
Developments 2-30
Pre-Automobile Neighborhoods. 2-31
Imperviousness in Pre-Automobile Era 2-35
Pre-Expressway Neighborhoods. 2-35
Results for Pre-Expressway Era 2-35
Post-Expressway Neighborhoods 2-35
General Conclusions Regarding the Effect of Changing
Land Use 2-39
Components of Urban Land Use and Stormwater Problems. 2-45
Streets and Highways 2-45
Street Classification and Utilization 2-48
Recommendations for Residential Streets. 2-48
Streets and Stormwater Runoff 2-49
Parking 2-49
Lot Size 2-53
Dwelling Unit Footprint 2-53
Vll
-------
Covered Porches and Patios 2-54
Garages and Carports. 2-54
Driveways 2-54
Attached, Front Facing Garage 2-55
Attached, Side or Rear Facing Garage 2-55
Detached Garage in Rear of Lot 2-55
Pervious Area on Property 2-55
Alleys 2-56
Sidewalks 2-56
Curb and Gutter and Swales 2-57
Planting Strip Between Street and Sidewalk 2-57
Overall Right of Way 2-57
Will Americans Reduce Auto Use?. 2-58
Summary and Conclusions 2-58
References 2-60
Chapter 3 Sustainable Urban Water Management 3-1
James P. Heaney, Len Wright, and David Sample
Introduction 3-1
Systems View of Urban Water Management 3-1
Sustainability Principles of Urban Water Infrastructure 3-3
Urban Water Budget 3-6
Literature Review 3-6
Dry Weather Urban Water Budget 3-8
Indoor Urban Residential Water Use 3-9
Toilet Flushing 3-13
Clothes Washing 3-14
Showers and Baths 3-14
Faucet Use 3-14
Dishwashers 3-14
Water Use for Cooling. 3-15
Outdoor Urban Residential Water Use. 3-15
Infiltration and Inflow 3-17
Summary of Sources of Dry-Weather Flow into Sanitary and
Combined Sewers 3-17
Quantities of Precipitation in Urban Areas 3-20
Vlll
-------
Results of Water Budget Case Studies .3-20
Arizona 3-20
Germany 3-24
Melborne, Australia .3-25
Adelaide, Australia 3-26
Simulated Monthly Urban Water Budgets for Denver and
New York 3-31
General 3-31
Water Use 3-31
Indoor Water Use 3-31
Outdoor Water Use 3-32
Total Water Use 3-32
Wastewater 3-35
Stormwater Runoff 3-38
Summary Water Budgets 3-38
Future Urban Water Scenarios. 3-39
References 3-43
Chapter 4 Source Characterization .4-1
Robert Pitt
The Source Concept 4-1
Sources and Characteristics of Urban Runoff Pollutants. 4-2
Chemical Quality of Rocks and Soils 4-5
Street Dust and Dirt Pollutant Sources 4-6
Characteristics 4-6
Street Dirt Accumulation 4-8
Washoff of Street Dirt 4-12
Observed Particle Size Distributions in Stormwater. 4-27
Atmospheric Sources of Urban Runoff Pollutants .4-28
Source Area Sheetflow and Particulate Quality. .4-35
Source Area Particulate Quality 4-35
Warm Weather Sheetflow Quality. .4-35
Other Pollutant Contributions to the Storm Drainage System 4-48
IX
-------
Sources of Stormwater Toxicants. 4-48
Analyses and Sampling 4-49
Potential Sources 4-53
Results 4-53
References 4-60
Chapter 5 Receiving Water and Other Impacts 5-1
Robert Pitt
Desired Water Uses Versus Stormwater Impacts 5-1
lexicological Effects of Stormwater .5-2
Ecological Effects of Stormwater. 5-3
Fates of Stormwater Pollutants in Surface Waters. .5-8
Human Health Effects of Stormwater. .5-9
Groundwater Impacts from Stormwater Infiltration 5-10
Constituents of Concern .5-10
Nutrients 5-10
Pesticides 5-10
Other Organics 5-11
Pathogenic Microorganisms. 5-12
Heavy Metals and Other Inorganic Compounds 5-12
Salts 5-13
Recommendations for Protection of Groundwater During
Stormwater Infiltration 5-13
References 5-20
Chapter 6 Collection Systems 6-1
James P. Heaney, Len Wright, and David Sample
Introduction 6-1
Problems Commonly Associated with Present Day
Collection Systems 6-3
Combined Systems 6-4
Inflow and Infiltration 6-6
Inflow 6-6
-------
Infiltration 6-7
Inflow/Infiltration Analysis and Design Challenges. 6-8
Sanitary Sewer Overflows 6-18
Separate Stormwater Collection Systems and Non-Point
Sources 6-20
Solids and Their Effect on Sewer Design and Operation 6-21
Predicting Pollutant Transport in Collection Systems. 6-25
Characteristics and Treatability of Solids in Collection
Systems 6-26
Innovative Collection System Design - The State of the Art 6-26
Current Innovative Technologies - Review of Case Studies. 6-27
Data Management, SCADA, Real Time Control 6-27
Sanitary Sewer Technology - Vacuum Sewers 6-29
Low Pressure Sewers 6-30
Small Diameter Gravity Sewers 6-33
Black Water/Gray Water Separation Systems 6-33
Waste/Source Separation .6-33
Compostinq 6-35
VV...|VVV.....^2 w -ww
Combined Systems for the Future?. 6-35
Future Directions: Collection Systems of the 21st Century. 6-35
Future Collection System Scenarios 6-36
H i g h D e ns ity Areas 6-36
Suburban Development 6-37
References 6-38
Chapter 7 Assessment of Stormwater Best Management
Practice Effectiveness 7-1
Ben Urbonas
Introduction 7-1
Objectives in the Use of Best Management Practices for
Stormwater Quality Management 7-2
Non-Structural Best Management Practices. 7-5
Structural Best Management Practices .7-6
Minimized Directly Connected Impervious Area 7-6
Water Quality Inlets 7-8
XI
-------
Infiltration Practices 7-8
Filter Basins and Filter Inlets. 7-9
Swirl-Type Concentrators 7-9
Extended Detention Basins 7-9
Retention Ponds 7-9
Wetlands 7-10
Stormwater Quality Management Hydrology 7-10
An Assessment of Best Management Practice Effectiveness. 7-12
Non-Structural Best Management Practices 7-12
Pollutant Source Controls. .7-13
Public Education and Citizen Involvement Programs 7-14
Street Sweeping, Leaf Pickup and Deicing Programs 7-15
Local Government Rules and Regulations. 7-15
Elimination of Illicit Discharges. 7-15
Structural Best Management Practices: Design
Considerations 7-16
Local Climate 7-16
Design Storm 7-16
Nature of Pollutants 7-16
Operation and Maintenance 7-18
On-Site or Regional Control 7-18
Structural Best Management Practices: Performance 7-19
Minimized Directly Connected Impervious Area 7-19
Grass Swales 7-20
Grass Buffer Strips 7-20
Porous Pavement 7-21
Percolation Trenches 7-21
Infiltration Basins 7-22
Media Filter Basins and Filter Inlets. .7-22
Water Quality Inlets 7-23
Swirl-Type Concentrators 7-24
Extended Detention Basin s 7 -24
Retention Ponds 7-25
Wetlands 7-26
Summary on Best Management Practices Effectiveness. 7-28
Non-Structural Best Management Practices 7-28
Structural Best Management Practices. 7-29
Xll
-------
The Definition of Effectiveness. 7-29
Research and Design Technology Development Needs 7-30
Design Robustness. .7-31
Runoff Impacts Mitigation 7-31
Summary of the Usability of the Evaluated Best
Management Practices 7-33
Stormwater Systems of the Future. .7-35
Use of Combined Wastewater and Storm Sewer Systems 7-36
Use of Separate Stormwater Systems. 7-37
Closing Remarks 7-39
References 7-41
Chapter 8 Stormwater Storage-Treatment-Reuse Systems 8-1
James P. Heaney, Len Wright, and David Sample
Introduction 8-1
Stormwater Treatment 8-1
Effect of Initial Concentration 8-1
Effect of Change of Storage. 8-1
Effect of Mixing Regime 8-1
Effect of Nature of the Suspended Solids. 8-2
Essential Features of Future Wet-Weather Control Facilities 8-2
High-Rate Operation of Wastewater Treatment Plants 8-2
Stormwater Reuse Systems 8-2
Introduction 8-2
Previous Studies 8-3
Estimating the Demand for Urban Irrigation Water. 8-7
Urban Water Budgets 8-7
Water Budget Concepts 8-8
Methods of Analysis 8-11
Results 8-15
Conclusions 8-22
References 8-23
Xlll
-------
Chapter 9 Urban Stormwater and Watershed Management:
A Case Study 9-1
James P. Heaney, Len Wright, and David Sample
Overview 9-1
Watershed Planning Methodologies. .9-1
Contemporary Principles of Watershed Management 9-2
American Water Resources Association 9-2
Water Environment Federation 9-3
U.S. Environmental Protection Agency 9-3
Case Study of Urban Stormwater Management within
a Watershed Framework: 9-3
Introduction 9-3
Hydrology 9-4
j v'vsyj '
Introduction 9-4
Precipitation Analysis. 9-7
Streamflow Stations. 9-8
North Boulder Creek 9-8
Middle Boulder Creek 9-8
South Boulder Creek 9-16
Groundwater 9-17
Land Use and Growth Management in Boulder Valley. 9-17
General 9-17
Relative Importance of Urban Land Use. 9-18
Water Management Infrastructure. 9-23
Storage 9-23
Canals 9-23
Control Works 9-23
Pipelines 9-24
Imports and Exports 9-24
Current Water Management System 9-24
Water Quantity 9-24
XIV
-------
Municipal Water Supply and Wastewater Return .9-24
Agricultural Water Supply. 9-25
Flood Control .9-25
Greenway Program 9-29
Hydropower 9-32
Instream Flow Needs. 9-32
Importation of Water .9-34
Overall Water Budget for Boulder. .9-34
Sources .9-35
Sinks .9-35
Annual Water Budget .9-35
Monthly Water Budget .9-36
Daily Water Budget .9-41
Hourly Water Budget .9-41
Conclusions Drawn from the Water Budget 9-44
Urban Stormwater Quality .9-45
Stormwater Pollution in Boulder. 9-45
Agricultural Water Quality. .9-45
Forest Fires .9-45
Highway Runoff. 9-45
Mining Runoff 9-46
Urban Stormwater Quality. 9-46
Recreation and Water Quality in Boulder Creek 9-47
Wastewater Characteristics 9-47
Removal Efficiencies 9-51
Sanitary Sewer Overflows 9-51
0 vera 11 Rece i vi ng Water Q ua I ity I m pacts 9-51
Upper Section-Boulder Creek Immediately Above the City 9-55
Middle Section-Boulder Creek at 28th St 9-55
Lower Section-Boulder Creek Below 75th St 9-55
Risk-Based Analysis of Urban Runoff Quality. .9-56
Covariance Between Concentration and Flow .9-57
Covariance Between Upstream Flow and Urban Runoff. 9-57
References 9-61
XV
-------
Chapter 10 Cost Analysis and Financing of Urban Water
Infrastructure 10-1
James P. Heaney, David Sample, and Len Wright
Introduction 10-1
Demand for Water Infrastructure. .10-1
Effect of Density on Imperviousness .10-1
Effect of Density on Pipe Length .10-1
Water Supply 10-6
Wastewater .10-7
Stormwater. 10-7
Optimal Scale of the Urban Water System .10-7
Costs of Infrestructure Com ponents .10-11
Cost of Piping 10-11
Cost of Treatment .10-18
Cost of Storage. .10-21
Summary of Costs for Urban Stormwater Systems. .10-23
Financing Methods .10-23
Tax Funded System .10-24
Service Charge Funded System .10-25
Exactions and Impact Fees .10-26
Special Assessment Districts 10-26
Conclusions on Finance .10-26
References 10-27
Chapter 11 Institutional Arrangements 11-1
Jonathan Jones, Jane Clary, and Ted Brown
Introduction 11-1
Existing Models of Stormwater Management Institutions. .11-1
Required Characteristics of Stormwater Management Institutions. 11-4
Specific Issues to be Addressed by Stormwater Management
Institutions .11-5
Financing 11-5
Staffing: Inter-Disciplinary Approach 11-7
Administrative Authority .11-7
Regulatory Flexibility 11-8
XVI
-------
ClearRegulationsandStandard s. .11 -8
Leqal Challenges .11-10
_V^2ซ. w IV...V. . ^VV . . v
Reqional Solutions 11-10
C3 w ซซ ซ
Total RiskManagement .11-12
Maintenance .11-12
Monitoring/Evaluation .11-12
Modeling and Performance Auditing .11 -14
Nonstructural Source Control Strategies. .11-15
Retrofitting 11-15
Technology Transfer. .11-16
Guidance for Practices Such as Riparian Corridor
Preservation and Restoration .11-16
Public Involvement and Education .11 -17
Conclusion .11-18
References 11-19
Chapter 12 Summary and Conclusions 12-1
James P. Heaney, Robert Pitt, and Richard Field
Summary and Conclusions .12-1
Chapter 2: Principles of Integrated Urban Water Management .12-1
Chapter 3: Sustainable Urban Water Management .12-1
Chapter4: Source Characterization .12-1
Chapter 5: Receiving Water and Other Impacts .12-2
Chapter 6: Collection Systems .12-3
Chapter 7: Assessments of Stormwater Best Management
Practices Technology .12-3
Chapter 8: Stormwater Storage-Treatment-Reuse Systems .12-4
Chapter 9: Urban Stormwater and Watershed Management:
A Case Study 12-4
Chapter 10: Cost Analysis and Financing of Urban Water
Infrastructure 12-5
Chapter 11: Institutional Arrangements .12-5
Appendix Innovative Stormwater Management in New
Development: Planning Case Study A-l
Brian W. Mack, Michael F. Schmidt, and Michelle Solberg
Introduction A-1
Background. A-1
The Master Planning Process A-3
Program Goals A-3
XVll
-------
Flood Control A-5
Water Quality Control A-5
Ecosystem Management A-5
Levels of Service A-6
Methodology A-9
Stormwater Modeling A-9
Hydrologic ModeJ A-9
Hydraulic Model A-9
Water Quality Model A-10
Hydrologic Parameters A-10
Subbasin and Hydrologic Unit Areas. A-11
Rainfall Intensities and Quantities. A-11
Rainfall for Water Quality Modeling A-11
Rainfall for Runoff Modeling A-11
Soil Types and Capabilities A-13
Overland Flow Parameters A-14
Land Use and Impervious Areas. A-15
Hydraulic Parameters A-16
Structures/Facilities A-17
Stage-Area Relationships. A-19
Stage and Discharge Data A-19
Floodplains and Floodways A-21
Water Quality Parameters A-22
Selection of Water Quality Loading Factors. A-22
Identification of Pollutants A-23
Selection of Stormwater Pollution Loading Factors A-23
Land Use Load Factors. A-24
Open / Nonurban Land Use Load Factors. A-25
Water Bodies A-25
Major Roads A-25
XVlll
-------
Recommendation of Stormwater Pollutant Loading
Factors A-25
D e I ive ry Rat i o/Trave I T i m e. A-2 7
Point Source Discharge A-27
Best Management Practice Pollutant Removal Efficiencies. A-27
Surface Water Quality Classifications A-28
Historical Water Quality Monitoring Data A-30
Evaluation of Best Management Practices A-32
Best Management Practice Considerations A-32
Alternative Best Management Practices A-33
Structural Stormwater Controls. A-33
Non-Structural Source Controls A-33
Operation and Maintenance (O&M) A-34
Regional Versus Onsite Structural Best Management Practice. A-34
Onsite Approach A-34
Regional Approach A-35
Best Management Practice Implementation Considerations A-40
Recommended Best Management Practices A-43
Introduction A-43
Pretreatment Best Management Practices A-44
Minimization of Directly Connected Impervious Area A-44
Landscaped Swales and Grass-Lined Swales. A-44
Curb Connections to Swales A-46
Capture Ratios of Swales A-49
Oil-Water Separators A-49
Sediment Forebays A-49
Source Reduction A-52
Wet Detention Location and Sizing Criteria A-52
Regional Facility Location Criteria A-52
Regional Facility Sizing Methodology A-52
Live Pool Volume A-53
Live Pool Volume Bleed-Down Requirements. A-53
XIX
-------
Permanent Pool Volume A-54
Flood Control Requirements A-56
Regional Stormwater System Review Considerations A-58
Water Quality Results A-58
Introduction A-58
Scenarios A-59
Future Land Use with Recommended Best Management
Practices A-59
Water Quantity Results A-62
Introduction A-62
Model Calibration A-62
Level of Service and Problem Area Definitions. A-63
Water Quantity Evaluation of Existing PSWMS A-64
Proposed Regional Wet Detention Facilities. A-67
Use of Existing Borrow Pits as Stormwater Facilities A-68
Flood Control Benefits A-68
Recommendations A-72
Introduction A-72
Capital Improvement Program for Structural Controls A-73
Review of Factors A-73
Technical Feasibility and Reliability. A-73
System Maintainability. A-73
Sociopolitical Acceptability. A-73
Economics A-73
Environmental Consistency. A-74
Financial Ability A-74
CIP S u m m a ry A-74
Project Phasing A-75
Operation and Maintenance A-75
Nonstructural Controls. A-79
Monitoring A-81
Recommended Monitoring Program A-81
XX
-------
Rainfall A-81
Water Quality A-81
Water Quantity. A-81
Mosquito Control A-82
Data Sources and Bibliography. A-83
XXI
-------
Tables
2-1 Changing patterns of automobile use in the U.S., 1915-1996 2-3
2-2 Case studies on "urbanizing" suburbs and areas where infill
has successfully occurred 2-14
2-3 Case studies using intermodal transportation policies that
consider environmental impacts 2-15
2-4 Types of storms contributing to stormwater runoff in
Chicago, IL 2-23
2-5 Site coverage for three land uses in Olympia, WA 2-26
2-6 Attributes of 20th century neighborhoods in the U.S 2-31
2-7 Attributes of dwelling units located on traditional grid street
network-total imperviousness. 2-34
2-8 Attributes of dwelling units located on traditional grid street
network-directly connected imperviousness. 2-34
2-9 Attributes of dwelling units located on traditional grid street
network-total imperviousness. 2-37
2-10 Attributes of dwelling units located on traditional grid street
network-directly connected imperviousness. 2-37
2-11 Attributes of thirteen contemporary one story houses-total
imperviousness 2-38
2-12 Attributes of thirteen contemporary one story houses-directly
connected imperviousness 2-38
2-13 Relationship between street length and dwelling unit density
for a five acre rectangular block of dimensions 660 feet
by 300 feet 2-40
2-14 Effect of dwelling unit density on CA in the Rational formula 2-41
2-15 Relationship between dwelling unit density and area per lot 2-42
2-16 Street mileage in the U.S 2-48
2-17 Condensed summary of national design standards for
residential streets 2-50
2-18 Relationship between number of dwelling units, traffic
generation, and residential congestion 2-50
2-19 Parking demand ratios for selected land uses and activities 2-52
3-1 Summary of indoor water use for 12 cities in North America 3-10
3-2 Summary of indoor and outdoor water use in Boulder,
Denver, Eugene, Seattle, and San Diego .3-11
3-3 Summary of indoor and outdoor water use in Phoenix,
Scottsdale, Waterloo, Walnut Valley, LosVirgenes,
and Lompoc 3-11
3-4 Number of toilet flushes per day and proportion related
to fecal flushes 3-13
3-5 Typical lot sizes and irrigable area, King County, WA 3-16
3-6 Annual precipitation and days with rain for selected U.S. cities. 3-22
3-7 Attributes of two neighborhoods in Melbourne, Australia 3-25
XXll
-------
3-8 Simulated performance of modified urban systems. .3-26
3-9 Assumed common attributes of representative
neighborhoods in Denver, CO and New York, NY. .3-31
3-10 Assumed indoor water use for Denver, CO and
New York, NY neighborhoods. .3-31
3-11 Estimated monthly outdoor water use in Denver, CO and
New York, NY 3-32
3-12 Total monthly water use for representative residential
areas in Denver, CO and New York, NY 3-33
3-13 Total monthly wastewater flows for Denver, CO and
New York, NY 3-37
3-14 Monthly precipitation and runoff for Denver, CO and
New York, NY 3-38
3-15 Final monthly water budget for Denver, CO. 3-41
3-16 Final monthly water budget for New York, NY. 3-42
4-1 Uses and sources for organic compounds found in
stormwater. 4-4
4-2 Common elements in the Lithosphere .4-5
4-3 Common elements in soils 4-6
4-4 Street dirt loadings and deposition rates 4-11
4-5 Suspended solids washoff coefficients. .4-27
4-6 Summary of reported rain quality. .4-30
4-7 Atmosphere dustfall quality. .4-31
4-8 Bulk precipitation quality 4-33
4-9 Urban bulk precipitation deposition rates. 4-34
4-10 Summary of observed street dirt mean chemical quality 4-37
4-11 Summary of observed particulate quality for other source areas 4-38
4-12 Sheetflow quality summary for other source areas 4-39
4-13 Sheetflow quality summary for undeveloped landscaped and
freeway pavement areas. .4-45
4-14 Source area bacteria Sheetflow quality summary .4-46
4-15 Source area filterable pollutant concentration summary. 4-47
4-16 Numbers of samples collected from each source area type. 4-48
4-17 Toxic pollutants analyzed in samples 4-50
4-18 Fraction of samples rated as toxic .4-52
4-19 Stormwater toxicants detected in at least 10% of the source area
sheetflow samples 4-55
4-20 Relative toxicity of samples using Microtox 4-59
5-1 Groundwater contamination potential for stormwater pollutants .5-15
6-1 Variations of infiltration allowances among cities. 6-7
6-2 Comparison of average daily wastewater and infiltration for
one mile of 8 inch sanitary sewer based on 500 gpd/idm 6-11
6-3 Causes of SSOs in Fayetteville, AR 6-19
XXlll
-------
6-4 Causes of SSOs in Miami, FL 6-19
6-5 Typical design storm frequencies 6-20
6-6 Comparison of recommended minimum sewer grades and
velocities over the years 6-23
6-7 Recommended critical shear stress to move sewer deposits 6-24
6-7 Annual operating costs of vacuum and gravity sewer
systems as of 1995 6-30
6-9 Pump data and O&M costs for low pressure sewer systems 6-32
7-1 Sensitivity of the BMP capture volume in Denver, CO. 7-12
7-2 BMP pollutant removal ranges in percent 7-29
7-3 An assessment of design robustness technology for BMPs 7-32
7-4 Summary assessment of structural BMP effectiveness
potential 7-34
8-1 Water budget calculations for San Francisco, CA .8-12
8-2 Water storage tank calculations for San Francisco, CA 8-15
8-3 Summary of annual data for selected stations .8-20
9-1 Boulder Creek watershed streamflows on Main Boulder
Creekbelow Broadway in Boulder, CQ .9-6
9-2 Monthly precipitation in Boulder, CO, 1949-1993. 9-10
9-3 Summary of monthly and annual storm event statistics for
Boulder, CO, 1949-1993 .9-11
9-4 Summary of surface water records for Boulder Creek
Watershed .9-14
9-5 Land use in the City of Boulder, CO service area -1995 9-19
9-6 Drainage areas for Boulder and Boulder Creek Watershed .9-22
9-7 Comparison of water use and wastewater flows, 1992 .9-27
9-8 Recreational activities supported by flows in Boulder Creek .9-31
9-9 Overall water budget for calendar year 1992 (flow in cfs) 9-37
9-10 Measured and computed monthly flowrates in 1992 9-39
9-11 Monthly flows in Boulder Creek at 28th St. for calendar
year 1992 9-40
9-12 Monthly flows in Boulder Creek for calendar year 1992,
above, within and below the City of Boulder (in cfs) 9-42
9-13 Total sources of flow, Boulder Creek, CO, 1992 (in cfs) .9-43
9-14 Trends in annual performance of 75th St. WWTP, 1988 -1994 9-53
9-15 Trends in monthly performance of 75th St. WWTP .9-53
10-1 Effect of dwelling unit density and irrigation rate on indoor
and outdoor water use .1.0-2
10-2 Effect of dwelling unit density on wastewater and
infiltration/inflow .10-2
10-3 Effect of dwelling unit density and runoff rates on quantities
of stormwater runoff. .10-2
XXIV
-------
10-4 Sanitary sewer pipe in place for various city sizes. .10-4
10-5 Street mileage in the U.S. -1995. .10-5
10-6 Summary of water pipe diameters and lengths in Boulder, CO .10-6
10-7 Typical capital cost equations for water resources facilities .10-12
10-8 Sanitary sewer pipe costs and flow rates. .10-14
10-9 Estimated 1998 sanitary sewer pipe costs per dwelling unit
for various dwelling unit densities .10-17
10-10 Cost equations for CSO control technology .10-19
10-11 Present (1998) value of cost of treating stormwater runoff. .10-21
10-12 Estimated (1998) storage cost per dwelling unit .10-21
A-1 Existing levels of Service for Water Quantity. A-8
A-2 Global Morton Infiltration Parameters A-14
A-3 Impervious by land Use Category. A-17
A-4 Field Estimated Normal Pool and Seasonal High Water
Elevations A-20
A-5 Event Mean Concentrations and Impervious Percentages
Recommended for the Watershed Management Model A-26
A-6 Average Annual Pollutant Removal rates for Retention
Basins, Detention Basin and Swale BMPs A-29
A-7 Annual Trophic State Index Results A-31
A-8 1994 Summary of Lake Secchi Disk Measurement
Chlorophyll-A Concentrations and Nitrogen and
Phosphorus Concentrations. A-32
A-9 Biological Quality of Selected lakes in Orange County A-32
A-10 BMP Selection Feature Requirements vs. Benefits A-42
A-11 Average Annual Loadings for Existing and future Land Use
Conditions With Recommended BMPsforthe Future
Condition Entire Lake Hart Study Area A-61
A-12 Comparison of Reported and simulated Peak Surface
Water Elevations A-64
A-13 Excessive Velocity Determination for Future Land Use. A-67
A-14 Changes in Surface Area of Sites Currently Existing as
Borrow Pits A-72
A-15 Conceptual Capital Cost Estimate A-77
A-16 Annual Operation and Maintenance Cost Summary. A-79
XXV
-------
Figures
2-1 Trends in U.S. population and ownership of automobiles 2-3
2-2 Trends in vehicles per capita in the U.S 2-4
2-3 Trends in vehicle miles per capita in the U.S 2-4
2-4 Rainfall-runoff relationships for unit area, Chicago, IL 2-24
2-5 Flow sources for example medium density residential areas
Having clayey soils, Milwaukee, Wl 2-24
2-6 Relation of the coefficient of runoff for urban areas to
imperviousness 2-26
2-7 Imperviousness as a function of developed population density 2-27
2-8 Example urban lot 2-29
2-9 Typical unit residential area, Chicago, IL 2-32
2-10 Aerial view of 10 blocks in an older neighborhood in
Boulder, CQ 2-33
2-11 Relationship between street length and dwelling unit
density for a five acre rectangular block of dimensions
660 feet by 330 feet 2-40
2-12 Relationship between dwelling unit density and area per lot 2-43
2-13 Watershed imperviousness and the storm runoff coefficient 2-43
2-14 Effect of dwelling unit density on imperviousness 2-44
3-1 Early view of the systems approach to urban water
management 3-4
3-2 Water budget for urban water systems. .3-5
3-3 The urban hydrologic system .3-8
3-5 Hourly variability of indoor water use in 88 houses,
Boulder, Co 3-12
3-6 Hourly variability in total residential water use for 88
houses, Boulder, Co 3-19
3-6 DWF., I/I and total wastewater flow, Boulder, CO, 1995 3-20
3-7 Front yard of Casa del Agua 3-23
3-8 Back yard of Casa del Agua 3-24
3-9 Consumption of water in Adelaide, Australia according
to quality 3-28
3-10 Availability of wastewaters in Adelaide, Australia according
to quality 3-29
3-11 Typical monthly water supply and demand, Adelaide,
Australia 3-30
3-12 Flow chart of proposed integrated water system for
Adelaide, Australia 3-30
3-13 Average water use, Denver, CO. 3-34
3-14 Average water use, New York, NY. 3-34
3-15 Monthly residential wastewater discharge, Denver, CQ 3-36
3-16 Monthly residential wastewater discharge, New York, NY. 3-36
XXVI
-------
4-1 Deposition and accumulation of street dirt 4-10
4-2 Particle size distribution of HDS test (high rain intensity,
dirty, and smooth street) 4-18
4-3 Particle size distribution for LCR test (light rain intensity,
clean, and rough street) 4-18
4-4 Washoff plots for HCR test (high rain intensity, clean,
and rough street) 4-19
4-5 Washoff plots for LCR test (light rain intensity, clean,
and rough street) 4-20
4-6 Washoff plots for HDR test (high rain intensity, dirty,
and rough street) 4-21
4-7 Washoff plots for LDR test (light rain intensity, dirty,
and rough street) 4-22
4-8 Washoff plots for HCS test (high rain intensity, clean,
and smooth street) 4-23
4-9 Washoff plots for LCS test (light rain intensity, clean,
and smooth street) 4-24
4-10 Washoff plots for HDS test (high rain intensity, dirty,
and smooth street) 4-25
4-11 Washoff plots for LCS replicate test (light rain intensity,
clean, and smooth street) 4-26
4-12 Tenth percentile particle sizes for stormwater inlet flows 4-29
4-13 Fiftieth percentile particle sizes for stormwater inlet flows 4-29
4-14 Ninetieth percentile particle sizes for stormwater inlet flows 4-29
6-1 Typical entry points of inflow and infiltration 6-8
6-2 Annual contribution of I/I 6-9
6-3 Monthly contribution of I/I 6-10
6-4a Comparison of infiltration flow rates and residential flow
rates for a one mile long, eight inch sanitary sewer
(high population density) .6-12
6-4b Comparison of infiltration flow rates and residential flow
rates for a one mile long, eight inch sanitary sewer
(medium population density) 6-13
6-4c Comparison of infiltration flow rates and residential flow
rates for a one mile long, eight inch sanitary sewer
(low population density) 6-14
6-5 Histogram of average annual residential wastewater and
I/I rates on a per capita basis from 102 U.S. cities. 6-15
6-6 Estimated occurrence of SSO by cause 6-19
6-7 Typical vacuum sewer system schematic 6-29
6-8 Per capita construction costs for different sanitary sewer
systems at various population densities 6-31
6-9 Components of small diameter gravity sewer (SDGS)
system 6-34
XXVll
-------
7-1 BMPs in series to minimize urban stormwater runoff
quality impacts 7-4
"y~
7-2 Comparing traditional and minimized directly connected
impervious area drainage 7-7
7-3 Ratio of events captured as a function of the normalized
detention volume. 7-11
7-4 Total phosphorous "percent removal efficiency" and
effluent concentrations for a peat-sand filter as a
function of influent concentration 7-17
8-1 Concept of stormwater reuse residential storage system .8-8
8-2 Monthly precipitation for selected stations in the U.S.,
means and extremes 8-9
8-3 Water budgets for selected stations in the U.S .8-10
8-4 Water budget for San Francisco, CA .8-12
8-5 Cities used in water balance analysis 8-16
8-6 Utilization of stormwater by region 8-18
8-7 Water deficit by region 8-21
8-8 Projected residential stormwater storage tank size for
studied locations 8-22
9-1 Boulder Creek Watershed, CO. .9-5
9-2 Monthly inflows of Boulder Creek to Boulder, CO. 9-7
9-3 Mean annual precipitation in Boulder, CO 9-9
9-4 Mean monthly precipitation in Boulder, CO 9-9
9-5 Relative frequency for runoff producing events in
Boulder, CO 9-11
9-6 Runoff producing events per month in Boulder, CO. 9-12
9-7 Average rainfall duration per event in Boulder, CO .9-12
9-8 Average rainfall per event for Boulder, CO. 9-13
9-9 Average runoff producing rainfall per month for Boulder, CO. 9-13
9-10 Boulder Creek streamflow at Orodell, CO 9-15
9-11 Land use in the City of Boulder, CO service area, 1995 .9-19
9-12 Boulder open space chronology of events. .9-20
9-13 Boulder open space and public lands 9-27
9-14 Monthly water use for Boulder, CO, 1992 .9-28
9-15 Monthly wastewater volumes for Boulder, CO, 1992 .9-28
9-16 Monthly wastewater and Boulder Creek flows, 1992 9-20
9-17 Boulder Creek potential flood inundation 9-31
9-18 Flow in Boulder Creek at the Orodell gauging station,
December 25, 1994 9-33
9-19 OveralI water budget for calendar year 1992 .9-38
9-20 Boulder Creek monthly flows in 1992 .9-39
9-21 Monthly flows in Boulder Creek at 28th St. for calendar
year 1992 9-40
XXVlll
-------
9-22 Monthly flows in Boulder Creek for calendar year 1992,
above, within, and below the City of Boulder. .9-42
9-23 Total sources of flow for Boulder Creek, CO, 1992 .9-43
9-24 Effect of flow on BOD load and concentration, Boulder
WWTP, 1990-1995 9-49
9-25 Effect of flow on SS load and concentration, Boulder
WWTP, 1990-1995 .9-50
9-26 Influent flow to Boulder WWTP, 1990-1995 .9-52
9-27 Influent vs. effluent SS concentrations, Boulder 75th St.
WWTP .9-54
9-28 Influent vs. effluent BOD concentrations, Boulder 75th St.
WWTP 9-54
9-29 Boulder WWTP flow vs. flow in Boulder Creek .9-59
10-1 Pervious and impervious area as a function of dwelling
unit density 10-3
10-2 Lot width as a function of dwelling unit density .10-3
10-2 Effect of population on the ratio of length of large pipes
to length of small pipes .10-5
10-4 Total costs of wastewater collection and treatment systems. .10-9
10-4 Service scale versus capital costs for components of
a sewerage system .10-9
10-5 Service scale versus operating costs for components
of a sewerage system .10-10
10-6 Effect of varying density of development on the minimum
sewerage system cost/service and scale at which the
minimum occurs .10-10
10-7 1998 sewer construction costs per foot of length as a
function of pipe diameter. .10-15
10-9 Typical flows versus pipe diameter .10-15
10-10 Sewer construction costs per foot of length versus
design flow rate .10-16
10-11 Effect of dwelling unit density on sanitary sewer
construction costs in wet areas. .10-16
10-12 Effect of dwelling unit density on 1995 sanitary sewer
construction costs in dry areas. .1.0-17
10-13 Construction costs for CSO controls .10-19
10-14 Operation and maintenance costs for CSO controls .10-20
10-15 Cost of a ground level prestressed concrete storage tank
in 1995 as a function of volume .10-22
10-16 Monthly stormwater management fees. .10-25
A-1 Southeast Annexation Area Vicinity Map. A-2
A-2 Study Area and PSWMS A-4
A-3 Water Quantity LOS A-7
A-4 Raingauge Locations A-12
XXIX
-------
A-5 Existing PSWMS Model Schematic Map A-18
A-6 BMP Treatment Train Concept A-36
A-7 Design for Retention/Detention Facility. A-37
A-8 Onsite vs. Regional BMPs A-38
A-9 Typical Multi-Use Stromwater Facility A-41
A-10 Minimization of DCIA and Uses of Grass Lined Swales A-45
A-11 Landscaped Retention Pretreatment Swales with Raised/
Inlets A-47
A-12 Roadside Swales A-48
A-13 Percent Annual Runoff Volume Captured for Medium
Density Residential A-50
A-14 Typical Wet Pond with Forebay A-51
A-15 Problem Identification Map. A-66
A-16 Conceptual Regional Facility Map A-69
A-17 Regional Wet Detention Facility Locations A-70
A-18 Alternative PSWMS Model Schematic Map A-71
A-19 Capital Improvements Plan Map. A-76
XXX
-------
Abbreviations and Acronyms
A
AASHTO
ac-ft
ADT
AMSA
APWA
ASCE
AWRA
AWWA
AWWARF
BASINS
BCW
BMP
BOD
C
CofV
CCA
COD
CSO
CY
DBO
DCIA
DSS
DU
DUD
DWF
EPA
FEMA
FHA
FHWA
fps
ET
gpcd
gpd/idm
CIS
ha
HCR
HCS
HDR
HDS
HOV
HUD
I
Area
Association of State Highway and Transportation Officials
Acre-foot
Average daily traffic
Association of Metropolitan Sewerage Agencies
American Public Works Association
American Society of Civil Engineers
American Water Resources Association
American Water Works Association
American Water Works Association Research Foundation
Better Assessment Science Integration Point and Nonpoint
Sources
Boulder Creek Watershed
Best management practice
Biochemical oxygen demand
Runoff coefficient (in Rational method)
Coefficient of variation (standard deviation/mean)
Copper, chromium, arsenic
Chemical oxygen demand
Combined sewer overflow
Calendar year
Design-build-operate
Directly connected impervious area (See IA)
Decision support systems
Dwelling unit
Dwelling unit density
Dry weather flow
U.S. Environmental Protection Agency
Federal Emergency Management Agency
Federal Housing Administration
Federal Highway Administration
Feet per second
Evapotranspiration
Gallons per capita per day
Gallons per day per inch diameter per mile
Geographic information system
Hectare
High rain intensity, Clean, and Rough street
High rain intensity, Clean, and Smooth street
High rain intensity, Dirty, and Rough street
High rain intensity, Dirty, and Smooth street
High occupancy vehicle
U.S. Department of Housing and Urban Development
Imperviousness
XXXI
-------
IA
IBDU
I/I
ITE
ISS
J
kl
I
L
Ib/ft2
LCE
LCR
LCS
LDR
LPS
m
MCTT
mgd
ml
mm
MMI
MTBE
MTBSC
MVS
N/m2
NAREUS
NCRS
NMC
NPDES
NPS
NSF
NURP
NWS
O&M
OIA
OWRR
P
PAH
PD
PET
POC
PSCO
R
RCRA
ROW
Impervious area (See DCIA)
Isobutylidene diurea
Infiltration and/or inflow
Institute of Transportation Engineers
Integrated storm-sanitary system
Julian day number (e.g., J=365 for December 31)
Kiloliter
Liter
Length of street per dwelling unit
Pound per square foot
Life-cycle engineering
Light rain intensity, Clean, and Rough street
Light rain intensity, Clean and Smooth street
Light rain intensity, Dirty, and Rough street
Low pressure sewers
Meter
Multi-chambered treatment train
Million gallons per day
Milliliter
Millimeter
Man-machine interface
Methyl-tert-butyl ether
Mean time between service calls
Modern vacuum system
Neuton per square meter
North American End Use Study
National Resource Conservation Service (formerly, SCS, Soil
Conservation Service)
Nine minimum controls
National Pollution Discharge Elimination System
Non-point source
National Science Foundation
Nationwide Urban Runoff Program
National Weather Service
Operation and maintenance
Other impervious area
Office of Water Resources Research
Precipitation (inches)
Polycyclic aromatic hydrocarbons
Population density
Potential evapotranspiration
Purgable organic carbon
Public Service Company of Colorado
Runoff volume
Resource Conservation and Recovery Act
Right of way
XXXll
-------
RPE
RTC
SCADA
SCS
SDC
SDGS
SOV
STD
STEP
SS
SSES
SSO
STORM
THM
TND
TOO
TSS
UF
ULI
USEPA
USGS
UV
UWRRC
VMT
VOC
WARMF
WEF
WET
WSIUA
WWF
Runoff producing event
Real time control
Supervisory control and data acquisition
Soil Conservation Service (now the NRCS, National Resource
Conservation Service)
System development charges
Small diameter gravity sewer
Single occupancy vehicle
Standard deviation
Septic tank effluent pumping
Suspended solids
Sewer System Evaluation Survey
Sanitary sewer overflow
Storage, Treatment, Overflow and Runoff Model
Trialomethane
Traditional neighborhood development
Total organic carbon
Total suspended solids
Micrometer
Urea formaldehyde
Urban Land Institute
U.S. Environmental Protection Agency
U.S. Geological Survey
Ultraviolet
Urban Water Resources Research Council (of ASCE)
Vehicle miles traveled
Volatile organic compound
Watershed Analysis Risk Management Framework
Water Environment Federation
Whole effluent toxicity
Water sustainability in urban areas
Wet weather flow
XXXlll
-------
Acknowledgments
This document was prepared for the U.S. Environmental Protection Agency (EPA)
under Cooperative Agreement Nos. CX824932 and CX824933. The support of the
project by the EPA Offices of Water, Wastewater Management, and Research and
Development; the EPA National Risk Management Research Laboratory; the Urban
Water Resources Research Council of the American Society of Civil Engineers; and the
University of Alabama at Birmingham is acknowledged and appreciated.
Stuart G. Walesh, Ph.D., P.E., an independent consultant, peer-reviewed and edited
this report. Peer review comments were also provided by Professor Richard M. Ashley,
Ph.D. of the University of Abertlay Dundee, Scotland. The cooperation and helpful
suggestions provided by Chi-Yuan Fan, P.E., DEE, Project Officer, is acknowledged.
Furthermore, the contributions of all of the following individuals are acknowledged and
appreciated:
Ted Brown, Wright Water Engineers, Inc. Denver, CO.
Jane Clary, Wright Water Engineers, Inc., Denver, CO.
Richard Field, P.E., U.S. Environmental Protection Agency, National Risk Management
Research Laboratory, Water Supply and Water Resources Division, Edison, NJ.
James P. Heaney, Ph.D., Department of Civil, Environmental, and Architectural
Engineering, University of Colorado at Boulder, Boulder, CO.
Jonathan Jones, P.E., Wright Water Engineers, Inc., Denver, CO.
David Sample, Department of Civil, Environmental, and Architectural Engineering,
University of Colorado at Boulder, Boulder, CO.
Brian W. Mack, P.E., Camp Dresser and McKee Inc., Maitland, FL.
Robert Pitt, Ph.D., P.E., DEE, Department of Civil and Environmental Engineering, The
University of Alabama at Birmingham, Birmingham, AL.
Michael F. Schmidt, P.E., Camp Dresser and McKee Inc., Maitland, FL.
Michelle Solberg, Camp Dresser and McKee Inc., Maitland, FL.
Ben Urbonas, P.E., Denver Urban Drainage and Flood Co/ntrol District, Denver, CO.
Len Wright, Department of Civil, Environmental, and Architectural Engineering,
University of Colorado at Boulder, Boulder, CO.
In addition, Melissa Lilburn, graduate student at the University of Alabama at
Birmingham and Steve Burian, graduate student at the University of Alabama, along
XXXIV
-------
with Stephan Nix, Ph.D. and Rocky Durrans, Ph.D. professors at the University of
Alabama, contribution to chapters 4 and 5 are also acknowledged and appreciated.
Helen Egidio assisted to finalize the manuscript, and Stephanae Liik diligently restored
and developed an electronic version of the most complex figures.
It is acknowledged and appreciated the quick and meticulous work of the City of Boulder
Open Space CIS Laboratory and Hydrosphere, both of whom replaced severely
damaged figures.
XXXV
-------
Chapter 1
Introduction
James P. Heaney, Robert Pitt, and Richard Field
Introduction
Stormwater has traditionally been considered a nuisance, requiring rapid and complete
drainage from areas of habitation. Unfortunately, this approach has caused severe
alterations in the hydrological cycle in urban areas with attendant, mostly negative,
changes in receiving water conditions and uses. This historical "water as a common
enemy" approach has radically affected the way urban dwellers relate to water. For
example, most residents are not willing to accept standing water near their homes for
significant periods of time after rain has stopped.
However, a new, innovative approach to stormwater management is beginning to
appear. There are many examples where engineers, planners, landscape architects
and others have successfully integrated water into the urban landscape. In many
cases, water has been used as a focal point in revitalizing downtown areas. Similarly,
many arid areas are looking at stormwater as a potentially valuable resource, with
stormwater being used for on-site beneficial uses, instead of being quickly discharged
as a waste.
New actual and potential innovative approaches to stormwater management are
described in this report. Overviews of individual chapters are presented below.
Chapter 2: Principles of Integrated Urban Water Management
The purpose of this chapter is to review the literature on innovative urban
developments, in general, evaluate principles of sustainability, and present the urban
stormwater management problem within this broader context. The focus of this report is
new urban developments and these developments are at the neighborhood scale.
Control methods include source controls at the individual parcel level.
Trends in urbanization during the 20th century are described including the impact of the
automobile and subdivision regulations. Urban sprawl has often been the result of such
changes. Possible emerging land use forms are described that might be more
sustainable than present systems. Issues are presented to help decide whether smaller
or larger scale infrastructure systems are preferable. Finally, the sources of runoff in
urban areas are described along with a description of their relative importance.
Chapter 3: Sustainable Urban Water Management
Water supply, wastewater, and stormwater systems are explored in this chapter, first
individually and then in an integrative manner. Key areas of potential integration of
these three functions are reuse of wastewater and stormwater to reduce the required
net import of water for water supply. The literature review summarizes previous and on-
1-1
-------
going work nationally and internationally to develop more sustainable urban water
management systems. A systems view of urban water management was first
advocated in the late 1960's. This approach is summarized. Principles for sustainable
urban water infrastructure systems are presented.
Urban water budgets provide a way to evaluate the relative importance of the various
components of the urban water system. The results of a recently completed national
residential water use study are described along with the results of several water budget
studies from Europe and Australia. Then, monthly water budgets for Denver, CO and
New York City, NY are presented. Lastly, some alternative future urban water
scenarios are described ranging from the status quo to aggressive water conservation
and reuse programs.
Chapter 4: Source Characterization
The sources of the stormwater pollutants and flows that are likely to be preventing
beneficial uses must be recognized and quantified before an effective stormwater
management strategy can be implemented. This chapter gives an overview of the
obvious stormwater pollutant sources in urban areas, especially natural sources (soils,
atmospheric dustfall, and rain) and the washoff of contaminated dirt from pavements
(the most popular location for source control efforts). Included in Chapter 4 are
summaries of actual sheetflow runoff quality obtained during rains from numerous
source areas (roofs, landscaped areas, parking and storage areas, driveways,
sidewalks, and streets) for commercial, industrial, and residential land use areas. The
chapter concludes describing a study that investigated toxic heavy metal and organic
pollutant sources. Information and ideas presented in this chapter can be used to
identify significant sources of problem pollutants and understand how stormwater can
be better controlled at critical source areas and/or at a downstream outfall.
Chapter 5: Receiving Water and Other Impacts
A critical element to be investigated as part of a stormwater management program is an
understanding of the local receiving water problems. This chapter reviews many types
of problems that have been identified and documented during studies throughout the
country. The list of potential problems is diverse and long, although relatively few may
be relevant for any given geographic area. Some of the most common types of
receiving water problems that have been investigated relate to aquatic life uses.
Numerous studies have compared aquatic life (usually fish and benthic
macroinvertebrates) in urban streams with reference streams. Most of the
investigations examined toxic pollutant causes of the noted aquatic organism
differences, but recent investigations focused more on habitat issues caused by
stormwater discharges (e.g., contaminated and fine-grained sediments, unstable
streambeds, variable and high flows, and destruction of refuge areas).
Human health issues associated with stormwater discharges are also reviewed.
Potential groundwater impacts caused by inadvertent and by designed subsurface
disposal of stormwater are also examined. Chapter 5 includes emerging tools that
1-2
-------
many States are using to measure receiving water problems, especially bioassessment
procedures that integrate numerous relatively inexpensive field measurement
components.
Chapter 6: Collection Systems
Stormwater and other wastewater collection systems are a critical link in the urban
water cycle, especially under wet-weather conditions. In the context of pollution control,
these systems transport sanitary wastewater, stormwater, industrial wastewater, non-
point source pollution, inflow, and infiltration. Understanding the problems associated
with modern sewer collection systems is enhanced by reviewing the history of collection
systems in the U.S. Problems associated with present day collection systems are
described including the challenge of infiltration and inflow. The emerging issue of
sanitary sewer overflows is discussed. The importance of understanding the nature of
sewer solids is described with emphasis on the role of solids in determining sewer
design criteria. Innovative sewer design and monitoring systems are discussed.
Chapter 7: Assessment of Stormwater Best Management Practice Technology
The use of stormwater controls to manage the quality and quantity of urban runoff has
become widespread in the U.S. and in many other countries. As a group they have
been labeled best management practices, or BMPs. Structural BMPs are designed to
function without human intervention at the time wet weather flow is occurring, that is,
they are expected to function unattended during a storm and to provide passive
treatment. Nonstructural BMPs, as a group, are a set of practices and institutional
arrangements, both with the intent of instituting good housekeeping measures that
reduce or prevent pollutant deposition on the urban landscape.
Much is known about the technology behind these practices, much is still emerging and
much remains yet to be learned. Many of these controls are used without full
understanding of their limitations and their effectiveness under field conditions.
Uncertainties in the state of practice associated with structural BMP selection, design,
construction and use are further complicated by the stochastic nature of stormwater
runoff and its variability with location and climate. Examination of precipitation records
throughout the U.S. reveals that the majority of individual storms are relatively small,
often producing less precipitation and runoff than used in the design of traditional storm
drainage networks. Chapter 7 describes a number of structural and non-structural
BMPs with emphasis on their effectiveness in removing pollutants and in mitigating flow
rates. BMP effectiveness in addressing some of the impacts of urban runoff on
receiving water systems is also discussed.
Chapter 8: Stormwater Storage-Treatment-Reuse Systems
The overall effectiveness of a variety of stormwater BMP's is evaluated in the previous
chapter. Two other aspects of control of stormwater: high-rate treatment and the
potential effectiveness of using stormwater for supplemental irrigation, are described in
Chapter 8. Presented is a review of ways to evaluate the tradeoff between storage and
treatment of wet-weather flows. Then the potential for high-rate operation of
1-3
-------
wastewater treatment plants during wet-weather periods is discussed. Stormwater
reuse offers the possibility of significantly reducing water demand for irrigation and toilet
flushing. The approximate size of on-site storage needed and how it varies with
location is presented. A monthly water budget is used as part of this to estimate
storage needs.
Chapter 9: Urban Stormwater and Watershed Management: A Case Study
Interest in watershed management has waxed and waned over the past century.
During the 1980's, primary reliance was placed on a command and control approach for
addressing water resources problems including Stormwater. A strong move back to the
watershed management approach began a few years ago. Watershed analysis and
planning methodologies are reviewed.
A detailed case study of Boulder Creek Watershed (BCW) and Boulder, CO is
presented. (This case study emphasizes the analysis aspect of urban Stormwater and
watershed management. Appendix A in this report is a case study that emphasizes the
planning aspect of urban Stormwater and watershed management). With the beginning
of mining in 1858, the water and land associated with various forms of development had
a significant impact on BCW. The watershed has been drastically altered by activities
such as mining, urbanization, agriculture and hydropower development. BCW suffered
serious early Stormwater pollution from the original mining activities.
Thus, nonpoint pollution is an old problem in BCW. The watershed has also been
adapted to provide water supply, flood control, recreation, and instream flow needs.
The adaptations are both structural and nonstructural. Structural interventions include
construction of reservoirs, canals, pipelines, pump stations, hydropower generation,
water and wastewater collection and treatment systems, flood control levees, instream
and wetland restoration, and imports and exports of water. Nonstructural interventions
include flood warning systems, floodplain management, water rights enforcement, water
conservation programs, and education about watershed protection.
The end result of all of these interventions is a complex watershed system that has
been adapted to serve the needs of society as well as the natural system. This level of
development and adaptation is typical of watersheds in the U.S. and other developed
areas. Thus a watershed should be dealt with as a system in contrast with isolating
system components and ignoring the system's complexity. While the focus of this
report is urban Stormwater quality management, these other considerations should also
be borne in mind.
Chapter 10: Cost Analysis and Financing of Urban Water Infrastructure
This chapter summarizes water, wastewater, and Stormwater infrastructure costs for
cities in the U.S. While the main theme of this report is Stormwater, some of the
innovative ideas proposed would reuse Stormwater for reducing water supply demands
(e.g., for irrigation water). The effect of dwelling unit density on the demand for water
infrastructure is presented. Previous efforts to find the optimum scale of urban water
1-4
-------
systems are described. Summary cost functions for a variety of water resources
facilities are presented.
Stable funding is an essential ingredient in developing and maintaining viable urban
water organizations, whether they are stormwater utilities, watershed organizations, or
other organizational forms. Integrated management offers the promise of improved
economic efficiency and other benefits by combining multiple purposes and
stakeholders. However, the benefits from integrated management exacerbate problems
of financing these more complex organizations because ways must be found to assess
each stakeholder's "fair share" of the cost of this operation. An overview of utility
financing in the water, wastewater, and stormwater areas is presented.
Chapter 11: Institutional Arrangements
Stormwater Management Institutions of the 21st century face many challenges. Federal
stormwater permitting requirements will affect most cities. Funding and staffing are
likely to remain tight, even though stormwater regulations and requirements continue to
expand. Stormwater management will be only one of a long list of issues that must be
addressed by local governments. Given the time and budget constraints that staff will
face, local governments will have to decide where stormwater management lies relative
to other priorities. This is no easy task, given that the benefits of stormwater
management can be elusive to quantify.
New stormwater management facilities must be financed and constructed. The public
must be better educated on the significance of stormwater issues and stakeholders
should be increasingly involved in urban water management. Research must lead to
new technologies for treating and retaining stormwater runoff. Institutions will need to
issue guidance on complicated and often controversial issues such as riparian corridor
preservation, impervious area limitations, conservation easements, innovative zoning
techniques and other subjects. Given these challenging tasks, Chapter 11 briefly
characterizes the existing models of stormwater management institutions, identifies five
essential characteristics of future stormwater management institutions, and describes
specific technical and administrative issues that these stormwater management
institutions must address.
Further, existing stormwater regulations are transitioning from the promulgation and
implementation stages to the enforcement stage, where local governments may face
legal challenges, particularly as a result of land use restrictions. Coordination among
local, state, federal and private entities is and will continue to be a challenge.
Stormwater management institutions have to address both water quality and quantity
issues. In some cases, this will require retrofitting existing stormwater quantity
structures to address stormwater quality issues and to improve their drainage and flood
control function.
A planning case study to illustrate innovative stormwater management in new
development is presented in Appendix. It is a condensed version of the Southeast
1-5
-------
Annexation Area Lake Hart Basin Master Stormwater Management Plan (LHMSMP),
City of Orlando, Orange County, FL. The general goals of the LHMSMP are the
development of an integrated stormwater, wetland, and open space management
system that would balance preservation of natural systems with land development. The
general goals are to be accomplished by meeting the following three key objectives in a
cost-effective manner: flood control, pollution control, and ecosystem management
(which includes wetlands protection, aquifer recharge, and water conservation).
1-6
-------
Chapter 2
Principles of Integrated Urban Water Management
James P. Heaney
Introduction
The purpose of this chapter is to review the literature on innovative urban
developments, in general; evaluate principles of sustainability; and present the urban
stormwater management problem within this broader context.
The Neighborhood Spatial Scale
The spatial scales for urban developments to be evaluated in this report are defined as
follows:
1. Individual parcel: the smallest spatial scale consisting of an individual lot that
may contain a house, apartment, commercial, industrial, or public activity.
2. Block: collection of parcels bounded by streets. For example, in higher density,
older neighborhoods with gridiron streets, the typical area of a block is 1/8 x 1/16
of a mile or five acres. Blocks tend to be larger in area for contemporary lower
density developments with block sizes being as large as 20 acres in size.
3. Subdivision: single land development, typically with the same land uses.
Subdivisions are assumed to range in size from 25 to 100 acres.
4. Neighborhood: mixture of residential, commercial, public, and perhaps industrial
land uses. The neighborhood is assumed to be an integrated, partially self-
sustained, urban system. Typical sizes would be 100-1,000 acres.
5. New Town: cluster of neighborhoods designed to be largely self-sustaining in that
the town provides sufficient employment opportunities for the local residents.
Population sizes range from 20,000 to 60,000 people.
While the scope of this report are developments with populations less than 50,000
people, the area can either begreenfield (previously undeveloped land) orbrownfield
(urban redevelopment).
Trends in Urbanization
Historical Patterns
Certain background information helps to understand and evaluate future neighborhood
stormwater systems. Examples are understanding historical land use patterns, factors
stimulating changes in those land use patterns, and projecting expected future patterns
of urban land use and the extent to which urban infrastructure might influence, or be
influenced, by these changes.
Cities evolve in response to the inhabitants' needs for mutual self-protection,
commerce, education, and cultural exchange. The late 1800's signaled the end of the
"pioneer era" in the United States during which people migrated from place to place in
2-1
-------
search of a better way of life. For the first 20 years of the 20th century, infrastructure in
cities focused on non-transportation related needs. However, the growing importance
of the automobile, beginning in the 1920's, forced city managers to devote an increasing
portion of their budgets to accommodating this new mode of transportation. Prior to
World War II, U.S. cities developed around the concept of mixed neighborhoods as part
of villages, towns, and cities. Beginning in the late 1940's, suburbia began to dominate
urban America. Early suburbia had its origins in the late 19th century with urban
dwellers seeking to escape the blighted conditions of cities. Suburban living in the late
19th century was made possible by commuter trains that provided reasonable access to
cities from outlying areas.
Impact of the Automobile
The automobile is having a profound impact on urban developments during the 20th
century. A summary of trends in population and automobile use in the United States
from 1915 to 1994 is shown in Table 2-1. During this period, the U.S population grew
by a factor of 2.6 from 100 to 261 million people and the number of automobiles grew by
a factor of 80 from 2.5 million to nearly 200 million. The most dramatic growth in
automobiles occurred since World War II. For example, from 1945 to 1955, the number
of automobiles doubled from 31 million to 62.8 million. From 1955 to 1995, the number
of automobiles tripled to over 200 million vehicles. The trends in growth of population
and automobiles, shown in Figure 2-1, indicate that the rate of increase of vehicles is
much greater than population growth.
The trend in vehicles per capita is shown in Figure 2-2. At present, there are 0.76
vehicles per capita. Perhaps, this is a saturation level based on the percentage of the
population that is older than the minimum driving age. For example, 79.9% of the U.S.
population is over 13 years old (National Safety Council 1995).
The vehicle miles traveled (VMT) per capita has continued to rise at a steady rate since
1945 as shown in Figure 2-3. Projections for the State of Colorado indicate that the
1995 VMT of 10,000 is expected to increase to 11,130 by the year 2020 (Yuhnke 1997).
The average American drives twice as much as the average European or Japanese
citizen (Kunstler 1996). Americans use cars for 82% of their trips compared to 48% for
Germans, 47% for the French, and 45% for the British (Kunstler 1996). Between 1960
and 1990, Americans commuting by car increased from 69.5% to 86.5% while
commuting by public transit decreased from 12.6% to 5.3% and walking decreased from
10.4% to 3.9% (Goldstein 1997).
With only 5% of the world's population, the United States consumes a quarter of the
world's oil, half of which is used in motor vehicles (Kunstler 1996). Over 60,000 square
miles of U.S. land is paved over which is 2% of the total surface area and 10% of the
arable area (Kunstler 1996). The American public has subsidized this development
through a combination of incentives such as large defense expenditures to protect oil
producing countries, subsidized highway construction, and "free" parking. Auto tolls
2-2
-------
Table 2-1. Changing patterns of automobile use in the U.S., 1915-1996 (TetraTech
1996).
Year
1915
1920
1925
1930
1935
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1994
No. of
Vehicles
millions
2.5
9.2
21.1
26.7
26.5
32.5
31.0
49.2
62.8
74.5
91.8
111.2
137.9
161.6
177.1
192.9
199.4
No. of
Drivers
millions
3.0
14.0
30.0
40.0
39.0
48.0
46.0
62.2
74.7
87.4
99.0
111.5
129.8
145.3
156.9
167.0
175.1
Vehicle
Miles/yr.
Billions
122
206
229
302
250
458
606
719
888
1120
1330
1521
1774
2148
2347
Population
millions
100
107
115
123
127
132
132
151
164
180
194
204
215
227
239
249
261
Drivers/
Population
3.0%
13.1%
26.2%
32.5%
30.7%
36.3%
34.7%
41 .2%
45.5%
48.6%
51.1%
54.7%
60.3%
63.9%
65.6%
67.1%
67.1%
Vehicles/
Population
0.03
0.09
0.18
0.22
0.21
0.25
0.23
0.33
0.38
0.41
0.47
0.55
0.64
0.71
0.74
0.77
0.76
Vehicles
miles/
capita
1064
1672
1801
2285
1888
3030
3690
3997
4588
5494
6178
6694
7420
8626
8992
1SSQ ZXQ
Figure 2-1. Trends in U.S. population and ownership of automobiles.
2-3
-------
1910 1920 1930
1940 1950 1960 1970 1980 1990 2000
Year
Figure 2-2. Trends in vehicles per capita in the U.S.
1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Year
Figure 2-3. Trends in vehicle miles per capita in the U.S.
2-4
-------
and gas taxes cover only about 9 to 18% of the cost of transportation (Kunstler 1996).
Goldstein (1997) estimates that 25% or more of newly-developed land is committed to
roads, parking, driveways, and garages.
The preceding discussion indicates the dominant impact of the automobile on
contemporary urban settlements. In order to accommodate more cars and higher rates
of utilization, the sizes and proportion of property devoted to vehicles has increased
dramatically. One example is the shift from one to two and even three car garages.
Parking and other support services have similarly expanded. A key question for the
future is whether these trends will continue. If they do, then wet-weather problems will
continue to grow in relative importance as will air pollution and noise problems.
Impact of Subdivision Regulations
Southworth and Ben-Joseph (1995) present an overview of suburbia evolution since
1820. They trace the evolution of the current design standards for suburbia, with
particular emphasis on city streets. They bemoan the consequences of current
standard practices stating (Southworth and Ben-Joseph 1995):
Attempts to reshape the form of the American city are
often thwarted by the standards and procedures that
have become embedded in planning and development.
Particularly troublesome are standards for streets that
virtually dictate a dispersed, disconnected community
pattern providing automobile access at the expense of
other modes. The rigid framework of current street
standards has resulted in uniform, unresponsive
suburban environments.
The current residential street design standards which are accepted virtually throughout
the United States necessitate a large amount of impervious area per family which
consists of wide streets, sidewalks, and driveways.
Contemporary Neighborhoods and Urban Sprawl
Urban areas in the United States are using land four to eight times faster than the
growth in population. The New York metropolitan area's population increase over the
past 25 years has been only 5%, but the developed land has increased by 61 %,
replacing nearly 25% of the region's forests and farmlands (Peirce 1994). Cities are
spreading over the natural landscapes far faster than population increases or economic
progress requires, while older urban districts with their valuable infrastructures are
under used or abandoned (Barnett 1993).
In spite of an aggressive program to control urban sprawl and acquire greenways,
Portland, OR has grown by nearly 25% since 1980 while expanding its urban area by
only 1%. Without such management strategies, the Chicago area's population has
grown only 4% in the past 20 years but expanded its urban land by 35%. Between
2-5
-------
1960 and 1990, the population of the Baltimore metropolitan area increased by 33% but
the amount of land in the region used for urban purposes grew fivefold-by 170% (Katz
1997).
The subdivision is the basic building block of current land use and each parcel within
the subdivision is designed to maximize its own identity and privacy. According to
Kunstler (1996), the reigning metaphor for the "good life" in the United States is:"... a
modest dwelling all our own, isolated from the problems of other people."
However, these properties tend to be much larger than would be suggested by the word
"modest" because they attempt to provide a variety of traditional community functions
within their individual boundaries such as parks (front and back yard), parking (garages
and driveways), and recreation (swimming pools, play areas). Each of these units
exists in isolation.
Zoning laws are the chief public instrument used to separate functions in contemporary
urban communities. Building the equivalent of Main Street USA in modern America is
virtually impossible. It would violate current zoning law provisions such as setbacks,
parking requirements, and mixing of land uses. Each major land use function is
separated from the others requiring motorized transportation (typically an automobile) to
get from one area to another.
Urban sprawl has been a widely debated topic during the past 25 years as automobile-
dominated urban transit has become pervasive. Real Estate Research Corporation
(1974) analyzed the costs of sprawl for a variety of land use scenarios ranging from
uniform low density development to high density, clustered developments. As part of
the large on-going effort to protect Chesapeake Bay, the effect of sprawl on land use
has been quantified and its implications discussed. This study defined sprawl as
(Chesapeake Bay Foundation 1996):
the haphazard scattering of homes and businesses across the landscape,
beyond already developed areas, far from cities and towns.
an ineffective use of the land, difficult to service with infrastructure and
transportation, requiring extensive use of automobiles, and consuming large land
areas (CH2M Hill 1993).
Residential development at a density of less than three dwelling units per acre
(CH2MHNI 1993).
Tetra Tech (1996) defines urban sprawl as:
Current development patterns, where rural land is
converted to urban uses more quickly than needed to
house new residents and support new businesses, and
2-6
-------
people become more dependent on automobiles.
Sprawl defines patterns of urban growth which include
large acreage of low-density residential development,
rigid separation between residential and commercial
uses, minimal support for non-motorized transportation
methods, and a lack of integrated transportation and
land use planning.
The National Commission on the Environment (1993) criticizes contemporary urban
land use pattern by stating:
Meanwhile, sprawling housing developments, shopping
centers, highways, and myriad other developments have
proceeded virtually unfettered by any sense of respect
for the environment and humankind's relation to it. As a
result, pollution from non-point sources continues to
grow and is increasingly difficult to control; biological
diversity is destroyed as habitats are fragmented and
eliminated; sprawl development blighted the landscape
and precludes cost-effective and environmentally
beneficial means of providing transportation and other
services; and inner cities at the core of metropolitan
areas increasingly are home to people who have been
abandoned as hopeless by the rest of U.S. society.
The impacts of sprawl in the Chesapeake Bay area include (Chesapeake Bay
Foundation 1997):
1. Five to seven times the sediment and phosphorus as a forest.
2. Nearly twice as much sediment and nitrogen as compact development.
3. Each person uses four to five times as much land as 40 years ago.
4. Twice as much road building as compact development.
5. Three to four times as many automobile trips per day.
6. Much more air pollution as compact development.
7. Lower tax revenues than the cost of providing these services.
8. Induced relocation of people from central cities and inner suburbs.
Historical Infrastructure Development Patterns
Early infrastructure systems tended to be smaller in size with customers providing some
or all of the necessary services or participating in smaller utilities to provide water
supply, wastewater, and stormwater services as separate entities. Early transportation
systems were often private toll roads. Citizens also formed cooperatives to share the
cost of building and maintaining these roads.
The first major call for governmental participation in road construction came in the late
2-7
-------
19th century in response to requests from the bicycle community to provide improved
roads. Prior to the automobile, railroads provided much of the transportation
infrastructure for trips of any significant distance.
Regionalization of urban wastewater infrastructure began in earnest in the 1960's and
early 1970's with the federal government providing large subsidies for construction of
new wastewater treatment plants and interceptor sewers. Under this program, the
urban areas were required to demonstrate that the proposed system was the most cost-
effective. Typically, the preferred solution was to build very large regional systems to
serve the entire metropolitan area. From a regulatory viewpoint, the agencies strongly
preferred larger regional systems since they were easier to administer as opposed to
dealing with numerous individual cities and suburbs. The availability of federal
subsidies in the range of 75% of the construction cost had a major influence on the
decision that "bigger is better". Analogous central systems emerged in water supply,
stormwater, and transportation.
Interceptor Sewers and Urban Sprawl
Binkley et al. (1975) evaluated the effect of federally subsidized construction of large
interceptors on urban sprawl. The federal government paid 75% of the initial capital
cost of interceptors to provide for the existing and future populations. They felt that this
subsidy encouraged overdesigning the interceptor sewers. Excess capacity is paid by
existing residents who derive little or even negative benefit from it. One alternative
funding option is to subsidize only that portion of the interceptor that serves the existing
population. Additional capacity would have to be paid by owners of the benefiting
property.
This study analyzed 52 interceptor projects. The following conclusions were reached:
About one half of the total federal investment benefited future growth, not existing
customers.
The costs of excess capacity averaged $145 per capita and was as high as $658
per capita, measured in 1975 dollars.
Design project periods with a median of 50 years were used. It would be more
efficient to use shorter periods of, say 25 years, to reduce uncertainty and to give
the existing communities more control over future growth patterns.
Based on this evaluation, Binkley et al. (1975) make the following recommendations:
1. Provide no federal funds for excess capacity. Future growth should pay its own
way. Subsidizing this growth will encourage sprawl. Reevaluate interceptor
staging of project design in rapidly growing areas. Using shorter design periods
reduces the tendency to subsidize future growth. Excess capacity does impose
extra cost, especially if it is not used.
2. Use realistic standards for per capita flows. EPA recommended average sewage
flows of 100 to 125 gpcd when actual flows average 40-60 gpcd.
2-8
-------
3. Improve population forecasting techniques
4. Require consideration of environmental effects of interceptor-induced land use.
Increase public participation in the project so that existing stakeholders better
understand the environmental and financial implications of the projected project.
Federal Housing and Urban Development Programs
Federal government policies to promote urban economic development have evolved
over the past 50 years. Following World War II, urban renewal programs aimed at
building affordable housing flourished. The Clinton administration relies on the
establishment of empowerment zones and enterprise communities (Moss 1997). These
programs have focused on the bricks and mortar aspects of the problem. The Clinton
administration's empowerment zone is modeled on the "enterprise zone" concept used
in Britain where public investment is attracted by eliminating government regulations
and taxes in the worst areas of the city (Moss 1997). According to Moss (1997), the
migration of population from the cities to the suburbs is the result of numerous forces
including racial and ethnic bias, the construction of high-speed expressways, crime, the
decline of urban public schools, and the cultural appeal of low density, single-family
housing.
Engel et al. (1996) discuss how the U.S. Dept. of Housing and Urban Development
(HUD) and EPA are changing to better integrate their respective missions. They trace
the origins of the environmental movement in the United States to late-19th century
concerns about poor public health and sanitation conditions in cities and to the need to
protect open space and wildlife in undeveloped areas. Early public interventions in
housing were brought about by public health concerns about overcrowding, open
spaces and urban parks, light and air, sanitary facilities, potable water, and housing and
building codes (Engel et al. 1996). The Housing and Urban Development Act of 1968
was intended to have HUD take the lead in implementing a comprehensive urban
strategy. The implementation of this act emphasized construction of housing.
Concurrently, major environmental initiatives came on line as a result of numerous
legislative mandates. Interestingly, there was little interaction between housing and
urban policy advocates and environmental organizations during the 1970s and 1980s
and the two programs developed separately. In 1993, the New York Citizens Housing
and Planning Council held a conference on housing and environment. Critics argued
that environmental regulations were "...endangering the economic viability of the
existing housing stock and the rehabilitation or new construction of low-and moderate-
income housing." (Engel et al. 1996). This initial effort stimulated other workshops and
the development of joint activities between EPA and HUD in areas of common interest
such as brownfields.
Engel et al. (1996) synthesize the current situation into four categories arranged in
ascending order of difficulty:
2-9
-------
1. Procedural reforms: Concern exists that existing environmental regulations,
particularly federal mandates, are unduly restrictive and cumbersome. They
need to be made more flexible and better integrated into the local planning and
permitting process.
2. Balancing of social goals: A natural tension exists between developers and
regulators. Strong federal environmental regulation is intended to provide a
check against too much control by local development interests. However, these
regulations and associated liability have strongly discouraged redevelopment of
older sections of urban areas by encouraging builders to go to new areas where
environmental cleanup is not an issue. Unfortunately, this contributes to urban
sprawl.
3. Urban risk analysis: The comparative risks of environmental stressors need to
be prioritized based on the cost effectiveness of reducing these risks. Progress
is being made in this area in that individual risk assessments are being done,
such as use-based cleanup standards for brownfields. However, it is still difficult
for local authorities to develop their own priorities on relative risks because
environmental regulations are organized by individual media and pollutants.
Trade-offs may not be permitted.
4. Allocation of costs: The issue of who pays for environmental cleanup is at the
heart of current debates. During the 1970's, the federal government paid a large
share of these control costs. However, this is no longer the case. As of 1990,
the federal government was only paying about 30% of pollution control costs
(Engel et al. 1996). A significant part of the residual cost falls on local residents,
many of whom have limited ability to pay.
Federal Transportation Programs
The federal government has provided the bulk of the financing for the interstate systems
that has had a major impact on urbanization since the late 1950's. This support has
continued and has been a major inducement for promoting automobile use in urban
areas (Littman 1998).
Summary of the Impacts of Federal Urban Programs
Beginning in the 1930's, federal programs to insure mortgages, and associated
guidelines for "good" subdivision design, have resulted in widespread adoption of
zoning and land use ordinances that foster lower density suburban development.
Transportation agencies at all levels have promoted automobile use by providing large
subsidies for this mode of transportation and mandating "free parking" and generous
widths on little used streets. USEPA construction grants for wastewater treatment
during the 1970's encouraged construction of large interceptor sewers and centralized
wastewater treatment plants. The large amount of "excess capacity" in these systems
encouraged low density development as cities sought customers to utilize this available
capacity. Liability concerns with renovating brownfields in urban areas encouraged
2-10
-------
migration away from the core city to greenfield areas. Recent years have seen a
rekindling of interest among federal agencies to look at urban systems in a more unified
manner in order to promote more sustainable communities.
Possible New Approaches
Neo-traditional Neighborhoods
One attempt to develop modified urban land use patterns is called the New Urbanism
school. New urbanism is also called neo-traditional planning, traditional neighborhood
development, low density urbanism, or transit oriented development (Kunstler 1996).
The key component of the "new approach" is to return to the pre World War II practice
of designing urban neighborhoods with a mix of land uses rather than segregating land
uses by function as currently exists. Features of traditional neighborhood developments
(TND) include the following (Chellman 1997):
1. Mixed land uses.
2. Gridiron street pattern to maximize circulation. The goal is to maximize
connectivity of streets, not the opposite.
3. Most TND streets are designed to minimize through traffic by using tee
intersections.
4. Alleys.
5. Garages in rear of house facing alley.
6. Smaller front yard with porches to reflect the increased friendliness of
neighborhood.
7. Higher densities that promote alternative forms of transportation to the
automobile. Typical TND densities in the United States are 6-10 dwelling units
per acre.
8. Designed to maximize non-motorist mobility for residents and visitors.
9. Residential streets are designed for shared use; they are not designed merely
to optimize automobile movement. Examples of narrower streets in traditional
neighborhoods include (Chellman 1997, p. 25) two lane-two parking lane
streets with a 25 foot curb to curb dimension (Seattle, WA), 28 to 32 feet wide
(Georgetown in Washington, D.C.), 21 feet wide (San Francisco, CA), 22 feet
wide (Madison, Wl), 26 to 30 feet wide (Portsmouth, NH), and 18 to 28 feet
wide (Portland, OR). As Chellman (1997) points out, the narrower streets
reduce traffic speeds to 10-20 mph, thus improving safety for other users.
10. The scale of the design is based on the primary user being a pedestrian, not an
automobile driver. For example, signs are smaller.
11. TNDs are sized based on walkability. Thus, they range in size from 40 to 125
acres.
12. Most commercial units have residences located on upper floors of the TND
project.
13. On-street parking is allowed.
2-11
-------
A prominent example of a neo-traditional community is Celebration, a new development
by Disney Corporation near Orlando, FL. This 4,900 acre development will house
20,000 residents in a mix of land uses. These new communities try to reduce the
impact of the automobile on urban settlements. Smaller streets are used in the
neighborhoods. Alleys with garages are used so that streets will be lined with front
porches and lawns, not garage doors and driveways. Open space including pocket
parks are an integral component of these new communities. Ben-Joseph (1995)
presents several examples of such developments in the Netherlands, Germany,
England, Australia, Japan, and Israel. Another example in the U.S. is Seaside, FL
(Mohney and Easterling, eds. 1991).
The preceding examples of "new urbanism" reflect current attempts to convince
Americans that alternative options exist. However, many long-term examples already
exist in older cities of the United States and Europe.
Newsweek (1995), in an article based on interviews with leading New Urbanism
proponents, Andres Duany, Elizabeth Plater-Zyberk, Peter Calthorpe, and Henry Turley,
summarizes 15 basic tenets of the new urbanism:
1. Give up big lawns: they increase sprawl, require large amounts of irrigation
water, and increase alienation.
2. Bring back the corner store: a simple development that both brings local
residents together and a convenience that does not require a 10-mile trip to the
supermarket.
3. Make the streets skinny: plan neighborhood streets for walking not driving.
4. Drop the cul-de-sac: although a "dead-end" neighborhood prevents through
traffic, it chokes that one road that connects the neighborhood with the rest of
the world.
5. Draw boundaries: limit the city's physical size; don't let population increase
cause sprawl.
6. Hide the garage: neighborhoods are for living, not parking.
7. Mix housing types: avoid monoculture neighborhoods and invite diversity
through development.
8. Plant trees curbside: beautify the places we travel and walk.
9. Put a new life into old malls: plan shopping centers not entirely around the
consumer, but strive to bring together a community.
10. Plan for mass transit: encourage alternatives to the automobile.
11. Link work to home: break the idea that one has to travel a great distance to
work.
12. Make a town center: focus a development around a public center
13. Shrink parking lots: business can share parking.
14. Turn down the lights: light streets for the pedestrian, not the automobile.
15. Think green: instead of endless manicured green carpets, invite nature into the
community.
2-12
-------
The wave of interest in New Urbanism concepts of urban planning has rekindled the
debate regarding the pros and cons of traditional neighborhood developments.
Chellman (1997) presents an overview of the debate and evaluates the transportation
aspects of traditional neighborhood development. Ewing (1996) evaluates new urban
developments and compares them to traditional developments. He presents a list of
best development practices for land use, transportation, housing, and environmental
practices. No work was found that evaluated the impact of neo-traditional development
on urban water infrastructure. Accordingly, a preliminary evaluation of this topic is
presented in this report.
Related EPA Activities Dealing with Urban Growth Patterns
In addition to the activities of the National Risk Management Research Laboratory that
is sponsoring this study, other groups within US EPA are interested in issues of urban
development and its environmental impacts. These groups are discussed here.
Green Development
U.S. EPA's Office of Wetlands, Oceans and Watersheds is developing the Green
Development approach to make urban growth and development work with existing
environmental resources. Tetra Tech (1996) compiled a list of case studies of
innovative urban development. The case studies are divided into the following
categories:
Urbanizing suburbs and areas where infill has successfully occurred (See Table
2-2).
Intermodal transport policies that consider environmental impact (See Table 2-3).
EPA's air quality control program is encouraging methods to reduce the demand for
vehicle travel by a variety of means including charging systems (ICF Incorporated and
Apogee Research Inc. 1997).
Green development achieves its goals using the following (Tetra Tech 1996):
1. Flexible zoning and subdivision regulations.
2. Management of growth through agriculture and natural resources preservation.
3. Comprehensive and integrated site planning.
4. Reduction in site imperviousness.
5. Restoration of the site hydrologic regime to mimic the natural or predevelopment
condition.
6. Maintenance of surface water and groundwater quality and minimization of the
generation and off-site transport of pollutants.
7. Minimization of disturbance of riparian habitat functions.
8. Preservation of terrestrial habitat ecological functions and maximizing
conservation of woodland and vegetative cover.
9. Use of compact, pedestrian-friendly development practices.
2-13
-------
Studies of Chesapeake Bay
The Chesapeake Bay Foundation (1996) advocates the following principles to avoid
sprawl:
1. Channel development into "growth areas," that is, compact mixed-use
patterns in and adjacent to existing cities and towns.
2. Create "growth boundaries" to keep sprawl out of open lands where
farming, forestry and recreational activities should prevail.
3. Maintain existing highways, improve local roads, and use transit to
connect and organize land uses in growth areas.
4. Revitalize existing towns and cities.
Table 2-2. Case studies on "urbanizing" suburbs and areas where infill has
successfully occurred (Tetra Tech 1996).
Case Study Name
California Infill Development Program
Downtown Master Plan*
Florida Main Street Program
Grand Central Square
Memorial Park
Mizner Park
River Place
Uptown District
Ballston
Main Street
Downtown Redlands
Whittier Boulevard
The Eastward Ho! Initiative
Fearrington
Fairview Village
Downtown area
Downtown area
Revitalization Plan
The Florida Avenue Project
The Jordan Tract
North Boulder
South Martin County
Master Plan
Montgomery Village
Lake Park Village
Oak Ridges Moraine
Peaks Branch
Dorsey Woods
Location
California
City of West Palm Beach, FL
State of Florida
Los Angeles, CA
Richmond, CA
Boca Raton, FL
Portland, OR
San Diego, Ca
Arlington, VA
Huntington Beach, CA
Redlands, CA
East Los Angeles, CA
South Florida
Near Chapel Hill, NC
Near Portland, OR
Mashpee, Ml
Boca Raton, FL
Orlando, FL
Miami, FL
Mount Pleasant, SC
Boulder, CO
Martin County, FL
Port Royal, SC
Montgomery Township, NJ
Union County, NC
Toronto, Canada
Dallas, TX
Arlington, VA
Economic Analysis
Included?
No
No
No
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Yes
2-14
-------
Brownfield Redevelopment
The US EPA is promoting the redevelopment of brownfields in older urban areas. A
review of this program highlights many of the challenges of reversing the trend from
continued development of green fields on the periphery of urban areas to
redevelopment of existing areas. Challenges include technical, socio-economic, and
liability issues as discussed below. Barnette (1995) lists three advantages of
redeveloping brownfields:
Brownfields are properly zoned and thus well suited for industrial and commercial
use.
The civil infrastructure and utilities necessary for industrial operations are already
in place at many brownfield sites.
Brownfield redevelopment preserves the nation's virgin land and natural
resources.
Table 2-3. Case studies using intermodal transportation policies that consider
environmental impacts (Tetra Tech 1996).
Case Study Name
Effects of Interstate 95 on Breeding Birds
For Animals. It's the Road to Safety
Haymount
Skinny-Streets & One-sided Sidewalks: A Strategy... Paradise
I-287 it and They Will Drive On It
For Many, Gas Guzzler is Necessary Tool, Not a Toy
The Road Less Noisy: How America is Muffling the Highways
Portland's Pedestrian Master Plan
City of Toronto
City of Seattle Bicycle Program
State of Washington Transportation Planning
Core Area Requirements to Support Non-Auto Trips, New Jersey
Transit
Designing for Transit, Integrating Public Transportation and
Land Development
Guide to Land Use and Public Transportation
The Citizen Transportation Plan for Northeastern Illinois
Transit-Supportive Land Use Planning Guidelines*
TCEA-Transportation Concurrency Exception Area
Smart Development Program
The Crossings
Old Pasadena
North Thurston UGMA
North Boulder
South Martin County
Revegetation along US 189
Stream Restoration in Boulder
Rail Plan on the Wrong Track
MSHA Grown, Don't Mow Program
Location
Maine
Washington, DC
Caroline, Co., VA
Olympia, WA
Wanaque, NJ
Cllifton Park, NY
Colorado
Portland, OR
Toronto, Canada
Seattle, WA
Washington
New Jersey
San Diego Metropolitan Area
Snohomish County, WA
Chicago Region, IL
Ontario, Canada
Delray Beach, FL
State of Oregon
Mountain View, CA
Pasadena, CA
Thurston County, WA
Boulder, CO
Martin County, FL
Provo Canyon, UT
Colorado
Maryland
Maryland
Modes Provided ($)1
A
A
T,A
A
A($)
A($)
A($)
P
T,A
B
T,A,P
T,A,P
TAP
T
T,A($)
TAP
T,A,P,B
T,A($)
T,A,P($)
TAP
TAP
T,A
TAP
T
P,B
T($)
T
1) A: Auto, B: Bicycle, P: Pedestrian, T: Transit, $: Economic analysis included.
2-15
-------
Collatin and Bartsch (1996) discuss three major concerns regarding brownfield
redevelopment: the high cost of cleanup, the uncertainty about liability and procedures,
and a negative public attitude towards old facilities. Cleanup costs are an upfront cost
for developers and include required site environmental assessments for all properties.
Given the initial assessment, the developer still faces major uncertainties about the
ultimate final cost. Thus, lending institutions are understandably reluctant to become
involved in such high-risk ventures. Review procedures are complicated by not having
clear guidelines on the required level of control and the extent of the public review
process. Lastly, the above concerns and a recent history of negative attitudes towards
these properties further reduces their desirability. Amedudzi et al. (1997) provide an
overview of brownfield redevelopment issues at the federal, state, and local levels.
The follow existing brownfield demonstration projects are explicitly linked to urban water
systems (Colatin and Bartsch 1996):
1. Birmingham, AL: Link environmental protection approaches involving flood
control and stormwater/groundwater contamination reduction with remediation
of soil and site-specific contamination, and develop consortium of community
leaders to direct resources to targeted areas.
2. Erie County, NY: Brownfield cleanup as part of a large waterfront
redevelopment project.
3. Laredo, TX: Seek conversion of brownfield into waterfront recreation area
near campus of a community college.
4. Lima, OH: Focus on remediating and redeveloping 200-acre industrial park
and support ongoing river corridor redevelopment activities in order to
enhance water quality and provide greenspace.
5. Pritchard, AL: Remediate extensive organic chemical contamination of city's
water supply by using State Enterprise Zone tax credits to encourage
investment.
Sustainability Principles for Urban Infrastructure
A general guiding principle for designing innovative urban stormwater management
systems for the 21 st century is that they promote sustainable development. A popular
general definition of sustainable development is:
Development that meets the needs of the present
without compromising the ability of future generations
to meet their own needs (World Commission on
Environment and Development 1987).
2-16
-------
The following principles are suggested for sustainable infrastructure systems for the 21st
century:
1. Ideally, individual urban activities should minimize the external inputs to
support their activities at the parcel level: For water supply, import only
essential water for high valued uses such as drinking water, cooking, showers
and baths. Reuse wastewater and stormwater for less important uses such
as lawn watering and toilet flushing. Minimize the demand for water by
utilizing less water intensive technologies where possible. For transportation,
minimize the generation of impervious areas, especially directly connected
impervious areas, for providing traffic flow and parking in low use areas.
2. Minimize the external export of residuals from individual parcels and local
neighborhoods: For wastewater, export only highly concentrated wastes that
need to be treated off-site. Reuse less contaminated wastes such as shower
water for lawn watering. For storm water, minimize off-site discharge by
encouraging infiltration of less contaminated stormwater and using cisterns or
other collection devices to capture and reuse stormwater for lawn watering
and toilet flushing.
3. Structure the economic evaluation of infrastructure options to maximize the
incentive to manage demand by using commodity use charges instead of
fixed charges: For water supply, assess charges based on the cost of service
with emphasis on commodity charges. Charges should be a combination of a
level of service that specifies flow, quality, and pressure. For wastewater,
assess charges based on the cost of service with emphasis on commodity
charges. Charges should be a combination of a level of service that specifies
flow and quality. For stormwater, assess charges based on the cost of
providing stormwater quality control for smaller storms and flood control for
larger storms. Charges should be based on the imperviousness with higher
charges for directly connected imperviousness and the nature of the use of
the impervious areas and their pollutant potential. Some charge should be
assessed for pervious areas. Credit should be given for on-site storage and
infiltration. For transportation, assess charges for transportation related
imperviousness directly to users as fees per mile for travel and fees per hour
for parking in order to encourage demand management and switch to more
sustainable modes of transportation.
4. Assess new development for the full cost of providing the infrastructure that it
demands, not only within the development, but also external support services.
5. Implement policies to make drivers pay the full cost of using personal
automobiles.
2-17
-------
The following list of other goals provides additional criteria for more sustainable new
communities. These topics overlap and can be consolidated down to a much smaller
set of principles.
1. Re-develop vacant or low-density development within currently developed areas
at higher intensities.
2. Design comprehensive, mixed-use neighborhoods instead of isolated pods,
subdivisions and developments. The spaces between neighborhoods should
consist of functional open space such as farms, grazing areas, gardens, parks,
playgrounds, bikeways, jogging trails and the like.
3. Encourage telecommuting and the infrastructure necessary to make it work.
4. Do a comprehensive accounting of infrastructure costs that reflects social and
environmental costs as well as economic costs. Current investments based on
partial and incomplete accounting systems are considered to be factors in urban
sprawl and the inability of infrastructure capacity to keep pace with these urban
development patterns.
5. Develop a community designed for people first, that does not damage the natural
environment, that enables a healthy, active lifestyle, where human interaction is
an everyday event (Goldstein 1997).
6. Housing, stores, and employment will be accessible (less than 20 minutes) to
each other by walking, biking and transit (Goldstein 1997):
7. With regard to environmental impacts, the City of Dreams will have the following
benefits (Goldstein 1997):
a. Reduce energy demand by 75%.
b. Reduce water use by 65%.
c. Reduce solid waste by 90%.
d. Reduce air pollution by 40%.
Much general information on this subject is available on the internet, (e.g., see Smart
Growth Network-www.smartgrowth.org).
Sustainability and Optimal Size of Infrastructure Systems
While the notion that "bigger is better" still persists, some argue that these systems are
not sustainable. Problems with larger systems include:
1. Large organizations are necessary to manage these systems.
2. Large organizations with monopoly powers tend to be inefficient and less
responsive to changing needs.
3. Complex cost sharing arrangements need to be developed to fairly charge
each group for its share of the cost of the system.
4. Complex political institutions are needed to govern these systems that cross
city, county, and even state boundaries.
5. Part of the savings associated with regional systems results from transferring
problems from area to area so as to take better advantage of the assimilative
capacity of the receiving environment. While such solutions may reduce
2-18
-------
costs overall, they may be highly objectionable to citizens in those parts of the
service area that receive a disproportionate share of the negative effects of
such transfers, (e.g., added flood hazard , traffic noise, more polluted water).
6. Large regional systems are inefficient if recycling of treated wastewater and
stormwater is desired since it is necessary to pipe and pump this water back
through the entire system.
7. The failure of larger systems causes more serious consequences since larger
areas are affected and illicit discharges are concentrated at fewer points.
8. Customers are less aware of the nature of the problems that they cause and
are therefore less receptive to their responsibility to better manage their
demand for the service.
9. The strong tendency for urban sprawl that has accompanied the creation of
these regional systems makes them even less efficient due to the added
distribution costs associated with more dispersed development.
10. It is necessary to build large amounts of excess capacity into these regional
systems. Thus, the existing customers pay this added cost. The primary
beneficiaries of this largesse are new customers. Correspondingly, the
governing agency has a strong incentive to promote the growth of the area to
help pay for this unused capacity.
11. Regional systems serve a heterogeneous group of customers including
domestic, commercial, and industrial users. Thus, the nature of the wastes
are harder to predict and the design must be upgraded accordingly. The use
of a regional system encourages off-site discharge of wastes instead of
prevention or treatment at the source.
12. Once established, it is difficult to restructure large organizations who enjoy
monopoly power to provide the infrastructure service.
Given the above concerns, one of the main themes of this report is the need to rethink
this basic "bigger is better" premise that has guided water infrastructure development
during the past 30 years. Perhaps, bigger is not better.
Models for Evaluating Future Infrastructure
Beginning in the 1960's, large-scale efforts were made to develop urban planning
models that link land use, transportation, and infrastructure including environmental
impacts. Large simulation models were developed to support these efforts. These
models included the critical interaction between provision of infrastructure and land use.
This is particularly important in showing the impact of transportation on land use. These
early models were severely limited due to use of relatively primitive computers, lack of
good databases, and poor knowledge of the underlying cause-effect linkages of urban
dynamics (Lee 1973). Few urban models were developed after the early 1970's but a
renaissance in the development and use of these models began to occur in the early
1990s (Wegener 1994). The resurgence of interest in urban planning models in the
1990's is partially due to the renewed recognition of the need to link transportation-land
use models to urban environmental systems models.
2-19
-------
Integrated urban models to evaluate the overall efficacy of alternative growth scenarios
do not exist. However, there are individual models for water, wastewater, stormwater,
and transportation. These models need to be integrated with each other and with land
use models at both the micro (neighborhood) scale as well as the macro (urban area)
scale. Preliminary evaluations using simple models are presented in this report.
Research Initiatives Related to Urban Infrastructure
Until recently, research support has been unavailable for evaluating alternative
infrastructure systems. However, the National Science Foundation has initiated
research programs in this area. Zimmerman and Sparrow (1997) summarize the results
of an NSF sponsored workshop on integrated research for civil infrastructure. This is
the third workshop on this subject since 1993. The participants strongly recommended
a holistic view of infrastructure development. Sustainable infrastructure is defined as:
"Achieving a balance of human activity (including human settlements and population
growth) with its surroundings, so as not to exceed available resources."
Infrastructure sustainability is discussed around four topics:
1. Life-cycle engineering (LCE), that is, a process that incorporates into design
the "true costs" of construction, operation, maintenance, renewal, and any
other requirements over the expected lifetime of the facility. LCE includes
design, construction, and repair, rehabilitation, reconstruction, retirement, and
removal. Current costing methods and related institutions hamper LCE in the
following ways:
a. Incentives and statutory restrictions often favor "least-first-cost"
contracting.
b. New capital projects are often favored politically over maintenance or
rebuild contracting.
c. Tight budgets preclude field inspections, favor corrective over
preventive maintenance, and encourage the use of minimal
specifications for materials and structures.
2. Technology investment
a. Mechanisms are needed to integrate infrastructure design,
construction and maintenance. For example, integrated utility corridors
provide a way to reduce the life cycle cost of infrastructure, particularly
maintenance of subsurface infrastructure.
b. Innovative approaches for technology investment at every point in the
life cycle of infrastructure systems, (e.g. develop more durable
materials, better monitoring and diagnostic techniques, better designs,
and more rational methods for determining design safety factors
throughout the lifetime of the infrastructure).
2-20
-------
3. Performance measures
a. Research is needed on the appropriate adaptation of process control
management procedures in conjunction with advanced probabilistic
and reliability methods for urban infrastructure systems.
b. Research is needed on proper output performance measures for
infrastructure and how it relates to costs.
c. Performance measures need to be supported by direct monitoring of
the physical state of the system and changing public expectations for
use, capacity, and performance.
4. Project management
a. A new generation of simulation and optimization models are needed to
address both the new "intelligent" infrastructure, new model
characteristics, and new cultures of the consumers.
b. Encourage Design-Build-Operate (DBO) contracting mechanisms that
will promote the evaluation of projects on a life-cycle basis. At present,
using least cost criteria for design and construction leads to much
higher maintenance costs over the life of the project. If the designer
and builder also has to operate the infrastructure, they will have the
proper incentives to minimize the entire life cycle cost, and not just the
initial cost. Such procedures are already being used in Europe and
Japan.
Transportation/Land Use Strategies to Alleviate Congestion
Congestion in urban transportation systems can be alleviated by expanding the capacity
of the existing system. The capacity of the existing system can be expanded by
improved traffic engineering and rescheduling work hours, also, demand can be
managed by providing added incentives to use alternative modes of transportation,
managing parking availability, promoting more transportation efficient land use patterns,
and/or encouraging trip reduction through telecommuting or work at home options
(Deakin,1995).
Projected Future Trends
Projected general trends are:
1. Continuing migration of population to cities throughout the world. By the year
2000, more than half of the world's population will live in cities. These cities
will continue to grow in size with numerous mega-cities developing throughout
the world. Okun (1991) summarizes the migration of people to urban areas
around the world. In 1950, less than 30% of the world's population lived in
cities. This percentage will exceed 50% by the year 2000. In developed
countries such as the U.S., over 75% of the people live in cities.
2. The spatial settlement patterns of future urban development may differ
significantly from current patterns. Population is being redistributed away
from the core of the cities. Modern telecommunications could have a
2-21
-------
profound impact on settlement patterns and transportation needs.
3. Public expectations about levels and types of service are continually changing as
standards of living and life styles change.
4. The magnitude and distribution of investments in infrastructure are changing.
Government subsidies of infrastructure are decreasing in some areas, (e.g.,
wastewater treatment plants), and increasing in other areas, (e.g., major
highways and interstate expressways). The timing and lengths of budgetary
cycles are changing with efforts to better integrate life cycle costs into new
design and construction.
Origins of Stormwater in Urban Areas
Introduction
The purpose of this section is to evaluate the nature of the quantity of stormwater runoff
in urban areas and to evaluate the relative importance of various sources. Water quality
impacts are evaluated in Chapter 5.
Stormwater falls onto pervious or impervious areas. Runoff occurs after the infiltration
capacity has been exceeded. Impervious areas have a very small amount of initial
storage capacity whereas pervious areas have much larger initial storage capacities
depending on the soil type and antecedent conditions.
A primary goal of sustainable water infrastructure systems is to maximize the
management of the problem at the source, that is, the parcel or local level. Thus, it is
important to understand the movement of water at this scale. An evaluation of the
nature of the rainfall-runoff relationship at the neighborhood level is presented in the
next section. Then, detailed discussions of the nature of impervious and pervious areas
are presented in the later sections.
Rainfall-Runoff Relationships at the Neighborhood Scale
An integrated urban stormwater management program should provide a sustainable
solution to the problem of handling storms of all sizes from micro-storms to major floods.
Early studies in Chicago showed that most of the annual volume of runoff is associated
with smaller storms as indicated in Table 2-4 (APWA 1968). For this Chicago
catchment, 10.8 inches of runoff resulted from 34.7 inches of precipitation that occurred
during 122 events. About 50% of the runoff resulted from precipitation of 0.5 inches or
less, that roughly corresponds to storms that occur, once a month, on the average.
Nearly 75% of the runoff volume is from storms that result from precipitation of one inch
or less. Thus, the key point is that these smaller storms account for the majority of the
runoff volume. Similar results were reported later by Heaney et al. (1977) and Roesner
etal. (1991).
Early studies in Chicago by Harza Engineering and Bauer Engineering (1966)
demonstrated that runoff is a nonlinear function of precipitation as shown in Figure 2-4.
Up to rainfalls of two inches with corresponding runoff of about 0.6 inches, the
2-22
-------
relationship is linear with contributions only from the impervious areas, approximately an
equal mix of runoff from directly connected roofs and streets and alleys. For rainfalls
greater than two inches, runoff from pervious areas begins and becomes the major
source for rainfalls greater than four inches.
Pitt and Voorhees (1994) show the nature of runoff for a residential area in Milwaukee
as shown in Figure 2-5. For this case study, all of the runoff came from streets,
driveways, and roofs up to precipitation depths of 0.1 inches. In this range, about 80%
of the runoff came from transportation related imperviousness. As the rainfall depths
increase, the landscaped areas become more significant sources of total runoff. At the
one inch depth, landscaped areas contribute about 40% of the runoff.
These relative contributions are site specific but it is safe to conclude that the initial
runoff is the runoff from the directly connected impervious areas. Impervious area (IA)
is defined as land area that infiltrates less than 2% of precipitation that falls onto its
surface directly or runs onto this surface. Directly connected impervious area (DCIA) is
the IA that drains directly to the storm drainage system.
Table 2-4: Types of storms contributing to stormwater runoff in Chicago, IL (APWA
1968).
Precipitation
(inches)
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
3.0
Total
Average
Runoff
(inches)
0.03
0.09
0.15
0.21
0.28
0.35
0.42
0.49
0.56
0.63
0.7
0.76
1.26
Events
per year
78.00
19.80
9.60
5.20
3.20
2.40
1.30
0.92
0.53
0.36
0.22
0.14
0.53
122.20
Precipitation
(inches/yr.)
7.80
5.94
4.80
3.64
2.88
2.64
1.69
1.38
0.90
0.68
0.46
0.32
1.59
34.73
Runoff
(inches/yr.)
2.34
1.78
1.44
1.09
0.90
0.84
0.55
0.45
0.30
0.23
0.15
0.11
0.67
10.84
%of
Runoff
21.6
16.4
13.3
10.1
8.3
7.8
5.0
4.2
2.7
2.1
1.4
1.0
6.2
Cumulative
% of Runoff
21.6
38.0
51.3
61.4
69.7
77.4
82.4
86.6
89.3
91.4
92.9
93.8
100.0
2-23
-------
2.5
I
u
c
c 1.5
I
' Runoff from Strซซts and Alleys
' Runoff from Directly Connected Hoofs
Runoff from Pervious Araa
Figure 2-4. Rainfall-runoff relationships for unit area, Chicago,IL (Harza and Bauer,
1966).
0.01
Rain Depth (inches )
Figure 2-5. Flow sources for example medium density residential areas having clayey
soils, Milwaukee, Wl (Pitt and Voorhees, 1994).
2-24
-------
Imperviousness has been suggested as a good single indicator of the extent of
urbanization as far as stormwater impacts are concerned (WEF-ASCE 1998). For
example, Schueler (1994) shows the dependence of the runoff coefficient on
imperviousness. This relationship is based on evaluation of more than 40 runoff
monitoring sites as part of the Nationwide Urban Runoff Program (NURP) studies. While
a generally positive trend is evident in Figure 2-7, a large variability remains indicating
that imperviousness alone is not an adequate predictor of runoff.
Population density has been used to predict imperviousness as shown in Figure 2-8
(Heaney et al. 1977). A primary unresolved source of variability in these results is the
use of different bases for defining the service area. Some of these studies used small
areas on the scale of blocks while others used aggregate data for much larger areas
that included other land uses such as schools, parks, and commercial areas. Thus, the
results vary widely.
Previous Studies of Imperviousness
Schueler (1996) cites the results of a recent study by the city of Olympia, WA which
shows the components of imperviousness for a variety of land uses as shown in Table
2-5. Road related imperviousness is seen to comprise 63% to 70% of the total.
Schueler (1995) contends that cluster development can reduce the imperviousness by
10-50% depending on the lot size and road network. Arnold and Gibbons (1996) show
an example of the effect of cluster development in reducing imperviousness from 17.5%
to 10.7%. Schueler (1995) presents a detailed analysis of the relationship between land
use and imperviousness. He discusses alternative street designs, parking provisions,
expected imperviousness, pollutant loads, and BMP options for control.
Debo and Reese (1995) show how to adjust SCS curve numbers based on the
proportion of imperviousness that is directly connected. Unit pollutant loadings are
often expressed in terms of curb lengths. Novotny and Olem (1994) show a relationship
between percent imperviousness and curb length per unit area. The American Public
Works Association (1968) estimated curb length as a function of population density.
The use of population density as the independent variable is subject to significant error
because it can be defined in several ways. The density varies significantly depending
upon whether open space or other land uses such as streets are included in the area.
2-25
-------
LL.
U.
O
K
u.
O
UJ
3
ง
1
h
2
i
C
[
y
L
C
u
y
C
4
0
I.U
? 0.8
o
ฃ 0.7
ง 0.6
0.5
i 0.4
i
: 0.3
j
>
3 0.2
i 0.1
3
f
A
I*-'
*
^>
,
*
,
>
^
x^
*
*
ป
/
*
*
/
/'
.
i
/
A.
<
/'
,
'
I
/
/
*
0 10 20 30 40 50 60 70 80 90 100
% IMPERVIOUS
Figure 2-6. Relation of the coefficient of runoff for urban areas to imperviousness
(Schueler1994).
Table 2-5. Site coverage for three land uses in Olympia, WA (Schueler 1996).
Surface Coverage Type
1 . Streets
2. Sidewalks
3. Parking/driveways
4. Roofs
5. Lawns/landscaping
6. Open space
Total impervious surface (1-4)
Road-related impervious surface (1-3)
(Road-related as a percentage of total
impervious coverage)
Average Approximate Site Coverage, %
High Density
Residential
(3-7 units/acre)
16
3
6
15
54
n/a
40
25
(63%)
Multifamily
(7-30 units/acre)
11
5
15
17
19
34
48
31
(65%)
Commercial
3
4
53
26
13
n/a
60
86
(70%)
2-26
-------
0 10 20
persons / hectare
30 40 50
60 70 80
100
90
80
70
OT
OT
2>
OT
D
o
60-
Ul
O
Of
Ul
Q_
40
30
20
10
A
GRAHAM ET ซ.
WASHINGTON, D. C
WASHINGTON, D. C
O ONTARIO
IMPERVIOUSNESS DUE TO STREETS ONLY
0 5 10 15 20 25 30 35
DEVELOPED POPULATION DENSITY, PD persons / acre
Figure 2-7. Imperviousness as a function of developed population density (Heaney et
al. 1977).
2-27
-------
Sources of Urban Runoff
A sketch of a contemporary residential lot and associated right of way (ROW) is shown
in Figure 2-8. Each parcel consists of the development on the lot itself plus the
adjacent development in the right of way that provides infrastructure services for this
parcel, plus services for adjacent parcels. For this illustration, the overall area of the lot
plus the ROW is summarized below:
Overall lot plus ROW area, sq. ft. = 7,020
Lot area, sq. ft. = 4,980
ROW area, sq. ft. = 2,040
For this case, about 71 % of the total area is devoted to the lot and the ROW occupies
the remaining 29%. This is close to a rule of thumb that says that the ROW occupies
about 25% of the developable land area. When calculating development densities, it is
important to define whether the denominator is the lot area only, the lot plus ROW area,
or lot plus ROW plus other land uses including open space.
The percent imperviousness for the lot and ROW is 50.4% while it is only 38.2% for the
lot only. The most dramatic statistic is the breakdown of imperviousness by function.
Only 34% of the imperviousness is due to the living area itself. Nearly 60% of the
imperviousness is due to providing for vehicles. The remaining 7% of the
imperviousness is due to sidewalks.
The directly connected imperviousness (DCIA) is the most important component as far
as causing stormwater runoff quantity and quality problems. About 80% of the DCIA is
due to vehicle related imperviousness, predominantly the street and the portion of the
driveway that drains to the street. While this percentage will vary, this illustration does
indicate the dominance of vehicle related DCIA in contemporary urban development. It
is now standard practice to discharge roof runoff onto pervious areas, particularly in
lower density developments with well drained soils. Thus, rooftops are no longer the
predominant source of DCIA; rather streets and driveways have grown in relative
importance as the number of vehicles has increased. It is instructive to examine a cross
section of residential land use to generate a database from which more general
inferences can be made regarding how imperviousness is affected by land use.
Categories of Urban Catchments
A popular way to classify urban land uses is to define various categories of residential
land use, (e.g., low density, commercial, industrial, and public land uses). Associated
with each land use is an estimated imperviousness. A limitation of such general
measures is that they don't provide a breakdown on the nature of the imperviousness.
Another limitation is lack of specificity in how the area is defined as discussed above. A
2-28
-------
60,000
40,000
HOUSE
- 20,000
GARAGE
DRIVEWAY
20,000
83,000
SIDEWALK
2,000
8,000
2,000
STREET CCNTERLINC
17,000
Figure 2-8. Example urban lot.
2-29
-------
more functional way to partition urban areas is by the nature of the imperviousness and
whether it is directly connected to the storm drainage system. For residential areas, the
total land area can be divided into two major components: residential lots, and right-of-
way, as shown in Figure 2-8. The lot portion of the area is divided into the following
components:
1. House
2. Garage
3. Part of driveway
4. Yard
5. Walkway to dwelling unit
6. Pool
7. Deck/shed
The ROW portion of the area is divided into the following components:
1. One half of street consisting of driving and parking lanes
2. Curb and gutter, part of which is used as part of the parking lane
3. Pervious area between curb and sidewalk
4. Sidewalk
5. Pervious area between sidewalk and property line.
6. One half of an alley in some neighborhoods
7. Part of driveway
How Imperviousness Varies for Different Types of Urban Developments
Neighborhoods are the heart of urban development and the objective is to develop
sustainable neighborhoods. Commercial, industrial and public areas can be part of the
neighborhood or separate entities. For the purposes of this discussion, three categories
of 20th century neighborhoods are defined: pre-automobile, pre-expressway automobile,
and post-expressway automobile. The general attributes of these categories are shown
in Table 2-6.
Pre-automobile neighborhoods were laid out and developed prior to 1920 and did not
include accommodation of the automobile as an important design factor. With
automobile use becoming significant in urban areas during the period from the 1920's to
1950's, the federal government encouraged the development of suburban type
subdivisions with driveways and garages. The massive federally supported urban
expressway program began in the late 1950s and now affects virtually every major
community in the United States. The availability of expressways and the provision of
"free" parking at destination points greatly accelerated the trend towards individual
automobile travel in cities and surrounding areas. The term "automobile" is used to
cover all categories of personal motor vehicles.
2-30
-------
Table 2-6. Attributes of 20th century neighborhoods in the U.S.
Neighborhoods
Population Density
Street Connectivity
Alleys
Driveways
Parking
Dwelling Unit Size
Garages
Cars/dwelling unit
People/dwelling
unit
VMT/cap-year
Sidewalks
Type of sewer
system
Pervious
areas/dwelling unit
Land uses
Covered porches
Patios
Commercial
Industrial
Pre-
Automobile
High
High
Typical
Rare
On-street
Smaller
No
0
4-5
Negligible
Yes
Combined
Low
Mixed
Very popular
Rare
Neighborhood/
Strip
Neighborhood/
Separate
Pre-
expressway
Medium
Medium
Rarer
Some
On and off
street
Medium
One car
1
3-4
2,000-3,000
Yes
Mixed
Medium
Hybrid
Less popular
More popular
Strip
development
Neighborhood/
Separate
Post-
expressway
Low
Low
Very rare
Typical
Mainly off-
street
Larger
Two-three car
1-4
2-3
8,000-10,000
Yes
Separate
High
Separated
Less popular
Very popular
Shopping
Center
Separate
Pre-Automobile Neighborhoods
The approach taken is to evaluate a variety of residential land use patterns at the block
or subdivision level and to vary the housing density for these units in order to calculate
how directly connected (DCIA) and other (OIA) imperviousness varies as land use
changes. A standard gridiron block with data from Chicago, IL and Boulder, CO is
used. Two standard Chicago blocks are shown in Figure 2-10 (APWA 1968). This five
acre block contains 36 houses (popularly called bungalows in Chicago) within the five
acre block or an overall average density of 7.2 dwelling units per gross acre. Because
of the high density and soils with limited infiltration capacity, the downspouts from the
rooftops are connected directly to the sewers. The total imperviousness is about 57%.
The DCIA is about 40% with the houses contributing about one half of the DCIA.
Land use in an older neighborhood in Boulder, CO is shown in Figure 2-10. The block
size is identical to the Chicago blocks, (i.e., five acres in area) with a length of 660 feet
2-31
-------
and a width of 330 feet. However, unlike the homogeneous lot and house sizes in
Chicago, the Boulder lots and houses vary widely in size and shape. The alleys in
Boulder are semi-improved.
A spreadsheet was set up to estimate the nature of the imperviousness for these
traditional gridiron street patterns. Six different housing densities are placed on these
five acre blocks ranging from a high of 14.2 to a low of 2.4 dwelling units per gross acre.
All lot sizes are identical within a given category. The results are shown in Tables 2-7
for total imperviousness and 2-8 for directly connected imperviousness.
-ALLEY-
\/'
IA
X
H
J
I
I
]
I
[
'
]
[
']
I
^ r.uik LIIIST
I
(
Lsfrao! Unซ J
iX
X
[x]
X
Y
K
_
X
X
18
Let* at
Y
,/"\
33 s
X
KMT
1
X
CM
V
1
,33-,
^
-Tyjj
ra
calLo!
X
Dim en
\/*
/ \
3 ion 5
1^^
X
H
-ALLEY-
O
O Citeh B*ซ)n
Figure 2-9. Typical unit residential area, Chicago, IL (APWA, 1968).
2-32
-------
Figure 2-10. Aerial view of 10 blocks in an older neighborhood in Boulder, CO.
2-33
-------
Table 2-7. Attributes of dwelling units located on traditional grid street network-total imperviousness.
DwElliv:
BlKl
Lwng
Arai
Owfcfl
IHatat
Fomrrt
Lwng
taa
Giragt
Roof
firnmiy
m MV
Strtrt
WfUHJ
iq.lt.ni
Alty
TiansMrt
TiUI
Pervraus
Jrta
Toil Moul
sq.fLffli
Im | lirag |
Calif Trrh TaH
nw iri IIMR
9:0
1170
1171)
1.170
515
is:
a:
igt
m
T'S
fli
391
259
m
-.a
1.KH
?,ปi
1.1851
2JM
3.53*
1.7P
',802
WIS
i5!6
nl:l'
SJOBl
ซ**
5M*
2JE
386
i!4
257
911
IMS
653
tout
1jQ47
1.J3
211
42
70!
238
1.7W !
2.646
V682
WM j
5fiS*
2.11
y\
;. H:tEK wt" HMriW/'girage h lint.
1500
1100
2*0
20
2,ซQ
a:
33:
no
0
mo
M03
.:H
2.W5
9T
990
1.3ซ;
M*
1,693
*S3*
4,1*1
5,137
HUH
18.1:0
52 K
1.71
!,ซ77
2,102
1.S4J
2523
2SB
3,725
HHI
2 ฃ5
20
SJ
KT
1.WB
6.019
S.W7
25J
1.W3
Table 2-8. Attributes of dwelling units located on traditional grid street network-directly connected imperviousness.
IMS'
BtMt
LwtiS
An*
Rwf
Slit*
)q.lliCW
MiV
ปซJU
^.HiW
DC
Vt*
ToW
tm
%DC
OCU
Pjrtrj Tnffie
KC
1.17D
1.170
$:o
1.17B
MS
is?
209
2?B
139
HI
1745
24C6
1.343
J.645
UHOj
3.0J51
38 S*
38.9%
41.1J
I 58
1. 12
HI
}JS
I.C40
HO
w
1JM7
1.H
701
15?
299
399*
I.I!
4(0
7N
TSO
Hfl
SO
190
150
1.4JB
m
1305
24
I.BI-:
11ซ1
mi
2.9(0
28M
3,9*1
B..075
10.8SO
18,150
29.S
312
5.53
til
ซJ
MK
T?1 I.883
m \m
1.M!. :i,8S
HHI
KO
1,19
77B
119
rw;
2.381
33
ซi nse
ta
.xrg aii
tM
53*
11.1%
00*
32 S*
1TJ*
Tail
i-:oo*
2.COO
Sป
657
0
:5i
IM6
6.C19
Or*)!
Diimny
M.IK
4,4%
Hit
SEC
T2
Kl
ttt
2-34
-------
Imperviousness in Pre-Automobile Era
Categories 1 to 3 in Tables 2-7 and 2-8 represent the pre-automobile era and are all
served by alleys. Densities range from 5.2 to 14.4 dwelling units per acre. Garages are
assumed to exist although they probably were used for other purposes and were called
sheds. The total imperviousness for these three land uses is about 58% and the DCIA
is about 40%. The rooftops are directly connected to the sewer because of the higher
densities and lack of sufficient pervious areas to receive the roof runoff. The transition
point at which roof runoff can be discharged onto pervious areas needs to be
determined based on local conditions. Even for this pre-automobile condition,
transportation related imperviousness is over twice the imperviousness caused by the
living area. However, walkways (front, rear, and side) are a significant part of the
transportation component.
Pre-Expressway Neighborhoods
Large-scale development began after World War II with communities such as Levittown,
NY (Southworth and Ben-Joseph 1997). This residential street is typical of the design
standards for suburban developments, (i.e., wide streets with curb and gutter, sidewalks
on both sides of the street, paved driveways, and garages or carports). Most newer
suburban communities followed federal street standards promulgated by FHA during the
1930's.
Results for Pre-Expressway Era
Cases 4 to 6 in Tables 2-8 and 2-9 represent developments that accommodate the
automobile. The first phase of this transition was to eliminate alleys and construct side
drives to garages in the rear of the house. Then, garages were attached directly to the
house, and lastly the houses grew in size. The number of dwelling units per gross acre
ranges from 2.4 to 4.8. The declining dwelling unit densities reduced total
imperviousness to 41 to 54%, less than traditional developments, but not
proportionately less. The DCIA ranges from 22 to 29%, a significant decrease from 38
to 41 % associated with earlier developments. The major reduction in DCIA is due to
disconnecting roof downspouts and eliminating alleys. However, the DCIA area per
dwelling unit increases substantially from an average of about 1,800 to 3,200 square
feet due to the larger garages, driveways, and lot sizes.
Post-Expressway Neighborhoods
The availability of expressways allowed people to move even farther from the core
urban areas. The major impact of the expressways is the need for more vehicles per
family and with cheaper land and increased economic prosperity associated with a
healthy economy and the trend towards two working parents, house and lot sizes
continued to grow. Thus, contemporary houses have larger garages and driveways,
and more street frontage per house. A sample of 24 contemporary homes taken from
Sunset (1992) was used to evaluate the expected nature of imperviousness in
contemporary housing. The sample consisted of 13 single story houses and 11 two
story houses.
2-35
-------
One Story Houses: The results for the single story houses are shown in Tables 2-9 and
2-10 for total imperviousness and DCIA, respectively. No explicit street pattern is
assumed for this development. Thus, the street and sidewalk areas are
underestimated, probably by 10-15%. Development densities range from 2.0 to 5.4
houses per acre. The results indicate that total imperviousness is relatively insensitive
to housing density and ranges from 36 to 48%. Total imperviousness actually increases
as dwelling unit density decreases due to larger garages, longer driveways and more
street length per house. On the average, the living area constitutes 41 % of the total
imperviousness, but only 22% of the DCIA. Thus, the transportation component
dominates as the primary source of total, and more importantly, directly connected
imperious area.
Measured in absolute terms in terms of total impervious area per house, the results
indicate that total impervious area per house increases from about 4,000 square feet to
almost 8,700 square feet as the living area goes from 1,272 square feet to 4,284 square
feet. Parking is responsible for most of the total impervious area for vehicles, an
average of 2,041 square feet of parking compared to an average of 811 square feet for
traffic movement. Only about half of the impervious area for parking is directly
connected. Thus, its impact is lessened. Overall, streets constitute over 61% of the
DCIA. The street is used both for parking and traffic flow.
Two-story Houses: The results for the two story houses are shown in Tables 2-11 and
2-12 for total imperviousness and DCIA, respectively. No explicit street pattern is
assumed for this development. Thus, the street and sidewalk areas are
underestimated, probably by 10-15%. Development densities range from about 2.9 to
6.9 houses per acre. The results indicate that total imperviousness is relatively
insensitive to housing density and ranges from 31 to 80%. Total imperviousness
actually increases as dwelling unit density decreases due to larger garages, longer
driveways and more street length per house. On the average, the living area
constitutes 37% of the total imperviousness, but only 20% of the DCIA. As before, the
transportation component dominates as the primary source of total and more
importantly, directly connected imperious area.
Measured in absolute terms in terms of total impervious area per house, the results
indicate that total impervious area per house increases from about 2,800 square feet to
almost 6,376 square feet as the living area goes from 1,193 square feet to 3,728 square
2-36
-------
Table 2-9. Attributes of dwelling units located on traditional grid street network-total imperviousness.
(rvjril rrw M, r>x-ซi
IM*}
l**v Km
Ehtk
IMtitii
IMig
Rwt
sun
1.
11 aw
1 II7D
2 sป
190
3ป
K
s:
SI
JOI
Trunpiit
iq It.ftl
(VMW*
lป
i IDS f.sas; '-.HB
2S8* 1.5&I 2,516.
118? 1.?B7 t.3ป:
aoso
HllMllf
Prtinj
584% 20i
791
5H
ra
J. H>JM1 * 1* d- !-},'ซ' iWW
5 Hajsi
1. Uvd
I.M
MOD
1400
K!
1SSO
3.1ซ
2'5
5;-?'
s;j
Till
ra
SX
I.4D9
!B
2.ซ6
*12
901
I.T94
V'K
StM
JWJ
50
MM
4.H1
S.Itf
10.722
ซ.ซ*
HLMi,
211
5TI
9,075
IOJปD
rt.9*.
1 .-
2.1*
1.7BI
1,ซJ?
HE
771
2SS
jซa
S.725
N<*1
Jio
320
40'i
5.56"
203
.cm
J9EO
Table 2-10. Attributes of dwelling units located on traditional grid street network-directly connected imperviousness.
rwftl,
I; arw
.V3*CA1i"r
311'*
111%
DK
KM
'fr*
>-J
Hey
AM
TtW
*ปป
J4.1K ป}
;iv n
9}
11*
7JK
M4
1K :s 2.611
2-37
-------
Table 2-11. Attributes of thirteen contemporary one story houses-total imperviousness.
Number
1
2
3
4
5
a
7
8
9
10
11
12
13
Mean
%DCIA
Uwa
Area
sq ft.
1,3??
1.283
1,300
1,413
1,438
L458
1.533
2,000
2,130
2,400
2,*S3
3,755
4,294
2*,OC%
Living*
porch/storage
sq, Ft.
1 w
1.300
1,560
1468
1,476
1458
1.689
2,000
2.280
2.660
3,208
3,835
4384
2,109 2.222
25, W%
Garage
Ro-of
sq.lt
462
400
441
4B4
2S.WW
Driveway
sq.n.
640
600
860
aoo
400 400
400 eeo
576
672
B2B
550
450
500
900
600
1.000
1.200
rea aoo
30 1 .200
S2Q aoo
loa.wi
Street
sq.ft.
1,309
1.224
1,173
1,411
1.139
V309
1.190
1.428
1,486
2,006
2,0*0
2,210
'.SHS
1 ,S33
zs.w*
Walkway;
sq.ft.
38S
290
245
116
236
as
250
120
340
490
500
550
495
151
Transport
sq. Ft,
2Sป
2.484
2.733
3513
2,17-4
2.874
2.515
3J20
2,965
4.IMS
4,190
4.128
4.30*
3.20*
Impervious
Total
*q. H.
3.868
3.764
4.299
4678
3,652
032
4.205
5320
5,245
6.706
7.398
8.263
8,688
5,426
Pervtou*
Total
sq.ft.
5,858
4,78*
4,671
t.C33
4.3BB
5.SC1
4, ess
S.C36
8,6Se
1 1.936
13,002
12,537
?i.>ซ
7. 90S
Onnd
Total
sq ft.
9,356
6.5fl8
B,37C
e,711
B,g>*o
8,933
8,990
S3, lie
13,904
16.944
%
Tซ4ซl
Impervious
Am
Imp. Area
Transport/
Lining
40 3% 2.12
*t3*
47.S%
482%
454%
436%
1.91
1.76
1.BO
U7
1 97
47.3% 1 .49
3S.&%
W7%
38.0%
1.AA
130
1.52
2D,4'30 36.3%: 1.31
aDjJM
22,230
397% 1.10
381%
Oil
13,111 42 0% 2
ATM for uซlปic(eซ
Parking
sq. ft.
1,718
t.576
1,373
IJMfl
1,336
1,896
1.636
:,J>*4
',833
2, a94
2,810
j.eoa
:,766
2,041
Traffic Total
iq. ft. sq, ft
&93
548
S21
?4?
W3
9S3
Sffi
756
792
LQ92
1,080
1,170
1,053
2.411
2.224
2.404
26ป
1,939
2.585
2.:-eซ
3,0ซ
2,625
3.55^
3.6M
3.JT8
3.819
S11 2.8S1
Table 2-12. Attributes of thirteen contemporary one story houses-directly connected imperviousness.
Nuwfcer
1
2
3
4
5
&
7
8
9
10
11
12
13
Msan
Living
Area
to.fi.
Living-*
|.'i-,-h-.,l,v,i.-|
M.Jt
,272 [ 318
,2ซ3! 325
,300
.418
,428
,453
JHI
2,000
390
417
370
369
422
SOD
2,180 1 970
2,4oo i ees
2,966
3,735
l.iK
2109
80?
984
1,066
5K
Carage
Roof
*fl,W.
116
100
110
121
100
100
144
168
132
136
113
192
[M
flriv, '.v, ,,
ซ,ft
160
150
220
200
100
220
125
22G
190
250
300
200
300
130 200
Shoot
ซfcft,
'.3U9
,224
,173
.411
,139
.308
,190
1,428
,4ซe
7.C06
2.CUO
2,210
.aay
',533
Walkway
mrt.
71
$5
61
79
56
71
63
ao
3S
123
125
133
121
88
Transpon
mft.
.665
.519
.5*5
.811
.liป
.700
,522
.901
.$$1
2.51$
25? S
2,740
2.M3
1,ปป
DC Imperv.
Total
*o, n.
2.928
Z.S22
JB65
3.229
2.82S
1.158
3.211
3.901
4.043
4.813
SMfi
S.47C.
s.aw
4.059
Htrv.
Tola!
Sttrft,
6.928
5,?46
6.1 06
6.432
4,214
6,775
5,nR(l
C-.4GO
6,361
13.726
14,855
-4.320
;i,J/8
9.:72
Grand
Tolal
*gjl.
y.Die
6,568
BJ?J
9.711
6,040
3.933
8,990
13,356
l3Jj
-------
feet. Most of the total impervious area for vehicles is for parking, an average of 1,725
square feet of parking compared to an average of 662 square feet for traffic movement.
Only about half of the impervious area for parking is directly connected. Thus, its
impact is lessened. Overall, streets constitute over 63% of the DCIA. The street is
used both for parking and traffic flow.
General Conclusions Regarding the Effect of Changing Land Use
Three 20th century land use patterns: pre-automobile, pre-expressway, and post-
expressway, were evaluated. The major trend over the century has been towards
decreased development densities. Densities greater than about eight dwelling units per
acre are difficult to achieve with automobiles since insufficient parking by contemporary
standards is available. Therefore, the earlier impact of the automobile was to retrofit
existing neighborhoods and foster growth in nearby suburbs that could accommodate
automobiles as a major user of land. The development of expressways allowed people
to move even farther out of the core urban areas. This movement resulted in even
more dependence on automobiles and led to even lower development densities. Thus,
the overall results of the above analysis can be captured by showing the effect of
density on infrastructure utilization. The results are summarized below.
Higher densities significantly reduce the lengths of streets, water mains, sanitary and
storm sewers needed per dwelling unit as shown in Table 2-13 and Figure 2-11 for the
five acre block studied as part of traditional developments. The general equation for
feet of street per dwelling unit for this five acre case is:
L= Equation 2-1
DUD
where L = feet of street per dwelling unit, and
DUD = dwelling units per gross acre.
The length shown in Equation 2-1 consists of one half of the street frontage per dwelling
unit plus a prorated share of the side street length. Urban sprawl is considered to be lot
densities of three per acre or less. As indicated by Figure 2-11 , the street length per
dwelling unit increases rapidly at lower densities reaching 100 feet per dwelling unit at
two units per acre, four times the length at eight units per acre. This length per dwelling
unit is a critical parameter because the street, water main, sanitary sewer, and storm
sewer lengths all increase in the same proportion.
The service area per household increases according to the same type of relationship as
for infrastructure length, that is:
A 4356ฐ ^ *' O O
A = Equation 2-2
DUD
where A = square feet of area per dwelling unit, and
DUD = dwelling units per gross acre.
2-39
-------
Table 2-13: Relationship between street length and dwelling unit density for a five acre
rectangular block of dimensions 660 feet by 330 feet.
DUD
Dwelling
Unit Density
(dwelling
units/acre)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Street Length
Per Dwelling
Unit
(feet)
99.0
66.0
49.5
39.6
33.0
28.3
24.8
22.0
19.8
18.0
16.5
15.2
14.1
13.2
Density in Units/Acre
Figure 2-11. Relationship between street length and dwelling unit density for a five acre
rectangular block of dimensions 660 feet by 330 feet.
2-40
-------
The results are shown in Table 2-14 and Figure 2-12. Lot area per dwelling unit is also
a critical parameter in determining infrastructure costs. Larger lots generate an
increased demand for lawn watering, the largest source of variability in urban water
supply.
Another significance of lot area is that storm sewer peak design flows for small
catchments are typically calculated using the Rational formula,
= CiA
Equation 2-3
where Q = peak discharge rate,
C = runoff coefficient that depends on the land use,
/ = rainfall intensity, and
A = drainage area.
Q increases linearly with drainage area in Equation 2-3. The only offsetting factor is if
the runoff coefficient decreases as A increases. The runoff coefficient is often assumed
to equal the imperviousness as shown in Figure 2-13. Using a database of DUD as a
function of total and DCIA developed as part of this study, a relationship between
imperviousness and DUD was derived. The results, shown in Figure 2-14, indicate that
total imperviousness decreases from about 60% at a DUD of 10 to about 40% at a DUD
of two. The net effect, shown in Table 2-15 is more than a three-fold increase in CA
and, therefore, peak discharge rate, as densities decrease from 10 to two DU/gross
acre.
Table 2-14. Effect of dwelling unit density on CA in the Rational formula
DUD
Dwelling Unit
Density
(dwelling
units/acre)
2
10
A
Lot Area
Per Dwelling
(sq. ft.)
21,780
4,356
I
Imperviousness
(%)
40
60
CA
In
(sq. ft.)
8,712
2,616
The preceding results imply that serving contemporary lower density residential
developments is significantly more expensive per dwelling unit than it is for higher
density developments. Is this cost reflected in the charges for services rendered? If the
new users paid system development charges (SDC) that covered the cost of the local
improvements, then a significant part of this added cost is equitably assigned. Most of
the charges for water supply are assessed based on water use. Per capita indoor water
use is fairly constant. However, outdoor water use depends on the demand for
irrigation water which ranges from insignificant in the northeastern U.S. to dominant in
the arid southwestern U.S. If irrigation is not a significant water use and SDC's were
2-41
-------
not assessed, then the lower density developments are being subsidized since they
require more piping per unit of water delivered. If irrigation is significant, then the equity
of the charges depends on the charge for outdoor water use. Wastewater charges are
either fixed per household or assessed based on indoor water use. This charging
procedure is unfair to people living in higher density areas since they use less piping per
family. Stormwater charges are a fixed amount per month, or are based on impervious
area. Only in the latter case are charges assessed in proportion to the contribution to
the problem.
Table 2-15: Relationship between dwelling unit density and area per lot.
DUD
(Dwelling Unit
Density)
(dwelling
units/acre)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Lot Area
(sq. ft.)
21,780
14,520
10,890
8,712
7,260
6,223
5,445
4,840
4,356
3,960
3,630
3,351
3,111
2,904
2-42
-------
25,000
6810
Dwelling Units/Acre
Figure 2-12. Relationship between dwelling unit density and area per lot.
1
0.9
0.8
+-ป
S 0.7
'o
E 0.6
0)
O 0.5
it 0.4
O
0.3
0.1
10
20
30
40
50
60
70
80
90
100
Watershed Imperviousness ( % )
Figure 2-13. Watershed imperviousness and the storm runoff coefficient (WEF/ASCE
1998).
2-43
-------
.2 0.5
I
E 0.4
Dwelling Units/Acre
Figure 2-14. Effect of dwelling unit density on imperviousness.
In summary, overall dwelling unit density is a good measure of the impact of residential
development on infrastructure. Densities above about eight dwelling units per acre are
difficult to achieve in areas that are dependent on the automobile for transportation
since there is insufficient space to accommodate the automobile with existing land use
zoning requirements.
The quantity of stormwater runoff per person has grown dramatically during the past
century. The following factors are the major causes of this growth:
1. The introduction of automobiles into cities: Automobiles are very inefficient
people movers in cities with regard to the space and generation of pollutants. A
vehicle weighing 2,500 to 4,000 pounds is used to carry a 150 pound person
around the city. This vehicle is only used about 1-5% of the time. When not in
use, it must be parked. Each off-street parking space uses 300-400 square feet
of impervious area. In residential areas, transportation related imperviousness
accounts for over 65% of total imperviousness and nearly 80% of the DCIA.
Within residential neighborhoods alone, about 1.25 to 2.0 square feet of
impervious area is generated for transportation for every square foot of living
area. Similar ratios exist for commercial areas.
2. The trend towards larger houses: House sizes have grown significantly in the
past 40 years from about 1,000 square feet to over 2,000 square feet as families
move to outlying areas.
3. The trend towards larger lots: Lot sizes have also grown significantly as families
provide recreation and open space on each lot as opposed to using common
2-44
-------
areas. Lot sizes have also had to grow to accommodate larger garages and
driveways.
4. The trend towards smaller families: Smaller family sizes and larger houses
cause the need for support infrastructure per capita to increase accordingly.
5. The green trend of providing more open space as part of the development: This
open space further reduces densities and increases sprawl. Properly designed,
some or all of this open space could provide essential water infrastructure
functions such as stormwater retention.
Given that demands for stormwater management have increased dramatically due to
the pervasive influence of the automobile, the trend towards lower density sprawl
development, and the desire for open space, can any of these patterns be changed?
The individual sources of imperviousness and their nature are discussed in the following
sections.
Components of Urban Land Use and Stormwater Problems
The components of urban land use are examined in this section. For each component,
the relative importance as a source of stormwater quantity and quality problems is
discussed. The controllability of stormwater from each component is then analyzed.
Streets and Highways
Urban street patterns have changed during the 20th century, with the automobile having
a major influence on street design at all levels. Southworth and Ben-Joseph (1995)
summarize this evolution. They trace the major change in philosophy for street design
to the 1930s when the federal government became involved in developing guidelines for
subdivisions as part of its program to insure home mortgages. The traditional pattern is
the gridiron with typical block dimensions of 1/8 by 1/16 of a mile as was shown earlier.
The most radical departure from this pattern was the Radburn development in New
Jersey that used narrower streets in the neighborhood.
In 1936, the Federal Housing Administration (FHA) rejected the grid pattern for
residential neighborhoods, and has continued this policy of preferring other street
layouts (Southworth and Ben-Joseph 1995). Their primary reasons for rejecting the
gridiron pattern are:
1. It requires more paved area than necessary because all residential
streets are built to the same specifications.
2. It requires more expensive type of pavement since the traffic is
dispersed throughout the neighborhood and thus the streets must be
designed to a higher standard.
3. This heavier traffic demand creates a hazard.
2-45
-------
4. The gridiron layout is monotonous and uninteresting.
The FHA recommended a hierarchical street pattern. For residential streets, they
recommended curvilinear alignments, cul-de-sacs, and courts. Desirable design criteria
promulgated by the FHA included (Southworth and Ben-Joseph 1995):
1. Layout should discourage through traffic.
2. Minimum width of a residential street should be 50 feet with 24 feet of
pavement, eight foot planting/utility strips and four foot walks.
3. Cul-de-sacs are the most attractive street layout for family dwellings.
4. Minimum setbacks for streets should be 15 feet.
5. Front yard should avoid excessive planting, for a more pleasing and
unified effect along the street.
These early FHA guidelines had a tremendous influence on residential development in
the United States because of their financial leverage over developers and home buyers.
The Institute of Transportation Engineers (ITE) has also had a major influence on
residential street design. Their perspective is heavily influenced by traffic flow and
parking considerations. They recommend (Southworth and Ben-Joseph 1995):
1. Right of way minimum of 60 feet.
2. Pavement width of 32-34 feet.
3. Cul-de-sacs should have a maximum length of 1,000 feet with a 50-
foot radius at the end.
4. Parking lanes should be 8 feet in width.
The influence of these street design standards on drainage and stormwater
quality does not seem to have been a significant factor in the decision making
process.
The American Association of State Highway and Transportation Officials (AASHTO) has
been responsible for developing the design standards for highways and streets. The
primary reference is A Policy on Geometric Design of Highways and Streets (AASHTO
1984).
According to Khisty (1990), 10-13 foot lane widths predominate in the United States with
12 feet being the most common. The use of 11 foot lane widths is acceptable in urban
2-46
-------
areas due to higher right-of-way costs. Ten-foot lane widths are only acceptable on low
speed urban streets.
Ewing (1996) divides residential streets into the categories of arterial, collector/sub-
collector, and access. Four types of residential streets (i.e., non-arterials) exist. They
are:
1. Collector
2. Sub-collector
3. Access-looped
4. Access-dead end
Southworth and Ben-Joseph (1997) provide a history of urban streets, a critique on
current practices, and project the expected nature of streets in urban areas. They
estimate that, worldwide, more than one third of all developed urban land is devoted to
roads, parking lots, and other automobile infrastructure. In the urban U.S., about one
half of the land is used for this purpose. In automobile oriented cities like Los Angeles,
the percentage increases to two thirds (Hanson 1992, Renner 1988). These estimates
are compatible with the results presented in the previous section.
Traditional gridiron street patterns were rejected as bad practice beginning in the 1930's
based on recommendations from the federal government. They are enjoying a
comeback as part of the interest in the new urbanism. Chellman (1997) provides a
current summary of the pros and cons of traditional streets for neighborhoods. Features
of traditional streets include a high degree of connectivity that maximizes mobility for
non-motorists.
Transportation engineers tend to design streets to maximize convenience for the
automobile subject to safety constraints. Recently, designers have attempted to recast
the purpose of streets as multi-purpose components of the community with much more
of a pedestrian orientation. Shared streets provide a multi-purpose use of residential
streets. These streets have gained favor internationally but have not yet gained
widespread acceptance in the U.S. Key impediments in the U.S. include dependency
on automobiles, and concerns of liability if existing street standards are changed.
Portland, OR is one of the few cities in the U.S. that is rethinking its approach to
residential streets with its skinny streets program (Southworth and Ben-Joseph 1997).
They have reduced street widths to 20-26 feet and have installed many traffic calming
devices.
Streets have the potential to play a major role in stormwater management. Walesh
(1989, Chapter 5) presents an analysis of the ability of a typical urban street, with curb
and gutter, to temporarily convey or store stormwater runoff from major runoff events.
Skokie, IL implemented an innovative approach to its streets by using them to
intentionally convey and store stormwater in a controlled fashion so that combined
sewers do not surcharge and back up into basements (Walesh and Carr, 1998).
2-47
-------
Stormwater control is achieved in this cost-effective system using on-street berms
coupled with catch basin flow regulators and, where needed, subsurface tanks.
Street Classification and Utilization
The Federal Highway Administration (FHWA) tabulates a variety of street related
statistics that can be obtained on the internet at http:/www.bts.gov/cgi-
bin/stat/final_out.pl. Results for urban areas in the United States are shown in Table 2-
16. The major traffic carrying components of the highway system constitute only about
9% of the road mileage in urban areas. Local streets that carry little traffic constitute the
bulk of the mileage, nearly 70%. Parking is allowed on the lesser used streets; thus,
most of the parking is associated with local and collector streets. While the interstates,
freeways, other expressways, and principal arterial streets constitute only 9.1% of the
miles, they carry 58% of the traffic. At the other extreme, local streets, constituting
69.5% of the street length, carry only 13.8% of the traffic. Thus, in terms of managing
imperviousness, the lesser used local streets are the prime candidates for evaluating
whether they could be reduced in size.
The results of Table 2-16 also suggest that the primary sources of traffic related
stormwater pollution are the intensively used street systems. This may suggest a
control strategy of providing more treatment for these intensively used streets. This
much smaller impervious area may be more amenable to control than trying to deal with
the entire impervious area of the city.
Table 2-16: Street mileage in the U.S.
Urban
Interstate
Other
freeways/expressways
Other principal arterial
Minor arterial
Collector
Local
Total Urban
Miles of
road
13,307
9,022
53,044
89,013
87,918
574,119
826,423
% of urban
1.6%
1.1%
6.4%
10.8%
10.6%
69.5%
100.0%
Recommendations for Residential Streets
Southworth and Ben-Joseph (1997) recommend the following principles for future
residential streets:
1. Support varied uses of residential streets including children's play and adult
recreation.
2-48
-------
2. Design and manage street space for the comfort and safety of residents.
3. Provide a well-connected, interesting pedestrian network.
4. Provide convenient access for people who live on the street, but discourage
through traffic; allow traffic movement, but do not facilitate it.
5. Differentiate streets by function.
6. Relate street design to the natural and historical setting.
7. Conserve land by minimizing the amount of land devoted to streets.
Contemporary texts on highway engineering do not deal with urban runoff problems.
Khisty (1990) cautions of the need to evaluate air pollution and noise impacts as part of
highway design. He doesn't mention highway runoff as a problem. Wright and
Paquette (1996) describe conventional highway drainage design but do not discuss
stormwater quality problems or the detrimental off-site impacts from highway runoff.
The FHWA has sponsored several studies to address the issue of stormwater problems
associated with highways. Young et al. (1996) present a detailed overview of highway
runoff quality problems. For a more current view from FHWA on whether they consider
highway runoff to be a serious problem, see
http://www.tfhrc.gov/hnr20/runoff/runoff.html.
Streets and Stormwater Runoff
Whether residential streets are laid out in a grid-iron, curvilinear, or cul-de-sac format
does not appear to have a major impact on the quantity of stormwater runoff per capita.
The curvilinear and cul-de-sac layouts tend to have a larger impact per capita because
of lower development densities. Schueler (1995) summarizes current national design
standards for residential streets as shown in Table 2-17. Parking requires about eight
feet of space and traffic lanes require about 10-12 feet per lane. Thus, streets with two
way traffic and parking on both sides of the street would be 36 to 40 feet wide, if multi-
purpose use is not incorporated in the design.
Average daily traffic (ADT) in vehicles per day is the common indicator of the utilization
of streets for traffic. Schueler (1995) summarizes the expected traffic flow for various
ADTs assuming 10 trips per dwelling unit per day and that the number of trips in the
peak hour is 10% of the daily trips. The results are presented in Table 2-18 (Schueler
1995). As Schueler points out, for ADTs of 25 or less, it is reasonable to share parking
and traffic lanes. Unfortunately, many cities have adopted regulations that require wide
residential streets even in areas with little or no traffic.
Parking
The Institute of Transportation Engineers (ITE) recommends (Southworth and Ben
Joseph, 1995) that on-street parking lanes should be eight feet in width and that
driveway widths should be a minimum of 10 feet for one car, with a 20 foot-wide curb
cut (five-foot flare on each end). According to Shoup (1995), off-street parking space
per vehicle ranges from 300 to 350 square feet per space. This square footage
includes the space itself, the access aisles, and the entry, exit area.
2-49
-------
Table 2-17. Condensed summary of national design standards for residential streets
(Schueler1995).
Design Criteria
Residential Street Categories
Minimum Street Width
Additional Right of Way
Design Speed, Level Terrain
Curb and Gutter
Cul-de-sac Radii
Turning Radii in Cul-de-sac
AASHTO
1
26ft
24ft
30 mph
generally required
30ft
20ft
ITS
3, depending on
use density
22-27 ft>2 du
28-34 ft @2-6 du
36 ft< 6 du
24ft
30 mph
generally required
40ft
25ft
HEADWATER STREETS
4, depending on ADT
16 ft (<1 00 ADT)
20 ft (100-500 ADT)
26 ft (500-3000 ADT)
32 ft (>6 du/ac)
8 to 16 ft
15 to 25 mph
not required on collectors
30ft
17ft
Table 2-18. Relationship between number of dwelling units, traffic generation, and
residential congestion (Schueler 1995).
No. of Single
Family Homes
5
10
25
20
75
100
150
300
Average
Daily Trips
50
100
250
500
750
1000
1500
3000
Peak Trips
Per Hour
5
10
25
50
75
100
150
300
Minutes between
cars (average)
30
15
6
3
2
1.5
1
30 sees
Minutes between
cars (peak)
12
6
4
1.5
45 sees
35 sees
20 sees
1 0 sees
Shoup (1995) and Wilson (1995) summarize the origin of parking "requirements" in
urban areas and the overall impact. According to Shoup (1995), motorists report free
parking for 99 percent of all automobile trips. About 95% of automobile commuters say
that they park free at work. A primary reason for such high use of cars to commute to
work is that employers pay for parking. The average for seven case studies of the
impact of parking fees on driving behavior is that 72 cars are driven to work per 100
employees if the employer pays for parking while only 53 cars are driven to work per
100 employees if the employee pays for parking (Shoup 1995). Recent state
legislation in California requires employers to allow non-auto using employees to
receive an equivalent cash payment to the amount of the subsidy for parking.
2-50
-------
Between 1975 and 1993, the average number of parking spaces required by cities per
1,000 square feet of office space increased from 3.6 to 3.8 spaces (Shoup 1995).
According to Wilson (1995), zoning codes typically require between three and five
spaces per 1,000 gross square feet of office building area, with four spaces being the
most popular requirement. At 350 square feet per parking space, this corresponds to
1.05 to 1.75 square feet of parking per square foot of office space. Similar ratios have
been obtained for residential areas.
The actual estimate of saturation demand for parking is 2.4 spaces per 1,000 square
feet of office space for driver paid parking to 3.1 spaces per 1,000 square feet for
employer paid parking (Shoup 1995). According to Shoup (1995), over 91 % of cities
required more than this saturation demand. Wilson (1992) estimated an average
requirement of 4.1 spaces per 1,000 square feet in southern California, with the average
peak parking demand being only 56% of this capacity.
The primary justification for high parking requirements is to avoid spillover of parking
from one parcel of land to others. However, if all facilities are designed for peak
demand, often specified as the demand that only occurs 15 to 30 hours per year, then,
by definition, large amounts of excess capacity will exist in the system since these
peaks are not coincident. According to the Urban Land Institute (1982), specifying a
design hour of the 20th busiest hour of the year, leaves spaces vacant more than 99%
of the time and leaves half the spaces vacant at least 40% of the time.
Existing parking guidelines have evolved from observing practice around the United
States. However, the database is observations on consumer behavior in lots where
parking is provided free of charge. Thus, the existing standards are for the demand for
parking if parking is free. According to Shoup (1995), virtually no research has been
done to determine the optimal amount of parking since parking requirements are usually
mandated by the local government agency. If a private developer was free to establish
the amount of spaces to provide for his development, the developer would be expected
to do a benefit-cost analysis and determine the number of spaces such that his net
revenue was maximized.
Many residential streets carry relatively few vehicles each day. For example, streets
serving less than 25 homes are so lightly traveled each day ( and during peak hours)
that shared parking and moving lanes make sense
The requirement for parking is typically estimated from the ITE parking manual (1987).
Sample parking requirements are shown in Table 2-19, from Schueler (1995).
According to Arnold and Gibbons (1996), the City of Olympia, WA found not only
parking oversupply with vacancy rates of 60-70%, but also developers building an
average of 51 % more spaces than required by the City of Olympia.
2-51
-------
Table 2-19. Parking demand ratios for selected land uses and activities (Schueler
1995).
[Land Use
[Parking Space Ratio Used [Range |
Single Family Homes
Townhouses
Professional Office
Hotel/Motel
Retail
Convenience Store
Shopping Center
Movie Theatre
Gas Station
Industrial
Golf Course
Nursing Home
Day Care Center
Restaurant
Marina
Health Club
Church
High School
Medical/Dental Office
2 spaces/du
2.25 spaces/du
1 space/200 sf gfa
1 space/guest room
1 space/250 sf gfa
1 space/300 sf gfa
1 space/200 sf gfa
1 space/4 seats
2 spaces/pump (and 3 spaces)
1 space/1 000 sf gfa
4 spaces/hole
1 space/3 beds
1 space/8 children
1 space/50 sfg la
0.5 space/slip
1 space/1 00 gfa+es
1 space/5 seats
many diverse ratios
1 space/1 75 sf gfa
1.5-2.5
1.5-2.5
150-330
0.8-1.25
200-300
1 00-500+es
150-250
3.3-5
500-1200
3-6.5
2-4+es
4-10+es
0-200
0.26-0.7+es
100-150
4-6
100-225
Notes: du=dwelling unit, sf=square feet, gla=gross leasable area, es= employee
spaces, gfa=gross floor area.
A popular treatment option for parking lots is to deploy street sweepers. Street
sweepers are also used for aesthetic purposes. Street sweepers pick up solids and
debris. They are much less effective in removing other pollutants. Of course, street
sweeping has no impact on the quantity of stormwater runoff. Another potentially
effective method is to use porous or permeable pavement to reduce the runoff rates
from parking areas.
An important question with regard to parking is the tradeoff between on-street and off-
street parking. With contemporary subdivision design, the house has a two or three car
2-52
-------
garage, a driveway, and parking on the street in front of the house. In some cities,
overnight parking on streets is prohibited, thereby increasing the need for off-street
parking. A careful reexamination of these policies might show that current
neighborhood parking requirements are overly conservative.
Lot Size
Lot sizes and associated dwelling unit densities were discussed previously with regard
to estimating imperviousness. Lot size is seen to be a very good overall indicator of the
amount of infrastructure needed to support residential development. Trends toward
more automobiles and larger houses and a desire for "privacy" have resulted in much
larger lot sizes. Demand for larger lot sizes might be reduced if the full costs of these
larger lots were assessed on the property owners. In addition to promulgating
regulations with regard to right-of-ways, cities often specify lot densities and minimum
requirements (Schueler 1995). These minimum setback and related requirements
further reduce allowable densities. As with right of ways, it is advisable to revisit these
requirements for larger lot sizes.
Dwelling Unit Footprint
Urban dwelling units vary greatly in size as illustrated by these typical units and size
ranges:
1. Single room: 100-300 sq.ft.
2. Studio apartment: 300-500 sq. ft.
3. One-bedroom unit: 400-700 sq. ft.
4. Two-bedroom unit: 600-1,200 sq. ft.
5. Three-bedroom unit: 1,200-2,500 sq. ft.
6. Four-bedroom unit: 1,800-4,000 sq. ft.
Because of increasing affluence and more affordable housing, the median size of
dwelling unit per family has steadily increased since World War II. For example, the
median size of home increased from 912 square feet in 1948 to 1,113 square feet in
1963 (ULI 1968, p. 38).
The footprint of the dwelling unit (DU) is the amount of land it occupies. For single
story DU's, the sizes of the DU and the footprint are very similar. The footprint is slightly
larger due to roof overhang. The footprint is much less than the DU area if multiple
level construction is used.
Stormwater runoff from buildings depends upon the roof area and whether the roof
downspouts are directly connected to the storm sewer system. At densities of eight or
more units per gross acre, the roof area should probably be connected directly to the
stormwater control system because insufficient pervious area exists on the property
itself. Treatment of roof runoff consists of controlling sources of atmospheric deposition,
changing to more benign roofing materials, periodic cleaning of gutters, and
2-53
-------
disconnecting downspouts. The primary demand management approach is to
encourage smaller roof areas by constructing multi-level buildings.
Covered Porches and Patios
The footprint of the DU is increased if covered porches are included in the house.
Covered porches are an icon of traditional neighborhood development. One reason that
porches fell out of favor is traffic noise. Porches add imperviousness to the property
and appear to be regaining popularity. However, porches are a minor source of
imperviousness and much of this imperviousness is not directly connected. Thus, no
detailed evaluation of porches is included.
Patios may be constructed of permeable or impermeable material. They typically drain
to adjacent pervious areas. Also, patios are not a major source of pollutant loadings.
Thus, no separate analysis of patios is included.
Garages and Carports
Garages have emerged as an important land use in urban areas during the 20th century.
Automobiles require about 200 square feet of garage space per car. As the number of
automobiles has continued to increase, so has the number of garage spaces in DU's.
Two and three car garages are now the norm for new house construction. The primary
runoff from garage areas is from the rooftop. Thus, the impact depends upon whether
the roof downspouts are directly connected to the sewer system or discharge to
adjacent imperviousness such as driveways.
Treatment of roof runoff consists of controlling sources of atmospheric deposition,
changing to more benign materials, and disconnecting downspouts. The primary
demand management technique for garages and carports is to reduce the demand for
the number of cars. In the United States, there are over 200 million cars for 250 million
people. This corresponds to about one vehicle for every licensed driver in the United
States. It is possible to have the number of cars per capita continue to increase as
people have more than one car per capita.
Driveways
Driveways have become an important source of imperviousness in the 20th century as
new developments had to accommodate a growing number of automobiles. The ITE
(Southworth and Ben Joseph 1995) recommends minimum driveway widths of 10 feet
for one car, with a 20 foot-wide curb cut (five-foot flare on each end). Driveways
associated with garages are also an important land use. Four types of driveways need
to be considered based on the location and orientation of the garage:
1. Attached, front facing garage
2. Attached, side facing garage
3. Attached, rear facing garage
4. Detached garage in rear of lot
2-54
-------
Attached, Front Facing Garage: If the garage faces the street and is attached
to the house, then the driveway width is usually the width of the number of garage
spaces, or about 9-10 feet of width per car. The length of the driveway depends on the
house setback. Minimum driveway lengths are dictated by having sufficient length so
that a car can pull into the driveway and not block the sidewalk. Thus, a minimum
driveway length is the sum of the distance from the street to the sidewalk (0-15 feet)
plus the width of the sidewalk (four-six feet) if there is one plus the length of a car space
or about 20 feet, or a total minimum driveway length of 20-41 feet. The extra house
setback distance must be added to this minimum distance to get the total distance. For
many houses, the paved area for the driveway exceeds the impervious area of the
garage. Some, if not all, of the driveway drains to the street, thereby creating a
significant source of directly connected impervious area.
Attached, Side or Rear Facing Garage: If the garage entrance faces the side
of the house, then a narrower driveway from the street to the house can be used, (e.g.,
12 feet). However, this savings in width is offset by the need to provide a turning area
so that the cars can maneuver to enter and exit the garage. This added turning area
adds significant paved area.
Detached Garage in Rear of Lot: If the garage is detached and located at or
near the rear of the lot, then a longer driveway is needed to extend from the street to the
rear of the house. The width of this driveway increases in front of the garage to allow
cars to enter the various bays. Of course, if an alley exists, then the driveway distance
is minimal.
As a low intensity use, driveways are good candidates for porous and permeable
pavements or simply paving only parallel strips for the wheels. Another effective control
is to route driveway runoff onto adjacent pervious areas instead of directly to the street.
This can be done by putting a crown on the driveway as is done for streets.
An effective demand management to reduce the demand for driveways is to reduce the
demand for automobiles. Another possibility is to better utilize on-street parking.
Pervious Area on Property
The pervious area on the property is used primarily for lawns, gardens, and wooded
areas. This land is used for aesthetic appeal, and recreation for people and pets.
Under proposed innovations, this pervious area will be used more intensively to infiltrate
stormwater from adjacent impervious areas as well as from precipitation directly onto its
surface. At present, pervious areas do receive some of the runoff from impervious
areas, primarily from roofs, patios, and some parts of the driveway. Thus, it is important
to determine the infiltration capacity of these soils. The infiltration capacity depends on
the soil type. Pervious areas can be graded to provide some on-site detention of
stormwater, that could then be reused for lawn watering or other purposes. Prince
George's County (1997), MD has developed the idea of "functional landscapes" for on-
site management of stormwater.
2-55
-------
Alleys
Alleys are regaining popularity as part of new urbanism designs. Alleys can be found in
older neighborhoods. They provide access for garages and garbage pickup and other
deliveries. Alleys eliminate the need for driveways and thereby permit narrower lot
widths. Typical alley widths range from 12 to 16 feet. In addition to this pavement
width, aprons to the garages on either side of the alley are needed.
Boulder, CO specifies a 20 foot right-of-way width for alleys. The width of the alley is
controlled by the required turning radius for vehicles entering and exiting from the
garages and open parking areas. From a safety point of view, alleys greatly minimize
the traffic and pedestrian safety hazards associated with vehicles entering and backing
out of driveways onto the street. Runoff from alleys is directly connected to the storm
sewer system. The runoff moves along the alley by overland flow until it reaches the
street inlet. Treatment options would be the same as for other impervious areas with
low traffic and parking rates. The demand for alleys can be eliminated by using
driveways. The tradeoff on the amount of pavement used for alleys vs. driveways
depends on the lot geometry.
Sidewalks
Attractive sidewalks are an inducement to walking. According to Chellman (1997),
about 10% of Americans walked to work in 1960. By 1990, the percentage walking to
work had decreased to 4%. Sidewalks are an integral part of older cities. With lower
density urban development, the need for sidewalks is less critical. If the housing density
is very low, then people can walk in the street. Also, a single sidewalk can be used
instead of having a sidewalk on either side of the street. Sidewalks can be located
adjacent to the street or separated by a six to seven foot wide planting area. The ITE
(Southworth and Ben Joseph, 1995) recommends sidewalks with a minimum width of
five feet on both sides of the street. Sidewalks are typically constructed of reinforced
concrete.
The ULI (1968) recommends sidewalks on both sides of the street if the density
exceeds six houses per net acre. They recommend five foot wide sidewalks along
collector streets and four foot sidewalks on minor streets. Chellman (1997)
recommends sidewalk widths of five feet to provide sufficient room for pedestrians to
pass without crowding.
Sidewalks typically drain to pervious areas allowing the runoff to infiltrate into the
ground. The notable exception is when the sidewalks are located immediately adjacent
to the streets; then the sidewalk runoff becomes directly connected since the drainage
goes directly onto the streets. A traditional treatment is sweeping the sidewalk areas to
keep them clean and to provide trash containers to discourage littering. Sidewalks can
be eliminated if the street is safe for non-vehicular use. See the section on streets for a
discussion on this topic.
2-56
-------
Curb and Gutter and Swales
The curb and gutter serves a number of functions in residential street design including
drainage, providing a barrier for vehicles going from the lot to the street or vice versa,
and aesthetics. Two primary types of curb and gutter are the barrier curb and the rolling
curb. An alternative is to eliminate curb and gutter and allow street runoff to flow onto
adjacent pervious areas. The curb and gutter are about two feet in width. The ITE
(Southworth and Ben Joseph, 1995) recommends vertical curb with gutters. Rolled
curbs are not recommended. However, the ULI (1968) recommends rolled curbs for
most residential areas because they avoid curb cuts for driveways.
According to Khisty (1990), curbs are used for the following reasons:
1. Drainage control
2. Pavement-edge delineation
3. Right-of-way reduction
4. Aesthetics
5. Delineation of pedestrian walkways
6. Reduction of maintenance operations
Planting Strip Between Street and Sidewalk
Many subdivision regulations require a planting strip to separate the sidewalk and the
street. The ITE (Southworth and Ben Jospeh 1995) recommends planting strips on
both sides of the street with a minimum width of six to seven feet and with the planting
strip draining towards the street. A 1990 revision of these standards decreased the
minimum planting width to five feet. Boulder, CO specifies an eight foot wide planting
area. Planting strips with a width of 15 feet are popular in the western suburbs of
Chicago. These planting strips provide a buffer between the street and sidewalk. They
also provide a planting area within the right of way for trees. Early subdivision
regulations promulgated by the federal government suggested two trees should be
planted on each lot. Drainage from these planting areas is directed towards the street.
No citations could be found regarding how these areas could function as part of the
stormwater drainage system. They could be expected to attenuate noise and air
pollution effects to a limited degree.
Overall Right of Way
Required right of way width dimensions for Boulder, CO are (Boulder 1982):
1. Bikeway: 12ft
2. Alley: 20ft
3. Residential: 48ft
4. Residential collector: 68ft
5. Collector: 81 ft
6. Arterial: 130ft
7. Freeway: Use AASHTO standards
2-57
-------
To this base are added medians, added travel lanes and speed changing lanes, and
turn lanes. These right-of-way requirements are typical. The key control option is to
take a hard look at existing right-of-way requirements, especially in residential areas, to
see whether the requirements could be modified to reduce the generation of impervious
area that is providing little or no added value and to encourage the more effective use of
pervious areas within the right-of-way.
Will Americans Reduce Auto Use?
Dittmar (1995) outlines a broader context for transportation planning that incorporates
some of the above concepts for developing more sustainable transportation systems. In
his conclusions, he discusses the feasibility of reversing the trend since World War II of
increasing reliance on the automobile. Dittmar says:
In discussions of the issues with transportation
officials, their most frequent initial assertion is that
Americans love cars and cherish driving, and that any
reform effort is therefore somehow doomed. Running a
close second are the assertions that Americans are
voting with their gas pedals by choosing exurbia, and
that building more roadways is simply giving folks what
they want. I don't believe this is true. People are
responding to a set of signals our society gives them by
building ring roads and beltways, subsidizing free
parking and suburban development through utility
infrastructure, and providing tax incentives that favor
car use and suburban home ownership. These signals
favor continued sprawl and reliance on cars. Changing
these endemic signals by creating incentives to live in
the city, eliminating tax biases toward cars, and
enhancing livability can send the public new signals.
With regard to streets, parking, and other major sources of imperviousness, engineers
have been the ones who have promulgated these regulations. Hopefully, they can also
take the lead in modifying them to create more sustainable communities.
Summary and Conclusions
The results of this discussion on the nature of imperviousness in urban areas show that
the quantity of urban stormwater generated per dwelling unit has increased dramatically
during the 20th century due to the trend towards more automobiles which require more
streets and parking, and the trend towards larger houses, all combined on larger lots.
Commercial and industrial areas likewise need much more parking per unit of office
space than they did before automobiles. Interestingly, the square footage for residential
and commercial areas is less than the support parking requirements. Modern practices
dictate devoting more of the city landscape to parking than to human habitat and
commercial activities. The net result of this major shift in urban land use is low density
2-58
-------
sprawl development that generates over three times as much stormwater runoff per
family than did pre-automobile land use patterns. Much of these requirements for more
and wider streets and parking have been mandated in order to improve the
transportation system. Ironically, unlike water infrastructure, these services are not
charged directly to the users. Rather, they are subsidized by the general public
including non-users. Options for changing this pattern are presented in Chapter 3.
2-59
-------
References
AASHTO. (1984). A Policy on Geometric Design of Highways and Streets. Washington,
D.C.
Akbari, H., S. Davis, S. Sorsano, J. Huang, and S. WinnettEds. (1992). Cooling Our
Communities-A Guidebook on Tree Planting and Light-Colored Surfacing. U.S.
Environmental Protection Agency, Washington, D.C., 217 p.
Amekudzi, A.A., N.O. Attohokine, and S. Laha (1997). Brownfields Redevelopment
Issues At The Federal, State, And Local Levels. J. Environmental Systems, Vol. 25(2),
p. 97-121.
American Public Works Association (1968). The Causes and Remedies of Water
Pollution From Surface Drainage in Urban Areas-Research Project No. 120. Final
Report to Federal Water Pollution Control Administration-WP-20-15, Washington, D.C.
Arnold, Jr., C.L. andC.J. Gibbons (1996). Impervious Surface Cover-The Emergence
Of A Key Environmental Indicator. Jour, of the American Planning Assoc., Vol. 62, No.2,
p. 242-258.
Barnett, J. (1992). Sustainable Development: How To Make It Work. Architectural
Record, June, p. 32.
Barnette, C.H. (1995). Revitalizing Brownfield Sites. Iron Age New Steel, 1:6, p. 88.
Ben-Joseph, E. (1995). Changing The Residential Street Scene. Journel of the
American Planning Association. Vol. 61, No.4, autumn. P.504-515
Binkley, C., B. Collins, L. Kanter, M. Alford, M. Shapiro and R. Tabors (1975).
Interceptor Sewers and Urban Sprawl. Lexington Books, Lexington, MA. 118 p.
Bookout, L.W. (1992). Neotraditional Town Planning-The Test Of The Marketplace.
Urban Land, Vol. 51, June, p. 12-17.
Bookout, L.W. (1994). Valuing Landscape, Site Planning, And Amenities. Urban Land,
Vol.53, Nov., p. 39-43.
Booth, D. and L. Reinelt (1993). Consequences Of Urbanization On Aquatic Systems-
Measured Effects, Degradation Thresholds, And Corrective Strategies. Proc. Watershed
Management. WEF, Alexandria, VA.
Boulder, CO. (1982). Design Criteria and Standard Specifications. 11/9.
Boulder, CO. (1993). 5/26/93 Memo On Downtown Parking.
2-60
-------
Calthorpe, P. (1993). The Next American Metropolis-Ecology, Community and the
American Dream. Princeton Architectural Press.
CH2M Hill (1993). Cost of Providing Government Services to Alternative Residential
Patterns. Report for the Chesapeake Bay Program's Subcommittee on Population
Growth and Development. USEPA, Contract No. 68WO-0043.
Chellman, C.E. (1997). Traditional Neighborhood Development Street Design
Guidelines. Institute of Transportation Engineers. Washington, D.C., 43 p.
Chesapeake Bay Foundation (1996). Growth, Sprawl and the Bay-Simple Facts About
Growth and Land Use. Chesapeake Bay Foundation. September.
Clark, R. (1983). Economics Of Regionalization: An Overview. ASCE. New York, NY.
Colatins, E. and C. Bartsch (1996). Industrial Site Reuse And Urban Redevelopment-
An Overview. Cityscape: A Jour, of Policy Development and Research. Vol. 2, No. 3, p.
17-61.
Deakin, E. (1995). Land Use and Transportation Planning in Response to Congestion
Problems: A Review and Critique. Transportation Research Record 1237. p. 77-86.
Debo, T.N. and A.J. Reese (1995). Municipal Storm Water Management. Lewis
Publishers. Boca Raton, FL. 756 p.
Dittmar, H. (1995). A Broader Context for Transportation Planning. Jour, of the
American Planning Assoc. Vol. 61, No. 1, p. 7-13.
Engel, D., E. Stromberg and M.A. Turner (1996) Toward A National Urban
Environmental Policy. Cityscape: A Jour, of Policy Development and Research, Vol. 2,
No. 3, p. 1-16.
Ewing, R. (1994). Characteristics, Causes And Effects Of Urban Sprawl: A Literature
Review. Environmental and Urban Issues. Vol. 21, Winter, p. 1-15.
Ewing, R. (1996). Best Development Practices. Planners Press. American Planning
Association. Chicago, IL.
Ewing, R. (1998). Best Development Practices-A Primer. USEPA. Washington, D.C.
Ferguson, B.K. (1994). Stormwater Infiltration. Lewis Publishers. Boca Raton, FL.
269 p.
FHWA. (1997). Ultra-urban BMPs. Draft.
2-61
-------
FHWA. Undated. Is Highway Runoff a Serious Problem?
www.tthrc.gov/hnr20/runoff/runoff.html.
Forbes, T.W. (1981). Human Factors in Highway Traffic Safety Research. Malabar, FL.
Robert G. Kreiger Publishing Co.
Geltman, R.B. (1997). Brownfield Financing Strategies. Environmental Regulation and
Permitting. Spring, p. 5-7.
Goldstein, H (1997). A City of Dreams. Colorado Commons. Spring, P.42-44
Graham, Jr., E. (1944). Natural Principles of Land Use. Greenwood Press. New York.,
NY.
Hanousek, D. et al. (1996). Project Infrastructure Development Handbook. ULI.
Washington, D.C. 178 p.
Hanson, M. (1992). Automobile Subsidies And Land Use. Jour, of the American
Planning Assoc. 58:1.
Harza Engineering Company and Bauer Engineering Company, Incorporated (1966).
Flood and Pollution Control: A Deep Tunnel Plan for the Chicago Metropolitan Area.
Hawken, P. (1993). Ecology and Commerce. HarperCollins. New York, NY.
Heaney, J., W. Huber, and S. Nix (1977). Storm Water Management Model: Level I-
Preliminary Screening Procedures. U.S. Environmental Protection Agency. EPA-
600/2-76-275. Cincinnati, OH.
Howard, E. (1965). Garden Cities of Tomorrow. Reprint, F.J. Osborn, Ed. MIT Press.
Cambridge, MA. Originally published in 1878.
Huang, Y.J., H. Akbari and H.G. Taha (1990). The Wind-Shielding And Shading
Effects Of Trees On Residential Heating And Cooling Requirements. 1990 ASHRAE
Trans. (Atlanta, GA). Also Livermore Berkeley Lab Report 24131.
ICF Incorporated and Apogee Research Inc. (1997). Opportunities to Improve Air
Quality through Transportation Pricing Programs. US Environmental Protection
Agency. EPA-420-R-97-004. Washington, D.C.
Institute of Transportation Engineers (1965-90). Traffic Engineers Handbook. ITE.
Washington, D.C.
2-62
-------
Institute of Transportation Engineers (1987). Parking Generation. 2nd Ed. ITE.
Washington, D.C.
Institute of Transportation Engineers (1989). Residential Street Design and Traffic
Control. Prentice-Hall. Englewood Cliffs, NJ.
James, W. Ed. Current Practices in Modelling the Management of Stormwater Impacts.
Lewis Press. Boca Raton, FL.
Kandelaars, P., H. Opschoor, and J. van den Bergh (1996). A Dynamic Simulation
Model For Materials-Product-Chains: An Application To Gutters. J. Environmental
Systems. Vol. 24(4), p. 345-371.
Katz, B. (1997). Brookings National Issues Forum on Metropolitan Solutions to Urban
and Regional Problems, www.smartgrowth.org/library/katz.html.
Katz, P. (1994). The New Urban ism-Toward and Architecture of Community. McGraw-
ill. New York, NY.
Khisty, C.J. (1990). Transportation Engineering. Prentice-Hall, Inc. Englewood Cliffs,
NJ.
Knapp, G. (1998). The Determinants of Residential Property Values: Implications for
Metropolitan Planning. Jour, of Planning Literature. 12, 3.
Kunstler, J. H. (1996). Home From Nowhere. Simone and Schuster, New York, NY
Lee, Jr., D.B. (1973) Requiem For Large-Scale Models. Journal of the American
Institute of Planners. Vol. 39, p. 163-178.
Limpert, R. (1994). Motor Vehicle Accident Restoration and Cause Analysis. 4th Ed.
Charlottesville, VA. The Michie Co.
Littman, T. (1998). Transportation Cost Analysis: Techniques, Estimates, and
Implications. Victoria Transport Policy Institute. Victoria, BC.
Marsh, G.P. (1970). The Earth as Modified by Human Action, Arno Press (originally
published in 1874 as Man and Nature.
McHarg, I. (1971). Design with Nature. Doubleday. Garden City, NY.
Mohney, D. and Easterling, K., Editors (1991: Seaside; Making a Town in America.
Princeton University Architectural Press, New York, New York
2-63
-------
Moss, M.L. (1997). Reinventing The Central City As A Place To Live And Work.
Housing Policy Debate. Vol. 8, Issue 2, p. 471-490.
National Commission on the Environment (1993). Choosing a Sustainable Future, p.
114. Nation. Island Press. Washington, DC. 180 pages.
National Safety Council (1995). Accident Facts. Itasch, IL
Newsweek (1995). 15 Ways to Fix the Suburbs. May 15
Novotny, V. and H. Olem (1994). Water Quality-Prevention, Identification, and
Management of Diffuse Pollution. Van Nostrand Reinhold. New York, NY. 1054 p.
O'Connor, K.A. (1996). Institutional Framework For Water Quality Over The Past
Century, in WEF Watershed 96. Alexandria, VA. p. 1019.
Oglesby, C.H. and R.G. Hicks (1982). Highway Engineering. 5th Ed. J.Wiley and
Sons. New York, NY.
Oknn, D.A. (1991) Reclaimed Water: An Urban Resource. Water Science and
Technology. Vol. 24, No. 9, p. 352-362.
Papacostas, C.S. and Prevedouros (1987). Transportation Engineering and Planning.
2nd Ed. Prentice-Hall. Englewood Cliffs, NJ.
Parente, M. and M.E. Hulley (1994). Stormwater Pollution at a Major Highway
Interchange. Chapter 10 in (missing ?????)
Peirce, Neil (1994). The Dawn Of Civic Environmentalism. Tampa Tribune. Jan. 10.
Pitt, R. andVoorhees, J. (1994). Source Loading and Management Model (SLAMM).
Department of Civil and Environmental Engineering. University of Alabama at
Birmingham.
Prince George's County (1997). Low-Impact Development Design Manual. Prince
George's County, MD.
Real Estate Research Corporation (1974). The Cost of Sprawl. U.S. Government
Printing Office. Washington, D.C.
Renner, M. (1988). Rethinking The Role Of The Automobile. World Watch Institute.
Washington, D.C.
Repogle, M. (1991). Sustainability: A Vital Concept For Transportation Planning And
Management. Jour, of Advanced Transportation. 25, No. 1, p. 9.
2-64
-------
Risse, E.M. (1989). The American Settlement Pattern of the 21st Century-Where are
the "Sub"urbs Going, www.smartgrowth.org/library/risse/html.
Roesner, L.A., et al. (1991). Hydrology of Urban Runoff Quality Management. Proc.
18th National Conf Water Resources Planning and Management. Symposium Urban
Water Resources. American Society of Civil Engineers. New York, NY.
Schueler, T. et al. (1992). Watershed Restoration Sourcebook. Metro. Washington
Council of Governments. Washington, D.C.
Schueler, T.R. (1994). Site Planning For Urban Stream Protection. Watershed
Protection Techniques. 1,3: 137-140.
Schueler, T.R. (1995). Site Planning for Urban Stream Protection. Metro. Washington
Council of Governments. Washington, D.C. 232 p.
Shoup, D.C. (1995). An Opportunity To Reduce Minimum Parking Requirements. Jour.
American Planning Assoc. Vol. 61, No. 1, p. 14-28.
Smith, W. (1964). The Low-Rise Speculative Apartment. Research Report 25.
Berkeley: University of California Center for Real Estate and Urban Economics.
So, F.S. and J. Getzels, Eds. (1987). The Practice of Local Government Planning. 2nd
Edition. International City Managers Association. Washington, DC
Southworth, M. and E. Ben-Joseph (1995). Street standards and the shaping of
suburbia. American Planning Assoc. Journal. Vol. 61, No. I, p. 65-81.
Southworth, M. and E. Ben-Joseph (1997). Streets and the Shaping of Towns and
Cities. McGraw-Hill. New York, NY.
Sunset (1992). Best Home Plans. Sunset Publishing Co. Menlo Park, CA.
Tetra Tech (1996). Green Development Literature Search: Summary and Benefits
Associated with Alternative Development Approaches. USEPA. Washington, D.C.
www.smartgrowth.org/bibliographies/greenlit_search/case_examples.html.
Thomson, N.R., E.A. McBean, I.B. Mostrenko, and W.J. Snodgrass (1994).
Characterization of Stormwater Runoff from Highways. Chapter 9 in James, W. Ed.
Current Practices in Modelling the Management of Stormwater Impacts. Lewis Press.
Boca Raton, FL.
Urban Land Institute (1968). The Community Builders Handbook. Urban Land Institute.
Washington, D.C. 526 p.
2-65
-------
Urban Land Institute (1989). Project Infrastructure Development Handbook. ULI.
Washington, D.C. 175 p.
Urban Land Institute (1982). Parking Requirements for Shopping Centers.
Washington, D.C. Urban Land Institute.
Urbonasetal. (1990). Optimization Of Stormwater Quality Capture Volume. In Urban
Stormwater Quality Enhancement-Source Control. Retrofitting and Combined Sewer
Technology. ASCE. New York, NY.
USEPA. (1991). Proposed Guidance Specifying Management Measures for Sources of
Nonpoint Pollution in Coastal Areas. May.
Wagener, M. (1994). Operational Urban Models: State Of The Art. Journal of the
American Planning Association. Vol. 60, No. 1, p. 17-19.
Walesh, S.G. (1989). Urban Surface Water Management. Wiley and Sons. New York,
NY.
Walesh, S.G., and R. Carr (1998). Controlling Stormwater Close To The Source: An
Implementation Case Study. American Public Works Congress. Las Vegas, NV.
September.
Walter, B., L. Arkin and R. Crenshaw (1992). Sustainable Cities Concepts And
Strategies For Ecocity Development. Ecohome Media, p. 178.
Water Environment Federation-American Society of Civil Engineers (1998). Urban
Runoff Quality Management. WEF Manual of Practice N. 23. ASCE Manual and
Report on Engineering Practice No. 87. Alexandria, VA and Reston, VA. 259 p.
Wilson, R. (1992). Suburban Parking Economics and Policy: Case Studies of Office
Worksites in Southern California. Report No. FTA-CA-11-0036092-1. Washington,
D.C. U.S. Dept. of Transportation.
Wilson, R.W. (1995). Suburban Parking Requirements: A Tacit Policy For Automobile
Use And Sprawl. Jour, of the American Planning Assoc. 61,1:29-42.
World Commission on Environment and Development (1987). Our Common Future
Wright, P.M. and R.J. Paquette (1996). Highway Engineering. J. Wiley and Sons. New
York, NY.
Young, G. K., Stein, S., Cole, P., Kammer, T., Graziano, F., and Bank, G. (1966).
Evluation and Management of Highway Runoff Quality. Publication No. FHWA-PD-96-
2-66
-------
032. Federal Highway Administration. Washington, DC, p.480.
Huhnke, B. (1997). Take a Deep Breath. Colorado Commons. Spring pp. 20-21.
Zimmerman, R. and Sparrow, R. (1997). Workshop in Integrated Research for Civil
Infrastructure. Final report to NSF, Washington, DC
2-67
-------
Chapters
Sustainable Urban Water Management
James P. Heaney, Len Wright, and David Sample
Introduction
Water supply, wastewater, and stormwater systems are explored in this chapter, first
individually and then looking at them in an integrative manner. Key areas of
potential integration of these three functions are in reuse of wastewater and
stormwater to reduce the required net import of water for water supply. The
literature review summarizes previous and on-going work nationally and
internationally to develop more sustainable urban water management systems.
Systems View of Urban Water Management
The mid 1960's were a period of great change in the water resource field in the
United States. The 1964 Water Resources Research Act established the Office of
Water Resources Research (OWRR) with a mission of promoting interdisciplinary
research because the individual federal agencies were only looking at their
mandated piece of the total water system. Also, the 1965 Water Resources
Planning Act established river basin commissions to better integrate water resources
planning across federal agencies. Great strides were made in urban water and
environmental management during the 1960's and 1970's because of strong federal
support for research, a national mood to look at revitalizing our cities and restoring
the environment, and the concomitant emergence of the systems approach and
essential computer hardware and software.
The leadership in urban water resources during the early years can be traced to the
ASCE Urban Water Resources Research Council (UWRRC) headed by M.B.
McPherson. With funding from OWRR and the National Science Foundation (NSF),
the UWRRC sponsored research conferences and numerous research projects
dealing with a wide variety of urban water resources issues. The early results are
published in McPherson et al. (1968). They pointed out that:
A single aspect research approach is totally
inadequate and, indeed, is entirely inappropriate, for
resolving multi-aspect problems. The former
simplistic approach of regarding a unit of water as a
fixed entity, such as stormwater, must be abandoned
for that same unit at a different point in time will be
categorized as water supply, recreation, esthetics,
etc., perhaps several times before leaving a given
metropolis.
The ASCE UWRRC defined urban water resources to consist of:
3-1
-------
1. Urban water uses:
Water supply (domestic, commercial, agricultural and for fire
protection).
Conveyance of wastes (from buildings and industries).
Dilution of combined and storm sewerage system effluents and
treatment plant effluents (by receiving bodies of water).
Water-oriented recreation and fish management.
Aesthetics (such as landscaped creeks and ponds in parks and
parkways).
Transportation (commercial and recreational).
Power generation.
2. Protection of urban areas from flooding:
Removal of surface water at the source.
Conveyance of upstream surface water through the area.
Barricading banks, detaining or expressing flow natural streams to
mitigate spillover in occupied zones of flood plain.
Flood proofing of structures.
3. Manipulation of urban water:
Groundwater recharge.
Recycling of water.
4. Pollution abatement in urban areas:
Conveyance of sanitary sewage and industrial wastes in separate
sewerage systems.
Interception of sanitary sewage and industrial wastes.
Interception and treatment of storm sewer discharges or combined
sewer overflows.
Reinforcing waste assimilative capacity of receiving water bodies.
Treatment of sanitary wastes at point of origin.
5. Interfacial public services:
Snowstorm and rainstorm traffic routing.
Street cleaning scheduling.
Snow removal strategies.
Lawn irrigation conservation.
Air pollution control.
The review of the integrated approach to urban water systems, which was in vogue
in the late 1960's and 1970's, indicates that these researchers had scoped the
problem very well. The spatial scale for these early systems studies tended to be
macro in that it encompassed the entire urban area with a view towards finding the
most cost-effective overall system. This approach was compatible with federal
infrastructure funding patterns that required that the funded projects be part of an
overall transportation or wastewater master plan for the entire urban area.
3-2
-------
A systems approach to urban water management was described by Jones in 1971
(see Figure 3-1). McPherson (1973) argued that developing an urban water budget
was an essential first step in using a systems approach as shown in Figure 3-2.
Concurrently, researchers at Resources for the Future were stressing the use of a
materials balance approach for inventorying and evaluating the generation and
disposal of "residuals" or the quality constituents associated with transport in the air
or water (Kneese, Ayres, and d'Arge 1970). A more recent summary of the residual
management approach and a comprehensive catalog of models is presented in
Basta and Bower (1982). Heaney (1994) presents an overview of these early
studies.
Sustainability Principles for Urban Water Infrastructure
With regard to urban development in general and urban water systems in particular,
Grottker and Otterpohl (1996) list the following general principles for providing
sustainable development:
For the same or more activities, use less energy and material.
Do not transfer problems in space or time to other persons.
Minimize degradation of air, water, and land.
Application of these principles to urban water systems yields the following principles
(Grottker and Otterpohl 1996):
1. Minimize the distance of water and wastewater transportation.
2. Use stormwater from roofs, preferably for water supply, instead of infiltrating
or
discharging it.
3. Do not mix the human food cycle with the water cycle. Do not mix waste
waters
of different origin.
4. Decentralize urban water systems and do not allow human activities with
water if
local integration into the water cycle is not possible.
5. Increase the responsibility of individual humans for their impacts on local
water and wastewater systems.
3-3
-------
THE SYSTEMS APPROACH TO URBAN WATER RESOURCES
THE URBAN COMPLEX IS THE BASIC SYSTEM:
The urban complex is people and serves people.
THE URBAN WATER RESOURCE IS A SUBSYSTEM IN THE BASIC URBAN
SYSTEM:
To address the urban water resource as an independent system, even for
convenience, may lead to dangerously narrow conclusions.
TRADITIONAL THINKING OF WATER SUPPLY, DISTRIBUTION, SEWAGE,
FLOOD CONTROL, AND RECREATION AS SUB-ORDERS MAY BE
INAPPROPRIATE:
These are interdependent service functions.
Perhaps the following breakdown might prove better:
The complete water cycle.
The environment, including people.
The ecology, including people (if separable from environment).
Public and private economies.
Management.
GENERALIZATIONS AT THE SUB-SUB-SUBSYSTEMS LEVEL COULD DEFEAT
THE OBJECTIVES OF THE SYSTEMS APPROACH:
The progress of science is measured by development of details. Research
contributions typically come from multiple minute steps-not from giant
strides forward.
Rewarding concepts, innovations and improvements will originate essentially
at the sub-sub-subsystem level.
TEMPTATIONS TO GENERALIZE, TO INERRELATE ONLY WITHIN THE FINITE
CAPABILITY OF A MACHINE, AND TO IGNORE "INTANGIBLE"
RELATIONSHIPS LACKING HARD DATA, MUST BE AVOIDED:
Neither a model nor a machine can think.
Man cannot excuse his failure to think.
Figure 3-1. Early view of the systems approach to urban water management (Jones
1971).
3-4
-------
1 I
I * 1= * =1 *
Figure 3-2. Water budget for urban water systems (McPherson 1973).
Sustainability has become popular as a general goal of future societies in general
and environmental and economic systems in particular. A recent issue of Water
Science and Technology featured numerous articles by European authors on the
theme of "Sustainable Sanitation" (Henze et al. 1997). They could not find an
operational definition of sustainability as it applies to urban water problems. Several
authors did strongly advocate taking an holistic view of urban water systems
ranging from water supply to wastewater and stormwater collection, treatment, and
disposal.
Clark, Perkins, and Wood (1997) have developed and applied concepts of
sustainability to evaluating alternative futures for the water system in Adelaide,
Australia. This effort is the largest known case study of a group that is taking an
integrative look at this problem. The purpose of the Water Sustainability in Urban
Areas (WSIUA) project is to investigate the feasibility and benefits of progressive
replacement of the existing large scale, single purpose water systems with replicated
small scale, multipurpose water systems. These water systems consist of water
supply, wastewater and stormwater. The key concepts explored in this study are
3-5
-------
(Clark etal. 1997):
1. Adoption of a long planning cycle compatible with the life span of major
components of the water systems.
2. Planning water systems to achieve multiple objectives-environmental,
social,
and economic.
3. Viewing water as a valuable resource warranting conservation and
efficient
utilization.
4. Undertaking water planning which seeks efficiency gains through taking a
total water cycle approach on a local and regional basis as the best
means of meeting multiple objectives.
5. Integrating water systems as appropriate to achieve efficiencies through
infrastructure cost sharing.
6. Localizing water systems to achieve efficiencies through maximizing local
opportunities.
7. Utilizing rainwater capture, effluent recycling and groundwater storage to
maximize system resilience.
8. Franchising the operation of small scale systems as the best means of
balancing cost competition with maintenance of adequate reliability
and
public health standards.
9. Recognizing the organizational and social implications of integrated local
water systems.
Urban Water Budget
Literature Review
Water budgets have become popular in recent years as water professionals attempt
to do more holistic evaluations of urban water systems. Grimmond et al. (1986)
present a schematic of the components of the urban water budget as shown in
Figure 3-4.
Stephenson (1996) cites three impacts of urbanization on stormwater runoff:
Increased stormwater runoff.
Recession of the water table.
Shorter response time due to imperviousness.
He compares the water budgets of an undeveloped catchment with an urbanized
catchment in Johannesburg, South Africa. The results show the expected increase
in direct runoff and the need to import water for water supply. He also cites an urban
water budget of a suburb of Vancouver, B.C. (Grimmond and Oke 1986).
Nelen et al. (1996) describe the planning of a new development for about 10,000
people in Ede, Netherlands. The three underlying environmental principles are
3-6
-------
sustainability, quality, and ecology. This area has a high groundwater table so
groundwater management is an important part of the project. They plan to
incorporate water-conserving hardware and divert the more polluted stormwater into
the sanitary sewer. In addition, they are considering a dual water supply system.
Fujita (1996) describes efforts in Japan to encourage stormwater infiltration. The
multiple objectives of this approach include:
1. River flow maintenance.
2. Springwater restoration.
3. Water resources guarantee.
4. Ground subsidence prevention.
5. Groundwater salination prevention.
Herrmann and Klaus (1996) do general water and nutrient budgets for urban water
systems including stormwater. Imbe et al. (1996) performs a water budget analysis
to determine the impact of urbanization on the hydrological cycle of a new
development near Tokyo, Japan. This development is trying to minimize hydrologic
impacts by encouraging infiltration systems and storing rainwater. Mitchell et al.
(1996) describes a water budget approach to integrated water management in
Australia. Budgeting is done at the individual parcel, neighborhood, and wider
catchment scale. On-site management options include providing rain and graywater
storage.
Clark et al. (1997) uses a water budget approach to evaluate decentralized urban
water infrastructure for Adelaide, Australia.
3-7
-------
PRECIPITATION
-------
and 12 weeks in a colder period. Readings were taken every 10 seconds and
converted into individual water using events using specially developed software.
This work was finished in April 1998. This project is referred to as the North
American End Use Study (NAREUS) project. Descriptions of this effort can be found
in DeOreo et al. (1996), Harpring (1997), Mayer et al. (1997), Stadjuhar (1997), or by
visiting the homepage of Aquacraft atwww.aquacraft.com. The summary results of
this water use study are presented in Table 3-1 that describes overall water use in
the 12 cities, and Tables 3-2 and 3-3 that present the city summaries for each
sampling period so that the reader can see the difference between the results for the
warmer versus the colder periods.
Indoor Urban Residential Water Use
The results of the NAREUS project indicate an average indoor water use of 63.2
gallons per capita per day (gpcd) with a range from 49 to 73 as shown in Table 3-1.
Perusal of Tables 3-2 and 3-3 indicates that indoor water use does not vary
significantly between winter and summer. Indoor residential water use per capita is
quite stable in the United States reflecting the fact that indoor water use is for
relatively essential purposes. These results are quite similar to previous studies of
indoor water use. Based on a nationwide evaluation, Maddaus (1987) concluded
that indoor residential water use averaged 60 gpcd. Studies of the expected value
of wastewater into sewers likewise report an average of 60 gpcd. Toilets account for
the largest percentage of indoor water use in all three studies followed by
clotheswashers, showers, and faucets. The basis for the results shown in these
three studies is described below.
Indoor water use does not vary significantly over the year. Some daily variability
occurs between weekdays and weekends. The hourly distribution of indoor
residential water use is shown in Figure 3-5 (Harpring 1997). Peak usage occurs
during the early morning hours of 7 am to 10 am. Most of this peak is due to toilet
and shower use. Toilet flushing continues at a similar rate for the rest of the day and
into the evening. On the other hand, showers are taken primarily in the morning.
Peak clothes washing activity occurs from 9 am to 1 pm. In general, water use in
houses declines during the middle of the day because fewer people are at home.
Use increases in the evening as people return home and prepare dinner, and then
reaches its lowest level between midnight and 6 am when people are asleep.
Interestingly, the British studies show use during the early morning hours for dish
and clothes washing. The explanation for this usage pattern is that customers are
taking advantage of lower electric rates during these hours (Edwards and Martin
1995). A general discussion of expected future trends in indoor water use follows.
3-9
-------
Table 3-1 .Summary of indoor water use for 12 cities in North America
ia vmjป n g^ons |
Uf V CftttflWY
&nthป
CMIM* WMtwre
CoaMri
DMh WBhws
F*UCซl*
D*inkjrtjS water'
Hat Tubs
L**i"
Showers
TOME
MM OR
Outdoor
TOTAL
2.42
Souldf
Colorado
' ':;.
\S 76
a IE
142
1047
0.37
002
338
13 17
:> sf.
6502
73.40
M.S 42
2,T4
Dmvtr
Colorado
I 51
1465
034
1 07
336
0.37
000
662
i: 73.
; " 9r.
64.46
1 15 59
I8O07
cr capita
2.*
Euwnt
I 29
16 n;'
000
1.26
9.70
0.37
000
3 70
I 3 'J
20.29
71 41
52 59
U4i.ll)
pe- dsy
2,ป
6**ti*
Wiahlnaton
Q.66
10 32
000
032
636
037
OOD
4 14
10.10
14. 64
4362
i? 19
Win
27J
San &tgo
CซHorrai
.:< :?
^r 77
000
033
93B
037
0 10
4.56
9.14
1502
5621
6657
122 n>
t.*3
Tar-ps
Flomfi
i ;;
13 *9
0 10
060
10 2E
037
000
9.75
992
15 16
6078
i375
S*4 5J
2ซซ
Phffltren
A<1?ซnป
0 :;.:
1 --s .=Jj
1.50
0.75
623
o .'.;
005
1245
11 BO
1700
6S.65
I06.50
177 If,
3.34
Somvda**'
Tซmpi ,AZ
C-K
>- -'f
245
1 05
98J
037
0.20
I430
11.75
1705
7270
16360
>w .so
3.12
Wrttrloo
Ont*no
: ,:.',,:
12 70
000
075
9.51
037
000
6 20
3 15
I7_50
61 3D
1340
3,ป
Wjlunt valley
CriMbmla
! '-',
1390
002
0.80
1051
037
030
7 35
11.80
16 10
63 15
8655
W JO
3.0T
Ln VlrjjปnM
CHWomii
I 26
1930
0.05
037
991
037
026
9 25
11 06
1422
6394
16376
2*1
Lempoc
Crtfomii
1 41
1575
OOD
062
7E4
D.S7
DOS
8.48
1146
14.59
81.43
3761
JSi Jซ
2,ป
Avcntyt a#
12 cltln
1 IIJ
li 3d
038
090
931
0.37
008
797
1132
18.66
63 19
B28I
Mil ill)
030
StA D*v Of
12 cltln
0 >j
1 59
073
025
1 13
-
011
3..J7
1 65
2.18
650
4972
ซ M
011
Cs*f Of
Vgrlrtign
0 ^:'J
0 11
202
023
0 12
-
1.24
042
D 15
0.13
0 IQ
060
<ซ of tool
' ...:."-
22 64 K,
061%
1 43K,
14 745i
0 ^i'i;.
013%
1262%
17 769i
26 4094
100 OOK,
"Dnndng iwjlBr at I 4 Irters psr
"Leaks are assumed to be irrJixir Trey Ktualif ars a ccrtunatjon of indMr
""Unhtwwn is ^amrt to be cutdocr It is Drtu^ty a combinalicn of indmr and oitdwr
3-10
-------
Table 3-2. Summary o\ Indoor and uutduui water use In BtmldH, Denver, Eugtn*, Seattle, and San Diego
GALLONS PER CAPITA PER DAY
(rxcni.dnill-ii unl
NN
attorns
Cn>lhซป Viunti
PUB mi in in
TOWtj
FtoHfta
Cwrf**ป
"Hi [uฑ*
UMPfcMpi*
LHtg
NDOOfl
knawan
**ซn*^Ppซ*
BOULDER. CO
6fl1-ซJW6
y^
i
us
i .
i
107
tu
pri
25
61 i
iifl
01
UhtoMnl 19
Dk/TDCOft TOTAL
TOTAL
1451
in -JilM*
134
124
.
a i
to 9
01
00
0"
4 J
@3 1
73u
0 1
0 J
734
ซli
Avtilut
113
118
1 4
20T
IOC
[12
00
00
3.4
JEJ
715
0 1
DS
764
I4J4
DENVER, CO EUGENE, OK
' :
14 Mi7ae
.
ซ 7
i ,
1
104
OJ
00
00
n
573
Ida
ir
2Ti
S2
sSl
U4JOM7
14
104
i.. ;
-
I
109
:
00
133
Ky
Si
ar
11
\ ;
1IBO
-^^^
; -
12.. 5
VJT
0.1
00
9 T
S3 0
36.7
4 T
n
33- T
MS
six aty
Avir^*
II!
14 1
1 u
v-
0.1
00
01
c:
611
jjSj
il
i j
692
1403
Table 3-3. Summary ol Indoor and uulduui water use in Phutfnin.. Scutlsiiale. Waleiluo, Walnut Valley, Las Vnyeires. and Ltxnpot-
GALLONS PER CAPITA PER DAY
Pft vcnli4Nfli-is u-il
IBM
IllWJ^i
riiiTttun WinltoTO
PHOENIX, AZ
4J39.6T1SH7
177
Da
135
14 f)
Orari Wltf*!*^
Tad*u IT i
FMfta
CwUm
IHUIl^M
IV^TWJ
Lull
HDOOfl
e.9
2"S
00
01
!ซ!
712
bt^M4in< IMd
.amnnmgriiiili
UTk'Oiiin
OUTDOOf: TQT4L
TOTJIL
15
20
I453
!--
I1*.11rtas?| tmnat
. ,.
1 1
112
150
Oi
lflฃ
95
0'.
0 1
1 1
Ifl J
M1
' .
5)
05
Til
1S7ซ
2S&
10
11 9
j*j
DO
17 0
9T
1 5
61
flft
12!
oer
. -'
jg
11
i. -; '.
-
SCOTTSDALEiTEMPE.AZ
OlKiftMiT
. _:
1 1
120
1.3 ?
1.1
iaa
10 1
n
01
Oi
JM
7JI
.;_
Ml 4
39
"4 r 'j
.
ia0.12ftBA97
24*
0:
11-.
14 ;-
10
17 j'
97
0 3'
Oi
Id
'55
T17
701
04
2C
TQJ
AvtnQt
2J4
10
1 1 ซ
137
1,1
171
IBS
2 *'
a:
ft .*.
145
T27
1534
**
1B36
238 *
WATERLOO, OHT
RB1W1M7
3 Ofi
u
T-,
1? j
07
164
m.B
00
00
56
T 5
(\ > i
341
01)
1 2
.:. .
'
'$ &
UV
M
13?
as
ia b
99
ao
00
50
5 1
(11 >.
10
11 I'l
o:.
i &
totnat
2-12
14
82
12.7
es
175
99
00
00
53
52
613
12 d
Ol]
05
134
3SJ
WALNUT VALLEY. CA | LAS V1R5ENES, CA
Tjraซiz8r|<ซ.iyraflG
3Jr3-
14
11O
13?
05
156
114
ao
05
1f.
S9
020
.. .
^6
2 2
160.1
H3 1
J2i
OJ
112
14 c
07
I'.C-
10.4
00
01
1 J
7 F'
W J-
ne
OJ
ID
Awngt J9fiBซraB7
yg
1 1
I1B
us
06
161
IDS
DO
03
14
7<
ซy
ail
18
ICi
|M
HUT
i 1
1 4
95
153
07
rij
100
01
05
04
90
019
. y; -
lOi
19
_:i; i
3603
CT.i,iaiป
304
1 j
12 f
173.
1.0
151
9.7
OC
0.!
8.2J
09 3-
a. 7
24
2.7
38. 7
ICB 1
Mtnr
3.03
13
1 1 1
103.
O'j
14 1
io.r
0 1
02
fli
93
JHS
I'r
ซ4
23
i.S :
.:. .
LOHPOC.CA
9Sซ-!3fl7
2?a
1 1
121
1C 2
09
15 Jl
e.a
00
01
08
GO
620
S07
00
04
61.1
K21.MMS
2 A3
17
TO?
\ri 3.
0
13 H
9.0
00
00
0 >
89
M4
130
00
Jj(
14. :
T4i
Ann*
2. SI
14
115
159
OJ
M6
S.2
ao
01
.'i ?
!,!
MJ
36 ft
0 0
10
37 6
SBJ
SNOty
Anngc
ID
13
110
145
OS
16 1
BC
DT
01
1 S
P9
G'. .:
414
3.4
1C
ซB_4
1817
3-11
-------
PRECIPITATION (p)
PIPED WATER
SUPPLY
-------
Toilet Flushing: Toilet flushing is the most regular and predictable of all
of the indoor water uses with an average of 16.7 gpcd and a range from 14.2 to 20.7
gpcd. Residents and guests will use the toilets every few hours if they are home.
The only significant break in this pattern is during the night when people are asleep.
Day to day variation in toilet flushing depends upon how many people are home at a
given time. More people would be expected to be home on weekends and in the
summer when school is not in session. Toilet flushing generates the black water that
is the main source of pollutants at the wastewater treatment plant. The low
variability of toilet use is good news from a design point of view since it is then only
necessary to design for relatively small peaking factors. Also, low quality water can
be used for toilet flushing. Thus, it is a good candidate for using reclaimed
wastewater or stormwater.
Conservation options for toilets have focused on reducing the volume per flush from
four to five gallons to 1.6 gallons which is mandated nationally in the plumbing
codes. An important concern with regard to lower volume per flush is that people
would double or triple flush. Based on a nationwide study of toilet flushing, Mayer et
al. (1997) conclude that double flushing is a minor problem with low-flush toilets,
occurring only about 6% of the time. Also, it does not appear that people will change
their flushing patterns. British studies of the nature of toilet flushing indicate that
only about 25 % of toilet flushes are to dispose of fecal material as shown in Table
3-4 (Friedler et al. 1996).
Table 3-4. Number of toilet flushes per day and proportion related to fecal flushes
(Friedler etal. 1996)
Flushes/day
Fecal related
Other
Total
Week Day
0.87
2.24
3.11
Weekend Day
1.09
2.43
3.52
The diurnal pattern of fecal related flushes indicates that the majority take place
between 6 am and 9 am. Thus, the savings result from fewer gallons per flush and
not fewer flushes per day. The associated pollutant load would remain constant;
accordingly, the wastewater concentrations would increase. Some concern exists
that odors from sewers would be further intensified with the implementation of water
conservation (Joyce 1995).
The volume per flush can be reduced to 0.5 gallons using pressurized systems.
This technology may gain more widespread use in the future. Future toilets include
the currently mandated low-flush (1.6 gallons) and ultra low-flush (0.5 gallons)
conventional toilets. Johnson et al. (1997) describe an innovative toilet wherein
feces and urine are collected in separate compartments. This toilet reduces water
use and allows more efficient treatment of the two separate waste streams. Dual
flush toilets are employed in Australia wherein the user selects whether to use more
3-13
-------
or less flushing water depending upon the need.
Clothes Washing: Clothes washers use an average of 14.3 gpcd with a
range from 10.8 to 16.3 gpcd. The traditional Monday wash day has been replaced
by a more uniform pattern of clothes washing which is done throughout the day with
peaks in the morning and early afternoon as was shown in Figure 3-4. More efficient
clothes washers are expected to reduce water use per load by about 25 percent.
The timing on clothes washing could be affected by electric or water utility rates,
which provide time of day incentives and disincentives. As mentioned earlier, water
users in Great Britain apparently wash late at night to take advantage of lower
electricity rates.
Showers and Baths: Showers (11.2 gpcd) are much more popular than
baths (1.2 gpcd) for all 12 cities in the NAREUS study. For Boulder, CO, the morning
shower is the predominant time for this activity as shown in Figure 3-5 (Harpring
1997). The other peak in showering occurs during the evening. Showers are taken
on a daily basis in Boulder. Thus, no significant variability occurs from day to day.
Drainage from showers can be used for lawn watering during the growing season of
year. It is a significant source of reclaimable water and the timing of its entry into the
wastewater collection system can be estimated accurately because the shower
water is not stored during use.
The main conservation option for showers is to use low-flow shower heads. Results
to date indicate only limited reduction in water use since users did not set the older
shower heads to the higher flow rates. Federal law mandates a maximum flow rate
for showers of 2.5 gallons per minute (gpm). Results of the NAREUS study indicate
that most people set their shower flow rate below this level. Thus, conservation
savings may not be that significant (Mayer et al. 1997). No significant change in
duration of showers has been observed with the lower flow rate showers. Showers
are also important as a major user of hot water.
Faucet Use: Faucet use includes drinking water, water for washing and
rinsing dishes, flushing solids down the garbage disposal, shaving, and numerous
other personal needs. Faucet use averages 9.3 gpcd with a range from 6.9 to 10.5
gpcd. No breakdown among these uses is available although one can make
educated guesses as to the amounts of water used for these purposes. Best
estimates of actual drinking water use are in the range of 1.0 to 2.0 liters per capita
per day with a mean of 1.4 liters per day (Cantor et al. 1987). Garbage disposals
add about one gpcd to total indoor consumption (Karpiscak et al. 1990). Faucet use
requires the highest water quality because it is the potable water source. Overall,
faucet use is a small proportion of total use, which suggests the possibility of
separate treatment and distribution systems for this source. Also, faucet use is
relatively common during the day so equalizing storage requirements are low.
Dishwashers: Dishwashers are a relatively minor water use and newer
dishwashers are being designed to use less water to conserve energy and water.
3-14
-------
Present per capita water use averages only 0.9 gpcd.
Water Use for Cooling: For some houses, and for many commercial
and industrial establishments, water use for cooling is a significant part of the water
budget. Swamp coolers are used in the more arid areas of the United States.
Karpiscak et al. (1994) estimate that residential evaporative coolers use about six
gpcd in Tucson, AZ. Because of the relatively small number of houses using coolers,
the average usage is quite low, only 0.4 gpcd.
Outdoor Urban Residential Water Use
Whereas indoor residential water use is very constant across the United States and
does not vary seasonally, irrigation water use varies widely from little use to being
the dominant water use. Also, it varies seasonally. The 12 cities in the NAREUS
are not a representative sample of the United States with regard to climate types.
Also, the amount of natural precipitation that occurred during the study periods can
have a significant impact on the results. Nevertheless, the results certainly suggest
the potential major impact of irrigation on average and peak water use.
A detailed evaluation of irrigation water use as a potential reuse of urban stormwater
is presented in Chapter 8. This section only introduces the subject. Irrigation water
use follows a definite pattern of high use rates in the morning and evening with low
use rates during the day and late at night. Thus, these customers are following the
common recommendations to not water during the middle of the day. Watering late
at night is discouraged because of the noise from the sprinklers.
For the entire NAREUS study, outdoor water use averaged 82.8 gpcd, significantly
more than the indoor water use of 63.2 gpcd. Studies of overall residential water
use in Boulder and Denver show that outdoor water use averaged over the entire
year exceeds indoor water use. Thus, outdoor water use can be a significant
component of total annual average water use.
For the NAREUS study, Waterloo, Ontario is representative of conditions in the
northeastern part of North America. During the summer, the outdoor water use
averaged 25.3 gpcd compared to indoor water use of 62.3 gpcd. As expected the
outdoor water use became negligible in the colder months, averaging only 1.5 gpcd
in October.
At the other extreme, outdoor water use in Las Virgenes, CA averaged 299 gpcd,
nearly five times the indoor water use of 61.6 gpcd during the summer sampling
period. Thus, for residential areas in the more arid and warmer parts of the country,
lawn watering is the largest single use on an annual average basis and is the
dominant component of peak daily and hourly use during the summer months.
In the arid areas, evapotranspiration requirements are much greater than natural
rainfall. In warmer parts of the country, even those with abundant rainfall, such as
Florida, irrigation water use rates are high because of the long growing season
3-15
-------
which includes some dry periods. Irrigation water use is a major input to the urban
water budget during the growing season. A growing number of people are installing
automatic sprinkling systems. These systems tend to use more water than manual
systems (Mayer 1995). Also, the timers on these systems are seldom adjusted.
Thus, lawn watering occurs even during rainy periods. Experience with soil moisture
sensors to control sprinkling use has been mixed. Automatic sprinkling systems do
offer the potential for more efficient use of water if they are properly calibrated and
operated (Courtney 1997).
The hourly pattern of total residential water use (indoor plus outdoor) for Boulder,
CO is shown in Figure 3-5 (Harpring 1997). The study period from late May to early
June included some rainy days. Peak hourly use between 6 and 8 am is caused
predominantly by irrigation. Comparison of Figures 3-4 (indoor only) and 4-5 (total)
indicates the importance of irrigation. The indoor water use at 6 am is about 7.5
gallons per house while the total water use at the same time is about 41 gallons per
house. Thus, irrigation constitutes over 80% of the peak hourly use.
Options for reducing outdoor water use include using less water-loving plants,
applying water more efficiently, reducing the irrigated area, and using nonpotable
water including stormwater runoff and treated wastewater (Courtney 1997).
Irrigation use has an indirect effect on urban runoff because it causes much wetter
antecedent conditions, which increases the portion of rainfall that runs off. Sakrison
(1996) projects a potential decrease of 35% in the demand for irrigation water in
King County, WA if the higher density urbanization occurs. For King County, the
main way that water use is managed is by restrictions on outdoor water use for
landscaping. A maximum permissible evapotranspiration is allotted that forces the
property owner to reduce the amount of pervious area devoted to turf grass.
Stormwater run-on to the pervious area can be used for an extra credit. The
amounts of irrigable area for three typical single family lot sizes are shown below.
The advantage of clustering is obvious from inspection of Table 3-5. The amount of
irrigable area per house is reduced from 5,000 sq. ft. to 1,500 sq. ft., a reduction of
70%. This is the main savings in water use. However, from a stormwater runoff
point of view, the imperviousness would increase.
Table 3-5. Typical lot sizes and irrigable area, King County, WA (Sakrison 1996).
Density
Low
Medium
High
Lot Size,
(sq.ft.)
10,000
7,000
4,500
Irrigable Area Per lot
(sq. ft.)
5,000
3,000
1,500
% of total
50
43
33
Lawn watering has increased in the U.S. as population migration occurs to warmer,
more arid areas. Also, urban sprawl means much larger irrigable area per dwelling
3-16
-------
unit. Lawn watering needs are a dominant component of peak water use in urban
areas. Reuse of treated wastewater and stormwater for lawn watering appears to be
a very attractive possibility for more sustainable communities.
Infiltration and Inflow
Infiltration and inflow are major issues in urban stormwater management. For
example, the results of studies of Boulder, CO indicate that I/I is the major source of
flow during high flow periods, which might cause SSOs (Heaney et al. 1996).
Indeed, the actual sewage flow in the system is 8-10 mgd whereas flows reach 45-
50 mgd during peak periods as shown in Figure 3-6. Thus, I/I is over four times the
amount of legitimate dry weather flow (DWF). For Boulder, evidence exists that the
I/I is clean ground water since pollutant concentrations drop as sewage flow
increases. Thus, pollutant loads remain relatively constant. I/I is discussed in detail
in Chapter 6.
Summary of Sources of Dry-Weather Flow into
Sanitary and Combined Sewers
Based on a sampling of nearly 1,200 houses in 12 North American cities, in which
flows were measured for four weeks in each house, very accurate information is
available on indoor water use patterns. Indoor residential water use averages 63.2
gpcd and remains constant throughout the year. Commercial, industrial, and public
uses need to be added to this amount to estimate total water use. Essentially all of
the indoor water use enters the sanitary or combined sewers. Outdoor water use is
an important, and highly variable, water use.
Outdoor water use exceeds indoor water use on an annual average in more arid
parts of the country. It also the primary cause of peak summer water use, and can
range as high as five to six times indoor water use during these periods. Because of
its seasonal nature, outdoor water use is a major component of the peak design flow
as is water for firefighting.
Water conservation practices can reduce water use significantly, particularly outdoor
water use. The increasingly high cost of treating water should encourage a new look
at dual water systems and more aggressive reuse systems. Infiltration and inflow
are the main unknowns in designing sanitary sewer systems. I/I varies widely within
a city and across cities. Contemporary practice still allows much higher peak flows
to account for this uncertainty.
The primary source of degraded water quality for residential uses is toilet flushing
which accounts for about 30% of the DWF. Faucet water is also of concern,
especially where garbage grinders are used. Thus, about 50 % of the DWF could be
classified as "blackwater". The remaining sources including showers, baths,
clotheswashers, and dishwashers would be classified as "graywater". The largest
source of illicit "wastewater" is I/I which can range from a small fraction to several
times DWF.
3-17
-------
The conclusion from this simple water budget is that only a small portion of the
wastewater entering sewers requires a high level of treatment. The remaining water
could receive less treatment or does not need treatment because it is probably the
infiltration of clean groundwater. This mass balance indicates that innovative
changes in current practices may be very cost-effective.
3-18
-------
Indoor Use Type Volume vs. Time
Total Toilet
Shower
Faucet
D Dishwasher
D Other
Clotheswasher
U Bath
Time (hr)
Figure 3-5. Weekday variability in total residential water use for 88 houses, Boulder, Co. (Harpring 1997).
3-19
-------
50 -r
Q ซ
1
u_
40
35
30
*J !0
I 15
i
ra
Infilration /Inflow
Dry Weather Flow
0*'11.195
OWMflS
IOi'26'SS
Figure 3-6. DWF.,
1996).
and total wastewater flow, Boulder, CO, 1995 (Heaney et al.
Quantities of Precipitation in Urban Areas
Annual precipitation amounts for selected U.S. cities are listed in Table 3-6. The
results of water budgets presented in the literature and water budgets for Denver
and New York are presented in the remaining sections of this chapter.
Results of Water Budget Case Studies
Arizona
Two demonstration projects in Arizona provide examples of the results of aggressive
water and energy conservation. The first project, which began in 1985, is located in
Tucson, AZ, and is a demonstration house called Casa del Agua. The layout of the
house and lot are shown in Figures 3-7 and 3-8 (Foster et al. 1988). Stormwater
runoff from the impervious surfaces is directed to the adjacent pervious areas to
provide supplemental irrigation water. Roof runoff is collected in rain cisterns with a
total capacity of 14,000 gallons. Casa del Agua is a three bedroom, two-bathroom
residence that has been retrofitted to incorporate low water use fixtures and water
reuse systems. All graywater from the washing machine, tub, shower, lavatories,
and one side of the kitchen sink is directed into a collection sump where it receives
treatment (filtration) and then is stored until needed. Rainwater is a very high quality
water source and is low in total dissolved solids making it ideal for use for
evaporative cooling (Foster et al. 1988). It is also used for toilet flushing. The
problem with rainwater, in Tucson, is that the supply is small and highly variable.
The average annual precipitation for Tucson is only 11 inches (Karpiscak et al.
1990).
3-20
-------
The baseline water use for an average Tucson house indicates a total daily use of
105 gallons per capita, of which 68 gpcd is for indoor use. All of this water is
supplied from the municipal system. By comparison, the goal of the water
conservation project was to import only 37 gpcd and to use 12 gpcd from rainwater
and 30 gpcd from recycled graywater. The main reduction in indoor water use was
to be achieved by flushing toilets with recycled water. The actual water use during
the first year of the study was reduced by 33%. The total water use was broken
down as follows: city water (77%), gray water (24%), and rain water (4%).
Rainwater use was less than expected due to below average rainfall.
Graywater use was less than expected due to insufficient storage for gray water,
necessitating its discharge periodically to the sanitary sewer. After four years of
operation with some adaptation to improve performance, the use of municipal water
was reduced by 66%. A key change was to convert one of the two 7,000 gallon
rainwater collection tanks to a graywater storage tank (Karpiscak et al. 1990). As a
result, very little graywater was discharged to the sanitary sewer system, greatly
reducing the dry-weather wastewater flow to the WWTP. The use of graywater
storage over the year indicates seasonal variability in the utilization with the storage
full, or nearly full, in spring and then emptying during the main water use summer
period of the year.
In addition to Casa del Agua, in Tucson, a newer demonstration house opened in
Phoenix, AZ in May 1993. It is called Desert House and is located at the Desert
Botanical Garden (Karpiscak et al. 1994). The goal of this demonstration house is to
reduce energy and water use by 40%. This design will also focus on reducing peak
summer water use. The main savings in indoor water use is due to reductions in
toilet, shower, and washing machine use. The main reduction in outdoor water use
results from using graywater for lawn watering. This 1,657 square foot, one story,
single family
house is equipped with 1.5 gallon per flush toilets, 2.75 gallons per minute
showerheads, and faucet aerators. Roof runoff goes to a 4,750 gallon cistern. The
design size of the cistern had decreased significantly from the original size of 14,000
gallons in Casa del Agua. Desert House is designed for high visitor use so it is not
operated in as routine a manner as Casa del Agua.
3-21
-------
Table 3-6. Annual precipitation and days with rain for selected U.S. cities (US EPA
1979).
State
AL
CT
FL
GA
KY
LA
MA
MD
NC
NY
NY
OH
OH
PA
PA
TN
IA
IL
IN
Ml
MN
MO
MO
NE
TX
TX
TX
Wl
CO
NM
UT
AK
AZ
CA
CA
DC
HI
NV
OR
WA
WA
City
Birmingham
Harford
Miami
Atlanta
Louisville
New Orleans
Boston
Baltimore
Charlotte
Buffalo
New York
Cincinnati
Cleveland
Pittsburg
Philadelphia
Nashville
Des Moines
Chicago
Indianapolis
Detroit
Minneapolis
St. Louis
Kansas City
Omaha
Austin
Dallas
Houston
Milwaukee
Boulder
Albuquerque
Salt Lake City
Anchorage
Phoenix
Los Angeles
San Francisco
Washington
Honolulu
Las Vegas
Portland
Seattle
Spokane
Region
East
East
East
East
East
East
East
East
East
East
East
East
East
East
East
East
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Midwest
Rocky Mtn.
Rocky Mtn.
Rocky Mtn.
West
West
West
West
West
West
West
West
West
West
Mean
Max
min
Annual Precipitation, in.
53.52
42.43
57.48
47.14
41.47
63.54
42.77
44.21
43.38
35.65
42.37
39.34
32.08
36.87
42.48
45.00
31.06
33.49
39.69
30.95
24.78
36.46
34.07
25.90
32.58
34.55
45.26
27.57
18.57
8.13
14.74
14.71
7.42
14.62
20.78
40.78
23.96
4.35
39.91
34.10
17.19
3330
63.54
4.35
Annual Days w/ Rain
118
128
127
115
122
120
128
112
110
165
119
134
156
146
115
120
105
120
124
130
113
104
98
94
81
80
103
119
87
58
87
126
34
35
67
107
99
25
149
164
118
109
165
25
Average in/day
0.45
0.33
0.45
0.41
0.34
0.53
0.33
0.39
0.39
0.22
0.36
0.29
0.21
0.25
0.37
0.38
0.3C
0.28
0.32
0.24
0.22
0.35
0.35
0.28
0.40
0.43
0.44
0.23
0.21
0.14
0.17
0.12
0.22
0.42
0.31
0.38
0.24
0.17
0.27
0.21
0.15
031
0.53
0.12
3-22
-------
Figure 3-7. Front yard of Casa del Agua (Foster et al. 1988)
1) grape vine will grow over the lattice for more complete shade, 2) main entry
defined and visually separated from street/driveway, 3) reed covered entry arbor
provides shade from the west sun, 4) Rhus lancea, 5) Cassia phyllodinea, 6)
Lantana montevidensis, 7) perimeter of yard is bermed to contain the rain and direct
it to the plants, 8) cobblestone driveway directs rain to plants.
3-23
-------
Figure 3-8. Back yard of Casa del Agua (Foster et al. 1988).
1) evaporative cooler, 2) new aluminum gutter, 3) new filon greenhouse roof, 4)
existing gravel roof, 5) new filon porch roof, 6) new aluminum downspout, 7) pipe
from downspout to filter, 8) concrete filter box with screen, 9) rain cisterns (14,000
gallons total), 10) cistern access, 11) supply to pump, 12) graywater cistern (800
gallons), 13) supply to pump, 14) overflow to sewer, 15) seat walls, 16) brick paving
defined and visually separated from street/driveway, 17) kalanchoe species, 18)
herb garden, 19) Acacia pennacula.
Germany
According to Grottker and Ottterpohl (1996), "the separation of feces and urine from
the domestic waste water is identified as the most important step to a sustainable
water concept." A 100-unit housing complex in Lubeck-Flintenbreite, Germany is
being built using this concept. Key components of this innovative project are:
1. Storm water of private properties is re-used for toilet flushing, washing-
3-24
-------
machines and irrigation in gardens. The overflow of stormwater storage is
connected to the infiltration trenches of the road drainage. Two
advantages of this approach are less potable water consumption and less
detergent consumption.
2. Storm water from roads and other public surfaces is drained by infiltration
depressions with trenches to the small creek. This method increases
evaporation and retention of storm runoff.
3. Graywater is treated in aerated sand filters or constructed wetlands. The
overflow is connected to the infiltration trenches of the public road
drainage. Two advantages of this approach are using a simple treatment
technique with high efficiency and waste water runoff retention.
4. Feces and other organic matter from households are transported by a
vacuum system to a semi-central aerobic reactor with sludge storage,
where the organic matter of 100 living units is treated. Vacuum toilets are
used as inlets. Further, collected organic matter/waste is added to the
anaerobic reactor. The treated sludge is stored and later carried to a
farm. Three advantages of this approach are no I/I problem, less pollution
in the treated sludge yields very high fertilizer, and biogas can be used in
a semi-central heating system
This new system will be completely monitored for two years to do a final evaluation.
Melbome, Australia
Mitchell et al. (1996) used a daily water budget simulation model to evaluate the
impact of on-site water management. They evaluated water use for two blocks in
Melbourne, Australia. The attributes of each block are shown in Table 3-7.
Table 3-7. Attributes of two neighborhoods in Melbourne, Australia (Mitchell et al.
1996).
Attribute
Rainfall, mm/vr
Rain, davs/vr
Evaporative demand, mm/vr.
Soil Type
Area, so m
Roof plan area, sa m
Paved area, sq m
Garden area, sa m
Peoole/house
Type of garden
Neighborhood
Essendon
591
196
1054
clay
750
203
113
434
3
standard
Scores by
887
215
1054
silty clay
750
203
113
434
3
standard
The following retrofits were evaluated in these two areas:
3-25
-------
13 kiloliter rain tank for storage of roof runoff for laundry, toilet, and garden
water uses. Spillage is directed to the storm drainage network.
Graywater from bathrooms and laundry is used for gardening through a
sub-surface irrigation system. Overflows go to the wastewater sewer.
The simulated performance of the modified system is summarized in Table 3-8
(Mitchell et al. 1996).
Table 3-8 Simulated performance of modified urban systems (Mitchell et al. 1996).
Attribute
Water demand, kl/yr
Reduced demand for imported water, %
Reduced off-site stormwater runoff, %
Reduced wastewater runoff, %
Usage from rainwater tank, kl/yr
Rain tank deficit/demand
Use of graywater, kl/yr
Graywater deficit/demand
Neighborhood
Essendon
278
41
56
11
84
0.48
28
0.65
Scoresby
265
49
49
8
107
0.3
24
0.65
The reduction in demand for imported water was 41 and 49% for the two systems
while off-site stormwater runoff was reduced by 56 and 49% for the two
neighborhoods. These results indicate the potentially major impact of on-site water
management on overall water use.
Adelaide, Australia
Adelaide is typical of other cities in that the water supply, wastewater, and
stormwater infrastructure systems have developed independently of each other and
now exist as large centralized systems. Adelaide has a separate sewer system.
The demand for water in Adelaide, shown in Figure 3-9, indicates that direct contact
needs are about 52 GL/a, 8 GL/a for process and manufacturing, 82 GL/a for
gardens and other irrigation, and 18 GL/a for toilet flushing, or a total of 157 Gl/a.
Thus, the majority of the water demand does not require high quality water. The
potentially available local supply, shown in Figure 3-10, indicates 30GL/a from roof
runoff, 95 GL/a from hillside runoff, 61 GL/a from street runoff, 52 GL/a from
graywater effluent, and 24 GL/a from blackwater effluent, or a total of 260 GL/a.
Thus, on the average, the potential local supply exceeds the demand, and the
possibility exists for a locally sustainable system if the necessary storage, treatment,
and redistribution facilities could be provided.
The monthly variability in demand, rural runoff, effluent, and urban runoff are shown
in Figure 3-11. The present centralized system utilizes 550 kl per person in storage.
According to calculations of Clark et al. (1997), the decentralized system would
require only 150 kl per person to provide adequate water during a one in a 100 year
drought. The overall proposed water budget components for the Adelaide system is
shown in Figure 3-12.
3-26
-------
Urban wastewater is being reused at several locations in Australia, (e.g., Rouse Hill
near Sydney), with a first stage of 25,000 dwellings (Law 1997) and on a small scale
at New Haven Village in Adelaide with 67 dwellings. New Haven Village is an
innovative development of 65 medium density affordable dwellings that is designed
as an implementation of the integrated approach (Clark et al. 1997). Key water
management features include on-site treatment and reuse of household effluent, an
innovative stormwater drainage system, and demonstration technology for an
underground sub-surface irrigation system. With on-site treatment and reuse of
household sewage and stormwater runoff, virtually no water leaves the site. The
wastewater plant is located underground. Treated water is used for irrigation and
toilet flushing, thereby reducing water demand by 50%. Two 22,500 liter
underground storage tanks provide effluent storage. Sludge is disposed to a sludge
thickening plant on site. Street widths have been reduced from 12.4 meters to only
6.8 meters. The stormwater is captured in a 40,000 liter underground concrete tank.
Overflows go to an infiltration trench, and finally to a retention area for extremely
heavy rainfalls. The tank delivers stormwater to the treatment plant at night for
treatment.
Other larger demonstration projects are underway in Australia. Notable projects
include New Brompton Estate in which roof runoff is being stored in an underground
aquifer. Overall, the studies by Clark et al. (1997) demonstrate the feasibility of
water self-sufficiency for the City of Adelaide with an annual rainfall of 600 mm,
which is typical of average rainfall conditions in the United States.
3-27
-------
Contact Consumption
Process and
Manufacturing
Gardens and Other
Irrigation
Low Grade (toilet flush,
etc.)
Fotal=
157 GlL/a
0 10 20 30
40 50
GL/a
60 70
Increasing
Quality
90
Figure 3-9. Consumption of water in Adelaide, Australia according to quality (Clark,
1997).
3-28
-------
Roof Runoff
Hillsface Runoff
Street Runoff
Graywater Runoff
Blackwater Effluent
Tota
1=260 GL/a
Increasing
Quality
0 10 20 30 40 50 60 70 80 90 100
GL/a
Figure 3-10. Availability of wastewaters in Adelaide, Australia according to quality
(Clark, 1997).
3-29
-------
50.00
o.oo I I I I Kl I I I I I I 1 r KKr I I I I I I
JMMJSNJMMJSN
Month
Figure 3-11. Typical monthly water supply and demand, Adelaide, Australia (Clark
1997).
| Siln
Reuse of
Storm Wat*;1
1
1 Jnik ng WEcerl
i
I
Ihunan iซir:g 1
1
Coniutiซr
L';.jtK-
1
I
] I ป^ I
Figure 3-12. Flow chart of proposed integrated water system for Adelaide, Australia
(Clark etal. 1997).
3-30
-------
Simulated Monthly Urban Water Budgets for Denver and New York
General
This section presents the results of monthly simulations of water budgets for cities
with climates similar to New York and Denver. The results should not be construed
to be accurate representations of actual conditions in these two cities. The purpose
of presenting these case studies is to show the relative importance of the various
terms in the water budget and to show the impact of climatic conditions. The
common assumptions for the comparative studies of representative urban
neighborhoods in Denver and New York are presented in Table 3-9.
Table 3-9. Assumed common attributes of representative neighborhoods in Denver,
CO and New York, NY.
Area, acres
Roof area, acres
Driveway area, acres
Local street area, acres
Major street area, acres
Lawn area, acres
Directly connected imperviousness, DCI, %
People
Impervious
Area
Total
15
10
10
5
Impervious
Area Directly
Connected
5
5
10
5
100
60
25
1,000
Water Use
Indoor Water Use
Assumed per capita water use estimates for the two cities are shown in Table 3-10.
Table 3-10. Assumed indoor water use for Denver, CO and New York, NY
neighborhoods.
Item
Toilets
Showers
Baths
Faucet-drinking
Faucet-other
Dishwashers
Clothes washers
Leaks
Total
Flow
(gpcd)
16
10
1
1
9
2
14
7
60
%of
Total
26.6
16.7
1.7
1.7
15.0
3.3
23.3
11.7
100
Black
Water
(gpcd)
16
10
1
1
9
2
14
1
54
Gray
Water
(gpcd)
6
6
The land use for the two representative neighborhoods is typical low density
3-31
-------
residential. The same population density of 10 persons per acre is used for the
Denver and New York because since the purpose of this exercise is to illustrate the
impact of rainfall and climate.
Outdoor Water Use
The estimated outdoor water use for the two cities is shown in Table 3-11.
Table 3-11. Estimated monthly outdoor water use in Denver, CO and New York, NY.
Month
1
2
3
4
5
6
7
8
9
10
11
12
Mean
Denver
(gpcd)
0
0
15
50
90
175
210
175
70
20
0
0
67
New York
(gpcd)
0
0
0
0
40
70
100
70
30
0
0
0
26
Inspection of Table 3-11 indicates that the per capita outdoor water use of 67 gpcd
for this prototype area in Denver exceeds the indoor water use of 60 gpcd whereas
average annual outdoor water use on New York of 26 gpcd is less than one half of
the indoor water use because New York receives more annual precipitation and has
lower evapotranspiration needs than Denver. Peak water use occurs during the
summer in both locations and most of that peak is caused by lawn watering.
Denver's peak monthly outdoor water use of 210 gpcd is over three times the indoor
water use during July. Thus, urban lawn watering is the dominant component in
peak water use in most urban areas. Peak water use is an important factor in sizing
water infrastructure.
Total Water Use
Total water use (indoor plus outdoor) for Denver and New York is shown in Table 3-
12.
3-32
-------
Table 3-12. Total monthly water use for representative residential areas in Denver,
CO and New York, NY.
Total Water Use for Denver
Month
1
2
3
4
5
6
7
8
9
10
11
12
Black
Water
(gpcd)
17
17
17
17
17
17
17
17
17
17
17
17
Gray
Water
(gpcd)
43
43
43
43
43
43
43
43
43
43
43
43
Total
(gpcd)
60
60
60
60
60
60
60
60
60
60
60
60
Outdoor
(gpcd)
0
0
15
50
90
175
210
175
70
20
0
0
Total
(gpcd)
60
60
75
110
150
235
270
235
130
80
60
60
[Mean |17 |43 |60 |67
127
Total Water Use for New York
Month
1
2
3
4
5
6
7
8
9
10
11
12
Black
Water
(gpcd)
17
17
17
17
17
17
17
17
17
17
17
17
Gray
Water
(gpcd)
43
43
43
43
43
43
43
43
43
43
43
43
Total
(gpcd)
60
60
60
60
60
60
60
60
60
60
60
60
Outdoor
(gpcd)
0
0
0
0
40
70
100
70
30
0
0
0
Total
(gpcd)
60
60
60
60
100
130
160
130
90
60
60
60
[Mean
43
60
26
Histograms of monthly water use for Denver and New York are shown in Figures 3-
13 and 3-14. Per capita indoor residential water use is the same for the two cities
with only 17 gpcd of the water use producing black water and 43 gpcd of gray water.
There is very little monthly variability in indoor water use. On the other hand,
outdoor water use varies widely over the year and is the predominant cause of peak
water use.
3-33
-------
1.150
o
D Outdoor
D Graywater
D Blackwater
34567
Months
9 10 11 12
Figure 3-13. Average water use, Denver, CO.
160
140
100
a
o
Q.
o
20
-
DOutdoor
1 Graywater
II Blackwater
-
1 2 3456 7 8 9 10 11 12
Months
Figure 3-14. Average water use, New York, NY.
3-34
-------
Wastewater
Wastewater or DWF = indoor water use residual + I/I. Nearly all of indoor water use
enters the sanitary sewer system. Small losses in indoor water use, (e.g., from
taking water on a picnic), are probably offset by the discharge to the sewer system
of fluids brought into the house that are poured down the drains (e.g. leftover soft
drink). Thus, it is reasonable to assume that 100% of the indoor water use, or its
equivalent, enters the wastewater system. Salient assumptions used in the Denver-
New York analysis are:
Indoor water use residuals: Assume 100% of indoor water use goes to
the sanitary or combined sewer. This component is DWF.
Infiltration/inflow: I/I = base infiltration + rain-induced inflow and infiltration.
Infiltration varies widely depending on construction and maintenance
practices. Sanitary sewers are designed for two to six times DWF with the
base sewer infiltration assumed to be 60 gpcd. Rain-induced infiltration, in
gpcd, is computed as follows:
Denver, I = 60 times P(monthly inches)
New York, I = 20 times P(monthly inches)
The estimated I/I is presented for illustrative purposes and does not
necessarily represent actual I/I for these two cities.
The total estimated wastewater flows for Denver, CO and New York, NY are shown
in Figures 3-15 and 3-16 and Table 3-13. As with indoor and outdoor water use,
black water and gray water associated with indoor water use are essentially constant
throughout the year. However, I/I varies widely over the year and determines the
design capacity for the wastewater network. Traditionally, I/I has been accepted as
part of normal sewer flows. This topic is evaluated in Chapter 6.
3-35
-------
c
O
[
[
[
3 I/I
IGraywater
DBIackwater
1 23456789 10
Months
11 12
Figure 3-15. Monthly residential wastewater discharge, Denver, CO.
Q. 80
O
10 11 12
Months
Figure 3-16. Monthly residential wastewater discharge, New York, NY.
3-36
-------
Table 3-13. Total monthly wastewater flows for Denver, CO and New York, NY.
Denver
Month
1
2
3
4
5
6
7
8
9
10
11
12
Total
Mean
Precip.
(inches)
0.5
0.7
1.3
1.5
2.0
2.5
2.4
2.2
1.2
1.0
0.7
0.6
17.0
1.38
Black
Water
(gpcd)
17
17
17
17
17
17
17
17
17
17
17
17
17
Gray
Water
(gpcd)
43
43
43
43
43
43
43
43
43
43
43
43
43
I/I
(gpcd)
30
42
78
90
120
150
144
132
72
60
42
36
83
Total
(gpcd)
90
102
138
150
180
210
204
192
132
120
102
96
143
New York
Month
1
2
3
4
5
6
7
8
9
10
11
12
Total
Precip.
(inches)
3.0
4.0
4.0
3.0
3.0
3.5
4.0
3.8
4.2
4.0
3.8
3.0
43.0
Black
Water
(gpcd)
17
17
17
17
17
17
17
17
17
17
17
17
Gray
Water
(gpcd)
43
43
43
43
43
43
43
43
43
43
43
43
I/I
(gpcd)
60
80
80
60
60
70
80
76
84
80
76
60
Total
(gpcd)
120
97
97
77
77
87
97
93
101
97
93
77
[Mean
3.61
17
43
72
93
3-37
-------
Stormwater Runoff
The final component of the urban water budget to be estimated is the quantity of
stormwater runoff. General characteristics of the study areas were shown in Table
3-9.
The runoff volume, R, from precipitation, P, is estimated as R = C*P where C =
runoff coefficient. This coefficient is assumed to equal the directly connected
imperviousness, I. For this example, I = 0.25. The estimated monthly precipitation
and runoff for Denver and New York are shown in Table 3-14.
Table 3-14. Monthly precipitation and runoff for Denver, CO and New York, NY.
Month
1
2
3
4
5
6
7
8
9
10
11
12
Total
Denver
Precipitation
(inches)
0.5
0.7
1.3
1.5
2.0
2.5
2.4
2.2
1.2
1.0
0.7
0.6
16.6
Runoff
(inches)
0.13
0.18
0.33
0.38
0.50
0.63
0.60
0.55
0.30
0.25
0.18
0.15
4.15
New York
Precipitation
(inches)
3.0
4.0
4.0
3.0
3.0
3.5
4.0
3.8
4.2
4.0
3.8
3.0
43.3
Runoff
(inches)
0.75
1.00
1.00
0.75
0.75
0.88
1.00
0.95
1.05
1.00
0.95
0.75
10.83
Summary Water Budgets
Water use and wastewater flows are typically expressed in terms of gallons per day.
Stormwater runoff is usually expressed in inches averaged over the entire
catchment. All flows were converted to inches averaged over the 100 acre
catchment with 1,000 residents. The common assumed values, presented earlier in
this analysis, are:
1. Population
2. Area, acres
3. Indoor water use, gpcd
4. Runoff coefficient
5. Conversion factors:
1,000
100
60
0.25
7.48 gallons = 1 cu ft
43,560sqft= 1 acre
The summary results for Denver, CO and New York, NY are presented in Tables 3-
15 and 3-16. Denver results indicate a natural input from precipitation of 16.6
inches per year and imported water of 17.15 inches per year, slightly more than the
natural input. The majority of the imported water is used for lawn watering. On the
output side for Denver, I/I at 11.19 inches is the largest source of the 19.26 inches of
3-38
-------
water going to the WWTP. Urban runoff contributes an additional 4.15 inches of
water leaving the system. Nearly 40% of the urban runoff falls on roofs and
driveways. A good portion of that water could be retained on-site and infiltrated
and/or used for lawn watering. Urban runoff alone is insufficient to provide sufficient
water for lawn watering. However, urban runoff and graywater do provide enough
water to meet essentially all of the lawn watering needs.
New York results indicate a natural input from precipitation of 43.3 inches per year
and imported water of 11.57 inches per year, slightly more than a quarter of the
natural input. The majority of the imported water is used for indoor purposes. On
the output side for New York, I/I at 9.69 inches is the largest source of the 17.76
inches of water going to the WWTP. Urban runoff contributes an additional 10.83
inches of water leaving the system. Nearly 40% of the urban runoff falls on roofs
and driveways. A good portion of that water could be retained on-site and infiltrated
and/or used for lawn watering. Urban runoff alone is sufficient to provide sufficient
water for lawn watering.
Future Urban Water Scenarios
Future scenarios for urban water use and wastewater discharges include
combinations of the following futures. Water use estimates in gallons per capita per
day include the pro rata additional nonresidential use, which is included in the per
capita figure.
Status Quo: This scenario means continuing the current pattern of water
use and wastewater disposal. The nationally mandated compulsory use
of low flush toilets should reduce per capita consumption by 10-15 gpcd.
Legitimate sewage quantities should be in the 75-90 gpcd range. This per
capita figure includes the added water use of non-residential customers
averaged over the residential population. I/I would add another 50 to 400
gpcd to these flows. Solids loading will remain the same; thus, DWF
concentrations will increase accordingly.
Significant indoor water conservation: This scenario means replacing
existing plumbing systems with water conserving devices including low-
flush toilets, low flow rate shower heads, lower water using appliances.
Expected sewage quantities are in the 50-65 gpcd range. Some I/I control
is expected which reduces I/I to 25 to 300 gpcd. Increased DWF
concentrations are expected.
Gray water systems with aggressive I/I control: This scenario is defined
as the preceding scenario with on-site use of gray water for lawn watering
and toilet flushing. Expected sewage quantities are in the 30-45 gpcd
range. Also assumed is aggressive I/I control, which reduces I/I to 25 to
100 gpcd. Much higher DWF concentrations will occur.
Thus, future water conservation and I/I control practices can be expected to have a
significant impact on wastewater discharges or dry-weather flow. Having to deal
with much lower volumes of water opens up opportunities for innovative stormwater
3-39
-------
management. For example, Pruel (1996) suggests storing DWF on-site during wet-
weather periods. If only black water has to be stored, then this option becomes
more attractive.
3-40
-------
Table 3-15. Final monthly water budget for Denver, CO.
Monthly
(All values are in inches)
Month
1
2
3
4
5
6
7
8
9
10
11
12
Total
Precip-
itation
0.5
0.7
1.3
1.5
2.0
2.5
2.4
2.2
1.2
1.0
0.7
0.6
16.6
Indoor
Water
Use
0.69
0.62
0.69
0.66
0.69
0.66
0.69
0.69
0.66
0.69
0.66
0.69
8.07
Outdoor
Water
Use
0.00
0.00
0.17
0.55
1.03
1.93
2.40
2.00
0.77
0.23
0.00
0.00
9.08
Total
0.69
0.62
0.86
1.22
1.71
2.60
3.08
2.68
1.44
0.91
0.66
0.69
17.15
DWF
0.69
0.62
0.69
0.66
0.69
0.66
0.69
0.69
0.66
0.69
0.66
0.69
8.07
I/I
0.34
0.43
0.89
0.99
1.37
1.66
1.64
1.51
0.80
0.69
0.46
0.41
11.19
Total
1.03
1.05
1.58
1.66
2.06
2.32
2.33
2.19
1.46
1.37
1.13
1.10
19.26
Urban
Runoff
0.13
0.18
0.33
0.38
0.50
0.63
0.60
0.55
0.30
0.25
0.18
0.15
4.15
Days/month
31
28
31
30
31
30
31
31
30
31
30
31
365
Annual
(All values are in inches)
Inputs:
Precipitation
Indoor use
Black water
Gray water
Outdoor use
Total
Outputs:
Wastewater
Legitimate
I/I
Urban runoff
Roofs
Driveways
Local streets
Major streets
Sub-total, outputs
Recharge to local
receiving waters and
groundwater
Total
2.29
5.78
0.83
0.83
1.66
0.83
16.60
8.07
9.08
33.75
8.07
11.19
4.15
23.41
10.34
33.74
Quality Aspects
High quality
Could use low quality
Need high quality
Need moderate quality
Requires high level of treatment
Requires modest level of
treatment
Requires little or no treatment
Requires little or no treatment
Requires little or no treatment
Requires little treatment
Requires moderate treatment
Good quality because of
subsurface infiltration
3-41
-------
Table 3-16. Final monthly water budget for New York, NY.
Monthly
(All values are in inches)
Month
1
2
3
4
5
6
7
8
9
10
11
12
Total
Precip-
itation
3.0
4.0
4.0
3.0
3.0
3.5
4.0
3.8
4.2
4.0
3.8
3.0
43.3
Indoor
Water
Use
0.69
0.62
0.69
0.66
0.69
0.66
0.69
0.69
0.66
0.69
0.66
0.69
8.07
Outdoor
Water
Use
0.00
0.00
0.00
0.00
0.46
0.77
1.14
0.80
0.33
0.00
0.00
0.00
3.5
Total
0.69
0.62
0.69
0.66
1.14
1.44
1.83
1.48
0.99
0.69
0.66
0.69
11.57
DWF
0.69
0.62
0.69
0.66
0.69
0.66
0.69
0.69
0.66
0.69
0.66
0.69
8.07
I/I
0.69
0.82
0.91
0.66
0.69
0.77
0.91
0.87
0.93
0.91
0.84
0.69
9.69
Total
1.37
1.44
1.60
1.33
1.37
1.44
1.60
1.55
1.59
1.60
1.50
1.37
17.76
Urban
Runoff
0.75
1.00
1.00
0.75
0.75
0.88
1.00
0.95
1.05
1.00
0.95
0.75
10.83
Days/month
31
28
31
30
31
30
31
31
30
31
30
31
365
Annual
(All values are in inches)
Inputs:
Precipitation
Indoor use
Black water
Gray water
Outdoor use
Total
Outputs:
Wastewater
Legitimate
Blackwater
Graywater
I/I
Urban runoff
Roofs
Driveways
Local streets
Major streets
Sub-total, outputs
Recharge to local
receiving waters and
groundwater
Total
2.29
5.78
2.29
5.78
2.17
2.17
4.33
2.17
43.30
8.07
3.50
54.87
8.07
9.69
10.83
23.41
26.29
54.87
Quality Aspects
High quality
Could use low quality
Need high quality
Need moderate quality
Requires high level of treatment
Requires modest level of treatment
Requires little or no treatment
Requires little or no treatment
Requires little or no treatment
Requires little treatment
Requires moderate treatment
Good quality because of
subsurface infiltration
3-42
-------
References
Basta, D.J. and B.T. Bower (Eds.) (1982). Analyzing Natural Systems: Analysis for
Regional Residuals-Environmental Quality Management. Resources for the Future,
Inc. Washington, D.C.
Cantor, K.P., R. Hoover, P. Hartageetal. (1987). Bladder cancer, drinking water
source, and tap water consumption. J. National Cancer Institute. 79(6): 1269-1279.
Clark, R., A. Perkins and S.E. Wood (1997). Water Sustainability in Urban Areas-An
Adelaide and Regions Case Study. Report One - An Exploration of the Concept.
Dept. of Environment and Natural Resources. Adelaide, Australia. Draft.
Courtney, B.A. (1997). An Integrated Approach to Urban Irrigation: The Role of
Shading, Scheduling, and Directly Connected Imperviousness. MS Thesis, Dept. of
Civil, Environmental, and Architectural Engineering. U. of Colorado. Boulder, CO.
Denver Water (1997). Comprehensive Annual Financial Report for the Year Ended
December 31, 1996. Denver, CO.
DeOreo, W., J. Heaney and P. Mayer (1996). Flow Trace Analysis to Assess Water
Use. Journal of the American Water Works Association. Jan., p. 79-80.
Edwards, K. and L. Martin (1995). A Methodology for Surveying Domestic Water
Consumption. Journal of the Chartered Institution of Water and Environmental
Management. Vol. 9, No. 5., p. 47-489.
Foster, K. E., M. M. Karpiscakand R. G. Brittain (1988a). Casa Del Agua: A
Residential Water Conservation and Reuse Demonstration Project in Tucson, AZ.
Water Resources Bulletin. 24(6): 1201-1206.
Foster, K. E., M. M. Karpiscakand R. G. Brittain (1988b). Casa Del Agua: A
Residential Water Conservation and Reuse Demonstration Project in Tucson, AZ.
Water Resources Bulletin. 24(6), p. 1201-1206.
Friedler, E., D.M. Brown, and D. Butler (1996). A Study of WC Derived Sewer
Solids. Water Science and Technology. Vol. 33, No. 9, p. 17-24.
Fujita, S. (1996). Measures to promote stormwater infiltration. Proceedings of the
7th International Conference on Urban Storm Drainage. Hannover, Germany, p.
407-412.
Grimmond, C. S. B., T. R. Oke and D. G.Steyn (1986a). Urban Water Balance 1. A
Model for Daily Totals. Water Resources Research. 22(10): 1397-1403.
3-43
-------
Grimmond, C. S. B. and T. R. Oke (1986b). Urban Water Balance 2. Results from a
Suburb of Vancouver, British Columbia. Water Resources Research. 22(10): 1404-
1412.
Grotter, M., and R. Otterpohl (1996). Integrated Urban Water Concept. Proceedings
of the 7th International Conference on Urban Storm Drainage. Hannover, Germany.
p. 1801-1806.
Harpring, J. S. (1997). Nature of Indoor Residential Water Use. MS Thesis, Dept. of
Civil, Environmental, and Architectural Engineering. U. of Colorado. Boulder, CO.
Heaney, J.P. (1994). Towards Integrated Urban Water System Management. Proc.
HEC Workshop on Future Directions of Urban Hydrology. Davis, CA.
Heaney, J.P., L. Wright and Samsuhadi (1996). Risk Analysis in Urban Stormwater
Quality Management, in Haimes, Y.Y., Moser, D.A., and E.Z. Stakhiv, (Eds.) Risk-
Based Decision Making in Water Resources VII. ASCE. New York, NY. p. 219-
248.
Henze, M., L. Somlyody, W. Schilling, and J. Tyson (Eds.) (1997). Sustainable
Sanitation. Water Science and Technology. Vol. 35, No. 9.
Herrmann, T. and U. Klaus (1996). Fluxes of nutrients in urban drainage systems:
assessment of sources, pathways and treatment technologies. Proceedings of the
7th International Conference on Urban Storm Drainage. Hannover, Germany, p.
761-766.
Imbe, M., T. Ohta and N. Takano (1996). Quantitative Assessment of Improvement
in Hydrological Water Cycle in Urbanized River Basin. Proceedings of the 7th
International Conference on Urban Storm Drainage. Hannover, Germany, p. 1085-
1090.
Johnson, H., T.A. Stanstrom, J.S. Svensson, and A. Sandin(1997). Source-
Separated Urine-Nutrient and Heavy Metal Contents Water Saving and Fecal
Contamination. Water Science and Technology. Vol. 35, No. 9, p. 45-152.
Jones, D. E. (1971). Urban Water Resources Management Affects the Total Urban
Picture. Chapter 1F in Albertson, M.L., Tucker, L.S., and Taylor, D.C. (Eds.)
Treatise on Urban Water Systems. Colorado State University. Ft. Collins, CO.
Joyce, J. (1995). Odor and Corrosion Control in Collection System: A Growing
Problem? Water Environment federation. Sewers of the Future. Alexandria, VA.
P.9-1 to 9-12.
Karpiscak, M. M., K. E. Foster and N. Schmidt (1990). Residential Water
Conservation: Casa Del Agua. Water Resources Research. 26(6):939-948.
3-44
-------
Karpiscak, M.M., R.G Brittain and K.E. Foster (1994). Desert House: A
Demonstration/Experiment in Efficient Domestic Water and Energy Use. Water
Resources Bulletin. Vol. 30, No. 2, p. 329-334.
Law, I. (1997). Domestic Non-potable Reuse - Why Even Consider it? Water,
May/June.
Kneese, A.V., R.U. Ayres and R.C. d'Arge (1970). Economics and the Environment-
A Materials Balance Approach. The Johns Hopkins Press. Baltimore, MD.
Maddaus, W.O. (1987). Water Conservation. American Waterworks Association.
Denver, CO.
Mayer (1995). Residential Water Use and Conservation Effectiveness: A Process
Approach. Master's Thesis, University of Colorado. Boulder, CO.
Mayer, P. W., W. B. De Oreo, J. 0. Nelson, E. Opitz and R. Allen (1997). North
American Residential End Use Study Progress Report to American Water Works
Association Research Foundation. Denver, CO.
McPherson, M.B. (1973). Need for Metropolitan Water Balance Inventories. Jour, of
the Hydraulics Div. ASCE. 99, HY10, p. 1837-1848.
McPherson, M.B. et al. (1968). Systematic Study and Development of Long-Range
Programs of Urban Water Resources Research. Report to Office of Water
Resources Research. NTIS No. PB 184 318. Washington, D.C.
Mitchell, V.G., R.G. Mein and T.A. McMahon (1996). Evaluating the Resource
Potential of Stormwater and Wastewater: an Australian Perspective. Proceedings of
the 7th International Conference on Urban Storm Drainage. Hannover, Germany, p.
1293-1298.
Nelen, A.J.M., A.C. deRidderand E.G. Hartman (1996b). Planning of a New Urban
Area in a Municipality of Ede. Using a New Approach to Environmental Protection.
Pruell, H.C. (1996). Combined Sewage Prevention System (CSPS) for Domestic
Wastewater Source Control. In Proceedings of the 7 International Conference on
Urban Storm Drainage. Hannover, Germany. P. 193-198.
Sakrison, R.G. (1996). New Urbanism, Growth Management and the Effect on
Metropolitan Water demands. Proc. of Conserv 96, ASCE, AWRA, and AWWA.
Orlando, FL. p. 19-26.
Sieker, F. and H-R. Verworn. (Eds.). Proceedings of the 7th International
Conference on Urban Storm Drainage. Hannover, Germany, p. 259-264.
3-45
-------
Stephenson, D. (1996). Evaluation of Effects of Urbanization on Storm Runoff.
Proceedings of the 7th International Conference on Urban Storm Drainage.
Hannover, Germany, p. 31-36.
Stadjuhar, L. (1997). Outdoor Residential Water Use. Master's Thesis, University
of Colorado. Boulder, CO.
US Environmental Protection Agency (USEPA) (1979). 1978 Needs Survey Cost
Methodology for Control of Combined Sewer Overflow and Stormwater Discharges.
EPA-430/9-79-002. Washington, DC.
3-46
-------
Chapter 4
Source Characterization
Robert Pitt
The Source Concept
Urban runoff is comprised of many separate source area flow components that are
combined within the drainage area and at the outfall before entering the receiving water.
Considering the combined outfall conditions alone may be adequate when evaluating
the long term, area-wide effects of many separate outfall discharges to a receiving
water. However, if better predictions of outfall characteristics (or the effects of source
area controls) are needed, then the separate source area components must be
characterized. The discharge at the outfall is made up of a mixture of contributions from
different source areas. The "mix" depends on the characteristics of the drainage area
and the specific rain event. The effectiveness of source area controls is, therefore,
highly site and storm specific.
Various urban source areas all contribute different quantities of runoff and pollutants,
depending on their characteristics. Impervious source areas may contribute most of the
runoff during small rain events. Examples of these source areas include paved parking
lots, streets, driveways, roofs, and sidewalks. Pervious source areas become important
contributors for larger rain events. These pervious source areas include gardens,
lawns, bare ground, unpaved parking areas and driveways, and undeveloped areas.
The relative importance of the individual sources is a function of their areas, their
pollutant washoff potentials, and the rain characteristics.
The washoff of debris and soil during a rain is dependent on the energy of the rain and
the properties of the material. Pollutants are also removed from source areas by winds,
litter pickup, or other cleanup activities. The runoff and pollutants from the source areas
flow directly into the drainage system, onto impervious areas that are directly connected
to the drainage system, or onto pervious areas that will attenuate some of the flows and
pollutants, before they discharge to the drainage system.
Sources of pollutants on paved areas include on-site particulate storage that cannot be
removed by usual processes such as rain, wind, and street cleaning. Atmospheric
deposition, deposition from activities on these paved surfaces (e.g., auto traffic, material
storage) and the erosion of material from upland areas that directly discharge flows onto
these areas, are the major sources of pollutants to the paved areas. Pervious areas
contribute pollutants mainly through erosion processes where the rain energy dislodges
soil from between vegetation. The runoff from these source areas enters the storm
drainage system where sedimentation in catchbasins or in the sewerage may affect
their ultimate discharge to the outfall. In-stream physical, biological, and chemical
processes affect the pollutants after they are discharged to the ultimate receiving water.
4-1
-------
Knowing when the different source areas become "active" (when runoff initiates from the
area, carrying pollutants to the drainage system) is critical. If pervious source areas are
not contributing runoff or pollutants, then the prediction of urban runoff quality is greatly
simplified. The mechanisms of washoff and delivery yields of runoff and pollutants from
paved areas are much better known than from pervious urban areas (Novotny and
Chesters 1981). In many cases, pervious areas are not active except during rain events
greater than at least five or ten mm. For smaller rain depths, almost all of the runoff and
pollutants originate from impervious surfaces (Pitt 1987). However, in many urban
areas, pervious areas may contribute the majority of the runoff, and some pollutants,
when rain depths are greater than about 20 mm. The actual importance of the different
source areas is highly dependent on the specific land use and rainfall patterns.
Obviously, in areas having relatively low-density development, especially where
moderate and large sized rains occur frequently (such as in the Southeast), pervious
areas typically dominate outfall discharges. In contrast, in areas having significant
paved areas, especially where most rains are relatively small (such as in the arid west),
the impervious areas dominate outfall discharges. The effectiveness of different source
controls is, therefore, quite different for different land uses and climatic patterns.
If the number of events exceeding a water quality objective are important, then the small
rain events are of most concern. Stormwater runoff typically exceeds some water
quality standards for practically every rain event (especially for bacteria and some
heavy metals). In the upper midwest, the median rain depth is about six mm, while in
the southeast, the median rain depth is about twice this depth. For these small rain
depths and for most urban land uses, directly connected paved areas usually contribute
most of the runoff and pollutants. However, if annual mass discharges are more
important (e.g. for long-term effects), then the moderate rains are more important.
Rains from about 10 to 50 mm produce most of the annual runoff volume in many areas
of the U.S. Runoff from both impervious and pervious areas can be very important for
these rains. The largest rains (greater than 100 mm) are relatively rare and do not
contribute significant amounts of runoff pollutants during normal years, but are very
important for drainage design. The specific source areas that are most important (and
controllable) for these different conditions vary widely.
This chapter describes sources of urban runoff flows and pollutants based on many
studies as found in the literature. This chapter also reports on the specific source area
sampling activities conducted as part of this research funded by the USEPA for use in
this report.
Sources and Characteristics of Urban Runoff Pollutants
Years of study reveal that the vast majority of stormwater toxicants and much of the
conventional pollutants are associated with automobile use and maintenance activities
and that these pollutants are strongly associated with the particulates suspended in the
stormwater (the non-filterable components or suspended solids). Reducing or
modifying automobile use to reduce the use of these compounds, has been difficult with
the notable exception of the phasing out of leaded gasoline. Current activities,
4-2
-------
concentrated in the San Francisco, CA area, focus on encouraging brake pad
manufacturers to reduce the use of copper.
The effectiveness of most stormwater control practices is, therefore, dependent on their
ability to remove these particles from the water, or possibly from intermediate
accumulating locations (such as streets or other surfaces) and not through source
reduction. The removal of these particles from stormwater is dependent on various
characteristics of these particles, especially their size and settling rates. Some source
area controls (most notably street cleaning) affect the particles before they are washed-
off and transported by the runoff, while others remove the particles from the flowing
water. This discussion, therefore summarizes the accumulation and washoff of these
particulates and the particle size distribution of the suspended solids in stormwater
runoff to better understand the effectiveness of source area control practices.
Table 4-1 shows that most of the organic compounds found in stormwater are
associated with various human-related activities, especially automobile and pesticide
use, or are associated with plastics (Verschueren 1983). Heavy metals found in
stormwater also mostly originate from automobile use activities, including gasoline
combustion, brake lining, fluids (e.g., brake fluid, transmission oil, anti-freeze, grease),
undercoatings, and tire wear (Durum 1974, Koeppe 1977, Rubin 1976, Shaheen 1975,
Solomon and Natusch 1977, and Wilbur and Hunter 1980). Auto repair, pavement
wear, and deicing compound use also contribute heavy metals to stormwater (Field et
al. 1973 and Shaheen 1975). Shaheen (1975) found that eroding area soils are the
major source of the particulates in stormwater. The eroding area soil particles, and the
particles associated with road surface wear, become contaminated with exhaust
emissions and runoff containing the polluting compounds. Most of these compounds
become tightly bound to these particles and are then transported through the urban
area and drainage system, or removed from the stormwater, with the particulates.
Stormwater concentrations of zinc, fluoranthene, 1,3-dichlorobenzene, and pyrene are
unique in that substantial fractions of these compounds remain in the water and are less
associated with the particulates.
All areas are affected by atmospheric deposition, while other sources of pollutants are
specific to the activities conducted on the areas. As examples, the ground surfaces of
unpaved equipment or material storage areas can become contaminated by spills and
debris, while undeveloped land remaining relatively unspoiled by activities can still
contribute runoff solids, organics, and nutrients, if eroded. Atmospheric deposition,
deposition from activities on paved surfaces, and the erosion of material from upland
unconnected areas are the major sources of pollutants in urban areas.
4-3
-------
Table 4-1
1983).
Uses and sources for organic compounds found in stormwater (Verschueren
COMPOUND
Phenol
N-Nitroso-di-n-propylamine
Hexachloroethane
Nitrobenzene
2,4-Dimethylphenol
Hexachlorobutadiene
4-Chloro-3-methylphenol
Pentachlorophenol
Fluoranthene
Pyrene
Di-n-octylphthalate
EXAMPLE USE/SOURCE
gasoline, exhaust
contaminant of herbicide Treflan
plasticizer in cellulose esters, minor use in rubber and insecticide
solvent, rubber, lubricants
asphalt, fuel, plastics, pesticides
rubber and polymer solvent, transformer and hydraulic oil
germicide; preservative for glues, gums, inks, textile, and leather
insecticide, algaecide, herbicide, and fungicide mfg., wood preservative
gasoline, motor and lubricating oil, wood preservative
gasoline, asphalt, wood preservative, motor oil
general use of plastics
Many studies have examined different sources of urban runoff pollutants. These
references were reviewed as part of this study and the results are summarized in this
section. These significant pollutants have been shown to have a potential for creating
various receiving water impact problems, as described in Appendix D (???) of this
report. Most of these potential problem pollutants typically have significant
concentration increases in the urban feeder creeks and sediments, as compared to
areas not affected by urban runoff.
The important sources of these pollutants are related to various uses and processes.
Automobile related potential sources usually affect road dust and dirt quality more than
other particulate components of the runoff system. The road dust and dirt quality is
affected by vehicle fluid drips and spills (e.g., gasoline, oils) and vehicle exhaust, along
with various vehicle wear, local soil erosion, and pavement wear products. Urban
landscaping practices potentially affecting urban runoff include vegetation litter, fertilizer
and pesticides. Miscellaneous sources of urban runoff pollutants include firework
debris, wildlife and domestic pet wastes and possibly industrial and sanitary
wastewaters. Wet and dry atmospheric contributions both affect runoff quality.
Pesticide use in an urban area can contribute significant quantities of various toxic
materials to urban runoff. Many manufacturing and industrial activities, including the
combustion of fuels, also affect urban runoff quality.
Natural weathering and erosion products of rocks contribute the majority of the
hardness and iron in urban runoff pollutants. Road dust and associated automobile use
activities (gasoline exhaust products) historically contributed most of the lead in urban
runoff. However, the decrease of lead in gasoline has resulted in current stormwater
lead concentrations being about one tenth of the levels found in stormwater in the early
1970s (Bannerman et al. 1993). In certain situations, paint chipping can also be a major
source of lead in urban areas. Road dust, contaminated by tire wear products and zinc
plated metal erosion material, contributes most of the zinc to urban runoff. Urban
landscaping activities can be a major source of cadmium (Phillips and Russo 1978).
Electroplating and ore processing activities can also contribute chromium and cadmium.
4-4
-------
Many pollutant sources are specific to a particular area and on-going activities. For
example, iron oxides are associated with welding operations and strontium, used in the
production of flares and fireworks, would probably be found on the streets in greater
quantities around holidays, or at the scenes of traffic accidents. The relative
contribution of each of these potential urban runoff sources, is, therefore, highly
variable, depending upon specific site conditions and seasons.
Specific information is presented in the following subsections concerning the qualities of
various rocks and soils, urban and rural dustfall, and precipitation. This information is
presented to assist in the interpretation of the source area runoff samples collected as
part of this project.
Chemical Quality of Rocks and Soils
The abundance of common elements in the lithosphere (the earth's crust) is shown in
Table 4-2 (Lindsay 1979). Almost half of the lithosphere is oxygen and about 25% are
silica. Approximately eight percent is aluminum and five percent is iron. Elements
comprising between two percent and four percent of the lithosphere include calcium,
sodium, potassium and magnesium. Because of the great abundance of these
materials in the lithosphere, urban runoff transports only a relatively small portion of
these elements to receiving waters, compared to natural processes. Iron and aluminum
can both cause detrimental effects in receiving waters if in their dissolved forms. A
reduction of the pH substantially increases the abundance of dissolved metals.
Table 4-2. Common elements in the Lithosphere (Lindsay 1979).
Abundance
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Element
O
Si
Al
Fe
Ca
Na
K
Mg
P
C
Mn
F
S
Cl
Ba
Rb
Zr
Cr
Sr
V
Ni
Concentration
in Lithosphere
(mg/kg)
465,000
276,000
81 ,000
51 ,000
36,000
28,000
26,000
21 ,000
1,200
950
900
625
600
500
430
280
220
200
150
150
100
4-5
-------
Table 4-3, also from Lindsay (1979), shows the rankings for common elements in soils.
These rankings are quite similar to the values shown previously for the lithosphere.
Natural soils can contribute pollutants to urban runoff through local erosion. Again, iron
and aluminum are very high on this list and receiving water concentrations of these
metals are not expected to be significantly affected by urban activities alone.
Table 4-3. Common elements in soils (Lindsay 1979).
Abundance
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Element
O
Si
Al
Fe
C
Ca
K
Na
Mg
Ti
N
S
Mn
P
Ba
Zr
F
Sr
Cl
Cr
V
Typical
Minimum
(mg/kg)
230,000
10,000
7,000
7,000
400
750
600
1,000
200
30
20
200
100
60
10
50
20
1
20
Typical
Maximum
(mg/kg)
350,000
300,000
550,000
500,000
30,000
7,500
6,000
10,000
4,000
10,000
3,000
5,000
3,000
2,000
4,000
1,000
900
1,000
500
Typical
Average
(mg/kg)
490,000
320,000
71 ,000
38,000
20,000
13,700
8,300
6,300
5,000
4,000
1,400
700
600
600
430
300
200
200
100
100
100
The values shown on these tables are expected to vary substantially, depending upon
the specific mineral types. Arsenic is mainly concentrated in iron and manganese
oxides, shales, clays, sedimentary rocks and phosphorites. Mercury is concentrated
mostly in sulfide ores, shales and clays. Lead is fairly uniformly distributed, but can be
concentrated in clayey sediments and sulfide deposits. Cadmium can also be
concentrated in shales, clays and phosphorites (Durum 1974).
Street Dust and Dirt Pollutant Sources
Characteristics
Most of the street surface dust and dirt materials (by weight) are local soil erosion
products, while some materials are contributed by motor vehicle emissions and wear
(Shaheen 1975). Minor contributions are made by erosion of street surfaces in good
condition. The specific makeup of street surface contaminants is a function of many
conditions and varies widely (Pitt 1979).
Automobile tire wear is a major source of zinc in urban runoff and is mostly deposited
on street surfaces and nearby adjacent areas. About half of the airborne particulates
4-6
-------
lost due to tire wear settle out on the street and the majority of the remaining
particulates settle within about six meters of the roadway. Exhaust particulates, fluid
losses, drips, spills and mechanical wear products can all contribute lead to street dirt.
Many heavy metals are important pollutants associated with automobile activity. Most
of these automobile pollutants affect parking lots and street surfaces. However, some
of the automobile related materials also affect areas adjacent to the streets. This
occurs through the wind transport mechanism after being resuspended from the road
surface by traffic-induced turbulence.
Automobile exhaust particulates contribute many important heavy metals to street
surface particulates and to urban runoff and receiving waters. The most notable of
these heavy metals has been lead. However, since the late 1980s, the concentrations
of lead in stormwater has decreased substantially (by about ten times) compared to
early 1970 observations. This decrease, of course, is associated with significantly
decreased consumption of leaded gasoline.
Solomon and Natusch (1977) studied automobile exhaust particulates in conjunction
with a comprehensive study of lead in the Champaign-Urbana, IL area. They found that
the exhaust particulates existed in two distinct morphological forms. The smallest
particulates were almost perfectly spherical, having diameters in the range of 0.1 to 0.5
|j,m. These small particles consisted almost entirely of PbBrCI (lead, bromine, chlorine)
at the time of emission. Because the particles are small, they are expected to remain
airborne for considerable distances and can be captured in the lungs when inhaled.
The researchers concluded that the small particles are formed by condensation of
PbBrCI vapor onto small nucleating centers, which are probably introduced into the
engine with the filtered engine air.
Solomon and Natusch (1977) found that the second major form of automobile exhaust
particulates were rather large, being roughly 10 to 20 |j,m in diameter. These particles
typically had irregular shapes and somewhat smooth surfaces. The elemental
compositions of these irregular particles were found to be quite variable, being
predominantly iron, calcium, lead, chlorine and bromine. They found that individual
particles did contain aluminum, zinc, sulfur, phosphorus and some carbon, chromium,
potassium, sodium, nickel and thallium. Many of these elements (bromine, carbon,
chlorine, chromium, potassium, sodium, nickel, phosphorus, lead, sulfur, and thallium)
are most likely condensed, or adsorbed, onto the surfaces of these larger particles
during passage through the exhaust system. They believed that these large particles
originate in the engine or exhaust system because of their very high iron content. They
found that 50 to 70 percent of the emitted lead was associated with these large
particles, which would be deposited within a few meters of the emission point onto the
roadway, because of their aerodynamic properties.
Solomon and Natusch (1977) also examined urban particulates near roadways and
homes in urban areas. They found that lead concentrations in soils were higher near
roads and houses. This indicated the capability of road dust and peeling house paint to
4-7
-------
contaminate nearby soils. The lead content of the soils ranged from 130 to about 1,200
mg/kg. Koeppe (1977), during another element of the Champaign-Urbana lead study,
found that lead was tightly bound to various soil components. However, the lead did not
remain in one location, but it was transported both downward in the soil profile and to
adjacent areas through both natural and man-assisted processes.
Street Dirt Accumulation
The washoff of street dirt and the effectiveness of street cleaning as a stormwater
control practice are highly dependent on the available street dirt loading. Street dirt
loadings are the result of deposition and removal rates, plus "permanent storage." The
permanent storage component is a function of street texture and condition and is the
quantity of street dust and dirt that cannot be removed naturally or by street cleaning
equipment. It is literally trapped in the texture, or cracks, of the street. The street dirt
loading at any time is this initial permanent loading plus the accumulation amount
corresponding to the exposure period, minus the re-suspended material removal by
wind and traffic-induced turbulence. Removal of street dirt can occur naturally by winds
and rain, or by human activity (e.g., by the turbulence of traffic or by street cleaning
equipment). Very little removal occurs by any process when the street dirt loadings are
small, but wind removal may be very large with larger loadings, especially for smooth
streets (Pitt 1979).
Figure 4-1 shows very different street dirt loadings for two San Jose, CA residential
study areas (Pitt 1979). The accumulation and deposition rates (and therefore the
amounts lost to air) are quite similar, but the initial loading values (the permanent
storage values) are very different. The loading differences were almost solely caused
by the different street textures.
Table 4-4 summarizes many accumulation rate measurements obtained from
throughout North America. In the earliest studies (APWA 1969; Sartor and Boyd 1972;
and Shaheen 1975), the initial street dirt loading values after a major rain or street
cleaning were assumed to be zero. Calculated accumulation rates for rough streets
were, therefore, very large. Later tests measured the initial loading values close to the
end of major rains and street cleaning and found that they could be very high,
depending on the street texture. When these starting loadings were considered, the
calculated accumulation rates were, therefore, much lower. The early, uncorrected,
Sartor and Boyd accumulation rates that ignored the initial loading values were almost
ten times the correct values shown on this table. Unfortunately, most urban stormwater
models used these very high early accumulation rates as default values.
The most important factors affecting the initial loading and maximum loading values
shown on Table 4-4 were found to be street texture and street condition. When data
from many locations are studied, it is apparent that smooth streets have substantially
less loadings at any accumulation period compared to rough streets for the same land
use. Very long accumulation periods relative to the rain frequency resultant in high
street dirt loadings. During these conditions, the wind losses of street dirt (as fugitive
4-8
-------
dust) may approximate the deposition rate, resulting in relatively constant street dirt
loadings. At Bellevue, WA, typical interevent rain periods average about three days.
Relatively constant street dirt loadings were observed in Bellevue because the frequent
rains kept the loadings low and very close to the initial storage value, with little observed
increase in dirt accumulation over time (Pitt 1985). In Castro Valley, CA, the rain
interevent periods were much longer (ranging from about 20 to 100 days) and steady
loadings were only observed after about 30 days when the loadings became very high
and fugitive dust losses caused by the winds and traffic turbulence moderated the
loadings (Pitt and Shawley 1982).
An example of the type of research conducted to obtain the values shown in Table 4-4
was conducted by Pitt and McLean (1986) in Toronto. They measured street dirt
accumulation rates and the effects of street cleaning as part of a comprehensive
stormwater research project. An industrial street with heavy traffic and a residential
street with light traffic were monitored about twice a week for three months. At the
beginning of this period, intensive street cleaning (one pass per day for each of three
consecutive days) was conducted to obtain reasonably clean streets. Street dirt
loadings were then monitored every few days to measure the accumulation rates of
street dirt. Street dirt sampling procedures developed by Pitt (1979) were applied.
Powerful industrial vacuums (two units, each having two HP, combined with a "Y"
connector, and using a six inch wide solid aluminum head) were used to clean many
separate subsample strips across the roads which were then combined for physical and
chemical analyses.
In Toronto, the street dirt particulate loadings were quite high before the initial intensive
street cleaning period and were reduced to their lowest observed levels immediately
after the last street cleaning. After street cleaning, the loadings on the industrial street
increased much faster than for the residential street. Right after intensive cleaning, the
street dirt particle sizes were also similar for the two land uses. However, the loadings
of larger particles on the industrial street increased at a much faster rate than on the
residential street, indicating more erosion or tracking materials being deposited onto the
industrial street. The residential street dirt measurements did not indicate that any
material was lost to the atmosphere as fugitive dust, probably because of the low street
dirt accumulation rate and the short periods of time between rains. The street dirt
loadings never had the opportunity to reach the high loading values needed before they
could be blown from the streets by winds or by traffic-induced turbulence. The industrial
street, in contrast, had a much greater street dirt accumulation rate and reached the
critical loading values needed for fugitive losses in the relatively short periods between
the rains.
4-9
-------
2,000
5
u
a
a
tarn
'5
a
o
ฃ
*tssi
w
a
12
"5
ca
"5
o
Lo;-
500
Dep
10 15 20
25
30
Figure 4-1. Deposition and accumulation of street dirt (Pitt 1979).
4-10
-------
Table 4-4. Street dirt loadings and deposition rates.
Smooth and Intermediate Textured Streets
Reno/Sparks, NV-good condition
Reno/Sparks, NV - good with smooth gutters (windy)
San Jose, CA - good condition
U.S. nationwide - residential streets, good condition
U.S. nationwide - commercial street, good condition
Reno/Sparks, NV - moderate to poor condition
Reno/Sparks, NV - new residential area (construction)
Reno/Sparks, NV- poor condition, with lipped gutters
San Jose, CA - fair to poor condition
Castro Valley, CA - moderate condition
Ottawa, Ontario - moderate condition
Toronto, Ontario - moderate condition, residential
Toronto, Ontario - moderate condition, industrial
Believue, WA - dry period, moderate condition
Believue, WA - heavy traffic
Believue, WA - other residential sites
Average:
Range:
Rough and Very Rough Textured Streets
San Jose, CA - oil and screens overlay
Ottawa, Ontario -very rough
Reno/Sparks, NV
Reno/Sparks, NV- windy
San Jose, CA - poor condition
Ottawa, Ontario - rough
U.S. nationwide - industrial streets (poor condition)
Average:
Range:
Initial Loading
Value
(grams/curb-meter)
80
250
35
110
85
200
710
370
80
85
40
40
60
140
60
70
150
35-710
510
310
630
540
220
200
190
370
190-630
Daily
Deposition
Rate
(grams/curb-meter-day)
1
7
4
6
4
2
17
15
4
10
20
32
40
6
1
3
9
1 -40
6
20
10
34
6
20
10
15
6-34
Maximum
Observed
Loading
(grams/curb-meter)
85
400
>140
140
140
200
910
630
230
290
Na
100
351
>230
110
140
>270
85-910
>710
Na
860
>1 ,400
430
Na
370
>750
370 - >1 ,400
Days to Observed
Maximum
Loading
5
30
>50
5
5
5
15
35
70
70
Na
>10
>10
20
30
30
>25
5-70
>50
Na
35
>40
30
Na
10
>30
10->50
Reference
Pitt and Sutherland 1982
Pitt and Sutherland 1982
Pitt 1979
Sartor and Boyd 1 972 (corrected)
Sartor and Boyd 1 972 (corrected)
Pitt and Sutherland 1982
Pitt and Sutherland 1982
Pitt and Sutherland 1982
Pitt 1979
Pitt and Shawley 1982
Pitt 1983
Pit and McLean 1986
Pit and McLean 1986
Pitt 1984
Pitt 1984
Pitt 1984
Pitt 1979
Pitt 1983
Pitt and Sutherland 1982
Pitt and Sutherland 1982
Pitt 1979
Pitt 1983
Sartor and Boyd 1 972 (corrected)
4-11
-------
Washoff of Street Dirt
The Yalin equation relates the sediment carrying capacity to runoff flow rate (Yalin
1963). Yalin stated that sediment motion begins when the lift force of flow exceeds a
critical lift force. Once a particle is lifted, the drag force of the flow moves it downstream
until the weight of the particle forces it back down. The Yalin equation is used to predict
particle transport, for specific particle sizes, on a weight per unit flow width basis. It is
used for fully turbulent channel flow conditions, typical of shallow overland flow in urban
areas. The receding limb (tail) of a hydrograph may have laminar flow conditions, and
the suspended sediment carried in the previously turbulent flows would settle out. The
predicted constant Yalin sediment load would therefore only occur during periods of
rain, and, the sediment load would decrease, due to sedimentation, after the rain stops.
The critical particle bedload tractive force, the tractive force at which the particle begins
to move, can be obtained from the Shields' diagram. However, Shen (1981) warned
that the Shields' diagram alone cannot be used to predict "self-cleaning" velocities,
because it gives only a lower limit below which deposition will occur. It defines the
boundary between bed movement and stationary bed conditions. The Shields' diagram
does not consider the particulate supply rate in relationship to the particulate transport
rate. Reduced particulate transport occurs if the sediment supply rate is less than the
transport rate. The Yalin equation by itself is, therefore, not sensitive to particulate
supply; it only predicts the carrying capacity of flowing waters.
Besides the particulate supply rate, the Yalin equation is also very sensitive to local flow
parameters (specifically gutter flow depth). Therefore, a hydraulic model that can
accurately predict sheetflow across impervious surfaces and gutter flow is needed.
Sutherland and McCuen (1978) statistically analyzed a modified form of the Yalin
equation, in conjunction with a hydraulic model for different gutter flow conditions.
Except for the largest particle sizes, the effect of rain intensity on particle washoff was
found to be negligible.
The Yalin equation is based on classical sediment transport equations and requires
some assumptions concerning the micro-scale aspects of gutter flows and street dirt
distributions. The Yalin equation, as typically used in urban stormwater evaluations,
assumes that all particles lie within the gutter and no significant washoff occurs by
sheetflows traveling across the street towards the gutter. The early measurements of
across-the-street dirt distributions made by Sartor and Boyd (1972) indicated that about
90 percent of the street dirt was within about 30 cm of the curb face (typically within the
gutter area). These measurements, however, were made in areas of no parking (near
fire hydrants because of the need for water for the sampling procedures that were used)
and the traffic turbulence was capable of blowing most of the street dirt against the curb
barrier (or over the curb onto adjacent sidewalks or landscaped areas) (Shaheen 1975).
In later tests, Pitt (1979) and Pitt and Sutherland (1982) examined street dirt
distributions across the street in many additional situations. They found distributions
similar to Sartor and Boyd's observations only on smooth streets, with moderate to
4-12
-------
heavy traffic, and with no on-street parking. In many cases, most of the street dirt was
actually in the driving lanes, trapped by the texture of rough streets. If extensive on-
street parking was common, much of the street dirt was found on the outside edge of
the parking lanes, where much of the resuspended (in air) street dirt blew against the
parked cars and settled to the pavement.
Another process that may result in washoff less than predicted by Yalin is bed armoring
(Sutherland et al. 1982). As the smaller particulates are removed, the surface is
covered by predominantly larger particulates which are not effectively washed-off by
rain. Eventually, these larger particulates hinder the washoff of the trapped, underlying,
smaller particulates. Debris on the street, especially leaves, can also effectively armor
the particulates, reducing the washoff of particulates to very low levels (Singer and
Blackard1978).
Observations of particulate washoff during controlled tests using actual streets and
natural street dirt and debris are affected by street dirt distributions and armoring. The
earliest controlled street dirt washoff experiments were conducted by Sartor and Boyd
(1972) during the summer of 1970 in Bakersfield, CA. Their data were used in many
stormwater models (including SWMM, Huberand Heaney 1981; STORM, COE 1975;
and HSPF, Donigian and Crawford 1976) to estimate the percentage of the available
particulates on the streets that would wash off during rains of different magnitudes.
Sartor and Boyd used a rain simulator having many nozzles and a drop height of 1.5 to
two meters in street test areas of about five by ten meters. Tests were conducted on
concrete, new asphalt, and old asphalt, using simulated rain intensities of about five and
20 mm/hr. They collected and analyzed runoff samples every 15 minutes for about two
hours for each test. Sartor and Boyd fitted their data to an exponential curve, assuming
that the rate of particle removal of a given size is proportional to the street dirt loading
and the constant rain intensity:
dN/dt = krN
where: dN/dt = the change in street dirt loading per unit time
k = proportionality constant (1/hr)
r = rain intensity (in/hr)
N = street dirt loading (Ib/curb-mile)
This equation, upon integration, becomes:
N = N0e-krt
where: N = residual street dirt load (after the rain)
NO = initial street dirt load
t = rain duration (hr)
Street dirt washoff is, therefore, equal to N0 minus N. The variable combination rt, or
4-13
-------
rain intensity (in/hr) times rain duration (t), is equal to total rain depth (R), in inches.
This equation then further reduces to:
N = N0e-kR
Therefore, this equation is only sensitive to the total depth of the rain that has fallen
since the beginning of the rain, and not rain intensity. Because of decreasing
particulate supplies, the exponential washoff curve also predicts decreasing
concentrations of particulates with time since the start of a constant rain (Alley 1980 and
1981).
The proportionality constant, k, was found by Sartor and Boyd to be slightly dependent
on street texture and condition, but was independent of rain intensity and particle size.
The value of this constant is usually taken as 0.18/mm, assuming that 90 percent of the
particulates will be washed from a paved surface in one hour during a 13 mm/hr rain.
However, Alley (1981) fitted this model to watershed outfall runoff data and found that
the constant varied for different storms and pollutants for a single study area. Novotny
(as part of Bannerman et al. 1983) also examined "before" and "after" rain event street
particulate loading data from the Milwaukee Nationwide Urban Runoff Program (NURP)
project and found almost a three-fold difference between the constant value of k for fine
(<45 |j,m) and medium sized particles (100 to 250 |j,m). The calculated values were
0.026/mm for the fine particles and 0.01/mm for the medium sized particles, both much
less than the "accepted" value of 0.18/mm. Jewell et al. (1980) also found large
variations in outfall "fitted" constant values for different rains compared to the typical
default value. Either the assumption of the high removal of particulates during the 13
mm/hr storm was incorrect or/and the equation cannot be fitted to outfall data (most
likely, as this would require that all the particulates are originating from homogeneous
paved surfaces during all storm conditions).
This washoff equation has been used in many stormwater models, along with an
expression for an availability factor. An availability factor is needed, because N0 is only
the portion of the total street load available for washoff. This availability factor (the
fraction of the total street dirt loading available for washoff) is generally used as 1.0 for
all rain intensities greater than about 18 mm/hr and reduces to about 0.10 for rains of
one mm/hr.
The Bellevue, WA urban runoff project (Pitt 1985) included about 50 pairs of street dirt
loading observations close to the beginnings and ends of rains. These "before" and
"after" loading values were compared to determine significant differences in loadings
that may have been caused by the rains. The observations were affected by rains
falling directly on the streets, along with flows and particulates originating from non-
street areas. The net loading differences were, therefore, affected by street dirt washoff
(by direct rains on the street surfaces and by gutter flows augmented by "upstream"
area runoff) and by erosion products that originated from non-street areas that may
have settled out in the gutters. When all the data were considered together, the net
4-14
-------
loading difference was about 10 to 13 g/curb-m removed. This amounted to a street dirt
load reduction of about 15 percent, which was much less than predicted using either of
the two previously described washoff models. Very large reductions in street dirt
loadings during rains were observed in Bellevue for the smallest particles, but the
largest particles actually increased in loadings (due to deposited erosion materials
originating from off-street areas). The particles were not source limited, but armor
shielding may have been important. Most of the particulates in the runoff were in the
fine particle sizes (<63 |j,m). Very few particles greater than 1000 |j,m were found in the
washoff water. Care must be taken to not confuse street dirt particle size distributions
with stormwater runoff particle size distributions. The stormwater particle size
distributions are much more biased towards the smaller sizes, as described later.
Suspended solids washoff predictions for Bellevue conditions were made using the
Sutherland and McCuen modification of the Yalin equation and the Sartor and Boyd
equation. Three particle size groups (<63, 250-500, and 2000-6350 |j,m), and three
rains, having depths of 5, 10, and 20 mm and 3-hr durations, were considered. The
gutter lengths for the Bellevue test areas averaged about 80 m, with gutter slopes of
about 4.5%. Typical total initial street dirt loadings for the three particle sizes were: 9
g/curb-m for <63 urn, 18 g/curb-m for 250-500 urn, and 9 g/curb-m for 2000-6350 ^m.
The actual Bellevue net loading removals during the storms were about 45% for the
smallest particle size group, 17% for the middle particle size group, and minus six
percent (six percent loading increase) for the largest particle size group. The predicted
removals were 90 to 100% using the Sutherland and McCuen method, 61 to 98% using
the Sartor and Boyd equation, and 8 to 37% using the availability factor with the Sartor
and Boyd equation. The ranges given reflect the different rain volumes and intensities
only. There were no large predicted differences in removal percentages as a function of
particle size. The availability factor with the Sartor and Boyd equation resulted in the
closest predicted values, but the great differences in washoff as a function of particle
size was not predicted.
The Bellevue street dirt washoff observations included effects of additional runoff water
and particulates originating from non-street areas. The additional flows should have
produced more gutter particulate washoff, but upland erosion materials may also have
settled in the gutters (as noted for the large particles). However, across-the-street
particulate loading measurements indicated that much of the street dirt was in the street
lanes, not in the gutters, before and after rains. This particulate distribution reduces the
importance of these extra flows and particulates from upland areas. The increased
loadings of the largest particles after rains were obviously caused by upland erosion,
but the magnitude of the settled amounts was quite small compared to the total street
dirt loadings.
In order to clarify street dirt washoff, Pitt (1987) conducted numerous controlled washoff
tests on city streets in Toronto. These tests were arranged as an overlapping series of
23 factorial tests, and were analyzed using standard factorial test procedures described
by Box et al. (1978). The experimental factors examined included: rain intensity, street
4-15
-------
texture, and street dirt loading. The differences between available and total street dirt
loads were also related to the experimental factors. The samples were analyzed for
total solids (total residue), dissolved solids (filterable residue: <0.45 |j,m), and SS
(particulate residue: >0.45 |j,m). Runoff samples were also filtered through 0.45 |j,m
filters and the filters were microscopically analyzed (using low power polarized light
microscopes to differentiate between inorganic and organic debris) to determine
particulate size distributions from about 1 to 500 |j,m. The runoff flow quantities were
also carefully monitored to determine the magnitude of initial and total rain water losses
on impervious surfaces.
The total solids concentrations varied from about 25 to 3000 mg/l, with an obvious
decrease in concentrations with increasing rain depths during these constant rain
intensity tests. No concentrations greater than 500 mg/l occurred after about two mm of
rain. All concentrations after about 10 mm of rain were less than 100 mg/l. Total solids
concentrations were independent of the test conditions. A wide range in runoff
concentrations was also observed for SS, with concentrations ranging from about 1 to
3000 mg/l. Again, a decreasing trend of concentrations was seen with increasing rain
depths, but the data scatter was larger because of the experimental factors. The
dissolved solids (<0.45 |j,m) concentrations ranged from about 20 to 900 mg/l,
comprising a surprisingly large percentage of the total solids loadings. For small rain
depths, dissolved solids comprised up to 90 percent of the total solids. After 10 mm of
rain depth, the filterable residue concentrations were all less than about 50 mg/l.
Manual particle size analyses were also conducted on the suspended solids washoff
samples, using a microscope with a calibrated recticle. Figures 4-2 and 4-3 are
examples of particle size distributions for two tests. These plots show the percentage of
the particles that were less than various sizes, by measured particle volume (assumed
to be similar to weight). The plots also indicate median particle sizes of about 10 to 50
|j,m, depending on when the sample was obtained during the washoff tests. All of the
distributions showed surprisingly similar trends of particle sizes with elapsed rain depth.
The median size for the sample obtained at about one mm of rain was much greater
than for the samples taken after more rain. The median particle sizes of material
remaining on the streets after the washoff tests were also much larger than for most of
the runoff samples, but were quite close to the initial samples' median particle sizes.
The washoff water at the very beginning of the test rains, therefore, contained many
more larger particles than during later portions of the rains. Also, a substantial amount
of larger particles remained on the streets after the test rains. Most street runoff waters
during test rains in the 5 to 15 mm depth category had median suspended solids
particle sizes of about 10 to 50 |j,m. However, dissolved solids (less than 0.45 |j,m)
made up most of the total solids washoff for elapsed rain depths greater than about five
mm.
These particle size distributions indicate that the smaller particles were much more
important than indicated during previous tests. As an example, the Sartor and Boyd
(1972) washoff tests (rain intensities of 50 mm/h for two hour durations) found median
4-16
-------
particle sizes of about 150 |j,m which were typically three to five times larger than were
found during these tests. They also did not find any significant particle size distribution
differences for different rain depths (or rain duration), in contrast to the Toronto tests,
which were conducted at more likely rain intensities (3 to 12 mm/hrfortwo hours).
The particulate washoff values obtained during these Toronto tests were expressed in
units of grams per square meter and grams per curb-meter, concentrations (mg/l), and
the percent of the total initial loading washed off during the test. Plots of accumulative
washoff are shown on Figures 4-4 through 4-11. These plots show the asymptotic
washoff values observed in the tests, along with the measured total street dirt loadings.
The maximum asymptotic values are the "available" street dirt loadings (N0). The
measured total loadings are seen to be several times larger than these "available"
loading values. As an example, the asymptotic available total solids value for the HDS
(high intensity rain, dirty street, smooth street) test (Figure 4-10) was about 3 g/m2 while
the total load on the street for this test was about 14 g/m2, or about five times the
available load. The differences between available and total loadings for the other tests
were even greater, with the total loads typically about ten times greater than the
available loads. The total loading and available loading values for dissolved solids were
quite close, indicating almost complete washoff of the very small particles. However,
the differences between the two loading values for SS were much greater. Shielding,
therefore, may not have been very important during these tests, as almost all of the
smallest particles were removed, even in the presence of heavy loadings of large
particles.
The actual data are shown on these figures, along with the fitted Sartor and Boyd
exponential washoff equations. In many cases, the fitted washoff equations greatly
over-predicted suspended solids washoff during the very small rains (usually less than
one to three mm in depth). In all cases, the fitted washoff equations described
suspended solids washoff very well for rains greater than about 10 mm in depth.
Table 4-5 presents the equation parameters for each of the eight washoff tests for
suspended solids. Pitt (1987) concluded that particulate washoff should be divided into
two main categories, one for high intensity rains with dirty streets, possibly divided into
categories by street texture, and the other for all other conditions. Factorial tests also
found that the availability factor (the ratio of the available loading, N0, to the total
loading) varied depending on the rain intensity and the street roughness, as indicated
below:
Low rain intensity and rough streets: 0.045
High rain intensity and rough streets, or low rain intensity and smooth streets:
0.075
High rain intensity and smooth streets: 0.20
Obviously, washoff was more efficient for the higher rain energy and smoother
pavement tests. The worst case was for a low rain intensity and rough street, where
4-17
-------
only about 4.5% of the street dirt would be washed from the pavement. In contrast, the
high rain intensities on the smooth streets were more than four times more efficient in
removing the street dirt.
Particle size ( microns )
Figure 4-2. Particle size distribution of HDS test (high rain intensity, dirty, and smooth
street) (Pitt 1987).
Particle size ( microns )
Figure 4-3. Particle size distribution for LCR test (light rain intensity, clean, and rough
street) (Pitt 1987).
4-18
-------
0.2
~ 2.5 f
"E 2.0 +
CTI
t
O
(S
1.5-
1.0-
0.8-
-------
3.0
E
t
o
(S
3
2
"55
o>
E
ra
It
o
v>
I
0.05
3
'ซ; 0.03
ฃ 0.02
o
ฃ
(ft
0.005
0.75 g/mj
01
345
0 ' 1 '2 ' 3 '4 ' 5
0 '1 '2 '3 U '5
Figure 4-5. Washoff plots for LCR test (light rain intensity, clean, and rough street) (Pitt 1987).
4-20
-------
o>
It
o
.c
H
ซ
w
o>
JS
"o
10.0-
8.0
S.O
3.0
2.0
1.0
0.0
0.5
0.3
0.2
0.1
0.08
0.05-
0.03
0.02
12.8 g/m'
10 ' 15 ' 20
E
CB
It
o
SI
m
a
3
T3
10.0
5.0
3.0
2.0
1.0. .
0.5
0.3
0.2
0.1+ +
* 0.05
fj 0.03
.| 0.02
(0
ฐ- 0.01
0.005
11.9
0 '5 ' 10 ' 15 ' 20
Rain (mm)
M
re
0.8
0.5
0.3
0.2
0.1-
ง 0.08
* 0.05 4-
ฃ 0.03-
(i>
*j-ป
E 0.02-
0.01
0.92 g/nT
10 ' 15 ' 20
Figure 4-6. Washoff plots for HDR test (high rain intensity, dirty, and rough street) (Pitt 1987).
4-21
-------
E
en
It
o
JC
m
a
o>
3
TJ
'w
ฃ
"5
4^
O
0.1 -
10.0
8.0
E
ra 3.0
2.0
It
o
o>
3
1.0
0.8
0.5
10.5
E
O)
"m.*
It
O
M
re
0.5 .
0.3
0.2
0.1
0.08
0.05
0.03
0.02
0.01
0.68 g/m
0 1
3 4
Rain (mm)
Figure 4-7. Washoff plots for LDR test (light rain intensity, dirty, and rough street) (Pitt 1987).
4-22
-------
3.0 T
0.3
r-+
*J
E
ni
fc
o
M
ni
ซ
1
ฃ
1
u
c
ro
a.
2.0
1.5 '
1.0 -
0.0
0.7 '
0.6 -
0.5 '
0.4
I
1.8 g/m2
I
I
1
I
I
1
I"""
10 " 15 " 20
0 5 10 15 20
0.05
10 15 20
Rain (mm)
Figure 4-8. Washoff plots for HCS test (high rain intensity, clean, and smooth street) (Pitt 1987).
4-23
-------
o
JC
w
0)
15
*U
O
2.0
1.0 '
0.5
0.3
0.2
0.1
0.05
0.03
0.02
0.01 *^
2.0 i
2.3 g/m'
01 23456
0123456
Rain (mm)
0.4
0.3
0.2
cC"*
E
oi
0.1
t 0.08
ฃ
M
ง 0.05
0)
13
ro
0.03 -
0.02
S 0-01
ฃ 0.008
0.005 -
0.40 g/mj
2 -3 4 5 6
Figure 4-9. Washoff plots for LCS test (light rain intensity, clean, and smooth street) (Pitt 1987).
4-24
-------
15.0
E
en
>" "*
t
o
JI
(fl
a
a>
1
i-r
o
E
wfe
CB
fc
o
JC.
m
a
o>
10.0
8.0
5.0
3.0
2.0
1.5
3
U
t
TO
CL
0.4
12.6 g/mz
10 " 15 ' 20
10 " 15 ' 20
0.1
0 "5 ' 10 ' 15 ' 20
Rain (mm)
Figure 4-10. Washoff plots for HDS test (high rain intensity, dirty, and smooth street) (Pitt 1987).
4-25
-------
2.0
ซ 1-0
^g 0.8 ^
CO
0.5 4
8=
o
.c
w
3
1/1
o>
CO
4MP
o
0.3
0.2
0.1
0.08
0.05
0.03
0.02
2.42 g/m2
01 23456
0.01
01 23466
Rain (mm)
0.01
0 ' 1
3 '4 '5 '6
Figure 4-11. Washoff plots for LCS replicate test (light rain intensity, clean, and smooth street) (Pitt 1987).
4-26
-------
Table 4-5. Suspended solids washoff coefficients (Pitt 1987)1.
Test
condition
code
HCR
LCR
HDR
LDR
HCS
LCS
HDS
LCS
Rain
intensity
category
high
low
high
low
high
low
high
low
Street dirt
loading
category
clean
clean
dirty
dirty
clean
clean
dirty
clean
Street
texture
category
rough
rough
rough
rough
smooth
smooth
smooth
smooth
Calculated k
(1/hr)
0.832
0.344
0.077
0.619
1.007
0.302
0.167
0.335
Standard
error for k
(1/hr)
0.064
0.038
0.008
0.052
0.321
0.024
0.015
0.031
Ratio of available
load to total initial
load
0.11
0.061
0.032
0.028
0.26
0.047
0.13
0.11
1) Note:
N = N0e-kR
where: N = residual street dirt load, after the rain (Ib/curb-mile)
NO = initial street dirt load (Ib/curb-mile)
R = rain depth (inches)
k = proportionality constant (1/hr)
Observed Particle Size Distributions in Stormwater
The particle size distributions of stormwater greatly affect the ability of most controls to
reduce pollutant discharges. This research included particle size analyses of 121
stormwater samples from three states that were not affected by stormwater controls
(southern New Jersey as part of the inlet tests; Birmingham, AL as part of the MCTT
pilot-scale tests; and in Milwaukee and Minocqua, Wl, as part of the MCTT full-scale
tests). These samples represented stormwater entering the stormwater controls being
tested. Particle sizes were measured using a Coulter Multi-Sizer Me and verified with
microscopic, sieve, and settling column tests.
Figures 4-12 through 4-14 are grouped box and whisker plots showing the particle sizes
(in Lim) corresponding to the 10 , 50th (median) and 90th percentiles of the cumulative
distributions. If 90% control of SS was desired, for example, then the particles larger
than the 90th percentile would have to be removed. The median particle sizes ranged
from 0.6 to 38 iim and averaged 14 iim. The 90th percentile sizes ranged from 0.5 to 11
Lim and averaged 3 iim. These particle sizes are all substantially smaller than have
been typically assumed for stormwater. In all cases, the New Jersey samples had the
smallest particle sizes, followed by Wisconsin, and then Birmingham, AL, which had the
largest particles. The New Jersey samples were obtained from gutter flows in a
residential semi-xeroscaped neighborhood, the Wisconsin samples were obtained from
several source areas, including parking areas and gutter flows mostly from residential,
4-27
-------
but from some commercial areas, and the Birmingham samples were collected from a
long-term parking area.
Atmospheric Sources of Urban Runoff Pollutants
Atmospheric processes affecting urban runoff pollutants include dry dustfall and
precipitation quality. These have been monitored in many urban and rural areas. In
many instances, however, the samples were combined as a bulk precipitation sample
before processing. Automatic precipitation sampling equipment can distinguish
between dry periods of fallout and precipitation. These devices cover and uncover
appropriate collection jars exposed to the atmosphere. Much of this information has
been collected as part of the Nationwide Urban Runoff Program (NURP) and the
Atmospheric Deposition Program, both sponsored by the USEPA (EPA 1983a).
This information must be interpreted carefully, because of the ability of many polluted
dust and dirt particles to be resuspended and then redeposited within the urban area.
In many cases, the measured atmospheric deposition measurements include material
that was previously residing and measured in other urban runoff pollutant source areas.
Also, only small amounts of the atmospheric deposition material would directly
contribute to runoff. Rain is subjected to infiltration and the dry fall particulates are likely
mostly incorporated with surface soils and only small fractions are then eroded during
rains. Therefore, mass balances and determinations of urban runoff deposition and
accumulation from different source areas can be highly misleading, unless transfer of
material between source areas and the effective yield of this material to the receiving
water is considered. Depending on the land use, relatively little of the dustfall in urban
areas likely contributes to stormwater discharges.
Dustfall and precipitation affect all of the major urban runoff source areas in an urban
area. Dustfall, however, is typically not a major pollutant source but fugitive dust is
mostly a mechanism for pollutant transport, as previously mentioned. Most of the
dustfall monitored in an urban area is resuspended particulate matter from street
surfaces or wind erosion products from vacant areas (Pitt 1979). Point source pollutant
emissions can also significantly contribute to dustfall pollution, especially in industrial
areas. Transported dust from regional agricultural activities can also significantly affect
urban stormwater.
Wind transported materials are commonly called "dustfall." Dustfall includes
sedimentation, coagulation with subsequent sedimentation and impaction. Dustfall is
normally measured by collecting dry samples, excluding rainfall and snowfall. If rainout
and washout are included, one has a measure of total atmospheric fallout. This total
atmospheric fallout is sometimes called "bulk precipitation." Rainout removes
4-28
-------
100
80
60
40
20
NJ Wl
AREA
AL
Figure 4-12. Tenth percentile particle sizes for stormwater inlet flows.
40
30
Q 20
UJ
10
NJ
Wl
AREA
AL
Figure 4-13. Fiftieth percentile particle sizes for stormwater inlet flows.
15
10
NJ
Wl
AREA
AL
Figure 4-14. Ninetieth percentile particle sizes for stormwater inlet flows.
4-29
-------
contaminants from the atmosphere by condensation processes in clouds, while washout
is the removal of contaminants by the falling rain. Therefore, precipitation can include
natural contamination associated with condensation nuclei in addition to collecting
atmospheric pollutants as the rain or snow falls. In some areas, the contaminant
contribution by dry deposition is small, compared to the contribution by precipitation
(Malmquist 1978). However, in heavily urbanized areas, dustfall can contribute more of
an annual load than the wet precipitation, especially when dustfall includes
resuspended materials.
Table 4-6 summarizes rain quality reported by several researchers. As expected, the
non-urban area rain quality can be substantially better than urban rain quality. Many of
the important heavy metals, however, have not been detected in rain in many areas of
the country. The most important heavy metals found in rain have been lead and zinc,
both being present in rain in concentrations from about 20 iig/l up to several hundred
iig/l. It is expected that more recent lead rainfall concentrations would be substantially
less, reflecting the decreased use of leaded gasoline since these measurements were
taken. Iron is also present in relatively high concentrations in rain (about 30 to 40 iig/l).
Table 4-6. Summary of reported rain quality.
Suspended solids, mg/l
Volatile suspended solids, mg/l
Inorganic nitrogen, mg/l as N
Ammonia, mg/l as N
Nitrates, mg/l as N
Total phosphates, mg/l as P
Ortho phosphate, mg/l as P
Scandium, ug/l
Titanium, ug/l
Vanadium, ug/l
Chromium, ug/l
Manganese, ug/l
Iron, ug/l
Cobalt, ug/l
Nickel, ug/l
Copper, ug/l
Zinc, ug/l
Lead, ua/l
Rural-Northwest
(Quilayute,
WA)1
<0.002
nd
nd
<2
2.6
32
0.04
nd
3.1
20
Rural-Northeast
(Lake George,
NY)1
nd
nd
nd
nd
3.4
35
nd
nd
8.2
30
Urban-
Northwest
(Lodi, NJ)2
1
3
6
44
45
Urban-
Midwest
(Cincinnati, OH)3
13
3.8
0.69
0.24
Other
Urban3
0.7
0.3
<0.1
Continental
Avg. (32
locations)1
nd
nd
nd
nd
12
nd
43
21
107
1) Rubin 1976
2) Wilbur and Hunter 1980
3) Manning et al. 1976
4-30
-------
The concentrations of various urban runoff pollutants associated with dry dustfall are
summarized in Table 4-7. Urban, rural and oceanic dry dustfall samples contained
more than 5,000 mg iron/kg total solids. Zinc and lead were present in high
concentrations. These constituents can have concentrations of up to several thousand
mg of pollutant per kg of dry dustfall. Spring et al. (1978) monitored dry dustfall near a
major freeway in Los Angeles, CA. Based on a series of samples collected over several
months, they found that lead concentrations on and near the freeway can be about
3,000 mg/kg, but as low as about 500 mg/kg 150 m (500 feet) away. In contrast, the
chromium concentrations of the dustfall did not vary substantially between the two
locations and approached oceanic dustfall chromium concentrations.
Table 4-7. Atmosphere dustfall quality.
Constituent, (mg
constituent/kg total solids)
PH
Phosphate-Phosphorous
Nitrate-Nitrogen, jxg/l
Scandium, jxg/l
Titanium, jxg/l
Vanadium, jxg/l
Chromium, jxg/l
Manganese, jxg/l
Iron, jxg/l
Cobalt, jjg/l
Nickel, jxg/l
Copper, jxg/l
Zinc, jjg/l
Lead, jxg/l
Urban'
5
380
480
190
6700
24000
48
950
1900
6700
Rural/
suburban1
3
810
140
270
1400
5400
27
1400
2700
1400
Oceanic '
4
2700
18
38
1800
21000
8
4500
230
Near freeway
(LA)2
4.3
1200
5800
34
2800
500' from
freeway (LA)2
4.7
1600
9000
45
550
1) Summarized by Rubin 1976
2) Spring 1978
Much of the monitored atmospheric dustfall and precipitation would not reach the urban
runoff receiving waters. The percentage of dry atmospheric deposition retained in a
rural watershed was extensively monitored and modeled in Oakridge, TN (Barkdoll et al.
1977). They found that about 98% of the lead in dry atmospheric deposits was retained
in the watershed, along with about 95% of the cadmium, 85% of the copper, 60% of the
chromium and magnesium and 75% of the zinc and mercury. Therefore, if the dry
4-31
-------
deposition rates were added directly to the yields from other urban runoff pollutant
sources, the resultant urban runoff loads would be very much overestimated.
Tables 4-8 and 4-9 report bulk precipitation (dry dustfall plus rainfall) quality and
deposition rates as reported by several researchers. For the Knoxville, KY, area
(Betson 1978), chemical oxygen demand (COD) was found to be the largest component
in the bulk precipitation monitored, followed by filterable residue and nonfilterable
residue. Table 4-9 also presents the total watershed bulk precipitation, as the
percentage of the total stream flow output, for the three Knoxville watersheds studies.
This shows that almost all of the pollutants presented in the urban runoff streamflow
outputs could easily be accounted for by bulk precipitation deposition alone. Betson
concluded that bulk precipitation is an important component for some of the constituents
in urban runoff, but the transport and resuspension of particulates from other areas in
the watershed are overriding factors.
Rubin (1976) stated that resuspended urban particulates are returned to the earth's
surface and waters in four main ways: gravitational settling, impaction, precipitation and
washout. Gravitational settling, as dry deposition, returns most of the particles. This
not only involves the settling of relatively large fly ash and soil particles, but also the
settling of smaller particles that collide and coagulate. Rubin stated that particles that
are less than 0.1 |j,m in diameter move randomly in the air and collide often with other
particles. These small particles can grow rapidly by this coagulation process. These
small particles would soon be totally depleted in the air if they were not constantly
replenished. Particles in the 0.1 to 1.0 |j,m range are also removed primarily by
coagulation. These larger particles grow more slowly than the smaller particles
because they move less rapidly in the air, are somewhat less numerous and, therefore,
collide less often with other particles. Particles with diameters larger than 1 |j,m have
appreciable settling velocities. Those particles about 10 |j,m in diameter can settle
rapidly, although they can be kept airborne for extended periods of time and for long
distances by atmospheric turbulence.
The second important particulate removal process from the atmosphere is impaction.
Impaction of particles near the earth's surface can occur on vegetation, rocks and
building surfaces. The third form of particulate removal from the atmosphere is
precipitation, in the form of rain and snow. This is caused by the rainout process where
the particulates are removed in the cloud-forming process. The fourth important
removal process is washout of the particulates below the clouds during the precipitation
event. Therefore, it is easy to see that re-entrained particles (especially from street
surfaces, other paved surfaces, rooftops and from soil erosion) in urban areas can be
readily redeposited through these various processes, either close to the points of origin
or at some distance away.
Pitt (1979) monitored airborne concentrations of particulates near typical urban roads.
He found that on a number basis, the downwind roadside particulate concentrations
were about 10% greater than upwind conditions. About 80% of the concentration
4-32
-------
increases, by number, were associated with particles in the 0.5 to 1.0 iim size range.
However, about 90% of the particle concentration increases by weight were associated
with particles greater than 10 iim. Pitt found that the rate of particulate resuspension
from street surfaces increases when the streets are dirty (cleaned infrequently) and
varied widely for different street and traffic conditions. The resuspension rates were
calculated based upon observed long-term accumulation conditions on street surfaces
for many different study area conditions, and varied from about 0.30 to 3.6 kg per curb-
km (one to 12 Ib per curb-mile) of street per day.
Table 4-8. Bulk precipitation quality.
Constituent (all units
mg/l except pH)
Calcium
Magnesium
Sodium
Chlorine
Sulfate
PH
Organic Nitrogen
Ammonia Nitrogen
Nitrite plus Nitrate-N
Total phosphate
Potassium
Total iron
Manganese
Lead
Mercury
Nonfilterable residue
Chemical Oxygen
Demand
Zinc
Copper
Urban
(average of
Knoxville
St. Louis &
Germany)1
3.4
0.6
1.2
2.5
8.0
5.0
2.5
0.4
0.5
1.1
1.8
0.8
0.03
0.03
0.01
16
65
Rural
(Tennessee)1
0.4
0.1
0.3
0.2
8.4
4.9
1.2
0.4
0.4
0.8
0.6
0.7
0.05
0.01
0.0002
Urban
(Guteburg,
Sweden) ?
2
1
0.03
0.05
10
0.08
0.02
1) Betson 1978
2) Malmquist 1978
4-33
-------
Table 4-9. Urban bulk precipitation deposition rates (Betson 1978)1.
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Constituent
Chemical oxygen demand
Filterable residue
Nonfilterable residue
Alkalinity
Sulfate
Chloride
Calcium
Potassium
Organic nitrogen
Sodium
Silica
Magnesium
Total Phosphate
Nitrite and Nitrate-N
Soluble phosphate
Ammonia Nitrogen
Total Iron
Fluoride
Lead
Manganese
Arsenic
Mercury
Average Bulk
Deposition Rate
(kg/ha/yr)
530
310
170
150
96
47
38
21
17
15
11
9
9
5.7
5.3
3.2
1.9
1.8
1.1
0.54
0.07
0.008
Average Bulk
Prec. as a % of
Total Streamflow
Output
490
60
120
120
470
360
170
310
490
270
130
180
130
360
170
1,100
47
300
650
270
720
250
1) Average for three Knoxville, KY, watersheds.
Murphy (1975) described a Chicago study where airborne particulate material within the
city was microscopically examined, along with street surface particulates. The
particulates from both of these areas were found to be similar (mostly limestone and
quartz) indicating that the airborne particulates were most likely resuspended street
surface particulates, or were from the same source.
PEDCo (1977) found that the re-entrained portion of the traffic-related particulate
emissions (by weight) is an order of magnitude greater than the direct emissions
4-34
-------
accounted for by vehicle exhaust and tire wear. They also found that particulate
resuspensions from a street are directly proportional to the traffic volume and that the
suspended particulate concentrations near the streets are associated with relatively
large particle sizes. The medium particle size found, by weight, was about 15 |j,m, with
about 22% of the particulates occurring at sizes greater than 30 |j,m. These relatively
large particle sizes resulted in substantial particulate fallout near the road. They found
that about 15% of the resuspended particulates fall out at 10 m, 25% at 20 m, and 35%
at 30 m from the street (by weight).
In a similar study Cowherd et al. (1977) reported a wind erosion threshold value of
about 5.8 m/s (13 mph). At this wind speed, or greater, significant dust and dirt losses
from the road surface could result, even in the absence of traffic-induced turbulence.
Rolfe and Reinbold (1977) also found that most of the particulate lead from automobile
emissions settled out within 100 m of roads. However, the automobile lead does widely
disperse over a large area. They found, through multi-elemental analyses, that the
settled outdoor dust collected at or near the curb was contaminated by automobile
activity and originated from the streets.
Source Area Sheetflow and Particulate Quality
This section summarizes the source area sheetflow and particulate quality data
obtained from several studies conducted in California, Washington, Nevada, Wisconsin,
Illinois, Ontario, Colorado, New Hampshire, and New York since 1979. Most of the data
obtained were for street dirt chemical quality, but a relatively large amount of parking
and roof runoff quality data have also been obtained. Only a few of these studies
evaluated a broad range of source areas or land uses.
Source Area Particulate Quality
Particulate potency factors (usually expressed as mg pollutant/kg dry particulate
residue) for many samples are summarized on Tables 4-10 and 4-11. These data can
help recognize critical source areas, but care must be taken if they are used for
predicting runoff quality because of likely differential effects due to washoff and erosion
from the different source areas. These data show the variations in chemical quality
between particles from different land uses and source areas. Typically, the potency
factors increase as the use of an area becomes more intensive, but the variations are
slight for different locations throughout the country. Increasing concentrations of heavy
metals with decreasing particle sizes was also evident, for those studies that included
particle size information. Only the quality of the smallest particle sizes are shown on
these tables because they best represent the particles that are removed during rains.
Warm Weather Sheetflow Quality
Sheetflow data, collected during actual rain, are probably more representative of runoff
conditions than the previously presented dry particulate quality data because they are
not further modified by washoff mechanisms. These data, in conjunction with source
area flow quantity information, can be used to predict outfall conditions and the
magnitude of the relative sources of critical pollutants. Tables 4-12 through 4-15
4-35
-------
summarize warm weather sheetflow observations, separated by source area type and
land use, from many locations. The major source area categories are listed below:
1. Roofs
2. Paved parking areas
3. Paved storage areas
4. Unpaved parking and storage areas
5. Paved driveways
6. Unpaved driveways
7. Dirt walks
8. Paved sidewalks
9. Streets
10. Landscaped areas
11. Undeveloped areas
12. Freeway paved lanes and shoulders
Toronto warm weather sheetflow water quality data were plotted against the rain volume
that had occurred before the samples were collected to identify any possible trends of
concentrations with rain volume (Pitt and McLean 1986). The street runoff data
obtained during the special washoff tests reported earlier were also compared with the
street sheetflow data obtained during the actual rain events (Pitt 1987). These data
observations showed definite trends of solids concentrations verses rain volume for
most of the source area categories. Sheetflows from all pervious areas combined had
the highest total solids concentrations from any source category, for all rain events.
Other paved areas (besides streets) had total solids concentrations similar to runoff
from smooth industrial streets. The concentrations of total solids in roof runoff were
almost constant for all rain events, being slightly lower for small rains than for large
rains. No other pollutant, besides SS, had observed trends of concentrations with rain
depths for the samples collected in Toronto. Lead and zinc concentrations were highest
in sheetflows from paved parking areas and streets, with some high zinc concentrations
also found in roof drainage samples. High bacteria populations were found in sidewalk,
road, and some bare ground sheetflow samples (collected from locations where dogs
would most likely be "walked").
Some of the Toronto sheetflow contributions were not sufficient to explain the
concentrations of some constituents observed in runoff at the outfall. High
concentrations of dissolved chromium, dissolved copper, and dissolved zinc in a
Toronto industrial outfall during both wet and dry weather could not be explained by wet
weather sheetflow observations (Pitt and McLean 1986). As an example, very few
detectable chromium observations were obtained in any of the more than 100 surface
sheetflow samples analyzed. Similarly, most of the fecal coliform populations observed
in sheetflows were significantly lower than those observed at the outfall, especially
during snowmelt. It is expected that some industrial wastes, possibly originating from
metal plating operations, were the cause of these high concentrations of dissolved
4-36
-------
metals at the outfall and that some sanitary sewage was entering the storm drainage
system.
Table 4-15 summarizes the very little filterable pollutant concentration data available,
before this EPA project, for different source areas. Most of the available data are for
residential roofs and commercial parking lots.
Table 4-10. Summary of observed street dirt mean chemical quality (mg constituent/kg
solids).
Constituent
P
TKN
COD
Cu
Pb
Zn
Cd
Cr
Residential
620 (4)
540 (6)
1100 (5)
710 (1)
810 (3)
1030 (4)
3000 (6)
290 (5)
2630 (3)
3000 (2)
100,000 (4)
150,000 (6)
180,000 (5)
280,000 (1)
180,000 (3)
170,000 (2)
162 (4)
110 (6)
420 (2)
1010 (4)
1800 (6)
530 (5)
1200 (1)
1650 (3)
3500 (2)
460 (4)
260 (5)
325 (3)
680 (2)
<3 (5)
4 (2)
42 (4)
31 (5)
170 (2)
Commercial
400 (6)
1500 (5)
910 (1)
1100 (6)
340 (5)
4300 (2)
110,000 (6)
250,000 (5)
340,000 (1)
210,000 (2)
130 (6)
220 (2)
3500 (6)
2600 (5)
2400 (1)
7500 (2)
750 (5)
1200 (2)
5 (5)
5 (2)
65 (5)
180 (2)
Industrial
670 (4)
560 (4)
65,000 (4)
360 (4)
900 (4)
500 (4)
70 (4)
References; location; particle size described:
(1) Bannermanetal. 1983 (Milwaukee, Wl) <31jjm
(2) Pitt 1979 (San Jose, CA) <45 urn
(3) Pitt 1985 (Bellevue, WA) <63 ^m
(4) Pitt and McLean 1986 (Toronto, Ontario) <125 jxm
(5) Pitt and Sutherland 1982 (Reno/Sparks, NV) <63 ^m
(6) Terstriep et al. 1982 (Champaign/Urbana, IL) >63 j^m
4-37
-------
Table 4-11. Summary of observed participate quality for other source areas (means for
<125 Lim particles) (mg constituent/kg solids).
Residential/Commercial Land
Uses
Roofs
Paved parking
Unpaved driveways
Paved driveways
Dirt footpath
Paved sidewalk
Garden soil
Road shoulder
Industrial Land Uses
Paved parking
Unpaved parking/storage
Paved footpath
Bare ground
P
1500
600
400
550
360
1100
1300
870
770
620
890
700
TKN
5700
790
850
2750
760
3620
1950
720
1060
700
1900
1700
COD
240,000
78,000
50,000
250,000
25,000
146,000
70,000
35,000
130,000
110,000
120,000
70,000
Cu
130
145
45
170
15
44
30
35
1110
1120
280
91
Pb
980
630
160
900
38
1200
50
230
650
2050
460
135
Zn
1900
420
170
800
50
430
120
120
930
1120
1300
270
Cr
77
47
20
70
25
32
35
25
98
62
63
38
Source: Pitt and McLean 1986 (Toronto, Ontario)
4-38
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data).
Pollutant and Land Use
Total Solids (ma/I)
Residential:
Commercial:
Industrial:
Susoended Solids (ma/I)
Residential:
Commercial:
Industrial:
Dissolved Solids (ma/I)
Residential:
Commercial:
Industrial:
Roofs
58(5)
64(1)
18(4)
95(1)
190(4)
113(5)
22(1)
13(5)
4(5)
42(10
5(5)
109(5)
Paved Parking
1790(5)
340 (2)
240(1)
102(7)
490 (5)
1660(5)
270 (2)
65(1)
41(7)
306 (5)
130(5)
70(2)
175(1)
61(7)
184(5)
Paved
Storage
73(5)
270 (5)
41(5)
202 (5)
32(5)
68(5)
Un paved
Parking/Storage
1250(5)
730 (5)
520 (5)
Paved
Driveways
510(5)
506 (5)
440 (5)
373 (5)
70(5)
133(5)
Un paved
Driveways
5620 (5)
4670 (5)
950 (5)
Dirt
Walks
1240(5)
810(5)
430 (5)
Paved
Sidewalks
49(5)
580 (5)
20(5)
434 (5)
29(5)
146(5)
Streets
325 (5)
235 (4)
325 (4)
1800(5)
242 (5)
242 (5)
1300(5)
83(5)
83(4)
83(5)
500 (5)
4-39
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data) (Continued).
Pollutant and Land Use
BODs (ma/I)
Residential:
Commercial:
COD (ma/l)
Residential:
Commercial:
Industrial:
Total Phosohorus (ma/I)
Residential:
Commercial:
Industrial:
Roofs
3(4)
7(4)
46(5)
27(1)
20(4)
130(4)
55(5)
0.03 (5)
0.05(1)
0.1 (4)
0.03 (4)
0.07 (4)
<0.06 (5)
Paved Parking
22(4)
11 (1)
4(8)
173(5)
190(2)
180(4)
53(1)
57(8)
180(5)
0.16(1)
0.15(7)
0.73 (5)
0.9 (2)
0.5 (4)
2.3 (5)
Paved
Storage
22(5)
82(5)
0.7 (5)
Un paved
Parking/Storage
247 (5)
1.0(5)
Paved
Driveways
178(5)
138(5)
0.36 (5)
0.9 (5)
Un paved
Driveways
41 8 (5)
3.0 (5)
Dirt
Walks
0.20 (5)
Paved
Sidewalks
62(5)
98(5)
0.80 (5)
0.82 (5)
Streets
13(4)
174(5)
170(4)
174(5)
322 (5)
0.62 (5)
0.31 (4)
0.62 (5)
1.6(5)
4-40
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data) (Continued).
Pollutant and Land Use
Total Phosphate (ma/I)
Residential:
Commercial:
Industrial:
TKN (ma/I)
Residential:
Commercial:
Industrial:
Ammonia (ma/I)
Residential:
Commercial:
Industrial:
Roofs
<0.04 (5)
0.08 (4)
0.02 (4)
<0.02 (5)
1.1 (5)
0.71 (4)
4.4 (4)
1.7(5)
0.1 (5)
0.9(1)
0.5 (4)
1.1 (4)
0.4 (5)
Paved Parking
0.03 (5)
0.3 (2)
0.5 (4)
0.04 (7)
0.22 (8)
0.6 (5)
3.8 (5)
4.1 (2)
1.5(4)
1.0(1)
0.8 (8)
2.9 (5)
0.1 (5)
1.4(2)
0.35 (4)
0.38(1)
0.3 (5)
Paved
Storage
<0.02 (5)
0.06 (5)
3.5 (5)
0.3 (5)
0.3 (5)
Un paved
Parking/Storage
0.13(5)
2.7 (5)
<0.1 (5)
Paved
Driveways
<0.2 (5)
<0.02 (5)
3.1 (5)
5.7 (5)
<0.1 (5)
<0.1 (5)
Un paved
Driveways
0.10(5)
7.5 (5)
<0.1 (5)
Dirt
Walks
0.66 (5)
1.3(5)
0.5 (5)
Paved
Sidewalks
0.64 (5)
0.03 (5)
1.1 (5)
4.7 (5)
0.3 (5)
<0.1 (5)
Streets
0.07 (5)
0.12(4)
0.07 (5)
0.15(5)
2.4 (5)
2.4 (4)
2.4 (5)
5.7 (5)
<0.1 (5)
0.42 (4)
<0.1 (5)
<0.1 (5)
4-41
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data) (Continued).
Pollutant and Land Use
Phenols (mq/l)
Residential:
Industrial:
Aluminum (na/l)
Residential:
Industrial:
Cadmium (|oa/l)
Residential:
Commercial:
Industrial:
Chromium (|xa/l)
Residential:
Commercial:
Industrial:
Roofs
2.4 (5)
1.2(5)
0.4 (5)
<0.2 (5)
<4(5)
0.6(1)
<4(5)
<60 (5)
<5(4)
<5(4)
<60 (5)
Paved Parking
12.2(5)
9.4 (5)
3.2 (5)
3.5 (5)
2(5)
5.1 (7)
0.6 (8)
<4(5)
20(5)
71(4)
19(7)
12(8)
<60 (5)
Paved
Storage
30.0 (5)
2.6 (5)
0.38 (5)
3.1 (5)
<5(5)
<4(5)
<10(5)
<60 (5)
Un paved
Parking/Storage
8.7 (5)
9.2 (5)
<4(5)
<60 (5)
Paved
Driveways
9.7 (5)
7.0 (5)
5.3 (5)
3.4 (5)
5(5)
<4(5)
<60 (5)
<60 (5)
Un paved
Driveways
7.4 (5)
41(5)
<4(5)
70(5)
Dirt
Walks
<0.4 (5)
<0.03 (5)
<1(5)
<10(5)
Paved
Sidewalks
8.6 (5)
8.7 (5)
0.5 (5)
1.2(5)
<4(5)
<4(5)
<60 (5)
<60 (5)
Streets
6.2 (5)
24(7)
1 .5 (5)
14(5)
<5(5)
<5(5)
<4(5)
<60 (5)
49(4)
<60 (5)
<60 (5)
4-42
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data) (Continued).
Pollutant and Land Use
Coccer (ua/l)
Residential:
Commercial:
Industrial:
Lead (ua/l)
Residential:
Commercial:
Industrial:
Roofs
10(5)
<5(4)
110(4)
<20 (5)
<40 (5)
30(3)
48(1)
17(4)
19(4)
30(1)
<40 (5)
Paved Parking
100(5)
40(2)
46(4)
1 1 0 (7)
480 (5)
250 (5)
200 (2)
350 (3)
1090(4)
146(1)
255 (7)
54(8)
230 (5)
Paved
Storage
20(5)
260 (5)
760 (5)
280 (5)
Un paved
Parking/Storage
120(5)
210(5)
Paved
Driveways
210(5)
40(5)
1400(5)
260 (5)
Un paved
Driveways
140(5)
340 (5)
Dirt
Walks
20(5)
30(5)
Paved
Sidewalks
20(5)
30(5)
80(5)
<40 (5)
Streets
40(5)
30(4)
40(5)
220 (5)
180(5)
670 (4)
180(5)
560 (5)
4-43
-------
Table 4-12. Sheetflow quality summary for other source areas (mean concentration and source of data) (Continued).
Pollutant and Land Use
Zinc (nq/l)
Residential:
Commercial:
Industrial:
Roofs
320 (5)
670 (1 )
180(4)
310(1)
80(4)
70(5)
Paved Parking
520 (5)
300 (5)
230 (4)
133(1)
490 (7)
640 (7)
Paved
Storage
390 (5)
310(5)
Unpaved
Parking/Storage
410(5)
Paved
Driveways
1000(5)
310(5)
Unpaved
Driveways
690 (5)
Dirt
Walks
40(5)
Paved
Sidewalks
60(5)
60(5)
Streets
180(5)
140(4)
180(5)
910(5)
References:
(1) Bannerman et al. 1983 (Milwaukee, Wl) (NURP)
(2) Denver Regional Council of Governments 1983 (NURP)
(3) Pitt 1983 (Ottawa)
(4) Pitt and Bozeman 1982 (San Jose)
(5) Pitt and McLean 1986 (Toronto)
(7) STORET Site #590866-2954309 (Shop-Save-Durham, NH) (NURP)
(8) STORET Site #596296-2954843 (Huntington-Long Island, NY) (NURP)
4-44
-------
Table 4-13. Sheetflow quality summary for undeveloped landscaped and freeway
pavement areas (mean observed concentrations and source of data).
Pollutants
Total Solids, mg/l
Suspended Solids, mg/l
Dissolved Solids, mg/l
BOD5, mg/l
COD, mg/l
Total Phosphorus, mg/l
Total Phosphate, mg/l
TKN, mg/l
Ammonia, mg/l
Phenols, jjg/l
Aluminum, jjg/l
Cadmium, jxg/l
Chromium, jxg/l
Copper, jxg/l
Lead, jxg/l
Zinc, jxg/l
Landscaped Areas
388 (4)
100 (4)
288 (4)
3 (3)
70 (3)
26 (4)
0.42 (3)
0.56 (4)
0.32 (3)
0.14(4)
1 .32 (3)
3.6 (4)
1.2 (3)
0.4 (4)
0.8 (4)
1.5 (4)
<3 (4)
10 (3)
<20 (4)
30 (2)
35 (3)
<30 (4)
10(3)
Undeveloped Areas
588 (4)
400 (1)
390 (4)
193 (4)
72 (1)
54 (4)
0.40 (1)
0.68 (4)
0.10 (1)
0.26 (4)
2.9 (1)
1.8 (4)
0.1 (1)
<0.1 (4)
11 (4)
<4 (4)
<60 (4)
40 (1)
31 (3)
<20 (4)
100 (1)
30 (2)
<40 (4)
100 (1)
100 (4)
Freeway Paved Lane and
Shoulder Areas
340 (5)
180 (5)
160 (5)
10 (5)
130 (5)
0.38 (5)
2.5 (5)
60 (5)
70 (5)
120 (5)
2000 (5)
460 (5)
References:
(1) Denver Regional Council of Governments 1983 (NURP)
(2) Pitt 1983 (Ottawa)
(3) Pitt and Bozeman 1982 (San Jose)
(4) Pitt and McLean 1986 (Toronto)
(5) Shelly and Gaboury 1986 (Milwaukee)
4-45
-------
Table 4-14. Source area bacteria sheetflow quality summary (means).
Pollutant and
Land Use
Fecal Coliforms
(#/100ml)
Residential:
Commercial
Industrial:
Fecal Strep
(#/100ml)
Residential:
Commercial:
Industrial:
Pseudo, Aerug
(#/100ml)
Residential:
Industrial:
Roofs
85(2)
<2(3)
1400(4)
9(3)
1600(4)
170(2)
920 (3)
2200 (4)
17(2)
690 (4)
30,000 (4)
50(4)
Paved
Parking
250,000 (4)
2900 (2)
350 (3)
210(1)
480 (5)
23,000 (6)
8660 (6)
190,000(4)
1 1 ,900 (2)
>2400 (3)
770(1)
1 1 20 (5)
62,000 (6)
7300 (4)
1900(4)
5800 (4)
Paved
Storage
100(4)
9200 (4)
<100(4)
2070 (4)
100(4)
5850 (4)
Unpaved
Parking/
Storage
18,000(4)
8100(4)
14,000(4)
Paved
Driveways
600 (4)
66,000 (4)
1900(4)
36,000 (4)
600 (4)
14,300(4)
Unpaved
Driveways
300,000 (4)
21 ,000 (4)
100(4)
Dirt
Walks
1800(4)
600 (4)
Paved
Sidewalks
1 1 ,000 (4)
55,000 (4)
3600 (4)
3600 (4)
Streets
920 (3)
6,900 (4)
100,000(4)
>2400 (3)
7300 (4)
45,000 (4)
570 (4)
6200 (4)
Land-
scaped
3300 (4)
43,000 (4)
21 00 (4)
Un-
developed
5400 (2)
49(3)
16,500(2)
920 (3)
Freeway
Paved
Lane and
Shoulders
1500(7)
2200 (7)
References:
(1) Bannerman et al. 1983 (Milwaukee, Wl) (NURP)
(2) Pitt 1983 (Ottawa)
(3) Pitt and Bozeman 1982 (San Jose)
(4) Pitt and McLean 1986 (Toronto)
(5) STORE! Site #590866-2954309 (Shop-Save-Durham, NH) (NURP)
(6) STORE! Site #596296-2954843 (Huntington-Long Island, NY) (NURP)
(7) Kobriger et al. 1981 and Gupta et al. 1977
4-46
-------
Table 4-15. Source area filterable pollutant concentration summary (means).
Roof Runoff
Solids (mg/l)
Phosphorus (mg/l)
Lead (ng/l)
Paved Parking
Solids (mg/l)
Phosphorus (mg/l)
TKN (mg/l)
Lead (jxg/l)
Arsenic (ng/l)
Cadmium (jjg/l)
Chromium (jxg/l)
Paved Storage
Solids (mg/l)
Residential
Total
64
58
0.054
48
Filterable
42
45
0.013
4
Filterable
(%)
66(1)
77(3)
24(1)
8(1)
Commercial
Total
240
102
1790
0.16
0.9
0.77
146
54
0.38
0.62
11.8
73
Filterable
175
61
138
0.03
0.3
0.48
5
8.8
0.095
0.11
2.8
32
Filterable
(%)
73(1)
60(4)
8(3)
19(1)
33(2)
62(5)
3(1)
16(5)
25(5)
18(5)
24(5)
44(3)
Industrial
Total
113
490
270
Filterable
110
138
64
Filt.
(%)
97(3)
28(3)
24(3)
References:
(1) Bannerman et al. 1983 (Milwaukee) (NURP)
(2) Denver Regional Council of Governments 1983 (NURP)
(3) Pitt and McLean 1986 (Toronto)
(4) STORET Site #590866-2954309 (Shop-Save-Durham, NH) (NURP)
(6) STORET Site #596296-2954843 (Huntington-Long Island, NY) (NURP)
4-47
-------
Other Pollutant Contributions to the Storm Drainage System
The detection of pentachlophenols in the relatively few samples previously analyzed
indicated important leaching from treated wood. Frequent detections of polycyclic
aromatic hydrocarbons (PAHs) during the U.S. Environmental Protection Agency's
Nationwide Urban Runoff Program (EPA 1983a) may possibly indicate leaching from
creosote treated wood, in addition to fossil fuel combustion sources. High
concentrations of copper, and some chromium and arsenic observations also indicate
the potential of leaching from "CCA" (copper, chromium, and arsenic) treated wood.
The significance of these leachate products in the receiving waters is currently
unknown, but alternatives to these preservatives should be considered. Many cities use
aluminum and concrete utility poles instead of treated wood poles. This is especially
important considering that utility poles are usually located very close to the drainage
system ensuring an efficient delivery of leachate products. Many homes currently use
wood stains containing pentachlorophenol and other wood preservatives. Similarly, the
construction of retaining walls, wood decks and playground equipment with treated
wood is common. Some preservatives (especially creosote) cause direct skin irritation,
besides contributing to potential problems in receiving waters. Many of these wood
products are at least located some distance from the storm drainage system, allowing
some improvement to surface water quality by infiltration through pervious surfaces.
Sources of Stormwater Toxicants
This project included the collection and analysis of 87 urban stormwater runoff samples
from a variety of source areas under different rain conditions as summarized in Table 4-
16. All of the samples were analyzed in filtered (0.45 urn filter) and non-filtered forms to
enable partitioning of the toxicants into "particulate" (non-filterable) and "dissolved"
(filterable) forms.
Table 4-16. Numbers of samples collected from each source area type.
Local Source
Areas 1
Roofs
Parking Areas
Storage Areas
Streets
Loading Docks
Vehicle Service Area
Landscaped Areas
Urban Creeks
Detention Ponds
Residential
5
2
na
1
na
na
2
Commercial/
Institutional
3
11
2
1
na
5
2
Industrial
4
3
6
4
3
na
2
Mixed
19
12
1) All collected in Birmingham, AL.
4-48
-------
Analyses and Sampling
The samples listed in Table 4-16 were all obtained from the Birmingham, AL, area.
Samples were taken from shallow flows originating from homogeneous source areas by
using several manual grab sampling procedures. For deep flows, samples were
collected directly into the sample bottles. For shallow flows, a peristaltic hand operated
vacuum pump created a small vacuum in the sample bottle, which then gently drew the
sample directly into the container through a Teflon tube. About one liter of sample
was needed, split into two containers: one 500 ml glass bottle with Teflon lined lid was
used for the organic and toxicity analyses and another 500 ml polyethylene bottle was
used for the metal and other analyses.
An important aspect of the research was to evaluate the effects of different land uses
and source areas, plus the effects of rain characteristics, on sample toxicant
concentrations. Therefore, careful records were obtained of the amount of rain and the
rain intensity that occurred before the samples were obtained. Antecedent dry period
data were also obtained to compare with the chemical data in a series of statistical
tests.
All samples were handled, preserved, and analyzed according to accepted protocols
(EPA 1982 and 1983b). The organic pollutants were analyzed using two gas
chromatographs, one with a mass selective detector (GC/MSD) and another with an
electron capture detector (GC/ECD). The pesticides were analyzed according to EPA
method 505, while the base neutral compounds were analyzed according to EPA
method 625 (but only using 100 ml samples). The pesticides were analyzed on a
Perkin Elmer Sigma 300 GC/ECD using a J&W DB-1 capillary column (30m by 0.32 mm
ID with a 1 |j,m film thickness). The base neutrals were analyzed on a Hewlett Packard
5890 GC with a 5970 MSD using a Supelco DB-5 capillary column (30m by 0.25 mm ID
with a 0.2 |j,m film thickness). Table 4-17 lists the organic toxicants that were analyzed.
Metallic toxicants, also listed in Table 4-17, were analyzed using a graphite furnace
equipped atomic absorption spectrophotometer (GFAA). EPA methods 202.2 (Al),
213.2 (Cd), 218.2 (Cr), 220.2 (Cu), 239.2 (Pb), 249.2 (Ni), and 289.2 (Zn) were followed
in these analyses. A Perkin Elmer 3030B atomic absorption spectrophotometer was
used after nitric acid digestion of the samples. Previous research (Pitt and McLean
1986; EPA 1983a) indicated that low detection limits were necessary in order to
measure the filtered sample concentrations of the metals, which would not be achieved
by use of a standard flame atomic absorption spectrophotometer. Low detection limits
would enable partitioning of the metals between the solid and liquid phases to be
investigated, an important factor in assessing the fates of the metals in receiving waters
and in treatment processes.
4-49
-------
Table 4-17. Toxic pollutants analyzed in samples.
Pesticides
Detention Limit
= 0.3 |jg/l
BHC (Benzene
hexachloride)
Heptachlor
Aldrin
Endosulfan
Heptachlor epoxide
DDE (Dichlorodiphenyl
dichloroethylene)
ODD (Dichlorodiphenyl
dichloroethane)
DDT (Dichlorodiphenyl
trichloroethane)
Endrin
Chlordane
Phthalate Esters
Detention Limit = 0.5 |jg/l
Bis(2-ethylhexyl) Phthalate
Butyl benzyl phthalate
Di-n-butyl phthalate
Diethyl phthalate
Dimethyl phthalate
Di-n-octyl phthalate
Polycyclic Aromatic Hydrocarbons
Detention Limit = 0.5 |jg/l
Acenaphthene
Acenapthylene
Anthracene
Benzo (a) anthracene
Benzo (a) pyrene
Benzo (b)
fluoranthene
Benzo (ghi) perylene
Benzo (k)
fluoranthene
Chrysene
Dibenzo (a,h)
anthracene
Fluoranthene
Fluorene
Indeno (1 ,2,3-cd) pyrene
Naphthalene
Phenanthrene
Pyrene
Metals
Detention Limit
= 1 |Jg/l
Aluminum
Cadmium
Chromium
Copper
Lead
Nickel
Zinc
The Microtox 100% sampletoxicity screening test, from Azur Environmental
(previously Microbics, Inc.), was selected for this research after comparisons with other
laboratory bioassay tests. During the first research, 20 source area stormwater
samples and combined sewer samples (obtained during a cooperative study being
conducted in New York City) were split and sent to four laboratories for analyses using
14 different bioassay tests. Conventional bioassay tests were conducted using
freshwater organisms at the EPA's Duluth, MN, laboratory and using marine organisms
at the EPA's Narraganssett Bay, Rl, laboratory. In addition, other bioassay tests, using
bacteria, were also conducted at the Environmental Health Sciences Laboratory at
Wright State University, Dayton, OH. The tests represented a range of organisms that
included fish, invertebrates, plants, and microorganisms.
The conventional bioassay tests conducted simultaneously with the Microtox
screening test for the 20 stormwater sheetflow and combined sewer overflow (CSO)
samples were all short-term tests. However, some of the tests were indicative of
chronic toxicity (e.g., life cycle tests and the marine organism sexual reproduction tests),
whereas the others would be classically considered as indicative of acute toxicity (e.g.,
Microtox and the fathead minnow tests). The following list shows the major tests that
were conducted by each participating laboratory:
1. University of Alabama at Birmingham, Environmental Engineering Laboratory
Microtox bacterial luminescence tests (10-, 20-, and 35-minute exposures)
using the marine Photobacterium phosphoreum.
4-50
-------
2. Wright State University, Biological Sciences Department
Macrofaunal toxicity tests:
Daphnia magna (water flea) survival; Lemma minor (duckweed) growth;
and Selenastrum capricornutum (green alga) growth.
Microbial activity tests (bacterial respiration):
Indigenous microbial electron transport activity;
Indigenous microbial inhibition of p-galactosidase activity;
Alkaline phosphatase for indigenous microbial activity;
Inhibition of p-galactosidase for indigenous microbial activity; and
Bacterial surrogate assay using 0-nitrophenol-p-D-galactopyranside
activity and Escherichia coli.
3. EPA Environmental Research Laboratory, Duluth, MN
Ceriodaphnia dubia (water flea) 48-h survival; and
Pimephales promelas (fathead minnow) 96-h survival.
4. EPA Environmental Research Laboratory, Narragansett Bay, Rl
Champia parvula (marine red alga) sexual reproduction (formation of cystocarps
after 5 to 7 d exposure); and
Arbacua punctulata (sea urchin) fertilization by sperm cells.
Table 4-18 summarizes the results of the toxicity tests. The C. dubia. P. promelas,
and C. Parvula tests experienced problems with the control samples and, therefore,
these results are therefore uncertain. The A. pustulata tests on the stormwater
samples also had a potential problem with the control samples. The CSO test results
(excluding the fathead minnow tests) indicated that from 50% to 100% of the samples
were toxic, with most tests identifying the same few samples as the most toxic. The
toxicity tests for the stormwater samples indicated that 0% to 40% of the samples were
toxic. The Microtox screening procedure gave similar rankings for the samples as the
other toxicity tests.
Laboratory toxicity tests can result in important information on the effects of stormwater
in receiving waters, but actual in-stream taxonomic studies should also be conducted.
A recently published proceedings of a conference on stormwater impacts on receiving
streams (Herricks 1995) contains many examples of actual receiving water impacts and
toxicity test protocols for stormwater.
4-51
-------
Table 4-18. Fraction of samples rated as toxic.
Sample series
Microtox marine bacteria
C. Dubia
P. promelas
C. parvula
A. punctulata
D. magna
L. minor
Combined sewer
overflows
(%)
100
60
O1
100
100
63
501
Storm water
(%)
20
O1
O1
O1
O1
40
0
1) Results uncertain, see text
All of the Birmingham samples represented separate stormwater. However, as part of
the Microtox evaluation, several CSO samples from New York City were also tested to
compare the different toxicity tests. These samples were collected from six CSO
discharge locations having the following land uses:
1. 290 acres, 90% residential and 10% institutional.
2. 50 acres, 100% commercial.
3. 620 acres, 20% institutional, 6% commercial, 5% warehousing, 5% heavy
industrial, and 64% residential.
4. 225 acres, 13% institutional, 4% commercial, 2% heavy industrial, and 81%
residential.
5. 400 acres, 1% institutional and 99% residential.
6. 250 acres, 88% commercial. 6% warehousing, and 6% residential.
Therefore, there was a chance that some of the CSO samples may have had some
industrial process waters. However, none of the Birmingham sheetflow samples could
have contained any process waters because of how and where they were collected.
The Microtox screening procedure gave similar toxicity rankings for the 20 samples as
the conventional bioassay tests. It is also a rapid procedure (requiring about one hour)
and only requires small (<1 ml) sample volumes. The Microtox toxicity test uses
marine bioluminescence bacteria and monitors the light output for different sample
concentrations. About one million bacteria organisms are used per sample, resulting in
highly repeatable results. The more toxic samples produce greater stress on the
bacteria test organisms that results in a greater light attenuation compared to the control
sample. Note that the Microtox procedure was not used during this research to
determine the absolute toxicities of the samples or to predict the toxic effects of
stormwater runoff on receiving waters. It was used to compare the relative toxicities of
4-52
-------
different samples that may indicate efficient source area treatment locations, and to
examine changes in toxicity during different treatment procedures.
Potential Sources
A drainage system captures runoff and pollutants from many source areas, all with
individual characteristics influencing the quantity of runoff and pollutant load.
Impervious source areas may contribute most of the runoff during small storm events
(e.g., paved parking lots, streets, driveways, roofs, and sidewalks). Pervious source
areas can have higher material washoff potentials and become important contributors
for larger storm events when their infiltration rate capacity is exceeded (e.g., gardens,
bare ground, unpaved parking areas, construction sites, undeveloped areas). Many
other factors also affect the pollutant contributions from source areas, including: surface
roughness, vegetative cover, gradient and hydraulic connections to a drainage system;
rainfall intensity, duration, and antecedent dry period; and pollutant availability due to
direct contamination from local activities, cleaning frequency/efficiency, and natural and
regional sources of pollutants. The relative importance of the different source areas is
therefore a function of the area characteristics, pollutant washoff potential, and the
rainfall characteristics (Pitt 1987).
Important sources of toxicants are often related to the land use (e.g., high traffic
capacity roads, industrial processes, and storage area) that are unique to specific land
uses activities. Automobile related sources affect the quality and quantity of road dust
particles through gasoline and oil drips/spills, deposition of exhaust products, and wear
of tire, brake, and pavement materials (Shaheen 1975). Urban landscaping practices
potentially produce vegetation cuttings and fertilizer and pesticide washoff.
Miscellaneous sources include holiday firework debris, wildlife and domestic pet wastes,
and possible sanitary wastewater infiltration. In addition, resuspension and deposition
of pollutants/particles via the atmosphere can increase or decrease the contribution
potential of a source area (Pitt and Bozeman 1982, Bannerman et al. 1993).
Results
Table 4-19 summarizes the source area sample data for the most frequently detected
organic toxicants and for all of the metallic toxicants analyzed. The organic toxicants
analyzed, but not reported, were generally detected in five, or less, of the non-filtered
samples and in none of the filtered samples. Table 4-19 shows the mean, maximum,
and minimum concentrations for the detected toxicants. Note that these values are
based only on the observed concentrations. They do not consider the non-detectable
conditions. Mean values based on total sample numbers for each source area category
would therefore result in much lower concentrations. The frequency of detection is
therefore an important consideration when evaluating organic toxicants. High detection
frequencies for the organics may indicate greater potential problems than infrequent
high concentrations.
Table 4-19 also summarizes the measured pH and SS concentrations. Most pH values
were in the range of 7.0 to 8.5 with a low of 4.4 and a high of 11.6 for roof and concrete
4-53
-------
plant storage area runoff samples, respectively. This range of pH can have dramatic
effects on the speciation of the metals analyzed. The SS concentrations were generally
less than 100 mg/l, with impervious area runoff (e.g., roofs and parking areas) having
much lower SS concentrations and turbidities compared to samples obtained from
pervious areas (e.g., landscaped areas).
Out of more than 35 targeted compounds analyzed, 13 were detected in more than 10%
of all samples, as shown in Table 4-19. The greatest detection frequencies were for
1,3-dichlorobenzene and fluoranthene, which were each detected in 23% of the
samples. The organics most frequently found in these source area samples (i.e.,
polycyclic aromatic hydrocarbons (PAH), especially fluoranthene and pyrene) were
similar to the organics most frequently detected at outfalls in prior studies (EPA 1983a).
Roof runoff, parking area and vehicle service area samples had the greatest detection
frequencies for the organic toxicants. Vehicle service areas and urban creeks had
several of the observed maximum organic compound concentrations. Most of the
organics were associated with the non-filtered sample portions, indicating an
association with the particulate sample fractions. The compound 1,3-dichlorobenzene
was an exception, having a significant dissolved fraction.
In contrast to the organics, the heavy metals analyzed were detected in almost all
samples, including the filtered sample portions. The non-filtered samples generally had
much higher concentrations, with the exception of zinc, which was mostly associated
with the dissolved sample portion (i.e., not associated with the SS). Roof runoff
generally had the highest concentrations of zinc, probably from galvanized roof
drainage components, as previously reported by Bannerman et al. (1983). Parking and
storage areas had the highest nickel concentrations, while vehicle service areas and
street runoff had the highest concentrations of cadmium and lead. Urban creek
samples had the highest copper concentrations, which were probably due to illicit
industrial connections or other non-stormwater discharges.
Table 4-20 shows the relative toxicities of the collected stormwaters. A wide range of
toxicities was found. About 9% of the non-filtered samples were considered highly toxic
using the Microtox toxicity screening procedure. About 32% of the samples were
moderately toxic and about 59% were considered non-toxic. The greatest percentage
of samples considered the most toxic were from industrial storage and parking areas.
Landscaped areas also had a high incidence of highly toxic samples (presumably due to
landscaping chemicals) and roof runoff had some highly toxic samples (presumably due
to high zinc concentrations). Treatability study activities indicated that filtering the
samples through a range of fine sieves and finally a 0.45um filter consistently reduced
sample toxicities. The chemical analyses also generally found much higher toxicant
concentrations in the non-filtered sample portions, compared to the filtered sample
portions.
4-54
-------
Table 4-19. Stormwater toxicants detected in at least 10% of the source area sheetflow samples (iig/l, unless
otherwise noted).
Total samples
Roof
areas
N.F.'
12
F.z
12
Parking
areas
N.F.
16
F.
16
Storage
areas
N.F.
8
F.
8
Street
runoff
NF
6
F.
6
Loading
docks
N.F.
3
K
3
Vehicle
service
areas
N.F.
5
F.
5
Landscaped
areas
N.F.
6
F.
6
Urban
creeks
N.F.
19
K
19
Detention
ponds
NF.
12
F.
12
Base neutrals (detection I mlt = 0.5 |ig/l)
1 ,3-Dichlorobenzene detection frequency = 20% N.F. and 13% F.
No. detected3
Mean4
Max.
Min.5
Fluoranthene detection frequency = 20% N.F. and 12% F.
No. detected
Mean
Max.
Min.
Pyrene detection frequency = 17% N,F, and 7% F.
No. detected
Mean
Max.
Min.
Benzo(b)fluoranthene detection frequency = 15% N.F. and 0% F.
No. detected
Mean
Max.
Min.
Benzo(k)fluoranthene detection frequency = 11% N.F. and 0% F.
No. detected
Mean
Max.
Min.
Benzo(a)pyrene detection frequency = 15% N.F. and 0% F.
No. detected
Mean
Max.
Min.
52
88
14
3
23
45
7.6
1
28
4
76
260
6.4
0
4
99
300
34
2
20
23
17
2
9.3
14
4.8
0
0
0
0
3
34
103
3.0
3
37
110
3.0
3
40
120
3.0
3
53
160
3.0
3
20
1
3.0
3
40
120
3.0
2
13
26
2.0
2
2.7
5.4
2.0
2
9.8
20
2.0
0
0
0
1
16
1
4.5
1
8
0
0
0
1
14
0
0
0
0
0
0
1
5.4
1
0.6
1
1.0
1
14
1
15
1
19
1
3.3
1
0.5
1
0.7
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
48
72
6.0
3
39
53
0.4
3
44
51
0.7
2
98
110
90
2
59
103
15
2
90
120
60
2
26
47
4.9
2
3.6
6.8
0.4
2
4.1
7.4
0.7
0
0
0
3
29
54
4.5
3
13
38
0.7
2
5.3
8.2
2.3
1
30
1
61
1
54
2
5.6
7.5
3.8
2
1.0
1.3
0.7
0
0
0
0
2
93
120
65
1
130
1
100
2
36
64
8.0
2
55
78
31
2
73
130
19
0
0
0
0
0
0
1
27
2
10
14
6.6
2
31
57
6.0
0
0
0
1
21
1
6.6
1
5.8
0
0
0
4-55
-------
Table 4-19. Stormwater toxicants detected in at least 10% of the source area sheetflow samples (iig/l, unless
otherwise noted).Continued.
Total samples
Roof
areas
N.F.'
12
F'
12
Parking
areas
NF
16
F.
16
Storage
areas
NF.
8
F.
8
Street
runoff
N.F.
6
F.
6
Loading
docks
NF.
3
F.
3
Vehicle
service
areas
N.F.
5
F.
5
Landscaped
areas
N.F.
6
F.
6
Urban
creeks
NF.
19
F.
19
Detention
ponds
NF.
12
F.
12
Bis(2-chloroethyl) ether detection frequency = 12% N.F. and 2% F.
No. detected
Mean
Max.
Min.
Bis(chloroisopropyl) ether detection frequency = 13% N.F. and 0% F.
No. detected
Mean
Max.
Min.
Naphthalene detection frequency = 11% N.F. and 6% F.
No. detected
Mean
Max.
Min.
Benzo(a)anthracene detection frequency = 10% N.F. and 0% F.
No. detected
Mean
Max.
Min.
Butylbenzyl phthalate detection frequency = 10% N.F. and 4% F.
No. detected
Mean
Max.
Min.
Pest
Chlordane detection frequency = 11% N.F. and 0% F.
No. detected
Mean
Max.
Min.
42
87
20
3
99
150
68
2
17
21
13
1
16
1
100
Iclde
2
1.6
2.2
0.9
1
17
2
0
0
0
0
s (c
0
2
20
39
2.0
3
130
400
3.0
1
72
3
24
73
3.0
2
12
21
3.3
et e c
2
1.0
1.2
0.8
0
0
1
6.6
0
1
3.3
tlor
0
0
0
0
0
0
llrr
3
1.7
2.9
1.0
0
0
0
0
0
It =
0
1
15
0
0
0
0
0.3
1
0.8
0
0
0
0
0
iig'
0
0
0
0
0
0
I)
0
0
0
0
0
0
0
0.8
1
45
6.0
2
120
160
74
2
70
100
37
2
35
39
31
2
26
48
3.8
1
1
23
4.9
0
1
82
0
2
9.8
16
3
0
1
56
4.5
1
85
1
49
1
54
1
130
0
0
3.8
0
0
0
0
0
1
200
65
2
59
78
40
1
300
1
61
1
59
0
0
0
1
6.7
0
0
0
1
15
0
2
43
68
18
0
1
13
0
0
0
2
12
17
6.6
0
0
0
4-56
-------
Table 4-19. Stormwater toxicants detected in at least 10% of the source area sheetflow samples (ng/l, unless
otherwise noted).Continued.
Total samples
Roof areas
NF.'
12
F'
12
Parking
areas
NF
16
F.
16
Storage
areas
NF
8
F.
8
Metals (detection II
Street
runoff
NF
6
ml t =
F.
6
1 iig/l
Loading
docks
NF
3
)
F.
3
Vehicle
service
areas
NF
5
F.
5
Landscaped
areas
NF.
6
F.
6
Urban
creeks
NF.
19
F.
19
Detention
ponds
NF.
12
F.
12
Lead detection frequency = 100% N.F. and 54% F.
No. detected
Mean
Max.
Min.
Zinc detection frequency = 99% N.F. and 98% F.
No. detected
Mean
Max.
Min.
Copper detection frequency = 98% N.F. and 78% F.
No. detected
Mean
Max.
Min.
Aluminum detection frequency = 97% N.F. and 92% F.
No. detected
Mean
Max.
Min.
Cadmium detection frequency = 95% N.F. and 69% F.
No. detected
Mean
Max.
Min.
Chromium detection frequency = 91% N.F. and 55% F.
No. detected
Mean
Max.
Min.
41
170
1.3
12
250
1580
11
11
110
900
1.5
12
6850
71300
25
11
3.4
30
0.2
7
85
510
5.0
1
1.1
12
220
1550
9
7
2.9
8.7
1.1
12
230
1550
6.4
7
0.4
0.7
0.1
2
1.8
2.3
1.4
16
46
130
1.0
16
110
650
12
15
116
770
10
15
3210
6480
130
15
6.3
70
0.1
15
56
310
2.4
8
2.1
5.2
1.2
16
86
560
6
13
11
61
1.1
15
430
2890
5.0
9
0.6
1.8
0.1
8
2.3
5.0
1.1
8
105
330
3.6
8
1730
13100
12
8
290
1830
10
7
2320
6990
180
8
5.9
17
0.9
8
75
340
3.7
7
2.6
5.7
1.6
7
22
100
3.0
6
250
1520
1.0
6
180
740
10
7
2.1
10
0.3
5
11
32
1.1
6
43
150
1.5
6
58
130
4.0
6
280
1250
10
6
3080
10040
70
6
37
220
0.4
5
9.9
30
2.8
4
2.0
3.9
1.1
6
31
76
4.0
5
3.8
11
1.0
6
880
4380
18
5
0.3
0.6
0.1
4
1.8
2.7
1.3
3
55
80
25
2
55
79
31
3
22
30
15
3
780
930
590
3
1.4
2.4
0.7
3
17
40
2.4
1
2.3
2
33
62
4.0
2
8.7
15
2.6
1
18
3
0.4
0.6
0.3
0
5
63
110
27
5
105
230
30
5
135
580
1.5
5
700
1370
93
5
9.2
30
1.7
5
74
320
2.4
2
2.4
3.4
1.4
5
73
230
11
4
8.4
24
1.1
4
170
410
0.3
3
0.3
0.5
0.2
1
2.5
6
24
70
1.4
6
230
1160
18
6
81
300
1.9
5
2310
4610
180
4
0.5
1
0.1
6
79
250
2.2
1
1.7
6
140
670
18
6
4.2
8.8
0.9
5
1210
1860
120
2
0.6
1
0.1
5
2.0
4.1
1.4
19
20
100
1.4
19
10
32
<1
19
50
440
<1
19
620
3250
<5
19
8.3
30
<0.1
19
62
710
<0.1
15
1.4
1.6
<1
19
10
23
<1
17
1.4
1.7
<1
19
190
500
<5
15
0.2
0.3
<0.1
15
1.6
4.3
<0.1
12
19
55
1
12
13
25
<1
12
43
210
0.2
12
700
1570
<5
12
2
11
0.1
11
37
230
<0.1
8
1.0
1.0
<1
12
14
25
<1
8
20
35
<1
12
210
360
<5
9
0.5
0.7
0.4
8
2.0
3.0
<0.1
4-57
-------
Table 4-19. Stormwater toxicants detected in at least 10% of the source area sheetflow samples (iig/l, unless
otherwise noted).Continued.
Total samples
Roof
areas
N.F.'
12
F'
12
Parking
areas
NF
16
F.
16
Storage
areas
NF.
8
F.
8
Street
runoff
N.F.
6
F.
6
Loading
docks
N.F.
3
F.
3
Vehicle
service
areas
NF.
5
F.
5
Landscaped
areas
NF.
6
F.
6
Urban
creeks
N.F.
19
F.
19
Detention
ponds
N.F.
12
F.
12
Nickel detection frequency = 90% N.F. and 37% F.
No. detected
Mean
Max.
Min.
Other constituents (alw
PH
Mean
Max.
Min.
Suspended solids
Mean
Max.
Min.
16
70
2.6
ays i
6.9
8.4
4.4
14
92
0.5
0
lete
14
45
130
4.2
ct ed
7.3
8.7
5.6
110
750
9.0
4
5.1
13
1.6
, a n
8
55
170
1.9
1 1 yzc
8.5
12
6.5
100
450
5.0
1
87
d o
5
17
70
1.2
1 1 y f
7.6
8.4
6.9
49
110
7.0
0
3 r n
3
6.7
8.1
4.2
o n -
7.8
8.3
7.1
40
47
34
1
1.3
lite
5
42
70
7.9
red s
7.2
8.1
5.3
24
38
17
1
31
amp
4
53
130
21
les)
6.7
7.2
6.2
33
81
8.0
1
2.1
18
29
74
<1
7.7
8.6
6.9
26
140
5.0
16
2.3
3.6
<1
11
24
70
1.5
8.0
9.0
7.0
17
60
3.0
8
3.0
6.0
<1
1) N.F.: concentration associated with a nonfiltered sample.
2) F.: concentration after the sample was filtered through a 0.45 j^m membrane filter.
3) Number detected refers to the number of samples in which the toxicant was detected.
4) Mean values based only on the number of samples with a definite concentration of toxicant reported (not on the total number of samples analyzed).
5) The minimum values shown are the lowest concentration detected, they are not necessarily the detection limit.
4-58
-------
Replicate samples were collected from several source areas at three land uses
during four different storm events to statistically examine toxicity and pollutant
concentration differences due to storm and site conditions. These data indicated
that variations in Microtox toxicities and organic toxicant concentrations may be
partially explained by rain characteristics. As an example, high concentrations of
many of the PAHs were associated with long antecedent dry periods and large
rains (Barren 1990).
Table 4-20. Relative toxicity of samples using Microtox (non-filtered).
Local Source
Areas
Roofs
Parking Areas
Storage Areas
Streets
Loading Docks
Vehicle Service Areas
Landscaped Areas
Urban Creeks
Detention Ponds
Highly
Toxic
(%)
8
19
25
0
0
0
17
0
8
Moderately
Toxic
(%)
58
31
50
67
67
40
17
11
8
Not
Toxic
(%)
33
50
25
33
33
60
66
89
84
Number
of
Samples
12
16
8
6
3
5
6
19
12
All Areas
32
59
87
J
Microbics suggested toxicity definitions for 35 minute exposures:
Highly toxic - light decrease >60%
Moderately toxic - light decrease <60% & >20%
Not toxic - light decrease <20%
4-59
-------
References
Alley, W. M. (1980). Determination of the decay coefficient in the exponential
washoff equation. International Symposium on Urban Runoff. University of
Kentucky. Lexington, KY. July.
Alley, W. M. (1981). Estimation of impervious-area washoff parameters. Water
Resources Research. Vol. 17, No. 4, pp 1161-1166.
American Public Works Association (1969). Water Pollution Aspects of Urban
Runoff. Water Pollution Control Research Series WP-20-15. Federal Water
Pollution Control Administration. January.
Bannerman, R., K. M. Baun, P. E. Bohn, and D. A. Graczyk (1983). Evaluation
of Urban Nonpoint Source Pollution Management in Milwaukee County,
Wisconsin. PB 84-114164. U.S. Environmental Protection Agency. Chicago, IL.
Bannerman, R., D. W. Owens, R. B. Dodds, and N. J. Hornewer (1993). Sources
of pollutants in Wisconsin stormwater. Water Science and Technology. Vol. 28,
No. 3-5, pp. 241-259.
Barkdoll, M. P., D. E. Overton, and R. P. Beton (1977). Some effects of dustfall
on urban stormwater quality. Water Pollution Control Federation. 49(9): 1976-84.
Barren, P. (1990). Characterization of Polynuclear Aromatic Hydrocarbons in
Urban Runoff. Master's Thesis. The University of Alabama at Birmingham
Department of Civil Engineering. Birmingham, AL.
Betson, R. P. (1978). Precipitation and streamflow quality relationships in an
urban area. Water Resources Research. 14(6): 1165-1169.
Box, G. E. P., W. G. Hunter, and J. S. Hunter (1978). Statistics for
Experimenters. John Wiley and Sons. New York, NY.
COE (U.S. Corps of Engineers). Hydrologic Engineering Center. (1975). Urban
Storm Water Runoff: STORM. Generalized Computer Program. 723-58-L2520.
Davis, CA. May.
Cowherd, C. J., C. M. Maxwell, and D. W. Nelson (1977). Quantification of Dust
Entrainment from Paved Roadways. EPA-450 3-77-027. U.S. Environmental
Protection Agency. Research Triangle Park, NC. July.
Denver Regional Council of Governments (1983). Urban Runoff Quality in the
Denver (Colorado) Region. Prepared for the U.S. EPA. Washington, DC. PB85-
101640. September.
4-60
-------
Donigian, A. S., Jr. and N.H. Crawford (1976). Modeling Nonpoint Pollution from
the Land Surface. EPA-600/3-76-083. U.S. Environmental Protection Agency.
Athens, GA. July.
Durum, W. H. (1974). Occurrence of some trace metals in surface waters and
groundwaters. In Proceeding of the Sixteenth Water Quality Conference. Am.
Water Works Assoc., etal. Univ. of Illinois Bull. 71(108). Urbana, IL.
EPA (1982). Methods for Organic Chemical Analyses of Municipal and Industrial
Wastewater. Environmental Monitoring and Data Support Laboratory. EPA-
600/4-82-057. U.S. Environmental Protection Agency. Cincinnati, OH.
EPA (1983a). Results of the Nationwide Urban Runoff Program. Water Planning
Division. PB 84-185552. Washington, D.C. December.
EPA (1983b). Methods for Chemical Analysis of Water and Wastes. EPA-600/4-
79-020. U.S. Environmental Protection Agency. Cincinnati, OH.
Field, R., E.J. Struzeski, Jr., H.E. Masters and A.M. Tafuri (1973). Water
Pollution and Associated Effects from Street Salting. EPA-R2-73-257. U.S.
Environmental Protection Agency. Cincinnati, OH. May.
Gupta, M., D. Mason, M. Clark, T. Meinholz, C. Hansen, and A Geinopolos
(1977). Screening Flotation Treatment of Combined Sewer Overflows Volume I -
Bench Scale and Pilot Plant Investigations. EPA-600/2-77-069a. U.S.
Environmental Protection Agency. Cincinnati, OH. August.
Herricks, E. E. (1995). Stormwater Runoff and Receiving Systems: Impact,
Monitoring, and Assessment. CRC/Lewis Publishers. Boca Raton, FL.
Huber, W.C. and J.P. Heaney. (1981). The USEPA Storm Water Management
Model, SWMM: A ten-year Perspective. Second international Conference on
Urban Storm Drainage. Urbana, IL. June.
Jewell, T.K., D.D. Adrian and D.W. Hosmer (1980). Analysis of stormwater
pollutant washoff estimation techniques. International Symposium on Urban
Storm Runoff. University of Kentucky. Lexington, KY. July.
Kobriger, N.P., T.L. Meinholiz, M.K. Gupta, and R.W. Agnew(1981).
Constituents of Highway Runoff. Vol. 3. Predictive Procedure for Determining
Pollution Characteristics in Highway Runoff. FHWA/RD-81/044. Federal
Highway Administration. Washington, D.C. February.
4-61
-------
Koeppe, D. E. (1977). comp. Vol. IV: Soil-water-air-plant studies. In:
Environmental Contamination by Lead and Other Heavy Metals. G. L. Rolfe and
K. A. Peinbold, eds. Institute for Environmental Studies. Univ. of Illinois.
Urbana-Champaign, IL. July.
Lindsay, W. L. (1979). Chemical Equilibria in Soils. John Wiley and Sons. New
York, NY.
Malmquist, Per-Arne (1978). Atmospheric Fallout and Street Cleaning - Effects
on Urban Stream Water and Snow Prog. Wat Tech., 10(5/6): 495-505.
Pergamon Press. Great Britain. September.
Manning, M.J., R.H. Sullivan, and T.M. Kipp (1976). Nationwide Evaluation of
Combined Sewer Overflows and Urban Stormwater Discharges. Vol. Ill:
Characterization of Discharges. U.S. Environmental Protection Agency.
Cincinnati, OH. October.
Murphy, W. (1975). Roadway Particulate Losses: American Public Works Assoc.
Unpublished.
Novotny, V. and G. Chesters (1981). Handbook of Nonpoint Pollution Sources
and Management. Van Norstrand Reinhold Company. New York, NY.
PEDCo-Environmental, Inc. (1977). Control of Re-entrained Dust from Paved
Streets. EPA-907/9-77-007. U.S. Environmental Protection Agency. Kansas
City, MO.
Phillips, G. R., and R. C. Russo (1978). Metal Bioaccumulation in Fishes and
Aquatic Invertebrates: A Literature Review. EPA-600-3-78-103, U.S.
Environmental Protection Agency. Duluth, MN. December.
Pitt, R. (1979). Demonstration of Nonpoint Pollution Abatement Through
Improved Street Cleaning Practices. EPA-600/2-79-161. U.S. Environmental
Protection Agency. Cincinnati, OH. August.
Pitt, R. (1983). Urban Bacteria Sources and Control in the Lower Rideau River
Watershed. Ottawa, Ontario. Ontario Ministry of the Environment. ISBN 0-
7743-8487-5. 165pgs.
Pitt, R. (1985). Characterizing and Controlling Urban Runoff through Street and
Sewerage Cleaning. U.S. Environmental Protection Agency. Storm and
Combined Sewer Program. Risk Reduction Engineering Laboratory.
EPA/600/S2-85/038. PB 85-186500. Cincinnati, OH. June.
4-62
-------
Pitt, R. (1987). Small Storm Urban Flow and Particulate Washoff Contributions
to Outfall Discharges. Ph.D. dissertation submitted to the Department of Civil
and Environmental Engineering. University of Wisconsin - Madison.
Pitt R. and M. Bozeman (1982). Sources of Urban Runoff Pollution and Its
Effects on an Urban Creek. EPA 600/S2-82-090. U.S. Environmental Protection
Agency. Cincinnati, OH.
Pitt, R. and G. Shawley (1982). A Demonstration of Non-Point Source Pollution
Management on Castro Valley Creek. Alameda County Flood Control and Water
Conservation District (Hayward, CA) for the Nationwide Urban Runoff Program.
U.S. Environmental Protection Agency. Water Planning Division. Washington,
D.C. June.
Pitt, R. and R. Sutherland (1982). Washoe County Urban Stormwater
Management Program. Volume 2, Street Particulate Data Collection and
Analyses. Washoe Council of Governments. Reno, NV. August.
Pin, R. and J. McLean (1986). Toronto Area Watershed Management Strategy
Study. Number River Pilot Watershed Project. Ontario Ministry of the
Environment. Toronto, Ontario.
Pitt, R., M. Lalor, R. Field, D.D. Adrian, and D. Barbe (1993). Investigation of
Inappropriate Pollutant Entries into Storm Drainage Systems, A User's Guide.
EPA/600/R-92/238. U.S. Environmental Protection Agency. Cincinnati, OH.
Rolfe, G.L. and K.A. Reinhold (1977). Vol. I.- Introduction and Summary.
Environmental Contamination by Lead and Other Heavy Metals. Institute for
Environmental Studies. University of Illinois. Champaign-Urbana, IL. July.
Rubin, A. J., ed. (1976). Aqueous-Environmental Chemistry of Metals. Ann
Arbor Science Publishers. Ann Arbor, Ml.
Sartor J. and G. Boyd (1972). Water Pollution Aspects of Street Surface
Contaminants. EPA-R2-72-081, U.S. Environmental Protection Agency.
November.
Shaheen, D.G. (1975). Contributions of Urban Roadway Usage to Water
Pollution. 600/2-75-004. U.S. Environmental Protection Agency. Washington,
D.C. April.
Shelley, P.E. and D.R. Gaboury (1986). Estimation of pollution from highway
runoff - initial results. Conference on Urban Runoff Quality - Impact and Quality
Enhancement Technology. Henniker, NH. Edited by B. Urbonas and L.A.
Roesner. Proceedings published by the American Society of Civil Engineering.
New York, NY. June.
4-63
-------
Shen, H.W. (1981). Some basic concepts on sediment transport in urban storm
drainage systems. Second International Conference on Urban Storm Drainage.
Urbana, IL. June.
Singer, M.J. and J. Blackard (1978). Effect of mulching on sediment in runoff
from simulated rainfall. Soil Sci. Soc. Am. J., 42:481-486.
Solomon, R.L., and D.F.S. Natusch (1977). VoUII: Distribution and
characterization of urban dists. In: Environmental Contamination by Lead and
Other Heavy Metals. G. L. Rolfe and K. G. Reinbold, eds. Institute for
Environmental Studies. Univ. of Illinois. Urbana-Champaign, IL. July.
Spring, R. J., R. B. Howell, and E. Shirley (1978). Dustfall Analysis for the
Pavement Storm Runoff Study (I-405 Los Angeles). Office of Transportation
Laboratory. California Dept. of Transportation. Sacramento, CA. April.
Sutherland, R., and R.H. McCuen (1978). Simulation of urban nonpoint source
pollution. Water Resources Bulletin. Vol. 14, No. 2, pp 409-428. April.
Sutherland, R., W. Alley, and F. Ellis (undated). Draft Users' Guide for
Particulate Transport Model (PTM). CH2M -HILL. Portland, OR for the U.S.
Geological Survey.
Terstriep, M.L., G.M. Bender, and D.C. Noel (1982). Final Report - NURP
Project, Champaign, Illinois: Evaluation of the Effectiveness of Municipal Street
Sweeping in the Control of Urban Storm Runoff Pollution. State Water Survey
Division. Illinois Dept. of Energy and Natural Resources. Champaign-Urbana,
IL. December.
Verschueren, K. (1983). Handbook of Environmental Data on Organic
Chemicals, 2nd edition. Van N Reinhold Co. New York, NY.
Wilber, W. G., and J.V. Hunter (1980). The Influence of Urbanization on the
Transport of Heavy Metals in New Jersey Streams. Water Resources Research
Institute. Rutgers University. New Brunswick, NJ.
Yalin, M.S. (1963). An expression for bed load transportation. Journal of the
Hydraulics Division, Proceedings of the American Society of Civil Engineers. Vol
89, pp 221-250.
4-64
-------
Chapters
Receiving Water and Other Impacts
Robert Pitt
Desired Water Uses Versus Stormwater Impacts
The main purpose of treating stormwater is to reduce its adverse impacts on receiving
water beneficial uses. Therefore, this report on wet-weather flow management systems
includes an assessment of the detrimental effects that runoff is actually having on a
receiving water.
Urban receiving waters may have many beneficial use goals, including:
1. Stormwater conveyance (flood prevention).
2. Biological uses (e.g., warm water fishery, biological integrity).
3. Non-contact recreation (e.g., linear parks, aesthetics, boating).
4. Contact recreation (swimming).
5. Water supply and irrigation.
With full development in an urban watershed and with no stormwater controls, it is
unlikely that any of these uses can be obtained. With less development and with the
application of stormwater controls, some uses may be possible. Unreasonable
expectations should not be placed on urban waters, because the cost to obtain these
uses may be prohibitive. With full-scale development and lack of adequate stormwater
controls, severely degraded streams will be common.
Stormwater conveyance and aesthetics should be the basic beneficial use goals for all
urban waters. Biological integrity should also be a goal, but with the realization that the
natural stream ecosystem will be severely modified with urbanization. Certain basic
controls, installed at the time of development, plus protection of stream habitat, may
enable partial realization of some of these basic goals in urbanized watersheds. Careful
planning and optimal utilization of stormwater controls are necessary to obtain these
basic goals in most watersheds. Water contact recreation, consumptive fisheries, and
water supplies are not appropriate goals for most urbanized watersheds. These higher
uses may be possible in urban areas where the receiving waters are large and drain
mostly undeveloped areas.
In general, monitoring of urban stormwater runoff has indicated that the biological
beneficial uses of urban receiving waters are most likely affected by habitat destruction
and long-term pollutant exposures (especially to macroinvertebrates via contaminated
sediment). Documented effects associated from acute exposures of toxicants in the
water column are rare (Field and Pitt 1990, Pitt 1995).
5-1
-------
Receiving water pollutant concentrations resulting from runoff events and typical
laboratory bioassay test results have not indicated many significant short-term receiving
water problems. As an example, Lee and Jones-Lee (1993) state that exceedences of
numeric criteria by short-term discharges do not necessarily imply that a beneficial use
impairment exists. Many toxicologists and water quality experts have concluded that
the relatively short periods of exposures to the toxicant concentrations in stormwater are
not sufficient to produce the receiving water effects that are evident in urban receiving
waters, especially considering the relatively large portion of the toxicants that are
associated with particulates (Lee and Jones-Lee 1995a and 1995b). Lee and Jones-
Lee (1995a and 1995b) conclude that the biological problems evident in urban receiving
waters due to stormwater discharges are mostly associated with illegal discharges and
that the sediment bound toxicants are of little risk. Mancini and Plummer (1986) have
long been advocates of numeric water quality standards for stormwater that reflect the
partitioning of the toxicants and the short periods of exposure during rains.
Unfortunately, this approach attempts to isolate individual runoff events and does not
consider the accumulative adverse effects caused by the frequent exposures of
receiving water organisms to stormwater (Davies 1995, Herricks 1995 and Herricks et
al. 1996). Recent investigations have identified acute toxicity problems associated with
short-term (about 10 to 20 day) exposures to adverse toxicant concentrations in urban
receiving streams (Crunkilton et al. 1997). However, the most severe receiving water
problems are likely associated with chronic exposures to contaminated sediment and to
habitat destruction.
The effects of stormwater on receiving waters are very site specific. Accordingly, site
investigations of local waters are highly recommended to understand the magnitude and
like cause of the problems. Burton and Pitt (1996) have prepared a book that details
site investigation procedures that can be used for local waters. The following is a
summary of recent work describing the toxicological and ecological effects of
stormwater.
Toxicological Effects of Stormwater
The need for endpoints for toxicological assessments using multiple stressors was
discussed by Marcy and Gerritsen (1996). They used five watershed-level ecological
risk assessments to develop appropriate endpoints based on specific project objectives.
Dyer and White (1996) also examined the problem of multiple stressors affecting toxicity
assessments. They felt that field surveys rarely can be used to verify simple single
parameter laboratory experiments. They developed a watershed approach integrating
numerous databases in conjunction with in-situ biological observations to help examine
the effects of many possible causative factors. Toxic effect endpoints are additive for
compounds having the same "mode of toxic action", enabling predictions of complex
chemical mixtures in water, as reported by Environmental Science & Technology
(1996a). According to EPA researchers at the Environmental Research Laboratory in
Duluth, MN, there are about five or six major action groups that contain almost all of the
compounds of interest in the aquatic environment. Much work still needs to be done,
5-2
-------
but these new developing tools may enable improved prediction of in-stream toxic
effects of stormwater.
Ireland et al. (1996) found that exposure to ultraviolet (UV) radiation (natural sunlight)
increased the toxicity of PAH contaminated urban sediments to C. dubia. The toxicity
was removed when the UV wavelengths did not penetrate the water column to the
exposed organisms. Toxicity was also reduced significantly in the presence of UV when
the organic fraction of the stormwater was removed. Photo-induced toxicity occurred
frequently during low flow conditions and wet weather runoff and was reduced during
turbid conditions.
Johnson et al. (1996) and Herricks et al. (1996) describe a structured tier testing
protocol to assess both short-term and long-term wet weather discharge toxicity that
they developed and tested. The protocol recognizes that the test systems must be
appropriate to the time-scale of exposure during the discharge. Therefore, three time-
scale protocols were developed, for intra-event, event, and long-term exposures. The
use of standard whole effluent toxicity (WET) tests were found to over-estimate the
potential toxicity of stormwater discharges.
The effects of stormwater on Lincoln Creek, near Milwaukee, Wl, were described by
Crunkilton et al. (1997). Lincoln Creek drains a heavily urbanized watershed of 19 mi2
that is about nine miles long. On-site toxicity testing was conducted with side-stream
flow-through aquaria using fathead minnows, plus in-stream biological assessments,
along with water and sediment chemical measurements. In the basic tests, Lincoln
Creek water was continuously pumped through the test tanks, reflecting the natural
changes in water quality during both dry and wet weather conditions. The continuous
flow-through mortality tests indicated no toxicity until after about 14 days of exposure,
with more than 80% mortality after about 25 days, indicating that short-term toxicity
tests likely underestimate stormwater toxicity. The biological and physical habitat
assessments supported a definitive relationship between degraded stream ecology and
urban runoff.
Rainbow (1996) presented a detailed overview of heavy metals in aquatic invertebrates.
He concluded that the presence of a metal in an organism couldn't tell us directly
whether that metal is poisoning the organism. However, if compared to concentrations
in a suite of well-researched biomonitors, it is possible to determine if the accumulated
concentrations are atypically high, with a possibility that toxic effects may be present.
Allen (1996) also presented an overview of metal contaminated aquatic sediments.
Allen's book presents many topics that would enable the user to better interpret
measured heavy metal concentrations in urban stream sediments.
Ecological Effects of Stormwater
A number of comprehensive and long-term studies of biological beneficial uses in areas
not affected by conventional point source discharges have typically shown impairments
5-3
-------
caused by urban runoff. The following paragraphs briefly describe a variety of such
studies.
Klein (1979) studied 27 small watersheds having similar physical characteristics, but
having varying land uses, in the Piedmont region of Maryland. During an initial phase of
the study, they found definite relationships between water quality and land use.
Subsequent study phases examined aquatic life relationships in the watersheds. The
principal finding was that stream aquatic life problems were first identified with
watersheds having imperviousness areas comprising at least 12 percent of the
watershed. Severe problems were noted after the imperviousness quantities reached
30 percent.
Receiving water impact studies were also conducted in North Carolina (Lenet et al.
1979, Lenet and Eagleson 1981, Lenet et al. 1981). The benthic fauna occurred mainly
on rocks. As sedimentation increased, the amount of exposed rocks decreased, with a
decreasing density of benthic macroinvertebrates. Data from 1978 and 1979 in five
cities showed that urban streams were grossly polluted by a combination of toxicants
and sediment. Chemical analyses, without biological analyses, would have
underestimated the severity of the problems because the water column quality varied
rapidly, while the major problems were associated with sediment quality and effects on
macroinvertebrates. Macroinvertebrate diversities were severely reduced in the urban
streams, compared to the control streams. The biotic indices indicated very poor
conditions for all urban streams. Occasionally, high populations of pollutant tolerant
organisms were found in the urban streams, but would abruptly disappear before
subsequent sampling efforts. This was probably caused by intermittent discharges of
spills or illegal dumpings of toxicants. Although the cities studied were located in
different geographic areas of North Carolina, the results were remarkably uniform.
During the Coyote Creek, San Jose, CA, receiving water study, 41 stations were
sampled in both urban and nonurban perennial flow stretches of the creek over three
years. Short and long-term sampling techniques were used to evaluate the effects of
urban runoff on water quality, sediment properties, fish, macroinvertebrates, attached
algae, and rooted aquatic vegetation (Pitt and Bozeman 1982). These investigations
found distinct differences in the taxonomic composition and relative abundance of the
aquatic biota present. The non-urban sections of the creek supported a comparatively
diverse assemblage of aquatic organisms including an abundance of native fishes and
numerous benthic macroinvertebrate taxa. In contrast, however, the urban portions of
the creek (less than 5% urbanized) affected only by urban runoff discharges and not
industrial or municipal discharges, had an aquatic community generally lacking in
diversity and was dominated by pollution-tolerant organisms such as mosquitofish and
tubificid worms.
A major nonpoint runoff receiving water impact research program was conducted in
Georgia (Cook et al. 1983). Several groups of researchers examined streams in major
areas of the state. Benke et al. (1981) studied 21 stream ecosystems near Atlanta
5-4
-------
having watersheds of one to three square miles each and land uses ranging from 0 to
98% urbanization. They measured stream water quality but found little relationship
between water quality and degree of urbanization. The water quality parameters also
did not identify a major degree of pollution. In contrast, there were major correlations
between urbanization and the number of species found. They had problems applying
diversity indices to their study because the individual organisms varied greatly in size
(biomass).
CTA (1983) also examined receiving water aquatic biota impacts associated with urban
runoff sources in Georgia. They studied habitat composition, water quality,
macroinvertebrates, periphyton, fish, and toxicant concentrations in the water, sediment,
and fish. They found that the impacts of land use were the greatest in the urban basins.
Beneficial uses were impaired or denied in all three urban basins studied. Fish were
absent in two of the basins and severely restricted in the third. The native
macroinvertebrates were replaced with pollution tolerant organisms. The periphyton in
the urban streams were very different from those found in the control streams and were
dominated by species known to create taste and odor problems.
Pratt et al. (1981) used basket artificial substrates to compare benthic population trends
along urban and nonurban areas of the Green River in Massachusetts. The benthic
community became increasing disrupted as urbanization increased. The problems were
not only associated with times of heavy rain, but seemed to be affected at all times.
The stress was greatest during summer low flow periods and was probably localized
near the stream bed. They concluded that the high degree of correspondence between
the known sources of urban runoff and the observed effects on the benthic community
was a forceful argument that urban runoff was the causal agent of the disruption
observed.
Cedar swamps in the New Jersey Pine Barrens were studied by Ehrenfeld and
Schneider (1983). They examined nineteen wetlands subjected to varying amounts of
urbanization. Typical plant species were lost and replaced by weeds and exotic plants
in urban runoff affected wetlands. Increased uptakes of phosphorus and lead in the
plants were found. The researchers concluded that the presence of stormwater runoff
to the cedar swamps caused marked changes in community structure, vegetation
dynamics, and plant tissue element concentrations.
Medeiros and Coler (1982) and Medeiros et al. (1984) used a combination of laboratory
and field studies to investigate the effects of urban runoff on fathead minnows.
Hatchability, survival, and growth were assessed in the laboratory in flow-through and
static bioassay tests. Growth was reduced to one half of the control growth rates at
60% dilutions of urban runoff. The observed effects were believed to be associated with
a combination of toxicants.
The University of Washington (Pederson 1981, Richey etal. 1981, Perkins 1982,
Richey 1982, Scott et al. 1982, Ebbert et al. 1983, Pitt and Bissonnette 1983, and Prych
5-5
-------
and Ebbert undated) conducted a series of studies to contrast the biological and
chemical conditions in urban Kelsey Creek with rural Bear Creek in Bellevue, WA. The
urban creek was significantly degraded when compared to the rural creek, but still
supported a productive, but limited and unhealthy salmonid fishery. Many of the fish in
the urban creek, however, had respiratory anomalies. The urban creek was not grossly
polluted, but flooding from urban developments had increased dramatically in recent
years. These increased flows markedly changed the urban stream's channel by
causing unstable conditions with increased stream bed movement, and by altering the
availability of food for the aquatic organisms. The aquatic organisms were very
dependent on the few relatively undisturbed reaches. Dissolved oxygen concentrations
in the sediments depressed embryo salmon survival in the urban creek. Various
organic and metallic priority pollutants were discharged to the urban creek, but most of
them were apparently carried through the creek system by the high storm flows to Lake
Washington. The urbanized Kelsey Creek also had higher water temperatures
(probably due to reduced shading) than Bear Creek. This probably caused the faster
fish growth in Kelsey Creek.
The fish population in the urbanized Kelsey Creek had adapted to its degrading
environment by shifting the species composition from coho salmon to less sensitive
cutthroat trout and by making extensive use of less disturbed refuge areas. Studies of
damaged gills found that up to three-fourths of the fish in Kelsey Creek were affected
with respiratory anomalies, while no cutthroat trout and only two of the coho salmon
sampled in the forested Bear Creek had damaged gills. Massive fish kills in Kelsey
Creek and its tributaries were also observed on several occasions during the project
due to the dumping of toxic materials down the storm drains.
There were also significant differences in the numbers and types of benthic organisms
found in urban and forested creeks during the Bellevue research. Mayflies, stoneflies,
caddisflies, and beetles were rarely observed in the urban Kelsey Creek, but were quite
abundant in the forested Bear Creek. These organisms are commonly regarded as
sensitive indicators of environmental degradation. One example of degraded conditions
in Kelsey Creek was shown by a specie of clams (Unionidae) that was not found in
Kelsey Creek, but was commonly found in Bear Creek. These clams are very sensitive
to heavy siltation and unstable sediments. Empty clam shells, however, were found
buried in the Kelsey Creek sediments indicating their previous presence in the creek
and their inability to adjust to the changing conditions. The benthic organism
composition in Kelsey Creek varied radically with time and place while the organisms
were much more stable in Bear Creek.
Urban runoff impact studies were conducted in the Hillsborough River near Tampa Bay,
FL, as part of the U.S. EPA's Nationwide Urban Runoff Program (NURP) (Mote Marine
Laboratory 1984). Plants, animals, sediment, and water quality were all studied in the
field and supplemented by laboratory bioassay tests. Effects of salt water intrusion and
urban runoff were both measured because of the estuarine environment. During wet
weather, freshwater species were found closer to Tampa Bay than during dry weather.
5-6
-------
In coastal areas, these additional natural factors made it even more difficult to identify
the cause and effect relationships for aquatic life problems. During another NURP
project, Striegl (1985) found that the effects of accumulated pollutants in Lake Ellyn
(Glen Ellyn, IL) inhibited desirable benthic invertebrates and fish and increased
undesirable phyotoplankton blooms.
The number of benthic organism taxa in Shabakunk Creek in Mercer County, NJ,
declined from 13 in relatively undeveloped areas to four below heavily urbanized areas
(Garie and Mclntosh 1986 and 1990). Periphyton samples were also analyzed for
heavy metals with significantly higher metal concentrations found below the heavily
urbanized area than above.
Many of the above noted biological effects associated with urban runoff are likely
caused by polluted sediments and benthic organism impacts. Examples of heavy metal
and nutrient accumulations in sediments are numerous. In addition to the studies noted
above, DePinto et al. (1980) found that the cadmium content of river sediments can be
more than 1,000 times greater than the overlying water concentrations and the
accumulation factors in sediments are closely correlated with sediment organic content.
Another comprehensive study on polluted sediment was conducted by Wilber and
Hunter (1980) along the Saddle River in New Jersey where they found significant
increases in sediment contamination with increasing urbanization.
The effects of urban runoff on receiving water aquatic organisms or other beneficial
uses is very site specific. Different land development practices create substantially
different runoff flow characteristics. Different rain patterns cause different particulate
washoff, transport and dilution conditions. Local attitudes also define specific beneficial
uses and, therefore, current problems. There are also a wide variety of water types
receiving urban runoff and these waters all have watersheds that are urbanized to
various degrees. Therefore, it is not surprising that urban runoff effects, though
generally dramatic, are also quite variable and site specific.
Claytor (1996a) summarized the approach developed by the Center for Watershed
Protection as part of their EPA sponsored research on stormwater indicators (Claytor
and Brown 1996). The 26 stormwater indicators used for assessing receiving water
conditions were divided into six broad categories: water quality, physical/hydrological,
biological, social, programmatic, and site. These were presented as tools to measure
stress (impacting receiving waters), to assess the resource itself, and to indicate
stormwater control program implementation effectiveness. The biological communities
in Delaware's Piedmont streams have been severely impacted by stormwater, after the
extent of imperviousness in the watersheds exceeds about 8 to 15%, according to a
review article by Claytor (1996b). If just conventional water quality measures are used,
almost all (87%) of the state's non-tidal streams supported their designated biological
uses. However, when biological assessments are included, only 13% of the streams
were satisfactory.
5-7
-------
Changes in physical stream channel characteristics can have a significant effect on the
biological health of the stream. Schueler (1996) stated that channel geometry stability
can be a good indicator of the effectiveness of stormwater control practices. He also
found that once a watershed area has more than about 10 to 15% effective impervious
cover, noticeable changes in channel morphology occur, along with quantifiable impacts
on water quality and biological conditions.
Stephenson (1996) studied changes in streamflow volumes in South Africa during
urbanization. He found increased stormwater runoff, decreases in the groundwater
table, and dramatically decreased times of concentration. The peak flow rates
increased by about two-fold, about half caused by increased pavement (in an area
having only about 5% effective impervious cover), with the remainder caused by
decreased times of concentration.
Fate of Stormwater Pollutants in Surface Waters
Many processes may affect urban runoff pollutants after discharge. Sedimentation in
the receiving water is the most common fate mechanism because many of the
pollutants investigated are mostly associated with settleable particulate matter and have
relatively low filterable concentration components. Exceptions include zinc and
1,3-dichlorobenzene, which are mostly associated with the filtered sample portions.
Particulate reduction can occur in many stormwater runoff and CSO control facilities,
including (but not limited to) catchbasins, swirl concentrators, fine mesh screens, sand
or other filters, drainage systems, and detention ponds. These control facilities (with the
possible exception of drainage systems) allow reduction of the accumulated polluted
sediment for final disposal in an appropriate manner. Uncontrolled sedimentation will
occur in relatively quiescent receiving waters, such as lakes, reservoirs, or slow moving
rivers or streams. In these cases, the wide dispersal of the contaminated sediment is
difficult to remove and can cause significant detrimental effects on biological processes.
Biological or chemical degradation of the sediment toxicants may occur in the typically
anaerobic environment of the sediment, but the degradation is quite slow for many of
the pollutants. Degradation by photochemical reaction and volatilization (evaporation)
of the soluble pollutants may also occur, especially when these pollutants are near the
surface of aerated waters (Callahan et al. 1979, Farmer 1993). Increased turbulence
and aeration encourages these degradation processes, which in turn may significantly
reduce toxicant concentrations. In contrast, quiescent waters would encourage
sedimentation that would also reduce water column toxicant concentrations, but
increase sediment toxicant concentrations. Metal precipitation and sorption of
pollutants onto suspended solids increases the sedimentation and/or floatation potential
of the pollutants and also encourages more efficient bonding of the pollutants to soil
particles, preventing their leaching to surrounding waters.
Receiving waters have a natural capacity to treat and/or assimilate polluted discharges.
This capacity will be exceeded sooner (assuming equal inputs), resulting in more
5-8
-------
degradation, in smaller urban creeks and streams, than in larger receiving waters.
Larger receiving waters may still have ecosystem problems from the long-term build up
of toxicants in the sediment and repeated exposures to high flowrates, but these
problems will be harder to identify using chemical analyses of the water alone, because
of increased dilution (Pitt and Bissonnette 1983).
In-stream receiving water investigations of urban runoff effects need a multi-tiered
monitoring approach, including habitat evaluations, water and sediment quality
monitoring, flow monitoring, and biological investigations, conducted over long periods
of time (Pitt 1991). In-stream taxonomic (biological community structure) investigations
are needed to help identify actual toxicity problems. Laboratory bioassay tests can be
useful to determine the major sources of toxicants and to investigate toxicity reduction
through treatment, but they are not a substitute for actual in-stream investigations of
receiving water effects. In order to identify the sources and treatability of the problem
pollutants, detailed watershed investigations are needed, including both dry and wet
weather urban drainage monitoring and source area monitoring.
An estimate of the actual pollutant loads (calculated from the runoff volumes and
pollutant concentrations) from different watershed areas is needed for the selection and
design of most treatment devices. Several characteristics of a source area are
significant influences on the pollutant concentrations and stormwater runoff volumes.
The washoff of debris, soil, and pollutants depends on the intensity of the rain, the
properties of the material removed, and the surface characteristics where the material
resides. The potential mass of pollutants available to be washed off will be directly
related to the time interval between runoff events during which the pollutants can
accumulate.
Human Health Effects of Stormwater
Water Environment & Technology (1996b) reported on an epidemiology study
conducted at Santa Monica Bay, CA, that found that swimmers who swam in front of
stormwater outfalls were 50% more likely to develop a variety of symptoms than those
who swam 400 m from the same outfalls (Haile et al. 1996). This was a follow-up study
after previous investigations found that human fecal waste was present in the
stormwater collection systems. Environmental Science & Technology (1996b) also
reported on this Santa Monica Bay study. They reported that more than 1 % of the
swimmers who swam in front of the outfalls were affected by fevers, chills, ear
discharges, vomiting and coughing, based on surveys of more than 15,000 swimmers.
The health effects were also more common for swimmers who were exposed on days
when viruses were found in the outfall water samples.
Water Environment & Technology (1996a) reported that the fecal coliform counts
decreased from about 500 counts/100 ml to about 150 counts/100 ml in the Mississippi
River after the sewer separation program in the Minneapolis and St. Paul area of
Minnesota. Combined sewers in 8,500 ha were separated during this 10-year, $332
million program.
5-9
-------
Groundwater Impacts from Stormwater Infiltration
Prior to urbanization, groundwater recharge results from infiltration of precipitation
through pervious surfaces, including grasslands and woods. This infiltrating water is
relatively uncontaminated. With urbanization, the permeable soil surface area through
which recharge by infiltration could occur is reduced. This results in much less
groundwater recharge and greatly increased surface runoff. In addition, the waters
available for recharge generally carry increased quantities of pollutants. With
urbanization, new problematic sources of groundwater recharge also occur, including
recharge from domestic septic tanks, percolation basins and industrial waste injection
wells, and from agricultural and residential irrigation.
The following paragraphs (from Pitt et al. 1994 and 1996) describe the stormwater
pollutants that have the greatest potential of adversely affecting groundwater quality
during inadvertent or intentional stormwater infiltration. Also included are suggestions
on ways to minimize these potential problems.
Constituents of Concern
Nutrients
Nitrates are one of the most frequently encountered contaminants in groundwater.
Groundwater contamination of phosphorus has not been as widespread, or as severe,
as for nitrogen compounds. Whenever nitrogen-containing compounds come into
contact with soil, a potential for nitrate leaching into groundwater exists, especially in
rapid-infiltration wastewater basins, stormwater infiltration devices, and in agricultural
areas. Nitrate has leached from fertilizers and affected groundwaters under various turf
grasses in urban areas, including golf courses, parks and home lawns. Significant
leaching of nitrates occurs during the cool, wet seasons. Cool temperatures reduce
denitrification and ammonia volatilization, and limit microbial nitrogen immobilization and
plant uptake.
The use of slow-release fertilizers is recommended in areas having potential
groundwater nitrate problems. The slow-release fertilizers include urea formaldehyde
(UF), methylene urea, isobutylidene diurea (IBDU), and sulfur-coated urea. Residual
nitrate concentrations are highly variable in soil due to soil texture, mineralization,
rainfall and irrigation patterns, organic matter content, crop yield, nitrogen
fertilizer/sludge rate, denitrification, and soil compaction. Nitrate is highly soluble (>1
kg/I) and will stay in solution in the percolation water, after leaving the root zone, until it
reaches the groundwater.
Pesticides
Urban pesticide contamination of groundwater can result from municipal and
homeowner use of pesticides for pest control and their subsequent collection in
stormwater runoff. Pesticides that have been found in urban groundwaters include: 2,4-
D, 2,4,5-T, atrazine, chlordane, diazinon, ethion, malathion, methyl trithion, silvex, and
simazine. Heavy repetitive use of mobile pesticides on irrigated and sandy soils likely
5-10
-------
contaminates groundwater. Fungicides and nematocides must be mobile in order to
reach the target pest and hence, they generally have the highest contamination
potential. Pesticide leaching depends on patterns of use, soil texture, total organic
carbon content of the soil, pesticide persistence, and depth to the water table.
The greatest pesticide mobility occurs in areas with coarse-grained or sandy soils
without a hardpan layer, having low clay and organic matter content and high
permeability. Structural voids, which are generally found in the surface layer of finer-
textured soils rich in clay, can transmit pesticides rapidly when the voids are filled with
water and the adsorbing surfaces of the soil matrix are bypassed. In general, pesticides
with low water solubilities, high octanol-water partitioning coefficients, and high carbon
partitioning coefficients are less mobile. The slower moving pesticides have been
recommended in areas of groundwater contamination concern. These include the
fungicides iprodione and triadimefon, the insecticides isofenphos and chlorpyrifos and
the herbicide glyphosate. The most mobile pesticides include: 2,4-D, acenaphthylene,
alachlor, atrazine, cyanazine, dacthal, diazinon, dicamba, malathion, and metolachlor.
Pesticides decompose in soil and water, but the total decomposition time can range
from days to years. Literature half-lives for pesticides generally apply to surface soils
and do not account for the reduced microbial activity found deep in the vadose zone.
Pesticides with a 30 day half life can show considerable leaching. An order-of-
magnitude difference in half-life results in a five- to ten-fold difference in percolation
loss. Organophosphate pesticides are less persistent than organochlorine pesticides,
but they also are not strongly adsorbed by the sediment and are likely to leach into the
vadose zone, and the groundwater.
Other Organics
The most commonly occurring organic compounds that have been found in urban
groundwaters include phthalate esters (especially bis(2-ethylhexyl)phthalate) and
phenolic compounds. Other organics more rarely found, possibly due to losses during
sample collection, have included the volatiles: benzene, chloroform, methylene chloride,
trichloroethylene, tetrachloroethylene, toluene, and xylene. PAHs (especially
benzo(a)anthracene, chrysene, anthracene and benzo(b)fluoroanthenene) have also
been found in groundwaters near industrial sites.
Groundwater contamination from organics, like from other pollutants, occurs more
readily in areas with sandy soils and where the water table is near the land surface.
Removal of organics from the soil and recharge water can occur by one of three
methods: volatilization, sorption, and degradation. Volatilization can significantly reduce
the concentrations of the most volatile compounds in groundwater, but the rate of gas
transfer from the soil to the air is usually limited by the presence of soil water.
Hydrophobic sorption onto soil organic matter limits the mobility of less soluble
base/neutral and acid extractable compounds through organic soils and the vadose
zone. Sorption is not always a permanent removal mechanism, however. Organic re-
solubilization can occur during wet periods following dry periods. Many organics can be
at least partially degraded by microorganisms, but others cannot. Temperature, pH,
5-11
-------
moisture content, ion exchange capacity of soil, and air availability may limit the
microbial degradation potential for even the most degradable organic.
Pathogenic Microorganisms
Viruses have been detected in groundwater where stormwater recharge basins were
located short distances above the aquifer. Enteric viruses are more resistant to
environmental factors than enteric bacteria and they exhibit longer survival times in
natural waters. They can occur in potable and marine waters in the absence of fecal
coliforms. Enteroviruses are also more resistant to commonly used disinfectants than
are indicator bacteria, and can occur in groundwater in the absence of indicator
bacteria.
The factors that affect the survival of enteric bacteria and viruses in the soil include pH,
antagonism from soil microflora, moisture content, temperature, sunlight, and organic
matter. The two most important attributes of viruses that permit their long-term survival
in the environment are their structure and very small size. These characteristics permit
virus occlusion and protection within colloid-size particles. Viral adsorption is promoted
by increasing cation concentration, decreasing pH and decreasing soluble organics.
Since the movement of viruses through soil to groundwater occurs in the liquid phase
and involves water movement and associated suspended virus particles, the distribution
of viruses between the adsorbed and liquid phases determines the viral mass available
for movement. Once the virus reaches the groundwater, it can travel laterally through
the aquifer until it is either adsorbed or inactivated.
The major bacterial removal mechanisms in soil are straining at the soil surface and at
intergrain contacts, sedimentation, sorption by soil particles, and inactivation. Because
of their larger size than for viruses, most bacteria are, therefore, retained near the soil
surface due to this straining effect. In general, enteric bacteria survive in soil between
two and three months, although survival times up to five years have been documented.
Heavy Metals and Other Inorganic Compounds
Heavy metals and other inorganic compounds in stormwater of most environmental
concern, from a groundwater pollution standpoint, are aluminum, arsenic, cadmium,
chromium, copper, iron, lead, mercury, nickel, and zinc. However, the majority of these
compounds, with the consistent exception of zinc, are mostly found associated with the
particulate solids in stormwaters and are thus relatively easily removed through
sedimentation practices. Filterable forms of the metals may also be removed by either
sediment adsorption or are organically complexed with other particulates.
In general, studies of recharge basins receiving large metal loads found that most of the
heavy metals are removed either in the basin sediment or in the vadose zone.
Dissolved metal ions are removed from stormwater during infiltration mostly by
adsorption onto the near-surface particles in the vadose zone, while the particulate
metals are filtered out at the soil surface. Studies at recharge basins found that lead,
zinc, cadmium, and copper accumulated at the soil surface with little downward
movement over many years. However, nickel, chromium, and zinc concentrations have
5-12
-------
exceeded regulatory limits in the soils below a recharge area at a commercial site.
Elevated groundwater heavy metal concentrations of aluminum, cadmium, copper,
chromium, lead, and zinc have been found below stormwater infiltration devices where
the groundwater pH has been acidic. Allowing percolation ponds to go dry between
storms can be counterproductive to the removal of lead from the water during recharge.
Apparently, the adsorption bonds between the sediment and the metals can be
weakened during the drying period.
Similarities in water quality between runoff water and groundwater has shown that there
is significant downward movement of copper and iron in sandy and loamy soils.
However, arsenic, nickel, and lead did not significantly move downward through the soil
to the groundwater. The exception to this was some downward movement of lead with
the percolation water in sandy soils beneath stormwater recharge basins. Zinc, which is
more soluble than iron, has been found in higher concentrations in groundwater than
iron. The order of attenuation in the vadose zone from infiltrating stormwater is: zinc
(most mobile) > lead > cadmium > manganese > copper > iron > chromium > nickel >
aluminum (least mobile).
Salts
Salt applications for winter traffic safety is a common practice in many northern areas
and the sodium and chloride, which are collected in the snowmelt, travel down through
the vadose zone to the groundwater with little attenuation. Soil is not very effective at
removing salts. Salts that are still in the percolation water after it travels through the
vadose zone will contaminate the groundwater. Infiltration of stormwater has led to
increases in sodium and chloride concentrations above background concentrations.
Fertilizer and pesticide salts also accumulate in urban areas and can leach through the
soil to the groundwater.
Studies of depth of pollutant penetration in soil have shown that sulfate and potassium
concentrations decrease with depth, while sodium, calcium, bicarbonate, and chloride
concentrations increase with depth. Once contamination with salts begin, the
movement of salts into the groundwater can be rapid. The salt concentration may not
decrease until the source of the salts is removed.
Recommendations to Protect Groundwater During Stormwater Infiltration
Table 5-1 is a summary of the pollutants found in stormwater that may cause
groundwater contamination problems for various reasons. This table does not consider
the risk associated with using groundwater contaminated with these pollutants.
Characteristics of concern include high mobility (low sorption potential) in the vadose
zone, high abundance (high concentrations and high detection frequencies) in
stormwater, and high soluble fractions (small fraction associated with particulates which
would have little removal potential using conventional stormwater sedimentation
controls) in the stormwater.
The contamination potential is the lowest rating of the influencing factors. As an
example, if no pretreatment was to be used before percolation through surface soils, the
5-13
-------
mobility and abundance criteria are most important. If a compound was mobile, but was
in low abundance (such as for VOCs), then the groundwater contamination potential
would be low. However, if the compound was mobile and was also in high abundance
(such as for sodium chloride, in certain conditions), then the groundwater contamination
would be high.
If sedimentation pretreatment was to be used before infiltration, then much of the
pollutants will likely be removed before infiltration. In this case, all three influencing
factors (mobility, abundance in stormwater, and soluble fraction) would be considered
important. As an example, chlordane would have a low contamination potential with
sedimentation pretreatment, while it would have a moderate contamination potential if
no pretreatment was used. In addition, if subsurface infiltration/injection was used
instead of surface percolation, the compounds would most likely be more mobile,
making the abundance criteria the most important, with some regard given to the
filterable fraction information for operational considerations.
Table 5-1 is only appropriate for initial estimates of contamination potential because of
the simplifying assumptions made, such as the likely worst case mobility measures for
sandy soils having low organic content. If the soil was clayey and had a high organic
content, then most of the organic compounds would be less mobile than shown on this
table. The abundance and filterable fraction information is generally applicable for
warm weather stormwater runoff at residential and commercial area outfalls. The
concentrations and detection frequencies would likely be greater for critical source
areas (especially vehicle service areas) and critical land uses (especially manufacturing
industrial areas).
5-14
-------
Table 5-1
1996).
Groundwater contamination potential for stormwater pollutants (Pitt et al.
Categories
Nutrients
Pesticides
Other
organics
Pathogens
Heavy
metals
Salts
Compounds
Nitrates
2,4-D
y-BHC (lindane)
malathion
atrazine
chlordane
diazinon
VOCs
1 ,3-dichloro-
benzene
anthracene
benzo(a)
anthracene
bis (2-
ethylhexyl)
phthalate
butyl benzyl
phthalate
fluoranthene
fluorene
naphthalene
penta-
chlorophenol
phenanthrene
pyrene
enteroviruses
Shigella
Pseudomonas
aeruginosa
protozoa
nickel
cadmium
chromium
lead
zinc
chloride
Mobility
(sandy/low
organic soils)
mobile
mobile
intermediate
mobile
mobile
intermediate
mobile
mobile
low
intermediate
intermediate
intermediate
low
intermediate
intermediate
low/inter.
intermediate
intermediate
intermediate
mobile
low/inter.
low/inter.
low/inter.
low
low
inter./very
low
very low
low/very low
mobile
Abundance
in storm-water
low/moderate
low
moderate
low
low
moderate
low
low
high
low
moderate
moderate
low/moderate
high
low
low
moderate
moderate
high
likely present
likely present
very high
likely present
high
low
moderate
moderate
high
seasonally
high
Fraction
filterable
high
likely low
likely low
likely low
likely low
very low
likely low
very high
high
moderate
very low
likely low
moderate
high
likely low
moderate
likely low
very low
high
high
moderate
moderate
moderate
low
moderate
very low
very low
high
high
Contamination
potential for
surface infilt.
and no
pretreatment
low/moderate
low
moderate
low
low
moderate
low
low
low
low
moderate
moderate
low
moderate
low
low
moderate
moderate
moderate
high
low/moderate
low/moderate
low/moderate
low
low
low/moderate
low
low
high
Contamination
potential for
surface infilt.
with sediment-
ation
low/moderate
low
low
low
low
low
low
low
low
low
low
low?
low
moderate
low
low
low?
low
moderate
high
low/moderate
low/moderate
low/moderate
low
low
low
low
low
high
Contamination
potential for
sub-surface
inj. with
minimal
pretreatment
low/moderate
low
moderate
low
low
moderate
low
low
high
low
moderate
moderate
low/moderate
high
low
low
moderate
moderate
high
high
high
high
high
high
low
moderate
moderate
high
high
5-15
-------
The stormwater pollutants of most concern (those that may have the greatest adverse
impacts on groundwaters) include:
1. Nutrients: nitrate has a low to moderate groundwater contamination potential
for both surface percolation and subsurface infiltration/injection practices
because of its relatively low concentrations found in most stormwaters.
However, if the stormwater nitrate concentration was high, then the
groundwater contamination potential would also likely be high.
2. Pesticides: lindane and chlordane have moderate groundwater contamination
potentials for surface percolation practices (with no pretreatment) and for
subsurface injection (with minimal pretreatment). The groundwater
contamination potentials for both of these compounds would likely be
substantially reduced with adequate sedimentation pretreatment. Pesticides
have been mostly found in urban runoff from residential areas, especially in
dry-weather flows associated with landscaping irrigation runoff.
3. Other organics: 1,3-dichlorobenzene may have a high groundwater
contamination potential for subsurface infiltration/injection (with minimal
pretreatment). However, it would likely have a lower groundwater
contamination potential for most surface percolation practices because of its
relatively strong sorption to vadose zone soils. Both pyrene and fluoranthene
would also likely have high groundwater contamination potentials for
subsurface infiltration/injection practices, but lower contamination potentials
for surface percolation practices because of their more limited mobility
through the unsaturated zone (vadose zone). Others (including
benzo(a)anthracene, bis (2-ethylhexyl) phthalate, pentachlorophenol, and
phenanthrene) may also have moderate groundwater contamination
potentials, if surface percolation with no pretreatment, or subsurface
injection/infiltration is used. These compounds would have low groundwater
contamination potentials if surface infiltration was used with sedimentation
pretreatment. Volatile organic compounds (VOCs) may also have high
groundwater contamination potentials if present in the stormwater (likely for
some industrial and commercial facilities and vehicle service establishments).
The other organics, especially the volatiles, are mostly found in industrial
areas. The phthalates are found in all areas. The PAHs are also found in
runoff from all areas, but they are in higher concentrations and occur more
frequently in industrial areas.
4. Pathogens: enteroviruses likely have a high groundwater contamination
potential for all percolation practices and subsurface infiltration/injection
practices, depending on their presence in stormwater (likely if contaminated
with sanitary sewage). Other pathogens, including Shigella, Pseudomonas
aeruginosa, and various protozoa, would also have high groundwater
contamination potentials if subsurface infiltration/injection practices are used
without disinfection. If disinfection (especially by chlorine or ozone) is used,
5-16
-------
then disinfection byproducts (such as trihalomethanes or ozonated bromides)
would have high groundwater contamination potentials. Pathogens are most
likely associated with sanitary sewage contamination of storm drainage
systems, but several bacterial pathogens are commonly found in surface
runoff in residential areas.
5. Heavy metals: nickel and zinc would likely have high groundwater
contamination potentials if subsurface infiltration/injection was used.
Chromium and lead would have moderate groundwater contamination
potentials for subsurface infiltration/injection practices. All metals would likely
have low groundwater contamination potentials if surface infiltration was used
with sedimentation pretreatment. Zinc is mostly found in roof runoff and other
areas where galvanized metal comes into contact with rainwater.
6. Salts: chloride would likely have a high groundwater contamination potential
in northern areas where road salts are used for traffic safety, irrespective of
the pretreatment, infiltration or percolation practice used. Salts are at their
greatest concentrations in snowmelt and early spring runoff in northern areas.
It has been suggested that, with a reasonable degree of site-specific design
considerations to compensate for soil characteristics, infiltration can be very effective in
controlling both urban runoff quality and quantity problems (EPA 1983). This strategy
encourages infiltration of urban runoff to replace the natural infiltration capacity lost
through urbanization and to use the natural filtering and sorption capacity of soils to
remove pollutants.
However, potential groundwater contamination through infiltration of some types of
urban runoff requires some restrictions. Infiltration of urban runoff having potentially
high concentrations of pollutants that may pollute groundwater requires adequate
pretreatment, or the diversion of these waters away from infiltration devices. The
following general guidelines for the infiltration of stormwater and other storm drainage
effluent are recommended in the absence of comprehensive site-specific evaluations:
1. Dry-weather storm drainage effluent should be diverted from infiltration
devices because of their probable high concentrations of soluble heavy
metals, pesticides, and pathogenic microorganisms.
2. Combined sewage overflows should be diverted from infiltration devices
because of their poor water quality, especially high pathogenic microorganism
concentrations, and high clogging potential.
3. Snowmelt runoff should also be diverted from infiltration devices because of
its potential for having high concentrations of soluble salts.
5-17
-------
4. Runoff from manufacturing industrial areas should also be diverted from
infiltration devices because of its potential for having high concentrations of
soluble toxicants.
5. Construction site runoff must be diverted from stormwater infiltration devices
(especially subsurface devices) because of its high SS concentrations, which
would quickly clog infiltration devices.
6. Runoff from other critical source areas, such as vehicle service facilities and
large parking areas, should at least receive adequate pretreatment to
eliminate their groundwater contamination potential before infiltration.
7. Runoff from residential areas (the largest component of urban runoff from
most cities) is generally the least polluted urban runoff flow and should be
considered for infiltration. Very little treatment of residential area stormwater
runoff should be needed before infiltration, especially if surface infiltration is
through the use of grass swales. If subsurface infiltration (e.g., French drains,
infiltration trenches, dry wells) is used, then some pretreatment may be
needed, such as by using grass filter strips, or other surface filtration devices.
All other runoff should include pretreatment using sedimentation processes before
infiltration, to both minimize groundwater contamination and to prolong the life of the
infiltration device (if needed). This pretreatment can take the form of approaches such
as grass filters, sediment sumps, and wet detention ponds depending on the runoff
volume to be treated and other site specific factors. Pollution prevention can also play
an important role in minimizing groundwater contamination problems, including reducing
the use of galvanized metals, pesticides, and fertilizers in critical areas. The use of
specialized treatment devices can also play an important role in treating runoff from
critical source areas before these more contaminated flows commingle with cleaner
runoff from other areas. Sophisticated treatment schemes, especially the use of
chemical processes or disinfection, may not be warranted, except in special cases,
especially considering the potential of forming harmful treatment by-products (such as
THMs and soluble aluminum).
Most past stormwater quality monitoring has not been adequate to completely evaluate
groundwater contamination potential. The following list shows the parameters that are
recommended to be monitored if stormwater contamination potential needs to be
considered, or infiltration devices are to be used. Other analyses are appropriate for
additional monitoring objectives (such as evaluating surface water problems). In
addition, all phases of urban runoff should be sampled, including stormwater runoff, dry-
weather flows, and snowmelt.
Contamination potential:
- Nutrients (especially nitrates)
- Salts (especially chloride)
5-18
-------
- VOCs (if expected in the runoff, such as from manufacturing industrial
or vehicle service areas, could screen for VOCs with purgable organic
carbon, POC, analyses)
- Pathogens (especially enteroviruses, if possible, along with other
pathogens such as Pseudomonas aeruginosa, Shigella, and
pathogenic protozoa)
- Bromide and total organic carbon, TOC (to estimate disinfection by-
product generation potential, if disinfection by either chlorination or
ozone is being considered)
- Pesticides, in both filterable and total sample components (especially
lindane and chlordane)
- Other organics, in both filterable and total sample components
(especially 1,3 dichlorobenzene, pyrene, fluoranthene, benzo (a)
anthracene, bis (2-ethylhexyl) phthalate, pentachlorophenol, and
phenanthrene)
- Heavy metals, in both filterable and total sample components
(especially chromium, lead, nickel, and zinc)
Operational considerations:
- Sodium, calcium, and magnesium (in order to calculate the sodium
adsorption ratio to predict clogging of clay soils)
- Suspended solids (to determine the need for sedimentation
pretreatment to prevent clogging)
The Technical University of Denmark (Mikkelsen et al. 1996a and 1996b) has been
involved in a series of tests to examine the effects of stormwater infiltration on soil and
groundwater quality. They found that heavy metals and PAHs present little groundwater
contamination threat, if surface infiltration systems are used. However, they express
concern about pesticides, which are much more mobile. Squillace et al. (1996) along
with Zogorski et al. (1996) presented information concerning stormwater and its
potential as a source of groundwater MTBE contamination. Mull (1996) stated that
traffic areas are the third most important source of groundwater contamination in
Germany (after abandoned industrial sites and leaky sewers). The most important
contaminants are chlorinated hydrocarbons, sulfate, organic compounds, and nitrates.
Heavy metals are generally not an important groundwater contaminant because of their
affinity for soils. Trauth and Xanthopoulus (1996) examined the long-term trends in
groundwater quality at Karlsruhe, Germany. They found that the urban landuse is
having a long-term influence on the groundwater quality. The concentration of many
pollutants have increased by about 30 to 40% over 20 years. Hutter and Remmler
(1996) describe a groundwater monitoring plan, including monitoring wells that were
established during the construction of an infiltration trench for stormwater disposal in
Dortmund, Germany. The worst case problem expected is with zinc, if the infiltration
water has a pH value of 4.
5-19
-------
References
Allen, H. E., editor (1996). Metal Contaminated Aquatic Sediments. Ann Arbor Press.
Chelsea, Ml. 350 pgs.
Benke, A.C., G.E. Willeke, F.K. Parrish and D.L. Stites (1981). Effects of Urbanization
on Stream Ecosystems. School of Biology. Environmental Resources Center. Report
No. ERG 07-81. Georgia Institute of Technology. Atlanta, GA.
Burton, G.A. and R.E. Pitt (to be published in 1998). A Manual for Conducting
Evaluations of the Effects of Urban Runoff on Aquatic Life. CRC Press.
Callahan, M.A., M.W. Slimak, N.W. Gabel, I.P. May, C.F. Fowler, J.R. Freed, P.
Jennings, R.L. Durfee, F.C. Whitmore, B. Maestri, W.R. Mabey, B.R. Holt, and C. Gould
(1979). Water Related Environmental Fates of 129 Priority Pollutants. U.S.
Environmental Protection Agency. Monitoring and Data Support Division. EPA-4-79-
029a and b. Washington D.C.
Claytor, R.A. and W. Brown (1996). Environmental Indicators to Assess the
Effectiveness of Municipal and Industrial Stormwater Control Programs. Prepared for
the U.S. EPA, Office of Wastewater Management. Center for Watershed Protection.
Silver Spring, MD. 210 pgs.
Claytor, R.A (1996a). An introduction to stormwater indicators: an urban runoff
assessment tool. Watershed Protection Techniques. Vol. 2, no. 2, pp. 321 - 328.
Spring.
Claytor, R.A (1996b). Habitat and biological monitoring reveals headwater stream
impairment n Delaware's Piedmont. Watershed Protection Techniques. Vol. 2, no. 2,
pp. 358 - 360. Spring.
Cook, W.L., F. Parrish, J.D. Satterfield, W.G. Nolan and P.E. Gaffney (1983). Biological
and Chemical Assessment of Nonpoint Source Pollution in Georgia: Ridge-Valley and
Sea Island Streams. Department of Biology. Georgia State University. Atlanta, GA.
Crunkilton, R., J. Kleist, J. Ramcheck, W. DeVita, and D. Villeneueve (1997).
Assessment of the response of aquatic organisms to long-term in-situ exposures to
urban runoff. Presented at the Effects of Watershed Developments and Management
on Aquatic Ecosystems conference. Snowbird, UT. August 4-9, 1996. Edited by L.A.
Roesner. ASCE. New York, NY.
CTA, Inc. (1983). Georgia Nonpoint Source Impact Assessment Study: Blue
Ridge/Upland Georgia Cluster, Piedmont Cluster, and Gulf Coastal Plain Cluster.
Georgia Environmental Protection Division. Dept. of Natural Resources. Atlanta, GA.
5-20
-------
Davies, P.M. (1986). Toxicology and chemistry of metals in urban runoff. In: Urban
Runoff Quality: Impact and Quality Enhancement Technology. Engineering Foundation
Conference. Henniker, NH. ASCE. New York, NY.
DePinto, J.V., T.C. Young and S.C. Martin (1980). Aquatic sediments. Journal of
Water Pollution Control Federation. Vol. 52. No. 6. pp 1656-70. June.
Dyer, S.D. and C.E. White (1996). A watershed approach to assess mixture toxicity via
integration of public and private databases. Abstract Book: SETAC 17th Annual
Meeting, pg. 96. Washington, D.C. Nov. 17-21.
Ebbert, J.C., J. E. Poole, and K.L. Payne (1983). Data collected by the U.S. Geological
Survey during a study of urban runoff in Bellevue, WA. 1979-82. Preliminary U.S.
Geological Survey Open-File Report. Tacoma, WA.
Ehrenfeld, J.G. and J.P. Schneider (1983). The Sensitivity of Cedar Swamps to the
Effects of Non-Point Pollution Associated with Suburbanization in the New Jersey Pine
Barrens. U.S. Environmental Protection Agency. Office of Water Policy. PB8-4-
136779. Washington, D.C. September.
Environmental Science & Technology (1996a). Toxicity of aquatic mixtures yielding to
new theoretical approach. Vol. 30, no. 4, pp. 155a - 156a. April.
Environmental Science & Technology (1986b). News Briefs. Vol. 30, no. 7, pg. 290a.
July.
EPA (U.S. Environmental Protection Agency) (1983). Results of the Nationwide Urban
Runoff Program. Water Planning Division. PB 84-185552. Washington, D.C.
December.
Field, R., and R. Pitt (1990). Urban storm-induced discharge impacts: US
Environmental Protection Agency research program review. Water Science and
Technology. Vol.22, No. 10/11.
Garie, H.L. and A. Mclntosh (1986). Distribution of benthic macroinvertebrates in a
stream exposed to urban runoff. Water Resources Bulletin. Vol. 22. No. 3. pp. 447-
455.
Garie, H.L. and A. Mclntosh (1990). Distribution of benthic macroinvertebrates in a
stream exposed to urban runoff. Water Science and Technology. Vol. 22, No. 10/11.
Haile and the Santa Monica Bay Restoration Project (1996). An Epidemiological Study
of Possible Adverse Health Effects of Swimming in Santa Monica Bay. Santa Monica
Bay Restoration Project. Monterey Park, CA. October.
5-21
-------
Herricks. E.E., editor (1995). Stormwater Runoff and Receiving Systems: Impact,
Monitoring and Assessment. Conference of the Engineering Foundation/ASCE held in
1991 in Mt. Crested Butte, CO. Lewis/CRC Press. Boca Raton. 458 pgs.
Herricks, E.E, I. Milne, and I. Johnson (1996). A protocol for wet weather discharge
toxicity assessment. Volume 4, pg. 13-24. WEFTEC'96: Proceedings of the 69tK
Annual Conference & Exposition. Dallas, TX.
Mutter, U. and F. Remmler (1996). Stormwater infiltration at a site with critical subsoil
conditions: Investigations of soil, seepage water and groundwater. 7th International
Conference on Urban Drainage. Hannover, Germany. Edited by F. Sieker and H-R.
Verworn. International Association on Water Quality, London, pp. 713 - 718 . Sept. 9 -
13.
Ireland, D.S., G.A. Burton, Jr., and G.G. Hess (1996). In-situ toxicity evaluations of
turbidity and photoinduction of polycyclic aromatic hydrocarbons. Environmental
Toxicology and Chemistry. Vol. 15, no. 4, pp. 574-581. April.
Johnson, I., E.E. Herricks, and I. Milne (1996). Application of a test battery for wet
weather discharge toxicity analyses. Volume 4, pg. 219-229. WEFTEC'96:
Proceedings of the 69th Annual Conference & Exposition. Dallas, TX.
Klein, R.D(1979). Urbanization and stream quality impairment. Water Resources
Bulletin. Vol. 15. No. 4. August.
Lee, G.F. and A. Jones-Lee (1993). Water quality impacts of stormwater-associated
contaminants: focus on real problems. Water Science and Technology. Vol. 28, No. 3-
5, pp. 231-240.
Lee, G.F. and A. Jones-Lee (1995a). Deficiencies in Stormwater quality monitoring, in:
Stormwater NPDES Related Monitoring Needs. Edited by H.C. Torno. Proceedings of
an Engineering Foundation Conference. Mt. Crested Butte, CO. August 1994. ASCE.
New York, NY.
Lee, G.F. and A. Jones-Lee (1995b). Issues in managing urban Stormwater runoff
quality. Water/Engineering Management. Vol. 142, No. 5. pp. 51-53. May.
Lenet, D.R., D.L. Penrose, and K. Eagleson 1979). Biological Evaluation of Non-Point
Sources of Pollutants in North Carolina Streams and Rivers. North Carolina Division of
Environmental Management, Biological Series #102. North Carolina Dept. of Natural
Resources and Community Development. Raleigh, NC.
5-22
-------
Lenet, D. and K. Eagleson (1981). Ecological Effects of Urban Runoff on North
Carolina Streams. North Carolina Division of Environmental Management, Biological
Series #104. North Carolina Dept. of Natural Resources and Community Development.
Raleigh, NC.
Lenet, D.R., D.L. Penrose, and K.W. Eagleson (1981). Variable effects of sediment
addition on stream benthos. Hydrobiologia. Vol. 79. pp. 187-194.
Mancini, J. and A. Plummer (1986). Urban runoff and water quality criteria. In: Urban
Runoff Quality - Impact and Quality Enhancement Technology. Edited by B. Urbonas
and L.A. Roesner. Engineering Foundation Conference. Henniker, Hew Hampshire.
ASCE. NY. pp. 133-149. June.
Marcy, S. and J. Gerritsen (1996). Developing diverse assessment endpoints to
address multiple stressors in watershed ecological risk assessment. Abstract Book:
SETAC 17th Annual Meeting, pg. 96. Washington, D.C. Nov. 17-21.
Medeiros, C. and R.A. Coler (1982). A Laboratory/Field Investigation into the Biological
Effects of Urban Runoff. Water Resources Research Center. University of
Massachusetts. Amherst, MA. July.
Medeiros, C., R.A. Coler, and E.J. Calabrese (1984). A laboratory assessment of the
toxicity of urban runoff on the fathead minnow (Pimephales promelas). Journal of
Environmental Science Health. Vol. A19. No. 7. pp. 847-861.
Mikkelsen, P.S., H. Madsen, H. Rosgjerg, and P. Harremoe's (1996a). Properties of
extreme point rainfall III: Identification of spatial inter-site correlation structure.
Atmospheric Research.
Mikkelsen, P.S., K. Arngjerg-Nielsen, and P. Harremoe's (1996b). Consequences for
established design practice from geographical variation of historical rainfall data.
Proceedings: 7th International Conference on Urban Storm Drainage. Hannover,
Germany. Sept. 9-13.
Mote Marine Laboratory (1984). Biological and Chemical Studies on the Impact of
Stormwater Runoff upon the Biological Community of the Hillsborough River, Tampa,
FL. Stormwater Management Division, Dept. of Public Works. Tampa, FL. March.
Mull, R. (1996). Water exchange between leaky sewers and aquifers. 7th International
Conference on Urban Storm Drainage. Hannover, Germany. Sept. 9-13, 1996. Edited
by F. Siekerand H-R. Verworn. IAHR/IAWQ. SuG-Verlagsgesellschaft. Hannover,
Germany, pp. 695-700.
5-23
-------
Farmer, K.D. (1993). Photo and Biodegradation of Pyrene and Benzo(a)pyrene in a
Model of the Near Surface Environment. Ph.D. dissertation. Department of
Environmental Health Science. The University of Alabama at Birmingham. 299 pgs.
Pedersen, Edward Robert (1981). The Use of Benthic Invertebrate Data for Evaluating
Impacts of Urban Stormwater Runoff. Masters thesis submitted to the College of
Engineering. University of Washington. Seattle, WA.
Perkins, M. A. (1982). An Evaluation of Instream Ecological Effects Associated with
Urban Runoff to a Lowland Stream in Western Washington. U.S. Environmental
Protection Agency. Corvallis Environmental Research Laboratory. Corvallis, OR. July.
Pitt, R. and M. Bozeman (1982). Sources of Urban Runoff Pollution and Its Effects on
an Urban Creek. EPA-600/52-82-090. U.S. Environmental Protection Agency.
Cincinnati, OH. December.
Pitt, R.E., and P. Bissonnette (1983). Bellevue Urban Runoff Program, Summary
Report. PB84237213. Water Planning Division. U.S. Environmental Protection
Agency. Washington, D.C. December.
Pitt, R. E. (1991). Biological effects of urban runoff discharges, in: Effects of Urban
Runoff on Receiving Systems: An Interdisciplinary Analysis of Impact, Monitoring, and
Management, Engineering Foundation Conference. Mt. Crested Butte, CO. ASCE.
New York, NY.
Pitt, R., S. Clark, and K. Parmer (1994). Protection of Groundwater from Intentional and
Nonintentional Stormwater Infiltration. U.S. Environmental Protection Agency.
EPA/600/SR-94/051. PB94-165354AS. Storm and Combined Sewer Program.
Cincinnati, Ohio. 187 pgs. May.
Pitt, R. (1995). Effects of urban runoff on aquatic biota. In: Handbook of Ecotoxicology
(Edited by D.J. Hoffman, B.A. Rattner, G.A. Burton, Jr. and J.Cairns, Jr.). Lewis
Publishers/CRC Press. Boca Raton, FL. pp. 609-630.
Pitt, R., S. Clark, K. Parmer, and R. Field (1996). Groundwater Contamination from
Stormwater Infiltration. Ann Arbor Press. Chelsea, Ml. 218 pages.
Pratt, J.M., R.A. Coler and P.J. Godfrey (1981). Ecological effects of urban Stormwater
runoff on benthic macroinvertibrates inhabiting the Green River, Massachusetts.
Hydrobiologia. Vol. 83. pp. 29-42.
Prych, Edmund A. and J.C. Ebbert (undated). Quantity and Quality of Storm Runoff
from Three Urban Catchments in Bellevue, WA. Preliminary U.S. Geological Survey
Water Resources Investigations Report. Tacoma, WA.
5-24
-------
Rainbow, P.S. (1996). Chapter 18: Heavy metals in aquatic invertebrates. In:
Environmental Contaminants in Wildlife: Interpreting Tissue Concentrations. Edited by
W.N. Beyer, G.H. Heinz, and A.W. Redmon-Norwood. CRC/Lewis Press. Boca Raton,
FL. pp. 405-425.
Richey, Joanne Sloane (1982). Effects of Urbanization on a Lowland Stream in
Western Washington. Doctor of Philosophy dissertation. University of Washington.
Seattle, WA.
Richey, Joanne Sloane, Michael A. Perkins, and Kenneth W. Malueg (1981). The
effects of urbanization and stormwater runoff on the food quality in two salmonid
streams. Verh. Internat. Werein. LimnoL Vol. 21, Pages 812-818. Stuttgart, Germany.
October.
Schueler, T. (editor) (1996). Stream channel geometry used to assess land use
impacts in the Pacific Northwest. Watershed Protection Techniques. Vol. 2, no. 2, pp.
345-348. Spring.
Scott, J.B., C.R. Steward, and Q.J. Stober (1982). Impacts of Urban Runoff on Fish
Populations in Kelsey Creek, WA. Contract No. R806387020. U.S. Environmental
Protection Agency. Corvallis Environmental Research Laboratory. Corvallis, OR. May.
Squillace, P.J., J.S. Zogorski, W.G. Wilber, and C.V. Price (1996). Preliminary
assessment of the occurrence and possible sources of MTBE in groundwater in the
United States, 1993 - 94. Environmental Science & Technology. Vol. 30, no. 5, pp.
1721 -1730. May.
Stephenson, D. (1996). Evaluation of effects of urbanization on storm runoff. 7th
International Conference on Urban Storm Drainage. Hannover, Germany. Sept. 9-13,
1996. Edited by F. Siekerand H-R. Verworn. IAHR/IAWQ. SuG-Verlagsgesellschaft.
Hannover, Germany, pp. 31-36.
Striegl, R.G. (1996). Effects of stormwater runoff on an urban lake, Lake Ellyn at Glen
Ellyn, IL. USGS open file report 84-603. Lakewood, CO.
Trauth, R. and C. Xanthopoulos (1996). Non-point pollution of groundwater in urban
areas. 7th International Conference on Urban Drainage. Hannover, Germany. Edited
by F. Sieker and H-R. Verworn. International Association on Water Quality, London.
pp. 701-706. Sept. 9-13.
Water Environment & Technology (1996a). News Watch: Sewer separation lowers
fecal coliform levels in the Mississippi River. Vol. 8, no. 11, pp. 21 -22. November.
Water Environment & Technology (1996b). Research Notes: Beachgoers at Risk from
Urban Runoff. Vol. 8, no. 11, pg. 65. November.
5-25
-------
Wilber, W. G., and J. V. Hunter (1980). The influence of urbanization on the transport of
heavy metals in New Jersey Streams. Water Resources Research Institute. Rutgers
University. New Brunswick, NJ.
Zogorski, J.S., A.B. Morduchowitz, A.L. Baehr, B.J. Bauman, D.L. Conrad, R.T. Drew,
N.E. Korte, W.W. Lapham, J.F. Pankow, and E.R. Washington (1996). Fuel
Oxygenates and Water Quality: Current Understanding of Sources, Occurrence in
Natural Waters, Environmental Behavior, Fate, and Significance. Office of Science and
Technology. Washington, D.C.
5-26
-------
Chapters
Collection Systems
James P. Heaney, Len Wright, and David Sample
Introduction
Stormwater and wastewater collection systems are a critical link in the urban water
cycle, especially under wet-weather conditions. In the context of pollution control, these
systems transport sanitary wastewater, stormwater, industrial wastewater, non-point
source pollution, and inflow/infiltration (I/I).
Research in the area of collection systems as a means of wet-weather pollution control
is showing signs of renewed activity, especially in Europe and Japan (Henze et al.
(1997), Sieker and Verworn (Ed.) 1996, Ashley (Ed.) 1996, Bally et al. (Ed.) 1996).
Case studies of recent applications of innovations in this country are also receiving
attention, as evidenced by recent Water Environment Federation technical conferences
(WEF1994a, 1994b, 1995a, 1995b, 1996) and a recent EPA seminar (USEPA 1996b).
By applying new technology and revisiting traditional urban water problems with a fresh
outlook, advances are being made in a wide variety of sewer related areas. By
reviewing successful applications of research in recent projects, a vision of successful
wet-weather management of collection systems of the future may be formulated.
An historical review of collection systems in the U.S. helps with understanding the
problems associated with modern sewer collection systems. Many of the early sewers,
including some from before the turn of the century, are still in service. As cities grew,
the need for stormwater and wastewater conveyance became a necessity to protect
human health. Stormwater and sanitary waste were generally conveyed to the nearest
natural water body. In fact, the modern word "sewer" is derived from the old English
word meaning "seaward" (Cayman 1996).
In the late nineteenth and early part of the twentieth century, these conveyance systems
were "intercepted" into a smaller conveyance sized to accommodate a multiple of the
estimated dry weather sanitary flow (Moffa 1990, Foil et al. 1993, Metcalf and Eddy
1914). The first construction of an intercepting combined sewer in this country was in
Boston in 1876 (Foil et al. 1993). The intercepted sewage was usually transported to a
primitive treatment plant consisting of solids and floatables removal via screening and
settling (Metcalf and Eddy 1914).
During this period there was considerable debate between proponents of separate
systems and those who favored CSS. The appeal of the combined system was one of
economics, especially in areas where rainfall intensity was high enough to regularly
flush the sewers, greatly alleviating the need for regular cleaning (Metcalf and Eddy
1914). While engineers in England were strongly advocating separate systems as early
as 1842, primarily for sanitation reasons, engineers in America were divided. An
6-1
-------
important engineering monograph of the time by Dr. Rudolph Hering is quoted in
"Design of Sewers" by Metcalf and Eddy (1914):
The advantages of the combined system over a separate
one depend mainly on the following conditions: Where
rain-water must be carried off underground from
extensive districts, and when new sewers must be built
for the purpose, it (combined sewers) will generally be
cheaper. But more important is the fact that in closely
built-up sections, the surface washings from light rains
would carry an amount of decomposable matter into the
rain-water sewers, which, when it lodges as the flow
ceases, will cause a much greater storage of filth than in
well-designed combined sewers which have a
continuous flow and generally, also, appliances for
flushing.
Thus problems associated with settled solids (e.g., maintenance costs and odor
problems) were a primary reason for the spread of combined sewers in this country at
the turn of the century.
Separate systems were advocated for areas with potable water concerns. Perhaps the
"link" between wastewater and stormwater with drinking water in the urban water cycle
was more evident under early 20th century conditions, when pumping costs were too
great to accept the volume of combined sewage, and when rainwater did not require
removal (Metcalf and Eddy 1914). One of the first separate systems designed in this
country was in Memphis, TN following a yellow fever outbreak in 1873 when more than
2,000 persons died. Unfortunately, this system was apparently designed without regard
to English experience and had significant design problems associated with it (Metcalf
and Eddy 1914, Foil et al. 1993).
Separate sewer systems became more widely accepted as receiving water quality
decreased and potable water supplies were threatened. They were designed primarily
for newer urban areas, but later were also used as a means of doing away with
combined systems. Separate systems, consisting of sanitary and storm sewers, remain
the norm in the U.S.
However, NPS pollution has become more of a concern for urban areas (as well as in
rural agricultural areas), separate untreated stormwater conveyance is now being
questioned as an acceptable design practice. For example, sewer separation, a
common mitigative action for areas with severe CSO problems, has been shown in
some areas to be an infeasible solution for reducing water quality impacts. In
Cincinnati, OH separation of the combined system was evaluated as a design
alternative and shown to be an ineffective means of controlling the total solids load to
the receiving water due to the polluted stormwater runoff from the untreated separate
6-2
-------
storm sewers (Zukovs et al. 1996). Conversely, separation has been an effective CSO
abatement alternative in other urban areas (e.g., Minneapolis, MN). These cases
indicate the site specificity of runoff, specifically with regard to land-use density and
local rainfall characteristics. Clearly, a new look at some of these age old urban water
management problems is in order.
Skokie, IL offers one example of a "new look." Faced with a massive basement flooding
problem caused by combined sewer surcharging, Skokie found traditional sewer
separation to be technically feasible but unacceptably costly. Accordingly, controlled on
and below street storage of stormwater was found to be a cost-effective (one-third the
cost of separation) solution. Flow and storage control is achieved with a system of
street berms and flow regulators. The premise of this retrofit system, which is almost
completely implemented throughout the 8.6 square mile community, is that "out of
control" stormwater is the root cause of combined sewer problems. As a side benefit,
the Skokie system includes numerous pollutant-trapping sumps (Walesh and Carr
1998).
Problems Commonly Associated with Present Day Collection Systems
As described above, some collection systems in use today in the U.S. represent over
100 years of infrastructure investment. During that period the technical knowledge of
the nature of wastewater has increased and the public expectation of the performance
and purpose of collection systems has changed. What was considered state-of-the-art
pollution control in 1898 is no longer acceptable. The societal goals which the engineer
attempts to satisfy with a combination of technical feasibility and judgment have
undergone drastic changes in the last 30 years (Harremoes 1997). Present day
collection systems; many of which were designed and constructed in older periods
when performance expectations and technical knowledge were less advanced than
today, now must perform to today's elevated standards. At the same time, sprawling
urban growth has strained infrastructure in many areas, exacerbated by poor cradle-to-
grave project management (Harremoes 1997). Designers of new collection systems
must recognize and address the problems of past designs.
The current status of collection system infrastructure in the U.S. represents a
combination of combined, sanitary and separate storm sewers. These collection
systems vary in age from over 100 years old to brand new. While general design
practices in the U.S. today are not drastically different than 30 years ago, current
innovative research in Europe and Japan suggest that broad societal goals such as
"sustainability" are not being achieved by current design practices in the U.S. Old
combined sewers discharge raw sewage to receiving waters. I/I is a costly and wasteful
problem associated with sewers. Sanitary sewer overflows (SSOs) discharge raw
sewage from failed or under-designed separate systems. NPS pollution associated with
urban areas is discharged from separate storm sewers. Proper transport of solids in
sewers is still a misunderstood phenomenon, causing significant operational problems
such as clogging, overflows, and surcharging.
6-3
-------
This section provides an overview of the problems commonly associated with collection
system infrastructure currently in use in the U.S. Designers of new collection systems
must recognize these problems and address them with modern tools. Unsustainable
design practices must not be allowed to be perpetuated in the field of urban water
management. The useful life of the infrastructure is too long to simply design big
systems to compensate for uncertainty. Following this section are sections describing
innovative technologies being investigated and ways they might be used in the 21st
century.
Combined Sewer Systems
CSS now constitute one of the remaining large-scale urban pollution sources in many
older parts of major cities (Moffa 1990). In large urban areas, raw sewage, combined
with stormwater runoff, regularly discharges to receiving waters during wet-weather.
Water quality problems arise from NPS pollution in the stormwater portion of the
discharge mixing with the sanitary wastes associated with the combined sewer. Low
dissolved oxygen, high nutrient loads, fecal matter, pathogens, objectionable floatable
material, toxins, and solids all are found in abundance in combined sewage (Moffa
1990). This mixture has led to some of the more difficult control problems in urban
water management. However, CSS problems of today are the result of technology
dating back to 1900 and earlier.
The traditional way to control CSO is to first maximize the efficiency of the existing
collection system. This may include an aggressive sewer cleaning policy to maximize
conveyance and storage properties of the system, reducing the rate of stormwater
inflow, a re-evaluation of control points (frequently resulting in raised overflow weirs to
maximize in-line storage in a static sense), and alterations of the wastewater treatment
plant's operating policy to better accommodate short-term wet-weather flows (Gross et
al. 1994). These measures were instituted as requirements for CSO discharge permits
in 1994 by the EPA. The "Nine Minimum Control (NMC) Requirements" are (USEPA
1995b):
1. Proper operation and regular maintenance programs for the sewer system
and CSO points.
2. Maximum use of the collection system for storage.
3. Review and modification of pretreatment programs to assure CSO impacts
are minimized.
4. Maximization of flow to the WWTP.
5. Prohibition of dry-weather CSO discharges.
6. Control of solids and floatables.
7. Pollution prevention programs that focus on contaminant reduction activities.
8. Public notification to ensure that the public receives adequate notification of
CSO occurrences and impacts.
9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO
controls.
6-4
-------
In creating these permit requirements, the EPA has mandated that all owners must, at a
minimum, adhere to these relatively low cost management activities.
These measures were frequently not enough, and less passive means of controlling
CSO have been adopted in many cities. Storage of combined sewage, both in-line and
off-line, has been used in a number of locations to capture frequent storms and the "first
flush" of large events. As the capacity in the collection system and treatment works
increases when the runoff subsides, the stored combined sewage is returned to the
system for treatment (Field 1990). While not completely doing away with CSO (e.g.,
overflows occur when storage capacity is exceeded), storage of combined sewage has
been a cost effective CSO control method (Walker et al. 1994).
Sewer separation has also been used in the U.S. This means of CSO control is
expensive and is usually reserved for limited areas where severe overflow effects are
concentrated in dense urban areas. As stated earlier, this means of control is not
always adequate if polluted stormwater is discharged untreated. Traditional approaches
of CSO mitigation including storage and separation are well documented in the literature
and for detailed information the reader is referred to Moffa, 1990; USEPA, 1991 a, 1993,
1995a, 1995b, 1995c, 1996a; WEF 1994a.
Other CSO control technologies that have been used on a more limited basis include
high-rate treatment in the form of vortex or "swirl" separation technology (frequently in
combination with storage), disinfection (including chlorination and ultra violet), micro
screening, receiving water storage methods (including the flow-balance or the "Swedish
method" developed by Karl Dunker), wetland treatment, floatable traps, and operation
optimization techniques such as real time control (Field 1990; WEF 1994a; Seiker and
Verworn (Ed.) 1996). Included in the category of CSO control technologies used on a
limited basis is the previously mentioned on and below street storage of stormwater with
the purpose of eliminating surcharging (Loucks and Morgan 1995, Walesh and Carr
1998).
An interesting development regarding CSSs is that due to contaminated stormwater
runoff from urban areas that require treatment, combined systems are now at least
being considered for new urban areas in some parts of Europe. CSS may in fact
discharge less pollutant load to receiving water than separate systems where
stormwater is discharged untreated and sanitary wastewater is treated fully. In southern
Germany, CSSs are being designed with state-of-the-art BMPs to reduce the volume of
stormwater entering the system. With reduced stormwater input, the number and
volume of overflows are reduced over a traditional "old-fashioned" CSO, thus only
discharging CSO during large, infrequent events, when the receiving water is most likely
to be at high flow conditions also. This concept is discussed in more detail in
subsequent sections of this chapter titled "Innovative Collection System Design - The
State of the Art" and "Future Directions: Collection Systems of the 21st Century."
6-5
-------
Inflow and Infiltration
Separate sanitary sewers serve a large portion of the sewered population in the U.S.
These sewers are generally of smaller diameter than combined or storm sewers, and
serve residential, commercial and industrial areas. While sanitary systems are not
specifically designed to carry stormwater, per se, stormwater and groundwater do enter
these systems. This is a common and complicated problem for sewer owners. So
common, in fact, that the design of sanitary sewers must include I/I capacity, which may
actually exceed pure sanitary flow rates (ASCE/WPCF 1982). The capacities of many
collection systems are being exceeded well before the end of their design life, resulting
in by-passes, overflows, surcharging and reduced treatment efficiency (Merril and Butler
1994).
Inflow
Inflow is defined as surface water entering the sewer via manholes, flooded sewer
vents, leaky manholes, illicitly connected storm drains, basement drains (probably illicit
in most areas) and by means other than groundwater. Inflow is usually the result of
rain and/or snowmelt events.
Inflow, contrasted with infiltration, is generally easier to control by enforcement of
regulations and through proper design of the sewer/surface water interface
(ASCE/WPCF 1982). For example, in areas prone to nuisance flooding (such as
development in riparian land), careful design of sewer vents and manholes can limit the
amount of storm drainage entering the sanitary sewer. Water tight, elevated vents must
be above a certain flood elevation, and solid manhole covers with half-depth pickholes
will greatly reduce chances for surface waters leaking into the sewer (ASCE/WPCF
1982). Tests performed on manhole covers submerged in one inch of water indicate as
much as 75 gpm leakage into the sewer depending on the number and size of holes
through the cover (ASCE/WPCF 1982).
Enforcement of regulations restricting impervious areas from draining into the sewer will
limit the amount of illicit stormwater entering the sewer (ASCE/WPCF 1982). A1000
sq. ft. roof area may contribute nearly 11 gpm during a one inch/hour rain storm
(ASCE/WPCF 1982). Foundation drains may also contribute drainage water that will
quickly overload sanitary sewer systems. A careful examination of local conditions and
regulations must be made before determining design inflow rates for a sanitary sewer.
Frequently, regulations are difficult and expensive to enforce, and costly provisions may
have to be made to eliminate illicit connections. As such, the costs of treating and
pumping inflow must be weighed against the costs of enforcement and mitigative
actions such as yard regrading, and expensive foundation drains. Every sanitary sewer
will have some point at which the present value of mitigative actions is greater than the
present value of future pumping and treatment costs. Inflow reduction beyond this point
is not cost effective (ASCE/WPCF 1982).
6-6
-------
Infiltration
Infiltration is defined as water that enters the sewer via groundwater. This usually
occurs through leaky sewer pipe joints, manholes and service connections. Being a
function of groundwater head above the sewer leak, infiltration can result from
stormwater and/or snowmelt infiltrating into the ground and into the sewer. Thus a wet-
weather event can trigger both inflow (usually a faster response to the system) and
infiltration in the form of groundwater (ASCE/ WPCF 1982). During wet-weather, a fast
increase in flow rate in the sewer is due to inflow and a delayed response during or
following wet-weather is caused by storm-induced infiltration. This wet-weather-
dependent I/I in a separate sanitary sewer may behave nearly as fast as a CSS and, in
turn, trigger SSOs (Miles et al. 1996). Infiltration can also occur purely as a function of
groundwater elevation, independent of wet-weather. During dry weather the night-time
minimum flows found in the sewer are from pure infiltration. Infiltration is usually much
more difficult and costly to control than inflow. A typical sanitary sewer with likely
sources of I/I indicated is shown in Figure 6-1.
Current design standards usually require that a certain amount of infiltration be
accounted for in the design of a gravity sanitary sewer. Infiltration rates are given in
units of volume per time per mile of pipe, normalized by the diameter of the pipe. In the
U.S., values are reported in units of gpd/inch diameter/mile (gpd/idm). The joint ASCE-
WEF design guidance for gravity sewers gives general guidelines for the volume of
infiltration that should be used in capacity calculations for the a sewer at the end of its
design life. Variations of local guidelines in the U.S. are presented in Table 6-1.
Table 6-1. Variations of infiltration allowances among cities (ASCE/WPCF 1982).
Cities Reporting
Number
4
4
1
2
1
63
11
16
21
5
Total = 128
%
3.1
3.1
0.8
1.6
0.8
49.2
8.6
12.5
16.4
3.9
Total = 100.0
Allowance
(gpd/idm)
1500
1000
800
700
600
500
450 to 300
250 to 150
100
50
Weighted Average = 422
3;
Note: gpd/idm x 0.000925 = rrr/day/cm diam/km
6-7
-------
Defective
Cleanout
Faulty Manhole
Frame/Chirnmey Seal
Deteriorated Manhole
Foundratlon Drain
Connected to
Building Laterals
Storm Drain
faulty Lateral Connection
to Sanitary Sewer
Deteriorated or
Misaligned Joint
Cracked or
Broken Pipe
Figure 6-1. Typical entry points of inflow and infiltration ( USEPA 1991 a).
Inflow/Infiltration Analysis and Design Challenges
In existing sewers, the relative amount of I/I may be dramatic. Relative I/I contributions
on an annual and monthly scale, respectively, are shown in Figures 6-2 and 6-3. The
effect of groundwater elevation is evident in the annual analysis shown in Figure 6-2,
where infiltration increases with groundwater. Inflow, on the other hand, tends to be a
function of rainfall intensity, as seen in Figure 6-3.
A comparison was made of typical wastewater inputs versus the infiltration rates shown
in Table 6-1 for an eight inch sanitary sewer. Typical wastewater flows were calculated
for three population densities using 60 gpcd (DeOreo et al. 1996). Lateral spacing was
assumed to be 50 ft. (high density), 100 ft. (medium density), and 150 ft. (low density).
Each lateral was assumed to receive waste flows from four persons, thereby
discharging 240 gpd. The results are shown in Figure 6-4. The conclusion from this
theoretical comparison based on reasonable values is that typical infiltration rates
allowed in the U.S. are a significant portion of the total wastewater flow.
6-8
-------
UJ
a:
Ill
D
o
01
o
UJ
I
UJ
Recorded Wastewater Flow
Total Infiltration / Inflow
Theoretical Wastewater Production Rate
TIME
1 Year
Figure 6-2. Annual contribution of I/I ( USEPA 1991).
6-9
-------
LU
iii
I
UJ
CO
Q
UJ
0
UJ
I
Inflow
Recorded Wastewater Flow
Non-Rainfall Day
Wastewater Flow
Maximum
Infiltration
"Theoretical Wastewater Production Rate
TIME
1 Month
Figure 6-3. Monthly contribution of I/I ( USEPA 1991 a).
6-10
-------
From Table 6-1, 50% of U.S. cities allow 500 gpd/idm or more. Table 6-2 shows the per
capita I/I contribution for the three population densities for 500 gpd/idm. The results
emphasize that infiltration is a significant portion of the wastestream, even using
"moderate" rates such as 500 gpd/idm for an eight inch pipe.
Another comparison was made by using design values based on tributary area. Pre-
1960s sewers were designed for 2,000 to 4,000 gal/acre/day I/I. Current design
practice is 1,000 gal/acre/day. By comparison, per capita waste flow before 1960 was
assumed to be 200 to 400 gal/capita/day, and the modern design value is 100
gal/capita/day (Heaney et al. 1997). The conclusion is that collection systems are
designed for two to 10 times the dry-weather flow (Heaney et al. 1997). Therefore most
of the sewer capacity presently "in the ground" is there to accommodate I/I (Heaney et
al. 1997).
Table 6-2. Comparison of average daily wastewater and infiltration for one mile of 8
inch sanitary sewer based on 500 gpd/idm.
Population
Density
Low
Medium
High
Lateral
Spacing
(ft)
150
100
50
Population
(four persons
per lateral)
141
211
422
Per Capita
Waste-
water
(gpd)
60
60
60
Total
Waste-
water
(gpd)
8,460
12,660
25,320
Infil.
(gpd)
4,000
4,000
4,000
Total
(gpd)
12,460
16,660
29,320
Infil.
(%)
32%
24%
14%
Per
Capita
Infil.
(gpd)
28
19
9.5
A review of 10 case studies in USEPA (1990) indicates that peak waste flows ranged
from 3.5 to 20 times the average dry-weather flow (DWF). System surcharges would
typically occur as the ratio reached 1:4 or 1:5 (USEPA 1990). Petroff (1996) estimated
that I/I accounts for almost one half of the average flows to WWTPs in the United
States. Houston, TX, measures peaking factors of 1:30 with maximum ratios reaching
1:50(Jengetal. 1996).
An example of the problems associated with reporting extraneous flows is found in a
survey of 102 municipal wastewater management agencies from across the U.S. The
survey was conducted by the Association of Metropolitan Sewerage Agencies (AMSA)
and reported in AMSA (1996). The distribution of per capita wastewater flows and I/I
from this survey is shown in Figure 6-5. The average per capita wastewater flow is 87.4
gpcd and average annual I/I is 37.4 gpcd (AMSA 1996).
6-11
-------
(Q
0)
100%
90%
80%
v>
c
(V
^ 70%
ฃ
Ut
" 60%
O 50%
U.
o 40ฐ/0
Wastewater
Waste water calculated by assumin 4 persons per lateral
connection, @ 60 gpcd. I /1 calculated for 8 inch sanitary
sewer pipe. High density equals one lateral connection every
50 feet for this example.
200
400
00
800
1000
1200
1400
1600
Average I/I Rate: gallons per day per inch diameter mile (gpd/idm)
Figure 6-4a. Comparison of infiltration flow rates and residential flow rates for a one mile long, eight inch sanitary
sewer (high population density).
6-12
-------
100% T
C 60 %
^ 50 %
O
"t 40 %
O
Wastewater calculated by assumin 4 persons per lateral
connection, (f> 60 gpcd. I /1 calculated for 8 inch sanitary
sewer pipe. Medium density equals one lateral connection
every 100 feet for this example.
Wastewater
200 400 600 800 1000 1200
Average I/I Rate: gallons per day per inch diameter mile (gpd/idm)
1400
1600
Figure 6-4b. Comparison of infiltration flow rates and residential flow rates for a one mile long, eight inch sanitary
sewer (medium population density).
6-13
-------
C
0)
Q
O
I
0%
Wastewater
Wastewater calculated by assumin 4
persons per lateral connection,
60 gpcd. I /1 calculated for 8 inch
sanitary sewer pipe. Low density
equals one lateral connection every
150 feet for this example.
200 400 600 800 1000 1200
Average I/I Rate: gallons per day per inch diameter mile (gpd/idm)
1400
1600
Figure 6-4c. Comparison of infiltration flow rates and residential flow rates for a one mile long, eight inch sanitary
sewer (low population density).
6-14
-------
Estimated Residential GPCD for Wastewater
0.25 T
20 40 60 80 100 120 140 160 180 200 220 240 260 280
30 50 70 90 110 130 150 170 190 210 230 250 270 290
Gallons Per Capita Per Day, 1996
Estimated GPCD for Infiltration/Inflow
0.3 T
0.2
0
I"-1
a>
0ฃ
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190
Gallons Per Capita Per Day, 1996
Figure 6-5. Histogram of average annual residential wastewater and I/I rates on a per
capita basis from 102 U.S. cities (AMSA 1996).
6-15
-------
Actual residential wastewater use, however, was found by DeOreo et al. (1996) to be 60
gpcd with little variance. Also, the I/I flow values reported in the AMSA survey are lower
than reported I/I values on a national basis reported from other sources (e.g., Petroff
1996). It is likely that I/I values are under-reported in the AMSA survey, the difference
being in inflated residential rates. For instance, the difference of reported residential
and actual wastewater is 27.4 gpcd (87.4 - 60 gpcd). Added to the average reported I/I
value, 37.4 gpcd, the result is an average annual I/I flow of 64.8 gpcd from across the
nation. This value is in closer agreement with other sources, and highlights the fact that
I/I can be a nebulous, imprecise quantity to estimate.
Methods of I/I detection are usually part of a complete Sewer System Evaluation Survey
(SSES), which may include flow monitoring, pipe and manhole inspection, smoke
testing, dye trace testing, and remote video surveys to isolate areas of high I/I (Rudolph
1995). These methods provide data that help locate areas with deteriorated sewers.
Further analysis will identify areas contributing the most volume per sewer length and,
therefore, the most likely areas for rehabilitation. Various methods are available for
rehabilitation, including sewer lining, sealing, and reconstruction. Traditional
approaches to I/I rehabilitation may be found in USEPA (1991 a), ASCE/WPCF (1982),
WEF/ASCE (1994), Read and Vickridge (Ed.) (1997).
Fixing an I/I problem can be an expensive rehabilitation project. It is only cost effective
when the present value of the future costs of pumping and treating the I/I exceed the
rehabilitation costs over the design life of the sewer including rehabilitation (WPCF
1982). Some older sanitary sewers may in fact have been designed to accept
infiltration in order to dewater areas that may suffer damages from a high groundwater
table. Other failing sewers may be providing the same function, though not originally
designed to function this way. The added costs of damages resulting from high
groundwater tables must be accounted for in an I/I evaluation. I/I rehabilitation policy
must address this potential problem, as residents are likely to blame the I/I rehabilitation
as "causing" groundwater flooding if they have been accustomed to this benefit for
sometime.
One problem associated with estimating and measuring I/I in existing sewers is the
lumping or combining of inflow and infiltration. While both are sources of extraneous
flow, they originate from different sources, tend to impact the system on greatly different
time scales, and have different remedial measures. A likely reason that inflow and
infiltration are combined together is the typical downstream "lumped" flow measurement
at the WWTP headworks. For cost purposes, because inflow and infiltration are both
extraneous to the waste stream, I/I are treated together.
This combining has led to confusion in reporting measured values in terms of average
or peak flows for design or costing calculations. For pumping and treatment costs,
average annual volumes are used for power and equipment cost estimation. In this
case, reporting I/I together is correct. For other purposes, flow rates are important.
Lack of frequency and duration of peak flows has exacerbated the uncertainty
6-16
-------
associated with extraneous flows. For example, the values in Table 6-1 were taken
directly from a modern design guidance. While the figures in Table 6-1 only represent
infiltration, there is little or no discussion as to whether these flows are an average flow
over a year, a season, or day. If these are taken to be design allowances for additions
to existing sewers, what is the return period of the rates given? This has design
ramifications for the expected performance of the system at the end of its design life
and the frequency of failure (e.g., surcharging and overflows).
Estimation of flow for wastewater design purposes has historically been more of an art
than a science. While recent research has shown little variability in residential
wastewater flows (DeOreo et al. 1996), designers have had to estimate peak and
average I/I flows such as presented in Table 6-1 and 6-2 and in Figures 6-2 and 6-3.
For new sewer design, inflow into the system can be expected to be insignificant if a
surface drainage system is designed properly and if illicit connections are reduced by
enforcement of local regulations (ASCE/WPCF 1982, Tchobanoglous 1981).
Expected infiltration rates at the end of the project life are uncertain and, therefore, must
be estimated by the designing engineer. The uncertainty is due to site specitivity of soil
and groundwater conditions and uncertainty of the expected future performance of
modern construction techniques. For estimating peak infiltration rates, old systems
range from 10 m3/ha-d for 5,000 ha service area to 48 m3/ha-d for 10 ha service area,
and new systems range from 3 m3/ha-d for 5,000 ha service area to 14 m3/ha-d for 40
ha service area (Tchobanoglous 1981). The assumption is that performance has
increased due to improved construction. While this is very likely true, to truly estimate
life cycle costs the designer needs additional information on the frequency and duration
of infiltration rates. The absence of a definition for "peak" in terms of time period (e.g.,
hour, day, season) and frequency (e.g., equaled or exceeded once every ten years) is
very important for estimating performance. This information can only come from long-
term, continuous measurement. Likewise, "average" infiltration rates for new sewers,
without a definition of the return period or the duration of the average range from 2
m3/ha-d for 5,000 ha service area to 9 m3/ha-d for 40 ha service area (Tchobanoglous
1981). In the future, after a period of time when actual extraneous flows have been
continuously measured for a variety of systems and in a variety of areas, flow/duration
information will be available to reduce the uncertainty in extraneous flow estimation.
Until that time, collection systems owners will continue to operate under a large cloud of
uncertainty.
Reducing the amount of I/I in new sewers for the entire life of the collection system to
near zero is imperative. This is critical from a variety of viewpoints. From a pure cost
standpoint, the costs of treating I/I over a long period of time are large. From a design
standpoint, the expected I/I from current systems near the end of their useful life may
exceed sanitary flow and "drive" the design. In other words, if I/I can not be reduced to
near zero, the designer must increase sewer design capacity to account for it. The
sewer owner pays for a larger system than is required by societal demand, and then
must pay to treat the I/I over the entire project life. Clearly this is not cost efficient or
6-17
-------
sustainable if the system can be constructed and designed from the outset as "tight".
Generally, the added costs of l/l-proofing the sewer will be far less during original
construction than being forced to pay for expensive rehabilitation projects well into the
lifespan of the system. As an integral part of overall urban water management, I/I
control for new collection systems should be considered a major design objective.
In most cases, excessive I/I can be traced to poor construction techniques and
materials and/or poor enforcement of policies regarding illicit connections. Current
bidding practice is designed to minimize initial costs on the part of municipalities.
However, the goal should be to minimize life-cycle costs given a certain level of
performance over the entire project life. For the sewer owner of the 21 st century (who
may not be a public entity), measures must be taken to ensure that the construction and
design contractors have a vested interest in the acceptable long-term performance of
the collection system.
Sanitary Sewer Overflows
When the capacity of a sanitary sewer is exceeded, untreated sewage may discharge to
the environment. SSO may be due to excessive I/I, from an under-designed (or over-
developed) area releasing more sanitary flow than the system was designed for, from a
sewer blockage, or from a malfunctioning pump station. The distribution of SSO causes
from a sample of six communities is shown in Figure 6-6. An SSO can occur at the
downstream end of a gravity sewer near the headworks of a WWTP or at relief points
upstream in the system. These relief points may have been designed into the system,
or retrofitted to alleviate a problem, or unexpected surcharging through manholes,
basements or sewer vents. SSO causes from two case studies, in Fayetteville, AR, and
Miami, FL, are shown in Tables 6-3 and 6-4. These data show that I/I is a significant
cause of SSO, again reinforcing the importance of the need for data measurement
discussed in the previous section.
SSOs are undesirable under any circumstance because they result in relatively high
concentrations of raw sewage flowing directly to surface waters. Wet-weather SSOs
may behave in a fashion similar to CSOs in extreme cases, though rehabilitation of the
system is different. Instead of treating overflow (as is often the case of CSOs where the
CSS provides primary drainage), wet-weather SSOs are more typically treated by
attempting to remove wet-weather sources or removing hydraulic-capacity bottlenecks.
Dry-weather SSOs are especially unwanted because the receiving water may not be
running as high as during wet-weather, thus triggering more severe water quality
degradation. Heaney et al. (1997) address a more detailed discussion of the
relationship between wet-weather triggered overflows and receiving water assimilative
capacity.
6-18
-------
Insufficient System
Capacity
Power
Failure
Pipe
Breaks
Based on a sample
of six communities.
The causes of SSOs can
vary significantly from
community to community.
Infiltration
and Inflow
Pipe
Blockages
Figure 6-6. Estimated occurrence of SSO by cause ( USEPA 1996b).
Table 6-3. Causes of SSOs in Fayetteville, AR (Jurgens and Kelso 1996).
Cause of SSO
I/I
Roots
Grease
Roots/grease
Other
Total (%)
Number of SSOs
1991 (%)
39
19
25
6
11
100
161
1992(%)
36
24
13
7
20
100
123
Table 6-4. Causes of SSOs in Miami, FL ( Clemente and Cardozo 1996).
Cause of SSO
Pipe breaks (deterioration and accidental)
Pump station failures
Insufficient capacity due to wet-weather
Pipe blockages
Total
Percent of Total
36
30
19
15
100
6-19
-------
For new collection systems, the reasons for SSOs need to be thoroughly understood.
Relief points for excessive flow during wet-weather events in sanitary sewers should not
be a design concern if I/I is truly minimized. Likewise, if land use management plans
are properly coordinated with system design and operation, then sewer capacity should
not cause SSOs. However, surcharging due to clogging may occur even under the
most rigorous of maintenance programs. Therefore, a pipe failure analysis should be
conducted in the design phase to understand the reliability of the system. Relief points
near the headworks of the WWTP should also be part of the design, to protect the
treatment plant from possible excessive flows from unexpected sources. For example,
a failure scenario could include a water main break that floods the sewer, or extreme
surface water flooding that enters via non-illicit means, such as external sewer. In
general, an integrated urban water management program of the future will have a
minimum of SSOs, but collection system owners and regulators should at some point in
the project life expect that some form of discharge due to surcharging will occur.
Separate Stormwater Collection Systems and Non-Point Sources
Separate storm sewers of one form or another can be found in virtually every
municipality in the U.S. They are typically designed to collect stormwater from
urban/suburban areas to prevent nuisance flooding (e.g., usually storms with return
frequencies less than 10 years). This "level of protection" from flooding replaces an
economic efficiency analysis that would ideally be performed on the basis of the worth
of the potential damages resultant from flooding (ASCE/WEF 1993). The selection of
return period is related to the exceedance probability of the design storm and not the
reliability (or probability of failure) of the drainage system (ASCE/WEF 1993). Typical
different levels of protection depending on the land use of the service area are
presented in Table 6-5.
Table 6-5. Typical design storm frequencies (ASCE 1993).
Land Use
Minor Drainage Systems
Residential
High value commercial
Airports (terminals, roads, aprons)
High value downtown business areas
Major Drainage System Elements
Design Storm Return
Period
(years)
2-5
2-10
2-10
5-10
<100
A more thorough analysis of the expected performance of a drainage system would
include a continuous mathematical simulation of the response of the system over an
extended period of time using measured rainfall in the service area. This analysis
would provide a more accurate estimation of the expected return period at which the
capacity of the drainage system would be exceeded and the magnitude of the
6-20
-------
exceedances. This information may be used in conjunction with property values to
estimate the distribution of expected damages that result from system exceedance thus
providing a more rational basis of design (USAGE 1994). In addition, the quality of the
discharged stormwater may be mathematically simulated, which would provide
information that could be used for receiving water management decisions. A detailed
account of the benefits of continuous storm drainage accounting is provided in Heaney
and Wright (1997).
Typical elements of a stormwater system include curbs, gutters, catchbasins,
subsurface conveyance to a receiving water, sometimes first passing through a passive
treatment facility such as a dry detention pond, a wet pond, and/or through a
constructed wetland (ASCE/WEF 1993). This typical system may have open channels
or swales instead of catchbasins and pipes.
Separate storm sewers may transport various forms of diffuse or NPS pollution to the
receiving water. The amount and type of contaminant transported is heavily dependent
on the land use of the tributary area, the rainfall/snowmelt characteristics of the area,
and the type of storm sewer. Recent studies have shown a relationship between the
impervious tributary area and receiving water quality. While the volume and time to
peak of storm hydrographs have long been known to be adversely impacted by
imperviousness, the water quality degradation aspects of imperviousness are still not
completely understood.
Solids and Their Effect on Sewer Design and Operation
The fundamentals of modern sewer design haven't changed in many respects since the
beginning of the century. Review of "Design of Sewers" by Metcalf and Eddy (1914),
indicates that the fundamentals of minimum and maximum velocities, grade, flow rate
prediction, and solids transport were in place at the turn of the century after hundreds
of years of trial and error designs dating back to ancient civilizations. Modern design
has significantly refined the information used in design, but the basic engineering
criteria have remained, much to the credit of early sanitary engineers.
The purpose of sewer collection systems has always been to safely transport unwanted
water and solids. Historically, sewer design has focused primarily on the volume and
flow rate of the fluid, and has assumed solids will be carried with the fluid if certain
"rules-of-thumb" regarding velocity are followed. This imprecise method of designing for
solids transport has been a costly and significant source of maintenance needs over the
years in the U.S. and elsewhere.
Recent research conducted in Europe (Ashley (Ed.) 1996) has focused on the age-old
question of transport of solids in sewers. The flow rate, velocity and size of pipe are all
important in determining the amount and size distribution of solids a particular sewer will
carry. Therefore, along with flow rate, the solids transport question is one of the most
fundamental questions that must be addressed when calculating costs. It is a vexing
question, because solids transport is a function of flow rate, velocity, pipe size, pipe
6-21
-------
material, gradient, solids concentration, size distribution of the solids, and type of solid
(e.g., colloidal or non-colloidal, and grit). Also important is the question of solids
transformation in the collection system. Fundamental research conducted in Europe
has shed some light on this issue (Ashley (Ed.) 1996, Sieker and Verworn (Ed.) 1996,
Ackers etal. 1996).
A historic reference to a minimum design velocity is found in Metcalf and Eddy (1914),
where an early sewer design in London is cited as using a value of 2.2 fps to avoid
unwanted deposition in sewers. Other early work on minimum grades for various pipe
sizes was done by Col. Julius W. Adams in designing the Brooklyn sewers in 1857-59
(Metcalf and Eddy 1914). Col. Adams' recommended sewer grades are shown in Table
6-6, and compared with modern values found in Gravity Sanitary Sewer Design and
Construction (ASCE/WPCF 1982). These early designers recognized that the minimum
mean velocity to avoid deposition was dependent on the pipe diameter.
However, in the 1994 WEFTEC proceeding "Collection Systems: Residuals and
Biosolids Management", a paper entitled "Two feet per second ain't even close" by P. L.
Schafer discusses the problems associated with deposition in large diameter sewers
due to using a "rule-of-thumb" design value of two fps (Schafer 1994). Modern design
guidelines still state: "Accepted standards dictate that the minimum design velocity
should not be less than 0.60 m/sec (2 fps) or generally greater than 3.5 m/sec (10 fps)
at peak flow." (ASCE/WPCF 1982). One problem with this recommendation is the lack
of peak flow definition. Should this be the seasonal, monthly, daily, or hourly peak flow?
The frequency and duration of the flushing flow are critical to the proper performance of
the sewer. Ideally, a settled sewer particle at the furthest end of the collection system
will be re-entrained into the waste stream and carried to the WWTP. Clearly the
minimum velocity design problem has not been resolved.
Sewers that exhibit sediment deposition are prone to a multitude of problems over time.
Excess sedimentation promotes clogging, backwater and surcharging and may promote
corrosion by producing hydrogen sulfide (Schafer 1994). Because sedimentation
problems are more likely to occur in larger diameter sewers, such as trunk sewers, the
associated costs of sewer failure may be substantially greater than in a smaller
diameter pipe. In combined systems, the in-line storage that is taken up in a heavily
sediment-laden trunk or interceptor sewer will tend to increase the volume and
frequency of overflow events (Mark et al. 1996). In addition, the deposited sediments in
combined systems represent a build up of pollutants, that may resuspend during wet-
weather (Gent et al. 1996).
6-22
-------
Table 6-6. Comparison of recommended minimum sewer grades and velocities over
the years.
Source
Balzalgette,
London, c. 1852
(1)
Roe, London, c.
1840 (1)
New Jersey Board
of Health, 1913(1)
u
u
Metcalf and Eddy,
1914(2)
u
WPCF/WEF1982
(3)
WEF/ASCE1992
(4)
Acker etal. 1996
(5)
a
it
it
it
it
it
it
Type of sewer and pipe
diameter
Large intercepting sewers -
combined system
Large intercepting sewers -
combined system
8" - Sanitary sewer (n =
0.013)
12" - Sanitary Sewer (n =
0.013)
24" - Sanitary Sewer (n =
0.013)
Combined systems
Sanitary systems
Sanitary systems
Storm sewers
150mm (5.9 in)
225 mm (8.85 in)
300mm (11. 8 in)
450 mm (17.7 in)
600 mm (23.6 in)
750 mm (29.5 in)
1000mm (39.3 in)
1800mm (70.8 in)
Minimum
Slope
(ft/ft)
0.002
0.004
0.0022
0.0008
0.0062
0.0043
0.0032
0.0024
0.0021
0.0022
0.0025
0.0028
Minimum
Velocity
(fps)
2.2
2.5
2.0
2.0
2-3
2.2
2.36
2.46
2.59
2.95
3.48
4.43
6.66
Note:
1. Col. Julius W. Adams (c. 1859) in Metcalf and Eddy (1914)
2. Metcalf and Eddy (1914)
3. ASCE/WPCF(1982)
4. ASCE/WEF(1992)
5. Ackers etal. (1996)
6-23
-------
The movement of solid material in flowing water is a complex phenomenon that
depends on the nature of the solid particles, the nature of the flow, and the nonlinear
interaction between the two. A solid particle undergoes acceleration from the force of
gravity, from the average advective motion of the water, and from the local turbulent
motions of the water. Particles may be suspended in the water column of the sewer,
deposited along the bed of the sewer, or slowly move along the bedload of the sewer.
Once deposited under low flow conditions, a particle may resuspend into the water
column under high flow conditions. In addition, a particle may exhibit cohesive
properties, adjoining with other particles both in suspension or in the bed after
deposition. Sewer particles may be organic, with low specific gravity and break down
both physically and biologically while in the sewer.
When considering sewer collection systems, the proper transport of solids is crucial to
a correctly functioning system. There are distinct areas where deposition should be
avoided, (e.g., the conduit network) and also areas where deposition is desired, (e.g.,
treatment works). The system should function under a wide range of hydraulic
conditions and under a wide range of solid loadings. The solids may also vary widely in
character, which may alter the performance of the sewer.
To avoid deposition, a common design method is to calculate the shear stress required
to move the largest size of particle expected in the sewer under average or high flow
conditions (Schafer 1994). This assumes that the frequency of the high flow is enough
to avoid excessive deposition and the subsequent creation of a permanent bed layer.
The critical shear stress of a particle is defined as the minimum boundary stress
required to initiate motion (Schafer 1994). Chow (1959) indicates that shear stress is a
function of the specific weight of water and the hydraulic radius and invert slope of the
sewer. Various values of critical shear stress have been recommended, depending on
the maximum size of particle found in the sewer. Values of critical shear stress
recommended by various researchers are shown in Table 6-7.
Table 6-7. Recommended critical shear stress to move sewer deposits (Schafer 1994).
Recommended critical
shear stress
N/m2
4
4
1.5 to 2.0
1 to 2
3 to 4
2.5
6 to 7
Ib/ft2
0.08
0.08
0.03 to 0.04
0.02 to 0.04
0.06 to 0.08
0.05
0.12to0.14
Reference
Lynse 1 969
PaintaM972
Schultz1960
Yao1974
Yao
Nalluri1992
Nalluri1992
Conditions
Sanitary sewers
Sanitary sewers
German work
Sanitary sewers with small grit size
Storm sewers
Sand with weak cohesiveness
Sand with high cohesiveness
Note: 1 N/m2 equals 0.02064 Ib/ft2
6-24
-------
Schafer (1994) recommends that the lower end of the shear stress range in Table 6-7 is
adequate only for waste streams with small particle size and limited grit, and when
flushing flows may be expected daily. The high end of the range is appropriate when
the waste stream contains heavy grit and gravel, as is common in combined or storm
sewers (Schafer 1994). Table 6-7 indicates that commonly used design values for the
minimum flushing velocities in sewers are not adequate to scour grit from large sewers.
Consider, for example, a 48 inch diameter sewer transporting a reasonable load of grit.
Minimum velocities in the range of 4.0 fps are required to flush deposited grit, far
greater than the 2.0 fps recommended in some design guidelines. However, European
research shows that bed stress is the most important criterion, and a minimum bed
shear stress of 2N/m2 is required to ensure sediment transport (Ashley and Verbanck,
1997).
Uncertainty in key design parameters is the source of unnecessary cost. If under-
designed, operation and maintenance costs are likely to be high. If over-designed,
additional unnecessary capital costs are incurred as are high maintenance costs due to
solids deposition at low flows. Just as this was shown to be true in the discussion of I/I,
so it is also true for designing sewers for solids transport.
However, in addition to the lack of high quality frequency/duration information regarding
flows, the designer concerned with solids transportation must also contend with a
physical process about which only the rudimentary nature is known. The relationship
between the solids concentration, the distribution of settling velocities, and the dynamics
of movement are not well understood for gravity pipe flow. Operational costs will be
incurred if the frequency and duration of velocities are not enough to regularly cleanse
the pipes. Deposition in uncleaned sewers will cause SSOs. Thus environmental costs
are also incurred. If over-designed, the sewers will remain clean, however additional
excavation and material costs will be incurred.
While attempts have been made to estimate costs of I/I and SSOs on a national basis,
there are no cost estimations of improperly designed sewers. It is likely that these
costs, if known, would dwarf those for I/I and SSOs. As is the case with I/I estimation,
new systems that record and store operational data will be invaluable to improving
design techniques for solids transport.
Predicting Pollutant Transport in Collection Systems
A problem associated with present day collection systems is that, given the current state
of computer simulation technology and knowledge, simulating pollutant transport
correctly through a complex collection system is very difficult. This is especially true if
complex hydrodynamics and continuous simulation are required. Due to the complex
nature of the governing hydrodynamic equations, coupled with sediment transport
equations, continuous simulation of the response of a collection system is nearly
impossible for realistic system configurations. However, the designer of new collection
system should realize that this will likely not be true in the near future. Data retrieval via
Supervisory Control And Data Acquisition (SCADA) systems should be considered a
6-25
-------
major system component in collection systems of the 21 st century. Data acquisition will
be imperative for real time control and advanced simulation/optimization and designers
of new collection systems must recognize that the technology available at the end of the
project life of the collection system will be far advanced from what is available today.
To properly simulate pollutant discharges from a sewer system, a model must have the
ability to simulate the movement of solids in sewers (Gent et al. 1996). Research
conducted in the UK has shown four types of sewer transport (Gent et al. 1996):
1. Suspended transport (occurs at or slightly slower than the flow rate).
2. A dissolved or very fine rate (occurs at the ambient flow rate).
3. A dense near-bed layer (occurs during periods of low flow).
4. A course bed load layer (occurs during periods of high flow or in steep
sewers).
The near bed and bed layer are the primary pollutant transport mechanisms and are
also the main sources of deposition (Gent et al. 1996). Current trends in mechanistic
modeling of collection systems indicate that these transport mechanisms will be part of
future mathematical models. It should be assumed that future collection systems will
have extensive data collection systems and that computational capabilities will be
advanced to the point of accurately simulating pollutant behavior in a pipe network.
Characteristics and Treatability of Solids in Collection Systems
When considering the transport and/or treatment of solids in sewers, the cumulative
effect of gravity on the overall particle distribution must be measured. Sewer solids may
occur in a wide range of specific gravities and an equally wide range of shapes. The
settling characteristics of the entire distribution of solids must be known to properly
establish solids behavior in pipes, pumping stations and treatment works. Due to the
site specific nature of solids, local data on settling velocities are greatly preferred over
literature values.
Several forms of measurement tests have been developed and Pisano (1996) provides
a summary of the currently accepted techniques. All methods provide estimates of the
distribution of settling velocities for a particular solids sample. However, the results are
a function of the protocol used and, therefore, not absolute. Pisano (1996) shows an
example plot of settling characteristics for various forms of sewer samples. Data show
a wide range of "treatability," that is, ability to settle as determined in laboratory tests.
When considering design of new systems that include wet-weather treatment, a
standardized measure of settling velocity distribution data will be needed.
Innovative Collection System Design - The State of the Art
Recent work in all aspects of sewer collection systems, from design and facilities-
planning level research to construction and operation and maintenance, shows promise
for greatly improved collection system performance for the next century. In addition,
drastically new technologies are being considered which may greatly affect the future
6-26
-------
configuration of urban water management. Some innovators in the field are advancing
ideas to replace water-intensive waste removal systems.
This section provides an overview of many aspects of sewer concepts. It is generally
organized in terms of increasing innovation. In other words, the first examples remain
closest to present day systems and the last innovations described deviate furthest from
current design concepts. The reader is reminded that this section is an overview of
innovative ideas in the field of waste management. Many of these ideas are only now
being tested and inclusion in this guidance should not be misunderstood as a
recommendation by the authors or the USEPA. References are provided for the
interested reader to follow up on performance testing in the future. The section
following this one attempts to provide these technologies in a future scenario-type
context.
During the past decade, many changes in the understanding of global and local effects
of urbanization, population growth, and land use have brought about a concern for
future generations. This concern is manifested in a concept for future development
called "sustainability" which is discussed in Chapter 3 of this report. While there are
many interpretations of the concept of, engineers have attempted to bring the
fundamental concepts to the practitioners and policy makers. In the field of urban water
management, sustainability concepts are being used to critique current water
management practices, and bring fresh ideas of waste management to decision
makers. Henze et al. (Ed.) (1997) provide the most recent work in this area. Innovative
collection system concepts attempt to reconcile problems discussed in the earlier
section of this chapter titled "Problems Commonly Associated with Present Day
Collection Systems." While rethinking the whole concept of transporting urban wastes
via underground water-driven sewers.
Recent literature in the area of sewer innovations were surveyed from WEF (1994a),
WEF (1994b), WEF (1995a), WEF (1995b), WEF (1996), Sieker and Verworn (Ed.)
1996, Ashley (Ed.) 1996, Bally et al. (Ed.) (1996), Henze et al. (1997), USEPA (1991 a),
and USEPA (1991b). An especially important summary of vacuum, pressure and small
diameter gravity sewers is presented in USEPA (1991b).
Current Innovative Technologies - Review of Case Studies
Data Management, SCADA, Real Time Control
Many fields, including that of urban water management, have barely been able to keep
up with the rapid technological and computational advances of the past decade. This
has been exacerbated in the U.S. by the relative longevity of civil infrastructure works
and the amount of infrastructure already in place, the majority being constructed in the
20th century. As the end of the project life of many of these works is approaching, and
as new urban areas are being contemplated for certain high-growth sections of the U.S.,
practitioners and researchers in the field of urban water management have a unique
window of opportunity. Now is the time to take advantage of the latest in technological
6-27
-------
advances and to use the past two decades as a model to predict what the future may
bring in terms of technology.
The information age has changed the way in which resources are managed. This fact
will be more apparent in new collection systems and waste management of the 21st
century. New systems will be operationally data intensive due to a higher level of
control. The current level of control in WWTPs may be seen as extending into the
collection system. The increase in data quality and quantity will have positive effects on
simulation for design, simulation for operation and for real time control of the system.
These innovations should decrease costs and environmental impacts and maximize
utility of the system.
Seattle, WA was one of the first major municipal sewer owners in the U.S. to use real
time measurements of the collection system in a control scheme (Gonwa et al. 1994,
Vitasovic et al. 1994). Vitasovic et al. (1994) describes the use of Real Time Control
(RTC) in Seattle for CSO control purposes. Vitasovic (1994) states the goal of the
program succinctly:
... the idea behind RTC of CSO's is fairly straightforward:
the conveyance system is controlled in real time with
the objective of maximizing the utilization of in-line
storage available within the system. The cost of the
control system is often a fraction of the cost required for
alternatives that include construction of new storage
facilities.
The Seattle experience highlights the need for some form of system simulation to test
control procedures off-line and to provide a higher level of system knowledge on-line
than from data measurement alone (Vitasovic et al., 1994). A SCADA system provides
automation one level above manual process level control and interfaces data retrieval
systems with a relational database (Vitasovic et al., 1994, Dent and Davis 1995). Under
the SCADA level of control, operators usually manage the system from a centralized
location using Man-Machine Interface (MMI) software, receiving data from the SCADA
while maintaining a supervisory level of control over the system (Vitasovic et al., 1994,
Dent and Davis 1995). A higher level of automation may be used if a computer
controller is used to change system operation. This can include simple control
algorithms such as if-then and set-level points, or may be as advanced as providing on-
line non-linear optimization (e.g., genetic algorithms).
Other successful applications of RTC in the U.S. include Lima, OH, Milwaukee, Wl, and
Cleveland, OH. Gonwa et al. (1994) provide a summary of the Milwaukee upgrade of
an existing RTC. One new feature of the upgrade was additional control applied to the
headwords of the WWTP.
The hydraulic grade line of the Milwaukee system modified by the RTC upstream of the
6-28
-------
WWTP resulted 1,5000,000m3 inline storage volume during peak storm diversions to
ISS after interceptor storage is maximized. In other words, the RTC provides control of
the system to maximize pipe storage before diverting to the Inline Storage System.
RTC is used in combination with storage facilities to minimize overflows.
Most applications of RTC, SCADA, automated system optimization and other advanced
data management techniques are currently used in collection systems designed before
the computer/information-age revolution. For new collection system designs, it is
imperative that designers understand the physical/structural requirements of long-term
high-quality data measurement. Successful designs will have adaptivity "built-in". The
ability to change operational procedures as technological advances become available
will greatly extend the useful life of future collection systems. In other words, future
collection systems will have many critical "high information points" that, used in
conjunction with control and simulation, will facilitate operating the system for optimal
utilization. The tools used to accomplish this task will change during the project life of
the system because of the longevity of infrastructure in contrast with the rapidity of
computer technological advances. A successful design will anticipate these changes.
Sanitary Sewer Technology - Vacuum Sewers
Hassett (1995) provides a summary of current vacuum sewer technology. A typical
vacuum sewer configuration is shown in Figure 6-7.
Central Vacuum and Pumping Station
Wastewater to
Treatment Plant
Figure 6-7. Typical vacuum sewer system schematic (Hassett 1995).
6-29
-------
Vacuum sewers are typified by shallow pipelines that make them attractive for high-
groundwater areas and for alignments that would require expensive rock excavation for
gravity lines. Such systems are also useful in flat countries such as the Netherlands.
Being completely sealed, vacuum lines also do not have any I/I - a remarkable benefit
that begs the question: If vacuum sewer lines can be constructed water tight, why can't
gravity lines? Vacuum systems do show promise, however, especially with recent
advances in lifting capabilities. A recent installation in an Amtrak station in Chicago, IL
used a valve configuration that achieved over 20 feet of vacuum lift (Hassett 1995).
Another advantage of these systems is that vacuum toilets function with less than a
third of water per flush than do modern low-flush toilets, using only 0.3 to 0.4 gallons per
flush, compared with 1.5 to 6.0 gallons for toilets connected to gravity sewers.
Hassett (1995) provides a cost comparison for vacuum sewers for an actual project
location in Virginia. The service area was assumed flat with a three foot depth-to-
groundwater, an area of 750 acres (300 hectares), and approximately 750 residential
units housing 3,000 people. The density was then varied to provide the construction
cost information presented in Figure 6-8 and the operating costs shown in Table 6-8.
Hassett (1995) notes that the operating costs of any of the system configurations is only
4 to 6% of the present value of the capital components and is, therefore, unlikely to be a
decision factor. This observation may not be true in countries with higher energy costs.
Table 6-8. Annual operating costs of vacuum and gravity sewer systems as of 1995
(Hassett 1995).
Type of Sanitary
Sewer System
Gravity (Dry)
Gravity (Wet)1
Modern Vacuum
High Lift Vacuum
Cost (1 995 $U.S.)
Labor
26,000
28,000
42,000
34,000
Materials
3,000
28,000
10,000
3,000
Power
4,000
4,000
8,000
8,000
Total
33,000
60,000
60,000
45,000
(1) Wet means that the system includes lift stations and is
below the water table.
A major advantage of these systems (along with pressure sewers) is their adaptability to
monitoring and control. The use of pressure instead of gravity flow simplifies flow
measurement. Control of these system is more exact than with gravity systems,
thereby making them suited for overall system optimization by RTC.
Low Pressure Sewers
Another modern collection system technology that has been used in the U.S. is the low
pressure sewer used in conjunction with a grinder pump (Farrell and Darrah 1994).
These systems use a small grinder-pump typically installed at each residence. The
grinder pump reduces solids to 1/4 to 112 inch maximum dimension (Farrell and Darrah
6-30
-------
10000
9000
8000
7000
6000
5000
4000
3000
2000
a.
is
a
^
0)
a.
(0
1000
900
800
700
600
500
400
300
200
100
W1VS
Gravity (wet)
VS 2001
Gravity (dry)
20 25
(8) (10)
40 50
(16) (20)
100
(40)
200 250
(80) (100)
Population Density
Persons per Hectare
(Persons per Acre)
Figure 6-8. Per capita construction costs for different sanitary sewer systems at
various population densities (Hassett 1995). (Note: MVS means modern vacuum
system and VS 2001 represents 21st century vacuum system).
6-31
-------
1994). Like vacuum systems, these low-pressure grinder systems feature water tight
piping, thus virtually eliminating I/I. A full system in Washington County, MD went on-
line in 1991. Water use, rainfall and wastewater flows were monitored and wastewater
flows were found to be 110 to 130 gpcd, with no measurable increase during or
following wet-weather events (Farrell and Darrah 1994).
A demonstration facility in Albany, NY was installed in 1972, where per capita flows
were only 34 gpd. One purpose of this demonstration was to determine the effect of
grinding solids on settleability. The conclusion was that there was no effect on
settleability and treatability as compared with solids transported via a traditional gravity
sewer (Farrell and Darrah 1994). Other demonstrations found no significant differences
in grease concentrations (Farrell and Darrah 1994). The LPS pipe was excavated after
several years of service, and no significant build-ups of solids were noted in the pipes
(Farrell and Darrah 1994).
LPS systems have over a 20 year track record. As with most new technologies,
engineers were hesitant to specify these sewers despite smaller capital expenditures
due to the lack of long-term experience (Farrell and Darrah 1994). The reliability and
costs of operating and maintaining the pumps were a major impediment to widespread
use. Reliability of LPS systems has increased dramatically since the first commercial
installation at a marina in the Adirondack mountains in NY (Farrell and Darrah 1994). In
the 1972 Albany demonstration project (which only lasted 13 months), the mean time
between service calls (MTBSC) for pump maintenance was 0.9 years (Farrell and
Darrah 1994). An LPS system installed in 1986 in Bloomingdale, GA. averaged 10.4
years between service calls (Farrell and Darrah 1994) over an eight year period. Pump
operation and maintenance (O&M) costs and MTBSC for five LPS collection systems
are shown in Table 6-9 (Farrell and Darrah 1994).
Table 6-9. Pump data and O&M costs for low pressure sewer systems (Farrell and
Darrah 1994).
Location
Cuyler, NY
Fairfield Glade, TN
Pooler/Bloomingdale, GA
Pierce County, WA
Sharpsburg/Keedysville, MD
Number of
Pumps
41
955
998
900
780
Average Age
(years)
17
16
11
9
5
Annual O&M
($/pump)
53.00
36.07
13.24
51.00
18.00
MTBSC
(years)
4.6
5.6
10.4
7.9
>20
As with vacuum systems, LPS systems are well suited for control and monitoring due to
the use of pressure rather than gravity to drive the system. This may be a significant
advantage over gravity system in the future for RTC applications.
6-32
-------
Small Diameter Gravity Sewers
These systems consist of a system of interceptor tanks, usually located on the property
served, a network of small diameter collector gravity sewers (USEPA 1991 b). The
interceptor tanks remove settleable solids and grease from the wastewater. Effluent
from each tank is discharged to the collector sewer via gravity or by pumping (septic
tank effluent pumping (STEP)) (USEPA 1991 b). A typical system layout is shown in
Figure 6-9.
This system has the advantage of not having to transport appreciable solids (USEPA
1991 b). Cost savings therefore result from having a lower required velocity and from
less cleaning costs. Also, peak flows are attenuated in the tank. Therefore, the
average to peak flow rate from wastewater is far less than for a standard gravity sewer
(USEPA 1991 b).
Otherwise, these systems function much the same as traditional gravity sewers. They
have been used in rural areas to replace existing septic tank discharge. They are also
used in developing countries to share costs (Mara, 1996) where they have been known
as settled sewerage. A problem associated with these sewers is I/I. The use of old
septic tanks tends to increase the amount of rainfall induced infiltration (USEPA 1991 b).
Black Water/Gray Water Separation Systems
A more drastic break with modern systems is that of water separation at the household
level. This has been a relatively active research area in recent years because of its
appeal from a water conservation standpoint. Water from faucets, showers,
dishwashers and clothes washers drains to a separate on-site filtration device. The
filtered as water is then typically used for outdoor irrigation. This may be especially
advantageous in arid areas where on-site stormwater detention for outdoor use does
not meet the evapotranspiration needs on an average annual basis.
Waste/Source Separation
Recent research in Europe has focused on the separation of household waste in a
variety of ways (Henze et al. (Ed.) 1997). The goal of these systems is to promote
nutrient recycling and limit entropy gain (a goal for sustainability) via dilution. Urine
separation is perhaps the most radical departure, where urine is tanked on site and
converted to fertilizer (Hanaeus et al. 1997). Human urine contains 70% of the
phosphorus and 90% of the nitrogen found in wastewater from toilets (Hanaeus et al.
1997). This technology is still in the formulation phase and has only been tested on a
limited basis. Research shows it may have applicability for certain waste management
applications.
6-33
-------
RAW WASTE
/ 7 ~~ Service
Settleable Solids Soluble Bod Lateral
Effluent
Inlet
Scum
Sludge
I I Outlet
Figure 6-9. Components of small diameter gravity sewer (SDGS) system (USEPA
1991b).
6-34
-------
Composting
On-site composting has been attempted at an ecovillage in Sweden (Fittschen and
Niemczynowicz 1997). Toilet wastes were deposited in an on-site composting tank.
The results of this experiment were less than desirable for a variety of reasons. The
system is user-intensive, demanding a level of expertise beyond that of average
residents. Technically it was only partially acceptable because the resulting compost
was only of mediocre quality for agricultural use. The system was found to be socially
unacceptable and was energy intensive as electricity was used to dry the compost
(Fittschen and Niemczynowicz 1997). Again, this technology is in the testing phase,
though it may hold promise for specific applications.
Combined Systems for the Future?
While old CSS are considered a major source of urban pollution, there is some recent
activity in the area of new CSS. Where urban areas have significant amounts of NPS
pollution that requires treatment, it may be possible to design a CSS to capture most of
the annual storm volume for treatment at a WWTP, without discharging raw sewage
during major events. Lemmen et al. (1996) describe a concept for a sewer system in
the Netherlands that has connections between the storm drainage network and the
sanitary collection system.
Walesh and Carr (1998) and Loucks and Morgan (1995) describe use of controlled
storage of stormwater on and below streets to control surcharging and solve basement
flooding in a CSS. The premise of this approach is that stormwater flow rate, not
volume, is the principal cause of surcharging of CSS and resulting basement flooding
and CSO. On and below street storage of stormwater, strategically placed throughout
the CSS, reduces peak stormwater flows to rates that can be accommodated in the
CSS without surcharging. The two large scale, constructed, and cost effective projects
described by Walesh and Carr and by Loucks and Morgan were retrofits. However, the
success of these projects suggests integrating the design of streets and CSS in newly
developing high intensity areas.
Future Directions: Collection Systems of the 21st Century
New ideas for managing the entire urban water cycle in an integrated fashion are being
formulated. This section synthesizes various aspects of recent research into a vision of
what the near future may hold for collection systems in the 21 st century. In order to
synthesize these ideas, probable contextual factors within which collection systems will
operate must be examined.
The definitive settlement type of the second half of the 20th century in the U.S. has
been urban sprawl. In the U.S., this land use has been brought on largely by zoning
and the proliferation of the automobile. Recent ideas regarding resource allocation
seem to indicate that, while the automobile is not likely to disappear in this country in
the next 50 years, its function may change. The "new urbanism" is likely to have mixed
land use areas typified by neighborhoods where specific land use types may not
dominate a specific urban catchment. Neighborhoods replace zoned land use types in
6-35
-------
the new urbanism and, as such, present a variety of opportunities for innovative urban
water management.
The main premise of this discussion is that new urban development in the 21st century
will begin to follow the patterns of the "new urbanism" in terms of land use and
transportation. The other guiding premise is that design will be control-driven, that is to
say that new systems will be designed to be controlled far beyond that which is
presently used in wet-weather management. Therefore, the following scenarios
describe possible future collection systems for new urban areas that integrate source
control, system control, data management, life-cycle costs, environmental costs, and
social acceptability.
Future Collection System Scenarios
High Density Areas
Areas with the highest levels of urban NPS will require stormwater treatment, much as
they do today. A form of CSS, or an integrated storm-sanitary system (ISS) (Lemmen
et al. (1996), will capture a large portion of the annual runoff volume from dense urban
areas. Storm runoff will be reduced by source control and infiltration BMPs and the
residual of small events will be transported to the WWTP. Large events will be throttled
out of the ISS, before mixing with sanitary waste, and discharged to receiving waters.
This new system will have the best of both CSS and separate systems. The advantage
of the combined system has been treatment of small runoff producing events, including
snowmelt. However, the disadvantage has always been the discharge of raw sewage
to receiving waters during large events. With the advantage of control technology, as
the sewers and/or the WWTP reach capacity, the stormwater is diverted directly to
receiving waters, without mixing with sanitary and industrial wastes.
This system will have a high degree of built in control. The data stream begins with
local radar observations. This information is combined with real-time ground level
measurements of rainfall. These data will be used to predict the rainfall patterns over
the catchment for the next half hour. The SCADA system receives information
regrading the present state of the sanitary and storm portions of the waste stream.
Quality as well as quantity are monitored. Performance of high rate treatment devices
operating on the discharged stormwater is monitored. A critical innovation is the
integration of the WWTP performance, operation and control into the system. Operation
of the WWTP now extends to the collection system. Rainfall information in conjunction
with the state of the system and receiving water data are used to predict potential
outcomes of the wet-weather event using a system simulation model. Coupled with a
non-linear optimization routine, an optimal control scheme is determined on-line and
changes in system control are relayed back to the system via the SCADA system.
The system response is fed back to the SCADA and continuous control is maintained
throughout the wet-weather event. This "feedback" loop provides the municipality with
rapid response for flashy summer events and provides urban flood control
6-36
-------
simultaneously with water quality control. In addition, the time series of wet-weather
data are now stored in a relational database, spatially segregated to interface with static
geography stored in a CIS.
Suburban Development
Outlying from the new urban centers, suburban type development still exists. While less
dense than the city, new suburban development contains some of the mixed land uses
found in the urban center. The collection system serving this area is far different from
the city, however, because the NPS pollution is not so severe as to warrant full
treatment at the WWTP. BMPs and source control innovations have reduced the
stormwater impacts on the receiving water. Regional detention is used for flood control
and water quality enhancement while possibly providing recreation.
Sanitary wastes are transported via pressure sewers to collector gravity lines at the
city's border. The use of pressure sewers has reduced suburban I/I to near zero. In
addition, the new sanitary LPS sewers are very easy to monitor, as the age-old problem
of open channel flow estimation is avoided by using pressure lines. This provides
added certainty in the flow estimation and lends itself very well to control. Technology
borrowed from the water distribution field has achieved a great level of system reliability
and control. In fact, the sewer now mirrors the water distribution network, essentially
providing the inverse service.
6-37
-------
References
Ackers, J., D. Butler, S. John and R. May (1996). Self-Cleansing Sewer Design: The
CIRIA Procedure. In Sieker, F. and H.R. Verworn (Ed.). Proceedings of the Seventh
Annual Conference on Urban Storm Drainage. Hannover, Germany. September 9-13,
1996. Vol. II. IAER/IAWQ Joint Committee on Urban Storm Drainage.
American Society of Civil Engineers and Water Pollution Control Federation (1982).
Gravity Sanitary Sewer Design and Construction. ASCE No. 60. WPCF No. FD-5.
ASCE. New York, NY. WPCF. Washington DC.
American Society of Civil Engineers and Water Environment Federation (1993). Design
and Construction of Urban Stormwater Management Systems. ASCE No. 77. WEF No.
FD-20. ASCE. New York, NY. WEF. Washington DC.
Ashley, R.M. (Ed.) (1996). Solids in sewers. Water Science & Technology. Vol.33.
No. 9. Association of Metropolitan Sewerage Agencies (AMSA). (1996).
Ashley, R.M. and Verbanck, M.A. (1997) Physical Processes in Sewers. In Emscher
Congress: 'Water Management in Conurbations' June 19 and 20, 1997, Bottrop,
Germany.
Association of Metropolitan Sewerage Agencies (AMSA) (1996). The AMSA Financial
Survey, 1996, A National Survey of Municipal Wastewater Management Financing
Trends. AMSA. Washington, DC.
Bally, D., T. Assano, R. Bhamidimarri, K.K. Chin, W.O.K. Grabow, E. R. Hall, S. Ohgaki,
D. Orhon, A. Milburn, C. D. Purdon and P. T. Nagle. (Ed.) (1996). Water Quality
International '96 Part 2. Water Science & Technology. Vol. 34. No. 3-4.
Chow, V.T. (1959). Open Channel Hydraulics. McGraw-Hill Book Co. New York, NY.
Clemente, A.J. and R.WCardozo (1996). Dade county's mandated improvement
program to reduce sanitary sewer overflows. In USEPA. National Conference on
Sanitary Sewer Overflows (SSOs). EPA/625/R-96/007. Office of Water. Washington,
DC.
Collins, E. (Ed.) (I 994). On-site wastewater treatment. Proceedings of the Seventh
Annual International Symposium on Individual and Small Community Sewage Systems.
Atlanta, GA. December 11-13, 1994. American Society of Agricultural Engineers. St.
Joseph, Ml.
Dent, S.D, and D. Davis (1995). Database management model for SCADA systems. In
James, W (Ed.). Modem Methods for Modeling the Management of Stormwater
Impacts. Computational Hydraulics International. Guelph, Ontario, Canada.
6-38
-------
DeOreo, W., J. Heaney and P. Mayer (1996). Flow trace analysis to assess water use.
Journal of the American Water Works Association. Jan., p. 79-80.
Farrell, R.P., and G. Grey Darrah (1994). Pressure sewers - a proven alternative
solution for a variety of small community sewage disposal challenges. In Collins, E.
(Ed.). OnSite Wastewater Treatment. Proceedings of the Seventh Annual International
Symposium on Individual and Small Community Sewage Systems. Atlanta, GA.
American Society of Agricultural Engineers. St. Joseph, Ml.
Fittschen, I., and J. Niemczynowicz (1997). Experiences with dry sanitation and
greywater treatment in the ecovillage Toarp, Sweden. In Henze, M., L. Somlyody, W.
Schilling, and J. Tyson (Ed). Sustainable Sanitation. Water Science & Technology.
Vol. 35, No. 9. Elsevier Science Ltd. Oxford, UK.
Foil, J. L., J. A. Cerwick, and J. E. White (1993). Collection systems past and present.
Water Environment and Technology. December.
Field, R. (1990). Combined sewer overflows: control and treatment. In Moffa, P.E.
Control and Treatment of Combined Sewer Overflows. Van Nostrand Reinhold. New
York, NY.
Cayman, M. (1996). A glimpse into London's early sewers. Cleaner Magazine. Cole
Publishing Inc. Three Lakes, Wl.
Gent, R., B. Crabtree and R. Ashley (1996). A review of model developments based on
sewer sediments research in the UK. In Ashley, R. (Ed.). Solids in Sewers. Water
Science & Technology. Vol. 33. No. 9.
Gonwa, W., N. Schultz, L. Paulus, and V. Novotny (1994). Improved collection system
real time control for Milwaukee MSD. In WEF. WEFTEC '94 Proceedings of the Water
Environment Federation 67th Annual Conference and Exposition. Chicago, IL. October
15-19,1994. Part 1: Collection Systems, volume 111. Water Environment Federation.
Alexandria, VA.
Gross, C.E., N. Huang, J.T. Mauro and E.D. Driscoll (1994). Nine minimum control
requirements for combined sewer overflows. In WEF. A Global Perspective for
Reducing CSOS: Balancing Technologies, Costs, and Water Quality. WEF Specialty
Conference Series Proceeding. July 10-13, 1994. Louisville, KY. Water Environment
Federation. Alexandria, VA.
Hanaeus, J., D. Hellstrom and E. Johansson (1997). A study of a urine separation
system in an ecological village in northern Sweden. In Henze, L., Somlyody, W.
Schilling and J. Tyson (Ed.). Sustainable Sanitation. Water Science & Technology.
Vol. 35. No. 3. Elsevier Science Ltd. Oxford, UK.
6-39
-------
Harremoes, P. (1997). Integrated water and waste management. In Henze, L,
Somlyody, W. Schilling and J. Tyson (Ed.). Sustainable Sanitation. Water Science &
Technology. Vol. 35. No. 3. Elsevier Science Ltd. Oxford, UK.
Hassett, A. (1995). Vacuum sewers - ready for the 21 st Century. In WEF. Sewers of
the Future. WEF Specialty Conference Series Proceeding. September 10-13, 1995.
Houston, TX. Water Environment Federation. Alexandria, VA.
Heaney, J., D. Sample and L. Wright (1997). Class notes, EPA project meeting and
modeling workshop. March 24-26, (1997). Environmental Protection Agency. Edison,
NJ.
Heaney, J. and L. Wright (1997). On integrating continuous simulation and statistical
methods for evaluating urban stormwater systems. In James, W. (Ed.). Advances in
Modeling the Management of Stormwater Impacts. Vol. 5. Computational Hydraulics
International. Guelph, Ontario, Canada.
Henze, M., L. Somlyody, W. Schilling and J. Tyson (Ed.) (1997). Sustainable sanitation.
Water Science & Technology. Vol.35. No. 3. Elsevier Science Ltd. Oxford, UK.
James, W. (Ed.) (1997). Advances in modeling the management of stormwater
impacts. Vol. 5. Computational Hydraulics International. Guelph, Ontario, Canada.
James, W. (Ed.) (1995). Modem Methods for Modeling the Management of Stormwater
Impacts. Computational Hydraulics International. Guelph, Ontario, Canada.
Jeng, K., M.J. Bagstad, and J. Chang (1996). New collection system modeling
techniques used in Houston. In USEPA. National Conference on Sanitary Sewer
Overflows (SSOs). EPA/625/R-96/007. Office of Water. Washington, DC.
Jurgens, D.E. and H.M. Kelso(1996). Sewer rehabilitation: the techniques of success.
In USEPA. National Conference on Sanitary Sewer Overflows (SSOs).
EPA/625/R96/007. Office of Water. Washington, DC.
Lemmen, G., D. de Bijil, and M. Maessen (1996). A new development in the City of
Dordrecht: sewerage and drainage masterplan of Buitenstad. In Sieker, F. and H.R.
Verworn (Ed.). Proceedings of the Seventh Annual Conference on Urban Storm
Drainage. Hannover, Germany. September 9-13, (1996). Vol. II. IAHR/IAWQ Joint
Committee on Urban Storm Drainage.
Loucks, E. D. and M. G. Morgan (1995). Evaluation of the Wilmette runoff control
program. Proceedings of Integrated Water Resources Planning for the 21st Century.
American Society of Civil Engineers. New York, NY. May.
6-40
-------
Mara, D. (1996). Low Cost Urban Sanitation. Wiley. New York, NY
Mark, 0., U. Cerar and G. Perrusquia (1996). Prediction of locations with sediment
deposits in sewers. In Ashley, R. (Ed.). Solids in Sewers. Water Science &
Technology. Vol. 33. No. 9.
Merril, M. Steve and R. Butler (1994). New dimensions in infiltration/inflow analysis. In
WEF. A Global Perspective for Reducing CSOs: Balancing Technologies, Costs, and
Water Quality. Water Environment Federation Specialty Conference Series
Proceedings. July 10-1 3, 1994. Louisville, KY. WEF. Alexandria, VA.
Metcalf, L., and H. P. Eddy (1914). American Sewerage Practice: Volume I Design of
Sewers. Mcgraw-Hill. New York, NY.
Miles, S. W., J. L. Dom, and R.E. Tarker Jr. (1996). An I/I analysis and prediction
method to help guide separate sanitary sewer improvement programs. In WEF. Urban
Wet Weather Pollution: Controlling Sewer Overflows and Stormwater Runoff. WEF
Conference Proceedings. Quebec City, Canada. June 16-19, 1996. WEF. Alexandria,
VA.
Moffa, P. E. (Ed.) (1990). Control and Treatment of Combined Sewer Overflows. Van
Nostrand Reinhold. New York, NY.
Petroff, R.G. (1996). An analysis of the root causes of SSOs. In USEPA. National
Conference on Sanitary Sewer Overflows (SSOs). EPA/625/R-96/007. Office of Water.
Washington, DC.
Pisano, W.C. (1996). Summary: United States "sewer solids" settling characterization
methods, results, uses and perspectives. In Ashley, R. (Ed.). Solids in Sewers. Water
Science & Technology. Vol. 33. No. 9.
Read, G. F., and I. G. Vickridge (Ed.) (1997). Sewers - Rehabilitation and New
Construction, Repair and Renovation. Arnold, London, UK.
Rudolph, R.S., E.T. Kelly and J.D. Sharon (1995). A guide to efficiently isolate I/I
sources related to basement flooding occurrences. In WEF. Sewers of the Future.
WEF Specialty Conference Series Proceeding. September 10-13, 1995. Houston, TX.
Water Environment Federation. Alexandria, VA.
Schafer, P. L. (1994). Two feet per second ain't even close. In WEF. WEFTEC'94:
Collection Systems and Residuals & Biosolids Management. Proceedings of the Water
Environment Federation 67th Annual Conference and Exposition. Chicago, IL. October
15-19, (1994). WEF. Alexandria, VA.
6-41
-------
Sieker, F. and H. R. Verworn(Ed.) (1996). Proceedings of the Seventh Annual
Conference on Urban Storm Drainage. Hannover, Germany. September 9-13, (1996).
Vols. 1, II and III. IAHR/IAWQ Joint Committee on Urban Storm Drainage.
Tchobanoglous, G. (1981). Wastewater Engineering: Collection and Pumping of
Wastewater. McGraw-Hill. New York, NY.
United States Army Corps of Engineers (USAGE) (1994). Risk-Based Analysis for
Evaluation of Hydrology/Hydraulics and Economics in Flood Damage Reduction
Studies. Circular No. 1105-2-205. Department of the Army. Washington, DC.
USEPA (1990). Rainfall Induced Infiltration into Sewer Systems. Report to Congress.
EPA/430/09-90/005. Office of Water. Washington, DC.
USEPA (1991 a). Sewer System Infrastructure Analysis and Rehabilitation. EPA/625/6-
91/030. Office of Water. Washington DC.
USEPA (1991 b). Manual: Alternative Wastewater Collection Systems. EPA/625/1 -
91/024. Office of Water. Washington DC.
USEPA (1993). Manual: Combined Sewer Overflow Control. EPA/625/R-93/007.
Office of Water. Washington, DC.
USEPA (1995a). Combined Sewer Overflows: Guidance For Long-Term Control Plan.
EPA 832-B-95-002. Office of Water. Washington, DC.
USEPA (1995b). Combined Sewer Overflows: Guidance For Nine Minimum Controls.
EPA 832-B-95-003. Office of Water. Washington, DC.
USEPA (1995c). Combined Sewer Overflows: Screening and Ranking Guidance. EPA
832-B95-004. Office of Water. Washington, DC.
USEPA (1996a). Combined Sewer Overflows: Guidance For Monitoring And Modeling.
EPA 832-B-97-001 Draft. Office of Water. Washington, DC.
USEPA (1996b). National Conference on Sanitary Sewer Overflows (SSOs).
EPA/625/R96/007. Office of Water. Washington, DC.
Vitasovic, Z., J. Dumont, R. Fitzgerald and J. Mackenzie (1994). Comprehensive
approach to real time control of CSOs. In WEF. A Global Perspective for Reducing
CSOs: Balancing Technologies, Costs, and Water Quality. WEF Specialty Conference
Series Proceeding. July 10-13, 1994. Louisville, KY. Water Environment Federation.
Alexandria, VA.
6-42
-------
Walesh, S.G. and R. W. Carr (1998). Controlling stormwater close to the source: an
implementation case study. American Public Works Congress. Las Vegas, NV.
September.
Walker, D.E., J.B. Golden, D.R. Bingham, E.D. Driscoll, and D.J. Murray (1994).
Design considerations for off-line, near surface storage/treatment facilities. In WEF. A
Global Perspective for Reducing CSOs: Balancing Technologies, Costs, and Water
Quality. WEF Specialty Conference Series Proceeding. July 10-13, 1994. Louisville,
KY. Water Environment Federation. Alexandria, VA.
Water Environment Federation (WEF) (1994a). A Global Perspective for Reducing
CSOs: Balancing Technologies, Costs, and Water Quality. WEF Specialty Conference
Series Proceeding. July 10-13, 1994. Louisville, KY. Water Environment Federation.
Alexandria, VA.
WEF (1994b). WEFTEC '94 Proceedings of the Water Environment Federation 67th
Annual Conference and Exposition. Chicago, IL. October 15-19, 1994. Parti:
Collection Systems. Volume III. Water Environment Federation. Alexandria, VA.
WEF (1995a). Sewers of the Future. WEF Specialty Conference Series Proceedings.
September 10-13, 1995. Houston, TX. Water Environment Federation. Alexandria,
VA.
WEF (1995b). WEFTEC '95 Proceedings of the Water Environment Federation 68th
Annual Conference and Exposition. Miami Beach, FL. October 21-25, 1995. WEF.
Alexandria, VA.
WEF (1996). Urban Wet Weather Pollution, Controlling Sewer Overflows and
Stormwater Runoff Proceedings. June 16-19, 1996. Quebec City, Quebec, Canada.
WEF. Alexandria, VA.
WEF/ASCE(1994). Existing Sewer Evaluation & Rehabilitation. WEF FD-6. ASCE
No. 62. Water Environment Federation. Alexandria, VA.
Zukovs, G., D. Cuthbert, W. Pisano, M. Umberg, and T. Quinn (1996). Watershed
based CSO planning in greater Cincinnati. In Sieker, F. and H.R. Verwom (Ed.).
Proceedings of the Seventh Annual Conference on Urban Storm Drainage. Hannover,
Germany. September 9-13, 1996. IAHR/IAWQ Joint Committee on Urban Storm
Drainage.
6-43
-------
Chapter?
Assessment of Stormwater Best Management Practice Effectiveness
Ben Urbonas
Introduction
The use of stormwater practices to control and manage the quality and quantity of urban
runoff has become widespread in U.S. and in many other countries. As a group they
have been labeled as best management practices or BMPs. Current literature
describes a variety of techniques to reduce pollutants found in separate urban
stormwater runoff (that is, not CSS). Many of these same practices can also be applied
for areas served by CSS to reduce the frequency of combined sewer overflows (CSOs)
during wet weather and to enhance quality of the CSOs when they do occur.
Structural BMPs are designed to function without human intervention at the time wet
weather flow is occurring, thus they are expected to function unattended during a storm
and to provide passive treatment. Nonstructural BMPs as a group are a set of practices
and institutional arrangements, both with the intent of instituting good housekeeping
measures that reduce or prevent pollutant deposition on the urban landscape.
Much is known about the technology behind these practices, much is still emerging and
much remains yet to be learned. Currently many of these controls are used without full
understanding of their limitations and their effectiveness under field (i.e., real world)
conditions, as opposed to regulatory expectations or academic predictions or beliefs. In
addition, the uncertainties in the state of practice associated with structural BMP
selection, design, construction and use are further complicated by the stochastic nature
of stormwater runoff and its variability with location and climate. Where one city may
experience six months of gentle, long-duration rains; another will experience many
convective and frontal rainstorms followed by severe winter snows that melt in the
spring; while still another will experience few, mostly convective storms. At the same
time, examination of precipitation records throughout the U.S. reveals that the majority
of individual storms are relatively small, often producing less precipitation and runoff
than used in the design of traditional storm drainage networks.
A number of structural and non-structural BMPs are discussed in this chapter focusing
on their effectiveness in removing pollutants and in mitigating flow rates. BMP
effectiveness in addressing some of the stipulated impacts of urban runoff on receiving
water systems is also discussed.
7-1
-------
After much literature review Roesner, Urbonas and Sonnen (1989) concluded the
following:
Among all these devices the most promising and best
understood are detention and extended detention
basins and ponds. Less reliable in terms of predicting
performance, but showing promise, are sand filter beds,
wetlands, infiltration basins, and percolation basins. All
of the latter appear to be in their infancy and lack the
necessary long-term field testing that would provide
data for the development of sound design practices.
Information published since 1989 has expanded very little understanding of structural
BMPs and their performance. However, urban water professionals may be on a verge
of a breakthrough in identifying and possibly quantifying some of the linkages between
the urban runoff processes and its effects on various aspects of receiving systems.
This should lead to a better understanding of how and why various types of BMPs may
be able to moderate some of the effects on receiving systems. It is unlikely, however,
that BMPs and other techniques will be able to eliminate all of the effects on receiving
systems that are caused by the growth in population world wide, especially the
population growth of urban areas.
Objectives in the Use of Best Management Practices for Stormwater Quality
Management
The comprehensive - quantity and quality - approach to stormwater management is
relatively new. Prior to the late 1960's the primary goal was to rapidly drain municipal
streets and to convey this drainage to the nearest natural waterway. This practice
evolved into the use of detention when the municipal engineers began to recognize that
the cost of urban drainage systems became prohibitive as more and more of the
watershed urbanized. Also, some began to recognize the deleterious effects that
uncontrolled urban drainage had on the stability of the receiving stream. One of the first
states to require the control of smaller runoff events, namely the peak runoff rate from
the two-year design storm, was Maryland. In the late 1970's, Maryland was also the
first to require stormwater quality BMPs, including stormwater infiltration. As a result, it
and some of the other states like Florida became early field test beds for these facilities.
Although much has yet to be learned before engineers can design for a specific
performance, BMP knowledge is evolving. Currently, the design professional and the
planner have to think in terms of how to best manage stormwater runoff in order to limit
damage to downstream properties, reduce stream erosion, limit the effects on the flora
and fauna of the receiving streams and integrate stormwater systems into the
community.
As the field of stormwater management expanded in its scope, water quality became an
increasingly important consideration at many locations in the U.S. Structural BMPs
cannot do the job alone without the cooperation and participation of the public.
Prevention and good housekeeping became two operative words and practices. They
7-2
-------
are now considered as important as the use of structural BMPs and may be the only
affordable approaches for much of the currently urbanized landscape.
Figure 7-1 conceptually summarizes four basic objectives for stormwater quality
management. The first objective includes the concepts of prevention and load
reduction. This is followed by the use of other non-structural and structural measures.
The following four objectives provide an integrated and balanced approach to help
mitigate the changes in stormwater runoff flows that occur as land urbanizes and to help
mitigate the impacts of stormwater quality on receiving systems:
1. Prevention: Practices that prevent the deposition of pollutants on the urban
landscape including changes in the products that, when improperly used or
accidentally spilled, deposit pollutants on the urban landscape and changes in
how the public uses and disposes of these types of products.
2. Source control: Preventing pollutants from coming into contact with
precipitation and stormwater runoff.
3. Source disposal and treatment: Reduction in the volume and/or rate of
surface runoff and in the associated constituent loads or concentrations at, or
near their source.
4. Follow-up treatment: Interception of runoff downstream of all source and on-
site controls using structural BMPs to provide follow-up flow management
and/or water quality treatment.
Whenever two or more of these objectives are implemented in series within a
watershed, they form a treatment train. A long line of discussions among some
regulators and stormwater professionals indicates a belief that the implementation of
more than one of these objectives in a treatment train fashion (Livingston et al., 1988,
Roesner et al. 1991, Schueler et al., 1991, Urbonas and Stahre 1993, WEF & ASCE
1998) will result in better quality stormwater reaching the receiving waters. Whether this
is true or not has not been conclusively field tested. Intuitively this assertion makes
sense, but whether the use of a set of structural BMPs or the use of more than one of
these objectives in various combinations has any significant or measurable mitigation of
urban runoff effects on the receiving waters has yet to be answered. Obtaining the
answer will require well designed and controlled field studies, with each taking place
over a number of years. Nevertheless, each set of practices appears to add to the
arsenal of tools that help manage stormwater runoff and its quality. If nothing else, their
use probably adds to the quality of urban life and the enjoyment of the receiving waters
into which urban runoff drains.
7-3
-------
Stormwater
Pollution
J
Prevent Reduce Polutant Deposition
on Urban Landscape
Source Controls
Onsile Structural Controls
I
(Minimizing Directly Connected Impervious Areas,
Wet Ponds, Constructed Wetlands, Grass Buffer
Strips, Grass-Lined Swales, Modular Block
Pavement, Filtration)
F oil own p Structural Controls
(Serves Larger Area than Onsite Controls:
Wet Ponds, Dry Ponds, Constructed Wetlands,
Filter Basins)
c
Receiving Waters
J
Figure 7-1. BMPs in series to minimize urban stormwater runoff quality impacts
(UD&FCD1992).
7-4
-------
Non-Structural Best Management Practices
Non-structural BMPs include a variety of institutional and educational practices that,
hopefully, result in behavioral changes which reduce the amount of pollutants entering
the stormwater system and, eventually, the receiving waters into which it drains. Some
of these non-structural practices deal with the land development and redevelopment
process. Others focus on educating the public to modify behavior that contributes to
pollutant deposition on urban landscapes. Others search out and disconnect illicit
wastewater connections, control accidental spills, and enforce violations of ordinances
designed to prevent the deposition of pollutants on the urban landscape and its
uncontrolled transport downstream. Among a variety of practices, non-structural BMPs
include:
1. Discontinuing or reducing the use of products that have been identified as a
problem (e.g., use of phosphorous free or low phosphorous detergents,
limiting the application of pesticides, calibrating the application of sand and
salt applicators to road surfaces in winter).
2. The adoption and implementation of building and site development codes to
encourage or require the installation of structural BMPs for a new
development and significant redevelopment projects.
3. Adoption and implementation of site disturbance/erosion control programs.
4. Minimizing the DCIA in new development including the use of landscaped
areas for the discharge of stormwater from impervious surfaces, grass
buffers, and roadside swales instead of curb and gutter.
5. Public education on the proper uses and disposal of potential pollutants such
as household chemicals, paints, solvents, motor oils, pesticides, herbicides,
fertilizers, and antifreeze.
6. Effective street sweeping and leaf pickup and efficient street deicing
programs.
7. Detection and elimination of illicit discharges from wastewater lines to
separate storm sewers.
8. Enforcement of the operation and maintenance requirements of privately
owned stormwater management facilities, including on-site structural BMPs
and non-structural programs.
9. Providing the needed operation and maintenance for publicly owned BMPs.
7-5
-------
Structural Best Management Practices
Stormwater runoff quality enhancement begins with the avoidance and prevention of
pollutant deposition onto the urban landscape (Urbonas and Stahre 1993). It is likely
that structural BMPs cannot do the job alone and be fully effective. Structural BMPs
need to be viewed as only a supplement to the "good housekeeping measures" being
practiced within a community. Once the development and implementation of a non-
structural program is in progress, the use of the BMPs discussed in this section can be
considered.
Minimized Directly Connected Impervious Area
This practice is listed under the structural BMPs because it can be provided only when
land is being developed (i.e., changed from agricultural or an undeveloped state to an
urban development) and when significant amounts of older urbanized areas undergo
redevelopment. Retrofitting this BMP into developed areas is probably not generally
feasible because of the great expense and the physical disruption of neighborhoods and
their residents.
Minimizing DCIA relies on the construction of urban streets, parking lots and buildings
using a non-traditional template. Figure 7-2 illustrates two hypothetical areas, one using
traditional drainage practices and the other the minimal DCIA concept. Instead of
elevated landscape islands in a commercial areas, this concept uses landscaped areas
that are lower than the adjacent street and parking lot grades to intercept, detain and
convey surface runoff. Also, porous pavement parking pads can be used to intercept
surface runoff from impervious paved areas. This concept for new land development
includes an extensive use of swales, grass buffer strips, porous pavement, and random
placements of infiltration basins (infiltration areas) whenever site conditions permit. Not
all of the features illustrated in Figure 7-2 are feasible at all sites, nor is this concept
feasible for all development sites or land use types. Site conditions such as local
geology, soils, groundwater levels, terrain slopes, soil stability, meteorology, land uses
and development policies need to be fully evaluated to determine if this practice is
feasible.
The intent is to slow down the rate of stormwater runoff and to encourage infiltration. In
so doing, surface runoff volumes during small storms can be reduced somewhat for the
majority of sites and totally eliminated under most favorable site conditions.
7-6
-------
Commercial Lot
Roof Drains v
to Parking Lot \
Storm Sewer
Inlet (typ) x
1 V **
<
J
wwwi mum mmnm
\
X
%
WWII
I Office 1
/Building -\
If Flat Roof %,?
V$* <*^\
\Parking Lot
/
^jLฃw
* |K\^\\
* i in
J\ \ 4 \ \
\\ -* \
tJ 1
t
\
**
\
3.
Landscape
/ Area (typ)N.
/ \SidewalkN
J Sti
WW WWWi WWWI iWWW WWWI WWII
%
\
ซป
cet
m wwwt
f f
House
V * N
/^ s /
\ \
u *
Sidewalk ^ S%
J Jf\ \^
DS_V
|
Curb
IWWI
Gutter
Manhole ' ^ Storm Sewer
TRADITIONAL SITE AND STREET DRAINAGE DESIGN
Grass
Swale
(for large flows)
NOTE: Elimination of storm sewer system
and increasing swale capacity would
elevate this to Level 3.
Office
Building -
Flat Roof
kTVQOvVi. ^ป - 4v\>\TT^i\>\\ swaie \\XTV^.\\I- 4V\k^^v\yy^
"f__/_ f ~L _ -%.-} ^
Shallow^" % stmm Sewm wuS "f
Culvert Storm Sewer
MINIMIZING DIRECTLY CONNECTED IMPERVIOUS AREAS
Manhole
Figure 7-2. Comparing traditional and minimized directly connected impervious area
drainage (UD&FCD 1992).
7-7
-------
Water Quality Inlets
Water quality inlets are single or multi-chambered underground sediment or sediment
and oil separation vaults. Some are simple catch basins with a depressed bottom
where the heavier sediments settle before stormwater enters the downstream
conveyance system. Others are more complex, equipped with more than one chamber,
have lamella plates and/or are designed to separate solids, floatables, oils and greases
from water. These type of devices have been in use for years and primarily serve very
small tributary catchments.
Infiltration Practices
This group of structural BMPs include swales, grass buffer strips, porous pavement,
percolation trenches, and infiltration basins. Water that infiltrates can sometimes drain
to the groundwater table. As a result, this practice has to be used with caution and may
not be appropriate for sites that have gasoline stations, chemical storage areas and
other activities that that can contaminate land surfaces and the groundwater below.
Each of these practices is described in more detail as follows:
1. Grass Swale: The slower the flow in a grass swale, the more pollutants will
be removed from stormwater through sedimentation and the straining of
surface runoff through the vegetative cover. Also, the slower the flow, the
more time stormwater has to infiltrate into the ground. The ultimate in slow
flow is a swale that acts as a linear detention basin.
2. Grass buffer strip: To remove the heavier sediment particles, a grass buffer
strip has to have a flat surface with a healthy turf-form ing grass cover.
Pollutants are removed from stormwater primarily through sedimentation and
the straining of stormwater runoff through the vegetative cover. In arid and
semi-arid climates, grass buffer strips need to be irrigated (UD&FCD 1992).
3. Porous Pavement: Porous pavement has been used in the U.S. and Europe
since the mid-1970s. It is constructed either of monolithically poured porous
asphalt or concrete, or modular concrete paver blocks.
4. Percolation Trench: A percolation trench is a rock filled trench that
temporarily stores stormwater and percolates it into the ground. A percolation
trench typically serves small impervious tributary areas of two hectares or
less.
5. Dry Well: A dry well is a rock filled vertical well that temporarily stores
stormwater in order to allow it time to percolate into the ground. It is similar in
operation to a percolation trench. Dry wells are sometimes used to penetrate
an impermeable layer near the surface to provide a stormwater conduit to a
permeable soil layer that lies below it. Dry wells typically serve small
impervious tributary areas of two hectares or less.
7-8
-------
6. Infiltration Basin: An infiltration basin intercepts and temporarily stores
stormwater on its surface, where it eventually infiltrates into the ground. An
infiltration basin often serves a small developed catchment, one with less than
four hectares of tributary impervious surface.
Filter Basins and Filter Inlets
The use of media filter basins, mostly sand filters, for stormwater quality enhancement
was first reported by Wanielista et al. (1981) and Veenhuis et al. (1988). Since then the
use of filters has expanded, with most uses reported in the State of Delaware, the
Washington DC area, Alexandria, VA and the Austin, TX area (City of Austin 1988,
Livingston et al. 1988, Anderson et al. Undated, Chang et al 1990, Truong et al. 1993,
Belletal. 1996).
Recently, media filters such as peat-sand mix, sand-compost mix and goetextiles have
also been tested and proposed for use (Farham and Noonan 1988, Galli 1990, Stewart
1989). An ingenious sand filter inlet has been suggested by Shaver and Baldwin
(1991). In most of the suggested filter designs, a detention volume is provided
upstream of the filter media. This volume captures the runoff and permits it to flow
through the filter at a flow rate compatible with its size and hydraulic conductivity.
Swirl-Type Concentrators
These complex underground vaults are designed to create circular motion within the
chamber to encourage sedimentation and the removal of oil and grease. They are also
often equipped with trash skimmers and traps. Swirl concentrators are designed to
effectively process up to a design flow rate and to by-pass higher flow rates.
Extended Detention Basins
Detention basins hold storm water temporarily (i.e., detain). They are sometimes called
dry detention basins or ponds because they drain out, for the most part, completely after
the runoff from a storm ends and then they remain "dry" until the next runoff event
begins. The joint use of the terms "dry-pond" is an oxymoron and, for the sake of
consistent terminology, the expression detention basin is suggested.
Retention Ponds
Retention ponds have a permanent pool. Some are equipped with a formal surcharge
detention volume above this pool. Processes that are known, or are suspected to be at
work in a retention pond are sedimentation, flocculation, agglomeration, ion exchange,
adsorption, biological uptake through microbial and plant ingestion and eutrophication,
remobilization, solution, and physical resuspension of particulates. In the main body of
the pond, particulate pollutants are removed by settling and nutrients are removed by
phytoplankton, algal and bacterial growth in the water column. Marsh plants around the
perimeter of the pond provide the biological media to help remove nutrients and other
dissolved constituents and trap small sediment and algae in the water column.
7-9
-------
Wetlands
Currently, the use of wetlands as stormwater quality enhancing facilities is an emerging
technology. Wetlands can be used as source controls or as follow-up treatment
devices. A wetland basin, in essence, is another form of an extended detention basin or
a retention pond. As a result, all of the constituent removal processes listed for an
extended detention basin and a retention pond should also apply to a wetland basin.
A wetland channel is similar to a grass-lined channel, except it is designed to develop
wetland growth on its bottom and is typified by a flat longitudinal slope, wide bottom and
slow flow velocities during the two-year and smaller storm runoff events. A wetland
channel, to a smaller degree and depending on specific site conditions and design,
probably has many of the constituent removal characteristics of a wetland basin.
Stormwater Quality Management Hydrology
Urbonas, Guo and Tucker (1990) observed that capture volume effectiveness in the
Denver, CO area reached a point of diminishing returns. This point, referred to by some
as the "knee of the curve," was later defined as the point of maximized capture volume
(Urbonas and Stahre 1993). Figure 7-3 indicates that this is the point where rapidly
diminishing returns begin to occur. Beyond this point the number of events and the total
volume of stormwater runoff fully captured during an average year decrease
significantly as the detention volume is increased.
Although the number of storms, and their characteristics such as intensity, volume,
duration, seasons, and storm separation vary with location, a pattern of diminishing
returns was observed by Roesner et al (1991), Guo and Urbonas (1996) Urbonas et al
(1996 a), Heaney and Wright (1997) and others. This seems to be the case for all
precipitation gauging sites analyzed, regardless of the hydrologic regions in U.S. in
which they are located. The other finding was that the maximized capture volume, once
determined for a given site, captured 80 to 90% of all runoff events and runoff volumes
at the site. This volume was also sufficient to capture the "first flush" of storm runoff
during the larger events that exceed the design capture volume.
Table 5.1 in WEF & ASCE (1998) lists the maximized capture volumes at six study sites
studied by Roesner et al. (1991) located in different hydrologic regions of U.S. They
observed that 1.0 watershed inches (25.4 mm) of storage volume captured more than
90% of all the runoff volume at all six sites and that 0.5 watershed inches (13 mm) of
available storage volume captured over 90% of the runoff at the four residential
neighborhoods among the six sites.
7-10
-------
3
HM
Q.
TO
O
*c
Qi O
i3 1
"O
-------
The need to focus on TSS removal by BMPs has been recently reinforced by DiToro et
al. (1993) and Cerco (1995). They both studied bottom sediment in receiving waters
and found that sediment deposits in Chesapeake Bay can have a benthic oxygen
uptake. Thus, TSS reduction in stormwater runoff can be the primary reason for
selecting and sizing many structural BMPs.
Table 7-1. Sensitivity of the BMP capture volume in Denver, CO (Urbonas et al. 1990).
Capture Volume to
Maximized Volume
Ratio
0.7
1.0
2.0
Percent of Annual
Runoff Volume
Captured
75
85
94
Percent of Average
Annual TSS
Removed
86
88
90
Thus, in order to be effective in the removal of most constituents found in stormwater,
structural BMPs need to focus on the frequently occurring smaller events. As a result,
detention and retention facilities, wetlands, infiltration facilities, media filters, water
quality inlets, swirl concentrators and possibly swales need to be designed to
accommodate the runoff volumes and flow rates that result from smaller storm events.
It has been recommended that the capture volume for water quality enhancement and
for the protection of receiving stream integrity be somewhere between the runoff volume
from a mean storm event (Driscoll et al.,1989) and the maximized volume (Urbonas et
al. 1990, Hall et al.,1993, Guo and Urbonas 1996). Furthermore, this volume should be
released over an extended period of time, namely, somewhere between 12 to 48 hours
(Grizzard et al. 1986, Urbonas et al., 1990, Urbonas and Stahre 1993).
Other design considerations, however, come into play when dealing with the removal of
nutrients and dissolved constituents. The permanent pool volume of ponds, the volume
and the surface area of wetlands and other biochemical dependent BMPs (e.g., peat-
sand mix filter) need to be designed and sized on considerations other than only
capture volume (Hartigan 1989, Lakatos and Mcnemer 1987, Galli 1990).
Nevertheless, even these facilities are likely to benefit from a surcharge capture volume
sized as discussed in the preceding.
An Assessment of Best Management Practice Effectiveness
Non-Structural Best Management Practices
Non-structural BMPs rely on human behavioral changes to reduce the amount of
pollutants that enter a separate stormwater system, which transports untreated
stormwater and the pollutants it contains to receiving waters such as arroyos, gullies,
brooks, streams, lakes, estuaries, and reservoirs. As a result, quantifying the amounts
of various constituents (some of which may be pollutants) that non-structural practices
eliminate from being delivered to these receiving waters is very difficult.
7-12
-------
Some of these practices directly affect the types and numbers of structural BMPs that
are going to be used as land development and redevelopment takes place. As a
surrogate measure, the effectiveness of the structural controls, and the percentage of
the total urban landscape within a community or a watershed these controls intercept,
can be used to quantify the effectiveness of the regulatory, non-structural practices.
On the other hand, how does one measure the amount of pollutant load that does not
reach the receiving systems because of educating the public or a change in behavior?
USEPA (1993) goes into much discussion and detail on what to do and how to do it, but
does not provide reliable methods for quantifying the effectiveness of non-structural
BMPs in reducing pollutant loads reaching the receiving waters of this nation.
The discussion that follows attempts to address some of the issues and questions
regarding non-structural BMP effectiveness. It draws on many discussions involving
municipal public works and park department officials in Colorado and other states.
Some of it interprets and adds to the issues discussed by USEPA (1993).
Unfortunately, no field data is known to exist on the effectiveness of many of these
practices on reducing the pollutant loads reaching receiving waters. However, several
field studies are underway, the most prominent known study being the one in Portland,
OR. Hopefully, with sufficient data from well controlled field investigations, some of the
outstanding questions will begin to be answered.
Pollutant Source Controls
For this practice to be effective, widespread changes must occur in the use of various
potentially polluting products. It is insufficient for a single city or metropolitan area to
discontinue the use of a product it believes to pollute its waterways because such a
product will be brought in from outside from adjacent communities where it is still being
used. For example, requiring that only phosphorous free or low phosphorous
detergents be sold will only work if such a ban is state or nation wide.
On the other hand, municipalities and industries can, through proper training and
licensing, probably reduce the amount of certain types of pollutants applied to their
landscapes. Through changes in the traditional ways some of these institutions handle
and apply various materials to the urban landscape in their daily maintenance and
operation activities, loads of various materials reaching the surface waters can probably
be reduced. For example, proper application of pesticides and herbicides and
minimizing their overspray will reduce the amount of these chemicals applied on the
vegetated and adjacent impervious surfaces. Also, the calibration of equipment to
minimize the rate of salt and other deicing chemicals being applied to road surfaces in
winter should also reduce the loads of these chemicals reaching the receiving waters
and groundwater when ice and snow melts. Other possible municipal practices that can
help reduce pollutant loads reaching the receiving waters could include the licensing
and training of pesticide and herbicide applicators; controls on how and where
commercial carpet cleaners dispose of their waste water; building codes requiring rain
covers over fueling pumps, mechanical maintenance areas, and chemical storage and
loading areas; and proper storage and handling of garbage disposal bins at food
7-13
-------
handling institutions such as restaurants and other commercial and industrial activities.
Intuitively, all of these can reduce the amount of pollutants applied to the urban
landscape. However, to what degree these practices actually reduce the amount of
various pollutants reaching the receiving waters, or if the quantities being reduced
actually make a difference to the water quality of the receiving waters, has yet to be
quantified. If only insignificant gains in receiving water are in fact possible, are all or
any of these practices remotely cost effective? These questions still need carefully
designed field studies to answer. One question that remains is how aggressively should
municipalities pursue such non-structural controls and practices before answers about
their effectiveness are in. Should the municipalities focus primarily on practices they
know work well for the site specific conditions of their community?
Public Education and Citizen Involvement Programs
The goal of public education according to those involved in the field is to modify
behavior. That is also the stated goal of US EPA (1993). To be effective, modifications
are needed in how a large majority of individuals use and dispose of fertilizers,
pesticides, herbicides, crankcase oil, antifreeze, old paint, grass clippings and many
other products that contain toxicants, nutrients or oxygen demanding substances. To
what degree and in what numbers changes in behavior can be achieved through public
education has yet to be answered.
The belief is that the more aggressive the education program, the more effective it
should be. This has to be questioned, since there probably is a point of diminishing
returns. Where that point is has yet to be determined and will probably be, to one
degree or another, a function of the economic, social, ethnic, educational and language
makeup of the population being targeted. For public education to work, the target public
has to care, or has to be convinced to care. Simple distribution of information through
mass media or through written materials is not likely to achieve widespread acceptance
of the message or results in terms of water quality improvements.
Walesh (1993, 1997) advocates a proactive public involvement program that goes
beyond public education, which tends to be one-way "communication," and instead
reaches for public involvement, which constitutes to two-way communication. Guiding
principles of these public involvement programs include:
A public interaction program, or lack thereof, is often the principal reason for
the successful implementation of an urban water program or the failure to
implement it.
The success of a public involvement program is determined more by the total
number of different "publics" that participate than by the told number of
individuals involved.
Essential to the success of a water management effort is agreement between
the public and the water professionals on what problems are to be prevented
7-14
-------
or mitigated.
In addition to public education and involvement efforts, communities need to have
programs in place that make it convenient for the public to dispose of unwanted
household products and toxicants. Disposal centers with easy access need to be in
place so the public can, in fact, follow through on what is being asked of them.
Street Sweeping, Leaf Pickup and Deicing Programs
Field tests by US EPA (1983) demonstrated that street sweeping reduced by very little
the concentrations of constituents reaching receiving waters. It may be possible,
however, that strategically scheduled sweepings at key periods of the year can reduce
constituent loads available for wash off by stormwater. For example, in the midwest,
sweeping in the fall and in late winter months can reduce the leaf litter and street
deicing products reaching receiving waters. With current technology, street sweeping is
most effective in picking up coarse sediment and litter, thus enhancing the aesthetics of
stormwater discharges.
Local Government Rules and Regulations
Well drafted ordinances, rules, regulations and criteria and their enforcement can
provide the basis for an effective stormwater management program especially in
providing structural BMPs and erosion and sediment control for new land development
and redevelopment. Such local ordinances, rules and regulations can help reduce
impacts of urban runoff from newly urbanizing lands by providing for and/or requiring:
1. Installation of structural BMPs as land develops or redevelops. This is less
expensive than retrofitting structural BMPs later.
2. Enforcement of site disturbance and erosion control programs.
3. Encouragement of the use of minimized DCIA in new development including
the use of landscaped areas, grass buffers, and roadside swales instead of
curb, gutter and storm sewer whenever site conditions and land uses permit.
4. Maintenance for publicly owned BMPs.
5. Enforcement of the operation and maintenance of privately owned stormwater
management facilities, including on-site structural BMPs and non-structural
measures.
Elimination of Illicit Discharges
Untreated wastewater discharged through illicit connections is a public health concern,
which justifies efforts to find and eliminate illicit wastewater connections. Illegal
dumping, however, because to its covert nature, is extremely difficult to control and
soliciting the help of the public to report suspicious or apparently illegal activities may be
one way for extending its effectiveness.
7-15
-------
Structural Best Management Practices: Design Considerations
Many factors influence the effectiveness of any structural stormwater BMP installation.
Although progress has been in understanding how some of these controls perform,
selecting, sizing, designing, operating and maintaining effective BMPsforthe purpose
they are intended to serve is still a challenge. Many BMPs are used without full
understanding of their limitations and their effectiveness under field conditions, which
often differs from regulatory expectations or modeled predictions. This is particularly
the case when addressing the effects of urbanization on the receiving waters.
What is a particular BMP supposed to address? Is it the removal of suspended solids,
or is it the removal of dissolved metals or is it the organic matter in the sediment that
can settle on the bottom and cause sediment oxygen demand on the water column?
Which of these or other "problems" is most important when selecting a single BMP or a
group of BMPs? For instance, recent bottom sediment studies reveal that these
sediments can have a significant benthic oxygen uptake and may be the cause of
oxygen sags and suppression of micro invertebrate populations in the receiving waters
(Cerco 1995, DiToro and Fitzpatric 1993). If that is the case, the removal of sediment
may be the primary reason for selecting the BMP instead of nutrients that have also
been linked to oxygen sags. Or should the selection of the BMP be driven by the need
to reduce flow rates and volumes of runoff from urbanizing areas? These and other
factors need to be considered in planning for maintenance and/or the restoration, or
determining the inability to attain a desired restoration level, and recommending a family
of BMPs for use in any given watershed.
Local Climate
As a first step, one needs to consider local climate. If the treatment control relies on a
"wet" condition for vegetation and biological processes, the site needs adequate
ambient precipitation throughout all seasons. In arid and semi-arid areas, such as the
southwest, such treatment controls are not practical unless supplemental water is
provided to make up for the evapotranspiration during dry seasons. Thus, when
assessing the effectiveness of structural controls, the suitability of the practice for the
local climate and meteorology must be considered.
Design Storm
The use of an appropriate design storm to size a facility is probably one of the most
important considerations. Often some designers and regulators believe that the bigger
the design storm the more effective the control facility will be. That often is far from the
truth. Controls designed to improve stormwater quality and to control downstream flow
rates need to be matched with the type of facility being used, local hydrology and the
receiving system needs. Use of an appropriate design hydrology to design each control
facility is assumed in developing the various assessments of BMPs that follow.
Nature of Pollutants
The nature of stormwater pollutants has to be considered when selecting and sizing
BMPs. Most BMPs are suited for the reduction in suspended solids and of the
dissolved fraction of constituents that attach to these particles. If, however, the removal
7-16
-------
of nutrients and dissolved constituents is the goal, the family of suitable BMPs is much
smaller. The concentration of a constituent in the water column has an effect on the
"efficiency" reported for the BMP. When high concentrations are present the BMP will
typically show higher percentages of removal than when low inflow concentrations are
encountered. For this reason, the reporting of effectiveness in terms of percent
removed has to be questioned. This is evident when the water quality of the effluent is
very good and the percent removal is low. This may be because the inflow
concentration of the constituent of concern is also low.
Figure 7-4 compares the "efficiency of removal" in percent to the actual effluent
concentrations for total phosphorous by a sand-peat filter as a function of influent
concentration for one set of field tests. Tests for other constituents at this same site
produce somewhat less definitive relationships, but a similar general trend was
observed. Figure 7-4 is probably one of the more dramatic illustrations of the fact that
the influent concentration affects the percent removal rate. It implies that a
mathematical relationship can be developed for this site. It may even be possible to
develop similar relationships for other BMPs and other sites, but that has yet to be
demonstrated with sufficient variety of field data. Although a similar form for such an
equation may possible, the regression coefficients are likely to differ for each
constituent, each BMP type and, possibly, for each site. Nevertheless assuming such a
relationship is possible, Figure 7-4 suggests a general form such as % Removed =
100*[1- (c/Cj)k], in which c and k are regression constants and C\ is the influent
concentration.
100.0
0.2
0.3 0.4 0.5 0.6
Influent Concentration, mg/l
0.7
0.8
Figure 7-4. Total phosphorous "percent removal efficiency" and effluent concentrations
for a peat-sand filter as a function of influent concentration. (Farnham and Noonan
1988).
7-17
-------
Based on the preceding discussion, the definition of effectiveness should be based on
more than "percent removal" of a constituent. It may be more appropriate to judge
effectiveness against ranges of realistic effluent concentrations or some other
parameter established by local watershed studies. It is not appropriate, however, to
base this judgment on water quality standard developed for continuous dry weather
flows, or on fixed percent removals of a constituent.
Often a community judges the "effectiveness" of a BMP by what other attributes it
possesses, or what uses, other than stormwater management, it offers to the
community. Thus, the incorporation of one or more other uses, namely multiple uses,
such as active and passive recreation, enhancing or protecting wildlife habitat, flood
control, and ground water recharge, into the BMPs design often is considered by the
local residents as an "effective" facility. In contrast, a single-purpose, well functioning
stormwater management facility sometimes is judged by its neighbors as a "nuisance."
Operation and Maintenance
Operation and maintenance practices, or lack thereof, can significantly influence the
actual effectiveness of structural BMPs. Most treatment controls do not require active
operation of mechanical or chemical systems equipment, but all need adequate
maintenance. Provision of such maintenance is assumed in the assessment
discussions that follow. Also assumed in these discussions is that appropriate soil
erosion controls are being vigorously practiced within the tributary catchment. If not,
even the best designs can be rendered inoperative because of large sediment loads
generated by uncontrolled construction sites.
On-Site or Regional Control
Another issue that needs to be considered is whether a BMP is used as an on-site or as
a regional control. Very large numbers of on-site controls, sometimes exceeding
several hundred or even several thousand, may be in place within any urban watershed.
Reliably quantifying their cumulative hydrologic impacts on receiving waters becomes
virtually impossible. Water quality, however, can be improved by both regional and on-
site controls.
The degree of improvement for the cumulative effect in numerous on-site controls is,
however, less predictable than with regional controls. This is because large numbers of
on-site controls seriously complicate the quality assurance efforts during their design
and construction. Large numbers of on-site controls are designed by a variety of
individuals, which are then constructed by a variety of different contractors under
varying degrees of quality control. Furthermore, very large numbers of BMPs will be
maintained and operated in a variety of ways that are virtually impossible to anticipate
or to effectively control.
Wiegand et al. (1989) estimated that regional controls are more cost effective because
fewer controls are less expensive to build and to maintain than a large number of on-
site controls. Regional controls can provide treatment for existing and new
developments and can capture runoff from public streets, which is often missed by
7-18
-------
many of the on-site controls (Urbonas and Stahre 1993).
The major disadvantage of regional stormwater controls, such as detention basins, is
that they require advanced watershed planning. Even when such a plan exists, the
necessary up-front financing may be out of phase with the land development that is
occurring in the watershed. Often the use of on-site controls is the only practical
institutional, financial and political alternative.
Structural Best Management Practices: Performance
A number of the most commonly used structural BMPs are discussed next. Each is
evaluated as to its effectiveness in addressing water quality, control of runoff volume
and ability to moderate runoff rates in the receiving system. Also, when appropriate,
some or all of the other points mentioned above are addressed.
Minimized Directly Connected Impervious Area
This practice has been around for a long time. However, up until recently it was
recognized or defined as a stormwater management practice. In fact, it has been
considered as inadequate and inappropriate for "good drainage" in urban areas. For
certain types of urban land uses this practice can be a very effective stormwater BMP.
Unfortunately there are no data to show how much the implementation of minimized
DCIA reduces surface runoff volumes, peaks and pollutant loads. The exact
performance of this practice depends on which types of components show on Figure 7-
2 are used at the site, the exact nature of the local geology, the type of soils and
vegetative cover, and the nature of local climate. Under ideal conditions, surface
stormwater runoff from low to medium density single family residential areas can be
virtually eliminated for small rainstorms (i.e., storms with less than 13 to 25 mm (0.5 to
1.0 inch) of rainfall).
On the whole, this is a very effective stormwater BMP for low to medium density
residential developments and for smaller commercial sites. Minimized DCIA is not a
very effective BMP for high density residential developments and high density
commercial zones, such as central business districts. This BMP demands that much of
the land area of the development have a pervious surface, free of buildings and solid
pavement. It may also not be appropriate for use when the general terrain grades are
steeper that six percent. With highly erodeable soils, minimized DCIA may require even
flatter terrain slopes.
This is one of the very few BMPs that, when used appropriately, can moderate the flow
effects of urbanization in receiving waters, especially from the smaller storms. Also, for
low to medium density developments, it can save on the cost of drainage systems and
could be cost effective because the cost of storm drainage systems are reduced. In
addition, with the use of stabilized shoulders, the surface area of pavement on public
streets can be less than is used for a traditional street cross-section, thereby saving on
initial construction and on its maintenance.
7-19
-------
If misused, minimized DCIA can result in many problems to local residents that are
often the result of poor drainage. Such problems include boggy mosquito breeding
areas, poor snow removal and hazardous roadside ditches. On steeper slopes, erosion
along some roadside and backyard swales has been observed. Also, property owners
have been observed paving and filling poor draining, eroding or deep swales fronting
their yards. Local policing and enforced preservation of the swales may be needed to
prevent their loss through actions of local residents. Such enforcement is not a
politically popular prospect for locally elected officials, especially if the citizens believe
they are eliminating a problem on their front lawn.
This practice not be used for industrial and commercial sites that may be susceptible to
spillage of soluble pollutants such as gasoline, oils, or solvents. The concern is
prevention of soil and groundwater contamination.
Grass Swales
Removal rates exceeding 80% of TSS by grass swales are suggested by Whallen and
Cullum (1988). Others suggest lower removal rates, on the order of 20 to 40%
(UD&FCD 1992). The higher rates suggested by Whallen and Cullum may be possible
when soils have very high infiltration rates and very slow flow velocities occur (i.e., less
than 0.15 m/s). Grass swales appear to be best suited when terrain slopes are less
than 3% to 4%, although some have suggested their use with terrain slopes as high as
6%. The limitations of site overlot grading during land development make the effective
use of swales at higher slopes not practical. The use of swales is an integral part of the
minimized DCIA practice.
The use of grass swales as stormwater collectors, instead of curb-and-gutter, slows the
runoff process and can, under certain site conditions, also reduce the volume of runoff.
Unless the swale is underlain by a clay layer, it is not recommended for use at industrial
and commercial sites that may be susceptible to spillage of soluble pollutants such as
gasoline, oils, and solvents for fear of soil and groundwater contamination.
Grass Buffer Strips
Grass buffer strips can remove larger particulates and promote local infiltration,
provided the flow is kept very shallow and slow. Under ideal conditions, removals of 10
to 20% of suspended solids have been suggested (UD&FCD 1992). Buffer strips are an
integral part of the minimized DCIA practice and are also an important part, of a number
of practices that act in combination with each other. Thus the use of grass buffer strips
is suggested whenever site conditions and land uses permit, upstream of swales,
infiltration, percolation, wetlands, retention, and detention type of BMPs.
The use of grass buffer strips can slow surface runoff and, under certain site conditions,
also reduce the volume of runoff, especially from small storms. Unless the grass buffer
strip is underlain by a clay layer, it is recommended that it not be used at industrial and
commercial sites that may be susceptible to spillage of soluble pollutants such as
gasoline, oils, and solvents for fear of soil and groundwater contamination.
7-20
-------
Porous Pavement
Field evidence indicates that properly designed modular pavement block porous
pavement may be the only form of porous pavement that has a proven long-term
successful performance record. This type of pavement has been in use since the mid-
1970's with very few reported problems (Day et al. 1981, Smith 1984, and Pratt 1990).
When porous pavement begins to clog, the simple removal and replacement of the soil
or sand media in the pavement's openings can return it to full function.
On the other hand, Schueler et al. (1991) and others have reported that monolithic
porous pavement surfaces tends to seal within one or two years after their installation.
Once sealed, return the pavement to an acceptable working level is virtually impossible
without total replacement of the pavement. Estimates of constituent removals for
modular porous pavement range from 65 to 95%, depending on the constituent being
monitored and the nature of local site and meteorological conditions.
The use of porous pavement can slow surface runoff and, under certain site conditions,
reduce the volume of runoff, especially from the smaller storms. Unless porous
pavement is underlain by an impermeable membrane and the stormwater is collected
by an underdrain for surface discharge or post-treatment, the use of porous pavement
not be considered for industrial and commercial sites that may be susceptible to spillage
of soluble pollutants such as gasoline, oils, and solvents, for fear of soil and
groundwater contamination.
Percolation Trenches
When properly operating, percolation trenches can remove up to 98% of the suspended
solids in the stormwater and many of the constituents that are associated with these
particulates. It has also been asserted that these facilities can also remove significant
faction of nutrients, metals and other constituents from surface runoff. However, there
is a concern that groundwater contamination may occur.
When operating, percolation trenches can reduce the volume of stormwater surface
runoff. In fact, they can virtually eliminate direct surface runoff from small storms (i.e.,
less than 13 to 25 mm (0.5 to 1.0 inches) of precipitation).
Schueler et al. (1991) report that about 50% of percolation trenches constructed in the
eastern U.S. have failed. He did not report on the nature and reason of these failures,
although clogging within the trench and of its infiltrating surfaces were suspected. Two
comprehensive field inspections, one in 1986 and the other in 1990, of percolation
trenches were performed by the State of Maryland (Pensyl and Clement 1987, Lindsey
et al., 1991). During the 1990 inspection of 88 percolation trenches, 51 % showed signs
of partial or major failure. Also reported was the fact that 31 % of those failures occurred
between 1986 and 1990. Although only 45% of installations reported a need for
sediment removal maintenance, the inspectors reported a high incidence of sediment
entering these trenches. Discussions with stormwater professionals working in the
eastern U.S. indicates that the failure rate may actually be higher in 1996 than was
originally reported by Schueler et al (1991) and Lindsey et al. (1991).
7-21
-------
It is possible to postulate from the inspectors' descriptions that clogging of percolation
trench surfaces and groundwater mounding are the two most likely contributors to the
reported failures. Groundwater mounding can develop under and around a percolation
trench, actually surfacing within the trench (Stahre and Urbonas 1990, Colorado Storm
Water Task Force 1990).
Clearly, the use of this practice should not be encouraged until sound engineering
design guidance is adopted, possibly similar to the methodology suggested by Urbonas
and Stahre (1993), including pre-filtration of stormwater before it enters a trench and the
use of a comprehensive groundwater hydrologic investigation during design.
Furthermore, percolation trenches should not be used at industrial and commercial sites
that may be susceptible to spillage of soluble pollutants such as gasoline, oils, and
solvents for fear of soil and groundwater contamination.
Infiltration Basins
Properly operating infiltration basins can remove anywhere from zero to as high as 70 to
98% of the pollutants found in stormwater, depending on the constituent and site
conditions. Also, when operating, infiltration basins can reduce the volume of
stormwater runoff and virtually eliminate direct surface runoff for small storms (i.e., less
than 0.25 to 0.5 inches of precipitation).
Two comprehensive field inspections, one in 1986 and the other in 1990, of infiltration
basins were performed by the State of Maryland (Pensyl and Clement 1987, Lindsey et
al. 1991). During the 1990 inspection, 73% of the 48 installations inspected were
judged as "failed." The inspectors reported that only 41 % of the inspected infiltration
basins needed sediment removal maintenance. From the inspectors' descriptions,
groundwater mounding appears to have contributed to some of the reported failures.
Their rate of failure implies a lack of sound engineering in their design and/or
construction. Lack of maintenance may have contributed to some of the reported
failures, but the findings by Lindsey et al. (1991) suggest that other factors were at work
in many of the reported failures.
This practice should not be encouraged until sound engineering design guidance is
adopted, possibly similar to the methodology suggested by Urbonas and Stahre (1993).
When operating properly, infiltration basins can reduce the volume of stormwater
surface runoff. In fact, they can virtually eliminate direct surface runoff from small
storms (i.e., less than 13 to 25 mm (0.5 to 1.0 inches) of precipitation).
Infiltration basins not be used for industrial and commercial sites that may be
susceptible to spillage of soluble pollutants such as gasoline, oils, and solvents for fear
of soil and groundwater contamination.
Media Filter Basins and Filter Inlets
Filters can be very effective BMPs where land area is at a premium, but they need
regular maintenance. When they are undersized or are left unmaintained, media filters
accumulate a layer of fine sediment on their surface and seal. Once clogged, a media
7-22
-------
filter drains at very slow rate and stormwater runoff either ponds upstream of the filter or
bypass it (Urbonas et al. 1996b). Either condition is unacceptable. In the first case the
ponding water may be a nuisance or create dangerous situations. In the latter, only a
fraction of the stormwater that arrives at the filter actually receives the treatment
efficiencies typically reported for sand filters.
To compensate for this potential problem, oversizing the filters or providing stormwater
capture detention volume upstream that is sized in balance with the filter's clogged flow-
through rate is necessary. Both approaches, that is, oversizing and upstream detention,
might be used. Oversizing the filter can also reduce the necessary frequency of
maintenance. Providing an extended detention basin for pretreatment is suggested by
Urbonas and Ruzzo (1986) and Chang et al. (1990). Field experience with designs that
have a full presettlement detention basin appear to have much longer life before the
filter surface requires cleaning and/or the media needs replacement.
Tests using media other than sand, such as peat, peat-sand mix, compost-sand mix
show them to clog faster than sand filters (Galli 1990, Stewart 1989). This means their
longevity at acceptable hydraulic flow through rates may be very poor and they may be
even less attractive and functional than filters using sand as the media for filtration.
When a media filter is located within an underground vault, such as a water quality inlet,
it is out-of-sight-and-out-of-mind and is likely to not receive the needed maintenance
attention of a visible surface facility. Regular inspection programs are a must if media
filters are used in order to assure their continued proper operation.
A media filter basin or inlet, without an upstream detention basin, has no effect on
stormwater runoff flow rates. As a result, these facilities have no potential for
attenuating increases of runoff rates from urban areas.
Sand filter inlets suggested by Shaver and Baldwin (1991), while effective, are
expensive to construct. Above ground filter basins are also significantly more expensive
to build than detention basins. It has been argued that media filters are most likely to be
used where land costs are very high. However, comparisons of filters, designed with
clogging and minimal maintenance in mind, to detention basins and retention ponds
revealed that the filters require similar land areas to construct as do detention basins. If
this is the case, as recent findings have suggested (Urbonas et al. 1996 b), the cost of
functional media filters may actually be more than detention basins. Also, based on the
analysis of various unit operations and filter clogging processes measured under
laboratory and field conditions, Urbonas (1997) suggested an engineering design and
analysis procedure for stormwater runoff sand filters. This procedure provides for
design and water quality performance by accounting for runoff probabilities, suspended
sediment loads in stormwater, volumes processed by the filter and volumes bypassing it
and the maintenance (i.e., cleaning) for the filter media.
Water Quality Inlets
Episodic evidence reported by a number of observers over a number of years and more
7-23
-------
recently confirmed by Schueler et al. (1991) through field tests, indicates poor
performance by water quality inlets (i.e., sand and oil and grease traps). These devices,
depending on their complexity, can be very expensive to construct and to maintain and
appear to offer very little water quality enhancement in return. Also, these devices
provide no peak flow or volume control capability. Additional, research and
development efforts are likely to occur in this area.
Swirl-Type Concentrators
Swirl concentrators are designed to process stormwater up to a stated design flow rate
and to by-pass flows that exceed this rate. When they work properly, swirl
concentrators can remove the heavier sediment particles and many of the floatables
found in stormwater. They have not been shown to be effective in the removal of
neutrally buoyant solids such as plastic bags, oils, greases or very small or light
suspended particles. Also, they have been known to perform below expectations for
larger and smaller flow rates than the specific design rate.
New commercial devices such as StormCeptor are currently being field tested and
objective results on their performance should begin to show up in literature within the
next two years. These devices can be expensive to construct and to maintain. Swirl
concentrators provide no peak flow or volume control capability unless they have a
detention basin upstream of them to equalize flows.
Extended Detention Basins
The performance of a relatively large number of extended detention basins have been
documented by field and laboratory tests. For example, removal rates for TSS range
from 10 to 90%, depending on the constituent being sampled, the geometry of the
installation, and the local climate. For properly sized and designed extended detention
basins, removal rates for TSS, lead and other undissolved constituents are only
somewhat less than observed for retention ponds and wetlands. Although
sedimentation is the main treatment process in these basins, other associated
processes are known, or are suspected, to be at work. These include flocculation,
agglomeration, ion exchange, adsorption, physical resuspension of particulates, and
solution.
According to Grizzard et al. (1986), to serve as a water quality enhancing BMP, a
detention basin needs to hold stormwater runoff for much longer periods of time than a
detention basin that is used for the purpose of controlling peak runoff rates. Thus the
term extended detention basin has been coined. For the smaller storms, namely the
storms that produce somewhere between the mean and the 90th percentile surface
runoff volumes, the minimum emptying time of the captured volume needs to be
between 24 to 48 hours (Grizzard et al. 1986, Urbonas et al. 1990, Urbonas and Stahre
1993). To be most effective for water quality enhancement and to mitigate some of the
effects of increased surface runoff from an urbanizing area, the longer of the suggested
drain times needs to be used with the larger design storm (i.e., probably exceeding 13
to 20 mm [0.5 to 0.75 inches] of precipitation) and the shorter drain times with the
smaller events (i.e., probably less than 13 mm [0.5 inches] of precipitation).
7-24
-------
Extended detention basins can be designed to control the flow rates from a wide range
of small to large storm runoff events. However, the most difficult storm events to control
are the small ones from small tributary areas. The outlet needed to throttle flows down
to very low levels needs to have very small openings, which are susceptible to clogging.
Control of the larger events is accomplished by the detention volumes that surcharge
the water quality extended detention volume. Also, an extended detention basin does
not reduce the volume of the runoff that enters it.
Retention Ponds
Hartigan (1989) stated that retention ponds can remove 40%-60% of phosphorus and
30%-40% of total nitrogen. Other studies show lesser annual removal rates. Studies in
Washington, DC area by Schueler and Galli (1992), indicate that the permanent pools
characteristic of retention ponds can act as heat sinks resulting in warm water releases
and, therefore, retention ponds may not be appropriate for use if they discharge to
streams that support trout. Often a retention pond is sized to remove nutrients and
dissolved constituents, while any pool that may be associated with an extended detention
basin is much smaller and is provided for aesthetics, namely, to cover the solids settling
areas with water.
The major features of a state-of-the-art design of a retention pond includes a permanent
pool and an emergent wetland vegetation bench called the littoral zone. The pond
provides a volume of water where the solids can settle out during the storm event (i.e.,
active sedimentation period) and during the periods between storms (i.e., quiescent
sedimentation period). Sedimentation can also remove that fraction of nutrients and
soluble pollutants that adhere to sediment particles. The littoral zone provides aquatic
habitat, enhances the removal of dissolved constituents through biochemical processes
and helps to minimize the formation of algae mats. Sometimes the pond has surcharge
detention storage volume above it that can be used for flood control and to enhance
sedimentation during storm runoff periods.
Retention ponds, on the average, can do a noticeably better job at the removal of
nutrients than extended detention basins. However, the reported variability in
performance ranges for retention ponds indicate that much remains to be learned about
their performance. This knowledge will be needed to develop a reliable design
guidance for nutrient removals. Nevertheless, the use of retention ponds appears to be
more effective than extended detention basins, filters, swirl concentrators, swales,
buffer strips, and other BMPs. A possible exception is constructed wetlands when
nutrient loading is of concern, namely for urban watersheds that are tributary to
reservoirs and lakes and to tidal embayments and estuaries.
For retention ponds to be effective in the removal of nutrients, the permanent pool has
to have two to seven times more volume than an extended detention basin (Hartigan
1989), depending on local meteorology and site conditions. As a result, more land area
is needed than is required for a detention basin and costs can be 50% to 150% higher
than for an extended detention. This increase may not be as significant if the pond has
7-25
-------
surcharge storage for drainage or flood control peak-shaving.
Retention ponds can be more aesthetic than extended detention basins because
sediment and debris accumulate within the permanent pool and are out-of-sight. Large
retention basins are sometimes used as property value amenities, sometimes permitting
surcharge in the "lake front" property cost. However, if the tributary area does not have
sufficient runoff during the year, detention ponds can dry out or become unsightly "bogs"
and become a nuisance to the adjacent property owners.
Thus, some of the issues to consider when choosing a retention pond are:
1. Can the tributary catchment sustain a sufficient base flow to maintain a
permanent pool?
2. Are the receiving waters immediately downstream particularly sensitive to
increased effluent water temperatures that can result from sun's warming of
the pond?
3. Do existing wetlands at the site restrict the design of the permanent pool of
the pond?
4. Are water rights available for the evapotranspiration losses in states with a prior
appropriation water rights laws?
Retention ponds can be designed to control the flow rates from a wide range of small to
large storm runoff events. As with extended detention basins, the most difficult storm
runoff events to control are the small ones, especially the ones from small tributary
catchments. The outlet needed to throttle flows down to very low levels needs to have
very small openings, which are susceptible to clogging. Control of the larger events is
accomplished by the detention volumes that surcharge above the permanent pool.
However, a retention pond does not appreciably reduce the volume of the runoff that
enters it.
Wetlands
Properly designed and operated wetlands, on the average, can remove significant
percentages of total phosphorous, nitrogen, TSS and other constituents from urban
stormwater runoff (Strecker et al. 1990). However, when compared statistically to other
BMPs, wetlands appear to remove most of the constituents found in stormwater to
about the same percentages that one can expect from extended detention basins and
retention ponds. The claim that wetland basins are more effective in the removal of
nutrients from stormwater is probably true for some installations, while other
installations appear to be less effective.
The ranges in the performance data reported for wetland basins tell us that much has to
be learned about how wetlands function and what constitutes a reliable design,
especially for nutrient removals. Well controlled field investigations are needed to
7-26
-------
identify which field conditions and design parameters produce consistently good
pollutant removals.
For example, Walesh (1986) describes the planning and design of a restored wetland in
series with a sedimentation pond intended to substantially reduce the transport of
suspeded solids and phosphorous into an urban lake. Oberts et al. (1989) presents the
results of a 29 month monitoring study of the system during which 19 rainfall and four
snowmelt events were monitored. Total phosphorous removals were at or above 50%
for rainfall events. The sedimentation pond-wetland system removed 90% the total
suspended solids for all monitored rainfall and snowmelt events. The successful
performance of the system, which, incidentally, exceeded the performance of four other
similar systems in the area, was attributed to several factors. For example, pre-settling
of stormwater runoff in the sedimentation pond prior to discharge into the restored
wetland is important. The volume of the permanent storage pool should be at least 2.5
times the runoff volume generated from the mean summer storm. The area of the
permanent pool in the sedimentation basin should be about two percent of the
impervious area of the watershed and the pool should have the maximum depth of over
four feet.
There are little data in literature on the performance of wetland channels. As a result,
current estimates of their effectiveness are speculation and educated guesses.
Extrapolations from limited data (Urbonas et al. 1993) suggest that properly sized and
designed wetland channels compare well with the performance of wetland basins for
nutrient removal during small storm runoff events and during dry weather flow periods.
Another claim found in the literature is that the removal of nutrients by wetlands
requires regular harvesting of wetland basins. This claim, however, does not appear to
be well substantiated by field data. In fact, the limited information that is available
shows regular harvesting to be of questionable value in increasing nutrient removal
rates. Mechanisms in addition to plant uptake appear to be responsible for nutrient
uptake in nutrient removals by wetlands.
The actual mechanisms for the removal of phosphorous and of nitrogen by wetlands are
probably different. Phosphorous removals are most likely associated with the removal
of solids, including ionic adhesion to solids and uptake of the dissolved fractions by
algae (i.e., eutrophication). When algae die, they are deposited on the bottom "muck"
or benthos, taking along some of the phosphorus with them. However, these benthal
deposits can release phosphorous under reducing conditions. Much of the
phosphorous in the benthos, however, becomes permanently trapped and unavailable
for release to the water column. Thus, the removal of the accumulated benthos (i.e.,
mucking out) has to take place occasionally to keep wetland basins and wetland
channels operating satisfactorily.
Although the removal of nitrogen is, in part, the byproduct of algae and other plant
uptake, nitrites and nitrates appear to be too mobile for effective removal rates by this
process alone. Aerobic and anaerobic denitrification appears to also take place within
7-27
-------
wetlands. This process takes place in wetlands used for the polishing of wastewater
treatment plant effluent, mostly in the root zones and on the biological film that is found
on all wetland plants and their roots. Much of the current wetland treatment technology
was developed for the treatment of wastewater (Nichols 1983, Kedlec and Hammer
1980) and has not had the benefit of the development for use under the vastly different
conditions that occur during wet weather conditions. However, even for the uniform flow
and loading conditions of a wastewater treatment plant, wetlands have a limit in how
much nutrient loading they can accumulate before degradation in performance is
experienced (Watson, et al. 1989). Much has yet to be learned about the actual bio-
chemical processes at work in wetlands, especially for the treatment of stormwater,
before it is possible to design them with confidence for stormwater treatment.
A wetland basin can be designed to control the flow rates from a substantial portion of
small storm runoff events and to also control the flow rates from most large storm runoff
events. The approach is to design them for the flow control function like one would
design a retention pond.
Wetland channels can help control the flow rates of the smaller runoff events, however
to a lesser degree than a wetland basin, an extended detention basin or a retention
pond. Wetland technology is emerging as a viable tool for stormwater management but
suffers from lack of prolonged field studies. Such studies are needed to answer
questions such as how different wetland design configurations respond to stormwater
loadings over an extended number of years when operating in the wide variety of
climates, geologic settings and meteorological conditions found in the U.S.
Summary on Best Management Practice Effectiveness
Non-Structural Best Management Practices
A quantified assessment of how much effect non-structural BMPs have on the receiving
water quality or the enhancement of its aquatic life has yet to be made. So far many
surrogate measures have been used in an attempt to quantify their effectiveness. For
example, the measure of gallons of oil recycled has been used to demonstrate how
"effective" this non-structural BMP is, but this does not in any way quantify the number
of gallons of oil this program eliminates from being transported to the receiving waters
by the stormwater system. In other words, a surrogate measure may or may not have
any relationship to the BMP's effectiveness in reducing any specific pollutant from
reaching the receiving waters or determining the impact on the receiving system.
Most of the suggested practices are supported by good intentions. For the most part
they are a collection of common sense practices and measures. This leads to the belief
that non-structural BMPs should provide a positive benefit when implemented and used,
but data are needed to quantify the costs and benefits. If nothing else, non-structural
BMPs should result in a cleaner looking urban landscape.
7-28
-------
Structural Best Management Practices
The Definition of Effectiveness
Much more field performance data are available for structural than for non-structural
BMPs. Table 7-2 summarizes the removal "efficiencies" of several structural BMPs
most frequently used in the U.S. The table includes the information found through
extensive literature reviews conducted for this report and by a Colorado task force
(Colorado Storm Water Task Force 1990) and the Denver, Co area Urban Drainage and
Flood Control District (UD&FCD 1992). What is of note are the wide ranges in the
reported percent removals. Despite that, when properly designed for local soil,
groundwater, climate and site geology, all BMPs will remove pollutants from stormwater
to some degree. What is in question is how much at any given site and for how long will
the BMP continue to function at those performance levels.
Table 7-2. BMP pollutant removal ranges in percent. (Bell et a I. 1996, Colorado Storm
Water Task Force, 1990, Harper & Herr 1992, Lakatos & McNemer 1987, Schueler
1987, Southwest 1995, Strecker et al. 1990, UD&FCD 1992, USGS 1986, US EPA
1983, Veenhuis et al. 1989, Whipple & Hunter 1981).
Type of Practice
Porous Pavement
Grass Buffer Strip
Grass Lined Swale
Infiltration Basin
Percolation Trench
Retention Pond
Extended Detention
Wetland Basin
Sand Filters (fraction
flowing through filter)
TSS
80-95
10-20
20-40
0-98
98
91
50-70
40-94
14-96
Total P
65
0-10
0-15
0-75
65-75
0-79
10-20
(-4)-90
5-92
Total N
75-85
0-10
0-15
0-70
60-70
0-80
10-20
21
(-129)-
84
Zinc
98
0-10
0-20
0-99
95-98
0-71
30-60
(-29)-82
10-98
Lead
80
n/a
n/a
0-99
n/a
9-95
75-90
27-94
60-80
BOD
80
n/a
n/a
0-90
90
0-69
n/a
18
60-80
Bacteria
n/a
n/a
n/a
75-98
98
n/a
50-90
n/a
n/a
Note: The above-reported removal rates represent a variety of site conditions and influent-effluent
concentration ranges. Use of the averages of these rates for any of the reported constituents as design
objectives for expected BMP performance or for its permit effluent conditions is not appropriate. Influent
concentrations, local climate, geology, meteorology and site-specific design details and storm event-
specific runoff conditions affect the performance of all BMPs.
The current definition of "effectiveness" in terms of percent removal is flawed, whether it
is defined as the reduction in concentration or as the load of a constituent removed from
stormwater runoff. A better measure needs to be developed to define how well a
specific structural BMP is performing. This point was illustrated earlier by the example
for the removal of phosphorous by a sand-peat filter. That example showed that the
"percent removal" increased with the concentration of phosphorous in the influent while
the concentrations in the effluent remained constant. As a result, "worst" performance
was attributed to the storm runoff that had the cleanest water entering the filter.
7-29
-------
Ironically, one can argue that a performance standard based on percent removals would
be met most frequently when the watershed was kept in the most unclean condition,
while the watershed with the best use of source controls would produce the worst
performance record for the filter. This, despite the fact the filter's effluent was identical
for both.
The nature of a redefined performance measure has yet to be determined. Such a
standard will most likely be tailored for each structural BMP. It will have to address
more than one question since the purpose for the selection and use of each BMP will
vary with the local goals and objectives. As an example, is the BMP needed primarily to
remove floating trash and sediment or is the removal of phosphorous or nitrogen the
main goal, or is it the mitigation of increased runoff rates or volumes the main reason for
the selection of the BMP? These and other, yet to be identified questions and issues
will need to be addressed when developing a new "effectiveness" matrix for each BMP
and its design.
Research and Design Technology Development Needs
While much is known about the performance of some of the discussed BMPs, such as
retention ponds and extended detention basins, much more must be learned. For some
BMPs, insight into their pollutant removal mechanism and characteristics is just
beginning. For some areas of the U.S. there may even be sufficient information to
relate BMP performance to a set of design parameters such as the size and
imperviousness of the tributary watershed. This does not deny the fact that all BMPs
can still benefit from well conceived and well controlled prolonged field studies.
An approach towards a systematic approach for performing field evaluations of BMPs
was suggested by Urbonas (1995). Although there appears to be a significant number
of BMP tests in the U.S. and other countries, what is lacking is a consistent scientific
approach and the reporting of key design and tributary watershed parameters for the
BMPs being tested. As a result of the data acquisition approach suggested by Urbonas,
the American Society of Civil Engineers and the USEPA in 1996 entered into a
cooperative agreement to define the data and information needs for such studies, to
develop a data base software package for field investigators to use, to find and extract
existing data on BMP performance, and to complete an initial evaluation of such data by
the end of 1999.
To have significance, and to identify issues that arise over the near term, field
investigations of BMPs probably need at least five years of data gathering, otherwise
important performance information is likely to be missed. For some BMPs, performance
is affected by maintenance and/or operations. For others, the maintenance needs will
not become apparent for several years and prolonged testing is the only way to answer
the question of how their performance will vary over time. Yet for other BMPs,
performance may change over time. Such information will be needed to decide if and
when such BMPs will need to be replaced or rehabilitated. Only when such information
and much field performance data are available, are fully analyzed, and reliable
relationships between performance and design parameters are quantified, will
7-30
-------
practitioners be in a position to design BMPs with performance expectations in mind. At
this point there are too many unanswered questions on how to design BMPs for a
stated performance level, whatever it may yet turn out to be. Among the questions that
need to be answered are what kind of operations and maintenance are needed to
provide the desired level of performance, what are the life cycle costs, and will they
provide the desired results in the receiving waters for which they were selected or
minimize the impacts of urbanization on those receiving waters?
Design Robustness
Robustness of BMP design technology is a factor that integrates what is known today
about design. Robustness needs to be recognized when judging various BMPs for use.
High robustness of design technology implies that, when all of the design parameters
are correctly defined and quantified, the design has a high probability of performing as
intended. In other words, the design technology is well established and has undergone
the test of time. Low robustness implies that there are many uncertainties in how the
design will perform over time. All facilities are assumed to be properly operated and
maintained when judging design robustness.
Table 7-3 is an edited version of the collective opinion of many senior professional
engineers involved in the development of the 1998 WEF & ASCE manual of practice for
the selection and design of stormwater quality controls. The differences between this
table and Table 5.6 of the MOP are based on further evaluation of the issues
considered during the assessments at the time the MOP was being prepared. The
weakest design link actually governs the overall design robustness of each BMP.
Runoff Impacts Mitigation
The emerging theme in the environmental community is the need for stormwater
surface runoff flow control in urban and urbanizing areas. This concept has a long
history of study and discussion in stormwater engineering literature. Changes in
surface runoff hydrology with urbanization have been discussed by the engineering
community now for over 20 years (McCuen 1974, Hardtand Surges 1976, Urbonas
1979, Glidden 1981, Urbonas 1983, Walesh 1989). The challenge until now has been
to control the peak runoff rates for drainage and flood control purposes. This focus led
to the control of peaks from larger storms such as the 5-, 10- or/and the 100-year flow
rates. Use of on-site and regional detention became popular in some areas of the U.S.
7-31
-------
Table 7-3. An assessment of design robustness technology for BMPs1.
BMP Type
Swale
Buffer (filter) strip (2)
Infiltration basin (2)
Percolation trench
Extended detention (dry)
Retention pond (wet)
Wetland
Media filter
Oil separator
Catch basin inserts
Monolithic porous pavement
(2)
Modular porous pavement
(2)
Hydraulic
Design
High
Low-
Moderate
Low-High
Low-
Moderate
High
High
Moderate-
High
Low-
Moderate
Low-
Moderate
Uncertain
Low-
Moderate
Moderate-
High
Removal of Constituents in
Stormwater
TSS/Solids
Low-
Moderate
Low-
Moderate
High
High
Moderate-
High
High
Moderate-
High
Moderate-
High
Low
n/a
Moderate-
High
Moderate-
High
Dissolved
None-Low
None-Low
Moderate-
High
Moderate-
High
None-Low
Low-Moderate
Low-Moderate
None-Low
None-Low
n/a
Low-High (3)
Low-High (3)
Overall
Design
Robustness
Low
Low
Low-
Moderate
Low-
Moderate
Moderate-
High
Moderate-
High
Moderate
Low-
Moderate
Low
n/a
Low
Low-
Moderate
Notes:
1) Weakest design aspect, hydraulic or constituent removal, governs overall design robustness.
2) Robustness is site-specific and very much maintenance dependent.
3) Low-to-moderate whenever designed with an underdrain and not intended for infiltration.
4) Moderate-to-high when site conditions permit infiltration.
and Canada. In the early 1970s the State of Maryland was the first to require the
control of the two-year peak flow rate for the stated purpose of controlling stream
widening and erosion that were observed to take place after urbanization. However,
Maryland acknowledges that the success of these requirements was well below
expectations.
What is clear is that scientifically untested policies have little chance of success, despite
their good intentions. They can lead to waste of resources and provide little or no
environmental benefit, especially when applied through regulatory mandates. A better
approach would be to develop long term field test beds before nationwide requirements
7-32
-------
or guidance on runoff flow controls are promulgated. Too much variety in community
needs, ecological integrity protection, fiscal resources, physical settings of the receiving
waters, climates, and geology exist throughout the U.S. to suggest a generic
methodology. These type of decisions best rest at the specific watershed level and the
state in which it is located.
The current demand by some for runoff flow controls has to be approached very
carefully, lest resource (primarily in the form of land area and urban sprawl)
consumption occurs without the commensurate environmental return. It is also possible
to set up policies that physically cannot be met, such as "no increase in surface runoff
volume." Although some sites, under certain rainfall regimes, may be able to meet this
standard after urbanization, this is probably not a realistic expectation at all sites, at all
times.
Some of the BMPs discussed here can provide peak runoff rate mitigation. Others can
provide mitigation of surface runoff peak rates and of runoff volume increases. None
can totally eliminate the effects of urbanization. The most promising candidates for
mitigating peak flow rates are the ones that capture runoff volume and release it over an
extended period of time. These include retention ponds with extended detention
surcharge volume over their permanent pool, extended detention basins, wetland
basins and any other BMP that captures and slowly releases surface runoff.
Runoff volume reduction is much more difficult to achieve. Some of the BMPs
discussed here can do so whenever site conditions permit. Trying to use such BMPs
for volume reduction proposed under unfavorable site conditions is not only unwise, it is
a gross denial of reality and physical limitations of the practices and the site conditions.
For instance, these practices have only a limited potential for volume reduction when
the development site is very steep, or has very tight or highly erosive soils, or is located
in a region that cannot support a healthy and robust vegetative ground cover.
Nevertheless, each of the BMPs is rated in the next section for their potential ability to
reduce surface runoff flow rates and volumes.
Summary of the Usability of the Evaluated BMPs
Table 7-4 was designed to consolidate the foregoing discussion. It contains ranking
scores from 1 through 5, with 5 being the score for the highest positive aspect and (-5)
indicating the highest negative aspect of each BMP. As an example, potential for failure
is considered to be a negative aspect, while the potential for mitigating the increases in
surface runoff volume is considered a positive aspect. The rankings are based not only
on what is reported in the literature, but also are based on experience in stormwater
management. Clearly, the scores are somewhat subjective and further discussion and
study are needed.
At any rate, the composite average rating scores reveal a ranking that integrates all of
the aspects discussed and considered so far. Note the groupings of the BMPs. All
ratings were ranked from one through 16 and then were segregated into five groups,
7-33
-------
Table 7-4. Summary assessment of structural BMP effectiveness potential.
Structural BMP Type
Minimized DCIA (2)
Extended Detention Basin
Retention Pond (3)
Wetland Basin (3)
Porous Pavement:
Modular w/ Underdrain
Infiltration Basin (2)
Wetland Channel (3)
Porous Pavement:
Modular w/ Infiltration (2)
Media Filter
Percolation Trench (2)
Grass Swale (2)
Grass Buffer Strip
(Grass Filter Strip) (3)
Swirl-type Concentrator
Dry Well (2)
Porous Pavement:
Monolithic(2)
Water Quality Inlet
"S
a
CH
rt (U
ง o
S 3
^13
S 2
3
4
4
4
5
5
4
5
3
3
3
3
2
3
3
2
"3
g
a
o
O
f
Q '1
^3 3
bp .5
Sn hS
1
3
3
2
5
2
2
5
5
4
1
1
4
4
3
3
Design
Technology
Robustness
O
CS
d
^p
d
a
cS
o
bo
"o
PH
4
4
4
4
4
3
4
4
3
3
3
2
3
2
2
3
>-.
s
a
J-H
ta
Cง
4
4
4
3
3
4
2
4
4
4
1
1
2
2
3
1
B
u
H
ซ
1 ง
PH hS
-1
-3
-4
-3
-2
-1
-2
-2
-2
-1
-2
-1
-2
-1
-3
-1
a3
CS
d
3
S
^o '-g
'% 'a
"S o
p i C^
-3
-2
-2
-2
-2
-4
-2
-4
-1
-5
-2
-2
-1
-5
-4
-1
bo
a
a
s
^H
o
u
bo
t-H
1)
>
<1
1.09
0.97
0.97
0.85
0.70
0.64
0.58
0.61
0.27
0.09
0.09
0.09
0.03
-0.09
-0.18
-0.36
bo
a
^H
t-H
o gp
,V i-H
PH
-------
four with positive average ratings and one with negative ratings. The BMPs with the
best average ratings were put into Group 1 and those with the lowest ratings into Group
5. These five groupings are as follows:
Group 1: Minimized Directly Connected Impervious Area
Extended Detention Basin
Retention Pond
Wetland Basin
Group 2: Modular Porous Pavement With an Underdrain
Infiltration Basin
Wetland Channels
Group 3: Modular Porous Pavement With Infiltration
Media Filter
Group 4: Percolation Trench
Grass Swale
Grass Buffer (Filter) Strip
Swirl Concentrator
Group 5: Dry Well
Monolithic Porous Pavement
Water Quality Inlets
Stormwater Systems of the Future
Stormwater management in urban centers of the U.S. is in the process of
metamorphosis. The shift is away from rapid disposal of surface runoff. Instead
governing bodies are looking at urban Stormwater runoff impacts on the receiving
waters and how to minimize these impacts to a "maximum extent practicable."
Urbanization affects the environment, including the nature and quality of the receiving
waters. This inescapable fact is driven by population growth. Although some believe
that such impacts can be eliminated, the laws of conservation of space, matter and
energy consign challenge such beliefs. Therefore, society has to find ways to make
wise and cost effective choices to minimize the impact of population growth and its
resultant urbanization on the receiving waters. Too ambitious a program can have
profound economic impacts on the public and can become economically and politically
self defeating. At the same time, doing nothing can have a profound detrimental effect
on the receiving waters that also translates to harsh economic impacts on the local
public as well.
As much as some may wish it was not so, barring major natural disasters continued
urban growth has to be assumed as a given. How Stormwater runoff from this growth is
managed will define how urban centers will evolve in the next century. The challenge is
to find systems and their components that both serve the environment and the needs of
7-35
-------
the urban communities to the maximum practicable level desired by the U.S. Congress,
the individual states and the local municipal populations. Doing this requires learning
how to moderate impacts of urbanization on each receiving system as it relates to the
local geography, geology and climate, realizing that all impacts cannot be eliminated.
At the same time, the systems should not have draconian impacts on urbanization, a
natural effect of population growth. With these thoughts as background, the following
ideas are offered as possible stormwater management systems of the future.
Use of Combined Wastewater and Storm Sewer Systems
Some have suggested the return to the use of combined wastewater and stormwater
systems, that is CSS. The suggestions range from complete coverage of all new urban
areas by such systems to the limiting of their use to only high density commercial and
industrial areas. Most of these suggestions include detention elements to modulate flow
rates into such systems and to limit the size of the conveyance sewers and treatment
works. Such systems would result in the first flush of larger storms and all runoff from
smaller storms being captured and treated through publicly owned wastewater
treatment plants before release to the receiving systems. Much of the stormwater
entering headwater streams would be diverted to such systems, thus reducing the
impacts of increased stormwater runoff into these streams.
On the other hand, these systems would have occasional combined sewer overflows.
In the process of diverting stormwater runoff from the headwater streams, other
hydrologic changes will likely occur, such as groundwater depletion and reduced base
flows in perennial streams. The biggest drawback to these systems is the cost of their
construction, operation, and maintenance. Much bigger sewers would be needed to
transport stormwater to a treatment plant, even with detention, than are needed to
deliver stormwater to the nearest receiving waterway. The treatment plant also needs
much greater capacity to handle the 10 to 30 percent of the days during any given year
when wet weather flows actually occur. Combined systems need a much higher level of
maintenance than separate sewer and storm sewer systems. Also, these systems will
require an increased use of non renewable resources (i.e., electric power, petroleum
based fuels and chemicals) to treat stormwater. Whether these added costs are
justified will depend on site specific conditions such as the receiving waters and the
impacts on them that are being mitigated, the community's size and economic strength.
With the foregoing in mind one scenario for a stormwater system of the future would
consist of a hybrid system, one that serves part of the urban area with a combined
wastewater and separate stormwater system and the remaining part with a separate
stormwater system. More specifically it would consist of the following:
1. The use of good housekeeping, and non-structural BMPs, is well
established and practiced, with especially strong emphasis on control of
illegal and illicit discharges of contaminants and the control of erosion during
construction.
7-36
-------
2. Major facility needs of the stormwater management system would be based
on a watershed, or sub-watershed level master planning process. The
community would be involved in the process.
3. The process would account for future growth, drainage system and other
infrastructure needs of the community and integrate all of these with
community needs such as open space, recreation, jobs, and transportation.
Impacts, growth trends, costs, maintenance needs, benefits and other
issues and needs would be identified and, when possible, quantified.
4. Use of the minimized DCIA elements wherever practicable and possible in
residential areas and commercial parts of the community and in areas such
as parks, golf courses, playgrounds, playing fields, churches, and recreation
centers.
5. An extensive use of surface infiltration and flow retardance elements such
as grass buffers, swales, porous pavement, and infiltration basins when site
geology and site conditions permit.
6. Extensive use of on site or regional extended detention basins, retention
ponds and/or wetland basins for all urbanizing areas, whether connected or
not, to the CSS.
7. Sized to capture a water quality volume to also help mitigate increases in
surface runoff from small events.
8. When the drainage system and public safety requires, provide for a
surcharge flood control detention above the water quality capture volume.
9. All high density commercial areas, gasoline stations, other commercial
areas subject to surface contamination by chemicals or high concentrations
of nutrients, and industrial areas subject to chemical surface contamination
be connected to a combined sewer system.
10. All connections to the CSS would be made through water quality capture
volume basins.
11. All releases from the water quality capture basins connected to the CSS
would be controlled by an intelligent real-time flow management system
designed to meet the conveyance and the treatment plant system's
capacities.
Use of Separate Stormwater Systems
Use of a hybrid combined wastewater and stormwater system may not be the best or
practical option for the majority of communities in U.S. As discussed earlier, these
7-37
-------
systems are likely to be more expensive, in terms of life cycle costs, to build and
operate than two separate systems, one for wastewater and the other for stormwater.
When a hybrid combined system is not a cost effective or practical solution, what is left
is a separate stormwater management system that uses various management and land
use development practices to control stormwater runoff quality and quantity as close to
the source as practicable. The goal of an ideal separate stormwater management
system of the future would be to select stormwater management components that best
mitigate the impacts of urbanization on the receiving waters for the community in a most
practical and cost effective manner. Similar to the hybrid combined system, a separate
stormwater system of the future would capture the first flush of larger storms and all
runoff volume from smaller storms. The captured volume would receive passive
treatment by the BMP before stormwater is released to the receiving systems within or
downstream of the community. Such a system could significantly reduce the impacts of
increased stormwater runoff and its contaminants on these receiving waters.
With the foregoing, a possible scenario for a stormwater system of the future is as
follows:
1. The use of good housekeeping, non-structural BMPs, is well established and
practiced, with especially strong emphasis on illegal and illicit discharges of
contaminants and the control of erosion during construction.
2. Major facility needs of the stormwater management system would be based
on a watershed, or sub-watershed level master planning process. The
community would be involved in the process. The process would account for
future growth, drainage system needs and other compatible use needs of the
community. Impacts, growth trends, costs, maintenance needs, benefits, and
other issues and needs would be identified and, when possible, quantified.
3. Use of minimized DCIA elements wherever practicable and possible in
residential areas and areas such as parks, golf courses, playgrounds, playing
fields, and recreation centers.
4. An extensive use of surface infiltration and flow retardance elements such as
grass buffers, swales, porous pavement, and infiltration basins when site
geology and site conditions permit.
5. Extensive use of on site or regional extended detention basins, retention
ponds and/or wetland basins for all urbanizing areas.
Sized to capture a water quality volume and to also help mitigate
increases in surface runoff from small events.
When the drainage system and public safety requires, provides for a
7-38
-------
surcharge flood control detention above the water quality capture volume.
6. All high density commercial areas, gasoline stations, other commercial areas
subject to surface contamination by chemicals or high concentrations of
nutrients, and industrial areas subject to chemical surface contamination be
addressed on a site-by-site basis to reduce stormwater runoff flow rates and
contaminants to maximum extent practicable. Some of these sites may need
special treatment measures for the pollutants being generated on the site
such as special media filters, and chemical additives.
All runoff from the areas subject to contamination be routed through water
quality capture volume basins. These basins may need to be oversized if
the pollutants are of major concern for environmental and public health
protection.
All such water quality capture basins would be occasionally audited for
compliance to insure that the needed operation and maintenance is being
provided. Also, occasional grab samples of the effluent would be taken
and tested by their owners.
Closing Remarks
This chapter discusses many issues that relate to BMPs and what is known about their
effectiveness in stormwater management. Much of this discussion is based on a
plethora of information that is "supported" by a number of local field investigations
designed to test a given BMP's "effectiveness" at the specific site. Still needed is a
national approach, similar to NURP, that would systematize a large number of
investigation into a cohesive, well controlled, program to learn about various BMP
functions, physical mechanisms, biochemistry, and design parameters.
Also needed is a better measure of "effectiveness. The current measure in terms of
"percent pollutant removal" has no sound technical basis. This is the case whether the
effectiveness is measured in term of constituent load reductions or in terms of reduction
in concentrations. Lack of a sound definition can lead to findings that may appear to be
inconsistent and non-transferable, when in truth, the differences may not be that large if
a better measure of effectiveness is used. Another area of need is improving on the
design robustness for various BMPs. Until that is done, expecting a specific
performance from any given BMPs is unrealistic. Design robustness should improve as
more is learned about what design parameters are most important when selecting,
sizing and designing each type of BMP.
Urban stormwater management has to consider the safety and welfare of the citizens
living in urban areas. Issues of efficient site drainage, control of nuisances caused by
inadequate drainage, hazards posed by large storm events and the floods they create,
and cost and benefits received for the expenditure of public dollars have to be
considered along with stormwater quality and impact on the receiving water quality,
7-39
-------
integrity and biology. As a result, sound stormwater management has to address not
only runoff impact mitigation associated with urbanization, but also the public and
community needs as well
The preceding discussion summarizes the potential usability of BMPs. All of this is
based on information in need of enrichment. Nevertheless, it should provide a basis for
understanding the current BMP state of-of-practice and state-of-the-art and,
accordingly, serve as a guide for planners and engineers.
7-40
-------
References
Anderson, D.L., R.L. Siegrist, and R.J. Otis (undated). Technology Assessment of
Intermittent Sand Filters. Office of Research and Development. Environmental
Protection Agency. Cincinnati, OH.
Bell, W., L, Stokes, L.J. Gavan, and T. Nguyen (1996). Assessment of the Pollutant
Removal Efficiencies of Delaware Sand Filter BMPs. City of Alexandria, Department of
Transportation and Environmental Services. Alexandria, VA.
Cerco, C.F. (1995). Response of Chesapeake Bay to nutrient load reductions. Journal
of Environmental Engineering. Vol. 121, No. 8.
Chang, G.C., J.H., Parrish, C. Soeur, and A.S. Librach (1990). Removal Efficiencies of
Stormwater Control Structures. Dept. of Environmental and Conservation Services. City
of Austin, TX.
City of Austin (1988). Environmental Criteria Manual. Environmental and Conservation
Services. Austin, TX.
Colorado Storm Water Task Force (1990). BMP Practices Assessment for the
Development of Colorado's Stormwater Management Program. Final Report to
Colorado Water Quality Control Division. Denver CO.
Day, G.E., D.R. Smith, and J. Bowers (1981). Runoff and Pollution Characteristics of
Concrete Grid Pavements. Bulletin 135, Virginia Water Resources Research Center.
Blacksburg, VA.
DiToro, D.M. and J.J. Fitzpatric (1993). Chesapeake Bay Sediment Flux Model.
Prepared for U.S. Environmental Protection Agency and U.S. Corps of Engineers
Baltimore District.
Driscoll, E.D., G.E., Palhegyi, E.W. Strecker, and P.E. Shelley (1989). Analysis of
Storm Events Characteristics for Selected Rainfall Gauges Throughout the United
States. U.S. Environmental Protection Agency. Washington, DC.
Farnham, R.S. and T. Noonan (1988). An Evaluation of Secondary Treatment of
Stormwater Inflows to Como Lake, MN Using A Peat-Sand Filter. EPA Proj. S-005660-
02. Environmental Protection Agency. Chicago, IL.
Galli, J. (1990). Peat-Sand Filters: A Proposed Stormwater Management Practice for
Urbanized Areas. Metropolitan Washington Council of Governments. Washington, DC.
7-41
-------
Glidden, M.W. (1981). The Effects of Stormwater Detention Policies on Peak Flows in
Major Drainageways. Master of Science Thesis. Dept. of Civil Engineering. University
of Colorado at Denver. Denver, CO.
Grizzard, T.J., C.W., Randall, B.L. Weand, and K.L. Ellis (1986). Effectiveness of
extended detention ponds. Urban Runoff Quality - Impact and Quality Enhancement
Technology. Urbonas, B.R. and Roesner, L.A., Editors. American Society of Civil
Engineers.
Guo, J.C.Y. and B. Urbonas (1996). Maximized detention volume determined by runoff
capture ratio. J. Water Resources Planning and Management. Vol. 122, No. 1, p. 33-
39.
Hall, M.H., D.L. Hockin, and J.B. Ellis (1993). The Design of Flood Storage Reservoirs.
Butterworth Heineman, London.
Hardt, R.A. and S.J. Surges (1976). Some Consequences of Area Wide Runoff Control
Strategies in Urban Watersheds. Technical Release No. 48. Charles W. Harris
Hydraulics Laboratory. University of Washington. Seattle, WA.
Harper, H. and J. Herr (1992). Treatment Efficiencies of Detention with Filtration
Systems. Environmental Research and Design, Inc. Orlando, FL. 164pp.
Hartigan, J.P. (1989). Basis for design of wet detention basin BMPs. Design of Urban
Runoff Quality Controls. American Society of Civil Engineers. New York, NY, p. 122-
144.
Heaney, J.P. and L.T. Wright (1997). On integrating continuous simulation and
statistical methods for evaluating urban stormwater systems. Modeling the
Management of Stormwater Impacts. W. James, editor. Computational Hydraulics
International. Guelph, Ontario, Canada, p.44-76.
Kedlec, R.H. and D.E. Hammer (1980). Wetland Utilization for Management of
Community Wastewater. 1979 Operations Summary, Houghton Lake Water Treatment
Project. NTISPB80-170061.
Lakatos, D.F. and L.J. Mcnemer(1987). Wetlands and Stormwater Pollution
Management. Wetland Hydrology. Proceedings of the National Wetland Symposium.
Chicago, IL.
Lindsey, G., L. Roberts, and W. Page (1991). Stormwater Management Infiltration
Practices in Maryland: A Second Survey. Maryland Dept. of the Environment.
Baltimore, MD.
7-42
-------
Livingston, E. H., et al (1988). The Florida Development Manual: A Guide to Sound
Land and Water Management. Department of Environmental Regulation. Tallahassee,
FL.
McCuen, R.H. (1974). A regional approach to urban stormwater detention.
Geophysical Research Letters. 74-128, p. 321-322. American Geophysical Union.
Washington, DC.
Neufeld, C.Y. (1996). An investigation of Different Media for Filtration of Stormwater.
Masters Thesis. Department of Civil Engineering. University of Colorado at Denver,
CO.
Nichols, D.S. (1983). Capacity of wetlands to remove nutrients from wastewater.
Journal of Water Pollution Control Federation. Vol. 55, No. 5. Pp. 495-505.
Oberts, G.L., P.J. Wotzka, and J.A. Hartsoe (1989). The Water Quality Performance of
Select Urban Runoff Treatment Systems. Metropolitan Council of the Twin Cities Area.
St. Paul, MN. June.
Pensyl, K. and P.F. Clement (1987). Results of the State of Maryland Infiltration
Practices Survey. Sediment and Stormwater Div. Maryland Dept. of the Environment.
Baltimore, MD.
Pitt, R., M., Liburn, S. Nix, S.R. Durrans, and S. Burian (1997). Guidance Manual for
Integrated Wet Weather Flow (WWF) Collection and Treatment Systems for Newly
Urbanized Areas (New WWF Systems). Report prepared for U.S. Environmental
Protection Agency. Risk Reduction Engineering Laboratory. Office of Research and
Development. Cincinnati, OH.
Pratt, C.J. (1990). Permeable pavement for stormwater quality enhancement. Urban
Stormwater Quality Enhancement. American Society of Civil Engineers. New York,
NY. p. 131-155.
Roesner, L.A., H.E. Burgess, and J.A. Aldrich (1991). The hydrology of urban runoff
quality management. Proceedings of a Water Resources Planning and Management
Conference. American Society of Civil Engineers. New Orleans, LA.
Roesner, L.A., B.R. Urbonas, and M.B. Sonnen, Editors (1989). Design of Urban
Runoff Quality Controls. American Society of Civil Engineers.
Schueler, T. (1987). Controlling Urban Runoff: A Practical Manual for Planning and
Designing Urban BMPs. Metropolitan Washington Council of Governments.
Washington, D.C.
7-43
-------
Schueler, T.R. and J. Galli (1992). The Environmental Impact of Stormwater Ponds.
Effects of Urban Runoff on Receiving Systems. American Society of Civil Engineers.
Schueler, T.R., P.A. Cumble, and M.A. Heraty (1991). Current Assessment of Urban
Best Management Practices: Techniques for Reducing Non-point Source Pollution in
the Coastal Zones. (Review Draft). Metropolitan Washington Council of Governments.
Washington, D.C.
Shaver, E. and R. Baldwin (1991). Sand Filter Design for Water Quality Treatment.
Delaware Department of Natural Resources and Environmental Control. Dover, DE.
Smith, D.R. (1984). Evaluation of concrete grid pavements in United States.
Proceedings Second Conference on Concrete Block Paving. Delft, Australia. Society
of Civil Engineering.
South Florida Water Management District. Technical Publication 88-9. West Palm
Besch, FL.
Southwest Florida Water Management District (1995). Proceedings of the 4th Biennial
Stormwater Research Conference. Southwest Florida Water Management District
(editor and publisher). Brooksville, FL.
Stahre, P. and B. Urbonas (1990). Stormwater Detention for Drainage, Water Quality
and CSO Management. Prentice Hall. Englewood Cliffs, NJ.
Stewart, W. (1989). Evaluation and full-scale testing of a compost biofilter for
Stormwater runoff treatment. Presented at the Annual Conference of the Pacific
Northwest Pollution Control Association. Seattle, WA.
Strecker, E.W., G.E. Palhegyi, and E.D. Driscoll (1990). The use of wetlands for control
of urban runoff pollution in USA. Proceedings of the Fifth International Conference on
Urban Storm Drainage. Osaka, Japan.
Truong, H.V., C.R., Burrell, M.S. Phua, and R.D. Dallas (1993). Application of
Washington DC Sand Filter for Urban Runoff Control. District of Columbia
Environmental Regulation Administration. Washington, DC.
Urban Drainage & Flood Control District (1992). Urban Storm Drainage Criteria Manual:
Volume 3 - Best Management Practices. Denver, CO.
Urbonas, B. and P. Stahre (1993). Stormwater - Best Management Practices and
Detention. Prentice Hall. Englewood Cliffs, NJ.
7-44
-------
Urbonas, B., L.A., Roesner, and J.C.Y. Guo (1996a). Hydrology for Optimal Sizing of
Urban Runoff Treatment Control Systems. Water Quality International, International
Association for Water Quality. London, England.
Urbonas, B.R. (1979). Reliability of design storms in modeling. Proceedings,
International Symposium on Urban Storm Runoff Modeling. University of Kentucky.
Lexington, KY.
Urbonas, B.R. (1983). Potential effectiveness of detention policies. Southwest Urban
Stormwater Symposium. Texas A &M. Austin, TX.
Urbonas, B.R. (1995). Recommended parameters to report with BMP monitoring data.
J. Water Resources Planning and Management. Vol. 121, No. 1, pp. 23-34.
Urbonas, B.R. (1997). Hydraulic design of sand filters for stormwater quality. Flood
Hazard News. Denver, CO.
Urbonas, B.R., and W. Ruzzo (1986). Standardization of detention pond design for
phosphorus removal. Urban Runoff Pollution. NATO ASI Series Vol. G10. Springer-
Verlag, Berlin.
Urbonas, B.R., J. Doerfer, and L.S. Tucker (1996b). Stormwater sand filters: a solution
or a problem? APWA Reporter. May Issue. Washington DC.
Urbonas, B.R., C.Y. Guo, and L.S. Tucker (1990). Optimization of stormwater quality
capture volume. Urban Stormwater Quality Enhancement. American Society of Civil
Engineers.
Urbonas, B.R., B. Vang, and J. Carlson (1993). Joint pond-wetland system
performance in Colorado. Water Policy and Management: Solving the Problems.
Proceedings of the 21st Annual Conference of the Water Resources Planning and
Management Division. The American Society of Civil Engineers. New York, NY.
US EPA (1983). Results of the Nationwide Urban Runoff Program. Final Report. U.S.
Environmental Protection Agency. NTIS Access No. PB84-18552. Washington DC.
USGS (1986). Constituent Load Changes in Urban Stormwater Runoff Routed Through
a Detention Pond - Wetland System in Central Florida. Water Resources Investigation
85-4310. U.S. Geological Survey. Tallahassee, Fl.
Veenhuis, J., J. Parish, and M. Jennings (1989). Monitoring and design of stormwater
control basins. Design of Urban Runoff Quality Controls. American Society of Civil
Engineers. New York, NY.
7-45
-------
Walesh, S.G. (1986). Case studies of need-based quality-quantity control projects.
Proceedings of Urban Runoff Quality-Impact and Quality Enhancement Technology. An
Engineering Foundation Conference. American Society of Civil Engineers. New York,
NY.
Walesh, S.G. (1997). DAD (decide-announce-defend) is out, POP (public owns project)
is in. Water Resources Education Training and Practice: Opportunities for the Next
Century. American Water Resources Association. Keystone, CO. June 1997.
Walesh, S.G. (1993). Interaction with the public and government officials in urban water
planning. Hydropolis - The Role of Water in Urban Planning. Proceedings of the
International UNESCO-IMP Workshop. Wageningen, The Netherlands and Emscher
Region, Germany. March-April.
Walesh, S.G. (1989). The hydrologic cycle in the urban environment. Chapter 2 in
Urban Surface Water Management. John Wiley and Sons. New York, NY.
Wanielista, M.P., Y.A., Yousef, H.H. Harper, and C.L. Cassagnol (1981). Detention with
effluent for stormwater management. Proceedings of the 2nd International Conference
of Urban Stormwater Management. Urbana, IL.
Watson, T.J., S.C., Reed, R.C., Kadlec, R.L. Knight and A.E. Whitehouse (1989).
Performance Expectation and Loading Rates for Constructed Wetlands. Constructed
Wetlands for Wastewater Treatment: Municipal, Industrial, and Agricultural. Lewis,
Chelsea, Ml.
WEF & ASCE (1998). Urban Runoff Quality Management. Water Environment
Federation Manual of Practice No. 23 and American Society of Civil Engineers Manual
and Report on Engineering Practice No. 87. WEF. Alexandria, VA. ASCE. Reston,
VA.
Whallen, P.J. and M.G. Cullum (1988). An Assessment of Urban Land Use: Stormwater
Runoff Quality Relationships and Treatment Efficiencies of Selected Stormwater
Management Systems.
Whipple, W. and J.V. Hunter (1981). Settleability of urban runoff pollution. Journal,
Water Pollution Control Federation. Vol. 53, No. 12, pp. 1726-1731.
Wiegand, C., T. Schueler, W., Chittenden, and D. Jellick (1989). Cost of urban quality
controls. Design of Urban Runoff Quality Controls. American Society of Civil
Engineers. New York, NY.
7-46
-------
Chapters
Stormwater Storage-Treatment-Reuse Systems
James P. Heaney, Len Wright, and David Sample
Introduction
The overall effectiveness of a variety of stormwater BMP's was evaluated in Chapter 7.
Two other aspects of control of stormwater: high-rate treatment and the potential
effectiveness of using stormwater for supplemental irrigation are described in this
chapter.
Stormwater Treatment
Because of the dynamic nature of stormwater flows and water quality, most control
systems are a hybrid of temporary storage and high-rate treatment. For a given level of
stormwater control, the engineer can accomplish this objective using various
combinations of storage and treatment. Much has been written on this subject and
methods for finding the optimal combination of storage and treatment have been
developed. Heaney and Wright (1997) provide a summary of these methods. Several
unresolved issues remain with regard to evaluating the performance of these treatment
systems.
Effect of Initial Concentration
As pointed out in Chapter 7, the effect of initial concentration on the performance of wet-
weather controls should not be ignored. A high percent removal for a control will usually
occur if the initial concentration is high. Separate and combined stormwater flows
exhibit wide variability from storm to storm as well as within a given storm. The effect of
initial concentration on performance can be evaluated directly by finding the order of the
reaction as well as the rate constant (Heaney and Wright 1997).
Effect of Change of Storage
Another complication in dealing with treatment of wet-weather flows is that the control
units are typically filling and emptying during and following the storm. Thus, it is vital to
properly measure the change in storage at short time intervals to incorporate this
important factor. The effect of changing storage is captured in the calculated detention
time for each parcel of water.
Effect of Mixing Regime
Another critical assumption is the type of mixing that takes place in the treatment
reactor. Two limiting cases are plug flow wherein the parcels simply queue through the
reactor and complete mixing wherein the incoming parcel instantaneously mixes with
the water already in the reactor.
8-1
-------
Effect of Nature of the Suspended Solids
The nature of the suspended solids changes during the storm and can vary widely. The
solids can range over several orders of magnitude from coarse solids to fine colloids.
Pisano and Brombach (1996) present a summary of efforts to date to characterize wet-
weather solids.
Essential Features of Future Wet-Weather Control Facilities
Given the large variability in the quantity and quality of wet-weather flows and the filling
and emptying of treatment reactors, direct monitoring of the wet-weather inflows and the
status of the control units is of fundamental importance. Unfortunately, few such
systems have been built in the United States. The Europeans are more advanced in
trying to evaluate and optimize wet-weather control systems.
High-Rate Operation of Wastewater Treatment Plants
High-rate operation of WWTPs during and following wet-weather events is an important
option to evaluate as part of the overall stormwater management program for combined
and for separate systems that are affected by I/I. It is possible to model the expected
performance of these systems using the GPS-X WWTP software from Hydromantis,
Inc., or similar programs, to do continuous simulation of the effect of wet-weather flows
on DWF treatment plants. Mangeot (1996) performed a preliminary feasibility study
using GPS-X to evaluate the Boulder WWTP during the 1995 high-flow year. High-
rate operation of the WWTP during these wet periods and periods with high I/I due to
seasonably high groundwater tables appears to be a very attractive option to consider.
Not much research has been done on this problem and there are only a few literature
citations on results of attempting to model the dynamics of WWTP operation during high
flow periods. Some questions remain regarding the ability of GPS-X to properly handle
the hydraulics associated with wet-weather flows. However, it is possible to show with
direct measurements for the Boulder WWTP, that the plant is capable of operating
effectively over a wide range of influent flows and concentrations. Because the influent
is already so dilute, caution should be exercised in requiring a specified percent removal
under these wet-weather conditions.
Stormwater Reuse Systems
Introduction
At present, there is much interest in local management of stormwater from smaller,
more frequent events. The primary on-site option is to encourage infiltration of
stormwater from roofs, driveways, parking lots, and streets. This infiltrated water
increases the moisture in the unsaturated zone and raises the groundwater table which
can provide benefits in terms of increasing base flows in streams and providing storm
water to help meet the ET needs of the local vegetation. Higher groundwater levels can
have negative effects on basements and on sanitary and combined sewers. This
section explores the possibility of the reuse of urban stormwater for irrigation water
which is a major component of urban water use.
8-2
-------
Previous Studies
As water supplies become more stressed, water conservation and reuse become more
attractive options. Wastewater disposal costs also encourage more water reuse.
Asano and Levine (1996) provide a historical perspective and explore current issues in
wastewater reclamation, recycling, and reuse, and outline requirements of a stormwater
and wastewater reuse feasibility study. Lejano et al. (1992) summarize the benefits of
water reuse as the following:
1. Water supply related:
a. Supplements regional water supply, eliminating need to develop additional
supplies.
b. Provides more reliability than the usual supply and is less affected by
weather.
c. Provides a locally controlled supply, reducing dependence on state or
regional politics.
d. Avoids the operating costs of water treatment and delivery.
e. Eliminates social and environmental impacts of diverting water from
natural drainageways.
f. Eliminates impacts of constructing large-scale water storage and
transmission facilities.
2. Wastewater related:
a. Avoids the capital and operating costs of disposal facilities.
b. Avoids the costs of advanced treatment facilities needed to meet state and
federal discharge requirements.
Urban wet weather flow management needs to be viewed within the context of overall
urban water management. Such an integrated framework was proposed in the late
1960s and is regaining favor in the mid-1990s. Changes in urban water use are
occurring because of aggressive water conservation practices which will significantly
reduce indoor and outdoor water use.
As discussed in Chapter 3, per capita indoor residential water use is very stable at an
average of 60 gpcd. Aggressive hardware changes such as low flush toilets should
reduce this usage rate to 35-40 gpcd. Only a small proportion of this indoor waste is
black water. Most of it is graywater that could be reused on-site for lawn watering and
other non-potable purposes. Peak water use in most cities is heavily influenced by
urban lawn watering. This outdoor water use does not require potable quality. As the
cost of water treatment continues to increase, dual water systems become more of a
possibility, particularly with a decentralized infrastructure.
California has been a focal point of reuse activity for some time. Ashcraft and Hoover
(1991) found that reclaimed water in southern California is selling at prices ranging from
$303/ac-ft to $366/ac-ft, with costs of operation and maintenance of treatment facilities
running from $10/ac-ft to $95/ac-ft. The authors argue that "avoided costs," such as
8-3
-------
those associated with wastewater disposal should be included in cost calculations.
Mallory and Boland (1970) developed a hydrologic and economic optimization model of
a stormwater reuse system in a new town in Maryland. Their system used a network of
subdivision level detention ponds. Subpotable reuse required a dual distribution system
to deliver it to households. They found that the net capital cost of such a system
(scaled up to 1998 dollars) was $560/dwelling unit for a potable reuse system, and
$1175/dwelling unit for the subpotable system. This compares favorably with
$950/dwelling unit for a conventional system, the differential of 23% premium for
subpotable reuse due mainly to the dual distribution system. When pollution control
costs are included for stormwater quality, an additional cost of $640/dwelling unit was
calculated, making the investment in the subpotable system more attractive.
Requa et al. (1991) developed a wastewater reuse cost model for screening purposes
in northern California. More recently, Tselentis and Alexopoulou (1996) describe a
feasibility study of effluent reuse in the Athens, Greece metropolitan area. Uses
considered were: crop irrigation, irrigation of forested areas, industrial water supply and
domestic non-potable use. The most cost-effective scenario was distribution for crop
irrigation near the route of the current discharge point.
At the other extreme, Haarhoff and Van der Merwe (1996) describe direct potable reuse
of reclaimed wastewater in Windhoek, Namibia. Law (1996) describes the Rouse Hill
project in Sydney, Australia, in which a dual non-potable distribution system was
installed in a new community in 1994. Oron (1996) developed an integrative economic
model, arguing that the optimal cost of a reuse system is a function of treatment
method, cost of treatment, transportation and storage costs (pipelines and tanks),
environmental costs, and the selling price of reused wastewater. New initiatives for
reusing stormwater flows for urban residential and industrial water supply systems in
Australia were described by Anderson (1996a, 1996b).
Mitchell, Mein, and McMahon (1996) used a water budget approach to integrate storage
and reuse of urban stormwater and treated wastewaters for two neighborhoods in
suburban Melbourne, Australia. The authors developed an urban water balance model
to determine the impact of stormwater and wastewater reuse; and suggest its
application at a number of scales. They determined that water demand from reservoirs
in Australia could be halved through the use of this resource.
Nelen, DeRidder, and Hartman (1996) described the planning of a new development for
about 10,000 people in Ede, Netherlands that considers a dual water supply system.
Storing the treated wastewater on-site during wet weather periods can be more
attractive than only using black water for reuse (Pruel, 1996). Herrmann and Hase
(1996) described rainwater utilization systems in Bavaria, Germany that save drinking
water and reduce roof run-off to the sewerage system. The impact of urbanization on
the hydrological cycle of a new development near Tokyo, Japan was performed by
Imbe, Ohta, and Takano (1996).
8-4
-------
Much of this work has focused upon using treated wastewater from a single effluent
plant. The problem then becomes one of finding demand centers for the wastewater
that are typically located quite some distance away. This becomes a nonlinear form of
the transhipment problem, in which demand and distance are cost drivers in a nonlinear
objective function.
Many researchers have started to focus on less centralized systems, including
Tchobanoglous and Angelakis (1996). Decentralized systems can take advantage of the
segregation between wet weather flow, graywater, and blackwater, and possibly utilize
less contaminated waters closer to their points or origin. Of the three, stormwater runoff
is usually the least contaminated prior to central collection. This may avoid construction
of additional treatment systems, pipelines, and other infrastructure and present
significant cost savings.
From the wet weather flow quality management perspective, there is much interest in
local management of wet weather flow from smaller, more frequent events, as these
events tend to have more pollutants associated with them. The primary on-site option is
to encourage infiltration of this stormwater flow from roofs, driveways, parking lots, and
streets.
Herrmann et al. (1996) found that rainwater utilization (using roof runoff water directed
into a storage tank) could provide from 30-50% of total water consumption of a
residence and reduce heavy metals (in stormwater runoff not reused) by 5-25%.
Wanielista (1993) developed design curves in order to determine the storage retention
volumes necessary to achieve given proportions of reuse. The design curves are based
on a daily water-balance model. The main objectives for this practice in the State of
Florida are the costs avoided of using municipal or pumped groundwater for irrigation
purposes. From the regulatory viewpoint, the main objective is to discharge some of the
stormwater onto the land and thereby get credit for 100% removal of this pollutant
source.
Field (1993) did a cost-effectiveness study of the reuse of urban stormwater to meet a
variety of differing demands for a hypothetical urban area. The proposed uses varied
in their water quality needs, as did the corresponding treatment system designated for
that use. Nowakowska-Blaszcyzyk and Zakrzewski (1996) project increases in
suspended solids, nitrates, COD, BOD, and lead from rainfall routed through the
following sources: roofing, parking areas, streets, storm sewers, infiltration through
lawns, and infiltration through sand. The lowest values tended to be from roof runoff.
Karpiscak, Foster, and Schmidt (1990) detail the application of stormwater and
graywater reuse techniques at a single residence in Tucson, AZ.
Harrison (1993) developed a spreadsheet model to estimate the amount of stormwater
captured in a detention pond that could be reused for irrigation in Florida. His work is
an application of earlier work by Harper (1991). The Southwest Florida Water
8-5
-------
Management District is interested in stormwater reuse as a way of increasing the
treatment efficiency of detention systems. Their current design calls for storing the first
inch of runoff and draining the pond over a five-day period. They are considering going
to an average residence time of 14 days to improve performance from removal rates of
50 to 70 % with a five-day drawdown time. Reusing stormwater would give them a
100% treatment efficiency.
Harrison (1993) uses a daily water budget to estimate the amount of captured urban
runoff that could be used for irrigation. The basic storage equation is:
= R + P + F-RU-D-ET Equation8.1
dt
where
= the change in storage.
R = runoff volume.
P = direct precipitation onto the pond.
F = water inflow through sides and bottom of the pond which can be negative.
RU =reuse volume.
D = pond outflow.
ET= pond evapotranspiration.
Harrison assumes that there is no net subsurface flow into or out of the pond, i.e., F = 0.
All values are converted into inches over the equivalent impervious drainage area. A
daily time step is used. A minimum precipitation volume of .04 inches is assumed to be
needed to produce runoff. This method is identical to the STORM-type calculations
with the exception that STORM uses an hourly time step and, in this case, outflows
occur either by reuse or direct discharge of the excess water. Harrison does not
indicate what he assumed for a pond drawdown rate in addition to the irrigation release.
The final results are expressed as a production function showing the percent of the
irrigation demand that is satisfied for various combinations of pond size and irrigation
reuse rates. The primary purpose of the stormwater reuse study in Florida was to
minimize the pond outflow and thereby achieve increased pollutant removal efficiency
by infiltrating the water locally. Lawn watering was more of a by-product.
Courtney (1997) explored the potential effectiveness of stormwater runon systems for
meeting irrigation needs in Boulder, CO. She used an hourly simulation model that
mimicked the operating policy of the University of Colorado's automatic irrigation
system. The overall imperviousness of the campus is about 60% so there is ample
opportunity for infiltrating some of this storm water. The results of this study indicate
that, while much of the stormwater can be infiltrated, it is unclear how much of this water
will ultimately be used to satisfy ET. During and immediately following the storm, the ET
8-6
-------
needs have already been satisfied. Without detailed concurrent groundwater and soil
moisture monitoring data, it is not possible to estimate the longer term fate of this
captured stormwater. If this stormwater could be directed to local or regional storage
ponds, it could be reused later for irrigation. Some of this reuse already happens on the
University of Colorado at Boulder campus because some of the stormwater drains to
the local irrigation ponds.
Estimating the Demand for Urban Irrigation Water
Urban Water Budgets
One of the most prevalent themes advanced in the recent literature in stormwater
management is to limit the generation of runoff from urban areas through the use of
BMPs and on-site control of stormwater particularly in frequent small storm events
(Mitchell et al. 1996). This section evaluates residential on-site control.
Butler and Parkinson (1997) suggest that reuse of the stormwater resource provides for
a more sustainable urban drainage infrastructure by minimizing available stormwater
that could possibly be mixed with wastewater; as well as attempting to minimize the use
of expensive drinking water for irrigation purposes. Pitt et al. (1996) suggests that
residential stormwater (i.e. roofs and driveways, not streets) generally has the least
amount of contamination and advocates infiltration of residential stormwater as a means
of disposal with few environmental impacts.
In keeping with this theme, a possible model of a residential on-site control system is
shown in Figure 8-1. Precipitation falls on roofs and driveways and is channeled, with
some losses, into a storage tank. The storage tank varies in size depending upon the
location. Water is taken from the tank for irrigation of landscape surfaces; some is used
for evapotranspiration, some is lost to infiltration, and some is lost to runoff. In essence,
this model is an irrigation, or water deficit demand, model.
Oarage
= 400 sf.
rEvaporation,Runoff Loss*
Lfrom Impervious Area
Rainfall Input
Roof
- 1500 sf.
'
Storage TanN
= Variable Size
Landscaping
= 5000 Sf.
Irrigation
Driveway
= BOO sf.
Figure 8-1. Concept of stormwater reuse residential storage system.
8-7
-------
Irrigation demand is determined mainly from ET requirements. In order to calculate ET, daily or
monthly water budgeting is performed. By examining the water balance of one residential parcel
in differing climatic zones, the efficacy of the option of on site reuse of stormwater can be
evaluated across the U.S. This section introduces the reader to climatic water balance models,
and existing databases for use with these models, develops a parcel level storage/demand
analysis using the results from the climatic model and compares results regionally across the
U.S.
Water Budget Concepts
The early efforts by Thornthwaite (1948) may have been the first work in climatology in
which, by an analytical method, differing characteristics such as rainfall, temperature,
and the number of daylight hours in a day were combined to yield regional climatic
projections. The number of daylight hours in a day are a function of the latitude of the
location, whereas monthly precipitation and temperature are functions of the climate of
the location. Average monthly precipitation in the U.S. varies widely with location, as
can be seen in Figure 8-2. For example, in comparing the rainfall signature of San
Francisco, CA with Memphis, TN, San Francisco has dry summers and wet winters;
whereas Memphis appears to have wet springs, with some precipitation falling in every
month of the year. Extreme monthly precipitation is also shown in Figure 8-2. San
Francisco appears to have much less variability than Memphis.
The Thornthwaite method keeps track of precipitation, calculated potential
evapotranspiration (PET), and calculated actual ET on a daily or monthly basis,
calculating water deficit, water surplus, soil moisture recharge, and soil moisture
utilization by integrating areas under the plotted curves. The graphical representation of
this process is a water budget, examples of which are plotted in Figure 8-3, compiled
from Mather (1978).
For example, for San Francisco, in January, the precipitation far exceeds the PET (and
ET, at this point they are equal). Up until mid February, the soil moisture is being
recharged. This occurs until soil moisture capacity is reached, then the rest of the
rainfall exceeding PET is surplus (and available for runoff). For San Francisco, the
annual surplus is about 4.3 inches. When PET exceeds rainfall (and is greater than ET)
in April through October, there are two integrals of importance; the area between PET
and ET is the water deficit, or 10.1 inches, and the area between ET and precipitation is
what is being drawn from the soil moisture storage. Then, in October, when
precipitation exceeds PET, the area between the precipitation curve and PET goes to
soil moisture recharge. The annual total PET for San Francisco is 26.6 inches, ET is
16.6 inches, and precipitation is 20.8 inches. Memphis, also shown in Figure 8-3, has
an annual total PET of 39.2 inches, ET of 32.5 inches, precipitation of 45.8 inches, a
water deficit of 6.7 inches, and a surplus of 13.2 inches. It is readily apparent that the
climate, and the subsequent irrigation needs for each location, are significantly different.
8-8
-------
MONTHLY PRECIPmON
MEANS AMD EXTREMES
Figure 8-2. Monthly precipitation for selected stations in the U.S., means and extremes (USGS 1970).
8-9
-------
Precipitation
r-
^^ Potential Evaportranspiration
1 1 Actual Evaportranspiration
| | Water Deficiency
|| | | || Water Surplus
|/XX| Soil Moisture utilization
Soil Moisture Recharge
I I I I I I I I I I I
JFMAMJJASOHDJ
J FMAMJJASOHOJ
J FMAMJJASOHD
" I I I I I I I I I I I I
J FMAMJJASOHDJ
Figure 8-3. Water budgets for selected stations in the U.S. (Mather 1978).
8-10
-------
Methods of Analysis
The Thornthwaite and Mather temperature based method (Thornthwaite 1948, Mather
1957, and Willmott 1977) was used to calculate monthly PET, projected ET, water
deficit, water surplus, and runoff (for undeveloped areas). Other methods, developed
later, require more information, such as net radiation measurements, wind speed, or
humidity. Such methods are usually found to be more accurate in arid areas (Yates
1996). An even better approach to the daily water balance model is suggested by
Vorosmarty et al. (1996) and explained in detail in Vorosmarty et al. (1989, 1991). This
work is a continuation of the work of Mather and Thornthwaite at the University of
Delaware.
In the work in this section, the Thornthwaite (or other temperature or radiation based
PET model) is used as above, but the soil moisture term is actually modeled as well as
the PET. The result is a series of coupled differential equations that are solved by a
Runge Kutta algorithm. The input data then reduced to soil and vegetation type. The
Thornthwaite method was chosen for this analysis because of the simplicity of the
algorithm, as well as the availability of both monthly and daily precipitation and
temperature data. Daily data are available for most locations from the National Climatic
Data Center.
The water budget procedure is presented in Table 8-1 and graphically in Figure 8-4 for
San Francisco, CA. The reader may use the table to follow along the calculations step
by step. The mean precipitation, mean temperature, and mean PET (for comparative
purposes) are input parameters, and can be found in rows 10, 11, and 29, respectively.
The first step is the calculation of the Julian Day Number. This was done by starting
with the number 15 and adding 30 to each successive month in row 12. Next, the
geodesic variables are calculated by the following formula:
0 = 27^Latitude]/360 Equation 8.2
and
<5=.4093sin[(27r/365y-1.405] Equation 8.3
where platitude in radians in Equation 8.2, <5also in radians, is the earth-sun
declination angle in Equation 8.3, and J is the Julian day number (e.g., December
31 =365). These formulas are used in rows 12 and 13. Next the following term is
calculated:
cos = arccos[- tan 0tan S[ Equation 8.4
using the terms calculated above. cos is the sunset hour angle in radians (Equation 8.4).
This is calculated for each month in row 15. Next, the total day length in hours is
calculated in Equation 8.5 as follows:
N, = 24cos/7t Equation 8.5
8-11
-------
Table 8-1. Water budget calculations for San Francisco, CA.
8
9
10
11
12
13
15
16
17
18
19
20
21
22
73
24
25
76
77
28
79
30
31
32
33
C
Meteoroloaical variable
Davs in month
Mean Precipitation, mm
Mean Temperature, mm
Julian Dav Number
delta, radians
Omegas, radians
Ni, hours
I
alpha
Thornthwaite Model:
Thornthwaite PET, mm
P-PET. mm
Storaaei mm
Chanae in storaae. mm
Calculated ET, mm
Water Deficit, mm
Water Surplus, mm
Runoff, mm
P-ET, mm
Measured PET, mm
nitial Storaae. mm
Storaae Maximum, mm
Error, mm
% error
D
Jan
31
lie
10.4
15
-0.37
1.26
9.64
3.03
1.39
30
86
15C
60
30
0
26
26
86
31
90
15C
1
E
Feb
28
93
11.7
45
-0.24
1.38
10.53
3.62
1.39
35
58
150
0
35
0
58
58
58
35
0
F
Mar
31
74
12.6
75
-0 05
1.53
11.72
4.05
1 39
48
26
150
0
48
0
26
26
26
49
1
G
Aor
30
37
13.2
105
0.16
1.70
12.96
4.35
1.39
55
-18
133
-17
54
1
0
0
-17
59
4
H
Mav
31
16
14.1
135
0.33
1.84
14.02
4.80
1.39
67
-51
94
-39
55
13
0
0
-39
70
3
I
Jun
30
4
15.1
165
0.41
1.91
14.60
5.33
1.39
75
-71
59
-35
39
35
0
0
-35
78
3
J
Jul
31
0
14.9
19E
0.38
1.89
14.41
5.22
1.39
75
-75
36
-73
23
52
0
0
-23
79
4
K
Aua
31
1
15.2
22E
026
1.77
13.56
5.38
1.39
72
-71
22
-14
15
58
0
0
-14
77
5
L
Seo
30
6
16.7
25E
0.06
1.62
12.38
6.21
1.39
73
-67
14
-a
14
59
0
0
-E
75
2
M
Oct
31
23
16.3
28E
-O.V
1.46
11.14
5.98
1.39
65
-42
11
-4
27
39
0
0
-4
66
1
N
Nov
30
51
14.1
31 E
-0.31
1.32
10.05
4.80
1.39
47
4
15
4
47
0
0
0
4
48
1
O
Dec
31
10E
11.4
34E
-0 4C
1.23
9.43
3.48
1.39
34
74
89
74
34
C
C
C
74
35
1
P
Sum (mm)
36E
52ฃ
57.50
677
-148
92^
-1
42C
256
10ฃ
10ฃ
70S
26
3.68%
Q
Sum (inches)
20.8
26.6
-5.8
364
O.C
16.6
10.1
4.3
4 3
27.6
'Thornthwaite PET, mm
Precipitation
'Calculated ET
Water Deficit
Water Surplus
Soil Moisture Utilization
Soil Moisture Recharge
i
Figure 8-4. Water budget for San Francisco, CA.
8-12
-------
and is shown in row 16. Then the following parameters are calculated in Equations 8.6
and 8.7:
Equation 8.6
oc= (6.75* 1(T7)/3 -(7.71 * 1(T5)/2 + (1.79*l(T2)+.49 Equation 8.7
where n= number of months (or days) in question. These are calculated in rows 17 and
18, the sum of / is calculated by adding all the values of / for the previous 12 months
shown in row 17 and is shown in cell P17 . Since T (temperature) can be negative, in
those cases, / and PET are set to zero. / represents an annual heat index for the area
in question. Then, actual values for potential evapotranspiration, PET, storage, S,
evapotranspiration, Et, and undeveloped runoff, R are calculated using the Equation
8.8:
PET, = 16fJ2
101
Equation 8.8
where fl = the fraction of the number of days in the month / divided by the average days
N-
in a month, 30; and /2 =-, the fraction of the number of hours in a day divided by the
base of 12 hours in a day. This is calculated in row 20. Next, the soil moisture storage
is calculated. This is not to be confused with tank storage, which will be calculated
later. The soil moisture storage is modeled as an offline reservoir that leaks when the
soil moisture field capacity is reached. Equations 8.9 and 8.10 compute storage in
month / as follows:
if Pt > /^(surplus condition) Equation 8.9
St = St_, exp
(PET, - P,
*Jmo^
if P, < PET, (deficit condition) Equation 8.10
in which S, is the soil moisture storage term for month /, P, is precipitation term for month
/, and Smax is the maximum storage availability found in cell D31. The initial storage
term for month 0 is found in cell D30. The calculated S, for each month is found in row
22. The change in storage, or AS = S, - S,^ is calculated in row 23. Next, actual
evapotranspiration is calculated by Equations 8.11 and 8.12:
Et, = PET, if Pt > PET, Equation 8.11
Et,=P,+8,^-8, \iP,
-------
and can be found in row 24. Finally, runoff is computed by Equation 8.13,
R = Pi-Eti-AS Equation 8.13
and is shown in row 27. In cases in which R<0, runoff is then set to zero.
The parameters for which the least amount of information is usually available are the
initial storage term (when /=1) and the maximum soil moisture storage. In this case, an
equal Smax of 150 mm was used and the initial storage term was determined by using
the calculated S, for December (and iterating if necessary). Water deficit was calculated
by subtracting the estimated ET from the calculated PET in months in which PET
exceeds rainfall (otherwise there is no deficit). This is shown in row 25. Water surplus
was calculated by Equation 8.14:
SUt =Pt- PETi - AS,, if Pt > PET, Equation 8.14
and is shown in row 26. The percent error is calculated by taking the absolute value of
the difference between the calculated PET and measured PET, summing for the 12
months, and dividing by the sum of the measured PET for 12 months, and is shown in
cell P33. For San Francisco, the error is 3.68%, indicating that there is a reasonably
good fit with the Thornthwaite model.
The tank calculations for San Francisco are shown in Table 8-2. Using a parcel size of
10,000 sq. ft. (cell D36), and a 1500 sq. ft. house (cell D37), 400 sq. ft. garage(cell
D38), an 800 sq. ft. driveway (cell D39), and an irrigated area of 5000 sq. ft. (cell D40),
an irrigation demand model was developed in which 80% of the runoff from the house,
garage, and driveway was recovered into a storage tank (unless spilled), converting mm
of runoff into gallons by multiplying by the impervious areas and conversion factors.
This is shown for each month in row 42. These criteria are approximately equal to the
dimensions used in the "Casa Del Agua" house in Tucson, AZ (Foster, et al.,1988 and
Karpiscak et al., 1990). For purposes of this exercise, runoff from the roof, garage, and
driveway are assumed to be channeled into the proposed cistern, which is assumed to
be 80% efficient at capturing rainfall (which is consistent with the "Casa Del Agua"
case). An initial guess of 100 gallons was given for the storage tank to initiate the
calculations.
Water requirements of the landscaped vegetation were assumed to be similar to that
predicted by the deficit calculations using the Thornthwaite procedure and losses due to
runoff and infiltration were considered negligible. The cumulative volume was then
calculated, assuming that the tank initially is empty and that cumulative volume cannot
exceed the size of the storage tank, subtracting actual use in the previous month from
the storage volume. This is shown in row 43. Next, the potential use or demand for the
water was calculated by multiplying the deficit by the irrigated area and converting the
number into gallons. This is shown in row 44. The actual use from the storage tank,
8-14
-------
shown in row 45, is equal to the potential use if it does not exceed the cumulative
volume. This procedure is followed in the Table 8-2 for San Francisco.
Table 8-2. Water storage tank calculations for San Francisco, CA.
35
36
37
38
39
40
41
4?
43
44
45
46
47
C
Stormwater calculations:
size of lot, square footage
sauare footaae of house
sauare footaae of aaraae
sauare footaae of drive and sidewalk
sauare footaae of landscaoina
Size of tank, aallons
Urban Runoff into tank, aallons
Cumulative volume, aallons
Potential Use from tank, gallons
Actual Use from tank, aallons
Difference
% used
D
10000
1500
400
800
5000
14311
6149
6149
0
0
E
4930
11079
0
0
F
3923
14311
0
0
G
1961
14311
127
127
H
848
14184
1570
1570
I
212
12741
4316
4316
J
0
9995
6333
6333
K
53
7978
7089
7089
L
318
7222
7222
7222
M
1219
7089
4783
4783
N
2703
9528
0
0
0
5725
14311
0
0
P
31439
31439
0
100%
Next, the potential use and actual use are summed for the 12 month period and the
difference taken (cell P46). The percentage of the resource used is in cell P47.
Because the objective is to maximize the use of the stored stormwater volume, this
difference is minimized by successfully selecting larger volumes until the difference is
zero or remains constant. In cases in which the difference is zero, the EXCEL function
GoalSeek may be used to simplify iterations. If the difference remains constant and not
zero, it indicates that it is not possible to meet 100% of the irrigation demand with the
available storage, regardless of the tank's volume.
The volume calculated is based upon historically averaged rainfall in a month; a
perhaps more accurate method would be to use daily temperature and rainfall data to
develop a daily PET model, using several years of data, after developing an
autocorrelation model for the precipitation input, and do a Monte Carlo analysis. This
would enable the user to capture droughts and probably increase the size of the tank to
achieve a greater degree of reliability.
Results
The methodology outlined in the previous section was applied to the cities shown in
Figure 8-5. The user can easily create a new worksheet for any city not shown, and
copy the database information into it. Then the user may copy the bottom part of any of
the existing worksheets containing the model, adjust the initial storage and the latitude
to the desired location, and iterate the solution on the tank size, following the procedure
in the previous section. By plotting PET, precipitation, and projected ET over the year,
and then comparing these numbers to the water deficit, water surplus, and soil moisture
storage data, an illustrative plot of the average climatology of a location can be done.
Such a plot is given for the city of San Francisco, CA in Figure 8-5.
8-15
-------
San Francisco
Boston
J
New York
WASHINGTON
Los Angeles
Miami
Figure 8-5. Cities used in water balance analysis.
Notice that the winter rain period in which soil moisture is being recharged by the high
precipitation which is much greater than ET at that time of the year. The water surplus
occurs when the soil cannot store any more water and results in runoff (in natural,
undeveloped areas), and coincides with the early spring flood/landslide season in San
Francisco. During the late spring and summer, as precipitation becomes almost
negligible, available soil moisture is utilized by vegetation for ET purposes. Because
the ET is less than PET, there is a deficit that is also shown in Figure 8-4. The deficit is
the integral of the PET less the calculated actual ET. This area is calculated month by
month in Table 8.2. By comparing Figure 8-4 with the chart for San Francisco in Figure
8-2, it is apparent that the calculations of Mather (1978) and Thornthwaite (1948) have
been reproduced.
The amount of the stormwater resource able to be used in each region was plotted in
the bar graph shown in Figure 8-6. Most eastern (and western coastal) cities were able
to use nearly 100% of the resource. Of course, in using a monthly time step, flooding
events are not part of the model. The Rocky Mountains and semi-arid southwest were
able to achieve over 90% and the desert southwest (Phoenix) was only able to achieve
24%. Supplemental water would need to be provided in these locations, if reused water
is desired to meet irrigation demand, graywater would have to supplement the reused
stormwater.
The projected average water deficit for each region are plotted in Figure 8-7. The
highest deficit was the desert southwest, with a low rainfall and high PET, followed by
the semiarid southwest, then by the Rocky Mountain west, then the northwest,
8-16
-------
1UU.UU
90.00 -
80.00 -
,_ 70.00 -
1
I 60.00 -
S
ฐ 50.00 -
o
is
= 40.00 -
+J
s?
30.00 -
20.00 -
10.00 -
X
X
X
X
X
X
X
X
X
X
/
X
X
/
^^^^H
X
X
X
^^^^H
/ ,
X
X^
^^^^H
X
X
X
^^^^H
/
x7
X
^^^^m
s
/
7|
/
X
^^^^H
x^"
~7\
X
r
Northwest West-Rocky Mtn Southwest Desert South west-Semiarid
Region
Figure 8-6. Utilization of stormwater by region.
8-17
-------
4O.ULT
40.00-
35.00-
30.00-
tn
9)
.C
o
c 25.00-
*;
o
ซ=
-------
southeast, midwest, and northeast.
The annual precipitation, calculated PET, water deficit, and an estimate of the percent
error of the Thornthwaite model for each studied city is found in Table 8-3. There may
be some variation between these values and other published data depending upon the
location of the measurement, as well as the length of the data record. This may affect
the error calculation as well. The Thornthwaite model, as stated previously, tends to
give better results in non arid areas. The station chosen for Seattle, WA is probably at a
higher elevation than published data for the city of Seattle, as the value for precipitation
in Table 8-3 is much higher than expected.
The projected storage tank size for each location is plotted in Figure 8-8. San Antonio,
TX had the largest tank size, at 25,000 gallons, followed by Dallas, TX at about 17,500
gallons, then Denver, CO at 15,500 gallons. Areas with very dry summers and wet
winters such as San Francisco, CA and Los Angeles, CA tended to be next, at around
14,500 gallons. Most areas in the humid east were under 5,000 gallons, except in
locations where ET needs outstripped available precipitation, such as in Tampa, FL at
9,000 gallons. The reason very high water deficit areas such as Phoenix, AZ did not
result in the largest tanks is that no available storage would have any benefit, that is, the
ET needs far exceed available rainfall.
This data compares favorably with Pazwash and Boswell (1997) who found the same
nationwide trends when their results are scaled up to the same lot size. They found that
the arid southwest tended to require smaller tanks than the rest of the country, due to
the lack of available rainfall. Average tank size for other areas ranged from 4320
gallons in the northeast to 6750 in the southeast.
8-19
-------
Table 8-3. Summary of annual data for selected stations.
City
Atlanta
Boston
Charlotte
Chicago
Dallas
Denver
Houston
Jacksonville
Los Angeles
Memphis
vliami
Minneapolis
New Orleans
slew York
3hoenix
Portland
Salt Lake City
San Antonio
San Francisco
Seattle
Tampa
Washington
State
GA
MA
NC
IL
TX
CO
TX
FL
CA
TN
FL
MN
LA
NY
AZ
OR
UT
TX
CA
WA
FL
DC
Annual
Precipitation
(in)
47.1
47.5
43.4
33.2
34.6
15.0
45.3
53.3
14.7
45.7
59.8
24.8
63.5
42.4
7.2
41.9
13.9
27.9
20.8
64.1
50.6
40.8
Annual PET
(in)
37.5
22.3
36.8
26.7
39.0
23.5
50.0
48.8
39.1
39.2
57.1
22.3
50.4
29.1
52.6
25.4
25.5
48.0
26.6
24.1
52.7
32.2
Annual ET
(in)
33.4
21.8
33.4
24.1
30.8
14.9
43.0
48.4
14.8
32.5
54.3
20.9
50.2
27.4
7.6
18.9
13.3
27.9
16.6
17.8
48.8
30.4
Annual
Water
Deficit
(in)
4.0
0.5
3.3
2.5
8.2
8.6
7.0
0.5
24.3
6.7
2.8
1.4
0.2
1.7
44.9
6.5
12.2
20.1
10.1
6.3
3.9
1.8
Annual
Water
Surplus
(in)
13.7
25.6
10.0
9.1
4.0
0.0
2.3
5.2
0.0
13.2
6.0
4.3
13.3
14.9
0.0
23.0
0.6
0.0
4.3
46.3
1.8
10.4
% Error of
Model
(%)
8.10
15.17
8.43
3.73
25.60
6.76
16.24
19.35
18.16
7.84
14.21
12.13
16.04
3.27
15.88
9.71
8.15
13.84
3.68
10.48
15.21
3.27
8-20
-------
25000-
20000-
(0
o
ns 15000-
O
_c
c
03
0 10000-
*'o'o
-------
Conclusions
In summary, in many areas of the country, particularly in humid areas, enough
stormwater can be collected to satisfy average irrigation demands. If driveway areas
are eliminated due to possible problems with water quality and ease of collection, the
result will be a larger tank size, however, irrigation demand may still be satisfied in a
majority of cases. In arid areas, particularly those with high ET requirement, stormwater
reuse may not be justified by itself. In these cases, the option of combining storage with
treated graywater may be worth considering.
A possible enhancement in the technique could be to apply the model to a daily time
series and developing an autoregessive time series model of the PET, ET, and
precipitation for each city. Next, a Monte Carlo analysis can be performed to determine
that, given the historical data series, a tank sized by this procedure will serve, say, 90%
of the ET needs of the parcel. Such an analysis and computer model was developed
for rural regions of India by Vyas (1996). An extrapolation of this work to
urban/suburban areas of the U.S. needs to be done. In addition, consideration of a
daily time step model may be more realistic in this effort. The effect of using several
years of data will be to enlarge the tank, as the tank size will increase in order to serve
ET needs during more extreme events, such as droughts.
8-22
-------
References
Anderson, J.M. (1996a). Current water recycling initiatives in Australia: scenarios for
the 21st century. Water Science Technobgy. (G.B.), 33: 10-11, 37-43.
Anderson, J.M. (1996b). The potential for water recycling in Australia: expanding our
horizons. Desalination, 106: 1-3, 151-156.
Asano, T., and A. D. Levine (1996). Wastewater reclamation, recycling and reuse:
past, present, andfuture. Water Science Technology. (G.B.), 33: 10-11, 1-13.
Ashcraft, J. G., and M. G. Hoover (1991). Water reuse-implementation and costs in
southern California. In Water Supply and Water Reuse: 1991 and Beyond.
Proceedings of the AWRA Conference. Denver, CO.
Butler, D. and J. Parkinson (1997). Towards sustainable urban drainage. Water
Science and Technology. 35 (9), 53-63.
Courtney, B.A. (1997). An Integrated Approach to Urban Irrigation: The Role of
Shading, Scheduling, and Directly Connected Imperviousness. MS Thesis.
Department of Civil, Environmental, and Architectural Engineering. University of
Colorado. Boulder, CO.
Field, R. (1993). Reclamation of Urban Stormwater. Integrated Stormwater
Management. Field, R., M.L. O'Shea, and K.K. Chin (Ed.), p.307.
Foster, K. E., M. M. Karpiscak, and, R. G. Brittain (1988). Casa Del Agua: a
residential water conservation and reuse demonstration project in Tucson, AZ. Water
Resources Bulletin. 24(6): 1201-1206.
Grimmond, C. S. B. and T. R. Oke (1986). Urban water balance 2: Results from a
suburb of Vancouver, British Columbia. Water Resources Research. 22(10): 1404-
1412.
Grimmond, C. S. B., T. R Oke, and D. G. Steyn (1986a). Urban water balance 1: a
model for daily totals. Water Resources Research. 22(10): 1397-1403.
Haarhoff, J., and B. Van der Merwe (1996). Twenty-five years of wastewater
reclamation in Windhoek, Namibia. Water Science Technobgy. (G.B.), 33: 10-11, 25-
35.
Harper, G. (1991). Reuse of Stormwater: Design Curves for Florida. MS Thesis.
University of Central Florida. Orlando, FL.
8-23
-------
Harrison, T.J. (1993). Stormwater Reuse Design Curves for Southwest Florida Water
Management District. In SWFMD. Proceedings of 3rd Biennial Stormwater Research
Conference. Brooksville, FL.
Heaney, J.P. and L.T. Wright (1997). On Integrating Continuous Simulation and
Statistical Methods for Evaluating Urban Stormwater Systems. Chapter 3 in James, W.
(Editor). Advances in Modeling the Management of Stormwater Impacts. Vol. 5. CHI.
Guelph, ON, Canada. P. 44-76.
Heaney, J.P., L.T. Wright, D. Sample, B. Urbonas, B. Mack, M. Schmidt, M. Solberg, J.
Jones, J. Clary, and T. Brown (1998). Development of Methodologies for the Design of
Integrated Wet-Weather Flow Collection/Control/Treatment Systems for Newly
Urbanizing Areas. Draft Rep. to U.S. EPA. Natl. Risk Manage. Res. Lab. Cincinnati,
OH.
Herrmann, T., and K. Hase (1996). Way to get water rainwater utilization or long-
distance water supply? A holistic assessment. In Proc. of the 7th Int. Conf. Urban
Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint Committee Urban Storm
Drainage.
Herrmann, T., U. Schmida, U. Klaus, and V. Huhn (1996). Rainwater utilization as
component of urban drainage schemes: hydraulic aspects and pollutant retention. In
Proc. 7th Int. Conf. Urban Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint
Committee Urban Storm Drainage.
Imbe, M., T. Ohta, and N. Takano (1996). Quantitative assessment of improvement in
hydrological water cycle in urbanized river basin. In Proc. of the 7th Int. Conf. Urban
Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint Committee Urban Storm
Drainage.
Karpiscak, M. M., K. E. Foster, and N. Schmidt (1990). Residential water conservation:
Casa Del Agua. Water Resources Research. 26: 6, 939-948.
Law, I. B. (1996). Rouse HillAustralia's first full scale domestic non-potable reuse
application. Water Science Technology. (G.B.), 33: 10-11, 71-78.
Leemans, R. (1988). Dataset developed during the YSSP summary program 1988, at
NASA. Laxenburg, Austria for the BIOSPHERE.
Lejano, R. P., F. A. Grant, T. G. Richardson, B. M. Smith, and F. Farhang (1992).
Assessing the benefits of water reuse: applying a cost-benefit allocation procedure.
Water Environment & Technology. 4 (8), 44-50.
Mallory, C. W., and J. J. Boland (1970). A system study of storm runoff problems in a
new town. Water Resources Bulletin. 6 (6), 980-989.
8-24
-------
Mangeot, E.F. (1996). City of Boulder Wastewater Treatment Plant Model Stormwater
Surge Analysis Using GPX-X. Independent Study for Professor Silverstein.
Department of Civil, Environmental, and Architectural Engineering. University of
Colorado. Boulder, CO.
Mather, J. R.(1978). The Climatic Water Budget in Environmental Analysis. D. C.
Heath and Company. ISBN: 0-669-02087-7.
Mitchell, V.G., R.G. Mein, and T.A. McMahon (1996). Evaluating the resource potential
of stormwater and wastewater: an Australian perspective. In Proc. of the 7th Int. Conf.
Urban Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint Committee Urban
Storm Drainage.
Nelen, A.J.M., A.C. de Ridder, and E.G. Hartman (1996). Planning of a new urban area
in a municipality of Ede using a new approach to environmental protection. In Proc. of
the 7th Int. Conf. Urban Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint
Committee Urban Storm Drainage.
Nowakowska-Blaszczyk, A., and J. Zakrzewski (1996). The sources and phases of
increase of pollution in runoff waters in route to receiving waters. In Proc. 7th Int. Conf.
Urban Storm Drainage. Hannover, Germany. IAHR/IAWQ Joint Committee Urban
Storm Drainage.
Oron, G. (1996). Management modeling of integrative wastewater treatment and reuse
systems, wastewater reclamation and reuse 1995. Water Science Technology. (G.B.),
33: 10-11,95-105.
Pazwash, H., and S. Boswell (1997). Management of roof runoff conservation and
reuse. Proc. 24th ASCE Water Resources Planning and Management Annual Conf.,
Aesthetics on the Constructed Environment. Houston, TX. 784.
Pisano, W.C. and H. Brombach (1997). Solids Settling Curves. Water Environment
Technology. Vol. 8, No.4, P 27-33.
Pitt, R., R. Field, M. Lalor, and M. Brown (1996). Groundwater Contamination from
Stormwater Infiltration Chelsea, Ml. Ann Arbor Press.
Pruel, H.C. (1996). Combined sewage prevention system (CSPS) for domestic
wastewater source control. In Proc. of the 7th Int. Conf. Urban Storm Drainage.
Hannover, Germany. IAHR/IAWQ Joint Committee Urban Storm Drainage.
8-25
-------
Requa, A., J. M. Kelly, J. A. Burgh, and M. Manzione (1991). Successful
implementation of an urban landscaping recycled water program. In Water Supply and
Water Reuse: 1991 and Beyond. Proceedings of the Conference of the AWRA.
Denver, CO.
Tchobanoglous, G., and A. Angelakis (1996). Technologies for wastewater treatment
appropriate for reuse potential for application in Greece. Water Science Technology.
(G.B.), 33: 10-11, 15-24.
Thornthwaite, C. W. (1948). An approach toward a rational classification of climate.
Geographical Review, volume 38 pp. 55-94.
Tselentis, Y., and S. Alexopoulou (1996). Effluent reuse options in Athens metropolitan
area: a case study. Water Science Technology. (G.B.), 33: 10-11, 127-137.
U.S. Geological Survey (1970). The National Atlas of the United States of America.
Reston, VA.
Veldkamp. R. G., T. Hermann, V. Colandini, L. Terwel, and G. D. Geldof (1997). A
decision network for urban water management. Water Science Technology. (G.B.) 36:
8-9, 111-115.
Vorosmarty, C. J. and B. Moore (1991). Modeling basin-scale hydrology in support of
physical climate and global biogeochemical studies: an example using the Zambezi
River. Surveys in Geophysics, volume 12, pp. 271-311.
Vorosmarty, C. J., C. J. Willmott, B. J. Choudhury, A. L. Schloss, T. K. Stearns, S. M.
Robeson, and T. J. Dorman (1996). Analyzing the discharge regime of a large tropical
river through remote sensing, ground-based climatic data and modeling. Water
Resources Research. 32(10):3137-3150.
Vorsomarty, C. J., B. Moore, A. L. Grace, M. P. Gildea, J. M. Melillo, B. J. Peterson, E.
B. Rastetter, and P. A. Steudler (1989). Continental scale models of water balance and
fluvial transport: an application to South America. Global Biogeochemical Cycles.
3(3):241-265.
Vyas, V. (1996). Monte-Carlo simulation of rainwater harvesting systems. Raindrop.
December, 1996 and web page
http://www.geocities.com/RainForest/Canopy/4805/FAQ.html.
Wanielista, M. (1993). Stormwater Reuse: An Alternative Method of Infiltration. In Proc.
National Conf. on Urban Runoff Management: Enhancing Urban Watershed
Management at the Local, County, and State Levels. U.S. EPA. Cincinnati, OH.
8-26
-------
Willmott, C. J. (1977). WATBUG: A FORTRAN IV Algorithm for Calculating Climatic
Water Budget. Water Resources Center. Delaware University; Contribution Number
23, Report Number 1. Publications in Climatology Vol. XXX, No. 2.
Yates, D. N. (1996). WatBal: an integrated water balance model for climate impact
assessment of river basin runoff. Water Resources Development. 12(2): 121-139.
8-27
-------
Chapter 9
Urban Stormwater and Watershed Management: A Case Study
James P. Heaney, Len Wright, and David Sample
Overview
Interest in watershed management has waxed and waned over the past century. The
concept of integrated water and land management was first articulated in the western U.S.
by John Wesley Powell in a report to the Congress in 1878 (Peterson 1984). However,
Congress rejected his idea and continued to use an ad hoc approach to authorizing
projects. During the 20th century, interest in watershed planning has come and gone
several times. Following World War I, unified planning at the river basin scale flourished
with major studies and implementation on numerous river basins, (e.g., the creation of the
Tennessee Valley Authority). The National Resources Planning Board provided the
leadership for these efforts (Viessman and Welty 1985). Increased environmental
awareness during the 1960's and 1970's led to expanded efforts to evaluate water quality
and related problems on a regional level. During the 1980's, primary reliance was placed
on a command and control approach for addressing water resources problems. A strong
move back to the watershed management approach began a few years ago, (e.g., see the
Proceedings of Watershed 93 and Watershed 96, WEF, 1993, 1996). While it is
axiomatic that integrated, holistic, sustainable infrastructure systems are very desirable,
demonstrated success stories of how such systems might function effectively are rare
(Heaney 1993).
Watershed Planning Methodologies
Early watershed planning efforts focused on developing "master plans" which, once
approved, would serve as a blueprint for management in the basin. Prior to computers,
such efforts faced severe technological limitations in bringing together large amounts of
information and analyzing alternatives in a systematic manner. The widespread availability
of mainframe computers in the 1960's and associated computer-based simulation and
optimization techniques led to large-scale efforts to develop "rational" master plans
(Maass et al. 1962). Integrated river basin planning models were developed as early as
1971. An updated summary of these quantitative methodologies is contained in Mays and
Tung (1992) and Wurbs (1994). The thrust in developing better planning methodologies
was in devising ever-more complex models, (e.g., three dimensional lake models,
nonlinear programming models). Unfortunately, the sophistication of the models greatly
outstripped the availability of data. Nevertheless, models have had a strong positive
influence in water resources planning (Office of Technology Assessment 1982).
Dissatisfaction with rational planning models and major improvements in metrology led to
the more recent shift to data rather than model driven approaches wherein the analyst
attempts to match the models with the data. These information driven approaches are
9-1
-------
often classified as Decision Support Systems (DSS) (Loucks 1995). Contemporary
DSS's contain a mixture of simulation and optimization models, databases, geographical
information systems, typically with a graphics front-end to integrate these systems. The
DSS should incorporate real-time control systems if they have been installed. The DSS is
more than a series of interfaced programs. It also embodies a different philosophy of
planning. Rather than focusing on "solving" the "problem", the DSS provides an
operational framework in which continuous process improvement is stressed.
Contemporary Principles of Watershed Management
During recent years, several national and regional groups have articulated new principles
of water and environmental management. A summary of these positions follows.
American Water Resources Association
The American Water Resources Association (AWRA) represents the largest collection of
professionals dealing with water resources problems. They published the following list of
seven guiding principles of water resources management (Anonymous 1992):
1. Water problems should be approached in a holistic way with the
watershed as the basic planning unit; and the water requirements of
natural systems within the watershed must be fully integrated into water-
management decisions.
2. The framework for policy making must be flexible and adaptive to
changing conditions, needs, and values, yet provide a level of
predictability and timeliness needed to support management and
investment decisions; management strategies must focus on appropriate
geography to effectively deal with the problems at hand; and the public
must understand the nature of the problems and how resource managers
intend to solve them.
3. The States play a key role in water management and should be
delegated responsibility for specific water-related Federal programs;
authority and accountability should be decentralized to the lowest capable
level of government while ensuring oversight and enforcement of these
programs; obstacles to meaningful intergovernmental partnerships, such
as overlapping missions, jurisdictional boundaries, and responsibilities,
must be overcome.
4. Water policy development should express a preference for negotiation,
market-like approaches, and performance standards and should include
more consultation, cooperation, and concurrence between all levels of
government and non-governmental entities with interests in the policies.
9-2
-------
5. Federal, State, and local participation should be encouraged in the
development of each other's program policy development,
implementation, and administration; more leadership capacity needs to
be developed among politicians, water professionals, and the public to
champion concerns and reforms.
6. Freshwater is a fundamental integrating ingredient in natural resources
management and an essential building block for a competitive and
healthy economy.
7. The goal of freshwater sustainability should be a guiding principle for
future water-resource management.
Water Environment Federation
The WEF is the professional organization, which represents the water quality field. They
have been conducting a major initiative called Water Quality 2000. The output of the third
phase of their effort is the result of an 18-month consensus process that included more than
100 experts representing a wide variety of interests. This report calls for a national water
policy that will improve protection of surface and ground waters by combining the following
three interrelated strategies (WEF 1993):
1. Pollution prevention.
2. Increased individual and collective responsibility for protecting water resources.
3. Reorientation of water research programs and institutions along natural
watershed boundaries.
U.S. Environmental Protection Agency
The U.S. EPA has adopted a watershed approach to water quality management (US EPA,
1991). This posture represents a revisiting of their earlier leanings in this direction.
Case Study of Urban Stormwater Management within a Watershed Framework
Introduction
The benefits and challenges of using an integrated, watershed-based approach to water
and environmental management can be demonstrated using a case study with meaningful
data and models. BCW, which includes the City of Boulder, was selected for this purpose.
A map of BCW is shown in Figure 9-1. BCW is a textbook watershed with its origins in the
Rocky Mountains from where it flows out of the mountains through the Front Range of
Colorado.
With the beginning of mining in 1858, the water and land associated with development
activities have had a significant impact on BCW. The initial mining activities altered
streamflows, greatly increased erosion and pollution, and forever altered the "natural"
hydrology. From 1858 to the present, BCW has been drastically altered by activities such
9-3
-------
as mining, urbanization, agricultural activities, and hydropower development. BCW
suffered serious stormwater pollution from mining activities beginning in the 1860s. Thus,
nonpoint pollution is an old problem in BCW.
BCW has also been adapted to provide water supply, flood control, recreation, and
instream flow needs. These interventions are both structural and nonstructural. Structural
interventions include construction of reservoirs, canals, pipelines, pump stations,
hydropower generation, water and wastewater collection and treatment systems, flood
control levees, instream and wetland restoration, and imports and exports of water.
Nonstructural interventions include flood warning systems, floodplain management, water
rights enforcement, water conservation programs, and education about watershed
protection.
The end result of all of these interventions is a complex watershed system, which has been
adapted to serve the needs of society as well as the natural system. This level of
development and adaptation is typical of watersheds in the U.S. and other developed
areas. Dealing with the watershed as a system is essential in contrast with trying to isolate
one component of it and assume away all of the complexity that is associated with this
system. While the focus of this report is urban stormwater quality management, these other
considerations should also be kept in mind. The components of BCW are discussed in the
following sections.
Hydrology
Introduction
BCW can be partitioned into three main sources: North Boulder Creek, Middle Boulder
Creek, and South Boulder Creek, as shown in Figure 9-1. According to WBLA, Inc.
(1988), the general water budget for the system inflows, under natural conditions, is as
follows:
Source Percent of Total
North Boulder Creek 20
Middle Boulder Creek 30
South Boulder Creek 40
Other Tributaries 10
Total 100
9-4
-------
Figure 9-1. Boulder Creek Watershed, CO. City of Boulder 1998. (Reprinted Courtesy of Hydrosphere)
9-5
-------
The total estimated natural inflow averaged 140,000 acre feet per year. The natural inflow
is estimated by correcting the observed historical inflows for development activities such
as storage, imports, and exports. The reconstructed expected natural inflows of Boulder
Creek at Broadway, which is located at the upstream end of the City of Boulder, are shown
in Table 9-1 and Figure 9-2.
The natural inflow averages 108 cfs. Depletions have reduced this natural flow to an
average of 52 cfs, or 48% of the natural inflow. The monthly pattern of inflows, shown in
Table 9-1 and Figure 9-2, indicates the dominant influence of the spring runoff in supplying
water to the downstream portion of BCW. About 72 % of the annual runoff occurs during
May, June, and July. The traditional low flow period of concern for water quality
management occurs in late summer when the stream temperatures are high and flow in the
receiving water is low. The lowest historical flows occur in October at the end of the
irrigation season as shown in Table 9-1. The average flow at Broadway in October is 10
cfs. However, these inflows at Broadway do not necessarily pass through the city. Much of
this inflow is diverted between Broadway and 75th St., the downstream end of the City of
Boulder.
Table 9-1. Boulder Creek watershed streamflows on Main Boulder Creek below
Broadway in Boulder, CO (WBLA Associates 1988).
Month
January
February
March
April
May
June
July
August
September
October
November
December
Avg.
Natural
(cfs)
15
18
22
58
250
435
252
105
52
40
30
20
108
Historical
(cfs)
33
33
22
35
115
180
90
25
20
10
25
35
52
Natural
(%)
1.2
1.4
1.7
4.5
19.3
33.5
19.4
8.1
4.0
3.1
2.3
1.5
100
Historical
(%)
2.5
2.5
1.7
2.7
8.9
13.9
6.9
1.9
1.5
0.8
1.9
2.7
48.0
9-6
-------
500
1
10 11
23456789
Month of Year
I I Natural Inflow Historical Inflow
Figure 9-2. Monthly inflows of Boulder Creek to Boulder, CO.
Precipitation Analysis
The average annual precipitation in Boulder is 18.2 inches with about two thirds of this
occurring between April and September. Total annual precipitation has ranged from 10 to
28 inches. Annual and monthly total precipitation data are presented in Figures 9-3 and 9-
4 and Table 9-2. May is the wettest month of the year.
Storm event statistics were tabulated using NWS hourly rainfall data. A storm event is
defined as ending when it hasn't rained for six consecutive hours. An estimated minimum
storm event precipitation of 0.15 inches is needed to initiate runoff. The relative frequency
distribution for these runoff producing events (RPE) is shown in Figure 9-5. An average of
29.27 RPEs occur per year. The monthly distributions of storm events is shown in Table 9-
3 and Figures 9-6 to 9-9. An average of 2.44 RPEs occur per month with as little as 1.3
RPEs in January to a high of 3.6 RPEs in May. The average RPE volume/month is 1.25
inches. The mean volume per RPE is 0.49 inches. The mean event duration is 5.8 hours
and the mean interevent time is 318 hours. Overall, RPEs occur less than 2% of the year.
For Boulder, the precipitation falling from November to March is typically occurs as snow.
9-7
-------
Streamflow Stations
A summary of available stream gauging stations is presented in Table 9.4. A brief
summary of the individual watersheds and stream gauging stations follows.
North Boulder Creek
The flows in North Boulder Creek are directly affected by seven city owned reservoirs with
a total storage capacity of about 7,000 acre feet (WBLA 1988). The City diverts water
from North Boulder Creek via the Silver Lake and Lakewood pipelines. Natural flows at
Lakewood average 21,800 acre feet per year over about 31 square miles of drainage or
about 0.97 cfs/mi2. As shown in Table 9-1, development has had a major impact on North
Boulder Creek with a combination of storage and direct diversions. The natural flow below
Lakewood of 31.25 cfs has been reduced by about one third due to man's activities with no
flow in the stream during the colder months of the year. No long-term stream gauging
stations exist for North Boulder Creek. The only available record is a few years of data on
the upper parts of the North Boulder Creek Watershed. Flows in North Boulder Creek are
affected by upstream storage and a major diversion of water for the City of Boulder's water
supply system via the Lakewood pipeline. Natural flows for North Boulder Creek can be
estimated based on its hydrologic similarity to Middle Boulder Creek above Nederland.
Middle Boulder Creek
According to WBLA (1988), Middle Boulder Creek flows essentially undisturbed into
Barker Reservoir at Nederland. The average runoff is about 1.55 cfs/mi2. Barker Dam and
associated diversions for water supply and hydropower exert a drastic influence on Middle
Boulder Creek downstream of Barker Dam. The City diverts water for water supply and
Public Service Company of Colorado diverts water for hydropower, both via the Barker
pipeline. As shown in Table 9-1, the natural outflow has decreased from about 108 cfs to
less than 52 cfs, a loss of over half of the natural flow in the stream. Wth current diversions,
only about one or two cfs of flow reach the confluence of North Boulder Creek and Middle
Boulder Creek during the colder months of the year.
The flows of Middle Boulder Creek as it enters the City are dominated by PSCO
hydropower releases and diversions by a large number of agricultural ditches. Historically,
during dry years, extended periods of flows less than one cfs have been experienced
below Broadway due to agricultural diversions and Boulder's exchange operations (WBLA
1988). Winter flows fluctuate wildly due to hydropower releases with flows ranging from 2
to 140 cfs over a single day as shown in Figure 9-10.
9-8
-------
30
25
20
15
o
01 10
49 50 51 52 53 54 55 56 57 58 59 60 61 62 S3 84 65 66 6? 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93
Year
Figure 9-3. Mean annual precipitation in Boulder, CO.
3.5
O
E
2 2
C
o
'&
us
+J
"a.
'o
1.5
Figure 9-4. Mean monthly precipitation in Boulder, CO.
9-9
-------
Table 9-2. Monthly precipitation in Boulder, CO, 1949-1993.
Yr.
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
Mean
Max.
Min.
STD
CofV
Month
Jan
0.52
0.92
0.67
0.03
0.22
0.57
0.32
0.24
0.85
0.70
1.37
0.68
0.75
1.87
1.00
0.39
1.11
0.21
0.84
0.20
0.36
0.15
0.70
1.40
1.40
1.00
0.50
0.60
0.20
0.80
0.70
1.50
0.20
0.20
0.20
0.50
0.70
0.10
1.10
0.40
0.70
0.90
1.00
0.70
0.67
0.67
1.84
0.03
0.42
0.62
Feb
0.10
0.24
0.93
0.39
0.66
0.20
1.27
1.70
0.99
0.35
1.59
1.81
1.04
1.15
0.53
0.96
1.73
1.27
0.61
1.20
0.35
0.82
2.10
0.70
0.20
1.20
1.10
0.40
0.70
0.40
0.30
1.00
0.40
0.82
0.10
0.90
1.00
1.00
0.82
1.10
1.00
0.70
0.10
0.00
0.82
0.82
2.10
0.00
0.49
0.60
Mar
2.47
0.34
1.97
1.71
1.60
1.28
2.03
1.30
0.56
2.88
2.65
1.13
3.48
0.64
2.45
1.59
2.10
0.26
1.29
0.86
1.01
5.72
1.10
1.00
1.70
1.50
2.00
1.60
0.50
1.60
2.70
2.60
2.30
0.60
4.70
2.60
1.40
0.60
2.20
2.40
0.90
4.40
0.50
3.40
1.40
1.84
5.72
0.26
1.16
0.63
Apr
2.12
2.74
2.23
2.84
2.18
0.88
0.20
1.44
3.12
2.74
3.71
2.13
1.39
0.90
0.17
1.41
2.38
1.44
1.90
2.27
1.05
1.25
5.40
1.30
5.50
2.70
2.80
2.10
3.10
3.00
2.10
5.50
1.30
0.50
3.00
0.00
1.90
4.80
2.30
1.40
1.80
2.20
2.00
0.50
2.10
2.17
5.50
0.00
1.29
0.59
May
3.28
3.07
2.01
3.73
2.13
1.08
2.25
2.85
8.61
3.91
3.62
3.68
3.37
2.06
1.05
2.06
1.34
0.70
5.00
2.33
8.51
1.07
1.00
2.99
4.00
0.00
2.99
1.40
0.60
7.00
5.40
3.80
4.80
4.50
4.70
2.80
1.20
2.50
1.80
3.40
3.00
1.70
4.10
1.90
1.20
2.99
8.61
0.00
1.87
0.63
Jun
7.03
0.72
2.09
0.93
0.76
0.97
1.99
2.00
0.46
1.38
0.51
0.52
2.11
2.49
4.58
1.58
2.55
1.27
4.83
2.54
5.24
2.68
0.10
2.30
0.50
2.40
1.60
1.20
0.50
1.11
3.00
0.20
1.50
2.20
2.30
1.60
1.80
1.50
5.70
0.60
2.10
0.20
1.80
1.00
2.90
1.94
7.03
0.10
1.50
0.77
Jul
1.05
1.47
1.16
0.64
2.26
1.79
0.85
2.78
0.73
1.35
0.56
0.94
1.69
1.45
0.46
2.20
4.81
0.90
2.81
1.30
2.33
1.34
1.00
2.40
1.10
0.80
0.40
1.80
3.10
1.00
0.70
1.70
1.70
4.60
2.60
1.60
1.90
1.70
1.10
0.50
1.30
3.20
2.70
1.10
0.70
1.63
4.81
0.40
0.99
0.61
Aug
0.31
0.19
8.59
3.47
0.92
0.44
2.25
1.53
2.35
0.67
1.02
0.26
1.65
0.21
1.84
0.31
0.33
0.45
4.94
3.84
0.46
0.17
0.20
1.20
0.20
0.60
0.90
1.10
1.90
1.30
3.90
1.10
1.10
1.50
0.80
2.00
0.00
0.20
1.80
1.20
1.40
1.80
1.50
3.20
0.60
1.46
8.59
0.00
1.55
1.06
Sep
0.00
1.30
0.88
0.29
0.00
1.31
0.80
0.00
0.80
0.74
3.39
0.52
4.47
0.24
2.35
0.34
3.00
2.94
0.92
1.26
0.47
4.31
4.30
1.00
1.43
1.90
1.00
2.80
0.20
0.10
0.50
1.20
0.80
1.43
0.30
0.90
2.50
0.80
1.00
1.90
2.90
1.80
1.50
0.00
3.70
1.43
4.47
0.00
1.24
0.87
Oct
1.49
0.38
2.62
0.24
0.51
0.34
0.37
0.48
1.86
0.61
2.66
2.76
1.25
1.27
0.35
0.22
0.24
0.79
1.29
0.47
6.36
1.25
0.90
1.30
0.70
2.10
0.80
1.20
0.30
2.10
1.30
0.80
1.20
1.20
0.20
4.00
0.90
3.40
0.80
0.10
1.20
0.80
0.80
0.40
2.22
1.26
6.36
0.10
1.17
0.93
Nov
0.00
1.79
1.12
1.29
1.03
0.64
1.42
1.83
0.69
0.99
1.12
0.66
1.13
0.70
0.72
1.17
0.25
0.60
1.46
0.81
0.96
1.50
0.80
2.50
1.70
1.30
1.40
0.30
0.50
0.20
3.00
1.10
0.30
0.40
3.90
0.00
1.70
1.90
1.70
0.70
0.30
1.40
3.20
0.30
2.20
1.17
3.90
0.00
0.83
0.71
Dec
0.27
0.27
1.40
0.00
1.04
0.65
0.90
0.71
0.06
0.88
0.14
1.71
0.69
0.17
0.83
1.00
0.66
0.30
2.07
0.65
0.72
0.50
0.60
1.30
1.40
0.50
0.70
0.40
0.20
2.10
2.40
0.20
1.20
1.60
0.90
0.60
1.00
0.50
1.90
1.80
1.50
0.80
0.00
0.86
0.60
0.86
2.40
0.00
0.60
0.69
Total
18.6
13.4
25.7
15.6
13.3
10.2
14.7
16.9
21.1
17.2
22.3
16.8
23.0
13.2
16.3
13.2
20.5
11.1
28.0
17.7
27.8
20.8
18.2
19.4
19.8
16.0
16.2
14.9
11.8
20.7
26.0
20.7
16.8
19.5
23.7
17.5
16.0
19.0
22.2
15.5
18.1
19.9
19.2
13.4
19.1
18.24
28.00
10.20
4.15
0.23
9-10
-------
300
250
O 200
c
0)
3
D"
ฃ
100
0.1 10.210.310.4I0.5
[([([[[-II1
-31o.d1';K1OR1'j?1'ja1oa1 ^ * t -I'^o*
3.3 ' 3.4 "3.5" 3.6 '
Runoff in Inches
Figure 9-5. Relative frequency for runoff producing events in Boulder, CO.
Table 9-3. Summary of monthly and annual storm event statistics for Boulder, CO 1949-
1993.
Month
Jan
Feb
Mar
Apr
May
Jun
July
Aug
Sep
Oct
Nov
Dec
Total
Average
Events/mo.
1.31
1.47
3.13
3.20
3.58
2.84
3.16
2.31
2.33
2.11
2.16
1.67
29.27
2.44
Volume
Averag
e
(in./mo.)
0.49
0.60
1.54
1.84
2.48
1.68
1.36
1.15
1.16
1.06
0.98
0.65
14.97
1.25
Mean
(in./event
)
0.372
0.407
0.490
0.574
0.693
0.592
0.432
0.496
0.497
0.500
0.454
0.387
0.49
STD
(in./event
0.216
0.210
0.414
0.482
0.822
0.612
0.376
0.526
0.434
0.442
0.302
0.253
0.42
CofV
0.58
0.52
0.85
0.84
1.19
1.03
0.87
1.06
0.87
0.88
0.67
0.65
0.83
Duration
Mean
(hours
)
6.68
6.68
6.04
6.69
7.71
5.70
3.20
3.31
5.67
6.00
6.33
6.08
5.84
STD
(hours
)
5.212
6.885
6.460
5.308
9.192
6.125
2.421
2.718
5.445
5.696
5.264
5.253
5.50
CofV
0.781
1.031
1.070
0.794
1.192
1.074
0.757
0.822
0.961
0.949
0.832
0.864
0.93
Interevent Time
Mean
(hours
)
546
462
319
206
211
199
271
244
295
388
320
362
318.48
STD
(hours
)
455
444
428
179
263
231
270
258
303
425
371
288
326.32
CofV
0.834
0.961
1.341
0.872
1.248
1.162
0.999
1.058
1.029
1.095
1.158
0.795
1.05
Notes: Annual statistics based on total data set, not averages of monthly means.
9-11
-------
An event is defined as ending when six dry hours have elapsed.
9-12
-------
I3
Ul
_c
're
a:
IE
1 2 3 4 5 6 7 8 9 10 11 12
Month
Figure 9-6. Runoff producing events per month in Boulder, CO.
10
c
0)
a
"+-i
5 4
3
Q
I
'i 2
a:
1 2 3 4 5 6 7 8 9 10 11 12
Figure 9-7. Average rainfall duration per event in Boulder, CO.
9-13
-------
1234567
Month
Figure 9-8. Average rainfall per event for Boulder, CO.
10 11 12
2 3 4 5 6 7 8 9 10 11
Month
Figure 9-9. Average runoff producing rainfall per month for Boulder, CO.
12
9-14
-------
Table 9-4. Summary of surface water records for Boulder Creek Watershed.
ID
6726000
6726500
6725500
6726900
6725500
6727500
6729000
6729300
6725500
6730200
6730300
6730500
Name
N. Boulder C. @ Silver Lake
N. Boulder C. nr. Nederland
Boulder C. at Nederland
Bummers Gulch nr. El Vado
Boulder C. nr. Orodell
Fourmile C. at Orodell
S. Boulder C. nr. Rollinsville
S. Boulder C. at Pinecliff
S. Boulder C. nr. Eldorado Spgs.
Boulder C. at N. 75th St.
Coal R. nr. Plainview
Boulder C. @ Mouth nr. Longmont
Drainage
Area
(mi2)
8.7
30.4
36.2
3.87
102
24.1
42.7
72.7
109
304
15.1
439
Period of Record
From
1913
1929
1907
1983
1906
1947
1982
1910
1945
1979
1980
1986
1959
1927
1951
1978
To
1932
1931
Now
Now
Now
1953
Now
1918
1949
1980
Now
1949
1955
1990
Average Discharge
(cfs)
54.3
0.5
86.6
6.48
76
90.9
4.62
(cfs/miA2)
1.50
0.13
0.85
0.27
0.70
0.30
0.31
(inch/yr)
20.36
1.75
11.52
3.65
9.46
4.06
4.15
Upstream
Diversion
0
0
Yes, Boulder
?
Big Influence
Big Influence
None
Big Influence
Storage
(ac-ft.)
Small
0
11500
9
Much
Much
Source: Surface water records of the U.S. Geological Survey.
Flows strongly affected by numerous reservoirs and diversions.
9-14
-------
O
160.00
140,00
120.00
100.00
80.00
60.00
40.00
20.00
00.00
12/25/94 12/26/94 12/27/94 12/28/94 12/29/94
Date
12/30/94
12/31/94
1/1/95
Figure 9-10. Boulder Creek streamflow at Orodell, CO.
9-15
-------
The flows in the lower portion of Boulder Creek from 75th St. to its confluence with the St.
Vrain River are affected by wastewater treatment plant effluent, Colorado-Big Thompson
deliveries from the Boulder Creek Supply Canal, and numerous ditch diversions and return
flows. Low flows above 75th St. occur in May and October due to filling of Baseline,
Panama, Six-Mile, and Valmont reservoirs. Lowest flows in this section occur in late
summer due to diversions for irrigation. Winter flows have increased due to increased
releases by PSCO but with a wide range from 1 to 140 cfs over a daily cycle. This pulsed
flow occurs only a few hours per day for peaking power.
Middle Boulder Creek has a long-term gage at Nederland just upstream from Barker Dam.
This station provides the best estimate of what the unmodified alpine hydrology might look
like. Boulder Creek at Orodell includes the contribution of North Boulder Creek.
Streamflows at Orodell are affected by the upstream storage in Barker Dam and major
diversions for urban water supply and hydropower. Fourmile Creek at Orodell flows can
be added to the Boulder Creek at Orodell to get a good estimate of part of the inflow to the
urban portion of Boulder Creek.
Within the City of Boulder, numerous diversions take place. Many of the early diversions
were for irrigation. These diversions constitute a complex water network, which is difficult
to understand as will be discussed in the diversions section.
The Boulder Creek at N. 75th St. gage includes the direct flows in Boulder Creek as the
water moves through the City of Boulder. Other components are the sewage effluent from
the City, which discharges a few hundred feet above the gage, and numerous other
tributary inflows including part of the South Boulder Creek inflow, urban runoff, drainage
from local stream channels, and canal inflows to satisfy downstream water rights.
The gage on Boulder Creek at the mouth near Longmont is a discontinued station.
Fortunately, there is some overlap with the 75th St. station. Flows in this last section of the
stream are heavily affected by agricultural and urban withdrawals and return flows. This
section of Boulder Creek between 75th St. gage and Longmont typically loses flow.
South Boulder Creek
The natural runoff of South Boulder Creek at Eldorado Springs is estimated to be about
0.67 cfs/mi2 (WBLA 1988). The only current station for South Boulder Creek is at Eldorado
Springs where South Boulder Creek leaves the mountains. The flows at this station are
strongly affected by upstream Gross Reservoir, which is owned by the City of Denver and
diverts water from the basin. Downstream of Eldorado Springs, the flow in South Boulder
Creek is subject to numerous diversions. These diversions leave South Boulder Creek
without water during some months of the year. Because of the lack of stream gages, the
quantity diverted and where it enters Boulder Creek is speculative.
Groundwater
To date, relatively little attention has been given to groundwater and the interrelationship
between groundwater and surface water. This may change as competition for the available
9-16
-------
water continues to intensify. No active groundwater monitoring wells are maintained in the
study area.
Land Use and Growth Management in Boulder Valley
General
A comprehensive plan has been developed for Boulder Valley (City of Boulder Planning
Department and Boulder County Land Use Department 1990). This plan is updated
frequently. For planning purposes, the Boulder Valley is divided into the Service Area
which is the area serviced by the Boulder Utilities and the Planning Area which includes the
Service Area and outlying areas, typically open space areas. The breakdown of land use
for the Service Area is shown in Table 9-5 and Figure 9-11. The total service area is
17,225 acres. A roughly equal size of area constitutes the remainder of the total planning
area yielding a total planning area of about 35,000 acres.
The City of Boulder has a long tradition of open space land acquisition as chronicled in
Figure 9-12 (City of Boulder 1995). In response to rapid population growth during the
1950's and 1960's, Boulder established a "blue line" above which City water would not be
provided. The intended effect was to slow the rate of development in the foothills. In 1967,
Boulder became the first city in the United States to tax themselves for the acquisition,
management, and maintenance of open space land. The increase in the sales tax was
0.4%. In 1989, an additional 0.33% sales tax was approved by the voters for the same
purpose. As of 1993, 20,000 acres of land have been protected at a cost of $67 million.
By 1995, the total amount of open space land has reached 25,000 acres. The current
holdings of the open space program are shown in Figure 9-13.
An ecosystems approach has been used in prioritizing these land acquisitions. With
regard to water resources, this has resulted in acquisition of additional water rights which
can be used for instream flow needs, reduction in nonpoint loads from lands that would
otherwise have been developed, stream restoration, and acquisition of floodplains and
wetlands. Recreational use of these open space lands is very high. The 1993 annual level
of activity was about 1.7 million visits to this open space land. These recreational uses
include hiking, jogging, pet exercising, bicycling, wildlife viewing, horseback riding, and
fishing.
In addition to open space acquisition by the City of Boulder, Boulder County has had an
aggressive open space acquisition program. This program is supported by sales tax
revenues, which currently yield about $4 million per year for open space acquisition. To
date, Boulder County has acquired about 35,000 acres of land. Finally, a significant part of
the mountain portion of the Boulder Creek Watershed is owned by the U.S. Forest Service.
Thus, a very high percentage of the upper watershed land is in public ownership. This
provides an excellent opportunity for linked water and land management.
9-17
-------
In addition to the open space program, Boulder has an aggressive growth management
program. Before growth management, the expected built-out for the water supply system
was a population of 250,000. Growth management decisions have reduced this number
by 36% to 160,000 (WBLA 1988). This major reduction in growth, coupled with a major
open space acquisition program, has greatly reduced the potential impact of urbanization
on the water infrastructure system. In the long-run, this is probably the most effective water
management tool.
Relative Importance of Urban Land Use
The planning area for Boulder County was divided into 40 drainage basins as shown in
Table 9-6. The total drainage area upstream of Boulder is over 84,000 acres (Reaches 1
and 2). Virtually all of this land is undeveloped. Much of it is in public ownership including
large U.S. Forest Service holdings. The only current upstream activity is small urban areas,
the largest of which is Nederland, a small town located about 20 miles upstream.
The daily runoff was estimated for each of the basins within the City. The western part of
the City is grouped into Urban Runoff 1, which consists of eight small drainage areas
(Reaches 3-10), the largest of which is 68 acres. Then, Gregory Creek enters Boulder
Creek. It drains predominantly undeveloped land, much of it in the protected open space
program. The next area draining Boulder Creek is called Urban Runoff 2. It comprises
Reaches 12-26 and has a drainage area of 738 acres. Then, Bear Creek enters Boulder
Creek. Most of the drainage in Bear Creek is in the open space area. Next, Reaches 28-
31 enter Boulder Creek between Bear Creek and Goose Creek. About two thirds of
Goose Creek is urban. The last urban runoff group, Urban Runoff 4, enters Boulder Creek
between Goose Creek and Wonderland Creek. Then, Wonderland Creek and Fourmile
Creek enter Boulder Creek. Lastly, some nonurban lands drain to Boulder Creek between
Fourmile Creek and the Wastewater Treatment Plant.
9-18
-------
Table 9-5. Land use in the City of Boulder, CO service area - 1995 (City of Boulder
Planning CIS Laboratory, unpublished information).
Subcommunity
Central Boulder
North Boulder
U. of Colorado
Palo Park
Crossroads
South Boulder
East Boulder
Southeast Boulder
Gunbarrel
Total
% of Total
Area (acres)
Residential
2,010
1,268
85
396
252
1,649
147
1,862
1,113
8,782
51.0
Business
104
97
8
23
375
33
5
92
36
773
4.5
Industrial
0
63
0
0
69
176
1,242
43
1,074
2,667
15.5
Open Space
88
588
16
120
30
1,280
207
218
315
2,862
16.6
Parks
175
131
17
10
34
208
5
223
36
839
4.9
Public
154
55
508
63
11
110
196
186
19
1,302
7.6
Total
2,531
2,202
634
612
771
3,456
1,802
2,624
2,593
17,225
100.0
Residential (51.0%)
Business (4.5%)
Industrial (15.5%)
Public (7.6%)
Parks (4.9%)
Open Space (16.6%)
Figure 9-11. Land use in the City of Boulder, CO service area, 1995 (City of Boulder
planning CIS laboratory, unpublished information).
9-19
-------
1898 Purchase of Chautauqua Park at the foot of Flagstaff Mountain through a bond issue, the
beginning of the Boulder Mountain Parks System.
1907 Receipt of 1,600 acres on Flagstaff Mountain from a Congressional grant for the Mountain
Parks System.
1910 Frederick L. Olmstead suggests a program for preserving scenic Open Space lands.
1916 Purchase of 1,200 additional acres on Green Mountain and Bear Peak for the Mountain
Parks System.
1950-1960 Boulder's population nearly doubles from 19,999 to 37,718.
1959 Concerned citizens organize to form a group now known as PLAN-Boulder County.
1959 An amendment to the City Charter establishes a "blue line" above which City water will not
be supplied. Citizens who helped pass the amendment realized that this would slow
development of the foothills, but not stop it.
1960-1970 Boulder's population again nearly doubles from 37,718 to 68,870.
1963 PLAN Boulder County successfully campaigns for a bond issue to save the 160-acre
Enchanted Mesa from development. It is added to the Mountain Parks System.
1965 Citizens defeat a ballot proposal to extend services to a proposed development south of
Boulder.
1967 Boulder citizens vote to become the first city in the nation to tax themselves for the
acquisition, management, and maintenance of open space land. The measure to
permanently increase sales tax by four-tenths of one percent, or $0.004, passes with 61%
of the vote.
1971 An amendment to the City Charter authorizes the City to incur debt to acquire Open Space,
allowing for an expanded land acquisition program.
1973 City Council creates the Open Space Board of Trustees to set policies and priorities for
acquisition and management of Open Space land.
1978 Boulder Valley Comprehensive Plan (BVCP) states that Open Space shall provide "an
important framework for land use planning in the Boulder Valley."
1986 An amendment to the City Charter provides more permanent protection for Open Space
lands, and establishes the Open Space Board of Trustees and the Open Space
Department in the Charter, with support of 79% of the voters.
1989 Funding for the accelerated acquisition program passes with 76% of the vote. This adds
an additional 0.33 percent sales tax ($0.0033) for the 15-year period from 1990 through
2004.
1993
Authority to snend all Onen Snace sales tax revenues and continue to enter into debt for
Figure 9-12. Boulder open space chronology of events (City of Boulder, 1995).
9-20
-------
CITY OF BOULDER, COLORADO
Open Space and Related Public Lands
k
LEGEND
City Open Space Fed/State Lands SCALE
County Open Space i i City of Boulder 0.5 o 0.5 1 1.5 2 Miles
Mountain Parks A/Creeks
Figure 9-13. Boulder open space and public lands (City of Boulder, 1998).
9-21
-------
Table 9-6. Drainage areas for Boulder and Boulder Creek Watershed.
Individual Catchments
Reach
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Feet
Upstream
134,200
134,100
131,050
130,075
130,020
129,030
129,003
128,025
127,095
127,090
127,085
127,080
125,010
125,000
124,015
123,005
123,000
121,060
121,058
121,057
120,004
120,003
117,025
115,060
115,045
115,030
114,000
113,080
113,075
113,070
109,065
108,100
108,006
108,005
108,000
107,099
107,095
106,050
100,000
91,000
Individual
Name
Boulder C.
Sunshine Canyon C.
DFA 1
DFA 2
DFA 19
DFA 3
AFA C-5
AFA C-2
AFA C-6
AFA D-1
Gregory C.
AFA C-8
DFA 4
C-7
DFA 5
D-2
DFA 6
D-3
DFA 7
C-9
DFA 8
C-10
DFA 9
C-3
C-4
DFA 10
Bear Creek
E-1
DFA 11
E-2
DFA 15
Goose Creek
DFA 13
DFA 14
B
A
DFA 18
Wonderland C.
Fourmile Canyon C.
WW Treat. Pit.
Group
Name
Boulder C.
Sunshine Canyon C.
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Urban Runoff 1
Gregory C.
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Urban Runoff 2
Bear Creek
Urban Runoff 3
Urban Runoff 3
Urban Runoff 3
Urban Runoff 3
Goose Creek
Urban Runoff 4
Urban Runoff 4
Urban Runoff 4
Urban Runoff 4
Urban Runoff 4
Wonderland C.
Fourmile Canyon C.
WW Treat. Pit.
Total area above Boulder
Total area in Boulder
Total area below Boulder
Area (acres)
Total
83,200.0
1,165.0
24.9
22.5
9.6
67.2
67.7
50.9
22.3
66.3
1,465.6
20.0
35.6
48.5
42.6
176.2
41.9
48.7
19.8
15.9
23.8
8.1
45.7
30.7
91.2
89.2
5,273.6
99.1
46.1
166.3
52.9
3,494.4
23.8
193.8
255.3
237.5
18.2
1,222.4
6,419.2
500.0
84,365.0
20,537.5
104,902.5
Urban
0.0
0.0
24.9
22.5
9.6
67.2
67.7
50.9
22.3
66.3
315.4
20.0
35.6
48.5
42.6
176.2
41.9
48.7
19.8
15.9
23.8
8.1
45.7
30.7
91.2
89.2
1,456.0
56.0
26.1
94.0
29.9
2,294.1
18.6
151.7
199.8
185.9
14.2
430.5
781.5
65.2
0.0
7,188.2
7,188.2
Undev.
83,200.0
1,165.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1,150.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3,817.6
43.1
20.0
72.3
23.0
1,200.3
5.2
42.1
55.5
51.6
4.0
791.9
5,637.7
434.8
84,365.0
13,349.3
97,714.3
Imperviousness (decimal)
Average
0.04
0.04
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.139
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.50
0.167
0.30
0.30
0.30
0.30
0.342
0.40
0.40
0.40
0.40
0.40
0.202
0.096
0.10
Urban
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.3
0.3
0.3
0.3
0.5
0.4
0.4
0.4
0.4
0.4
0.5
0.5
0.5
Undev.
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
Aggregated Areas
Number
1
2
3
4
5
6
7
8
9
10
11
12
Station
134,200
134,100
128,924
127,085
120,830
114,000
112,073
108,100
107,641
106,050
100,000
91,000
Group Name
Boulder C.
Sunshine Canyon C.
Urban Runoff 1
Gregory C.
Urban Runoff 2
Bear Creek
Urban Runoff 3
Goose Creek
Urban Runoff 4
Wonderland C.
Fourmile Canyon C.
Wastewater Treatment Plant
Total Area
Acres
83,200.0
1,165.0
331.4
1,465.6
737.9
5,273.6
364.4
3,494.4
728.6
1,222.4
6,419.2
500.0
104,902.5
9-22
-------
Because of the open space land acquisition program, the public ownership of the
upstream drainage area, and the growth management program, Boulder has been able to
minimize the amount of urban runoff generation by minimizing urban land use. Only 7,200
acres out of a total of 20,500 acres in the local drainage generate urban runoff. With
upstream drainage of over 84,000 acres, only about seven percent of the land use in the
Boulder Creek Watershed above 75th St. is urban. Thus, urban runoff would be expected
to be a relatively small portion of the total runoff based on land use analysis.
Water Management Infrastructure
Storage
Natural storage in BCW consisted of a few alpine lakes. However, because of the highly
variable nature of the streamflow, construction of storage reservoirs was essential. Barker
Dam on Middle Boulder Creek was built in 1910. Seven storage reservoirs were built in
North Boulder Creek about the same time. Gross Reservoir on South Boulder Creek was
built by the City of Denver to store and divert water for its purposes. Wthin the plains
portion of BCW, numerous reservoirs have been built throughout the basin in order to store
water including Boulder Reservoir, Valmont Reservoir, and Baseline Reservoir. Boulder
Reservoir was built in 1954 at a cost of $1,190,800 as part of Boulder's contribution for
participating in the Colorado-Big Thompson Project, which brings water from the north into
Boulder Reservoir. Its original capacity was 12,700 acre feet. Overall, there are about 25
to 30 reservoirs in the valley, each one operated to accomplish local or specific objectives
within the overall water resources system.
Canals
An extensive canal network has been constructed during the past 140 years. Early canals
were built from the mountains to the valleys to maximize gravity flow. Coupled with the
storage reservoirs, these canals form a complex water delivery system. Many of the
"canals" were parts of the minor tributary system. Thus, the distinction between a
"receiving water" and a "canal" is a blurred one at best since these open canals also serve
as drainage ditches. This has implications for water quality management.
Control Works
A total of 27 major control works exist in the BCW. Two diversion structures are on North
Boulder Creek. These control structures control reservoir releases to the Lakewood
pipeline. The main control structure in the upper portion of Middle Boulder Creek is at
Barker Dam. This structure directs water into the pipeline, which is shared by the City of
Boulder and PSCO. In the valley portion of BCW, diversion structures exist at the mouth of
the canyon, at Broadway, and along the downstream portions of the main stem of Boulder
Creek. South Boulder Creek has 12 diversion structures on its banks. Each of these
diversion structures feeds water into a canal and/or reservoir system which may further
branch out to additional canals and associated control structures.
9-23
-------
Pipelines
Two major pipelines in the system are located in North Boulder Creek. Lakewood Pipeline
was originally installed to protect the City's water supply from contamination by mining
activities in the early 1900's. The other pipeline goes from Barker Dam on Middle Boulder
Creek to the PSCO generating facilities and the City's Betasso Water Treatment Plant.
This 50 cfs pipeline was originally constructed by PSCO which now shares it with the City
of Boulder. These two diversions have a major impact on streamflows in the mountain
portion of BCW.
Imports and Exports
The major importation of water occurs from the north as part of the Colorado-Big
Thompson and Windy Gap Projects. This water enters the Boulder Creek Watershed via
an open canal that discharges into Boulder Reservoir north of Boulder. The major export is
from Gross Reservoir on South Boulder Creek to the City of Denver. Also, numerous
diversions from Boulder Creek occur as the stream enters the city.
Current Water Management System
The current water management system bears little resemblance to the natural system.
Reservoirs, canals, diversion structures, and a complex prior appropriation water doctrine
have evolved to dictate the operation of the contemporary system.
Water Quantity
Area inhabitants have used BCW for virtually all purposes. Also, BCW has impacted
inhabitants through flooding and other undesirable factors. A summary of these activities is
presented below.
Municipal Water Supply and Wastewater Return
The City of Boulder began operating a water supply system in 1874. However, even at that
early date, much of the water had been preempted for agricultural and mining purposes.
Thus, the City's junior water right left them vulnerable during low flow periods. In response,
Boulder began to acquire some agricultural water rights and constructed more storage
capacity. In response to pollution from upstream mining activities, the City relocated its
intake upstream on two occasions. Finally, Boulder placed the intake in the headwaters of
the BCW and the water was transported to the City via the Lakewood pipeline, which was
completed in 1906. They also acquired the entire headwaters of the watershed to protect
the water from pollution.
This system functioned well until the serious drought of the early 1950's forced the City of
Boulder to further supplement their system with a water rights exchange agreement, which
allowed the City to use more upper basin water in exchange for providing an equivalent
amount of water downstream. Also, Boulder acquired significant storage rights in Barker
Reservoir from PSCO and the ability to transport this water to their treatment plant via a
pipeline. Finally, Boulder joined the Colorado-Big Thompson Project to obtain water from
the north. The City built Boulder Reservoir north of Boulder as part of this agreement.
9-24
-------
These acquisitions provided Boulder with a major improvement in the reliability of their
system. Relatively recent master plans for the water supply system have been prepared by
WBLA (1988) and Brown and Caldwell (1990).
The water demand for Boulder for 1992 was 19.73 mgd with peak monthly demand of
32.45 mgd in July as shown in Table 9-7. About 62% of the demand is for indoor use and
the remainder is for outdoor use. However, most of the summer water demand is for
outdoor use as shown in Table 9-7 and Figure 9-14.
Much of the urban water use is returned to Boulder Creek at 75th St. after treatment. For
1992, the average return flow from the treatment plant was 17.41 mgd. About 5.1 mgd of
this total is estimated to be infiltration as shown in Table 9-7 and Figure 9-15. Lastly, the
WWTP flow and the streamflow are compared in Table 9-7 and Figure 9-16. The WWTP
effluent flow is larger than the streamflow in the colder months of the year.
Agricultural Water Supply
Irrigation using Boulder Creek water is practiced in the valley portion of BCW. Major
diversions for agricultural water use occur at eight locations along Boulder Creek as it
moves through the City. For 1992, the average diversion for agriculture was 36.64 cfs.
These diversions have a major impact on the amount of flow in Boulder Creek because
they occur at the western end of the City.
Flood Control
Boulder has been plagued by flooding since its founding because the early settlers located
close to Boulder Creek to have easy access for water supply. Smith (1987) has chronicled
the evolution of Boulder's flooding problems since its inception. The first recorded flood
was in 1864. Subsequent floods in 1867, 1876, and 1885 caused the creek to spread a
mile and a half wide. The major flood of record occurred in 1894 with an estimated
discharge of 7,400 cfs. This flood did major damage to the town. Continued problems
with flooding prompted the City to hire consultants to make recommendations on how best
to manage the problem. Mr. Frederick Law Olmstead, Jr. proved to be the most prophetic.
In 1910, he recommended a plan, which is very similar to what the City adopted in 1985,
75 years later, that is, a linear park.
Flooding during the second decade of the 20th century broke the City's water line twice.
The City remained indecisive for many years in spite of a constant stream of consulting
studies, which recommended a wide variety of structural and non-structural solutions. As
the City procrastinated, the problem became potentially worse. Nevertheless, progress
was eventually made and Boulder has developed a sophisticated stormwater quantity and
quality management program.
9-25
-------
Table 9-7. Comparison of water use and wastewater flows, 1992.
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Avg.
% of Total
FLOWINMGD
Water Demand
Indoor
11.74
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.26
62.2
Outdoor
0.00
0.72
0.46
5.46
13.99
13.52
20.14
13.59
15.09
6.43
0.19
0.00
7.47
37.8
Total
11.74
13.03
12.77
Mil
26.30
25.83
32.45
25.90
27.40
18.74
12.50
12.31
19.73
100.0
Wastewater Treatment
Plant
Base
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
12.31
70.7
Infilt.
2.22
2.37
6.94
5.99
5.50
6.28
6.51
7.03
6.40
4.81
3.75
3.39
5.10
29.3
Total
14.53
14.69
19.25
18.31
17.81
18.59
18.82
19.34
18.71
17.12
16.06
15.70
17.41
100.0
Boulder Creek
Above WWTP
11.80
7.40
28.01
35.72
69.83
65.56
105.22
68.99
13.91
9.46
8.30
15.66
36.65
@ 75th St.
26.33
22.08
47.26
54.03
87.64
84.14
124.04
88.33
32.62
26.58
24.36
31.35
54.07
T3
OJ
m
1 2 3 4 5 6 7 8 9 10 11 12
Month
EH Indoor H Outdoor
Figure 9-14. Monthly water use for Boulder, CO, 1992.
9-26
-------
25
20
O)
15
10
Hlllllll'l
II II II II II II II II II II II II I
1 2 3 4 5 6 7 8 9 10 11 12
Month
EZI Base Flow H Infiltration
Figure 9-15. Monthly wastewater volumes for Boulder, CO, 1992.
150
100
TJ
O)
E
I
50
1 234 5 6 7 8 9 10 11 12
Month
H WWTP Boulder, CO. above WWTP
Figure 9-16. Monthly wastewater and Boulder Creek flows, 1992.
9-27
-------
9-28
-------
However, Boulder remains the most at risk community in Colorado for potential flooding
due to its development in relatively high hazard areas and the flashy nature of floods in this
area. Boulder has taken a benefit-cost-risk approach to stormwater management. Using
a combination of nonstructural and structural controls, they have delineated facilities which
can be built and remain in the floodplain. Typically, these buildings are public buildings
such as government offices and the library. A floodplain map, shown in Figure 9-17,
indicates that much valuable property in downtown Boulder and parts of University housing
remain at risk.
Greenway Program
With increased diversions over time, Boulder Creek was literally dried up by mid to late
summer. In the 1960's and 1970's, the community began to be concerned about rapid
growth. An outcome of that concern was a desire to maintain urban stream corridors as
community amenities. Described in this section is the manner in which this desire was
articulated in the 1978 Boulder Valley Comprehensive Plan.
An underlying principle was that the functional and aesthetic qualities of drainage courses
and waterways shall be preserved and enhanced in a manner compatible with a basically
non-structural approach to flood control. In particular, a non-containment approach to flood
management was to be followed for Boulder Creek.
Beginning in the 1970's, a succession of plans proposed a trail along the creek. The final
design, which emerged in the mid 1980's, called for restoring environmental features and
establishing a non-motorized corridor along the creek. A series of objectives were
identified including:
1. Create an offstreet non-motorized transportation system.
2. Preserve and enhance fish and wildlife habitat.
3. Protect ecologically sensitive areas.
4. Expand recreational use.
5. Protect water rights of multiple irrigation companies.
6. Maintain and improve flood carrying capacity of the waterway.
7. Protect water quality.
8. Provide opportunities for active and passive recreation.
The final design included strategies to revitalize the creek for fish, wildlife and recreation,
including engineering Whitewater boating features, enhancing fisheries habitat, and
developing paved and gravel pathways to serve bicyclists, walkers, joggers and the
disabled. A total of 65 fish habitat improvements were included. Structures included
upstream v-dams, angled boulder dams, boulder deflectors, s-dams, and double wing
deflectors. Ripple and pool areas provide desirable fish habitat especially during rapid
changes in flow due to hydropower generation.
9-29
-------
150
100
Oป
E
I
50
1234567
Month
CH WWTP
Figure 9-17. Boulder Creek potential flood inundation.
8 9 10 11 12
Boulder, CO. above WWTP
9-30
-------
BCW has a very high recreational value to the community, especially after its restoration
during the 1980's. A linear park with a bike path were constructed and much instream
restoration work was done to help return the stream to a more natural appearance. This
work has won a national award for innovative design. Also, Boulder's greenway is one of
eight nationally to be featured in a recent book on greenways (Smith and Hellmund, eds.
1993). The Boulder Creek linear park system is heavily used for activities such as walking,
jogging, biking and roller blading. Fishing, kayaking and tubing are popular in the upper
reaches of Boulder Creek within the City. Boulder Creek was used as the kayak course for
the 1995 Olympic Festival.
The original five-mile long Boulder Creek Greenway Project cost $3.3 million with about
$1.3 million coming from State Lottery funds. The program continues to grow to include the
rest of the Boulder Creek stream system. The current budget is over one million dollars per
year. The idea of greenways has spread to other areas. Mayor Webb of Denver has
made development of a greenway along the South Platte River as it moves through Denver
a cornerstone of his current term in office. The 10 mile long restoration is expected to cost
about $50 million and take ten years to complete.
With regard to the required flows for recreational uses, Boulder Creek, from the mouth of
the canyon to 55th St., can support the recreational activities listed in Table 9-8.
Table 9-8. Recreational activities supported by flows in Boulder Creek.
Activity
Swimming
Wading
Kayaking
Tubing
Fishing
Fisheries Maintenance
Flow Range
(cfs)
(1)
10-100
150-300
50-100
15-100
> 15 cfs
> 5 cfs
Months
(1)
June-September
June-July
July-August
May-September
May-September
October-April
1) Swimming is not supported because velocities are too high and temperature and depth are
too low.
Water quality has not been a major issue. The quality of the water is excellent. Urban
runoff quality has not been a major concern. Primary episodes to date deal with spills and
deliberate discharges of hazardous materials, such as paint, into the storm drains. In
contrast, maintaining minimum instream flows has been a high priority concern. Prior to a
major instream restoration effort in the mid 1980's, base flow in Boulder Creek as it moved
through Boulder was often zero. Thus, an obvious part of stream restoration was to have
adequate base flows, especially in late summer.
9-31
-------
Hydropower
Hydropower is an important component of the BCW water resource system. PSCO
provides most of the energy for the Boulder Valley and owns and operates Barker Dam on
Middle Boulder Creek. Water is released from Barker Dam to a pipeline, which is used to
transport the water to the generating facilities. The water is returned to Middle Boulder
Creek just upstream from the Orodell gage. PSCO also diverts water from South Boulder
Creek and Boulder Creek at 28th St. to Valmont Reservoir which is used for cooling water
for its electric generating facilities in Boulder. PSCO has agreements with the City of
Boulder for joint utilization of the storage in Barker Dam and for the pipeline to the
generating facilities.
Hydropower releases can cause major variability in flows in Boulder Creek. During the
winter months, flows are released only part of the day to meet early evening peaking
requirements. These flows are pulsed to permit efficient use of the turbines. The hourly
flows for Middle Boulder Creek at Orodell for late December 1994 are shown in Figure 9-
10. The daily flows range from near 0 cfs for most of the day to about 140 cfs for the early
evening hours. The flows for December 25, 1994 are shown in Figure 9-18. From
midnight to about 5 pm, the flow in Boulder Creek is a few cfs. From 5 pm to 9 pm, the flow
increases rapidly to about 136 cfs and then decreases rapidly back to 0 at about 9 pm.
This highly variable flow would be expected to have a significant impact on the fisheries
(WBLA 1988). Another concern is the diversion of Boulder Creek water at 28th St. to
replenish Valmont Reservoir during the non-irrigation season. This diversion reduces low
flows in the stream during fall and spring. Early fall, in particular, is a sensitive period for
the receiving water.
Instream Flow Needs
As development in BCW proceeded, more of the available water resource was
appropriated for the beneficial uses described above. These other uses left significant
sections of BCW with little or no water during parts of the year. The cumulative impact of
these diversions is that major problems occur with respect to fish and macroinvertebrate
survival in all but the peak flow months from May through July as follows (Rozaklis 1994):
1. North Boulder Creek: Zero flow past Lakewood from October-March.
2. Middle Boulder Creek: Zero flow below Barker Dam from October-April.
3. Main Boulder Creek: Inadequate flow through the City. Periods of low or zero
flow in late summer.
4. South Boulder Creek: Zero flow below Eldorado from November-March. Also,
zero flows during latter part of the summer.
9-32
-------
140.00
120.00
100.00
80.00
o
ง 60.00
40.00.
20.00
00.00
I I
12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/25/94 12/26/94 12/26/94
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00
Time
Figure 9-18. Flow in Boulder Creek at the Orodell gauging station, December 25, 1994.
9-33
-------
Recognition of this problem and the concomitant desire to restore Boulder Creek led the
City to embark on an aggressive program to increase low flows in BCW. After five years of
negotiations, the City was able to transfer its water rights to provide a minimum flow of 15
cfs in Middle Boulder Creek and minimum flows in other parts of the BCW system. This
water will be available for instream flow needs in all but the most serious droughts. If such
a drought occurs, the City can use this water for essential water needs. The present value
of these water rights transfers is about $14 million, a significant investment for the City of
Boulder.
Understandably, restoring base flows for instream needs is the top priority for a stream
restoration program. This water is of excellent quality. The next steps include:
1. Improved monitoring to verify that these instream flows are being maintained.
2. Improved accounting methods for tracking water movement through BCW.
3. Reducing extreme flow variability from pulsed hydropower releases.
4. Obtaining more capacity in Barker Reservoir to better manage instream flow
needs in Middle and South Boulder Creeks.
5. Increased attention to water quality management along with water quantity and
land management. Nonpoint pollution appears to be the most pressing concern.
Stream restoration is a vital part of the instream flow augmentation program. The required
flows to support various instream activities depends upon the nature of the stream. If the
stream has been channelized into a trapezoidal cross section, then it is not as desirable
from a fishing or boating point of view. With a restored stream system with ripples and
pools, the minimum required flow is about three to five cfs whereas it is about 15-20 cfs
without stream restoration. Similarly, the kayaking course with restoration requires
significantly less flow (20-30 cfs) instead of more than 100 cfs without restoration (Lacy
1995).
Importation of Water
Boulder Creek receives imported water from the Colorado-Big Thompson Project. This
water is delivered to Boulder Reservoir north of Boulder. Some of this water is used by the
City of Boulder with the balance directed to other users. The Boulder Supply Canal
transfers water from Boulder Reservoir to Boulder Creek just upstream of the Wastewater
Treatment plant. This water provides a major increase in the streamflow during the warmer
months of the year.
Overall Water Budget for Boulder
In order to understand integrated watershed management, a fairly complete water budget
for the urban area is essential (McPherson 1973). Calendar year 1992 was chosen
because of the availability of data. It was a drier than average year. The key sources and
sinks of the water budget are discussed first followed by presentation of annual, monthly,
daily, and hourly water budgets.
9-34
-------
Sources
1. Boulder Creek at Orodell: This input is measured by a USGS gage. The Orodell
station is downstream of North Boulder Creek and therefore includes this
source. The natural flow at Orodell has been significantly altered by upstream
diversions for municipal water use.
2. Fourmile Creek: This input is measured by a USGS gage.
3. South Boulder Creek: This input is not measured. It is assumed to be zero.
Except in wetter years, the entire flow in South Boulder Creek is utilized for
needs of area inhabitants.
4. Urban Runoff: This input is estimated based on a very rough estimate of
contributing land use. The estimate will be updated with better data.
5. Wastewater Treatment Plant: This input is measured. A significant part of the
wastewater flow is infiltration and inflow.
6. Boulder Reservoir: Deliveries to Boulder Creek to satisfy downstream water
users. This inflow enters Boulder Creek just upstream of the wastewater
treatment plant near 75th St.
Sinks
1. Diversions: These diversions occur at Canyon Mouth, Broadway, and along
Boulder Creek between Broadway and 75th St. These data are obtained from
the State Engineer's office.
2. Boulder Creek at 75th St.: These are measured flows at a USGS gage.
Annual Water Budget
The annual water budget for calendar year 1992 is shown in Table 9-9 and Figure 9-19.
The total estimated sources entering Boulder Creek above 75th St. are the upstream flow
of 54.55 cfs, the wastewater treatment plant return flow of 26.98 cfs, the Boulder Supply
Canal imported water from the CBT project of 29.29 cfs, and the estimated stormwater
runoff of 7.2 cfs. Urban runoff is estimated to be 6.17 cfs out of the total of 7.2 cfs of local
runoff. A simple rainfall-runoff relationship was used to estimate the runoff. This simple
method was used since the data on land use and imperviousness are only approximate.
Also, no direct rainfall-runoff measurements are available.
The sinks of water are the diversions from Boulder Creek. The total of diversions for
calendar year 1992 was 36.64 cfs averaged over the entire year. Most of these diversions
9-35
-------
occur during the irrigation season. This water budget ignores groundwater influences
since no data are available. Also, the inflow from South Boulder Creek is estimated to be
zero for 1992, a relatively dry year.
Of all of the above items, only the runoff is estimated. All of the other items in the water
budget are measured. The overall result of the annual water budget is an estimated total
sources of 118.0 cfs and total outflows of 120.9 cfs, leaving unaccounted for a total of 2.9
cfs of inflow. This inflow is some combination of stormwater runoff and groundwater inflow.
Lacking better measurements, the nature of this residual is unknown.
The error in the annual water budget is less than 3%. Thus, some statements can be made
about the expected relative importance of urban runoff. Urban runoff averages about six
cfs over the entire year. By comparison, the WWTP effluent is 26.98 cfs, over four times
larger. Of course, urban runoff occurs infrequently (about 2% of the time). Thus, it takes on
greater relative importance when it does occur.
Monthly Water Budget
The monthly water budget for CY 1992 is shown in Table 9-10 and is plotted on Figure 9-
20. The errors are random. The predictions follow the measured outflow fairly closely. The
monthly budgets reflect flow in Boulder Creek at 75th St., the downstream boundary of the
City. The flows within the City are significantly less since the Boulder Supply Canal and the
WWTP provide major inputs of water. The estimated monthly flow within the city (at 28th
St.) is shown in Table 9-11 and the associated time series is shown in Figure 9-21. Much
of the inflow to the city is diverted above 28th St. however, most of the urban runoff enters
Boulder Creek downstream of the city. Thus, the relative importance of urban runoff is still
small as shown in Table 9-10. Prevailing average monthly flows at 28th St. during the late
summer and early fall are in the 10 to 20 cfs range.
9-36
-------
Table 9-9. Overall water budget for calendar year 1992 (flow in cfs).
Sources, Average Flow Rate
1 Sunshine
2 Urban Runoff 1
3 Gregory
4 Urban Runoff 2
5 Bear Creek
6 Urban Runoff 3
7 Goose Creek
8 Urban Runoff 4
9 Wonderland C.
10 FourmileC.
11 WWTP
Total Urban & Other Runoff
Total Runoff
Upstream
WTPoff
Bo. Sp. Canal
Total Source
Sinks, Average Flow Rate
1 Anderson
2 Boulder Lefthand
3 Boulder White Rock
4 Farmers
5 Green
6 Silverlake
7 Butte Mill
8 N. Boulder Farm
Total Sinks
Computed Flow (sources-sinks)
Observed Flow @ 75th gage
Residual (observed-computed)
Urban
0.00
0.29
0.28
0.65
1.29
0.11
2.03
0.40
0.38
0.69
0.06
6.17
501
513
516
525
528
603
518
543
Other
0.08
0.08
0.27
0.01
0.08
0.01
0.06
0.40
0.03
1.03
7.20
54.55
26.98
29.29
3.97
2.43
9.59
7.48
2.71
1.23
2.11
7.10
118.02
36.64
81.38
84.24
2.86
9-37
-------
Total Urban Runoff
Total Other Runoff
Fourmile
Sunshine
0.00 %
Urban
C WWTP Runoff 1
11.17% Q.i3% 4.74 %
Wonderland
C
6.15%
Urban
Runoff 4
6.53 %
Goose cr
31.82 %
Gregory
4.51 %
Urban
Runoff 2
10.55 %
Bear C
19.83 %
Urban
Runoff 3
1.77 %
Urban
Runoff 1
WWTP sunshine rj.OQ %
3.00 % g.03 %
Gregory
"7.92%
Fourmile C
38.84 %
Urban
Runoff 2
0.00 %
Bear C
26.30 %
Wonderland
5.46% Runoff4 s.27%
1.10%
Sources
Diversions
Bo. Sp. Can
al
24.82 %
WTP eff.
22.86 %
Total Runoff
/ 6.10%
| Upstream
46.22 %
Figure 9-19. Overall water budget for calendar year 1992.
Anderson
11 % 2.
Boulder
Framers
20%
7%
3.
1 _ Boulder
WhiteRock
27%
9-38
-------
Table 9-10. Measured and computed monthly flowrates in 1992.
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Average Flow
(cfs)
Computed
38.45
38.94
72.74
62.79
125.03
101.63
182.38
149.47
43.79
49.75
54.35
52.69
Observed
40.74
34.28
71.71
83.47
135.35
127.13
192.35
140.52
50.77
41.13
37.70
48.52
Residual
-2.30
4.67
1.03
-20.68
-10.33
-25.51
-9.97
8.96
-6.97
8.62
16.65
4.17
Residual as %
Of Computed
-6
12
1
-33
-8
-25
-5
6
-16
17
31
8
Computed -ป- Observed
VI
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 9-20. Boulder Creek monthly flows in 1992.
9-39
-------
Table 9-11. Monthly flows in Boulder Creek at 28th St. for calendar year 1992.
Sources (cfs)
Sunshine
Urban Runoff 1
Gregory Urban
Other
Urban (Runoff 1 & Gregory)
Urban Runoff & Other
Upstream
Total Sources
Sinks (cfs)
501 Anderson
513 Boulder Lefthand
516 Boulder Wrock
525 Farmers
526 Green
603 SiN/erlake
543 N. BouFarm
Total Sinks
Flow at 28" Street
Month
Jan-92
0.03
0.09
0.09
0.03
0.18
0.23
13.67
13.90
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
13.90
Feb-92
0.00
0.00
0.00
0.00
0.00
0.00
16.20
16.20
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
16.20
Mar-92
0.30
1.08
1.03
0.30
2.11
2.72
21.96
24.68
5.69
0.00
0.00
0.00
0.00
0.00
0.00
5.69
16.27
Apr-92
0.02
0.07
0.07
0.02
0.14
0.18
54.57
54.75
11.76
1.94
7.85
0.00
0.00
0.00
0.70
22.25
32.50
May-92
0.10
0.37
0.35
0.10
0.72
0.92
137.90
138.83
6.58
8.61
37.22
11.68
5.87
1.80
16.19
87.96
50.87
Jun-92
0.04
0.14
0.13
0.04
0.28
0.36
133.30
133.66
6.54
11.47
45.03
26.63
6.92
3.58
19.58
119.75
13.91
Jul-92
0.05
0.19
0.18
0.05
0.37
0.48
109.77
110.25
5.87
1.95
22.92
29.51
5.99
3.90
23.82
93.96
16.29
Aug-92
0.17
0.62
0.59
0.17
1.21
1.56
69.13
70.69
4.02
3.23
1.97
16.51
8.18
3.02
15.70
52.63
18.06
Sep-92
0.00
0.00
0.00
0.00
0.00
0.00
33.63
33.63
3.66
1.70
0.00
4.99
3.78
2.47
7.57
24.17
9.46
Oct-92
0.04
0.15
0.14
0.04
0.29
0.38
23.45
23.83
3.23
0.33
0.00
0.00
1.65
0.00
1.22
6.43
17.40
Nov-92
0.17
0.59
0.56
0.16
1.15
1.47
15.03
16.50
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
16.50
Dec-92
0.05
0.18
0.17
0.05
0.34
0.44
24.06
24.50
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24.50
Urban (Runoff 1 & Gregory)
Flow at the 28th Street
60.00
50.00
40.00
30.00
0 20.00
10.00
Jn Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Figure 9-21. Monthly flows in Boulder Creek at 28th St. for calendar year 1992.
9-40
-------
The results of the monthly water budget show the dramatic influence of human activities on
the flows in Boulder Creek. The 1992 monthly flows above the City of Boulder, within the
City of Boulder, and downstream of the City of Boulder are shown in Table 9-12 and Figure
9-22. The streamflows differ dramatically. The inflow above the city is diverted before the
stream moves through much of the city. The flow downstream of the city is over four times
larger due to water import and the wastewater return flow. Thus, three distinctly different
hydrologic environments exist even though the total distance from above to below the city is
only about eight miles. The upper and within the city stations are only two miles apart. The
magnitude of the human-induced sources within the Boulder study area are shown in Table
9-13 and Figure 9-23. The wastewater treatment plant return flow is relatively constant at
26.97 cfs. However, the diversions and imports vary widely with virtually all of these flows
occurring during the irrigation season. On an annual average, the diversions are the
largest component followed by the imports. Recall that the estimated urban runoff is about
six cfs, far less than these values.
Daily Water Budget
Lastly, a daily water budget was done for calendar year 1992. The results are summarized
here. The predicted versus measured flows track fairly well. Notable differences occur
during storm periods, especially in the colder months, when the precipitation is actually
snow with entirely different runoff patterns. Critical water quality conditions occur during the
late summer and early fall so attention was focused on these months. The August results
indicate that the maximum actual daily flow at 75th St. was 250 cfs, one half of the
predicted maximum flow of 500 cfs. This peak was in response to the largest single rain
event of the year. Typical flows decreased from about 200 to 50 cfs over the month. The
dominant terms in the water budget for August are the import and export of water for
irrigation. Urban runoff is still a relatively small amount. Boulder Creek flows continued to
decrease in September to about 40 cfs. During October, the main source of flow in the
stream is the WWTP return flow. The Boulder Supply Canal deliveries declined as the
irrigation season began to end.
Hourly Water Budget
Only a few cfs of flow are available in Boulder Creek as it passes through the city in late
summer and early fall. However, it is important to understand the water budget, not only on
a daily basis, but also to do an hourly accounting. From October to March, PSCO releases
water to Boulder Creek in pulses for hydropower peaking purposes during the early
evening hours. Thus, while the average daily inflow might be 10 to 15 cfs, the actual flow
pattern is 140 cfs for two to three hours and zero flow the rest of the day as shown in Figure
9-18. Thus, the fish in Boulder Creek must adapt to very wide swings in flow even on an
hourly basis. Similar conditions would occur in other streams where hydropower is
generated. Such extreme daily flow swings would tend to have a more significant impact
on the fish than urban runoff because of their much greater frequency.
9-41
-------
Table 9-12. Monthly flows in Boulder Creek for calendar year 1992, above, within and
below the City of Boulder (in cfs).
Month
Jan-92
Feb-92
Mar-92
Apr-92
May-92
Jun-92
Jul-92
Aug-92
Sep-92
Oct-92
Nov-92
Dec-92
Average
(1)
(2)
(3)
Mean Monthly Flows in Boulder Creek, 1992
Above Boulder
13.67
16.20
24.68
54.75
138.83
133.66
110.25
70.69
33.63
23.83
16.50
24.50
55.10
Within Boulder
13.90
16.20
16.27
32.50
50.87
13.91
16.29
18.06
9.46
17.40
16.50
24.50
20.49
Below Boulder
40.74
34.28
71.71
83.47
135.35
127.13
192.35
140.52
50.77
41.13
37.70
48.52
83.64
1. Measured flow above Boulder. Stream mile = 25.5.
,th
2. Estimated flow at 28tn St. Stream mile = 23.5.
th
3. Measured flow below Boulder at 75 St. Stream mile = 17.5
<
Above
Within
Below
Nov81 Dec 91 Feb82 Apr 82 May 92 Jul 92 Sep 92 Oct92 Dec 92 Jan 93
Month
Figure 9-22. Monthly flows in Boulder Creek for calendar year 1992, above, within, and
below the City of Boulder.
9-42
-------
Table 9-13. Total sources of flow, Boulder Creek, CO, 1992 (in cfs).
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Local
Urban
Runoff
1.94
0.00
22.83
1.52
7.77
2.99
4.03
13.12
0.00
3.17
12.38
3.69
Other
Runoff
0.32
0.00
3.79
0.25
1.29
0.50
0.67
2.18
0.00
0.53
2.06
0.61
Total
Runoff
2.26
0.00
26.62
1.77
9.08
3.48
4.70
15.30
0.00
3.70
14.44
4.31
Upstream
Inflow
13.67
16.20
21.96
54.57
137.90
133.30
109.77
69.13
33.63
23.45
15.03
24.08
VWVTPeff
22.51
22.74
29.81
28.35
27.58
28.79
29.16
29.96
28.98
26.51
24.88
24.31
BsupCanal
0.00
0.00
0.03
0.35
45.40
62.47
137.97
91.65
7.72
2.51
0.00
0.00
Total
Sources
40.71
38.94
105.05
86.80
229.01
231.52
286.29
221.34
70.33
59.88
68.79
57.00
Runoff
(%)
4.77
0.00
21.73
1.75
3.39
1.29
1.41
5.93
0.00
5.30
18.00
6.48
Runoff
Producing
Rainfall
(inches)
0.41
0.00
4.82
0.31
1.84
0.61
0.85
2.77
0.00
0.67
2.53
0.78
Upstream Runoff
4-WWYP Effluent
-K- Boulder Supply Canal
Total Runoff
140.06
120.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 9-23. Total sources of flow for Boulder Creek, CO, 1992.
9-43
-------
Conclusions Drawn from the Water Budget
The results of examining the behavior of Boulder Creek each hour of calendar year 1992
provide dramatic testimony to the influence of man on this stream. Boulder Creek is typical
of streams in urban areas because of the intense level of human activities associated with
manipulating water resources as part of agricultural, industrial, mining, urban and/or other
activities. The following conclusions can be drawn from this water budget:
1. Given the wide variability in flows, even from hour to hour, it is not meaningful to
try to find a single "design event" to analyze the impact of urban runoff or any
other single term in the water budget.
2. A continuous water budget with a small time step, that is, hourly, is essential in
order to capture the reality of stream dynamics.
3. A process oriented approach is essential to accurately characterize what is
happening in complex urban stream systems. The Boulder Creek system has
evolved over the past 139 years and is a complex combination of facilities and
processes including reservoirs, canals, hydropower generation, imports,
exports, and instream flow releases. Statistical approaches can be used in
conjunction with continuous simulation but a process oriented continuous
simulation is essential in order to derive reliable information for risk analysis.
4. A primary purpose of human activities is to reduce the variance in streamflows.
The prior appropriations doctrine used in the West allows human activities to be
traced and to show how variance reduction occurs due to deliberate human
actions.
5. The hydrologic regime changes drastically over the eight mile reach of Boulder
Creek as it passes through Boulder. Thus, it is not meaningful to base policy
decisions on average conditions. The stream goes from being a rushing
mountain stream used for kayaking to a gentle valley stream flowing through
open space. Thus, the desirable flow regime varies accordingly.
6. Fish are permanent residents of Boulder Creek. Thus, from their perspective,
the flow frequency analysis should be done with a very short time step, say an
hour. Existing water quality standards, based on a seven day average low flow,
have little meaning to a fish population that has to live in a stream system with
flows ranging from 0 to 140 cfs over a single day.
7. The wide variety of stakeholders associated with Boulder Creek continue to
adapt the stream system and its management in light of changing attitudes and
values. The Boulder Greenways Program, implemented during the past decade,
is a dramatic example of these changes as is the City's recently enacted
instream flow improvement program.
9-44
-------
8. Population and land use management via the open space program have had a
major beneficial impact on Boulder Creek. Thus, an integrated appraisal of
land and water management is essential.
9. A risk analysis-based approach to the problem can be easily implemented using
the results of the continuous simulation model. The frequency distributions need
to reflect the appropriate averaging time for the affected species. For Boulder
Creek, an hourly time step is essential because of the dynamics of the forcing
functions on the system and the short travel times through the system.
Urban Stormwater Quality
Stormwater Pollution in Boulder
The City of Boulder inventoried nonpoint pollution sources within BCW(City of Boulder
1990). Results are summarized here under the headings of agricultural, forest fires,
highway, mining and urban runoff.
Agricultural Water Quality
Irrigation using Boulder Creek water is practiced in the lower valley portion of BCW.
Irrigation return flows and nonpoint runoff do not have a significant impact on Boulder
Creek above 75th St. because this agricultural water enters downstream. Agricultural
activities may impact water quality entering Boulder Reservoir.
Forest Fires
A large 4.5 square mile fire occurred during the summer of 1989 in the foothills area called
Sugarloaf Mountain. Subsequent heavy rains caused severe soil erosion in the immediate
area. Some of these impacts were felt in Boulder Creek with additional sediment
accumulations of up to 16 inches.
Highway Runoff
Sanding and salting of highways during the winter months increase loadings to the BCW.
Highway 119, which runs parallel to Middle Boulder Creek, is one of the prime concerns
due to the relatively heavy traffic and need for extensive ice control due to its mountainous
location. During the winter of 1987-1988, a total of 2,869 tons of sand and 201 tons of salt
were applied to 17 miles of Highway 119 between Nederland and the canyon mouth. An
equivalent amount is applied to county roads that intersect Highway 119. No specific
detrimental receiving water impacts have been documented to occur as a result of this
activity.
Mining Runoff
BCW was once actively mined. Some residual mine runoff occurs. Gravel mining in the
lower portions of BCW has also had an impact on the creek. These problems have been
9-45
-------
addressed. Some runoff quality problems from mining still exists during relatively wet
periods, such as 1995.
Urban Stormwater Quality
Nilsgard (1974) evaluated urban runoff in Boulder. He sampled an urban catchment that
drained to Boulder Creek near Broadway. Nilsgard noted the impact of stream diversions
on flows in the system. During dry-weather periods, virtually all of the streamflow was
diverted at Broadway just above where the storm drain entered Boulder Creek. Base flow
in the storm drain provided the only significant dry-weather flow in Boulder Creek at that
point. Nilsgard's data showed that urban runoff is equivalent to secondary effluent based
on annual loads were calculated. Unfortunately, Nilsgard did not explain how urban loads
were calculated. In contrast, analysis completed for this report indicates that urban runoff is
much less important than sewage effluent on an annual basis.
Bennett and Linstedt (1978) analyzed Boulder's stormwater quality with a limited sampling
program of an urban, suburban, agricultural, and natural area. They sampled six storm
events, most of which reflected winter snow conditions. Their results indicate that
urbanization appears to cause a decrease in water quality. They did not relate the variable
water quality to any beneficial uses. They also looked at treatability. Bennett and Linstedt
(1978) concluded that more studies are needed to understand the quality of urban runoff
and its impact on the receiving water.
Deacon and Vaught (1993) sampled Boulder Creek upstream of the City (Orodell), in the
city (Library and Scott Carpenter Park), and downstream (Valmont). Boulder Creek was
sampled in 1991 on April 23, May 30, July 31, September 27, December 6, and on
February 4, 1992. All of their results indicate a healthy aquatic environment in Boulder
Creek. Unfortunately, they did not describe the flow in the stream nor whether the sampling
was related to storm events.
The City of Boulder Stormwater Quality group has been monitoring water quality in Boulder
Creek for the past few years. Also, all of the over 1,000 outfalls into the Boulder Creek
stream system have been inventoried and checked for dry-weather flows. Generally,
Boulder's stormwater runoff is typical of other urban areas. No significant illicit sources of
storm drainage were identified.
Urban stormwater quality can be estimated using event mean concentration estimates,
which are based on a national database for the U.S. (Debo and Reese 1994). Also,
Denver has collected many samples of urban runoff quality as part of earlier studies of the
nature of urban runoff (NURP studies) and more recent NPDES sampling. Boulder has
also collected urban runoff quality samples. The national and Denver databases of
stormwater samples for suspended solids concentrations were evaluated to see how these
concentrations vary both spatially and temporally. A comparison of the means and
variances of the two datasets indicates no significant differences in the means or the
variances.
9-46
-------
The main controls for urban runoff and nonpoint runoff control in Boulder have been a very
aggressive land acquisition program, which has set aside about 60,000 acres during the
past 25 years. This open space program has the concomitant objective of limiting
population growth in the City of Boulder to 160,000 people instead of the earlier projection
of 250,000, a 36 % reduction in projected population. Another control is the Tributary
Greenway Program wherein the City has acquired riparian lands and created an award
winning linear park and greenbelt system, which is heavily used by residents and visitors.
A major stream restoration was done as part of this program. The key direct water related
component of this study was the City's commitment for instream flow needs with a
guaranteed minimum flow of 15 cfs in Middle Boulder Creek as it moves through the City.
The City has also installed stormwater detention systems to reduce pollutant loads from
some of its tributaries such as Goose Creek. These ponds are an integral part of the
Greenway program.
More complete analysis of Boulder's urban runoff quantity and quality is limited by the lack
of concurrent measurements of flow and quality from the major storm drains and tributaries.
The results of stormwater quality sampling indicate no major problems nor is there any
direct evidence of the link between urban runoff and stream impairment, (e.g., fish kills).
The City plans to install additional stream gages along Boulder Creek. This will greatly
improve the accuracy of estimates of the relative importance of urban runoff.
Recreation and Water Quality in Boulder Creek
Water quality has not been an impediment to recreation in Boulder Creek. The quality is
considered to be excellent and much use is made of the stream for kayaking, tubing, and
wading. The stream is not used for swimming due to its high velocity, cold temperature,
and shallow depths.
Wastewater Characteristics
An important question in analyzing dry and wet-weather quality management strategies is
to determine the relative importance of dry- and wet-weather sources. At the most
aggregate level, the annual loads from each of these sources can be estimated to obtain
the net load after adjusting for removal by treatment. An important question is to
characterize the relationship between WWTP flow and concentration. If infiltration and
inflow are "pure water," then a straight dilution effect would result.
Brown and Caldwell (1990) present monthly influent data for the Boulder WWTP for the
period from CY 1982 to CY 1985. The influent concentration of BOD as a function of
WWTP flow are shown in Figure 9-24. The negative relationship shows that concentration
decreases as flow increases.
Load as a function of flow is plotted in the upper part of Figure 9-24. The resulting scatter
plot indicates that the total load of BOD remains constant at higher flows. This result
indicates that, for BOD, a direct dilution effect is occurring. Thus, the added infiltration and
9-47
-------
inflow are of less concern since they are not causing any significant increase in the BOD
load. Figure 9-25, which is a similar plot for SS, reveals a negative correlation but a slight
increase in load as flow increases. Thus, the increased flows do cause an increase in the
solids load for the WWTP which may cause problems as flows continue to increase.
During the spring of 1995, a major wet weather period occurred with minor flooding and
some sewer surcharging. The daily influent flows to the Boulder WWTP from 1990 to June
1995 are shown in Figure 9-26. Influent flows reached over 45 mgd, well beyond any
inflows experienced prior to 1995. The WWTP was able to treat all flows without
bypassing.
The relationship between WWTP flows and influent quality for BOD are shown in the lower
part of Figure 9-24. The concentration decreases sharply as flow increases with influent
BOD's dropping from about 250 mg/l at lower flows to less than 50 mg/l at the higher flows.
The correlation coefficient for the flow-BOD relationship is -0.82. BOD load as a function
of flow during this critical period is shown in the upper part of Figure 9-26. It shows that
BOD load remains constant. Thus, the infiltration is simply "clean water" and provides a
direct dilution effect.
The results for suspended solids are similar. Figure 9-25 shows the negative correlation
coefficient of -0.55 with influent SS concentrations dropping from nearly 300 mg/l to less
than 100 mg/l at higher flows. For SS, the loads appear to be constant up to a flow of
about 30 mgd. However, beyond 30 mgd, the loads appear to increase significantly,
probably as a result of direct inflow of water to the sewers from surface sources.
This negative correlation is of critical importance in evaluating the impacts of wastewater
and urban runoff discharges on the receiving water. The negative covariance greatly
reduces the potential impact since there is a strong dilution effect as flow increases.
9-48
-------
*3
40
35
f.
- t/f
"!Q| 53
1|25
20
15
10
1
m
B
rfh ^ / I
0 B SB
B B B El
~ El
~ B
e
i i i i i Q i i
0 15 20 25 30 35 40 45 50
Flow, mgd
300
B) 25ฐ
E
ง 200
1
conceni
) PI
> o
Q
o
DQ
50
0
1
a- Corr. coef. = -.82
EP
H EL
~ B a H
ra
iฃJ
" BBH "^f1!. . . .
B H
B B m
H in
El
1 1 I 1 1 I 1
0 15 20 25 30 35 40 45 5
Flow, mgd
Figure 9-24. Effect of flow on BOD load and concentration, Boulder WWTP, 1990-1995.
9-49
-------
(0
80
70
60
50
ro
O 40
30
20
10
350
300
D)
E
c"
o
^
ra
250
200
C
-------
Removal Efficiencies
The removal efficiencies for the Boulder 75th St. WWTP during 1984 and 1985 were as
follows (B&C 1990):
Constituent
BOD
SS
Primary
41%
52%
Primary + Secondary
80%
80%
Removal efficiencies have improved significantly during the past five years as shown in
Table 9-14. In 1988, BOD and SS removal efficiencies were about 80 %, the same as the
mid-1980s performance. However, since 1989, treatment efficiencies have improved to
1994 removal efficiencies of 93.5% for BOD and 96.6 % for suspended solids, a
significant improvement.
Current (1994) variability in treatment plant performance is quite low as shown in Table 9-
15. The effluent SS and BOD show very consistent concentrations with coefficients of
variation (standard deviation/mean) of about 0.10. Even during the unprecedented wet
period of spring 1995, the WWTP produced high quality effluents as shown in Figures 9-27
for SS and Figure 9-28 for BOD. The effluent BOD and SS concentrations are
independent of flow rate. Thus, the Boulder WWTP is producing a uniformly high quality
effluent with little variability in performance even beyond its nominal design capacity.
Sanitary Sewer Overflows
The City of Boulder has not needed to bypass any of its sanitary sewage, even during the
record high flows of spring 1995. This event has a recurrence interval of about one in 25
years. Some localized surcharging of the sanitary sewers did occur for short periods.
Thus, Boulder does not presently have a serious sanitary sewer overflow problem.
Overall Receiving Water Quality Impacts
The water quality standards for the State of Colorado classify waters based on the
beneficial uses to be protected. The only direct water quality evaluations that have been
done are the standard receiving water quality calculations to determine the expected
impact of the wastewater treatment plant on Boulder Creek during the one in ten year,
seven day duration low flow. This approach to water quality management is extremely
narrow because it ignores all of the other components of the water budget and focuses on
a single, unusual point in time. As clearly pointed out in the water budget section, the
health of the stream is an integration of the continuous impacts overtime.
9-51
-------
1/1/90
1/1/91
12/31/94
12/31/95
Figure 9-26. Influent flow to Boulder WWTP, 1990 - 1995.
9-52
-------
Table 9-14. Trends in annual performance of 75th St WWTP, 1988 - 1994.
Year
1988
1989
1990
1991
1992
1993
1994
Permit
Limit
Flow
(mgd)
15.4
15.1
16.1
16.5
17.4
15.5
20.5
Inf. BOD
(Ib/day)
17036
16837
19045
20064
23942
23300
29065
(mg/l)
133
134
142
146
165
182
Effl. BOD
(Ib/day)
3727
2731
2332
2520
1943
1522
(mg/l)
29.02
21.69
17.37
18.31
13.39
10
BOD
Removal
(%)
78.1
83.8
87.8
87.4
91.9
93.5
Inf. SS
(Ib/day)
16981
15838
17837
18195
22635
26268
24371
29065
(mg/l)
132.21
123.31
138.88
141.67
176.24
181
189
Effl. SS
(Ib/day)
3304
1946
1048
1110
1109
909
833
(mg/l)
25.72
15.15
8.16
8.64
8.63
6
7
SS
Removal
(%)
80.5
87.7
94.1
93.9
95.1
96.5
96.6
Table 9-15. Trends in monthly performance of 75th St WWTP.
Month-Yr.
Jan-92
Feb-92
Mar-92
Apr-92
May-92
Jun-92
Jul-92
Aug-92
Sep-92
Oct-92
Nov-92
Dec-92
Jan-94
Feb-94
Mar-94
Apr-94
May-94
Jun-94
Jul-94
Aug-94
Sep-94
Oct-94
Nov-94
Dec-94
Days/mo.
31
29
31
30
31
30
31
31
30
31
30
31
31
28
31
30
31
30
31
31
30
31
30
31
Flow
(mgd)
14.5
14.7
19.2
18.3
17.8
18.6
18.8
19.3
18.7
17.1
16.1
15.7
13.80
13.40
14.30
16.20
16.30
16.80
17.40
17.00
16.40
15.50
15.10
13.30
Influent
BOD
(mg/l)
171
174
134
146
142
132
139
172
160
202
216
212
194
204
171
164
137
169
180
183
171
186
206
218
SS
(mg/l)
157
158
133
142
140
126
155
162
166
163
195
183
176
178
159
170
141
183
166
236
206
202
224
230
Effluent
BOD
(mg/l)
24
21
13
13
13
10
12
10
7
13
16
13
11
13
14
12
13
11
11
10
12
11
12
12
SS
(mg/l)
11
10
8
8
8
10
8
4
4
7
7
7
6
7
7
6
6
8
5
6
7
7
8
7
Statistics for CY 1994
Mean
Max
Min
SID
CofV
15.46
17.40
13.30
1.39
0.09
181.92
218.00
137.00
20.98
0.12
189.25
236.00
141.00
28.86
0.15
11.83
14.00
10.00
1.07
0.09
8.67
8.00
5.00
0.85
0.13
9-53
-------
~
O)
E
c"
o
+3
CO
"E
(D
O
C
O
O
h-
W
<+ป>
OJ
HI
1U
9
8
7
6
5
4
3
2
1
_ 0
H B H El H
a B a H0 0 B
B ElH H B 0 S H El
0 BBS B B a B
B B (gf*fep3 B^ B BB B B B
BBBBBElHBH B
B B B B
B
i i i i i
50
100 150 200 250 300
Influent SS concentration, mg/l
350
Figure 9-27. Influent vs. effluent SS concentrations, Boulder 75th St WWTP.
01 16
ฃ
c
.2 14
1
*.*
O
CO
12
10
C 8
V
I
LU
IEIIHI
m
El
El HH El
H El S El
El
El
Q
50
100 150 200
Influent BOD concentration, mg/l
250
300
Figure 9-28. Influent vs. effluent BOD concentrations, Boulder 75th St. WWTP.
9-54
-------
As pointed out in this case study, BCW is a complex water management system with
many competing and complementary uses including water quality management. The eight
mile stream section that runs through Boulder goes from a rushing mountain stream to a
much slower moving valley stream. Streamflows throughout BC are heavily influenced by
human activities. The upper reach is affected by storage and hydropower plant releases.
The middle reach is also impacted by heavy diversions during the warmer months of the
year. Lastly, the lower reach receives a major increase in flow due to water imports and
the return flow from the WWTP. The potential impacts of stormwater quality on Boulder
Creek are discussed here for the upper, middle, and lower sections of the creek.
Upper Section-Boulder Creek Immediately Above the City
This section of the creek does not receive any significant urban runoff. The upstream land
uses are almost all natural since the land is publicly owned and managed either by the U.S.
Forest Service or the City or County of Boulder. Thus, the runoff quality is excellent. Urban
runoff quality does not affect this section. The major impact on this section is the upstream
diversions and pulsing of flows that reduce the quantity of flow and increase the hourly
variability of flows. This section of the stream is used for kayaking and was the site of the
1995 Olympic Festival kayaking competition.
Middle Section-Boulder Creek at 28th St.
This section of the creek receives urban runoff from the immediately surrounding drainage
area. The concentration of this urban runoff would be typical of the reported values in the
literature. Only about 20% of Boulder's urban runoff enters the middle part of the stream.
This runoff is diluted by runoff from adjacent open space lands. Thus, the volume of urban
runoff is relatively small. The major impact in this middle section is the greatly reduced
flows in the stream because of upstream diversions as the water enters the city. Thus, less
dilution water is available. The City has implemented a major program to augment these
low flows and the stream has undergone restoration as part of the Greenways Program.
No significant urban runoff quality problems have been reported for this reach. Intensive
use is made of this section of the creek because of the creation of a Greenway about ten
years ago. Current activity levels exceed one million people per year. The stream
restoration recently won a national award.
Lower Section-Boulder Creek Below 75th St.
This section receives all of the urban runoff from Boulder. Some of this urban runoff has
received treatment in detention systems, (e.g., Goose Creek). It also receives the return
flow from the Wastewater Treatment Plant and imported water from the Colorado-Big
Thompson Project. Urban runoff is a relatively small source of water, less than 25% of the
WWTP effluent and only 20% of the Colorado-Big Thompson imported water. The WWTP
provides a consistently excellent effluent quality even during very high flow periods such as
the spring of 1995. The most sensitive time of the year for this section is early fall after the
imports have ceased and when the upstream flow is low. This section of the stream is not
presently accessible to the public. Thus, there is little recreational activity to report.
9-55
-------
Risk-Based Analysis of Urban Runoff Quality
The mixed concentration of a constituent in a stream can be calculated as follows:
Co = fCsQs +CrQr)/(Qs + Qr) Equation 9-1
where Co = downstream concentration, mg/l,
Cs = upstream concentration, mg/l,
Cr= concentration of added inflow, mg/l,
Qs = upstream flow, and
Qr= added inflow.
The added inflow can be of several types including:
1. Direct urban runoff.
2. Sanitary sewer overflow.
3. Wastewater effluent.
4. Imported water.
For Boulder Creek, direct urban runoff occurs at numerous places along the stream. There
are no sanitary sewer overflows. Wastewater effluent enters the stream downstream of the
City as does the imported water from the Colorado-Big Thompson Project.
Analysis of the terms in Equation 9-1 and there statistical properties is critical to
understanding the stream water quality impacts. The key factor which has been neglected
in the literature is the covariance of concentration and flow. Covariance is defined as:
s(xy) = (x-xb)(y-yb) Equation 9-2
where s(xy) = covariance between x and y,
x,y = two variables, and
xb, yb = means of x and y.
The correlation coefficient measures the extent of the covariance, or
r(xy) =[(x-xb)(y-yb)]/[(x-xb)*2*(y-yb)*2] Equation 9-3
where r(xy) = correlation coefficient between x and y with
_/ <=/-<= +1
The expected covariance patterns for the terms in Equation 9-1 are discussed in the
following:
9-56
-------
Covariance Between Concentration and Flow
For urban runoff, if a finite amount of material is on the land surface, say a parking lot, then
one would expect to see a negative covariance between concentration and flow. However,
if the source of material is large, say suspended solids from a construction area, then one
could indeed see a positive covariance. For most constituents, a negative covariance
between concentration and flow would be expected as was observed for the WWTP
influent. This negative covariance reduces the expected impacts of stormwater runoff
since a dilution effect occurs.
Covariance Between Upstream Flow and Urban Runoff
The following statistics on causes of 1994 beach closings in the U.S. were reported (Water
Environment and Technology 1995):
Cause Number
Sanitary Sewer Overflows 584
Stormwater Runoff 345
Combined Sewer Overflows 194
Agricultural Runoff 136
Wastewater Treatment Plant Malfunctions 106
While beach closings is not an issue for Boulder Creek, the above statistics do give some
indication of the relative importance of the various wet-weather sources and WWTP
malfunctions. In the case of oceans or large lakes, the covariance between the stormwater
runoff and the receiving water capacity would be expected to be zero. However, for
riverine systems, one would expect it to be positive, that is, when urban runoff is entering
the stream, the flow in the stream is increasing due to runoff from upstream concurrently
entering the system. For Boulder Creek and the City of Boulder, the following
combinations of wet-weather scenarios occur.
1. Worst Case: Localized rainfall over developed portion of the urban area only.
Low base flow in the stream. This situation can occur in late summer. Thus,
upstream flows would be low and most of the stream runoff would be urban
runoff. This situation would be expected to happen a few times a year
associated with light storms.
2. Typical Case: Moderate basin wide rainfall and runoff. This situation would be
associated with the more significant storm events. In this case, the urban runoff
would be a small part of the total runoff since only about 7% of the land use in
BCW is urban land use.
3. Significant Wet-Weather Events: Significant wet-weather events occur one to
five times per year. These events include the major flooding events, which are
rarer. Under this scenario, all of BCW would be expected to be contributing flow
9-57
-------
and infiltration entering the WWTP would be expected to be relatively high due to
the wet conditions. In this case, urban runoff would be an insignificant part of the
streamflow and water quality load.
Ideally, the probability density function for all of these scenarios can be developed.
However, insufficient data were available to make these judgments. It is possible to show
the covariance of streamflow and wastewater treatment plant flow. A total of 526 wetter
days from 1990 to mid 1995 were analyzed to compare the flow in the WWTP with the flow
in Boulder Creek immediately upstream of the WWTP and the imported water from the
Colorado-Big Thompson project. The results, shown in Figure 9-29, indicate a strong
positive covariance of streamflow and WWTP flow. The correlation coefficient is +0.81.
This covariance plot has significant implications for evaluating the impact of WWTP
bypasses or overflows during wet-weather periods. Current thinking is that CSO or SSO
should not occur more than a few (one to five) times per year. Thus, the system would
capture and treat all of the moderate storms. During the larger storms, part, not all, of the
larger events would be bypassed. How serious is this problem? If the covariance between
wastewater flows and receiving water flows is determined, then one could conclude that the
CSO and SSO volume is an insignificant part of the stream runoff during this very wet
period.
Thus, a relatively complex combination of the joint probabilities of undesirable conditions
may occur. This situation can be estimated with reliable continuous simulation or Monte
Carlo analysis. The results shown in Figure 9-29 indicate 23 days when the flow in the
WWTP was at least 40 cfs. This would correspond to about four events per year, well
within the current guidelines of the allowable number of overflows per year. But according
to the covariance analysis, if the WWTP flow is 40 cfs, then the Boulder Creek flow would
be over 500 cfs, or a dilution ratio of over 14:1. At a WWTP flow of 70 cfs, the expected
flow in Boulder Creek would be over 1600 cfs, a dilution ratio of over 23:1. This assumes
that all of the storm is bypassed. In reality, only part of the storm would be bypassed. If the
capacity of the plant was 50 cfs, then the bypass would be the difference. Thus, the
expected overflow for the 70 cfs case is 20 cfs, not the entire 70 cfs. Correspondingly, the
dilution ratio is about 80:1.
9-58
-------
80 T
2U
10 -
0
ซ w
III Illlll 1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Boulder Creek Flow (cfs)
Figure 9-29. Boulder WWTP flow vs. flow in Boulder Creek.
9-59
-------
The key point brought out by the risk analysis is that including the covariance among
concentration and flow and among flows is critical. All of these covariances help reduce
the impact of stormwater runoff. Negative covariance between concentration and flow
indicates that the concentrations decrease at higher flows. The positive covariance
between upstream flows and wastewater flows means that significant dilution capacity is
available during these wetter events. Also, overflow events do not bypass all of the event,
but only part of it. Thus, the impacts are even lower.
Ultimately, real-time water management will exist in urban areas. Thus, cities will be able
to deterministically manage the concentrations and the flows entering the receiving waters
throughout the year. The City of Boulder may have this capability in the next five to 10
years. This real-time control will reduce the probability of "worst case" conditions occurring
since the system can be managed to avoid these possibilities.
Overall, the benefit-cost-risk perspective provides valuable insights into the urban
stormwater quality problem and to evaluating urban water systems in general. A key
ingredient of improved water management is direct measurement of the behavior of the
system and the management flexibility to take advantage of multipurpose water and land
management opportunities. The City of Boulder and BCW offer numerous illustrations of
the benefits of this approach.
9-60
-------
References
Anonymous (1992). Hydata. 11,6.
Bennett, E.R. and K.D. Linstedt (1978). Pollutional Characteristics of Stormwater Runoff.
Colorado Water Resources Research Institute Completion Report No. 84. Fort Collins,
CO.
Brown and Caldwell (1990). Treated Water Master Plan, Phase 1, Final Report. City of
Boulder.
City of Boulder (1983). Boulder Reservoir-Development Master Plan. Boulder, CO.
City of Boulder (1990). Boulder Creek Basin Planning to Reduce Nonpoint Pollution by
Using Best Management Practices. Boulder, CO.
City of Boulder, (1998) Boulder Creek Watershed, CO. Hydrosphere, Boulder CO.
City of Boulder, (1998). Long Range Management Policies. City of Boulder Open Space
CIS Lab, R Graver, Boulder, CO,.
City of Boulder Planning Department and Boulder County Land Use Department (1990).
Deacon, J.R. and D.G. Vaught (1993). Assessment of Water Quality of Boulder Creek,
Boulder County, CO. Analysis of Water and Sediment Chemistry and Benthic Invertebrate
Communities. Research Project. U. of Colorado at Denver.
Debo, T. N. and A.J. Reese (1995). Municipal Storm Water Management. Lewis
Publishers. Boca Raton, FL.
Heaney, J.P. (1993). New Directions in Water Resources Planning and Management.
Water Resources Update. Fall.
Lacy, G. (1995). Personal communication with the Director of the Stream Restoration
Program. City of Boulder, CO.
Loucks, D.P. (1995). Developing and Implementing Decision Support Systems: A Critique
and a Challenge. Water Resources Bulletin. Vol. 31, No. 4.
Maass, A., et al. (1962). Design of Water Resource Systems. Harvard University Press.
Cambridge, MA.
Mays, L.W. and Y-K. Tung (1993). Hydrosystems Engineering and Management. McGraw-
Hill. New York, NY.
9-61
-------
McPherson, M.B. (1973). Need for metropolitan water balance inventories. Jour, of the
Hydraulics Div. ASCE. 99, HY10, p. 1837-1848.
Nilsgard, V. (1974). A Characterization of Urban Stormwater Runoff in Boulder, Colorado.
MS Thesis. Dept. of Civil, Environmental, and Architectural Engineering. U. of Colorado.
Boulder, CO.
Office of Technology Assessment (1982). Use of Models for Water Resources
Management, Planning, and Policy. Congress of the United States. Washington, D.C.
Peterson, M.S. (1984). Water Resource Planning and Development. Prentice-Hall.
Englewood Cliffs, NJ. 316 p.
Rozaklis, L. (1994). Boulder Creek instream flow program. Talk at U. of Colorado at
Boulder.
Smith, D.S. and P.C. Hellmund, (Eds.) (1993). Ecology of Greenways. U. of Minnesota
Press. Minneapolis, MN.
Smith, P. (1987). History of Flooding in Boulder. City of Boulder, CO.
USEPA (1991). The Watershed Protection Approach, An Overview. Office of Water. U.S.
Environmental Protection Agency. Washington, D.C. EPA/503/9-92/002.
Viessman, W., Jr. and C. Welty (1985). Water Management: Technology and Institutions.
Harper and Row Publishers. New York, NY.
WBLA (1988). Raw Water Master Plan. City of Boulder. Boulder, CO.
WEF(1993). Proceedings Watershed'93. WEF. Alexandria, VA.
WEF(1996). Proceedings Watershed'96. WEF. Alexandria, VA.
Wurbs, R.A. (1994). Computer Models for Water Resources Planning and Management.
IWR Report 94-NDS-7. U.S. Army Corps of Engineers. Alexandria, VA.
9-62
-------
Chapter 10
Cost Analysis and Financing of Urban Water Infrastructure
James P. Heaney, David Sample, and Len Wright
Introduction
The purpose of this chapter is to provide summary information regarding the cost of
water, wastewater, and stormwater infrastructure for U.S. cities. While the main theme of
this report is stormwater, some of the innovative ideas proposed relate to water supply.
An example is reusing stormwater for irrigation to reduce water supply demands.
Demand for Water Infrastructure
The effect of dwelling unit (DU) density on water use is shown in Table 10-1, on
wastewater is shown in Table 10-2, and on stormwater is shown in Table 10-3. The
wastewater table uses the indoor water supply as the estimate for base wastewater flows.
A range from two to 10 DU's per gross acre is used since most residential developments
fall within this range. Gross area is defined as the lot and the right-of-way in the
neighborhood only. It does not include open space or other land uses. The procedure
and the results are described next for the three components of urban water systems.
Effect of Density on Imperviousness
The effect of DU per acre on pervious and impervious areas was evaluated using the
database described in Chapter 3. The square feet of land devoted to pervious and
impervious areas, as a function of DU per acre, is shown in Figure 10-1. At two DU's per
acre, the total land area is about 21,800 square feet. About 12,000 square feet of this
land is pervious. At the other end of the scale, only 1,600 square feet of pervious area
exists for a density of 10 DU's per acre. The difference in pervious area per DU is
dramatic, even over this relatively small range of DU densities. Similarly, the impervious
area increases from about 2,750 square feet at 10 DU per acre to 9,800 square feet per
acre at two DU per acre, over a three-fold increase. Thus, even though the percent
imperviousness decreases as density decreases, the total imperviousness per DU
increases significantly.
Effect of Density on Pipe Length
Using the same database, the effect of density on lot width is shown in Figure 10-2.
Between three and 10 dwelling units per acre, the lot width varies linearly ranging from 25
feet at 10 DU per acre to 90 feet at three DU per acre. Below three DU per acre, the lot
width increases at a more rapid rate, reaching 140 feet at two DU/acre.
10-1
-------
Table 10-1. Effect of dwelling unit density and irrigation rate on indoor and outdoor water
use.
Percent of irrigable area that is watered:
Irrigation rate (inches/yr.):
Dwelling Unit
Density
(DU/acre)
2
4
6
8
10
Pervious Area
(sq.ft./DU)
14,000
5,500
3,100
1,900
1,400
Indoor'
Daily Use
(gal./DU)
180
180
180
180
180
75%
5
10
15
20
30
Annual average irrigation (gal./DU)
77
40
22
13
10
154
79
45
26
20
231
119
67
38
31
307
159
90
51
41
461
238
134
77
61
40
615
318
179
102
82
1) Assumed indoor water use in gallons per capita per day =60
Assumed number of people per dwelling unit =3
Table 10-2. Effect of dwelling unit density on wastewater and infiltration/inflow.
Dwelling
Units
Density
(DU/acre)
2
4
6
8
10
Indoor1
Daily Use
(gal./DU)
180
180
180
180
180
Lot Width
Or
Frontage
(ft./DU)
140
82
62
42
22
Assigned2
Feet of
Pipe
(DU)
70
41
31
21
11
I/I3
Daily
(gal./DU)
35C
205
155
105
55
1) Base wastewater flow is assumed to equal indoor water use from previous table.
2) Feet of pipe per dwelling unit is 0.5*feet of frontage per dwelling unit.
3) Assumed infiltration/inflow rate in gallons/day/foot = 5
Table 10-3. Effect of dwelling unit density and runoff rates on quantities of stormwater
runoff.
Runoff from impervious area (inches/yr.):
Dwelling
Units Density
(DU/acre)
2
4
6
8
10
Indoor Daily
Use
(gal./DU)
180
180
180
180
180
Impervious
Surface
(sq. ft/DU)
9,780
4,690
3,760
3,445
2,756
10
Daily
Runoff
(gal./DU)
167
80
64
59
47
20
Daily
Runoff
(gal./DU)
334
160
128
118
94
30
Daily
Runoff
(gal./DU)
501
240
193
176
141
4G
Daily
Runoff
(gal./DU)
668
32C
257
235
188
10-2
-------
X
I
\
,
J
5
\
\
IMP
\-
V
PERVIOL
V
ERVIOUS
<^
S
^
^
--*
Iฑ^
.__ 1
^^-1
=
* Total Area
Pervious Area
~ ซ -,
-^
~+ h
- JL
m
2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.
Dwelling Units/Acre
Figure 10-1. Pervious and impervious area as a function of dwelling unit density.
160.00
120.00
100.00
&
at
Li-
iS 80.00
_i
60.00
40.00
20.00
0.00 1.00 2.00 3.00
4.00 5.00 6.00
Dwelling Units/Acre
7.00 8.00 9.00 10.00
Figure 10-2. Lot width as a function of dwelling unit density.
10-3
-------
The total pipe length required to serve a given customer is the sum of the length
immediately in front of the property and a prorated share of the pipes in the system that
serve multiple users. The mix of pipes depends on the nature of the network and the size
of the system. The best general databases found on the network hierarchies, for
purposes of this report, were for sanitary sewers and street networks. Dames and Moore
(1978) conducted a national survey of 455 sewer construction projects. The final results
for sanitary sewer pipe lengths and diameters arranged by population size groups, are
presented in Table 10-4.
If local pipes are assumed to be 14 inches or less, then the ratio of large pipes to small
pipes can be determined as shown in the last column of Table 10-4. These ratios are
plotted as a function of population served in Figure 10-3. The ratios are seen to increase
from about 0.15 for a small system serving about 1,000 people to about 0.4 for systems
serving a population of 400,000.
Another measure of the reasonableness of the preceding ratio is obtained by looking at
the urban street systems having a geometry similar to pipe networks. The results of a
1995 national summary of urban streets is presented in Table 10-5. The ratio of larger
roads to local roads is 0.44 and the ratio of larger roads to collector and local roads is
0.25.
Lastly, an inventory of the water pipe network for Boulder, CO, shown in Table 10-6,
indicates ratios ranging from 0.17 to 0.41 depending upon how "small" is defined.
Boulder is a city of about 100,000. These comparative ratios for streets and water mains
indicate that the ratios based on the Dames and Moore study are reasonable.
Table 10-4. Sanitary sewer pipe in place for various city sizes (Dames and Moore 1978).
Population Range
From
500,000
250,000
100,000
50,000
25,000
10,000
2,500
To
>
500,000
250,000
100,000
50,000
25,000
10,000
Mileage of Various Pipe Sizes
<8"
1,094
4,860
5,010
10,061
9,233
19,041
23,987
8"-14"
39,649
26,123
34,824
29,925
34,609
47,946
74,257
15"-24"
14,971
7,420
5,662
6,108
6,749
7,264
12,740
>24"
12,646
4,990
4,610
5,236
3,402
2,218
3,787
Total
68,360
43,393
50,106
51,330
53,993
76,469
114,771
Feet of larger
pipe/feet of
Smaller pipe1
0.682
0.40
0.26
0.28
0.23
0.14
0.17
1) Assume neighborhood pipes are 14" in diameter or less. These pipes are considered
to be "small".
2) Sample calculation: (14,971+12,646)7(39,649) = 0.68
10-4
-------
Table 10-5. Street mileage in the U.S. -1995.
Urban
Interstate
Other freeways/expressways
Other principal arterial
Minor arterial
Collector
Local
Total Urban
Total Rural
Miles of
road
13,307
9,022
53,044
89,013
87,918
574,119
826,423
3,100,301
%of
urban
1 .6%
1.1%
6.4%
10.8%
10.6%
69.5%
100.0%
Source: STAT: State Transportation Analysis Tables, (http://www.bts.gov/cgi-
bin/stat/final_out.pl)
0.45
0.40
=S 0.25
E
ซ 0.20
0.05
150 200 250
Population served, 1000s
Figure 10-3. Effect of population on the ratio of length of large pipes to length of small
pipes.
10-5
-------
Table 10-6. Summary of water pipe diameters and lengths in Boulder, CO.
Diameter
(inches)
4
6
8
10
12
14
16
18
20
24
26
30
Total
Length,
(1000ft.)
107
517
806
1
288
14
132
19
35
59
2
34
2,014
Cumulative
Length,
(1000ft.)
107
624
1430
1431
1719
1733
1865
1884
1919
1978
1980
2014
Cumulative
%
5.3%
31.0%
71.0%
71.1%
85.4%
6.0%
92.6%
93.5%
95.3%
98.2%
98.3%
100.0%
Assume that all pipes <= 12" serve neighborhood systems
Length of smaller pipes in feet: 1431
Length of larger pipes in feet: 583
Ft. of larger pipe/ft, of smaller pipe = 0.41
If 12" is "small," the multiplier is 0.17
If 12" is "large," the multiplier is 0.41
Use average of 0.29
Water Supply
Based on the recent North American End Use Study (NAREUS) described in Chapter 3,
an average of 60 gpcd is used for indoor water use. Also, the assumed population per
dwelling unit is three persons, based on the NAREUS results. Indoor water use per DU is
independent of lot or house size.
Outdoor water use was estimated as a function of the pervious area. About 75% of the
pervious area is assumed to be the potentially irrigable area. The water budget
presented in Chapter 8 provides detailed information on the expected water deficits for
various cities in the United States. Based on calibration data for Denver, the deficits
shown in Table 8-3 should be doubled to reflect actual practice. Key reasons for the
differences include the fact that not much of the precipitation is viewed as being
"effective" by users. Also, they may over irrigate (Stadjuhar 1997). The resulting water
use in gallons/DU as a function of the irrigation rate in inches per year was shown in
Table 10-1.
10-6
-------
For a given irrigation rate, say 15 inches per year, which is similar to Denver practice, the
daily irrigation use exceeds the indoor water use at lower population densities. On the
other hand, at DU densities greater than six, the outdoor water use remains less than the
indoor water use even for high irrigation rates. The key factor that affects urban water
supply systems is the strong trend towards lower DU density and the corresponding large
increase in pervious area per DU. Thus, even with improved water conservation
practices, outdoor water demand has been increasing due to the lower population
densities associated with urban sprawl.
Wastewater
The base wastewater flow can be estimated as the indoor water use. The main source of
uncertainty in wastewater flows is the amount of I/I. While I/I is a complex process, most
predictive models use feet of sewer as a key explanatory variable. For this case, a rate of
five gallons per day per foot of pipe is used. The resulting sewer flows, shown in Table
10-2, indicate that I/I exceeds base wastewater flow as the population density decreases
below about five DU/acre. If the effect of population on pipe length per DU is included,
then the dominance of I/I becomes even more apparent. Of course, all of these
conclusions assume a constant I/I rate of five gallons per day per foot of pipe.
Stormwater
Stormwater runoff rates depend on local precipitation patterns and the extent of
imperviousness. As shown in Table 10-3, the impervious area per DU increases almost
by a factor of four as density decreases from 10 to two DU per acre. Thus, even though
the percent imperviousness might decrease, the total impervious area increases greatly
as densities decrease. For lower densities, the annual quantities of Stormwater exceed
indoor water use for most parts of the country. In addition, if storage of the first half inch
of runoff is required, then the storage area per DU increases significantly as densities
decrease. The feet of drainage pipe per DU can be estimated as a function of the lengths
calculated above for sanitary sewers. The length of storm sewer required per DU would
be less than for sanitary sewers in the more arid areas since overland flow on the street
can be used instead of pipes for some of the local travel.
Optimal Scale of the Urban Water System
The regionalization problem addresses the tradeoff between the economies of scale of
the treatment plant, and the spatial diseconomies of scale of pipeline distances, as
distances become large. For a description of this problem, the reader is referred to
Heaney (1997), Whitlach (1997), and Mays and Tung (1992).
Adams, Dajani and Gemmell (1972) evaluated the optimal size of service area for
wastewater collection and treatment systems. They show that the collection systems
exhibit diseconomies of scale because of the increasing lengths of pipe per unit of flow
while treatment plants exhibit economies of scale. Their results, presented in Figure 10-
4, show that the optimal size of wastewater service area decreases as population density
decreases and that the diseconomy is quite significant if one exceeds this size service
area.
10-7
-------
The lowest population density shown in this figure is 15 persons per acre, or about four to
five DU per acre. Sprawl is considered to occur at densities less than three units per
acre. These results strongly suggest that the optimal size wastewater service area for
contemporary low density developments is well within the neighborhood size suggested in
this report. Also, Adams, Dajani and Gemmell (1972) argue that decentralized
wastewater systems can provide better water quality than highly centralized systems
because they make better use of the assimilative capacity of the receiving water and
average out stochastic fluctuations in the performance of individual plants.
Clark (1997b) evaluates the effect of size on the least cost combination of collection and
treatment using data collected for the City of Adelaide, Australia. He uses a spreadsheet
model to calculate collection and treatment costs for systems ranging from on-site control
(all treatment-no collection) to a completely centralized system. The summary results for
capital costs, annual operation and maintenance (O&M), and total costs are shown in
Figures 10-5 to 10-7. All values are in 1997 Australian dollars.
The capital cost per service for treatment plants decreases rapidly from over $7,OOOA to a
minimum of around $1 ,OOOA at a very large system serving one million customers.
However, the unit treatment costs are only about $1,500A per service for 1,000 services
and about $1,10OA per service for 10,000 services. Thus, of the total cost savings of
about $6,500 per service as treatment goes from one to one million services, $6,OOOA or
over 90% of the total potential savings in treatment are achieved at the 1,000 service
size.
Offsetting the reduction in treatment plant costs per service is the increasing collection
system costs per service that range from zero to about $5,OOOA. Operating costs for
treatment are the most significant O&M cost. They decline from about $300A per service
per year for individual systems to $50A per service per year for one million services.
Here again, about 80% of the savings in O&M costs can be achieved by a system with
1,000 services. The total annualized cost (amortized construction plus O&M) for this case
study, shown in Figure 10-7, indicates continually decreasing unit costs for the originally
assumed density. However, virtually all of the economies of scale are realized in going
from 1 to 100 services. Further increases in the number of services bring only a small
added gain in savings. If density decreases, then a minimum cost is reached at about
100 services. Interestingly, Clark's (1997b) conclusions are similar to the results obtained
by Adams etal. (1972).
10-8
-------
10 20 30 40 50 60
Serwiee Area in Thousands of Acres
Figure 10-4. Total costs of wastewater collection and treatment systems (Adams et al.
1972). Curves represent average cost functions of collection and treatment (Numbers on
curves represent population densities of number of persons/acre).
8000
7000
6000
8 5000
ฃ
ai
m 4000
"ปปซ,
15
o
O 3000
"5
S.2000
m
O
1000
\
Sewers ;
Treatment Plants;
Connections I
Pumps i
\
10
100
1000
Services
10000
100000
1000000
Figure 10-5. Service scale versus capital costs for components of a sewerage system.
Costs are in 1997 Australian Dollars (Clark 1997b)
10-9
-------
200
150
1000
Services
Figure 10-6. Service scale versus operating costs for components of a sewerage
system. Costs are in 1997 Australian Dollars (Clark 1997b).
1200
Figure 10-7. Effect of varying density of development on the minimum sewerage system
cost/service and scale at which the minimum occurs. Costs are in 1997 Australian
Dollars (Clark 1997b).
10-10
-------
Costs of Infrastructure Components
Capital cost estimating equations for conveyance systems, pump stations, storage
facilities, water treatment, and wastewater treatment plants are shown in Table 10-7. The
general form of all of these cost equations is:
C = aXb Equation 10-1
where: C=cost, and
X=size
The two parameters, a and b, are determined from fitting a power function to the available
data. The traditional way to estimate a and b was by plotting the data on log-log paper
and finding the parameters of the resulting straight line approximation of the data in log-
log space. Now, it is simple to find a and b from a least squares regression that is built
into contemporary spreadsheets.
The exponent, b, represents the economies of scale factor. If b is less than 1.0, then unit
costs decrease as size increases. All of these equations shown economies of scale for
the output measures of either flow or volume. Pipe flow exhibits very strong economies of
scale with b <0.5. The economies of scale factor for treatment plants is about 0.7. A
generic economies of scale factor that has been used for years is b = 0.6 (Peters and
Timmerhaus 1980). All of the cost equations shown in Table 10-7 are updated to 1985.
In order to update them to 1998 $, the resulting estimated cost should be multiplied by
1.41.
Cost of Piping
Dames and Moore (1978) reviewed the results of 455 sewer construction projects as part
of a nationwide study of sewer costs. They summarize the average construction costs of
sanitary sewers per foot of pipe for pipes ranging in size from six to 72 inches. These
costs have been updated to 1998 values. Also, they estimate the range of design flows
for each pipe diameter. The results are shown in Table 10-8. A plot of construction costs
versus pipe diameter is shown in Figure 10-9. A linear relationship is apparent and this
line was forced through the origin. The resulting equation is:
C = 14.99 ID Equation 10-2
Where: C = construction cost/foot in 1998 $,
D = pipe diameter in inches.
Simply stated, pipe construction costs per foot may be estimated as $15 multiplied by the
pipe diameter in inches.
10-11
-------
Table 10-7. Typical capital cost equations for water resources facilities1.
Facility
A. Conveyance
1. Force main
2. Gravity mains
3. Open channel
4. Tunnel
B. Pump Station
1. Well Pump
2. Water Supply
3. Wastewater
C. Storage facilities
1. Reservoir
2. Covered concrete tank
3. Concrete tank
3. Earthen basin
4. Clean/veil
Below ground
Ground level
D. Water Treatment
1 . Package treatment
2. Conventional treatment
3. Direct filtration
4. Pressure filtration
5. Reverse Osmosis
6. Ion exchange
7. Lime softening
8. Corrosion cont.
9. Activated carbon
E. Wastewater treatment
1. Primary
2. Secondary
3. Tertiary
Units
$/ft
$/ft
$/ft-
mgd
$/ft-
mgd
$/ft
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1000$
1985 Cost Equation
Capital Cost1
C=6.97D119
C=5.08D119
C=150Q46
C=12.1Q41
C=4.44D114
C=72H64Q45
C=13H22Q44
C=3.8H37Q76
C=27HQ52
C=160V4
C=614V81
C=532V61
C=42V76
C=495V56
C=275V43
C=580Q64
C=680Q74
C=640Q62
C=402Q68
C=1430Q68
C=370Q68
C=1030Q68
C=32Q67
C=809Q67
C=2980Q62
C=4375Q68
C=11400Q72
Range
6
-------
The next relationship, called a production function, relates the input (pipe diameter) and
the output (pipe flow). The resulting curve, shown in Figure 10-9, indicates that flow
increases at the 2.64 power of pipe diameter, or
Q = 0.0005Z)2 6451 Equation 10-3
Where: Q=pipe flow in cfs
Algebraically, Equation 10-3 can be solved for D and the result substituted into Equation
10-2 to find C as a function of Q. Alternatively, as was done here, a power function was
fit to C as a function of Q. The result is shown in Figure 10-10 and Equation 10-4.
C = 217.66Q0 4JS5 Equation 10-4
Equation 10-4 demonstrates the strong economies of scale for pipe flow with an exponent
of 0.4385. Thus, the good news is that larger sewers are more cost effective in
transmitting flow. The bad news is that probably more feet of sewer pipe will be needed
per service to construct a more complex pipe network.
Hassett (1995) compares the initial cost of sanitary sewers as a function of population
density. His results for construction in wet and dry conditions are shown in Figures 10-11
and 10-12 respectively. Construction in wet conditions costs roughly twice the
construction costs for dry conditions. Costs per dwelling unit for two DU/acre range from
a high of $10,000 for wet conditions to $5,000 for dry conditions. At 10 DU/acre, costs
per DU are only $2,000 (wet) or $1,000 (dry). These results appear to be a bit unrealistic.
The negative exponent of nearly -1 suggests that total costs are fixed and that the costs
per unit are simply total costs divided by the number of units.
Results for sanitary sewer pipe costs as a function of DU densities are shown in Table 10-
9. The feet of pipe in front of the house were determined as described above. The
additional amount of "larger" pipe needed per foot of local pipe is estimated as a function
of population as described earlier. The unit costs of pipes were based on the 1978
Dames and Moore study updated to 1998. The results indicate the very strong influence
of dwelling unit density with base costs ranging from only $1,100 per DU at 10 DU/acre to
$7,000 per DU at 2 DU/acre. The effect of population is also seen to be quite significant
because of the higher unit cost for larger pipes and the extra feet per DU as population
increases.
10-13
-------
Table 10-8. Sanitary sewer pipe costs and flow rates (Dames and Moore 1978).
Pipe
Diameter
(inches)
6
8
10
12
15
18
21
24
27
30
36
42
48
54
60
66
72
Average
1998
Cost
($/foot)
56
101
111
139
172
221
278
292
320
419
506
588
710
793
983
1,047
1,136
Flow Range (mgd)
Min.
0
0.08
0.17
0.29
0.47
0.82
1.3
1.9
2.7
3.8
4.9
8
11.8
17
22.5
29.5
37.5
Max.
0.08
0.17
0.29
0.47
0.82
1.3
1.9
2.7
3.8
4.9
8
11.8
17
22.5
29.5
37.5
48
Mean
0.125
0.23
0.38
0.645
1.06
1.6
2.3
3.25
4.35
6.45
9.9
14.4
19.75
26
33.5
42.75
10-14
-------
$1,200
$1,000
$800
$600
$400
$200
20 30 40 50
Pipe diameter, inches
Figure 10-8. 1998 sewer construction costs per foot of length as a function of pipe
diameter.
30 40 50
Pipe diameter, inches
Figure 10-9. Typical flows versus pipe diameter.
10-15
-------
y = 217.66*
R2 = 0.99
10 15 20 25 30 35 40 45
Design flow rate, mgd
Figure 10-10. Sewer construction costs per foot of length versus design flow rate.
a
3 4000
y=16961X
R2= .99:
Dwelling Units per Acre
Figure 10-11. Effect of dwelling unit density on sanitary sewer construction costs in wet
areas (1996).
10-16
-------
4500
4000
3500
3000
2500
2000
1500
1000
500
h 7682.1X
P - QQ7Q
6 8 10
Dwelling Units per Acre
12
14
16
Figure 10-12. Effect of dwelling unit density on 1995 sanitary sewer construction costs in
dry areas (Hassett 1995).
Table 10-9. Estimated 1998 sanitary sewer pipe costs per dwelling unit for various
dwelling unit densities.
[Larger/smaller Ratio:
Dwelling
Unit
Density
(DU/acre)
2
4
6
8
10
Lot
Pipe
(feet/DU)
70
41
31
21
11
0.1 5| 0.2| 0.4
Added Larger Pipe (feet/DU)
for Various Population Sizes
1,000
10.5
6.15
4.65
3.15
1.65
1) Assumed Unit Cost for Pipe in $/ft:
"Small Pipe" 100
"Large Pipe" 300
10,000
14
8.2
6.2
4.2
2.2
100,000
28
16.4
12.4
8.4
4.4
Cost of
Small
Pipe1
$/DU
$7,000
$4,100
$3,100
$2,100
$1,100
Total Pipe Cost for
Various Population Sizes1
($/DU)
1,000
$10,150
$5,945
$4,495
$3,045
$1,595
10,000
$11,200
$6,560
$4,960
$3,360
$1,760
100,000
$15,400
$9,020
$6,820
$4,620
$2,420
10-17
-------
Cost of Treatment
The cost of treating stormwater varies widely depending on the local runoff patterns and
the nature of the treatment. Cost estimates for combined sewer systems are presented in
US EPA (1993) for swirl concentrators, screens, sedimentation, and disinfection. Capital
costs results are shown in Figure 10-13 and Table 10-10 and operating and maintenance
costs are found in Figure 10-14.
Typically, treatment will be combined with storage in order to dampen peak flows and
allow bleeding water from storage to the treatment plant. This treatment-storage approach
can be evaluated using continuous simulation and optimization to find the optimal mix of
storage and treatment (Nix and Heaney 1988). Ambiguities in such an analysis include
the important fact that treatment occurs in storage and storage occurs during treatment
for some controls (e.g., sedimentation systems). As shown in Table 10-3, average
stormwater flows can exceed dry weather wastewater flows for some lower DU density
situations.
In order to provide a planning level estimate of stormwater treatment costs as a function
of DU per acre and annual runoff, stormwater treatment is assumed to be comparable in
unit cost to primary treatment. The resulting stormwater treatment unit costs in 1998 $
are shown below:
Basic primary treatment: $0.50/1,000 gallons
Average primary treatment: $0.75/1,000 gallons
Refined primary treatment: $1.00/1,000 gallons
These unit treatment costs were multiplied by the estimated quantities of stormwater to
get the annual cost per DU. This annual cost is then multiplied by a present worth factor
of 10 to provide an estimate of the present value of this cost. The results of this cost
estimate for stormwater treatment are shown in Table 10-11 that presents the estimated
treatment costs per DU. These results indicate total costs per DU ranging from $129 for
high density areas with relatively low runoff to $1,829 for low density developments with
high runoff.
Similar analysis can be done for DWF including infiltration. A good first approximation
would be to use $1.50 per 1,000 gallons for treatment cost.
10-18
-------
1000
100
10
iUU
-., 10
I 1
s 0.1
0.01
100
2
IS 10
o
O
1 '
tj
s
o
O
0.01
I
EKB =
: ..-.-.-.-.-;
. .-.f--"
.--'--' ' :
1 10 100 1000
AMD !
CHEMICAL IREAlMtNl
EKR = 4508 -----
! .^-^"""
..^-^"""
...--" ; :
[
!Sป
f
1 10 100 1000
0.1 1 10 100
100
"5 10
I 1
-= 0.1
0.01
100
3?
- 10
s 1
I 0-1
0.01
1000
SCREENS
ENB =
10 100
10 100
1000
1000
Figure 10-13. Construction costs for CSO controls (US EPA 1993).
Table 10-10. Cost equations for CSO control technology (US EPA 1993).
CSO Control Technology
Storage basins
Deep tunnels
Swirl concentrators
Screens
Sedimentation
Disinfection
Cost Equation
C=3.637F826
C=4.982F795
C=0.176F611
C=0.072F"843
C=0.211F668
c=o.mv464
Applicable Design Range
0.15
-------
o
w
o
o
5
"g 10
(0
o
ซ
3
1 1
SCREENS
ENR = 4500
=
p
=^
MM*"
.-
iflSinn
-
*
-
_ *
j '
+ *
"X
10 0/F events /yr 1
30 0/F events /yr 1
1000
o
o
(ft
U)
o
o
O
O
3
100
10 100
Design Flow MGD
O
O
o_
w
ซ 100
M
O
o
5
1 10
B
O
15
3
1 1
DISINFECTION
ENR = 4500
O*
<**
il^^
^
<
ซ
E
0
^^
<<ฃ...,
ft-
^
.*
^-SJ
..-^
I
10 100
Design Flow MGD
SEDIMENTATION
CHEMICAL PRECIPITATION
ENR = 4500
,"
^
^
X
X
X
X
x1
X
X
'
#
'
*
^
^
ป
,
Sedimentation I
ied with Chemical Treatment
1
10
100
Design Flow MGD
1000
Figure 10-14. Operation and maintenance costs for CSO controls (US EPA, 1993).
10-20
-------
Table 10-11. Present (1998) value of cost of treating stormwater runoff.
Runoff from impervious area (inches/yr.):
Dwelling
Unit
Density
(DU/acre)
2
4
6
8
10
Indoor
Daily
Use
(gal/DU)
180
180
180
180
180
Impervious
Surface
(sq. ft/DU)
9,780
4,690
3,760
3,445
2,756
10
20
30
40
Present Value of Costs ($/DU)
457
219
176
161
129
914
439
352
322
258
1,372
658
527
483
387
1,829
877
703
644
515
Table 10-12. Estimated (1998) storage cost per dwelling unit1.
Dwelling
Unit
Density
(DU/acre)
2
4
6
8
10
Impervious
Surface
(sq. ft/DU)
9,780
4,690
3,760
3,445
2,756
Present
Value of
Cost
($/DU)
3,048
1,462
1,172
1,074
859
1) Runoff required to be stored in inches: 0.5
Cost of Storage
The total 1995 construction cost of a ground level prestressed concrete tank as a function
of its volume is shown in Figure 10-15. The average unit cost ranges from $1.00/gal. for
a 250,000 gallon tank to about $.25/gal. for a 10 million gallon tank.
Inspection of the cost curve indicates stronger economies of scale up to the two million
gallon size. The economies of scale factor for the portion of the curve up to two million
gallons in 0.51. The economies of scale factor above two million gallons is only 0.81,
while the average economies of scale factor is 0.62. The estimated cost of storage for
one million gallon systems using the equations in Table 10-7 indicates storage costs
ranging from about $.06/gal. for earthen basins to $.90/gal. for a covered concrete
storage tank.
10-21
-------
The costs of storage reported by US EPA for CSO control projects indicate much higher
unit costs as was shown in Figure 10-13. For a one million gallon facility, the unit costs
range from about $4/gal. to $6/gal. in 1998 $. Recent estimates for CSO storage costs in
New York City are about $9/gal. The cost of land has a major impact on the cost of
storage. The reported unit costs vary from excluding land costs to valuing land at its full
market value.
A preliminary estimate of the potential cost of storage per dwelling unit can be obtained
using a common stormwater detention rule to store and treat the first one half inch of
runoff. For the purpose of this exercise, a unit storage cost of $1.00 per gallon was used
and the runoff is calculated as the runoff from the impervious area. The results are
shown in Table 10-12. If on-site detention systems are used, then the cost of storage per
dwelling unit ranges from $859 for 10 DU/acre to $3,048 for 2 DU/acre.
3000000
2500000
2000000
1000000
500000
7
y = 101.4!
R2 = O.E
x
901
0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000 10000000
Volume in Gallons
Figure 10-15. Cost of a ground level prestressed concrete storage tank in 1995 as a
function of volume.
10-22
-------
Summary of Costs for Urban Stormwater Systems
The variability in the cost per DU for urban water supply is mainly due to the amount of
lawn to be watered and the need for irrigation water. In more arid parts of the U.S., most
of the water entering cities is used for lawn watering. The major factor affecting the
variability in wastewater treatment costs is the amount of I/I. The required lengths of pipe
for water supply and wastewater systems can be approximated based on DU and ratios
of the off-site pipe lengths to the on-site pipe lengths. Piping lengths per DU increase if
central systems are used because of the longer collection system distances.
The costs of stormwater systems per dwelling unit vary widely as a function of the
impervious area per DU and the precipitation in the area. The required stormwater pipe
length per DU is about equal to sanitary sewer lengths for higher density areas in wetter
climates. At the other extreme, very little use is made of storm sewers in arid areas and
runoff is routed down the streets to local outlets. Also, tradeoffs exist between pipe size
and the amount of storage provided. Consequently, generalizing the expected total cost
of stormwater systems is difficult. The following conclusions can be reached for
stormwater systems:
1. Urban sprawl has greatly increased the cost per DU for stormwater because of
the large increase in impervious area per dwelling unit. Early in the 20th
century, DU densities of 8-10 per acre were common. The associated
impervious area per DU was about 3,000 square feet. With contemporary low
density development in the range of two to four DU/acre, the square feet per
DU is about 7,500. Thus, the volume of runoff per DU has increased
dramatically.
2. If detention systems are needed, then storage costs per DU range from about
$850 for 10 DU/acre to over $3,000 per DU for 2 DU/acre.
3. If stormwater receives primary treatment, then the costs range from $129/DU to
$1,829/DU depending on runoff and DU density.
4. For wetter, higher density areas, stormwater piping costs range from
$1,100/DU to $15,400/DU depending upon density and population size.
5. The development of neighborhood stormwater management systems with
potential for reusing some of this water for non-potable purposes should be
explored.
Financing Methods
Stable funding is an essential ingredient in developing and maintaining viable urban water
organizations, whether they are stormwater utilities, watershed organizations, or some
other organizational form. Integrated management offers the promise of improved
economic efficiency and other benefits from combining multiple purposes and
stakeholders. However, the benefits from integrated watershed management exacerbate
10-23
-------
problems of financing these more complex organizations because ways must be found to
assess a "fair share" of the cost of this operation to each stakeholder (Heaney 1997).
Nelson (1995) provides a current overview of utility financing in the water, wastewater,
and storm water areas.
The main financing methods for urban stormwater systems are (Debo and Reese, 1995):
1. Tax funded systems
2. Service charge funded systems
3. Exactions and impact fee funded systems
4. Special assessment districts
Urban stormwater utilities have been a successful way to fund wet weather flow pollution
control systems (Benson 1992, Reese 1996). Roesner, Mack, and Howard (1996)
describe a wet weather flow master plan that formulates an integrated way to finance
necessary stormwater infrastructure for a new development near Orlando, FL. Henkin
and Mayer (1996) describe how EPA's Environmental Financial Advisory Board (EFAB)
and Environmental Financing Information Network (EFIN) can be used to create a
financing strategy for implementing comprehensive conservation and management.
One of the most promising financing alternatives for wet weather flow infrastructure needs
has been the development of a stormwater utility that can assess user fees (Ferris 1992,
Reese 1996, and Benson 1992). A good overview of stormwater utility financing is
provided in Debo and Reese (1995). Collins (1996) describes the formation of a county-
wide stormwater utility in Sarasota, FL. EPA used this county as its first stormwater
NPDES permit in the state.
Pasquel et al. (1996) describe the multifaceted funding mechanisms used by Prince
William County, VA to fund the county's watershed management program. The sources
include a stormwater management fee based upon density and area of impervious
surface, and development impact fees. The authors include a detailed discussion of the
major components of the fee structure. Nelson (1995) describes alternative methods for
calculating system development charges for a stormwater utility. Most systems use a
combination of these methods. The following sections briefly describe the fundamentals
of financing such systems.
Tax Funded System
Usually, the Public Works Department of a city is charged with maintaining and improving
stormwater systems. Projects are funded through the budget of the department, whose
source is mainly property tax revenue. However, if property taxes are used, then the
stormwater system must compete for funds directly with public safety, schools, and other
popular programs.
10-24
-------
Service Charge Funded System
The service charge funded system uses an algorithm that divides the budget for the
stormwater system by some weighting of the demand for service, (e.g., impervious areas
possibly with some reduction if the area is not directly connected). This new funding
method is being implemented because it has the advantage of separating the funding
needs according to the function on a user pays basis. Example fees/month per acre of
impervious surface from cities across the nation are shown in Figure 10-16 (Debo and
Reese 1995). Debo and Reese (1995) suggest the following monthly cost ranges per
residential customer for various levels of service:
1. $1.25-$2.00 for an incidental program
2. $2.50-$4.25 for a minimum level program
3. $3.33-$6.00 for a moderate level program
4. $6.00-$12.00 for an advanced level program
5. >$16.00 for an exception level program
Figure 10-16. Monthly stormwater management fees (adapted from Debo and Reese
1995).
10-25
-------
Exactions and Impact Fees
System development charges (SDC's) have emerged as the way to calculate the charges
to be levied against new developments. This system charges the developer or builder an
up-front fee that represents his equity buy-in to the stormwater system. Usually this fee is
calculated as a measure of the depreciated value of the system, plus system-wide
funding needs minus the existing users' share. The fee must be reasonable to avoid
court challenges. Nelson (1995) defines the rational nexus test of reasonableness of
SDCs. This tests requires:
A connection be established between new development and the new or
expanded facilities required to accommodate such development. This
establishes the rational basis of public policy.
Identification of the cost of those new or expanded facilities needed to
accommodate new development.
Appropriate apportionment of that cost to new development in relation to
benefits it reasonably receives.
Care must be taken where new development results in an increase in the level of service
for existing users. An important feature of this method is the ownership, or equity issue,
of existing users. Usually existing users are grouped into one class for ease of
calculation, however, in actuality, different groups joined at different points in time. At the
time of joining, some contractual agreement (written or unwritten) was initiated. Keeping
track of these agreements over time and space when setting impact fees is extremely
difficult and, if not carefully done, is a key weakness of the impact fee system. Because
of this added database need, and the wide variation in cost allocation methods for
apportioning costs, there can be wide fluctuations in impact fee calculations. These
shortcomings can be overcome, however, with better accounting and tracking of
information.
Special Assessment Districts
This system funds needs within a designated geographic area by dividing the funds,
usually equally, among the parcels within the area. Special assessment districts have a
unique advantage in that they can follow watershed or basin boundaries. The calculation
methods are inherently simple and, usually, the benefits and costs are roughly equally
distributed. The disadvantage to this method is that, usually, unless a flooding disaster
has occurred recently, the prospects for passage of such a district are usually very slim.
Conclusions on Finance
A variety of ways of financing stormwater management systems are available. They can
enable a community to manage both the traditional flooding and drainage problem and
also address issues of stormwater quality.
10-26
-------
References
Adams, B.J., J.S. Dajani, and R.S. Gemmell (1972). On the centralization of wastewater
treatment facilities. Water Resources Bulletin. 8(4), p. 669-678.
Benefield, L. D. et al. (1984). Treatment Plant Hydraulics and Environmental
Engineering. Prentice-Hall.
Benson, R. B. (1992). Financing stormwater utility user fees: where are we now. Water
Env. Technol. 4: 9, 59-62.
City of Boulder (1994). The 1994 Annual Utilities Report, Boulder, CO.
Clark, R. (1997a). An Exploration of the Concept, Unpublished Report #1 in the Water
Sustainability in Urban Areas: An Adelaide and Regions Case Study. Department of
Environment and Natural Resources. Adelaide, South Australia.
Clark, R. (1997b). Optimum Scale for Urban Water Systems, Unpublished Report #5 in
the Water Sustainability in Urban Areas: An Adelaide and Regions Case Study.
Department of Environment and Natural Resources. Adelaide, South Australia.
Clark, R. M. and R. M. Males (1986). Developing and applying the water supply
simulation model. Journal of the American Water Works Association. 78: 8,61-65.
Collins, P. S. (1996). Financing the future of storm water. Civil Engineering. 66: 3, 64.
Dames & Moore (1978). Construction Costs for Municipal Wastewater Conveyance
Systems: 1973-1977. US EPA Technical Report. Office of Water. EPA 430/9-77-014.
Debo, T. N. and A. J. Reese (1995). Municipal Storm Water Management. Boca Raton,
FL. CRC Press/Lewis Publishers.
Denver Water (1997). Comprehensive Annual Financial Report for the Year Ended
December 31, 1996. Denver, CO.
Ferris, J. B. (1992). Stormwater utilities: a successful financing alternative. Multi-
Objective Approaches to Floodplain Management. University of Colorado, Institute of
Behavioral Science. Natural Hazards Research and Applications Information Center. 78-
81.
Gilligan, C. (1996). Funding regional flood control improvements in Fort Bend County,
TX. In Proc. Watershed '96 Moving Ahead Together: Tech. Conf. & Expo. WEF.
Alexandria, VA.
10-27
-------
Gummerman, R. C. etal. (1979). Estimating Water Treatment Costs. EPA-600/2-79-
162a. Cincinnati, OH.
Hassett, A. (1995). Vacuum Sewers-Ready for the 21st Century. In WEF. Sewers of the
Future. WEF Specialty Conference Series Proceedings. September 10-15, 1995.
Houston, TX. Water Environment Federation. Alexandria, VA
Heaney, J. P. (1997). Cost allocation in water resources. Chapter 13 in Design and
Operation of Civil and Environmental Engineering Systems. Revelle, C. and A. E.
McGarity, (Eds). John Wiley & Sons. New York, NY.
Henkin, T., and J. Mayer (1996). Financing national estuary program comprehensive
conservation and management plans: How to identify and implement alternative financing
mechanisms. In Proc. Watershed '96 Moving Ahead Together: Tech. Conf. & Expo.
WEF. Alexandria, VA.
Integrated Utilities Group (1995a). Rate and PIF Review/Update, Volume 1: Report, for
Boulder Water, Wastewater, and Stormwater Utilities. Boulder, CO.
Integrated Utilities Group (1995b). Rate and PIF Review/Update, Volume 2: Appendixes,
for Boulder Water, Wastewater, and Stormwater Utilities. Boulder, CO.
Mayer, P. (1995). Residential Water Use and Conservation Effectiveness: A Process
Approach. M.S. Thesis. Dept. of Civil, Environmental, and Architectural Engineering.
U.of Colorado. Boulder, CO.
Mays, L. W. and Y-K. Tung (1992). Hydrosystems Engineering and Management.
McGraw-Hill. New York, NY.
Merkle, C. (1983). Cost Estimating in Water Resources. ME Report. University of
Florida.
Nagle, D.G., G.W. Currey, W. Hall, and J. L. Lape (1996). Integrating the point source
permitting program into a watershed management program. In Proc. Watershed '96
Moving Ahead Together: Tech. Conf. & Expo. WEF. Alexandria, VA.
Nelson, A. C. (1995). System Development Charges for Water, Wastewater, and
Stormwater Facilities. Boca Raton, FL. CRC Press/Lewis Publishers.
Nix, S.J. and J.P. Heaney (1988). Optimization of storage-release strategies. Water
Resources Research. 24, 11, p. 1831-1838.
Pasquel, F., R. Brawley, 0. Guzman, and M. Mohan (1996). Funding mechanisms for a
watershed management program. In Proc. Watershed '96 Moving Ahead Together: Tech.
Conf. & Expo. WEF. Alexandria, VA.
10-28
-------
Peters, M. and K. Timmerhaus (1980). Plant Design for Chemical Engineers. McGraw-
Hill. New York, NY.
R.S. Means (1996). Heavy Construction Cost Data. 10th Annual Edition. R.S. Means
Company, Inc. Kingston, MA.
Real Estate Research Corporation (1974). The Costs of Sprawl: Environmental and
Economic Costs of Alternative Residential Development Patterns at the Urban Fringe.
April, 1974.
Reese, A. J. (1996). Stormwater utility user fee credits. J. Water Res. Planning and
Management. 122: 1, 49.
Roesner, L.A., B.W. Mack and R.M. Howard (1996). Integrated storm water planning in
Orlando, FL. In Proc. of the 7th Int. Conf. Urban Storm Drainage. Hannover, Germany.
IAHR/IAWQ Joint Committee Urban Storm Drainage.
Schueler, T. (1995). Site planning for urban stream protection. Environmental Land
Planning Series. Center for Watershed Protection. Silver Spring, MD.
Scott, K., D. C. Wang, A. E. Eralp, and D. R. Bingham (1994). Cost estimation
methodologies for the 1992 CSO needs survey. In WEF A Global Perspective for
Reducing CSOs: Balancing Technologies, Costs, and Water Quality, a Specialty
Conference of the Water Environment Federation. WEF. Alexandria, VA.
Stadjuhar, L.E. (1997). Outdoor Residential Water Use. MS Thesis. University of
Colorado, Boulder, CO.
Urban Land Institute (1989). Project Infrastructure Development Handbook. Community
Builders Handbook Supplement Series.
US Army Corps of Engineers (1979). MAPS users guide and documentation. Draft
Engineering Manual. EM-1110-2-XXX. Washington, DC.
US Army Corps of Engineers (1981). Unpublished data on 87 reservoirs built between
1952 and 1981.
US EPA (1976). Areawide Assessment Procedures Manual. Appendix H. EPA 600/9-
76-014. Cincinnati, OH.
US EPA (1992). Manual, Wastewater Treatment/Disposal for Small Communities. US
EPA Off ice of Water. EPA/625/R-92/005. September, 1992.
US EPA (1993). Combined Sewer Control Manual. EPA/625/R-93-007.
10-29
-------
US EPA (1997). Response to congress on use of decentralized wastewater treatment
systems. US EPA Off ice of Water. EPA/832/R-097/001b. April, 1997.
Whitlach, E. (1997). Siting regional environmental facilities. Chapter 14 in Design and
Operation of Civil and Environmental Engineering Systems. Revelle, C., A. E. McGarity,
(Eds). John Wiley & Sons. New York, NY.
Young, G. K., S. Stein, P. Cole, T. Kammer, F. Graziano, F. Bank (1995). Evaluation and
Management of Highway Runoff Water Quality. Technical Report for the Federal
Highway Administration.
Zuniga, A. (1997). Model for Evaluating Water Infrastructure Cost: A methodology
applied to Costa Rica. Master's thesis. University of Colorado. Boulder, CO.
10-30
-------
Chapter 11
Institutional Arrangements
Jonathan Jones, Jane Clary, and Ted Brown
Introduction
Stormwater management institutions of the 21 ^ century must be equipped to face many
challenges. Federal stormwater permitting requirements will affect most cities, even those
under a population of 100,000. Funding and staffing are likely to remain tight, even though
stormwater regulations and requirements continue to expand. Stormwater management
will be only one of a long list of issues that must be addressed by local governments. Given
the time and budget constraints typically faced by municipal staffs, they will have to decide
where stormwater management lies relative to their other priorities. This is no easy task,
given that the benefits of stormwater management can be elusive to quantify.
Furthermore, existing stormwater regulations are transitioning from the promulgation and
implementation stages to the enforcement stage, where local governments may face legal
challenges, particularly as a result of land use restrictions. Coordination among local,
state, federal and private entities is and will continue to be a challenge. Stormwater
management institutions will increasingly have to address both water quality and water
quantity issues. In some cases, this will require retrofitting existing stormwater quantity
structures to address stormwater quality issues. New stormwater management facilities
will also need to be financed and constructed. Better education of the public on the
significance of stormwater issues will be necessary. Research will be needed to develop
new technologies for treating and retaining stormwater runoff. Institutions will have to issue
guidance on complicated and often controversial issues such as riparian corridor
preservation, impervious area limitations, conservation easements, innovative zoning
techniques and other subjects.
Given these challenging tasks, this chapter briefly characterizes the existing models of
stormwater management institutions. It then identifies five key characteristics that future
stormwater management institutions will need and describes specific technical and
administrative issues that these stormwater management institutions will have to address.
Existing Models of Stormwater Management Institutions
There are several existing "models" for stormwater management institutions, including
watershed-based committees, local governmental agencies (such as conventional city and
county public works departments and regional drainage and flood control districts),
stormwater utilities, and privatized institutions. While each of these models is primarily
locally based, each must function under federal and state regulations, as well as local
ordinances. Any of the models could be appropriate for a given area, depending on the
characteristics of the community and the watershed. Ultimately, the decision on what type
11-1
-------
of stormwater management organization is best for an area should be made by local
interest groups. This may involve incorporating stormwater management concepts into an
existing institution or creating a new institution (WEF and ASCE 1998). Key
characteristics of the four local stormwater management institutional models are briefly
highlighted below:
1. Watershed Based Committee/Institutions: "Watershed-based management is a
flexible framework integrating the management of all resources-land, biological,
water, infrastructure, human, economic-within a watershed" (Horneretal. 1994).
These geographically-based groups of multiple public and private entities join
together to pool resources and information, and develop and attain water-related
goals. The primary benefits are that the institution is geographically based, can
provide economies of scale and reduces the "piece-meal" approach to
stormwater management. The primary drawback is the difficulty in coordinating
a potentially large number of parties, establishing and determining authority, and
obtaining funds. The success of watershed-based institutions is also
significantly influenced by the size of the watershed (Schueler 1996).
2. Stormwater Utilities: Similar to water and wastewater utilities, municipalities
assess fees/taxes to support stormwater utilities and use these funds to
implement stormwater programs and facilities. The primary benefit is a steady
stream of revenue dedicated to stormwater that does not have to compete with
other programs and needs. The primary drawbacks are the lack of perceived
need for such institutions (as compared to water and wastewater utilities) and
the required creation of a new operating system that needs legal authorization to
exist, operate, and assess charges (Horner et al. 1994).
3. Local Agencies: Existing local agencies, such as public works departments and
urban drainage and flood control districts, can continue or expand to address
stormwater issues. The primary benefit is that, in many areas, these agencies
are already in place and have established authority. In addition, local
governments are already responsible for land development codes and
regulations with an established legal basis for reviewing and approving
development plans (Horner et al. 1994). In many cases, smaller basins or
subwatersheds are contained within the same political jurisdiction. These
subwatersheds are more easily managed than an entire watershed, which may
span multiple jurisdictions. A local government with already established
authority can manage multiple subwatersheds (Schueler 1996). The primary
drawbacks are limited public funding, the red-tape sometimes associated with
governmental agencies, and a fragmented approach if a watershed spans
several municipalities.
4. Privatization: This involves the developing, selling or partial sale of government-
owned enterprises or services. Benefits of privatization include a reduction in
11-2
-------
high "soft costs" associated with governmental organizations. Although
privatization has proven to be feasible and attractive in the water
treatment/distribution and wastewater treatment arenas, privatization of
stormwater systems is more problematic. Privatization requires a market-driven
service (Rendall 1996). Everyone in a community has the need for a water
supply and wastewater treatment and everyone is willing to pay a reasonable
price for these services. This is a situation that is potentially appealing to a
private business. By contrast, many citizens believe that they do not benefit from
expenditures on drainage and flood control systems and are unwilling to pay for
such services. A private business would normally not find this to be an
acceptable situation, unless the risk can be minimized. Privatization
experiences in the water and wastewater arena are not necessarily transferable
to the stormwater arena.
The stormwater management institution of the future may incorporate characteristics of
each of these models or may look like one of these models in one area and another model
elsewhere. The key to the stormwater management organization of the future is that it
needs to address local issues and be structured to fit local needs. For example, in many
areas, watersheds are contained in a relatively small geographic area; therefore, a
watershed-based approach has a limited scope and limited number of stakeholders where
coordination of stakeholders is a reasonable task. However, some watersheds, such as
the Chesapeake Bay area, may cover several states making a watershed approach more
difficult even though it makes the most sense physically. In some communities,
environmental issues rank as a higher priority than others. In these areas, a few extra tax
dollars a month toward a stormwater utility would be accepted.
The feasibility of innovative stormwater management systems is heavily dependent on
trends in federal regulations. At the federal level, responsibility for urban stormwater
management is spread among several agencies including the U.S. Environmental
Protection Agency (USEPA) (stormwater quality), the U.S. Army Corps of Engineers (flood
control and wetlands) and the Federal Emergency Management Agency (FEMA) (flood
control). Better integration of these agencies could have a significant positive impact on
urban water management (ASCE 1996b). An evaluation of the effect of federal regulations
is beyond the scope of this chapter. However, the suggestions presented here are
expected to be compatible with the existing federal regulatory framework. Similarly, state
involvement in stormwater management is often fragmented between water quality control
entities, water quantity entities and other regulatory programs.
Regardless of the "label" that stormwater management institutions receive, they will first
need to establish a long-range strategy by defining program objectives, assessing existing
conditions, and establishing a program framework. Next, they will need to select and
implement a complementary set of BMPs. Finally, they will need to evaluate the program
by assessing the effectiveness of these BMPs and then modify their strategy as needed
(WEF and ASCE 1998). Stormwater management institutions will be required to address
11-3
-------
both technical and administrative stormwater-related issues and have the characteristics
described in the remainder of this paper.
Required Characteristics of Stormwater Management Institutions
Urban stormwater management institutions for the 21st century will need to incorporate five
key concepts:
1. Integration: Given the probability of tight budgets and limited staffs, stormwater
institutions will need to coordinate a diversified staff to address both stormwater
quality and quantity issues. These personnel will also need to address related
engineering, scientific, legal and planning issues. If a watershed-based model
is chosen for an area, integration among various stakeholders in the watershed
is necessary for the success of the watershed program.
2. Flexibility: Functioning primarily at the local level, stormwater management
institutions will need to be flexible enough to meet the specific stormwater
challenges of their community and/or watershed. Stormwater management
cannot be approached from a "one-size fits all" perspective. Examples of
flexibility include consideration of area-specific receiving water characteristics
and alternative pollutant control approaches such as pollutant "trading."
3. Efficiency: These institutions must be able to function under tight budgets and
limited staffs, while the institutions' responsibilities grow under increased
stormwater permitting requirements. Technology such as geographic
information systems (CIS), the Internet and databases, should be used where
appropriate to efficiently transfer and share information between engineers,
planners, scientists, citizens, and others. Successful stormwater management
strategies and useful data should be shared throughout the country through
publications, conferences, the Internet and other means.
4. Effectiveness: Stormwater management institutions will need to implement
stormwater management practices and programs that result in both water quality
protection and water quantity control. Monitoring programs should be used to
assess the effectiveness of stormwater management practices. Institutions will
have to demonstrate that water quality is measurably improving in order to justify
stormwater-related expenditures.
5. Responsiveness: Stormwater management institutions will need to be able to
respond and adapt to changes in the field. Stormwater facility design criteria
must be modified periodically as new technologies become available and as
design standards are refined. Local government staff will also need to work
diligently to stay abreast of developments related to stormwater. Similarly,
considerable effort must be devoted to staying current with computer-based
technological advances.
11-4
-------
Specific Issues to be Addressed by Stormwater Management Institutions
Financing
The ability of stormwater management institutions to adequately fund and finance
stormwater-related expenditures will perhaps be the greatest challenge for these
institutions, particularly when the public resists new taxes and service fees. Funding is
needed to cover annual operating expenditures such as administration, maintenance and
debt service. Financing is needed to pay for capital improvements. Stormwater
management institutions will need to:
1. Function under decreased federal funding.
2. Coordinate with state, local and federal agencies and the private sector to
allocate funding among various water quality and quantity issues.
3. Prioritize expenditures to meet the growing water-related infrastructure
development and rehabilitation costs (i.e., determine the relative priorities of
CSO, SSO and urban stormwater management) (Schilling 1996).
4. Set specific and limited achievable goals, given the limited financing (Schueler
1996).
5. Develop a meaningful method of cost-benefit analysis (Jones and Jones 1989).
Traditional cost-benefit analysis does not normally occur for expenditures on
stormwater management projects, particularly on the water quality side. The
main quantifiable benefits of stormwater improvements include improved
property and recreational values (ASCE 1996b).
6. Allocate resources to ensure proper maintenance of stormwater facilities.
7. Educate the public to realize that drainage improvements are the financial
responsibility of those at the "top of the hill" as well as the "bottom of the hill."
The public often believes that those that are damaged by stormwater are those
who should pay. Members of the public who "live at the top of the hill" often find it
difficult to accept that they are partially responsible for flooding that is occurring
at the "bottom of the hill," and hence have an obligation to pay for drainage
improvements.
8. Involve local funding sources. Even if non-local funding is available, motivated
local water quality advocates are essential for progress in water quality
improvement.
11-5
-------
9. Develop methods for equitably assigning costs of multi-purpose/multi-group
stormwater management programs (Heaney 1986).
Identification of new funding and financing mechanisms may be required, including
allocating the costs of new infrastructure between public and private entities. Because the
current funding and financing of many watershed-based organizations is tenuous,
strategies should include sustaining these organizations, especially if they are being
considered for implementing stormwater regulatory compliance. In addition to traditional
tax-based and bonding approaches, the following funding and financing sources and/or a
combination of these strategies should be considered:
1. Public-Private Partnerships: involves pooling and matching public and private
funds. Watershed-based strategies can help to pool funds from multiple public
and private entities. Public funds need to be made available for watershed-
based initiatives.
2. Fee-in-lieu of: involves charging developers a fee in lieu of requiring
construction of certain site-specific BMPs. This fee can be put toward
construction of a more cost-effective regional facility.
3. Incentive Programs: provide adequate incentives to encourage developers to
implement appropriate BMPs or enter into watershed-based groups.
4. System Development Charges: fees charged to developers when development
occurs to help fund services and facilities previously constructed in anticipation
of their development. In other words, these deferred fees help recover costs of
capacity built into systems to accommodate expected development. SDCs are
best used in conjunction with other funding methods (Debo and Reese 1995).
Nelson (1995) provides detailed guidance on calculating SDCs.
5. Stormwater Utility: assesses fees/taxes to support stormwater programs and
uses these funds to implement stormwater programs and facilities.
6. Privatization: has been successful in the public water supply and municipal
wastewater treatment fields because there is an assured revenue stream and
because both services are real and perceived necessities. A key issue is "who
pays" and in what proportion.
7. Voluntary: through public education, voluntary pollution-prevention and reduction
should be encouraged to help states and localities upgrade nonpoint source
programs (USEPA 1996).
11-6
-------
Staffing: Inter-Disciplinary Approach
For a water quality and quantity management program to be effective, sufficient qualified
staff must be provided. In an era of shrinking funding, staffing will be a significant issue.
Better communication, coordination and delegation will be required among experts and
stakeholders such as aquatic biologists/ecologists, civil/water engineers, economists,
attorneys, planners, representatives of environmental and citizen's groups.
Staff members must be cognizant of stormwater quantity and quality management. The
subject matter has broadened to include water quality issues such as biology, sediment
and wet/dry weather distinctions. The ability to rapidly transfer and share information/data
through computerized systems, including the Internet, should be used to reduce redundant
efforts among staff members. Institutions will probably need to increasingly "farm-out" work
to private consultants, such as aquatic biologists, rather than maintain large staffs of
experts. Adjustments may also need to be made as stormwater permitting impacts smaller
cities that are able to maintain the staffs required to implement the permitting process.
Administrative Authority
For stormwater management institutions to be effective, they must have adequate state
and local legal authority to accomplish their mission. Authority is needed to create, adopt,
and enforce ordinances and regulations. Statutory authority must exist for local entities to
set up dedicated funding sources, such as a local utility (Horner et al. 1994).
For areas using a watershed approach, an area-wide agency or umbrella organization
having authority to require and direct actions by each member political subdivision is
needed. This type of authority is not available to most individual watershed management
organizations because of multiple jurisdictional involvement or lack of statutory authority.
States could assist in establishing appropriate authority by passing enabling legislation
and by assisting organizations seeking to address regional stormwater regulatory issues.
Considerations include:
The umbrella organization must have an independent and continuous source of
funding.
One entity must guide implementation.
The relative authorities and responsibilities of "overlapping" jurisdictions must be
determined up-front (Jones 1988).
In any event, public works officials are advised to interact regularly with their colleagues in
the city/county/watershed attorney's office because there will increasingly be questions
about the extent of the institutional legal authority.
11-7
-------
Regulatory Flexibility
The USEPA is increasingly demonstrating its willingness to consider alternatives to the
"one size fits all" regulatory approach on wet-weather issues. That is, the USEPA is willing
to consider a case-by-case approach. More flexibility and acknowledgment of regional
and local constraints should be integrated into the regulatory process. For example, many
of the regulatory considerations that apply to streams in humid areas of the U. S. have no
application to streams in arid or semi-arid environments (Harris et al. 1996, Stevens
1996). There is emerging recognition that standards and regulations should realistically
permit flexibility to respond sensibly to varying physical, biologic and economic conditions
and needs. This can be achieved by performing common sense comparisons of benefits,
costs, practicality, and cost-sharing alternatives.
A decision support system is necessary to enable flexibility in regulatory administration,
that is, a collection of approaches enabling water resource planners to select consistent,
appropriate actions with reasonable a priori estimates of the effectiveness of the
approach. New control approaches should be developed and demonstrated to enable
planners to reach protection goals. USEPA (1996) suggests that there would be value in
collating watershed management techniques with information such as on water quality
impacts, efficiencies, total costs and sustainability from research projects and
demonstrations.
In addition, innovative approaches, such as pollutant trading which has been widely applied
in the air arena, have also been applied to the water arena. The USEPA is in the process
of establishing a framework for watershed-based pollutant trading. This type of approach
incorporates market incentives to further water quality goals and adds flexibility to
stormwater regulation (WEF 1996).
Clear Regulations and Standards
Debo and Reese (1995) succinctly summarize the importance of good regulations for
achieving stormwater objectives:
The stormwater management structure must bring
together the institutional goals, objectives, and
administration and the technical solutions using models
and master plans by means of regulations, policies and
ordinances. When properly conceived, legal authority
spans the gap between the two by pairing institutional
goals or concerns with technical solutions through the
use of performance oriented criteria.
In the future, more stormwater quality regulation is likely to occur at the state and local level,
with a decreased role for the USEPA. As long as there is local commitment, knowledge,
and resources, water quality is best managed on a local and/or watershed-basis, with local
and state officials and staff making the key decisions. This approach is consistent with the
11-8
-------
philosophy that specific characteristics of receiving waters should dictate the necessary
quality of wet weather discharges. Clear regulations and standards support efficient and
effective functioning of a stormwater management institution. Regulatory considerations
include:
1. Local problems must be defined clearly to provide meaningful guidance and
leadership to all affected interests throughout the development of enabling
legislation, regulations, and design criteria.
2. Regulations should define functions and minimum performance objectives of
stormwater facilities.
3. Wet weather water quality criteria should be developed that are representative
of the specific receiving waternot merely generic water quality
criteria/standards.
4. Stormwater quality control programs should strive to protect designated
beneficial uses of receiving waters by directing controls at pollutants that impair
beneficial uses; however, it must be recognized that in some cases costs may
be prohibitive to obtain all beneficial uses (WEF and ASCE 1998).
5. Published design criteria for BMPs, in performance and/or specification terms,
must be provided.
6. Regulations must specify minimum submittal requirements for development
activities; identify construction inspection requirements and timing; provide for
short- and long-term maintenance; and provide for documentation of approvals,
special requirements and inspections.
7. Developers proposing construction must obtain water quality impact approvals.
There will be much more emphasis on erosion and sediment control in the
future, as communities recognize the significance of this problem and the
generally poor state of the practice at construction sites.
8. As wet weather criteria/standards become available within the next five to ten
years, the BMPs that are now being implemented may no longer be adequate.
Stormwater management institutions must plan to handle this scenario.
9. Effectiveness and implementability of nonpoint source regulations should be
considered.
10. If the evidence continues to accumulate that aquatic ecosystems are destined
to suffer significant damage beyond a certain percentage impervious area,
11-9
-------
communities are projected to increasingly adopt impervious area "caps," such
as the limitations that Austin, TX already has in place.
Legal Challenges
Stormwater management institutions are likely to function in an era of increasing litigation
related to "wet weather" issues. However, most programs should be able to stand these
tests if they are: not in violation of state legislation or municipal charters, equitable, fairly
enforced in the best interest of the general public, sound from the scientific and
engineering perspectives and well-documented (Debo and Reese 1995).
Nonetheless, much litigation will likely arise from land use-type issues, such as:
1. Impervious area limitations.
2. Maximum slope limitations.
3. Mandatory riparian zone setbacks.
4. Mandatory setbacks from regulatory wetlands.
5. Mandatory setbacks from sensitive environmental features, such as sinkholes in
karst terrain.
6. Lot size limitations.
For example, when a local government suggests allowing no more than 20% impervious
area within a given watershed to protect urban streams, objections from the development
community, governmental leaders and some citizens should be expected.
Regional Solutions
Regional solutions to stormwater issues encompass both physical and administrative
approaches including regional structural stormwater facilities, pollutant trading and
watershed approaches. Regional approaches to stormwater management should be
encouraged and enhanced through state policy and programs.
Watershed-based approaches are often regional by definition since many watersheds
incorporate numerous jurisdictions. Watershed/regional approaches to stormwater
management make sense from a hydrologic point of view, but are often constrained by
administrative issues such as funding, lack of legal authority, and staff continuity. Regional
planning entities, while not always organized around drainage basins, are logical entities to
address regional stormwater concerns. However, regional planning entities need to be
active and have the resources to support stormwater regulatory compliance.
Many communities have come to recognize that larger, "regional" stormwater
quantity/quality control facilities are preferable to numerous, smaller, on-site facilities for
reasons related to maintenance, appearance, functional effectiveness, including
multipurpose use, and cost effectiveness. Unfortunately, many such communities also lack
the up-front money necessary to secure optimal sites for regional facilities and to construct
11-10
-------
the facilities, even though they provide economies of scale in the long run. Stormwater
management institutions must help such communities obtain these sites.
Pollutant trading is one regional solution that has been employed in the air and water
realms. One critical aspect of successful pollutant trading programs is public relations,
including up-front development of partnerships and consensus (Toth 1996). Pollutant
trading systems, including both point and nonpoint sources, allow discharge sources to
exchange pollution control obligations in order to lower the joint costs of compliance. The
potential economic and environmental advantages of trading have drawn increasing broad-
based support. In May 1996, the USEPA issued draft guidelines to encourage and
facilitate watershed-based effluent trading. Successful trading systems require that
government provide three basic conditions: the creation and definition of an allowance, a
quantitative restriction on effluent discharge, and the creation and administration of a
system of allowance exchange (National Institutes of Water Resources 1996).
Podar et al. (1996) summarized progress of trading programs across the nation and
provides examples of such programs (Field et al. 1997). One example in Boulder, CO
involves the decision to improve stream flow, restore the riparian zone and install some
nonpoint source control measures rather than upgrade the municipal treatment facility to
remove more ammonia. Boulder has saved up to $3.5 million in capital costs and gained
improvements to the environment, including improved streambank stabilization, reduced
streambank erosion, improved filtration of runoff, improved fish habitat, more continuous
protected riparian zone for wildlife and increased wetland area. Pollutant trading programs
such as this one should be encouraged and solutions to administrative difficulties should
be shared nationally.
Interest in watershed approaches has also increased, as evidenced by over 300 papers
presented at the "Watershed '96" conference in Baltimore (Field et al. 1997). The
watershed approach is also being driven by federal natural resources management policy.
One of the key motivations for watershed-based approaches is enhanced local control and
improved economic efficiency. Cost-savings can be realized through coordinated
monitoring efforts and cost-effective pollutant removal for the watershed as a whole. Joint
efforts include the pooling of funds, expertise and capital. In many cases, the benefits of
joint efforts are multiplied beyond the initial savings. For example, the benefits of effective
monitoring enable better decision-making based on more accurate and complete data
(Brewer and Clements 1996).
Total Risk Management
Local governments are often involved with a variety of natural hazards, such as fire, wind,
landslides and earthquakes. Stormwater-related issues are just one category of the total
risks facing local governments. Risk management decision-support tools should be used
to optimize the use of various control strategies/technologies for stormwater management
including retrofitting, upstream pollution prevention, land management, and non-structural or
minimal structural approaches (USEPA 1996). For example, risk management
11-11
-------
approaches such as the Watershed Analysis Risk Management Framework (WARMF) can
be used to select management approaches based on cost, effectiveness and risk of failure
of various management alternatives (Chen et al. 1998). The stormwater management
institution should develop acceptable levels of risk on a watershed by watershed basis.
Maintenance
Even the best stormwater management programs and facilities fail without proper
maintenance. Resources must be allocated to ensure proper maintenance of stormwater
facilities. When requirements to install stormwater BMPs are imposed on private parties,
without the assurance that proper maintenance will be practiced, the facilities fail to
function, fall into disrepair, become unsightly and are viewed as a nuisance (Zeno and
Palmer 1986). The stormwater management institution should set up requirements and
guidance for appropriate maintenance. Clear policy should be developed clearly
specifying who is responsible for maintenance (Horner et al. 1994).
Monitoring/Evaluation
Regular monitoring and evaluation helps to determine whether the stormwater program is
achieving its goals and being administered in an efficient, cost-effective manner.
Procedures can include actual environmental monitoring such as water chemistry,
biological communities (e.g., aquatic life), and sediment chemistry. Monitoring program
objectives must be clearly identified when initiating the monitoring program (Horner et al.
1994). Stormwater monitoring should include quick and relatively inexpensive biological
tests to establish the toxicity of stormwater runoff. These tests and other chemical tests
(again, which are straight forward and inexpensive) will enable the determination of
problematic constituents in the stormwater by local stormwater institutions.
Clear guidance should be developed and distributed on developing practical monitoring
programs that represent a compromise between the number of samples suggested by
thorough statistical analysis and economic and resource considerations. Performance
assessment data from existing BMP databases can be used to determine the amount of
data required to evaluate the performance of new BMPs. Clear monitoring guidance is not
available for several biological and ecological properties of stormwater. As more data
become available, the role of BMPs in minimizing or reducing the potential toxicity of
stormwater runoff should be provided (WEF and ASCE 1998).
When determining pollutant removal guidelines, more emphasis should be placed on
defining the hydrologic and water quality characteristics of the receiving water. Moreover,
more public and private entities should have the capability to perform these baseline
studies, without an inordinate amount of training and at relatively low cost. A better
understanding of the receiving water characteristics would include:
Determining a suitable design flow representative of wet weather conditions.
11-12
-------
Enhancing the understanding of dose/frequency/response relationships. That is,
how often can the relevant organisms receive how much of a given pollutant?
Similarly, the use of ecological endpoints or "targets" should be increasingly used to define
objectives for urban stormwater quality management. This type of approach is consistent
with an overall, integrated watershed management approach that links studying streams,
groundwater, aquatic communities and other environmental components of interest. It also
includes studying municipal WWTP discharges, industrial waster sources, CSOs, sanitary
sewer overflows and discharges (WEF and ASCE 1998).
A variety of new monitoring approaches are available including a "stress-response"
framework, risk assessment approaches, environmental effects monitoring and other
methodologies. One innovative approach uses in situ probes and biomonitors that involve
putting organisms in place for brief periods of time to measure phenomena not measured
by typical chemical procedures or using special in situ organisms to detect impacts. One
challenge with biomonitoring-type approaches is increased difficulty with interpreting data,
whereas chemical monitoring allows easier comparison to water quality standards. As
monitoring systems develop over the next decade, a balance will need to be reached
between chemical and biological monitoring approaches (WEF and ASCE 1998).
Finally, stormwater management institutions should regularly evaluate the effectiveness of
monitoring programs and be willing to adapt to improve their effectiveness. This evaluation
should include analyzing results of water quality monitoring, return on expenditures (i.e.,
determining if money invested is providing benefits worth the costs), and public education.
Modeling and Performance Auditing
As a follow-up to monitoring and evaluation, modeling can be used to supplement
monitoring efforts with simulations that allow prediction of both discharge and receiving
water quality (WEF and ASCE 1998). However, selection of appropriate models and
collection of data necessary to run these models can be time-consuming and challenging in
some cases. A WEF and ASCE (1998) summary indicates that models can be used to
achieve the following objectives:
1. Characterize the urban runoff with regard to temporal and spatial detail, and
concentration/load ranges.
2. Provide input to a receiving water quality analyses.
3. Determine effects, magnitude , locations and combinations of control options.
4. Perform frequency analysis on quality parameters (to determine return periods
of concentration/loads).
5. Provide input to cost-benefit analyses.
11-13
-------
Although models do not replace a well-planned field monitoring program, they can
sometimes be used to extend and extrapolate measured data and enhance field-sampling
results.
Acquisition of high-quality data needed to support modeling affect the level of effort and
costs associated with the modeling effort. Two general types of data required for modeling
include input parameters needed in order for the model to function and data needed for
calibration and verification. Input parameters include both quantity and quality-related data.
Examples of quantity-related data include rainfall information, area, imperviousness and
runoff coefficient. Examples of quality-related data include constituent concentration,
median value and coefficient of variation, regression relationships, and buildup/washoff
parameters. Calibration and verification data may include sets of measured rainfall, runoff
and quality samples with which to test the model (WEF and ASCE 1998).
Nonstructural Source Control Strategies
Management institutions will need to place more emphasis on nonstructural source controls
because, in most cases, pollution prevention is more cost effective than pollution
correction. Historically, stormwater programs focused on flood control and structural
controls. In the future, multilevel stormwater management is needed that combines
nonstructural source controls with structural treatment controls (WEF and ASCE 1998).
Examples of source controls include: public education, recycling, stenciling stormwater
inlets, removing illicit discharges, pollution prevention practices for industrial and
commercial sites, modifying deploying methods and substituting products for lawn/garden
care and roadway chemicals, and non-toxic product substitution from materials of
construction and surface coatings/preservatives exposed to rainfall runoff (USEPA 1996).
Land use ordinances including cluster zoning, conservation easements, and mandatory
buffer zones are additional nonstructural strategies to protect stormwater quality.
Watershed-based organizations are particularly well suited to implementation of
nonstructural approaches. Innovative source control practices are expected to flourish in
the future in response to stormwater quality regulations just as RCRA compliance spawned
many activities that have eliminated/modified chemical usage.
Retrofitting
As the shift to recognizing the significance of stormwater quality issues continues to occur,
retrofitting of existing stormwater quantity structures to improve their quantity function and
also serve water quality purposes will occur. For example, to improve pollutant removal,
detention ponds must be changed to increase residence time, minimize short-circuiting,
and provide shallow littoral zones planted with appropriate native wetland plants. Dry
detention, used widely for flood control, typically provides little pollutant removal benefits
because of its short detention time, bottom discharge control, and paved channels. In
many locations, codes require that street curbs and gutters be used with storm sewers to
eliminate runoff ponding, even for short time periods. Many localities are eliminating this
11-14
-------
requirement to promote infiltration with grassed swales, decrease runoff volume, and
improve pollutant removal (Horner et al. 1994).
Walesh (1991, 1998) reviews the historic development of the use of storage for stormwater
management in the U.S. as the basis for the current retrofit potential. He stresses looking
at the possibility of retrofitting existing facilities for quantity-quality control before
constructing new facilities. Lower cost solutions may result. Various quantity-quality case
studies are provided. Walesh and Carr (1998) describe retrofitting a combined sewer
system, by means of controlled on and below street storage of storm water, to cost-
effectively solve basement flooding throughout an 8.6 square mile community.
Construction costs for the largely implemented system are one third of the cost of
traditional sewer separation.
Technology Transfer
Technological advances offer great potential to enhance stormwater management.
Conducting more "real time" analysis and system operation should increasingly become
more feasible (Schilling 1996, Field et al. 1997). CIS will increasingly be linked with
hydrologic modeling and decision support systems, thereby facilitating master planning.
For example, the USEPA recently released a package called BASINS (Better Assessment
Science Integrating Point and Nonpoint Sources) that provides links to nonpoint models
including HSPF and QUAL2E using ArcView (Lahlou et al. 1996). The ability to present
results of engineering analyses and to depict structural improvements will be greatly
enhanced through new technology, and this will be valuable for educating the public and
decision makers. Hydrologic computer models should be even easier to use than they are
now. Similarly, reliable stormwater quality software will likely be developed and be easy to
use. Even though stormwater management is expected to continue to occur primarily at
the local level, local staff should be able to take advantage of national databases with
design and implementation data to determine what measures are most appropriate for
their communities. For example, the USEPA and ASCE are in the process of developing
a national stormwater BMP database that will provide this type of information (ASCE
1996a).
Guidance for Practices Such as Riparian Corridor Preservation
and Restoration
More guidance is needed for practices such as riparian corridor preservation and
restoration. The virtues of this practice are becoming increasingly recognized, but the
difficulties and limitations should be discussed as well. In many urban areas, to
accomplish marked improvements in water quality and aquatic life, retrofitting stormwater
quality enhancements and stream habitat improvements is necessary. Retrofitting includes:
"restoring degraded urban water courses to either their original condition, or to a condition
that is ecologically and aesthetically satisfactory. This includes not only the prevention of
unwanted erosion, scour, and sediment deposition, but also the new methods for regaining
some of their aesthetic and ecological qualities and contributing to water quality
11-15
-------
enhancement, while at the same time retaining their flood carrying capacity (which is why
the streams were modified in the first place) (Torno 1989)."
Riparian corridor preservation is used as an example of the types of issues that need to be
considered when preparing guidance for these practices. The value of protecting,
restoring, and enhancing riparian corridors along streams in urban settings has been
widely recognized. However, specific guidance on how to preserve, restore, and/or
enhance riparian corridors has been lacking, particularly on the institutional side. In the last
few years, efforts have begun to develop this type of guidance and should continue. For
example, Herson-Jones et. al. (1995) recently provided guidance on riparian buffer
programs used to mitigate the impact of urban areas on nearby streams based on a
national survey and literature review. They recommend a step-by-step approach including
identifying program objectives, assessing site conditions, determining a program structure,
establishing minimum or standard width requirements, defining exceptions of rules for
increasing or decreasing the standard width and evaluating the potential water quality
benefits of the buffer program. They also address issues such as plan review and
inspection, long-term buffer management, maintenance, enforcement, construction, post-
construction and establishment of local ordinances.
Similarly, many federal agencies recently joined together to write Stream Corridor
Restoration: Principles, Process, Practices, which provides guidelines for stream
restoration and is expected to be released in 1998 (Tuttle and Brady 1996). A manual
focusing on the restoration of urban streams was produced in the midwest by a partnership
of federal, state and local government units (Newbury et al. 1998).
In conjunction with technical issues, guidance should address socioeconomic issues such
as:
1. Selecting a variable versus fixed width approach (a "variable width" approach to
delineating a buffer zone makes good sense technically, but a "fixed width"
approach is much easier to administer).
2. Convincing reluctant developers and other property owners of the merits of
leaving riparian zones undeveloped.
3. Legal aspects of buffer zone restrictions.
4. Promoting restoration of channels (Brown et al. 1996).
Public Involvement and Education
Public involvement is imperative to foster community ownership in stormwater programs
(Debo 1982, Walesh 1993, Wright 1982). The public must be better informed to recognize
that stormwater runoff is just as serious a source of pollution as CSOs. The public
perception must shift to recognize the need for stormwater management. Citizens must
11-16
-------
understand how everyday activities contribute to stormwater problems. Simple pamphlets
inserted into utility bills, books, videos, and displays at local events have been used
successfully. Special programs such as "adopt-a-stream," and "eco-neighborhoods" are
proving successful in encouraging citizens to buy into programs (Horner et al. 1994).
Furthermore, to obtain consensus and support needed for implementation of stormwater
management programs, watershed stakeholders must be involved in the program
development. Stakeholders can include agencies, organizations, and individuals that will
be affected by the program. The ideal group of stakeholders would include interested
citizens, developers, environmentalists, consultants, planners, property owners and public
agencies. Early and frequent stakeholder involvement is important to develop consensus
in what could otherwise be a controversial process. Issues on which participation should
be sought include: sharing data and mapping, setting priorities, establishing goals,
developing development criteria, measuring success, and reviewing and approving
stormwater programs (Schueler 1996, Walesh 1997).
An appropriate balance must be established between the need for adequate public input
versus excessive public involvement, which can actually impede progress. Given the
increasing knowledge and interest of stakeholders, Walesh (1997) notes that the old DAD
(decide-announce-defend) approach to urban water management must give way to the
more effective POP (public owns project) model.
Conclusion
Stormwater management institutions can incorporate a variety of characteristics of the
existing stormwater models or a combination of these models. The organization should be
locally based with adequate legal authority to create and enforce stormwater criteria and
regulations. Stormwater issues should be tackled on a limited geographic scale,
preferably at the subwatershed level. The stormwater utility approach is probably the most
reliable method for ensuring funds dedicated to stormwater management. Although the
future of privatization in the stormwater arena is not clear, market-based incentives such as
pollutant "trading" in a watershed will clearly become more popular. Watershed-based
organizations face a number of hurdles. Their role in educating the public regarding
stormwater issues could be significant. States could assist by performing more than a
permitting role with possible activities including providing guidance to and enhancing
regional cooperative efforts.
The stormwater management organization will be faced with challenges such as retrofitting
existing stormwater quantity structures to meet stormwater quality needs, developing
guidance for riparian corridor preservation, meeting legal challenges on land use
regulations, and monitoring and maintenance of stormwater structural and nonstructural
BMPs. The ability to rapidly share stormwater-related information through the use of
technology, such as the Internet and CIS, should help to facilitate progress in the
stormwater arena. Public involvement and education will also be keys to the success of
future stormwater management efforts.
11-17
-------
11-18
-------
References
American Society of Civil Engineers (1996a). Nationwide BMP evaluation protocols
parameters to report-final lists and suggested database structure. Letter from B. Urbonas
to J. Anderson. Memphis State University. September 13.
American Society of Civil Engineers (1996b). Proposal to develop guidance manual for
integrated wet weather flow collection and treatment systems for newly urbanized areas.
Submitted to USEPA, Region 2. March 4.
Brewer, K.A., and T. Clements (1996). Monitoring consortiums: a key tool in the
watershed approach. In Proceedings Watershed '96 Moving Ahead Together Technical
Conference and Exposition. June 8-12, 1996. Baltimore, MD. Water Environment
Federation. 21-23.
Brown, E., J. Jones, J. Clary, and J. Kelly (1996). Riparian buffer widths at rocky mountain
resorts. In Effects of Watershed Development and Management on Aquatic Ecosystems
Proceedings of an Engineering Foundation Conference. Snowbird, UT. August 4-9, 1996.
ed. L. A. Roesner. American Society of Civil Engineers. New York, NY. 278-294.
Chen, C. W., R. Goldstein, J. Herr, L. Ziemelis and L. Olmsted (1998). Uncertainty analysis
for watershed management. In Proceedings Watershed Management: Moving from
Theory to Implementation. May 3-6, 1998. Denver, CO. Water Environment Federation.
1097-1104.
Debo, T.N. (1982). Detention ordinances - solving or causing problems? In Proceedings
of the Conference on Stormwater Detention Facilities Planning, Design, Operation and
Maintenance. New England College. Henniker, N.H. August 2-6, 1982. ed. William
DeGroot. American Society of Civil Engineers. New York, NY. 332-341.
Debo, T.N. and A.J. Reese (1995). Municipal Storm Water Management. Lewis
Publishers. Boca Raton, FL.
Field, R., R. Pitt, C.Y. Fan, J. Heaney, M.K. Stinson, R.N. DeGuida, J.M. Perdek, M.
Borst, and K.F. Hsu (1997). Urban wet-weather flows. 1997 Water Environment
Federation Literature Review. (Draft in Progress).
Harris, T., J.F. Saunders, and W.M. Lewis (1996). Urban rivers in arid environments
unique ecosystems. In Effects of Watershed Development and Management on Aquatic
Ecosystems Proceedings of an Engineering Foundation Conference. Snowbird, UT.
August 4-9, 1996. ed. L. A. Roesner. American Society of Civil Engineers. New York, NY.
421-435.
11-19
-------
Heaney, J. P. (1986). Research needs in urban stormwater pollution. Journal of Water
Resources Planning and Management. 112(1).
Herson-Jones, L.M., M. Heraty, and B. Jordan (1995). Environmental Land Planning
Series: Riparian Buffer Strategies for Urban Watersheds. Prepared for US Environmental
Protection Agency Office of Wetlands, Oceans and Watersheds. December. Metro
Washington Council of Governments. Washington, D.C.
Horner, R., J. J. Skupien, H. Livingston, and H.E. Shaver (1994). Fundamentals of Urban
Runoff Management: Technical and Institutional Issues. August. Terrene Institute.
Washington, D.C.
Jones, D. E. (1988). Summary of institutional issues. In Design of Urban Runoff Quality
Controls. Proceedings of an Engineering Foundation Conference on Current Practice and
Design Criteria for Urban Quality Control. Potosi, MO. July 10-15 1988. eds. L. Roesner,
B. Urbonas, and M. Sonnen. American Society of Civil Engineers. New York, NY. 356-
358.
Jones, J. E., and D. E. Jones (1989). Stormwater quality institutional considerations. In
Urban Stormwater Quality EnhancementSource Control, Retrofitting and Combined
Sewer Technology. Proceedings of an Engineering Foundation Conference. Davos Platz,
Switzerland. October 22-27, 1989. ed. H. C. Torno. American Society of Civil Engineers.
New York, NY. 28-35.
Lahlou, M., L. Shoemaker, M. Paquette, J. Bo, S. Choudhury, R. Elmer, and F. Xia (1996).
Better Assessment Science Integrating Point and Nonpoint Sources-BASINS version 1.0.
User's Manual and CD. EPA Office of Water's Office of Science and Technology.
Washington, D.C. EPA-823-R-96-001.
National Institutes for Water Resources (1996). Effluent allowance trading: a new
approach to watershed management. Water Science Reporter. 1 -16.
Nelson, A. (1995). System Development Charges for Water, Wastewater, and Stormwater
Facilities. Lewis Publishers. Boca Raton, FL.
Newbury, R., M. Gaboury and C. Watson (1998). Field manual of urban stream restoration.
Illinois State Water Survey and Illinois Department of Natural Resources. Champaign, IL.
Podar, M.K., R.M. Kashmanian, D.J. Brady, H.D. Herzi, and T. Tuano (1996). Market
incentives: effluent trading in watersheds. In Proceedings Watershed '96 Moving Ahead
Together Technical Conference and Exposition. June 8-12, 1996. Baltimore, MD. Water
Environment Federation. 148.
11-20
-------
Rendall, C.R. (1996). Privatization: a cure for our ailing infrastructure? Civil Engineering.
66(12): 6.
Schilling, K. (1996). Wright Water Engineers Personal Communication with Kyle Schilling.
U.S. Army Corps of Engineers Institute of Water Resources.
Schilling, W. (1996). Potential and limitation of real time control. Proceedings 7th
International Conference on Urban Storm Drainage. Hannover, Germany. IAHR/IAWQ
Joint Committee on Urban Storm Drainage. 803.
Schueler, T.R. (1996). Crafting better urban watershed protection plans. Watershed
Protection Techniques. 2 (2): 329-337.
Stevens, M.A. (1996). South Platte in metropolitan Denvera river in transformation. In
Effects of Watershed Development and Management on Aquatic Ecosystems.
Proceedings of an Engineering Foundation Conference. Snowbird, UT. August 4-9, 1996.
ed. L. A. Roesner. American Society of Civil Engineers. New York, NY. 439-458.
Torno, H. C. (1989). Research Needs in Urban Hydrology. In Urban Stormwater Quality
EnhancementSource Control, Retrofitting and Combined Sewer Technology
Proceedings of an Engineering Foundation Conference. Davos Platz, Switzerland.
October 22-27, 1989. ed. H. C. Torno. American Society of Civil Engineers. New York,
NY. 568-571.
Toth, C.M. (1996). Realities of pollution control planning: St. Catherine's experience.
Proc. Urban Wet Weather Pollution: Controlling Sewer Overflow and Stormwater Runoff,
Specialty Conference. Quebec City, PQ, Canada. Water Environment Federation. 9-1.
Tuttle, R. W. and D. Brady (1996). Interagency stream corridor restoration handbook. In
Proceedings Watershed '96 Moving Ahead Together Technical Conference and
Exposition. June 8-12, 1996. Baltimore, MD. Water Environment Federation. 486-487.
USEPA Office of Research and Development, National Risk Management Research
Laboratory (1996). Wet weather flow research plan. Parts I and II. August 19, 1996.
Peer Review Draft.
Walesh, S. G. (1991). Retrofitting storm water facilities for quantity and quality control.
Proceedings of the International Conference on Urban Drainage Technologies. Dubrovnik,
Yugoslavia.
Walesh, S. G. (1993). Interaction with the public and government officials in urban water
planning. Hydropolis - The Role of Water in Urban Planning. Proceedings of the
International UNESCO-IHP Workshop. Wageningen, The Netherlands and Emscher
Region. Germany. March-April 1993.
11-21
-------
Walesh, S. G. (1997). DAD (decide-announce-defend) is out, POP (public owns project) is
in. Water Resources Education, Training and Practice: Opportunities for the Next Century.
American Water Resources Association. Keystone, CO. June 1997.
Walesh, S. G. (1998). Retrofitting stormwater storage facilities. Seminar presented to the
Indiana Society of Professional Land Surveyors. Valparaiso, IN. July 1998.
Walesh, S. G. and R. W. Carr (1998). Controlling stormwater close to the source: an
implementation case study. American Public Works Congress. Las Vegas, NV.
September 1998.
Water Environment Federation (1996). WEF comments on EPA watershed based effluent
trading draft framework. September 9. Letter to Comment Clerk. Water Docket MC-
4101. U.S. Environmental Protection Agency.
Water Environment Federation and American Society of Civil Engineers (1998). Urban
Runoff Quality Management. WEF Manual of Practice No. 23. ASCE Manual and Report
on Engineering Practice No. 87. Prepared by a Joint Task Force of the Water
Environment Federation and the American Society of Civil Engineers.
Wright, K. R. (1982). Stormwater detention: acceptance and rejection issues. In
Proceedings of the Conference on Stormwater Detention Facilities Planning, Design,
Operation and Maintenance. New England College. Henniker, N.H.. August 2-6, 1982.
ed. Wlliam DeGroot. American Society of Civil Engineers. New York, NY. 284-299.
Zeno, D.W. and C.N. Palmer (1986). Stormwater management in Orlando, FL. In Urban
Runoff QualityImpact and Quality Enhancement Technology Proceedings of an
Engineering Foundation Conference. New England College. Henniker, N.H. June 23-27,
1986. eds. B. Urbonas and L. A. Roesner. American Society of Civil Engineers. New
York, NY. 235-248.
11-22
-------
Chapter 12
Summary and Conclusions
James P. Heaney, Robert Pitt, and Richard Field
Summary and Conclusions
The purpose of this project is to conduct a thorough literature review of contemporary
and projected urban stormwater management practices in the U.S. and other parts of
the world. Based on this review, a framework for evaluating the effectiveness of
innovative stormwater management systems for the 21st century is presented.
Summaries and conclusions for the individual chapters are presented below.
Chapter 2: Principles of Integrated Urban Water Management
The results of the evaluation of the nature of imperviousness in urban areas show that
the quantity of urban stormwater generated per dwelling unit has increased dramatically
during the 20th century due to the trend towards more automobiles which require more
streets and parking, and the trend towards larger houses on larger lots. Commercial
and industrial areas need much more parking per unit of office space than they did
before automobiles. Modern practices dictate devoting more of the city landscape to
parking than to human habitat and commercial activities.
The net result of this major shift in urban land use is low density sprawl development
that generates over three times as much stormwater runoff per family than did pre-
automobile land use patterns. Much of these requirements for more and wider streets
and parking have been mandated in order to improve the transportation system.
Ironically, unlike water infrastructure, these services are not charged directly to the
users. Rather, they are subsidized by the general public including non-users.
Chapter 3: Sustainable Urban Water Management
More sustainable water systems can be achieved by promoting water conservation to
reduce the amount of water that must be imported into cities. Outdoor water use is the
largest source of variability in urban water use. Reuse of treated wastewater and
stormwater for nonpotable uses, such as toilet flushing and irrigation, would greatly
reduce urban water supply needs. Infiltration and inflow in sewers is the largest source
of variability in the quantity of wastewater going to the treatment plant. I/I amounts can
be reduced considerably by improved sewer design, installation, and operation and
maintenance practices. Urban stormwater varies in relative importance because of
climatic variability. On the average, it is of the same order of magnitude as urban
wastewater but it is much more variable.
Chapter 4: Source Characterization
The relative contributions of source areas for a specific pollutant are dependent on
several factors, including the characteristics of the source area and the rain energy and
volume. As expected, directly connected impervious areas contribute most of the runoff
12-1
-------
and pollutants during small rains. However, as the rain depth increases, non-paved
areas can become significant.
If the number of events exceeding a water quality objective are important, then the small
rain events are of most concern. Stormwater runoff typically exceeds some water
quality standards for practically every rain event (especially for bacteria and some
heavy metals). In the upper Midwest, the median rain depth is about six mm, while in
the Southeast, the median rain depth is about twice this depth. For these small rain
depths and for most urban land uses, directly connected paved areas usually contribute,
most of the runoff and pollutants. However, if annual mass discharges are critical (e.g.
for long-term effects) then the moderate rains are more important. Rains from about 10
to 50 mm produce most of the annual runoff volume in many regions of the U.S. Runoff
from both impervious and pervious areas can be very important for these rains. The
largest rains (greater than 100 mm) are relatively rare and do not contribute significant
amounts of runoff pollutants during normal years, but are very important for drainage
and flood control design. The specific source areas that are most important and
controllable for these different conditions vary widely.
Other important source area factors affecting stormwater management concern runoff
pollutant characteristics for the different areas. Particle size of particulates in the runoff
greatly affect many stormwater control practices, such as detention facilities and filters.
If the majority of the particles can be removed from stormwater, much of the potential
problem pollutants are also removed. Unfortunately, the actual particle sizes are
probably much smaller than typically assumed during the design of these facilities.
Chapter 5: Receiving Water and Other Impacts
Urban receiving water may have many beneficial uses, including:
Stormwater conveyance (flood prevention).
Non-contact recreation (e.g., linear parks, recreation, boating).
Biological uses (e.g., warm water fishery, biological integrity).
Contact recreation (e.g., swimming).
Water supply.
With full development in an urban watershed and with no stormwater controls, it is
unlikely that any of these uses can be fully obtained. With less development and with
the application of stormwater controls, some uses may be possible.
There are many instances of receiving water problems associated with urban
stormwater reported in the literature. Receiving water problems associated with urban
stormwater are highly varied. In watersheds that are lightly developed and have
relatively large receiving waters, the impacts are not as obvious as in heavily developed
watersheds in more arid areas.
12-2
-------
Chapter 6: Collection Systems
By applying new technology and revisiting traditional urban water problems with a fresh
outlook, advances are being made in a wide variety of sewer related areas. Integrated
storm/sanitary systems may emerge in the 21st century, that is, combined sewers may
be strategically designed into new urban development. Storm runoff will be reduced by
source control and infiltration BMPs and the residual of small events will be transported
to the WWTP. Large events will be throttled out of the integrated system, before mixing
with sanitary waste, and discharged to receiving waters. This new system will have the
best of both combined systems and separate systems. The advantage of the combined
system has been treatment of small runoff producing events, including snowmelt.
However, the disadvantage has always been the discharge of raw sewage to receiving
waters during large events. With the advantage of control technology, as the sewers
and/or the WWTP reach capacity, the stormwater could be stored and/or diverted
directly to receiving waters without mixing with sanitary and industrial wastes. Future
systems will have a high degree of built in control.
Outlying from the new urban centers, suburban type development still exists. While less
dense than the city, new suburban development will contain some of the mixed land
uses found in the urban center. The collection system serving this area will be far
different from the city, however, because the NPS pollution is not so severe as to
warrant full treatment at the WWTP. BMPs and source control innovations will reduce
stormwater impacts on the receiving water. Regional detention will be used for flood
control and water quality enhancement. Sanitary wastes will be transported via
pressure sewers to collector gravity lines at the city's border. The use of pressure
sewers will reduce suburban I/I to near zero. In addition, the new sanitary low pressure
sewers will be very easy to monitor because the age-old problem of open channel flow
estimation will be avoided by using pressure lines. This provides added certainty in the
flow estimation and facilitates control. Technology borrowed from the water distribution
field will achieve a great level of system reliability and control. In fact, the sewer will
now mirror the water distribution network, essentially providing the inverse service.
Chapter 7: Assessments of Stormwater Best Management Practices Technology
Much of this chapter's discussion is based on a plethora of information that is supported
by a number of local field investigations designed to test a given BMP's effectiveness at
the specific site. Still needed is a national approach, similar to NURP, that would
systematize the results of a large number of investigations into a coherent, well
controlled program to learn about various BMP functions, physical mechanisms,
biochemistry, and design parameters. Also needed is a better measure of
effectiveness. The current measure in terms of percent removal has limited value.
Another need is improvement in the design robustness for various BMPs. Until that is
done, expecting a specific performance from any given BMP is unrealistic. Design
robustness will improve as knowledge is gained on selecting, sizing and designing each
type of BMP. Urban stormwater management also has to consider the safety and
welfare of the citizens living in the urban areas. Issues of efficient site drainage, control
12-3
-------
of nuisances caused by inadequate drainage, the hazards posed by large storm events
and the floods they create, and costs and benefits received for the expenditure of public
dollars, have to be considered. As a result, sound stormwater management has to
address not only mitigating the runoff impacts of urbanization, but also the public and
community needs.
Chapter 8: Stormwater Storage-Treatment-Reuse Systems
In many parts of the country, particularly humid areas, enough stormwater can be
collected to satisfy average irrigation demands. If driveway areas are eliminated due to
possible problems with water quality and ease of collection, the result will be a larger
tank size, however, irrigation demand may still be satisfied in a majority of cases. In
arid areas, particularly those with high evapotranspiration requirements, stormwater
reuse may not be justified by itself. In these cases, combining storage with treated
graywater may be an option worth considering. An extrapolation of this work to
urban/suburban areas of the U.S. is needed.
Chapter 9: Urban Stormwater and Watershed Management: Analysis Case Study
The results of examining the behavior of Boulder Creek in Boulder, CO. each hour of
calendar year 1992 provide dramatic testimony to the influence of human activities on
this stream. Boulder Creek is typical of streams in urban areas because of the intense
level of activities associated with manipulating water resources as part of agricultural,
industrial, mining, urban and/or other interests. The following conclusions, many of
which can be extrapolated elsewhere, are drawn from this analysis:
1. Given the wide variability in flows, even from hour to hour, trying to find a
single "design event" to analyze the impact of urban runoff, or any other
single term in the water budget, is not reasonable.
2. A continuous water budget with a small time step (i.e., hourly) is essential in
order to capture the reality of stream dynamics.
3. A process oriented approach is needed to accurately characterize what is
happening in complex urban stream systems. The Boulder Creek system has
evolved over the past 140 years and is a complex combination of facilities
and processes such as reservoirs, canals, hydropower generation, imports,
exports, and instream flow releases.
4. The wide variety of stakeholders associated with Boulder Creek continue to
adapt the stream system and its management in light of changing attitudes
and values. The Boulder Greenways Program implemented during the past
decade is a dramatic example of these changes as is the City's recently
enacted instream flow improvement program.
12-4
-------
5. Population and land use management via the open space program have had
a major beneficial impact on Boulder Creek. Thus, an integrated appraisal of
land and water management is essential.
6. A key point brought out by the risk analysis is the importance of including the
covariance among concentration and flow and among flows. All of these
covariances help reduce the impact of stormwater runoff.
7. Ultimately, real-time water management will exist in urban areas. Thus, cities
will be able to deterministically manage the concentrations and the flows
entering the receiving waters throughout the year.
Chapter 10: Cost Analysis and Financing of Urban Water Infrastructure
The variability in the cost per dwelling unit for urban water supply is mainly due to the
amount of lawn to be watered and the need for irrigation water. In more arid parts of the
U.S., most of the water entering cities is used for lawn watering. The major factor
affecting the variability in wastewater treatment costs is the amount of infiltration and
inflow. The required lengths of pipe for water supply and wastewater systems can be
approximated based on dwelling unit density and ratios of the off-site pipe lengths to the
on-site pipe lengths. Piping lengths per dwelling unit increase if central systems are
used because of the longer collection system distances.
The costs of stormwater systems per dwelling unit vary widely as a function of the
impervious area per dwelling unit and the precipitation in the area. Urban sprawl has
greatly increased the cost per dwelling unit for stormwater because of the large increase
in impervious area per dwelling unit.
If detention systems are needed, then storage costs per dwelling unit range from about
$850 for 10 DU/acre to over $3,000 per DU for 2 DU/acre. If stormwater receives
primary treatment, then the cost per DU range from $129 to $1,829 as a function of
runoff and dwelling unit density. For wetter, higher density areas, stormwater piping
costs per dwelling unit range from $1,100 to $15,400 depending upon density and
population size. The development of neighborhood stormwater management systems
with potential for reusing some of this water for non-potable purposes should be
explored.
The main financing methods for urban stormwater systems are tax funded systems,
service charge funded systems, exactions and impact fee funded systems, and special
assessment districts. A variety of stormwater management financing systems are
available that enable a local community to manage the traditional flooding and drainage
problem, and also address issues of stormwater quality.
Chapter 11: Institutional Arrangements
Stormwater management institutions can incorporate existing stormwater models or a
combination of these models. The organization should be locally based with adequate
12-5
-------
legal authority to create and enforce stormwater criteria and regulations. Stormwater
issues should be tackled on a limited geographic scale, preferably at the subwatershed
level.
The stormwater utility approach is probably the most reliable method for ensuring funds
dedicated to stormwater management. Although the future of privatization in the
stormwater arena is not clear, market-based incentives such as pollutant "trading" in a
watershed will clearly become more popular. Watershed-based organizations face a
number of hurdles, however their role in educating the public regarding stormwater
issues and involving the public in decision making could be significant. States could
assist by performing more than a permitting role. Possible activities include providing
guidance to and enhancing regional cooperative efforts.
The stormwater management organization will be faced with challenges such as
retrofitting existing stormwater quantity structures to meet stormwater quality needs,
developing guidance for riparian corridor preservation, meeting legal challenges on land
use regulations, and monitoring and maintenance of stormwater structural and
nonstructural BMPs. The ability to rapidly share stormwater-related information through
the use of technology, such as the Internet and CIS, should help to facilitate progress in
the stormwater arena.
12-6
-------
Appendix
Innovative Stormwater Management in New Development:
Planning Case Study1
Brian W. Mack, Michael F. Schmidt, and Michelle Solberg
Introduction
Background
In March 1994, the City of Orlando, FL entered into a Joint Planning Agreement with
Orange County which facilitated the annexation of approximately 20 square miles
(11,500 acres) of primarily undeveloped land southeast of the Orlando International
Airport as shown in Figure A-1. Outlined in the Growth Management Plan Southeast
Annexation Study is the City's vision for the development of this area which includes
providing "opportunities for economic development, protecting natural resources, and
developing an integrated and efficient system of infrastructure and social service
delivery." Over the next 20 years, the entire Southeast Annexation Area is expected to
develop with a mixture of land uses. City planners will regulate the development of the
area, with the goal of creating a compact urban growth center. The growth center will
support the future development of Orlando International Airport and will contain land
uses such as office, service and industrial development, with housing to support the
employment generated by the airport expansion.
The stormwater element of this planning effort included the development of a Master
Stormwater Management Plan (MSMP) for the annexed area. The goals of the MSMP
are to provide regional flood control and water quality protection, protect existing
wetlands, and site regional facilities in such a manner that they meet both the City's and
private land owners' interests. Orlando will use the MSMP to guide development as it
occurs.
In November 1994, the City contracted with WBQ Design and Engineering Inc. to
provide engineering services for the Narcoossee Road Improvement Project. In August
1995, the City amended its contract with WBQ to include the development of an MSMP
also addresses the environmental goals of the City's Southeast/Orlando International
Airport Future Growth Center Plan (May 1995) for the Lake Hart Basin. The MSMP
would provide stormwater management for the projected future growth in the basin as
well as for the Narcoossee Road Improvement Project.
This is a condensed version of the Southeast Annexation Area Lake Hart Basin Master
Stormwater Management Plan, City of Orlando, Florida.
A-1
-------
Figure A-1. Southeast annexation area vicinity map. (Reprinted courtesy of the
City of Orlando, FL)
A-2
-------
In September 1995, WBQ contracted with Camp Dresser & McKee Inc. (COM) to
provide engineering services for the development of the Lake Hart basin MSMP. The
focus of this cooperative effort was to develop an MSMP with innovative options to
accomplish the general goals of the City of Orlando Urban Stormwater Management
Manual (OUSWMM). COM, working with the City, outlined a "watershed based" or often
called a "regional approach" to water quantity and water quality issues for this project.
This included an inventory and mapping of stormwater facilities and problems and an
evaluation of stormwater-related issues, alternatives, and solutions with emphasis on
the management of the Primary Stormwater Management System (PSWMS) within the
Lake Hart basin. The PSWMS is the major network of streams, lakes, wetlands,
bridges, and culverts that convey the majority of stormwater runoff southeasterly to
Lake Hart as shown in Figure A-2. This system must be operational so that the
proposed secondary systems (developments) within the basin can function as designed.
The MSMP will establish the framework for stormwater management within the Lake
Hart.
The Master Planning Process
Stormwater runoff can be controlled by natural or man-made systems of conveyance
and storage, guided development (land use controls), and the conservation of natural
systems. In urban, built-out conditions, a combination of all three methods of control is
necessary along with a proactive maintenance program to reach the stormwater
management goals of a community. In less urban, or rural areas, stormwater
management can be accomplished through land use controls and natural systems,
although some conveyance and storage facilities may be needed. To gauge how well
goals are achieved, levels of service (LOS) are established to quantify system
performance.
The control of runoff is, therefore, a mixture of storage and conveyance engineering,
land use controls, and ecosystems management. The three areas of runoff control are
not mutually exclusive nor distinct. For example, land use controls affect storage and
conveyance as well as natural systems. The interdependent development of
conveyance and storage engineering, maintenance programs, and possibly land use
controls can be of benefit to the City for planning of capital improvement programs.
Program Goals
The general goals of the Lake Hart MSMP are the development of an integrated
stormwater, wetland, and open space management system that would balance
preservation of natural systems with land development. The general goals are to be
accomplished by meeting the following three key objectives in a cost-effective manner:
flood control, pollution control, and ecosystem management (which includes wetlands
protection, aquifer recharge, and water conservation). A summary of each of these
A-3
-------
tnnmn Stornmater
Management Splem
IPilNMSI
Figure A-2. Study area and primary stormwater management system. (Reprinted
courtesy of the City of Orlando, FL)
-------
objectives is presented here and further details on how goals and objectives will be met
are contained in subsequent sections.
Flood Control
The flood control objective for the Lake Hart basin is locating regional facilities that will
provide proper storage and conveyance of peak flows and volumes as development
occurs. The facilities are to be located and conceptually designed to meet both the
City's and private landowners' interests to the extent practicable (e.g., aesthetics, cost,
ease of operation and maintenance). This requires close coordination with both the
public and private sectors.
Water Quality Control
The water quality control objective is to provide a regional system that will treat the
"first-flush" of runoff or reduce pollutant loads to the maximum extent practicable.
Because of the high groundwater table and the need for fill, a wet detention system
combined with pretreatment Best Management Practices (BMPs) for stormwater runoff
are considered to be the most cost-effective way to meet this objective.
Ecosystem Management
The objective of ecosystem management is to develop a regional system that will
protect healthy/pristine wetlands (abundant throughout the Lake Hart basin) and provide
potential landscape irrigation with surface water (pretreatment and reuse).
To implement a plan that will meet these objectives, the City requested that the Lake
Hart basin MSMP establish a framework for the design and review of proposed
stormwater management systems within the SEAA that could be beneficially used by
both City staff and developers. In general, the City wanted to supplement the
stormwater management requirements of the OUSWMM with innovative technology that
would address stormwater management in areas with extensively interconnected
wetlands and lakes and in areas that have a high seasonal groundwater table (low
infiltration potential). This framework would eventually be refined into a document
similar to the OUSWMM that would eventually become the Southeast Annexation Area
Stormwater Management Manual.
The City stressed the importance of training its staff to use the regional stormwater
management model developed for the PSWMS in the Lake Hart MSMP. The City will
use the stormwater model as a management tool to address regional stormwater
related issues which may include identifying and mitigating flooding impacts from
proposed land use changes as well as identifying the necessary phasing of proposed
regional facilities (dependent on development schedules and conceptual plan
approvals). To maintain the effectiveness of the stormwater model, City personnel will
need to perform periodic updates as appropriate.
This appendix documents the MSMP strategy developed for the Lake Hart basin that
can be implemented to control potential impacts to the natural stormwater system
A-5
-------
resulting from man's activities. The strategy includes a combination of land
development regulations, capital improvement projects, and shared private and public
partnerships (integrated resource planning) as needed to achieve the desired LOS for
flood protection and water quality protection. The plan also discusses the phasing of
recommended improvements to help the City implement proposed regulations and
capital improvement projects in a cost-effective and timely manner.
Levels of Service
Proper LOS decisions are an essential component of the Lake Hart basin MSMP. While
LOS includes retrofit, the decisions are primarily for new development. The LOS
decisions will directly affect the size and cost of regional facilities and structures in the
PSWMS. The OUSWMM defines primary conveyance facilities as "systems designated
as outfalls from, or connections between, natural lakes and artificial regional detention
facilities." For the purposes of this case study, the primary conveyance facilities are the
PSWMS.
After discussions with City staff, the LOS criteria presented in OUSWMM were
amended to more clearly define existing problem areas in the Lake Hart basin. Figure
A-3 illustrates the four LOS criteria considered for this study. They were formulated to
protect or enhance public safety. For example, Class D provides for flood protection of
first-floor elevations (FFE), while Class B provides control of flood waters so that one-
half of the road is not flooded (arterial road crowns). Table A-1 lists water quantity LOS
goals used to define potential problem areas (retrofit needs) in the Lake Hart basin
MSMP.
A-6
-------
CUSS A
ClASSR
CLASS C
GLISSD
Figure A-3. Water quantity levels of service. (Reprinted courtesy of the City of Orlando, FL)
A-7
-------
Table A-1. Existing Levels of Service For Water Quantity1
Structure/Facility
Houses/Buildings
Arterial Roads2
Collector Roads3
Minor Roads4
10-Year
10-Year
-------
Methodology
Stormwater Modeling
The primary aspect of this Lake Hart basin (MSMP) is the proper evaluation of water
quantity (flooding) and water quality. A good understanding of water quantity helps
determine the most effective methods of controlling flooding and protecting public
safety. A proper understanding of water quality and its control is essential to ensuring
the high quality of environmental protection desired by the City. Recent versions of the
RUNOFF and EXTRAN blocks of the United States Environmental Protection Agency
Stormwater Management Model (EPA-SWMM, Version 4.3) for water quantity were
used because these models best meet the requirements of the program. The models
have been verified in Stormwater master plan uses throughout Florida.
The hydrologic model, RUNOFF, simulates rainfall, runoff, and infiltration characteristics
of an area. It also performs simple hydrologic routing in channels, pipes, and lakes
where gradients are known. RUNOFF output is electronically delivered to EXTRAN,
which is a hydraulic routing model. EXTRAN provides dynamic flood routing in
channels, lakes, and control structures such as bridges, culverts, and weirs. EXTRAN
accounts for conservation of mass, energy, and momentum thereby predicting looping,
flow reversals, and similar phenomena should they occur.
The water quality modeling framework involves identification of the water quality
problems addressed by the modeling study, the structure of the model software, and the
assumptions and guidelines used with the model to represent the Lake Hart basin. The
Watershed Management Model (WMM) was used for the water quality analysis because
this model provides evaluations consistent with EPA, NPDES and SFWMD permit
requirements.
Hydrologic Model
The RUNOFF block of the EPASWMM, which was originally developed by COM,
simulates the rates of runoff developed from subbasins using a kinematic wave
approximation. Hydrologic routing techniques are then used to route the overland flows
through the pipe, culvert, and channel as required. Program results can be saved for
input to the EXTRAN block of Stormwater Management Model (SWMM) to perform
hydraulic routing in downstream reaches. A more complete documentation of the
model's background and theory can be found in the SWMM 4.3 user's manual.
Hydraulic Model
SWMM EXTRAN is a hydraulic flow routing model for open channel and/or closed
conduit systems. It uses a link-node (conduit-junction) representation of the Stormwater
management system in an explicit finite difference solution of the equations of gradually
varied, unsteady flow. EXTRAN receives hydrograph input at specific junctions by file
transfer from a hydrologic model, such as RUNOFF or TR20, and/or by manual input.
The model performs dynamic routing of Stormwater flows through the PSWMS to the
points of discharge or outfalls. Since it is dynamic, it simultaneously considers both the
A-9
-------
storage and conveyance aspect of stormwater management facilities. The program will
simulate branched or looped networks; backwater due to tidal or nontidal conditions;
free-surface flow; pressure flow or surcharge; flow reversals; flow transfer by weirs,
orifices, and pumping facilities; and storage at online or off-line facilities. Types of
conduits that can be simulated include circular, rectangular, horseshoe, elliptical, and
basket handle pipes, plus trapezoidal or irregular channel cross sections. Simulation
output takes the form of water surface elevations and inundated areas at each junction
and flows and velocities at each conduit. The SWMM 4.3 user's manual includes further
details.
Water Quality Model
WMM is a screening level water quality model used to develop relative projections of
long-term pollutant loadings on an annual basis. Relative comparisons of land use and
BMP implementation impacts on pollutant loads can be made. Application of the
screening level model incorporates detailed data collected for each hydrologic unit used
in the water quality model SWMM. WMM was applied to provide a relative evaluation of
nonpoint source pollution management strategies that address water quality problems
over long-term periods. WMM is a spreadsheet model for estimating annual nonpoint
source loads from direct runoff based upon land use specific event mean concentrations
and runoff volumes. Data required to use the nonpoint source model include event
mean concentrations (EMCs) for each pollutant type, land use, average annual
precipitation, annual baseflow, and average baseflow concentrations. A detailed
discussion of the methodology applied in WMM can be found in the COM WMM users
manual (COM, 1992).
The WMM model does not consider the potential in-lake or in-stream chemical,
biological, or physical modification of the pollutants, nor is it intended for this purpose.
WMM estimates the total load from runoff (and baseflow) to receiving waters and, as
such, represents the worst case (i.e., the loading without improvement or assimilation in
the receiving waters). As a next step, ecological management planning can define
biological water quality levels of service so that in critical areas, more detailed, in-lake
and in-stream water quality modeling can be completed to augment the Lake Hart
MSMP results.
For the Lake Hart basin MSMP, WMM was used to generate estimates of average
annual pollutant loadings for existing and future conditions based upon local rainfall
statistics. The model relies upon EMC factors for different land use categories to
calculate pollution loadings. Because the model is spreadsheet based, it can be easily
applied to screen the pollutant loading reductions that can be achieved by various BMP
alternatives. A series of different BMP alternatives can be screened to identify BMP
requirements that will adequately mitigate existing and projected long-term water quality
problems within the watershed.
Hydrologic Parameters
Hydrologic model parameters used for the model simulations are described below.
A-10
-------
Subbasin and Hydrologic Unit Areas
For modeling purposes, the Lake Hart basin was subdivided into 51 subbasins for which
land use, soil, and topographic characteristics were compiled. Subbasin area averaged
approximately 150 acres with a minimum of 17 acres and a maximum of 1300 acres.
For the alternative evaluations, these subbasins were further partitioned into 103
hydrologic units to account for the proposed regional facilities.
Rainfall Intensities and Quantities
There are three rainfall stations within the vicinity of the Lake Hart study area. The
Boggy Creek rain gauge and the Lake Hart rain gauge are maintained and operated by
Orange County, FL. The third rain gauge is the Orlando-McCoy Airport (Orlando
International Airport) Station Number 6628 and 6638, and is monitored by the U.S.
Department of Commerce, National Climatic Data Center. The Boggy Creek rain gauge
is approximately one mile to the west of the study area and has been recording rainfall
data at five minute intervals since August 1987. The Lake Hart rain gauge is
approximately one mile to the southeast of the study area (within the same basin) and
has been in existence since March 1995. The station at the Orlando International
Airport station is one mile east of the study area and records rainfall data in 15 minute
intervals. The average annual rainfall for the 1942 to 1993 period of record is 49.7
inches. The general locations of these rain gauges are shown on Figure A-4.
Rainfall For Water Quality Modeling
Wet and dry season rainfall quantities for determining nonpoint source pollutant loading
projections were also determined. The rainfall volume for the wet season, which occurs
from June through September, is approximately 28.1 inches. The rainfall volume for the
dry season, which occurs from October through May, is approximately 21.6 inches.
Rainfall for Runoff Modeling
Design rainfall data for the Lake Hart MSMP were obtained from the OUSWMM and the
South Florida Water Management District in the form of rainfall quantities and
distributions (30-minute intervals) for each design storm (2-, 10-, 25-year, 24-hour, and
the 100-year, 72-hour). Rainfall quantities are:
10O-Year/72-Hour -14.4 inches of rainfall
25-Year/24-Hour - 8.6 inches of rainfall
10-Year/24-Hour - 7.4 inches of rainfall
2-Year/24-Hour - 4.8 inches of rainfall
A-11
-------
BIJI
IB E
I 28 I
m i
m i
31 I
34 E
RAIHGAOGE LOCATIONS
(IRflHfiE CQUHTV F1QRIDA
DEMONS 0ROHCI COUIW RUlGDUli IDClIlfllS
ฉ SPRIHl IAXE
ฎ UKI inunno
(ฃ> puanc HORKS
UMBUlflIHE
UKI HUH
@ UKI
OIUUDI-NGBOV
U> EBII
ฉ IHTUHD
CD utii
ฉ SHINGU
ฉ BDBDf
ฉ ISA
Figure A-4. Rain gauge locations. (Reprinted courtesy of the City of Orlando, FL)
A-12
-------
For the 2-, 10-, and 25-year, 24-hour design storm events the Soil Conservation Service
Type II Florida modified rainfall distribution (also called Type III) was selected based on
the requirements of OUSWMM. The 100-year, 72-hour rainfall distribution was taken
from the SFWMD permit manual. Rainfall intensities were then generated for each
design storm.
Soil Types and Capabilities
Soils data are used to evaluate stormwater runoff, infiltration, and recharge potential for
pervious areas. Information on soil types was obtained from the National Resources
Conservation Service (NCRS), formerly the Soil Conservation Service (SCS). Each soil
type has been assigned to a soil association, a soils series, and to one of the four
Hydrologic Soil Groups (HSG) designated A, B, C, or D. HSG A is comprised of soils
having very high infiltration potential and low runoff potential. HSG D is characterized
by soils with a very low infiltration potential and a high runoff potential. The other two
categories fall between the A and D soil groups.
For the Lake Hart study area, the majority of the soils types are within Smyrna-
Bassinger-St. Johns soil association which are characterized by nearly level, poorly
drained, and very poorly drained soils that are sandy throughout. The soils in the
vicinity of Lake Nona, Red Lake and Buck Lake are classified as part of theSmyrna-
Pomello-lmmokalee association which are nearly level and have poorly drained soils to
very well drained soils that are sandy throughout.
The predominant soils series within these subbasins include Sanibel Muck which has a
depth to seasonal high groundwater table between zero and one foot and Smyrna Fine
Sands which has a depth to seasonal high groundwater of one foot above the ground
surface to one foot below the ground surface. The remainder of the soils are classified
as part of the Pomello Fine sands which have a depth to seasonal high groundwater
table between two and 3.5 feet or the St. Johns Fine Sands which have a depth to
seasonal high groundwater table between zero and one foot.
Soil infiltration rates were taken from the NRCS Soil Survey for Orange County, FL
based upon the soil hydrologic group. The RUNOFF Block of SWMM uses both soil
storage and infiltration rates. Soil capacity (or soil storage) is a measure of the amount
of storage (in inches) available in the soil type for a given antecedent moisture
condition. The average antecedent moisture condition (AMC II) was used for all design
storm analyses. Soil capacities were estimated based on available depth-to-water-table
data and the use of equations as outlined in the SFWMD manual which uses equations
developed by the NRCS. The high water table and low infiltration capacity conditions
were considered in the best management practice (BMP) evaluations in subsequent
sections to ensure that chosen alternative would function properly.
The Horton soil infiltration equation was used to simulate rain water percolation into the
soil. The Horton equation uses an initial infiltration rate to account for moisture already
in the soil, a maximum infiltration rate, and a decay infiltration rate. Additionally, a total
A-13
-------
maximum infiltration depth is computed based on the moisture capacity of the soil. In
this study, the maximum depth was determined from the information provided in the Soil
Survey of Orange County which documents seasonal high water tables or depths to the
impervious layer (first impermeable boundary condition).
Once these infiltration parameters were computed and calibrated for each HSG,
area-weighted parameter values were computed based on the percent of each HSG
within a catchment. Detailed information on the use of the Morton infiltration equation is
described in the SWMM 4.3 users manual.
Table A-2 lists the global infiltration parameters used to calculate the hydrologic input
data used in this study. The global Morton infiltration equations presented in Table A-2
resulted in peak water surface elevations similar to those predicted by the Federal
Emergency Management Agency (FEMA). This is based on COM experience with over
30 stormwater management programs in Florida, including extensive calibration and
verification to historic storms.
Table A-2. Global Morton Infiltration Parameters
Hydrologic
Soil
Group
A
B
C
D
Maximum
Infiltration
Rate
(in/hr)
14.0
10.0
7.0
5.0
Minimum
Decay
Rate
(in/hr)
0.75
0.50
0.25
0.10
Decay
Rate
(1/sec)
0.000556
0.000556
0.000556
0.000556
Maximum
Soil
Storage
(in)
5.4
4.0
3.0
1.4
In order to manage the volume of data required to generate the SWMM RUNOFF data
sets, spreadsheets were developed to semi-automate the process. Flow path data,
land use data (including percent imperviousness), soil data, and tributary area
measurements for each subbasin were input into a spreadsheet. The spreadsheet
calculated area-weighted averages using the global Morton infiltration parameters and
the hydrologic data to generate subbasin information that could be directly input to the
SWMM RUNOFF data set.
Overland Flow Parameters
The RUNOFF module of SWMM uses overland flow data in the form of width, slope,
and Manning's roughness coefficient to create a physically based overland flow runoff
plane to route runoff to conduits and storage for further routing. The overland flow
length (L) is the weighted-average travel length to the point of interest. The need for
weighting becomes apparent when considering areas with odd geometry where a long,
thin portion of the area may bias the hydraulic length. For ponded areas, the point of
interest chosen was the centroid of ponding. For areas where ponding does not occur,
A-14
-------
the point of interest is the outflow from the area. Overland flow length is used to better
estimate subbasin width for the RUNOFF overland flow routing by use of the equation:
A=LW
where:
A = subbasin area (sq. ft.)
L = overland flow length (ft.)
W = overland flow width (ft.)
Overland flow slope is the average slope over the hydraulic length and is calculated by
dividing the difference in elevation by the hydraulic length. Length and slope
information were obtained from 1985 aerial photogrammetry one-foot topographic data.
These data were augmented by available subdivision plans and survey data.
Land Use and Impervious Areas
Land use data are used to estimate impervious areas for use in runoff calculations.
Existing land use for the portion of the Lake Hart basin annexed by the City was
obtained from 1985 aerial photography (1 in = 200 feet), 1995 aerial photography, and
as-built information provided by the major property owners within the study area.
The majority of the study area consists of undeveloped lands (55%), wetlands (24%),
and water bodies (15%). The remaining six percent of the total is a mixture of low
density residential, golf course, commercial and major road land uses. Of the major
property owners within the study area, only Lake Nona has constructed phases of their
development plan.
The estimate of future land use was compiled from information provided by each of the
major property owners within the basin and from information provided by the City of
Orlando Planning Department. The developable land in the basin is projected to
become low density residential (17% of study area), medium density residential (17% of
study area), and supporting industrial/commercial land uses (12% of study area). The
balance of the developable land (9%) is planned for schools, high density residential,
golf courses and open space.
Using the existing and future land use data and the source maps, the percentage of
each land use category within each subbasin was determined. Note that the future land
use scenario represents a combination of City of Orlando information and the desires of
the major property owners within the study area. The City has not adopted a future land
use plan for this area.
The percent imperviousness of each subbasin is one of the parameters used by the
SWMM RUNOFF model to determine the volume and rate of surface water runoff. For
this study, a percent imperviousness value for each of the eleven land use categories
was determined. A summary of the eleven land use categories is presented in Table A-
A-15
-------
3. Additionally, the table lists the percent of Directly Connected Impervious Area (DCIA)
and the percent of Non-DCIA (NDCIA) assigned to each land use category. The DCIA
represents all the impervious surfaces which are directly connected to the stormwater
system. The NDCIA represents the impervious surfaces that have a pervious buffer
between them and the stormwater system.
Hydraulic Parameters
PSWMS (refer again to Figure A-2) for the Lake Hart basin consists of a series of
interconnected lakes, streams, and wetlands that discharge to 10 different discharge
points from the study area. There are 15 miles of open channels/interconnected
wetlands (51 model segments), 33 structure crossings (e.g., culverts, bridges), and 35
existing storage areas representing lakes and depressional areas. Additional detention
ponds were modeled for future land use. Characteristic data of this system were
obtained from as-built drawings, field reconnaissance, one-foot contour topographic
maps, and survey.
A necessary task of any stormwater master plan is the creation of a simplified
representation of the actual system for input into the stormwater models. This task
typically begins with the development of a model schematic which also aids in checking
input data and interpreting output data. An overall RUNOFF/EXTRAN existing model
schematic of the PSWMS for the entire Lake Hart study area is shown in Figure A-5.
The schematic shows the hydrologic unit load points for inflow, conveyance channels,
and structures, as well as the storage and linking junctions. It also illustrates how the
RUNOFF and EXTRAN programs were set up to simulate each area's runoff
hydrograph and the routing of the runoff through the stormwater management system.
Identification numbers for various system elements are also shown on the schematic.
The schematic provides a quick reference for correlations between the actual physical
situation and the modeled system.
A-16
-------
Table A-3. Imperviousness by Land Use Category
Land Use Category
1 . Forest, Open, & Park
2. Agricultural & Golf Courses
3. Low Density Residential
4. Medium Density Residential
5. High Density Residential
6. Institutional
7. Industrial
8. Commercial
9. Wetlands
10. Water bodies
1 1 . Major Roads
Impervious1
(%)
1
1
25
35
65
50
80
90
100
100
98
DCIA2
(%)
1
1
12.5
25
55
45
80
90
100
100
98
NDCIA3
(%)
0
0
12.5
10
10
5
0
0
0
0
0
Pervious
(%)
99
99
75
65
35
50
20
10
0
0
2
Notes:
1) Total Impervious Area
2) Directly Connected Impervious Area (DCIA)
3) Non-Directly Connected Impervious Area (NDCIA)
Structures/Facilities
A major component of this study was the inventory of the stormwater management
structures along the PSWMS. This information forms the foundation for the model
representation of the hydraulic system. The hydraulic characteristics of the structures
and facilities in the Lake Hart study area were collected from design drawings of
improvements (e.g., culverts, bridges, detention ponds) that have occurred within the
study area.
A-17
-------
Figure A-5. Existing PSWMS nodal schematic map. (Reprinted courtesy of the
City of Orlando, FL)
A-18
-------
Stage-Area Relationships
Stage-area information was developed by planimetering topographic contours for major
depressional areas which could not be uniformly incorporated into channel/wetland
cross sections. This process was done to more accurately reflect floodplain storage.
The same procedure was applied to the existing detention ponds. Stage-area
relationships for existing facilities were obtained from topographic data shown on the
as-built plans provided by the property owners within the basin. The volume of storage
was internally calculated by stormwater models using the trapezoidal method.
Stage and Discharge Data
A desirable component of any water resources investigation is the availability of
measured stages and/or discharges at selected points of interest, or the availability of
calibrated hydrologic/hydraulic models from the area to serve as a "reality check" or
verification. Stages and/or discharges are used in conjunction with known rainfall
amounts/distributions and other hydrologic/hydraulic conditions to calibrate and verify
models. These calibrated and verified models can then be used in evaluations of
present problem area solutions or future conditions planning. Data in at least hourly
intervals are often desired so that relatively short-term, yet potentially damaging, flood
peaks can be predicted and planned for. For the Lake Hart basin, there are limited
stage data and no discharge data available for use in the master planning process. The
data that are available are summarized in the following paragraphs.
Lake Nona (575 acres), Red Lake (120 acres), and Buck Lake (115 acres) are the three
major water bodies within the basin. These three lakes collect the majority of
stormwater runoff from the basin which is then discharged from the lakes into a series of
streams and wetlands that meander toward Lake Hart. These three lakes become
hydraulically connected when their water level exceeds an elevation of 75.5 ft-National
Geodetic Vertical Datum (NGVD). During periods of high rainfall, Lake Nona will also
discharge into Mud Lake through a channel system located on the southwest side of the
lake.
The normal water surface elevations and the seasonal high water surface elevations for
Lake Nona, Red Lake, and Buck Lake were obtained from the Orange County Lake
Index and through field inspection. The index reports a normal water elevation of 77.6
feet-NGVD for the three lakes. Orange County also took nine random measurements of
the water surface elevation in Buck Lake between the years 1970 and 1975. The
highest recorded water surface elevation was 77.8 feet-NGVD which was recorded on
July 1, 1974. The FEMA also estimated the 100-year peak water surface elevation for
these three lakes to be 79.6 feet-NGVD.
Wetland jurisdiction limits extend from the lake's open water body landward to where
the dominance of cypress (Taxodium distichum), bay (Gordonia lasianthus), and tupelo
trees (A/yssa sp.), ferns (Osmunda spp.) and shiny lyonia (Lyonia lucida) disappear.
Upland areas include the canopy tree layer dominated by slash pine (Pinus elliottii),
scrub live oak (Quercus geminata), and turkey oak (Quercus laevis), while saw palmetto
A-19
-------
(Serenoa repens) dominate the understory. Extending the seasonal high water line and
normal pool elevations landward would provide a reasonable wetland boundary around
each lake. Hydric soils and hydrologic indicators would also need to be assessed to
confirm the wetland jurisdiction line.
Biological indicators of wetland water levels were also used to approximate the normal
pool and seasonal high water elevations at five sites within the Lake Hart basin. This
was done using SWFWMD guidelines. The wetland jurisdictional determination
methodologies implemented by Florida Department of Environmental Protection, and St.
Johns River Water Management District (SJRWMD), and U.S. Army Corps of Engineers
were also used to determine plant community zonation (i.e., obligate, facultative and
facultative upland plant species) and to approximate temporal water inundations and
conditions.
Using these guidelines, hydric soils characteristics, hydrophilic vegetation, and other
biological information were compared with known topographic elevations to estimate
normal pool and seasonal high water levels. No water level recorders or staff gages
were present or were installed. The results of the field inspection for the five sites are
summarized in Table A-4.
Table A-4. Field Estimated Normal Pool and Seasonal High Water Elevations
Site No.
(invert)
1
2
3
4
5
Normal Pool
(feet-NGVD)
78.1
74
76.9
79
73.1
Seasonal High
(feet-NGVD)
78.6
75.4
77.7
80
75.1
Existing Water Level
(feet-NGVD)
77.3
73.3
76.4
78.7
72.4
Indicators
Used
Stain line
Moss line
Stain line
Moss line
Stain line
Moss line
Stain line
Stain line
Moss line
The results of the biological indicators at the five sites indicate that the maximum
difference between the normal pool and seasonal high water elevations range from 0.5
feet to two feet. Various constrictions (e.g., inadequately sized culverts, culverts in
A-20
-------
poor condition, or inverts above than the 100-year flood event) may cause flow
constrictions. The biological indicators provide fluctuation patterns, not duration.
The biological results provide a difference of water level fluctuation indicators for
specific wetland species that adapt to prolonged inundation (i.e., adventitious roots and
epiphytic algae) or are intolerant to sustained inundation (foliose lichens). Facultative
and obligate plant indicators that occur along the landward extent of the wetlands can
assist in the determination of the normal pool and seasonal high water levels. Many
aquatic plants occur in specific horizontal zones along the slope and the changing water
levels. Each species has adapted to a specific inundation period (duration). These
hydrologic factors were used to differentiate the water distribution pattern and the extent
of wetlands around each lake.
Floodplains and Floodways
A floodplain is the area inundated, or flooded, by a particular rain or tidal event.
Floodplains are usually described by their frequency of occurrence (e.g., 25-year or
100-year). FEMA establishes nationwide flood levels and flood insurance standards.
The FEMA flood insurance study (FIS) for Orange County, FL and associated Flood
Insurance Rate Maps (FIRMs) identify portions of the Lake Hart basin annexed by the
City as flood prone and provide estimates of the 100-year flood stages in order to
provide guidance for home building and road elevations. For this study, available data
were compiled in order to estimate stormwater flood boundary conditions for
subsequent evaluations.
The City of Orlando requires that a Floodplain Development Permit be obtained for any
development activities for any building or structure located in an area of special hazard.
The general requirements for the permit application require that the applicant submit
drawings to scale showing the nature, location, dimensions, and elevations of the area
in question; existing and proposed structures; fill; storage or materials; and drainage
facilities. Specifically, the following information is required:
Base flood elevation (100-year flood)
Habitable flood elevation
Nonresidential floodproofing elevation
Floodproofing certification
Alteration of watercourse
Once this information is received, the City Engineer will review the application for
compliance and issue a permit as appropriate. The City Engineer's review includes
notification of other applicable regulatory agencies prior to any alteration or relocation of
a watercourse, the verification of flood and structure elevations, determination of
whether a building or development is within an Area of Special Hazard based on the
applicable FEMA FIS and accompanying maps, and advise an applicant whether or not
a Letter of Map Amendment or Revision from FEMA is required.
A-21
-------
OUSWMM also has requirements for development in the floodplain. For example,
encroachment will be allowed in the 100-year floodplain with compensating storage. All
proposed developments within the 100-year floodplain as delineated on an official FIRM
or as determined by the City Engineer need to comply with these requirements:
City will establish the 10O-year/24-hour base flood elevation
If the area is not in a 100-year flood prone area, an analysis will be done to
determine the 100-year elevation
The design storm event to be used to establish the 100-year on-site elevation
shall be a 10O-year/72-hour event of 14.4 inches of rainfall
The minimum finished floor elevation shall be one foot above the 100-year
elevation
Floodproofing may be substituted for elevating finished floor elevations for
commercial and industrial developments
Compensating flood storage must be provided for all floodwater displaced by
development below the elevation of the 10O-year/24-hour flood (generally,
between the 100-year flood elevation and the wet season water table)
Compensating storage may be claimed in retention/detention ponds when they
are above maintained water elevations and they can be inundated during the
100-year flood.
Off-site increases in flood stage will not be allowed by encroachment within a
floodway.
Details on each of these summaries can be found in the appropriate chapters of the City
Code and OUSWMM.
Water Quality Parameters
The following paragraphs discuss state surface water classifications, historical water
quality data in the study area, trends exhibited by the data, and the methodology used
to estimate nonpoint source pollutant loads. Data from the EPA's STOrage and
RETrieval (STORET) database are included as appropriate.
Selection of Water Quality Loading Factors
In order to meet the objectives of the Lake Hart MSMP, pollutants that may affect water
quality were identified and quantified. This section identifies stormwater related-
pollutants in the study area and describes the methodology for determining appropriate
event mean concentrations (EMCs) for use in the WMM.
A-22
-------
Identification of Pollutants
The major sources of pollutants in a watershed are typically stormwater runoff from
urban and agricultural areas, discharges from wastewater treatment plants (WWTPs)
and industrial facilities, and contributions from improperly installed or maintained septic
tanks. Stormwater runoff pollution and septic tank loadings have been historically
referred to as nonpoint source pollution (NPS). A WWTP or industrial discharge is
typically referred to as point source pollution because it releases pollution into streams
at a discrete point. The Lake Hart MSMP targets the pollutants which are most
frequently associated with stormwater including:
1. Sediment
Total suspended solids (TSS)
Total dissolved solids (TDS)
2. Oxygen demand
Biochemical oxygen demand (BOD)
Chemical oxygen demand (COD)
3. Nutrients
Total phosphorus (TP)
Dissolved phosphorus (DP)
Total Kjeldahl nitrogen (TKN)
Nitrate + nitrite nitrogen (N03+N02)
4. Heavy metals
Lead (Pb)
Copper (Cu)
Zinc (Zn)
Cadmium (Cd)
Estimates of the annual loads of these pollutants are required as part of the National
Pollution Discharge Elimination System (NPDES) stormwater permitting analysis.
Selection of Stormwater Pollution Loading Factors
The nonpoint pollution loading module of WMM computes nonpoint pollution loads
based on factors which relate local land use patterns and rainfall and percent
imperviousness in a watershed to pollutant loadings. Nonpoint pollution loading factors
(e.g., pounds/acre/year) for different land use categories are based upon annual runoff
volumes and EMCs for different pollutants. The EMC is a flow-weighted average
concentration and is defined as the sum of individual measurements of stormwater
pollution loads divided by the storm runoff volume. Selection of EMCs factors depends
upon the availability and accuracy of local monitoring data, as well as the effective
transfer of literature values for nonpoint pollution loading factors to a particular study
area. Reviewed here are monitoring data collected throughout Florida, as well as
A-23
-------
available literature values for estimating event mean concentrations for use in the Lake
Hart MSMP.
Over the past 15 years, nonpoint pollution monitoring studies throughout the U.S. have
shown that "per acre" discharges of urban stormwater pollution (e.g., nutrients, metals,
BOD, fecal coliforms) are positively related to the amount of imperviousness in the land
use (i.e., the more imperviousness the greater the nonpoint pollution load) and that the
EMC is relatively consistent for a given land use. Soil types affect hydrology more than
EMC, especially in areas dominated by impervious surfaces.
Land Use Load Factors
Recommended EMCs for the urban land use categories (residential, commercial, and
industrial) in this plan are based upon a detailed analysis of available monitoring data
recently collected under the EPA NPDES Part II Stormwater Permit application process.
The process was conducted between November 1990 and May 1993 for over 34
NPDES municipal stormwater applications throughout the country including the states of
Florida and Georgia. As part of the permit application process, representative
stormwater outfalls were monitored in cities and counties with populations greater then
100,000. These "representative" outfalls typically discharged stormwater from areas
with predominantly residential, commercial, or industrial land uses. Each outfall was
monitored and sampled during a minimum of three separate storm events. The analysis
included a total of 98 storm events that were monitored by selected cities and counties
under the Florida Stormwater NPDES permitting process. Previously, the EPA
sponsored Nationwide Urban Runoff Program (NURP) monitored stormwater pollution
from urban areas in about 80 storm events in Tampa during 1978-1983.
Under the NPDES permitting process, flow-weighted composite samples were collected
during storm events according to detailed sampling protocols prescribed by the EPA.
Samples were analyzed for about 140 pollutants including those targeted for the Lake
Hart MSMP. Statistical analyses of available NPDES data were used to determine
appropriate EMCs for watershed management applications. Data from the City of
Orlando NPDES monitoring sites were included in this analysis.
Some citrus and cattle growing/pasture land use exists or has existed in the study area.
The pasture land use is in the northwest portion of the study area and the citrus is in the
southeast. These two land uses are not well monitored nor documented for water
quality in the literature. In particular, pasture EMCs can range dramatically if cattle are
allowed to free range through streams and wetlands for water and forage. EMCs for
total P can range from 0.3 mg/l to 1.0 mg/l or higher.
Total N can range from 1.45 mg/l to over 5 mg/l. Therefore, the most applicable central
Florida values were used for these land uses to estimate existing land use pollutant
loadings from these highly variable sources.
A-24
-------
For central and south Florida, provides estimates of stormwater EMCs based on a
literature review of monitoring studies performed at various sites in Florida. Dade
County also prepared a literature review of selected EMC values to be used in the Dade
County Stormwater Management Master Plan.
Open/Nonurban Land Use Load Factors
The only open/nonurban monitoring site included in the Florida NPDES sites analyzed
was monitored by Sarasota County. This site did not include cattle pasture/growing or
citrus.
Water Bodies
The primary sources of pollution to water bodies are runoff from upstream areas and
pollutants associated with precipitation falling on the water surface. Since pollution
discharged from upstream areas is already accounted for by the other land use
category loading factors, loading factors for water bodies consider only the pollution
derived from precipitation.
Urban atmospheric monitoring studies performed under NURP and other studies have
documented that there is a pollution load associated with precipitation. Pollutant
loading factors for water bodies were derived from the Tampa NURP atmospheric
monitoring studies and a report containing a compilation of atmospheric deposit data.
The loading factors used in this plan differ from those used in the Lake Hart MSMP
based on an update of more recent and extensive data.
Major Roads
Highway runoff data reported by the Federal Highway Administration (FHWA) were
considered for application to the major highway land uses in Florida watersheds. The
FHWA study analyzed stormwater runoff monitoring data obtained at 31 highway sites
covering a total of 993 separate storm events. Highway stormwater runoff data were
collected under several previous studies during the past 10 to 15 years. Also, many of
the previous FHWA monitoring studies were performed during periods when the use of
leaded gasoline was more prevalent than today. These studies demonstrated that
highway runoff may contain solids, metals, nutrients, oil and grease, bacteria, and other
pollutants.
Recommendation of Stormwater Pollutant Loading Factors
From the databases described above, EMCs obtained from water quality monitoring
studies completed in the state of Florida were used in this evaluation. These EMC
values were compared with those obtained from studies throughout the eastern United
States. Based on this comparison, the final EMC values were selected. These EMC
values represent the best available information (most recent up-to-date database) and
are applicable for pollutant load estimates in the City of Orlando. Table A-5 presents
the recommended event mean concentrations and impervious percentages for the Lake
Hart MSMP. Listed with each pollutant group is the reference source for these
recommended EMCs.
A-25
-------
Table A-5. Event Mean Concentrations and Impervious Percentages Recommended for the Watershed Management
Model
Land Use Category
1 Forest, Open and Park
2. Agriculture and Golf
3. Low Density Residential
4. Medium Density Residential
5. High Density Residential
6, Institutional
7. Industrial
8- Commercial
9. Wetlands
10. Waterbodies
1 1 . Major Roadways
Avg.
Percent
Imp.
1 .00%
1 .00%
25.00%
35,00%
65.00%
50,00%
80.00%
90,00%
100.00%
100.00%
98.00%
Oxygen Demand and Sediment
( mg/L)
BOD
1
4
15
9
8
7
14
8
5
3
11
COD
51
51
71
65
53
50
83
53
51
22
99
TSS
11
55
27
59
42
41
77
42
5
5
121
IDS
100
100
286
59
141
114
130
141
100
100
189
SOURCE
A.B
A.B
0
c
c
c
c
c
A.B.E
D,E
C
Nutrients
(mg/L)
TP
0.05
0.34
0,44
0.45
0,20
0.15
0,28
0.20
0.19
0.17
0.40
DP | TKN
0.004
0.23
0.33
0.27
0,09
0,08
0.20
0.09
0.10
0.09
0.15
0.94
1.74
1.34
1,77
1.03
1,24
1.47
1.03
1.10
1.10
1.51
N023
0.31
0.58
0.63
0.27
0.67
1.05
0.40
0.67
0.40
0.20
0.34
SOURCE
A
A
C
C
c
c
c
c
A,B,E
E
C
Heavy Medals
( mg / L )
Pb
0.000
0.000
0.002
0.013
0.011
0.012
0.023
0.011
0.006
0,006
0.039
Cu
0.000
0.000
0.009
0.007
0,022
0.018
0.024
0.022
0.003
0.003
0.022
Zn
0.000
0.000
0.051
0.057
0,065
0,079
0.132
0.065
0.005
0.005
0.189
Cd
0.000
0.000
0,002
0.001
0,001
0.001
0,001
0.001
0.000
0.000
0.002
Source
B
B
C
C
C
c
c
c
A,B,E
E
C
SOURCES:
NOTES:
A: "Estimation of Stormwater Loading Rate Parameters," Harvey H. Harper, 1992, Table 21.
B: Nationwide Urban Runoff Program ( NURP ), 1983.
C: NPDESPartll Stormwater Permit Applications for the Cities of Jacksonville, St. Petersburg and Orlando, and the Counties of Palrn Beach and Sarasota, 1992-93.
D. "Washington Metropolitan Area Urban Runoff Demonstration Project," Northern Virginia Planning District Commission, January 1983, Table 24,
E: Mean concentrations reported for wetfall monitored as part of the Tampa NURP study and Mote Marine data compilation.
1. Dissolved - P concentrations for wetlands and Watercourses /Waterbodies are generally 55 percent of the recommended total - P concentration
( Harper, 1992; Florida NPDES data, 1992 -1993 ).
2. TKN and N02 + N03 concentrations for the non-urban land use categories were assumed to be 75 percent and 25 percent, respectively, of the recommended
total - N concentration ( Florida NPDES data, 1992 -1993 }.
3. Averages reported are based on parametric statistics with a lognormal distribution.
4. Concentrations reported below the detection limits were assumed to 50% of the detection limits for the statistical analysis.
5. Golf courses were not explicitly included in the NPDES monitoring networks.
A-26
-------
WMM converts the EMCs described above into nonpoint pollution loading factors
(expressed as pounds/acre/year) based on the runoff volume for each land use within a
watershed. Pollution loading factors vary by land use and the percent imperviousness
associated with each land use. The pollution loading factor MLU is computed for each
land use (LU) based on the EMCs presented in Table A-5 using the following equation:
ML = EMCL*RL*K
Where:
MLU = loading factor for land use LU (Ib/ac/year)
EMCiu = event mean concentration in runoff from land use LU (mg/l).
EMCi varies by land use and by pollutant
RLU = total average annual surface runoff from land use LU
(in/year)
K = 0.2266, a unit conversion constant ((lb-l)/(mg-ac-in))
The total annual pollution load from a watershed is computed by multiplying the
pollutant loading factor by the acreage in each land use and summing for all land uses.
Delivery Ratio/Travel Time
Wet-weather travel times on the order of 24 hours or more are typically required to
achieve significant decay of pollutants during instream transport. While in-stream
settling occurs on an annual basis, theresuspension of sediments in streams is likely to
carry pollutants downstream. Therefore, in order to provide more conservative
estimates of the nonpoint source loads, a delivery ratio of 100 percent was assigned to
all areas within the City of Orlando for pollutants suspended in the water column.
Point Source Discharge
Pollutant loadings from point source dischargers, such as regional WWTPs, are usually
estimated to determine the relative contributions of point versus nonpoint pollution
loadings. The Lake Nona wastewater treatment facility is within the study area.
However, it is not considered to be a point source discharge because effluent from the
WWTP is discharged into a holding pond that is used for slow-rate spray irrigation at the
golf course so that it does not directly discharge into the PSWMS.
BMP Pollutant Removal Efficiencies
WMM applies a constant removal efficiency for each pollutant to all land use types to
simulate treatment BMPs. Recommended pollutant removal efficiencies for retention
basin, detention basin, and swale BMPs are discussed below.
The design of retention systems is generally based on a specified diversion volume.
Relying on extensive field investigations and simulations using 20 years of rainfall data,
average yearly pollutant removal efficiencies were estimated for fixed diversion volumes
for onsite (small) watersheds, as presented in Table A-6. The diversion depth is the
A-27
-------
depth of runoff water which must be stored and percolated from the total upstream
drainage area that discharges to the retention pond.
The EPA NURP study monitored several wet detention ponds serving small urban
watersheds in different locations throughout the U.S. For wet detention ponds with
significant average hydraulic residence times (e.g., two weeks or greater), average
pollutant removal rates were on the order of 40 to 50% for total-P and 20 to 40% for
total-N. For other pollutants which are removed primarily by sedimentation processes,
the average removal rates were as follows: 80 to 90% for TSS; 70 to 80% for lead; 40
to 50% for zinc; and 20 to 40% for BOD or COD.
Pollutant removal efficiencies for dry extended detention ponds are based on settling
behavior of the particulate pollutants. Table A-6 summarizes average pollutant removal
efficiencies for dry extended detention ponds based on settling column data and field
monitoring data. Settling column data from NURP studies and from the FHWA study
were evaluated to establish the removal efficiencies for TSS and metals.
Removal efficiencies for the nutrients were determined by evaluating the results of two
field monitoring studies of dry extended detention ponds in the metropolitan
Washington, D.C. region. These efficiencies are applied to the percentage of total
annual pollutant washoff captured for treatment in the extended dry detention pond.
The removal efficiencies summarized in Table A-6 for swales represent swales
designed for infiltration and capture of 80 percent of the annual runoff volume. These
efficiencies are based upon NURP findings and COM experience. Finally, the pollutant
removal rates for retention swale pre-treated upstream of a wet detention pond are
based on retaining the first 0.25 inches over the tributary area coupled with full wet
detention treatment.
Surface Water Quality Classifications
Section 403.021 of Florida Statutes declares that the public policy of the state is to
conserve the waters of the state to protect, maintain, and improve the quality thereof for
public water supplies, for the propagation of wildlife, fish, and other aquatic life, and for
domestic, agricultural, industrial, recreational, and other beneficial uses. It also
prohibits the discharge of wastes into Florida waters without treatment necessary to
protect those beneficial uses of the waters. Furthermore, Congress, in Section
101(a)(2) of the Federal Water Pollution Control Act, as amended, declared that
achievement by July 1, 1983 of water quality sufficient for the protection and
A-28
-------
Table A-6. Average Annual Pollutant Removal Rates for Retention Basin, Detention
Basin and Swale BMPs (Note: All values are percent.)
BODS
COD
TSS
IDS
Total-P
Dissolved-P
N02+N03
TKN
Cadmium
Copper
Lead
Zinc
Extended Dry
Detention 1
30
30
90
0
30
0
0
20
80
60
80
50
Wet
Detention 2
40
40
90
40
50
70
30
30
80
70
80
50
Retention3
90
90
90
90
90
90
90
90
90
90
90
90
Swales 4
30
30
80
10
40
10
40
40
65
50
75
50
Retention
Swales
With Wet
Detention5
76
76
96
76
80
88
76
72
92
88
92
80
NOTES:
1. Extended dry detention basin efficiencies assume that the storage capacity of the extended detention pool
is adequately sized to achieve the design detention time for at least 80 percent of the annual runoff
volume. For most areas of the United States, extended dry detention basin efficiencies assume a storage
volume of at least 0.5 inches per impervious acre.
2. Wet detention basin efficiencies assume a permanent pool storage volume which achieves average
hydraulic residence time of at least two weeks.
3. Retention removal rates assume that the retention BMP is adequately sized to capture at least 80 percent
of the annual runoff volume from the BMP drainage area. For most areas of the United States, the required
minimum storage capacity of the retention BMP will be in the range of 0.50 to 1.0 inch of runoff from the
BMP drainage area, but the required minimum storage capacity should be determined for each location.
4. Source: California Stormwater Best Management Practice Handbooks, (COM, et. al., 1993). These
efficiencies are applied to the percentage of total annual pollutant washoff captured for treatment in the
extended dry detention pond BMP.
5. This efficiency reflects removal efficiencies for series BMPs with 0.25 inches of retention swale pre-treated
upstream of a wet detention pond.
propagation offish, shellfish, and wildlife, as well as for recreation in and on the water,
is an interim goal to be sought wherever attainable. Congress further states, in Section
101(a)(3), that it is the national policy that the discharge of toxic pollutants in toxic
amounts be prohibited.
A-29
-------
Therefore, the present and future most beneficial uses of all waters of the state have
been designated by the FDEP using the classification system set forth in Chapter
62-302, of the Florida Administrative Code. These water quality standards and
associated criteria have been established to protect designated uses which are:
1. OFW Outstanding Florida Waters, which include waters in state and federal
parks, wildlife refuges, and other environmentally sensitive areas.
2. Class I: Potable Water Supplies.
3. Class II: Shellfish Propagation or Harvesting.
4. Class III: Recreation, Propagation and Maintenance of a Healthy, Well-Balanced
Population of Fish and Wildlife.
5. Class IV: Agricultural Use.
6. Class V: Navigation, Utility, and Industrial Uses.
Accordingly, the FDEP has established minimum, general, and specific criteria for
surface waters in the state. These criteria provide limits for various detectable sources
of pollution (e.g., nutrients, metals, organics). Water quality data are needed to
document adverse impacts to Water bodies/watercourses and flora/fauna. Stormwater
generates nonpoint source pollutant loads which can degrade water quality.
Traditionally, water quality data are collected in regular intervals (e.g., quarterly) to
record ambient conditions in a given location. However, stormwater sampling is needed
during specific storm events to properly monitor for the "flush" of pollutants in rivers and
streams.
By using these water quality data, water classifications, and criteria, recommendations
can be made regarding the BMPs to use to achieve the standards established for, or
mitigate the adverse impacts to, the receiving body of water. The following sections
discuss available water quality data and potential water quality trends in the study area.
The receiving waters in this study area are Lake Hart, Red Lake, Buck Lake and Lake
Nona which are designated as Class III waters.
Historical Water Quality Monitoring Data
Historical water quality data are available for Lake Nona, Red Lake, and Buck Lake.
The following paragraphs present a brief summary of current water quality.
To measure water quality of Florida lakes, an index of bio-physical and chemical
parameters (trophic classification system) has been developed. Lakes containing
similar (cluster) analysis results of seven indicators (primary production (pp), chlorophyll
a (CHA), total organic nitrogen (TON), total phosphorus (TP), Secchi disc transparency
A-30
-------
(SD), conductivity (COND), and a cation ratio (CR) due to Pearsall (1922)) were
classified into four trophic levels and ranked (Brezonikand Shannon, 1971). The
trophic state index is delineated by numerical values into four classes: oligotrophic (0-
49), mesotrophic (50-60), eutrophic (61-69), and hypereutrophic (70-).
The Orange County Environmental Protection Department conducted annual water
quality studies for all the county lakes beginning in 1990 to the present. The
department measures four of the original seven parameters: chlorophyll a (a component
of algae), Secchi depth (water clarity or transparency), total phosphorus, and total
nitrogen (nutrient indicators). As a natural lake ages (eutrophication), a shift from
oligtrophic (few nutrients) to eutrophic (well nourished) conditions occurs. Industrial,
agricultural, and urbanization activities around a lake accelerate this process. Table A-7
provides the annual trophic state index (TSI) results of the calculations which rank the
Lake Hart basin.
The TSI results show that natural eutrophication has occurred basin wide. Each lake
shows a slight increase in value during the five year study. Red Lake and Lake Nona
have retained their oligotrophic status. Buck Lake and Lake Whipporwill have recently
changed from oligotrophic to mesotropic conditions. Lake Hart has maintained a
mesotrophic level being within five increments of the range. In contrast, the two
oligotrophic lakes have no or minimum urbanization activities. Overall the water quality
in Lake Nona, Red Lake and Buck Lake is good. The Orange County TSI survey
showed that Lake Nona was ranked second out of 136 lakes, with Buck Lake 68, Lake
Whipporwill 76, and Lake Hart 109. The results are summarized in Table A-8.
Biological quality of selected lakes in Orange County were measured in 1994. Table A-
9 provides the Diversity Index (a measurement of the variety of biological organisms
which exists within a community), Equitability (a measurement of the distribution of the
various types of biological organisms within a community and Taxa Richness (an
average number of the species present at the site sampled.
Table A-7. The Annual Trophic State Index Results for the Lake Hart Basin
Lake Name
Buck
Hart
Nona
Red
Whipporwill
1990
45
53
30
39
34
1991
50
20
44
38
1992
54
56
15
44
52
1993
50
57
28
49
46
1994
50
58
22
40
51
A-31
-------
Table A-8. 1994 Summary of Lake Secchi Disk Measurements, Chlorophyll-a
Concentrations and Nitrogen and Phosphorus Concentrations in the Lake Hart Basin
Lake Name
Buck
Hart
Nona
Red
Whipporwill
Secchi
Diskm
1.8
0.5
3.8
2.3
1.3
Chlor-a
ug/l
7.5
2.9
1.6
3.5
9.5
N02-
N03
mg/l
0.02
0.1
0.01
0.02
0.02
TKN
mg/l
0.95
1.06
0.27
0.64
0.55
TN mg/l
0.97
1.16
0.28
0.66
0.57
TPC-4
mg/l
0.03
0.03
0
0.02
0.02
TSI
Index
50
58
22
40
51
Source: Orange County Environmental Protection.
The results of the lakes in Table A-9 reflect a moderate pollution condition (eutrophic) in
comparison to other lakes in central Florida. The results of the next two lakes are
outside the Lake Hart basin that show one lake with eutrophic conditions and one lake
with oligotrophic conditions, respectively. Lake Rowena was sampled on January 13,
1993, had a TSI of 57, a Diversity Index of 1.38, an Equitability of 0.3, and a Taxa
Richness of 12. Lake Wauseon was sampled on December 29, 1993 had a TSI of 30, a
Diversity Index of 3.2, an Equitability of 0.52, and a Taxa Richness of 30.5.
Table A-9. Biological Quality of Selected Lakes in Orange County
Lake
Hart
Whipporwill
Date
2/8/93
2/8/93
Diversity
Index
2.45
2.52
Equitability
0.64
0.67
Taxa
Richness
11
12
Source: Orange County Environmental Protection.
Evaluation of Best Management Practices
Best Management Practices Considerations
Best Management Practices (BMPs) are techniques, approaches, or designs that
promote sound use and protection of natural resources. Various types of BMPs are
discussed extensively in Chapter 6 of the FDER Land Development Manual 1989. This
A-32
-------
section summarizes alternatives which can be used to control flooding and avoid water
quality problems.
Alternative Best Management Practices
BMPs that were considered for use in the Lake Hart basin MSMP are listed below
where they are grouped as structural (constructed facilities) and non-structural
(regulations or ordinances):
Structural Stormwater Controls
1. Extended dry detention ponds
2. Wet detention ponds (with and without retention swales)
3. Exfiltration trenches
4. Shallow grassed swales
5. Retention basins
6. Porous pavement
7. Water quality inlets
8. Underdrains and stormwater filter systems
9. Alum injection
10. Aeration
11. Skimmers
Non-Structural Source Controls
1. Land use planning
2. Public information programs
3. Stormwater management ordinance requirements
4. Fertilizer application controls
5. Pesticide use controls
6. Solid waste management
7. Street sweeping
8. Aquifer recharge and minimization of directly connected impervious
area
9. Illicit connections (non-stormwater discharges) identification and
removal
10. Control of illegal dumping
11. Erosion and sediment
12. Source control on construction sites
13. Operation and maintenance
The use of a specific BMP depends on the site conditions and objectives such as water
quality protection, flood control, aquifer recharge, or volume control. In many cases,
there are multiple goals or needs for a given project. Therefore, BMPs can be "mixed
and matched" to develop a "treatment train." The treatment train concept maximizes
the use of available site conditions from the point of runoff generation to the receiving
water discharge in order to maximize water quantity (flood control), water quality
(pollutant load reduction), aquifer recharge, and wetlands benefits.
A-33
-------
The City currently applies the treatment train concept for wet detention facilities as
described in OUSWMM. The runoff generated by the first inch of rainfall is stored in an
off-line retention facility that is separate from the detention facility. Once the retention
volume is exceeded, stormwater runoff flows into a separate detention facility for flood
control where it is gradually discharged to receiving water as necessary. For the South
East Annexation Area (SEAA), the City will consider alternative innovative options to
meet the goals of OUSWMM. This is discussed in further detail in this "Evaluation of
Best Management Practices."
Figure A-6 and Figure A-7 show, respectively, a schematic flowchart of the treatment
train concept and the City's "two pond" wet detention system.
Operation and Maintenance (O & M)
A recent survey by FDEP reported that nearly 70% of existing treatment facilities in
Florida are not properly maintained and, therefore, do not provide the intended pollutant
removal effectiveness. Because of this, one of the most effective non-structural BMPs
is routine maintenance of existing treatment facilities. For publicly owned treatment
facilities, routine maintenance and inspection should be considered for facilities that are
within water quality sensitive basins. For the other "non-critical" areas, maintenance of
treatment facilities may be considered on an as needed basis based on periodic
inspection reports.
For privately owned facilities, maintenance is not typically performed by a municipality.
There are several options that can be pursued by a municipality to help insure that
proper maintenance is being conducted. These options may include a certification
program initiated by a municipality that requires all approved private subdivision ponds
to be recertified by the owner on a predetermined time interval. The re-certification may
be done by a state certified/trained inspector or engineer. Enforcement of maintenance
of privately owned facilities is one of the most difficult problems for a municipality. A
potential enforcement measure is City intervention, after sufficient notification, where
critical maintenance is done by the City and the cost of the maintenance is billed to the
owner. Another option would be to consider stormwater utility credits for certified
maintenance and rehabilitation.
Regional Versus Onsite Structural Best Management Practices
In much of the undeveloped portions of the City of Orlando, regional detention of flood
control and water quality protection for relatively flat areas with high water tables appear
to be the solution of choice because they provide the needed multiple benefits. The
following discussion is provided for detention pond applications, which tend to be cost-
effective where sited regionally.
Onsite Approach
In the case of future urban development, the onsite (also known as piecemeal approach
to stormwater control) involves the delegation of responsibilities for BMP deployment to
local land developers. Each developer is responsible for constructing a structural BMP
A-34
-------
at the development site to control nonpoint pollution loadings from the site. Detention
pond BMPs provided onsite typically have contributing areas of 20 to 50 acres. The
local government is responsible for reviewing each structural BMP design to ensure
conformance with specified design criteria, for inspecting the constructed facility to
ensure conformance with the design, and for ensuring that a maintenance plan is
implemented for the facility. The onsite approach is illustrated in Figure A-8.
Regional Approach
The regional approach to stormwater control involves strategically siting regional
structural BMPs to control nonpoint pollution loadings from multiple development
projects. The front-end costs for constructing the structural BMP are assumed by the
developer and/or the local government entity that administers the regional BMP plan.
BMP capital costs can then recovered from upstream developers on a pro-rata basis as
development occurs. Individual regional BMPs are phased in as development occurs
rather than constructing all regional facilities at one time. Maintenance responsibility for
regional structural BMPs can be assumed by the developer (or designee with certified
maintenance bonds) or by the local government. The regional approach addresses
concurrence for the entire watershed while the onsite approach does not address this
issue. The regional approach is also shown in Figure A-8.
In developing stormwater and watershed management programs during the 1970s, local
governments often elected to use the piecemeal approach because it required no
advanced planning and, therefore, appeared relatively easy to administer. While the
lack of planning requirements does give the piecemeal approach an up-front advantage,
in comparison with the regional approach, the long term disadvantages outweigh this
benefit.
A regional BMP system offers benefits that are equal to or greater than onsite BMP
benefits at a lower cost. Most of the advantages of the regional approach over the
onsite approach can be attributed to the need for fewer structural facilities that are
strategically located within the watershed. The specific advantages of the regional
approach are summarized below
A-35
-------
Slept
Step 2
Step 3
Step 4
RUNOFF
GENERATION
CONVEYANCE
AND
PRE-TREATMEHT
AIDITIINAL
TREATMENT
AND
ATTENUATION
FINAL
TREATMENT
AND
ATTEHDATION
OISCHMGE
Tt
RECEIVING
WATERS IF
NECESSARY
MINIMIZE DICA
TO REDOCCE
DIRECT RUNOFF
SWALES PREFERRED.
PIPES IF NECESSARY
(OFF-LINE IF POSSIBLE!
SWALES DETECTION,
OR RETENTION
(OFF-LINE IF POSSIBLE)
RETENTION OR DETECTION.
(CONTROL PEAK FLOW AND
VOLDME IF POSSIBLE)
NOTES:
1. DICA IS DIRECTLY CONNECTED IMPERVIOUS AREA.
2. RECHARGE/INFILTRATION SHOULD BE ATTAINED WHEREVER POSSIBLE.
3. MULTI-STEP TREATMENT MAXIMIZES REMOVAL OF BOTH SUSPENDED AND DISSOLVED POLLUTANTS.
Figure A-6. Best management practice "treatment train" concept (Reprinted Courtesy of the City of Orlando,
FL).
A-36
-------
MINIMUM RETENTION POND VOLUME = { O.5 / 12 " } x I FT x DRAINAGE AREA IN ACRES
INFLOW TO RETENTION
L
DETENTION PONDS
OVERFLOW WEIR
I
I
DETENTION BHSIN MUST BE DESIGNED
FOR n PRE/P03T
DEVELOPMENT RUNOFF DIFFERENCE
SO THflT RUNOFF IS LIMITED
IN QUflNITY TOPRE DEVELOPMENT
CONDITION OR SYSTEM RESTRRINTS
1
1
I
Q
-MI m- .=
RETENTION PCM? MINIMUM
CAPACITY RUNOFF FROM
I tT INCH OF RAINFALL
( NOT LESS THAN 1/2")
EKFILTRDTION SYSTEM
OUTFHLLWITH
POND
DRDWDOWN
FOR
CLEHNINQ
[IF REQUIRED]
OUTFLOW FROM
UNDERDRDIN SYSTEM
EXISTING
II.
ij.
CONTROL STRUCTURE
SYSTEM
Figure A-7. Design for retention/detention facilities (Reprinted Courtesy of the City of Orlando, FL).
A-37
-------
ONSITE
(Each developer provides RVIP on dtvi'lopnienl sile)
REGIONAL
(Strategically locale*! by hical "ovtrrnnmiO
Versus
ALTERNATIVES FOR BMP DEPLOYMENT
Figure A-8. Onsite versus regional best management practices (Reprinted Courtesy of the City of Orlando,
FL).
A-38
-------
Reduction in maintenance costs: Since there are fewer stormwater detention
facilities to maintain, the annual cost of maintenance programs are significantly
lower. Moreover, because the regional detention facility recommended in the
master plan can be designed to facilitate maintenance activities, annual
maintenance costs are further reduced in comparison with onsite facilities.
Examples of cost saving design features that are typically only feasible at
regional BMP facilities include: access roads that facilitate the movement of
equipment and work crews onto the site (by comparison, detention facilities
implemented under the onsite approach are often located in residential
backyards), additional sediment storage capacity (e.g., sedimentforebay) to
permit an increase in the time interval between facility clean-out operations, and
onsite disposal areas for sediment and debris removed during clean-out.
Greater reliability: A regional BMP system will be more reliable than an onsite
BMP system because it is more likely to be maintained. With fewer facilities to
maintain and design features that reduce maintenance costs, the regional BMP
approach is much more likely to result in an effective long-term maintenance
program. Due to the greater number of facilities, the onsite BMP approach tends
to result in a large number of facilities that do not get adequate maintenance and,
therefore, soon cease to function as designed. Many municipalities start off with
the onsite approach but eventually switch to the regional approach to address the
lack of maintenance of the onsite systems and to increase the overall
effectiveness of the stormwater management program. Regional facilities,
however, cannot be so large that incremental water quality protection is lost. For
instance, if a regional detention facility is at the bottom of a 10 square mile basin,
no water quality protection would be provided to the upstream rivers and streams
as urbanization occurs. This could be detrimental to the existing plants and
wildlife species. Another problem with an excessively large regional facility is the
impact of the facility on existing wetlands. In rural areas, an excessively large
pond would inundate large wetland areas which would make permitting of the
structures extremely difficult. Experience shows that a regional pond should be
limited to a 100 to 600 acre tributary area.
Opportunities to manage existing non-point pollution loadings: Nonpoint pollution
loadings from existing developed areas can be affordably controlled at the same
regional facilities that are sited to control future urban development. This is
because the provision of additional storage capacity to control runoff from
existing development in the facility's contributing area is reasonable in cost as a
result of economies-of-scale. By comparison, the costs of retrofitting existing
development sites with onsite detention BMPs to control existing nonpoint
pollution loadings may be prohibitively expensive.
Fairness to land developers: Land developers recognize that
economies-of-scale available at a single regional BMP facility should produce
lower capital costs in comparison with several onsite detention facilities. They
A-39
-------
also tend to prefer the regional BMP approach because it eliminates the need to
set aside acreage for an onsite facility other than pretreatment and conveyance
to the regional pond. This could permit an increase in the number of dwelling
units within the development site while still providing sufficient stormwater
management. The additional cost of a pond sized for future development can be
passed on to the developer. Developers can "buy" into the regional system and
eliminate on-site BMP requirements, thus minimizing cost to the public. Regional
facilities also offer the ability to maximize mining of fill material which will be
necessary in the Lake Hart basin.
Multi-purpose uses: Regional facilities can often be landscaped to offer
recreational and aesthetic benefits. Jogging and walking trails, picnic areas, ball
fields, and canoeing or boating are some of the typical uses. For example,
portions of the facility used for flood control can be kept dry, except during floods,
and used for exercise areas, football or soccer fields and softball or baseball
diamonds. Wildlife benefits can be provided in the form of islands or
preservation zones which allow observation of nature within the park schemes.
Gradual swales can also be worked into the park concept to provide pretreatment
around paved areas, such as parking lots or access roads. Figure A-9 illustrates
a typical multi-purpose stormwater facility.
Best Management Practices Implementation Considerations
In determining the best stormwater management facility or combination of facilities
(treatment train), various factors need to be considered. Examples are:
Physical constraints or requirements of the site such as permeability of the soil,
the location of the wet season high water table, and the amount of land available
on the site to construct the facility.
Permitability of the facility or facilities.
Needed benefits to solve problems and guide future development in a given
area.
Benefits provided by the facility such as control of peak discharge for flood
control, reduction in the total volume of discharge, groundwater recharge, erosion
control, wetlands management, reduction of pollutant loads to receiving waters,
and/or optimized maintenance. Table A-10 lists requirements and benefits that
can be used as a guide in the selection of a stormwater BMP type.
-------
RUNOFF
Park and Recreation
Lake
Final Treatment
and Flood Control
( Canoeing and Fishing )
r
n
Park Facilities
and Parking
Pretreatments and
Additional Flood Control
( Ballfields. Hiking,
Jogging, and Biking )
m ป
Recharge
Where Possible
Figure A-9. Typical multi-use stormwater facility (Reprinted Courtesy of the City of Orlando, FL).
A-41
-------
Table A-10. BMP Selection Features:: Requirements Versus Benefits
BEST MANAGEMENT PRACTICE
Extended Dry Detention
Ponds
Wet Detention
Exfiltration Trenches
Shallow Grassed Swales
Retention Basins
Filtration
Requirements:
1. Available Space
1. Available Space
2. Water Table at or
Near Pond Normal Pool Level
3. Relatively Impermeable
Soils
1. Limited Space
Available
2. Water Table > 2
=t Below Trench Bottom
3. Highly Permeable
Soils
1. Moderate to Limited
Space Available
2. Water Table > 1-2 Ft
3elow Swale Bottom
3. Permeable Soils
1. Available Space
2. Water Table > 2-3
Ft Below Basin
Bottom
1. Available
Space
2. Minimal Base
=low
Benefits:
1. Peak Discharge
Control
2. Load Reduction
for Suspended Pollutants
3. Multiple-Use Park
Areas
1. Peak Discharge
Control
2. Load Reduction for
Dissolved and Suspended
Pollutants
3. Aesthetic Permanent
Pool and Fountain
4. Wildlife Habitat
5. Multi-Use ParkAreas
1. Aquifer Recharge
2. Pollutant Load
Reduction On-Line
1. Peak Discharge
Control
2. Volume Discharge
Control
3. Aquifer Recharge
4. Pollutant Load
Reduction Off-Line or On-Line
5. Pre-Treatment
1. Peak Discharge
Control
2. Volume
Discharge Control
3. Aquifer
Recharge
4. Pollutant Load
Reduction Off-Line or
On-Line
5. Multiple-Use
ParkAreas
2. Aquifer
Recharge
/\-42
-------
Recommended Best Management Practices
Introduction
The previous section titled "Evaluation of Best Management Practices" presented a
discussion of various BMP types, and their benefits and limitations. The recommended
BMPs, as discussed in the section, are proposed to become the foundation for a South
East Annexation Area (SEAA) Stormwater Management Manual (SWMM). As already
noted, two general categories of controls can be implemented to improve or enhance
stormwater runoff with respect to water quality and water quantity (flooding). Structural
controls are constructed facilities that treat, store, or convey stormwater runoff. Non-
structural controls, on the other hand, focus on the prevention of pollution and the
reduction of runoff. This section presents the recommended BMP treatment train.
The BMPs discussed in the previous section were screened for applicability to the Lake
Hart basin study area based on site constraints, cost-effectiveness, efficiency,
maintenance requirements, and current OUSWMM guidelines. Since the basin is
largely undeveloped with few existing problems, the focus of the alternative analysis
was planning regional facilities for the control of runoff from future development (quality
and quantity control). The Lake Hart basin has the following physical characteristics:
1. Relatively flat terrain.
2. High groundwater table.
3. Need for flood storage.
4. Need for treatment of solids and soluble pollutants.
5. Need for fill for development and improvement projects.
Because of these physical characteristics, wet detention BMPs were considered to be
the most appropriate control measures to meet the program goals.
Based on the LOS goals of the program, system constraints, SFWMMD permitting
requirements, the Narcoossee Road improvements, and developer needs, a BMP
Treatment Train has been formulated with three major components: DCIA minimization,
pretreatment (0.25 inches) and regional wet detention ponds.
OUSWMM requires that wet detention facilities use a two pond system. The first pond
uses retention to provide water quality treatment and the second separate pond uses
detention for flood control. Because of the high groundwater table in the Lake Hart
basin developable areas (typically one to two feet below the ground surface), deeper
retention pond systems (two to four feet) may not function as desired. Therefore,
shallow pretreatment practices may be incorporated into landscaping swales and lot
grading plans as an alternate. The BMP treatment train would build upon the
foundations of OUSWMM by providing nearly equivalent innovative technology
considerations for areas with these site constraints:
Lakes as receiving waters.
Karst topography.
-------
Twenty-four percent of the basin is comprised of wetlands.
The BMP treatment train for the Lake Hart basin would consist of several pretreatment
practices primarily within the secondary stormwater management system in series with
regional wet detention ponds protecting the PSWMS. This innovative approach will
achieve both the water quantity and water quality goals of OUSWMM while allowing for
a cost-effective regional facility concept for future development. In addition, this
concept is consistent with annexation agreements between the City, County, and local
land owners. The recommended BMPs (pretreatment and wet detention) for the Lake
Hart basin are discussed below.
Pretreatment Best Management Practices
The pretreatment BMPs are a series of structural and non-structural controls that will
provide a reduction in runoff volumes and/or pollutant loads from urbanized areas prior
to their discharge into the regional wet detention ponds and the downstream wetlands.
The structural pretreatment BMPs will provide treatment for approximately 0.25 inch of
runoff over the tributary area. Structural controls include retention swales with raised
inlets to allow overflows, wet detention ponds, and oil-water separators for individual
areas. Non-structural BMPs include reducing DCIA by diverting rooftops and portions of
driveways and parking lots to shallow, grassed, or landscaped swale areas, and runoff
pollutant source reduction methods - many of which are voluntary but would help to
achieve benefits. The recommended pretreatment BMPs are discussed below.
Minimization of Directly Connected Impervious Area
Minimizing DCIA involves ensuring that as much runoff as possible from impervious
areas is routed over relatively large pervious areas and, in some cases, choosing an
alternative surface to pavement or concrete that allows for some degree of infiltration.
Figure A-10 is an illustration of a parcel that has been modified to convert a portion of
the DCIA into non-directly connected impervious area by rerouting the roof gutters over
the lawn (properly graded between houses). A portion of the DCIA could be converted
to pervious area by using a porous surface.
Landscaped Swales and Grass-Lined Swales
Landscaped swales should be used around parking lots, houses, and other structures.
The swales will provide pretreatment and also provide conveyance to larger secondary
or primary stormwater management systems. Properly designed swales are useful for
proper grading around houses as well as detention/retention prior to discharge into a
/\-44
-------
Shallow
Swales
Graded to
Regional
Facilities
Shallow
Swales
Graded to
Regional
Facilities
Rooftop Runoff
i la Lot Line
Road
PLAN VIEW
Figure A-10. Minimization of directly connected impervious area and use of grass lined swales. (Reprinted
Courtesy of the City of Orlando, FL).
-------
secondary or primary system. Fill from the shallow swale area may be used elsewhere
on the property to improve the grading plan. Landscaped swales would typically be 0.5
to 1.0 foot deep and should have side slopes no steeper than 4:1 (H:V), with side slopes
of 6:1 or greater being less noticeable and more attractive.
Grass-lined swales should be constructed around parking lots and commercial centers
as recessed planters for landscaping. The swales could be part of the landscaping and
incorporate raised inlets into the design, which will allow for the initial 0.25 inch retention
volume for pretreatment. Although groundwater tables in the developable area are
generally within one to two feet of the surface, recovery times for retention volumes of
approximately 0.25 inch should be sufficiently small to allow the use of limited retention.
Minimum infiltration rates of 0.1 inch/hour are expected to be advisable, allowing a
relatively quick drawdown. Swales incorporated within commercial areas can enhance
aesthetics and be used as credit towards green space and landscaping requirements.
Figure A-11 shows an example of a landscaped swale with a raised inlet. Runoff will
serve to reduce irrigation needs.
Curb Connections to Swales
Connections from the curbs to roadside swales should be provided to route street flow
to grass-lined swales before discharge to the secondary or primary stormwater
management system. Because roadway runoff may contain a greater pollutant load
than runoff most other surfaces, providing swale pretreatment of roadway runoff will
reduce pollutant loads to the regional ponds and improve the overall efficiency of the
BMP treatment train. The swale space required for pretreatment of roadway runoff in
roadside swales can be incorporated into OUSWMM green space requirements and be
used to enhance the aesthetics of the roadways.
The connections between the curb and the swale can be implemented in two ways.
The first method is to provide regularly spaced flumes in the curb as the connection to
the swale. This method would be less expensive and will be aesthetically appealing.
Another way, as illustrated in Figure A-12, is to provide a four to six inch diameter pipe
approximately every 200 feet between the curb and the swale. This method may
provide better erosion control at the edge of the curb by preventing water from flowing
over the turf between the curb and the swale. The disadvantage to this method is the
potential for clogging of the small pipes and thus the requirement for increased
maintenance.
-------
Raised Inlets
IB"
I I I I
,1,1,1,1,
PLflH VIEW
Figure A-11. Landscaped retention pretreatment swales with raised inlets (Reprinted Courtesy of the City of
Orlando, FL).
/\-47
-------
SECTION VIEW
6:1 SI ID
SLOPES
Figure A-12. Use of pipe to convey roadway runoff to roadside swale (Reprinted Courtesy of the City of
Orlando, FL).
-------
Capture Ratios of Swales
The Storage, Treatment, Overflow, and Runoff Model (STORM) was used to evaluate
the effectiveness of the pretreatment swales at capturing a percentage of the annual
runoff and, therefore, the annual pollutant volume. STORM is a continuous simulation
model developed by COM for the United States Army Corps of Engineers (USACOE)
Hydrologic Engineering Center (HEC) that translates a continuous, long-term rainfall
record (1942 through 1993 was used for this study) into a series of runoff events based
on hydrologic conditions, routes the runoff through a "treatment facility," and calculates
statistics on outputs such as runoff volumes and pollutant loads.
In the mode used for this analysis, the characteristics of the treatment facility were
described by a storage volume(e.g., 0.25 inches) and a treatment rate. The treatment
rate in this case is equal to the infiltration rate in the swale normalized to the total
contributing area. Characteristic swales were established for both residential and
commercial areas using the swale configuration previously discussed. Because there
will be variability based on site conditions and application, a range of treatment rates
and storage volumes around the expected values were used to establish the sensitivity
to the results. Results from these simulations are shown in Figure A-13 for medium
density residential areas. The average annual runoff volume capture ratio is
approximately 60% for a 0.25 inch retention volume and typical soils in the area.
Treatment efficiencies for the BMP treatment train were adjusted accordingly since the
wet detention ponds would treat and attenuate about 40% of the average annual runoff
volume.
Oil-Water Separators
Potential sources of high oil and grease, such as gas stations and light industrial land
uses, should be required to provide either oil-water separation devices or off-line
retention. Off-line retention offers additional pollutant removal benefits beyond oil and
grease removal, provides additional volume control, and requires typical maintenance.
However, off-line retention is also more space intensive and may result in groundwater
contamination if sufficient quantities of pollutants are released into the retention basin.
Oil-water separators require less space and initial capital expense. They need to be
maintained at least monthly and offer some control of floating and settleable solids.
Sediment Forebays
Sediment forebays should be designed into the regional wet detention ponds. Forebays
are designed to be easier to maintain than the rest of pond. The use of forebays will
lower maintenance costs and extend the time between maintenance dredging of the
remainder of the pond. Figure A-14 shows a typical forebay.
-------
Medium Density Residential Area
0% 10% Z0% 3D% 40% 50% ED% 7D % BD% 90%
Percent of Dnnual Runoff Uolume Captured
4 OJJ5 in Jnr infiltration rale -*- 0.1 in Jnr Infiltration rale -a- 0.2 in I hi infiltration rate
1DD%
Figure A-13. Percent of annual runoff volume captured for medium density residential (Reprinted Courtesy of
the City of Orlando, FL).
A-50
-------
Littoral Zone
25 to 50 % of Total Surface
Forebay
Side Slope No Steeper than 4:1
-M1
Embankment Side Slope
No than 3 :1
Embankment
*- Access to Outlet
or Flatter
Permanent w.S.
Average Depth
ot SJD it
12 ft (max.)
SECTION A1-A
Overflow for
Larger Storms
Inflow
S
Energy Dissipator
\
Solid Driving Surface
Adapted from : Urban Drainage and Flood Control District
Derived Colorado, " Urban Drainage Criteral Manual -
3 - Best Management Practices - Stormvjater "
September 1992
Littoral Zone / Berrn
Emergency Spillway Flood Level
ฎ Spillway Crest
(e.g. 100 yr)
Embankment
Spillway Crest
Flared
Culvert
Outflow
Cutoff
Collars
irSjX*
*iL* .
NOT TO SCALE
Provide
Bottom Drain
Outlet Works
(see )
Figure A-14. Typical wet pond with forebay (Reprinted Courtesy of the City of Orlando, FL).
A-51
-------
Source Reduction
Control of pollutants at the source of generation is a very effective and economical
pretreatment BMP. Source reduction requests for illicit corrections and illegal dumping
are needed for the EPA NPDES permit order. Source reduction relies almost entirely
on the education of citizens living and working in the area. Examples of education
programs for source reduction of pollutants are fliers instructing how to use the minimal
amount of lawn fertilizer and pesticide and stenciled messages on storm drains.
Wet Detention Location and Sizing Criteria
The following paragraphs discuss the general criteria used to site the proposed regional
facilities as well as the methodologies used to size them.
Regional Facility Location Criteria
A major component of this MSMP was the cooperative effort between the City of
Orlando and private property owners during the siting of the proposed regional facilities.
This was accomplished through a series of group and individual meetings with the major
property owners and their engineers to discuss the advantages and disadvantages of
each proposed regional facility location. Criteria discussed during these meetings
included siting the regional facilities such that program goals of flood control, water
quality protection, aquifer recharge and wetland protection could be achieved. In
addition, other implementation considerations were incorporated, such as maximizing
road frontage, developable property, waterfront property, and tributary area served.
Additionally, accessibility of the regional facilities by maintenance crews was considered
during the siting process. From an environmental perspective, the regional facilities
were sited adjacent to wetlands (wherever possible) and conceptually designed with V-
notched weirs that would discharge into the wetlands in such a manner that the existing
wetlands would be preserved.
Coordination of the Narcoossee Road widening project with proposed development in
the study area was also a key factor in siting the proposed regional facilities. There are
potentially seven regional ponds that would provide stormwater management for both
Narcoossee Road and surrounding proposed developments. By serving a dual
purpose, fewer ponds would be required which represents capital operation and
maintenance cost savings to both the City and private property owners.
Regional Facility Sizing Methodology
The proposed regional facilities were sized using the guidelines documented in the City
of Orlando Urban Stormwater Management Manual (OUSWMM) and the SFWMD
Management and Storage of Surface Waters (MSSW) Permit Information Manual
Volume IV. A discussion of these guidelines and their application to wet detention is
present below. Two volumes are used in sizing a wet detention system. They are the
live pool (sometimes called treatment pool volume) and the permanent pool.
Combined, these two components have a regulated discharge to detain water and settle
pollutants to achieve the desired water quality goals.
A-52
-------
Live Pool Volume
Chapter 5.2.1 of the SFWMD MSSW Permit Information Manual provides guidelines on
determining the required treatment pool volume for a wet detention system. The
requirements state that "wet detention volume shall be provided for the first inch of
runoff from the developed project, or the total runoff of 2.5 inches times the percentage
of imperviousness, whichever is greater". The same criterion is used in Chapter 2.8.4 of
the OUSWMM. Therefore the live pool volume computed for each of the proposed
facilities was determined using the following equations:
Maximum of
V SUB L ~ = ~ { Rl*A*Ia } OVER { 12 ~ inch 'foot }
V SUB L ~ = ~ { R2*A } OVER { 12 ~ inch 'foot }
or
where:
VL = Live pool volume (acre-feet)
R1 = 2.5 inches of rainfall
R2 =1.0 inches of runoff
A = Tributary area (acres)
la = Average impervious area (percent)
(NDCIA + DCIA)/100
NDCIA = Non directly connected impervious area (percent)
DCIA = Directly connected impervious area (percent)
Because of the high seasonal groundwater tables identified for the study area, the
maximum treatment pool depth was assumed to be one foot above the permanent pool
to ensure proper flood protection. This criterion became one of the key elements in
determining the pond surface area requirements.
Live Pool Volume Bleed-Down Requirements
The criteria in the OUSWMM manual also requires that 50% of the live pool volume can
be discharged in the first 60 hours following a storm event with total volume recovery
occurring in 14 days. The bleed-down requirements presented in the SFWMD MSSW
Permit Information Manual Volume IV (Chapter 7.2) are for a release of no more than
0.5 inches per 24 hours.
The SFWMD basis of review requires that bleed-down mechanisms be V-notches for
wet detention systems. The discharge through a V-notch opening is a weir can be
estimated by:
A-53
-------
Q ~ = ~ 2.5*tan ( 2 ) *H SUP { 2.5 }
where:
Q = Discharge (cfs)
= Angleof V-notch (degrees)
H = Head on vertex of notch (feet)
Since SFWMD criteria specified that this bleed-down mechanism be sized to discharge
one-half inch of detention volume in 24-hours, the following formula provides the
required size:
~ = ~ 2*tan SUP {-1} ~ {( 0.492*Vdet )} OVER H SUP {2.5}
where:
= V-notch angle (degrees)
Vdet = One-half inch of detention volume (acre-feet)
H = Vertical distance from weir crest to vertex angle (feet)
For the Lake Hart MSMP, the SFWMD criteria were used for sizing the V-notch control
weirs.
Permanent Pool Volume
Chapter 2.8.4 of the OUSWMM manual lists the following requirements for the
permanent pool volume:
"The volume in the permanent pool (below the maintained water level) must be
sufficient to provide a residence time of at least 14 days. This volume may be
determined as 2-inches over the impervious portion of the drainage basin, plus
%-inch over the pervious portion of the drainage basin"
"A littoral shelf shall be incorporated into the facility from maintained water level
or a depth of 2.5 feet at a slope no steeper than 6:1"
"The facility shall be configured such that the mean depth is 3 to 10 feet.
Recommended depth ratios are:"
Percent Area Depth, feet
<10 >8
50-70 4-8
25-50 0-4
A-54
-------
Using these requirements, the permanent pool volume was calculated as follows:
Vp~ = ~ {[A*Ia*R3+A*(l-Ia)*R4]} OVER (12 ~ inch'foot)
where:
Vp = Required permanent pool volume (acre-feet)
A = Tributary area (acres)
la = Average impervious area (percent)
(NDCIA + DCIA)/100
R3 = 2.0 inches of rainfall over the impervious area
R4 = 0.5 inches of rainfall over the pervious area
There are no specified permanent pool volume requirements identified in the SFWMD
MSSW Permit Information Manual. However, the SFWMD has identified similar criteria
to that in the OUSWMM for geometric considerations of a wet detention system
(Chapter 7.4). A summary of these criteria are as follows:
The facility must have a minimum wet detention surface area of 0.5 acres.
The wet detention facility should have a 2:1 length to width ratio (applicant
can request a waiver of this criteria if there is a single owner, or the entities
involves have a full time maintenance staff with an interest in maintaining the
areas for water quality purposes).
The littoral area should be shallower than six feet as measured below the
control structure elevation. The littoral area shall be 20% of the wet detention
area or 2.5% if the total wet detention area (including side slopes) plus the
contributing area. The SFWMD also recommends that 25 to 50% of the wet
detention area be deeper than 12 feet.
Side slopes shall not be steeper than 4:1.
Bulkheads shall be allowed for no more than 40% of the shoreline length, plus
compensating littoral zone must be provided.
For planning purposes, the required depth of the permanent pool for each facility was
estimated for the OUSWMM criteria or as 70% of the area would have a depth of six
feet and 30% of the area would have a depth of one foot which results in an average
depth of 4.5 feet. Individual ponds could be constructed deeper to the SFWMD
maximum values if additional fill is needed. This would provide a longer residence time.
Aerating fountains are also recommended to control water quality (higher dissolved
oxygen).
A-55
-------
Flood Control Requirements
Chapter 2.9 of the OUSWMM lists the flood control requirements of the City. These
requirements are summarized as follows:
The additional volume of runoff generated by development shall be controlled
and released at a rate not to exceed the peak rate for the site in the
undeveloped condition. The design criterion shall be the 25-year/24-hour
storm event.
For landlocked primary basins, volumetric controls apply. The excess runoff
from development for the 10O-year/24-hour storm event shall be held on-site.
Normally, the detention for flood control must be accomplished in an area
separate from that used to provide pollution abatement. For the Lake Hart
MSMP, this criterion was modified to include a second alternative by the City
to allow single ponds with the pretreatment of 0.25 inches runoff onsite.
Chapter 2.10 of the OUSWMM addresses flood prone areas. Definitions included in this
section include:
The floodplain is the area inundated during the 10O-year/24-hour storm event.
The floodway is that portion of the floodplain which must be clear of
encroachment in order to limit the increase in flood stage to one foot.
The requirements for flood prone areas as presented in this section are summarized as
follows:
Encroachment will be allowed within the 100-year floodplain, with
compensating storage.
All development within the 100-year floodplain established by FEMA or the
City shall comply with the following:
If the project is not within a 100-year flood prone area, an analysis shall be
performed to establish the site's 100-year elevation.
The design storm event to establish the 100-year onsite elevation shall be the
10O-year/72-hour storm event.
The minimum finished floor elevation shall be at least one foot above the
elevation from the 10O-year/24-hour storm, or at the maximum stage for the
10O-year/72-hour storm.
A-56
-------
For commercial or industrial developments, flood proofing may be substituted
for elevating the finished floor (careful consideration should be given prior to
implementing this alternative).
Compensating storage must be provided for all floodwater displaced by
development below the 10O-year/24-hour storm event. Compensating
storage may be claimed in the retention/detention ponds provided it is above
the maintained water elevations and berm elevations are such that the pond
can be inundated during the 100-year storm and still provide 25-year flood
protection.
Off-site increases in flood stage and/or velocity will not be allowed by
encroachment within a floodway. (The 10O-year/72-hour design storm top
width in flow should be considered as the floodway along the wetland
tributaries.)
A letter of map revision will be required for development within the defined
FEMAfloodplain.
Chapter 6 of the SFWMD MSSW Permit Information manual lists water quantity criteria.
A summary of these criteria area is as follows:
Offsite discharge rate is limited to rates not causing adverse impacts to
existing offsite properties and historic discharge rates, rates determined in
previous SFWMD permit actions, or rates specified in SFWMD criteria.
Unless otherwise specified by SFWMD permits or criteria, a 25-year/72-hour
storm event shall be used in computing offsite discharge rates. Alternate
discharge rates can be requested from the SFWMD if adequate justification
can be provided.
Building floors shall be above the 100-year flood elevation as determined
from the FEMA FIRM or from the 10O-year/72-hour storm event. Lower
elevations will be considered by the SFWMD for non-residential uses.
In cases where flood protection of roads is not specified by local government,
the 5-year/24-hour storm event shall be used for flood protection. The
minimum roadway crown elevation shall be at least two-feet higher than the
control elevation.
No net encroachment into the floodplain, between the average wet season
water table and that encompassed by the 100-year event, which will
adversely affect the existing rights of others, will be allowed.
A-57
-------
Based on these criteria, the regional facilities were sized so that peak flows and
elevations from the 25-year/24-hour and 10O-year/72-hour design storm events were
not increased at any of the ten discharge points. This was accomplished using the
stormwater model developed for this study.
Regional Stormwater System Review Considerations
A critical element in the implementation of the Lake Hart basin MSMP will be the review
by the City of the stormwater facility design plans from developers to ensure that
recommendations for the Lake Hart basin are being satisfied. Ultimately a detailed
checklist should be prepared that will assist reviewers in determining if the
recommendations are being met. The items listed below are an outline for a preliminary
checklist to be filled in by the designer and used by the reviewers:
1. Basin number.
2. Tributary area (ac).
3. Land use and soil parameter consistency.
4. Pretreatment volume (ac-ft).
5. Pond treatment volume (live and permanent pools, ac-ft).
6. Forebay.
7. Pond flood volume (ac-ft, this can include the live treatment volume).
8. Connection to PSWMS (method).
9. Control structure (details).
10. Flow, stage, and velocity (summaries).
After the completion of this study, the checklist and more detailed statistics could be
produced to provide the step-by-step outline needed for implementation.
Water Quality Results
Introduction
The Lake Hart basin MSMP included an evaluation of nonpoint source pollutant loads
caused by land use changes and their associated BMPs. The nonpoint source
pollution assessment was performed to estimate the annual average and seasonal
stormwater pollutant loads for the twelve EPA NPDES indication parameters, including
biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended
solids (TSS), total dissolved solids (TDS), total nitrogen (TN), total Kjeldahl nitrogen
(TKN), total phosphorus (TP), dissolved phosphorus (DP), cadmium (Cd), copper (Cu),
lead (Pb), and zinc (Zn). From this analysis, a base set of pollutant loads was
established under existing land use conditions with the existing BMPs. Under future
land use conditions, pollutant load projections are made with both the existing and
proposed BMPs and compared to the existing loads. The relative changes in present
and future pollutant load projections are used as an indicator of the potential for water
quality impacts. This comparison then helps to identify the effectiveness of SFWMD
and City criteria for controlling pollutant load increases as well as assisting in
determining the level of control that will be required in the future.
A-58
-------
Scenarios
Average annual nonpoint pollutant source loads from the study area were projected
using the Watershed Management Model (WMM) described earlier. NPS pollutant
loadings projected with WMM are based on annual runoff volumes and storm event
mean concentrations (EMCs) for each pollutant type and each land use category.
Pollutant loads were projected under both present and future land use conditions using
the following scenarios:
Existing land use with existing BMPs: This scenario is best described as
"existing conditions" and will be used in the evaluation as the baseline for
comparison.
Future land use with existing BMPs: This scenario represents the loading
from future land uses if no new BMPs are built. When compared with the
results from existing land uses in the existing BMPs, this scenario illustrates
the increases in loading due to future growth if such growth is not regulated.
Future land use with existing BMPs and proposed BMPs: This scenario
represents the loading for future land uses once the proposed regional wet
detention facilities with pretreatment have been constructed. When
compared with the results from future land uses without control, this scenario
illustrates the reduction in pollutant loading from the implementation of the
recommended plan.
The recommended BMP Treatment Train is discussed in the previous section titled
"Recommended Best Management Practices." The removal efficiencies composite of
retention swales and wet detention is based on the average annual runoff volume
capture estimated with STORM.
Future Land Use with Recommended BMPs
As discussed earlier, a BMP treatment train is recommended for the future development
in the Lake Hart basin in order to minimize water quality impacts. The primary structural
controls are 0.25 inch of pretreatment swale retention volume in series with regional wet
detention ponds. Removal efficiencies were calculated for these BMPs in series based
on primarily a volumetric reduction from the retention plus an additional removal of the
remaining pollutants from the wet detention ponds. Combined removal efficiencies
were projected to range from 72% for TKN to 96% for TSS. The average annual and
seasonal pollutant loads under existing and future land use (with recommended BMPs)
conditions are presented in Table A-11.
Compared to existing loads, future annual nonpoint source oxygen demand loads with
the recommended BMPs are projected to increase for BOD and decrease for COD and
future annual sediment loadings are projected to decrease or remain approximately the
same. BOD loads are projected to be approximately 1.1 times greater than existing
A-59
-------
loads and COD loads are projected to decrease by approximately 0.9 times. TSS loads
under future conditions with the recommended BMPs are projected to be approximately
0.4 times the existing TSS loads and IDS loads are projected to be approximately 0.9
times.
Total average annual nonpoint source nutrient loadings are projected to decrease for
one of the four constituents. The other three are projected to decrease only slightly,
therefore, remaining virtually the same. Total-P, TKN and NC^+NOs are projected to
approximately remain the same. Dissolved-P is projected to be approximately 0.9 times
the existing loads.
Annual nonpoint source heavy metal loadings are projected to decrease for one of the
four constituents. Only one constituent increases and the other two remain
approximately the same. Lead, is projected to be approximately 0.7 times lower. Zinc
loadings are projected to be approximately 1.3 times greater. Copper and cadmium
remain approximately the same as existing loads.
In summary, five of the 12 constituents are projected to decrease and five are projected
to remain the same under future land use conditions with the recommended BMPs.
Loadings of two of the constituents are projected to be greater than existing loadings.
The constituents projected to increase are BOD and zinc. BOD increases can be
controlled by the use of fountains (i.e., oxygenation) in the wet detention ponds. Slight
increases in zinc loadings are not expected to be a problem because wetland plants
utilize this metal in a beneficial manner. As previously shown, the overall pollutant
loadings from future land use conditions with the recommended BMPs suggest that the
recommended BMPs will be effective at minimizing future impacts to water quality.
A-60
-------
Table A-11. Average Annual Loadings for Existing and Future Land Use Conditions with Recommended Best
Management Practices for the Future Condition
Basin: Entire Lake Hart Study Area
Constituent
BOD
COD
TSS
IDS
Total P
Dissolved P
TKN
NO2+NO3
Lead
Copper
Zinc
Cadmium
Runooff (ac-ft/yr)
Runoff (in/yr)
% Impervious
Basin Area (acres)
Existing Land Uses With Existing BMP's
Wet Season Loads in
Surface Runoff
(Ibs/yr)
90,687
997,277
214,771
2,361,045
3,906
1,916
25,203
7,652
125
66
196
1
8,529
14
Dry Season Loads
in Surface Runoff
(Ibs/yr)
69,821
767,815
165,355
1,817,796
3,007
1,475
19,404
5,891
96
51
151
1
6,567
10
Annual Loads in
Surface Runoff
(Ibs/yr)
160,508
1,765,092
380,126
4,178,841
6,913
3,391
44,608
13,544
221
116
347
2
15,096
24
41
7,578
Future Land Uses With Recommended BMP's
Wet Season Loads
in Surface Runoff
(Ibs/yr)
102,622
890,577
85,860
2,171,423
3,795
1,658
24,713
7,434
90
64
248
1
12,372
20
Dry Season Loads in
Surface Runoff
(Ibs/yr)
79,009
685,665
66,105
1,671,803
2,921
1,276
19,027
5,724
69
49
191
1
9,526
15
Annual Loads in
Surface Runoff
(Ibs/yr)
181,631
1,576,242
151,965
3,843,226
6,716
2,934
43,741
13,158
159
113
439
2
21,898
35
68
7,578
A-61
-------
Water Quantity Results
Introduction
The driving force behind the need for the Lake Hart Basin MSMP was the City's desire
to identify stormwater infrastructure needs in this urbanizing basin. Infrastructure needs
include improvements necessary to resolve existing problems in the PSWMS as well as
avoid potential problems resulting from proposed development. In this study area
includes over 4,500 acres of developable property. In terms of water quantity, problems
may be in the form of building or road flooding or areas with excessive velocities that
could cause significant erosion. For these types of analyses, stormwater model
calibration is valuable. Model calibration is essentially a "reality check" to show that the
modeled system adequately represents the actual system.
Once SWMM was calibrated, it was used in this plan to identify current levels of service
(LOS) and infrastructure needs to accomplish the desired LOS. This was done by
comparing peak flood stages from the model results with known critical elevations, such
as top-of-road elevations, and any resulting overtopping was compared to the desired
level of service for the determination of potential flooding problems and infrastructure or
ordinance needs. Likewise, peak velocities in each element in the system were
compared to threshold values for the determination of potential excessive velocity
problems. Another important element of this study was establishing PSWMS flood
stages under future land use conditions and existing hydraulic conditions. Existing and
future flood stages are important for guiding future development and determining the
relative
Model Calibration
Model calibration refers to the adjustment of model parameters so that the model results
(e.g. peak water surface elevations) are in reasonable agreement with a set of observed
data. A reasonable range of values for the adjustment of parameters is established
through review of the hydrologic literature, and adjustments outside of those ranges are
only made if some unusual hydrologic condition exists. The model is considered
well-calibrated when it is in reasonable agreement with the data for a comparable
independent event without any model adjustments. This process is called model
verification. Calibration and verification are desirable to establish a "reality check" of
predicted stages, flows, and velocities.
The two primary data requirements for model calibration are gauged rainfall and runoff
for the study area. When selecting a calibration storm, the rainfall and runoff data must
be sufficiently documented in appropriate time intervals so that variations in rainfall
intensity and the associated runoff can be described. Data should be recently acquired
so that the current conditions existing in the study area are accurately represented.
Additionally, to account for the spatial distribution inherent in Florida rainfall, data should
be available at various rainfall stations throughout the study area.
A-62
-------
For this study, three rainfall stations were identified within one mile of the study area
(Boggy Creek rain gauge, Lake Hart rain gauge, and the Orlando International Airport
rain gauge). These three stations record rainfall data on a continuous basis. Because
of their proximity to the study area, they were considered to be acceptable for use in
model calibration. The data collection phase of the Lake Hart Basin MSMP revealed
that flow data were not available for any site in the study area and stage data were
limited.
Based on the available data, a normal water surface elevation of 77.0 feet-NGVD was
selected as a initial condition in the stormwater model for Lake Nona, Red Lake, and
Buck Lake. The normal water surface elevation presented in the Orange County Lake
Index Report (77.6 feet-NGVD) was reduced based on the historical measurements
obtained from Orange County.
A sensitivity analysis was performed to determine the influence the normal water
surface elevation has on the simulated peak water surface elevations in Lake Nona,
Red Lake, and Buck Lake. The normal water surface elevations selected for the three
lakes were 75.5 ft-NGVD for the low end of the range (known invert elevation of
discharge point) and 77.6 ft-NGVD for the upper end of the range (normal water surface
elevation reported by Orange County). Using these ranges, the 10O-year/72-hour
design storm event was simulated for existing land use conditions. The resulting peak
water surface elevation ranges were 78.3 to 80.0 ft-NGVD for Lake Nona and 79.4 to
80.1 ft.-NGVD for both Red Lake and Buck Lake.
Using the selected normal water surface elevation of 77.0 ft-NGVD, the simulated 25-
year/24-hour peak water surface elevations for Lake Nona, Red Lake, and Buck Lake
(from this study) were 78.5, 78.8, and 78.8 ft-NGVD, respectively. This is within 0.2 feet
of the 25-year/24-hour peak water surface elevation for Lake Nona and within 0.1 feet of
the 25-year/24-hour peak water surface elevations for Red Lake and Buck Lake
obtained from the Lake Nona conceptual permit issued by the SFWMD.
Level of Service and Problem Area Definitions
For the 10O-year/72-hour design storm event, the simulated peak water surface
elevations were 79.5, 79.7, and 79.7 ft-NGVD for Lake Nona, Red Lake, and Buck
Lake, respectively. For Lake Nona, the simulated 100-year/72-hour peak water surface
elevation is 0.1 feet less than the 100-year peak water surface elevation obtained from
FEMA. For Red Lake and Buck Lake, the 10O-year/72-hour peak water surface
elevation simulated as part of this study is 0.1 feet more than the 100-year peak water
surface elevation reported by FEMA. A summary of these comparisons is presented in
Table A-12. Based on the results of this comparison, the model was considered
calibrated for master planning purposes.
A-63
-------
Table A-12. Comparison of Reported and Simulated Peak Surface Water Elevations
Location
Model Node
Lake Nona
Red Lake
Buck Lake
10930
10870
10830
25-Year Design Storm
SFWMD1994
Permit
(ft-NGVD)
78.7
78.7
78.7
COM 1996
(ft-NGVD)
78.5
78.8
78.8
Elevation
Difference
(ft-NGVD)
-0.2
-0.1
-0.1
100-Year Design Storm
FEMA1989
(ft-NGVD)
79.6
79.6
79.6
COM 1996
(ft-NGVD)
79.5
79.7
79.7
Elevation
Difference
(ft-NGVD)
-0.1
0.1
0.1
Water Quantity Evaluation of Existing PSWMS
The PSWMS for the Lake Hart Basin was modeled in RUNOFF and EXTRAN to
determine and quantify potential problem areas under existing and future land use
conditions, using the 2-, 10-, and 25-year/24-hour design storm events and the 100-
year/72-hour design storm event. As appropriate for master planning, existing
structures within the PSMS were assumed to be in a maintained condition. This
maintenance is costed and summarized in the "Recommendations" section of this
appendix. It is also important to understand what a frequency of a design storm (e.g.,
25-year frequency) event implies. A 25-year frequency does not mean that the rainfall
event will occur once every 25 years. A 25-year frequency means the event has a 4%
(1 in 25) chance of occurring or being exceeded in any given year.
Resultant flood stages in the PSWMS were developed for the existing and future land
use scenarios. Increases in depth from existing to future land use conditions range
from approximately 0.0 ft to 0.4 ft. The relatively small increases in stage, despite the
increases in imperviousness, are a result of two conditions. First, the PSWMS has a
very large storage capacity in the lakes and wetlands with very flat floodplains, so
increases in flow rates will not cause large increases in stage. Second, because the
seasonal high groundwater table is close to the surface over much of the study area
(limited soil storage capacity), the decrease in pervious area from present to future land
use conditions does not result in a large loss of storage in the soil column. The high
groundwater table causes the pervious areas of the basin to effectively become
impervious after minimal rainfall.
Therefore, regulating floodplain storage and floodway conveyance in this basin, along
with the regional wet detention ponds and identified capital improvements, is important.
Based on the level of service criteria previously discussed, deficiencies in the PSWMS
were:
Problem P-1 is the flooding of Narcoossee Road by 0.3 feet during the two-
year design/24-hour storm event and by as much as 1.2 feet during the 100-
year/72-hour design storm event (model node 10895). This problem is
A-64
-------
caused by the tailwater condition established for node 10905 from Orange
County stage data, field inspection, and 1 foot photogrammetry. The location
of this problem area is shown on Figure A-15.
The peak simulated velocities for in the PSWMS elements are presented in
Table A-13 for the two-year and 10-year events under future land use
conditions. High velocities for lower return period events are an indicator of
potentially excessive erosion which can cause structure failure and degrade
water quality.
A-65
-------
P-4 PROBLEM AREA
IDENTIFICATION
ROAD IMPROVEMENT
. CULVERT ENTRANCE AND
EXIT ARMORMG CHANNEL
STREAM BANK ARMORING
EXTRAN CONDUIT
EXTRAN WEIR CONNECTION
ฎ EXTRAN LNKING JUNCTION
S EXTRAN STORAGE JUNCTION
O PROPOSED REGIONAL
FACILITY JUNCTION
Figure A-15. Problem area identification map (Reprinted courtesy of the City of
Orlando, FL).
A-66
-------
Table A-13. Excessive Velocity Determination for Future Land Use
Channel ID
11080
11060
10970
10885
10870
10851
10811
10801
10492
10491
10290
Channel
Typed)
C
N
C
C
C
C
C
C
C
C
C
2-Year
Event (2)
2
2
2
2
2
2
10-Year
Event (2)
2
1
2
2
2
2
2
2
2
2
2
Problem ID(3)
P-2
P-3
P-4
P-5
P-6
P-7
P-8
P-9
P10
P-10
P-11
(1) Channel Type: C = culvert, bridge, storm sewer, or paved channel. N = natural earthen channel.
(2) Problem Type: 1 = Natural channel velocity > 3ft/sec. 2 = Culvert, bridge, sewer, or channel velocity > 7
ft/sec.
(3) Velocity problem areas have been assigned Ids.
Proposed Regional Wet Detention Facilities
The siting of the proposed regional wet detention facilities was accomplished through a
cooperative effort between the City of Orlando and the major property owners in the
study area. Through this cooperative work effort, regional facilities were strategically
located to meet public, private, and environmental interests to the maximum extent
practicable. Through this process, a total of 52 wet detention ponds, nine of which are
existing borrow pits, were conceptually designed for this study area. The facilities
provide regional flood control and water quality protection associated with urbanization.
Conceptually, stormwater runoff would be collected in a pretreatment and conveyance
system and delivered to the proposed regional facility, treated (via wet detention),
attenuated for peak flow and velocity, and discharged into the PSWMS through a V-
notch weir/swale spreader system.
A conceptual plan view of a proposed facility is presented in Figure A-16. As can be
seen in the figure, the proposed regional facilities were located along existing wetlands
in an elongated manner. The wet detention facilities can also provide other benefits
such as waterfront property, potential recreational areas, and hydrate wetlands thus
protecting them from potential development impacts.
A-67
-------
The locations of the proposed regional wet detention facilities in the study area are
presented on Figure A-17. The facility footprints shown on the figure represent the 100-
year/72-hour peak water surface elevation predicted to occur at each site using the
stormwater model developed for this study.
Use of Existing Borrow Pits as Stormwater Facilities
Existing waterbodies may be used for detention purposes as long as the SFWMD
grading criteria pertaining to ponds or lakes near wetlands are met (Section 4.10 of the
SFWMD MSSW Permit Application Manual Volume IV). Additionally, the SFWMD
requires that side slopes be no steeper than 4:1 to a depth of two feet below the control
elevation. Existing borrow pit acreage within the study area and, if necessary,
increased surface area requirements are presented in Table A-14. As previously
stated, there are nine existing borrow pits identified as potential regional wet detention
facilities. These include potential sites P, V, RR, TT, UU, VV, SS, ZZ, and WW shown
on Figure A-18.
Flood Control Benefits
The proposed regional facilities were evaluated using SWMM for each design storm
event under future land use conditions. The resulting peak water surface elevations
were determined from the hydraulic analyses. The elevations are compared to existing
and future land use conditions without the proposed regional facilities. The simulated
peak water surface elevation for the 2-, 10-, 25-year/24-hour design storm events and
the 10O-year/72-hour design storm event under future land use conditions with the
proposed regional facilities are less than or equal to the simulated peak water surface
elevations under existing land use conditions at almost every point within the study
area*
A-68
-------
Figure A-16. Typical wetlands and ponds layout (Reprinted courtesy of the City of Orlando, FL).
A-69
-------
ป: :: :: tซ
ru *. J": i ,,,v :
10930I
Lake Nona
10830 , ,,2,
Buck Lake ) [
LEBEND.
PROPERTY BOUNDMY
HTDROLOGIC BOUNDARY
SU8&ASW OESIBNAT10N
EXISTING LAKE
WETLAND BOUNDARY
PROPOSED FACILITY
LOCATION
PROPOSED FACILITY
LOCATION CEXBTWG
BORROW PIT]
(21520) POND B
"""E- THE PODS HAW BEEN
DfMHN AROUNO THE CURRENT
DE1UNO BOUMMnES.1HCSE SHAPES
MAT CHANGE ONCE ACTUAL HEILAMD
BOMDARffS HAVE SEEN
Figure A-17. Proposed regional wet detention facilities (Reprinted courtesy of the
City of Orlando, FL).
A-70
-------
Lake
Vtttippoorwill -J---^:1j--=^ฃ=ฃ--i-:t*i#f
1 " if-^ --tffrt
LESFNO;
^^ PROPERTY BOUNDARY
HYDROLO61C
WETLAND BOUNDARY
LAKE
EXTRAN CONDUIT
EXTRAN WEIR CONNECTION
'1 '.r^?-^;^
ฎ EXTRAN LINING JUNCTION
El EXTRAN STORAGE JUNCTION
D PROPOSED RESIONAL
FACILITY JUNCTION
Figure A-18. Alternative PSWMS nodal schematic (Reprinted courtesy of the City
of Orlando, FL).
A-71
-------
Table A-14. Changes in Surface Area of Sites Currently Existing as Borrow Pits
Existing Surface Required Surface Increase in Surface
Area of Borrow Pit Area for 1 00-YR Area of Borrow Pits
Pond Node ID (Acres) (Acres) (Acres)
21170 (P)
21 230 (V)
21450(RR)
21460 (SS)
21470(TT)
21480 (UU)
21490(VV)
21500(WW)
21530(ZZ)
33
32
6
12
22
9
26
5
36
34
33
12
15
22
15
27
12
37
1
1
6
3
O1
6
1
7
1
1. The existing surface area is greater than what is required. Therefore, no increase in the surface
area of the existing site is necessary.
Peak flows at the discharge points of the study area were also compared to show that
downstream (Orange County) peak flows and peak water surface elevations are
controlled under post-development conditions. With the proposed facilities, significant
flow rate reductions are obtained when compared to flow rates simulated under future
land use conditions without the regional facilities. The predicted flow reductions
obtained by incorporating the proposed facilities into the PSWMS are also below those
predicted at the discharge points from the study area under existing land use conditions.
This analysis shows that the proposed regional wet detention facilities are effective in
providing flood control for future development.
Recommendations
Introduction
A summary of the recommendations for the Lake Hart basin MSMP is provided in this
section. The Capital Improvements Program (CIP) is outlined along with operation and
maintenance considerations, nonstructural controls, and stormwater monitoring.
A-72
-------
Capital Improvement Program for Structural Controls
Review of Factors
As previously discussed, six major factors were considered in the formulation of the CIP
program recommendations. These factors are:
1. Technical feasibility and reliability
2. System maintainability
3. Sociopolitical acceptability
4. Economics
5. Environmental consistency
6. Financial ability
Technical Feasibility and Reliability
The recommendations have been formulated to be feasible and reliable from a technical
standpoint. Flooding problems are solved within the level of service guidelines defined
for this study and cost-effective water quality control is provided (pretreatment and wet
detention). Conveyance solutions are all gravity-driven and regional storage of water
(swales, ponds) is proposed as needed for proposed development and the Narcoossee
Road Improvement Project.
System Maintainability
The proposed project needs to address operation and maintenance (O&M) issues. For
example, the proposed regional approach promotes the need for fewer stormwater
management facilities compared to the onsite approach which requires many ponds to
achieve the same level of service. The larger regional facilities are more likely to be
maintained on a regular basis.
Sociopolitical Acceptability
The recommendations address flooding and water quality concerns and are consistent
with existing regulations. Public information may become an important aspect of the
recommendations in the future since improved watershed protection can be achieved
though public education and involvement. The recommended plan reduces nonpoint
loads to the lakes, maintains or lowers existing flood stages, and does not adversely
impact healthy wetlands which are a large component of the PSWMS.
Additionally, because the Lake Hart MSMP serves City, public, and private developer
interests, the project needed to be conducted cooperatively between interested parties
to the extent practicable. This was accomplished through coordination meetings with
City staff, regulatory agency staff, and private developers.
Economics
The recommended plan provides sound technical, environmental, and social benefits,
as well as providing for the most cost-effective water quantity and water quality controls.
The recommendations appear to be cost-effective for joint private/public funding
A-73
-------
partnership of stormwater management capital improvement projects as development
occurs.
Environmental Consistency
The recommendations have been formulated to minimize wetland impacts and to
promote aquifer recharge, where possible. No ponds or BMPs were sited in known
wetlands.
Financial Ability
An important consideration in this project is the ability to fund the recommended plan.
Funding of the regional facilities will likely be a public/private venture. The project
needs to have a reasonable chance of being funded without causing financial hardship.
Because of the large number of recommended regional facilities, phasing of capital
improvements will be concurrent with the development phasing in the basin.
CIP Summary
Based on these six criteria, 52 regional wet detention facilities (nine are modified
existing borrow pits) are recommended for the Lake Hart basin. Each facility would
serve a dual purpose of flood control and water quality protection. The location of each
facility reflects the cooperative siting efforts between the City and private land owners.
Because of the high groundwater table in the study area, it is recommended that
pretreatment be provided (0.25 inches) upstream of each facility instead of the retention
requirements for wet detention facilities in OUSWMM. The pretreatment requirement is
considered to be applied innovative technology for the basin and is viewed as an
enhancement to OUSWMM.
In addition to the proposed regional facilities, it is recommended that the Narcoossee
Road (Problem P-1 at model node 10895) crossing of the tributary flowing southward
from Red Lake to Lake Whippoorwill be raised to an elevation above the 25-year/24-
hour designs storm event under future land use conditions with the proposed regional
facilities in place (77.8 ft-NGVD).
Based on the results of the December 5, 1995 field inspection, it is also recommended
that the culvert and conveyance channel under the dirt road just downstream of Red
Lake be restored. The culvert and approach channel appeared to be in poor condition
from cattle traffic.
Excessive velocities were identified in 11 conduits in the basin. All but one of the
conduits (11060) is a culvert pipe. Conduit 11060 is an excavated drainage canal. For
this canal, visual inspection for erosion problems should be made and where erosion is
evident the bank should be stabilized. For the closed conduits (culvert crossings),
channel bank and bottom armoring is recommended for a distance of 30 feet upstream
and downstream of the culvert crossing. Three of the culverts with high velocities are
associated with outlet works from existing facilities within the Lake Nona development
A-74
-------
(Model nodes 10850, 10810, and 10800). Armoring downstream of these structures
should be done as part of these capital improvements.
A map showing the overall recommended CIP plan is presented in Figure A-19. CIP
planning level costs for these improvements are summarized in Table A-15.
Project Phasing
Phasing of capital improvements was based on scheduled and planned construction
projects. The first planned change in the basin is the City's Narcoossee Road
Improvement Project scheduled for construction in 1997. In order to address
stormwater management for this project, the proposed regional facilities that can serve
both new development and Narcoossee Road are going to be constructed first. The
City will develop a cost sharing plan with private development for these dual purpose
facilities. The first phase of pond construction will serve Narcoossee Road (funded by
City). Private land owners can then expand these facilities as development occurs.
The remaining facilities should be built as development plans are approved and
scheduled for construction. The City plans to use the stormwater model developed for
this Lake Hart basin MSMP to identify which facilities will be needed for each new
development. The phasing of these structures will require coordination between City
staff and land developers planning to build within the basin.
Operation and Maintenance
Operation and maintenance are critical elements of the MSMP. Control measures that
are not maintainable provide short-lived, expensive solutions. Additionally, stormwater
management systems that are not adequately maintained cannot be relied upon to
provide the desired levels of service. The control measures recommended were
developed with consideration of maintenance issues. For example, forebays have been
recommended for all regional wet detention facilities to reduce the maintenance
requirements and extend the effectiveness of the facilities. The City is considering
taking over the operation and maintenance responsibility for the regional facilities
constructed under a cost sharing program. The City would fund the cost of the
operation and maintenance through their existing stormwater utility.
A-75
-------
@ FLOW-VELOCITY
STAGE RECORDER
CULVERT ENTRANCE AND
EXIT ARMORING CHANNEL
STREAM BANK ARMORING
EXTRAN CONDUIT
EXTRAN WEK CONNECTION
ฎ EXTRAN LINKMG JUNCTiON
B EXTRAN STORAGE JUNCTKi
Q PROPOSED REGIONAL
FACILITY JUNCTION
Figure A-19. Capital Improvements Plan Map (Reprinted courtesy of the City of
Orlando, FL).
A-76
-------
Table A-15. Conceptual Capital Cost Estimate for Lake Hart Basin Southeast
Annexation Area
City Ponds
Subtotal
Developer
Ponds
Pond ID
21 250 (X)
21 260 (Y)
21300(CC)
21450(RR)
21175(AAA)
21 020 (A)
21 030 (B)
21040ฉ
21045(0)
21 060 (E)
21 040 (F)
21 080 (G)
21 090 (H)
21100(1)
21110 (J)
21120(K)
21130(L)
21140(M)
21150(N)
21160(O)
21170(P)
21180(Q)
21190(R)
21200(3)
21210(T)
21 220 (U)
21 230 (V)
21 240 (W)
21 270 (Z)
21280(AA)
21290(BB)
21310(DD)
21320(EE)
21330(FF)
21340(GG)
21350(HH)
21360(11)
21370(JJ)
21380(KK)
21390(LL)
241 00 (MM)
21410(NN)
21 420 (CO)
21430(PP)
21440(QQ)
21460(SS)
21470(TT)
21480(UU)
Capital Cost ($)
984,000
2,234,000
1 ,485,000
662,000
521 ,000
5,886,000
1,133,000
764,000
1 ,456,000
325,000
644,000
430,000
150,000
545,000
634,000
400,000
195,000
951 ,000
447,000
591 ,000
241 ,000
165,000
447,000
272,000
150,000
545,000
582,000
190,000
371 ,000
529,000
899,000
1 ,320,000
1 ,786,000
1 ,035,000
1 ,425,000
560,000
1 ,583,000
605,000
651 ,000
1 ,035,000
885,000
771 ,000
1 ,674,000
945,000
1 ,200,000
1 ,771 ,000
189,000
182,000
470,000
A-77
-------
Table A-15. Continued.
Pond ID
Capital Cost i
21490 (W)
21500(WW)
21510 (XX)
21520(YY)
21530(ZZ)
119,000
589,000
1,816,000
1,861,000
182,000
Subtotal
35,710,000
Channel
Armoring
Ponds
P-2
P-3
P-4
P-5
P-10
P-11
13,000
33,000
13,000
13,000
76,000
13,000
Subtotal
161,000
Total
41,757,000
1 City pond
capital costs include $15,000/acre for land acquisition
(land acquisition costs are not included in developer pond
costs).
2
3 Capital costs
are for stormwater related facilities only and do not include
stormwater related utility rehabilitation and replacement.
4
5 Costs are in
1996 dollars.
6
7 These costs
include a 40% contingency for engineering, surveying,
permitting, and contractor's overhead and profit as well as
mobilization and standard contingencies.
8
9 Excavation
costs may be reduced by the use or sale of fill material.
10
1 1 Field verification
of problem areas is recommended prior to channel
armoring.
A-78
-------
Annual operation and maintenance costs are summarized in Table A-16. These costs
include the costs associated with maintaining the existing facilities and recommended
control measures.
Table A-16. Annual Operation and Maintenance Cost Summary for Lake Hart Basin
Southeast Annexation Area
Item
1) Maintain 53 regional facilities. This includes labor and equipment to provide
annual grounds maintenance and inspection of control structures, channels, silt
levels, erosion, and vegetation.
Also included are three mowings per year and removal of excess silt and
Vegetation every five to seven years.
2) Maintain 33 bridges/culverts within the primary stormwater management
system (once every two years with annual inspection).
TOTAL ANNUAL OPERATION AND MAINTENANCE COSTS
Cost
($/yr.)
424,000
33,000
457,000
1. Routine maintenance of natural channels was not considered since the majority of the PSWMS
consists of natural wetlands.
2. Maintenance of channels for a distance of 50 ft. upstream and downstream of culverts is included in
culvert maintenance costs.
3. Problem ID P-6, reach 10870, is a small trail crossing which should be maintained if an erosion
problem is identified from field inspection.
Nonstructural Controls
Nonstructural controls were considered to help control both water quantity and water
quality aspects of stormwater. Nonstructural controls are not constructed capital
projects but rather are source controls, ordinances, and regulations that depend on
participation by municipalities and residents to minimize the water quantity and quality
impacts associated with development. A summary of recommended nonstructural
controls follows:
1. Public information program
2. Fertilizer application control
3. Pesticide and herbicide control
4. Solid waste management and control of illegal dumping
5. Directly connected impervious area (DCIA) minimization
6. Water conservation landscaping
7. Illicit connections - identification and removal
8. Erosion and sediment control on construction sites
9. Stormwater management ordinance requirements
10. Stormwater management system maintenance
A-79
-------
The following provisions are recommended to supplement the existing OUSWMM
1. 100-Year Floodplain Protection: This provision already exists in OUSWMM,
but
2. because of its importance in preventing future flooding, it is re-emphasized in
this section of the report. To assure proper flood hazard management, it is
recommended that compensating storage be required for all construction,
development, or site alteration so that existing 100-year floodplain storage in
the City is maintained; and therefore, flood stages are not increased or moved
onto adjacent lands by the development.
3. Aquifer Recharge: Although the potential for aquifer recharge in this basin is
low due to the soils and the groundwater table, the overall concept is an
important consideration. A general consideration is to retain the first three
inches of runoff over the DCIA on SCS Hydrologic Group A soils and two
inches of runoff over the DCIA on SCS Hydrologic Group B soils. In addition,
it is recommended that swale pretreatment for these areas be provided to
increase the amount of soil treatment before discharge into the aquifer.
4. First-Floor Elevations: Variances to construct dwelling first-floor elevations
below the 100-year floodplain should not be allowed or variances should be
deed-recorded with sale of the property. Variances encourage people to build
in flood prone areas around lakes and streams. It is inevitable that these
dwellings will eventually be flooded. This can cause public pressure on the
City to drain wetlands and regulate or drain lakes - a policy that is
inconsistent with fishery habitat, aquifer recharge, and water quality.
5. Floodway Management: SFWMD allows the filling of a floodway as long as it
does not cause more than a one-foot increase in the flood stage within the
floodway (Federal Emergency Management Agency standard). This can
have a severe cumulative impact on property in or adjacent to the floodway
farther downstream. It is recommended that floodway encroachment be
prohibited. It is recommended that no net encroachment be allowed within
the future land use top-width-in-flow for the 100-year storm.
6. Water Quality It is recommended that the City continue to require water
quality performance standards as outlined in Chapter 40, Florida
Administrative Code, that are based upon receiving water classifications, until
more detailed watershed specific data are known from monitoring and/or state
water policy mandates from the Florida legislature occur.
7. Reuse: The conservation of water resources is increasingly encouraged
where it is applicable. The use of landscaped swales is recommended to
promote reuse of some of the stormwater runoff.
A-80
-------
Monitoring
A comprehensive monitoring program includes many facets of data collection and is
used to accurately define the hydrologic and hydraulic characteristics of a watershed.
This report recommends that the City augment existing monitoring data with an overall
program in order to provide additional data necessary to evaluate the stormwater
quantity and quality of the Lake Hart basin. The monitoring program should address the
following:
1. Identification of rainfall and flow/stage data at key points of interest to calibrate
and verify model analysis tools.
2. Current status of water quality including ambient data, dry weather flow from
stormwater outfalls, and wet weather runoff as event mean concentration (EMC)
values for land use types.
3. Trends in water quality due to land use changes and BMP implementation.
4. Regulatory assistance with state and federal permitting.
5. Compliance monitoring to document permit compliance.
The City can benefit from a monitoring program that addresses the preceding. A
monitoring program will support implementation of the Lake Hart basin MSMP and the
NPDES MS4 program. The overall monitoring program recommended for the City is
described below.
Recommended Monitoring Program
Rainfall
This plan recommends that the City supplement the existing rainfall stations operated
and maintained by Orange County and NOAA (airport rain gauge) with two stations.
One would be combined with the stage recorder proposed for Lake Nona and the other
would be combined with the flow-velocity recorder proposed at Moss Park Road. These
rainfall stations should record rainfall data at a minimum of 15-minute intervals. The
general locations of these stations are presented in Figure A-18.
Water Quality
It is recommended that the City maintain the ambient water quality monitoring program
conducted by Orange County for Lake Nona, Red Lake, and Buck Lake as to further
document the long-term water quality.
Water Quantity
The City should consider a joint effort with USGS to establish a stream gauge
monitoring program for the Lake Hart basin. Daily stages should be recorded for Lake
A-81
-------
Nona, Red Lake, and Buck Lake. Stations that measure flow and velocity are also
recommended on the downstream side of Moss Park Road (model node 10500), the
downstream side of Narcoossee Road (flows from Buck Lake, model node 10530), and
on the downstream side of the Central Florida Greenway (flows from Red Lake to Lake
Whippoorwill, model node 10890). Stream gauges at these locations will help the City
monitor flow from the major tributaries that outfall into Orange County. It is
recommended that the City propose that USGS establish, operate, and maintain the
gauge and data. The locations of these facilities are also presented on Figure A-18.
Mosquito Control
As part of the evaluation of various alternatives, it is recommended that the City
consider the potential for mosquito breeding. Some minor modifications and
considerations in the design of various BMPs are needed to minimize the breeding of
mosquitoes. The primary concern is stagnant water, which provides a breeding ground
for mosquito larvae. Water that stands for periods of greater than 72 hours provides a
suitable environment for the breeding of mosquito larvae.
To effectively control mosquitoes, it is suggested that the following guidelines be
considered for the design of BMPs in the Lake Hart basin:
1. Use only Hydrologic Group A soils (or well drained Hydrologic Group B or C
soils, water table at least one to two feet below grade) for retention type
facilities (e.g., shallow grassed swales). It is suggested that seasonal high
groundwater tables and soils be tested for each area on a case-by-case basis
to verify that complete storage recovery will occur within 72 hours
2. For wet ponds, use a minimum depth of greater than 18 inches so that
minnows can be sustained. Additionally, maintain vegetative density low
enough for minnows to access (minnows feed on mosquito larvae)
3. When developing a site for a detention or infiltration pond, use a minimum of
20 feet for the buffer/maintenance strip.
A-82
-------
Data Sources and Bibliography
Referenced reports, studies, digital data, and maps were obtained and reviewed for this
study. This section is intended to be a data bibliography which lists the sources and
types of data used. The following references were evaluated for potential applicability
to this Lake Hart MSMP.
1993 Annual Report, Orange County Environmental Protection Department,
1993.
Orange County, Environmental Protection Department, 1993 Lake Ranking for
Orange County Lakes by Trophic State Index, by (April 1994).
1994 Orange County lake ranking by tropic state index, Orange County
Environmental Protection Department, 1995.
Aerial (color) photogrammetry maps by Belt Collins, FL from Lake Nona
Corporation (2.5 inches = 1 mile and 2.33 inches = 1 mile, March 1994).
Aerial photogrammetry maps for Lake Hart-Lake Mary Jane Drainage Basin with
1 foot contours from Orange County, Florida (1 inches = 200 feet, 1985).
Aerial photogrammetry maps from Orange County, FL (1 inch = 300 feet, 1990).
Applications for Development Approval for Developments of Regional Impact
(DRIs) for Lake Nona, Lake Hart, St. James Park, and Campus Crusade.
Basis of Review for Environmental Resource Permit Applications with the South
Florida Water Management District (August 1995).
Brunetti Bal Bay Tract Concept Plan prepared by Berryman and Henigar
(1 inch = 600 feet, August 1994).
City of Orlando Engineering Standards Manual Second Edition from the Public
Works Department (June 1993).
City of Orlando Florida Southeast Annexation Area Lake Hart Basin Master
Stormwater Plan, February 1996, prepared by Camp Dresser & McKee Inc. and
WBQ Design & Engineering, Inc.
City of Orlando Florida Southeast Annexation Stormwater Management Needs
Assessment, June 1995, prepared by Camp Dresser & McKee Inc. This report
was the first phase of the Lake Hart MSMP.
Digital FEMA MAP of the Lake Hart Study Area from the City of Orlando, FL.
A-83
-------
Digital soils file of the Lake Hart area from the City of Orlando, FL.
Eastern Beltway - Bee Line Interchange Plans from the Orlando-Orange County
Expressway Authority.
Eastern Beltway roadway and drainage as-built plans from the Orlando-Orange
County Expressway Authority.
Eastern Beltway roadway and drainage plans from the Orlando-Orange County
Expressway Authority (Sections 454, 455, and 457).
Existing Drainage Map of Randall/Johnson Trust Property from Miller-Sellen
Associates, Inc.
Existing Survey in the Lake Hart Area. This survey was completed for the Boggy
Creek watershed study which includes cross-sections between Lakes Nona, Red
and Buck and of the Myrtle Bay Area.
Existing Survey in the Lake Hart Area from Transportation Engineering, Inc.
(1995).
Existing Survey in the Lake Hart Area computed by DeGrove Surveyors from
FEMA(1992).
FEMA; FIS for the Unincorporated Area in Orange County, FL (December 8,
1989).
Flood Insurance Rate Maps from Federal Emergency Management Agency
(FEMA) (Panels: 400, 425, 550 and 575).
Future Development Plan for Randall/Johnson Trust from Miller-Sellen
Associates, Inc.
Greendale Master Plan prepared by Davis and Associates (1" = 300', May 1994).
Growth Management Plan Southeast Annexation Study approved October 17,
1994 from the City of Orlando, FL..
Lake Hart Master Plan Development Plan from Post, Buckley, Schuh and
Jernigan (1 inch = 1333 feet, 1994).
A-84
-------
Lake Nona Application for Conceptual Approval Surface Water Management
Permit with the South Florida Water Management District prepared by Miller and
Einhouse, Inc. from Lake Nona Corporation (October 1988).
Lake Nona Construction Plans and as-builts for stormwater facilities provided by
Lake Nona Corporation.
Lake Nona Master Drainage Plan for Phase 1-A (1 inch = 300 feet, December
1988).
Lake Nona Preliminary Master Plan 6 Future Development Plan prepared by Belt
Collins, Florida from Lake Nona Corporation (1" = 1000', September 1994).
Lake Nona Preliminary Master Plan 6 Future Development Plan prepared by Belt
Collins, Florida from Lake Nona Corporation (1 inch = 1000 feet, March 1995).
Lake Nona South Existing Conditions Drainage Map prepared by Einhouse and
Associates, Inc. from Lake Nona Corporation (1 inch = 600 feet).
Lake Nona Surface Water Management Permit Modification Application for
Conceptual Permit No. 48-00195-S with the South Florida Water Management
District prepared by Miller and Einhouse, Inc. from the Lake Nona Corporation.
La Vina Trust Land Use Plan prepared by Burkett Engineering, Inc. (1 inch = 300
feet, May 1995).
Master Drainage Plan of Randall/Johnson Trust Property from Miller-Sellen
Associates, Inc. (1 inch = 400 feet).
Miscellaneous Permits in the Southeast Study Area from the South Florida Water
Management District.
Narcoossee Road Construction Plans for the City of Orlando from WBQ Design
& Engineering, Inc. (May 1995).
Narcoossee NW, Narcoossee, St. Cloud North, and Pine Castle Fish and Wildlife
Service National Wetland Inventory Maps (1988).
Narcoossee NW, Narcoossee, St. Cloud North, and Pine Castle USGS
Quadrangle Maps 7.5 minute series (photo revised: 1980, 1970, 1987 and 1980,
respectively).
Orange County Future Land Use Maps Series of the Lake Hart Study Area from
Orange County, FL (August 1993).
A-85
-------
Orange County Lake Index, 1995 Report from Orange County Public Works.
Orlando/Orange County Joint Planning Area Map from City of Orlando Planning
and Development Department (May 1994).
Orlando Urban Stormwater Management Manual (OUSWMM) prepared by Dyer,
Riddle, Mills, and Precourt, Inc. Volume 2 Design Criteria, Second Edition from
the City of Orlando, Florida.
Physical and Chemical Data and Plankton Summaries for Lakes Nona, Red and
Buck for the period of record from (1972 -1994), from Orange County Pollution
Control Department.
Rainfall data for the period of record (1974-1992) at the Orlando-McCoy Airport
in Florida, rain gauge from the National Climatic Data Center (NCDC).
Rainfall data for the period of record (1987-1995) at the Boggy Creek rain gauge
and for the period of record (1995) at the Lake Hart rain gauge from the
Stormwater Management Department of Orange County, FL.
Randall/Johnson Trust conceptual approval permit from the South Water
Management District (Control Number: 48-00653-S, January 1992).
Realignment of Dowden Road Plans provided by Busch Properties.
Seventh International Conference on Urban Storm Drainage, Hannover,
Germany, 9-13 September 1996. Proceedings Volume I, II, III.
Soil Survey of Orange County, FL, 1989. This is a typical United States
Department of Agriculture Soil Conservation Service (SCS) soils report that
provides various surficial-layer soils information for the County. Total soil
storage, infiltration rates, and data on surficial "hard pan" layers were used for
this study.
South Florida Water Management District, Management and Storage of Surface
Waters Permit Information Manual, Volume IV (May 1994).
Southeast/Orlando International Airport Future Growth Center Plan Conceptual
Framework from the City of Orlando Planning and Development Department
(May 1995).
Southeast Study Area Map with property owners boundaries from the City of
Orlando Planning and Development Department (November 1993).
A-86
-------
Southeast Study Area Map with the property owners proposed roadways and the
City of Orlando's preferred roadways from the City of Orlando Planning and
Development Department (June 1995).
Survey completed by Regional Engineers, Planners and Surveyors, Inc. (REPS)
for use in the Stormwater Modelling (October 1995).
Upper Kissimmee River Watershed Map of Major Basins from the South Florida
Water Management District (SFWMD) (8.5 inches x 11 inches).
Urban Drainage and Flood Control District, Denver, Colorado, "Urban Storm
Drainage Criteria Manual - Volume 3 - Best Management Practices - Stormwater
Quality", September 1992.
Water Quality Data Summary for Lakes Nona, Red, and Buck prepared by
Envirosmiths, Inc. (November 1994).
A-87
------- |