Street Storage System
for
Control of Combined Sewer Surcharge
Retrofitting Storm water Storage
Into
Combined Sewer Systems
by
Stuart G. Walesh
Valparaiso, IN 46385-2979
Contract No. 8C-R416-NTSX
Project Officer
Carolyn R. Esposito
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
Cinncinnati, OH 45268
-------
Disclaimer
The U.S. Environmental Agency through its Office of Research and Development
funded and managed the research described here under Contract No. 8C-R416-NTSX.
It has been subjected to the Agency's peer and administrative review and has been
approved for publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendations for use.
wp/epastdiscl
11
-------
Foreword
The U.S. Environmental Protection Agency is charged by Congress with protecting the
Nation's land, air and waste 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
wp/epastfore
in
-------
Abstract
A case study approach, based primarily on two largely implemented street storage
systems, is used to explain the concept through construction and operation aspects of
street storage systems. More specifically, the case studies address analysis and
design approaches, the regulatory and funding framework, public involvement,
construction costs, operation and maintenance procedures, and system performance.
Street storage refers to the technology of temporarily storing stormwater in urban areas
on the surface (off-street and on-street) and, as needed, below the surface close to the
source. Close to the source means where the water falls as precipitation and prior to its
entry into the combined, sanitary, or storm sewer system. The idea is to accept the full
volume of stormwater runoff into the sewer system but greatly reduce the peak rate of
entry of stormwater into the system. System components include street berms, flow
regulators, and surface and subsurface stormwater storage sites.
By eliminating or greatly reducing surcharging in combined sewer systems, street
storage has the potential to cost effectively and simultaneously mitigate basement
flooding and CSO's. Other possible benefits of street storage are mitigating SSO's,
eliminating surface flooding, reducing peak flows at WWTP's, and controlling non-point
source pollution.
This report was submitted in fulfillment of Contract No. 8C-R416-NTSX by prime
contractor Stuart G. Walesh with the assistance of subcontractors Earth Tech, Inc. and
Donald Roecker under the sponsorship of the U.S. Environmental Protection Agency.
This report covers a period from July 7, 1998 to May 1, 1999, and work was completed
as of May 1, 1999.
wp/epastabst
IV
-------
Table of Contents
Disclaimer ii
Forward iii
Abstract iv
Table of Contents v
Tables xvi
Figures xvii
Abbreviations and Acronyms xx
Acknowledgments xxii
Chapter 1 Introduction 1-1
Combined Sewer System Challenge in the U.S 1-1
CSO Policy of the USEPA 1-1
Objectives of the Policy 1-1
Nine Minimum Controls 1-2
Long-Term CSO Control Plan 1-3
Traditional Approach: Store/Treat Combined Sewage or
Separate the Sewer System 1-3
A New Approach: Store Stormwater Before it Combines With
Sanitary Sewage 1-5
Scope of this Evaluation 1-5
Case Study Approach 1-5
Quantity and Quality: Seeking Optimum Means of
Simultaneously Mitigating Flooding and Pollution 1-5
Retrospective Details with Prospective Purpose 1-9
Initiatives 1-10
Terminology 1-10
-------
Abbreviations, Acronyms and Glossary 1-12
Chapter2 Case Study Communities: SkokieandWilmette, IL 2-1
Basis of Selection of Case Study Communities 2-1
Familiarity of the Investigators with the Projects 2-1
On-Going Relationships with Personnel in the Case
Study Communities 2-1
Opportunity to Study a Large, Long-Standing Street
Storage Project 2-1
Supplemental Communities 2-2
Description of Skokie, IL 2-2
Location 2-2
Relationship to the Metropolitan Water Reclamation
District of Greater Chicago 2-2
Land Use and Population 2-7
Soils and Groundwater 2-7
Topography and Drainage Patterns 2-7
Climate 2-8
Brief History of Skokie with Emphasis on Development of
Its Drainage System 2-8
Skokie's Historic Combined Sewer System Basement
Flooding Problems 2-12
Previous Studies of Ways to Solve Skokie's Combined Sewer
System Basement Flooding Problems 2-13
Study Completed in 1967 Recommending Relief Sewers. ...2-13
Study Completed in 1973 Recommending Deep
and Shallow Tunnels 2-14
Study Completed in 1974 Recommending Downspout
Disconnection and Catch Basin Restrictors 2-15
Study Completed in 1978 Recommending Deep and
Shallow Tunnels and Relief Sewers 2-17
Study Completed in 1981 Providing Additional
Insight into System Inadequacies 2-18
Study Completed in 1981 Suggesting Combinations of
Traditional and Innovative Measures 2-21
VI
-------
Study Completed in 1982 Recommending a Street
Storage System 2-22
Observations Regarding the Studies to Solve Skokie's
Combined Sewer System Basement Flooding Problem 2-24
Occurrence of a Series of Evolving Studies 2-24
Initial Focus on Traditional Solutions 2-24
Gradual Recognition of the Water Pollution Control
Purpose of TARP 2-24
Description of Wilmette, IL 2-25
Location 2-25
Relationship to the Metropolitan Water Reclammation
District of Greater Chicago 2-25
Land Use and Population 2-27
Topography and Drainage Patterns 2-27
Brief History of Wilmette with Emphasis on Development of
Its Drainage System 2-29
Wilmette's Historic Combined Sewer System Basement
Flooding and Peak Discharge Problem 2-29
Previous Studies of Ways to Solve Wilmette's Combined
Sewer System Problems 2-30
Study Completed in 1991 Recommending Relief
Sewers 2-30
Value Engineering Study Completed in 1992
Recommending Street Storage 2-31
Study Completed in 1992 Recommending Street
Storage 2-31
Study Completed in 1992 Recommending Refined
Street Storage 2-31
Observations Regarding Studies to Solve Wilmette's
Combined Sewer System Problems 2-32
Chapter 3 The Concept Through Construction Process for Street
Storage Systems: Skokie and Wilmette, IL 3-1
Status of Urban Stormwater Management 3-1
Vll
-------
Two Fundamentally Different Approaches: Conveyance-
Oriented and Storage-Oriented 3-1
Conveyance-Oriented Approach 3-1
Storage-Oriented Approach 3-3
Comparison of Features 3-3
Historic Development of the Storage-Oriented
Approach 3-4
Emergency and Convenience Systems 3-5
The Convenience (Minor) System 3-5
The Emergency (Major or Overflow) System 3-7
Combined Convenience and Emergency System....3-7
The Possibility of Retrofitting Stormwater Storage Into
Already Developed Areas 3-10
Distinction Between Analysis and Design: Diagnosis and
Then Prescription 3-10
Chronological Mode of Presentation 3-11
The Concept of Street Storage 3-14
Conveyance Capacity of Urban Streets 3-14
Street Cross Sections 3-14
Analysis Procedure 3-14
Results 3-18
Storage Capacity of Urban Streets 3-20
Analysis Procedure 3-20
Results 3-24
Using Street Storage and Conveyance Capacity in
Combined Sewer Systems 3-24
Bringing the Street Storage Concept to Reality: Berms, Flow
Regulators, and Subsurface Storage 3-26
Berms 3-26
Berms Contrasted with Bumps and Humps 3-26
Berms: The Negative Perception Problem 3-32
Vlll
-------
The Possibility of Integrating Stormwater
Berms and Speed Hump Functions 3-33
Flow Regulators 3-34
Combined Function of Berms and Flow Regulators 3-38
Subsurface Storage 3-41
Apply Screening Criteria to Determine Likely Applicability of a
Street Storage System 3-46
Select an Initial Pilot or Implementation Area Within the
Combined Sewer System 3-46
Need for Phased Implementation 3-46
Prioritization Factors 3-46
Establish Performance Criteria 3-48
Need for Performance Criteria: Analysis and Design 3-48
Variation in Performance Criteria 3-48
Skokie Performance Criteria 3-49
Wilmette Performance Criteria 3-50
Analyze Existing System Using Monitoring 3-51
Skokie Monitoring 3-52
Wilmette Monitoring 3-53
Analyze Existing System and Perform Preliminary Design
Using Computer Models 3-53
A Complex System: Need for Computer Modeling 3-53
Analysis and Preliminary Design for the HSSD in
Skokie 3-54
Phase I-Analysis of Static Conditions 3-54
Phase II -Analysis of Sewer Capacity 3-55
Phase 111 - Prelim inary Design of Street Storage 3-57
Results 3-59
Analysis and Preliminary Design in Wilmette 3-61
Modification of the Stormwater Management
Model 3-61
Application of the Model 3-63
Results 3-64
IX
-------
Review Flow Regulator Availability and Performance 3-64
Essentiality of Flow Regulators 3-64
Skokie Flow Regulator Study 3-64
Purpose 3-65
Literature Search and Interviews 3-65
Design of the Field Study 3-67
Equipment Acquisition and Installation 3-67
Observation Procedures 3-72
Rainfall 3-72
Resistance to Plugging 3-72
Costs 3-72
Maintenance 3-74
Conclusions for Skokie 3-74
Complete Design of the Street Storage System 3-74
Construction 3-76
Skokie Construction 3-76
Wilmette Construction 3-79
Phase 1: Greenleaf Avenue Relief Sewer 3-79
Phase 2: Eastside Relief Sewer 3-79
Phase 3: Eastside Relief Sewer 3-79
Phase 4 3-79
PhaseS 3-80
Chapter4 Other Examples of Street Storage Systems 4-1
Purpose 4-1
Cleveland, OH: Puritas Avenue - Rock River Drive Area 4-2
Background 4-2
Results 4-2
Parma, OH: Ridge Road Area 4-4
Background 4-4
Results 4-5
Chicago, IL: Jeffery Manor Neighborhood 4-5
-------
Background 4-5
Results 4-6
Chapters Regulatory and Financial Framework: Complying with
Regulations and Funding Construction 5-1
Motivated by Need but Subject to Regulatory and Financial
Constraints and Opportunities 5-1
Federal and State Regulatory and Funding Framework
Within Which Skokie and Wilmette Functioned 5-3
Today's Regulatory and Funding Framework: Review of Outside
Capital Funding Programs, Techniques and Strategies....5-4
Overview 5-4
Outside Capital Funding from Users 5-5
Outside Capital Funding from State and Federal
Agencies 5-5
Outside Capital Funding from the U.S. Congress:
Direct Legislation 5-8
Initial Capital Funding for the Skokie Street Storage System 5-11
On-Going Local Capital Funding of the Skokie Street Storage
System Through the Bond Market 5-12
Skokie Downspout Disconnection Ordinance and Program 5-14
The Downspout Problem 5-14
The Downspout Solution 5-14
Educational Value 5-17
Downspout Disconnection Process Used in Skokie 5-17
Skokie Stormwater Control Ordinance 5-18
Regulations of the Metropolitan Water Reclammation
District of Greater Chicago 5-19
Chapters Stakeholder Involvement 6-1
Two Public Works Challenges 6-1
Purpose of this Chapter 6-1
XI
-------
A Characteristic of Wet Weather Problems: Widely
Fluctuating Public Interest 6-2
More on the Need for Stakeholder Involvement 6-2
Identification of Stakeholders 6-4
Types of Stakeholder Involvement 6-6
Examples of Stakeholder Involvement Techniques 6-11
Skokie and Wilmette Approaches 6-11
Additional Tactics 6-12
Chapter/ Inspection and Maintenance 7-1
Essentiality of Inspection and Maintenance 7-1
Inspection and Maintenance Procedures for Skokie's Street
Storage System 7-2
Surface and Subsurface Storage and Dewatering
Facilities 7-2
Flow Regulators 7-3
Street Berms 7-4
Street Ponding Areas 7-5
Safety of Inspection and Maintenance Personnel 7-6
Chapters Construction Costs 8-1
Purpose 8-1
Skokie Construction Costs 8-1
Wilmette Construction Costs 8-5
Unit Costs 8-5
Skokie and Wilmette Unit Costs 8-5
Discussion of Unit Costs 8-7
Intangible Costs 8-8
Xll
-------
Chapters Performance of Street Storage Systems 9-1
Performance: The Ultimate Test 9-1
Broad Interpretation of Performance 9-1
Means of Assessing Performance 9-2
Summary of Interviews with Skokie, IL Officials 9-3
Participants 9-3
Process 9-3
Results 9-4
Financing 9-4
Effectiveness of the System in Mitigating Basement
Flooding 9-4
Public Education and Involvement 9-5
Litigation 9-5
Claims 9-5
Operation of Emergency Vehicles 9-5
Operation of Motor Vehicles 9-6
Operation and Maintenance (O&M) 9-6
Monitoring 9-8
Downspout Disconnection 9-8
Pavement Deterioration 9-9
Icing of Streets When Rainfall or Snowmelt Occurs
During Freezing Temperatures 9-9
Interaction With Other Government Entities 9-9
Summary of Interviews With Wilmette, IL Officials 9-10
Participants 9-10
Process 9-10
Results 9-11
Financing 9-11
Effectiveness of the System in Mitigating Basement
Flooding 9-11
Public Education and Involvement 9-11
Litigation 9-12
Claims 9-12
Operation of Emergency Vehicles 9-12
Operation of Motor Vehicles 9-12
Operation and Maintenance (O&M) 9-13
Downspout Disconnection 9-13
Pavement Deterioration 9-13
Icing of Street When Rainfall or Snowmelt Occurs
During Freezing Temperatures 9-13
Xlll
-------
Interaction With Other Government Entities 9-14
Rainfall - Flooding Incidents 9-14
Typical Lim ited Data 9-14
June20-21, 1987 Rainfall -Flooding Event in Skokie 9-14
August 13-14, 1987 Rainfall - Flooding Event in
Skokie 9-15
August 4, 1989 Rainfall - Flooding Event in
Skokie and Wilmette, IL 9-15
May8,1996 Rainfall-Flooding Event in Skokie 9-18
Augusts, 1999 Rainfall-Flooding Event in Skokie 9-18
Economic and Financial Impact on Skokie 9-19
Potential Impact of a Street Storage System on the
Frequency and Volume of Com bined Sewer Overflows 9-20
Chapter 10 Discussion 10-1
Lessons Learned: How Other Communities Might Benefit
From A Street Storage System 10-1
Lessons Learned About Analysis and Design 10-1
Lessons Learned About Regulatory Compliance and
Project Financing 10-2
Lessons Learned About Stakeholder Involvement 10-3
Lessons Learned About Evaluating System
Performance 10-4
Lessons Learned About Operation and Maintenance 10-4
Criteria For Screening Applicability of Street Storage 10-4
Purpose of Screening Criteria 10-4
Qualifications of Evaluators 10-5
Interpreting the Screening Information 10-5
Chapter 11 Conclusions and Recommendations 11-1
XIV
-------
Street Storage: A New Technology for Affordable Mitigation
of CSS Problems 11-1
Recommended Research 11-2
Integration of Speed Humps and Street Berms 11-2
Street Storage to Reduce CSOs and Peak Flows at
WWTPs 11-3
Costs and Benefits of Street Storage Versus
Traditional Approaches 11-3
Further Improvement to Hanging Traps 11-4
Street Storage as Part of New Combined Sewer
Systems 11-5
Impact of a Street Storage on Non-Point Source
Pollution 11-6
Appendices
A Questions Used to Prompt Discussion With Skokie
Officials A-1
B Criteria for Screening the Applicability of Street
Storage B-1
C Trouble Shooting Guide for Underground and Surface
Storage Basins with Gravity Dewatering C-1
D Trouble Shooting Guide for Stormwater Storage
Basins-Dewatering Pump Stations D-1
E Standard Maintenance Procedures for Submersible
Dewatering Pumps - Stormwater Storage Basins E-1
F Exploratory Analysis of the Impact of a Street Storage
System on the Frequency and Volume of
Combined Sewer Overflows F-1
G Construction Costs for Skokie Street Storage System
Adjusted to 1999 G-1
Glossary
Cited References
Bibliography
wp/epasttoc
xv
-------
Tables
1 -1 Proven methods are available to solve pollution and/or flooding problems
in combined sewer systems 1-4
1 -2 Seven of 22 large CSS communities explicitly reported basement or
street and other surface flooding 1-8
3-1 Depth, cross-sectional area, and cumulative volume data for half of Easy
Street 3-22
3-2 Rainfall and depth of ponding for Easy Street 3-22
3-3 Components of the Skokie street storage system 3-77
8-1 Total construction costs for the Skokie, IL street storage system 8-2
8-2 Unit construction costs for the Skokie and Wilmette street storage systems 8-6
XVI
-------
Figures
1-1 Control of peak rates of stormwater runoff can, in concept, mitigate
surcharging of combined sewer systems 1-6
2-1 Skokie and Wilmette, IL lie immediately north of the City of Chicago 2-3
2-2 Map of Skokie, IL 2-4
2-3 The North Shore Channel, which bounds Skokie on the east, and its
contiguous linear parks provide an amenity for area residents 2-5
2-4 The deep tunnel is primarily a pollution control system in that it mitigates
combined sewer overflows to the North Shore Channel 2-6
2-5 Each Skokie catch basin is a manhole-type structure with a sump 2-9
2-6 Skokie is partitioned into three easterly draining combined sewer districts 2-10
2-7 Map of portion of Wilmette, IL served by combined sewer system 2-26
2-8 Brick streets account for half of the street length in Wilmette that was
targeted for street storage 2-28
3-1 Conveyance and storage approaches to stormwater management 3-2
3-2 Historic development and use of storage facilities for stormwater
management in the U.S 3-6
3-3 Emergency and convenience system applied to an urban street 3-9
3-4 Emergency and convenience system applied along a channel and
floodplain 3-9
3-5 Successful application of a street storage system requires a systematic
analysis and design process that begins with understanding the
concept and concludes with construction 3-12-3-13
3-6 The photographs of urban streets in Skokie (top) and Wilmette (bottom)
suggest their potential stormwater conveyance and storage function 3-15
3-7 Selected street cross sections from Skokie, IL 3-16
3-8 Typical street and lawn cross section representative of actual Skokie cross
sections 3-17
3-9 Depth versus discharge relationships for typical street and lawn cross
sections 3-19
3-10 Typical urban street plan showing the area tributary to the east side of a
one block segment of Easy Street 3-21
3-11 Depth versus volume relationship for Easy Street and lawn cross section 3-23
XVll
-------
3-12 Control of peak rates of stormwater runoff can, in concept, mitigate
surcharging of combined sewer systems 3-25
3-13 Mid-block berm in Skokie intended to direct the flow of stormwater runoff 3-27
3-14 Berm across an intersection in Skokie 3-28
3-15 A berm under construction in Skokie showing relocated inlet, raised
curb and gutter, m illed concrete surface and an asphalt lift 3-29
3-16 Bumps and humps are vehicle control devices and the gentler berm is a
stormwater control device 3-30
3-17 Typical configuration of an inlet, catch basin and manhole in the Skokie
combined sewer system 3-36
3-18 A flow regulator installed in a catch basin illustrates the basic function
of the regulator 3-37
3-19 Longitudinal profile of a street showing how a berm and flow regulator
function as the outlet works of a temporary street storage facility 3-39
3-20 Strategic placement of berms and flow regulators along a street facilitates
use of the street's capacity to temporarily and in a controlled fashion
store stormwater 3-40
3-21 The street storage approach uses temporary, controlled ponding of
stormwater in contrast with the common unintentional, uncontrolled
and unexpected ponding resulting in damage and vehicular
interference 3-42
3-22 Actual street ponding in Skokie (top) and Wilmette (bottom) 3-43
3-23 Subsurface storage facilities are positioned within the right of way, above
the combined sewer and temporarily store stormwater, not combined
sewage 3-44
3-24 Subsurface storage facilities range from simple oversized lengths of storm
sewer to, as shown here, large structures assembled from precast
reinforced concrete sections 3-45
3-25 Phase I, a simple static condition analysis, was used to determine if high
stages on the North Shore Channel caused basement flooding in the
HSSD 3-56
3-26 Computer model used for analysis and preliminary design in the Skokie
HSSD 3-58
3-27 Depth and duration of street ponding as a function of recurrence interval 3-60
3-28 Examples of Hydro-Brake flow regulators available in the early 1980's
illustrating the basic operation of vortex-type regulators 3-66
3-29 Photograph of Scepterflow regulator 3-68
3-30 Photograph of solid cover with orifices 3-69
3-31 Photographs of horizontal orifice plate flow regulator before and after
installation 3-70
3-32 Hanging trap flow regulator 3-71
3-33 Streets were intentionally flooded to test the performance of flow regulators 3-73
3-34 Typical street berm design in Skokie, IL 3-75
3-35 Street storage accounts for half of the total stormwater storage in Skokie 3-78
XVlll
-------
4-1 Street storage system proposed for the Jeffery Manor neighborhood in
Chicago, IL 4-7
5-1 Downspouts connected to the house sewer, as shown on the left side,
permit roof water to directly and immediately enter the combined
sewer system and increase surcharging 5-15
5-2 A disconnected downspout 5-16
6-1 The "Hydroillogical" cycle 6-3
6-2 Breadth of stakeholder involvement 6-5
6-3 A street storage project is likely to have many stakeholders, all of whom
should be involved from the outset 6-7
6-4 No communication and announcing decisions are increasingly unacceptable
ways of serving the public 6-8
6-5 The goal in stakeholder involvement goes beyond providing information,
it is meaningful interaction 6-9
8-1 Distribution of construction costs for the Skokie street storage system
showing the relatively small cost of the berm-flow regulator
installations 8-3
8-2 Construction costs for Skokie's street storage system are about one-third
the estimated cost of sewer separation 8-4
9-1 Shear gate with orifice flow regulator as used in Wilmette, IL 9-14
wp/epasttabfig
XIX
-------
Abbreviations and Acronyms
CCI
cfs
CMP
CSO
CSS
CUP
CWA
DPW
EDA
ELSSD
ENR
EPA
gpd
HSSD
HUD
IDOT
IEPA
ILLUDAS
ITE
mph
MSDGC
MSSD
MWRDGC
NMC
POTW
RHS
RUS
SAM
SASAM
SRF
333
SWMM
TARP
USDA
Construction Cost Index (provided by ENR)
Cubic feet per second
Corrugated metal pipe
Combined sewer overflow
Combined sewer system
Chicago Underflow Plan
Clean Water Act
Director of Public Works
U.S. Department of Commerce Economic Development
Administration
Emerson-Lake Streets Sewer District
Engineering New Record (Source of the CCI)
Environmental Protection Agency (same as USEPA)
Gallons per day
Howard Street Sewer District
U.S. Department of Housing and Urban Development
Illinois Department of Transportation
Illinois Environmental Protection Agency
Illinois Urban Drainage Area Simulator
Institute of Transportation Engineers
Miles per hour
Metropolitan Sanitary District of Greater Chicago (now the
MWRDGC)
Main Street Sewer District
Metropolitan Water Reclamation District of Greater Chicago
(formerly MSDGC)
Nine minimum controls
Publicly-owned treatment works
Rural Housing Service
Rural Utilities Service
System Analysis Model
Surface and Street Analysis Model
State Revolving Fund
Sanitary sewer system
Storm Water Management Model
Tunnel and Reservoir Plan
U.S. Department of Agriculture
XX
-------
USEPA U.S. Environmental Protection Agency (same as EPA)
WWF Wet weather flow
WWTF Wastewater treatment facility
wp/epastabbr
xxi
-------
Acknowledgments
The support of the project by the Office of Research and Development, U.S.
Environmental Protection Agency is acknowledged and appreciated.
Mr. Robert W. Carr and Mr. Michael C. Morgan of Earth Tech conducted the computer
simulation study of the effect of street storage on the volume and frequency of
combined sewer overflows. They also participated in interviews; provided construction
costs, implementation schedules and other information about the Skokie and Wilmette
projects; and reviewed all chapters of this report. Mr. Donald F. Roecker, Special
Project Consultant, prepared most of the funding text in Chapter 5 and reviewed related
sections of this report. Ms. Vicki Farabaugh of Creative Computing created or
assembled the graphical content of this report and did the word processing.
Many Skokie and Wilmette, IL officials gave generously of their time and knowledge as
part of interviews conducted for this project. Their efforts are acknowledged and
appreciated.
Also worthy of recognition are personnel of Donohue and Associates and Rust
Environment and Infrastructure, predecessor firms of Earth Tech. Many individuals in
all three firms contributed to the creation and implementation of street storage systems
in Skokie and Wilmette.
The cooperation of Ms. Carolyn R. Esposito, Work Assignment Officer, Water Supply
and Water Resources Division, National Risk Management Research Laboratory, U.S.
Environmental Protection Agency, is appreciated and acknowledged.
wp/epastack
XXll
-------
CHAPTER 1
INTRODUCTION
Combined Sewer System Challenge in the U.S.
Much work remains to be done to solve the overflow and basement flooding problems
caused by surcharging of combined sewer systems (CSS) in approximately 1000 U.S.
communities. These communities, 60% of which are small in that they have
populations of less than 10,000, have a total population of about 40 million or
approximately 15% of the country's total. About 85% of the CSS municipalities are in
eleven northeastern, midwestern and far western states. Within these communities are
10,000 combined sewer overflow (CSO) points and an unknown number of historic and
potential basement flooding situations (Dwyer, T. 1998).
Most combined sewer municipalities face the challenge of how to mitigate overflows
and/or basement flooding and the attendant water pollution, health risks, and monetary
damages. The challenge is further defined by recognizing that the combined sewer
problem must be solved to comply with state and federal regulations, recognize the
realities of fiscal responsibility, and earn public acceptance.
Presented in this manual is a description and evaluation of what has proven, within a
specific set of circumstances, to be one way of meeting the CSS challenge. More
specifically, the technology described in this manual solved surcharging, complied with
regulations, proved to be cost effective and earned public support.
CSO Policy of the USEPA
Objectives of the Policy
Three objectives guide the U.S. Environmental Protection Agency's (USEPA) CSO
policy (USEPA 1994). They are:
"...ensure that if CSOs occur, they are only as a result of wet weather."
1 -1
-------
"...bring all wet weather CSO discharge points into compliance with the
technology-based and water quality-based requirements of the Clean Water
Act (CWA)."
"...minimize water quality, aquatic biota, and human health impacts from
CSOs."
According to the USEPA (1994):
Permitees with CSSs that have CSOs should immediately
undertake a process to accurately characterize their sewer
systems, to demonstrate implementation of the nine
minimum controls, and to develop a long-term CSO control
plan.
Nine Minimum Controls
Permitees with CSOs should, according to the EPA (1994), submit appropriate
documentation demonstrating implementation of the nine minimum controls (NMCs),
including any proposed schedules for completing minor construction activities. The
nine minimum controls are:
2. proper operation and regular maintenance programs for the sewer system and
the CSOs;
3. maximum use of the collection system for storage;
4. review and modification of pretreatment requirements to assure CSO impacts
are minimized;
5. maximization of flow to the publicly-owned treatment works (POTW) for
treatment;
6. prohibition of CSOs during dry weather;
7. control of solid and floatable materials in CSOs;
8. pollution prevention;
9. public notification to ensure that the public receives adequate notification of
CSO occurrences and CSO impacts; and
10. monitoring to effectively characterize CSO impacts and the efficacy of CSO
controls.
John and Wheatley (1998) focus on the minimum and interim aspects of the NMCs
when they state that the NMCs were:
...not expected to require major capital expenditures and
directed state environmental agencies to formulate their own
strategies for bringing CSOs into compliance with water
quality standards and other CWA requirements. The
minimum controls can reduce CSO impacts on water quality
but were not seen as a long-term solution.
1 -2
-------
Long-Term CSO Control Plan
Permitees with CSOs are, according to the EPA (1994), responsible for developing and
implementing long-term CSO control plans that will ultimately result in compliance with
the requirements of the CWA. The long-term plans should consider the site-specific
nature of CSOs and evaluate the cost effectiveness of a range of control
options/strategies. The minimum elements of the long-term control plan are:
Characterization, monitoring, and modeling of the combined sewer system.
Public participation.
Consideration of sensitive areas.
Evaluation of alternatives.
Cost/performance considerations.
Operational plan.
Maximizing treatment at the existing POTW treatment plants.
Implementation schedule.
Post-construction compliance monitoring program.
Traditional Approach: Store/Treat Combined Sewage or Separate the Sewer
System
Traditional and proven structural methods for resolving CSS flooding and pollution
problems include, as shown in Table 1-1, separation, in-system storage, end-of-pipe
storage, and deep tunnels. All the traditional solutions address the pollution problem
while separation and in-system storage can also mitigate flooding problems, especially
basement flooding caused by surcharging of combined sewers.
The premise of the traditional and proven solutions is to generally accept the rate of
stormwater flow into the system. The resulting mixture of stormwater, sanitary sewage
and other components is then controlled with methods such as in-system storage, end-
of-pipe storage, and deep tunnels.
The Association of Metropolitan Sewage Agencies, in a study of 21 large U.S.
communities having CSS's, reported that "storage is the most common approach taken
to reduce the volume and frequency of overflows" (AMSA, 1994, p. 17). Storage in this
context includes the in-system, end-of-pipe, and deep tunnels approaches listed in
Table 1-1. Interestingly, nine of the 21 communities have constructed (Chicago, IL and
Milwaukee, Wl) or plan to construct tunnels. Two of the 21 studied communities,
Minneapolis-St. Paul, MN and Hartford, CT have made major commitments to sewer
separation.
1 -3
-------
Table 1-1. Proven methods are available to solve pollution and/or flooding problems in
combined sewer systems.
Method
Separation
In-System Storage1
End-of-pipe Storage1
Deep Tunnels
Problem Solved
Pollution
•
•
•
•
Flooding
•
•
1) Storage of combined sewage.
1 -4
-------
A New Approach: Store Stormwater Before It Combines With Sanitary Sewage
Wet weather problems in CSSs are caused by the peak rate of stormwater runoff, not
necessarily by the runoff volume. Wet weather flooding and pollution problems would
often not occur, or would be much less severe, if the peak flows of stormwater could be
lessened. Peak flows are often the principal culprit, not the volume of stormwater
runoff.
This suggests a fundamentally different approach having the following premise: reduce
the peak flow rates of stormwater before it enters the combined sewer system. Accept
the full volume of stormwater into the CSS, but greatly reduce the peak rate of entry.
Figure 1-1 illustrates, in conceptual fashion, this stormwater-oriented approach to
reducing surcharging in CSS and, therefore, mitigating flooding and pollution. Chapter
3 includes a detailed description of the conceptualization, development, design and
construction of the street storage approach.
Scope of This Evaluation
Case Study Approach
This manual documents a case study-based evaluation of the use of on-street and
related storage of stormwater to reduce the surcharging of combined sewers and, in
turn, mitigate basement flooding and CSOs. The focus of the evaluation is capturing,
analyzing, and presenting what has been learned through the concept-through-
operation process over 18 years in primarily two communities. Synopses of several
other applications are included as supplemental ways to learn about the street storage
system approach.
The scope of this manual is broad. The evaluation includes many and varied aspects
of the case studies such as analysis and design approaches, regulatory and funding
framework, public involvement, operation and maintenance procedures and costs,
construction costs, and performance of the system. The scope of this manual is also
deep, that is, detailed. Each of the preceding topics are covered in depth. The scope
of this manual is also broad in that it addresses both flooding and pollution caused by
surcharging of CSS's. This quantity and quality issue is discussed in the next section.
Quantity and Quality: Seeking Optimum Means of Simultaneously Mitigating
Flooding and Pollution
Most CSS studies, reports and guidelines that are not community or site-specific,
address only or mainly the need to reduce pollution caused by CSOs. Lost in this focus
on pollution caused by surcharging of CSSs is the frequent parallel problem of
basement and other flooding caused by surcharging of CSSs.
1 -5
-------
Dry Weather
Inlet/Catchbasin
Turf, Concrete,
Asphalt Surface
Combined
Sewer
" Is
Surcharged
Wet Weather without
Stormwater Control
Inlet/Catchbasin
Turf, Concrete,
Asphalt Surface
Combined
Sewer
Surcharged
Wet Weather with
Stormwater Control
Temporary
Storage
Inlet/Catchbasin
•. -•• accept flow rates
(mostly Stormwater) =•'.•. .-•••'•
the sewer
Turf, Concrete,
Asphalt Surface
C°SS,!l?d
Surcharged
Figure 1-1. Control of peak rates of Stormwater runoff can, in concept, mitigate
surcharging of combined sewer systems.
1-6
-------
As an indication of the possible local importance of basement and other flooding in
CSS communities, consider the community-specific information provided in an
assessment report prepared by the Association of Metropolitan Sewerage Agencies
(AMSA, 1994). Described in this report are "CSO control programs" in 21 communities
across the U.S. Although the focus of the report is clearly on CSS water quality, that is,
pollution problems, water quantity problems, that is, flooding, are clearly evident in
some of the 21 communities. The report states (AMSA, 1994, p. 15):
In many of the cities, basement flooding during
wet weather is also a problem that influences
CSO improvements and frequently impacts
the selected control strategy (emphasis
added).
Flooding data on the previously mentioned 21 communities plus others is summarized
in Table 1-2. Some type of flooding attributed to the CSS is explicitly reported by seven
of the communities. Given the preceding quote, flooding problems may be under
reported.
As an example of emphasis on pollution control in CSSs to the essential exclusion of
flood control, consider the USEPA manual on combined sewer overflow control
(USEPA, 1993). The stated purpose is to provide "...information to assist in selecting
and designing control measures for reducing pollutant discharges from CSOs" (USEPA,
1993, p. 1). Although most of the report focuses on controlling combined sewage, there
are scattered brief references to components of street storage. Examples are inlet
restriction and attendant street ponding (p. 7), flow slipping (p. 7) and regulators (p. 38).
Several possible explanations can be offered for the strong focus on pollution caused
by CSSs to the exclusion of addressing basement and other flooding problems.
First, pollution will almost always be a problem in CSSs while basement and other
flooding problems are less likely to occur as evidenced by the AMSA (1994)
assessment. Basements are essentially not present in some communities because of
factors such as high groundwater levels and the presence of shallow bedrock. The
actual severity and frequency of basement flooding, regardless of cause, is likely to be
greater than reported because building owners may fear loss of property value if
flooding of their basements is documented. However, when basements exist within a
CSS, the resulting flooding by combined sewage can be a serious and repeated health
risk and create large monetary losses.
1 -7
-------
Table 1-2. Seven of 22 large CSS communities explicitly reported basement or street
and other surface flooding (AMSA, 1994 except where other source is indicated).
City
Atlanta, GA
Boston, MA
Chicago, IL
Cincinnati, OH
Cleveland, OH
Columbus, GA
Detroit, Ml
Fort Wayne, IN1
Hartford, CT
Louisville, KY
Milwaukee, Wl
Minneapolis-St. Paul,
MN
New York, NY
Philadelphia, PA
Portland, OR
Providence, Rl
Richmond, VA
Sacramento, CA
San Francisco, CA
Seattle, WA
Washington, DC
Wayne County, Ml
Type of Flooding Explicitly Reported As being Attributed to the CSS
Street and/or Other
Surface Flooding
M
M
M
Basement Flooding
M
M
M
M
M
Undifferentiated
Flooding
M
1)WERF, 1998, pp. 14-15
1 -
-------
Second, the USEPA and counterpart state "environmental" agencies (e.g., Indiana
Department of Environmental Management) tend to be concerned with pollution
abatement. In contrast, flood control and drainage are within the mission of the COE
and counterpart state agencies (e.g., Indiana Department of Natural Resources).
These flood control oriented agencies typically do not address problems in CSSs.
Agency missions understandably drive agency programs. A possible negative aspect of
exclusive or excessive focus on pollution abatement in CSSs is that less than optimum
solutions may result. For example, a community's CSO problem may be successfully
resolved by end-of-pipe storage or end-of-pipe connection to "deep tunnels" while the
basement flooding problem continues.
Optimum solutions are more likely to arise if the entire drainage system or watershed is
examined from the outset in terms of defining the problem (pollution and flooding),
determining the causes, and then finding the most cost-effective solution. The scope of
this manual is holistic in that it stresses the possibility of simultaneously addressing
quality and quantity, that is, pollution abatement and flood control.
Retrospective Details With Prospective Purpose
Because of the case study approach, the details of this manual are retrospective. That
is, the emphasis is on history—what was done, why it was done, how it worked.
However, in as much as municipal officials are the principal audience of this manual, the
overall thrust is prospective. That is, how could other communities benefit from the
concept-through-operation experience of the case study communities?
Each municipality has a unique meteorological, physical, socio-economic, political and
regulatory profile. Therefore, only some of the knowledge gained from the case studies
described in this manual will be transferable to any given community. However, given
the breadth and depth of knowledge presented in this manual, if even a small part is
directly applicable to a given municipality, that municipality will gain much. Stated
differently, the specifics documented in this manual should prevent "reinventing the
wheel" in other communities. The theme of relevance to other CSS municipalities is
woven throughout this manual. Perhaps some communities will investigate the street
storage option as a result of successes enjoyed by the case study municipalities.
In addition to having a prospective thrust to serve municipalities, this manual is also
prospective for the benefit of researchers. Possible research topics are identified, (see
Chapter 11), based on the case study experience, with the hope that additional
investigations might be conducted.
1 -9
-------
Initiatives
As noted, this is a case study-based manual and, therefore, the details are largely
retrospective. Accordingly, new research efforts were generally beyond the scope of the
evaluation, with two specific exceptions.
The first exception to the retrospective focus of this manual is a literature search. Efforts
were made to find, document and incorporate relevant papers, articles, and personal
contacts not already discovered during the conduct of the two projects. Because the
technology was considered innovative when first applied to the case study communities
in the 1980's, a major effort was undertaken at that time to find relevant literature and
knowledgeable individuals. Results of those efforts were included in early project
documents and are summarized in this manual. The additional literature and resource
search carried out for this evaluation was conducted to enhance the value of the
manual. Findings of the literature search are included throughout this manual as
supplements to the two case studies.
The second exception to the retrospective focus of this manual is the special analysis of
the hypothetical impact of the control technology on the volume and frequency of CSOs
and on peak flows at wastewater treatment plants. Basement flooding by combined
sewage, not CSOs, was the major CSS concern in the two case study communities.
However, the implemented solution may have the potential to mitigate CSOs and related
problems. Therefore, that potential was studied in an exploratory fashion to further
enhance the value of this manual. That study is described in Appendix F and the results
are summarized in Chapter 9.
Terminology
Several terms have been used in recent years to describe controlling peak rates of
stormwater flow as a means of reducing surcharging in CSS's. Utilization of different
terms for essentially the same system can and probably has led to some confusion.
Accordingly, various terms are discussed here for purposes of clarification and to show
commonality among various research, development and engineering design efforts in
the U.S. and elsewhere. A specific terminology and its definition is then set forth for use
in this manual.
Terms in use include:
Runoff Control. This terminology has been in use in the U.S. since at least the
early 1980's. In fact, it was used in most of the written and spoken
communication throughout the two principal case studies which are described in
this manual. See for example, the numerous Donohue & Associates citations in
the Cited References. However, this term, while suggesting stormwater, is too
general. Many aspects of stormwater management could be called "runoff
1 -10
-------
control."
Inlet Control. This terminology appears in the title of writings by Hides (1994)
and Pisano (1989) and is also used by Harza Engineering (1981). While inlet
modification may be part of the overall stormwater control system, it is typically
just one component. For example, other possible components are street berms
and subsurface storage tanks. Therefore, the term inlet control is undesirable
because it suggests an unrealistically simple approach.
Source Control. This term, which was used by Kaufman and Lai (1978) and
Walesh (1996), has appeal because the stormwater is to be temporarily stored
as close as possible to the source, that is, to where it falls as precipitation.
Unfortunately, this quantity-oriented use of "source control" conflicts with the
predominantly quality-oriented use of "source control" in amendments to the
Clean Water Act. In these amendments, "source control" is strongly associated
with non-point source pollution.
Micromanagement of Stormwater. This terminology, used by Carr and
Walesh (1998), focuses on the local, detailed, intersection-by-intersection
analysis and design process that is needed when attempting to reduce peak
stormwater flows in existing urban areas. This analysis and the resulting design
and construction of numerous, small structures may be characterized as "micro"
when compared to the "macro" approach typically used in stormwater system
analysis and design. "Macro," in this context, refers to larger subbasins used in
the analysis and the smaller number of larger structures, such as detention or
retention facilities, typically designed and constructed. On the negative side,
the term "micromanagement" is not, in and of itself, very descriptive. Additional
description is needed to communicate the concept.
Street Storage. This term has proved to be highly descriptive. It readily
suggests the unconventional, but potentially effective use of streets to
temporarily store stormwater. On the negative side, while on-street storage is
typically an important aspect of reducing peak stormwater flow into a CSS, it is
not the only form of storage. Other possibilities include off-street surface
storage and storage below streets and parking lots. The short hand term "street
storage" was selected for use in this manual. It appears in the title.
Street storage means:
a system that mitigates surcharging of CSSs,
SSSs and stormwater systems by temporarily
storing stormwater in a controlled fashion on the
surface (mainly on-street but some off-street)
and, as needed, below streets. Stormwater is
stored close to the source, that is, where it falls
as precipitation, and prior to its entry into the
1 -11
-------
sewer system. The full volume of stormwater
runoff Is accepted Into the sewer system but
peak rates are reduced, as a result of the
storage, to flow that can be accommodated
without surcharging.
Abbreviations, Acronyms and Glossary
Many abbreviations and acronyms are used, for the purposes of efficiency and
communication, in this manual. In the interest of assisting the reader, the first use of an
abbreviation or acronym in the manual is accompanied by its definition. After that
introduction, the abbreviation or acronym is used in the remainder of the manual. For
easy reference, a complete list of abbreviations and acronyms is included near the front
of this manual.
Some readers may not be familiar with all the technical, regulatory and other terms used
in this manual. Accordingly, a Glossary appears near the end of this document.
Selected definitions were drawn from the "Glossary of Wet Weather Flow Terms"
(USEPA, 1998) and from other sources, as indicated in the Glossary.
wp/epastchl
1 - 12
-------
CHAPTER 2
CASE STUDY COMMUNITIES:
SKOKIE AND WILMETTE, IL
Bases of Selection of Case Study Communities
Skokie and Wilmette, IL, the two principal case study communities, were chosen for this
manual primarily for three reasons, as described here. Because this manual describes
case studies of a newer technology, an opportunistic approach was taken to finding
principal and supplemental case study communities whose experiences could be of
value to other communities. The identified case study communities in effect provided
"laboratories" in which the new street storage technology could be studied.
Familiarity of the Investigators With the Projects
Each member of the four-member engineer team that conducted this investigation
contributed significantly to the engineering, financing or other aspects of one or both of
the two principal street storage system projects. By choosing the Skokie and Wilmette,
IL as the two principal case study communities, optimum use was made of the first
hand experience of the investigators.
On-Going Relationships With Personnel in the Case Study Communities
Three of the four engineer members of the team that conducted this investigation have
maintained on-going relationships with personnel in at least one of the two principal
case study communities. This proved to facilitate ready access to data, information,
and suggestions originating within the two communities.
Opportunity to Study a Large, Long-Standing Street Storage Project
The Skokie, IL street storage system is the largest known application of this technology
in the U.S. and possibly beyond. Furthermore, parts of the Skokie system have been in
operation since 1983, providing many years of operating experience. By choosing
Skokie for this case study, the manual captures the best known overall example of the
street storage technology.
2- 1
-------
Supplemental Communities
As a supplement to using Skokie and Wilmette as the principal case study
communities, other smaller scale applications of street storage, or components of it,
were sought. These applications is presented in Chapter 4.
The remainder of this chapter is devoted to detailed descriptions of Skokie and
Wilmette, IL. Pertinent information on supplemental communities that have
implemented street storage or some aspect of it is presented when those communities
are discussed.
Description of Skokie, IL
A detailed description of Skokie, IL is presented to provide context and data for
understanding the case studies. Included in the description are physical attributes,
meteorology, and history of CSS problems and proposed solutions to them.
Location
The general location of the 8.6 square mile Village of Skokie is shown on Figure 2-1. It
is immediately north of the City of Chicago. Figure 2-2 is a map of Skokie showing
major features. Skokie is bounded on the south by Lincolnwood, on the west by Miles
and Morton Grove, on the north by Wilmette, and on the east by the North Shore
Channel and Evanston. As suggested by Figure 2-3, which is a photo of the North
Shore Channel, the channel and its associated linear parks are an amenity for area
residents.
Relationship to the Metropolitan Water Reclamation District of Greater Chicago
Skokie lies entirely in the service area of the Metropolitan Water Reclamation District of
Greater Chicago (MWRDGC). At the beginning of the Skokie street storage project,
this agency was named the Metropolitan Sanitary District of Greater Chicago (MSDGC).
Essentially all of Skokie is served by a CSS. Combined stormwater runoff and sanitary
sewage generated within Skokie flow generally eastward to interceptors and TARP
(Tunnel and Reservoir Plan), also called the deep tunnel system, which is owned and
maintained by the MWRDGC. As shown schematically on Figure 2-4, the interceptor
parallels the North Shore Channel. The tunnel, which parallels and lies 200 feet below
the North Shore Channel, is intended to capture, via drop shafts, combined sewage that
is in excess of the interceptor capacity. As suggested by Figure 2-4, the deep tunnel is
primarily a pollution control system. It mitigates CSOs but has minimal impact on
basement flooding caused by surcharged combined sewers.
2-2
-------
Wl
IL
0 10 M I
Wilmette>
Skokie
Lake Michigan
IN
Figure 2-1. Skokie and Wilmette, IL lie immediately north of the City of Chicago.
2-3
-------
c
ro
^
O
2!
o
w
^
o
Figure 2-2. Map of Skokie, IL (Source: Donohue, 1982b, p. 13).
2-4
-------
Figure 2-3. The North Shore Channel, which bounds Skokie on the east, and its
contiguous linear parks provide an amenity for area residents.
2-5
-------
Building with
Basement
Building without
Basement
North Shore
Channel
i
Combined
Trunk
Sewer
Interceptor
Sewer
Normal
Stage
Deep
Tunnel
Figure 2-4. The deep tunnel is primarily a pollution control system in that it mitigates
combined sewer overflows to the North Shore Channel.
2-6
-------
Most drop shaft connections were provided to relieve the MWRDGC interceptors and
not directly serve individual communities. However, proactive Chicago area
communities such as Arlington Heights, Evanston, Miles, Skokie, and Wilmette were
able to negotiate with the MWRDGC to provide drop shaft connections with agreed
upon capacities to serve their CSSs. As a condition of placing these drop shafts, the
communities were required to limit peak discharges to TARP. These conditions gave
added impetus to Skokie and Wilmette, the two principal case study communities, to
consider the street storage system.
Land Use and Population
Skokie is completely developed. Land use is about 80 percent residential, 10 percent
industrial and 10 percent commercial. The population is about 60,000 persons with an
overall population density of 11 people per acre and a population density in residential
areas of approximately 14 people per acre (Nakai and Carr, 1993). There are about
20,000 single family residences in Skokie (Raasch, 1989b).
Soils and Groundwater
Skokie soils are primarily from glacial deposits of the Pleistocene series. These glacial
deposits have an approximate depth of 60 feet and consist of many types of materials.
About 25 percent of the community has sandy soils, while the remainder has clay soils.
Groundwater levels are generally 10 to 15 feet below ground level in sandy areas. An
exception is isolated perched lenses of shallower ground water (Nakai and Carr, 1993).
Topography and Drainage Patterns
"The land ...generally slopes eastward toward the North Shore Channel. Slopes vary
from 0.1 to 1 percent and the overall slope in many areas of the Village is a flat 0.2
percent. Surface runoff ...flows from the front lawn and driveway areas to the street.
Flow in the street is along the curb line and gutters to the nearest inlet. Inlets are
generally located midblock and at intersections. Due to the extremely flat conditions,
few areas have a continuous drainage pattern from block to block" (Nakai and Carr,
1993).
Trunk sewers in the combined system range in diameter from 30 inches to a maximum
of 84 inches. Lateral sewers which are connected to trunk sewers vary in diameter
from 12 to 27 inches. Combined sewage is carried from Skokie through three 84-inch
trunk sewers to the MWRDGC interceptor sewer. When the interceptor capacity is
exceeded each trunk sewer overflows first to the MWRDGC deep tunnel and then to
the North Shore Channel (Nakai and Carr, 1993).
Stormwater leaves the street by flowing into an inlet, none of which have sumps, and
2-7
-------
generally there are two inlets connected to a catch basin. As shown in Figure 2-5,
catch basins are manhole-type structures containing some standing water in a sump at
all times. The pipe conveying flow from the catch basin to the combined sewer is
configured so as to form a trap preventing backup of sewer gases into the catch basin.
Catch basins are generally located between the curb and sidewalk and have either a
grated or solid manhole cover (Walesh and Schoeffmann, 1984).
Skokie is partitioned into three combined sewer districts. They are, as illustrated in
Figure 2-6, the 1,255 acre Howard Street Sewer District (HSSD) in the southern part of
the community; the 2,300 acre Main Street Sewer District (MSSD) in the central part,
and the 1,955 acre Emerson Lake Streets Sewer District (ELSSD) in the northern part.
As indicated earlier, the three districts drain generally easterly and flow into an
interceptor sewer along the deep tunnel beneath the North Shore Channel (Nakai and
Carr, 1993).
Climate
Skokie's climate is classified as continental, typical of a location in middle latitudes (42
degrees north latitude), but somewhat modified by the proximity of Lake Michigan which
is two miles east of the community. Because of the lake, the climate is moderated
relative to inland locations. Nevertheless, winters are cold, with an average snowfall of
about 36 inches as snow, and summers are warm and sometimes humid. "All seasons
are marked by occasionally intense storms that accompany changes from one air mass
to another. Runoff from these storms, particularly in the spring and early summer,
causes flooding in the Skokie area" (Donohue, 1982a, p. 29-31).
Nakai and Carr (1993) indicate that precipitation "...occurs as rain, sleet, hail, and snow
and ranges from showers of trace quantities to brief intense storms to longer duration
rainfall or snowfall events. Precipitation is distributed throughout the year with an
average annual total of 33.3 inches." For a one-hour storm, the 1, 10, and 100-year
recurrence interval rainfall amounts are 1.18, 2.10, and 3.56 inches, respectively. Fora
24-hour storm, the 1, 10, and 100-year amounts are 2.51, 4.47 and 7.58 inches,
respectively (Huff and Angel, 1989, pp. 29-30).
Brief History of Skokie with Emphasis on Development of Its Drainage System
Sewer surcharging and basement flooding problems that gradually developed in Skokie
can be traced back to the unique circumstances associated with development of the
community. Most of what is now Skokie was under waters of Lake Michigan in
prehistoric times. The community lies between two ridges approximately three miles
apart and the area was mostly swamp when the first explorers arrived in the sixteen
hundreds and found the Potawatomi Indians living there.
2-8
-------
Catch Basin
Outlet Pipe to
Combined Sewer
Inflow Pipe
from Inlet
^
1
1
y
9
' >
^
1
Figure 2-5. Each Skokie catch basin is a manhole-type structure with a sump.
2-9
-------
North Shore
Channel
7
1 M I
Figure 2-6. Skokie is partitioned into three easterly draining combined sewer districts.
2-10
-------
As the area became populated in the 1800's, the need for drainage and sanitary waste
disposal became critical. Construction of the North Shore Channel in 1910, as part of
the overall plan to provide the Chicago metropolitan area with an adequate drainage
system, provided an outlet for sewers to serve Skokie. The first trunk sewer was
constructed in 1886 to drain what is now the downtown area and carried both
stormwater and sewage to the channel. Skokie's combined sewer system had begun.
The prime reason for the severity of the present basement flooding problem in Skokie is
tied to the 1920's—the land boom days in Skokie. Major roads from Chicago were
being paved and a rapid transit line extended through Skokie. As farm land was
subdivided into building lots, population rose from 760 in 1920 to 4,200 in 1930. In
preparation for the anticipated building boom, the majority of streets, sidewalks, water
mains and sewers were constructed. The contemporary technology resulted in the
construction of a combined sewer system with its outfall at the North Shore Channel. In
1927, a treatment plant and interceptor sewer system were constructed to handle dry
weather sanitary flows, but the remaining mainly combined sewage flowed into the
channel.
The depression of the 1930's brought the land boom in Skokie to an immediate halt.
The constructed infrastructure was left essentially unused for the next 20 years.
However, development anticipated in the 1920's finally occurred in the years following
World War II. The majority of development and building took place in the 1950's as
Skokie's population exploded from 14,800 in 1950 to 59,400 in 1960 (Walesh and
Schoeffmann, 1984).
Not only did the community commit to an entire CSS but, trunk sewers were,
unfortunately, undersized. More specifically (Consoer, Townsend & Associates, 1967):
Because of limitations on financing, the original
trunk sewer improvements were of an
introductory nature and restricted in size. The
lateral sewers were, however, installed to then
standard practice. All of these sewers were
combined storm and sanitary type.
It had been anticipated that additions to the
combined sewers would be installed at
intervals as buildings were constructed in the
vacant areas. However, this program was not
followed and as of today, all of the trunk
sewers are deficient in capacity for an
acceptable level of service. Basement flooding
is prevalent during medium to heavy storms,
and damaging street flooding also occurs
2- 11
-------
during the heavier storms.
In summary, this brief history highlights the community's early commitment to combined
sewers and the need, driven by finances, to undersize trunk sewers. This history also
provides a seque to the next major section of this chapter which describes problems
caused by Skokie's undersized CSS.
Skokie's Historic Combined Sewer System Basement Flooding Problems
Several surveys over about a decade in the 1960's and 1970's documented widespread
basement flooding in Skokie. According to Donohue (1982a):
Previous studies by Consoer, Townsend &
Associates, 1967 and 1973; the Village of
Skokie, 1974; and by Harza Engineering
Company, 1978, have included surveys to
determine the extent of basement backup
flooding in the Village of Skokie. These
surveys were generally conducted by sending
post cards to residences requesting
information on their flooding history.
The 1967 survey received responses from over
9,000 residences with slightly in excess of 54
percent indicating that they had basement
backup problems during major storms.
The 1978 survey resulted in about 2,500
responses, a response rate of only 11 percent.
Approximately 15 percent of those responding,
indicated they had basement flooding from
recent rains which were less intense than a 2-
year frequency storm. These backup problems
were spread somewhat uniformly over most of
the community. Interestingly, about 20 percent
of the residences having flooding problems
also indicated they had at least one flood
protection device that obviously didn't work
properly.
The 1974 survey by the Village was conducted
only in the Fairview South area. During the
survey, a questionnaire was mailed to each
residence and Village personnel attempted to
interview every homeowner. These efforts
resulted in a 72 percent coverage of the 471
2- 12
-------
units and 47 percent Indicated they had
basement flooding during heavy rainfall.
Again, a large percent of the people with some
type of flood control equipment indicated they
still had basement backup flooding problems.
Viewed collectively, the three surveys (1967, 1974 and 1978) suggest a community-
wide basement flooding problem caused by surcharging of the CSS. At least half of the
residences appeared to experience basement flooding in larger storms. Furthermore,
basement flooding occurred in a smaller but significant fraction of residences during
frequent, minor storms.
Previous Studies of Ways to Solve Skokie's Combined Sewer System Basement
Flooding Problems
Skokie commissioned or conducted studies over a 15 year period to find a cost-
effective solution to the growing basement flooding problem. Summarized here are the
essential aspects of seven studies including the recommendations. This summary
serves to illustrate how traditional solutions were repeatedly proposed but not
implemented. This process, in turn, set the stage for Skokie's receptivity to a new
approach.
Study Completed in 1967 Recommending Relief Sewers
Consoer, Townsend & Associates (1967) conducted this community-wide investigation.
Donohue (1982a, pp. 15-16) provides this summary:
This study reviewed the sewer system
deficiencies and backup problems in
basements throughout the Village. It reviewed
several alternative solutions to these sewer
backup problems and recommended an
overflow relief sewer system for the entire
Village with an estimated 1967 cost of $22.0
million (Note: The 1999 cost would be $123
million using the Engineering News Record
[ENR] Construction Cost Index [CCI]). In the
Howard Street Sewer District the report
recommended a major relief sewer along
Laramie Avenue from Farwell Avenue to
Brummel Street (48-inch to 102-inch diameter),
then eastward along Brummel Street from
Laramie Avenue to Hamlin Avenue (108-inch
to 144-inch diameter), then two blocks south
along Hamlin Avenue to Howard Street, and
2- 13
-------
east along Howard Street to the North Shore
Channel (144-inch diameter). These sewers
were never installed.
The proposed relief sewers were designed so
that the combined capacity of the existing trunk
sewers and the new relief sewers would be
such that runoff from about a 15-year storm
could be accepted from non-restricted areas
and the actual maximum possible runoff could
be accepted from restricted flat areas.
Study Completed in 1973 Recommending Deep and Shallow Tunnels
With the "deep tunnel" being imminent, Skokie retained Consoer, Townsend &
Associates (1973) to carry out another community-wide investigation with emphasis on
solving basement flooding problems. The following summary is provided by Donohue
(1982a, pp. 16-17):
In October 1972, the Board of Trustees of the
Metropolitan Sanitary District of Greater
Chicago (MSDGC) adopted the "Chicago
Underflow Plan" (CUP). (This plan is later
referred to as Tunnel and Reservoir Plan,
TARP). The plan consisted of construction of
120 miles of conveyance tunnels intercepting
the overflows from all existing combined
sewers in the Chicago land area. One of the
planned underflow tunnels paralleled the North
Shore Channel and was scheduled for
installation in the first phase of construction of
the underflow plan. This provided a new outlet
for the combined sewage flow from the Skokie
sewer system and radically changed relief
sewer concepts for the Village of Skokie. The
1973 Consoer, Townsend study analyzed the
sewer facility needs for the Village of Skokie in
conjunction with the CUP.
This report recommended a system of deep
and shallow tunnels connecting to the MSDGC
main tunnel along the North Shore Channel.
The 1973 estimated cost was $31 to $35
million (Note: The 1999 cost range would be
2- 14
-------
$98 to $111 million using the ENR CCI). The
system within the Village of Skokie included a
major deep tunnel in an east-west direction
down Main Street draining towards the North
Shore Channel and several shallow tunnels in
north-south directions draining to this deep
tunnel. The Howard Street area would be
served by shallow tunnels leading north along
Laramie Street and Keeler Avenue. The report
presented design data and cost estimates on
systems sized for both the 10-year and 100-
year storms. None of these deep or shallow
tunnels have been constructed.
The study also analyzed the effect that the
CUP would have on the existing trunk sewers if
no relief sewers were provided. The report
concludes that the North Shore Channel
underflow tunnel will have a minor impact on
Skokie flooding without supplementary
channels or relief sewers being installed,
except for several blocks near the outlet.
Study Completed in 1974 Recommending Downspout Disconnection and Catch
Basin Restrictors
Unlike all the other studies summarized in this section, this one was conducted by
Skokie personnel. Donohue (1982b, pp. 17-18) contains this summary:
This study was completed by the Village of
Skokie to determine the probable relief that
could result from downspout disconnection in
the Fairview South area and catch basin
restrictions. The restrictors were "half-moons"
inserted into catch basin outlet pipes which
effectively reduce their discharge capacity by
one half. Twenty-seven percent of the
downspouts in the area were found to be
disconnected at the beginning of the study.
Detailed surveys were conducted by mailing
questionnaires to residents of the Fairview
South area and collecting these questionnaires
by survey teams in the field. The survey
2- 15
-------
covered 72 percent of the residences and
showed that of those surveyed, 47 percent
have basement backup problems during heavy
rainfalls. The survey also asked if residences
had some type of flood control equipment
installed. Of the 355 residences surveyed, 86
percent indicated that they had some type of
flood control equipment installed. However, a
large percentage of these residences still
experienced sewer backup problems due to
inadequacies or malfunctioning of their flood
control equipment. Another question checked
the citizen response to the acceptability of a
future downspout disconnection program.
Sixty-nine percent of the 355 residences
surveyed voiced a willingness to participate in
a downspout disconnection program.
Recommendations of the study were: 1) New
catch basin restrictors should be installed at 86
locations to reduce the pipe diameter from
eight inches to four inches thereby reducing
the discharge capacity of the catch basins by
75 percent. The cost was estimated to be
$1,274. 2) A downspout disconnection
program should be instituted and all
residences in the study area except those
fronting on Laramie and Pratt Avenues should
be disconnected. Cost for this program was
estimated at $19,728. The net effect of this
downspout disconnection program would be a
49 percent reduction in the demand placed on
the sewer system. The study stated that the
additional stormwater directed into the street
by the disconnected downspouts and stored in
the street by the restricted catch basins could
be stored without causing major hazards to
vehicular traffic in all areas of Fairview South
except the west and south boundary streets,
Laramie Avenue and Pratt Avenue,
respectively. This study used the five and 10-
year storms to analyze street flooding
characteristics.
2-16
-------
As a result of this study, Skokie proceeded with a downspout disconnection program
with the goal of disconnecting 95 percent of those in the HSSD in 1982. Also in
keeping with the study's innovative recommendation, some restrictors were installed in
catch basins. Unfortunately, most were removed because of plugging and
maintenance problems (Donohue, 1982b, p. 18).
Study Completed in 1978 Recommending Deep and Shallow Tunnels and Relief
Sewers
The entire Skokie CSS was the target of another study, this one conducted by Harza
Engineering Company (1978). As with the 1973 study, this investigation was carried
out with the understanding that TARP would eventually be a reality and, therefore,
provide an improved outlet for Skokie's CSS. The following summary is provided by
Donohue (1982b, pp. 18-19):
This study analyzed the combined sewer
system in the Village of Skokie and reviewed
alternative ways to improve the system
performance and mitigate existing problems.
The study related that the lateral sewers,
characteristically about two blocks long with a
maximum diameter of 18 inches, would have
sufficient capacity such that backups in
basements would occur only about once in 25
years if the downstream branch sewers were
adequate to handle the lateral sewer
discharges. These existing branch sewers,
however, have about one-half of the capacity
needed to convey the flow which the lateral
sewers can deliver. The large trunk sewers
into which the branch sewers flow have less
than one-half of the capacity required to
convey the flow from the branch and lateral
sewers. Thus, the overall sewer system
capacity decreases drastically in a downstream
direction causing a flow constraint and
resulting in under utilization of the upstream
features of the sewer system.
Mitigation concepts that were investigated
included homeowner protection devices,
reduced rate of stormwater runoff into the
sewer system, separate storm sewer systems,
and increased capacity of the existing sewers.
2- 17
-------
The report recommended that the Village
proceed with a program to increase the
capacity of the existing sewers. This increased
capacity would be accomplished by
construction of a system of deep and shallow
tunnels connecting to the MSDGC main stream
tunnel system. Installation of some parallel
branch sewers to convey additional flow to the
tunnel system was also recommended. This
system was sized to provide conveyance
capacity for runoff from a 10-year frequency
storm with Phase I of TARP in place and
functioning. The 1978 cost estimate for these
improvements was $78 million (Note: The 1999
cost would be $168 million using the ENR
CCI). None of the improvements have been
constructed.
Study Completed in 1981 Providing Additional Insight Into System Inadequacies
The MSDGC (now the MWRDGC) studied the performance of the ESSD after two
summer of 1981 storms caused basement and street flooding (Paintal, 1981). This
investigation, as summarized in the following Donohue description (1982b, pp. 19-21),
characterizes the capacity problems in and other aspects of the CSS:
The MSDGC completed a study analyzing the
performance of the Emerson Street Sewer
District during two heavy storms that occurred
over the Skokie area in the months of July and
August 1981. These storms produced runoff
rates which exceeded the capacity of the local
sewer system resulting in street and basement
flooding. The purpose of this study was to
analyze those storms relative to the capacity of
the Emerson Street sewer system. This
system is a 1,740 acre area in the northern
part of the Village of Skokie and is fairly similar
in structure to the Howard Street system. The
study analyzed the following:
• The frequency of the July 12 and
August 14, 1981 storms.
• The sensitivity to flooding of the local
2- 18
-------
sewer system relative to the water
level elevation in the North Shore
Channel.
• The ejects of downspout
disconnection and house flood
control-pumping systems on lateral
sewer flows.
Although this analysis was performed on the
Emerson Street District, most of the results and
conclusions are pertinent to the Howard Street
Sewer District and are summarized as follows:
• Submergence of the sewer outlet at
the North Shore Channel does not
affect the sewer capacity
significantly if the water level in the
channel does not rise above
elevation 5+/- Chicago City Datum.
• The storms of July 12 and August 14
had a frequency of recurrence of
once in 40 years and once in five
years, respectively. The Emerson
Street sewer, had it been designed
for a five-year storm, would have
adequate capacity to handle the
flows generated by the above
storms. The Lawler Avenue sewer
(a local lateral similar to the laterals
in the Howard Street District), had it
been designed for a two-year storm,
would have conveyed the flows
generated by these storms.
• In order to negotiate the storms, the
Emerson Street sewer should have a
capacity of 1 to 1.2 cubic feet per
second (cfs) per acre in comparison
to the actual capacity of 0.13 to 0.2
cfs per acre. The capacity of the
sewer is about one-fifth of what was
required.
• Had the sewer been of adequate
capacity, the flow at the outlet would
2- 19
-------
have been 1,600 cfs from its service
area of 1,740 acres. That is equal to
0.92 cfs per acre. It is noted that
TARP (Phase I) is designed for 1.0
cfs per acre drainage intensity.
• The results of an analysis of the
Lawler Avenue (south) sewer to
study the effect of downspout
disconnection and individual house
flood control pumping systems on
the performance of the sewer system
indicated that:
> For short duration storms the
disconnection of downspouts
from the sewer system reduces
the flow in the sewer
significantly if the flow from the
downspouts is directed to lawns
and other porous areas.
> The flood control pumping
system protects the house but
overloads the sewer system due
to pumping during periods of
peak flow and wet weather. If
every house in the area has this
kind of system, the pumpage
alone will account for about 50
percent of sewer capacity
depending on the size of the
lateral sewer.
Additional analyses were completed in an
addendum to this report. The addendum
reviewed the effect that TARP - Phase I would
have in reducing sewer surcharging particularly
in the lower reaches of the Emerson Street
District. This analysis concluded, had TARP -
Phase I been in place during the July 12, 1981
storm, sewer surcharging and basement
flooding would have been eliminated or
considerably reduced within about 10 percent
2-20
-------
or 170 acres of the Emerson Street sewer
service area which is near the sewer outfall at
the North Shore Channel. A similar reduction
in surcharging would be felt in the Howard
Street Sewer District with TARP - Phase I
completed. The actual reduction in number of
basements flooded will be somewhat less in
the Howard Street district since development
nearest the North Shore Channel is
predominately industrial and commercial with
no basements.
Study Completed in 1981 Suggesting Combinations of Traditional and Innovative
Measures
Harza Engineering Company, which had completed a system wide study in 1978, was
called on again to explore options (Harza, 1981). Now the principal stimulus for another
study was greatly reduced probability of USEPA funding. The following summary is
provided by Donohue (1982b, pp. 21-22):
Harza Engineering Company completed a
supplemental study of flood control alternatives
in 1981. This was a follow-up to their 1978
report which recommended implementation of
a system of relief sewers that would connect to
the Metropolitan Sanitary District of Greater
Chicago's main tunnel under the North Shore
Channel. Implementation of the relief sewers
was predicated on a significant amount of
funding coming from the USEPA. Since
funding from the USEPA was no longer
probable, this supplemental study was
undertaken to identify solutions that could be
implemented without federal aid.
2-21
-------
Alternatives discussed in the study were
grouped into conveyance, flood protection,
inlet control, and combinations of these
concepts. The conveyance concepts included
relief tunnels and sewers (estimated cost of
$160 million for 10-year capacity), separate
sewers (estimated cost of $120 million), and
sewer lining (not adequate alone). Flood
protection consisted of individual flood
protection devices such as overhead sewers
(estimated cost of $75 million). The review of
inlet control looked at some typical depths of
street flooding that would be anticipated if inlet
controls were installed at the inlets without
significant subsurface or other off-street
storage. The cost of inlet controls alone,
without storage, was estimated at $2 million.
Combinations of the above were packaged to
provide alternatives with the best features of
each single approach to maximize benefits for
targeted expenditure levels. Various
combinations of inlet controls with storage and
conveyance improvements were estimated to
range as high as $60 million (Note: The 1999
cost of the separate storm sewers would be
$203 million using the ENR CCI. This is
consistent with earlier IEPA (Park, 1990)
estimates).
Study Completed in 1982 Recommending a Street Storage System
Skokie retained Donohue and Associates in January 1982 to undertake a preliminary
engineering study of what was then called runoff control but, for purposes of this case
study manual and as explained in Chapter 1, is referred to as a street storage system.
The HSSD was selected for this preliminary engineering project as an initial study area.
Included in the scope of services for this project, which was completed in July 1982,
were data inventory, hydrologic-hydraulic modeling, development of alternatives with
cost estimates, and implementation recommendations (Donohue, 1982a, 1982b).
As the preliminary engineering project proceeded, nine alternatives were created for the
HSSD. They ranged from flow regulators only to various combinations of flow
regulators, underground storage and relief sewers. All alternatives "...were intended to
minimize sewer backup into basements and maximize utilization of available street
flooding capacity" (Donohue, 1982b, p. 3). This was the first time that utilization of
street storage was the sole basis for solving Skokie's basement flooding problem. The
series of previously discussed studies had evolved to the point where the innovative,
2-22
-------
lower cost, street storage concept was explored in detail. The idea was to focus on the
cause of CSS surcharging, that is, stormwater runoff, and explore ways to intentionally
store stormwater on streets in a controlled fashion. Traditional approaches were, at
least for the duration of this preliminary engineering study, held in abeyance.
The recommended street storage system consisted of approximately 1200 flow
regulators, 24 supplemental storage facilities, and a relief sewer. (The constructed
project required only 10 supplemental storage facilities). The storage and sewer
facilities were sized, in this preliminary engineering study, for a 10-year recurrence
interval storm. Flow regulators would range in location and function from modification
of existing inlet grates to orifice type or energy dissipating type flow regulators installed
in the sewer lines leading from catch basins or inlets to the sewer system.
Storage facilities were recommended for all areas where street ponding would exceed
the depth at which damage to adjacent private property could occur. This below street
or off-site storage will reduce street ponding depths to just below damaging levels.
The estimated mid-1982 construction cost for the recommended HSSD street storage
system was $11,220,000. This cost was much less than the cost of traditional
approaches and, as a result, was attractive to community decision makers.
Opportunities to improve the cost-effectiveness of the design and reduce the total
construction cost would be available as more detailed designs were prepared.
Additional maintenance costs associated with the recommended street storage system
were projected to be minimal.
A pilot program was recommended during the design and initial construction phase of
implementation. The pilot program would evaluate various types of flow regulating
devices and assess their operational aspects and maintenance requirements.
A monitoring program was recommended to evaluate the existing uncontrolled system
and the performance of the pilot street storage system. The following five types of data
collection and analyses were recommended: rainfall, sewer flow, street ponding, depth
in storage facilities, and foundation drainage flow.
Unlike the recommendations in previous studies, the preceding recommendations were
implemented. The commitment to finally take action was probably due to a combination
of growing severity of the basement flooding problem and the promised low cost of the
street storage system. The gradual, successful implementation of the
recommendations in the preliminary engineering study, led to more recommendations
which were in turn implemented. As of 1999, the street storage system has been
almost completely implemented throughout the 8.6 square mile community. And, as
explained in Chapter 9, the system performs very well. The details of the planning,
design, testing, construction, financing and operation of the Skokie street storage
system are presented in the remainder of this manual.
Observations Regarding the Studies to Solve Skokie's Combined Sewer System
Basement Flooding Problem
2-23
-------
The Skokie experience in conducting a series of studies to solve its basement flooding
problem contain ideas that can be advantageously transferred to other communities.
Consider the three observations discussed here.
Occurrence of a Series of Evolving Studies
In an attempt to solve its growing basement flooding problem, Skokie commissioned or
conducted a series of seven evolutionary studies over a period of 15 years. This
pattern of serial, evolutionary studies is common in the public works environment.
The evolutionary nature of the Skokie studies is readily illustrated. For example, the
1967 study recommended relief sewers whereas the 1973 study, informed by the
MSDGC's adoption of TARP, recommended tunnels that could connect to the TARP
system. Recognizing that USEPA funding was probably no longer available, the 1981
study explored more innovative, low cost options, including street storage.
The study-no action, study-no action, etc. pattern is especially characteristic of wet
weather problems. This is caused by the random, episodic nature of such problems.
One or more damaging episodes occur, adversely affected citizens express concern,
and community officials take action by initiating a study. By the time the study is
completed and recommendations made, the intensity of interest in solving the problem
has diminished, especially in light of implementation costs. In contrast with the random,
episodic nature of CSS, SSS, stormwater system and other wet weather problems,
most public service problems persist or at least are much less episodic, until solved.
Examples are deteriorating streets, poorly performing schools, deteriorating quality of
water supply, and inadequate police protection.
Initial Focus on Traditional Solutions
Most of the earlier studies considered and recommended traditional solutions to
Skokie's basement flooding problem. Examples are relief sewers and tunnels.
Widespread consideration of—but not necessarily recommendation of—innovative
options was stimulated by lack of external funding. Reductions in or limitations of
financial resources encourages creativity.
Gradual Recognition of the Water Pollution Control Purpose of TARP
The series of studies and the improved understanding of TARP gradually led to the
realization that while the massive, expensive TARP would mitigate CSOs it would have
minimal impact on the basement flooding problem. For example, the MSDGC's 1981
study concluded that basement flooding would have been eliminated in less than 10
percent of Skokie buildings had TARP been in place during the two summer 1981
storms. Unless something was done, post-TARP Skokie would still have a massive
basement flooding problem because of its CSS.
2-24
-------
Description of Wilmette, IL
A description of Wilmette, IL is presented as a basis for understanding the case
studies. Less detail is provided for Wilmette than for the previously described Skokie,
for three reasons. First, some of what applies to Skokie also applies to Wilmette given
that the latter is contiguous with and north of the latter. Second, more background
information is needed for the much larger and longer duration Skokie project because it
is emphasized in this case study manual. Third, less background documentation is
available for Wilmette.
Location
As indicated on Figure 2-1, the Village of Wilmette is contiguous with and immediately
north of Skokie. Figure 2-7 is a map of Wilmette showing major features. Besides
being bounded on the south by Skokie and Evanston, Wilmette is bounded on the west
by Glenview, on the north by Kenilworth and Northfield and on the east by Lake
Michigan. The North Shore Channel, which as previously noted forms the east
boundary of Skokie, passes through an eastern extremity of Wilmette before
discharging into Lake Michigan. As also is the case in Skokie, the North Shore
Channel, or more specifically, land paralleling it is an amenity for Wilmette. These
lands include a public golf course and Gillson Park.
Relationship to the Metropolitan Water Reclammation District of Greater Chicago
Combined sewers serve the 2.0 square mile portion of Wilmette lying east of Ridge
Road. Note that this CSS area is slightly less than one fourth of the CSS area in
Skokie. The rest of Wilmette, which lies west of Ridge Road, is served by a separate
sewer system (Loucks and Morgan, 1995). The Wilmette description presented in the
remainder of this section applies primarily to the CSS area.
Wilmette's CSS lies in the service area of the MWRDGC. Combined sewers generally
flow eastward. Connections to MWRDGC interceptors occur in the central portion of
the CSS along Green Bay Road and on the east end of the CSS along Sheridan Road
and the North Shore Channel. The Wilmette CSS is connected to TARP via two drop
shafts along the North Shore Channel (SEC Donohue, December 1992, pp. 4-5). The
initial CSS did not contain many trunk sewers because of the large number, relative to
Skokie, of connections to MWRDGC interceptors.
2-25
-------
Isabella S tteetr
ViDage Ld
Figure 2-7. Map of a portion of Wilmette, IL served by combined sewer system.
2-26
-------
Land Use and Population
Approximately 80 percent of the fully developed Wilmette CSS is occupied by single
family residences. The remainder is commercial and multiple family dwelling units. The
2.0 square mile CSS has a population of 11,300 and contains approximately 3500
buildings. The overall population density is 9 people per acre and the population
density in residential areas is about 11 people per acre. To reiterate, the area is
completely developed (SEC Donohue, December 1992, p. 4).
Note that the Wilmette and Skokie CSSs are similar when compared on the basis of
type and intensity of land use. Each is fully developed, about 80 percent single family
residential, and has an overall density of about 10 people per acre (Skokie: 11,
Wilmette: 9).
Topography and Drainage Patterns
As noted earlier, the general drainage direction within the Wilmette CSS is eastward.
Longitudinal street slopes are very flat. For example, 364 street segments within the
CSS having a total length of 36.2 miles were examined. A street segment would
typically be one block in length. Because of traffic volume, safety considerations or
steep longitudinal slopes, 24% of the streets were determined to be not suitable for
street storage. However, of the remaining 76% of street segments, 66% had
longitudinal slopes of less than 0.25% (0.25 feet per 100 feet), 21% had longitudinal
slopes of 0.25% to 0.50%, and only 13% had longitudinal slopes in excess of 0.50%
(SEC Donohue, June, 1992, pp. 12-16).
One way in which Wilmette differs from Skokie is the presence of some brick streets.
Of the 26.2 lineal miles of streets available for street storage, 50% are constructed of
brick, 48% of asphalt, and 2% of concrete (SEC Donohue, June, 1992, p. 15). Figure
2-8 shows one of Wilmette's brick streets. They are highly valued because of their
appearance. The brick streets were fully incorporated into the street storage system
without compromising their aesthetic values. For example, a mid-block berm is shown
on Figure 2-8.
The CSS contains about 33 miles of sewers that vary from eight to 72 inches in
diameter. Smaller sewers—less than 30 inches in diameter—are generally formed of
clay tile while the sewers larger than 48 inches in diameter are made of reinforced
concrete. Combined sewers in the 30 to 48 inch diameter range could be clay or
concrete. No combined sewers are constructed of brick (SEC Donohue, December,
1992, p. 4).
2-27
-------
Figure 2-8. Brick streets account for half of the street length in Wilmette targeted for
street storage.
2-28
-------
Brief History of Wilmette with Emphasis on Development of Its Drainage System
Partly as a result of the Chicago fire of 1871, the population of what is now Wilmette
increased to over 300 which was the number required for incorporation. Wilmette was
incorporated in 1872 and its first water and sewer systems were built in 1893-94. The
combined sewer system, which was the accepted type of sewer system at that time,
discharged into Lake Michigan.
As noted earlier, Wilmette, contrasted with Skokie, originally did not contain many trunk
sewers because of numerous connections to MWRDGC interceptors. The entire
system was generally under capacity. Relief sewers were constructed prior to 1960, but
they were also undersized.
This discharge location and the shape of the Wilmette lakefront changed in the 1908 to
1910 period with construction of the North Shore Channel and the interceptor system.
Spoil from the channel construction was used to create a landfill, north of the North
Shore Channel, which is now Gillson Park. Therefore, Wilmette, like Skokie and many
other Chicago area communities, made a major historic commitment to combined
sewers and they proved to be undersized.
Wilmette's Historic Combined Sewer System Basement Flooding and Peak
Discharge Problem
Like Skokie, Wilmette had a long-standing, widespread basement flooding in its CSS.
SEC Donohue (December, 1992, p. 2) provides this description:
The combined sewer area of the Village of
Wilmette... experiences basement flooding
during moderate and heavy rainfalls. A
postcard survey conducted following a heavy
rain in August 1989 reported that nearly 800
buildings (23%) in the combined sewer area
were flooded during this storm. More recent
community surveys indicate that a substantially
greater number of homes are actually
impacted. These surveys indicate that over
60% of the buildings in the combined sewer
area have been affected by basement flooding
at one time or another.
A subsequent report by Rust (November, 1993, p. 1) reports the preceding and notes
that, besides property damage, flooding of basements with combined sewage exposes
residents to health problems. According to this report, basement and street flooding
problems "...occur regularly every one to two years during intense rain storms." The
2-29
-------
report also notes that, as a result of uncontrolled street flooding, emergency vehicles
have been delayed during storms.
As Wilmette sought a solution to its basement and street flooding problem in the early
1990's, it also had to resolve a related problem. As explained by Loucks and Morgan
(1995), Wilmette needed to reduce the peak discharge from its sewer system:
...to facilities of the MWRDGC. The MWRDGC
is responsible for transportation, treatment and
eventual discharge of sewage flows in
Wilmette and 185 other communities.
Approval from MWRDGC is required for all
system modifications and new discharge
connections. Projects consisting only of relief
sewers are generally unacceptable. Hydraulic
simulations were used to demonstrate a
reduction of 28 percent in the peak discharge
from the village. A maximum total peak
release rate was negotiated with MWRDGC
which serves as a constraint on the system
design.
Reduction in peak flow from the CSS, which was not an issue in the planning and early
design of the Skokie street storage system, was a factor in the planning and design of
the Wilmette system. The added value achieved in Wilmette is significant. It points to
the potential for a street storage system to serve other functions such as reducing peak
flows in interceptor sewers and at WWTFs.
Previous Studies of Ways to Solve Wilmette's Combined Sewer System Problems
Several studies were carried out in the early 1990's. Key studies are briefly described
here as an explanation of how and why Wilmette decided to implement a street storage
system in its 2.0 square mile CSS.
Study Completed in 1991 Recommending Relief Sewers
According to SEC Donohue (June, 1992, p. 5), RJN Environmental Associates, Inc.
completed a facility plan for Wilmette in 1991. Focusing on solving the basement
flooding problem, the plan "...recommended construction of combined relief sewers to
increase the existing combined sewer system capacity to transport a 10-year storm
event without surcharging." The estimated 1991 construction cost was $65,000,000.
The 1999 cost would be $81 million using the ENR CCI.
Value Engineering Study Completed in 1992 Recommending Street Storage
2-30
-------
Donohue & Associates, Inc. and Lewis & Zimmerman Associates, Inc. were retained by
Wilmette to participate in a value engineering study of the previous study (SEC
Donohue, June 1992, p. 5; SEC Donohue, December 1992, p. 2). Completed in
January 1992, the value engineering study concluded that what is defined as street
storage in this report "...appeared to offer a higher level of protection against basement
flooding at a cost of $46,000,000 or substantially less than the $65,000,000
recommended in the RJN facility plan."
Study Completed in 1992 Recommending Street Storage
Wilmette retained Donohue & Associates in March of 1992 to "...determine the
technical and economic feasibility of using runoff control techniques such as temporary
street ponding to relieve basement flooding problems in the east side areas" (SEC
Donohue, June 1992, p. 5). The scope of services for this project was similar to that of
the preliminary engineering study completed by Donohue for Skokie in 1982.
Completed in June 1992, the study concluded that "...a stormwater runoff control
program consisting of temporary street ponding along with relief sewers will provide a
cost-effective level of protection against basement flooding in the combined sewer area
east of Ridge Road" (SEC Donohue, June 1992, p. 1). The report went on to point out
significant potential cost savings over the previously recommended conventional relief
sewer system. More specifically, the report stated:
The estimated cost for a system of temporary
street ponding berms and relief sewers which
provide full protection against basement
flooding and dedicated runoff storage capacity
for a 10-year event is $28,000,000. ... The
estimated cost of the 10-year ...capacity runoff
control program ...is substantially less than the
$65,000,000 10-year capacity combined relief
sewer alternative recommended in the 1991
RJN facility plan.
Study Completed in 1992 Recommending Refined Street Storage
Wilmette commissioned SEC Donohue (formerly Donohue & Associates) to conduct
this preliminary engineering study based on the favorable findings of the previous
feasibility study. One change in approach was to use a more sophisticated hydrologic-
hydraulic model. The USEPA Stormwater Management Model (SWMM) was now used
rather than the Illinois Urban Drainage Area Simulator (ILLUDAS). The principal
purpose of SWMM was to represent the dynamics of flow in the system, that is, to
rigorously simulate surcharging and backwater effects and the interaction between
sewer flows and storage. Also used for the first time in Wilmette was SEC Donohue's
2-31
-------
Surface and Street Analysis Model (SASAM). It simulated on-street conveyance and
storage of stormwater (SEC Donohue, December 1992, pp. 8-9).
This refined study concluded that a system of street storage and relief sewers could
control the 10-year storm for a construction cost of $31,000,000. The 1999 cost would
be $37 million using the ENR CCI. Thus, this refined study essentially confirmed the
preceding study (SEC Donohue, December 1992, p. 9). Details of additional planning,
design, financing and construction of the Wilmette street storage system are presented
in the remainder of this manual.
Observations Regarding Studies to Solve Wilmette's Combined Sewer System
Problems
As with Skokie, a series of studies led to the decision to implement street storage in
Wilmette's CSS. Also like Skokie, some of what was learned in the process of
conducting the studies might be transferable to other communities faced with CSS
problems. Two observations based on Wilmette's experience are essentially the same
as the first two of the three observations presented earlier based on Skokie's
experience. They are:
• Occurrence of a series of evolving studies prior to making a commitment.
• Initial focus on traditional solutions.
Wilmette's studies differed from Skokie's in one way: they sought to solve flooding while
also reducing the peak discharge from the Wilmette CSS to the MWRDGC system.
This gave added impetus, as the studies proceeded, to exploring means to temporarily
store stormwater for gradual release. Relief sewers alone would not suffice.
wp/epastch2
2-32
-------
CHAPTER 3
THE CONCEPT THROUGH CONSTRUCTION PROCESS
FOR
STREET STORAGE SYSTEMS
Status of Urban Stormwater Management
As briefly noted in Chapter 1, the street storage system mitigates surcharging of CSSs
by managing stormwater—by reducing peak rates of stormwater before it enters the
combined sewer system. Accordingly, a brief review of the status of urban stormwater
management, with emphasis on detention, that is, temporary storage of stormwater, is
appropriate. The following review is taken from Walesh (1989, pp. 20-31) and other
sources as indicated.
Two Fundamentally Different Approaches: Conveyance-Oriented and
Storage-Oriented
The state of the art of stormwater management has evolved to the point where there
are two fundamentally different approaches to controlling the quantity, and to some
extent the quality, of stormwater runoff. Using a "before and after" format. Figure 3-1
illustrates selected characteristics of the two available approaches.
Conveyance-Oriented Approach
The first to the two approaches is the more traditional conveyance-oriented stormwater
system. Systems designed in accordance with this approach provide for the collection
of stormwater runoff, followed by the immediate and rapid conveyance of the
stormwater from the collection area to the discharge point to minimize damage and
disruption within the collection area. Principal components of conveyance-oriented
stormwater systems are culverts, storm sewers, and channels supplemented with inlets
and catch basins.
3-1
-------
Figure 3-1. Conveyance and storage approaches to stormwater management
(Source: Walesh, 1989, p. 26).
3-2
-------
A potentially effective, newer approach to stormwater control is the storage-oriented
system. Its function is to provide for the temporary storage of stormwater runoff at or
near the point of origin, with subsequent slow release to downstream storm sewers or
channels. This approach minimizes damage and disruption both within and
downstream of the site. One or more storage facilities are the principal elements in a
storage-oriented system. These principal elements are often supplemented with
conveyance facilities, such as culverts, storm sewers, inlets, and catch basins, which
transport stormwater to storage facilities and gradually convey flow from those facilities.
Comparison of Features
A principal advantage of the traditional conveyance-oriented approach is applicability to
both existing and newly developing urban areas, contrasted with the storage-oriented
approach. Storage is more difficult to retrofit into already developed areas because of
space limitations. Although retrofitting storage into developed areas is difficult, it is not
impossible and it is sometimes cost effective as clearly demonstrated by the Skokie and
Wilmette projects.
Other advantages of the conveyance-oriented approach are rapid removal of
stormwater from the service area, minimal operation and maintenance requirements
and costs, and accepted analysis and design procedures. Principal advantages of the
storage-oriented approach are possible cost reductions in newly developing urban
areas, prevention of downstream adverse flooding and pollution associated with
stormwater runoff, and potential for multiple-purpose uses.
Neither the conveyance-oriented approach nor the storage-oriented approach is
inherently better. Both approaches should be considered, at least when a project or
development is at the conceptual level.
The conveyance- and storage-oriented approaches to stormwater management are not
necessarily mutually exclusive within the same hydrologic-hydraulic system. Depending
on the circumstances, the two approaches may be compatible and integrated use of the
two approaches may lead to a more optimum stormwater management system. One
example of the joint use of the conveyance-oriented facilities in one portion of a
watershed and storage-oriented facilities in another portion. Another example of the
combined use of the two approaches is to use conveyance-oriented facilities for the
convenience system and storage-oriented facilities for the emergency system. The
later approach is illustrated by the Skokie and Wilmette projects where the preexisting
combined sewers are the convenience system and new street surface storage and
underground tank storage constitute the emergency system. The convenience (minor)
and emergency (major) systems are discussed in a later section of this chapter.
Historic Development of the Storage-Oriented Approach
3-3
-------
Understanding of the status of stormwater management is informed by its history.
Furthermore, to the extent that contemporary use of storage sometimes targets both
the quantity and quality of stormwater, that history is very relevant to street storage and
possible implication of street storage for control of nonpoint source pollutants. The
following historical account is based on Walesh (1989, pp. 29-31) and other cited
sources.
The original motivation for using the newer storage-oriented approach over the
traditional conveyance-oriented approach was that the former offered cost advantages.
Most documented examples of the cost advantage of the storage-oriented approach
over the conveyance-oriented approach relate to newly developing areas (e.g.,
Poertner, 1974). More recently, however, there have been situations in which already
developed areas are being retrofitted with a storage-oriented system at significantly less
cost than that of a traditional conveyance-oriented system. Examples include the
Skokie and Wilmette projects.
A complete comparison of conveyance-oriented and storage-oriented systems for a
particular location must consider all costs and benefits, tangible and intangible. For
example, reduction in developable land and possible safety hazards to children with the
storage-oriented system are costs, while increased land values for areas contiguous to
attractive storage facilities are a benefit. Cost analyses must be conducted on a
case-be-case basis. Documented case studies and experience suggest that storage
facilities should be at least considered for controlling the quantity of stormwater runoff
because of the potential for cost savings.
After initial use of storage facilities for the single purpose of controlling the quantity of
stormwater runoff, storage facilities found increased use as multiple-purpose
developments. In addition to their primary surface water control function, storage
facilities were designed to provide, or be part of, sites for recreation including such
activities as fishing, boating, tennis, jogging, ski touring, sledding, and field sports.
Well-planned, well-designed, and well-operated storage facilities were also found to
have aesthetic value for contiguous and nearby residential areas.
In addition to the obvious erosion and sedimentation problems often associated with
urbanization, studies conducted in the 1970's indicated that urban stormwater runoff
contributes a significant part of some of the pollutants finding their way to surface
waters. For example, an early study conducted in Durham, NC, compared the quality of
urban runoff with that of secondary municipal sewage treatment effluent on the basis of
weight per unit area per year (Colston, 1974). On an annual basis, the urban runoff
contributed 91 percent of the chemical oxygen demand, 89 percent of ultimate
biochemical oxygen demand, and 99 percent of the suspended solids.
Many measures were suggested for controlling urban area nonpoint-source pollution in
general and erosion and sedimentation in particular. The use of storage was one of
these measures. The state of the art of using storage facilities to control the quality of
urban stormwater runoff is still under development.
3-4
-------
In summary, storage facilities are being increasingly used for controlling the quantity of
runoff because of the cost advantages and because of their recreation and aesthetic
values. They are also being increasingly designed to accomplish a third function of
controlling the quality of stormwater runoff.
The evolution of using the storage-oriented approach in surface water management is
summarized in Figure 3-2. Beginning with the single quantity control function, storage
facilities have evolved so that they now can serve three compatible functions: quantity
control; recreation, aesthetic, and other supplemental uses; and quality control.
Street storage systems, which make heavy use of storage, have served the quantity
control function as demonstrated by the Skokie and Wilmette applications. Street
storage also has the potential to serve the quality control function relative to nonpoint
source pollution. This possibility is discussed in Chapter 11.
Emergency and Convenience Systems
The increasingly accepted emergency and convenience system approach to
stormwater management is an integral part of the street storage approach.
Accordingly, a brief overview of the emergency-convenience system is provided. This
overview is taken from Walesh (1989, pp. 31-34) and other cited sources.
The stormwater system may be thought of as two systems, one functionally and
physically superimposed on the other. One system, the convenience or "minor" system,
contains components that accommodate frequent, small runoff events. The other
system, the emergency or "major" or overflow system, consists of components that
control infrequent but major runoff events. Although many of the components are
common to both the convenience and emergency system, their relative importance in
the two systems varies significantly.
The Convenience (Minor) System
Stormwater systems have traditionally been designed to convey all the design runoff
without street flooding, parking lot or other ponding, or basement backup associated
with frequent, small runoff events—up to about the five- or 10-year recurrence
interval—from an urban area with no damage and little or no disruption or even
3-5
-------
AESTHETIC,
AMP
Figure 3-2. Historic development and use of storage facilities for stormwater
management in the U.S. (Source: Walesh, 1989, p. 31).
3-6
-------
unimportant.
The Emergency (Major or Overflow) System
Major runoff events—such as 50- or 100-year recurrence interval events—will also
inevitably occur in urban areas. Accordingly, some stormwater control systems are
designed to control major event runoff rates and volumes in such a manner that
although temporary disruptions and inconvenience will occur, widespread danger and
damage will be avoided. This is accomplished by allowing for temporary storage and
conveyance of stormwater on parking lots and streets, within public open space areas,
and in other suitable low-lying areas; by establishing building grades well above street
grades; and by designing streets and roadways to serve as open channels providing for
the temporary storage and conveyance of runoff as it moves through the urban area
toward a safe discharge point.
The emergency system is sometimes called the major system because it is designed to
control runoff from "major" rainfall events. Sometimes the emergency system is
referred to as the overflow system because it is the system that begins to function when
the capacity of the convenience system is exceeded and it overflows.
Most surface water control systems, however, are not explicitly designed to
accommodate major runoff events. Nevertheless, major runoff events occur and the
emergency system will, by default, function during such events with sometimes
catastrophic damage and disruption.
Combined Convenience and Emergency System
The ideal surface stormwater system is planned and designed to include both the
emergency and convenience systems in anticipation of the inevitable occurrence of
both major and minor runoff events. In a combination system, essentially complete
control of minor runoff events is achieved to minimize disruption and damage during
smaller, frequently occurring rainfall events. Emergency components of the system are
designed to accept some temporary disruption and inconvenience during relatively
infrequent events. Jones (1967) provided a very readable and convincing early
explanation of the convenience-emergency system concept.
Figure 3-3 illustrates the emergency and convenience system concept applied to a
typical urban street cross section. This is essentially the manner in which the
emergency system appears in the street storage system described in this report. The
variation is that with street storage system, the receiving sewer is a combined
sewer—not a separate storm sewer. Figure 3-4 illustrates the emergency and
convenience system applied to a channel-floodplain passing through an urban area.
Components in the stormwater system can be examined from the perspective of
whether or not they function, how they function, and the relative importance of their
3-7
-------
functioning under both convenience and emergency conditions. Consider, for example,
stormwater inlets located along the curbs and gutters of urban streets. For minor runoff
events, such inlets are normally designed to pass essentially all the discharge conveyed
to them, but under major events they should be expected to intercept only a small
portion of the flow moving along the gutter. Thus, whereas inlets are key elements in a
convenience system, they are of little importance in an emergency system.
Note, however, that catch basins—inlets with sumps—are of great importance in the
Skokie and Wilmette street storage systems. Their operation is not left to chance.
Flow regulators are installed in the catch basins.
Streets are graded longitudinally and laterally to provide, during minor runoff events, for
rapid runoff of stormwater to curbs and inlets or to roadside ditches. During major
events, however, the longitudinal slope of the streets and the relative elevation of the
streets and contiguous residences and commercial and industrial structures must be
designed such that the street functions as a large, paved open channel or reservoir
which temporarily conveys or stores stormwater runoff. Thus, whereas the street is one
of many components in a surface water system during minor runoff events, it becomes
a key element in the surface water system during major events.
Streets are certainly key elements in the street storage systems described in this report.
However, unlike the situation in the design of new development, the basic topography
of the streets and contiguous areas is already defined. It provides a physical constraint
within which the street storage system must be designed. That design includes some
refinements in the topography in the form of street berms.
3-8
-------
CONVENIENCE
SYSTEM OPetZATIWG
EMEEGrENICY
SYSTEM OPEEATTIKlCt
Figure 3-3. Emergency and convenience system applied to an urban street
(Source: Walesh, 1989, p. 33).
FLOOPPLAIW
C.ONJVEWIEWCE (MIWOE)
SYSTEM OPERATlKJOr
"SVSTeM
Figure 3-4. Emergency and convenience system applied along a channel and
floodplain (Source: Walesh, 1989, p. 33).
3-9
-------
Stormwater storage facilities have, as described in the preceding section, proven to be
technically sound, economically attractive, and environmentally acceptable elements in
urban stormwater management systems. However, they have been used primarily as
preventive measures in newly developing areas in contrast with use as remedial
measures in developed areas.
Widespread, frequent—one or more times per year—basement flooding is common in
existing, old, and intensely developed urban areas, served by CSSs. Traditional and
proven remedial measures to CSS basement and surface flooding problems include, as
noted in Chapter 1, separation and in-system storage of combined sewage.
A fundamentally different alternative to remedying combined sewer surcharging and
surface flooding is retrofitting the existing system to include storage. More specifically,
it is feasible under certain conditions to implement a carefully engineered system of
surface and sub-surface storage facilities to control the rate at which stormwater flows
into the combined sewer system so it does not exceed the capacity of the existing
sewers, thereby mitigating basement and other flooding.
The largely implemented Skokie and Wilmette projects have demonstrated the
technical and economic feasibility of retrofitting stormwater storage into CSSs.
Furthermore, retrofitted stormwater storage can also have other benefits such as
reducing peak flows of combined sewage to regional wastewater agencies, mitigating
inflow to SSSs, solving flooding problems in separate sewer systems, and managing
nonpoint source pollution.
Retrofitting is not limited to CSSs. It can also be applied to the stormwater portion of
separate sewer systems for purposes such as improving quantity and/or quality control,
reducing safety hazards and enhancing recreation facilities and aesthetic values.
Retrofitting stormwater facilities has been explored by and reported on by Walesh
(1991, 1992, 1993 and 1998).
Distinction Between Analysis and Design: Diagnosis and Then Prescription
An important integrating theme of this chapter is describing, using mainly case studies,
tools and techniques for analyzing the root causes of problems in CSSs and
designing solutions to these problems. A medical analogy helps to appreciate the
difference between analysis and design. Analysis in engineering, like diagnosis in
medicine, strives to get beyond symptoms. In medicine, symptoms may be a fever or
pain. In CSSs, symptoms may be flooded basements or overflows into surface waters.
In both medicine and engineering, symptoms may appear to be problems or, in fact, be
problems to those who are adversely affected, but they are not the root causes. In
medicine, the cause of fever may be an infection and in engineering the cause of a
symptom like basement flooding may be inadequate flow carrying capacity of selected
sections of combined sewers.
3-10
-------
Once the medical diagnosis or engineering analysis has gotten beyond symptoms to
causes, remedies or solutions can be explored. Medical doctors prescribe solutions
and engineers design solutions.
Walesh (1989, p. 317) elaborates on this two step analysis and design, or diagnosis
and prescription, process. His discussion is directly applicable to CSSs. Two
fundamental questions must be addressed in all but the most trivial CSSs. First, how
does the existing system function, that is, what is the cause or what are the causes of
the CSS problems such as basement flooding, surface flooding and CSOs? This, the
problem definition phase, must use but look way beyond and below symptoms such as
the number of basements flooding, the location of street inundation, and the frequency
of overflows. The first step, that is, the analysis or diagnosis phase, focuses on finding
causes. A clear understanding of the cause of a problem tends to lead to its solution.
The second fundamental question is: How can the CSS be modified or altered to
eliminate or mitigate the causes of the problems and to prevent similar or new problems
from occurring in the future? The process of answering this question may be called
design or prescription.
Why the emphasis on the two part analysis and design, or diagnosis and prescription
process? Answer: CSSs are complex and there is a tendency to rush to judgement as
to causes so that a community can "get on" with implementing solutions. Furthermore,
there is also a pattern, as shown by the Skokie and Wilmette studies discussed in
Chapter 2, to favor, if not exclusively consider, traditional solutions to CSS problems.
Superficial analyses combined with a predisposition to employ traditional solutions can
lead to unnecessarily costly solutions to CSS problems.
Ideas and information presented in this chapter are intended to show the long term
value of a careful, deliberate, multi-faceted (e.g., monitoring, computer modeling, pilot
studies) analysis and design process. The "pay off" for a community can be a
cost-effective solution to its CSS problems.
Chronological Mode of Presentation
The remainder of this chapter is structured in a chronological fashion. Using Skokie,
Wilmette and, occasionally other communities, the steps that may be needed to
implement a street storage system are described in the approximate order they would
occur. Figure 3-5 illustrates the overall process. The description begins with the
understanding of the concept of a street storage system and concludes with
3-11
-------
Study the concept
of a street storage system
I
Apply screening criteria
to determine
likely applicability
of a street storage system
Street
storage likely
to be
applicabl
Select
an initial
pilot or
implementation
area within
the CSS
I
Explore other
solutions
Figure 3-5 (1 of 2). Successful application of a street storage system requires
a systematic analysis and design process that begins with understanding the
concept and concludes with construction.
3-12
-------
i
Establish performance
criteria
1
I
Analyze existing
system and
perform preliminary
engineering using
computer models
1
Analyze existing
system using
monitoring
Street
storage likely
to be
applicable
Explore other
options
Review flow regulator
availability and
performance
Complete design of
street storage
system
Construct street
storage system
Figure 3-5 (2 of 2). Successful application of a street storage system requires a
systematic analysis and design process that begins with understanding the concept
and concludes with construction.
3-13
-------
constructing the system.
All of the steps followed in Skokie, the first large scale application of street storage, are
not likely to be needed in other communities. For example, the laboratory and field
testing of various flow regulators that was necessary for the Skokie project would
probably not be needed in other applications. However, the Skokie laboratory and field
testing is fully described here so that the process and especially the results are
available for possible use by others.
The Concept of Street Storage
Fundamental to understanding the street storage system concept is appreciating the
capacity of urban streets to carry and store stormwater. Accordingly, this section begins
with discussions of the flow capacity and the storage capacity of an urban street.
Figure 3-6 shows one photograph of a typical asphalt covered street in Skokie and a
typical brick street in Wilmette. These photographs suggest the potential stormwater
conveyance and storage functions of urban streets.
Conveyance Capacity of Urban Streets
Urban streets can be a vital element in the previously described emergency stormwater
system by conveying stormwater to a safe discharge point during a major rainfall-runoff
event. The Manning open channel flow equation is available for calculating depth
versus discharge relationships for urban streets.
Street Cross Sections
Some Skokie street cross sections, including the adjacent parkway, sidewalk and lawn
up to the street side of residences, are shown in Figure 3-7. A typical half cross section
of a street, based in part on the configurations of the actual street cross sections shown
in Figure 3-7, is presented in Figure 3-8. Longitudinal slopes, S0, of 0.1, 1.0, and 3.0
percent are assumed for the subsequent analysis.
Analysis Procedure
The objective is to determine, assuming normal depth, the flow capacity of the street
cross section for a range of depths and a range of longitudinal slopes. The total flow in
the half section can be determined as the sum of the flow in subsection A of Figure 3-8,
the street portion of the cross section, and subsection B, the lawn portion of the cross
section. With this approach, the Manning equation becomes
-------
Figure 3-6. The photographs of urban streets in Skokie (top) and Wilmette (bottom)
suggest their potential stormwater conveyance and storage function.
3-15
-------
Figure 3-7. Selected street cross sections from Skokie, IL (Source: Donohue,
1982b, p. 65)
3-16
-------
PATUM ——J
Figure 3-8. Typical street and lawn cross section representative of actual Skokie
cross sections (Source: Walesh, 1989, p. 191).
3-17
-------
J
= 1.495o°'5
\ UA nB }
where Q^ = discharge in subsection A
QB = discharge in subsection 6
S0 = longitudinal slope for both subsections (dimensionless)
AA = flow cross-section area in subsection A
RA = hydraulic radius for subsection A = AA /PA, where PA = the wetted
perimeter
nA = Manning roughness coefficient for subsection A
AB = flow cross-sectional area in subsection 6
RB = hydraulic radius for subsection 6 = AB /PB, where PB = the wetted
perimeter
nB = Manning roughness coefficient for subsection 6
Assume the depth of flow at the gutter of 0.5 ft. Then
AA = (0.5)(0.5)(20) = 5ft2
PA = 0.5+ (202 + 0.52)°'5 = 20.5ft
= 0.244 ft
(5x02442/3)
= L495.0'5 V ; + 0 =
Substituting SO = 0.1, 1.0, and 3.0 percent yields half-street discharges of 7.1, 22.4,
and 38.8 ft3/sec, respectively. The corresponding average velocities are, 1.42, 4.48,
and 7.76 ft/sec, respectively. The preceding process is repeated for depths at the
gutter of 1.0 and 2. Oft.
Results
Depth versus discharge relationships for the complete street cross section, including
adjacent lawns, are summarized in graphic form in Figure 3-9. A separate curve is
presented for each of the three longitudinal slopes.
3-18
-------
111
u.
Figure 3-9. Depth versus discharge relationships for typical street and lawn cross
sections (Source: Walesh, 1989, p. 192).
3-19
-------
The analysis indicates that streets can carry very large flows relative to typical storm
sewers at similar slopes. For example, consider the case with a depth at the gutter of
1.0 ft. For the three longitudinal slopes, flows on the full width of street and adjacent
lawn areas are approximately 14 to 18 times greater than those that would be carried in
a 24-inch diameter reinforced-concrete pipe laid at the same slope and flowing full.
The preceding analysis suggests that better use could be made of streets by designing
them to be channels that function as part of the emergency stormwater system. Using
streets for temporary stormwater conveyance is one aspect of the street storage
system.
Storage Capacity of Urban Streets
Urban streets can also constitute a vital element in the emergency stormwater system
by temporarily storing stormwater until it can be safely discharged to storm or combined
sewers. Actual street cross sections shown in Figure 3-7 suggest the volume of storage
available.
Analysis Procedure
Consider again the typical street cross section presented in Figure 3-8 and cross
sectional areas calculated and presented in the previous section titled "Conveyance
Capacity of Urban Streets." A plan view of a typical single-family residential area with
paved streets and curb and gutter is shown in Figure 3-10.
Consider the east half of the 600-ft-long section of Easy Street and the directly tributary
area of 67,500 ft2. The runoff coefficient for the area is 0.5; that is, half of the rainfall on
the total tributary area is directed toward the east half of Easy Street.
Assuming that the street has a zero longitudinal slope, the cross-sectional area of the
east side of the street and cumulative storage on the east side of the street may be
calculated as a function of depth of water relative to the gutter. Results are presented
in Table 3-1 and Figure 3-11. The depth versus volume relationship for the east side of
the 600-ft-long street has a shape similar to the depth versus volume relationship for a
natural river valley. That is, as depth increases, the relative volume of incremental
storage per unit of depth increases at least over the first one foot of depth.
Assume rainfall amounts of 0.5, 1.0, 2.0, and 4.0 in., which may be typical of moderate
to very severe rainfall events. Assuming that half of the rainfall is directed to and
remains in the street, the depth versus storage relationship presented in Figure 3-11
can be used to determine the depth of ponded water or each rainfall amount. The
results are presented in Table 3-2.
3-20
-------
/
/
/
/
/
/
/
f
/
/
/
/
/
/
/
/
/
/
/
I
/
/
//
Figure 3-10. Typical urban street plan showing the area tributary to the east side
of a one block segment of Easy Street (Source: Walesh, 1989, p. 193).
3-21
-------
Table 3-1. Depth, cross-sectional area, and cumulative volume data for half of Easy
Street (Source: Walesh, 1989, p. 194).
Depth at
Gutter (ft)
0.0
0.5
1.0
2.0
Cross-Sectional Area
on East Side of Street
(ft3)
0.0
5.0
18.33
65.00
Cumulative Storage on East
Side of Street1
(ft3)
0
3,000
11,000
39,000
(acre-ft)
0
0.07
0.25
0.90
1) for600-ft. street segment and assuming zero longitudinal grade.
Table 3-2. Rainfall and depth of ponding for Easy Street1 (Source: Walesh, 1989, p.
194).
Rainfall
(in.)
0.50
1.00
2.00
4.00
Runoff
(in.)
0.25
0.50
1.00
2.00
(ft3)
1,410
2,810
5,625
11,250
Depth of Ponding
in Street Relative
to Gutter (ft.)
0.30
0.45
0.75
1.00
1) Assumes zero longitudinal grade.
3-22
-------
2,0 -,
Figure 3-11. Depth versus volume relationship for Easy Street and lawn cross
section (Source: Walesh, 1989, p. 194).
3-23
-------
Results
As indicated, even with four inches of rainfall, and assuming that two inches of runoff is
stored in the street, the peak depth of street ponding relative to the gutter would be one
foot.
The simple analysis suggests that streets with low longitudinal grades have the capacity
to store large volumes of stormwater runoff. Situations may arise where new streets
can be designed to store stormwater, or existing streets can be retrofitted to serve a
storage function as part of the emergency system. The latter retrofitting idea is one
aspect of the street storage system.
Using Street Storage and Conveyance Capacity in Combined Sewer Systems
Attention now turns to CSSs. As briefly noted in Chapter 1, wet weather problems in
CSSs, such as basement flooding, street flooding, and CSOs, are caused by peak rates
of stormwater runoff, not necessarily by the runoff volumes. Midwestern experience
suggests that wet weather flooding and pollution problems would often not occur, or
would be much less severe, if the peak flows of stormwater could be lessened. Peak
flows are often the principal culprit, not the volumes of stormwater runoff.
This suggests a fundamentally different approach having the following premise: reduce
the peak flow rates of stormwater before it enters the combined sewer system. Accept
the full volume of stormwater into the stormwater runoff into the CSS, but greatly
reduce the peak rate of entry. Figure 3-12 illustrates, in conceptual fashion, this
stormwater-oriented approach to reducing surcharging in CSS and, therefore, mitigating
flooding and pollution.
But where and how can stormwater runoff be temporarily stored and otherwise
controlled to reduce peak flows into the CSS? Urban streets have significant storage
and conveyance capacity, as just illustrated, in this chapter. That storage capacity and
conveyance capacity can be effectively utilized to answer the question of where and
how to temporarily store stormwater.
Because of their storage capacity, some streets can be used to temporarily store
stormwater before it mixes with sanitary sewage and surcharges the CSS. Because of
their conveyance capacity, other streets can be used to convey stormwater from street
segments with low surface storage capacity to street segments with high surface
storage capacity. Streets in effect become a rectilinear conveyance and storage
system that are activated under emergency conditions, that is, when the capacity on
one or more segments of the CSS is exceeded.
3-24
-------
Dry Weather
Inlet/Catchbasin
Turf, Concrete,
Asphalt Surface
Combined
Sewer
Surcharged
Wet Weather without
Stormwater Control
Inlet/Catchbasin
Turf, Concrete,
Asphalt Surface
Combined
Sewer
Is
Surcharged
Wet Weather with
Stormwater Control
Temporary
Storage
Inlet/Catchbasin
•- -' accept flow rates
(mostly Stormwater) -;-".v
the sewer
Turf, Concrete,
Asphalt Surface
Combined
••' Sewer
Figure 3-12. Control of peak rates of Stormwater runoff can, in concept, mitigate
surcharging of combined sewer systems.
5-25
-------
Bringing the Street Storage Concept to Reality: Berms, Flow Regulators, and
Subsurface Storage
Capitalizing on street storage and conveyance capacity requires three elements that
operate in a integrated fashion. These elements are berms, flow regulators and
subsurface tanks. In this section, first berms and then regulators are described. Their
integrated function is then explained. Finally, subsurface storage facilities, which also
use regulators, are discussed.
Berms
Berms Contrasted With Bumps and Humps
A berm is a low structure constructed across a street, from curb to curb, and intended
to temporarily impound water on its upstream side. The crest or top of the berm, when
viewed along the longitudinal axis of the street, is horizontal. It is, in effect, a spillway.
Figure 3-13 is a photograph of a mid-block berm in Skokie. The berm is identified by
the asphalt overlay. A berm that lies across a Skokie intersection is shown in Figure
3-14. This berm may also be identified by the asphalt overlay. A berm under
construction is shown in Figure 3-15. The construction process typically consists of:
Relocating inlets, if needed.
Raising the curb and gutter, which has been done in Figure 3-15.
Milling the street surface. The concrete has been milled in Figure 3-15.
Placing lifts of asphalt to form the berm. At least one lift has been placed
in Figure 3-15.
The term berm was selected early in the Skokie street storage project to distinguish it
from bumps and humps, two established types of vehicle speed control devices. The
essential features of bumps, humps and berms are illustrated in Figure 3-16.
According to the Institute of Transportation Engineers (1997, p. 1):
3-26
-------
Direct the flow
of stormwater
Figure 3-13. Mid-block berm in Skokie intended to direct the flow of stormwater
runoff.
5-27
-------
Temporarily
store
stormwater
Figure 3-14. Berm across an intersection in Skokie.
3-28
-------
Figure 3-15. A berm under construction in Skokie showing relocated inlet, raised curb
and gutter, milled concrete surface and an asphalt lift.
3-29
-------
Bump
3» . 4
Purpose: Low Speed
Control
Berm
Hump
., 1 3"-4" ,.
12' '
Purpose: Intermediate
Speed
Control
32'
Purpose: Stormwater Control
Figure 3-16. Bumps and humps are vehicle control devices and the gentler berm
is a stormwater control device.
3-30
-------
of three to six inches with a length (in the
direction of vehicle movement) of one to three
feet. Speed bumps are typically found on
private roadways and parking lots and do not
tend to exhibit consistent design parameters
from one installation to another... A bump
causes significant driver discomfort at typical
residential speeds and generally results in
vehicles slowing to five mph or less at the
bump.
Also, according to the ITE (1997, p. 1):
A speed hump is a raised area in the roadway
pavement surface extending transversely
across the travel way... speed humps normally
have a maximum height of three to four inches
with a travel length of approximately 12 feet...
Within typical residential speed ranges, humps
create a gentle vehicle rocking motion that
causes some driver discomfort and results in
most vehicles slowing to 15 mph or less at
each hump and 25 to 30 mph between
properly spaced humps in a system.
Some speed humps have a flat top, that is, a plateau shape with gradual approaches
on both ends. This configuration tends to protect long wheel base vehicles like fire
trucks (Velazquez, 1992). Recognizing that speed humps control vehicle speeds
without the presence of police personnel, the humps have been called "sleeping
policemen" (ITE, 1997, p. 1).
In the interest of more fully understanding speed humps, consider their benefits and
drawbacks, as noted by Elizer (1996), and Haynes (1998). Some of these positive and
negative features can also be applied to berms when they are viewed from a vehicular
perspective.
Principal speed hump benefits are:
1. Reduced vehicle speeds.
2. Less accidents.
3-31
-------
3. Diversion of traffic to more desirable routes; for example, from a local
street being used as a short cut to an arterial street.
4. Less traffic noise with the possible exception of more noise from trucks.
5. Less air quality impact and energy use than stop signs.
6. Support by most local residents.
Some speed hump drawbacks include:
1. Undesired traffic diversions; for example, from arterial to local streets.
2. Interference with the rapid response of police, firefighters, paramedics
and other emergency vehicles.
3. Negative aesthetic impact of humps and related signs and markings.
4. Concern with street sweeping and plowing, ice formation and other
maintenance and repair functions.
5. Fear of increased liability exposure attributed to claims of vehicle damage
and injury to bicyclists.
6. Poor design and construction resulting from the misperception that humps
are simple. ITE (1997) provides detailed design guidance.
Given the possible benefits and drawbacks to speed humps, some municipalities have
taken a systematic approach to optimize their use. During the 1994 to 1997 period, 217
people were killed in automobile crashes in Montgomery County (Haynes, 1998).
Accordingly, the county installed more than 1000 humps on 300 residential streets as a
partial solution to the excessive number of automobile accidents. Thousand Oaks, CA,
which is one of the first U.S. cities to use speed humps, installed them and studied their
effects. Their conclusion: if the hump is more than two inches high, drivers will seek
alternate routes (Velazquez, 1992). Boulder, CO addressed the issue of interference
with emergency vehicles by banning speed humps on emergency routes (Haynes,
1998).
Berms: The Negative Perception Problem
The suggestion of building structures across streets to control stormwater often elicits
negative reactions, especially from engineers and other personnel responsible for the
design, construction and maintenance of streets. The driving public may also express
concern. One way to deal with this is to note that across street structures are
commonly used in urban areas to control the speed of vehicles. For example, ITE
(1997, p. 5) provides a "partial listing of jurisdictions with speed hump experience" in the
United States and Canada. Included in the partial list are 52 communities in 17 states
and three provinces. (ITE (1997, p. 5) also notes that speed humps are also used in at
least 14 countries outside of the U.S. In other words, humps, engineered cross-street
structures, are widely used in the transportation field.
Note that a berm has a much gentler slope than a hump in the direction of travel.
3-32
-------
Accordingly, berms cause even less discomfort than humps. Clearly, berms are vastly
different than bumps when measured in terms of driver discomfort.
The Possibility of Integrating Stormwater Berms and Speed Hump
Functions
Although the berms, as used extensively in Skokie and Wilmette, differ markedly in
function from the humps used widely in traffic control, berms and humps are very
similar in form. This suggests that traffic engineers and other personnel responsible for
urban streets should be receptive to the idea of using berms to control stormwater. In
fact, the convergence of the stormwater berm and the speed hump suggests the
possibility of retrofitting existing urban areas with these simple structures for the dual
purposes of stormwater and traffic control. Going one step further, convergence of the
form and function of berms and humps opens the possibility of designing these
structures into new urban development to optimize stormwater and traffic management.
The previously mentioned ITE (1997) document is described as a recommended
practice of the ITE. Interestingly, the only mention of stormwater in this document is a
brief caution to not interfere with drainage. More specifically, ITE (1997, p. 20) states:
Speed humps should be installed with
appropriate provisions made for roadway
drainage... Ideally, a hump should be installed
immediately on the downside of an existing
drain inlet. If this is not feasible the
construction of a bypass drain or other
treatment to route water around the hump
should be considered.
On the more positive side, and in keeping with the idea integrating stormwater
berms/speed hump structures into new development, ITE notes that speed humps
could be designed into new streets. The guidelines state (ITE, 1997, p. 27):
It is desirable in the planning of new residential
subdivisions to configure and design local
streets to minimize excessive speed, excessive
volumes, and cut-through traffic from outside
the immediate neighborhood. However, where
adequate subdivision planning and street
design control cannot be achieved, and one of
the aforementioned problems is considered
likely, it may be appropriate to include speed
humps as part of new street construction after
consideration of less restrictive design or traffic
3-33
-------
control techniques.
Flow Regulators
For purposes of this manual, a flow regulator is a passive, gravity device that regulates
the flow of stormwater into a combined sewer. Because it restricts flow, a flow regulator
must be designed in combination with storage which is usually located immediately
upstream.
Donohue (March 1984a, p. 3-1) identifies three common features of flow regulators:
A common feature of flow regulators is that
they are gravity devices operating without
external energy sources or external control.
That Is, they are Intended to be simple devices
requiring no control and minimal attention.
A second characteristic shared by most flow
regulators Is that they are designed and
installed to achieve the desired flow reduction
while minimizing the likelihood of blockage by
debris relative to that which could occur with a
conventional orifice. Some flow regulators
result in less flow passing the control section
for a given head or head range than would
occur with a simple orifice.
A third feature of flow regulators is the need to
specify three parameters for design. The first
parameter is the maximum discharge and the
second parameter Is the corresponding design
head. The third parameter is installation
requirements such as available space and
expected orientation of the device.
Many flow regulators have been developed and tested. A discussion of the
configuration and performance of various flow regulators appears later in this chapter.
For the purposes of this section, flow regulators are viewed as a generic device having
the preceding three features.
As further explained by Donohue (March 1984a, p. 3-1), "flow regulators may be
installed in a variety of locations in an urban stormwater-wastewater system including:
in storm inlets and catch basins to cause temporary ponding on streets or in depressed
3-34
-------
areas; at the outlets of subsurface and surface detention facilities to induce temporary
subsurface and surface storage; and within ...sewers to utilize available in-system
storage."
The meaning of the terms inlet and catch basin, as used for example in the preceding
paragraph, are important for purposes of this report. As explained by Donohue (March
1984a, p. 3-1):
Inlets collect runoff from the land surface and
discharge via a pipe. Inlets do not have a
sump. That Is, the discharge pipe Is at the
bottom of the inlet. Catch basins receive flow
from inlets and, occasionally, directly from the
land surface and discharge to the sewer
system. Catch basins have a sump created by
the outlet pipe being several feet above the
bottom of the basin. This sump serves to trap
leaves and other debris and requires periodic
removal and cleaning.
A typical Skokie configuration of an inlet, a catch basin and a manhole on a combined
sewer is shown in Figure 3-17. The configuration is shown in plan and section. Note
that, in a properly operating system, the transition from stormwater runoff to combined
sewage occurs in the pipe connecting the catch basin to the manhole. A trap, as
shown in Figure 3-17, is required to prevent sewer gases from being a problem near the
catch basins.
Figure 3-18 uses a flow regulator installed in a catch basin to illustrate the regulator's
function. Comparison of the two head-discharge relationships indicates that for any
given head on the catch basin outlet, the flow regulator results in significantly less flow
out of the catch basin. This flow restriction or reduction must be accomplished without
blocking of the flow regulator with debris carried by the stormwater.
Although the function of a flow regulator is illustrated in Figure 3-18 using a catch basin
installation, flow regulators can be installed in other places. Example locations, as
noted earlier, are in stormwater inlets and at the outlets of surface and subsurface
storage facilities.
3-35
-------
SIDEWALK
CATCH
BASIN
TV
INLET
-CURB
- COMBINED SEWER
e. >STREET
MANHOLE
PLAN
SIDEWALK
CATCH
BASIN CURB-
MANHOLE
/ \
_JZ.
^cr-— ^
SECTION
COMBINED
SEWER
Figure 3-17. Typical configuration of an inlet, catch basin and manhole in the Skokie
combined sewer system (Source: Donohue, March, 1984a, p. 3-2).
3-36
-------
Head
Street
Catch Basin
Outlet Pipe to
Combined Sewer
I1
Inflow Pipe
from Inlet
Static
Level
Discharge
Figure 3-18. A flow regulator installed in a catch basin illustrates the basic function
of the regulator.
3-37
-------
In Wilmette's CSS, a pair of special catch basins were constructed immediately
upstream of beams and fitted with flow regulators. These catch basins were connected
to a single new manhole on the adjacent combined sewer. In some cases, as
described in the Chapter 9 section titled "Summary of Interviews with Wilmette, IL
Officials," shear gate flow regulators were placed at the downstream end of pipes
connecting the catch basins to the combined sewer manholes.
In summary, suitable catch basins and manholes already existed in Skokie and the
catch basins needed only to be fitted with flow regulators. Existing inlets often had to
be moved or new ones installed. In Wilmette, new catch basins, which also served as
inlets, had to be constructed as did new manholes on the adjacent combined sewer.
Combined Function of Berms and Flow Regulators.
Functioning together, berms and flow regulators become, in what more traditional
stormwater management is called, an outlet works. The berm-flow regulator
combination, like the outlet works on a traditional stormwater detention basin, is sized
and configured to temporarily store stormwater to achieve a desired attenuation of the
stormwater runoff hydrograph.
Figure 3-19 shows how a berm on a street and a flow regulator in a catch basin cause
temporary ponding of water on the street during and immediately after a runoff event.
During and immediately after the event, the peak flow from the catch basin is limited, by
the design of the flow regulator and the berm, to what can be conveyed by the receiving
combined sewer without surcharging. After, the event, the temporarily stored water
drains by gravity through the catch basin.
Figure 3-20 takes the description of the combined function of berms and flow regulators
one step further. Shown here is a hypothetical profile, with great vertical exaggeration,
along the longitudinal axis of a street. Berms and flow regulators (the flow regulators
are not shown) are strategically placed to take advantage of the storage capacity along
the length of the street. Low points, which are also storage areas, are used with peak
outflow of stormwater to the CSS also being governed by flow regulators.
Recall the earlier brief discussion of a common adverse reaction to constructing berms
across streets. This was answered, in part, by noting that stormwater berms have even
less impact on vehicles than do the engineered and widely used speed humps.
A similar negative reaction is frequently expressed in response to the suggestion of
intentionally storing stormwater on streets. Experiences in Skokie, Wilmette and
elsewhere indicate that this initial objection may be offset by offering the following three
points for consideration:
-------
of
Controlled
to
Combined
Sewer
Catch
Note: Not to scale and great vertical exaggeration
Figure 3-19. Longitudinal profile of a street showing how a berm and flow regulator
function as the outlet works of a temporary street storage facility (Source: Adapted
from Loucks and Morgan, 1995).
3-39
-------
ROADWAY BERMS
PEAK STAGE
NOTE: GREATLY EXAGGERATED VERTICAL SCALE
Figure 3-20. Strategic placement of berms and flow regulators along a street
facilitates use of the street's capacity to temporarily and in a controlled fashion
store stormwater.
3-40
-------
Urban Streets often flood anyway, especially in flat topography typical of
CSSs. That flooding is unintentional, uncontrolled and unexpected and
can cause damage and excessive disruption of vehicular traffic as
indicated by the upper portion of Figure 3-21.
Stormwater "flooding" in the street storage system is controlled, that is,
the peak stage and lateral extent are predetermined by the design of
berms and flow regulators. The idea of street temporary controlled
storage of stormwater is illustrated in the lower portion of Figure 3-21.
The goal is to prevent damage to adjacent properties and not
unnecessarily disrupt vehicular traffic.
Controlled stormwater on streets is much preferred over uncontrolled
combined sewage in basements.
Shown in Figure 3-22 are photographs of actual street storage in Skokie and Wilmette.
Note that the ponding is shallow, does not prevent vehicular movement, and is
contained within the public right-of-way.
Subsurface Storage
Subsurface storage facilities are expensive, but sometimes necessary, components of
a street storage system. They are used for temporary storage of stormwater beneath
those streets and parking lots where the required surface storage would cause damage.
Subsurface storage is used only where absolutely needed because of the typical high
cost per unit volume of storage. Accordingly, street storage systems will typically have
very few subsurface storage facilities relative to on-street and other surface facilities.
Skokie's 8.6 square mile street storage system, for example, contains only 83
subsurface storage facilities compared to 871 berms and 2,900 flow regulators.
Figure 3-23 illustrates the function of subsurface storage. The facility lies within the
public right-of-way and is positioned above the combined sewer. Its outlet is controlled
by a flow regulator. Stormwater, not combined sewage, is temporarily stored in the
facility.
Actual subsurface storage facilities range from simple to complex configurations
depending on the volume of storage required and site constraints. Some facilities are
simply oversized lengths of storm sewer while others are large rectangular structures
extending the length of a block and the width of the street. An example of the latter is
illustrated in Figure 3-24. Shown is the construction of a subsurface storage facility
composed of precast, reinforced concrete sections.
3-41
-------
Unintentional, uncontrolled and
unexpected surface flooding
J L
Temporary, controlled surface ponding
within street right-of-ways
Figure 3-21. The street storage approach uses temporary, controlled ponding of
stormwater in contrast with the common unintentional, uncontrolled and unexpected
ponding resulting in damage and vehicular interference.
3-42
-------
Figure 3-22. Actual street ponding in Skokie (top) and Wilmette (bottom).
3-43
-------
Combined
Sewer
Flow
Regulator
Reinforced
Concrete Box
Dry Weather
Combined
Sewer
" Flow
Regulator
Reinforced
Concrete Box
Wet Weather
Figure 3-23. Subsurface storage facilities are positioned within the right of way, above
the combined sewer and temporarily stored stormwater, not combined sewage.
3-44
-------
**%
Figure 3-24. Subsurface storage facilities range from simple oversized lengths
of storm sewer to, as shown here, large structures assembled from precast
reinforced concrete sections.
3-45
-------
Apply Screening Criteria to Determine Likely Applicability of A Street Storage
System
Refer to the section in Chapter 10 titled "Criteria for Screening the Applicability of Street
Storage." The screening criteria are based largely on ideas and information presented
in this report, that is, the criteria reflects experience with the successful implementation
of street storage systems. Included in the previously noted section of Chapter 10 are
an explanation of the purpose of the screening criteria, comments about the
qualifications of evaluators, reference to the actual criteria which are presented in
Appendix B, suggestions for interpreting the information.
Select an Initial Pilot or Implementation Area Within the Combined Sewer System
Need for Phased Implementation
Traditional public works projects, such as streets and highways, wastewater collection
and treatment, and water supply treatment and distribution, are often implemented in a
phased manner. Budgetary constraints are usually the reason for prioritization and
phasing. That is, there is a need to spread capital costs over a period of years so that
they match revenues.
Phasing means prioritization. If costs are the principal reason for phasing, then a
phased public works project begins with the most cost-effective component. However,
other factors can establish priorities including physical constraints, regulatory
compliance, and political considerations.
When non-traditional approaches, such as street storage, are an integral part of a
public works project, another important reason arises for phasing. That reason is the
need to be cautious as the new technology is gradually conceptualized, planned,
designed, tested, refined, understood, and accepted. Phased implementation was
heavily used in the Skokie street storage project because it is the first large scale
application of the street storage system in the U.S.
The key to effective phasing is selection of the first or pilot implementation area. The
purpose of this section of the chapter is to offer suggestions, based on the Skokie,
Wilmette and other experiences, on factors to consider in selecting the physical area for
the first phase of a street storage project and then prioritizing subsequent phases.
Prioritization Factors
Many factors could be weighed in selecting an initial implementation area and
prioritizing subsequent areas. Factors to use and their relative weights will depend on a
given community's physical, regulatory, and socio-economic situation. In picking an
initial implementation area or the next area in order of decreasing priority, consider
3-46
-------
selecting an area that:
Includes a complete drainage system or watershed. The analysis and
design process requires, for any point in the system, consideration of all
significant conveyance and storage components upstream of that point.
The entire 1255 acre HSSD, one of three combined sewer districts in
Skokie, was selected as the initial area. It is a CSS watershed that
discharges to the interceptor sewer system of the MWRDGC. While
selecting a head water portion of this sewer district would have been
acceptable, choosing a middle or lower portion of the district would conflict
with this factor.
Best satisfies the screening criteria for street storage. These criteria are
introduced in the preceding section of this chapter, elaborated on in
Chapter 10, and attached as Appendix B.
Has a high concentration of basement flooding or other problems. By
using this approach, and assuming implementation proceeds through
construction, the selected area is likely to be very cost effective. That is,
the ratio of problems solved to dollars expended should be higher than if
other areas with less concentrated problems are selected.
Reflects stakeholder input. An advisory committee of stakeholders might
be formed to help select the initial implementation area. Stakeholder
groups to be represented on the advisory committee might include
homeowners, business people, educators, environmentalists, and
regulators. Technical and other support should be provided by the
community possibly with the assistance of their engineering consultant. In
Skokie, the HSSD was selected by the community and then a consulting
engineering firm was retained (Donohue, 1982a, p. 11).
Has characteristics typical of other areas. Skokie, for example, selected
portions of four streets covering approximately ten blocks within the HSSD
for testing of flow regulators. The referenced pilot study is discussed in
detail later in this chapter. One requirement for the testing of flow
regulators was that the selected areas have a number of inlets and catch
basins per unit area approximating that of the HSSD. In addition, street
cross sections and widths in the selected areas were to be representative
of the HSSD (Donohue, 1984a, pp. 3-13, 3-14). As further suggested by
this Skokie example, use of one or more small pilot study areas within the
overall initial implementation area may be prudent.
Offers cost or other advantages if quick action is taken. As an example of
this opportunity factor, one of several candidate CSS drainage areas may
be slated for near future street resurfacing. Given that street geometry is
3-47
-------
critical to street storage, that CSS drainage area may be the logical place
to begin implementation of street storage.
Establish Performance Criteria
Need for Performance Criteria: Analysis and Design
Before a CSS can be diagnosed, that is, analyzed to determine the cause of problems,
the desired performance must be defined. The desired performance serves as the
benchmark against which the severity of CSS problems and the nature of their causes
can be measured.
Likewise, the prescription of solutions to a CSS's problems, that is, planning and
design, cannot be undertaken until the desired performance of the CSS is defined.
Variation in Performance Criteria
Presented in this section of the chapter are examples of performance criteria used in
the Skokie and Wilmette and other street storage systems. While there are some
commonalities, the presented performance criteria show significant variations. This is
to be expected for the following three reasons:
1. The street storage technology is relatively new and, therefore, rapidly
evolving. Something learned in one project, or one phase of a given
project, may change the performance criteria for the next project, or next
phase of a given project.
2. Special circumstances. For example, a community with many tree-lined
streets is likely to include in their performance criteria provisions intended
to protect that amenity.
3. Different level of service expectations. Some communities have higher
expectations for the level of public services that they receive and are
willing to pay for.
Performance criteria presented here are not necessarily recommended for other
communities. Rather, they are offered as examples of what some communities have
developed to be consistent with their familiarity with the street storage technology, their
special circumstances and their level of service expectations. Each community
contemplating use of the street storage system should formulate their own performance
criteria, possibly using the criteria presented here as a guideline.
Skokie Performance Criteria
3-48
-------
Performance criteria for Skokie's street storage system were first formulated in 1982 as
part of the preliminary engineering for the HSSD (Donohue, 1982a, p. 5-1). They were
slightly modified as part of a refinement of the HSSD preliminary engineering
(Donohue, 1984, pp. 5-1, 5-2), the preliminary engineering for the MSSD (Donohue,
1987b, pp. 6-1, 6-2) and the preliminary engineering for the Emerson and Lake Streets
Sewer District (Donohue, 1987a, pp. 5-1, 5-2). These criteria changed relatively little
during this five year preliminary engineering period. Therefore, the performance criteria
for the Emerson and Lake Streets are presented here as being representative of the
Skokie approach.
The explicitly documented Skokie performance criteria may be summarized as follows:
1. The street storage system should be designed for the 10-year recurrence
interval storm.
2. Reduce surcharging of sewers to prevent sewage backup caused by
overloading of the municipal sewer system. The preliminary design of the
alternatives is developed with the concept of defining maximum
stormwater runoff rate into the sewers while preventing damaging sewer
surcharging.
3. Make utilization of available street ponding capacity without causing flood
damage to adjacent private development. Berms are to be used to detain
stormwater on upland streets.
4. Minimize ponding on state and county highways. Stormwater ponding is
discouraged on such streets. In locations where street storage on nearby
streets could increase ponding depth on or near state and county
highways, roadway berms are to be use to prevent ponding on the state or
county highways. Storage facilities or relief sewers are to be used in
no-pond areas to accommodate stormwater in excess of sewer capacity.
5. Establish maximum permissible flood stage for each street on a
block-by-block basis. This stage, referred to as the "critical" elevation, is
the highest stage which can be tolerated on the block without incurring
flood damage such as first floor flooding and the flow of surface water
through windows into basements or into below grade garages. In most
cases the sidewalk elevation at the lowest point in the block is the critical
elevation.
6. Confine temporarily stored stormwater within the right-of-way during the
10-year recurrence interval design storm. Right-of-way typically extends
from the back of the sidewalk on one side of the street to the back of the
3-49
-------
sidewalk on the other side. Limit the maximum depth of ponding for the
10-year storm to the lesser of six inches at the street centerline or nine
inches at the gutter invert.
7. TARP Phase I provides a discharge point that will carry the stormwater
runoff from a 10-year recurrence interval storm.
8. A gravity operated stormwater system is preferred to a pumped system.
Minimal use of electrical and mechanical controls and equipment is
desirable. A simple gravity operated system reduces the likelihood of
failure and minimizes future operation and maintenance costs.
9. Storage of excess runoff should be accomplished first in off-street areas,
second on streets, and last in underground storage facilities. Park and
private property may also be considered assuming proper arrangements
can be made.
10. Downspouts from one and two family residences are assumed to be
disconnected from the CSS and to discharge to the land surface or storm
sewer system in all street storage areas and in all areas without street
storage but having storm sewers and/or stormwater storage facilities.
Industrial, commercial and multi-family buildings and any buildings with
internal drainage systems are excluded from this assumption.
Wilmette Performance Criteria
The explicitly documented performance criteria for Wilmette's street storage system
may be summarized as follows:
1. "Alleviate basement flooding for the 10-year frequency storm event" (Rust,
November 1993, p. 1).
2. "Reduce private property flooding (outside of the Village right-of-way) for
the 10-year frequency storm event" (Rust, 1993, p. 1).
3. "Limit inconvenience to residents in accessing their property during major
rainfall events" (SEC Donohue, December 1992, p. 7).
4. Confine street storage to public right-of-way (SEC Donohue, June 1992,
p. 6).
5. Limit ponding depths to a maximum of six inches on the crown of a street
and a maximum 12 inches above the gutter invert. Allow no ponding on
sidewalks (SEC Donohue, June 1992, p. 7).
6. Exclude designated streets or street segments from ponding. These
3-50
-------
streets were selected based on high traffic volume and/or proximity to
schools, places of business, and access to or from elderly housing or fire
and police stations (SEC Donohue, June 1992, pp. 7-8).
7. Generally consider berms only on streets with flat longitudinal
grades—0.5% or less (SEC Donohue, June 1992, p. 16).
8. "Limit inconvenience to the community during the construction process"
(SEC Donohue, December, 1992, p. 7).
9. "Limit increases in hydraulic loading on the North Shore Channel" (SEC
Donohue, December 1992, p. 7).
10. "Limit increases in pollutant loading on the North Shore Channel" (SEC
Donohue, December 1992, p. 7).
11. Limit peak flow discharged to TARP to the negotiated rate for the 10-year
design rainfall events (Morgan, 1999).
Although not documented in the available Wilmette reports (SEC Donohue, June 1992;
SEC Donohue, December 1992; and Rust, November 1993) other important
performance criteria, in addition to the preceding list, were apparently applied in
Wilmette. These seem to include the previously presented Skokie performance criteria
8, 9 and 10.
Analyze Existing System Using Monitoring
The suggested systematic analysis and design process for a street storage system
should include, as shown in Figure 3-5, monitoring data. That data may already exist
from previous studies, may be collected as part of a special monitoring effort, or be a
combination of the two. Regardless of data origin, the data should be used in parallel
with the previous described computer modeling. Ideally, iteration should occur between
modeling and monitoring as suggested by the dashed two-way arrow in Figure 3-5.
For example, monitoring data should be used to calibrate hydrologic-hydraulic models.
Initial modeling results should be used to identify gaps in the monitoring program. See
Walesh (1989, Chapter 10) for a detailed discussion of the interplay between modeling
and monitoring. Both Skokie and Wilmette used monitoring during the analysis and
preliminary engineering process. Their efforts are described in the following sections.
Skokie Monitoring
This summary of the initial monitoring program is taken from Walesh and Schoeffmann
(1984). The monitoring program was conducted in 1983 to:
Better define the behavior of the existing CSS.
3-51
-------
Provide baseline information to evaluate the performance of the street
storage system, which would eventually be implemented.
Provide data for refinement of the ongoing computer modeling effort.
An overriding consideration was selection of equipment, training of Skokie personnel,
and installation of equipment in such a fashion that it could be moved to other sewer
districts, after one or more years of service in the HSSD.
A 41 unit monitoring system was installed. It consisted of three rainfall monitoring
stations; nine sewer flow monitoring stations with bottle racks installed at all nine
monitoring stations and continuous monitors installed in six of the stations; 20 street
ponding monitoring stations composed of 15 stations equipped with bottle racks and
five with specially designed recording devices; and 10 footing drain flow monitoring
stations, three of which were located in the HSSD and seven in adjacent sewer districts.
Installation, startup and calibration of equipment was carried out from January through
March, 1983. Training of the Village staff, which occurred in the February through April,
1983 period, included chart changing, battery replacement, calibration, parts
replacement and recording procedures. The monitoring system was operated as a joint
effort between Skokie and Donohue & Associates, its consulting engineering firm, until
the end of October, 1983. Additional, selective monitoring was conducted in 1984
within and outside of the HSSD.
The monitoring program revealed that precipitation exhibits significant spatial variation
across the HSSD with half of 16 monitored major storms exhibiting such a variation.
Dry weather flow values were found to be similar to those assumed in preliminary
analyses (which relied solely on computer modeling as described in subsequent
sections of this chapter) but exhibited significant spatial variation which was
subsequently included in the refined analyses. Foundation drain flows were determined
to be about one-third of the values assumed in the preliminary analysis. Accordingly,
foundation drain contributions were reduced from about 2,900 gallons per day per
house to about 1000 gallons per day per house.
Wilmette Monitoring
Flow monitoring was performed primarily to obtain data for calibration of SWMM. SEC
Donohue (December 1992, p. 8) describes the monitoring program as follows:
Flow meters were installed at five locations in
the... sewer system and operated from July 10,
1991 through September 9, 1991. Rainfall
over the flow metering period was measured
using a continuous recording rain gauge. Total
3-52
-------
rainfall for the flow monitoring period was 5.3
inches, the largest storm event was 1.6 inches,
and a number of smaller events were also
recorded.
A second purpose of the Wilmette monitoring program focused on system behavior
along the west boundary of the CSS. There was concern that MWRDGC interceptors
along this boundary might surcharge and impact the tributary portion of the CSS. No
surcharging occurred during the monitoring period. However, this observation was
qualified by the fact that no severe rainfalls occurred during the monitoring. This is an
example of using monitoring to diagnose system behavior.
Analyze Existing System and Perform Preliminary Design Using Computer
Models
A Complex System: Need for Computer Modeling
A typical combined sewer system is complex with its many and varied sanitary,
stormwater and other inflows and its tendency to surcharge. Overlay a rectilinear
system of street storage and conveyance components and the complexity increases.
Because of the complexity of the existing and possibly modified CSS, computer
modeling has proven to be a necessity. Hydrologic-hydraulic computer modeling was
heavily used in the Skokie and Wilmette projects. Computer modeling has been used
for both analysis and preliminary design, that is, diagnosis of problems and
development and prescription of solutions.
The models used and the manner in which they were used has naturally evolved, given
the approximately 15 year period during which analysis and design occurred in the
Skokie and Wilmette projects. Much was learned during this period as indicated by the
subsequent sections. Presented here are summaries of computer modeling
approaches used at various stages of the Skokie and Wilmette projects. Hopefully, the
ideas and information presented will be helpful to CSS communities contemplating the
use of computer modeling and the street storage approach.
Assuming a discrete event, contrasted with a continuous computer model (Walesh,
1989, pp. 321-324) is to be used, a design storm or design storms must be selected as
part of the modeling. This typically includes decisions on recurrence interval, duration,
volume, and hyetograph shape. Sensitivity analyses should be part of the process of
formulating the design storm or storms. Detailed discussion of design storms is beyond
the scope of this manual.
For in-depth discussion of design storms, see Walesh (1989, pp. 98-99, 112-113, 129,
304) and ASCE-WEF (1992, pp. 69-78, 226). An example of a sensitivity analyses
3-53
-------
used to determine the critical duration for a design storm is provided by Walesh (1989,
pp. 361-363).
Analysis and Preliminary Design for the HSSD in Skokie
A three-phased approach was used in the modeling and the analysis and preliminary
design of the HSSD. The following description of the approach is taken from Walesh
and Schoeffmann (1984).
Phase I was a simple static condition analysis, done without computer modeling, to
determine the effect of North Shore Channel flood stages on flooding in the HSSD.
Phase II was the steady-state hydraulic analysis of the sewer system, using a computer
modeling, to determine the capacity available for stormwater runoff. Phase III was the
determination of the location and extent of street flooding which would occur for various
recurrence interval storms and the location and size of supplemental surface storage
and relief sewers. This, the last phase was heavily dependent on computer modeling of
the dynamic hydrologic-hydraulic system.
Phase I - Analysis of Static Conditions
This analysis determined if flood levels on the North Shore Channel, the ultimate
receiving water for the HSSD CSS, would cause basement flooding solely as a result of
backwater. The analysis was motivated by the observation that surface and subsurface
storage of stormwater in the HSSD could not resolve basement flooding that resulted
solely from North Shore Channel backwater effects. The analysis was conducted to
determine if there were portions of the HSSD in which flood control could not be
achieved by a street storage system within the HSSD.
The procedure used in this analysis is illustrated in Figure 3-25. North Shore Channel
flood levels were obtained from the Corps of Engineers (Stadler, 1982) and the
MWRDGC (MSDGC, 1981). Elevations of inverts and crowns of sewers in the HSSD,
which were determined from sewer atlas maps and field surveys, were used to estimate
the elevations of basement floors. Basement floor elevations were then compared to
the flood levels.
The analysis concluded that there are no significant areas in which basement flooding
would result solely from backwater of the North Shore Channel. Therefore, flood
control within the HSSD might be achieved by an in-HSSD street storage system.
Phase II - Analysis of Sewer Capacity
The portion of the CSS capacity available for carrying stormwater runoff is a function of:
the total hydraulic capacity of the system as determined by pipe size, slope, and
3-54
-------
material; the quantity of sanitary flow, infiltration, and foundation drainage entering the
system; and the level to which the sewer can surcharge without causing basement
flooding or other damage. Capacity is also affected by the backwater effect of
downstream sewers. The maximum allowable surcharge level was set at the crown of
the sewers to avoid backup of combined sewage into basements.
For the sewer capacity analysis, flows representing foundation, sanitary and infiltration
components were established based on a concurrent monitoring program. Roof drains
were assumed to discharge to the land surface and no longer be directly connected to
the CSS as a result of the Village's largely completed downspout disconnection
program. The following flow components were used:
Foundation flow: 5,000 gpd/acre or 0.0075 cfs per acre based primarily
on monitoring.
Sanitary and infiltration flow in residential areas: a total of 3,000 gpd/acre
or 0.0047 cfs/acre for the western 90 percent of the HSSD and 6,000
gpd/acre or 0.0093 cfs/acre were used for the remainder of the HSSD
based on monitoring.
Sanitary and infiltration flow in industrial areas comprising the eastern
approximately 10 percent of the HSSD: 11,000 gpd/acre or 0.017 cfs/acre
based on monitoring.
3-55
-------
Building Building
with without
Basement Basement
\
" '•• \
Combined
Trunk ~? Normal
Sewer / Stage
Interceptor
Flood Stage Sewer
Figure 3-25. Phase I, a simple static condition analysis, was used to determine if
high stages on the North Shore Channel caused basement flooding in the HSSD.
3-56
-------
The intent of the analysis was to determine the maximum rate at which stormwater
runoff could be released into the CSS without exceeding the established surcharge
level. The analysis is analogous to establishing the maximum allowable release rate
from a conventional stormwater storage facility based on the capacity of downstream
conveyance works.
The sewer capacity analysis was carried out using the computer program System
Analysis Model (SAM), which permitted simulation of the entire HSSD and provided the
computational means of accounting for system surcharges and hydraulic grade lines for
each trunk and branch sewer (CH2M Hill, 1980). Refer to Figure 3-26 for a overview of
the computer modeling procedure. The dry weather module of SAM was used to
develop and input flows to the sewer system and the transport module was used to
combine and route the flows through the sewer system. The HSSD was represented in
the model as 101 subbasins, having an average area of 12 acres, and 161 sewer
segments, having an average length of 300 feet.
Foundation, sanitary and infiltration flows were input to the CSS. Increasing stormwater
runoff rates were then progressively added to the sewer system on a subbasin by
subbasin basis until the hydraulic grade line in the sewer met the established allowable
surcharge level.
The allowable runoff rates represent design conditions, that is, the maximum rate at
which stormwater can be released into the CSS without causing sewer surcharge and
basement flooding. For this no-surcharge condition, the maximum allowable
stormwater runoff rate ranged from 0.1 to 0.2 cfs per acre.
The resulting allowable stormwater runoff rates are extremely low. These unit area
rates are equivalent to the runoff from an impervious surface that would be generated
by a continuous rainfall intensity of only 0.1 inches per hour. Stated differently, the
computer modeling diagnosis revealed that the HSSD combined sewers had very little
capacity available for conveying stormwater runoff when allowance was made for
sanitary sewage, foundation flow and infiltration.
Phase III - Preliminary Design of Street Storage
This analysis determined the street ponding which would occur as a result of regulating
the rate at which stormwater runoff could enter the CSS. More specifically, this analysis
determined the location, depth, lateral extent, and duration of street ponding subject to
the allowable stormwater release rate and other constraints as described below.
-------
_ i
X t
V
.X,
A..
Figure 3-26. Computer model used for analysis and preliminary design in the
Skokie HSSD (Source: Donohue, 1982a, p. 45).
3-58
-------
A computer program, Street and Sewer Analysis Model (SASAM) was used for the
analysis. Refer again to Figure 3-26. Note the relationship between SASAM and SAM.
SASAM accepted historic or design rainfall hyetographs and computed runoff
hydrographs as a function of subbasin area, time of concentration, and type of land
cover using the British Road Research Laboratory Method (Stall, 1972). Flow in streets
and on adjacent parkways was routed using the Manning equation plus conservation of
mass to account for the conveyance capability of any given street section. Stormwater
which ponded on street surfaces and adjacent parkways and lawn was accounted for
by a reservoir routing procedure. Release of flow from the street surface to the sewer
system was set at the maximum allowable release rates which could be handled by the
sewer system as determined by Phase II. Examples of stage hydrographs produced by
SASAM are presented in Figure 3-27.
The HSSD was partitioned into 278 subbasins having an average size of 2.4 acres for
the Phase III analysis. Drainage area, percent directly connected impervious area, and
time of concentration were determined for each subbasin. The street system was
represented on a block-by-block basis requiring the use of 278 street segments.
Representative street cross-sections, some of which are shown in Figure 3-15, were
surveyed. Cross-sections extended from the street face of buildings on one side of the
street to the street face of buildings on the opposite side and varied significantly.
The first quartile storm distribution developed on the basis of historic rainfall data in the
Chicago area was used in the analysis (Illinois State Water Survey, 1976). Sensitivity
analyses using storm durations ranging from 30 minutes to 12 hours indicated that a six
hour duration was most critical.
The lowest sidewalk elevation in each block was selected as the critical elevation for
the block. The critical elevation is the maximum allowable ponding elevation under
design storm conditions.
The modeling process moved on a block-by-block basis in the downstream direction.
Excess water from each street was transferred to one or more adjacent downstream
streets. In this manner, ponding was maximized for each block. Use of street surface
berms was assumed for achieving stage control. Subsurface storage tanks were
strategically placed to store excess stormwater from groups of streets having
insufficient ponding capacity.
Results
Largely as a result of the preceding three phased analysis and preliminary design
process, the engineer recommended moving ahead with a street storage system
throughout the HSSD. Skokie accepted the recommendation and implementation of
street storage approach eventually encompassed the entire 8.6 square mile community.
-------
Z-YEAK R.t.EWNFAU. PISTKleUTIOM
EXAMPLES
09MPITI0KJ6 WITH WJW<9FP PATES
t2ESTfZie.net> TO PPBVEWT
W-YEAR R.I KAIWFW.U OI5TKI&UTIOW
1 10 11 12.
/X ~~T<^"
if/* -^c^N,
AB<7VB CUP& 7.O WiSUIZS
I 2 3
IUIOTH IM FEET
TIMB IW
Figure 3-27. Depth and duration of street ponding as a function of recurrence interval
(Source: Walesh and Shoeffmann, 1984).
3-60
-------
The three phased analysis and preliminary design approach developed for the HSSD
was subsequently used, with refinements, on the other two districts comprising Skokie.
Preliminary engineering was completed for both the MSSD and the ELSSD in 1987
(Donohue, May 1987a; Donohue, May 1987b). Thus, the substantial investment in
developing the computer modeling-based analysis and preliminary design methodology
for the HSSD yielded returns, not only on that district but also on the other two. As
described in the next section, some of the modeling approach developed for Skokie
was used in Wilmette.
Analysis and Preliminary Design in Wilmette
The USEPA Stormwater Management Model (SWMM) (Huber and Dickinson, 1992)
was modified for analysis and preliminary design of the Wilmette street storage system
(Loucks and Morgan, 1995). The modeling approach consisted of:
Hydrologic simulation using the SWMM RUNOFF module.
Street storage simulation using the SWMM EXTRAN module.
Sewer system simulation using the SWMM EXTRAN module.
The EXTRAN model of the Wilmette street storage system is a surface network of
storage junctions and berm overflows connected to a subsurface combined and relief
sewer system.
Modification of the Stormwater Management Model
3-61
-------
Street storage simulator required three innovations, including two modifications. As
explained by Loucks and Morgan (1995):
Three innovations were required in the
development of the street storage model.
First, the EXTRAN code was modified to
accept input of stage-storage relations for
storage junctions and to generate descriptive
storage junction output summaries of storage
junction levels and outflow. Second, it was
determined that the standard EXTRAN orifice
formulation did not adequately represent field
conditions for flow through a catch basin
restrictor. An alternate to the equivalent pipe
formulation was developed for use in the
EXTRAN model. Third, the EXTRAN weir
code was used to model flow overtopping of
the berms into adjacent street storage sites.
Each of the three SWMM innovations are now explained. This somewhat detailed
explanation is provided primarily because SWMM is widely used in modeling urban wet
weather conditions. Accordingly, communities contemplating a street storage system
may also be thinking of using SWMM.
In the standard use of EXTRAN, storage junction data are input in the form of a depth
and surface area relationships. Such a relationship is difficult to develop directly from
street storage sites. This problem was resolved as follows (Loucks and Morgan, 1995):
Available street storage volumes are from
street cross-sections using the end area
method. Software is available to compute
street storage at depth intervals of 0.1 feet.
The EXTRAN code was modified to accept
stage verus storage volume input and to print
an enhanced summary of storage junction
results. The summary provides the maximum
depth, storage and discharge for each storage
site and identifies whether an overflow from the
junction occurred.
The software referred to in the preceding quote is SASAM, the previously described
computer model used in the Skokie modeling. It was used to develop stage-storage
relationships in the Wilmette project.
3-62
-------
EXTRAN uses an equivalent pipe to represent an orifice. This representation differed
greatly from the manner in which flow regulators were to be installed in Wilmette catch
basins. For example, inherent in EXTRAN is the assumption that the water depth in the
upstream junction exceeds the orifice diameter and that upstream and downstream
junction elevations are about the same. This differs markedly from the expected
Wilmette flow regulator installations, as shown in Figure 3-19, where the flow regulators
are 1.5 to 4.5 feet below street grade and the receiving combined sewer is three to nine
feet below the flow regulators. EXTRAN provided no way to position an orifice well
below the storage junction invert. As explained by Loucks and Morgan (1995), the
complication was resolved as follows:
Laboratory tests by Spring (1983)
demonstrated that a PVC tee-restrictor in a
catch basin behaves as a classical orifice for a
wide range of heads. The flow for a particular
orifice area and head is given by formula
Q=Cda(2ghf2, where g is acceleration due to
gravity and Cd is a discharge coefficient found
to be 0.60 to 0.65. In the context of the
EXTRAN model, this formula is much better
suited to the EXTRAN weir code rather than an
equivalent pipe representation. The EXTRAN
weir code was modified to accept a new type
of weir representing a catch basin restrictor.
Data inputs are the orifice diameter, the depth
of the orifice below the ground, and the
discharge coefficient. This approach is
superior as long as there is no downstream
submergence. Even then it is still more
accurate than the equivalent pipe, but not as
stable computationally.
Berm overflow and flow exchange between adjacent street storage areas are important
phenomena in the street storage system. All stormwater flow and volume must be
accounted for. As explained by Loucks and Morgan (1995):
Berm overflow is employed to fully utilize
available storage and to convey stormwater to
relief sewer locations from individual ponding
areas, which may not have sufficient storage
volume. Simulation of berm overflow has been
implemented in the EXTRAN model using the
standard transverse weir input.
3-63
-------
Application of the Model
The previously described model was used for analysis, preliminary design, final design,
and post-construction verification. More specifically (Loucks and Morgan, 1995):
In the feasibility analysis, storage sites were
grouped together using a single storage
junction to represent ten or more ponding
areas. During design and construction, the
planning level models were refined to support
and verify the design of street storage location,
relief sewer configurations, relief sewer
connections to existing combined sewers, and
restrictor sizes. These models stretched the
traditional data limits of EXTRAN. Current
models representing the two completed
phases feature over 250 pipes and 350
junctions including more than 100 storage
junctions.
The model was calibrated against precipitation and flow data for July 13 and July 30,
1992 storm events, each of which had recurrence intervals of about three months.
Analyses of sensitivity of the system to design storm duration revealed that the six hour
event "...produced the greatest amount of system overflow and the most prolonged time
of widespread sewer surcharge." System analysis indicated that one-year frequency
and larger storm events surcharge the CSS and cause basement and street flooding
(Rust, November 1993, p. 4). This finding was consistent with Wilmette's historic
basement and street flooding problems.
Results
The engineer recommended implementing the street storage system in Wilmette as a
result of the previously described computer modeling based analysis and design
process. Wilmette accepted the recommendation and implementation of the street
storage approach will eventually encompass the entire 2.0 square mile CSS.
Review Flow Regulator Availability and Performance
Essentiality of Flow Regulators
Flow regulators, as explained earlier in this chapter, are an integral part of the street
storage system. They must be properly sized to achieve the desired stage-discharge
relationship at any given storage location.
3-64
-------
Equally important is selection of the type of flow regulator for a particular application.
Reason: relative to berms, subsurface tanks, relief sewers and other components, flow
regulators are most prone to failure. The most common failure mechanism is partial or
total plugging by debris carried in stormwater runoff. Plugging can, in turn, lead to
excessive upstream storage and stage and, after a rainfall event, prevent the gravity
drainage of stored stormwater. Therefore, the type of flow regulator selected must fit
the environment within which it is installed.
Skokie Flow Regulator Study
A flow regulator testing program was carried out in the early stages of the Skokie street
storage project. It had been recommended in the preliminary engineering study for the
HSSD (Donohue, 1982a, p. 115). At that time, in the early 1980's, little was known
about flow regulators. Flow regulators were viewed as likely pivotal components of the
evolving Skokie street storage program, and, therefore, a special flow regulator study
was warranted.
Presented here is a synopsis of the testing program based largely on Donohue (March
1984a). The first purpose of the synopsis is to sensitize potential uses of flow
regulators to flow regulator features so that informed decisions can be made. The
second purpose of this synopsis is to provide information about specific flow regulators.
Purpose
The overall purpose of the flow regulator study was an equitable and objective
evaluation of flow regulators under field conditions likely to be encountered in a
system-wide application of regulators in Skokie. Sometimes laudatory and occasionally
conflicting claims of equipment manufacturers and suppliers pointed to the need for a
comparative field test. Based on a literature search and personal contacts, such a test
had apparently never been carried out.
More specifically, the purpose of the flow regulator study was to: determine the initial
cost of commercially available flow regulators and devices specially fabricated by the
Village and others: evaluate flow regulator installation, removal and adjustment
requirements: and observe and evaluate the hydraulic and other performance
characteristics of flow regulators under a variety of field conditions.
Literature Search and Interviews
A literature survey and personal interviews identified the following five types of flow
regulators potentially applicable to the HSSD:
1. The commercially available Hydro-Brake unit as illustrated in Figure 3-28.
Flow enters the unit perpendicular to the outlet pipe, is turned through 90
degrees, and is discharged. The resulting turbulent flow pattern causes a
3-65
-------
much higher energy loss than would occur through an orifice of similar
diameter. Therefore, for a given head, the discharge through a
Hydro-Brake was half or less than half that which would occur through an
orifice having a cross-sectional area equal to the smallest free opening of
the Hydro-Brake. That is, although the Hydro-Brake and the orifice would
have similar ability to pass debris, the Hydro-Brake would reduce flows by
one-half or more.
As noted by Pisano (1989), the Hydro-Brake is an example of a vortex
flow throttling device. Vortex regulators were first developed in Denmark
in the mid 1970's. They were used in Denmark and Sweden to mitigate
basement flooding within CSSs.
3-66
-------
Low flow -
free discharge
(D.W.F.)
Controlled
flow
Low flow -
free discharge
(D.W.F.)
Controlled flow
•'•Low flow -
free discharge
(D.W.F.)
Controlled flow
Hydro-Brake Type 'C'
Hydro-Brake Type 'S'
with horizontal outlet
Hydro-Brake Type 'S'
with vertical outlet
Figure 3-28. Examples of Hydro-Brake flow regulators, available in the early 1980's,
illustrating the basic operation of vortex type regulators (Source: Hydro Group, 1982).
3-67
-------
2. The commercially available Scepter units. A photograph of one is shown
in Figure 3-29. The orifice is diamond shaped with a rectangular keyway
at the bottom. The principal purpose of the keyway is to keep buoyant
debris below the bottom of the diamond during dry periods. At the onset
of a runoff event, the device is expected to function such that buoyant
debris jammed against the keyway will rise, encounter the wider diamond
portion of the orifice, and immediately flow through the regulator.
3. Specially fabricated solid cover with orifices. Figure 3-30 is a photograph
of one of these devices. For a given head, a few small orifices reduce the
flow significantly compared to the flow through a standard inlet grate with
its many larger openings.
4. Horizontal orifice plate beneath the inlet grate as shown in the
photographs in Figure 3-31. The single, small orifice helps to trap leaves,
twigs and other debris carried by the stormwater before the material
reaches the underlying orifice.
5. Hanging trap flow regulator, as illustrated in Figure 3-32. This device,
which can be assembled from inexpensive, standard PVC units, features
an orifice that is always submerged.
Design of the Field Study
Portions of four streets, covering approximately ten lineal blocks on the west side of the
HSSD, were selected for the field phase of the flow regulator study. Factors considered
in selecting the test areas included: a variety of topographic features such as streets
with uniform and non-uniform longitudinal slopes; a range in type of street
cross-sections and street widths; an aerial density of inlets and catch basins similar to
that of the entire HSSD; a mix of residential and commercial streets; and the presence
of trees.
Equipment Acquisition and Installation
A total of 29 flow regulators were installed in the study area during the period of
January through April 1983. The Hydro-Brake and Scepter units were installed in both
catch basins and inlets. The hanging trap unit was applicable only to catch basins.
The orifice in the inlet grate and the horizontal orifice plate beneath the grate were
suited only to inlet installations.
3-68
-------
Figure 3-29. Photograph of Scepter flow regulator.
3-69
-------
Figure 3-30. Photograph of solid cover with orifices.
3-70
-------
Figure 3-31. Photographs of horizontal orifice plate flow regulator before and after
installation.
3-71
-------
• CATCH BASIN
OUTLET PIPE
ORIFICE RESTRICTOR
SHAPES
Figure 3-32. Hanging trap flow regulator (Source: Donohue, 1982a).
3-72
-------
Observation Procedures
The system of 29 flow regulators was observed by Skokie and Donohue personnel
during or immediately after a total of 15 rainfall-runoff events between March 18 and
September 20, 1983. In addition, regulator performance was observed during
intentional flooding tests conducted on October 18 and November 16, 1983. A
photograph of the intentional street flooding is shown in Figure 3-33. The field
observations of flow regulators focused on operation and maintenance factors such as
the tendency of the regulators to plug with leaves and other debris and the ease of
removing material from plugged regulators.
Rainfall
The average intensity of 60 percent of the rainfall events occurring during the six month
field tests exceeded 0.1 inches per hour which approximately corresponds to a unit
runoff rate of about 0.1 cfs per acre, the rate above which flow regulators had to
function as part of the HSSD street storage system to prevent damaging surcharging.
Therefore, the majority of rainfall events, and all intentional flooding tests, simulated
operational conditions.
Resistance to Plugging
From a plugging perspective, flow regulators were much more resistant to plugging
when placed in catch basins than inlets—the latter installations were 20 times more
likely to plug than the former. There was no significant difference in the operation
characteristics of Hydro-Brakes, Scepter units, and hanging traps placed in catch
basins—they all performed very well.
Although there were significant differences in the anti-plugging performance of inlet
installations of Hydro-Brakes, Scepter units, grate modifications and horizontal orifice
plates, the difference was of little practical significance because the incidence of
plugging was too high. That is, even a relatively low plugging frequency of inlet
installation is unacceptable for the street storage system. Leaves appeared to be the
principal cause of plugging of flow regulators. This dominance probably reflects the
large supply of leaves relative to other materials.
Costs
The cost of purchasing flow regulators varied widely. Cost ranges per unit in 1983 for
units appropriate to Skokie inlet or catch basin installations were:
-------
Figure 3-33. Streets were intentionally flooded to test the performance of flow
regulators.
3-74
-------
Hydro-Brake: $300 - $800
Scepter: $100-$130
Solid cover with orifice: $10 - $50
Horizontal orifice plate beneath inlet grate: $50 - $150
Hanging trap: $25 - $50
Given the good and similar operating characteristics of Hydro-Brakes, Scepter units,
and hanging traps, the hanging traps were clearly preferable because of their very low
costs.
Maintenance
The ease with which debris can be removed from plugged flow regulators was difficult
to quantify. The debris removal effort, listed in order of increasing difficulty, is
approximately as follows: modified grate flow regulators; horizontal orifice plate
positioned beneath the inlet grates; Hydro-Brake and Scepter flow regulators installed
in inlets; and Hydro-Brakes, Scepter units, and hanging traps installed in catch basins.
Conclusions for Skokie
1. Flow regulators should be installed in catch basins, rather than inlets.
2. Hanging trap flow regulators should be used throughout the HSSD, except
where the desired reduction and resulting orifice size is beyond the
effective lower range of the hanging trap regulator, in which case
Hydro-Brake flow regulators should be used.
3. A field-oriented flow regulator design process should be used to minimize
costs.
4. The design and installation of flow regulators should be done in
conjunction with other components of recommended street storage
system including roadway berms, subsurface storage tanks, and relief
sewers.
Complete Design of the Street Storage System
The goal of final design is to produce a set of plans and specifications to be used by
contractors for bidding and by the selected contractors for construction. Additional
hydrologic-hydraulic modeling is needed for tasks such as final sizing of flow regulators
and refinement of berm locations and heights. However, the final design process is
typical of that which might be done for an urban street. An example of the kind of detail
that results is shown in Figure 3-34.
3-75
-------
<5IPBWAU^ TO MBET
„ &
2 to
2
0
I
• EXIST)Wit
INUET
iiS
Figure 3-34. Typical street berm design in Skokie, IL (Source: Walesh, 1989, p. 401).
3-76
-------
Construction
Both Skokie and Wilmette are using a phased approach to construction. (For a
discussion of the advisability of phased implementation and suggested prioritization
factors, refer to the earlier section of the chapter titled "Select an Initial Implementation
Area Within the Combined Sewer System.") Each community's overall implementation
schedule, with emphasis on construction, is summarized here.
Skokie Construction
Skokie implemented the physical aspects of its street storage system according to the
following schedule:
1981: Initiate downspout disconnection
1983: Begin stakeholder involvement
1983: Test flow regulators in pilot areas
1983: Initiate base line monitoring
1983-1986: Construct HSSD
1988-1997: Construct MSSD
1989-1999: Construct ELSSD
Table 3-3 summarizes the components of the Skokie street storage system. Note the
heavy reliance on berm-flow regulator installations, which suggest, in turn, widespread
use of temporary, controlled street ponding.
The relative importance of street storage versus other storage is shown in Figure 3-35.
Overall, street storage accounts for half of the total stormwater storage capacity in
Skokie, the other half being subsurface storage and off-street surface storage.
Incidentally, in Wilmette essentially all of the storage is street storage because there
are no subsurface or off-street storage facilities.
The preceding observations about the dominance of street storage in Skokie and
Wilmette reinforce the discussion near the beginning of this chapter about the
significant storage and conveyance capacity of street, especially in a CSS. With
carefully engineered retrofitting, that storage and conveyance can be the basis for
cost-effective solutions to flooding and perhaps other wet weather problems in CSSs.
-------
Table 3-3. Components of the Skokie street storage system (Source: Carr, 1999).
Component
Flow Regulators
Berms
Off -Street
Surface Storage
Subsurface
Storage
Storm Sewer
Combined Sewer
Number
2,900
871
10
83
Length
(Feet)
64,000
29,000
3-78
-------
7,000
^ 6,000
15
,® 5,000
4,000
3,000
-------
Wilmette Construction
A five-phased construction program is underway in Wilmette. Three phases are
completed and two are planned. Two major considerations determined the priorities.
The first was functional dependence. For example, downstream relief sewers were
constructed before upstream relief sewers. The second of the two key prioritization
factors was cost effectiveness. That is, higher priority was given to areas with the most
severe problems. The five phases, with their actual construction costs (Phases 1, 2
and 3) and projected construction costs (Phases 4 and 5) are described below.
Phase 1: Greenleaf Avenue Relief Sewer
Included installation of approximately 6300 lineal feet of relief sewer (48" - 96") in
Greenleaf Avenue, connection to the deep tunnel, emergency overflow to the North
Shore Channel, and 165 berms and associated catch basins and flow regulators.
Cost: $10,358,000
Phase 2: Eastside Relief Sewer
Consisted of the continuation of relief sewers from Greenleaf Avenue, along 9th Street
and Forest Avenue to 15th Street. This tunneled sewer project consisted of
approximately 5600 lineal feet of 72", 54", and 48" diameter sewers. This phase also
included the construction of 50 berms and related catch basins and flow regulators.
Cost: $4,586,000
Cumulative Cost: $14,944,000
Phase 3: Eastside Relief Sewer
Included both construction of relief sewer to the south from Greenleaf Avenue and a
storm sewer system (including an outfall to the North Shore Channel) in the
Maple/Dupee portion of the Village. This Phase included the construction of 37 berms
and related catch basins and flow regulators.
Cost: $8,425,000
Cumulative Cost: $23,369,000
Phase 4: Eastside Lateral Relief Sewer
Will consist of the construction of relief sewers in 9th Street from Forest Avenue to
Chestnut; Ashland Avenue from 9th Street to 8th Street; 8th Street from Ashland
3-80
-------
Avenue to Chestnut Avenue; 12th Street from Forest Avenue to Ashland Avenue with
one block stubs on Elmwood, Greenwood, and Ashland; 17th Street from Lake Avenue
to Forest; and 17th Street from Forest Avenue to Elmwood Avenue. These sewers will
range in size from 18" to 36" in diameter.
Cost: $4,500,000
Cumulative Cost: $27,869,000
Phase 5: Eastside Lateral Relief Sewer
Will consist of relief sewers in 6th Street from Greenleaf Avenue to Elmwood Avenue;
Forest Avenue from 6th Street to Michigan Avenue; Elmwood Avenue from Sheridan
Road to Michigan Avenue; and Washington Avenue from Prairie to Green Bay Road. A
portion of the Phase 5 sewers will be constructed in Green Bay Road as part of the
Green Bay Road resurfacing project. This phase will also include storm sewers at
various locations across the Village. These sewers are proposed to pick up primarily
surface drainage from low lying areas.
Cost: $7,300,000
Cumulative Cost: $35,169,000
In summary, as of early 1999, the constructed three phases of the street storage
system in Wilmette's two square mile CSS consist of:
252 berms - catch basins - regulator installations. Over 98% of the
intended 717,540 ft3 (16.5 acre-feet) of street storage has already been
achieved.
Over 11,900 lineal feet of tunneled or conventionally constructed relief
sewer.
Incidental storm sewers.
The $23,369,000 total cost of the three completed phases consists of $18,946,000 or
81.1%, for relief sewers and $4,423,000 or 18.9%, for berms and associated catch
basins and flow regulators.
Because the CSS is essentially one system, all phases must be completed to achieve
the intended degree of flood control. The last two phases of the five phased program
are not yet constructed.
wp/epastch3
3-81
-------
CHAPTER 4
OTHER EXAMPLES
OF
STREET STORAGE SYSTEMS
Purpose
Using the well established and on-going Skokie and Wilmette, IL project; the previous
chapter presents a proven and practical street storage system concept through
construction and operation and maintenance process. Provided in this chapter of the
manual, are synopses of other street storage studies, designs and implementation.
The intent is to use other examples as supplemental, mini-case studies which provide
additional insight into street storage. Some of the additional examples were carried
through to implementation while other did not move or have not yet moved past the
feasibility stage. Nevertheless, each of the mini-case studies offers additional useful
ideas and information that may be useful to municipal officials.
In the early 1980's, near the beginning of the Skokie project, Donohue and Associates
personnel learned much about flow regulators from other communities. For example,
research revealed that vortex regulators had been installed in at least a dozen
Canadian and U.S. communities. Contacts were made with municipal personnel in six
communities that had vortex regulator experience. Donohue personnel also
communicated with Canadian and U.S. communities about their experience with other
types of flow regulators (Donohue, 1984a, pp. 3-3 to 3-13).
Missing, at that time, were completed, or largely completed, street storage systems that
included flow regulators, berms, surface and subsurface storage. The Skokie and
Wilmette case studies in the previous chapter provide examples of largely completed
street storage systems. This chapter's synopses of other projects which are, in effect,
street storage systems, provide additional examples.
4-1
-------
Cleveland, OH: Puritas Avenue - Rock River Drive Area
Background
This mid 1980's investigation was undertaken primarily to "...evaluate the ability of the
Hydro-Brake to effectively regulate specific design flows from stormwater storage
structures to such an extent that receiving sewers could be protected from surcharging
and creating CSO conditions" (Mathews et al., 1983, p. 2, see also Mathews et. al.,
1984). Although the study focused on the Hydro-Brake, one of the commercially
available flow regulators discussed earlier in Chapter 3, the study does provide insight
into the street storage system.
The overall combined sewer study area covered 115 acres of medium density
residential originally developed in the 1920's. Basement flooding caused by
surcharging of combined sewers was a problem. Within this area, three subsurface
tanks were constructed serving separate subareas having a total area of 9.0 acres
(Mathews et al., 1983, p. 2). The three tanks were located within the street curb lines
and above the combined sewers, that is, they were intended to be gravity devices and
to temporarily store stormwater runoff. The three tanks were constructed of corrugated
metal pipe (CMP). The first tank used 163 feet of 48 inch diameter CMP and provided
2000 cubic feet of storage. The second tank was formed from two parallel 87 by 63
inch corrugated metal arch pipes each 156 feet long for a total storage volume of
10,000 cubic feet. The third tank consisted of 170 feet of 95 by 67 inch corrugated
metal arch pipe and contained 5,800 cubic feet of storage. Inlets conveyed stormwater
to the subsurface tanks and flow regulators controlled flow out of the tanks (Mathews et
al., 1983, pp. 12-15).
The study included:
Filling and draining each tank to determine Hydro-Brake stage-discharge
relationships.
Monitoring of precipitation, water levels in tanks, and stormwater quality.
Simulation of tank inflow and outflow hydrographs for design storms of
prescribed recurrence intervals.
Pre and post-construction surveys of area residents with emphasis on
basement flooding.
Results
Numerous findings were reported. Some of the more significant observations relative to
this manual are (Mathews et. al., 1984):
4-2
-------
Hydro-Brake regulated storage tanks are
effective in alleviating sewer surcharge and
basement flooding problems.
By reducing the peak flow in the sewer system,
combined overflow pollutant loadings are
reduced because the first flush effect is
dampened.
For effective application of the Hydro-Brake
regulated technology, the design approach
must include accurate characterization of
drainage areas and sewer hydraulics to
properly identify site-specific release rate
requirements. The level of control desired
determines the required storage volume, and
the characteristics of the site determine
whether to employ above-grade or below-
grade storage, or a combination thereof.
Where surface ponding is an acceptable form
of stormwater storage, the application of
Hydro-Brakes alone is more cost-effective than
Hydro-Brakes used in conjunction with off-line,
below-grade storage structures. Both
applications, however, appear to be more cost-
effective than the other evaluated alternatives
where both surcharging and overflows are the
prevailing problems.
During the first 18 months of operation, the
Hydro-Brake control/detention structures
exhibited minimal maintenance requirements.
Solids deposition in the storage tanks was
negligible and did not increase significantly
with time.
Potentially useful ideas and information drawn from this Cleveland, OH project include:
Use of CMP for subsurface tanks.
Reduction of the first flush effect.
4-3
-------
Desirability, from a cost perspective, of using on-street storage rather than
below-street storage.
The likely cost-effectiveness and multiple purpose benefits (reducing
basement flooding and CSO's) of a street storage system.
Parma, OH: Ridge Road Area
Background
Ridge Road area "...is a topographic "dished" shaped area (30 acres) situated within the
lower portion of a 290 acre drainage system. The terrain in the watershed is hilly with
deep valleys..." (Pisano, 1989). The 290 acre area is highly developed in that it
contains 1200 homes and many commercial buildings. An over/under sewer system
serves the area. This is a special form of a combined sewer system common
throughout the Cleveland metropolitan area. The storm sewer is laid immediately
above the typically smaller diameter sanitary sewer. The two sewers share the same
trench and manholes and, therefore, there is a high likelihood of flow between the two
conduits..
As explained by Pisano (1989), the 30 acre area, known as the Triangle:
...endured severe basement flooding resulting
from the surcharging sanitary sewers during
heavy rainstorms (at least three to four
episodes per year). The cause of surcharge
stems from the undersized storm systems
which cannot handle storm flows, [they]
pressurize, surcharge and leak significant
amounts of clear water into the rock filled
"french drains" trench section. Since the sewer
joints in the sanitary sewer are invariably
cracked or broken, the surcharge condition
within the rock filled trench adversely affects
the sanitary sewer piping, ultimately resulting
in basement flooding. Basement flooding in
the Triangle is further exacerbated by the poor
hydraulic outlet conditions of the local sanitary
systems...
Due to the rolling terrain, there are numerous
"low valley pockets" throughout the entire 290
acre area. The storm drains are generally
inadequate. Surface water which cannot
4-4
-------
escape via major overload routes...
accumulates and severe street flooding results.
Therefore, the 290 acre drainage basin, and especially the Triangle, experienced
frequent and simultaneous basement and street flooding. The problems needed to be
solved.
Results
One partial solution was "...to construct a large underground off-line detention basin for
relieving the sanitary trunk sewer coming into the study area and to construct sanitary
relief sewers throughout the Triangle." This $2,200,000 project (mid 1980's costs)
would solve only the basement flooding problem. The surface flooding problem would
remain.
The alternative, which was implemented, is what is referred to in this manual as a street
storage system. The system includes downspout disconnection, berms, reconstructed
curbs, flow regulators, new catch basins, subsurface storage tanks, manhole
rehabilitation, and relief sewers. Construction costs in 1984 totaled $875,000 (or about
$3000 per acre in 1984 dollars) which is 40% of the cost of the partial solution.
According to Pisano (1989), "The project has mitigated surface water ponding and has
provided basement flooding protection throughout the entire 290 acre area... Although
not intended, spring sanitary sewer infiltration has been significantly reduced."
Possible valuable ideas and information based on the Parma, OH project are:
Potential applicability of the street storage system to hilly terrain.
Use of the street storage system to simultaneously mitigate basement and
surface flooding.
Cost effectiveness of the street storage system approach.
Chicago, IL: Jeffery Manor Neighborhood
Background
Jeffery Manor is a 470 acre CSS area on the southeast part of the City of Chicago.
Residential land use dominates with commercial, industrial and undeveloped land on
the perimeter. Streets have curb and gutter, are paved and most have sidewalks and
tree lined parkways. Local combined sewers, owned by the City of Chicago, range from
10 to 42 inches in diameter, and discharge to MWRDGC interceptor sewers. The entire
area is very flat (SEC Donohue, 1993).
4-5
-------
Jeffery Manor has a serious basement flooding problem caused by surcharging of the
CSS. Local and interceptor sewers do not have the capacity needed to carry flows
received during rainfall events. An additional exacerbating factor is excessive dry
weather flow in interceptor sewers that originate outside of and flow through Jeffery
Manor. Sewer crowns are about eight feet below street level and most basement floors
are five to six feet below street level. Therefore, a few feet of surcharging above sewer
crowns forces combined sewage into basements.
Results
Results of the feasibility study, as quoted (parenthetic comments added) from SEC
Donohue (1993, pp. 1-1 to 1-2) are:
...a temporary street storage system would
alleviate sewer surcharging in the Jeffery
Manor area caused by overloading of the local
collection system. The system was developed
under the assumption of greatly reduced flows
in the MWRDGC interceptor sewer entering
the Jeffery Manor area. This reduction in flow
will occur when tunnels or other relief sewer
projects are constructed. However, if flows in
the MWRDGC interceptor continue at current
levels, the proposed street storage system will
provide some relief to the existing flooding
problem, but will not perform to its maximum
capability.
The analysis for the five-year storm event
showed that the storage required to eliminate
sewer surcharging is 455, 280 cubic feet (970
cubic feet per acre). The proposed temporary
street ponding system entails development of
ponding areas on 74 city blocks ...to provide
328,570 cubic feet of storage. The ponded
stormwater would be held in place by 120
berms to be constructed across the streets
(See Figure 4-1). Construction required for
4-6
-------
i
Legend
»
1
t
«
I
r.«
•
•
I
. m
k^
§
t]
JJ
m
i*
•
t f
1 *>
I P
I P
1
t+
I
i
i
LJ
T
i.
/^
\ "^
|c
4
V,
\»B
y.1
1
i i
«*
i
i|
— \
^
Beim
Not to
Figure 4-1. Street storage system proposed for the Jeffery Manor neighborhood in
Chicago, IL (Source: SEC Donohue, 1993, p. 5-3).
4-7
-------
implementation consists of berm construction,
removal of existing stormwater inlets and
installation of new inlets with flow restrictors.
The estimated construction cost for the street
storage components is $1,860,000 (or $3960
per acre in 1993 dollars).
Although temporary ponding alone will greatly
improve the system capacity in Jeffery Manor,
additional facilities are required to provide a full
five-year level of protection. Approximately
60,000 cubic feet of additional storage is
needed in the southern part of the
neighborhood... This storage could possibly
be provided on the property of a closed
elementary school... Also a relief sewer is
needed... To provide a five-year level of
protection for the area after flows in the
MWRDGC interceptor are reduced by other
projects, street ponding, other storage and a
relief sewer are required at a probable
construction cost of $2,481,600 (or $5280 per
acre in 1993 dollars)... Street storage reduces
the required capacity of relief sewers, and can
result in millions of dollars in savings for
construction of sewers.
The recommended project has not been implemented. Possibly useful ideas and
information drawn from the Jeffery Manor feasibility study are:
The need to address interceptor sewer capacity as affected by contributions
from outside of the CSS area.
Cost effectiveness of the street storage system approach.
wp/epastch4 4-8
-------
CHAPTER 5
REGULATORY AND FINANCIAL FRAMEWORK:
COMPLYING WITH REGULATIONS AND
FUNDING CONSTRUCTION
Motivated by Need But Subject to Regulatory and Financial Constraints and
Opportunities
The principal reason to undertake the street storage projects in the communities of
Skokie and Wilmette, IL was to solve the serious problems of widespread flooding of
basements by combined sewage. Skokie and Wilmette had flooding problems that had
grown and festered long enough and the time for action had arrived, regardless of
regulatory requirements.
This stands in stark contrast to the situation in many CSS communities where projects
are planned and implemented primarily to comply with regulations and court,
administrative or consent orders intended to prevent pollution of receiving waters. The
fundamental challenge in Skokie and Wilmette was to take basement flooding, a
serious, widely shared local concern, and come up with an affordable alternative to the
proposed unaffordable relief sewers.
The initial objective in Skokie and Wilmette was to create a project that solved several
problems and package the project in such a way that it:
Eliminated basement flooding
Was compatible with MWRDGC policy
Was affordable to the community
Was supported by residents and users
Was supported by state agencies which control NPDES compliance
Might be eligible for outside capital agency funding.
With these objectives in mind, planning, design and construction could not proceed in a
vacuum. Many challenges had to be met, not the least of which were regulatory
requirements and related legal matters and the means by which construction would be
financed to make the improvements affordable. Some of the regulatory framework
5-1
-------
proved to be advantageous in that it offered opportunities to pursue certain funding
options.
Regulatory and financial issues are discussed together in this chapter because they are
highly interrelated. For example:
Federal and state regulations sometimes define a community's eligibility
for external funding in the form of loans and grants.
Past state and federal funding programs required ties to NPDES
compliance and schedules of implementation for identified construction
projects. In the case of Skokie and Wilmette, both projects were originally
expected to construct large relief sewers to flow into TARP. TARP was
grant eligible and the large relief sewers were not.
Working through the wastewater and stormwater permitting process
brings together local, regional, state and federal agency personnel. This
connection expands the local communities access to unique project
technical solutions as well as access to alternative funding sources.
Home rule jurisdiction, as defined by Illinois law, meant that Skokie's
elected and appointed officials did not have to get new voter approval on
some local borrowing. However, in the case of Skokie and Wilmette,
focusing on basement flooding elimination made proceeding with the
project easier at the local level.
Should the agency permitting process result in the creation of an
unaffordable project solution, the agency permitting staff themselves
become advocates for special funding. That special funding can come
from a change in program eligibilities or direct legislative appropriations.
Other crucial issues, such as analysis and design procedures, public involvement, and
inspection and maintenance are discussed in, respectively, Chapters 3, 6, and 7.
The next three major sections of this chapter focus primarily on complying with federal
and state regulations and obtaining funding through federal and state programs.
Sources for these sections are Roecker (1993, 1997, 1998a, and 1998b) plus additional
sources cited within these sections.
5-2
-------
Federal and State Regulatory and Funding Framework Within Which Skokie and
Wilmette Functioned
During the late 1970's, the Skokie and Wilmette combined sewer systems were
expected to be reconstructed and connected to the future Chicago TARP project. A
CWA Section 201 Facility Plan was prepared for both Skokie and Wilmette which
showed the cost of combined sewer correction program, consisting of large relief
sewers, to be very expensive. In the case of Skokie, the estimate was $100,000,000
based on 1980 dollars. Because of TARP's need for construction capital and the
MWRDGC's ability to win USEPA Construction Grant eligibility for the TARP project,
Skokie, Wilmette and all other MWRDGC contract communities combined sewer
separation projects were classified as ineligible for grant monies.
This ineligibility determination and the continued basement flooding stalled remedial
action in Skokie and Wilmette until affordable alternatives could be developed. In the
early 1980's, Skokie began looking for alternatives to the construction of relief sewers.
Working with their engineering firm, they began looking at their challenge in terms of a
stormwater management problem, rather than a relief sewer problem. This process
resulted in the creation of the Skokie street storage system approach.
Meetings were held at the state to review the concept and determine how Skokie and
the state could create a partnership. The partnership was necessary to change the
regulatory requirements associated with the existing CWA Section 201 Facility Plan and
to try to find a way to change or eliminate current funding ineligibility determinations.
Initial meetings with the state focused on the following;
Change the regulatory requirements associated with the previously
approved CWA Section 201 Facility Plan to eliminate NPDES compliance
issues associated with eliminating the relief sewers.
Look for local, state or federal funding sources which could assist in
demonstrating the new technologies or lower local cost impacts.
Look for state level project support which would later help bring in other
state and federal agency funding.
Today, the path cut by Skokie and followed by Wilmette, is different. The differences
can be characterized as follows and can be used by others to assess the regulatory and
financial process;
The initial regulatory challenge facing Skokie and Wilmette related to
TARP using all available USEPA Construction Grant dollars for their
project and leaving the two communities with an NPDES requirement to
build expensive relief sewers with no access to grant or low interest loan
money. Today, large percentage grants are not available to projects like
TARP and, therefore, communities are forced to focus on alternative,
lower cost and smarter projects at their initial stages of project planning.
The USEPA Construction Grants program has been replaced with the
5-3
-------
USEPA State Revolving Fund (SRF) program. In general, this program
provides low interest loans which must be paid back by the communities.
A new sense of fiscal responsibility has entered projects which has
resulted in longer term phased projects that become more affordable to
the users.
Demonstration projects, like Skokie and Wilmette, have become
showcases of what stormwater management can accomplish in CSS and
how it can save costs. More alternative technologies are becoming
available to those who seek them.
At the national level, the U.S. Congress has begun providing direct grant
assistance to those projects which can demonstrate unique qualities or
have unique characteristics. Most recently, successful projects tend to
deal with the large issue of "watersheds" as opposed to single issue
wastewater or stormwater challenges. The Skokie and Wilmette projects
provide good examples of a multi purpose, watershed-based approach.
Today's Regulatory and Funding Framework: Review of Outside Capital Funding
Programs, Techniques and Strategies
Overview
Since the 1950's, the U.S. Congress has provided capital funding for municipal water
related infrastructure. The capital funding assistance has ranged from full project
grants to subsidized long term loans. In the recent past, communities and authorities
have found that their water related projects have become more expensive and
government funding has diminished.
Based on recent Congressional actions, the future of state and federal sponsored water
related funding programs and initiatives are becoming known. That future includes
continued capital water related project funding opportunities for those communities and
projects that meet the criteria of a changing funding landscape.
Ideas, suggestions and insights contained in this chapter provide the tools needed by
communities to win needed capital water related funding. Addressed here is the
movement of available local, state and federal funds through existing and proposed
water related funding programs. Presented is information on the location of both
traditional and nontraditional funding opportunities. Communities are encouraged to
expand their water related project objectives to match the funding program objectives.
Both state and federal funding program objectives are highlighted in this chapter to give
community leaders important strategic information that can save time in review of
possible funding avenues.
Outside Capital Funding from Users
5-4
-------
The creative use of "special assessments" and "developer funds" offer unique capital
funding opportunities. Use of both "special assessments" and "developer funds" can
accomplish the following:
The ability to assess acreage that is receiving a benefit from an area-wide
project. In the case of an urban stormwater project, area-wide benefit can
easily be defined and assessed on a more uniform basis than the
traditional per-foot basis.
The ability to assess the capacity of a storage or treatment facility to all
users of the facilities on a uniform basis.
Since "special assessments" are property liens, federal agencies are
available to pay the assessments for the poor and elderly. Programs
continue to provide monies for these special user groups to make the
improvements affordable.
Including the needs of developers as a project planning objective can
enhance the project's usefulness, and bring a secondary benefit of
outside funding from the developer. Long term phased projects tend to
have the time available to search out these developers and negotiate
reasonable financial contributions which benefit the developer and the
community.
In the past several years, there is increased concern with making sure that all project
"stakeholders" are paying their fair share. In developing an outside capital funding
strategy, community leaders should make sure that all those benefiting or those who
will benefit are accounted for.
Outside Capital Funding from State and Federal Agencies
In order to understand what agency funds are available, a community must learn why a
agency provides funding. The following five points were developed from experience
and provide some insights:
Funding agencies fund their program objectives, not a community's
project
A community should develop its project's uniqueness during planning
Keep working with the agency until someone says "maybe"
Once funding is obtained, other agencies will follow
Spend some time getting to know representatives of agencies
To reiterate, of all the issues that are important to winning outside capital funding, the
single most important issue is understanding the funding program objective. As
community leaders start thinking about outside agency funding, they should define how
5-5
-------
their project will help the agency further its objectives.
The following list of funding programs contain current (1999) information regarding their
objective, funding, administration, and current program status. These programs provide
more than 90% of water related infrastructure funding throughout the country.
# U.S. Department of Agriculture (USDA), Rural Utilities Service (RUS) & Rural
Housing Service (RHS).
Objective: To provide safe and sanitary housing, including water related facilities
to small, rural municipalities (less than 10,000 pop.) serving lower income
persons.
Funding: FY 1999 funding levels were $763,977,000 in low interest loans and
$500,000,000 in direct grants for project costs and $25,000,000 in direct loans
and $25,000,000 in direct grants to low income elderly rural home owners for
special assessments.
Administration: Through a federal agency state headquarters office and several
district offices. The district offices review, screen and recommend individual
projects to the state office. If the state allocation is committed, a state can
submit a project to a national office for special funding consideration.
Status: These programs continue to receive increased funding. The district staff
engineers provide a very detailed review of proposed infrastructure and work to
lower capital costs and limit eligibilities on each project.
# U.S. Department of Housing & Urban Development Block Grant Program (HUD).
Objective: To provide viable urban communities with decent housing, a suitable
living environment and expanding economic opportunities for low to moderate
income residents.
Funding: FY 1999 set funding levels of $3,103,100,000 for their large
community entitlement program and $62,222,000 for their small community block
grant program.
Administration: Through a state agency normally located in the state capital.
Status: Past historic influence by Congress is said to have ended. Entitlement
recipients tend to receive small allotments that are spread over numerous
competing infrastructure needs with little money available for new water related
infrastructure, while the state-wide small community competition tends to provide
a more meaningful opportunity for water related funding.
# U.S. Department of Commerce Economic Development Administration (EDA).
Objective: To promote long-term economic development and assist in the
construction of infrastructure, including water related facilities, needed to initiate
and encourage the creation or retention of permanent jobs
5-6
-------
Funding: FY 1999 saw program funding of $160,000,000 for this program.
Administration: Through a federal agency headquartered in the federal regional
city with a very small state or multi state office. In addition, individual states also
have their own version of this job creation program that can provide direct state
assistance to worthy projects.
Status: While EDA was slated for termination by the 104th Congress, it remains
intact. Before funding water related infrastructure, EDA will want very detailed
information from the job creator and limits funding to projects that generally cost
less than $10,000 per permanent job created.
# U.S. Environmental Protection Agency (USEPA).
Objective: To provide financial incentives to communities to obtain and maintain
NPDES compliance and provide a long term source of financing for water related
infrastructure.
Funding: FY 1999 saw program funding of $2,125,000,000 for their water
related State Revolving Loan programs with additional grant monies available
from the USEPA Budget itself.
Administration: Through a federal agency headquartered in the federal regional
city with direct allocation of loan and grant monies to individual state pollution
control agencies.
Status: The State Revolving Fund programs are viable funding programs and
are beginning to expand eligibilities for watershed projects. Reauthorization of
the Clean Water Act was pending as of early 1999. However, the reauthorization
is expected to further expansion of the eligibilities to innovative watershed
programs that meet the objectives of pollution reduction together with flood
protection.
In addition to the USEPA's State Revolving Fund program several areas of the U.S.
Budget contain demonstration and implementation funding programs that can provide
grant assistance to projects that meet the specific funding objective contained in that
particular section. The USEPA (1993, EPA-814) provides the list of funding sources
which follows. Note: Section numbers refer to the Section of the existing Clean Water
Act and the numbers in parentheses refers to the funding program as described by the
Executive Office of the President and U.S. General Services Administration (U. S. GSA,
1998).
• Section 106 (66.419): This program provided state and interstate agencies
and Indian tribes with more than $115,000,000 in 1999 for prevention and
abatement of surface and groundwater pollution.
• Section 604(b) (66.454): This program provided States with $12,000,000 in
1999 to carry out water quality management planning.
5-7
-------
• Section 603(d) (66.458): This program provides States with up to 4% of their
State Revolving Fund (SRF) allocation to manage their programs. Nationally
this amounts to more than $80 million annually, and if the State's SRF
program involves water resource projects, the administration of these water
resource projects can come from this fund.
• Section 319(h) (66.460): This program provided $200,000,000 in 1999 to
State-designated lead non-point source (NPS) agencies to fund
implementation or construction of water resource related practices or
infrastructure. The 1999 federal allocation represents a 100% increase over
1998.
• Section 320(g) (66.456): This program provided $12,300,000 in 1999 to any
agency or individual for planning activities in designated estuaries.
• Section 104(b)(3) (66.463): This program provided $19,000,000 in 1999 to
any agency or individual for one to two year demonstration type projects,
including combined sewer overflow and stormwater discharge control
programs.
• Regional Initiatives: The USEPA regions spend in the area of $2 to $4 million
annually on projects that address watershed protection. Communities can
obtain a listing of current objectives from their regional USEPA office.
Working through these federal agencies and their state counterparts will provide
community leaders with an understanding of the administrative funding possibilities for
both current and future water related projects. In addition, the effort will produce the
background information needed by a community to consider taking their project to the
next step in the funding road. That step is the U.S. Congress.
Outside Capital Funding from the U.S. Congress: Direct Legislation
Over the past several years, a growing number of communities have sought direct
funding of their projects from Congress through the U.S. Congress' appropriations
process. In addition, various State Legislatures have begun providing direct funding of
special and unique projects.
5-8
-------
Since 1992, the U.S. Congress has provided $3,579,425,000 in direct grants for water,
watershed, groundwater and wastewater projects across the nation. If a community
works through the existing local, state and federal agency funding programs and the
project is still truly unaffordable or if it has some unique feature that distinguishes it from
other projects attempting to accomplish the same objectives, elected officials can help.
Certain projects may fall through the cracks either by poor management or
circumstances beyond their control. The U. S. democratic process has a strong sense
of fairness and when a case can be made demonstrating that the project has not had a
fair shake for available public funds, both the state and federal legislatures can help.
Special attention to the issues of the day and the concept of "fairness" leads to success
in the legislative arena. When dealing with its legislature, community leaders should
keep the following objectives in mind:
• Legislatures provide direct funding to win favor with large population areas for
future political purposes by correcting an actual or perceived public policy
injustice and removing unreasonable regulatory barriers which preclude
sound projects from proceeding.
• Legislatures provide direct funding to correct actual or perceived public policy
injustices for a project which would have been eligible for significant grant
funds in the past and was delayed beyond the control of the community.
As can be seen from a review of these two concepts, the key is to have spent the time
to review all funding options and have a project packaged to the point that
congressional funding is the last, but potentially promising resort. Using the information
provided in this chapter as an overall checklist for local, state, and federal agency
funding opportunities will serve communities well in covering the "other funding" bases.
Spending appropriate time to prepare a well written, concise project history, scope and
objectives document will serve to focus a community's project objective. The
community, its engineer, and state and congressional representatives should be
involved in the packaging process.
Below is a checklist of items to review before a community goes to the U.S. Congress
with its project. Community leaders should remember that they are looking to get their
representative's attention and have their project meet the objectives of the current line
item funding written and unwritten criteria.
I. Project factors to be completed before taking a project to U.S. Congress
A. Past site, environmental, and water quality issues addressed
1. The project is planned and on its way to being designed.
2. The community has reviewed other funding and understands why it is not
available.
5-9
-------
3. The state has supported the project in writing and has given it high priority.
B. Past agency issues have been addressed
1. The community addressed state concerns raised during the planning
process.
2. The community has or is continuing to work to secure all project permits.
C. The project is packaged
1. Unique project qualities have been determined.
2. The community knows all its lost opportunities for funding and the reasons.
3. The community has a well written one to two page summary describing the
project and needs.
4. Parallels to past congressionally funded projects have been developed by the
community.
5. The project's objectives have been packaged in a user-friendly format.
II. Recommended Washington-based activities
A. Develop the right team to present and monitor congressional actions
1. Set up a team representing the community that includes:
State congressional delegation representative
Local elected representative
Governor's office
Project owner's staff
Consulting engineer
Governmental affairs manager or consultant.
2. Make specific assignments to team members.
B. Make sure that the team understands the project and its objectives.
C. Meet with and/or communicate frequently with the community's congressional
delegation
D. Use the team's past experience to create new relationships with influential
congressional leaders, appropriate committee members and staff
E. Monitor the schedule of both the authorizing and appropriations committees
F. Develop, manage, and communicate with project team members frequently
G. Make responding to questions, inquiries, or requests a high priority
III. When a community "wins" funding
5-10
-------
A. Make sure that the entire congressional delegation gets credit
B. Work with the appropriate funding agency in the grant release process
1. That agency has control over grant percentages, the application or non-
application of rules, regulations, and program guidance.
2. Most funding agencies burdened with the grant release process are
understaffed and need community technical assistance to move quickly.
3. Be willing to share a small portion of the grant to cover necessary funding of
agency administrative costs of grant administration.
4. Keep very accurate records during the project because federal audits are
likely years after the project is complete.
Initial Capital Funding for the Skokie Street Storage System
As discussed earlier in this chapter, Skokie's initial capital funding plan had the
following two objectives:
Lessen the cost or eliminate the need to construct the $100,000,000 relief
sewer system that was recommenced by its existing CWA Section 201
Facility Plan.
Develop an innovative technical alternative to the relief sewers, work with
State and Federal agencies to win approval and secure some outside
funding to make the alternative affordable.
Skokie began work with the regional consulting engineering firm Donohue and
Associates, Inc., of Milwaukee, Wl (now Earth Tech, with corporate offices in Long
Beach, CA), who developed the innovative street storage system. Once this system
was documented in a feasibility study and the estimated capital cost was shown to be
only a quarter to a third of the cost of the relief sewers, Skokie called a meeting with the
State of Illinois.
The state was impressed with the technical approach and quickly realized that this
innovative technical alternative could be applied to other communities in the area and
result in a significant lowering of capital infrastructure cost. With this being the case,
the state became a partner in the project and began working with Skokie to find ways to
assist with making the project a reality.
While the USEPA's Construction Grants Program specifically made the relief sewer
alternative an ineligible project, the state had begun work on the new USEPA State
Revolving Loan Program which allowed the State more flexibility in making eligibility
decisions. After reviewing the water quality impacts and evaluating the technical merits
of the project, the state made the project and technology eligible for its low interest loan
program. Low interest loans were important catalysts in both the Skokie and Wilmette
5-11
-------
street storage projects.
The new funding program was entitled the "State of Illinois Water Pollution Control
Revolving Fund" (WPCRF). At its inception, it offered communities 20 year loan rates
equal to one-half the interest rate for which the State of Illinois could borrow monies.
Once Skokie began the project, it recognized that expanding the project objectives and
building a partnership with the state helped bring in outside capital to lower the cost of
the project and create a new project partner. This process was continued with the State
of Illinois Department of Transportation (IDOT). Skokie had a need to build street
storage infrastructure in and near to IDOT facilities. Working with IDOT and
demonstrating the positive impact of the street storage project on their facilities resulted
in the Village's receipt of additional direct grant dollars from the IDOT's own funding
programs. Another phase of Skokie's partnership with the state is grants received
under the Build Illinois program.
In the fourteen years Skokie has continued with the project, they have used a
combination of SRF loan monies, direct grant monies from the State of Illinois
Department Transportation, Build Illinois grants, and General Obligation local bond
monies to bring the project to where it is today. A general breakdown of these four
funding sources, is as follows:
Water Pollution Control Revolving Fund = $18,700,000
IDOT grants = 1,100,000
Build Illinois grant = 500,000
General Obligation bonding = 56,000,000
Total $76,300,000
On-Going Local Capital Funding of the Skokie Street Storage System Through the
Bond Market
Fishman (1998) reviewed the history of the Skokie street storage project with emphasis
on how it was financed on the local, non-agency front. As the project neared
completion in 1998, Fishman's paper provides a contemporary, insightful, outsider's
view of the systematic, prudent and persistent process followed by community leaders
to use the municipal bond market to finance project costs outside of agency funding
sources. The paper reviews the advantages of the phased implementation of the
system over an approximately 14 year period and provides insights into the
marketability and the investors desire to purchase municipal bonds for projects such as
this.
Even though the cumulative capital cost of the innovative street storage system was to
5-12
-------
be only about one-third the cost of more traditional sewer separation approaches, this
was the most expensive project ever undertaken by the community. Skokie faced a
great financial challenge.
From the outset, according to Fishman (1998, p. 181), Skokie enjoyed at least two
project financing advantages. First, the community had a high credit rating so that bond
issues typically drew multiple bidders. This yielded favorable interest rates. Second, as
an Illinois home-rule community, the community leaders did not have to get voter
approval for general obligation bonding.
As part of the street storage financing process, the community retained an individual
financial advisor. According to Fishman (1998, p. 182), the financial advisor's
responsibility was:
...to structure bond offerings on behalf of
issues so that they are legal and fair, as well
as attractive to both investors and dealers.
Then, at a pre-set time and under terms put
forth in his offering documents, he invites
would-be dealers to bid on the issue.
Moody's Investors Service was retained by Skokie to determine the community's
financial health. This is where the new and innovative nature of the street storage
system could have affected the capital financing process. Fishman (1998, p. 182)
explains that the soundness of any particular project in a community usually doesn't
affect the financial health assessment conducted by Moody's and other rating agencies:
...but in Skokie's case, the review would have
to account for the largely experimental and
expensive technology involved in the project.
...Moody's even made a few house calls to get
a feel for the intangibles that might not be
captured by the town's financials.
Apparently the "experimental" technology passed muster. Skokie funded the capital
cost of the project largely with a series of eight general-obligation bonds, the first of
which was issued in 1985. A total of $56 million was borrowed at interest rates ranging
from 4.5 to 7.2 percent. In 1998, Skokie:
...completed the last round of borrowing.
Seven bidders sought to issue bonds, and
Skokie got the lowest interest rates since the
project began over a decade ago (Fishman,
1998, p. 185).
Skokie Downspout Disconnection Ordinance and Program
5-13
-------
As suggested in the preceding sections of this chapter, federal and state regulations
often require that a community undertake costly projects. On the positive side, these
regulations also provide the creative, proactive community with opportunities for outside
funding.
While a community has little if any control over state and federal regulations, it does
have overall control over the creation and enforcement of local regulations. Skokie
created and enforced a special local regulation to successfully implement downspout
disconnection, the first concrete step in its program to mitigate basement flooding
caused by surcharging of combined sewers. Described here is the community's
systematic program, which started with information gathering and education, ended with
strict enforcements, and resulted in the disconnection of essentially all downspouts.
Portions of Skokie's approach may be useful to other communities.
The Downspout Problem
As shown in Figure 5-1, when downspouts are connected to the house sewer, they
permit roof water to directly and immediately enter the CSS. This aggravates combined
sewer surcharging and basement flooding problems.
The Downspout Solution
The adverse effects of directly connected downspouts can be partly mitigated by
disconnection the downspouts at ground level and directing their outlets toward
landscaped areas. A photograph of a disconnected downspout is provided as Figure 5-
2.
Paintal (1981), in his study of Skokie's ESSD, concluded that "for short duration storms
the disconnection of downspouts from the sewer system reduces the flow in the sewer
significantly if the flow from the downspouts is directed to lawns and other porous
areas." Skokie's 1974 study of a pilot area concluded that downspout disconnection
would substantially reduce the hydraulic load on the combined sewer system.
5-14
-------
Downspout
*~ Connected
toSewer inlet
but
Catch
Basin
House
Sewer
EXISTING CONDITIONS
Disconnected
Downspout •
'Combined
Sewer
SUBSURFACE TANK OPTION
Used Where Street Ponding
Capacity is Inadequate
STREET STORAGE SYSTEM
Figure 5-1. Downspouts connected to the house sewer, as shown on the left side,
permit roof water to directly and immediately enter the combined sewer system and
increase surcharging.
5-15
-------
Figure 5-2. A disconnected downspout.
5-16
-------
Educational Value
Even if downspout disconnection does not achieve a major reduction in the load on a
combined sewer system, it can have a positive community-wide educational effect.
Success of a downspout disconnection program requires participation, that is, specific
action, by essentially all property owners. Accordingly, they are likely to gain additional
understanding of the cause and effect relationship between stormwater runoff and
surcharging of the CSS. Armed with this knowledge, citizens are more likely to
understand the need for and give support to other much more costly components of a
street storage system. Examples of those other components are berms, flow
regulators, and underground tanks.
Downspout Disconnection Process Used in Skokie
This description is based on a paper by Walesh and Schoeffman (1984) which was
presented near the end of the disconnection program. The Skokie program began in a
regulatory manner with the September 1981 passage by the Board of Trustees of an
ordinance requiring the disconnection of all downspouts on one and two family
residences.
However, the initial strategy was to gather information and encourage volunteer action,
rather than emphasize enforcement. Questionnaires were sent to every involved
residence. This questionnaire set the groundwork for the subsequent two year
implementation effort. Residents were asked if their downspouts were already
disconnected, whether they needed assistance or advice, and whether they felt that
special circumstances made them eligible for an exception from the ordinance.
Based on the response from this survey, Skokie personnel began a comprehensive
program of assistance and inspection to determine where exceptions could be granted
and to find where compliance had been achieved. The initial inspection effort found
that volunteer action in response to previous recommendations to disconnect
downspouts had resulted in almost 50% compliance with the ordinance before its
passage.
In order to make the program manageable, residential areas of the community were
broken down into 21 housing districts, each containing approximately 700 residences
and covering an area of approximately one-half square mile. Each housing district was
dealt with separately and given a specific compliance date. Owners or occupants of
residences determined through inspection to be violating the ordinance were notified by
letter of the compliance date for their district. After expiration of the compliance date,
another inspection was made and a "warning citation" left at the residence by the
inspector. Two weeks after this warning, a final letter was sent to all non-complying
residents and citations requiring court appearances were issued.
5-17
-------
For a two year period, except during winter months, this process continued. At the
conclusion of the program, 99.9% compliance was achieved in that all but 18
residences out of the total of almost 14,000 satisfied the requirements. A total of 169
citations were issued requiring court action and 19 judgments of up to $500 were
entered by the court.
A review of the small number of exceptions granted under the ordinance indicates that
more than 90% of the roof water from one and two family homes in Skokie were
disconnected from the sewer systems. One reason for this small number of exceptions
is the specific criteria used to evaluate the need for an exception. Exceptions were
granted only if the downspout water could not be directed to a location where it would
drain away from all building structures with the use of an extension up to ten feet long
or where a necessary downspout extension would block a sidewalk or driveway.
Skokie Stormwater Control Ordinance
As explained by Donohue (1987a, p. 3-2):
Skokie adopted a stormwater control ordinance
in August 1977. This ordinance requires that
all new development limit the peak runoff rate
from the site to that of an undeveloped 2-year
frequency storm (C = 0.15). Excess
stormwater runoff, as determined by the
difference between the stormwater runoff from
the undeveloped area with a 2-year storm and
from the developed area with a 100-year
storm, shall be stored onsite in a stormwater
retention or detention facility.
All development that existed prior to the
effective date of the ordinance was exempt
from the stormwater control requirement
except certain off-street parking facilities and
developments that are destroyed or improved
by greater than 50 percent of the original value
of the structure before such damages were
incurred or improvements were made. The
ordinance also outlines minimum design and
construction criteria for onsite stormwater
retention/detention facilities and discusses
maintenance, administration, and enforcement.
This ordinance focuses primarily on new development but also applied to
redevelopment. Given that Skokie is essentially fully developed, as are many CSS
areas or communities, stormwater ordinances intended to prevent increased runoff
rates from new development will not typically have remedial effects. They can,
however, prevent aggravation of existing surcharging and related problems.
Skokie's stormwater ordinance provided a "safety factor" for the street storage system.
5-18
-------
In designing the street storage system to prevent combined sewer surcharging, the
ordinance allowed the assumption that any redevelopment in the community would be
restricted by the two year criterion.
Regulations of the Metropolitan Water Reclammation District of Greater Chicago
The "Manual of Procedures for Administration of the Sewer Permit Ordinance" was
adopted by the MWRDGC in 1970. Included are guidelines and criteria for the design
of sewerage within the agency's jurisdictional area. An MWRDGC permit is required for
a sewer system to discharge to the agency's system. The following provisions (quoted
from Donohue, 1982a, pp. 28-29) related to CSS:
1. Complete separation of sewers shall be provided within the property lines.
2. Detention shall be provided and/or permanent constrictions shall be built on
the stormwater sewer system to control flow into the existing combined
system in accordance with the requirements of the local government.
3. All downspouts or roof drains shall be discharged onto the ground or be
connected to storm or combined sewer.
4. Footing drains shall be connected to sump pumps and discharge shall be
made into storm sewers, combined sewers, or drainage ditches.
5. Floor drains in basements shall be connected to sump pumps and
discharged to sanitary or combined sewers.
6. Sump pumps shall be used for only one function, either to discharge
stormwater or to discharge sanitary sewage. If both functions are used in
one building, two pumps are required.
wp/epastch5
5-19
-------
CHAPTER 6
STAKEHOLDER INVOLVEMENT
Two Public Works Challenges
Two major challenges face today's public works personnel. The first is the challenge of
finding cost-effective solutions to increasingly complicated urban problems. The
second is communicating effectively with the public, recognizing the public's
increasingly elevated expectations relative to public facilities and services and the
public's growing understanding of technology and the environment. A premise of this
chapter is that many and varied stakeholders want to be involved in public works
decisions and should be given the opportunity to do so.
In retrospect, there was great need for meaningful communication with stakeholders in
the Skokie and Wilmette street storage projects. Two factors heightened the need for
stakeholder involvement. First, the technology was very new, especially for Skokie.
Second, many individuals, especially residents and business people scattered
throughout the CSS, would be directly affected. These were not remote projects.
Interestingly, and fortunately, both Skokie and Wilmette recognized the need for intense
communication. From the outset, both communities mounted proactive efforts to
interact with stakeholders. These efforts apparently played a major role in the success
of the two projects. As evidence of this, read the Chapter 8 summary of interviews and
comments with Skokie and Wilmette officials.
Purpose of this Chapter
Given the apparent importance of stakeholder involvement in the two street storage
projects described in this manual, the purpose of this chapter is to describe those
efforts. This documentation may be helpful to other communities. While communities
with a CSS should benefit from some of the specifics, many of the stakeholder
involvement efforts in Skokie and Wilmette are applicable to a wide range of public
works projects. Therefore, this chapter, unlike most other chapters of this manual, is
not focused primarily on street storage systems.
6-1
-------
A Characteristic of Wet Weather Problems: Widely Fluctuating Public Interest
The interest of the public and some elected and appointed government officials in wet
weather problems and opportunities tends to fluctuate widely, as illustrated in Figure 6-
1. The fluctuations parallel the random nature of major meteorologic events. Interest
usually is most intense during and immediately after a destructive problematic water
event such as basement or surface flooding, or CSOs.
Later, typically months later, when the initial studies/plans/preliminary engineering are
completed and recommendations made, interest has subsided. The zeal that
commissioned the investigations is not complemented with similar zeal to implement
the recommendations of those investigations. Maintaining stakeholder interest is one
challenge of a stakeholder involvement program.
The widely fluctuating interest associated with wet weather problems contrasts with a
morel level and continuous concern with most other areas of public works and services.
Examples are water supply pressure; condition of streets, especially presence of
potholes; level of police protection; and quality of public schools. Once problems
develop in these areas, they tend to persist and to receive persistent public attention
until they are solved.
More on the Need for Stakeholder Involvement
A public works effort that fails to include a stakeholder involvement program plans to
fail. Although said over a century ago, and in an entirely different context, the following
words of President Abraham Lincoln are appropriate: "With public sentiment, nothing
can fail; without it nothing can succeed. Consequently, he who molds sentiment goes
deeper than he who enacts statutes or pronounces decisions" (Helweg, 1985).
Grigg (1986) defines planning as "studying what to do" and distinguishes planning from
decision making or "deciding what to do." The point is that studying and deciding are
two different activities or processes, and, as exemplified by the preparation of a street
storage plan, the studying and deciding processes are usually carried out by different
groups. A team of professionals and technicians prepares the plan. Another group of
primarily appointed and elected officials, usually influenced by the public, typically
makes decisions based on the findings of the plan.
Because planning and deciding are different functions done by different groups, public
works personnel and their consultants must not be so presumptuous as to think that
their recommendations will be fully embraced by decision makers. The professionals
can greatly enhance the probability of acceptance of the recommendations if the work
is of high quality and if the professionals effectively communicate with all interested
individuals and groups.
6-2
-------
Wet Weather
Event
Procrastina tion
Pan±r
Plan
Figure 6-1. The "Hydroillogical" cycle
6-3
-------
A public interaction program, or lack thereof, is often the principal reason for the
successful implementation of a public works program or the failure to implement it. This
observation is supported by the work of Kurz (1973) and Rubin and Carbajal-Quintas
(1995) who describe six unsuccessful urban area planning efforts (not all water-related)
and conclude why they were not implemented. Deficiencies identified include a lack of
clearly presented objectives and standards; poor public involvement efforts; inadequate
coordination between government units and agencies; and a myopic approach to the
identification, development, and testing of alternatives. Kraft (1997) concludes that
failure to build public consensus is the reason for the failure of several public projects
that would have incorporated new ideas. Street storage is an example of a new idea.
Kraft lists causative "common pitfalls" similar to the preceding deficiencies. Avoiding
such deficiencies and pitfalls is the goal of a public interaction program, especially when
new, innovative technology is contemplated.
Perry (1996) advocates the preceding ideas using a "pro and con" model of public
communication. When the desirable "pro" approach is used, public works professionals
are proactive, proficient, and pro-people. In the undesirable "con" mode, the situation is
confrontational and confusing and messages are contrived.
Herrin and Whitlock (1992) somewhat harshly, but perhaps accurately, suggest that the
cause of some communication failures lies with engineers', and perhaps other
professionals', formal and informal education. According to them:
Engineers are taught very few skills in
interpersonal relationships, much less those of
public interface and involvement. We spend
little, if any, time addressing it at our
conferences and conventions. We then spend
thousands of hours and millions of dollars
defending our projects when threatened by
delays and possible blockage by public
intervention.
As noted by Viessman (1989), public sector problems "cannot be solved in the
technologic area only... Engineers must be society-wise as well as technology-wise."
Identification of Stakeholders
The success of a stakeholder involvement effort is determined more by the number of
different, legitimate stakeholders involved then by the total number of individuals
involved. Many subgroups with very different, often competing agendas typically
constitute the stakeholders. Breadth of stakeholder representation and involvement is
crucial as suggested by Figure 6-2.
6-4
-------
Figure 6-2. Breadth of stakeholder involvement is crucial (Source: USEPA, 1997).
6-5
-------
Public works officials should be especially wary of the temptation to exclude what they
regard as "extremist" elements from the deliberation process. These groups have a
right to be part of the process and to express their views. Attempts to exclude them are
likely to aggravate matters and precipitate or elevate conflict. In addition to affording
them their rights, inclusion of "extremist" organizations may lead to moderation of their
positions as their representatives are gradually exposed to data and information
developed during the management program and as they interact with spokespersons
for other segments of the public.
Presented in Figure 6-3 is a likely set of stakeholders for a street storage project. Note
the breadth of interests that are represented.
Types of Stakeholder Involvement
Priscoli (1989) suggests that interaction between public works professionals and the
public refers to a continuum of activities, programs, and techniques. The continuum
ranges from proactive public involvement (e.g., public information, advisory groups,
workshops) at one end of the spectrum to reactive conflict management (e.g.,
mediation, collaborative problem-solving, negotiation, and arbitration) at the other end.
The preceding suggests that stakeholder involvement should employ many and varied
programs and events.
Unfortunately, some professionals with public works responsibilities fail to appreciate
the importance of the communication challenge, or they recognize the challenge but are
not prepared to meet it. The traditional DAD approach, that is, public works
professionals adopt a decide-announce-defend mentality, is no longer appropriate. The
much more progressive and inclusive POP approach, that is, public owns project, is
more likely to be effective given the changing nature of the public's expectations and
knowledge (Walesh, 1999).
Speaking directly to civil engineers, and indirectly to all public project professionals,
Wakeman (1997) describes today's situation this way: "...broad sections of today's
public are concerned, vocal, and actively engaged in the formulation and
implementation of public policy, particularly policies regarding public facility construction
projects. Today's civil engineer must be ready to work on infrastructure projects from
many more perspectives than were required in earlier years."
Furthermore, stakeholder involvement is explicitly intended to be an iterative, two-way
process. The old DAD strategy is out. It is being replaced by the two-way POP
strategy in which concerns, ideas, and information flow freely between water resource
professionals and the individuals and organizations representing various interests.
Public interaction goes way beyond no communication (Figure 6-4) and announcing
decisions (Figure 6-4). Interaction even goes beyond public information (Figure 6-5),
6-6
-------
Local
Elected
Officials
Operation
and Maintenance
Personnel
Elected
State and
Federal
Representatives
Street
Storage
Project
Regulatory
Personnel1
Engineering
and Other
Consultants
Representatives
of
Contiguous
Communities
1) Local, regional, state, and federal entities.
Figure 6 - 3. A street storage project is likely to have many stakeholders, all
of whom should be involved from the outset.
-7
-------
Public
Consultants
and Public
Works
Personnel
NO COMMUNICATION
Consultants
and Public
Works
Personnel
DECISIONS
Public
ANNOUNCING DECISIONS
Figure 6-4. No communication and announcing decisions are increasingly unacceptable
ways of serving the public.
-------
Public
Consultants
and Public
Works
Personnel
PROVIDING INFORMATION
Consultants
and Public
Works
Personnel
Public
INTERACTION
Figure 6-5. The goal in stakeholder involvement goes beyond providing information,
it is meaningful interaction.
ppt/fig5-5
6-9
-------
which implies one-way communication from water professionals to the public. Public
interaction is truly two-way communication (Figure 6-5).
The importance of conducting the public interaction effort throughout a public works
program—from beginning to end—must be emphasized. Astrack et al (1984), Rubin et
al (1995) and Walesh (1993) emphasize the need to repeatedly interact with various
elements of the public beginning on "Day 1" and extending throughout the process. In
addition, the process should be highly visible to and easily accessible by the public.
Sargent (1972) uses the term "fishbowl planning" to suggest frequent and open
stakeholder involvement as the plan is being prepared.
The stakeholder paradigm presented in this chapter has three objectives (Walesh,
1989, 1993, 1999). They are:
The first objective is to demonstrate to the stakeholders that the public
works professionals are aware of the problems, at least in a general
sense; want to learn more about them; and want to seek solutions. In
other words, public works professionals need to demonstrate empathy
and concern. The public's position in the early part of a planning process
might be represented by the anonymous statement, "I don't care how
much you know until I know how much you care." Sometimes the most
vociferous citizens need an opportunity to vent their frustration with public
works problems and the apparent inability of responsible parties to solve
those problems. As stated by P. S. Hale, "We earned the public's distrust.
We'll have to work even harder to regain their trust" (Eschenbach and
Eschenbach, 1996). The interaction process must provide opportunities
to express frustration, to find empathy among the public works
professionals, and, hopefully, to enable frustrated individuals to become
positive participants in the problem defining and solving process.
The second objective of a stakeholder involvement program is to gather
supplemental data and information pertinent to the effort. Interested
citizens and officials, if informed about what they believe to be a
potentially useful public works effort, are likely to contribute photographs,
information on problems, ideas on solutions and other useful data and
information. Similarly, but on a larger scale and in a more formal manner,
various government units and agencies are likely to offer potentially useful
data, reports, funding opportunities and other information if they are
informed about the effort, are invited to contribute, and believe they will
benefit.
6-10
-------
The third and final objective of stakeholder involvement is to build a base
of support for rapid plan implementation. Enlightened citizens and
officials, who have been informed about a public works program and have
been given an opportunity to participate in it, are likely to become
supporters of the program, to help interpret it for others, and to otherwise
help implement it. Worthy goals are to have stakeholders exhibit pride of
authorship and a sense of ownership in the public works program.
Essential to the success of a public works effort is agreement between the public and
the professionals on what problems are to be mitigated or prevented. As stated by
Silberman (1977), "The objectives of a public participation program should be to assure
that the planners and the public have the same understanding of what the problems are
and that the proposed solutions are perceived as solutions by both the planners and the
public." Concurrence on problem definition is not as simple as it may seem. For
example, basement flooding in a CSS might be viewed as "the problem" by the public.
In contrast, public works personnel might view such flooding as the "symptom" of the
"real problem," namely, an inadequately sized CSS or localized constrictions in the
system.
Examples of Stakeholder Involvement Techniques
Skokie and Wilmette Approaches
Skokie and Wilmette used, and continue to use, an effective mix of stakeholder
involvement programs, events and supporting devices. Some of their strategies and
tactics may be of value to other communities.
Both communities used the strategy of starting the stakeholder involvement effort at the
beginning of the street storage projects, that is, when the projects were in the concept
stage. Second, the stakeholder involvement process was and is being continued
throughout the projects. A third shared strategy is that both communities used a variety
of communication tactics.
Stakeholder involvement tactics used or being used in Skokie and Wilmette include:
• Articles in the community's newsletter—"Newskokie" in Skokie and the
"Communicator" in Wilmette.
• Cable television programs.
• Surveys of residents. Wilmette had an excellent response on its survey of
residents in the CSS.
• Letters to residents.
6-11
-------
• Public meetings which were usually held at the Village Hall. In a spirit of
outreach, Wilmette conducted some meetings in resident's homes.
• Use of a committee of senior personnel, such as Skokie's Flood Task
Committee, to monitor and guide the engineering consultant's efforts (Walesh
and Schoeffmann, 1984).
• Physical models, like an operating, table top device created under the Skokie
project to illustrate surface and subsurface storage.
• Assigning one public works person to answer telephone inquiries.
• Special brochures
• Conduct of high visibility field pilot studies that included the construction of
berms, so that citizens can drive over and experience them, and the
temporary flooding of streets, so that citizens could observe the depth and
lateral extent of ponding.
• Video taping, for subsequent informational use, construction of facilities,
ponding on streets, and vehicles driving over berms (Walesh and
Schoeffmann, 1984).
• Brief discussions of the evolving street storage system as part of new
resident receptions. This approach was used in Wilmette.
Additional Tactics
Many and varied other tactics have been used for interacting with stakeholders. Ideas,
in addition to those presented in the preceding section, are (Walesh, 1999):
• Presentations to service clubs and other community groups: Knowledgeable
and influential community leaders are typically members of one or more civic
organizations such as service clubs, environmental groups, and professional
associations. Because of the frequency of their regular meetings—
sometimes two or more times per month—these groups are often receptive to
suggestions for speakers and programs. Such presentations can help to
expand knowledge of and support for a water management effort.
• School programs: By educating school children about water issues, a two-fold
result can be achieved. The students gain understanding and, to the extent
they share what they learned with their parents, the knowledge is
disseminated.
• Guided and self-guided tours: Interested individuals and groups, including
6-12
-------
news people, can be provided with guided tours of a project area, such as a
CSS. A single bus or van, preferably equipped with a public address system,
should be used for a guided tour so that all participants can easily travel
together and can be provided with an informative narrative between stops.
Self-guided tours are also possible if a written tour guide is available. Guided
and self-guided tours enhance understanding of the location and severity of
wet weather problems. Well-meaning citizens often have strong opinions
about environmental problems (e.g., combined sewer overflows) that they
have never seen or experienced. Tours also provide an opportunity for the
public works officials and their consultants to explain and show remedial and
preventive measures that are under consideration in the planning program.
Another benefit of guided tours is the spirit of camaraderie that typically
develops and the new interpersonal relationships that often result.
Briefings for newly-appointed or elected public officials: By being introduced
to issues and being provided with basic information on proposed, on-going or
completed public works projects, new public officials are more likely to be
supportive (Gilbert et al, 1981). Tactics include inviting them to join advisory
committees or to attend public meetings and providing them with special
briefings.
Preparation of media packages: Example contents are summaries of
regulations; descriptions with photographs of problems; brief discussions,
supplemented with photographs or graphics, of potential solutions; and
experiences of other communities.
Workshops: Public works officials and their consultants can conduct
workshops for interested citizens and public officials. These events provide
an opportunity for in-depth exploration of substantive topics such as issues,
findings, alternatives, recommendations, funding, and operations.
Electronic-based access and input: Email and websites (e.g., Tarn and
Murillo, 1997) offer exciting possibilities.
wp/epastch6
6-13
-------
CHAPTER 7
INSPECTION AND MAINTENANCE
Essentiality of Inspection and Maintenance
The experience of Skokie and Wilmette indicate that systematic maintenance is
essential to the effective functioning of a street storage system. Such a storage-
oriented system will malfunction, at least locally, if inlets or flow regulators become
obstructed with leaves, twigs, Styrofoam containers and other debris.
The preceding observation is also applicable to more traditional stormwater storage
facilities. It is not unique to a street storage system. The outlet works of a typical
stormwater detention basin should be carefully designed to minimize the potential for
blockage. Nevertheless, a systematic inspection and maintenance program is usually
required to further reduce the likelihood of malfunctioning to an acceptable level.
The point is that any stormwater storage system requires some sort of outlet control
structure or device. Even with thoughtful design, that outlet structure or device is
subject to failure without proactive inspection and maintenance.
Both Skokie and Wilmette report increased inspection and maintenance after
installation of their street storage systems. Refer, for example, to the Chapter 9
summaries of interviews with personnel from these communities. Quantifying the
increased inspection and maintenance effort is difficult, although Skokie personnel
described the overall effort as being "doubled." The increased effort is significant.
In considering the increased inspection and maintenance effort, the pre-system status
should be considered. Skokie, for example, carried out minimal catch basin inspection
and maintenance prior to construction of the street storage system. Evidence included
many completely filled sumps. Wilmette inspected and maintained catch basin sumps
only once every three years prior to the street storage system. These levels of
inspection and maintenance are substandard because they render the sumps
ineffectual in trapping solids. However, the catch basins functioned hydraulically.
Under street storage system conditions, sumps must be largely free of debris. Leaves,
twigs, Styrofoam containers and other debris trapped in catch basin sumps, if allowed
to accumulate too much, will begin to plug the orifices in the hanging traps. Stated
7-1
-------
differently, catch basin sump cleaning may be viewed as hydraulically optional in the
pre-street storage system mode. However, it is mandatory with the street storage
system in place.
Inspection and Maintenance Procedures for Skokie's Street Storage System
Recognizing the importance of system operation, Skokie commissioned the preparation
of a manual (Rust, September, 1995) to guide inspection and maintenance. This
manual was first prepared in June 1993, revised in November 1994 and September
1995, and was being revised again in 1999 as this manual was being written. The
specific purpose of the manual is to provide Department of Public Works personnel with
information needed to operate and maintain the street storage system.
Included in the manual are a synopsis of the history and function of the street storage
system, detailed description of system components, and detailed inspection and
maintenance procedures. This chapter draws on the detailed inspection and
maintenance procedures with the idea that they may be of interest to other CSS
communities contemplating a street storage system.
Inspection and maintenance procedures are arranged in the manual according to the
following six categories (quoted from Rust, September, 1995, Section 3.0).
1. Underground and surface storage basins - normal operation, inspection, and
trouble shooting.
2. Stormwater storage basins and dewatering pump stations - inspection and
trouble shooting guide.
3. Submersible dewatering pumps - standard maintenance procedures.
4. Flow regulators and catch basins - standard operating and maintenance
procedures.
5. Street berms and diverters - standard operating and maintenance
procedures.
6. Street ponding areas - standard operating and maintenance procedures.
Surface and Subsurface Storage and Dewatering Facilities
Summaries of the inspection and maintenance procedures for the first three categories
are presented, respectively, in Appendices C, D, and E of this manual. Referred to as
trouble shooting guides (the first two) or standard procedures (the third one), these
three inspection and maintenance procedures are made available in laminated card
format for Department of Public Works Personnel.
7-2
-------
Flow Regulators
Recall that two types of flow regulators are used in Skokie. They are the hanging trap,
which is widely used, and the vortex (Hydro-Brake and other) regulator, which is used
when the required orifice size is too small for use of the hanging trap. Flow regulator
inspection and maintenance procedures, quoted from Rust (September, 1995, Section
3.4), are:
1. Catch basins with hanging trap regulators should be inspected on a minimum
annual basis and maintained as required.
2. The best time for inspection is during the fall leaf season.
3. With a sounding pole, check the structure for an accumulation of grit in the
catch basin. There should be no accumulation of grit within one foot of the
bottom of the orifice.
4. Excessive floating material in the catch basin that reaches the orifice inlet
should also be removed.
5. Clean catch basins with hanging traps, and grit or floating material
accumulations, in the same manner as a normal catch basin.
6. Ponded water in the vicinity of a catch basin with a flow regulator is an
indicator of a clogged orifice.
7. If a street area is flooded because of a plugged regulator, dewater the area
and catch basin with a pump.
8. Clear the clogged trap by removing and replacing it, or by removing the plug
in the tee and rodding. Use confined space entry procedures if a person has
to enter the catch basin structure for any reason.
9. Use a similar strategy for inspection and maintenance of vortex regulators
installed in catch basins. To correct a clogged condition from a vortex
regulator, the entire device might have to be removed.
10. Record inspection and maintenance information on form provided.
7-3
-------
Street Berms
Inspection and maintenance procedures for berms, quoted from Rust (September
1995, Section 3.5), are:
1. At a minimum, the condition of the street berms should be inspected on an
annual basis. Inspect bituminous areas for the following features indicating
deterioration:
Rutting. A depression in the pavement parallel to the side of the street. A
depth of % inch is slight; % to 1 inch is moderate; greater than 1 inch, or such
to affect vehicle steering, is severe.
Raveling. Breaking of the surface with visibly loose pieces of aggregate.
Flushing. Asphalt mixture covers the aggregate on the pavement surface.
Corrugations. Ripples are visible in the pavement perpendicular to the
direction of traffic.
Alligator Cracking. Pavement cracks in a wire mesh-like pattern. Slight when
barely visible; moderate when some cracks exceed 1/4 inch in width; severe
when the sides of cracks become fully separated.
Transverse Cracking. Cracks in the pavement perpendicular to the direction
of traffic. Severity criteria the same as for alligator cracking.
Longitudinal Cracking. Cracks in the pavement parallel to the direction of
traffic. Severity criteria the same as for alligator cracking.
Patched Areas. Evidence of repaired potholes, utility cuts, or other failed
areas. Slight when level with the pavement with no sign of deterioration;
moderate when deteriorated, but not enough to slow traffic; severe when
deteriorated and deep enough to slow traffic.
2. Repair minor deteriorated areas in street berms in the same manner as a
typical street area.
3. For major damage to roadway berm areas, the surface should be scarified
down to the point where a stable sub-base is reached, and resurfaced to the
original grade. This work would typically not be done by Village staff, but
rather by an outside contractor.
4. Reference the record contract drawings to obtain the design grade
characteristics of each berm area.
7-4
-------
5. Record inspection and maintenance data on the form provided.
Street Ponding Areas
Procedures for inspection and maintenance of street ponding areas, quoted from Rust
(September 1995, Section 3.6) are:
1. At a minimum, the condition of the street ponding areas should be inspected
on an annual basis. Inspect bituminous areas for the following features
indicating deterioration:
Rutting. A depression in the pavement parallel to the side of the street. A
depth of % inch is slight; % to 1 inch is moderate; greater than 1 inch, or such
to affect vehicle steering, is severe.
Raveling. Breaking of the surface with visibly loose pieces of aggregate.
Flushing. Asphalt mixture covers the aggregate on the pavement surface.
Corrugations. Ripples are visible in the pavement perpendicular to the
direction of traffic.
Alligator Cracking. Pavement cracks in a wire mesh-like pattern. Slight when
barely visible; moderate when some cracks exceed 1/4 inch in width; severe
when the sides of cracks become fully separated.
Transverse Cracking. Cracks in the pavement perpendicular to the direction
of traffic. Severity criteria the same as for alligator cracking.
Longitudinal Cracking. Cracks in the pavement parallel to the direction of
traffic. Severity criteria the same as for alligator cracking.
Patched Areas. Evidence of repaired potholes, utility cuts, or other failed
areas. Slight when level with the pavement with no sign of deterioration;
moderate when deteriorated, but not enough to slow traffic; severe when
deteriorated and deep enough to slow traffic.
2. Repair minor deteriorated areas in street ponding areas in the same manner
as a typical street area.
3. For major damage to street ponding areas, the surface should be scarified
down to the point where a stable sub-base is reached, and resurfaced to the
original grade. This work would typically not be done by Village staff, but
rather by an outside contractor.
7-5
-------
4. Reference the design drawings to obtain the design grade characteristics of
each ponding area.
5. Record inspection and maintenance data on the form provided.
Safety of Inspection and Maintenance Personnel
The Skokie Department of Public Works uses a Safety Manual (Skokie, 1992) which
contains procedures to be followed by Village personnel. Much of the manual's content
is applicable to inspection and maintenance of the street storage system. As stated by
Rust (September, 1995, Section 4.0), with respect to safety and the street storage
system, "Topics of concern that should be reviewed by all workers performing
maintenance procedures include: traffic control; worksite safety; confined space entry;
safety equipment; and emergencies, first aid and hygiene."
wp/epastch7
7-6
-------
CHAPTER 8
CONSTRUCTION COSTS
Purpose
This chapter's purpose is to provide construction cost ideas and information which
might be useful to other CSS communities contemplating street storage. Accordingly,
presented are the total construction costs for those systems. Also included, for both
Skokie and Wilmette, are estimated construction costs if traditional solutions had been
implemented. These costs are compared to the much lower costs for the street storage
systems. Street storage costs are normalized and compared to normalized costs for
other options. The chapter concludes with a discussion of intangible costs.
Skokie Construction Costs
As shown in Table 8-1, the total construction cost for the Skokie street storage project,
which was to be completed in 1999, is projected to be $67 million. (This is the
cumulative construction costs not adjusted for inflation. As shown in Appendix G, total
construction costs converted to 1999 dollars using the ENR CCI is $78 million.) The
graphical presentation in Figure 8-1 emphasizes the differences in the relative costs of
berm-flow regulator installations, sewers and supplemental storage.
Comparison of Figure 8-1, which summarizes construction cost data, with Figure 3-35,
storage location data, suggests the cost effectiveness of temporary, controlled storage
of stormwater on streets. The berm-flow regulator installations in Skokie account for
only nine percent of the total construction cost while providing about half of the total
stormwater storage. In Wilmette, the berm-flow regulator installations account for all of
the stormwater storage.
A generalization to many CSS cannot be made based largely on in-depth experience
with two communities. Nevertheless, the Skokie and Wilmette case studies suggest
that retrofitted storage of stormwater on streets may be very cost effective. Therefore,
it should be at least considered at the outset of any urban project involving the control
of stormwater runoff.
Figure 8-2 compares actual construction costs for the Skokie street storage system to
the estimated cost if a traditional sewer separation project had been implemented.
8-1
-------
Table 8-1. Total construction costs for the Skokie, IL street storage system (Source:
Carr, 1999).
Element
Berm-flow regulator installations
Storm and combined sewers
Supplemental storage
Total:
Construction Cost
(Million $)
6
20
41
67
% of Total
8.9
29.9
61.2
100.0
8-2
-------
70
60
50
40
30
§ 20
0 10
Berms
Sewers
Supplemental Storage
Figure 8-1. Distribution of construction costs for the Skokie street storage system
showing the relatively small cost of the berm-flow regulator installations (Source:
Carr, 1999).
8-3
-------
Sewer Separation
Source Control
Figure 8-2. Construction costs for Skokie's street storage system are about one-third
the estimated cost of sewer separation (Source: Carr, 1999).
8-4
-------
These costs are adjusted to account for inflation during the Skokie construction period.
As noted, the projected construction cost of the Skokie street storage system, when
expressed in 1999 dollars as developed in Appendix G, is $78 million. As explained in
Chapter 2, sewer separation costs, expressed in 1999 dollars, were estimated to be
$203 million. Therefore, the street storage system cost was about 38% of sewer
separation. Skokie achieved a major construction cost saving by using the street
storage system approach.
Wilmette Construction Costs
The projected total construction cost for the Wilmette street storage system, with three
of five phases already constructed as of early 1999, is $35,169,000. As explained in
Chapter 3, this system will eventually include about 250 berm-flow regulator
installations, essentially all of which have been constructed, and tunneled and
conventionally constructed relief and storm sewers.
For cost comparison purposes, a 1991 facilities plan examined sewer separation and
relief combined sewer options (SEC Donohue, 1992, p. 5). Relief combined sewers
were recommended at an estimated construction cost then of $65 million. The 1999
cost would be $81 million using the ENR CCI. Therefore, the projected construction
cost of Wilmette's street storage system is about 43% the cost of the next best
identified option.
Unit Costs
One way to compare the costs of street storage to more traditional solutions of CSS
problems is to normalize the costs, that is, develop unit construction costs. Examples
of ways construction costs can be expressed on a unit basis are cost per acre, cost per
person, and cost per building. While normalization of costs helps with cost
comparisons, it does not reflect any economies of scale which may occur in the design
or construction process. For example, construction costs are likely to be less per unit
area if one contract is let for a large area than if two or more contracts are let.
Skokie and Wilmette Unit Costs
Table 8-2 presents various unit construction costs for the Skokie and Wilmette street
storage systems. As a point of reference, AMSA (1994, p. 19) reports the following unit
costs for sewer separation:
• Range: $15,000 - $176,000/acre
• Median: $21,000
According to AMSA, these costs are based on CSO work completed as of about 1994.
8-5
-------
Table 8-2. Unit construction costs for the Skokie and Wilmette street storage systems.
Item
Total Projected
Construction Cost (million $)
Area (square miles)
Construction Cost per Acre ($/acre)
Population in the CSS
Construction Cost per Person
($/person)
Number of Single Family Residences
Construction Cost per Single Family
Residence ($/residence)
Number of Buildings
Construction Cost per Building
($/building)
Skokie
781
8.6
14,200
60,000
1,300
20,000
3,900
Wilmette
35
2.0
27,300
11,300
3,100
3,500
10,000
1) Adjusted to 1999 using the ENR CCI.
8-6
-------
Adjusting the unit costs to 1999, using the ENR CCI, yields:
• Range: $16,600 - $195,000/acre
• Median: 23,300
The Skokie and Wilmette street storage unit costs of, respectively, $14,200/acre and
$27,300/acre are at the low end of the AMSA range. The Skokie unit cost is much less
than the AMSA median and the Wilmette unit cost is slightly above the AMSA median.
Discussion of Unit Costs
The preceding street storage system unit costs must be used cautiously. They are
based on construction experience in only two communities. The two communities are
similar in some ways. For example, flat street grades, the same climate and
approximately equivalent performance criteria such as the 10-year recurrence interval
design storm.
However, significant differences occur between the two communities and those
differences may affect unit costs. For example, while both street storage systems
include berms and relief sewers, Skokie's also includes subsurface storage.
Although both communities make intensive use of berms, many of Wilmette's are on
the highly valued brick streets and required very labor-intensive construction.
Furthermore, most of the required catch basins and combined sewer manholes already
existed in Skokie but had to be constructed in Wilmette, further adding to costs.
Having presented the previous caveat and with it in mind, this case study strongly
suggests that street storage, where physically feasible, is likely to be much less costly
than sewer separation and relief sewers, a traditionally more common means of solving
basement and other flooding. Stated differently, if basement and surface flooding is the
only or principal CSS problem faced by a community, street storage should be viewed,
from the outset, as a potential solution. So should separation and any other potential
solution. If CSO's are a problem, with or without basement and other flooding, street
storage should again be considered as an option, either alone or in combination with
traditional technologies.
Omitting street storage as an option in cases like preceding, either because of lack of
information about it or negative perception of it, could result in a community incurring
construction costs that are unnecessarily high. The suggested question to be asked by
a community and its stakeholders is: What is the most cost-effective means of
achieving the agreed-upon level of performance?
8-7
-------
Intangible Costs
The preceding costs are tangible, that is, they are quantifiable in monetary terms. They
are real costs. Other costs connected with resolving wet weather problems are
intangible. They cannot be expressed in monetary terms. Nevertheless, these costs
are very real. Lack of quantification does not make intangible costs less important but
does mean that they are more difficult to weigh by stakeholders in the comprehensive
decision-making process increasingly used in public works projects.
Stakeholders should identify and weigh all possible intangible costs associated with any
alternative. Examples of intangible costs that might be associated with one or more
potential solutions to CSS problems are:
• Noise, dust and other disruption during construction.
• Construction outside of the public right-of-way, that is, on private property.
• Loss of trees and the resulting aesthetic impact.
• Interference with or adverse re-routing of vehicular traffic after construction.
This could be the case with improperly designed berms.
• Few, if any, options for future physical adjustments.
Consider an example, recognizing that generalizations are problematic. Compare the
intangible costs of a sewer separation approach to a street storage system. Sewer
separation will probably result in much more noise, dust and other disruptions than
street storage. For example, separation is likely to involve opening up a street over the
length of many blocks. In contrast, street storage is constructed at discrete locations.
Sewer separation may require construction or reconstruction of building laterals outside
of the public right-of-way. Street storage construction is typically and readily confined to
the right-of-way. Separate sewers offer little opportunity for future, low cost
adjustments. In contrast, flow regulator changes and even berm modifications are
easily accomplished.
wp/epastch8
-------
CHAPTER 9
PERFORMANCE OF STREET STORAGE SYSTEMS
Performance: The Ultimate Test
The proof of a public works structure, facility or system is "in the doing." Does it
perform? Elected and appointed officials in CSS communities are much more likely to
consider a new process or technology if it has been proven in other similar
communities. Favorable performance will be even more highly valued if it is reported by
or originates with other public works officials.
This chapter documents available information on the performance (not projected
performance as has been done with computer modelling) of the street storage system
approach to mitigating basement and other flooding problems caused by CSS
surcharging. Most of the performance information is drawn from up to 15 years of
experience with the Skokie and Wilmette, IL systems. Supplemental performance
information is presented from other communities that have applied, usually on a smaller
scale, street storage technology.
Broad Interpretation of Performance
The word "performance" is broadly interpreted in the chapter as it should be given the
realities of the public works field. A public works structure, facility or system must meet
many criteria to be acceptable, especially if the structure, facility or system embodies a
fundamentally new approach.
Clearly, the street storage system should perform in a functional sense. That is, it
should substantially mitigate basement and other flooding caused by surcharged
combined sewers. A street storage system may also be expected, as was the case in
Wilmette, to reduce peak flows to the entity that operates an interceptor sewers system
and wastewater treatment plants. Another possible performance test of a street
storage system is its reduction in the frequency and volume of CSOs. Other likely
important performance factors are:
Economic feasibility, that is, do the benefits warrant the costs?
Financial feasibility, that is, can the system be financed?
9-1
-------
Public acceptance
Economic and financial impact on the community.
Likelihood of generating claims or prompting legal actions.
Impact on the effective operation of emergency and other vehicles.
Feasibility and cost of operation and maintenance.
Acceptance by local, regional, state and federal government agencies
having a stake in the system.
In searching for ideas on ways to evaluate performance of street storage in CSS,
reference was made to a summary of a series of five regional, AMSA-sponsored
workshops on the theme of CSO performance measures (AMSA and Limno-Tech,
1996). As is often the case with these events and the resulting documentation, the
summary report is totally devoted to the CSO problem. No mention is made of
basement flooding in CSSs, solutions to that problem, or ways of evaluating the
performance of implemented measures.
Means of Assessing Performance
Unlike a controlled laboratory test of a small prototype of a new device, testing of a new
large scale public works system is not typically carried out with intensive data collection.
Street storage and related storage of stormwater is such a large scale public works
system.
Accordingly, varied, qualitative and semi-quantitative means must be used to evaluate
the performance of the street storage system. Means of evaluation reported in this
chapter are:
Interviews with Skokie, IL officials
Interviews with Wilmette, IL officials
Rainfall event incidents
Study of economic and financial impacts
9-2
-------
Summary of Interviews With Skokie, IL Officials
Participants
Five Village of Skokie officials kindly agreed to be interviewed on December 14, 1998
as part of the EPA project. Interviewees were:
Ms. Jacqueline Gorell, Mayor
Mr. Albert J. Rigoni, Village Manager
Mr. Dennis York, Director of Public Works (DPW)
Mr. Eddy Nakai, Village Engineer
Mr. Frank Didier, Superintendent, Water and Sewer Division
Interviewees may be contacted through:
Village Hall
5127 Oakton Street
Skokie, IL 60077
Tel: 847-673-0500
Process
Stuart G. Walesh, Consultant, and Robert W. Carr of Earth Tech conducted two
interviews. The first involved Mayor Gorell and Manager Rigoni. The second interview
included DPW York, Engineer Nakai, and Superintendent Didier.
The objective of the comprehensive interviews was to obtain first hand ideas and
information on many aspects of the community's street storage system. Because four
of the five interviewees have been Skokie employees (A. Rigoni, E. Nakai and F. Didier)
or an elected official (J. Gorell) throughout the life of the project, the interviews proved
to be very fruitful. Value was added to the interview process by the participation of
DPW York who had been employed by Skokie for only several years and, therefore,
offered a fresh perspective and an objective review.
A list of questions was prepared by the interviewers prior to the interviews to facilitate a
thorough, wide-ranging discussion. The list was not given to the interviewees but was
used by the interviewers as an aid during the interviews. The questions are included as
Appendix A.
Interviewees were encouraged to be open and frank. As suggested by the wording of
most of the questions in Appendix A, both positive and negative views were sought in
the hope of extracting ideas and information that would be useful to representatives of
other communities contemplating street and related storage of stormwater.
Results
9-3
-------
Partly as a result of the prepared questions and the use of open-ended inquires, the
interviewees were generous, frank and informative with their comments. Key ideas and
information obtained or verified during the interviews are presented below.
Financing:
Bonding is the dominant means of financing, usually without referenda. Some
low interest loans have been obtained under the State Revolving Fund program
through the State of Illinois as described in Chapter 5.
There have been no large increases in taxes partly as a result of the phased
construction of the system.
On-going capital expenditures for system construction have been accepted
partly because of the system's success in solving problems and partly because
of the stability of the Board of Trustees and Skokie staff and citizen confidence
in the Board and staff.
Effectiveness of the System in Mitigating Basement Flooding:
Mayor Gorell: "Ultimately it makes your life easier... worth time, effort and
money."
Street storage is generally viewed as not a perfect solution. However, there
are no perfect solutions to stormwater and wet weather problems given the
random, episodic nature of meteorological events.
A serious storm might generate 60 telephone calls from residents and property
owners. In some cases, reported basement flooding may be caused by
seepage of infiltrated stormwater through basement floors and wall—not
necessarily back up of combined sewage.
They "would do it again" according to Mayor Gorell and Manager Rigoni.
DPW York, noting that the Skokie approach retrofits stormwater storage into
the system, stated that the project "makes good use of what is there."
One measure of the effectiveness of the street storage system is that news
media no longer come to Skokie when heavy rainstorms occur.
9-4
-------
Some building owners have installed their own systems, such as standpipes in
basement floor drains or overhead sewers as a backup system. Such building
owner actions tend to be prompted by major rainfall events—such as the
August, 1989 storm—in the interest of providing an "insurance policy." There is
concern with such actions, even though on private property, because they may
be implemented without adequate knowledge and result in serious structural
damage and risk to occupants. For example, as a result of standpipe
installation, excessive hydrostatic pressure may build-up under basement
floors and against basement walls. The floor may be raised and/or the walls
collapse inward.
Public Education and Involvement:
Although a major public education effort was mounted early in the project to
explain the function and benefit of the street storage system, on-going public
education is needed.
On-going public education mechanisms used in Skokie include letters to
citizens, cable television, and "Newskokie," the Village's newsletter (e.g.,
"Board Report" section, map of proposed street storage projects).
Litigation:
There has been no litigation as a result of the street storage system.
Claims:
One or two claims have been made to the Village.
In one case, the owner of an automobile requested reimbursement for alleged
water damage to his/her parked vehicle. The community denied the claim and
referred the individual to their automobile insurance carrier.
Operation of Emergency Vehicles:
There have been no complaints from any member of departments that use
emergency vehicles (e.g., fire, police).
There has been no damage to emergency vehicles as a resulting of driving
over berms.
9-5
-------
Operation of Motor Vehicles:
There have been no claims for damage to vehicles as a result of driving over
berms.
No accidents are known to have been caused by ice or water directly related to
the street storage system.
Operation and Maintenance (O&M):
Much more O&M is needed for effective operation of the street storage system
than was practiced prior to construction of the system.
Although complete statistics are not available to quantify the increased O&M,
the overall effort is described as having been doubled. One index is a doubling
of O&M personnel (from two to four) and an addition of a second Vac All.
Another way to portray the increased O&M effort is to note that, as a result of
the street storage system, Village personnel have progressed from cleaning
about 3000 catch basins to cleaning and maintaining approximately 10,000
structures (i.e., catch basins, inlets, berms and storage facilities.
About one-half of the approximately 3100 catch basins are cleaned each year
during the March through November period.
One reason for more maintenance is a reduction in flushing action
characteristic of CSS's and a corresponding increase in settling and
accumulation of solids in inlets, catch basins, and pipes connecting inlets to
catch basins. That is, the intentional, widespread introduction of street and
related stormwater storage reduces stormwater flow rates into and through
inlets, catch basins, connecting pipes and combined sewers. Thus the flow
reduction, which is highly desirable for mitigating basement flooding and
possibly CSO's, appears to be undesirable from the perspective of reducing
self cleaning of the CSS.
Catch basin sumps, which were not systematically cleaned prior to
implementation of the street storage project, are cleaned now because catch
basins are an even more essential part of the system.
A manual is being prepared to increase the effectiveness of O&M.
9-6
-------
The existence of only four pumping facilities in the entire system facilitates
O&M. Note: With the preceding exception, and as explained in Chapter 3, the
street storage system operates solely by gravity.
When plugging occurs, hanging trap flow regulators are much easier to rectify
than vortex regulators. If any difficulty is encountered in removing debris from
a hanging trap, the inexpensive device is simply broken off after which the
catch basin drains and a new hanging trap is inserted. A tee, on which the two
ends of the handle have been bent 90°, is used in an upside down fashion to
reach into the catch basin beneath the water level, "grab" the hanging trap and
pull up on it to break it off.
A problem peculiar to vortex regulators is that sticks tend to bridge across the
openings which, in turn, accumulates other debris. The initial bridging of vortex
regulator openings probably occurs because the openings are not always
submerged. In contrast, orifices on hanging trap regulators are always
submerged by at least a few inches of water and, therefore, are less likely to be
plugged by buoyant debris.
Newer model vortex regulators have two gaskets on the cylindrical portion
which inserts into the exit pipe from the catch basin. This has proven to be
better than the earlier model, which had one gasket. Two gaskets are
preferable because the regulator fits tighter and is less likely to fall out.
Because of the superior O&M performance of hanging trap flow regulators, the
Village would prefer to use more of them and less vortex regulators. This
would be feasible if the minimum orifice diameter for hanging traps could be
reduced to one inch.
Hanging trap resistance to plugging might be improved further and/or smaller
diameter orifices might be permissible by fitting the orifice end with a "bubble"
or hemispherically shaped screen or grate.
Plugging of regulators during any storm is relatively rare. For example, only
five to ten of the approximately 3000 regulators will experience blockage in a
runoff event.
A positive O&M feature of the street storage system, with emphasis on
continuous improvement in system operation, is the ability to make low cost,
physical adjustments to the system. Examples of such adjustments, which can
be motivated by observation of the system, are changing flow regulator sizes
and modifying, adding or removing berms. Low cost system adjustments or
"tweaking" may lead to higher levels of protection.
Because the street storage system has so many components distributed over a
large area (8.6 square miles), a user-friendly mapping system is very desirable.
9-7
-------
For example, one approach would be interactive computer-based maps that
would enable the user to easily obtain information about any component (e.g.,
the type and size of a particular flow regulator and the last time its catch basin
was cleaned) and to readily update the data base (e.g., document the cleaning
of a below-street tank).
Monitoring:
Occasional, focused monitoring of parameters such as rainfall intensity, and
dry and wet weather discharge in combined sewers, is very useful. It has, for
example, revealed great spatial rainfall variability over the 8.6 square mile
Village of Skokie.
Monitoring of stormwater levels in subsurface tanks, which has not been done,
is now desired. The principal interest is in determining if optimum use is being
made of available tank capacities.
If a system similar to Skokie's were to be planned, designed and constructed
"from scratch," consideration should be given to incorporating permanent
monitoring devices. An example of such a device would be pressure sensors
in the floors of tanks or other device to monitor the depth of stored water.
Another example would be permanent flow monitors in selected sewers.
Downspout Disconnection:
Refer to Chapter 5 for a description of Skokie's early 1980's community-wide
downspout disconnection program.
This measure helps the public understand the functioning—and
malfunctioning—of combined sewer systems when receiving high rates of
stormwater runoff. That is, more residents recognize the cause and effect
relationship between excessive rates of stormwater runoff and basement
flooding.
A mandatory downspout disconnection program should include an appeal
process. Some properties have special physical circumstances precluding
surface discharge of downspouts. For example, discharged stormwater may
flow onto neighboring properties.
9-8
-------
Skokie was too lenient with bringing business and commercial properties into
compliance with the community's downspout disconnection program. This was
done, in part, because of the larger cost of disconnecting downspouts within
some business and commercial buildings.
Pavement Deterioration:
There is no evidence of accelerated deterioration of asphalt or concrete
pavement as a result of the presence of the berms or the temporary ponding of
stormwater on the street. As noted in Chapter 3, street storage of stormwater
has occurred since 1985 in the Howard Street District, the first district in which
the street storage system was implemented.
Icing of Streets When Rainfall or Snowmelt Occurs During Freezing
Temperatures:
This is not a problem provided the system is maintained, that is, obstructions
do not prevent or greatly restrict stormwater flow into inlets.
Because it generates water slowly, snowmelt is not a problem.
Breaks in water mains during winter have occasionally caused freezing
conditions.
If an inlet or catch basin blockage exists during freezing conditions, a solution
is to dump a mixture of hot water and snow melting compound and "rod it" with
a jet truck.
Interaction With Other Government Entities:
The Illinois Environmental protection Agency (IEPA), after some discussion
and deliberation, decided to support the Skokie street storage system by
providing low interest loans under the state's revolving fund program. Refer to
Chapter 5 for details.
The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) is
a strong supporter of the Skokie project. One reason for MWRDGC support is
that the street storage type systems resolve the basement flooding problem
that remains after implementation of the Tunnel and Reservoir Plan (TARP).
Control of CSO's to protect surface water quality is TARP's primary purpose
and, as a result, there is a major residual basement flooding problem.
The Illinois Department of Transportation (IDOT) and Cook County, in contrast
with the preceding agencies, have not been supportive of the street storage
system. Their concern should be viewed in the context of these agencies'
roadway responsibilities and potential problems resulting from ponding of water
9-9
-------
on arterials under their jurisdiction.
Summary of Interviews With Wilmette, IL Officials
Participants
Three Village of Wilmette officials kindly agreed to be interviewed. Interviewees were:
Mr. George Sullivan, Chair, Wilmette Sewer Commission
Ms. Donna Jakubowski, Director of Public Works (DPW)
Mr. Robert S. Lewis, Village Engineer
Mr. Brad Enright, Sewer/Water Superintendent
Interviewees may be contacted through:
Village Hall
1200 Wilmette Avenue
Wilmette, IL 60091-0040
Tel: 847-853-7627
Process
Stuart G. Walesh, Consultant interviewed Chair Sullivan by telephone on February 4,
1999. S. Walesh and Michael C. Morgan, Earth Tech interviewed DPW Jakubowski
and Superintendent Enright in Wilmette on February 9, 1999. The second interview
that day was with Engineer Lewis.
As with Skokie, the objective of the comprehensive interviews was to obtain first hand
ideas and information on many aspects of the community's street storage system.
Because three interviewees have been Wilmette employees (D. Jakubowski and B.
Enright) or an elected official (G. Sullivan) throughout the life of the project, the
interviews proved to be very fruitful. Engineer Lewis, who had been with the community
less than a year at the time of the interview, provided fresh insight.
The previously mentioned list of questions (Appendix A) used for the earlier Skokie
interviews were subsequently used for the Wilmette interviews. The list was not given
to the interviewees but was used by the interviewers as an aid during the interviews.
Interviewees were encouraged to be open and frank. Both positive and negative views
were sought, as suggested by the wording of most of the questions in Appendix A. The
goal was to obtain ideas and information that would be useful to representatives of
other communities contemplating street and related storage of stormwater.
Results
9-10
-------
The interviewees were generous, frank and informative with their comments. Key ideas
and information obtained or verified during the interviews are presented below.
Financing:
Low interest loans were obtained through the State of Illinois as part of the
State Revolving Loan Fund is described in Chapter 5. Wilmette applied for
these loans based, in part, on learning of Skokie's success with this financing
mechanism. All of the street storage project was funded in this manner.
Sewer service charges, which are based on water use, have gradually
increased to generate needed revenue. However, the rates are still low relative
to similar neighboring communities
Effectiveness of the System in Mitigating Basement Flooding:
Chair Sullivan: "Excellent, demonstrably better..." However, the community is
waiting for a "huge rain" to further evaluate the performance of the system
before proceeding with implementation of the fourth and fifth phases of the five
phase program.
Few, if any complaints, about basement flooding were received from residents
of the CSS as a result of the August 1998 rainfall when about 2.75 inches fell.
Many streets filled with water, as expected, and this caused some citizen
concern. However, flooding was "drastically reduced" and the system "worked
just great."
Public Education and Involvement:
Chair Sullivan: "Get out in front in interacting with the public." The sewerage
commission budgeted specifically for information and publicity.
On-going public interaction efforts used in Wilmette include a survey of
residents; assigning one person in Public Works to answer telephone inquiries;
articles in the local weekly newspaper; new resident receptions; items in the
"Communicator," the Village's newsletter; programs on cable TV and meetings
at the Village hall and in citizen's homes.
There was little difficulty in earning community acceptance and approval of the
street storage system. This favorable result probably reflects the proactive
approach of community leaders in interacting with the public.
Litigation:
9-11
-------
There has been no litigation as a result of the street storage system.
A potential lawsuit did not materialize. In this situation a driver drove over a
berm, apparently at excessive speed, and damaged the vehicle's under
carriage. The initial issue, which was not pursued, was that the berms are
speed control devices and, therefore, require appropriate signs and street
markings. While it is true that signs and street markings are recommended by
ITE (1997, pp. 17-19), Wilmette's position was that the berms are designed
solely for flood control.
Claims:
No claims have been made as a result of the street storage system.
Operation of Emergency Vehicles:
One police car was damaged by "bottoming out" on one of the first berms
constructed in the community. This was attributed to an excessive longitudinal
slope on the first Wilmette berms. The vertical distance between the gutter
invert and the street crown is generally much greater in Wilmette than in
Skokie. That is, Wilmette streets typically have much more camber.
Therefore, in order to hold the same maximum longitudinal slope in Wilmette
as proved successful in Skokie, the longitudinal length of the Wilmette berms
must be longer than the Skokie berms. Stated differently, berm longitudinal
slope governs design, not berm longitudinal length. The problem with the initial
Wilmette berms was rectified by altering them.
There have been no subsequent problems with emergency vehicles.
Operation of Motor Vehicles:
There has been no unfavorable rerouting of vehicular traffic onto side streets.
However, berms are not generally located on high volume streets.
No accidents are known to have been caused by ice or water directly related to
the street storage system. Icing has not occurred.
Berms function as speed humps and favorably reduce speeds on some streets.
The berms do not impair driving when vehicles travel at speeds at or below the
established speed limit.
Parking patterns have been slightly altered by berms in that drivers tend to park
on or downstream of berms. Recall, as explained in Chapter 3 in the section
"Wilmette Performance Criteria," that street ponding depths for the design
storm are limited to a maximum of six inches on the street crown and a
9-12
-------
maximum of 12 inches above the gutter invert.
Operation and Maintenance (O&M):
Much more O&M is needed for effective operation of the street storage system
than was practiced prior to construction of the system.
Before the street storage system, catch basin sumps were cleaned about once
every three years. Now they are cleaned annually. Some sumps are probably
too shallow.
If precipitation lasts more than a couple of hours, crews usually are called out
to remove blockage of catch basin grates which is typically caused by leaves.
Crews drive the streets after most rainfalls.
Berms have not interfered with snow plowing and street sweeping operations.
Some flow regulators have become totally or partially plugged. Causes include
shallow catch basin sumps and leaves being raked into catch basins by area
residents. A negative result is stormwater being ponded on streets until the
blockage is removed by maintenance personnel. This problem was resolved
with a two step modification. Visualize an inlet-catch basin structure at the curb
line connected by a pipe to a manhole on the combined sewer. The first step
in the modification was to remove the hanging trap from the catch basin end of
the connecting pipe. The second step, as shown in Figure 9-1, was to add a
shear gate to the outfall end of the connecting pipe, that is, in the manhole on
the combined sewer. The shear gate is normally kept in the closed position but
contains an orifice sized to provide the allowable maximum flow of stormwater
into the combined sewer. If the orifice becomes blocked, the handle mounted
above it is used to open the shear gate and release the debris.
Downspout Disconnection:
Some property owners objected to the effort and cost of downspout
disconnection.
9-13
-------
8" FLEXIBLE BOOT
^'DUCTILE ]RON PIPE
8"BAND SEAL
COUPLING
•*- -
*, ^
&
S
&: \
HANDLE
OR3FEE
^SHEAR GATE
BOLTED FLANGE
CONNECTION
-N A
Figure 9-1. Shear gate with orifice flow regulator as used in Wilmette, IL.
9-14
-------
Downspout disconnection helped other citizens understand the
functioning—and malfunctioning—of combined sewer systems when receiving
high rates of stormwater runoff. They gained more appreciation of the cause
and effect relationship between stormwater runoff and basement flooding.
Pavement Deterioration
No pavement deterioration was reported. However, the Wilmette street
storage system has only been in place for several years. No streets segments
on which berms are located have been resurfaced since the berms were
constructed.
Icing of Streets When Rainfall or Snowmelt Occurs During Freezing
Temperatures:
No problems have occurred.
Interaction With Other Government Entities:
The IEPA supported the Wilmette street storage system by providing low
interest loans under the state's revolving fund program.
The MWRDGC is a strong supporter of the Wilmette project. According, to
Chair Sullivan, the MWRDGC "thinks it's wonderful."
Rainfall - Flooding Incidents
Typical Limited Data
Neither Skokie nor Wilmette have kept systematic records of rainfall event
characteristics (e.g., depth, duration, spatial variation, intensity, recurrence interval) or
basement flooding characteristics (e.g., number of buildings affected, location). This is
not unusual. Communities typically have neither the high priority need nor the
equipment and personnel means to obtain and analyze such data on an essentially
continuous basis over an extended period of time (e.g., years).
Instead, the rainfall event - flooding database in most communities is sporadic. It tends
to focus on major rainfall events because they are more likely to cause problems.
Flooding incident data is typically derived from citizen complaints and is limited in detail.
Under favorable circumstances, such information consists of the number of complaints
received and the corresponding location. Under less favorable circumstances, only
anecdotal information is available.
In spite of the typical paucity of rainfall event - flooding data, some value can be derived
from it in terms of assessing the performance of the system. The purpose of this
9-15
-------
section is to present and interpret some of the limited rainfall event and flooding data
that are available for the case study communities.
June 20 - 21, 1987 Rainfall - Flooding Event in Skokie
This event occurred during the special HSSD post-construction monitoring program.
Construction of the HSSD street storage system was completed in April 1987. The
monitoring program was conducted within the 1255 acre HSSD from June through
September 1987. The monitoring program's purpose was to assess the performance of
the street storage system and determine causes of scattered residual flooding
(Donohue, 1988, p. 1-1).
The event was determined to have a recurrence interval of 10 years on the east side
community and one year on the west side (Donohue, 1988, p. 5-1).
Village officials received about 20 reports of flooding as a result of the June 1987 event.
Most reported problems were in the eastern portion of the district. "Complaints included
sewer backups; street ponding areas too deep and extending into yards; and basement
flooding" (Donohue, 1988, p. 5-1, 5-4). At that time, approximately 4600 single family
residences were in the HSSD based on proportioning the community's single family
residences according to sewer district areas.
The system had performed very well based, in part, on the small number of complaints
relative to the number of single family residences. Furthermore, the number of HSSD
complaints with the street storage system in place was minuscule compared to the pre-
street storage system flooding problems described in Chapter 2.
However, given that this storm event was within the 10-year recurrence interval design
of the street storage system, a high degree of performance is expected. Causes of
flooding were determined to be the intentional absence of flow regulators on some
arterial streets, incorrect flow regulator sizes, improper berm construction and
obstructions in existing combined sewers. Specific corrective actions were
recommended (Donohue, 1988, p. 6-1).
August 13 -14, 1987 Rainfall - Flooding Event in Skokie
Also occurring during the special four month HSSD post-construction monitoring
program, this event greatly exceeded the design criteria for the street storage system.
A total of 7.5 inches of rainfall fell in 11 hours over an 18 hour period. The estimated
recurrence interval was 300 years (Donohue, 1988, p. 4-1). In addition to the extreme
rainfall, an extreme high stage occurred on the North Shore Channel, the ultimate
receiving stream for the HSSD. Backwater effects of this stage, which was four feet
higher than the stage used in designing the street storage system, probably caused
some of the flooding (Donohue, 1988, p. 5-4).
9-16
-------
Given the extreme severity of the August 13-14, 1987 rainfall relative to the design
conditions, the event provided an opportunity to assess the robustness of the street
storage system. About 85 reports of flooding within the HSSD were received by Skokie
officials. As with the June 1987 event, complaints included sewer backups, excessive
street ponding and basement flooding. Conclusion: The system performed very well
given that the storm greatly exceeded the design conditions.
August 4, 1989 Rainfall - Flooding Event in Skokie and Wilmette, IL
According to Skokie personnel (Rigoni, 1989), the August 4, 1989 storm generated 54
complaints from residents of the 1255 acre HSSD. Recall that approximately 4600
single family residences were in the HSSD. Therefore, flooding was reported for about
one percent of the residences. The complaints appeared to be "spread across the
entire HSSD without any noticeable pattern."
For comparison purposes Wilmette which, as explained in Chapter 2 is immediately
north of Skokie, experienced widespread basement flooding as a result of the same
August 1989 storm. Based on a postcard survey, nearly 800 buildings, or 23% of the
total in the CSS, were flooded (SEC Donohue, 1992, p. 2). About 0.63 structures per
acre in Wilmette reported basement flooding.
While Skokie was progressing with its street storage system, Wilmette had not yet
begun. Recall that Skokie residents reported 54 basement floodings throughout the
HSSD in their CSS or about 0.04 per acre. Therefore, the density of reported flooded
basements in Wilmette's CSS, which did not yet have a street storage system, was
about 16 times that of Skokie which had a street storage system in place in the HSSD.
In response to Skokie's request, Donohue & Associates "...reviewed the reported
basement flooding problems... and evaluated possible causes..." (Raasch, 1989a).
Contrary to the initial view that the flooding incidents lacked "any noticeable pattern,"
the Donohue analysis concluded that (Raasch, 1989a):
The largest cause of the continued flooding
problems was identified as runoff from streets
which do not have flow regulators to control
the rate at which runoff enters the sewer
system.
The review letter goes on to explain that Skokie and Donohue had decided during the
planning and design of the HSSD street storage system that "stormwater runoff on
selected streets or street segments would not be controlled with flow regulators
because intentional ponding was not desirable." Streets or street segments where
intentional street storage was deemed undesirable fell into three categories. They were
streets or street segments:
with high traffic volumes.
9-17
-------
under the jurisdiction of Cook County or IDOT, two government entities that
do not allow the new street storage technology.
on Skokie borders where street storage on the Skokie side of a street might
adversely affect neighboring communities.
In addition, street storage was not applied to those few streets or street segments
served by separate sanitary sewers. Other supplemental circumstances cited in the
Donohue letter were the possible impact of isolated combined sewage flow from
outside the HSSD, contributions of parks which were assumed in the system design to
not contribute runoff, and the recognition that some downspouts had not been
disconnected from the CSS.
To reiterate, the conclusion of reviewing the August 4, 1989 rainfall - flooding event was
that the scattered basement flooding incidents were attributed to the absence of street
storage on some streets and street segments plus other factors. Stated differently,
basement flooding was not caused by a failure of the street storage technology but
rather by the "failure" to apply it totally to the HSSD.
The Donohue review concluded recommending various refinements and remedial
actions. The principal suggestion was to revisit the original reasons for not applying
street storage to some streets and street segments and, if appropriate, add street
storage.
May 8, 1996 Rainfall - Flooding Event in Skokie
This rainfall was spatially varied with the most severe rainfall segment being 2.0 inches
in just over an hour at the west end of the HSSD which was an eight-year recurrence
interval. Wet antecedent soil conditions prevailed, because of intermittent rainfall over
the preceding two days, which increased the volume of stormwater runoff.
About 75 basement flooding calls were received from across the community with
approximately two-thirds occurring in the HSSD. Recall that there are about 20,000
single family residences in Skokie. If all 75 basement flooding complaints were from
single family residents, then basement flooding was reported for about 0.4% of the
residences. Factors causing basement flooding included unregulated inlets on IDOT
arterials, wet antecedent moisture conditions, and the fact that, as of 1996, the street
storage system was still being implemented in the MSSD and the ELSSD (Carr, 1999).
August 5, 1999 Rainfall - Flooding Event in Skokie
This rainfall was of one to three hours duration, as measured at five rain gauge
locations in Skokie. The event was rated as having a one to 16-year recurrence interval
depending on location. The storm was most severe in the HSSD.
Of the complaints received, 72 were determined to be basement flooding caused by
back-up of combined sewage through floor drains. Most were in the HSSD and MSSD.
9-18
-------
Given the small number of complaints, the street storage system performed well in light
of the severity of the storm. It exceeded the 10-year recurrence interval design criterion
for the street storage system. Additional explanatory factors include those noted under
the discussion of the May 8, 1996 event. They were unregulated inlets on the IDOT
arterials and the on-going construction of the street storage system in the ELSSD (Carr,
1999).
Economic and Financial Impact on Skokie
Fishman (1998) studied the history of Skokie's street storage project with emphasis on
how it was financed (as discussed in Chapter 5) and on the financial and economic well
being of the community. He notes the project was the most expensive ever undertaken
by Skokie. His findings highlight another dimension of the positive performance of the
street storage system in that it significantly enhanced the community's economic and
financial status.
Already at the beginning of the street storage project, Skokie had earned "high credit
ratings" because of excellent financial management. It was "one of only 232
municipalities in the nation with Moody's coveted Aa2 rating." Moody's refers to
Moody's Investor Services, an agency that rates a community's financial health for the
benefit of bond investors (Fishman, 1998, pp. 181-182). Now with the street storage
project almost completely implemented, "...Skokie's credit rating has been raised
another notch by Moody's..." apparently based, in part, in the success of the flood
control efforts (Fishman, 1998, p. 186).
Economic benefits of the street storage system include rejuvenation of downtown
businesses. Fishman (1998, p. 186) concluded that:
Downtown Skokie, where errant water once
drove businesses away, no longer looks
dilapidated; instead, it now resembles the
handsome, high-rent business districts of the
surrounding suburbs...
Individual homeowners have also reaped economic benefits. Anecdotal evidence from
real estate agents suggests that the street storage project has added $40,000 to the
value of an average house (Fishman, 1998, p. 186). The bottom line, according to
Fishman (1998, p. 178), is that "Skokie is cleaner, safer and much richer" as a result of
the street storage system.
9-19
-------
Potential Impact of a Street Storage System on the Frequency and Volume of
Combined Sewer Overflows
Chapter 1 of this manual explains that one of the initiatives undertaken during the
preparation of this manual is an exploratory analysis of the street storage system
technology on the volume and frequency of CSOs and peak flows at wastewater
treatment plants. Reductions in CSO volume and frequency and wastewater treatment
plant peak flows would enhance the performance of the street storage system.
The exploratory analysis is documented in Appendix F. Included are a description of
the methodology, presentation of results, and conclusions. Findings of the exploratory
study suggests that street storage systems have the potential to provide benefits
beyond mitigating basement flooding. Street storage technology may be able to
significantly reduce the volume and frequency of CSOs and peak flows at wastewater
treatment plants.
wp/epastch9
9-20
-------
Chapter 10
Discussion
Lessons Learned: How Other Communities Might Benefit From a Street Storage
System
In keeping with the theme of this manual—possible applicability of street storage as a
cost-effective solution to CSS problems in many communities—this chapter begins with
a lessons learned section. The lessons flow from ideas and information presented in
preceding chapters. The lessons learned section is directed primarily at elected and
appointed officials in communities having CSS flooding and/or overflow problems. For
convenience sake, the lessons learned are summarized here by the following six
categories:
Analysis and Design
Regulatory Compliance and Project Financing
Stakeholder Involvement
Evaluating System Performance
Operation and Maintenance
Lessons Learned About Analysis and Design
1. Establish and obtain concurrence on system performance criteria
before beginning the analysis and design process. Involve stakeholders in
defining the desired level of service.
2. Initial studies of CSS problems should focus on finding and defining the
causes. This diagnostic step should look beyond symptoms and seek out
causes. Computer modeling is likely to be needed given the complexity of
the typical CSS. Failure to conduct a thorough system analysis may lead to
subsequent misguided efforts targeted at solving the "wrong problem."
3. Consider, especially at the outset of the planning and preliminary design
phase, a wide range of potential solutions. Do not presume that
traditional, and very costly solutions, like separation, relief sewers and
tunnels are necessarily needed. Several to many years elapsed while
Skokie and Wilmette conducted a series of studies that contemplated only
10-1
-------
traditional solutions to their CSS problems.
4. Adopt, at least at the beginning of the analysis and design effort, a
multipurpose posture. Become aware of and define the causes of all CSS
problems—not just CSOs or basement flooding. Thinking globally is more
likely to lead to a cost effective, multipurpose project.
5. Use a phased approach to the concept through construction process. This
optimizes technical refinements and earns stakeholder acceptance.
6. Carefully prioritize the phases. Consider factors such as proceeding
downstream in each watershed, consistency with screening criteria
(Appendix B), severity of problems, stakeholder input, and windows of
opportunity.
7. In CSSs, view streets as potential partial solutions to flooding, CSO and
other problems. Given the typical low longitudinal grades of streets in CSS,
streets have significant potential storage capacity in a retrofit scenario.
8. Consider integrating the stormwater berm function and the speed hump
function into one stormwater management-speed control structure.
9. Avoid mechanical-electrical controls. Try to develop a simple, gravity
driven stormwater storage system.
10. Select flow regulators having a very low probability of plugging and
offering ease of maintenance.
Lessons Learned About Regulatory Compliance and Project Financing
1. View regulations positively. For example, they often help support a
community's eligibility claim for external funding in the form of loans and
grants from regulatory agencies.
2. Seek a comprehensive and innovative technical approach because it is
most likely to attract external funding.
3. Explore a wide range of established funding sources and seek ways to
meet the objectives of each. Investigate state and federal agencies as
sources of project grants and low interest, long term loans. Skokie, for
example received external financial assistance from IEPA, IDOT and Build
Illinois sources.
4. Consider seeking financial support in the form of a site specific line item
appropriation from the U.S. Congress. Having a distinctive project helps
10-2
-------
as does a team approach involving the community, its engineer, and state
and congressional representatives.
5. Phase the project because this enables the community staff and their
consultants to seek and leverage external financing in an optimum fashion.
This approach avoids needing a massive amount of funds in a short period
of time and allows "small wins" to spark new project and funding supporters.
6. Establish a downspout disconnection program using a combination of
education and ordinance enforcement. Expect the program to reduce
stormwater flow into the CSS and to increase citizen understanding of the
cause and effect relationship between stormwater and CSS surcharging.
7. Create a stormwater control ordinance. While it won't mitigate existing
CSS problems it can prevent exacerbation of those problems.
Lessons Learned About Stakeholder Involvement
1. Recognize that a street storage project has many and varied
stakeholders. This occurs because of the large areal extent of such a
project and because of regulatory compliance needs and external funding
possibilities.
2. Proactively plan, budget for and implement a stakeholder interaction
program. Begin at the outset of the street storage program and continue
through the program. Avoid a reactive position. Both Skokie and Wilmette
used this proactive, continuous approach.
3. Use a variety of communication mechanisms. Examples are
informational meetings, focus groups, surveys, newspaper and newsletter
articles, television and radio programs and websites.
4. Anticipate and respond proactively to likely initial negative reaction to
intentional storing of stormwater on streets. Note the streets often flood
anyway in an uncontrolled fashion, that street storage uses highly controlled,
temporary ponding and that stormwater in streets is preferred over combined
sewage in basements.
5. Expect and be prepared to proactively respond to initial negative
reaction to stormwater berms. They are likely to be incorrectly confused
with speed bumps. Explain that engineered speed humps (not bumps) are
widely used in urban areas throughout the U.S. and that stormwater berms
cause even less driver discomfort than speed humps.
10-3
-------
Lessons Learned About Evaluating System Performance
1. Think broadly when choosing criteria to evaluate the performance of a
street storage system. In Skokie, for example, the system performed very
well in reducing basement flooding. It also performed very well in that it had
a favorable economic impact on the community.
2. Obtain input from all stakeholders. Examples are elected and appointed
officials, citizens, business people, operation and maintenance personnel,
emergency vehicle operators, finance experts, and regulators.
3. Use the number and location of citizen complaints received during and
after storm events, along with storm severity data, as an index of system
performance. Consider doing pre- and post-project surveys.
Lessons Learned About Operation and Maintenance
1. Recognize that much more system wide maintenance is likely to be
needed once a street storage system is installed. Maintenance that may
have been optional before the street storage system, such as catch basin
cleaning, is mandatory with the street storage system in place.
2. Develop an operation and maintenance manual or other written
guidelines to encourage a systematic approach.
Criteria for Screening the Applicability of Street Storage
Purpose of Screening Criteria
Based largely on ideas and information presented in this manual, a set of street storage
screening criteria were created. These criteria appear as Appendix B. They are offered
for possible use by municipal officials and their consultants in making a preliminary
determination about the likely applicability of street storage as a solution to CSS
flooding and/or overflow problems in a particular community. Also included in the
screening criteria are sections for screening sanitary sewer and storm water systems.
These are included, because as noted in this manual, the street storage system could
be used to solve wet weather problems in sanitary sewer and stormwater systems.
10-4
-------
Assume that application of the preliminary screening criteria suggests that street
storage may be suited to a particular community, or a portion of the community. The
next steps might include, as they were in Skokie, selection of a pilot area; data
collection; hydrologic-hydraulic modeling, possibly including water quality modeling, with
and without street storage. If street storage continues to be promising, then the effort
might move to preliminary engineering, cost estimating, comparison to other options
and expansion to other areas. A detailed discussion of the street storage analysis and
design process is presented in Chapter 3.
Qualifications of Evaluators
Community officials, consultants or other persons responsible for applying the
screening criteria included as Appendix B should be very knowledgeable about the
physical aspects of the community. If they are, very little time—a matter of hours—will
be needed to fill in the form which follows and assess its significance. With few
exceptions, such as the short general information section, a simple and quick "check-
off" format is used.
In order to appreciate why certain information is being requested, individuals involved in
the screening should understand the premise, components, and benefits of street
storage. For that reason, these three aspects of street storage are summarized at the
beginning of the screening instrument.
Interpreting the Screening Information
Assume that the evaluator is, as suggested, knowledgeable about the physical features
of the community. Further assume that the evaluator understands, as also suggested,
the premise, components and benefits of a street storage system. Then the evaluator
should be in a good position to judge whether or not street storage is likely to be
applicable. If there is uncertainty, advice could be obtained from personnel in a
community that has a street storage system. Another approach would be a request
assistance from an engineering consultant experienced with street storage.
wp/epastch10
10-5
-------
Chapter 11
Conclusions and Recommendations
Street Storage: A New Technology for Affordable Mitigation of CSS Problems
Street storage, as documented in this manual using a largely case study approach, is a
relatively new and promising concept. Proven to be technically and cost effective in the
few communities where it has been systematically applied, street storage is becoming
one more technology in the array of technologies available for remedial or preventive
actions in CSSs.
Unlike traditional solutions to CSS problems, street storage may provide benefits that
transcend CSO control. That is, street storage has the potential to provide multiple
benefits in CSS communities. The first is mitigation of basement flooding caused by
surcharging of combined sewers. This potential benefit has been clearly demonstrated
by years of experience in Skokie, and Wilmette, IL.
The second problem that may be mitigated by the street storage system is CSOs and
excessive peak flows at WWTPs. Preliminary modeling studies conducted as part of
this case study project suggest that street storage alone or in combination with
traditional approaches, may cost effectively reduce the annual number and volume of
overflows.
Because a street storage system targets stormwater for control, the third benefit is the
potential to mitigate other stormwater related problems. Examples are inflow to sanitary
sewers and stormwater flooding.
Finally, because a street storage system contains many small storage facilities,
scattered throughout a system, it has the potential to manage non-point source
pollution. This observation is based on the premise that suspended solids are a major
component of non-point source pollution and that other potential pollutants tend to be
absorbed onto or adsorbed into the solids. The numerous well-maintained sumps in a
street storage system provide a means for removing solids and other pollutants in
stormwater. When the street storage approach is planned early and carefully tied to
water quality and health benefits, state revolving fund (low interest loan) eligibility can
be obtained.
Recommended Research
11-1
-------
Achieving the full potential of street storage for mitigation of flooding and for other
purposes requires research. Presented here are recommendations, informed by this
case study manual, for street storage research.
Integration of Speed Humps and Street Berms
Street berms, one component of the street storage system, are physically similar to
speed humps, which have proven to be effective devices for controlling vehicular
speeds on urban streets. This idea is developed in Chapter 3 in the section titled
"Berms and Humps: Different Functions But Similar Form."
While both speed bumps and street berms have been independently designed by civil
engineers and both have been constructed on urban streets, they apparently have
never been planned and designed in an integrated fashion to control vehicles and wet
weather flow. This conclusion is based on the literature review and information search
conducted for this case study. No evidence was found of traffic specialists and wet
weather specialists teaming to design an integrated hump-berm system.
Several possible explanations for this absence of a connection between speed humps
and street berms may be offered. First, street berms are relatively new and, therefore,
there has been little opportunity for a collaboration between hump and berm designers.
Second, a traditional principle of street and highway design is to remove stormwater
and snowmelt as quickly as possible from and beneath the pavement surface.
Reasons include vehicular safety and prevention of damage to pavements and their
bases. Therefore, the thought of intentionally storing water on a street may be viewed,
at least initially, as unacceptable. Recall that no incidents of risk to vehicles or damage
to pavement as a result of properly designed street storage of stormwater have been
reported in Skokie or Wilmette.
Therefore, preliminary research into the technical and economic feasibility of the
integrating planning and design of speed humps and street berms is
recommended. Each component has proven to be cost-effective and that cost
effectiveness might be enhanced if the two devices are part of an integrated design.
Joint application of humps for vehicle speed control and berms for stormwater control
should be examined in two nodes. One is retrofitting existing urban areas where speed
control and wet weather flow management are needed. Retrofitting is usually the way
these two devices are typically separately implemented. The other is integrating the
design of the form and function of humps and berms into new urban development to
optimize traffic and stormwater management.
Envisioned are traditional looking concrete or asphalt streets in a new development
which, on closer examination, are seen to include numerous berm-hump structures.
11-2
-------
Strategically placed and configured, the berm-hump structures were planned and
designed for the dual purpose of stormwater runoff vehicular speed management.
The recommended preliminary research into the integration of berms and humps
should include consideration of planning and design criteria and methodologies, public
agency acceptance, public acceptance, constructability, cost, and maintenance.
Street Storage to Reduce CSOs and Peak Flows at WWTPs
As noted, special hydrologic-hydraulic modeling conducted for this case study project
suggests that the street storage technology may help to significantly reduce the annual
number and volume of CSOs. Given the proven capability of a street storage system to
cost-effectively mitigate basement flooding, the need for some communities to mitigate
both basement flooding and CSOs, and the limited funds available to communities, the
possibility of using the street storage technology to cost-effectively solve two or more
problems warrants further study.
Consider, for example, a community where end-of-pipe storage is being considered to
mitigate CSOs. Assume the community also has a basement flooding problem. A
street storage system, implemented alone or in combination with reduced end-of-pipe
storage, might provide the most cost-effective overall solution to the hypothetical
community's two problems. Therefore, additional primarily modeling studies of the
role of street storage in reducing CSOs and peak flows at WWTPs is
recommended. The approach described in Appendix F is suggested, that is, select
actual CSSs and use computer modeling to determine the annual frequency and
volume of CSOs and the magnitude and frequency of peak flows with and without street
storage systems. These modeling studies could be integrated with the modeling
studies suggested under the next recommended research topic.
Cosfs and Benefits of Street Storage Versus Traditional Approaches
The Skokie and Wilmette case studies suggest that street storage, where physically
feasible, is likely to be much less costly than sewer separation and relief sewers in
solving basement and other flooding. Stated differently, if basement and surface
flooding is the only or principal CSS problem faced by a community, economics
indicates that street storage should be viewed, from the outset, as a potential solution.
So should separation and any other potential solution. If CSOs are a problem, with or
without basement and other flooding, street storage should again, because of costs, be
considered as an option, either alone or in combination with traditional technologies.
Needed is a rigorous comparison of the costs and benefits of street storage, sewer
separation, relief sewers, and end-of-pipe storage. While tangible and intangible costs
are obviously important in such a comparison, tangible and intangible benefits also
must be considered. This is because traditional CSS remedial methods tend to be
11-3
-------
single purpose (usually reduction of CSOs), whereas street storage is likely to be
multiple purpose. The lower cost of street storage coupled with more benefits may
make yield a very high economic advantage. However, relevant data, information and
insight are needed.
Therefore, research into the tangible and intangible costs and benefits of street
storage compared to traditional approaches is recommended. One approach
would be to retrofit, "on paper," street storage into one or more CSSs in which sewer
separation, relief sewers, or end-of-pipe storage has already been applied. Determine
tangible and intangible retrofit costs and compare to actual costs already incurred.
Similarly identify tangible and intangible benefits. Draw conclusions based on the costs
and benefits. Another approach would be to draw on historic tangible cost data for all
types of methodologies. Normalize the costs by presenting them on a unit cost basis
where the units might be acres, buildings, or persons. Again, make comparisons.
Further Improvement to Hanging Traps
Hanging traps have proven, based on years of experience in Skokie and Wilmette, IL,
to be a very effective way of controlling the rate of flow from catchbasins into combined
sewers. Positive attributes include low cost, very little maintenance and ease of
replacement. As noted in the Chapter 9 section titled "Summary of Interviews With
Skokie, IL Officials," maintenance personnel prefer the simple, low cost hanging trap
flow regulators over the much more costly vortex regulators.
More hanging trap regulators could be used if the minimum orifice diameter for hanging
traps could be reduced to one inch. Furthermore, as explained in Chapter 9, this might
be possible if the hanging traps were fitted with a "bubble" or hemispherically shaped
screen or grill. This screen or grill would prevent debris from reaching and blocking the
small orifice.
Therefore, research leading to development of an effective, low cost screen or
grill for hanging trap regulators is recommended. Various configurations could be
performance tested in a laboratory setting. Testing should include various sizes and
shapes of sumps, recognizing that sump depth and shape probably affect hanging trap
performance. A promising subset could then be field tested.
The hanging trap research might be extended to include optimizing the entire catch
basin. Water quality management would be the focus of this part of the research. For
ideas on improving catch basins, see Grottker (1989). There may be room for
improvement. Consider this conclusion based on Swiss studies (Conradin, 1989):
...the construction and operation of catch
basins is not really feasible from the economic
point of view. Nor would catch basins probably
11-4
-------
have much justification in the combined sewer
system, for ecological reasons, when streets
are cleaned frequently by the vacuum method.
Street Storage as Part of New Combined Sewer Systems
Since the 1930's and 1940's, U.S. sewage policy has embraced constructing separate,
as opposed to combined, sewer systems in newly urbanizing areas (Burian et al, 1999,
p. 7). Selection of this policy for new urban areas led to some major sewer separation
projects in the CSS portions of U.S. communities. Examples are Minneapolis-St. Paul,
MN and Hartford, CT (AMSA, 1994, p. 17).
While separate sewers have been the "system of choice" in the U.S. for several
decades, which may appear to be a long time, CSSs have been used throughout
western and eastern civilizations for many centuries. As an example, Burian et al
(1999, p. 4) states:
The Indus civilization, circa 3000 BC, presents
one example of a sewage system ahead of its
time. The dwellers of the city of Mohenjo-Daro
(now part of West Pakistan) used a simple
sanitary sewer system and had drains to
remove stormwater from the streets. The ruins
of this ancient system illustrate care taken to
construct the sewers that would make the
engineer of today envious. One feature of
note was the use of a cunette in the storm
drain to accommodate sanitary wastewater
flows, while the remaining capacity of the
channel was available for WWF.
Furthermore, CSSs are being constructed today in various countries. Examples are
Germany, Japan and Switzerland. Rather than continue to embrace a rigid SSS or
CSS stance, there appears to be some interest in the U.S. and elsewhere to consider
CSSs for certain types of new development (Burian et at., 1999, p. 11).
Interest in CSS for new development gets added impetus when the adverse water
quality impact of stormwater runoff is considered. With a CSS, at least some of the
stormwater would be captured and routed through treatment before release into the
receiving waters. Using a portion of Elizabeth, NJ, Kaufman and Lai (1978) studied
various types of sewer systems for pollution abatement and flood control purposes.
Hypothetical systems studied were a conventional separate storm and sanitary sewer
system; a conventional CSS; and an advanced CSS meaning that it included in-pipe
storage, satellite storage, and controlled flow routing. Unlike the street storage system
11-5
-------
described in this manual, storage meant storage of combined sewage, not stormwater.
One conclusion with respect to the advanced CSS was that a "combined sewer system
can be designed to discharge less pollutant than a conventional separate system in
which the storm sewers discharge all urban runoff directly to water courses" (Kaufman
and Lai, 1978, p. 4).
Given the apparent openness to at least considering CSSs in some types of new urban
development, the street storage technology becomes even more relevant. Its potential
function in new CSSs would be to reduce peak flows of stormwater into the CSS thus
reducing the size and cost of the combined sewers.
Therefore, integrating street storage into any known proposed or on-going
studies of new CSS is recommended. If such studies are not proposed or underway,
they should be.
Impact of a Street Storage System on Non-Point Source Pollution
As noted earlier in this chapter, the many well maintained sumps strategically placed
around a street storage system offer the potential to remove suspended solids as well
as absorbed and adsorbed potential pollutants from stormwater. This suggests the
value of knowing the pollutant removal performance of street storage systems for
possible multipurpose use in existing or new CSS and separate sewer systems.
Therefore, research into the pollutant removal effectiveness of street storage
systems is recommended. This research might include computer modeling,
laboratory, and field monitoring elements.
wp/epastch11
11-6
-------
Appendix A
Questions Used to
Prompt Discussion in
Interviews of Skokie Officials
1. Intentionally storing stormwater on streets is unusual, but, in your case, effective.
How do you explain the benefits of street storage to citizens and/or elected
officials? Stated differently, how do you know that street storage "works?"
2. In your view, what are the key guiding principles in dealing with the public on
problems and solutions in the public works field?
3. Street and supplemental storage of stormwater seems to be a cost-effective
(lowest cost) solution to basement flooding in Skokie. If you could go back to the
beginning of the project (early, 1980's), would you do it again? Or would you
"hold out" for a more traditional and more costlier solution?
4. When street storage of stormwater was initially proposed, concern was expressed
over accelerated deterioration of pavement. What is your experience?
5. When street storage of stormwater was initially proposed, concern was expressed
over dangerous icing of streets during freezing temperatures. What is your
experience?
6. Are you aware of any accidents caused by standing water?
7. When street storage of stormwater was initially proposed, concern was expressed
over interference with normal movement of vehicles. What is your experience?
8. When street storage of stormwater was initially proposed, concern was expressed
over interference with operation of emergency vehicles (e.g., police cars, fire
engines). What is your experience?
A-l
-------
9. Are you aware of any damage to vehicles directly related to the system or its
components?
10. What is the weakest "link" (e.g., hanging traps, berms, subsurface tanks, etc.) in
the physical system?
11. Has the Village encountered any legal (e.g., liability) problems as a direct result of
street storage?
12. Street and related storage of stormwater typically requires careful maintenance of
the drainage system. Examples include keeping inlet grates clear of debris,
removing sediment and other deposits from catch basin sumps, and cleaning
clogged flow regulators. To what extent has increased maintenance been a
financial/personnel burden?
13. How has your method of resolving basement flooding been received by
regulatory/operating agencies? That is, has your approach been an advantage,
disadvantage or "wash" with other governmental units?
14. How have you funded your "street storage" system? Anything
special/different/unique about this means of funding vis-a-vis other public works
projects?
15. Have there been any favorable or unfavorable effects on traffic flow such as
excessive speed reduction and unwanted diversion of vehicles to other streets?
wp/epastappa
A-2
-------
Appendix B
Criteria
For
Screening Applicability
Of
Street Storage
Note: Before using this screening instrument, please read the section in Chapter 10
titled "Criteria for Screening the Applicability of Street Storage." In order to appreciate
why certain information is being requested, the person(s) involved in the screening
should understand the premise, components, and benefits of street storage. For that
reason, these three aspects of street storage are summarized here.
PREMISE OF A STREET STORAGE SYSTEM
Temporarily store stormwater on the surface (off-street and on-street) and, as needed,
below the surface close to the source, that is, where it falls as precipitation and prior to
its entry into the combined, sanitary, or storm sewer system. Accept the full volume of
stormwater runoff into the sewer system but greatly reduce the peak rate of entry of
stormwater into the system.
COMPONENTS OF A STREET STORAGE
Downspout disconnection to slow down and possibly infiltrate
stormwater
Off-street surface storage of stormwater (conventional
detention/retention) with regulated outflow
On-street surface storage with regulated outflow achieved by an
optimum combination of on-street berms and catchbasin flow restrictors
Sub-surface storage of stormwater (tanks or oversized sewer segments
beneath streets and parking lots) with regulated outlet control using
restrictors
B-l
-------
BENEFITS OF A STREET STORAGE SYSTEM
Street storage technology has the potential, depending on the situation, to cost-
effectively mitigate one or more of the following wet weather condition problems:
Basement flooding caused by surcharging of combined and/or sanitary
sewers
Overflow of combined and/or sanitary sewers and resulting pollution of
receiving waters
Excessive peak flow at wastewater treatment plants
Nonpoint source pollution
Surface flooding caused by stormwater runoff and/or surcharging of
combined or sanitary sewers.
General Information About the Community
1. Name of community/government entity:
2. Name and affiliation of person(s) responsible for conducting screening:
Person Affiliation Telephone
Fax/
Email
3. Dates or period of screening:
4. Population of community/government entity:
B-2
-------
5. Area of community/government entity:
6. Overall longitudinal street grades (select one):
< 0.2% (0.2 feet per 100 ft. along the street centerline)
0.2 < 0.5%
0.5 < %
Comment:
Combined Sewer System Information
QUESTION
Are combined sewers
present in at least part
of the community?
If the answer to the first
question is "no," go to
the section titled
"Concluding Comments"
or go to the set of
questions under the
section titled "Sanitary
Sewer System
Information"
If the answer to the first
question is "yes," the
following questions
apply only to the areas
served by combined
sewers.
Are combined sewers
structurally sound?
Do basements flood
because of combined
sewer surcharging?
YES
OR
OFTEN
MAYBE
OR
SOMETIMES
NO
OR
RARELY
COMMENTS
B-3
-------
Do streets flood
because of combined
sewer surcharging?
Do combined sewers
overflow into surface
waters?
Are off-street sites
available for surface
detention/retention of
stormwater?
Is nonpoint source
pollution a concern?
Is the wastewater
treatment plant
operating at or over its
treatment capacity?
Is the wastewater
treatment plant
operating at or over its
treatment capacity?
Has the community
already decided on a
solution to its combined
sewer problems or is the
community still "open" to
alternative solutions?
Sanitary Sewer System Information
QUESTION
Is a separate sanitary
sewer system present in
at least part of the
community?
YES
OR
OFTEN
MAYBE
OR
SOMETIMES
NO
OR
RARELY
COMMENTS
B-4
-------
If the answer to the first
question is "no," go to
the section titled
"Concluding Comments"
or go to the set of
questions under the
section titled
"Stormwater System
Information"
If the answer to the first
question is "yes," the
following questions
apply only to the areas
served by sanitary
sewers.
Are sanitary sewers
structurally sound?
Do basements flood
because of backup or
sanitary sewage?
Do sanitary sewers
overflow into surface
waters?
Is infiltration (of
groundwater) into
sanitary sewers a
problem/cause of
problems?
Is inflow of stormwater
into sanitary sewers a
problem/cause of
problems?
Is the wastewater
treatment plant
operating at or over its
treatment capacity?
Has the community
already decided on a
solution to its sanitary
sewer problems or is the
community "open" to
alternative solutions?
B-5
-------
Stormwater System Information
QUESTION
Is a separate
stormwater system
present in at least part
of the community?
If the answer to the first
question is "no," go to
the section titled
"Concluding
Comments."
If the answer to the first
question is "yes," the
following questions
apply only to the areas
served by separate
stormwater system.
Are the storm sewers
structurally sound?
Are residential, business
and other buildings and
property damaged by
stormwater?
Are off-street surface
sites available for
surface
detention/retention of
stormwater?
Is nonpoint source
pollution a concern?
Does the community
have an erosion/
sedimentation/
stormwater control
ordinance?
Does the community
have a separate
stormwater service fee?
YES
OR
OFTEN
MAYBE
OR
SOMETIMES
NO
OR
RARELY
COMMENTS
B-6
-------
Has the community
already decided on a
solution to its
stormwater problems or
is the community "open"
to alternative solutions?
CONCLUDING COMMENTS
Additional ideas/concerns/questions/suggestions/etc.
wp/epastappb
B-7
-------
Appendix C
Trouble Shooting Guide
for
Underground and Surface Storage Basins
with
Gravity Dewatering
wp/epastappc
C-l
-------
UNDERGROUND AND SURFACE STORAGE BASINS WITH GRAVITY DEWATERING
NORMAL OPERATION, INSPECTION AND TROUBLESHOOTING GUIDE
Skokie, Illinois
NORMAL OPERATION
Storage structures with gravity drainage include relief sewers, underground vaults, and surface storage basins. The normal operating sequence of areas with
gravity drainage during a storm event is:
««» Rainfall runoff from the streets in these areas drains directly from the inlets to the underground or surface storage basins.
<» The basins provide additional sotrmwater runoff storage and protection from combined sewer surcharging and basement flooding.
««» The water is discharged by gravity from the storage basin to the combined sewer system. The discharge rate from the storage basin is controlled by a
restrictor device at the outlet end. A check valve at the outlet pipe prevents backflow of combined sewage into the separated stormwater runoff system.
INSPECTION AND TROUBLESHOOTING
CONDITION OBSERVED
POSSIBLE CAUSE
CORRECTIVE ACTION
Streets for basin area flooded
<» Rain stopped, streets not draining
««» Sewage odor after basins have drained
Dry Weather Inspection and Maintenance
<» Inspect street inlets for area basins
(Annually in fall).
««» Inspect condition of check valve and
orifice (Annually in fall).
<» Exercise bypass drain valve (Annually in
fall).
Very heavy rainfall filled storage basin.
Associated street inlets plugged.
Restrictor orifice is clogged
Basin has filled. Combined sewer still
surcharged.
Stagnant water in basin. Check valve not
working.
Extremely heavy rainfall could cause ponding on major streets.
Check for free flow of stormwater at inlets or flooded street
areas. Clear street inlets.
Check for free discharge at manhole where basin drainage re-
enters combined sewer system. Open bypass valve on street
for emergency drainage. Rod or flush out obstruction in orifice
or discharge pipe to combined sewer. Flush out basin drainage
area with city water.
Drainage will resume when combined sewers are no longer
surcharged. No action needed.
Check manholes with check valve. Check for and remove any
debris lodged in check valve.
Clean out any debris that would inhibit drainage into basin.
Clear out any debris lodged in check valve or orifice plate.
With valve open, inspect for accumulations of grit and sediment.
Flush out any excess accumulations with city water.
C-2
-------
Appendix D
Trouble Shooting Guide
for
Stormwater Storage Basins
Dewatering Pump Stations
wp/epastappd
D-l
-------
STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS
INSPECTION AND TROUBLESHOOTING GUIDE
Skokie, Illinois
CONDITION OBSERVED
POSSIBLE CAUSE
CORRECTIVE ACTION
STORMWATER BASINS
Rain Period - Basin Filling
<» Streets for area basins flooded
<» Rainfall without basins filling
Very heavy rainfall filled basin.
Associated street inlets plugged.
Combined sewers not surcharged.
<» Area 9 - light rain, combined sewer not Pumping low flow from Dempster Street.
surcharged, pumps running
Rain Over - Basin Draining
<» Rain stopped, basin not gravity draining Restrictor orifice is clogged.
Plug valve failed closed (Area 9)
Extremely heavy rainfall could cause ponding on major streets.
Secure appropriate traffic controls.
Check for free flow of stormwater at inlets or flooded street
areas. Clear street inlets.
Rain not sufficient to surcharge combined sewers. Verify by
checking that water level is below divider wall on siphon side of
inlet structures: 8Z.1 - Area 8; 9P.O - Area 9.
All flow entering the north basin in Area 9 from Dempster Street
must be pumped by the dewatering pumps to reach the
combined sewer on Skokie Boulevard. No action needed.
Check for free discharge at manhole where basin drainage re-
enters combined sewer system: Area 8 - Structure 8P.O (Oakton
Street at Skokie Boulevard); Area 9 - Structure 9P.2 (combined
gravity and pumped discharge). Dislodge clogged orifice by
rodding or flushing. In Area 8, bypass valve at vault 80.4 can be
opened.
Depress RESET at control panel to clear fail. If condition
remains, open plug valve using manual override. Call electrical
service contractor if valve operator or panel malfunction.
D-2
-------
STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS
INSPECTION AND TROUBLESHOOTING GUIDE
Skokie, Illinois
CONDITION OBSERVED
POSSIBLE CAUSE
CORRECTIVE ACTION
STORMWATER BASINS (Continued)
Basin Draining (Continued)
<» Basin drained to gravity point, pumps
won't start
<» Pumps operating, basin not draining
<» Sewage odor after basins have drained
Dry Weather Inspections
<» Prevent basin drain clogging
Additional rain surcharged the combined
sewer.
Pump Float Switch No. 6 or other controls not
working.
Restrictor orifice is clogged.
Pumps not pumping capacity.
Stagnant water in siphon. Check valve not
working.
Pumps won't start if combined sewers still surcharged. Verify
that water level is at top of divider walls at control structures.
Check float condition and levels. Manually trip floats with long
pike pole. Check for other pump failure conditions noted below.
See above for no gravity draining.
See pumping guidelines below.
Check manholes with check valve. Check for and remove any
debris lodged in check valve. Dewater siphons by opening drain
valve to remove stagnant water.
Clear any accumulated debris from basin drains. Remove
debris from perimeter of basin.
D-3
-------
STORMWATER STORAGE BASINS - DEWATERING PUMP STATIONS
INSPECTION AND TROUBLESHOOTING GUIDE
Skokie, Illinois
CONDITION OBSERVED
POSSIBLE CAUSE
CORRECTIVE ACTION
PUMPING STATIONS
««» Pump operating with severe noise or
vibration
««» Pumps operating but not pumping
capacity
Panel Alarm Indicators:
<» Pump Fail
««» Pump High Temperature
<» Pump High Moisture
<» Low Sump Level
<» High Basin Level
«{* Plug Valve Fail (Area 9)
Pump not seated properly.
Pump impeller or volute clogged.
Pump discharge clogged.
Basin dewatering drain plugged.
Power failure.
Other conditions indicated by specific alarm
lights:
Low cooling oil level.
Debris in impeller.
Pump motor seal failed.
Low level or normal pump cutout float switch
not working or hung up.
Very heavy rainfall filled basin.
Valve will not reach limit position (open or
close). Debris clogging valve.
Limits of valve out of adjustment.
Pull pump and re-seat on guide rail system.
Pull pump and unclog.
Check first manhole for pump discharge. Remove pump and
rod out or flush discharge line.
Verify by low sump level but considerable water remaining in the
basin to pump. Rod out or flush basin drain. Dewater with
alternate pump if necessary.
Pump RESET switch must be depressed before restarting
pumps in AUTOMATIC mode upon restoration of power after
power failure, circuit breaker trip, or any other type of failure
listed.
Pull pump and check cooling oil if pump repeatedly overheats.
Pull pump and remove debris from impeller.
Pull pump and inspect stator casing for moisture. Call pump
service representative if moisture is in motor housing.
With pumps in AUTOMATIC, use a long pike pole to manipulate
floats by hand to trip. Check for correct level of floats. Call
electrical service contractor if pump floats have become
inoperative.
Extremely heavy rainfall could cause ponding on major streets.
Secure appropriate traffic controls.
Manually open valve with override and manually start pumps to
flush out debris.
Refer to Limitorque valve operator manual or call electrical
service contractor.
D-4
-------
Appendix E
Standard Maintenance Procedures
for
Submersible Dewatering Pumps -
Stormwater Storage Basins
wp/epastappe
E-l
-------
SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS
STANDARD MAINTENANCE PROCEDURES
Skokie, Illinois
EQUIPMENT CONTRACTORS
PUMP SUPPLIER:
Hydroaire Incorporated
834 West Madison
Chicago, IL 60607
Phone: 312-738-3000
Fax: 312-738-3226
Project No.: AKFL 10280
ELECTRICAL PANEL INSTALLATION:
Aldridge Electric
28572 N. Bradley Road
Libertyville, IL 60048
Phone: 708-680-5200
Fax: 708-680-5298
PUMP LIST
LOCATION:
ITEM
Pump Tag No.
Make
Model No.
Impeller No.
Impeller Size
Horsepower
Flow, gpm
Head, feet
AREA 4
P-4-1 , 4-2
Flygt
CP-3085
438
4"
2.0
210
12.0
AREAS
P-8-1
Flygt
CP-3152
624
10"
14
2250
11.5
AREAS
P-8-2
Flygt
CP-3102
442
6"
5
450
18.5
AREA 9
P-9-1 , 9-2
Flygt
CP-3152
620
10"
14
3000
12.0
SAFETY PRECAUTIONS
1. Always lock out and tag the submersible pumping equipment before removing it from the sump for inspection or maintenance.
2. Use only the hoisting equipment recommended by the equipment manufacturer to remove the pumps from the sump.
3. Rinse the pump thoroughly with clean water before handling or inspecting the pump.
4. The pumps are designed to be removed from the sumps without anyone entering.
5. If for any reason it becomes necessary to enter the sump, follow proper confined space entry procedures.
6. If checking or changing the oil, hold a rag over the oil casing screw when removing it.
E-2
-------
SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS
STANDARD MAINTENANCE PROCEDURES (Continued)
Skokie, Illinois
MAINTENANCE PROCEDURES
DESCRIPTION FREQUENCY LUBRICANT/PARTS REMARKS
1. Inspect impeller and volute 12 months Replace severely worn impellers. Checkfor clogging and
remove debris if needed. Have service representative adjust
impeller clearance if needed.
2. Inspect motor seal for proper oil level and possible 12 months Cooling Oil Use Mobil Whiterex 309 or ordinary SAE 10W-30.
contamination. Replace oil containing water or if
cream-like.
3. Inspect the stator casing. 24 months Seal If oil or water is in the stator housing call the Flygt
representative.
4. Complete pump overhaul 5 years Interval recommended by manufacturer for overhaul. Best
performed for Skokie during winter dry weather months.
STATION INSPECTIONS
1. Inspect stations weekly during wet weather months or more frequently during heavy rain events. Note general condition of structure, surrounding ground or
grass area, control panel, and signs of forced entry or vandalism.
2. Record the pump hour meter readings and electric meter readings.
3. Observe the electrical panel for any alarm conditions: High water level, low water level, high temperature fail, seal leak. Record alarm occurrences on station
inspection form.
4. Check bottom of sump for debris buildup. Remove excess debris as required.
5. Alternate the pump sequence with the LEAD/LAG switches to obtain equal running time for the pumps at Area 9.
Notes:
a. The pump station for Area 8 should always have Pump No. 1 as the lead pump and Pump No. 2 as the lag pump. On this station, the pumps will
always have unequal run times.
b. When the pumps at the Area 4 station are set in the ALTERNATE position on the control panel, they will automatically alternate in sequence.
REFERENCE
Flygt Model CP Submersible Pump Installation and Maintenance Manual (provided with each pump).
Village of Skokie Operation and Maintenance Manual, Stormwater Runoff Control Facilities.
-------
SUBMERSIBLE DEWATERING PUMPS - STORMWATER STORAGE BASINS
INSPECTION FORM
Skokie, Illinois
Date
Hour Meters
Pump 1
Pump 2
Electric Meter
Comments
PUMP STATION AREA:
. AREA 4 (OAKTON AND FLORAL)
.AREA 8 (GABION POND)
.AREA 9 (EVANSTON GOLF CLUB)
E-4
-------
Appendix F
Exploratory Analysis
of the
Impact of a Street Storage System
on the
Frequency and Volume
of
Combined Sewer Overflows
Note:
This analysis and its documentation was
prepared by Robert W. Carr, PE and Michael
C. Morgan, PE of Earth Tech.
F-l
-------
Introduction
Street storage has been proven to substantially reduce basement flooding in various
communities.
It is reasonable to expect that street storage would have a positive impact on the
frequency and volume of CSOs and could be used to meet the Nine Minimum Controls
established by EPA. The primary purpose of this study was to complete an analysis to
evaluate the potential benefits of street storage with respect to reductions in the
frequency and volume of CSOs. The analysis was completed using hydrologic and
hydraulic computer modeling to represent the performance of the combined sewer
system. XP-SWMM computer modeling software was utilized to conduct the analysis.
To efficiently perform the analysis, data previously developed for the Village of Skokie
was utilized. The Village of Skokie has implemented a street storage program to
provide 10-year protection from basement flooding. The street storage improvements
were designed to function with TARP (the Tunnel and Reservoir Plan), deep tunnels
constructed to provide an overflow for flows in excess of the interceptor system
capacity. During dry weather, flows go from the Village's system to the MWRDGC's
interceptor system. During wet weather, flows fill the interceptor sewer system, and
then overflow into TARP. CSOs occur to the North Shore Channel when the capacity of
the connections between the local systems and TARP is exceeded or when TARP is
full.
Street storage combined with a deep tunnel solution to sewer capacity problems is
effective in reducing CSOs to waterways, but is not an option in most communities.
Therefore, the impacts the use of street storage independent of a TARP system need
to be evaluated. This study utilized the data developed for Skokie modified to exclude
TARP and replace it with discharge to a WWTP with CSOs to the adjacent waterway.
This provided information about a combined sewer system discharging directly to a
WWTP, as is the case for most existing combined sewer systems.
Two scenarios were evaluated in the study. The first scenario consisted of "pre-project"
conditions, or the combined sewer system without implementation of street or
subsurface storage. The second scenario represented conditions with street storage
and subsurface storage that has been implemented in a basin in Skokie with
characteristics representative of other combined sewer areas. The analysis
incorporated flows for dry and wet weather conditions with and without street storage
and was completed using the Emerson Street Sewer District (ESSD) basin of the
Village (see Figure F-1). A 45-year rainfall record was used as the basis for evaluating
potential CSO reductions attainable with street storage. The occurrence of CSOs was
defined using "typical" wastewater treatment plant capacity. The number and volumes
of combined sewer overflows was determined for scenarios with and without the street
storage.
F-2
-------
Figure F-1
Sewer Districts in Skokie
F-3
-------
Study Area Description
The Village of Skokie is located adjacent to and directly north of the City of Chicago.
The 5,510 acre area of the Village is divided into three sewer districts: the 1,255 acre
Howard Street Sewer District (HSSD) in the southern part of the Village; the 2,300 acre
Main Street Sewer District (MSSD) in the central part of the Village; and the 1,955 acre
Emerson and Lake Street Sewer District (ELSSD) in the northern part. As discussed
above, the 840 acre Emerson District was included in this analysis.
Precipitation occurs as rain, sleet, hail, and snow and ranges from showers of trace
quantities to brief intense storms to longer duration rainfall or snowfall events.
Precipitation is distributed throughout the year with an average annual total of
33.3 inches. Circular 172 prepared by the Illinois State Water Survey (1989) estimates
that for a one hour storm, the 1,10, and 100 year recurrence interval rainfall amounts
are 1.49, 1.94, and 2.08 inches, respectively. For a 24 hour storm, the 1, 10, and 100
year amounts are 2.21, 3.86 and 6.70 inches, respectively.
Soils in the area are primarily from glacial deposits of the Pleistocene series. These
glacial deposits have an approximate depth 60 feet and consist of many types of
materials. About 25 percent of the study area are sandy soils, while the remainder has
clay soils. Ground water levels tend to remain 10 to 15 feet below ground level in
sandy areas with the exception of isolated perched lenses of shallower ground water.
The land in the ESSD generally slopes eastward toward the North Shore Channel.
Slopes vary from 0.1 to 1 percent and the overall slope in many areas of the Village is a
flat 0.2 percent. Surface runoff flows from the front lawn and driveway areas to the
street. Flow in the street is along the curb line and gutters to the nearest inlet. Inlets
are generally located midblock and at intersections. Due to the extremely flat
conditions, few areas have a continuous drainage pattern from block to block. Trunk
sewers in the combined system range in diameter from 30 inches to a maximum of 84
inches. Lateral sewers which are connected to trunk sewers range in diameter from 12
to 27 inches.
Study Approach
Analysis Objectives
The focus of this study was to quantitatively evaluate the potential benefits of street
storage with respect to control of CSOs. The approach adopted for this study included
components intended to consider "typical" combined sewer systems. The following
study objectives were identified and incorporated into the impact analysis:
1. Evaluate the potential effects of street and underground storage for a typical
F-4
-------
community that contains a combined sewer service area. Use one sewer district in
the Village of Skokie as the basis for the analysis.
2. Assume that an overflow collection system such as TARP does not exist. The flows
discharged from the combined sewer system will be directed to the wastewater
treatment plant or overflow to a receiving stream.
3. Evaluate the effect of street storage on a community's ability to meet the Nine
Minimum Controls, that have been developed by USEPA for control of CSOs.
4. Evaluate the effect of street storage on the frequency and volume of combined
sewer overflows.
5. Evaluate the effect of street storage on the community's wastewater treatment
facilities.
Analysis Methodology
As previously discussed, detailed models were developed using SWMM to represent
the performance of the combined sewer system in the ESSD. Models were developed
to simulate performance of the system before and after the runoff control program was
implemented. SWMM is an excellent tool for conducting sewer system analysis,
however there are limitations to using the EXTRAN module of SWMM for continuous
simulation.
To overcome the limitations of the EXTRAN module while utilizing historical
precipitation, a two part approach was adopted for this analysis. The first part of the
analysis consisted of completing simulations using the SWMM models developed for
scenarios with and without street storage. Simulations were conducted to define the
minimum rainfall event threshold causing combined sewer overflow. Simulations were
completed for both scenarios using rainfall events selected to represent the range of
events contained in the historical series. The results of the simulations were used in
the second part of the analysis, which consisted of deriving CSO statistics from the
entire record of rainfall events. CSO occurrences, volumes and peak flows were
derived based on regression techniques applied to the simulation results of the
strategically selected rainfall events.
An outline of the procedure used for the impact study is summarized below:
1. Develop SWMM models for the ESSD basin to represent scenarios with and
without street storage.
2. Incorporate dry weather flows quantified from previously conducted flow
monitoring programs.
F-5
-------
3. Incorporate wet weather flows with runoff control facilities.
4. Verify model performance for the 10-year, 6-hour design rainfall event. Adjust
parameters as necessary to correctly represent expected system discharge and
storage volumes for the design event.
5. Develop model parameters to represent the scenario without runoff control
facilities.
6. Verify model performance for the 10-year, 6-hour design rainfall event using
earlier study results that quantified approximate surcharging depths.
7. Use the RAIN module of SWMM to convert the 45-year historical continuous
precipitation record from the NOAA station at O'Hare International Airport to
defined rainfall events.
8. Complete model simulations to determine which rainfall events will result in
CSOs for wet weather flows with and without runoff control facilities.
9. Select rainfall events for simulation that are representative of the historical
precipitation record. Complete model simulations for both scenarios using the
selected rainfall events. Tabulate model results to determine CSO peak flow
and CSO volume for each simulated rainfall event simulated.
10. Determine relationship for each scenario between CSO peak flows and CSO
volumes with corresponding rainfall event characteristics. Use defined
relationship to estimate CSO peak flow and CSO volume for all rainfall events in
the 45-year historical series (See no. 7 above).
11. Develop statistics to describe the occurrence of CSO peak flows and CSO
volumes to quantify the effects of street storage on CSOs.
Hydrologic and Hydraulic Computer Modeling
Hydrologic and hydraulic modeling supporting the runoff control program dates back to
the late 1980's. The original analysis of the ESSD was completed in 1987 using the
System Analysis Model (SAM) computer modeling software, which was originally
developed by CH2MHill. The analysis was limited to the major interceptors in the
ESSD. The SAM model was run on a VAX computer system. In 1992, the sewer
system model was converted into the HYDRA model, developed by Pizer, Inc.
XP-SWMM modeling software was used for this analysis. SWMM was selected
because it offers advantages in evaluating CSOs when compared to the capability of
models that were previously used for the ESSD. The hydraulic analysis capability of
the EXTRAN module of SWMM is superior to the other models. For example, SWMM
F-6
-------
explicitly solves the St. Venant equations for each model element at each time step
during the model simulation. The ability to explicitly represent system surcharging,
storage and volume are essential components to evaluating CSOs for a wide range of
rainfall events.
Model Parameters
Pipe and manhole data (pipe diameters, inverts and lengths, and manhole rim
elevations) were taken from the existing HYDRA model and input into the EXTRAN
module of SWMM. The dry weather flows, consisting of sanitary sewage and infiltration
were input as constant point flows into the EXTRAN module of SWMM. The wet
weather flows from foundation drains (0.007cfs/acre) and existing on-site detention
facilities (41 cfs) were input into the model as a constant flow in the EXTRAN module.
A flow rate of 2.0 cfs/acre was applied to the identified 26 acres of internal roof drains
using the acreage and the rainfall hyetograph in the RUNOFF module of SWMM.
Surface stormwater runoff was represented using the RUNOFF module. The ESSD
was divided into 73 subbasins, which were tributary to manholes in the model. The
area and percent impervious values were taken from previously completed analysis.
The subbasin widths were derived from measurements of each basin and a general
slope of 0.2 percent was used. The regulated catch basin flows were represented in
the EXTRAN module at each manhole by defining orifice links to control release rates
from each storage junction during the analysis. The non-regulated catch basin flows
were developed in the RUNOFF module and directed to the appropriate modeled
manholes in EXTRAN. The storage volume in each basin were determined and input
into the EXTRAN module using the stepwise linear area method.
Dry Weather Flow
Dry weather flows were considered to be sanitary sewage and infiltration. Sanitary
sewage is flow from residential, commercial or industrial buildings. The base average
daily residential flow was estimated based on the land use and the population served.
A per acre contribution was developed for each type of residential land, single family,
multi-family (2 to 4) and apartments. Residential flows varied from 0.006 to 0.02
cfs/acre.
The non-residential sanitary flows were divided into industrial and commercial flows.
Commercial flows are those flows from offices, gyms, laundries, schools, and other
commercial buildings. Sanitary flows from commercial buildings were estimated using
the size of the property. Industrial flows are those flows from manufacturing facilities,
warehouses, and other industrial buildings. Sanitary flows from industrial buildings
were also estimated using the size of the property. Commercial and industrial flows
varied from 0.04 - 0.02 cfs/acre.
Infiltration is primarily groundwater which enters the system through defective pipe and
manholes or other openings. Infiltration tends to be a steady-state flow as far as
F-7
-------
system modeling is concerned. The dry weather flows were all input as constant flows
because these flows are very small as compared to the wet weather flows.
Wet Weather Flows
Wet weather flows were considered to be foundation drains, roof drains, on-site
detention release rates and surface stormwater runoff. The first three components
were determined using flow monitoring and existing data. As part of the flow monitoring
program, foundation drains from individual homes in ESSD were monitored. This data
was determined to be similar to previous foundation flow monitoring data from the
Howard Street and Main Street Sewer Districts. The foundation flow was estimated to
be 0.007 cfs/acre and was input into the model as a constant flow.
The second wet weather flow component are roof drains. The Village required all
single-family residences to disconnect their downspouts. Buildings without downspouts
were assumed to have internal roof drains. It was decided to allow internal roof drains
to be connected directly to the combined sewer because of the cost to disconnect them.
A maximum peak flow rate of 2.0 cfs/acre was applied to the identified 26 acres of
internal roof drains. To maintain the rainfall dependent characteristics of flow from roof
drains, the roof area was represented as impervious tributary area in the model.
The third wet weather flow is the flow from existing on-site detention facilities. These
flows were represented by the design outflow rate as provided by the Village. Eighty
one (81) acres of existing on-site detention facilities were identified with a total release
rate of 41 cfs which was input into the model as constant point flows.
Stormwater Runoff
The first three wet weather flow inputs described above are considered to be fixed
flows, that is these flows can not be regulated or changed. The fourth and final wet
weather flow input is surface stormwater runoff. While the other types of wet weather
flows cannot be regulated, the street storage and subsurface storage system was
designed to control stormwater runoff component of wet weather flow.
Stormwater runoff was divided into two components, regulated catch basin flows and
non-regulated catch basin flows. Regulated catch basin flows require storage of the
surplus water not immediately allowed into the sewer within the project area. The
regulated catch basin flows and associated storage volumes were determined as part of
the runoff control program for the ESSD of Skokie. Non-regulated catch basin areas
allow the runoff from rainfall events up to the 10-year design rainfall event to enter the
sewer system without any restrictions. These non-regulated flows were only allowed on
arterial streets.
Regulated Catch Basin Flows
The first step of the analysis was to determine the capacity of the sewer system
F-8
-------
available for carrying stormwater runoff. The total hydraulic capacity of the sewer
system depends on the quantity of dry and wet weather flows and the level to which a
sewer can surcharge without causing basement flooding or other damage. This
capacity is also affected by the back water effect from limited capacity of downstream
sewers. The maximum allowable rates at which runoff can be released into the sewer
system were determined for all areas of the ESSD. These runoff rates ranged from
0.08 to 1.0 cfs per acre. Using the regulated runoff rate (cfs/acre) and the tributary
area, a maximum allowable regulated flow from each catch basin was determined.
Results of this analysis formed the basis for the design of the runoff control system and
for determining the sewer capacity available for those areas which could not be
regulated.
The second step was to determine the location and extent of intentional street ponding
which can be achieved through flow regulators and minor street grade modifications
(berms). Higher flows were allowed on streets with little storage available. Conversely,
on streets which could pond large stormwater volumes, the flows were regulated to use
the available storage capacity. The sewer capacity and the storage analyses were
conducted concurrently with each analysis providing input to the other. The product of
this analysis included delineation of street ponding elevations in allowable areas and
identification of the volume of additional runoff which must be detained in other storage
locations.
The third step was to site and size the additional storage facilities necessary to store
flows in excess of street ponding capacity and where street ponding was not feasible to
store runoff in excess of the regulated runoff rate. The locations and volumes of
detention facilities needed to store the remaining volume from step two were
determined. This step insured that the runoff control system for the ESSD would
reduce sewer surcharging to prevent sewer backup into the basement during the 10-
year recurrence interval storm.
Non-regulated Catch Basin Flows
The final component of the wet weather flows is the flow from non-regulated catch
basins. These catch basins are located on arterial streets and allow the runoff from a
10-year recurrence interval storm to enter the combined sewer system. The Village
designated the streets within the ESSD that were to be non-regulated streets.
Currently, the Village has reconsidered this assumption and is installing regulators to
restrict the runoff into the sewer system to that of a 10-year storm.
Wastewater Treatment Plant Description
The Village of Skokie does not own or operate a wastewater treatment plant (WWTP).
Conveyance and treatment facilities are provided by the MWRDGC. Dry weather flows
from the ESSD discharge to the MWRDGC interceptor located under McCormick
Boulevard. Wet weather flows discharge first to the interceptor sewer system, then to
F-9
-------
the TARP and if TARP is full, then to the North Shore Channel. To determine the
impact of street storage on the number and volumes of CSOs, a theoretical WWTP was
included in the analysis. Earth Tech recently completed a facility plan for the WWTP in
Gary, Indiana. Since Gary has a large combined sewer service area, it was used as a
basis for the theoretical WWTP for the ESSD. Theoretical ESSD flows were developed
by prorating average and peak flows from the Gary WWTP. The Gary WWTP treats an
average of 35.6 cfs on a dry day with a peak WWTP flow of 186 cfs. Flows larger than
186 cfs are bypassed into either the Little Calumet River or the Calumet River. The
average dry weather flow from the ESSD is 12 cfs. Using the same ratio of average dry
weather flow to peak capacity, the peak wet weather flow through the ESSD WWTP
would be 65 cfs. A review of the Skokie flows showed that the flows from on-site
detention facilities add up to 41 cfs. Therefore, the constant flows equal 53 cfs (12 cfs
dry weather and 41 cfs on-site detention facilities. The roof and foundation drains and
regulated catch basins also add additional flow. It was determined that 65 cfs was too
small to use for this analysis. Because many communities with large peaking factors,
both separate and combined systems, ie, Racine, Wl, Kenosha, Wl, Milwaukee, Wl and
the Greater Metropolitan Water Reclamation District of Greater Chicago, IL provide
either storage or a flow through clarifier (typically with disinfection) for a portion of the
flows that exceed the WWTP capacity. Therefore, it was decided to provide a flow
through clarifier to allow the ESSD facility to handle a peak wet weather flow of 100 cfs.
Therefore, the ESSD treatment facility assumed for this analysis accepts up to 100 cfs
prior to the occurrence of a combined sewer overflow.
Model Verification
Flow Monitoring Program
In 1986, a flow monitoring program was conducted in the ESSD. A total of flow
meters, rain gauges, and two foundation monitors were installed for months. This
flow monitoring program provided dry weather and wet weather flow data at strategic
points in the districts. In addition to sewer flows, a foundation drain monitoring program
was also done. This data was used to develop dry weather flows and verify wet
weather flows used in the hydraulic models. The parameter development completed
during previous analysis and observed system performance was used as the basis for
completing the SWMM models used in this analysis.
Design Storm Simulation
In addition to the flow monitoring data described above, simulation of the system design
rainfall event was used for model verification. The 10-year, 6-hour recurrence interval
rainfall event was the design storm for the design of the ESSD runoff control system.
Therefore, the 10-year, 6-hour rainfall event was simulated. The simulated storage
volumes and flows (sanitary, foundation drains, roof drains, existing on-site detention
facilities, and regulated catch basin flows) were compared and confirmed with expected
F-10
-------
results for the 10-year design storm. The regulated flows were confirmed by comparing
design parameters with simulation results for storage volumes and peak flows at
regulated manholes. The non-regulated catch basin flows were verified when the
simulated peak flow at the outfall matched the design peak flow of 300 cfs. At this point
the model was considered to be verified for use in performing additional analysis.
Combined Sewer Overflow Simulation
As previously discussed, detailed SWMM models were developed to represent the
performance of the combined sewer system in the Emerson Street study area. Models
were developed to simulate performance of the system before and after the runoff
control program was implemented. SWMM is an excellent tool for conducting sewer
system analysis, however there are limitations to using the EXTRAN Block of SWMM
for continuous simulation. Therefore, a two part approach was adopted for this analysis
to utilize the rigorous hydraulic analysis capability of the SWMM EXTRAN Block and
still obtain results for a long term period of recorded precipitation data. The first part of
the analysis consisted of completing simulations using the SWMM models developed
for both the pre-project scenario and the street storage scenario. Simulations were
conducted to define the minimum rainfall event threshold causing combined sewer
overflow. Simulations were then completed for both scenarios for approximately 25
rainfall events. The results of the simulations were used in the second part of the
analysis, which consisted of deriving CSO statistics from the entire record of rainfall
events. CSO occurrences, volumes and peak flows were derived based on the
regression techniques applied to the simulation results of the strategically selected the
rainfall events.
Historic Precipitation Record
Historic precipitation data from the NOAA station at Chicago O'Hare International
Airport (ORD) was obtained for the period WY1949 to WY1993. Initially, the
precipitation record was processed using the RAIN Block of SWMM. The RAIN Block
was used to read the continuous rainfall record and define individual rainfall events.
For the purpose of this study, a rainfall event was characterized as durations of
measured precipitation surrounded by 12-hour intervals during which precipitation was
not measured. The 12-hour interval was an arbitrary choice and deemed to be a
sufficient recovery time for the Emerson Street system. The continuous record was
processed by the RAIN block to gain information such as rainfall depth, maximum
rainfall intensity and average rainfall intensity to describe each rainfall event. This
information was used to correlate CSO occurrences with defined rainfall events. Table
F-1 presents a summary of the defined rainfall events according to rainfall depth and
maximum rainfall intensity.
The graphs depicted in Figure F-2, F-3 and F-4 were developed using the rainfall
events extracted from the historical precipitation record using the RAIN Block of
SWMM. The graphs include plots of rainfall depth, maximum rainfall intensity and
F-ll
-------
average rainfall intensity for the rainfall events defined in the historical record. As one
would expect, the graphs show significant scatter among the simple descriptors such
as rainfall depth and rainfall intensity. However, the graphs do indicate trends, upper
and lower limits and frequency characteristics that describe the historical rainfall events.
Use of rainfall events from a long term precipitation record was advantageous for a
number of reasons. For example, realistic rainfall patterns and system response is
represented with the use of recorded rainfall events instead of synthetic design rainfall
distributions. The frequent occurrence of CSOs also is better addressed by using a
historical precipitation record to derive frequency and performance statistics than by
using design rainfall events. Verification of the performance of a street storage system
with a variety of rainfall depths, durations and intensities was also an advantage gained
from using recorded rainfall.
Correlation of Combined Sewer Overflows and Rainfall
Rainfall events from the record were strategically selected to characterize CSO
occurrence for the study area while minimizing the number of simulations required.
Initially, simulations were conducted to define the minimum rainfall event threshold
causing combined sewer overflow. Simulations were then completed for both scenarios
for approximately 25 rainfall events. The simulated events were selected to be
representative of the variety in rainfall depth, maximum intensity and average intensity
present in the historical precipitation record. Particular emphasis was placed on
simulating rainfall events near the threshold at which overflows occur. This approach
was adopted to define performance for the most frequent rainfall events, which were
also believed to dominate the annual CSO statistics. The results of the simulations
were used as the basis for deriving CSO statistics from the entire record of rainfall
events. Table F-2 includes summary information for the simulated rainfall events and
Table F-3 presents simulation results for each rainfall event.
Table F-l
Rainfall Event Summary
Rainfall
Depth
(inches)
10.00
9.00
Number of
Occurrences
—
1
Cumulative
Subtotals
—
1
Maximum
Rainfall
Intensity
(inches/hour)
10.00
9.00
Number of
Occurrences
—
0
Cumulative
Subtotals
—
0
F-12
-------
8.00
7.00
6.00
5.00
4.00
3.00
2.50
2.00
1.50
1.00
0.50
0.20
0.10
0.05
0.02
0.01
0.00
0
0
0
0
5
15
27
37
96
241
575
888
624
490
532
280
456
1
1
1
1
6
21
48
85
181
422
997
1885
2509
2999
3531
3811
4267
8.00
7.00
6.00
5.00
4.00
3.00
2.50
2.00
1.50
1.00
0.50
0.20
0.10
0.05
0.02
0.01
0.00
0
0
0
0
0
1
0
2
13
37
205
657
687
689
761
413
805
0
0
0
0
0
1
1
3
15
52
257
914
1601
2290
3051
3464
4267
F-13
-------
Figure F-2
Rainfall Depth vs. Maximum Rainfall Intensity
H-
re L. _
c ^ 3
re .E 25-
^^^ ^^
.-? ^
3 W 1 c
c c LO
C -. =
X
7. if.
£ — :c
^.-. ..^
'
2.
^#
X "•<
:™.
50
"£ -
-• -_-"-
X
4.
%
/
'<..
50
/
\
/
6.
50
8.
50
X
10.
Rainfall Depth (in)
-------
Figure F-3
Maximum Rainfall Intensity vs.
Average Rainfall Intensity
c.
Is
C 0
(0 —
0
-.?.-
, -.]=
0
—£^^^-~|~^"j- v^-|~—
-X-
0.2 0.4 0.6 0.8 1
Average Rainfall Intensity (in/hr)
1.2
1.4
-------
Figure F-4
Rainfall Depth vs. Rainfall Intensity
c
O
I
'(5
o:
0.50
2.50
4.50 6.50
Rainfall Depth (in)
8.50
10.50
Maximum Intensity (in/hr) + Average Intensity (in/hr)
-------
Table F-2
Simulated Rainfall Events
Event Start Date
3/19/48
10/9/69
4/24/54
8/17/90
1 1/26/90
8/31/89
8/29/55
6/13/50
9/24/61
1 1/4/88
4/12/83
9/15/92
6/4/53
9/25/93
8/17/83
11/13/51
9/12/77
9/17/49
3/28/51
12/16/87
6/20/68
9/23/63
7/18/57
5/27/56
7/1/83
12/7/78
Event Duration
(hours)
19
33
8
10
10
18
16
4
22
7
18
15
23
11
1
5
11
23
5
20
4
18
12
16
3
3
Event Volume
(inches)
5.00
4.68
3.70
3.01
2.98
2.56
2.46
1.99
1.98
1.50
1.49
1.25
1.25
1.25
1.00
1.00
1.00
0.75
0.75
0.75
0.60
0.60
0.60
0.55
0.55
0.55
Maximum
Intensity
(inches/hour)
2.39
1.10
0.57
1.55
0.33
1.85
0.60
1.16
0.46
0.92
0.42
1.19
0.52
0.29
0.74
0.32
0.15
0.42
0.17
0.07
0.60
0.30
0.09
0.51
0.33
0.13
Average
Intensity
(inches/hour)
0.26
0.14
0.10
0.15
0.08
0.11
0.22
0.40
0.11
0.30
0.03
0.63
0.06
0.07
0.17
0.07
0.04
0.11
0.01
0.02
0.60
0.10
0.02
0.14
0.06
0.03
F-17
-------
Table F-3
Overflow Simulation Results
Event Start
Date
3/19/48
10/9/69
4/24/54
8/17/90
1 1/26/90
8/31/89
8/29/55
6/13/50
9/24/61
11/4/88
4/12/83
9/15/92
6/4/53
9/25/93
8/17/83
11/13/51
9/12/77
9/17/49
3/28/51
12/16/87
6/20/68
9/23/63
7/18/57
5/27/56
7/1/83
12/7/78
Pre-project Scenario
Peak
Overflow
(cfs)
464.5
353.1
116.2
427.7
61.8
418.9
114.0
225.7
66.8
177.8
67.1
199.5
51.2
45.1
141.6
34.8
—
37.1
—
—
73.1
21.7
—
35.8
—
~
Overflow
Volume
(acre-feet)
115.2
110.6
39.0
67.4
19.3
50.1
31.6
30.9
8.8
19.7
7.7
15.7
5.6
5.6
14.4
4.2
—
3.6
—
—
5.2
1.7
—
1.6
—
~
Street Storage Scenario
Peak
Overflow
(cfs)
278.3
229.7
86.3
233.7
55.3
223.7
82.7
150.2
16.9
113.3
—
119.0
26.0
33.9
95.9
25.9
—
22.1
—
—
42.3
11.4
—
9.1
—
~
Overflow
Volume
(acre-feet)
111.3
101.3
35.6
60.3
16.9
44.8
27.9
27.2
0.1
16.7
—
12.8
3.0
4.2
11.1
2.8
—
2.0
—
—
3.2
0.6
—
0.3
—
~
Overflow
Volume
Reduction
(%)
3.36
8.45
8.72
10.64
12.61
10.60
11.86
12.03
99.06
15.48
100.00
18.58
45.73
25.35
22.65
33.15
—
44.30
—
—
38.32
66.13
—
83.04
—
~
F-18
-------
The simulation results presented in Table F-3 formed the basis for determining CSO
occurrence and assigning CSO volumes to rainfall events contained in the historical
record. The relationship between rainfall event characteristics and CSO occurrence,
flow and volume was determined by regression of the simulated results. A third order
polynomial was fitted to the simulated CSO volumes using rainfall depth, maximum
intensity and average intensity. Figure F-5, F-6 and F-7 demonstrate the consistency
between simulated CSO data and predicted CSO data based on the regression
relationship.
Analysis Results
Annual statistics were generated for WY1949 to WY1993. Table F-4 presents the
computed statistics, which include annual number of CSO occurrences, annual CSO
volume without street storage, annual CSO volume with street storage, annual percent
reduction in CSO volume with street storage. In addition to the regression that was
completed to assign CSO occurrence and volume to historic rainfall events, the data
was further analyzed to investigate the relationships defining CSO peak flow and
reductions in CSO volume and peak flow attainable with provision of street storage.
Curve fitting techniques available in Microsoft EXCEL were used to quantify the
apparent relationships between various data sets.
Figure F-8 presents pre-project overflow volume plotted against overflow volume
reduction. The plot shows a well defined relationship between overflow volume
reduction and pre-project overflow volume and is well represented by the fitted power
function also shown in the figure. The data indicated significant reductions in overflow
volumes, especially for events producing overflow volumes that were less than 20 acre-
feet. As indicated in Figure F-8, street storage resulted in reductions of at least 20% for
overflow volumes of approximately 20 acre-feet. The trend in percent reduction
resulting with street storage increased dramatically as overflow volume decreases. The
potential benefits from street storage become even more apparent considering that the
average overflow volume for pre-project conditions was 15.9 acre-feet and the median
overflow volume was 10.0 acre-feet. Applying the fitted curve in Figure F-8, street
storage reduced overflow volumes for over half of the individual events by 30% or
greater.
Graphs were also developed to examine possible relationships between provision of
street storage and reductions in CSO peak flows. As shown in Figure F-9, there does
not appear to be a well defined trend between CSO peak flow and rainfall depth.
However, there does appear to be a trend in comparisons between CSO peak flow and
maximum rainfall intensity. Figure F-10 presents the CSO peak flows resulting from the
simulations compared with maximum rainfall intensity from each respective rainfall
event incorporated in the simulation. Figure F-10 also contains second order
polynomial curves fitted to the CSO peak flows for the pre-project scenario and the
F-19
-------
K)
O
200 -1
(0
100
-------
Figure F-6
Overflow Volume vs. Maximum Rainfall Intensity
Pre-project Scenario
-------
to
to
|
200
IB 100
2
t
0)
O
Figure F-7
Overflow Volume vs. Average Rainfall Intensity
Pre-project Scenario
0
0.2 0.4 0.6 0.8 1
Average Rainfall Intensity (in/hr)
1.2
1.4
x Predicted OF A Simulated OF
-------
Table F-4
Annual Overflow Statistics
Annual CSO
Statistics
Annual
Average
Annual
Median
Annual
Maximum
Annual
Minimum
Annual
Standard
Deviation
Pre-project Scenario
Number of
CSOs
12.62
12
23
6
4.00
CSO Volume
(acre-feet)
197.98
187.91
478.42
86.92
92.57
Street Storage Scenario
Number of
CSOs
11.24
10
22
5
3.69
CSO Volume
(acre-feet)
162.44
147.54
415.68
63.77
82.05
CSO Volume
Reduction
19.23
18.79
29.48
9.24
4.40
F-23
-------
Figure F-8
Overflow Volume Reduction vs. Overflow Volume
to
120
V 100
o
3
-------
-y 500 -i
.H. /inn
^•-^ H-UU
O^nn
_ ouu
CD 9nn
ȣ zuu
1 nn
v I UU
CD n
Figure F-9
Peak Overflow vs. Rainfall Depth
m * ^
^^, """" A
>
™™
zzzs; czz zzs .sfc ^|f I
=
!!
>
Q_ u n ^^ ^ ^ ^ '
01 2345
Rainfall Depth (in)
* Peak OF with Storage ^ Peak OF without Storage
6
-------
Figure F-10
Peak Overflow vs. Maximum Rainfall Intensity
to
0)
0
1 2 3
Maximum Rainfall Intensity (in/hr)
A Peak OF with Storage x Peak OF without Storage
— Poly. (Peak OF without Storage) Poly. (Peak OF with Storage)
-------
street storage scenario.
Conclusions
The graphs and tables summarizing the CSO simulation and annual statistics clearly
demonstrate that street storage does contribute to reducing both CSO volumes and
peak flows. The data indicated that street storage resulted in a reduction of overflow
volume of 30% or greater for approximately half of the overflow occurrences. This
trend is consistent with objectives included in the Nine Minimum Controls such as
treating the first flush and maximizing system storage.
Unfortunately, the results of this analysis did not indicate significant reduction in CSO
occurrence and frequency. The study area selected for this case study was based on
an area where street storage improvements have actually been constructed. This fact
lends credibility to the improvement components and street storage volumes
incorporated into the SWMM models developed for this study. It should be noted,
however, that the improvements in the Emerson Street study area were conceptualized
and developed to function with the MWRDGC TARP system. As a result, this system
provides significantly greater capacity to accept system discharge than would normally
be received by typical treatment plant capacities. The street storage system analyzed
for this study was optimized to work in conjunction with improved sewer system
capacity to provide protection to the residents for the 10-year design rainfall event. The
street storage system was not specifically developed or optimized for the specific
purpose of eliminating and reducing CSO impacts. It is probable that even greater
benefits might have been realized had control of CSOs been an original objective
during development of the street storage system.
Provision of street storage as a CSO control technology clearly offers benefits beyond
simply controlling CSO impacts. Street storage can provide a cost-effective means for
addressing capacity limitations in combined sewer systems that are not addressed by
any current CSO control technologies. Based on the potential identified in this case
study for street storage to contribute to reductions in both CSO volumes and peak
flows, additional research and investigation is recommended to further explore and
quantify the benefits of street storage with respect to CSO impacts. Additional research
and investigation should be formulated to quantify the benefits of street storage to
address CSO water quality, CSO impacts and compatibility with other CSO control
technologies. The following are specific examples of additional research and
investigation:
• Conduct monitoring of CSO effluent from areas with and without street
storage to evaluate potential water quality benefits attainable with
provision of street storage.
• Conduct analysis to determine the significance of different land use types
on the potential water quality benefits attainable with provision of street
F-27
-------
storage.
Conduct analysis to evaluate the compatibility of street storage with other
identified CSO control technologies. Evaluate potential design and cost
reductions for CSO control technologies resulting from implementation
with street storage.
Evaluate design modifications required for street storage systems
optimized for CSO control compared to street storage systems optimized
to prevent basement and surface flooding.
Conduct analysis to investigate the potential for implementing street
storage in various regions of the United States. Identify possible regional
limitations for implementing street storage for CSO control.
Conduct a sensitivity analysis to evaluate the impact of the size of the
WWTP along with the street storage on the amount of overflows. This will
allow us to further evaluate the effect of street storage on the community's
wastewater treatment facilities.
wp/epastappf
F-28
-------
Appendix G
Construction Costs
for
Skokie Street Storage System
Adjusted to 1999
G-1
-------
SYSTEM YEARS
COMPONENT OF
CONSTRUCTION
Roadway Berms
Roadway Berms
Tanks, Sewer
Relief Sewer
Roadway Berms
Surface Detention Facility
Tanks, Sewer, Surface
Detention Facility
Tanks, Sewer, Surface
Detention Facility
Roadway Berms
Tanks, Sewer, Surface
Detention Facility
Tanks, Sewer
Surface Detention Facility
Tanks, Sewer
Tanks, Sewer, Surface
Detention Facility
Tanks, Sewer
Tanks, Sewer
1984
1985
1985
1986-87
1988
1989
1989
1990
1990
1991-92
1992
1994
1993-94
1994-95
1995
1995
ORIGINAL ENR CONSTRUCTION
CONSTRUCTION INDEX COST
COST(1) FOR ADJUSTED
YEAR(S) TO
OF 1999(3)
CONSTRUCTION^)
$
42450
1325415
1689577
4930781
1547510
835771
7834524
4992485
1170665
4712949
2998451
946480
3153684
4422855
1686775
766109
4146
4195
4195
4351
4519
4615
4615
4732
4732
4910
4985
5408
5309
5440
5471
5471
$
61351
1893179
2413336
6790448
2051932
1085144
10172149
6321845
1482381
5751526
3604156
1048689
3559404
4871645
1847406
839065
-------
Tanks, Sewer
Relief Sewer
Sewer
Tanks, Sewer
Water Main
TOTALS:
1996-97 13100078 5723 13715825
1997-98 6887763 5873 7027324
1998 185023 5920 187273
1999 3508316 5992 3508316
66737661 78232393
Footnotes:
1) Based on actual costs with the exception of 19999 which is the engineer's estimate.
Source: Carr, 1999.
2) Engineering News Record (ENR) Construction Cost Indices were obtained from
The annual average value was used for one year construction periods.
The average of annual averages was used for two year construction periods.
3) ENR index used for 1999 (February) is:
5992
File Name: SkokieStreetStorageCosts
-------
Glossary
Note: Definitions are quoted from USEPA (August, 1998) except for terms denoted with
(*) at the end of the definition. Definitions of these terms are developed in this report or
taken from indicated sources.
Berm. A low structure constructed across a street, from curb to curb, and intended to
temporarily impound water on its upstream side. The crest or top of the berm when
viewed along the longitudinal axis of the street, is horizontal. It is in effect, a spillway.
n
Catch Basin. A chamber or well, usually at the street curbline, for the admission of
surface water to a sewer or subdrain, having at its base a sediment sump to retain grit
and below detritus the point of overflow; whereas, a stormwater inlet does not have a
sump and does not trap sediment.
Combined Sewer. A sewer receiving intercepted surface (dry- and wet-weather) runoff,
municipal (sanitary and industrial) sewage, and subsurface waters from infiltration.
Combined Sewer Overflow (CSO). Discharge of a mixture of stormwater and
domestic waste when the flow capacity of a sewer system is exceeded during
rainstorms.
Computer Model. A model in which the mathematical operations are carried out on a
computer.
Cost-Effective Solution. A solution to a problem that has been identified as being
financially optional (e.g., the solution associated with the knee-of-the-curve of a cost-
benefit relationship).
Detention. The slowing, dampening, or attenuating of flows either entering the sewer
system or within the sewer system by temporarily holding the water on a surface area,
in a storage basin, or within the sewer itself.
Flow Regulator. A passive, gravity device that regulates the flow of stormwater into a
combined sewer. (*)
-------
National Pollutant Discharge Elimination System (NPDES). The national program
for issuing, modifying, revoking and reissuing, terminating, monitoring, and enforcing
permits, and imposing and enforcing pretreatment requirements, under Sections 307,
402, 318, and 405 of the Clean Water Act.
Nonpoint Source. Diffuse pollution sources (i.e., without a single point of origin or not
introduced into a receiving stream from a specific outlet). The pollutants are generally
carried off the land by stormwater. Common nonpoint sources are agriculture, forestry,
urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city
streets.
Permit. An authorization, license, or equivalent control document issued by EPA or an
approved state agency to implement the requirements of an environmental regulation;
e.g., a permit to operate a wastewater treatment plant or to operate a facility that may
generate harmful emissions.
Pollutant. A contaminant in a concentration or amount that adversely alters the
physical, chemical, or biological properties of the environment. The term includes
pathogens, toxic metals, carcinogens, oxygen-demanding materials, and all other
harmful substances. With reference to nonpoint sources, the term is sometimes used
to apply to contaminants released in low concentrations from many activities that
collectively degrade water quality. As defined in the federal Clean Water Act, pollutant
means dredged spoil; solid waste; incinerator residue; sewage; garbage; sewage
sludge; munitions; chemical wastes; biological materials; radioactive materials; heat;
wrecked or discarded equipment; rock; sand; cellar dirt; and industrial, municipal, and
agricultural waste discharged into water.
Pollution. Generally, the presence of matter or energy whose nature, location, or
quantity produces undesired environmental effects. Under the Clean Water Act, for
example, the term is defined as the man-made or man-induced alteration of the
physical, biological, chemical and radiological integrity of water.
Publicly Owned Treatment Works (POTW). Any device or system used in the
treatment (including recycling and reclamation) of municipal sewage or industrial wastes
of a liquid nature that is owned by a state or municipality. This definition includes
sewers, pipes, or other conveyances only if they convey wastewater to a POTW
providing treatment.
Receiving Waters. Natural or man-made water systems into which materials are
discharged.
-------
Sewer. A channel or conduit that carries wastewater and stormwater runoff from the
source to a treatment plant or receiving stream. "Sanitary" sewers carry household,
industrial, and commercial waste. "Storm" sewers carry runoff from rain or snow.
"Combined" sewers handle both.
Source Control. A method of abating storm-generated or CSO pollution at the
upstream, upland source where the pollutants originate and/or accumulate.
Storm Sewer. A sewer that carries intercepted surface runoff, street wash and other
wash waters, or drainage, but excludes domestic sewage and industrial wastes except
for unauthorized cross-connections.
Stormwater. Stormwater runoff, snowmelt runoff, and surface runoff and drainage;
rainfall that does not infiltrate into the ground or evaporate because of impervious land
surfaces but instead flows onto adjacent land or watercourses or is routed into
drain/sewer systems.
Street Storage. A system that mitigates surcharging of CSSs, SSSs and stormwater
systems by temporarily storing stormwater in a controlled fashion on the surface (mainly
on-street but some off-street) and, as needed, below streets. Stormwater is stored
close to the source, that is, where it falls as precipitation, and prior to its entry into the
sewer system. The full volume of stormwater runoff is accepted into the sewer system
but peak rates are reduced, as a result of the storage, to flow that can be
accommodated without surcharging. (*)
Surface Runoff. Precipitation, snowmelt, or irrigation water in excess of what can
infiltrate the soil surface and be stored in small surface depressions; a major transporter
of nonpoint source pollutants.
Surface Water. All water naturally open to the atmosphere (rivers, lakes, reservoirs,
ponds, streams, impoundments, seas, estuaries, etc.) and all springs, wells, or other
collectors directly influenced by surface water.
Watershed Protection Approach (WPA). The U.S. EPA's comprehensive approach to
managing water resource areas, such as river basins, watersheds, and aquifers. WPA
has four major features: targeting priority problems, stakeholder involvement, integrated
solutions, and measuring success.
Watershed. A drainage area or basin in which all land and water areas drain or flow
toward a central collector such as a stream, river, or lake at a lower elevation.
-------
Wet-Weather Flow. Usually referred to as the flow in a combined sewer system with
stormwater, but may also constitute the flow in a separate storm or sanitary drainage
system with stormwater.
wp/epastglos
-------
Cited References
American Society of Civil Engineers and Water Environment Federation, Design and
Construction of Urban Stormwater Management Systems, 1992.
Association of Metropolitan Sewerage Agencies, Approaches to Combined Sewer
Overflow Program Development: A CSO Assessment Report, Washington, DC,
November, 1994.
Association of Metropolitan Sewage Agencies and Limno-Tech, CSO Performance
Measures as a Method of Tracking the Success of Control Efforts - Summary Report,
December, 1996.
Astrack, R. F., N. A. Baumann and G. L. Reynolds, "Managing a Public Involvement
Program," Water Resources Planning and Management Division Journal, American
Society of Civil Engineers, Vol. 110, No. 2, 1984, pp. 153-166. (*)
Burian, S. J., S. J. Nix, S. R. Durrans, R. E. Pitt, C. Y. Fan and R. Field, "Historical
Development of Wet-Weather Flow Management;" Journal of Water Resources
Planning and Management, American Society of Civil Engineers, Vol. 125, No. 1,
January/February, 1999, pp. 3-13.
Carr, R. W. and S. G. Walesh, "Micromanagement of Stormwater for Wet Weather
Control," Poster paper presented at WEFTEC '98, Water Environment Federation,
Orlando, FL, October, 1998.
Carr, R. W., Earth Tech, personal communication regarding Skokie street storage
system components and construction costs, 1999.
CH2M Hill, Inc., SAM Wastewater Collection System Analysis Model, Users Manual.,
August, 1980.
Colston, N. V., Jr., Characterization and Treatment of Urban Land Runoff, EPA-670/2-
74-096, 1974.
-------
Conradin, F., "Study on Catch Basins in Switzerland," In Proceedings of Urban
Stormwater Quality Enhancement - Source Control, Retrofitting, and Combined Sewer
Technology, Engineering Foundation Conference, American Society of Civil Engineers,
Davos Platz, Switzerland, October 22-29, 1989, pp. 199-214.
Consoer, Townsend & Associates, Comprehensive Engineering Study of the Storm
Flooding Problems in Skokie, IL, August 1967.
Consoer, Townsend & Associates, Engineering Report on Sewer Facilities Needed for
Conveyance of Skokie Combined Sewer Overflows to Main Tunnels of the Chicago
Underflow Plan, Village of Skokie, IL, December, 1973.
Donohue & Associates, Flow Regulator Pilot Study: Runoff Control Program - Howard
Street Sewer District, Village of Skokie, IL, March, 1984a.
Donohue & Associates, Preliminary Engineering: Runoff Control Program - Emerson
and Lake Street Sewer Districts - Village of Skokie, IL, May, 1987a.
Donohue & Associates, Preliminary Engineering: Runoff Control Program - Howard
Street Sewer District - Village of Skokie, IL, July, 1982a.
Donohue & Associates, Preliminary Engineering: Runoff Control Program - Howard
Street Sewer District - Village of Skokie, IL, Summary Volume, July 1982b.
Donohue & Associates, Preliminary Engineering: Runoff Control Program - Main Street
Sewer District - Village of Skokie, IL, May, 1987b.
Donohue & Associates, Post-Construction Monitoring -1987, Runoff Control Program,
Howard Street Sewer District, Village of Skokie, IL, April, 1988.
Dwyer, T., "Overview of the CSO policy and Guidance Documents," Paper presented at
the Small Communities Combined Sewer Overflow Workshop, Indianapolis, IN,
February 24-25, 1998.
Elizer, Jr., R. M. "Speed Bumps: Speed Bumps are Effective Strategy When
Addressing Residential Safety and Quality of Life Issues," Excerpts from an earlier
article, APWA Report, September, 1996, pp. 10-15.
Eschenbach, R. C. and T. G. Eschenbach, "Understanding Why Stakeholders Matter,"
Journal of Management in Engineering, American Society of Civil Engineers, Vol. 12,
No. 6, 1996, pp. 59-64.
-------
Fishman, T. C., "At the Corner of Wall Street and Main: The Flood of Money," Worth,
November, 1998, pp. 176-186.
Gilbert, J. B., W. 0. Maddaus and J. A. Yost, "Public Decision Making in Water
Conservation," Proceedings of Water Forum '81, American Society of Civil Engineers,
New York, NY, 1981, pp. 757-764.
Grigg, N. S., Urban Water Infrastructure: Planning, Management and Operation. Wiley
& Sons, New York, NY, 1986.
Grottker, M., "Pollutant Removal by Catch Basins in West Germany: State of the Art -
New Design," In Proceedings of Urban Stormwater Quality Enhancement - Source
Control, Retrofitting, and Combined Sewer Technology, Engineering Foundation
Conference, American Society of Civil Engineers, Davos Platz, Switzerland, October
22-29, 1989, pp. 199-214.
Harza Engineering Company, "Study of Flood Control Alternatives," Prepared for the
Village of Skokie, IL, October, 1981.
Harza Engineering Company, Study of the Combined Sewer Conveyance Problems:
Supplemental Study to the Infiltration/Inflow Analysis Portion of MSDGC Facilities
Planning, May, 1978.
Haynes, V. D., "Speed Bumps Raise Praise and Ire Among Communities," Chicago
Tribune, October 25, 1998.
Helweg, 0. J., Water Resources Planning and Management, Wiley & Son, New York,
NY, 1985.
Herrin, J. C. and A. W. Whitlock, "Interfacing With the Public on Water-Related Issues:
What TVA is Doing," Proceedings of Saving a Threatened Resource, American Society
of Civil Engineers, New York, NY, 1992, pp. 293-298.
Hides, S. P., "The Inlet Control System: A Common Sense Approach for Reducing CSO
Impacts," In Proceedings - A Global Perspective for Reducing CSO's: Balancing
Technologies, Costs, and Water Quality, Louisville, KY, July 10-13, 1994.
Huber, N. C. and R. Dickinson, Stormwater Management Model Version 4 User's
Manual, 2nd Printing, October, 1992.
Huff, F. A. and J. R. Angel, Frequency Distribution and Hydroclimate Characteristics of
Heavy Rainstorms in Illinois, Bulletin 70, State of Illinois Department of Energy and
Natural Resources, Champaign, IL, 1989.
-------
Hydro Group, "Hydro-Brake: Liquid Flow Controls," Brochure, February, 1982.
Illinois State Water Survey, Hydrometeorology of Heavy Rainstorms in Chicago and
Northeastern Illinois, Phase I - Historical Studies., Report on Investigation 82, 1976.
Institute of Transportation Engineers, Guidelines for the Design and Application of
Speed Humps, Washington, DC, 1997.
John, S. F. and N. J. Wheatley, "Environmental Negotiation: Lessons From the
Combined Sewer Overflow Policy," Paper presented at the Small Communities
Combined Sewer Overflow Workshop, Indianapolis, IN, February 24-25, 1998.
Jones, D. E., Jr., "Urban Hydrology -A Redirection," Civil Engineering, American
Society of Civil Engineers, August, 1967, pp. 58-62.
Kaufman, H. L. and F. Lai, Conventional and Advanced Sewer Design Concepts for
Dual Purpose Flood and Pollution Control: A Preliminary Case Study, Elizabeth, NJ,
EPA - 600/2-78-090, May 1978.
Kraft, W. H., "Building Consensus: How Tos and How Not Tos," Journal of Management
in Engineering, American Society of Civil Engineers, Vol. 13, No. 3, 1997, pp. 20-22.
Kurz, J. W., "Transformation of Plans Into Actions," Urban Planning and Development
Division Journal, American Society of Civil Engineers, Vol. 99, No. 2, 1973, pp. 184-
191.
Loucks, E. D. and M. C. Morgan, "Evaluation of the Wilmette Runoff Control Program,"
Proceedings of Integrated Water Resources Planning for the 21st Century, American
Society of Civil Engineers, Cambridge, MA, May 7-11, 1995.
Matthews, T. M., P. D. Pitts, Jr., and R. C. Larlham; Hydro Brake Regulated Storage
System for Stormwater Management - Project Summary, EPA-600/s2-83-097, January
1984.
Matthews, T. M., P. D. Pitts, Jr., and R. C. Larlham, Hydro Brake Stormwater Detention
System Demonstration in Cleveland, OH, EPA-600/2-83-097, 1983.
Metropolitan Sanitary District of Greater Chicago, Emerson Street Sewer Study -
Including Addendum, October, 1981.
Morgan, M. C., Earth Tech, personal communications regarding Wilmette performance
criterial and construction costs, 1999.
Nakai, E. H. and R. W. Carr, "Urban Stormwater Runoff Control System, Village of
-------
Skokie, IL," In Proceedings of the 20th Anniversary Conference of the Water Resources
Planning and Management Division, American Society of Civil Engineers, Seattle, WA,
May, 1993.
Paintal, A., "Emerson Street Sewer Study," Metropolitan Sanitary District of Greater
Chicago, October, 1981.
Park, J. B., "IEPA Loan Project Number L170181," memorandum to Village of Skokie
from Illinois Environmental Protection Agency, September/, 1990.
Perry, S. D., "Rx for Risk Communication," Civil Engineering, American Society of Civil
Engineers, August, 1996, pp. 61-63.
Pisano, W. C., "Inlet Control Concepts on Catchbasins: U.S. Experience," In
Proceedings of Urban Stormwater Quality Enhancement - Source Control, Retrofitting,
and Combined Sewer Technology, Engineering Foundation Conference, American
Society of Civil Engineers, Davos Platz, Switzerland, October 22-29, 1989.
Poertner, H. G., Practices in Detention of Urban Storm Water Runoff, Special Report
No. 43, American Public Works Association, Chicago, IL, 1974.
Priscoli, J. D., "Public Involvement, Conflict Management: Means to EQ and Social
Objectives," Water Resources Planning and Management Division Journal, American
Society of Civil Engineers, Vol. 115, No. 1, 1989, pp. 31-42.
Raasch, G. E., Project Manager, Donohue & Associates, "Letter to A. J. Rigoni, Village
Manager, Skokie, IL," October 30, 1989a.
Raasch, G. E., "Urban Storm Runoff Control System Case Study - Skokie, IL,"
Presented as part of the course Optimizing Your Storm Drainage System, Department
of Engineering Professional Development, University of Wisconsin, Denver, CO, April
24-26, 1989b.
Rigoni, A. J., Village Manager, Skokie, IL, "Letter to G. E. Raasch, Project Manager,
Donohue & Associates," September/, 1989.
Roecker, D. F., "1997 Capital Wastewater Funding Opportunities: A Survey of Available
State, Federal and Congressional Funding," Presented WEFTEC '97, the Water
Environment Federation's 70th Annual Conference & Exposition, Chicago, IL, 1997.
-------
Roecker, D. F., "1998 Capital Funding Sources," Utility Executive, Water Environment
Federation, Vol. 1, No. 1, May/June, 1998a.
Roecker, D. F., "Case Studies in Capital Wastewater Funding Using Innovative Funding
Techniques," Presented at WEFTEC '98, the Water Environment Federation's 71th
Annual Conference, Orlando, FL, October, 1998b.
Roecker, D. F., "Securing Capital Funds for Water Resources Projects," Presented at
the American Water Resources Association's 29th Annual Conference and Symposium,
Tucson, AZ, 1993.
Rubin, R. A. and B. Carbajal-Quintas, "Environmental Regulation and Public
Participation in Project Planning," Journal of Professional Issues in Engineering
Education and Practices, American Society of Civil Engineers, Vol. 121, No. 3, 1995,
pp. 183-186.
Rust Environment and Infrastructure, Amendment to 1991 Wastewater Facilities Plan
Appendix C, Design Memorandum, Preliminary Engineering for Stormwater Runoff
Control, Combined Sewer Area East of Ridge Road - Village of Wilmette, IL, November
1993.
Rust Environment & Infrastructure, Stormwater Runoff Control Facilities Operation and
Maintenance Manual, Village of Skokie, IL, September, 1995.
Sargent, H. L, Jr., "Fishbowl Planning Immerses Pacific Northwest Citizens in Corps
Projects," Civil Engineering, American Society of Civil Engineers, Vol. 42, No. 9, 1972,
pp. 54-57.
SEC Donohue, Amendment to the 1991 Wastewater Facility Plan, Village of Wilmette,
IL, December, 1992.
SEC Donohue, Stormwater Management Study and Feasibility Report for the Jeffery
Manor Area, Prepared for the Department of Sewers, City of Chicago, March, 1993.
SEC Donohue, Stormwater Runoff Control Feasibility Analysis, Combined Sewer Area
East of Ridge Road, Village of Wilmette, IL, June, 1992.
Silberman, E., "Public Participation in Water Resource Development," Water Resources
Planning and Management Division Journal, American Society of Civil Engineers, Vol.
103, No. 1, 1977, pp. 111-123.
Skokie, Village of, Department of Public Works, Safety Manual, August, 1992.
Spring, B. H., Hanging Trap and Scepter Orifice Tests, Department of Civil Engineering,
-------
Valparaiso University, December, 1983.
Stadler, Gerald, U. S. Army Corps of Engineers, Chicago District, Personal
Communication, March 17, 1982.
Tarn, W. and B. Murillo, "LA Story: Providing Public Services Online With CIS," Geo
Info Systems, Vol. 7, No. 7, 1997, pp. 26-27.
USEPA, Combined Sewer Overflow (CSO) Control Policy, EPA 830-B-94-001, April
1994.
USEPA, "Glossary of Wet Weather Flow Terms,"
Augusts, 1998.
USEPA, Manual: Combined Sewer Overflow Control, EPA/625/R-93/007, September
1993.
USEPA, "Top 10 Watershed Lessons Learned," EPA 840-F-97-001, October 1997, p.
50.
USEPA, Watershed Protection: Catalog of Federal Programs, EPA-841-B-93-002.
1993.
United States General Services Administration & Executive Office of the President,
7998 Catalog of Federal Domestic Assistance, Updated through December, 1998.
Velazquez, F., "Even a Lowly Hump Takes Good Engineering," Engineering Times, May
1992, p. 8.
Viessman, W. J., Jr., "Technology, Society and Water Management," Water Resources
Planning and Management Division Journal, American Society of Civil Engineers, Vol.
115, No. 1, 1989, pp. 48-51.
Wakeman, T. H., "Engineering Leadership in Public Policy Resolution," Journal of
Management in Engineering, American Society of Civil Engineers, Vol. 13, No. 1, 1997,
pp. 57-60.
Walesh, S. G., "DAD Is Out, POP Is In, Journal of the American Water Resources
Association, Vol. 35, Nol. 3, June 1999.
-------
Walesh, S. G., "Interaction With the Public and Government Officials in Urban Water
Planning," Proceedings of Hydro-polls - The Role of Water in Urban Planning, UNESCO-
IMP Workshop, Wageningen, The Netherlands and Emscher Region, Germany, March-
April, 1993, pp. 164-176.
Walesh, S. G., "Retrofitting Storm Water Detention Facilities for Quantity and Quality
Control," In Proceedings of the International Conference on Urban Drainage
Technologies, Dubrovnik, Yugoslavia, June, 1991.
Walesh, S. G., "Retrofitting Storm Water Facilities for Quantity and Quality Control,"
Presented at ASCE's Water Forum '92, American Society of Civil Engineers, Baltimore,
MD, August 1992.
Walesh, S. G., "Retrofitting a Detention Facility for Improved Quantity Control," Paper
presented at the International Symposium on Engineering Hydrology, American Society
of Civil Engineers, San Francisco, CA, July 1993.
Walesh, S. G., "Retrofitting Storm Water Facilities for Quantity and Quality Control,"
Seminar presented to the Indiana Society of Professional Land Surveyors, Valparaiso,
IN, July, 1998.
Walesh, S. G., "Source Control to Reduce Combined Sewer Surcharging," Paper
presented at the Annual Conference of the Michigan Water Environment Federation,
Mackinac Island, Ml, June, 1996.
Walesh, S. G. and M. L. Schoeffmann, "Surface and Sub-Surface Detention In
Developed Urban Areas: A Case Study," Paper presented at the conference Urban
Water- '84, American Society of Civil Engineers, Baltimore, MD, May 28-31, 1984.
Walesh, S. G., Urban Surface Water Management, John Wiley & Sons, New York, NY,
1989.
Water Environment Research Foundation, Wet Weather: Information for Wet Weather
Decision Makers, Vol. 3, Issue 2, 1998.
wp/epastref
-------
Bibliography
Aeppel, T., "Giant Sewage Storage Tank Shakes City," Wall Street Journal, January 22,
1996.
Association of Metropolitan Sewage Agencies and Limno-Tech, CSO Performance
Measures as a Method of Tracking the Success of Control Efforts - Workshop
Workbook, October and November, 1996.
Bingham, D., E. Driscoll, J. Golden, and D. Walker, Manual: Combined Sewer
Overflow, EPA/625/R-93/007, September 1993.
Carr, R. W. and E. H. Nakai, "Optimum Use of Existing Combined Sewer Systems,
Urban Stormwater Runoff Control Project," Village of Skokie, IL, Paper presented at
WEFTEC 94, 67th Annual Conference of the Water Environment Federation, Chicago,
IL, October 15-19, 1994.
Carr, R. W., and E. H. Nakai, "Runoff Control," Water Environment and Technology
Magazine, Vol. 7, No. 4, April 1995.
Des Plaines, IL, City of, "Flood Information Handbook: A Guide to Local, Interim
Solutions to a Regional Problem," February, 1973.
Donohue & Associates, Construction Cost Refinement, Runoff Control Program, Main
Street Sewer District, Main Street Sewer District, Village of Skokie, IL, January, 1989.
Donohue & Associates, Preliminary Engineering Addendum: Runoff Control Program -
Howard Street Sewer District - Village of Skokie, March, 1984.
Donohue & Associates, Monitoring -1983 Runoff Control Program - Howard Street
Sewer District - Village of Skokie, IL, March, 1984b.
Donohue & Associates, Monitoring -1984 Runoff Control Program - Howard Street
Sewer District, Village of Skokie, IL, April, 1985.
Donohue & Associates, Monitoring -1985 Runoff Control Program - Main Street Sewer
District, Village of Skokie, IL, February, 1986.
Donohue & Associates, Monitoring -1986 Runoff Control Program - Emerson & Lake
Street Sewer Districts, Village of Skokie, IL, December, 1986.
Evanston, City of, "Evanston's Flood and Pollution Problem," a brochure, no date but
-------
probably late 1970's.
Milligan, J. E., "Effective Subsurface Retention/Detention Systems," In North American
Water and Environment Congress, American Society of Civil Engineers, 1996.
Raasch, G. E., "Stormwater Detention - Controlling Peak Runoff," Paper presented at
the conference Designing the Future, Illinois Concrete Pipe Association, Carol Stream,
IL, April 13, 1988.
Rust Environment and Infrastructure, "Amendment to 1991 Wastewater Facilities Plan,"
Village of Wilmette, IL, November, 1995.
Rust Environment & Infrastructure, Combined Sewer Interceptor Outfall Flow Monitoring
Study, Village of Skokie, IL, May, 1993.
Rust Environment & Infrastructure, Project Manual for Combined Sewer Interceptor
Flow Meter Installation for the Village of Skokie, Cook County, IL, August, 1993.
Schoeffmann, M. L. and S. G. Walesh, "One Alternative to Flooded Basements," APWA
Reporter, American Public Works Association, Vol. 52, No. 3, March, 1985, pp. 6-7.
Stall, J. B. and M. L. Terstriep, Storm Sewer Design -An Evaluation of the BRRL
Method, Prepared for the Office of Research and Monitoring of the USEPA, October,
1972.
Stauss Engineering, 95% Plan Completion Valve Engineering Study Report -
Stormwater Detention Facilities - 1992 Construction Program, Village of Skokie, IL,
December, 1991.
Walesh, S. G. and R. W. Carr, "Controlling Storm Water Close to the Source: An
Implementation Case Study," Paper presented at APWA Congress, American Public
Works Association, Las Vegas, NV, September, 1998.
wp/epastbib
------- |