Coastal Stormwater Management
Through Green Infrastructure
A Handbook for Municipalities
&EPA
United States EPA 842-R-14-004
Environmental Protection
Agency December 2014
NATIONAL!
Office of Wetlands, Oceans and Watersheds
National Estuary Program
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Acknowledgements
EPA would like to thank the Massachusetts Bays National Estuary Program Director, Staff, and Regional
Coordinators for reviewing the document and providing useful and valuable input. This handbook was
developed under EPA Contract No. EP-C-11-009.
Cover Photo
Credit: Maureen Thomas, Town of Kingston, MA
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Table of Contents
1. Executive Summary 1
1.1. What is Green Infrastructure? 1
1.2. Benefits of Green Infrastructure 3
1.3. Regulatory Background 5
1.4. Green Infrastructure Maintenance 5
1.5. Incorporating Green Infrastructure into Existing Municipal Programs and Facilities 6
1.6. Massachusetts Bays National Estuary Program Technical Assistance 7
1.7. Case Study: Jones River Estuary and Kingston Bay Stormwater Assessment Project 9
1.8. Handbook Components 12
1.9. References 13
2. Watershed Assessment 15
2.1. Part 1: Identify and Engage Stakeholders 17
2.2. Part 2: Identify Study Watershed 18
2.3. Part 3: Identify Existing Hydrologic and Hydraulic Data 19
2.3.1. Types of Data 19
2.3.2. GIS Data for Massachusetts 20
2.3.3. Hydrologic and Hydraulic Data Summary 20
2.3.4. Additional Data Resources 21
2.3.5. Summary of Additional Data Resources 22
2.4. Part 4: Characterize Known Pollutant Loadings 22
2.5. Part 5: Identify Existing BMP and Green Infrastructure Practices 23
2.6. Part 6: Identify Additional Data Needs 24
2.6.1. Water Quality Sampling 24
2.6.2. Field Reconnaissance 24
2.6.3. Wetlands 25
2.7. Part 7: Identify Sources of Funding 25
2.8. References 28
3. Identifying Green Infrastructure Opportunities 29
3.1. Identification of Target Subwatersheds 30
3.2. Primary Screening of Potential BMP Locations 31
3.3. Secondary Screening and Prioritization 32
3.3.1. Prioritization Criteria 32
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3.3.2. Prioritization Methodology (Site Scoring) 35
4. Site Assessment, Planning, and Design 38
4.1. Site Planning and Design Principles 38
4.2. Preparing Conceptual Design Plans 43
4.2.1. Preliminary Geotechnical Investigation 43
4.2.2. Modeling and Optimization of BMP Placement for Green Infrastructure Sites 43
4.2.3. EPA Stormwater Calculator 44
4.2.4. Stormwater Management Optimization Tool 44
4.2.5. Conceptual Design Report 46
4.2.6. Conceptual Plan 47
4.3. References 48
5. Green Infrastructure Practices 49
5.1. Selecting Green Infrastructure BMPs (BMP Selection Matrix) 50
5.2. BMP Sizing 52
5.3. Common Green Infrastructure Practices 52
5.3.1. Vegetated Filter Strips 52
5.3.2. Bioretention 54
5.3.3. Constructed Stormwater Wetlands 56
5.3.4. Tree Box Filters 57
5.3.5. Sand Filters 60
5.3.6. Grassed Swales 62
5.3.7. Water Quality Swales 62
5.3.8. Cisterns and Rain Barrels 64
5.3.9. Green Roofs 65
5.3.10. Permeable Pavement 65
5.4. Cold Climate Considerations 68
5.5. BMP Construction and Post-Construction Issues 68
5.5.1. BMP Construction 68
5.5.2. Temporary Erosion and Sediment Control Practices 69
5.5.3. BMP Construction Inspection 71
5.5.4. BMP Inspection and Maintenance 72
5.6. References 74
6. Green Infrastructure Review Process 82
6.1. Local Review Process 82
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6.2. Massachusetts Plan Review and Permitting Process 83
6.3. Incentives 87
6.4. References 88
List of Tables
Table 1-1. Studies estimating percent increase in property value from green infrastructure 4
Table 2-1. Recommended sources of hydrologic and hydraulic data for watershed assessment 21
Table 2-2. Recommended additional data for use in watershed assessment 22
Table 3-1. Primary screening criteria for parcel-based and ROW green infrastructure opportunities 32
Table 3-2. Key secondary screening prioritization criteria for parcel-based and ROW green
infrastructure 33
Table 3-3. Prioritization criteria for small-scale green infrastructure opportunities 36
Table 3-4. Prioritization criteria for large-scale green infrastructure opportunities 36
Table 3-5. Prioritization criteria for ROW green infrastructure opportunities 37
Table 5-1. BMP selection matrix (Addapted from MassDEP 1997) 51
Table 5-2. Pollutant removal characteristics of vegetated filter strips 53
Table 5-3. Pollutant removal characteristics of bioretention 55
Table 5-4. Pollutant removal characteristics of flow-through planters 58
Table 5-5. Pollutant removal characteristics of sand filters 61
Table 5-6. Pollutant removal characteristics of water quality swales 63
Table 5-7. Pollutant removal characteristics of permeable pavement 67
Table 6-1. Planning Review Board supplemental checklist for green infrastructure plan review 84
List of Figures
Figure 1-1. Massachusetts Bays Program Regions 8
Figure 1-2. Rain garden off of Delano Ave. in Kingston, MA 11
Figure 1-3. Rain garden off of Delano Ave. in Kingston, MA during a storm event 11
Figure 2-1. Components of the watershed assessment process 16
Figure 4-1. Bioretention cell (Cape Cod) 39
Figure 4-2. Example of a bioretention curb pop-out (Portland, Oregon) 40
Figure 4-3. Steps to develop a green infrastructure-based site plan 42
Figure 4-4. Example watershed simulation setup in Opti-Tool with two subbasin and two BMPs 45
Figure 4-5. Example Opti-Tool output window for checking of optimization results 46
Figure 5-1. Vegetated filter strip at the edge of a parking lot 52
Figure 5-2. Bioretention area, or rain garden, on a residential property 54
Figure 5-3. Constructed stormwater wetland with wetland vegetation 56
Figure 5-4. Newly constructed tree box filter 58
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Figure 5-5. Below ground Delaware style sand filter installed in a parking lot 60
Figure 5-6. Grassed swale adjacent to a highway 62
Figure 5-7. Water quality swale adjacent to a highway 62
Figure 5-8. A 55-gallon rain barrel collecting rainwater from a residential rooftop 64
Figure 5-9. Vegetated green roof 65
Figure 5-10. Porous asphalt parking lot and permeable interlocking concrete pavers in the right-of-
way 66
Figure 5-11. Example of a bioretention area installed before permanent site stabilization with the
inset photo showing the clay layer clogging the mulch surface 70
Figure 5-12. Accumulated fines layer as a result of improper construction sequencing 70
Figure 5-13. Accurate grading and outlet elevations must be provided to achieve intended
hydrologic and water quality functions 71
Figure 5-14. Heavy equipment (especially wheeled equipment) should be operated outside the
excavated area to prevent compaction 72
Figure 5-15. For infiltrating practices, mitigate subsoil compaction by ripping grade to a depth of
12 inches 72
Figure 6-1. Sample planning review process, with (right) and without (left) green infrastructure
incentive 83
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1. Executive Summary
Coastal Stormwater Management through Green Infrastructure: A Handbook for Municipalities
(Handbook) is designed to assist coastal municipalities within the Massachusetts Bays Program
(MassBays) area to incorporate green infrastructure into their stormwater management planning as
they respond to MS4 stormwater permit requirements, review development proposals, and retrofit
existing municipal facilities and sites. The MassBays Program can assist those municipalities in using this
Handbook to facilitate the use of green infrastructure and address stormwater runoff.
The Handbook can also be applied more broadly by municipal infrastructure and resource managers
located in other States to provide them with a proven approach to planning for green infrastructure
implementation including a process for: 1) watershed assessment, 2) site identification and
prioritization, 3) site planning, 4) selecting appropriate green infrastructure practices, 5) developing
conceptual plans, and 6) effective plan review. Users can follow this handbook sequentially or use
portions of the handbook as needed for new or existing development situations.
Green Infrastructure Handbook Overview
Assess Watershed (Chapter 2)
Identify opportunities where green infrastructure can be used to provide water quantity and quality benefits to
restore, protect, and enhance the natural hydrology and ecosystem functions in the watershed.
Identify Green Infrastructure Opportunities (Chapter 3)
Determine the highest priority sites in a given municipality to provide the greatest water quality benefits.
Site Assessment, Planning, and Design (Chapter 4)
Use green infrastructure planning practices, including land use planning, site assessment, retrofit
considerations, and site design.
Identify Green Infrastructure Practices (Chapter 5)
Select the appropriate green infrastructure practice(s) using a BMP Matrix.
Green Infrastructure Review Process (Chapter 6)
Design review to verify proper design concepts to ensure successful construction and long-term operation.
1.1. What is Green Infrastructure?
Green infrastructure is a design strategy for handling runoff that reduces the volume and distributes
flows by using vegetation, soils, and natural processes to manage water and create healthier urban and
suburban environments. This is often best accomplished by creating a series of smaller retention or
detention areas that allow localized filtration utilizing a series of distributed treatment practices rather
than carrying runoff to a remote collection area for treatment in regional or centralized facilities (Lloyd
et al. 2002). At the scale of a city or county, green infrastructure refers to the patchwork of natural areas
that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a neighborhood or
site, green infrastructure refers to stormwater management systems that mimic nature by soaking up
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and storing water in a series of distributed practices, such as rain gardens, permeable pavements, and
green roofs. These neighborhood or site-scale green infrastructure approaches are often referred to as
low impact development (LID).
Green infrastructure strategies fall under two broad categories: planning practices and best
management practices (BMPs). Common site planning practices include site design planning based on
natural land contours and decreasing the impervious surface. Green infrastructure planning practices
include the following:
P Reducing impervious surfaces
P Disconnecting impervious areas
P Conserving natural resources
P Using cluster/consolidated development
P Using xeriscaping and water conservation practices
Green infrastructure practices use natural, vegetative processes to retain and infiltrate stormwater to
the extent feasible. Common BMPs used in green infrastructure include:
P Vegetated filter strips
P Bioretention
P Constructed stormwater wetlands
P Tree box filters
0 Green roofs
P Permeable pavement
Green infrastructure typically incorporates multiple practices using the natural features of the site in
conjunction with the goal of the site development. Multiple practices can be incorporated into the site
development to complement and enhance the proposed layout, while also providing water quality
treatment and volume reduction. These practices are discussed in detail in Section 5 of this handbook.
Green infrastructure offers a great degree of design flexibility, which makes it suitable for a wide variety
of sites and applications. Green infrastructure practices can often be integrated into a site utilizing
existing configurations including incorporating bioretention into landscaped areas, permeable pavement
in parking stalls or bike lanes, and green roofs on the rooftops of buildings. Specific to coastal
Massachusetts, limited space and high groundwater tables may prohibit the use of conventional
centralized stormwater management practices that require large surface areas and deep storage
capacity. Many green infrastructure practices can be designed to maximize water quality and quantity
benefits within a small footprint by distributing stormwater management practices and special design
considerations can be implemented to reduce ponding depths to compensate for limited distance to
groundwater or to prevent direct discharge into the groundwater (e.g., installation of an underdrain
system, Chapter 5 of this manual).
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Larger scale green infrastructure approaches may also incorporate natural features on the landscape,
such as wetlands, former wetland sites, or floodplains. In these cases, the design may involve land
management decisions including acquisition, easement designations, wetland restoration and
protection, and property buyout programs in flood prone areas. These measures can enhance the role
natural features play in storing rainfall, reducing peak runoff during storms, reducing the effects of
erosion, stabilizing soils, improving water quality, and sustaining surrounding aquatic environments.
The Greenseams program in Milwaukee, Wl illustrates a large scale green infrastructure alternative.
1.2. Benefits of Green Infrastructure
Green infrastructure restores the natural hydrologic processes of infiltration, percolation, and
evapotranspiration to reduce the adverse effects of urban stormwater runoff on receiving water bodies.
Green infrastructure practices have been shown to cost-effectively reduce the effects of stormwater
runoff by reducing pollutants such as sediment, bacteria, metals, nitrogen, and phosphorus; reduce
maintenance requirements; and provide multiple environmental, social, and economic benefits (Kloss
and Calarusse 2006). Some of the additional environmental, social, and economic benefits of green
infrastructure are listed below.
Water Quality Benefits. Green infrastructure principles and practices are designed to encourage
percolation and ground water recharge and can provide volume reduction. Green infrastructure
practices mainly use the interaction of the chemical, physical, and biological processes between soils
and water to filter out sediments and sorb constituents from stormwater. As stormwater percolates into
the ground, the soil captures the dissolved and suspended material in stormwater. When infiltration is
not feasible, water quality improvements can still be achieved through filtration utilizing sedimentation,
straining, and sorption processes as stormwater passes through small pore spaces (FHWA 2002).
When properly designed and maintained, green infrastructure has proven effective at reducing nutrients
and bacteria in stormwater runoff, two classes of pollutants of particular concern to coastal waters. Due
to water quality impairments linked to stormwater runoff pollution, many of Massachusetts' coastal
resources, including shellfish beds and bathing beaches, suffer closures. The implementation of green
infrastructure to manage and treat stormwater runoff has the potential to reduce closures and improve
the health of coastal resources. A summary of pollutant reduction efficiencies for a variety of green
infrastructure practices is included in Section 5.3.
Increased enjoyment of surroundings. Implementing green infrastructure practices to enhance
vegetation, preserve parking within the right-of-way (ROW), and add open or park space will help create
a more pedestrian-friendly environment that encourages walking and physical activity. A large study of
inner-city Chicago found that residents would use their courtyard more if trees were planted (Kuo 2003)
and residents living in greener, high-rise apartment buildings reported significantly more use of the area
just outside their building (Hastie 2003; Kuo 2003). Research has found that people in greener
neighborhoods judge distances to be shorter and make more walking trips (Wolf 2008).
Increased safety and reduced crime. Researchers examined the relationship between vegetation and
crime for 98 apartment buildings in an inner-city neighborhood and found the greener a building's
surroundings, the fewer total crimes (including violent and property crimes) and that levels of nearby
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vegetation explained 7 to 8 percent of the variance in crimes reported by building (Kuo and Sullivan
2001b). In investigating the link between green space and its effect on aggression and violence study
found that levels of aggression and violence were significantly lower among women who had some
natural areas outside their apartments (Kuo and Sullivan 2001a). Generally, when properly designed,
narrower, green streets increase safety by decreasing vehicle speeds and make neighborhoods safer for
pedestrians (Wolf 1998; Kuo and Sullivan 2001b).
Increased sense of well-being. There is a large body of literature indicating that green space makes
places more inviting and attractive and enhances people's sense of well-being. People living and working
with a view of natural landscapes appreciate the various textures, colors, and shapes of native plants,
and the progression of hues throughout the seasons (Northeastern Illinois Planning Commission 2004).
Desk workers who can see nature from their desks experience 23 percent less time off sick than those
who cannot see nature and report a greater job satisfaction (Wolf 1998). Habitat created by green
infrastructure attracts birds, butterflies, and other wildlife that add to the aesthetic beauty and appeal
of green spaces and natural landscaping. "Attention restorative theory" suggests that exposure to
nature reduces mental fatigue, with the rejuvenating effects coming from a variety of natural settings,
including community parks and views of nature through windows.
Reduced stormwater from preservation of open space. Adoption of green infrastructure into a site
facilitates preservation of open space. This reduces the amount of impervious cover and stormwater
runoff by retaining natural conditions that allow stormwater to infiltrate into the ground. In addition to
the reduction of stormwater runoff, open space can also treat stormwater runoff with little
maintenance needed (Massachusetts Land Trust Coalition).
Increased property values. Many aspects of green infrastructure can increase property values by
improving habitat, aesthetics, drainage, and recreation opportunities that can help restore, revitalize,
and encourage growth in economically distressed areas. Table 1-1 summarizes the recent studies that
have estimated the effect that green infrastructure or related practices have on property values.
Table 1-1. Studies estimating percent increase in property value from green infrastructure
Source
Percent Increase
in Property
Value
Notes
Ward et al. (2008)
3.5%-5%
Estimated effect of green infrastructure on adjacent properties
relative to those farther away in King County (Seattle),
Washington.
Shultz and Schmitz
(2008)
0.7%-2.7%
Referred to effect of clustered open spaces, greenways, and
similar practices in Omaha, Nebraska.
Wachter and
Bucchianer (2008)
2%
Estimated the effect of tree plantings on property values for select
neighborhoods in Philadelphia.
Anderson and Cordell
(1988)
3.5%—4.5%
Estimated value of trees on residential property (differences
between houses with five or more front yard trees and those that
have fewer), Athens-Clarke County, Georgia.
Voicu and Been (2009)
9.4%
Refers to property within 1,000 feet of a park or garden and within
5 years of park opening; effect increases overtime.
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Source
Percent Increase
in Property
Value
Notes
Espey and Owasu-
Edusei (2001)
11%
Refers to small, attractive parks with playgrounds within 600 feet
of houses.
Pincetl et al. (2003)
1.5%
Refers to the effect of an 11% increase in the amount of greenery
(equivalent to a one-third acre garden or park) within a radius of
200 to 500 feet from the house.
Hobden et al. (2004)
6.9%
Refers to greenway adjacent to property.
New Yorkers for Parks
and Ernst & Young
(2003)
8%-30%
Refers to homes within a general proximity to parks.
1.3. Regulatory Background
Several regulatory programs impact stormwater management and green infrastructure decisions in the
State of Massachusetts, including:
0 Massachusetts Stormwater Policy and Stormwater Management Standards - Developed by the
Massachusetts Department of Environmental Protection (MassDEP), these standards apply
when a wetlands or 401 permit is required. The ten stormwater management standards address
issues such as groundwater recharge, post-development peak discharge rates, and
redevelopment.
0 Small Municipal Separate Storm Sewer System Permit (MS4) - currently in draft and revision by
EPA Region 1, the "small communities" MS4 permit requires nearly all of MassBays communities
to develop a stormwater program that addresses six minimum control measures, including
removing barriers to application of green infrastructure principles.
P Construction General Permit (CGP) - issued by EPA, this permit applies to all projects (including
municipal construction projects) disturbing greater than one acre of land. Projects are required
to develop a stormwater pollution prevention plan (SWPPP) and implement practices that
control stormwater runoff from active construction.
P Multi-Sector General Permit (MSGP) - issued by EPA, this permit applies to certain categories of
industrial facilities and requires the development of a SWPPP and implementation of BMPs to
control stormwater runoff from industrial areas.
Additional information about these regulatory programs can be found on the MassDEP stormwater
website (http://www.mass.gov/eea/agencies/massdep/water/wastewater/stormwater.html).
1.4. Green Infrastructure Maintenance
The major goal of green infrastructure operation and maintenance is to ensure that BMPs are meeting
the specified design criteria for stormwater flow rate, volume, and water quality control functions. If
structural green infrastructure systems are not properly maintained, effectiveness can be reduced,
resulting in water quality impacts. Routine maintenance and any need-based repairs for a structural
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BMP must be completed according to schedule or as soon as practical after a problem is discovered.
Deferred BMP maintenance could result in detrimental effects on the landscape and increased potential
for water pollution and local flooding. Table 5-1 presents relative maintenance costs for different
categories and sizes of BMPs.
Training should be included in program development to ensure that maintenance staff has the proper
knowledge and skills. Most structural BMP maintenance work—such as mowing, removing trash and
debris, and removing sediment—is nontechnical and is already performed by property maintenance
personnel. More specialized maintenance training might be needed for more sophisticated systems.
Appendix C presents detailed information on proper BMP operation and maintenance.
With proper green infrastructure BMP maintenance, many benefits can be realized. The following
section highlights some of the major benefits of green infrastructure.
1.5. Incorporating Green Infrastructure into Existing Municipal Programs
and Facilities
Many communities in the Massachusetts Bays region are required to develop stormwater
management plans to comply with stormwater Phase II permit requirements, which include the
development of a program to address stormwater management in new development and
redevelopment (post-construction stormwater management). Municipalities can incorporate green
infrastructure concepts into their post-construction program by:
P Review your existing codes and ordinances. Some municipal codes can include barriers to green
infrastructure implementation. Review your codes by using EPA's Water Quality Scorecard
(http://www.epa.gov/dced/water scorecard.htm) or a similar checklist to identify barriers and
potential changes to your code.
P Establish a clear post-construction retention standard. Implement the Massachusetts
stormwater standards and encourage on-site retention to the extent practicable.
P Encourage green infrastructure practices. Chapter 5 of this Handbook describes common green
infrastructure practices that should be encouraged by municipal programs.
P Incorporate green infrastructure into municipal capital improvement projects. Lead by
example by including green infrastructure practices in new municipal projects, such as
incorporating bioretention into road or sidewalk projects.
P Develop a green infrastructure review process. Chapter 6 of this Handbook describes a green
infrastructure review process, including incentives.
P Review existing municipal facilities to determine if green infrastructure controls can be added.
Existing municipal facilities may have opportunities to include green infrastructure practices
with fairly minor changes. For example, a bioretention area could be added where an existing
grass swale exists.
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P Plan for maintenance of green infrastructure practices. Address maintenance by identifying
who will be maintaining the green infrastructure practices and requiring an operation and
maintenance plan.
For specific development projects, MassDEP's plan review and permitting process requires a Stormwater
Report to be submitted to document compliance with the state's Stormwater Management Standards
(as detailed in Chapter 3, Volume 1 of the Massachusetts Stormwater Handbook [2008]). Additional
information on the plan review process is in Section 6.1 of this handbook.
Also, EPA compiled a set of resources for planning for green infrastructure, including:
P Design and implementation resources to help practitioners better design, install, and maintain
practices: http://water.epa.gov/infrastructure/greeninfrastructure/gi design.cfm
P Modeling tools to assess green infrastructure performance, costs, and benefits:
http://water.epa.gov/infrastructure/greeninfrastructure/gi modelingtools.cfm
P EPA offers a Green Infrastructure Webcast Series and other training resources on their "Where
Can I Get More Training?" website:
http://water.epa.gov/infrastructure/greeninfrastructure/gi training.cfm
1.6. Massachusetts Bays National Estuary Program Technical Assistance
The Massachusetts Bays (MassBays) Program was formed in 1988, and became a National Estuary
Program (NEP) in 1990. Its mission is to facilitate partnerships that prompt local, state, and federal
action and stewardship, by convening stakeholders on the local and regional level, providing scientific
basis for management decisions, and informing decision makers about problems and solutions.
MassBays is one of 28 NEPs established and funded by EPA under §320 of the Clean Water Act (CWA).
Each NEP is led by a Management Committee made up of diverse stakeholders including citizens, local,
state, and federal agencies, as well as with non-profit and private sector entities. Using a consensus-
building approach and collaborative decision-making process, the Committee devises a long-term plan -
a Comprehensive Conservation and Management Plan (CCMP) - that contains specific targeted actions
tailored to the local priorities, designed to address water quality, habitat, and living resource challenges
as identified in CWA §320. Stormwater runoff is one of the largest sources of pollution faced by
MassBays and other NEPs.
Each NEP works within a geographic boundary or study area. The MassBays study area encompasses
approximately 1,100 linear miles of coastline, from the tip of Provincetown to the New Hampshire
border, and serves 50 coastal communities (Massachusetts EEA 2014). This includes Massachusetts Bay
and Cape Code estuaries. The area contains many important coastal resources such as shellfish beds,
salt marshes, seagrass beds, diadromous fish runs, and shorebird habitat and nesting sites. These
habitats support sensitive species and provide recreational and environmental benefits such as filtering
pollutants, serving as spawning and nursery areas, and buffering against storm damage. Polluted runoff
from Stormwater - excess nutrients, sediment, and chemicals - compromises these natural habitats.
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The MassBays Program is organized into 5 coastal subregions to facilitate implementation of its goals
and objectives. The 5 coastal subregions are (from north to south as shown in Figure 1-1): Upper North
Shore, Lower North Shore, Metro Boston, South Shore, and Cape Cod. A coordinator contracted in each
region provides technical and other assistance to local partners (Regional Coordinators). MassBays
Central staff - an Executive Director, Staff Scientist, and Communications Coordinator - are hosted by
the Massachusetts Office of Coastal Zone Management.
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MassBays can provide a range of support to municipal officials in its program areas to improve water
quality and address stormwater such as helping municipalities use this Handbook to facilitate the use of
green infrastructure. Through MassBays Regional Coordinators, you can receive technical support,
access embayment-specific water quality assessments and planning documents, and find connections to
state and federal funding agencies.
MassBays has a successful "Greenscapes" outreach and education program (greenscapes.org) for
homeowners and landscaping companies, and provides direct technical assistance to municipalities to
implement estuary-friendly stormwater treatment and control. Visit www.massbavs.org and use the
"Contact Us" link to find information for your local MassBays Program Regional Coordinator for
assistance.
1.7. Case Study: Jones River Estuary and Kingston Bay Stormwater
Assessment Project
Historically, Kingston Bay harbored a thriving shellfishing industry. But over time, deteriorating water
quality resulted in restrictions on shellfish harvesting. To restore what once was, the town of Kingston
applied for and received funding from MassBays in 2011 to evaluate the feasibility of installing green
infrastructure at stormwater outfalls that discharge into the Jones River and Kingston Bay. Kingston's
Conservation Agent worked with her counterpart in the town of Duxbury to lay out the process detailed
in this handbook.
Kingston contracted with local consulting firm ATP Environmental and identified nineteen outfalls into the
Jones River and related tributaries controlled by the Town. The outfalls were mapped and an estimate was
made of the "first flush" volume related to each. Distance from the mouth of the river, in river miles, and
distance from the Jones River itself were both determined as a way of assessing potential for adverse
impacts to the river and Kingston Bay. Two other outfalls controlled by Mass Highways on Route 3 and
discharging to the Jones River were also identified by the Town as outfalls of interest.
ATP recommended that 10 outfalls be sampled based upon the "first flush" volume generated from one
inch of runoff and the proximity of the discharge to Kingston Bay. One inch of runoff was used because
shellfish areas in Kingston Bay represent the natural resource of concern. Outfalls with elevated first flush
volumes discharging at or near the mouth of the River, or that were high in volume within 2 miles from the
mouth of the River, were selected to be sampled under two storm events. The Town added three other
local outfalls based upon their observations in the past, and two outfalls managed by Mass DOT.
Two rounds of wet weather sampling were performed in fall of 2011. Samples in both rounds were
analyzed for bacteria (fecal coliform and enterococci), and total suspended solids. The results of the two
sampling rounds were plotted and analyzed. Because of the wide disparity of bacteria values between
events at some locations, it was decided to calculate the geometric mean of values, rather than a simple
average, to assess the level of contamination. The geometric mean for fecal coliform counts ranged
from 52 cfu/100 ml to 13,856 cfu/100 ml with an average of 5,417 cfu/100 ml for all fifteen sample sites.
The geometric mean for enterococci ranged from 856 cfu/100 ml to 39,950 with an average of 16,962
cfu/100 ml for all fifteen sample sites. Total suspended solids values ranged from 6 mg/l to 33 mg/l with
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an average value of 17 mg/l across all fifteen sites. (Note: TSS values represent arithmetic average
values, not geometric mean values, because TSS values between sample rounds did not vary
significantly).
ATP performed an analysis to determine which of the Town-controlled outfalls represents the greatest
measurable threat to the shellfish areas in Kingston Bay at the mouth of the Jones River. A mass balance
was performed for each outfall using the three laboratory measured parameters selected for the study
(geometric mean or arithmetic average, as appropriate) and multiplying each by the "first flush" volume.
The greatest mass of fecal coliform units was measured at 9,995 million units. The greatest mass of
enterococci bacteria were 49,311 million units. The greatest volume of total suspended solids was
22,166 grams. The respective average values were 3,675 million units fecal, 11,568 million units
enterococci, and 8,861 grams TSS.
To reduce the number of outfalls be subject to preliminary design, ATP developed a relatively simple
matrix analysis incorporating four parameters: Pollutant Level (mass fecal units and mass enterococci
units); Proximity to Kingston Bay; and Constructability. Constructability refers to the probability that a
subsurface leaching system can be built with volume suitable to manage the first flush and was based, in
part, on the apparent public land available and soil characteristics as gleaned from the most recent
NRCS mapping. Within the matrix, each outfall was assigned a value from one to five for each of the four
parameters with 1 being not significant and 5 being significant. The individual scores were then added
up with the highest value representing outfalls that should move forward to preliminary design.
In an effort to begin the process of mitigating stormwater impacts, conceptual designs were developed
for ten catchment areas. Using first flush volumes calculated, a site specific BMP system that would
remove suspended solids and fecal coliform using infiltration systems, both surface and subsurface, was
developed. System headworks were sized to hold 10% of the first flush volume for settling purposes.
Consistent with the Massachusetts Stormwater Handbook, infiltration systems were sized using TR-55
analyses based upon the first flush (1" of runoff) which serves as the Required Water Quality Volume.
The "Dynamic Field" method was used to determine system size based upon an estimate of permeability
from the soils data gathered from NRCS sources.
Depending upon soil types and estimated depth to water table, surface and subsurface infiltration systems
were analyzed. In shallow-to-groundwater areas, such as near to outfalls, vegetated swales, surface
filtration systems, and rain gardens were proposed. Where first flush volumes were large, upgradient
subsurface systems were selected for conceptual design to capture flow and minimize the footprint of
surface systems. Subsurface systems were selected in locations where soils were permeable, groundwater
was deemed to be at depth, and/or where space was tight. In some locations a network of existing
catchbasins and drain manholes were worked into the conceptual design, while elsewhere, no system
existed apart from a simple catchbasin/outfall complex. Typical sedimentation units were comprised of
drain manholes with 4' sumps and septic tanks ranging in size from 1000 gallons to 1500 gallons.
Conceptual infiltration systems were predicated upon units manufactured by Cultec with varying heights
and sizes. Surface filtration systems sometimes were proposed to be constructed using imported sand with
underdrainage where soils were deemed not sufficiently permeable.
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Based upon the conceptual designs, a
materials quantity takeoff was performed
and a construction cost estimate developed
for each location. Construction costs were
increased by 15% to cover contingencies
and 25% to cover the cost of services for
final design and construction inspection.
The total construction cost, including final
engineering design, construction, and
construction inspection for all ten locations
was $556,392.
Based upon the matrix analysis results two
Source: Maureen Thomas, Town of Kingston
sites were selected for preliminary design. Fjgure ±_2 Rajn garden off of De,ano Ave jn Kingston/
Tasks to raise a design from "conceptual" to ma.
"preliminary" included a detailed
topographic and utility survey plotted to 20-scale, and refined design to ensure clearance with existing
watermains, sewage forcemains, and service connections. Two drawings were completed for the
Preliminary Designs. No stormwater infrastructure exists at either location so all systems were designed
to bypass flows in excess of the first flush along the street as flows currently do.
Preliminary design at the paved swale on
Delano Avenue was proposed to be
comprised of a trench drain at the toe of the
road, two 5' drain manholes with 4' sumps,
and two 18' diameter rain gardens. The site
is fairly tight with poor soils and narrow
public land but it appears, based upon
current understanding of property lines, that
a rain garden of some configuration is
possible on both sides of the proposed
trench drain. Final design will ensure that,
once the rain gardens are full, flows in
excess of the first flush will pass over the Source: Maureen Thomas, Town of Kingston
... , x J.l , F sure 1-3, Rain garden off of Delano Ave, in
trench drain and enter the Jones River as
Kingston, MA during a storm event,
they currently do. The final design will also
seek to manage any scour that might occur from the new system by specifying some combination of
riprap and hardy vegetation down gradient. Based on the preliminary designs, a total construction cost
estimate of $268,778 has been calculated for the two catchment areas. The total construction cost
includes 10% for construction contingencies and 25% for services related to design and construction
inspection. The total construction cost estimate to mitigate ail twelve outfalls is $825,170.
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1.8. Handbook Components
The checklist on the next page lists the major chapters of this Handbook, describes the goals of each
chapter, and lists the major activities within each chapter. Readers can also use this checklist to follow a
proven process to plan for implementing a green infrastructure approach, or refer directly to specific
chapters that meet their needs and are the most relevant to their situation.
INCORPORATING GREEN INFRASTRUCTURE INTO STORMWATER
MANAGEMENT PLANNING
WATERSHED ASSESSMENT (CH. 2)
Chapter Goal: To provide background on the regulatory requirements related to stormwater management,
conditions in the geographic region, contents of the Handbook, and green infrastructure concepts.
Identify stakeholders and roles.
I I
Q Identify study watershed or subwatershed.
Identify existing hydrologic and hydraulic data.
I I
Characterize known pollutant loadings.
Identify existing BMPs and green infrastructure practices.
I I
Identify additional data needs.
IDENTIFYING GREEN INFRASTRUCTURE OPPORTUNITIES (CH. 3)
Chapter Goal: To evaluate and prioritize each potential parcel and street segment for the potential
implementation of green infrastructure concepts and practices.
Identify target subwatershed(s).
Complete primary screening of potential BMP locations.
I I
Complete secondary screening and prioritization.
SITE ASSESSMENT, PLANNING, AND DESIGN (CH. 4)
Chapter Goal: To apply green infrastructure principles, concepts, and practices for a retrofit, redevelopment,
or new development site.
Review site planning and design principles.
Incorporate green infrastructure principles and concepts in a site design.
I I
Q Prepare conceptual design plans.
GREEN INFRASTRUCTURE PRACTICES (CH. 5)
Chapter Goal: To provide an overview of green infrastructure practices with guidance on selecting the
appropriate practice(s) for the selected site design.
Use "BMP Selection Matrix" to select green infrastructure BMPs.
Size green infrastructure BMPs.
I I
Q Review common green infrastructure practices.
Utilize resources referenced to develop a full design.
I I
Consider potential BMP construction and post-construction issues.
GREEN INFRASTRUCTURE REVIEW PROCESS (CH. 6)
Chapter Goal: To achieve effective implementation of green infrastructure concepts and practices by
developing effective and complete design plans and providing incentives for implementing green infrastructure
practices.
Incorporate a process for reviewing and approving green infrastructure.
Provide incentives to encourage green infrastructure.
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1.9. References
Anderson, L., and H. Cordell. 1988. Influence of trees on property values in Athens, Georgia (USA): A
survey on actual sales prices. Landscape and Urban Planning 15(1-2):153-164.
CMR (Code of Massachusetts Regulations), http://www.mass.gov/eea/agencies/dfg/dfw/laws-
regulations/cmr/.
Espey, M., and K. Owusu-Edusei. 2001. Neighborhood parks and residential property values in
Greenville, South Carolina. Journal of Agricultural and Applied Economics 33(3):487-492.
FHWA (Federal Highway Administration). 2002. Storm Water Best Management Practices in an
Ultraurban Setting: Selection and Monitoring. Federal Highway Administration, Washington, DC.
Hastie, C. 2003. The Benefit of Urban Trees. A summary of the benefits of urban trees accompanied by a
selection of research papers and pamphlets. Warwick District Council. Accessed April 8, 2014.
http://www.naturewithin.info/UF/TreeBenefitsUK.pdf.
Hobden, D.W., G.E. Laughton, and K.E. Morgan. 2004. Green space borders—a tangible benefit?
Evidence from four neighborhoods in Surrey, British Columbia, 1980-2001. Land Use Policy 21,
129-138.
Kloss, C., and C. Calarusse. 2006. Rooftops to Rivers - Green Strategies for Controlling Stormwater and
Combined Sewer Overflows. Natural Resource Defense Council, www.nrdc.org.
Kuo, F. 2003. The role of arboriculture in a healthy social ecology. Journal of Arboriculture 29(3).
Kuo, F., and W. Sullivan. 2001a. Aggression and violence in the inner city: Effects of environment via
mental fatigue. Environment and Behavior 33(4):543-571.
Kou, F., and W. Sullivan. 2001b. Environment and crime in the inner city: Does vegetation reduce crime.
Environment and Behavior 33(3):343-367.
Lloyd, S.D., T.H.F. Wong, and C.J. Chesterfield. 2002. Water Sensitive Urban Design—A Stormwater
Management Perspective. Industry Report No. 02/10. Cooperative Research Centre for
Catchment Hydrology, Melbourne, Australia.
MassDEP (Massachusetts Department of Environmental Protection). 2008. Massachusetts Stormwater
Handbook, http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-
stormwater-handbook.html.
Massachusetts EEA (Massachusetts Office of Energy and Environmental Affairs). 2014. About the Mass
Bays Program. Accessed October 8, 2014. http://www.mass.gov/eea/agencies/mass-bays-
prog ram/a bout-us.
Massachusetts Land Trust Coalition, http://www.massland.org. Accessed August 2014.
Northeastern Illinois Planning Commission (NIPC). 2004. Sourcebook on Natural Landscaping for Local
Officials. Accessed December 2012.
http://www.chicagowilderness.org/files/4413/3087/4878/natural landscaping sourcebook.pdf.
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New Yorkers for Parks and Ernst & Young. 2003. Analysis of Secondary Economic Impacts Resulting from
Park Expenditures. New Yorkers for Parks, New York, NY.
Pincetl, S., J. Wolch, J. Wilson, and T. Longcore. 2003. Toward a Sustainable Los Angeles: A Nature's
Services Approach. University of Southern California Center for Sustainable Cities, Los Angeles,
CA. http://sustainablecommunities.environment.ucla.edu/wp-
content/uploads/2012/10/Toward Sustainable LA 2003.pdf.
Shultz, S., and N. Schmitz. 2008. How Water Resources Limit and/or Promote Residential Housing
Developments in Douglas County. University of Nebraska-Omaha Research Center, Omaha, NE.
Accessed April 8, 2014. http://www.unorealestate.org/pdf/Water Study.pdf.
USFWS (U.S. Fish and Wildlife Service). 2014. Coastal Barrier Resources Act. Accessed March 24, 2014.
http://www.fws.gov/cbra/index.html.
Voicu, I., and V. Been. 2009. The effect of community gardens on neighboring property values. Real
Estate Economics 36(2):241-283.
Wachter, S. M., and G.W. Bucchianeri. 2008. What is a Tree Worth? Green-City Strategies and Housing
Prices. Real Estate Economics 36(2). SSRN: http://ssrn.com/abstract=1084652.
Ward, B., E. MacMullan, and S. Reich. 2008. The Effect of Low-impact Development on Property Values.
ECONorthwest, Eugene, OR.
Wolf, K. 1998. Urban nature benefits: Psycho-social dimensions of people and plants. Human Dimension
of the Urban Forest, Fact Sheet #1. Center for Urban Horticulture, University of Washington,
College of Forest Resources, Seattle, WA. http://www.naturewithin.info/UF/PsychBens-FSl.pdf.
Wolf, K. 2008. With Plants in Mind: Social Benefits of Civic Nature. Accessed April 8, 2014.
http://www.naturewithin.info/CivicEco/CivicNature BenefitCites.pdf.
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2. Watershed Assessment
A watershed assessment helps to identify opportunities where green infrastructure can be used to
provide water quantity and quality benefits to restore, protect, and enhance the natural hydrology and
ecosystem functions in the watershed; in this case, the Massachusetts coastal region (see Figure 1-1). It
includes an overview of multiple existing data resources. Additional detailed information for the steps
presented below is presented in Appendix A.
The overall goal of a watershed assessment is to identify opportunities where green infrastructure can be
used to provide water quantity and quality benefits to restore, protect, and enhance the natural hydrology
and ecosystem functions in the watershed. The purpose of a watershed assessment is therefore to:
P Evaluate current water quality conditions to determine overall health of streams.
P Identify sources of current water quality impairments.
P Address land use changes and predict effects future growth will have on water quality.
P Link activities in the watershed with impacts to water quality, hydrology, and habitat.
P Develop management strategies to restore and maintain water quality.
There is no "one size fits all" approach when it comes to watershed assessments. Watershed
assessments have varying levels of complexity depending on specific objectives, availability and
quantity/quality of existing data, results from previous studies, budget and funding, schedule,
watershed size, number of stakeholders and level of involvement, and other factors. However, all
watershed assessments should ask the following questions:
The watershed assessment addresses the following major questions:
(1) What are the most important impacts in the watershed?
(These include adverse impacts to water quality and hydrology.)
(2) What are the major stressors and sources linked to these impacts?
(3) Where in the watershed should green infrastructure efforts be focused?
Watershed assessments are typically initiated when an opportunity for restoration or enhancement is
recognized, or in response to a perceived problem related to a local water body. The sections below
provide an outline of the comprehensive watershed assessment approach and the types of data and
analyses required. Project-specific objectives and other factors described above will determine which of
the following categories should be included in the assessment and which are not relevant. Figure 2-1
outlines the components involved in the watershed assessment process, to be discussed in the following
sections. Detailed information on watershed assessment is provided in Appendix A. Note that the
watershed assessment is not a step-wise process - users can begin where it makes the most sense for
their particular situation (for example, collecting data before identifying the stakeholders).
MassBays provides an interactive map with access to more than 500 documents dated 1996 to 2013 on
its website at http://www.mass.gov/eea/agencies/mass-bavs-program/estuaries/. For each of the 47
embayments in the MassBays region, you will find a wealth of downloadable assessments and
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recommendations for action categorized by five topics: water quality, estuarine habitat protection,
continuity of estuarine habitat, invasive species, and climate change/vulnerability. This online resource
is a good first stop to find existing information about the subject watershed.
Part 1: Identify Stakeholders and Roles
Identify potential stakeholders and roles to engage the community and earn support for projects.
Part 2: Identify Study Watershed
¦ Define the watershed or subwatershed boundary.
• This establishes the limits of the study.
¦ Locate or create a geographic information systems (GIS) representation of the watershed.
• This will facilitate watershed assessment (Section 2) and pnoritization (Section 3).
Part 3: Identify Existing Hydrologic and Hydraulic Data
Search for existing data and studies that help characterize existing conditions in the study watershed.
Starting with a GIS-based desktop analysis can help reduce time and resources spent in the field.
¦ Locate water bodies in the study watershed.
• Identify waters that receive stormwater runoff and may benefit from BMPs.
¦ Characterize land use and land cover.
• This will help determine potential for runoff and pollutant loading.
¦ Identify areas of impervious coverage.
• These areas have the highest runoff rates (per unit area) compared to other land cover and could
provide retrofit opportunities.
¦ Characterize topography.
• Slope impacts the speed and path of stormwater mnoff and some BMPs are not appropriate where
steep slopes occur.
¦ Identify parcel data.
• This will help determine land ownership.
¦ Locate aerial photography dataset.
• This will allow for preliminary screening for BMP opportunities.
Part 4: Characterize Known Pollutant Loadings
identify and prioritize stormwater pollutant sources in the study watershed.
¦ Identify pollutants of concern or interest (beginning with 303(d) and TMDL pollutants).
¦ Identify potential pollutant sources.
¦ Estimate pollutant loadings.
• Pollutant loadings can be based on monitoring, land use-based estimates, or other methods.
¦ Develop site characterizations.
• Synthesize information in previous steps to facilitate site prioritization (Section 3).
Part 5: Identify Existing BMP and Green Infrastructure Practices
Identify any existing or planned green infrastructure projects in the study watershed.
Part 6: Identify Additional Data Needs
Identify data collection that may be necessary to address any data gaps identified in the previous steps.
This could include water quality sampling and site visits.
Source: Tetra Tech
Figure 2-1. Components of the watershed assessment process.
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2.1. Part 1: Identify and Engage Stakeholders
Formulate watershed assessment team by identifying potential stakeholders in the watershed
and their possible roles.
A good watershed assessment team should include members with a variety of disciplines or specialties.
Involving a variety of stakeholders with different backgrounds, experience, and expertise will make it
less likely that the assessment will overlook some important watershed factors. A key initial step is to
identify potential stakeholders in the watershed and their possible roles. The MassBays Regional
Coordinators convene a Local Governance Committee with representatives from multiple local agencies
and other community stakeholders; watershed associations and friends groups may also convene
stakeholders and can help bring them to the table for planning and siting. As the Massachusetts MS4
permit is put in place, towns will establish MS4 committees typically charged with oversight and
development of regional stormwater management programs and could serve important roles in the
stakeholder process.
General categories of stakeholders may include:
P Local businesses
P Landowners
P Local, regional, state, and federal agencies including the Department of Transportation
P Environmental groups
P Nonprofit and volunteer organizations
P Watershed and neighborhood associations
P Experts (consultants, engineers, scientists, and academics)
P People with local knowledge
When initiating a watershed assessment, contact a MassBays Regional Coordinator
(http://www.mass.gov/eea/agencies/mass-bavs-program/regions/) who can provide assistance and
connections with federal and state agencies, local nonprofits and community groups, and other towns
that have implemented green infrastructure projects.
The importance of earning community support for project goals cannot be overstated. From start to
finish, the assessment should make clear how and why various steps were taken. Stakeholders and
decision makers are more likely to trust the assessment's conclusions if they understand the reasons
why various approaches were taken, or if they were personally involved in gathering data and
information.
Possible methods for stakeholder involvement may include:
P Contact the MassBays Program
P Discuss the role of or engage local residents and business owners.
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P Work with local stakeholders to develop an understanding of:
- Awareness of green infrastructure/BMP facilities.
- Impacts of upstream pollutants and runoff to local waterways.
- Viable communication channels.
- Demographic variables.
P Develop outreach plan to increase community support and public awareness of green
infrastructure
P Use indirect communication channels such as websites, flyers, and billing inserts.
P Use direct channels such as events, workshops, and in-person visits.
P Develop advertising materials such as brochures, how-to guides, and social media posts.
The main goal of stakeholder involvement is to target and increase public awareness and ultimately
increase probability of success of project.
P EPA published the second edition of their guidance manual Getting in Step: Engaging
Stakeholders in Your Watershed. This manual can be very useful for guiding users through the
stakeholder involvement process
(www.epa.gov/owow/watershed/outreach/documents/stakeholderguide.pdf).
0 Community-Based Watershed Management: Lessons from the National Estuary Program
(www.epa.gov/nep) also contains valuable information about involving the public to address
coastal management issues.
2.2. Part 2: Identify Study Watershed
Define the watershed or subwatershed boundary.
As defined by EPA, "a watershed is the area of land where all of the water that is under it or drains off it
goes into the same place" (USEPA 2014). Watersheds are also called drainage basins, river basins, or
catchments. Watersheds can be very small or very large depending on the point of interest from which
they are drawn.
The local municipality leading the green infrastructure evaluation process typically directs the
watershed assessment team to focus their study in a particular watershed (or subwatershed) based on
existing knowledge of water quality, hydrology, or habitat issues prompting the assessment If a
geographic information system (GIS) based representation of the study watershed has not already been
created, this should be completed to facilitate assessment.
In many cases, cooperation among multiple local municipalities is necessary when it comes to green
infrastructure implementation because watersheds and subwatersheds typically do not adhere to
municipal boundaries. Accordingly, a single watershed or subwatershed could encompass multiple
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communities and cooperation among these multiple stakeholders is essential for achieving successful
outcomes in that particular watershed.
2.3. Part 3: Identify Existing Hydrologic and Hydraulic Data
Search for existing data that help characterize watershed or catchment hydrology and hydraulics.
Once the study watershed (or subwatershed) has been identified, a key component of the watershed
assessment process is to perform a detailed search for existing efforts characterizing the hydrology and
hydraulics of the target watershed. This might include previously collected monitoring data, modeling
efforts, watershed studies, and watershed management plans. Existing data and studies should be
evaluated for their relevance and summarized. Sources of previous watershed assessments and
watershed data can include local government, local organizations, and state agencies.
Data and results from previous studies and monitoring efforts can provide information to establish the
baseline conditions for hydrology and water quality in the watershed. Previous watershed delineations
and other assumptions should be evaluated, scrutinized, and confirmed appropriately before using them
in the watershed assessment and prioritization. When appropriate, data and results from previous
hydrology and hydraulic studies should be updated and supplemented with new data, if new data have
become available since the original study.
2.3.1. Types of Data
Relevant hydrologic and hydraulic data can include any pertinent data used to describe hydrologic and
hydraulic features of the watershed as well as characteristics that influence watershed hydrology and
hydraulics. These data types and potential resources for obtaining data are listed below, with detailed
descriptions provided in Appendix A:
P Locations of water bodies including streams, lakes, and wetlands
- Provides identification of surface waters that receive stormwater runoff and may benefit
from BMPs.
P Impervious surface coverage
- Used to identify potential areas where greatest stormwater runoff occurs.
P Land use and land cover, including vegetation
- Used to identify potential for runoff and pollution loading.
P Topography (elevation and slope)
- Elevation and slope determine speed and path of stormwater runoff, and excessive slopes
may prohibit green infrastructure installation.
P Soils (types, textures, and hydrologic soil groups)
- Used to evaluate infiltration capacity.
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P Parcel data
- Used to determine ownership when identifying sites for BMP opportunities.
P Aerial imagery
- Allows for preliminary screening of sites for BMP opportunities.
2.3.2. GIS Data for Massachusetts
Although there are other sources of spatial (GIS) data for Massachusetts, two of the more robust data
acquisition systems are described below. Both databases provide instant online access to free, high-
quality geospatial data.
2.3.2.1. MORIS
MORIS (Massachusetts Ocean Resource Information System) is an online spatial data mapping and
acquisition tool developed by the Massachusetts Office of Coastal Zone Management (CZM) in
partnership with MassGIS (described below), SeaPlan, Applied Science Associates, Charlton Galvarino,
and PeopleGIS (MORIS 2014). MORIS features an interactive web-based map application that allows the
user to zoom into an area of interest and download a wealth of data layers specific to that area. MORIS
contains much of the same data sources as MassGIS (described below), but is of particular interest to
MassBays communities due to its coastal focus.
P MORIS is accessed through the mass.gov website: www.mass.gov/eea/agencies/czm/program-
areas/mapping-and-data-management/moris/
2.3.2.2. MassGIS
The Commonwealth of Massachusetts maintains a database of GIS resources through its Office of
Geographic Information (MassGIS). Based on information provided by MassGIS, "the state legislature
has established MassGIS as the official state agency assigned to the collection, storage, and
dissemination of geographic data" and is responsible for coordinating GIS activity in the Commonwealth.
P The MassGIS geospatial library can be found at www.mass.gov/anf/research-and-tech/it-serv-
and-support/application-serv/office-of-geographic-information-massgis/.
P The MassGIS data system also includes an online viewer ("OLIVER") allowing users to quickly and
easily view available data layers for a particular area. It can be found at
http://maps.massgis.state.ma.us/map ol/oliver.php.
2.3.3. Hydrologic and Hydraulic Data Summary
Table 2-1 summarizes relevant data types, descriptions, and possible sources.
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Table 2-1. Recommended sources of hydrologic and hydraulic data for watershed assessment
Dataset
Type
Description
Source(s)
Subwatershed
boundary
GIS shapefile
Delineation of study watershed
Municipality
Hydrography
GIS shapefile
Locations of surface water features (lakes, ponds,
reservoirs, wetlands, rivers, streams)
MORIS, MassGIS
Land use and
land cover
GIS shapefile
Land use and land cover
MORIS, MassGIS
Impervious Area
Image file
Impervious surfaces including buildings, roads, and
parking lots
MORIS, MassGIS
Roads and
streets
GIS shapefile
Transportation (public and private roadways)
(if impervious surface data are insufficient)
MORIS, MassGIS
Elevation
GIS raster file
Elevation above or below sea level
MORIS, MassGIS
Soils
GIS shapefile
Spatial extent of soil types and HSGs
MassGIS
(alternately NRCS)
Parcels
GIS shapefile
Property boundaries and ownership
Municipality,
MORIS, MassGIS
Aerial imagery
Image file
True-color aerial photos
MORIS, MassGIS
2.3.4. Additional Data Resources
Additional data resources that can aid in the watershed assessment and characterization may include
the following:
P Locations and routing of existing stormwater structures and pipes
- New BMPs will become part of the existing stormwater infrastructure.
P Streamflow data and locations of streamflow gages
- Useful for understanding existing hydrologic behavior of the study watershed.
P Climate/rainfall data and locations of climate monitoring stations
- Used to develop understanding of climate and rainfall which impact BMP performance.
P Water quality data and locations of existing monitoring locations
- Useful for establishing baseline water quality conditions in the watershed.
P Locations of impaired waters and corresponding impairments, both within the watershed and
immediately downstream
- Used to identify known water quality problems.
P Environmentally sensitive areas, floodplains and floodways, water supplies, and dams
- These areas require special consideration.
The unique objectives and scope of the individual watershed assessment will determine the extent to
which each of these should be investigated and included in the assessment. Detail on each of these
resources is provided in Appendix A.
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2.3.5. Summary of Additional Data Resources
Table 2-2 summarizes relevant data types, descriptions, and possible sources.
Table 2-2. Recommended additional data for use in watershed assessment
Dataset
Type
Description
Source(s)
Storm drain map
GIS shapefile
(if available),
other
GIS, digital, or hardcopy map with locations and
dimensions of existing storm network including pipes,
road crossings, and culverts
Municipality
Climate stations
GIS shapefile
Locations of climactic data monitoring (e.g., NCDC or
NOAA, Global Historical Climatology Network [GHCN])
NOAA
Water quality
monitoring stations
GIS shapefile
Locations of water quality sampling (e.g., MassDEP
DWM)
MassGIS
303(d) waters
GIS shapefile
MassDEP Integrated List of Waters (303(d)) (most
recent available)
MORIS,
MassGIS
Shellfish sampling
stations
GIS shapefile
Stations designated by DMF's Shellfish Project for
water quality and shellfish samples
MORIS,
MassGIS
Coastal habitat
GIS shapefile
Core/critical habitat delineations
MORIS
ACECs
GIS shapefile
Areas of Critical Environmental Concern
MORIS,
MassGIS
Protected open
space
GIS shapefile
Conservation lands and recreational facilities
MORIS,
MassGIS
NHESP (various)
GIS shapefile
Natural Heritage & Endangered Species Program
habitats and natural communities
MORIS,
MassGIS
ORWs
GIS shapefile
Outstanding Resource Waters of the state
MORIS,
MassGIS
Priority natural
vegetation
GIS shapefile
Identified by NHESP as most critical to biological
diversity
MORIS,
MassGIS
NWI
GIS shapefile
National Wetlands Inventory - extent, types, and
locations of wetlands and deepwater habitats
MORIS,
MassGIS
FEMA flood
hazards
GIS shapefile
1 percent and 0.2 percent annual chance flood
boundaries and regulatory floodway
MORIS,
MassGIS
Dams
GIS shapefile
Locations of dams from Massachusetts ODS, ground-
truthed
MORIS,
MassGIS
Public water
supplies
GIS shapefile
Public surface and ground water supply sources
MassGIS
2.4. Part 4: Characterize Known Pollutant Loadings
Prioritize pollutant sources and develop a meaningful plan for green infrastructure
implementation focused on the highest priority sources in the target watershed or catchment
The purpose of this exercise is to characterize pollutant sources within the study watershed or
catchment. The goal is to build upon existing bodies of knowledge, such as relevant studies and efforts
within the target watershed or catchment, using supplemental research and local knowledge. Steps
used to identify and summarize known pollutant loadings include:
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P Identify pollutants of interest and concern (e.g., 303(d) and TMDL pollutants).
P Identify and characterize pollutant sources.
P Estimate pollutant loadings using existing monitoring data and other methods.
P Develop site characterizations.
P Identify significant data gaps (Section 2.6).
P Identify potential green infrastructure practices to address specific pollutants (this will be
addressed in subsequent sections of this guidance).
Site characterizations are essentially a synthesis of the information gathered in the previous steps, and
include an evaluation of any known activities that could be impacting stormwater runoff, an estimate of
impervious coverage, and the likelihood for discharge of pollutants of interest. Sites with the highest
known or suspected pollutant loadings should be prioritized for green infrastructure, or for further
monitoring to confirm the loading assumptions, respectively. These sites will be further prioritized for
green infrastructure in Section 3.
Supplemental detail on this process is provided in Appendix A. The site characterizations and estimated
pollutant loadings will be used to prioritize and target green infrastructure efforts. Higher
concentrations of pollutant loading might warrant a greater focus of BMPs.
2.5. Part 5: Identify Existing BMP and Green Infrastructure Practices
Identify existing or planned green infrastructure projects in the watershed or catchment.
Knowledge of any existing or planned projects is critical for developing a green infrastructure plan and
assessing the current condition of the watershed or catchment. It is possible that projects already in
place are significantly contributing to volume and pollutant load reduction. Further, to distribute green
infrastructure opportunities effectively throughout the watershed or catchment, areas in close proximity
to existing or planned green infrastructure implementation may be considered lower priority (see
Section 3.3). Available resources must be reviewed to identify the location and potential effect of any
existing green infrastructure practices or BMPs. All planned and existing BMPs must be considered in the
identification and prioritization of potential locations for green infrastructure to maximize the potential
water quality impacts of these improvements.
Potential sources of information for identifying existing BMPs include local municipalities, existing
databases and inventories, existing maps and GIS data, the Massachusetts Department of
Transportation (MassDOT), and physical site assessment.
Some municipalities maintain an electronic database or inventory, sometimes GIS-based, of existing
stormwater management practices, principally for maintenance purposes. Municipal employees or local
landowners can be good sources of knowledge for locating existing BMPs. It might be possible to obtain
existing maps, data, plans, and other information on existing green infrastructure practices directly from
municipalities or from local engineers or engineering firms with knowledge of when and where the
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BMPs were installed. MassDOT installs and maintains stormwater BMPs for the purpose of meeting
stormwater permit requirements related to runoff from state-owned transportation features. MassDOT
and local DOT offices might be able to provide information on locations and design of existing BMPs.
2.6. Part 6: Identify Additional Data Needs
Identify any additional data collection that might be necessary to
address data gaps identified in the watershed assessment process.
Field observations and additional monitoring may be used to verify assumptions regarding the pollutant
loading analysis, or to provide additional data for the watershed assessment and characterization of
pollutant sources where data gaps are identified. In watersheds or catchments with extensive existing
data resources, additional data collection might not be necessary.
An important consideration is that many grant programs require sufficient water quality data before
grants are awarded. This could serve as a key incentive for additional data collection when data gaps
have been identified.
2.6.1. Water Quality Sampling
Wet-weather observations and sampling can be used to confirm loading from key sources or drainage
areas where previous monitoring data are not available. Components can include water quality and
sediment analysis at selected sample sites to determine levels of bacteria, nutrients, organic
contaminants and metals or land use characterization to identify potential stressors. A biological
analysis can also be included as part of watershed or catchment monitoring, such as detailed habitat,
macroinvertebrate, and fish community assessments. The type of water quality sampling employed
depends on the specific pollutant(s) of concern and specific impacts to be addressed.
Many watersheds benefit from the presence of local organizations (such as watershed associations) that
develop their own volunteer monitoring programs. This can be an effective method for hands-on
community contribution to the assessment and can also conserve resources compared to contracting
out all of the monitoring work. However, effective training, supervision and scheduling are required for
the data to be rendered useful for watershed assessment. Section 2.1 described potential types of
watershed groups and other key stakeholders.
2.6.2. Field Reconnaissance
Sites identified as potential locations for green infrastructure as part of the watershed assessment can
be further evaluated through field visits to evaluate the accuracy of the GIS analysis and further
establish the priority of the site (Section 3). Field reconnaissance typically includes photo documentation
and documentation of site characteristics that can impact or prevent BMP design or construction, as
well as additional evaluation including:
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P Overall appearance
Gather information on overall site characteristics, including any perceived pollutant sources or
water quality or quantity concerns. (Refer to potential sources discussed in Appendix A.)
P Site configuration
Elements of the site that will determine the configuration and type of BMP, such as utilities,
right-of-way (ROW) width, curb configuration, existing landscaping, current use, and existing
drainage patterns.
P Slope
Verify visually to confirm that the slope is appropriate for green infrastructure.
Other factors to consider in the site identification process may include:
P Design complexity
Sites that require a more complex design should be avoided because they could prolong the
permitting process and complicate construction. Sites that might require extensive permits from
multiple regulatory agencies should also be avoided.
P Maintenance/accessibility
BMPs must be maintained at some level to function as designed. Sites should be evaluated for
ease of maintenance access.
2.6.3. Wetlands
Wetlands are valuable, sensitive resources that warrant careful attention in the watershed assessment
process. References that can be helpful in evaluating wetlands in the watershed context include:
P EPA Region 5 Wetlands Supplement: Incorporating Wetlands into Watershed Planning
P Watershed Approach Handbook: Improving Outcomes and Increasing Benefits Associated with
Wetland and Stream Restoration and Protection Projects
2.7. Part 7: Identify Sources of Funding
EPA also compiled a set of resources to help municipalities better understand the cost-benefits of green
infrastructure and to identify funding opportunities. They include:
P Cost-benefit resources to conduct cost benefit analyses of green infrastructure approaches.
Completed analyses demonstrate that the value of green infrastructure benefits can exceed
those of gray, http://water.epa.gov/infrastructure/greeninfrastructure/gi costbenefits.cfm
P Funding opportunities including federal funding sources and funding tools that project sponsors
can use to tap a variety of federal funding sources.
http://water.epa.gov/infrastructure/greeninfrastructure/gi funding.cfm
P Managing Wet Weather with Green Infrastructure Municipal Handbook: Funding Options.
http://water.epa.gov/infrastructure/greeninfrastructure/upload/gi munichandbook funding.pdf
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P EPA's report, Getting to Green: Paying for Green Infrastructure: Financing Options and Resources
for Local Decision-Makers, provides a summary of funding mechanisms available to support
stormwater management programs or finance individual projects, http://water.epa.gov/nep.
The report outlines financing options (mostly applicable to small parcel projects), examples of
municipal programs by type of funding source, and a list of additional resources for financing
green infrastructure projects.
Several possible funding sources for green infrastructure projects are outlined below. Contact your
MassBays Regional Coordinator to discuss possible funding opportunities and options.
MassBays Research and Planning Grants
Agency: Executive Office of Energy and Environmental Affairs (EEA)-Coastal Zone Management (CZM)
Description and Eligible Activities: The MassBays Research and Planning Program provides grants for
applied planning and research projects that protect coastal habitat, reduce stormwater pollution, protect
shellfish resources, manage local land use and growth, manage municipal wastewater, manage marine
invasive species, monitor marine and estuary waters, and adapt to the projected impacts of climate
change. Note: the program will be inactive in FY2015, to be evaluated and re-launched in FY2016.
Website: www.massbays.org
Eligible Applicants: Massachusetts cities, towns, and other public entities; academic institutions; and
certified 501(c) (3) non-profit organizations.
Clean Water Act S.604b Water Quality Management Planning Grant Program
Agency: Department of Environmental Protection (DEP)
Description and Eligible Activities: Assists regional planning agencies and other eligible recipients in
providing water quality assessment and planning assistance to local communities.
Website: http://www.mass.gOv/eea/agencies/massdep/water/grants/watersheds-water-qualitv.html#3
Eligible Applicants: Regional planning agencies, conservation districts, cities and towns
Coastal Pollution Remediation (CPR) Grants
Agency: Executive Office of Energy and Environmental Affairs (EEA)-Coastal Zone Management (CZM)
Description and Eligible Activities: The CPR Program provides funding to municipalities located within
the Massachusetts coastal watershed for planning / design and remediation including construction and
implementation to reduce stormwater pollution from paved surfaces, or for commercial boat waste
pumpout facilities. Municipalities may request up to $125,000 for stormwater planning /design
/remediation or commercial boat pumpout projects.
Website: http://www.mass.gov/eea/agencies/czm/program-areas/coastal-water-quality/cpr/
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Eligible Applicants: Municipalities located in the greater Massachusetts Coastal Watershed (see
http://www.mass.gov/eea/agencies/czm/program-areas/coastal-water-qualitv/cpr/coastal-watershed-
communities.html )
Clean Water Act S.319 grants
Agency: Department of Environmental Protection (DEP)
Description: This grant program is authorized under Section 319 of the federal Clean Water Act for
implementation projects that address the prevention, control, and abatement of nonpoint source (NPS)
pollution. In general, eligible projects must: implement measures that address the prevention, control,
and abatement of NPS pollution; target the major source(s) of nonpoint source pollution within a
watershed/subwatershed; contain an appropriate method for evaluating the project results; and must
address activities that are identified in the Massachusetts NPS Management Plan. Proposals may be
submitted by any interested Massachusetts public or private organization. To be eligible to receive
funding, a 40% non-federal match is required from the grantee
Website: http://www.mass.gOv/eea/agencies/massdep/water/grants/watersheds-water-quality.html#2
Eligible Applicants: Any Massachusetts public or private organization.
Massachusetts Environmental Trust
Agency: Executive Office of Energy and Environmental Affairs (EEA)
Description and Eligible Activities: The Trust supports cooperative efforts to restore, protect, and
improve water and water-related resources of the Commonwealth. Grants funds are generated through
the sale of environment themed license plates.
Website: http://www.mass.gov/eea/met
Eligible Applicants: Eligible organizations generally include 501(c)(3) nonprofit organizations and
municipalities. Unincorporated organizations may apply provided that they have an eligible fiscal sponsor.
Rivers and Harbors Grant Program
Agency: Department of Conservation and Recreation (DCR)
Description: Grants requiring matching funds for studies, surveys, design & engineering, environmental
permitting and construction that addresses problems on coastal & inland waterways, lakes, ponds and
great ponds. Grants are awarded in the following categories: 1) Coastal Waterways - for commercial and
recreational navigation safety & to improve coastal habitat by improving tidal interchange; 2) Inland
Waterways - to improve recreational use, water quality & wildlife habitats; 3) Erosion Control - to protect
public facilities and reduce downstream sedimentation; 4) Flood Control - to reduce flood potentials.
Contact: Kevin P. Mooney, (781) 740-1600 xl03
Wetlands and River Restoration and Revitalization Priority Projects
Agency: Department of Fish and Game (DFG)
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Description and Eligible Activities: These grants support sustainable river and wetland restoration
projects that restore natural processes, remove ecosystem stressors, increase the resilience of the
ecosystem, support river and wetland habitat, and promote passage of fish and wildlife through dam
and other barrier removal. Support is also provided for urban stream revitalization projects that improve
the inter-connection between water quality, aquatic ecology, physical river structure and land use,
taking into consideration the social, cultural and economic landscape.
Website: http://www.mass.gov/eea/agencies/dfg/der/aquatic-habitat-restoration/river-restoration/
Eligible Applicants: Open to public agencies and (c) (3) certified non-profit organizations, including, but
not limited to state agencies, cities and towns, regional planning agencies, watershed organizations, and
land trusts.
Buzzards Bay Watershed Municipal Mini-grant Program
Agency: Executive Office of Energy and Environmental Affairs (EEA)-Coastal Zone Management (CZM)
Description and Eligible Activities: The Buzzards Bay National Estuary Program offers these grants to assist
interested Buzzards Bay watershed municipalities in the protection of open space, rare and endangered
species habitat, and freshwater and saltwater wetlands, and to help restore tidally restricted salt marshes,
to purchase oil spill containment equipment, to restore fish runs, and to remediate stormwater discharges
threatening water quality. These funds have been made available in accordance with US EPA National
Estuary Program Cooperative Agreements and are part of an ongoing Buzzards Bay Watershed Municipal
Grant Program implemented by the Buzzards Bay National Estuary Program.
Website: www.buzzardsbay.org
Eligible Applicants: Eligible towns include Fall River, Westport, Dartmouth, New Bedford, Acushnet,
Fairhaven, Rochester, Mattapoisett, Marion, Wareham, Middleborough, Carver, Plymouth, Bourne,
Falmouth, and Gosnold. However, specific restoration and protection projects must lie principally within
the Buzzards Bay watershed.
Catalog of Federal Funding Sources for Watershed Protection (searchable database)
Website: https://ofmpub.epa.gov/apex/watershedfunding/f?p=fedfund:l
2.8. References
MORIS (Massachusetts Ocean Resource Information System). 2014. Accessed June 2014.
http://www.mass.gov/eea/agencies/czm/program-areas/mapping-and-data-
management/moris/
USEPA (U.S. Environmental Protection Agency). 2013. Getting in Step: Engaging Stakeholders in Your
Watershed (2nd edition). EPA 841-B-11-001. U.S. Environmental Protection Agency, Office of
Water, Nonpoint Source Control Branch (4503T), Washington, DC.
http://cfpub.epa.gov/npstbx/files/stakeholderguide.pdf.
USEPA (U.S. Environmental Protection Agency). 2014. What is a Watershed? U.S. Environmental
Protection Agency, Washington, DC. Accessed March 2014.
http://water.epa.gov/type/watersheds/whatis.cfm.
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3. Identifying Green Infrastructure Opportunities
This section of the Handbook provides an overview for determining the highest priority sites in a given
municipality. The green infrastructure opportunity evaluation and prioritization process will identify
specific parcel-based locations within the watershed where green infrastructure or green infrastructure
retrofits can be implemented that would provide water quantity and quality benefits in the watershed.
Step 1: Identification of Target Subwatersheds
This section builds on the information gathered in Section 2 (Watershed Assessment) to help
identify target subwatersheds where green infrastructure implementation will be most
effective.
Step 2: Primary Screening of Potential BMP Locations
This section outlines primary screening process, emphasizing publicly owned lands (including
publically-owned parcels and transportation right-of-ways) as creating the greatest opportunity
for green infrastructure.
Step 3: Secondary Screening and Prioritization
Opportunities identified in the primary screening process are prioritized based on their
suitability and potential to serve as effective green infrastructure sites. The prioritization criteria
vary depending on whether the opportunity is located within a public parcel or a transportation
right-of-way. This section also provides example scoring tables for ranking potential sites.
Identifying the best potential locations for green infrastructure implementation can be achieved through
a site-selection and prioritization process. The site screening and prioritization process is a desktop
analysis that systematically evaluates and prioritizes potential sites throughout the watershed. This
screening and prioritization process involves GIS-based analyses using the best available data that
considers landscape characteristics, jurisdictional attributes, water quality needs, and general site
sustainability. The advantage of this prioritization process is the ability to select cost-effective green
infrastructure locations that would provide water quantity and quality benefits to the watershed.
This green infrastructure site selection and prioritization process involves three primary steps:
(1) Identify target subwatersheds where green infrastructure implementation would be most
effective in addressing known priorities and providing water quantity and quality benefits to the
watershed (completed as part of watershed assessment per Section 2).
(2) Perform a primary screening to eliminate sites unsuitable for green infrastructure
implementation on the basis of physical and jurisdictional characteristics.
(3) Perform a secondary screening to prioritize potential sites based on suitability. Prioritization
identifies candidate sites that are ideal for green infrastructure implementation and most
effective in achieving priorities of the watershed.
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The green infrastructure opportunity evaluation and prioritization process will identify specific parcel-
based locations within the watershed where green infrastructure or green infrastructure retrofits can be
implemented that would provide water quantity and quality benefits to the watershed. Parcel-based
green infrastructure sites are opportunities for various types or combinations of green infrastructure
practices described in Section 5, from vegetated filter strips and planter boxes to bioretention areas and
constructed stormwater wetlands. Green infrastructure opportunities in rights-of-way (ROWs) require
the use of transportation layers rather than parcel layers. A right-of-way is a type of easement reserved
for transportation for the purpose of maintenance or expansion of existing services. ROW green
infrastructure opportunities are typically smaller in scale and include bioretention areas, permeable
pavement, or a combination thereof.
The following sections discuss the three steps in identifying parcel-based and ROW green infrastructure
opportunities sites in coastal Massachusetts.
3.1. Identification of Target Subwatersheds
To prioritize green infrastructure site opportunities, it is important to identify watershed priorities or the
watershed goals green infrastructure implementation is intended to achieve. These watershed priorities
or goals narrow the focus of green infrastructure implementation to areas where the impacts of green
infrastructure would be greatest. Target subwatersheds, where green infrastructure implementation will
be the most effective, can be subwatersheds with 303(d)-listed water bodies, with specific amenities or
habitats in need of restoration or preservation, with high land-based pollutant loadings, or with known
pollutant sources (based on the results of the watershed assessment in Section 2).
Coastal Massachusetts hosts dozens of aquatic habitats from sea grass beds to tidal flats to salt marshes
and dunes. These habitats support sensitive species and provide recreational and environmental
benefits such as filtering pollutants, serving as spawning habitat, and buffering against storm damage.
To protect these coastal resources, special habitat and water quality considerations can be used to
identify target subwatersheds. Habitat and water quality priorities specific to the region include bathing
beaches, designated shellfish growing areas (DSGAs), salt marsh restoration sites, seagrass beds,
diadromous habitats, intertidal habitats, and areas of critical environmental concern (ACECs). Geospatial
data that identify water quality, habitat, and coastal priorities that can be used to identify target
subwatersheds specific to the region are presented below:
P Designated Shellfish Growing Areas (DSGAs). A DSGA is an area of potential shellfish habitat.
Compiled by the Department of Fish and Game's Division of Marine Fisheries (DMF), there are
304 DSGAs which have classifications ranging from approved to prohibited areas.
P Salt Marsh Restoration Sites. Developed by the Massachusetts Office of Coastal Zone
Management (MCZM), these sites are located between Salisbury and Gloucester and were
compiled as part of the Parker River/Essex Bay ACEC Project.
P Areas of Critical Environmental Concern (ACECs). Designated by the Secretary of Energy and
Environmental Affairs (EEA), ACECs are coastal and inland areas that receive special recognition
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because of the quality, uniqueness, and significance of their natural and cultural resources.
MCZM and the Department of Conservation and Recreation compiled this data layer.
P7 Seagrass Beds. Seagrass beds are critical wetlands components of shallow marine ecosystems
along the Massachusetts coastline. MassDEP began a program to map the state's Submerged
Aquatic Vegetation (SAV) resources in the early 1990s. Since 1995 the MassDEP Eelgrass
Mapping Project has produced multiple surveys of SAV along the Massachusetts coastline.
P Biodiversity. The Massachusetts Natural Heritage and Endangered Species Program (NHESP)
and The Nature Conservancy's Massachusetts Program developed BioMap2 in 2010 as a
conservation plan to protect the state's biodiversity. BioMap2 is designed to guide strategic
biodiversity conservation in Massachusetts over the next decade by focusing land protection
and stewardship on the areas that are most critical for ensuring the long-term persistence of
rare and other native species and their habitats, exemplary natural communities, and a diversity
of ecosystems.
P Outstanding Resource Waters (ORWs). Designated waters protected under Massachusetts
Surface Water Quality Standards (314 CMR 4.00) because of their "outstanding socioeconomic,
recreational, ecological, and/or aesthetic values."
3.2. Primary Screening of Potential BMP Locations
Because structural BMPs at any scale involve identifying and setting aside land for stormwater
treatment, assessing opportunities on existing, publicly owned lands is especially important. Structural
treatment often can be integrated into parks or playing fields and street rights-of-way (ROWs) or
medians without compromising function, so opportunities for incorporating BMPs in recreation areas,
streets, and other public open spaces are typically prioritized and used as a first step in evaluating
available sites.
P The primary screening process uses GIS screening techniques to identify candidate locations
based on suitability and feasibility for green infrastructure implementation. Primary screening
rules out areas where green infrastructure implementation might be infeasible or costly and
focuses implementation on public parcels as being most cost-effective.
P The two primary factors considered in the primary screening process for parcel-based green
infrastructure opportunities include land ownership and slope. For right-of-way (ROW) green
infrastructure opportunities, road type, local topography, and depth to ground water can
significantly influence the practicality of designing and constructing these features. Table 3-1
summarizes details on the primary screening criteria for both parcel-based and ROW green
infrastructure opportunities.
The purpose of the primary screening process is to provide a base list of sites potentially suitable for
green infrastructure implementation. Prioritization of the remaining candidate sites occurs in the
secondary screening process as the next section describes.
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Table 3-1. Primary screening criteria for parcel-based and ROW green infrastructure opportunities
Primary Screening Criteria
Parcel-Based Opportunities
ROW Opportunities
¦ Parcel Ownership and Zoning/Land Use:
Land costs generally are minimized by using
existing public lands; therefore, most privately
owned parcels are eliminated as potential green
infrastructure sites. In some cases, private
universities and other private lands may be
retained for consideration and should be
considered on a case-by-case basis.
Depending on the available GIS data,
classifications such as zoning, land use, and
parcel ownership can be used to distinguish
public sites from private sites.
¦ Slope: Parcels where the slope exceeds 15
percent should be eliminated in the primary
screening process. Slope can be determined on
the basis of DEMs or other available
topography datasets. In areas where overall
slope ofthe parcel is in question, slope can be
verified through review of aerial imagery.
¦ Road Classification: High traffic volumes and high
speed limits are not favorable road conditions for
siting right-of-way (ROW) green infrastructure.
Freeways, highways, and major roads should be
screened out. Road classification data can be
obtained from Census TIGER road data, if local
road classification data are not available.
¦ Slope: Green infrastructure implementation on
streets with grades greater than 10 percent present
engineering challenges that substantially reduce
the cost-effectiveness ofthe retrofit opportunity.
Road segments with slopes greater than 10
percent should be screened out.
¦ Depth to Ground Water1: Shallow depths to
ground water indicate the potential for ground
water inflow, which will diminish the storage
capacity of green infrastructure practices. Roads in
areas where depth to ground water is less than 10
feet should receive a lower priority.
1 Coastal areas are commonly characterized by shallow ground water depths. In such cases, the "10 feet" rule of thumb may
not apply, and special consideration should be given to green infrastructure BMPs that are favorable for areas with high
water tables (see BMP Matrix, Table 5-1).
3.3. Secondary Screening and Prioritization
After primary screening, the remaining sites are prioritized based on their suitability and potential to
serve as effective green infrastructure sites with anticipated positive downstream impacts. Positive
downstream impacts and overall water quality and quantity benefits vary by watershed. In coastal
Massachusetts, for instance, downstream impacts should support the viability of bathing beaches,
shellfish beds, sensitive salt marsh, and other coastal habitat.
3.3.1. Prioritization Criteria
The secondary screening and prioritization process involves a GIS-based analysis to rank candidate sites
based on various prioritization criteria. Prioritization criteria are different for parcel-based green
infrastructure opportunities and ROW green infrastructure opportunities. Parcel-based green
infrastructure opportunities can also vary in scale. Small-scale parcel-based green infrastructure
opportunities typically consider sites for green infrastructure practices ranging from 500 to 2,000
square feet Large-scale parcel-based green infrastructure opportunities typically consider site for
green infrastructure practices of 0.1 acre and greater and require more available space for
implementation. Prioritization criteria for all parcel-based and ROW green infrastructure opportunities
are summarized in Table 3-2 and discussed in detail following the table. The following section describes
the prioritization methodology using these criteria.
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Table 3-2. Key secondary screening prioritization criteria for parcel-based and ROW green
infrastructure
Parcel-based green infrastructure
(small-and large-scale)
ROW green infrastructure
¦ Public ownership (except in special cases, per Table 3-1)
¦ Proximity to targeted subwatershed
¦ Proximity to environmentally sensitive or protected areas
¦ Infiltration capacity
¦ Parcel size (large-scale)
¦ Impervious parcel area
¦ Percent impervious
¦ Proximity to storm drainage networks
¦ Proximity to contaminated soils
¦ Proximity to existing BMPs
¦ Proximity to parks and schools
¦ Contributing drainage area (large-scale)1
¦ Drainage area percent imperviousness (large-scale)
¦ Known stormwater/MS4 capacity issues
¦ Proximity to targeted
subwatershed
¦ Infiltration capacity
¦ Available width
Note:
1Drainage areas need to be delineated for each potential green infrastructure opportunity. Identification of large-scale green
infrastructure opportunities can still be performed in lieu of drainage area size and percent imperviousness of the drainage
area; however, prioritization would significantly benefit from inclusion of these criteria.
Secondary screening criteria for parcel-based green infrastructure opportunities include:
P Public ownership: Publicly-owned (e.g., city- or town-owned) parcels are most favorable
because they avoid the cost of land acquisition or need for easement establishment and allow
for jurisdictions to have direct control over green infrastructure construction, maintenance, and
monitoring. These public parcels would be favored over other-owned public parcels such as
schools, universities, state facilities, and federal facilities. Certain types of private parcels (e.g.,
private universities) may be suitable and should be investigated on a case-by-case basis.
P Proximity to targeted subwatershed: Parcels within targeted subwatersheds will provide the
greatest effect on water quality and habitat enhancement. Parcels that drain to targeted
subwatersheds can also be prioritized because these locations will result in positive downstream
impacts.
P Proximity to environmentally sensitive or protected areas: For parcels located within an
environmentally sensitive or protected area, significant restrictions can apply, resulting in
construction complexity and elevated costs. Parcels within sensitive or protected areas are
considered low-priority sites; however, areas in close proximity to these sensitive or protected
areas are prioritized as green infrastructure and can treat the runoff before it drains to these
valuable areas.
P Infiltration capacity: Mapped hydrologic soil groups (HSGs) provide an initial estimate for the
infiltration rate and storage capacity of the soils on-site. Sites where mapped HSGs have high
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infiltration rates, and thus are most suitable for infiltration BMPs, receive higher priority. It is
important to note that soil maps are initial estimates and that field investigations would be
necessary to verify soil conditions.
P Parcel Size (large-scale): Parcel size is a useful indicator to determine if sufficient space is
available to implement an appropriately sized green infrastructure. The greater the parcel size,
the greater the opportunity for green infrastructure implementation.
P Impervious parcel area: Parcels representing a larger total impervious area typically generate
more runoff and greater pollutant loads. Green infrastructure implementation on these parcels,
therefore, has the greatest potential to result in water quality and habitat benefits.
P Percent impervious: Parcels with a higher percentage of impervious area relative to the size of
the parcel also typically produce more runoff. These sites are prioritized on the basis of the
greater potential to achieve volume reduction and water quality improvements, relative to their
overall parcel size.
P Proximity to the storm drainage network: Areas in close proximity to the storm drain network
are prioritized as they reduce potential construction costs. Green infrastructure on poor
draining soils requires underdrain systems that tap into existing infrastructure; therefore, siting
green infrastructure opportunities in proximity to the storm drain network can minimize cost
and reduce construction complexity.
P Contaminated sites: Areas near contaminated sites are of lower priority because of the
potential for increased costs and complications during implementation.
P Proximity to existing BMPs: To distribute green infrastructure opportunities effectively
throughout the watershed, areas in close proximity to existing or planned green infrastructure
implementation can be given a lower priority.
P Proximity to parks and schools: Areas closest to parks and schools are prioritized because these
sites provide a greater opportunity for public outreach and education.
P Contributing drainage area (large-scale): Given the size of the drainage area that could be
diverted and treated at each potential large-scale green infrastructure opportunity, sites that
capture and effectively treat runoff from the largest drainage areas are given higher priority.
P Drainage area percent imperviousness (large-scale): Contributing drainage areas with a higher
percentage of imperviousness produce increased runoff relative to the watershed size during
storms. Higher impervious drainage areas are prioritized for greater potential water quality and
habitat improvements.
P Known stormwater/MS4 capacity issues: Areas with known flooding or other issues related to
insufficient storm drain capacity or function should receive a higher priority.
P Municipality preference: In many cases, the local municipality may already have a list of one or
more potential sites considered favorable for green infrastructure consideration based on local
knowledge and any combination of factors listed above.
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Secondary screening criteria for ROW green infrastructure opportunities:
P Proximity to targeted subwatershed: Parcels within targeted subwatersheds will provide the
greatest impact to water quality and habitat enhancement. Parcels that drain to targeted
subwatersheds can also be prioritized as these locations will result in positive downstream
impacts.
P Infiltration capacity: Mapped HSGs provide an initial estimate for the infiltration rate and
storage capacity of the soils on-site. Sites where mapped HSGs have high infiltration rates, and
thus are most suitable for infiltration BMPs, receive higher priority. It is important to note that
soil maps are initial estimates and that field investigations would be necessary to verify soil
conditions.
P Available width: The width of the area between the curb and the sidewalk, often referred to as
the parkway, varies with road type because it accounts for the shoulders, parking lanes, and
sidewalks within ROWs. Standard parkway widths per road types vary across state and
municipal jurisdictions. Parkway widths can also have distinct zones that allow for parkway
edge, furnishings, throughways or walkways, and frontage areas. Green infrastructure
implementation in parkway widths can have varying limitations, but generally the greater the
parkway width, the more opportunity for sizeable green infrastructure implementation.
Parkway width criteria can be adjusted to reflect specific widths in a jurisdiction or county.
3.3.2. Prioritization Methodology (Site Scoring)
Green infrastructure opportunities are prioritized based on the prioritization criteria (Section 3.3.1)
using a scoring methodology. Scores range from 1 to 5, where 5 is the highest score assigned to indicate
higher priority. To emphasize priority based on potential load reduction and cost-effectiveness, scores of
5 are assigned to municipally owned parcels and sites located within target subwatersheds. A parcel or
road segment is assigned a score for each priority criterion and the sum of all scores is the total score.
Parcels or road segments with the highest total scores are priority green infrastructure opportunities.
Scoring thresholds for priority criteria vary for small-scale parcel-based green infrastructure
opportunities, large-scale parcel-based green infrastructure opportunities, and ROW green
infrastructure opportunities. Small-scale parcel-based green infrastructure opportunities have specific
parcel size, imperviousness, and impervious parcel area criteria (Table 3-3). Large-scale parcel-based
green infrastructure opportunities have specific parcel size, impervious parcel area, contributing
drainage area, and drainage area percent imperviousness (Table 3-4). ROW green infrastructure
opportunities have specific parkway width criteria (Table 3-5).
The secondary screening and prioritization process ranks candidate green infrastructure opportunities
based on their total scores. The highest total score represents sites that are most feasible, cost-effective,
and offer the greatest opportunity to provide water quality and habitat benefit. Beyond this desktop
prioritization analysis, sites are subject to field investigations to verify site conditions, evaluate potential
multi-benefit uses, and determine permitting and construction needs and costs.
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Table 3-3. Prioritization criteria for small-scale green infrastructure opportunities
Factor
Score (5 = Highest Priority, 1 = Lowest Priority)
5
4
3
2
1
Public ownership
City- or town-owned
public parcels and
ROWs
Other-owned public
parcels (schools and
universities, state
and federal facilities,
utilities, etc.) and
certain private
parcels.
Proximity to target
subwatershed1
Within target
subwatershed
Within
subwatershed
draining to
target
watershed
Proximity to
environmentally sensitive
or protected areas (feet)2
< 100, but not within
a sensitive or
protected area
Infiltration Capacity (HSG
soil type)
A, B
C
D
Impervious area (acres)
> 1
> 0.5
> 0.25
> 0.1
% Imperviousness
60%-80%
80%-90%
< 50%
Proximity to storm drainage
network (feet)
< 100
< 300
> 300
Proximity to contaminated
soils (feet)
> 100
< 100
Existing/proposed BMP
site proximity (miles)
> 5
4-5
3-4
2-3
<2
Proximity to parks and
schools (feet)
< 1,000
> 1,000
MS4 capacity issues
Known flooding
areas
No known
issues
Notes:
1 Parcels that do not drain to or are not within a target subwatershed receive a score of zero.
2 Parcels that are directly within or greater than 100 feet from an environmentally sensitive or protected area receive a score of
zero.
Table 3-4. Prioritization criteria for large-scale green infrastructure opportunities
Factor
Score (5 = Highest Priority, 1 = Lowest Priority)
5
4
3
2
1
Public ownership
City- or town-owned
public parcels and
ROWs.
Other-owned public
parcels (schools and
universities, state and
federal facilities, utilities,
etc.)
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Factor
Score (5 = Highest Priority, 1 = Lowest Priority)
5
4
3
2
1
Proximity to target
subwatershed1
Within target
subwatershed
Within
subwatershed
draining to
target
watershed
Proximity to
environmentally
sensitive or protected
areas (feet)2
< 100, but not
within a sensitive or
protected area
Infiltration Capacity
(HSG soil type)
A, B
C
D
Parcel size (acres)
> 200
150-200
100-
150
1-100
< 1
% Imperviousness
< 30%
30%-40%
> 40%
Proximity to storm
drainage network (feet)
< 100
< 300
> 300
Proximity to
contaminated soils (feet)
> 100
< 100
Existing/proposed BMP
Site Proximity (miles)
> 5
4-5
3-4
2-3
<2
Proximity to parks and
schools (feet)
<
1,000
> 1,000
Contributing drainage
area
> 250
> 150
> 100
> 50
< 50
Drainage area percent
imperviousness
> 70%
> 60%
> 50%
> 40%
< 40%
MS4 capacity issues
Known flooding
areas
No known
issues
Municipal Preference
Score based on municipal evaluation
Notes:
1 Parcels that do not drain to or are not within a target subwatershed receive a score of zero.
2 Parcels that are directly within or greater than 100 feet from an environmentally sensitive or protected area receive a score of
zero.
Table 3-5. Prioritization criteria for ROW green infrastructure opportunities
Factor
Score (5 = Highest Priority, 1 = Lowest Priority)
5
4
3
2
1
Proximity to target
subwatershed1
Within target
subwatershed
Within subwatershed
draining to target
watershed
Infiltration Capacity
(HSG soil type)
A, B
C
D
Parkway width (feet)
> 10
5-10
< 5
Notes:
1 Parcels that do not drain to or are not within a target subwatershed receive a score of zero.
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4. Site Assessment, Planning, and Design
This section of the Handbook contains green infrastructure planning practices, including land use
planning, site assessment, retrofit considerations, and site design examples. It also includes an overview
of conceptual design plans. Once the watershed assessment presented in Chapter 2 and potential sites
have been identified and prioritized using the guidance in Chapter 3, guidance provided in chapter 4
presents concepts for assessment and planning at the site scale to incorporate green infrastructure
concepts and practices into retrofit, redevelopment, and new development projects.
Part 1: Site Planning and Design Principles
This section describes the fundamental planning concepts of green infrastructure practices as
well as typical constraints and limitations when implementing green infrastructure. It also
provides an overview of the site assessment process. An accompanying example conceptual site
design is presented in Appendix B.
Part 2: Preparing Conceptual Design Plans
This section builds on information presented in Sections 2 and 3. Once sites have been
identified, further effectiveness assessment should be performed for the top sites to develop an
optimized conceptual design plan. This section provides an overview of preliminary geotechnical
investigation, modeling and optimization, and preparing a conceptual design report.
Green infrastructure practices use natural features to slow and filter stormwater runoff. Project
characteristics will define which green infrastructure BMPs are applicable. When determining the
appropriate green infrastructure requirements, project managers must consider characteristics such as
site location, existing topography and soils, and planning elements. These characteristics and their
impacts on design are important because green infrastructure BMPs are permanent features that can
affect other project elements; therefore, it is critical to conduct thorough site assessments to avoid the
need for redesign later. Incorporating green infrastructure early in the site design stage, whether new
construction or redevelopment, could reduce the need for and cost of traditional drainage infrastructure
by reducing the amount of stormwater to be conveyed off-site.
4.1. Site Planning and Design Principles
The following are the fundamental planning concepts of green infrastructure practices (Prince George's
County 1999):
1. Using hydrology as the integrating framework
Integrating hydrology during site planning begins with identifying sensitive areas, including streams,
floodplains, wetlands, steep slopes, highly permeable soils, and woodland conservation zones. For
redevelopment or retrofits this could involve evaluating existing soils, the level of disturbance of
those soils, and protecting any existing natural features. Through that process, the development
envelope—the total site area that affects the hydrology—is defined. This effort must include
evaluating both upstream and downstream flow paths and drainage areas that may be affected. For
redevelopment or retrofits this process could involve locating the existing storm drainage network.
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The functional value of natural wetlands and their value to ecosystems and watersheds where
they are located has been well documented. They serve to store rainfall, reduce peak runoff
during storms, and provide habitat for a diverse variety of plant and animal species. Wetlands
also improve water quality, reduce the effects of erosion by stabilizing soils, dampen the effects
of wave action in shoreline areas, and help sustain surrounding aquatic environments (Dennison
et al., 1993, Mitsch and Gosselink, 1986). Natural wetlands should be identified and protected
within the watershed and at the site scale. The Federal Clean Water Act helps to protect the
functions and values of Waters of the U.S. (including many natural wetlands). Section 404 of the
Clean Water Act regulates the discharge of dredged or fill material, while Section 402 (National
Pollutant Discharge Elimination System) regulates the discharge of pollutants into these
resources. CWA Section 402 authority addresses discharges of industrial and construction site
stormwater, municipal separate storm sewer systems, and stormwater that contributes to a
violation of water quality standards. States can play a role in implementing Clean Water Act
programs as well as implement their own wetlands protection programs.
Constructed stormwater wetlands are engineered to mimic the conditions and treatment
functions found in natural wetlands. For further information on constructed stormwater
wetlands, please refer to Section 5.3.3.
2. Use distributed practices
Distributed control of stormwater throughout the site can be accomplished by applying small -
scale green infrastructure BMPs throughout the site (e.g., bioretention in landscaped areas,
permeable pavement parking stalls). This might include preserving areas that are naturally
suited to stormwater infiltration and require little or no engineering. Such small-scale, green
infrastructure BMPs foster opportunities to maintain the natural hydrology even in highly
impervious areas, provide a much greater range of control practices, allow control practices to
be integrated into landscape design and natural
features of the site, reduce site development
and long-term maintenance costs, and provide
redundancy if one technique fails.
3. Controlling stormwater at the source
Undeveloped sites possess natural stormwater
mitigation functions such as interception,
depression storage, and infiltration. Those
hydrologic functions should be restored or
designed as close as possible to the disturbed
area (e.g., parking lot, building) to minimize and
then mitigate the hydrologic effects of site
development. Bioretention cells, as shown in
Figure 4-1, are an example green infrastructure
practice that can serve this function.
Source: Jo Ann Muramoto
Figure 4-1. Bioretention cell (Cape Cod).
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4, Using simple, non-engineered methods
Methods employing existing soils, native
vegetation, and natural drainage features can
be integrated into green infrastructure
designs. These designs integrate natural
elements into stormwater management and
limit structural material including concrete
troughs and vault systems. Examples include
bioretention cells, curb pop-outs, and
depressed medians, as shown in Figure 4-2.
5. Creating a multifunctional landscape
Urban landscape features such as streets,
sidewalks, parkways, and green spaces can be
designed to be multifunctional by
incorporating detention, retention, and
filtration functions such as curb pop-outs, as
shown in Figure 4-2.
Siting and selecting appropriate green infrastructure
practices is an iterative process that requires
comprehensive site planning with careful consideration of all nine steps detailed in Figure 4-3. A site
planner, landscape architect, or engineer can follow these steps in developing final site plans. The steps
are arranged on the basis of the anticipated design phases of site assessment, preliminary design, and final
design (Phases I, II, and III, respectively). Each step is an integral part of developing a site plan that mimics
natural conditions; however, some of the steps may not apply in a redevelopment or retrofit situation.
A thorough site assessment is needed initially to identify the development envelope and minimize site
alterations. The primary objective of the site assessment process is to identify limitations and development
opportunities specific to green infrastructure. For example, development opportunities include available
space, use of ROW as appropriate, and maximizing opportunities where properly infiltrating soils exist.
Constraints or limitations that need to be factored into site planning when implementing green
infrastructure practices include:
Slow-infiltrating soils (typically clays)
Soil contamination
Steep slopes
Adjacent foundations of structures
P Wells
Shallow bedrock
High seasonal water table
Coastal flooding and salinity
Source: Tetra Tech
Figure 4-2. Example of a bioretention curb
pop-out (Portland, Oregon).
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For both new development and redevelopment, in the preliminary site plan, the development envelope
(construction limits) is delineated. Applicable zoning, land use, subdivision, local road design regulations,
and other local requirements should be identified to the extent applicable at this stage (Step 1 in Figure
4-3). To make the best and most optimal use of green infrastructure techniques on a site, a
comprehensive site assessment must be completed that includes an evaluation of existing site
topography, soils, vegetation, and hydrology including surface water and ground water features. High-
quality ecological resources (e.g., wildlife habitat, mature trees) should also be identified for
conservation or protection. Coastal flooding and salinity can have an impact on the performance of the
green infrastructure practice, particularly vegetated practices. StormSmart Coasts
(www.mass.gov/eea/agencies/czm/program-areas/stormsmart-coasts/) provides information regarding
coastal erosion and flooding that should be considered in the site evaluation including a list of salt
tolerant coastal landscaping. With such considerations, the site assessment phase provides the
foundation for consideration of and proper planning around existing natural features and to retain or
mimic the site's natural hydrologic functions (Steps 2 and 3).
Phase II, site planning, covers Steps 4-7. Defining preexisting and site-specific drainage patterns is
essential for determining potential locations of green infrastructure BMPs (Step 4). For retrofit
scenarios, identifying the drainage patterns may include activities such as locating the downspouts from
a building, locating existing catch basins, and identifying the direction of flow in a roadway. Once natural
and existing hydrologic features are identified and slated to be preserved, areas can be designated for
clearing, grading, structures, and infrastructure (Step 5). After the preliminary site configuration has
been determined in light of the existing features, impervious area site plans (buildings, roadways,
parking lots, and sidewalks) can be evaluated for opportunities to minimize or reduce total impervious
area in the site planning phase (Step 6). The specific types of green infrastructure BMPs are determined
next (Step 7; e.g., a bioretention cell versus porous pavement for stormwater storage and infiltration).
Green infrastructure concepts and practices can be effectively implemented within the right-of-way to
reduce and treat runoff. Street layouts often can be designed to reduce the extent of paved areas, and
street widths can be narrowed to decrease the total impervious area as long as applicable street design
criteria are satisfied. Specific examples of alternative transportation options include narrow paved travel
lanes, consolidated travel lanes, and increased green parking areas. Green infrastructure practices can be
incorporated into horizontal deflectors (chicanes), intersection pop-outs, parking lanes, and bike lanes.
This approach is often referred to as a green street or complete street (USEPA 2008, City of Boston 2013).
In Phase III, final green infrastructure BMP footprints and sizes are estimated (Step 8). An iterative
process working between Steps 4 and 7 can help determine the final site layout for completing the
design process (Step 9). These steps are presented in more detail in Appendix B. When Step 6 is
complete, detailed determination of stormwater management practice selection and design that
considers BMP construction, and operation and maintenance (Section 5) should be made to complete
Phase III and the final site design process. Steps 8 and 9 assist in determining BMP sizing and final
design. Please refer to Appendix B for a complete example conceptual site design.
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Step 1: Identify Regulatory Needs
¦ Identify applicable zoning, land use, subdivision and other regulations
¦ Identify targeted pollutants and pollutants of concern
¦ Identify setbacks, easements, and utilities, and possible conflicts (e.g., traffic, flood control)
Step 2: Conduct Hydrologic and Geotechnical Survey
¦ Identify natural areas to be conserved or restored
¦ Conduct geotechnical survey including drainage characteristics,
hydrologic flow paths, and soil infiltration rates
Step 3: Protect Key Hydrologic Areas
¦ Protect areas of natural hydrologic function
¦ Protect possible areas for infiltration
Step 4: Use Drainage and Hydrology as a Design Element
¦ Identify the spatial layout of the site using hydrologic flow
paths as a feature
¦ Determine approximate conveyance and BMP locations
Step 5: Establish Clearing and Grading Limits
¦ Define the limits of clearing and grading
¦ Minimize disturbance to areas outside the limits of
clearing and grading
Step 6: Reduce/Minimize Total and Effective Impervious Area
¦ Evaluate conceptual design to reduce impervious surfaces
¦ Investigate potential for impervious area disconnection
Step 7: Determine Green Infrastructure BMPs
¦ Determine potential BMPs according to hydrologic and pollutant
removal process needs and cost estimates (see Chapter 5)
¦ Repeat Steps 4 through 7 as necessary to ensure that all
stormwater management requirements and project goals are met
Iterative design
process may require
revaluation of Steps 4-7
Step 8: Determine Approximate Size of Green Infrastructure BMP
¦ Determine the approximate BMP size using BMP sizing tool (Chapter 5 and the
Massachusetts Stormwater Handbook)
Step 9: Green Infrastructure Final Design
¦ Integrate conventional stormwater management needs
¦ Verify geotechnical and drainage requirements have been met
¦ Complete BMP Design (Chapter 5 and the Massachusetts Stormwater Handbook)
¦ Complete site plans
Construction Phase
Source: Tetra Tech
Figure 4-3. Steps to develop a green infrastructure-based site plan.
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4.2. Preparing Conceptual Design Plans
Preparing conceptual designs often begins with a site assessment and identification process similar to
that presented in Section 2 and Section 3. Once sites have been identified, further effectiveness
assessment should be performed for the top sites to develop an optimized conceptual design plan that
includes a site layout to identify the type, size, and location of potential green infrastructure practices
and to quantify, where possible, the potential effect of BMP implementation. The following sections
present a potential approach to developing conceptual design plans.
4.2.1. Preliminary Geotechnical Investigation
Because mimicking natural conditions is a fundamental concept of green infrastructure, an evaluation of
the local subsurface conditions beneath the potential sites should be performed as early in the design
process as possible to determine the feasibility and impact of infiltration. This task should involve a
review of readily available information, including published geologic literature and maps, topographic
maps, aerial photographs, and geotechnical investigations performed at nearby locations. The
preliminary investigation should include, at a minimum, an estimate of the feasibility of infiltrating.
Where possible, the following parameters should be determined or verified though field investigations:
P Infiltration rate of subgrade soils (ASTM D 3385 Standard Test Method for Infiltration Rate of
Field Soils Using Double Ring Infiltrometer, or a comparable method)
P Depth and texture of subsoils
P Depth to the seasonally high ground water table
P Structural capacity of soils
P Presence of expansive clay minerals
P Presence of compacted or restrictive layers
P Underlying geology
P Proximity to steep slopes
P Proximity to structural foundations, roadway subgrades, utilities, and other infrastructure
P Proximity to water supply wells
P Proximity to septic drain fields
Prior to design, further geotechnical investigations should be performed to verify estimates to ensure
viability of the project.
4.2.2. Modeling and Optimization of BMP Placement for Green Infrastructure Sites
Developing optimal conceptual designs for green infrastructure projects can be complex, requiring
consideration of multiple BMPs with multiple configurations and performance standards. The process
can be simplified by using a stormwater model and an optimization algorithm to consider all the design
alternatives. Modeling and optimization tools can be used to determine the optimal size and
combination of BMPs to maximize water quality and quantity benefits. Such tools allow the ability to
evaluate all feasible and economical design options to meet the water quantity and water quality goals
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of the project based upon all known design constraints (e.g., infiltration capacity, topography, utilities,
and infrastructure). The output from such a tool can be the optimized conceptual site layouts that
identify the type, size, and location of potential BMPs at each site. Tools that can be used to optimize
the site layout and evaluate impacts to water quality and quantity include EPA's System for Urban
Stormwater Treatment and Analysis INtegration (SUSTAIN), EPA's Stormwater Management Model
(SWMM), i-Tree (USDA Forest Service), EPA's Hydrological Simulation Program - FORTRAN (HSPF),
RECARGA (University of Wisconsin-Madison), BMP-DSS (Prince George's County, Maryland), EPA's
Stormwater Calculator, and others.
4.2.3. EPA Stormwater Calculator
The National Stormwater Calculator is an example of a simple to use tool for computing small site
hydrology for a single site or location. The tool estimates the amount of stormwater runoff generated
from a site under different development and control scenarios over a long term period of historical
rainfall. The analysis takes into account local soil conditions, slope, land cover and meteorology.
Different types of green infrastructure practices can be employed to help capture and retain rainfall on-
site.
The calculator's primary focus is informing site developers and property owners on how well they can
meet a desired stormwater retention target. It can be used to answer questions such as the following:
P What is the largest daily rainfall amount that can be captured by a site in either its
predevelopment, current, or post-development condition?
P To what degree will storms of different magnitudes be captured on site?
P What mix of LID controls can be deployed to meet a given stormwater retention target?
The calculator seamlessly accesses several national databases to provide local soil and meteorological
data for a site. The user supplies land cover information that reflects the state of development they wish
to analyze and selects a mix of LID controls to be applied. After this information is provided, the site's
hydrologic response to a long-term record of historical hourly precipitation is computed. This allows a
full range of meteorological conditions to be analyzed, rather than just a single design storm event. The
resulting time series of rainfall and runoff are aggregated into daily amounts that are then used to
report various runoff and retention statistics.
The calculator is most appropriate for performing screening level analysis of small footprint sites up to
several dozen acres in size with uniform soil conditions. The hydrological processes simulated by the
calculator include evaporation of rainfall captured on vegetative surfaces or in surface depressions,
infiltration losses into the soil, and overland surface flow. No attempt is made to further account for the
fate of infiltrated water that might eventually transpire through vegetation or re-emerge as surface
water in drainage channels or streams (USEPA 2013).
4.2.4. Stormwater Management Optimization Tool
An example of an optimization tool is the U.S. Environmental Protection Agency (USEPA) Stormwater
Management Optimization Tool (the Opti-Tool) is an Excel-based tool designed for improved
stormwater management decision-making. The Opti-Tool BMP simulation and optimization algorithms
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are from the U.S. EPA System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN)
model. The Opti-Tool provides a graphic user interface (GUI) for municipal engineers to set up green
infrastructure practice site layouts, optimize the size and configuration of green infrastructure practices,
review optimization results, and access background information for green infrastructure practice
performance simulation, optimization, BMP and operation and maintenance. With retention of all
essential SUSTAIN capabilities through an Excel environment, the Opti-Tool offers a user-friendly
alternative that does not rely on the ArcGIS platform. The main Opti-Tool window is shown in Figure 4-4
lZ| OplTool.WterU7.tr«mpar«nt O dim Microsoft Eictl
Specify
Watershed Information
BMP & Stream Network Sketch Design
1. Load Wairr>h«i Map |
i J
3. Land l« information
4. Pollutant Definitions
Sketch ami Model Setup
Step 5 Add Subwatershed/Junctions
Step 7 Add Stream/Conduits
9. Creat Fit# and Run
UnctionO
STRM2
4 unet«KT^ < *J
© STRM3
s
— p
—g
~W\
Editing Tool and Links
Figure 4-4. Example watershed simulation setup in Opti-Tool with two subbasin and two BMPs.
The Opti-Tool is developed with default parameters specified for USEPA Region I. Long-term runoff time
series from various hydrologic response units (HRUs) in the region are provided as default time series.
Green infrastructure practice water quality parameters were calibrated using observed data from the
University of New Hampshire Stormwater Center (UNHSC). It is expected that with these default
parameters the Opti-Tool will help maintain consistency across the region when assessing and reporting
the effectiveness of various green infrastructure practices. Green infrastructure practices embedded
within the Opti-Tool include biofiltration, dry ponds, grass swale, gravel wetland, infiltration basins,
infiltration trenches, and permeable pavement. Green infrastructure representations have been
calibrated to report effectiveness for TSS, TP, and Zn removal, all using data from the UNHSC. Efforts are
also under way to introduce TN into the water quality representation of the Opti-Tool.
With a flexible and generic structure, the Opti-Tool can be used for many evaluation scenarios. A user
may set up a model in the Opti-Tool to represent existing conditions in a watershed, regardless of
whether BMPs exist in the watershed or not. Similarly, the Opti-Tool can be used to represent post-
development watershed land use conditions without structural practice, in order to quantify the
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hydrologic and water quality changes as a result of the development. On the basis of the post-
development land use, a user may incorporate green infrastructure practices based on site conditions
and then creates an optimization setup for the Opti-Tool to search for the most cost-effective green
infrastructure practice configuration for the watershed. Lastly, the user may also use the Opti-Tool to
calibrate a certain green infrastructure practice using locally observed data to replace the default water
quality parameters provided in the tool. All of these are designed to provide a flexible and yet consistent
platform for stormwater practitioners in the region. An example window for checking the Opti-Tool
optimization output is shown in Figure 4-5.
fXI OptTool_latestl7_transparent_YX.xlsm - Microsoft Excel
Cost-Effectiveness Curve
$80 -|
$70 -
$60
$50
$40
$30
$20
$10
$0
Go Back to Watershed Sketch
~ AllSolutions ASelected Best Solution
C:\OptiT ool \Output
Best Solution
Reduction(%) Total Cost (Million S)
j 50 0% I
0%
30% 40% 50%
% Reduction
TP Annual Average Load
Decision Variables
9_Length
10_Length
11_Length
12_Length
13_Length
14_Length
15_Length
16_Length
41_Length
42_Length
43_Length
44_Length
45_Length
46_Length
47_Length
48_Length
49_Length
50_Length
51_Length
52_Length
53_Length
54_Length
55_Length
56_Length
57_Length
58_Length
59_Length
60 I
15.86
Values (ft)
8546
10848
425
2797
13894
4446
7352
4746
928
366
1197
992
2052
0
426
0
868
13244
628
3996
8684
17363
55472
480
1936
2061
58
9126
60 Length
Figure 4-5. Example Opti-Tool output window for checking of optimization results.
All of these are designed to provide a flexible and yet consistent platform for stormwater practitioners
in the region.
4.2.5. Conceptual Design Report
All analysis performed in the previous sections should be reviewed and incorporated into a full
conceptual design. Conceptual design reports should include, at a minimum, a discussion for each of the
following:
Project Description: An overview of the proposed location, recommended BMP types or green
infrastructure improvements, and BMP configurations should be included.
Drainage Area Limits: The drainage area for each project should be characterized providing relevant
design information including location, size, percent impervious, priority pollutants, watershed
impairments, and regulatory requirements.
Screening of Soils and Infiltration Rates: A screening of the local subsurface conditions at each site
should be performed to determine the feasibility of stormwater infiltration. Readily available
information, including published geologic literature and maps, topographic maps, aerial photographs,
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and geotechnical investigations performed at nearby locations should be reviewed and presented.
Based on information available, the feasibility of infiltrating stormwater at each site should be
considered and reported. However, prior to design, it should be necessary to perform geotechnical
investigations to verify estimates to ensure viability of the project.
Performance Specifications: Details required for designing the recommended BMPs or LID
improvements should be provided including recommended BMP type, site configuration, BMP
configuration, and design recommendations for BMP components to estimate the effectiveness of the
proposed green infrastructure design.
Concept Plan/Drawings: Conceptual drawings should include the approximate location and size of the
recommended BMP including details of BMP components and configuration.
Architectural Schematic Designs: One rendering per project is recommended to illustrate how the
proposed BMPs would be integrated into the site. The illustrations should indicate appropriate
landscaping on the surface and show how the BMPs are designed to function below the surface. The
renderings can be useful for presentations as part of the public outreach and encouragement activities.
Cost Estimate: A preliminary planning-level cost estimate for the full design and construction of the
recommended BMP should be included to assist in planning efforts.
Operation and Maintenance Requirements: Anticipated operation and maintenance requirements
based on the type, location, and configuration of the recommended BMP. Any anticipated operation
and maintenance concerns should be addressed. (BMP Operation and Maintenance is detailed in
Appendix C.)
Calculations: All assumptions and calculations used in developing the conceptual designs should be
included in the report.
Management Questions: A discussion of key management questions that could be addressed through
implementation of the conceptual design should be included in the report.
Plant Selection: Development of a plant palette with specific planting plans for the potential projects
should be included in the conceptual designs where appropriate. Choices for appropriate low water use
noninvasive plant material should be included. The impacts of the root depth and required plant spacing
of the recommended plant palettes should be considered in the development of the performance
standards.
4.2.6. Conceptual Plan
The more detail that is included in the conceptual design report, the more they will serve as effective
planning tools for a municipality. Providing details on BMP effectiveness, potential impacts to water
quality and quantity, and approximate costs provide greater value in budgeting for future
implementation projects to ensure reduction of runoff volumes and pollutant loading through the use of
green infrastructure concepts.
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4.3. References
MassDEP (Massachusetts Department of Environmental Protection). 1997. Massachusetts Stormwater
Handbook. Revised February 2008.
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-
handbook.html
Prince George's County. 1999. Low Impact Development Design Strategies: An Integrated Approach.
EPA-841-B-00-003. Prepared for the U.S. Environmental Protection Agency, Washington, DC, by
Prince George's County, MD, Department of Environmental Resources, Programs and Planning
Division, http://water.epa.gov/polwaste/green/upload/lidnatl.pdf
City of Boston. 2013. Boston Complete Streets.
http://bostoncompletestreets.org/pdf/2013/BCS_Guidelines.pdf
USEPA (U.S. Environmental Protection Agency). 2008. Managing Wet Weather with Green
Infrastructure, Municipal Handbook, Green Streets. EPA-833-F-08-009.
http://water.epa.gov/infrastructure/greeninfrastructure/upload/gi_munichandbook_green_stre
ets.pdf
USEPA (U.S. Environmental Protection Agency). 2013. National Stormwater Calculator User's Guide.
EPA/600/R-13/085. http://nepis.epa.gov/Adobe/PDF/P100GQQX.pdf
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5. Green Infrastructure Practices
This section of the Handbook provides a brief discussion of green infrastructure practices with a BMP
Selection Matrix to aid in the selection of the appropriate green infrastructure practice.
Part 1: Selecting Green Infrastructure BMPs (BMP Selection Matrix)
This section provides a detailed tool (Table 5-1) to aid project designers in considering and selecting
green infrastructure practices according to site characteristics and constraints. Cost estimates are
provided for planning purposes.
Part 2: BMP Sizing
This section provides an introduction to sizing green infrastructure practices, referring readers to the
Massachusetts Stormwater Handbook for BMP sizing standards.
Part 3: Common Green Infrastructure Practices
This section gives an overview of the function and treatment mechanisms of green infrastructure, and
provides detailed descriptions of many of the most commonly used practices. Each BMP description
includes a summary of pollutant removal mechanisms, BMP unit components, BMP-specific site
considerations, and more.
Part 4: BMP Construction and Post-Construction Issues
This section provides detailed information on considerations for BMP construction oversight and post-
construction inspection to ensure successful BMP execution and performance. BMP operation and
maintenance requirements are outlined in Appendix C.
Many of the design concepts discussed in Section 4 are useful to establish a foundation and framework
for implementing a comprehensive green infrastructure strategy. Thoughtful land use and site-specific
planning to minimize runoff can considerably decrease the size (and cost) of structural practices
required to meet regulatory requirements or minimize water quality impacts. Once a site's configuration
is optimized to reduce stormwater and pollutant sources, runoff from the remaining impervious surfaces
should be intercepted and treated by structural BMP practices that use one or more of three basic
mechanisms: infiltration, retention/detention, and biofiltration.
Each type of development, and the unique subwatershed in which it is located, present site-specific
challenges that make certain green infrastructure practices appropriate for some types of development
but not for others. For example, permeable pavement might be an effective and appropriate solution for
a low-rise office building; however, in a high-rise residential or office building with underground parking
and virtually no undeveloped areas, permeable pavement would not be an effective or appropriate
solution. In addition, downstream conditions on neighboring properties, manufactured slopes, the
location of structures and utilities, and other design aspects of a project can present unique challenges
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for designers and engineers, making what are otherwise effective green infrastructure solutions
inappropriate for the specific site.
5.1. Selecting Green Infrastructure BMPs (BMP Selection Matrix)
Table 5-1 is a tool to help project designers consider and select green infrastructure practices according
to site characteristics and constraints. Existing or expected site characteristics can be used to determine
individual practices or a suite of practices that might be appropriate in site design. In addition, relative
cost considerations can help project designers select specific BMPs, particularly between two or more BMPs
that achieve the project's goal and meet permit compliance requirements. Therefore, the table lists
dollar signs as qualitative costs for a relative comparison between types of BMPs rather than actual
values.
Estimated costs in this table cover all components of construction and operation and maintenance for
various-sized projects, but do not cover other conveyance needs that might be applicable. Cost
estimates are based on the design standards recommended in Volume 2, Chapter 2 of the
Massachusetts Stormwater Handbook (MassDEP 1997), and can vary widely by the necessary
configuration of the BMP and site constraints. These cost numbers are estimates and intended for
planning purposes only. The project manager must refine these numbers throughout the phases of
design to prepare a more accurate project construction estimate for bidding purposes. Cost estimates,
particularly the maintenance costs, do not account for cost savings that result from using integrated
practices (e.g., integrating bioretention areas into landscaping where the routine maintenance could be
included in the budget for typical landscape maintenance). Including various sizes of projects in the
maintenance costs attempts to include those costs in which an economy of scale has been observed.
The sizes selected for this analysis were as follows:
P Large BMP system = 4,000 square feet
P Medium BMP system = 2,000 square feet
P Small BMP system = 500 square feet
These categories are based on typically sized BMPs. The BMP system can include the application of
multiple BMPs implemented in a treatment train.
P Once individual or groups of BMPs have been selected using this matrix, consult Volume 2,
Chapter 2 of the Massachusetts Stormwater Handbook (MassDEP 1997) to develop detailed
designs.
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Table 5-1. BMP selection matrix (Addapted from MassDEP 1997)
Attribute
Pretreatment
Treatment
Conveyance
Other
Vegetated Filter
Strip
Bioretention3
Constructed
Stormwater Wetland
Tree Box Filter
Sand filter
Grassed Swale
Water Quality Swale
Cisterns/rain barrels
Vegetated (Green) Roof
Permeable Pavementb
(no UD)
(UD)
(no UD)
(UD)
(no UD)
(UD)
(no UD)
(UD)
Maximum allowable contributing
drainage area (acres)
< 1
< 5
>109
< 1
< 10
<2
<2
Rooftop
Rooftop (Self Treating
Area)
Self-Treating: No
Run-on
Self-Retaining:
Contributing run-on
drainage area to
permeable pavement
area ratio must be
less 2:1.
Soil infiltration rate (inches/hour)
N/A
> 0.5
< 0.5
N/A
> 0.5
< 0.5
N/A
> 0.5
< 0.5
Rooftop (Self Treating
Area)
N/A
> 0.5
< 0.5
Water table separation (feet)
>2
> 10
>2
At or below
permanent pool
elevation
N/A
> 10
>2
> 2
> 10
>2
N/A
N/A
> 10
>2
Depth to bedrock (feet)
>2
> 10
>2
At or below
permanent pool
elevation
N/A
> 10
N/A
>2
> 10
>2
N/A
> 10
>2
IMP slope
2-6%
< 0.5%
< 5%
< 0.5%
< 6%
<4%
<4%
N/A
< 45°
<4%
Pollutant
removal
Sediments
High
High
High
High
High
Medium
High
Pollutant removal
provided by
downstream IMP.
Refer to specific IMP
for removal efficiency
(although stormwater
volume reduction can
reduce total pollutant
loads if rainwater is
harvested and reused).
Pollutant removal of
green roofs generally
occur through
stormwater volume
reduction.
High
Nutrients
Low
Medium
Medium
Medium
Low
Low
Medium
Low
Trash
High
High
High
High
High
High
High
High
Metals
Medium
High
High
High
High
Medium
High
High
Bacteria
Low
High
High
High
High
Low
High
Medium
Oil & grease
Medium
High
High
High
High
Medium
High
Medium
Organics
Medium
High
High
High
High
Medium
High
Low
Pesticides
Medium
High
High
High
High
Medium
High
Medium
Runoff volume reduction
Low
High
Medium
None
Low
Medium
Low
Low
High
Medium
High
High
Medium
Peak flow control
Low
Medium
High
Low
Low
Low
Medium
Medium
Medium
Medium
Ground water recharge
Low
High
Low
None
N/A
Medium
Low
Low
High
Low
Medium
N/A
Medium
Low
Setbacks
(feet)
Structures
> 10
> 10
> 10
> 10
> 5
N/A
> 10
Steep slopes
> 50
> 50
> 50
> 50
> 50
N/A
> 50
Costs®
Construction
$
$-$$
$
$$
$ -$$
$
$-$$
$ -$$
$$$
\p\p - \p\p\p
O&M (small)
$$
\p\p - \p\p\p
$-$$
$$
\p\p - \p\p\p
$$
\p\p - \p\p\p
$$
$$
\p\p - \p\p\p
O&M (medium)
$
$ - $$9
$-$$
$-$$
$$
$ -$$
$-$$'
$-$$
$$
$$
O&M (large)
$
$ - $$9
$-$$
$-$$
$$
$ -$$
$-$$'
$-$$
$$
$-$$
Notes: UD = Underdrain, IMP = Integrated Management Practice, O&M = Operation and maintenance;a If lined, see planter box column;b If lined, see sand filter with underdrain column;c Separation depth from bottom of IMP to water table;d For tank outlet and overflow;e Costs are relative,
can be variable project to project, and are generalized;f Based on necessary regular landscape maintenance already required;g Minimum of 25-acre drainage area required for shallow marsh and basin/wetland systems.
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5.2. BMP Sizing
Green infrastructure BMPs are typically sized to manage runoff from frequent smaller storm events (most
often in the range of 1 to 2 inches of rainfall over 24 hours). The size of a BMP should be established using
the characterization of the drainage area and local hydrology. BMPs should be designed by applying either
volume- or flow-based design criteria. For further details regarding BMP sizing standards, refer to Volume
1 Chapter 1 and Volume 3 of the Massachusetts Stormwater Handbook (MassDEP 1997).
5.3. Common Green Infrastructure Practices
Regardless of their name, all green infrastructure practices are designed to manage stormwater by
mimicking natural processes and predevelopment hydrologic patterns. Infiltration, evapotranspiration,
filtration, retention/detention, reuse, etc., are one or more of the processes used by green infrastructure
practices. By understanding the different functions inherent to each BMP, designers can select practices to
target specific pollutant(s) of concern, which is an important consideration within impaired watersheds.
Although watershed-specific targets might be defined by local TMDLs and Watershed Protection Plans, site
constraints, pollutant fate and transport properties, BMP unit processes and performance, and the
stringency of permit requirements must all be evaluated to strategically match green infrastructure
practices with targeted pollutant treatment. Typical pollutants targeted for BMP treatment include
suspended solids, trash, heavy metals (e.g., copper, lead, zinc), nutrients, pathogens, and organics such as
petroleum hydrocarbons and pesticides. Refer to Chapter 2 of the Massachusetts Stormwater Handbook
(MassDEP 1997) for further details regarding these green infrastructure BMPs, including their benefits and
limitations, pollutant removal efficiencies, and required design information.
5.3.1. Vegetated Filter Strips
Vegetated filter strips are bands of dense,
perennial vegetation installed on a uniform
slope and designed to provide
pretreatment of runoff prior to discharging
into a BMP. Vegetated filter strips on highly
permeable soils can also provide
infiltration, improving volume reduction.
Increased infiltration can decrease the
necessary horizontal length. Such
characteristics make it ideal to use
vegetated filter strips as a BMP around
roadside shoulders, safety zones, or at the
edge of small parking lots. Figure 5-1
illustrates a vegetated filter strip installed at
the edge of a parking lot.
Source: Massachusetts Stormwater Handbook
Figure 5-1. Vegetated filter strip at the edge of a
parking lot.
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Vegetated filter strips are implemented for improving stormwater quality and reducing runoff flow
velocity. As water sheet flows across the vegetated filter strip, the vegetation filters out and settles the
particulates and constituents, especially in the initial flow of stormwater. Removal efficiency often
depends on the slope, length, gradient, underlying parent soil, and biophysical condition of the vegetation.
Although some assimilation of dissolved constituents can occur, filter strips are generally more effective
in trapping sediment and particulate-bound metals, nutrients, and pesticides. Nutrients that bind to
sediment include phosphorus and ammonium; soluble nutrients include nitrate. Biological and chemical
processes could help break down pesticides, uptake metals, and use nutrients that are trapped in the
filter. Vegetated filter strips also exhibit good removal of litter and other debris when the water depth
flowing across the strip is below the vegetation height. Maintenance of vegetative cover is important to
ensure that filters trips do not export sediment due to erosion of exposed ground (Winston et al. 2012).
Table 5-2 reports the water quality performance of vegetated filter strips.
Table 5-2. Pollutant removal characteristics of vegetated filter strips
Pollutant
Relative
removal
efficiency1
Median effluent
concentration
(mg/L unless
otherwise
noted)2
Removal processes
References
Sediment
High
(-195% to 91%)
19.1
Sedimentation and filtration.
Geosyntec Consultants and
Wright Water Engineering
2012; Knight et al. 2013;
Winston et al. 2011;
Metals
Medium
TAs: 0.94 pg/L,
TCd: 0.18 ua/L.
TCr: 2.73 ua/L.
TCu: 7.30 ua/L.
TPb: 1.96 ua/L
TNi: 2.92 ua/L
TZi: 24.3 ua/L
Removal with sediment.
Knight et al. 2013; Geosyntec
Consultants and Wright
Water Engineering 2012
Total
phosphorus
Low
(-126% to 40%)
0.18
Settling with sediment and
plant uptake.
Geosyntec Consultants and
Wright Water Engineering
2012; Knight et al. 2013;
Winston et al. 2011;
Total
nitrogen
Low
(TN: -17% to
40%,
TKN: -18% to
39%,
N02,3-N:-18% to
43%)
TN: 1.13,
TKN: 1.09.
NO2.3-N: 0.27
Sedimentation (TKN) and
plant uptake.
Geosyntec Consultants and
Wright Water Engineering
2012; Knight et al. 2013;
Winston et al. 2011;
Bacteria
Low (likely
exports
pathogens)
N/A
Limited sedimentation,
desiccation, predation, and
photolysis at surface.
USEPA 2012
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Underlined effluent concentrations were (statistically) significantly lower than influent concentrations, as determined by
statistical hypothesis testing on the available sampled data. Effluent concentrations displayed in italics were (statistically)
significantly higher than influent concentrations.
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5.3.2. Bioretention
Bioretention areas are landscaped, shallow
depressions that capture and temporarily store
stormwater runoff. Runoff is directed into the
bioretention area and then filtered through the
soil (often engineered soil) media. Figure 5-2
shows a bioretention area installed on a
residential property.
Bioretention areas usually consist of a
pretreatment system, surface ponding area,
mulch layer, and planting soil media. The
depressed area is planted with small-to medium-
sized vegetation including trees, shrubs, and
ground cover that can withstand urban
environments and tolerate periodic inundation
and dry periods. Plantings also provide habitat for beneficial pollinators and aesthetic benefits for
stakeholders. They can also be customized to attract butterflies or particular bird species. Ponding areas
can be designed to increase flow retention and flood control capacity.
Source: Massachusetts Stormwater Handbook
Figure 5-2. Bioretention area, or rain garden, on
a residential property.
Bioretention areas provide comprehensive pollutant load reduction at various depths through physical,
chemical, and biological mechanisms. Table 5-3 describes the effectiveness of bioretention for targeted
management of specific water quality constituents. Infiltration provides the most effective mechanism
for pollutant load reduction and should be encouraged where practicable. Treatment performance can
also be enhanced (particularly for nitrogen, pathogens, and other pollutants that are removed by
sorption) by installing deep media with slow infiltration rates (1 to 2 inches per hour) (Bright et al. 2010;
Hathaway et al. 2011; Hunt et al. 2012; Hunt and Lord 2006; Rusciano and Obropta 2007).
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Table 5-3. Pollutant removal characteristics of bioretention
Pollutant
Relative
removal
efficiency1
Median effluent
concentration
(mg/L unless
otherwise
noted)2
Removal processes
Min. rec.
media depth
for
treatment
References
Sediment
High
8J3
Settling in
pretreatment and
mulch layer, filtration
and sedimentation in
top 2 to 8 inches of
media.
1.5 feet
Hatt et al. 2008; Hunt et
al. 2012; Li and Davis
2008; Geosyntec
Consultants and Wright
Water Engineering 2012;
Stander and Borst 2010;
Metals
High
TCd: 0.94
ua/L. TCu:
7.67 ua/L.
TPb: 2.53
ua/L. TZn:
18.3 ua/L
Removal with
sediment and sorption
to organic matter and
clay in media.
2 feet
Hsieh and Davis 2005;
Geosyntec Consultants
and Wright Water
Engineering 2012; Hunt et
al. 2012
Hydro-
carbons
High
N/A
Removal and
degradation in mulch
layer.
N/A
Hong et al. 2006; Hunt et
al. 2012
Total
phosphorus
Medium
(-240% to
99%)
0.09
Settling with sediment,
sorption to organic
matter and clay in
media, and plant
uptake. Poor removal
efficiency can result
from media containing
high organic matter or
with high background
concentrations of
phosphorus.
2 feet
Clark and Pitt 2009; Davis
2007; Geosyntec
Consultants and Wright
Water Engineering 2012;
Hsieh and Davis 2005;
Hunt et al. 2006; Hunt
and Lord 2006; ; Li et al.
2010
Total
nitrogen
Medium
(TKN:
-5% to 64%,
Nitrate: 1%
to 80%)
TN: 0.90.
TKN: 0.60.
N02,3-N: 0.22
Sorption and setting
(TKN), denitrification
in IWS (nitrate), and
plant uptake. Poor
removal efficiency can
result from media
containing high
organic matter.
3 feet
Barrett et al. 2013; Clark
and Pitt 2009; Geosyntec
Consultants and Wright
Water Engineering 2012;
Hunt et al. 2006; Hunt et
al. 2012; Kim et al. 2003;
Li et al. 2010; Passeport
et al. 2009;
Bacteria
High
Enterococcus:
234 MPN/100
mL, E.colr. 44
MPN/100 mL
Sedimentation,
filtration, sorption,
desiccation, predation,
and photolysis in
mulch layer and
media.
2 feet
Hathaway et al. 2009;
Hathaway et al. 2011;
Hunt and Lord 2006; Hunt
et al. 2008; Hunt et al.
2012; Jones and Hunt
2010;
Thermal load
High
68-75 °F
Heat transfer at depth
and thermal load
reduction by volume
reduction (ET and
infiltration). IWS
enhances thermal load
reduction.
4 feet
Geosyntec Consultants
and Wright Water
Engineering 2012; Hunt et
al. 2012; Jones and Hunt
2009; Jones et al. 2012;
Winston et al. 2011;
Wardynski et al. 2013
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Underlined effluent concentrations were (statistically) significantly lower than influent concentrations, as determined by
statistical hypothesis testing on the available sampled data.
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5.3.3. Constructed Stormwater Wetlands
Constructed stormwater wetlands are engineered, shallow-water ecosystems designed to treat
stormwater runoff. Commonly implemented in low-lying areas, stormwater wetlands are well suited to
areas along river corridors where water tables are higher. Sediment and nutrients are efficiently reduced
by stormwater wetlands by means of sedimentation, chemical and biological conversions, and uptake by
wetland plant species. Stormwater
wetlands provide flood control benefits
by storing water and slowly releasing it
over 2 to 5 days. In addition to
stormwater management, stormwater
wetlands provide excellent plant and
wildlife habitat and can often be
designed as public amenities. To
preserve their effectiveness, MassDEP
requires placing a sediment forebay as
pretreatment for all constructed
stormwater wetlands. An example
constructed stormwater wetland is
presented in Figure 5-3.
Similar to natural wetlands, water quality improvement is effectively achieved in constructed wetlands
through physicochemical and biological processes as water is temporarily stored. Specific unit processes
include sedimentation, denitrification, and uptake. Consequently, the flow path through the wetland
should be maximized to increase residence time and contact with vegetation, soil, and microbes. Very
high sediment removal efficiencies have been reported for properly sized stormwater wetlands (50 to
80 percent reduction), with average effluent concentrations near 9 mg/L (Hathaway and Hunt 2010;
Geosyntec Consultants, Inc. and Wright Water Engineers, Inc. 2012). Subsequently, particle-bound
metals are thought to be reduced as sediment falls out of suspension, and significant reduction of total
copper, total cadmium, total lead, and total zinc is expected (although metals can dissociate from
sediment and organic matter into solution under anaerobic conditions; Newman and Pietro 2001;
Geosyntec Consultants, Inc. and Wright Water Engineers, Inc. 2012).
High phosphorus removal rates have been observed in stormwater wetlands, but, similar to metals,
phosphorus can desorb from sediments under anaerobic conditions (Hathaway and Hunt 2010).
Stormwater wetlands typically perform well for nitrate removal because the anaerobic conditions and
organic material in wetland sediment create an ideal environment for denitrification (converting nitrate
into nitrogen gas). Significant nitrate reduction is commonly observed in stormwater wetlands, but total
nitrogen reduction depends on the species and concentration of incoming nitrogen (Hathaway and Hunt
2010; Moore et al. 2011; Geosyntec Consultants, Inc. and Wright Water Engineers, Inc. 2012). Pathogen
removal in stormwater wetlands is expected because of predation, solar radiation, and sedimentation
(Davies and Bavor 2000; Struck et al. 2008; Geosyntec Consultants, Inc. and Wright Water Engineers, Inc.
Source: Massachusetts Stormwater Handbook
Figure 5-3. Constructed stormwater wetland with wetland
vegetation.
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2012); furthermore, wetlands tend to reduce bacteria more than do traditional wet detention ponds
(Davies and Bavor 2000).
The U.S. EPA recommends the following guidelines to help ensure successful constructed treatment
wetland projects:
P Construct treatment wetlands, as a rule, on uplands and outside floodplains in order to avoid
damage to natural wetlands and other aquatic resources, unless pretreated effluent can be used
to restore degraded systems.
P Consider the role of treatment wetlands within the watershed (e.g., potential water quality
impacts, surrounding land uses and relation to local wildlife corridors).
P Closely examine site-specific factors, such as soil suitability, hydrology, vegetation, and presence
of endangered species or critical habitat, when determining an appropriate location for the
project in order to avoid unintended consequences, such as bioaccumulation or destruction of
critical habitat.
P Use water control measures that will allow easy response to changes in water quantity, quality,
depth and flow.
P Create and follow a long-term management plan that includes regular inspections, monitoring
and maintenance
It is important to note that constructed stormwater wetlands may be subject to the Clean Water Act;
determinations are made by EPA and the U.S. Army Corps of Engineers on a case-by-case basis.
5.3.4. Tree Box Filters
A tree box filter is a concrete box containing porous soil media and vegetation that functions similarly to
a small bioretention area but is completely lined, must have an underdrain, and has one or more trees.
Runoff is directed from surrounding impervious surfaces to the tree box filter where it percolates
through the soil media to the underlying ground. If the runoff exceeds the design capacity of the tree
box filter, the underdrain directs the excess to a storm drain other device.
Tree box filters have been implemented around paved streets, parking lots, and buildings to provide
initial stormwater detention and treatment of runoff. Such applications offer an ideal opportunity to
minimize directly connected impervious areas in highly urbanized areas. In addition to stormwater
management benefits, tree box filters provide on-site stormwater treatment options, green space, and
natural aesthetics in tightly confined urban environments. Tree box filters are ideal for redevelopment
or in the ultra-urban setting and may be used as a pretreatment device. Figure 5-4 illustrates a tree box
filter shortly after construction.
Tree box filters are capable of consistent and high pollutant removal for sediment, metals, and organic
pollutants (e.g., hydrocarbons). Current research shows that pollutant removal is possible with
underdrains through the function provided at the surface and by the soil media.
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Source: Massachusetts Stormwater Handbook
Figure 5-4. Newly constructed tree box filter.
Table 5-4 reports the water quality performance of tree box filters.
Table 5-4. Pollutant removal characteristics of flow-through planters
Pollutant
Relative
removal
efficiency
1
Median
effluent
concentration
(mg/L unless
otherwise
noted )2
Removal
processes
Minimum
recommended
media depth
for treatment
References
Sediment
High
8J3
Settling in
pretreatment and
mulch layer, filtration
and sedimentation in
top 2 to 8 inches of
media.
1.5 feet
Geosyntec Consultants
and Wright Water
Engineering 2012; Hatt
etal. 2008; Hunt et al.
2012Li and Davis 2008;
Standerand Borst2010
Metals
High
TCd: 0.94ua/L,
TCu: 7.67ua/L,
TPb: 2.53|jg/L,
TZn: 18.3 ua/L
Removal with
sediment and
sorption to organic
matter and clay in
media.
2 feet
Geosyntec Consultants
and Wright Water
Engineering 2012; Hsieh
and Davis 2005; Hunt et
al. 2012
Hydro-
carbons
High
N/A
Removal and
degradation in
mulch layer.
N/A
Hong et al. 2006; Hunt et
al. 2012
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Pollutant
Relative
removal
efficiency
1
Median
effluent
concentration
(mg/L unless
otherwise
noted )2
Removal
processes
Minimum
recommended
media depth
for treatment
References
Total
phosphorus
Medium
(-240% to
99%)
0.09
Settling with
sediment, sorption
to organic matter
and clay in media,
and plant uptake.
Poor removal
efficiency can result
from media
containing high
organic matter or
with high
background
concentrations of
phosphorus.
2 feet
Clark and Pitt 2009;
Davis 2007; Geosyntec
Consultants and Wright
Water Engineering 2012;
Hsieh and Davis 2005;
Hunt etal. 2006; Hunt
and Lord 2006; Li et al.
2010
Total
nitrogen
Medium
(TKN: -5%
to 64%,
Nitrate: 1%
to 80%)
TN: 0.90.
TKN: 0.60.
N02,3-N: 0.22
Sorption and setting
(TKN), denitrification
in IWS (nitrate), and
plant uptake. Poor
removal efficiency
can result from
media containing
high organic matter.
3 feet
Barrett et al. 2013; Clark
and Pitt 2009;
Geosyntec Consultants
and Wright Water
Engineering 2012; Hunt
et al. 2006; Hunt et al.
2012; Kimet al. 2003; Li
et al. 2010; Passeport et
al. 2009;
Bacteria
High
Enterococcus'.
234 MPN/100
mL. E.coli: 44
MPN/100 mL
Sedimentation,
filtration, sorption,
desiccation,
predation, and
photolysis in mulch
layer and media.
2 feet
Geosyntec Consultants
and Wright Water
Engineering 2012;
Hathaway et al. 2009;
Hathaway et al. 2011;
Hunt and Lord 2006;
Hunt et al. 2008; Hunt et
al. 2012; Jones and Hunt
2010;
Thermal
load
High
68-75 °F
Heat transfer at
depth and thermal
load reduction by
volume reduction
(ET and infiltration).
IWS enhances
thermal load
reduction.
4 feet
Hunt et al. 2012; Jones
and Hunt 2009; Jones et
al. 2012; Wardynski et
al. 2013; Winston et al.
2011;
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Concentrations are based on bioretention performance data. Underlined effluent concentrations were (statistically)
significantly lower than influent concentrations, as determined by statistical hypothesis testing on the available sampled data.
Effluent concentrations displayed in italics were (statistically) significantly higher than influent concentrations.
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5.3.5. Sand Filters
A sand filter is a treatment system used to remove
particulates and solids from stormwater runoff by
facilitating physical filtration. It is a flow-through
system designed to improve water quality from
impervious drainage areas by slowly filtering runoff
through sedimentation and filtration chambers.
With increased detention time, the sedimentation
chamber allows larger particles to settle in the
chamber. The filtration chamber removes
pollutants and enhances water quality as the
stormwater is strained through a layer of sand. The
treated effluent is collected by underdrain piping
and discharged to the existing stormwater
collection system or another BMP. Sand filters can
be used in areas with poor soil infiltration rates, where ground water concerns restrict the use of
infiltration, or for high pollutant loading areas. Figure 5-5 shows a sand filter that has been installed at
the edge of a parking lot.
Sand filters are capable of removing a wide variety of pollutant concentrations in stormwater via
settling, filtering, and adsorption processes. Sand filters have been a proven technology for drinking
water treatment for many years and now have been demonstrated to be effective in removing urban
stormwater pollutants including total suspended solids, particulate-bound nutrients, biochemical
oxygen demand (BOD), fecal coliform, and metals (USEPA 1999). Sand filters are volume-based IMPs
intended primarily for treating the water quality design volume. In most cases, sand filters are enclosed
concrete or block structures with underdrains; therefore, only minimal volume reduction occurs via
evaporation as stormwater percolates through the filter to the underdrain. Table 5-5 reports the water
quality performance of sand filters.
Source: NCSU BAE
Figure 5-5. Below ground Delaware style sand
filter installed in a parking lot.
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Table 5-5. Pollutant removal characteristics of sand filters
Median effluent
concentration
Relative
removal
(mg/L unless
otherwise
Pollutant
efficiency1
noted)2
Removal processes
References
Sediment
High
81
Settling in pretreatment and
Barrett 2003, 2008, 2010;
(74% to 95%)
surface, filtration and
sedimentation in media.
Bell et al. 1995; Geosyntec
Consultants and Wright
Water Engineering 2012;
Horner and Horner 1995;
Metals
High
(14% to 87%)
TAs: 0.87ua/L.
TCd: 0.16ua/L.
TCr: 1.02ua/L.
TCu: 6.01 ua/L.
TPb: 1.69ua/L.
TNi: 2.20ua/L.
TZi: 19.9ua/L
Removal with sediment
(optional: sorption to organic
matter and clay amendments
in media).
Barrett 2010; Geosyntec
Consultants and Wright
Water Engineering 2012
Total
Low
0.09
Settling with sediment
Barrett 2010; Geosyntec
phosphorus
(-14% to 69%)
(optional: sorption to organic
matter and clay amendments
in media). Poor removal
efficiency can result from
media containing high
organic matter or with high
background concentrations of
phosphorus.
Consultants and Wright
Water Engineering 2012;
Hunt et al. 2012;
Total
Low
TN: 0.82,
Sorption and setting (TKN)
Barrett 2008; Geosyntec
nitrogen
(20%)
TKN: 0.57,
NO2.3-N: 0.51
and denitrification in IWS
(nitrate). Poor removal
efficiency can result from
media containing high
organic matter.
Consultants and Wright
Water Engineering 2012;
Hunt et al. 2012;
BOD
High
(-27% to 55%)
N/A
Sedimentation, filtration, and
biodegradation.
Barrett 2010
Bacteria
High (fecal
Fecal coliform:
Sedimentation, filtration,
Barrett 2010; Geosyntec
coliform:
542
sorption, desiccation,
Consultants and Wright
-70% to 54%,
MPN/100mL
predation, and photolysis in
Water Engineering 2012
fecal
surface layer.
streptococcus:
11% to 68%)
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Underlined effluent concentrations were (statistically) significantly lower than influent concentrations, as determined by
statistical hypothesis testing on the available sampled data. Effluent concentrations displayed in italics were (statistically)
significantly higher than influent concentrations.
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5.3.6. Grassed Swales
Grassed swales are shallow, open vegetated
channels designed to provide for
nonerosive conveyance with a longer
hydraulic residence time than traditional
curbs and gutters. Grass swales provide
limited pollutant removal by sedimentation
and gravity separation. Properly designed
grass swales are ideal when used adjacent
to roadways or parking lots, where runoff
from the impervious surfaces can be
directed to the swale via sheet flow. Swales
are effective for pretreatment of
concentrated flows before discharge to a
downstream BMP. A grassed swale installed
adjacent to a highway is depicted in Figure 5
Source: Massachusetts Stormwater Handbook
Figure 5-6. Grassed swale adjacent to a highway.
5.3.7. Water Quality Swales
Water quality swales are vegetated open
channels designed to convey runoff
without causing erosion while also
improving the water quality of stormwater
runoff. Water quality swales incorporate
specific features to enhance their
stormwater pollutant removal
effectiveness. There are both wet and dry
water quality swales. Dry swales promote
infiltration of the runoff and therefore
require porous soils. Wet swales contain
standing water and can use soils with poor
drainage or high ground water conditions. Source; Massachusetts Stormwater Handbook
The slope and cross-sectional area of the Figure 5-7. Water quality swale adjacent to a highway,
swale should sufficiently maintain
nonerosive flow velocities. Water quality swales may be used along roadways, at the edge of a parking
lot, or as parking lot islands. Figure 5-7 presents a water quality swale installed adjacent to a highway.
Although high sediment load reductions have been observed in well-constructed swales, performance is
highly variable and generally depends on flow rate, particle settling velocity (as determined by particle size
distribution), and flow length (Backstrom 2003; Backstrom 2006; Deletic and Fletcher 2006; Yu et al. 2001).
The sediment load reductions tend to be primarily associated with coarser sediment particles (sand) that do
not pose as great a threat to downstream aquatic life as finer sediment particles (Deletic 1999; Luell 2011;
Knight et al. 2013). Because swales offer minimal contact between runoff and sorptive surfaces, dissolved
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constituents and metals that tend to be associated with finer sediment particles (such as dissolved copper
and zinc) can be harder to remove (Zanders 2005). In some cases, swales have been shown to export heavy
metals (Backstrom 2003). USEPA (2012) reports that swales typically export pathogens. To achieve optimal
removal of fine sediment particles, minimum swale lengths of 246 feet and 361 feet have been
recommended, along with residence times of 5 tolO minutes (Backstrom 2003; Yu et al. 2001; Claytor and
Schueler 1996). Additionally, flow depth should not exceed the height of the vegetation. These design
parameters can make swales difficult to implement for water quality improvement in areas with limited
available footprint. Table 5-6 reports the water quality performance of swales.
Table 5-6. Pollutant removal characteristics of water quality swales
Pollutant
Relative
removal
efficiency1
Median effluent
concentration
(mg/L unless
otherwise
noted)2
Removal processes
References
Sediment
High
(20% to 98%)
13.6
Sedimentation and
filtration.
Deletic and Fletcher 2006, Yu et
al. 2001, Backstrom 2003,
Backstrom 2006, Geosyntec
Consultants and Wright Water
Engineering 2012
Metals
Medium
TAs: 1.17ua/L.
TCd: 0.31 ua/L.
TCr: 2.32ua/L.
TCu: 6.54ua/L.
TPb: 2.02ua/L.
TNi: 3.16ua/L.
TZi: 22.9ua/L
Removal with sediment.
Fassman 2012; Geosyntec
Consultants and Wright Water
Engineering 2012
Total
phosphorus
Low
0.19
Settling with sediment
and plant uptake.
Deletic and Fletcher 2006;
Geosyntec Consultants and
Wright Water Engineering 2012
Total
nitrogen
Low
TN: 0.71,
TKN: 0.62,
N02,3-N: 0.25
Sedimentation (TKN)
and plant uptake.
Deletic and Fletcher 2006;
Geosyntec Consultants and
Wright Water Engineering 2012
Bacteria
Low (typically
exports
pathogens)
E. coli: 4190
MPN/100 mL,
Fecal coliform:
5000 MPN/100
mL
Limited sedimentation,
desiccation, predation,
and photolysis at
surface.
EPA 2012, Geosyntec
Consultants and Wright Water
Engineering 2012
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Concentrations are based on vegetated swale performance data. Underlined effluent concentrations were (statistically)
significantly lower than influent concentrations, as determined by statistical hypothesis testing on the available sampled data.
Effluent concentrations displayed in italics were (statistically) significantly higher than influent concentrations
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5.3.8. Cisterns and Rain Barrels
Cisterns and rain barrels are containers that
capture rooftop runoff and store it for landscaping
and other nonpotable uses. With control of the
timing and volume, the captured stormwater can
be more effectively released for irrigation or
alternative grey water uses between storm events.
Rain barrels tend to be smaller systems that direct
runoff through a downspout into a barrel that
holds less than 100 gallons. As an example, Figure
5-8 shows a 55-gallon residential rain barrel.
Cisterns are larger systems that can be self-
contained aboveground or belowground systems
generally larger than 100 gallons and can direct
water from one or more downspouts. Belowground
systems often require a pump for water removal.
For the Massachusetts Bay and surrounding areas,
cisterns and rain barrels primarily provide control
of stormwater volume; however, water quality improvements can be achieved when cisterns and rain
barrels are used with other BMPs such as bioretention areas. Water in cisterns or rain barrels can be
controlled by permanently open outlets or operable valves depending on project specifications. Cisterns
and rain barrels can be a useful method of reducing stormwater runoff volumes in urban areas where
site constraints limit the use of other BMPs.
Because most rainwater harvesting systems collect rooftop runoff, the water quality of runoff harvested
in cisterns is largely determined by surrounding environmental conditions (e.g., overhanging vegetation,
bird and wildlife activity, atmospheric deposition,), roof material, and cistern material (Despins et al.
2009; Lee et al. 2012; Thomas and Greene 1993). Rooftop runoff tends to have relatively low levels of
physical and chemical pollutants, but elevated microbial counts are typical (Gikas and Tsihrintzis 2012;
Lee et al. 2012; Lye 2009; Thomas and Greene 1993). Physicochemical contaminants can be further
reduced by implementing a first-flush diverter (discussed later); however, first-flush diverters can have
little impact on reducing microbial counts (Lee et al. 2012; Gikas and Tsihrintzis 2012).
The pollutant reduction mechanisms of rain tanks are not yet well understood, but sedimentation and
chemical transformations area thought to help improve water quality. Despite limited data describing
reduction in stormwater contaminant concentrations in cisterns, rainwater harvesting can greatly
reduce pollutant loads to waterways if stored rainwater is infiltrated into surrounding soils using a low-
flow drawdown configuration or when it is used for alternative purposes such as toilet flushing or
vehicle washing. Rainwater harvesting systems can also be equipped with filters to further improve
water quality.
Source: Massachusetts Stormwater Handbook
Figure 5-8. A 55-gallon rain barrel collecting
rainwater from a residential rooftop.
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5.3.9. Green Roofs
Green roofs reduce runoff volume and rates by
intercepting rainfall in a layer of rooftop growing
media.
Rainwater captured in rooftop media then
evaporates or is transpired by plants back into
the atmosphere. Rainwater in excess of the
media capacity is detained in a drainage layer
before flowing to roof drains and downspouts.
Green roofs are highly effective at reducing or
eliminating rooftop runoff from small to medium
storm events. They can be incorporated into new
construction or added to existing buildings during
renovation or re-roofing.
In addition to stormwater volume reduction,
green roofs offer an array of benefits, including
extended roof life span (due to additional sealing,
liners, and insulation), improved building
insulation and energy use, reduction of urban
heat island effects, opportunities for recreation
and rooftop gardening, noise attenuation, air quality improvement, bird and insect habitat, and
aesthetics (Tolderlund 2010; Berndtsson 2010; Getter and Rowe 2006). Green roofs can be designed as
extensive, shallow-media systems or intensive, deep-media systems depending on the design goals, roof
structural capacity, and available funding. An example green roof is presented in Figure 5-9.
5.3.10. Permeable Pavement
Permeable pavement is a durable, load-bearing paved surface with small voids or aggregate-filled joints
that allow water to drain through to an aggregate reservoir. Stormwater stored in the reservoir layer can
then infiltrate underlying soils or drain at a controlled rate via underdrains to other downstream
stormwater control systems. Permeable pavement allows streets, parking lots, sidewalks, and other
impervious covers to retain the infiltration capacity of underlying soils while maintaining the structural
and functional features of the materials they replace.
Permeable pavement systems can be designed to operate as underground detention if the native soils
do not have sufficient infiltration capacity, or if infiltration is precluded by aquifer protection, hotspots,
or adjacent structures. Permeable pavement can be developed using modular paving systems (e.g.,
permeable interlocking concrete pavers, concrete grid pavers, or plastic grid systems) or poured in place
solutions (e.g., pervious concrete or porous asphalt). Some pervious concrete systems can also be
precast. In many cases, especially where space is limited, permeable pavement is a cost-effective
solution relative to other practices because it doubles as both transportation infrastructure and a BMP.
Figure 5-10 illustrates a porous asphalt parking lot.
Source: Massachusetts Stormwater Handbook
Figure 5-9. Vegetated green roof.
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Source: Massachusetts Stormwater Handbook and Sara P, Grady
Figure 5-10. Porous asphalt parking lot and permeable interlocking concrete pavers in the right-of-way.
Permeable pavement systems, when designed and installed properly, consistently reduce
concentrations and loads of several stormwater pollutants, including heavy metals, oil and grease, sedi-
ment, and some nutrients. The aggregate sub-base improves water quality through filtering and
chemical and biological processes, but the primary pollutant removal mechanism is typically load
reduction by infiltration into subsoils. Table 5-7 reports water quality performance of permeable
pavement.
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Table 5-7. Pollutant removal characteristics of permeable pavement
Pollutant
Relative
removal
efficiency1
Median effluent
concentration
(mg/L unless
otherwise noted)3
Removal processes
References
Sediment
High2
(32% to
96%)
13.2
Settling on surface and in
reservoir layer.
Bean et al. 2007; CWP 2007;
Fassman and Blackbourn 2011 Gilbert
and Clausen 2006; MWCOG 1983;
Pagotto et al. 2000; Roseen et al.
2009, 2011; Rushton 2001; Schueler
1987; Toronto and Region
Conservation Authority 2007;
Metals
High
(65% to
84%)
TAs: 2.50|jg/L,
TCd: 0.25|jg/L,
TCr: 3.73 pg/L,
TCu: 7.83ua/L.
TPb: 1.86ua/L.
TNi: 1.71 ua/L.
TZn: 15.0 ua/L
Removal with sediment
and possible sorption to
aggregate base course.
Bean et al. 2007; Brattebo and Booth
2003; CWP 2007; Dierkes et al. 2002;
Fassman and Blackbourn 2011;
Gilbert and Clausen 2006;MWCOG
1983; Pagotto et al. 2000; Roseen et
al. 2009, 2011; Rushton 2001;
Schueler 1987; Toronto and Region
Conservation Authority 2007;
Hydro-
carbons
Medium
(92% to
99%)
N/A
Removal in surface course
and aggregate layer.
Roseen et al. 2009, 2011
Total
phosphorus
Low
(20% to
78%)
0.09
Settling with sediment,
possible sorption to
aggregate, and sorption to
underlying soils.
Bean et al. 2007; CWP 2007; Gilbert
and Clausen 2006; MWCOG 1983;
Roseen et al. 2009, 2011; Rushton
2001; Schueler 1987; Toronto and
Region Conservation Authority 2007;
Yong et al. 2011
Total
nitrogen
Low
(-40% to
88%)
TKN: 0.80.
NO?.s-N: 0.71
Setting, possible
denitrification in IWS,
sorption in underlying soils
(TKN).
Collins etal. 2010; CWP 2007;
MWCOG 1983; Schueler 1987;
Bacteria
Medium
N/A
Sedimentation, filtration,
sorption, desiccation, and
predation in surface course
and reservoir layer.
Myers et al. 2009; Tota-Maharaj and
Scholz 2010
Thermal
load
Medium
58-73 °F
Heat transfer at depth,
thermal buffering through
profile, and thermal load
reduction by volume
reduction (infiltration). IWS
enhances thermal load
reduction.
Wardynski et al. 2013
1 This Handbook presents relative removal efficiencies (high, medium, low). Percent removal efficiencies from literature are also
included, where available, but can vary dramatically based on site specific conditions.
2 Run-on from adjacent surfaces with high sediment yield can cause premature clogging of the surface course or subsurface
interface. Permeable pavement should not be used to treat runoff from pervious surfaces or other areas with high sediment yield.
3 Underlined effluent concentrations were (statistically) significantly lower than influent concentrations, as determined by
statistical hypothesis testing on the available sampled data. Effluent concentrations in italics were (statistically) significantly
higher than influent concentrations.
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5.4. Cold Climate Considerations
Cold climates, such as in Massachusetts, present unique considerations for green infrastructure BMP
selection, design, and maintenance. In cold climate locations, freeze/thaw and snow plows are the
major concerns for permeable pavement. However, when well-designed, permeable pavement will
always drain properly and never freeze solid. Additionally, air voids present in permeable pavement
should allow sufficient space for moisture to freeze and expand. When snowfall occurs, municipalities
should ensure snow plow blades are raised sufficiently to prevent scraping of permeable pavement
surfaces. Sand should never be applied, as it can cause clogging and inhibit BMP function (USEPA, 2008).
Green infrastructure BMPs that incorporate vegetation are also subject so cold weather considerations.
Plants selected for these practices should flourish in the regional climate conditions, and salt-tolerant
species are most favorable for regions where road salt is applied in the winter (USEPA, 2008).
5.5. BMP Construction and Post-Construction Issues
Successful BMP execution and performance can be hindered when designers lack a complete
understanding of BMP requirements, construction is performed by inexperienced contractors, or as a
result of inadequate operation and maintenance over the long-term. To help prevent these issues, this
section provides considerations for BMP construction oversight and post-construction inspection; both
of which supplement the operation and maintenance discussion in Appendix C. It is recommended that
project managers include in the construction specifications the considerations presented below.
Incorporating important inspection and maintenance activities beginning with the planning and design
phase can significantly reduce the long-term operation and maintenance costs for permanent structural
stormwater controls. Because post-construction inspections and maintenance are essential to facility
function, it is important to ensure that necessary equipment, access, and methods to complete
maintenance and BMP evaluation tasks during the operation phase are considered during design.
5.5.1. BMP Construction
Essential functions of permanent BMPs (e.g., bioswales, stormwater wetlands) can be deteriorated by
common construction mistakes, such as soil compaction from heavy equipment, erosion and sediment
accumulation, or from construction performed in saturated soil conditions. Construction oversight and
inspection by a qualified inspector who is familiar with the functions of structural BMPs are highly
encouraged for quality control and assurance. Inspectors should verify that the proper temporary
erosion control practices are implemented in accordance with federal, state, and local regulations. In
addition, construction specifications should include the following practices to protect the permanent
green infrastructure BMPs from impairment during construction operations:
P Establish a protective zone around valued natural areas and trees that will be preserved.
P Minimize the use of heavy equipment, especially in areas where infiltration BMPs will be
present.
P Minimize soil disturbance and unprotected exposure of disturbed soils.
P Expose only as much area as needed for immediate construction.
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P As areas are cleared and graded, apply appropriate erosion controls to minimize soil erosion.
P Protect stormwater infiltration BMPs from unwanted sedimentation during the construction phase.
P Provide a temporary outlet to convey runoff down slope with sediment traps at outlets and
inlets.
P Minimize the movement of soil into the drainage system.
P Use sediment and erosion protection practices early in the site clearing and grading process to
reduce the sediment-laden runoff reaching soils intended for future infiltration.
P Protect future infiltration facilities from sediment from adjacent properties.
Sensitive areas that require protection should be delineated before grading and clearing starts. It is best
to indicate such restrictions on both the grading and erosion control plans. Areas of existing vegetation
that are planned for preservation should be clearly marked with a temporary fence. If trees have been
designated for preservation, equipment should be prohibited within the drip line to prevent root and
trunk damage. Trenching and excavating should not occur within the drip line, and trenches outside but
adjacent to the drip line should be filled in quickly to avoid root drying.
5.5.2. Temporary Erosion and Sediment Control Practices
Soil-disturbing activities at the construction site can increase erosion and sediment risks. Apply an
effective combination of temporary soil erosion and sediment controls to minimize the discharge of
sediments from the site or into a stormwater drainage system or natural receiving water. MassDEP's
Erosion and Sediment Control Guidelines for Urban and Suburban Areas: A Guide for Planners, Designers,
and Municipal Officials, provides detailed specifications for erosion and sediment control BMPs that are
applicable to all construction sites (MassDEP 2003). Properly applying the temporary controls (both on-
site and for drainage from off-site parcels with the potential to contribute sediment) is essential and can
help preserve the long-term capacity and functions of the permanent stormwater BMPs. Inspection and
maintenance of these temporary controls are required to ensure that they remain effective. These
controls are in addition to those in the Construction Period Pollution Prevention and Erosion and
Sedimentation Control Plan required as part of the Stormwater Report, or the Stormwater Pollution
Prevention Plan included as in the NPDES Construction General Permit, if applicable.
Proper construction sequencing can reduce the risk of clogging by excessive accumulation of fine
particles in the soil media layers. Designers should specify proper construction sequencing to minimize
potential disturbance to green infrastructure BMPs. During construction, the extent of exposed soil
should be limited to reduce site erosion by clearly specifying the timing and extent of permanent
vegetation establishment. Imported soil media should not be incorporated into BMPs until the drainage
area has been stabilized. Where the BMP is treating adjacent roadways or parking areas, soil media
should not be installed until at least the first course of pavement has been set to minimize the amount
of fines washed from the bedding layers into the BMP. A geotextile liner is not always sufficient to
prevent fines from migrating into and clogging the soil media layer; therefore, proper construction
sequencing is crucial. Figure 5-11 and Figure 5-12 are examples of the fines that can accumulate and clog
the soil media if proper construction sequencing is not followed.
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Source: NCSU BAE
Figure 5-11. Example of a bioretention area installed before permanent site stabilization with the
inset photo showing the clay layer clogging the mulch surface.
Source: NCSU-BAE
Figure 5-12. Accumulated fines layer as a result of improper construction sequencing.
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5.5.3. BMP Construction Inspection
It is essential to inspect all construction phases to ensure that BMPs are properly installed, especially
during critical elements such as inverts, inlets, outlets, overflow, and underdrains. Also, designers should
stipulate on the plans or specifications which types of materials cannot be substituted (e.g., engineered
media). If an element of a structural BMP system was not constructed properly, or the wrong materials
were used, the entire system could fail to achieve the desired stormwater benefits. Construction
inspection should be performed by the design professional of record or a certified inspector with
appropriate training and experience with BMP construction.
Accurate grading of stormwater infrastructure, including structural BMPs and hardscape areas, is critical
to ensure proper drainage and BMP function. Research has shown that structural practices with
insufficient storage capacity (as a result of inadequate outlet structure details or inaccurate grading)
might not perform to meet the targeted hydrologic or hydraulic function (Brown and Hunt 2011; Luell et
al. 2011). The designer and contractor should work together to ensure that the project is correctly built
to plan. Spot elevations of critical components should be clearly marked on construction plans for
verification during construction. If necessary, arrange for appropriate contractor training before starting
a BMP construction project, and make training available during construction as needed. It is important
to perform field surveys during construction activities to verify that as-built ponding depths have been
provided as designed (Figure 5-13); simply measuring the height of the outlet structure relative to the
ground surface is inadequate (Wardynski and Hunt 2012).
Source: Tetra Tech
Figure 5-13. Accurate grading and outlet elevations must be provided to achieve intended hydrologic
and water quality functions.
Construction activities inherently compact site soils, which can dramatically decrease infiltration rates.
Contractors should be properly instructed to minimize compaction by using tracked equipment,
excavating the last 12 inches using a toothed excavator bucket, and by minimizing the number of passes
over the proposed subgrade while operating the equipment outside of the BMP area where possible
(Figure 5-14). To the extent practicable, earth-moving activities should take place during dry conditions
to reduce the occurrence of smearing the soil surface, which can also reduce soil permeability.
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To mitigate compaction and partly restore
infiltration capacity (for practices that are
intended to infiltrate), the subgrade should
be treated by scarification or ripping to a
depth of 9-12 inches (Figure 5-15; Tyner et
al. 2009). A soil test might be required after
scarifying to verify that infiltration rates have
been restored. If the design infiltration rate is
not restored after scarifying or ripping,
trenches can be installed along the subgrade
to enhance infiltration. Trenches should be
constructed 1-foot-wide by 1-foot-deep on 6-
foot centers and filled with a 0.5-inch layer of
washed sand, then topped off with pea gravel
(Tyner et al. 2009).
Source: Tetra Tech
Figure 5-14. Heavy equipment (especially wheeled
equipment) should be operated outside the
excavated area to prevent compaction.
Many urban conditions, especially on retrofit
sites, have little or no organic material in the soil
structure as a result of compaction, impervious
cover, or lack of regeneration during the years
prior. Excavation also tends to unearth relatively
infertile subsoils. If engineered soil is not specified
a soil test (http://soiltest.umass.edu/services) is
recommended to determine the suitability of site
soils for plant growth, especially for practices
where vegetation will be planted in on-site
excavated soils (such as stormwater wetlands).
Amendment with 2 to 4 inches of topsoil could be
required to improve plant establishment.
Consultation with the landscape architect or
horticulture designer is recommended to verify
rooting depths and establish construction
guidance for the landscape contractor. The
planting plan should also include guidance on the
appropriate time of year to plant trees, shrubs,
and grass to reduce plant stress during establishment.
Source: NCSU-BAE
Figure 5-15. For infiltrating practices, mitigate
subsoil compaction by ripping grade to a depth
of 12 inches.
5.5.4. BMP Inspection and Maintenance
Regular inspection is vital for maintaining the effectiveness of structural BMPs. Generally, BMP
inspection and maintenance can be categorized as routine and as-needed. Routine activities, performed
regularly (e.g., monthly, biannually) ensure that the BMP is in good working order and continues to be
aesthetically pleasing. Routine inspection is an efficient way to prevent potential nuisance situations
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from developing and reduce the need for repair or maintenance. Routine inspection also reduces the
chance of degrading the quality of the effluent by identifying and correcting potential problems
regularly. Property maintenance personnel should be instructed to inspect BMPs during their normal
routines.
In addition to routine inspections, as-needed inspection and maintenance of all BMPs should be
performed after any event or activity that could damage the BMP, particularly after every large storm
event. Post-storm inspections should occur after the expected drawdown period for the BMP, when the
inspector can determine if the BMP is draining correctly.
Summary checklists with maintenance requirements are provided below in Section 5.5 for both
infiltration and biofiltration and filtration BMPs. Detailed BMP inspection checklists can include
minimum performance expectations, design criteria, structural specifications, date of implementation,
and expected life span. Recording such information will help the inspector determine whether a BMP's
maintenance schedule is adequate or requires revision and will allow comparison between the intended
design and the as-built conditions. Checklists also provide a useful way for recording and reporting
whether major or minor renovation or routine repair is needed. The effectiveness of a BMP might be a
function of the BMP's location, design specifications, maintenance procedures, and performance
expectations. Inspectors should be familiar with the characteristics and intended function of the BMP so
they can recognize problems and know how they should be resolved.
Green Infrastructure BMP Lifespan
BMP lifespan may vary greatly based on proper design, maintenance, hydraulic and pollutant
loading, and other factors. A lifespan of 20 years is generally assumed for stormwater BMPs, as
it provides a good horizon for stormwater planning (MDE, 2013).
Routine and as-needed BMP inspections consist of technical and nontechnical activities as summarized
below:
P Inspect the general conditions of the BMP and areas directly adjacent.
P Maintain access to the site including the inlets, side slopes (if applicable), forebay (if one exists),
BMP area, outlets, emergency spillway, and so on.
P Examine the overall condition of vegetation.
P Eliminate any possibility of public hazards (vector control, unstable public access areas).
P Check the conditions of inflow points, pretreatment areas (if they exist), and outlet structures.
P Inspect and maintain the inlet and outlet regularly and after large storms.
P Ensure that the pretreatment areas meet the original design criteria.
P Check the encroachment of undesirable plants in vegetated areas. This could require more
frequent inspections in the growing season.
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P Inspect water quality improvement components. Specifically, check the stormwater inflow,
conveyance, and outlet conditions.
P Inspect hydrologic functions such as maintaining sheet flow where designed, ensuring functional
pretreatment, maintaining adequate design storage capacity, and verifying proper operation of
outlet structures.
P Check conditions downstream of the BMP to ensure that flow is properly mitigated below the
facility (e.g., excessive erosion, sedimentation).
In every inspection, whether routine or as needed, the inspector should document whether the BMP is
performing correctly and whether any damage has occurred to the BMP since the last inspection.
Ideally, the inspector will also identify what should be done to repair the BMP if damage has occurred.
Documentation is very important in maintaining an efficient inspection and maintenance schedule,
providing evidence of ongoing inspection and maintenance, and detecting and reporting any necessary
changes in overall management strategies.
5.6. References
Backstrom, M. 2003. Grassed swales for stormwater pollution control during rain and snowmelt. Water
Science and Technology, 48(9):123-132.
Backstrom, M., Viklander, M., and Malmqvist, P.A. 2006. Transport of stormwater pollutants through a
roadside grassed swale, Urban Water Journal. 3(2):55-67.
Barrett, M.E., M. Limouzin, and D.F. Lawler. 2013. Effects of media and plant selection on biofiltration
performance. Journal of Environmental Engineering 139(4):462-470.
Barrett, M.E. 2003. Performance, Cost, and Maintenance Requirements of Austin Sand Filters. Journal of
Water Resources Planning and Management 129(3):234-242.
Barrett, M.E. 2008. Comparison of BMP performance using the International BMP Database. Journal of
Irrigation and Drainage Engineering 134(5):556-561.
Barrett, M.E. 2010. Evaluation of Sand Filter Performance. CRWR Online Report 10-07. Center for
Research in Water Resources, Bureau of Engineering Research, University of Texas at Austin.
Bean, E.Z., W.F. Hunt, and D.A. Bidelspach. 2007. Evaluation of four permeable pavement sites in
eastern North Carolina for runoff reduction and water quality impacts. Journal of Irrigation and
Drainage Engineering 133(6):583-592.
Bell, W., L. Stokes, L.J. Gavan, and T. Nguyen. 1995. Assessment of the Pollutant Removal Efficiencies of
Delaware Sand Filter BMPs. City of Alexandria, Department of Transportation and
Environmental Services, Alexandria, VA.
Berndtsson, J.C. 2010. Green roof performance towards management of runoff water quantity and
quality: A review. Ecological Engineering 36(4):351-360.
Brattebo, B.O., and D.B. Booth. 2003. Long-term stormwater quantity and quality performance of
permeable pavement systems. Water Research 37(18):4369-4376.
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Bright, T. M., Hathaway, J. M., Hunt, W. F., de los Reyes, F. L., and M.R. Burchell. 2010. Impact of
stormwater runoff on clogging and fecal bacteria reduction in sand columns. Journal of
Environmental Engineering 136(12):1435-1441.
Brown, R.A., D.E. Line, and W.F. Hunt. 2012. LID treatment train: Pervious concrete with subsurface
storage in series with bioretention and care with seasonal high water tables. Journal of
Environmental Engineering 138(6):689-697.
Brown, R.A., and W.F. Hunt. 2011. Underdrain configuration to enhance bioretention exfiltration to
reduce pollutant loads. Journal of Environmental Engineering 137(11):1082-1091.
Brown, R.A., and W.F. Hunt. 2010. Impacts of construction activity on bioretention performance. Journal
of Hydrologic Engineering 15(6):386-394.
Brown, R.A., and W.F. Hunt. 2011. Impacts of media depth on effluent water quality and hydrologic
performance of under-sized bioretention cells. Journal of Irrigation and Drainage
Engineering 137(3):132-143.
Center for Watershed Protection (CWP). 2007. National Pollutant Removal Performance Database.
Center for Watershed Protection, Ellicott City, MD.
Clark, S.E., and R. Pitt. 2009. Storm-water filter media pollutant retention under aerobic versus
anaerobic conditions. Journal of Environmental Engineering 135(5):367-371.
Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. The Center for Watershed
Protection. Ellicott City, MD.
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pavement and standard asphalt in eastern North Carolina. Journal of Hydrologic Engineering
13(12): 1146-1157.
Collins, K.A., W.F. Hunt, and J.M. Hathaway. 2010. Side-by-side comparison of nitrogen species removal
for four types of permeable pavement and standard asphalt in eastern North Carolina. Journal
of Hydrologic Engineering 15(6):512-521.
Davies, C.M., and H.J. Bavor. 2000. The fate of stormwater-associated bacteria in constructed wetland
and water pollution control pond systems. Journal of Applied Microbiology 89(2):349-360.
Davis, A.P. 2007. Field performance of bioretention: Water quality. Environmental Engineering Science
24(8):1048-1063.
Davis, A.P., W.F. Hunt, R.G. Traver, and M. Clar. 2009. Bioretention technology: Overview of current
practice and future needs. Journal of Environmental Engineering 135(3):109-117.
Davis, A.P., R.G. Traver, W.F. Hunt, R. Lee, R.A. Brown, and J.M. Olszewski. 2012. Hydrologic
performance of bioretention storm-water control measures. Journal of Hydrologic Engineering
17(5):604-614.
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DeBusk, K.M., W.F. Hunt, M. Quigley, J. Jeray, and A. Bedig. 2012. Rainwater harvesting: Integrating
water conservation and stormwater management through innovative technologies. World
Environmental and Water Resources Congress 2012: Crossing Boundaries, Proceedings of the
2012 Congress, pp. 3703-3710.
Deletic, A, and T.D. Fletcher. 2006. Performance of grass filters used for stormwater treatment - a field
and modeling study. Journal of Hydrology. 317:261-275.
Deletic, A. 1999. Sediment behaviour in grass filter strips. Water Science and Technology, 39(9):129-136.
Despins, C., K. Farahbakhsh, and C. Leidl. 2009. Assessment of rainwater quality from rainwater
harvesting systems in Ontario, Canada. Journal of Water Supply: Research and Technology—
AQUA 58(2):117-134.
Dierkes, C., L. Kuhlmann, J. Kandasamy, and G. Angelis. 2002. Pollution retention capability and
maintenance of permeable pavements. In Proc. 9th International Conference on Urban
Drainage, Global Solutions for Urban Drainage. September 8-13, 2002, Portland, OR.
Eck, B.J., R.J. Winston, W.F. Hunt, and M.E. Barrett. 2012. Water quality of drainage from permeable
friction course. Journal of Environmental Engineering 138(2): 174-181.
Fassman, E. 2012. Stormwater BMP treatment performance variability for sediment and heavy metals.
Separation and Purification Technology 84:95-103.
Fassman, E.A., and S.D. Blackbourn. 2010. Urban runoff mitigation by a permeable pavement system
over impermeable soils. Journal of Hydrologic Engineering 15(6):475-485.
Fassman, E.A., and S.D. Blackbourn. 2011. Road runoff water-quality mitigation by permeable modular
concrete pavers. Journal of Irrigation and Drainage 137(ll):720-729.
Ferguson, B.K. 1994. Stormwater Infiltration, Boca Raton: CRC Press.
Geosyntec Consultants and Wright Water Engineering. 2012. International Storm Water BMP Database
Pollutant Category Summary Statistical Addendum: TSS, Bacteria, Nutrients, and Metals. 2012.
International Storm Water BMP Database, http://www.bmpdatabase.org/.
Getter, K.L., and D.B. Rowe. 2006. The role of extensive green roofs in sustainable development.
HortScience. 41(5):1276-1285.
Gikas, G.D., and V. A. Tsihrintzis. 2012. Assessment of water quality of first-flush roof runoff and
harvested rainwater. Journal of Hydrology 466-467:115-126.
Gilbert, J.K., and J.C. Clausen. 2006. Stormwater runoff quality and quantity from asphalt, paver, and
crushed stone driveways in Connecticut. Water Research 40:826-832.
Harris, R.W. 1992. Arboriculture: integrated management of landscape trees, shrubs and vines (2nd ed.),
Englewood Cliffs: Prentice Hall.
Hathaway, J.M., and W.F. Hunt. 2010. Evaluation of storm-water wetlands in series in Piedmont North
Carolina. Journal of Environmental Engineering 136(1):140-146.
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Hathaway, J.M., W.F. Hunt, and S.J. Jadlocki. 2009. Indicator bacteria removal in stormwater best
management practices in Charlotte, North Carolina. Journal of Environmental Engineering
135(12): 1275-1285.
Hathaway, J.M., W.F. Hunt, A.K. Graves, and J.D. Wright. 2011. Field evaluation of bioretention indicator
bacteria sequestration in Wilmington, NC. Journal of Environmental Engineering 137(12):1103-
1113.
Hatt, B.E., T.D. Fletcher, and A. Deletic. 2008. Hydraulic and pollutant removal performance of fine
media stormwater filtration systems. Environmental Science & Technology 42(7):2535-2541.
Hatt, B.E., T.D. Fletcher, and A. Deletic. 2009. Hydrologic and pollutant removal performance of
stormwater biofiltration systems at the field scale. Journal of Hydrology 365(3-4): 310-321.
Hong, E., M. Seagren, and A.P. Davis. 2006. Sustainable oil and grease removal from synthetic
stormwater runoff using bench-scale bioretention studies. Water Environment Research.
78(2):141-155.
Horner, R.R. and C.R. Horner. 1995. Design, Construction, and Evaluation of a Sand Filter Stormwater
Treatment System. Part III. Performance Monitoring. Report to Alaska Marine Lines. Seattle, WA.
Hsieh, C.H., and A.P. Davis. 2005. Evaluation and optimization of bioretention media for treatment of
urban stormwater runoff. Journal of Environmental Engineering 131(11):1521-1531.
Hunt, W.F., and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance.
North Carolina Cooperative Extension, Raleigh, NC.
Hunt, W.F., A.R. Jarrett, J.T. Smith, and L.J. Sharkey. 2006. Evaluating bioretention hydrology and
nutrient removal at three field sites in North Carolina. Journal of Irrigation and Drainage
Engineering 132(6):600-608.
Hunt, W.F., J.T. Smith, S.J. Jadlocki, J.M. Hathaway, and P.R. Eubanks. 2008. Pollutant removal and peak
flow mitigation by a bioretention cell in urban Charlotte, NC. Journal of Environmental
Engineering 134(5):403-408.
Hunt, W.F., A.P. Davis, and R.G. Traver. 2012. Meeting hydrologic and water quality goals through
targeted bioretention design. Journal of Environmental Engineering 138(6):698-707.
Jones, M.P., and W.F. Hunt. 2009. Bioretention impact on runoff temperature in trout sensitive waters.
Journal of Environmental Engineering 135(8):577-585.
Jones, M.P., and W.F. Hunt. 2010. Effect of stormwater wetlands and wet ponds on runoff temperature
in trout sensitive waters. Journal of Irrigation and Drainage Engineering 136(9):656-661.
Jones, M.P., W.F. Hunt, and R.J. Winston. 2012. Effect of Urban Catchment Composition on Runoff
Temperature. Journal of Environmental Engineering. 138(12): 1231-1236.
Kim, H., E.A. Seagren, and A.P. Davis. 2003. Engineered bioretention for removal of nitrate from
stormwater runoff. Water Environment Research 75(4):355-367.
Knight, E.M.P., W.F. Hunt, and R.J. Winston. 2013. Side-by-side evaluation of four level spreader-
vegetated filter strips and a swale in eastern North Carolina.
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Kohler, M., M. Schmidt, F.W. Grimme, M. Laar, V.L. de Assungao Paiva, and S. Tavares. 2002. Green roofs
in temperate climates and in the hot-humid tropics—far beyond the aesthetics. Environment
and Health 13:382-391.
Lee, J.Y., G. Bak, and M. Han. 2012. Quality of roof-harvested rainwater - Comparison of different
roofing materials. Journal of Environmental Pollution. 162(2012)422-429.
Li, H., and A.P. Davis. 2008. Urban particle capture in bioretention media. I: Laboratory and field studies.
Journal of Environmental Engineering 143(6):409-418.
Li, H., L.J. Sharkey, W.F. Hunt, and A.P. Davis. 2009. Mitigation of impervious surface hydrology using
bioretention in North Carolina and Maryland. Journal of Hydrologic Engineering 14(4):407-415.
Li, M.-H., C.Y. Sung, M.H. Kim, and K.-H. Chu. 2010. Bioretention for Stormwater Quality Improvements in
Texas: Pilot Experiments. Texas A&M University in cooperation with Texas Department of
Transportation and the Federal Highway Administration.
Luell, S.K., W.F. Hunt, and R.J. Winston. 2011. Evaluation of undersized bioretention stormwater control
measures for treatment of highway bridge deck runoff. Water Science & Technology 64(4):974-
979.
Lye, D.J. 2009. Rooftop runoff as a source of contamination: A review. Science of the Total Environment
407:5429-5434.
MassDEP (Massachusetts Department of Environmental Protection). 1997. Massachusetts Stormwater
Handbook. Revised February 2008.
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-
handbook.html.
MassDEP (Massachusetts Department of Environmental Protection). 2003. Erosion and Sediment Control
Guidelines for Urban and Suburban Areas: A Guide for Planners, Designers, and Municipal
Officials. Department of Environmental Protection, Bureau of Resource Protection, Boston, MA.
MDE (Maryland Department of the Environment). 2013. Cost Efficiency and Other Factors in Urban
Stormwater BMP Selection.
http://www.mde.state.md.us/programs/Water/TMDL/TMDLImplementation/Documents/Regio
nal Meetings/Fall2013/presentations/Cost Efficiency WIP Fall Workshops 10312013.pdf.
Moore, T.C., W.F. Hunt, M.R. Burchell, and J.M. Hathaway. 2011. Organic nitrogen exports from urban
stormwater wetlands in North Carolina. Ecological Engineering 37(4):589-594.
MWCOG (Metropolitan Washington Council of Governments). 1983. Urban Runoff in the Washington
Metropolitan Area: Final Report, Urban Runoff Project, EPA Nationwide Urban Runoff Program.
Metropolitan Washington Council of Governments, Washington, DC.
Myers, B.R., S. Beecham, J.A. van Leeuwen, and A. Keegan. 2009. Depletion of E. coli in permeable
pavement mineral aggregate storage and reuse systems. Water Science and Technology
60(12):3091-3099.
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Newman, S., and K. Pietro. 2001. Phosphorus storage and release in response to flooding: implications
for Everglades stormwater treatment areas. Ecological Engineering 18(l):23-38.
Olszewski, J.M., and A.P. Davis. 2013. Comparing the Hydrologic Performance of a Bioretention Cell with
Predevelopment Values. Journal of Irrigation and Drainage 139(2):124-130.
Pagotto, C, M. Legret, and P. Le Cloirec. 2000. Comparison of the hydraulic behaviour and the quality of
highway runoff water according to the type of pavement. Water Research 34(18):4446-4454.
Passeport, E., W.F. Hunt, D.E. Line, R.A. Smith, and R.A. Brown. 2009. Field study of the ability of two
grassed bioretention cells to reduce stormwater runoff pollution. Journal of Irrigation and
Drainage Engineering 135(4):505-510. Ramsey, C.G. & H. R. Sleeper. 1988. Architectural Graphic
Standards (Eighth Ed.), Somerset, NJ: John Wiley & Sons.
Peck, S.W. and A. Johnston. 2006. The Green Roof Infrastructure Monitor 8(1).
http://www.greenroofs.org/resources/GRIM Spring2006.pdf.
Roseen, R.M., T.P. Ballestero, J.J. Houle, P. Avellaneda, J.F. Briggs, G. Fowler, and R. Wildey. 2009.
Seasonal performance variations for storm-water management systems in cold climate
conditions. Journal of Environmental Engineering 135(3):128-137.
Roseen, R.M., T.P. Ballestero, J.J. Houle, J.F. Briggs, and K.M. Houle. 2011. Water quality and hydrologic
performance of a porous asphalt pavement as a stormwater treatment strategy in a cold
climate. Journal of Environmental Engineering 138(l):81-89.
Rusciano, G. M., and C.C. Obropta. 2007. Bioretention column study: fecal coliform and total suspended
solids reductions. Transactions oftheASABE 50(4):1261-1269.
Rushton, B.T. 2001. Low-impact parking lot design reduces runoff and pollutant loads. Journal of Water
Resources Planning and Management 127(3):172-179.
Schroll, E., J. Lambrinos, T. Righetti, and D. Sandrock. 2011. The role of vegetation in regulating
stormwater runoff from green roofs in a winter rainfall climate. Ecological Engineering
37(4):595-600.
Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban
BMPS. Department of Environmental Programs, Metropolitan Washington Council of
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Schueler, T.R. 1995. Site Planning for Urban Stream Protection. Metropolitan Washington Council of
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Manual for Planning and Designing Urban BMPs. Metropolitan Washington Council of
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Schueler, T.R., P. A. Kumble, and M.A. Heraty. 1992. A Current Assessment of Urban Best Management
Practices, Techniques for Reduction Non-Point Source Pollution in the Coastal Zone. Metropolitan
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SEMCOG (Southeast Michigan Council of Governments). 2008. Low Impact Development Manual for
Michigan: A Design Guide for Implementers and Reviewers.
http://librarv.semcog.org/lnmagicGenie/DocumentFolder/LIDManualWeb.pdf. Accessed June 5,
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Stander, E.K., and M. Borst. 2010. Hydraulic test of a bioretention media carbon amendment. Journal of
Hydrologic Engineering 15(6):531-536.
Strecker, E.W., M.M. Quigley, B. Urbonas, and J. Jones. 2004. Analyses of the expanded EPA/ASCE
International BMP Database and potential implications for BMP design. In Proceedings of the
World Water and Environmental Resources Congress, American Society of Civil Engineers, Salt
Lake City, UT, June 27—July 1, 2004.
Street Tree Seminar, Inc. 1999. Street Trees Recommended for Southern California. Anaheim, California.
Struck, S.D., A. Selvakumar, and M. Borst. 2008. Prediction of effluent quality from retention ponds and
constructed wetlands for managing bacterial stressors in storm-water runoff. Journal of
Irrigation and Drainage 134(5):567-578.
Thomas, P.R., and G.R. Greene. 1993. Rainwater quality from different roof catchments. Water Science
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a Bioretention Swale. Interim Report #3. Seneca College, King City, Ontario.
Tota-Maharaj, K., and M. Scholz. 2010. Efficiency of permeable pavement systems for the removal of
urban runoff pollutants under varying environmental conditions. Environmental Progress and
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Wardynski, B.J., R.J. Winston, and W.F. Hunt. 2013. Internal water storage enhances exfiltration and
thermal load reduction from permeable pavement in the North Carolina mountains. Journal of
Environmental Engineering 139(2):187-195.
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North Carolina: Afield assessment. Journal of Environmental Engineering 138(12):1210-1217.
Winston, R.J., W.F. Hunt, S.G. Kennedy, J.D. Wright, and M.S. Lauffer. 2012. Field evaluation of storm-
water control measures for highway runoff treatment. Journal of Environmental Engineering
138(1): 101-111.
Winston, R.J., W.F. Hunt, D.L. Osmond, W.G. Lord, and M.D. Woodward. 2011. Field evaluation of four
level spreader-vegetative filter strips to improve urban storm-water quality. Journal of Irrigation
and Drainage Engineering 137(3): 170-182.
Winston, R.J., W.F. Hunt, and W.G. Lord. 2011. Thermal mitigation of urban stormwater by level
spreader—Vegetative filter strips. Journal of Environmental Engineering 137(8):707-716.
Wolf, D., and J.T. Lundholm. 2008. Water uptake in green roof microcosms: Effects of plant species and
water availability. Ecological Engineering 33:179-186.
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pervious pavements under variable drying and wetting regimes. Water Science and Technology
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runoff pollution. Journal of Water Resources Planning and Management. 127(3):168-171.
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6. Green Infrastructure Review Process
6.1. Local Review Process
Implementing green infrastructure development strategy from design concept to successful
construction and long-term operation requires an efficient and well-designed review and approval
process. The plan review and approval process helps ensure quality design and construction through the
planning, design, construction, and post-construction phases. Most site plan reviews for a specified
development are typically performed by a combination of a local planning commission, state or local
agency staff (including staff engineers), and governing boards, and are typically conducted to ensure the
following:
P The design will comply with local, state, and federal requirements
P Public facilities and infrastructure are adequate to serve future residents
P The development will not adversely impact the environment or adjacent neighborhoods
P Landscaping and screening are appropriate
P Structures and their locations are compatible with surrounding uses
Most municipalities follow a similar plan review process; although larger cities require approvals from
several departments, while smaller towns might only have a limited number of people involved.
Regardless, an efficient site plan review and approval process should involve continuous interaction
between the developer and reviewers from concept planning to final inspection. In a community that
has existing stormwater ordinances, site plan review and approval can include the following steps:
(1) Concept plan submittal and meeting between developer and reviewers
(2) Preliminary site plan and stormwater plan submittal, review, and approval
(3) Submittal of operations and maintenance agreements and performance guarantees for
stormwater BMPs
(4) Submittal of as-built documentation for stormwater BMPs
(5) Final inspection
(6) Issuance of certificate of occupancy
Designing a site for green infrastructure practices for either new or redevelopment requires a
reorganized process from the typical project approach. The site planning process presented in Section 4
is iterative and requires input from a geotechnical engineer, landscape architect, civil engineer, and the
building architect. Reviewers and developers (or their engineers) need to have a clear understanding of
the stormwater management goals for the community and the optimal green infrastructure practices for
a particular site to meet watershed-based targets. Green infrastructure encourages adaptive land use
such as minimizing impervious cover; a strategy that often requires interpretation of zoning, paving,
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parking, and sidewalk ordinances. Therefore, initiating meetings between developers and
regulatory/planning staff early in the planning process is an important strategy for successful and
efficient green infrastructure plan review. This early coordination helps determine and document
analysis criteria and stormwater management goals that vary by watershed and land use, which reduces
interpretation of stormwater management approaches during later stages of plan review. In addition, it
could potentially warrant the incentive for communities to offer expedited review to developers that
implement green infrastructure design to meet stormwater management goals.
An example project review process is offered in Figure 6-1, with a "traditional" review process on the
left, and a green infrastructure alternative review process which provides the incentive of expedited
review to encourage developers to use green infrastructure design. This type of flow chart, when
tailored to local permitting processes and requirements, can be shared with applicants to inform their
decision-making.
Figure 6-1. Sample planning review process, with (right) and without (left) green infrastructure
incentive.
6.2. Massachusetts Plan Review and Permitting Process
As part of the MassDEP's plan review and permitting process, a Stormwater Report must be submitted
to document compliance with the state's Stormwater Management Standards (as detailed in Chapter 3,
Volume 1 of the Massachusetts Stormwater Handbook [2008]). In addition to all plans and supporting
information/calculations, the Stormwater Report must also include a brief narrative describing
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environmentally sensitive site design and green infrastructure practices used within the development.
MassDEP also requires submittal of a checklist to help reviewers and developers ensure the Stormwater
Report is complete. Although the checklist includes a section for green infrastructure measures and
environmental sensitive design, a more detailed checklist is provided below for further evaluating
developments for green infrastructure implementation.
The checklist below (Table 6-1) is intended to assist municipal decision makers in evaluating both public
and private development projects that seek to implement green infrastructure design. While this does
not incorporate regulatory aspects, it can serve as a convenient tool for evaluating innovative
approaches to green infrastructure design and maintenance. Note that MassDEP has a separate,
general checklist to be submitted with its Stormwater Report available at
http://www.mass.gov/eea/docs/dep/water/laws/i-thru-z/swcheck.pdf.
Table 6-1. Planning Review Board supplemental checklist for green infrastructure plan review
Planning Review Board supplemental checklist for green infrastructure plan review
Site Evaluation
Provided?
Comments:
Provide vicinity map showing project boundary
superimposed on map showing adjacent streets and
nearby hydrologic features (streams, reservoirs, etc.) and
FEMA floodplain.
~ Yes
~ No
~ N/A
Identify targeted pollutant and flow attenuation needs.
~ Yes
~ No
~ N/A
Identify environmentally sensitive areas, areas that
provide water quality benefit.
~ Yes
~ No
~ N/A
Classify and map existing soils, including HSG.
~ Yes
~ No
~ N/A
Identify areas that are susceptible to erosion or sediment
loss.
~ Yes
~ No
~ N/A
Identify areas of high infiltration potential.
~ Yes
~ No
~ N/A
Provide total existing impervious area within the site
boundary, expressed in acres or square feet and as a
percentage of the total project area.
~ Yes
~ No
~ N/A
Provide total planned impervious area within the site
boundary, expressed in acres or square feet and as a
percentage of the total project area.
~ Yes
~ No
~ N/A
Minimize Site Impact
Provided?
Comments:
Develop previously disturbed land (urban infill, vacant
lots).
~ Yes
~ No
~ N/A
Preserve natural drainage ways.
~ Yes
~ No
~ N/A
Provide undisturbed buffer for creeks and waterways.
~ Yes
~ No
~ N/A
Provide details regarding planned slope protection
measures to improve geotechnical stability and mitigate
potential erosion.
~ Yes
~ No
~ N/A
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Planning Review Board supplemental checklist for green infrastructure plan review
Minimize grading and filling as much as possible.
~ Yes
~ No
~ N/A
Plan for phased development and clearing to limit soil
disturbance.
~ Yes
~ No
~ N/A
Incorporate existing drainage infrastructure into the
proposed stormwater management plan to extent
possible.
~ Yes
~ No
~ N/A
Minimize Impervious Area
Provided?
Comments:
Reduce roadway setbacks for buildings.
~ Yes
~ No
~ N/A
Cluster buildings.
~ Yes
~ No
~ N/A
Use minimum allowable road widths.
~ Yes
~ No
~ N/A
Include intersection deflectors (chicanes, pop-outs) in
roadway design.
~ Yes
~ No
~ N/A
Minimize number and dimensions of parking stalls.
~ Yes
~ No
~ N/A
Use shorter driveways for residences.
~ Yes
~ No
~ N/A
Limit sidewalks to one side of street where possible.
~ Yes
~ No
~ N/A
Reduce Effective Impervious Area
Provided?
Comments:
Downspouts directed to turf or landscaped areas.
~ Yes
~ No
~ N/A
Driveways graded to pervious areas.
~ Yes
~ No
~ N/A
Use grassed or landscaped swales instead of curb and
gutter.
~ Yes
~ No
~ N/A
Use pervious alternatives for low-traffic paved areas
(e.g., gravel, pavers, porous pavement, grassed parking).
~ Yes
~ No
~ N/A
Encourage mix-used developments that promote walking
versus driving.
~ Yes
~ No
~ N/A
Encourage Public Open Space
Provided?
Comments:
Provide high-value undisturbed open space in addition to
low-value land (e.g., steep slopes, wetlands).
~ Yes
~ No
~ N/A
Design compact residential lots with shared common
open space.
~ Yes
~ No
~ N/A
Increase residential unit densities through vertical
building or zero lot lines.
~ Yes
~ No
~ N/A
Maximize Infiltration
Provided?
Comments:
Locate green infrastructure practices on the relatively
lower runoff/higher infiltrating soil types.
~ Yes
~ No
~ N/A
Incorporate bioretention or infiltration features into
landscaping plan.
~ Yes
~ No
~ N/A
Extend drainage flow paths of swales as long as
possible.
~ Yes
~ No
~ N/A
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Planning Review Board supplemental checklist for green infrastructure plan review
Provide practices and guidelines to minimize soil
compaction.
~ Yes
~ No
~ N/A
Hydrologic Evaluation
Provided?
Comments:
Provide a detailed description of site design on-site and
how the proposed project maximizes use of green
infrastructure site design.
~ Yes
~ No
~ N/A
Provide tabulation of all impacted areas including
contributing drainage area, pervious area, slope, soil,
surface cover, and runoff coefficient.
~ Yes
~ No
~ N/A
Provide channel assessment for receiving streams
between the project discharge and the domain of
analysis.
~ Yes
~ No
~ N/A
Treatment Control (TC) BMPs
Provided?
Comments:
Provide details regarding the proposed project site
drainage network, including storm drains, concrete
channels, swales, detention facilities, stormwater
treatment facilities, natural and constructed channels,
and the method for conveying off-site flows through or
around the proposed project.
~ Yes
~ No
~ N/A
Provide narrative description of TC BMP selection
procedure based on soil infiltration potential,
hydromodification management criteria applicability, and
required pollutant removal efficiency.
~ Yes
~ No
~ N/A
Provide sizing calculation for each proposed BMP
including water quality design flow, design volume, outlet
design, overflow design, drawdown, ponding depth, etc.
~ Yes
~ No
~ N/A
Provide standard details for bioretention BMP facilities,
including underdrain design, soil mix specifications, and
overflow design.
~ Yes
~ No
~ N/A
Identify green roofs, if applicable, along with BMP-
specific design details.
~ Yes
~ No
~ N/A
Identify areas of proposed permeable pavement along
with applicable design details including underdrains, if
applicable.
~ Yes
~ No
~ N/A
Identify areas of active landscaping that will require
irrigation.
~ Yes
~ No
~ N/A
Identify rainwater harvesting facilities and standard detail,
if applicable.
~ Yes
~ No
~ N/A
Provide documentation regarding BMP operation and
maintenance, access easements, and certification to
accept maintenance responsibility.
~ Yes
~ No
~ N/A
Maintenance
Provided?
Comments:
Provide details regarding method for maintenance
extending into perpetuity (Homeowners Association,
Community Facilities District, etc.).
~ Yes
~ No
~ N/A
Provide details regarding the required BMP maintenance
activities and frequency required for each BMP.
~ Yes
~ No
~ N/A
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Planning Review Board supplemental checklist for green infrastructure plan review
Provide signed documentation providing for BMP
maintenance access into perpetuity if access is needed.
~ Yes
~ No
~ N/A
Sediment and Erosion Controls
Provided?
Comments:
Protect sensitive environmental features (e.g., streams,
ponds, buffers, wetlands, Natural Heritage Inventory
sites) from construction impacts.
~ Yes
~ No
~ N/A
Protect post-construction BMPs and from construction
runoff, such as from sediment clogging bioretention
areas.
~ Yes
~ No
~ N/A
Delineate locations and extents all features off-limits to
construction traffic, such as drip lines for protected
specimen trees and critical habitats.
~ Yes
~ No
~ N/A
6.3. Incentives
Municipalities can use a variety of incentives to encourage
green infrastructure implementation for new and existing
developments. Incentives can encourage developers to use
green infrastructure practices during the planning and
design process for new development projects. For existing
development, incentives can help property owners retrofit
their sites with new BMPs. In addition to the incentives listed
below, section 2.7 of this Handbook lists a number of grant
programs available to fund green infrastructure projects.
According to EPA, four common incentive mechanisms used
at the local level are fee discounts or credits, development
incentives, BMP installation subsidies, and awards and
recognition programs, as described below (USEPA 2012):
1. Stormwater fee discount or credit
Municipalities often charge a stormwater fee based on
the amount of impervious surface area on a property. If a
property owner decreases a site's imperviousness or adds
green infrastructure practices to reduce the amount of
stormwater runoff that leaves the property, the
municipality will reduce the stormwater fee or provide a
credit that helps the landowner meet a water quality
performance or design requirement.
2. Development incentives
Local governments can offer incentives that are only
available to a developer who uses green infrastructure
Definitions
Fee discounts or credits require a
stormwater fee that is based on
impervious surface area. If property
owners can reduce need for service by
reducing impervious area, the
municipality reduces the fee.
Development incentives are offered to
developers during the process of
applying for development permits. They
include zoning upgrades, expedited
permitting, reduced stormwater
requirements, and other incentives.
Rebates and installation financing
give funding, tax credits or
reimbursements to property owners who
install specific practices. These
incentives are often focused on
practices needed in certain areas or
neighborhoods.
Awards and recognition programs
provide marketing opportunities and
public outreach for exemplary projects.
These programs can include monetary
awards.
Source-. USEPA 2010
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practices. Some economic development corporations will use these incentives to encourage
development on targeted sites, such as redevelopment in downtown or underserved areas. For
example, cities might offer to waive or reduce permit fees, expedite the permit process, allow
higher density developments, or provide exemptions from local stormwater permitting
requirements for developers that use green infrastructure practices to meet stormwater
management goals.
3. Rebates and installation financing
To offset costs, cities might offer grants, matching funds, low-interest loans, tax credits, or
reimbursements to property owners who install specific green infrastructure practices or systems.
For example, some communities offer programs that subsidize the cost of rain barrels, plants and
other materials that can be used to control stormwater. Similarly, public improvements financed
through public and private partnerships can require green infrastructure implementation to meet
community goals.
4. Awards and recognition programs
More communities are holding green infrastructure design contests to encourage local participation
and innovation. Many communities highlight successful green infrastructure sites by featuring them
in newspaper articles, on websites and in utility bill mailings. Some also issue yard signs to recognize
property owners who have installed green infrastructure. Recognition programs can help to increase
property values, promote property sales and rentals, and generally increase demand for the
properties. Businesses receiving green awards can enhance sales materials to generate increase
revenue.
6.4. References
MassDEP (Massachusetts Department of Environmental Protection). 2008. Massachusetts Stormwater
Handbook, http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-
stormwater-handbook.html
USEPA (U.S. Environmental Protection Agency). 2010. Green Infrastructure Case Studies: Municipal
Policies for Managing Stormwater with Green Infrastructure. Accessed March 4, 2013.
http://www.epa.gov/owow/NPS/lid/gi case studies 2010.pdf.
USEPA (U.S. Environmental Protection Agency). 2012. Encouraging Low Impact Development: Incentives
Can Encourage Adoption of LID Practices in Your Community. Accessed March 4, 2013.
http://www.epa.gov/owow/NPS/lid/gi case studies 2010.pdf.
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Table of Contents
Appendix A Watershed Assessment Supplemental Information A-l
A. Watershed Assessment - Supplemental Information A-3
A.l Part 1: Identify Study Watershed A-3
A. 1.1 Principal Watersheds in Massachusetts A-3
A.2 Part 2: Identify Existing Hydrologic and Hydraulic Data A-4
A.2.1 Watershed Boundaries A-4
A.2.2 Water Bodies (Hydrography) A-5
A.2.3 Land Use/Land Cover and Impervious Surface A-6
A.2.4 Topography and Elevation A-6
A.2.5 Soils A-7
A.2.6 Parcels A-7
A.2.7 Aerial Photography A-8
A.2.8 Additional Data Resources A-8
A.3 Part 3: Characterize Known Pollutant Loadings A-13
A.3.1 Identify Pollutants of Concern A-13
A.3.2 Estimate Pollutant Loadings A-15
A.4 References A-17
Appendix B Example Green Infrastructure Conceptual Site Design B-l
B. Conceptual Site Design Watershed B-3
B.l Example Green Infrastructure Conceptual Site Design B-3
B.l.l Phase I - Site Assessment B-3
B.l.2 Phase II - Preliminary Design B-9
B.1.3 Phase III - Determine Final Design B-20
B.2 References B-22
Appendix C Green Infrastructure BMP Operation, Maintenance, and Monitoring C-l
C. BMP Maintenance and Monitoring - Supplemental Information C-3
C.l BMP Operation and Maintenance C-3
C.l.l Bioretention C-4
C.l.2 Water Quality Swale C-6
C.l.3 Tree Box Filter C-7
C.1.4 Sand Filter C-7
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C.1.5 Permeable Pavement C-7
C.1.6 Cisterns and Rain Barrels C-8
C.1.7 Constructed Stormwater Wetlands C-9
C.1.8 Green Roofs C-10
C.2 BMP Monitoring C-ll
C.2.1 Monitoring Hydrology C-12
C.2.2 Monitoring Water Quality C-17
C.2.3 Sample Collection and Handling C-17
C.3 References C-18
List of Figures
Figure A-l. Principal watersheds in Massachusetts (8-digit HUCs) A-3
Figure A-2. Cape Cod 8-dight subbasin showing 10- and 12-digit HUCs and megabasin
boundaries A-5
Figure B-l. Example capital improvement project conceptual site for green infrastructure B-3
Figure B-2. Identify applicable zoning requirements, utility easements, and site setbacks B-4
Figure B-3. Preservation of native soils and vegetation B-6
Figure B-4. Protect natural and sensitive areas (wetlands, native tree groves, steep hillside) and
conduct geotechnical survey to characterize infiltration capacity of soils B-7
Figure B-5. Identify and protect key hydrologic areas, such as infiltrating soils (blue area) and
wetlands (orange areas) B-9
Figure B-6. Identify ideal locations for green infrastructure implementation according to site
conditions B-10
Figure B-7. Establish grading envelope to protect natural areas and infiltrating soils B-12
Figure B-8. Site example demonstrating placement of pervious material (red) and opportunities
to minimize connected impervious area (yellow) B-13
Figure B-9. Bioretention incorporated into a pop-out (Kansas City, Missouri) B-15
Figure B-10. Example of an intersection pop-out B-16
Figure B-ll. Site plan indicating all possible BMP locations (blue areas) and types (annotated) B-19
Figure B-12. Completed site plan including iterations of Steps 4-7 and BMP sizing completed B-21
Figure C-l. Bioretention area clogged with sediment C-5
Figure C-2. Inlet sump to remove gross solids C-6
Figure C-3. Erosion caused by excessive flows in a bioswale C-7
Figure C-4. Plant growth, debris buildup, and puddles indicate that permeable pavement is
clogging. Prompt maintenance should be performed to prevent joints from fully
sealing C-8
Figure C-5. Self-cleaning inlet filters C-9
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Figure C-6. Outlet varied with weir boards C-10
Figure C-7. Outlet with a trash rack C-10
Figure C-8. White gravel indicates a no plant zone for a green roof C-ll
Figure C-9. Inflow pipe to bioretention area equipped with compound weir and bubbler for flow
measurement. Water quality sampling tube and strainer are visible inside pipe C-12
Figure C-10. Inlet curb cut with a v-notch weir C-13
Figure C-ll. Outlet of a roadside bioretention pop-out equipped with a V-notch weir for flow
monitoring C-13
Figure C-12. Underdrains from permeable pavement equipped with 30-degree V-notch weir
boxes and samplers for flow and water quality monitoring C-14
Figure C-13. Example of a bioretention underdrain outlet with sufficient drop to install a flow
monitoring weir without encountering tailwater C-15
Figure C-14. Poorly installed H-flume at the inlet to a bioretention area in which the invert of the
weir is too low, and tailwater from the bioretention will interfere with
measurement C-15
Figure C-15. Monitoring points C-16
Figure C-16. Example of manual (left) and tipping bucket (right) rain gauges C-16
List of Tables
Table A-l. Median EMCs for urban land uses (USEPA 1983) A-16
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Appendix A
Watershed Assessment
Supplemental Information
A-1
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A. Watershed Assessment-Supplemental Information
A.l Part 1: Identify Study Watershed
A.l.l Principal Watersheds in Massachusetts
Massachusetts contains eight major drainage areas [megahasins)—the Coastal, Connecticut,
Housatonic, Hudson, Merrimack, Narragansett, Piscataqua-Saimon Falls, and Thames River basins. These
megabasins can be further divided into 27 principal watersheds as shown in Figure A-l.
Figure A-l, Principal watersheds in Massachusetts (8-digit HUCs).
The 27 watersheds in the state can be further subdivided into smaller units depending on the scale and
area of interest for the study. Common practice is to use watershed delineations previously developed
by the U.S. Geological Survey (USGS) and Natural Resources Conservation Service (NRCS), by which
basins, watersheds, and subwatersheds are identified using a Hydrologic Unit Code (HUC) based on
scale. Section A.2.1 describes this watershed identification system in more detail.
In the case where HUC subwatersheds still exceed the scale of study, they can be further subdivided into
even smaller units at the local scale using other high-resolution datasets (e.g., NHDPIus catchments) or
by employing geospatial data such as contour lines, digital elevation models (DEMs), and aerial imagery
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to further subdivide watersheds to achieve desired sizes and extents. Using these existing data sources,
a geographic information system (GIS) based representation of the study watershed should be
developed (or obtained, if it already exists) to define the geographic scope and facilitate assessment.
A.2 Part 2: Identify Existing Hydrologic and Hydraulic Data
A.2.1 Watershed Boundaries
Section 2.1 provided a brief overview of watershed identification. Hydrologic watershed boundaries
describe the physical extent of watersheds. USGS and NRCS have developed the national Watershed
Boundary Dataset (WBD), which "defines the areal extent of surface water drainage to a point" (USGS
2014). The WBD data, provided by MassGIS, uses the HUC system in which watersheds are identified
using 2, 4, 6, 8, 10, or 12 digits depending on scale. For example, hydrologic regions use only a 2-digit
HUC while the smallest scale subwatersheds use a 12-digit HUC. The HUC describes where the unit is in
the country and the level of the unit, as outlined below (MassGIS 2014b).
First 2 digits: region (hydrologic region)
First 4 digits: subregion (megabasin)
First 6 digits: accounting units (basin)
First 8 digits: cataloging units (subbasin)
First 10 digits: watershed units (watershed)
Full 12 digits: subwatershed units (subwatershed)
The Massachusetts Ocean Resource Information System (MORIS) provides access to the same
watershed boundary datasets as MassGIS and is focused on the coastal zone.
It should be noted that additional HUC delineations are possible (for example, some states have
developed 14-digit HUCs); however, the HUCs indicated above are those currently developed for
Massachusetts. Per MassGIS, USGS developed HUCs up to 8 digits for the U.S. while the NRCS within
each state is developing the finer scale delineations (MassGIS 2014b).
The full number of HUC digits used defines the scale of the watershed or subwatershed, which depends
on the scale of the project. MassGIS provides access to NRCS 8-digit, 10-digit, and 12-digit HUC data as
well as 4-digit HUC data. As an example, Figure A-2 shows a portion of the Cape Cod 8-digit subbasin
(purple outline), specifically the South Shore Tributaries and Islands HUC-10 watershed, along with other
corresponding 10-digit (orange outline) and 12-digit (light grey outline) delineation scales. The thick
black outline represents megabasin boundaries (4-digit HUC).
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Figure A-2. Cape Cod 8-dight subbasin showing 10- and 12-digit HUCs and megabasin boundaries.
A.2.2 Water Bodies (Hydrography)
Hydrography data represent hydrographic (water-related) features in the watershed, including surface
water (lakes, ponds, and reservoirs), wetlands, bogs, flats, rivers, streams, and more (MassGIS 2014a).
MassGIS provides access to the Massachusetts Department of Environmental Protection (MassDEP)
hydrography dataset, which expands on the existing USGS 1:25,000 scale hydrography layer by adding
local stream resolution for enhanced detail, which is ideal for watershed assessment at the local scale.
MORIS is a one-stop shop for spatial hydrography data for coastal Massachusetts. MORIS provides
access to DEP rivers, streams, and water bodies (1:25,000), DEP wetlands (1:12,000), and National
Wetlands Inventory (NWI) streams and wetlands.
Local-, regional-, or state-level datasets are often the best option for hydrography; however, it is
important to know about alternative datasets such as the National Hydrography Data (NHD) and
NHDPIus datasets which might be better suited for the particular analysis, or can serve as supplemental
data sources. These are available at the following websites, respectively:
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¦ NHD (low-, medium-, or high-resolution):
http://nhd.usgs.gov/data.html
Data download available from:
ftp://nhdftp.usgs.gov/DataSets/Staged/States/
¦ NHDPIus (medium resolution):
www.horizon-systems.com/nhdplus/
The existence of streams, lakes, and other water bodies in the watershed with known water quality
impairments can be a key factor in determining appropriate locations for green infrastructure. This is
discussed in Section A.2.8.5.
A.2.3 Land Use/Land Cover and Impervious Surface
Vegetation, degree of land development, and other features can be observed and quantified in broad
terms from aerial photography, but more detailed spatial characterization is facilitated with GIS datasets
describing land use and land cover. A popular resource is the National Land Cover Database (NLCD), a
national dataset produced by the Multi-Resolution Land Characteristics Consortium (MRLC). The
database is updated at approximately 5-year intervals. NLCD 2011 was released in April 2014.
MORIS also provides access to land use and land cover datasets for the coastal zone. Land cover is based
on NOAA's Coastal Change Analysis Program (C-CAP). As of mid-2014, the most recent land cover
dataset on MORIS was from 2006, and the most recent land use dataset was from 2005. MORIS also
provides datasets indicating land use and land cover change over various time periods.
Land use analysis can indicate degree of impervious surface cover, which is often associated with
degraded physical and biological stream conditions. Breakdown of existing land use will also indicate
percentage of development, including residential, commercial, industrial, and institutional land uses.
Expected growth and development can be used to identify spatial distributions of projected land use
changes. Increases in development and impervious cover can have significant effects on water quality
and quantity, and areas with a high degree of development and impervious surface are generally
considered high priority for green infrastructure implementation.
A.2.4 Topography and Elevation
Topography is a description of the surface features of the watershed in terms of shape, aspect, slope,
and elevation. Locations with excessive slope might not be suitable for green infrastructure. Section 3
discusses the importance of topography and slope for green infrastructure site prioritization in greater
detail.
USGS topographic maps are a visual tool for analyzing the elevation and slope characteristics of a
watershed at a larger scale (1:24,000) and are available through MassGIS. For a more detailed
description of topography, digital elevation models (DEMs) are typically used for GIS-based analysis.
DEMs are spatial data in raster (gridded) format in which each cell (pixel) value represents an elevation
above (positive elevation) or below (negative elevation) sea level. MassGIS provides DEM data in
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squares with a resolution of 5 meters by 5 meters. USGS also maintains nationwide coverage of DEM
data at 30-meter, 10-meter, and 3-meter resolution (http://ned.usgs.gov/), available through the
NRCS/USDA Geospatial Data Gateway (GDG, http://datagateway.nrcs.usda.gov/). Note that 3-meter
resolution data are currently not available for all areas of the nation. DEM data can be used in GIS
software such as ArcGIS to calculate slope or render elevation contours.
MORIS also provides access to elevation data, including USGS topographic maps. Also included in MORIS
are elevation contours at an interval of 3 meters and an elevation grid at 1:5,000 scale.
A.2.5 Soils
An investigation of soils in the watershed should include descriptions of soil types, textures, and
hydrologic properties. For example, soils with higher infiltration capacities are generally better suited for
green infrastructure. For green infrastructure assessment purposes, soils are typically rated by
hydrologic soil group (HSG), which is a classification system NRCS developed to sort soils into four
categories (A, B, C, and D) based on runoff potential, water transmission, texture, hydraulic conductivity,
and other physical factors. Group A soils have the lowest runoff potential and Group D soils have the
highest runoff potential when thoroughly wet.
Green infrastructure is best suited for native soils with high infiltration capacities, which generally fit
into HSGs A, A/B, and B. The existence of clayey/silty soils can prohibit infiltration. As described in
Section 3.3, installing green infrastructure on poorly draining soils may require underdrain systems, soil
amendments, deep-rooted vegetation, or a combination of these, which increases construction
complexity.
MassGIS provides a NRCS SSURGO (Soil
Survey Geographic Database)-certified soils
data layer, with statewide coverage as of
November 2012. Soils data can be
downloaded for individual counties or as a
single statewide coverage. "SSURGO-
certified" indicates that NRCS has reviewed
and approved all of the soils data for quality
standards. Alternatively, soils data for
Massachusetts (and beyond) can be readily
downloaded from the NRCS/USDA Web Soil
Survey (http://websoilsurvey.nrcs.usda.gov)
or through the NRCS/USDA GDG.
Hydrologic Soil Groups (HSG)
HSG
Description
Soil textures
-
Low runoff potential
when wet
Sand, loamy sand,
or sandy loam
B
Moderately low
runoff potential
when wet
Silt loam or loam
c
Moderately high
runoff potential
when wet
I
Sandy clay loam
D
i
High runoff
potential when wet
Clay loam, silty clay
loam, sandy clay,
silty clay, or clay ,
L
J
A.2.6 Parcels
Parcel data are essential for identifying ownership when investigating potential green infrastructure
opportunities in the watershed. For example, vacant and publicly-owned parcels might provide greater
probability of successful implementation of green infrastructure than those that are currently under
private ownership for many reasons. This is discussed further in Section 3. MassGIS provides a recently
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completed (October 2013) dataset of property boundaries and information for all but a few
communities in the state, based on tax records. Parcel data ("Assessor's Parcels") are also available for
the coastal zone through MORIS.
A.2.7 Aerial Photography
Even for relatively small watersheds, it is not practical to visually inspect every parcel to match them
with the appropriate BMP option. It is recommended that the watershed assessment team employ a
systematic screening process based on the best available GIS data coupled with a targeted field
assessment. The screening process will incorporate knowledge from BMP experts regarding site
suitability to identify which sites are expected to offer the best opportunities for green infrastructure.
When combined with the other datasets outlined above, aerial photography can be an effective tool for
visually inspecting sites without physically visiting them. Inspection of aerial photos can enable
preliminary characterization of land use, vegetation, and impervious cover; identification of utilities such
as electric lines and easements; and other important features that can either facilitate or limit green
infrastructure. In general, "leaf-off" imagery is most desirable because it enables better visualization of
land use and land cover in areas with deciduous trees. Aerial photography should be used to screen out
locations in the watershed that are not suitable for green infrastructure due to obvious limitations.
MassGIS is perhaps the best place to start when searching for aerial imagery for Massachusetts. The
program currently provides access to USGS color orthoimagery for varying time periods for the entire
state. Aerial imagery was completed in April 2013 for three urban areas (metropolitan Boston,
Worcester, and Springfield). The 2013 imagery covers a large percentage of the state, and an index map
showing the area covered is available on MassGIS. For remaining areas of the state, MassGIS provides
color orthoimagery for 2008 or 2009, depending on area. Coverage area for the 2008 and 2009 data can
also be viewed on the MassGIS website.
MORIS offers numerous aerial imagery layers for viewing in its interactive mapping feature. However,
orthophotos currently cannot be downloaded through MORIS. Alternatively, it is possible that individual
counties and municipalities perform their own aerial imagery flyovers.
A.2.8 Additional Data Resources
A.2.8.1 Existing Stormwater Structures and Pipes
Local municipalities typically develop and maintain datasets which identify the locations and
specifications of stormwater pipes and features, and if so, these data should be readily available. Some
smaller municipalities might not possess spatial data for their stormwater drainage networks. In such
cases, it might be necessary to try to obtain engineering drawings ("as-builts") or rely on site visits to
attempt to identify and characterize existing storm features. Section 2.4 describes the process of
identifying existing green infrastructure and other stormwater BMPs. At present, MassGIS and MORIS do
not provide a statewide GIS dataset that identifies locations of stormwater pipes and features.
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A.2.8.2 Streamflow
Long-term continuously recorded stream gage data are most useful for watershed assessment. USGS
gauging stations record stream stage at 15-minute intervals then calculate a corresponding discharge
from a rating curve. The USGS National Water Information System (NWIS) provides instant access to
streamflow data at thousands of sites across the United States, including
http://nwis.waterdata.usgs.gov/nwis. In addition, the USGS Instantaneous Data Archive can be used to
access continuous streamflow data before October 1, 2007 (http://ida.water.usgs.gov/ida/).
MassGIS provides two datasets relevant to streamflow: one is "Stream-Gaging Stations" and the other is
"USGS Data-Collection Stations." However, the most reliable, up-to-date resource for locations of active
and discontinued gages is the USGS website. The NWIS Mapper can be used to quickly identify sites in
the area of interest, or for the entire state, at: http://maps.waterdata.usgs.gov/mapper/index.html.
Increasing development and impervious coverage in a watershed can significantly impact streamflow by
increasing both the magnitude of stormwater runoff (storm "peaks") and the rate at which it reaches
the stream. Analysis of streamflow data might provide clues on how the hydrology in the watershed
has changed over time because of development and help identify locations where green infrastructure
can help mitigate those impacts.
A.2.8.3 Climate and Precipitation
Appropriate characterization of precipitation patterns in the watershed will help determine suitable
types of green infrastructure. For example, some practices are better suited for climates with frequent
but low-intensity rainfall events, while others are designed for climates with infrequent but high-
intensity rainfall events.
Appropriate data should be obtained and analyzed to develop an understanding of the climate of the
watershed, particularly with respect to rainfall. Below is a list of several data sources, but note that
many others exist. (For example, some municipalities operate and maintain their own rain gauges.)
¦ National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC),
hourly and 15-minute
www.ncdc.noaa.gov/cdo-web/datasets
¦ NOAA's Climate Prediction Center (CPC) Hourly U.S. Precipitation (gridded)
www.esrl.noaa.gov/psd/data/gridded/data.cpc hour.html
¦ Massachusetts Hydrometeorological Networks (NCAR Earth Observing Laboratory)
www.eol.ucar.edu/proiects/hydrometnet/massachusetts/
¦ Community Collaboration Rain, Hail & Snow Network (CoCoRaHS), 1998-present
www.cocorahs.org/state.aspx?state=ma
¦ Mass.gov Precipitation Database (Office of Water Resources), monthly data for 176 stations, some
dating back to the 1800s
www.mass.gov/eea/agencies/dcr/water-res-protection/water-data-tracking/rainfall-program.html
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A.2.8.4 Water Quality
Analysis of water quality data will enable identification of existing water quality issues in the watershed.
Once the baseline water quality conditions and any current water quality concerns are identified, it will
be possible to begin to evaluate different green infrastructure practices for their potential to address
these water quality issues to restore and maintain water quality in the watershed.
Often, state and local agencies are the best source of water quality data. MassBays Regional
Coordinators should serve as primary points of contact for identifying sources of water quality
monitoring data, as well as to investigate the potential for partnering to obtain new data.
A source of water quality monitoring data might be local conservation or volunteer groups and
organizations with special interests within the watershed.
¦ Two great examples of volunteer monitoring efforts in the Massachusetts Bays region are the
North and South Rivers Watershed Association (www.nsrwa.org) and Salem Sound Coastwatch
(www.salemsound.org), two of the regional partners of the Massachusetts Bays Program
A.2.8.5 303(d)-Listed Water Bodies (Impaired Waters)
Per 314 CMR 4.00, MassDEP provides a detailed list of waters of the state with water use class,
designated use(s), and applicable minimum water quality standards ("Massachusetts Surface Water
Quality Standards") (www.mass.gov/eea/agencies/massdep/water/regulations/314-cmr-4-00-mass-
surface-water-qualitv-standards.html).
314 CMR 4.06 lists all waters of the state by major river basin or coastal drainage area and indicates
applicable reaches, water use class, and any special considerations (qualifiers) that may affect
application of the water quality criteria. An excerpt from 314 CMR 4.06 is shown below.
TABLE 24
SOUTH COASTAL DRAINAGE AREA (continued)
BOUNDARY MILE POINT CLASS QUALIFIERS
Jones River
Source to Wapping Pond 7.0-3.4 B Warm Water
High Quality Water
Wapping Road to Elm Street 3,4 - 2.5 B Warm Water
Cove. Herring, Iron Mine.
Second Hexiing. Stony, and
Third Herring Brook and Robinson Creek
Portion ill North River Corridor Outstanding Resource
Water
Under section 303(d) of the Clean Water Act, states are required to develop lists of waters that are
impaired by one or more pollutants. By definition, impaired waters do not meet water quality standards.
The 303(d) lists must be developed and updated every 2 years.
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An inventory of 303(d)-listed water bodies should be performed to identify streams, reservoirs, lakes,
and estuaries that do not fully support their designated uses, and to determine the extent to which the
impairment occurs (for example, the length of stream listed as impaired). These areas should be given
special attention and consideration. Causes of impairment should be reviewed to determine whether
green infrastructure could potentially provide a benefit in meeting designated uses. Knowledge of
impaired water bodies in the watershed might aid in prioritization. Designated uses might include
habitat for fish, other aquatic life, and wildlife; fish and shellfish consumption; primary (e.g., swimming)
and secondary (e.g., boating) contact recreation; and drinking water supply.
It is important to consult the most recently published 303(d) list because outdated listings might include
water bodies that have since been delisted, or might not include water bodies that have recently been
added. State 303(d) lists are submitted on even years but typically not approved until the following year.
The most recent 2012 303(d) list for Massachusetts (Integrated List) was finalized and approved in May
2013, and the 2014 303(d) list is expected to be available in 2015.
An inventory of existing and planned Total Maximum Daily Loads (TMDLs) for 303(d)-listed water
bodies should also be completed. The TMDL is the total amount of pollutant that can be assimilated by
the receiving water body while achieving applicable water quality standards. Established TMDLs for
water bodies in the watershed of interest will include detailed information on planned steps to improve
water quality to meet water quality standards and achieve designated uses.
¦ Information on TMDLs (both draft and completed) and the latest 303(d) list (Integrated List) are
made publicly available by MassDEP at
www.mass.gov/eea/agencies/massdep/water/watersheds/total-maximum-dailv-loads-tmdls.html
("Total Maximum Daily Loads").
¦ Mass.gov also provides an interactive mapping utility, which facilitates quick and easy viewing of
the statewide 2012 Integrated List of Waters, available at
www.mass.gov/eea/agencies/massdep/water/watersheds/2012-integrated-list-of-waters.html
("Interactive Mapping of the 2012 Integrated List of Waters").
A.2.8.6 Downstream Impairment
Water quality issues in waters downstream of the target watershed should also be considered, and
these downstream water bodies should be surveyed for existing impairments and TMDLs. Addressing
water quality impairments in upstream water bodies could provide mutual benefit for downstream
ones, and this should be considered when selecting sites for green infrastructure.
A.2.8.7 Environmentally Sensitive Areas
As described in Section 3.3.1, significant restrictions can apply for potential green infrastructure sites
that are located within an environmentally sensitive or protected area. This can result in construction
complexity and elevated costs. Locations within sensitive or protected areas are considered low-priority
sites, whereas areas in close proximity to these sensitive or protected areas are prioritized as green
infrastructure and can treat the runoff before it drains to these valuable areas.
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Environmentally sensitive areas in the watershed might include:
¦ Shellfish beds
¦ Sensitive salt marsh and other habitat
¦ Conserved lands (i.e., public parks, state and federal conservation lands, privately conserved lands,
etc.)
¦ Threatened and endangered species or species of special concern and their habitats
¦ Outstanding Resource Waters (ORWs)
¦ National Wetland Inventory (NWI) wetlands
¦ Recreational lakes and bathing beaches
MassGIS and MORIS provide many datasets that could be relevant and useful for identifying and
characterizing environmentally sensitive areas in the watershed.
A.2.8.8 Regulated Floodplains and Floodways
It is important to identify any potential locations in the watershed that are within regulatory floodways
and floodplains. The Federal Emergency Management Agency (FEMA) or appropriate local floodplain
management agency should be contacted for site-specific information. It is important to consider the
increased risk of flooding if green infrastructure is installed in these areas and the impact flooding could
have on the function and design of green infrastructure practices.
FEMA publishes National Flood Hazard Layer (NFHL) data, which incorporates Flood Insurance Rate Map
(FIRM) data. The FIRM is the basis for floodplain management, mitigation, and insurance activities for
the National Flood Insurance Program (NFIP). In recent years, a major effort has been undertaken to
update and upgrade all paper FIRMs into digital FIRMs (DFIRMs). The flood data classifies geographic
areas by flood risk, which determines whether flood insurance is required and the insurance rate
(MassGIS).
As of October 2013 final digital flood hazard data are available for a large area of the state, but there are
some coverage gaps. Coastal counties without final flood hazard data at this time include Barnstable
County and Nantucket County. A DFIRM status map can be viewed on MassGIS
(www.mass.gov/anf/docs/itd/services/massgis/nfhl-status.pdf).
Both MORIS and MassGIS provide access to FEMA National Flood Hazard data, which maps the various
FEMA flood risk classification zones, the regulatory floodway, and the flooding extent for the 1% and
0.2% annual chance (100-year and 500-year, respectively) probability events.
A.2.8.9 Water Supplies and Dams
It is important to identify any public water sources in the watershed and to consider ways in which water
supplies could be affected by green infrastructure, both with respect to water quality and quantity. Green
infrastructure could potentially provide water quality benefit by treating stormwater runoff before
pollutants are carried into public water supplies. In addition, green infrastructure can infiltrate
stormwater, which recharges ground water supplies and any water sources that are fed by ground water.
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Accordingly, locations of water supply intakes should be identified as well, if possible. Local municipalities
should serve as the first point of contact for identifying the locations of these features.
The MassGIS public water supply dataset identifies the locations of public community surface and
ground water supply sources and public non-community supply sources (as defined in 310 CMR 22.00).
The data layer is based primarily on information in the DEP's water quality testing system database, the
DEP's central database for tracking water supply data (MassGIS). Recharge areas for public water
supplies are defined in the Massachusetts Drinking Water Regulations, 310 CMR 22.02 (MassDEP 1997).
The Massachusetts dams dataset from MassGIS contains points derived from a dam safety database
maintained by the Massachusetts Office of Dam Safety (ODS). Most of the location information was
derived from historic data and has been ground-truthed. It is important to note that there are many
non-jurisdictional dams that are not in the ODS database.
A.3 Part 3: Characterize Known Pollutant Loadings
A.3.1 Identify Pollutants of Concern
Pollutants of concern should be identified by first determining which, if any, water bodies in the
watershed are listed as impaired, per the most recent 303(d) list, as described in Section A.2.8.5.
Further, it is necessary to determine whether any TMDLs have been developed to address specific
pollutants. As noted in Section A.2.8.5, a TMDL can provide some insight into proposed methods for
attaining water quality standards, which can be helpful for identifying areas in which certain types of
green infrastructure practices might provide some benefit.
The 303(d) list of impaired waters (Integrated List) generally provides information on known or
suspected causes of impairment, as does the TMDL report. However, green infrastructure
implementation does not necessarily depend on the existence of 303(d) impairments in the watershed.
Green infrastructure can be implemented for benefits not related to specific water quality regulations,
such as hydrologic benefits (i.e., residential flooding reduction) and the need to continue to maintain a
high standard of water quality in the face of increasing development. Municipalities might look to green
infrastructure as a means of achieving many different objectives.
It is important to recognize the many different known and potential sources of stormwater pollution in
the watershed to maintain a high standard of water quality, whether or not existing water quality
standards are currently being met. Keeping an inventory of activities in the watershed that could
potentially contribute to stormwater runoff pollution will facilitate a more efficient process for pollutant
control. Potential pollutant sources are discussed below.
A.3.1.1 Wastewater and Stormwater Facilities
Existing permitted water and stormwater facilities should be identified and catalogued. Locations and
detailed information on National Pollutant Discharge Elimination System (NPDES) permitted facilities is
readily available in online EPA databases, and a search should be conducted for such facilities within the
target watershed. EPA's Envirofacts system (www.epa.gov/enviro/) is the umbrella database of
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environmental data for a wide number of reporting systems and is an ideal starting point when
searching for information on existing facilities.
Some older municipalities operate combined storm and sanitary sewer systems, while others are
increasingly separating the two. Municipal separate storm sewer systems (MS4s) are regulated under
separate NPDES permits. Per EPA regulations, Phase I MS4s (generally larger cities such as Boston and
Worcester) are required to obtain individual permits and Phase II MS4s (generally smaller MS4s in
urbanized areas) are required to obtain permit coverage but are typically covered by a general permit.
Many municipalities across the country are developing stormwater utilities whereby residents and
commercial developments are charged a fee that funds the treatment and control of runoff before it is
discharged to surface waters. In any case, existing stormwater collection systems should be identified
and characterized because any proposed green infrastructure improvements in the watershed will
become an integral part of these systems. The locations of discharge points for stormwater collection
systems are especially important to identify, if possible. These are the locations where local Stormwater
Management Standards typically mandate that specific BMPs be implemented to control stormwater
quality and volume.
A.3.1.2 Residential Areas
Identify existing and potential sources of stormwater runoff pollution from residential sources. These
may include (USEPA 2003):
¦ Lawn care (fertilizers, pesticides, yard waste, landscaping waste, etc.)
¦ Septic systems (leaking and poorly maintained systems)
¦ Auto care (car washing and maintenance, auto fluids, etc.)
¦ Domestic pets (pet waste)
¦ Driveways, roads, and sidewalks (litter and debris, road salt, auto fluids, etc.)
A.3.1.3 Commercial Areas
Pollutants in stormwater runoff from commercial areas may include the following sources (USEPA 2003):
¦ Parking lots, roads, sidewalks, and driveways
¦ Chemical spills
¦ Automotive facilities
¦ Waste management (grease storage, dumpsters and trash containers, etc.)
A.3.1.4 Construction Operations
Ineffective erosion controls and construction vehicles can be sources of stormwater pollution. Erosion
on construction sites can cause sediment and debris to enter the stormwater system when erosion
controls are not properly installed and maintained. Construction equipment can also be a source of
sediment and grease or fluids if not properly maintained (USEPA 2003).
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A.3.1.5 Agricultural Operations
The existence of agricultural operations in the watershed can have important implications for stormwater
runoff. Therefore, these facilities must be identified and characterized. Principal agricultural operations in
the MassBays region include cranberry bogs. Main sources of stormwater runoff pollution include
fertilizers, pesticides, and herbicides. Irrigation and drainage may also have water quality impacts.
Efforts should also be made to characterize existing runoff and pollution control practices currently
being implemented at agricultural sites.
A.3.1.6 Golf Courses
Golf courses have the potential to contribute stormwater runoff pollution due to the use of fertilizers,
pesticides and herbicides, and other maintenance activities including equipment washing, fuel storage,
and irrigation.
A.3.1.7 Solid and Hazardous Waste and Toxic Releases
EPA's Envirofacts database can be consulted to identify any existing solid and hazardous waste and toxic
release facilities in the watershed. These sites may be classified under the following categories:
¦ Comprehensive Environmental Response, Compensation and Liability (CERCLA)
¦ Resource Conservation and Recovery Act (RCRA)
¦ Toxic Release Inventory (TRI)
The EnviroMapper is a service provided through EPA's Envirofacts website that enables the user to view
and select environmental data in a useful map format (www.epa.gov/emefdata/em4ef.home).
A.3.2 Estimate Pollutant Loadings
The watershed assessment process involves estimating relative pollutant loadings from various sources
in the watershed. This will facilitate identification of areas with relatively high pollutant loadings, which
might be better candidates for green infrastructure compared to areas with relatively low pollutant
loadings.
A.3.2.1 Pollutant Loadings based on Existing Monitoring Data
Section A.2.8.4 described identification of sources of existing water quality monitoring data, and Section
A.2.8.5 described how to identify impaired waters in the watershed. The data and information gathered
in those steps will be used in this section to characterize known pollutant loading in the watershed for
pollutants identified for action per Section 2.3.1.
A.3.2.2 Pollutant Loadings based on Land Use
In the absence of monitoring data, wet-weather loading for specific land uses can be estimated based on
local hydrology methods and recent local or regional efforts that quantify likely Event Mean
Concentration (EMC) ranges for a variety of land uses and sources. If regional literature is lacking,
published articles and studies can be referenced for pollutant EMC data. For example, EPA published
median EMCs for 10 pollutants and 4 different types of urban land uses (Table A-l) as part of the
Nationwide Urban Runoff Program (NURP).
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Table A-l. Median EMCs for urban land uses (USEPA 1983)
Pollutant
Units
Residential
Mixed
Commercial
Open/Non-Urban
Median
cov
Median
COV
Median
COV
Median
COV
BOD
mg/l
10
0.41
7.8
0.52
9.3
0.31
-
-
COD
mg/l
73
0.55
65
0.58
57
0.39
40
0.78
TSS
mg/l
101
0.96
67
1.14
69
0.85
70
2.92
Total Lead
pg/l
144
0.75
114
1.35
104
0.68
30
1.52
Total Copper
pg/l
33
0.99
27
1.32
29
0.81
-
-
Total Zinc
Mg/l
135
0.84
154
0.78
226
1.07
195
0.66
Total Kjeldahl
Nitrogen
Mg/l
1900
0.73
1288
0.5
1179
0.43
965
1
Nitrate + Nitrite
Mg/l
736
0.83
558
0.67
572
0.48
543
0.91
Total
Phosphorus
Mg/l
383
0.69
263
0.75
201
0.67
121
1.66
Soluble
Phosphorus
Mg/l
143
0.46
56
0.75
80
0.71
26
2.11
A/ofe: BOD = biochemical oxygen demand; COD = chemical oxygen demand; TSS = total suspended solids; COV=
coefficient of variation
Pollutant load is calculated by multiplying the total runoff volume by the EMC. Where water quality
treatment is of special concern (i.e., for discharge into environmentally sensitive areas), a simplified
method to estimate the runoff volume is to multiply the total impermeable surface area by the
appropriate rainfall depth (e.g., 1-inch, depending on local standards). In this case, the rainfall depth and
runoff volume are often referred to as the "water quality event" and "water quality volume",
respectively.
Local municipalities commonly publish stormwater manuals or guidance which prescribe specific
methods for estimating runoff volume. Local guidance should be consulted to ensure designs comply
with any applicable local stormwater codes and standards.
¦ The Massachusetts Stormwater Handbook contains specific information related to the Stormwater
Management Standards as established by the Stormwater Policy (MassDEP) and can be referenced
for specific guidance (www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-
stormwater-handbook.html).
¦ The handbook also provides a list of land uses with known higher potential pollutant loads, for
which the discharge of stormwater runoff should be eliminated or reduced "to the maximum
extent practicable."
After characterizing the estimated pollutant loading for the sources and areas, it will be possible to
prioritize the sources and areas based on their identified contributions to the watershed loading.
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A.4 References
MassDEP (Massachusetts Department of Environmental Protection). 1997. Massachusetts Stormwater
Handbook. Revised February 2008.
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-
handbook.html.
MassGIS (Massachusetts Office of Geographic Information). 2014a. MassGIS Data - MassDEP
Hydrography. Massachusetts Executive Office for Administration and Finance. Accessed March
2014. http://www.mass.gov/anf/research-and-tech/it-serv-and-support/application-serv/office-
of-geographic-information-massgis/datalayers/hd.html.
MassGIS (Massachusetts Office of Geographic Information). 2014b. MassGIS Data - NRCS HUC Basins
(8, 10,12). Massachusetts Executive Office for Administration and Finance. Accessed March
2014. http://www.mass.gov/anf/research-and-tech/it-serv-and-support/application-serv/office-
of-geographic-information-massgis/datalavers/nrcshuc.html.
USEPA (U.S. Environmental Protection Agency). 1983. Results of the Nationwide Urban Runoff Program:
Volume 1 - Final Report. EPA 832R83112. U.S. Environmental Protection Agency, Water Planning
Division, Washington, DC. http://www.epa.gov/npdes/pubs/sw nurp vol 1 finalreport.pdf.
USEPA (U.S. Environmental Protection Agency). 2003. After the Storm. EPA 833-B-03-002. U.S.
Environmental Protection Agency, Washington, DC. Accessed March 2014.
http://water.epa.gov/action/weatherchannel/stormwater.cfm.
USGS (U.S. Geological Survey). 2014. What is the WBD? U.S. Geological Survey, U.S. Department of the
Interior, Washington, DC. Accessed March 2014. http://nhd.usgs.gov/wbd.html.
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Appendix B
Example Green Infrastructure
Conceptual Site Design
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B. Conceptual Site Design Watershed
B.l Example Green Infrastructure Conceptual Site Design
A series of conceptual site renderings, starting with Figure B-l below, demonstrate the phases of site
assessment, preliminary design, and planning through the final designs and shows how the site changes
with each step. Figure B-l demonstrates a hypothetical site planned to include the construction of a
new library, adjoining parking lot, and a surrounding park. This example site will be used to illustrate the
steps described in the following sections.
Source'. Tetra Tech
Figure B-l. Example capita! improvement project conceptual site for green infrastructure.
B.l.l Phase I - Site Assessment
The first phase of site planning is composed of the site assessment. Steps 1 through 3 below delineate
the site assessment process.
B.l.1.1 Step 1: Identify Regulatory Needs
Green infrastructure implementation must be consistent
with the applicable federal, state, and local regulations.
Under the Wetlands Protection Act (Massachusetts
General Laws, Chapter 131, Section 40), and the
Massachusetts Clean Waters Act (Massachusetts General
Laws, Chapter 21, Sections 26-53), MassDEP uses its
authority to apply the Stormwater Management
Standards which promote green infrastructure techniques.
To Complete Step 1:
• Identify applicable zoning, land use,
subdivision, and other regulations.
• Identify setbacks, easements, and
utilities. (Call 811 for utility
location.)
• Identify targeted pollutants and
pollutants of concern.
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Identify applicable zoning land use, subdivision, and other local regulations
Zoning ordinances and comprehensive planning by any local government entity (county, city, and such)
provide a framework to establish a functional and visual relationship between growth and urbanization
(Prince George's County 1999). The Massachusetts Trial Court Law Libraries contain city and town
zoning requirements along with other land use bylaws and ordinances
(www.lawlib.state.ma.us/source/mass/bylaws,html). It is recommended that identified land uses also be
shown in a visual format similar to Figure B-2.
steep slope
^ setback
building
setback
wetland
.setback
wetland
wetland conservation transportation II high density public use zone
H zone zone II .1 residential
Source: Tetra Tech
Figure B-2. Identify applicable zoning requirements, utility easements, and site setbacks.
Identify setbacks, easements, and utilities
Defining the boundaries of the site (yellow-dashed line indicating parcel boundaries) also includes
identifying the required setbacks and any easements or utilities on the site. Municipal ordinances
provide the basic regulations regarding the size and scale of development, such as permitted density,
setbacks, and structure height on the basis of the applicable zoning code. Setbacks will restrict the
buildable area. Each city and town along the Massachusetts Bay has their own requirements regarding
setbacks, easements, and utilities, and local zoning codes should be consulted for this information
Planning and assessment must also include identifying easements on the site. Easements that could be
present are a road or sidewalk (ROW) easement; a public utility easement that allows a utility to run gas,
water, sewer, or power lines through a private property; or a railway easement. Local utilities
departments (e.g., electric, wastewater) should be consulted to determine whether utilities are above or
below ground and the required distance that site disturbance should be maintained from any utilities
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present. Easements on a site can be determined by consulting as-built drawings and records research;
these should be included on site drawings as illustrated in Figure B-2.
Identify targeted pollutant and flow alteration needs
The Stormwater Management Standards state that for-land uses with higher potential pollutant loads,
source control, and pollution prevention must be implemented in accordance with the Massachusetts
Stormwater Handbook (MassDEP 1997) to eliminate or reduce the discharge of stormwater runoff from
such land uses to the maximum extent practicable. If through source control or pollution prevention all
land uses with higher potential pollutant loads cannot be completely protected from exposure to rain,
snow, snowmelt, and stormwater runoff, the proponent shall use the specific structural stormwater
BMPs determined by MassDEP to be suitable for such uses as provided in the Massachusetts
Stormwater Handbook (MassDEP 1997). Stormwater discharges from land uses with higher potential
pollutant loads shall also comply with the requirements of the Massachusetts Clean Waters Act
(Massachusetts General Laws, Chapter 21, Sections 26-53), and the regulations promulgated
thereunder at 314 CMR 3.00, 314 CMR 4.00, and 314 CMR 5.00. Stormwater management systems must
be designed so that post-development peak discharge rates do not exceed predevelopment peak
discharge rates. The standard may be waived for discharges to land subject to coastal storm flowage as
defined in 310 CMR 10.04.
MassDEP identifies impaired water bodies in the state that warrant attention and additional resources.
Impaired bodies of water fail to meet water quality objectives and require development of
implementation plans targeted at both point source and nonpoint source pollution. Implementation
plans for TMDLs often target nonpoint source pollutants by requiring the incorporation of BMPs.
Implementing green infrastructure practices offers an effective tool used to enhance water quality to
the maximum extent practical. For that reason, site planning should include identifying any impaired
water or waters in the region and assessing pollutants of concern to allow planners and designers to
consider target pollutant reduction needs in the design phase.
B. 1.1.2 Step 2: Define Natural Site Features
Site planners and designers should consider how to
use existing natural features of the site in an effort
to retain natural hydrologic functions and
potentially reduce the cost of drainage
infrastructure. Identifying natural or sensitive areas
is an integral factor in defining the site area for
development and placing site needs and features
in the context of the overall watershed.
Naturally functioning areas
To enhance a site's ability to support source control and reduce runoff, natural areas that can infiltrate
stormwater should be identified in the site design process and conserved or restored. These areas can
intercept stormwater without engineered practices, thereby reducing the amount of runoff and the size
To Complete Step 2:
• Identify natural areas to be conserved or
restored.
• Conduct a geotechnical survey including
drainage characteristics, hydrologic flow
paths, and soil infiltration tests.
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and extent of drainage infrastructure. Such natural features can result in cost savings due to decreased
infrastructure costs.
The following are fundamental principles encouraging conservation and restoration of natural areas;
¦ Minimize site grading and the area of disturbance by isolating areas where construction will occur
(see Step 5). Doing so wiii reduce soil compaction from construction activities. In addition, reduced
disturbance can be accomplished by increasing building density or height.
¦ When possible, the site should be planned to conform to natural landforms and to replicate the
site's natural drainage pattern. Building roads and sidewalks on the existing contour ensures that
natural flow paths and hydrology continue to function.
¦ An essential factor in optimizing a site layout includes conserving natural soils and vegetation,
particularly in sensitive areas such as habitats of sensitive species, wetlands, existing trees,
hillsides, conservation areas, karst features, and existing water bodies. Such areas can be used as
natural features in site planning to avoid or reduce potential effects of development. Wetlands, for
example, provide habitat for several sensitive species, and off-site mitigation does not always
provide the same type or quality of habitat. Figure B-3 shows an example of native soils and
vegetation protected at a construction site.
Source: Tetra Tech
Figure B-3. Preservation of native soils and vegetation
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m In areas of disturbance, topsoil can be removed before construction and replaced after the project
is completed. When handled carefully, such an approach limits the disturbance to native soils and
reduces the need for additional (purchased) topsoil later.
¦ Impervious areas (e.g., square footage of parking lots, sidewalks, and roofs) should be minimized by
designing compact, taller structures; narrower streets; and using underground or under-building
parking.
In the example shown in Figure B-4, the natural and sensitive areas that should be considered for
protection during development are identified on the site map, including wetlands, high-quality
vegetation, and steep slopes (hillside).
Understand soils through geotechnical surveys
Any project that includes green infrastructure practices should include a soil evaluation or geotechnical
investigation. A licensed engineer with geotechnical expertise, a licensed geologist, engineering geologist,
hydrogeologist, or other licensed professional acceptable to the local jurisdiction should perform a detailed
evaluation of soils, shallow ground water and bedrock conditions. A soil evaluation including soil infiltration
testing is intended to identify and protect soils that provide greater infiltration as potential locations for
green infrastructure BMPs (Figure B-4). The presence and depth to the seasonal water table or shallow
bedrock should also be identified, which will inform BMP design under Phase II. In addition, natural drainage
characteristics and hydrologic flow paths should be identified. These features can be used in the design and
protected in future steps to maintain the site's natural drainage characteristics.
Source: Tetra Tech
Figure B-4. Protect natural and sensitive areas (wetlands, native tree groves, steep hillside) and
conduct geotechnical survey to characterize infiltration capacity of soils.
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B.l.1.3 Step 3: Protect Key Hydrologic Areas
Following the green infrastructure site planning concept of using hydrology as the integrating
framework, the key hydrologic areas such as hydrologic flow paths and infiltrating soils are protected. To
the extent possible, natural hydrologic functions of the site should be preserved. Applying green
infrastructure techniques results in a hydrologically
functional landscape that can function to slow runoff
rates, protect receiving waters, and reduce the total
volume of runoff.
Second only to flow regimes in ensuring proper hydrology,
healthy soils or media often serve as essential elements
for achieving green infrastructure functions and providing source control for stormwater treatment. For
example, upper soil layers are conducive to slowly filtering and storing stormwater, allowing unit processes
such as infiltration, sorption, evapotranspiration, and surface retention to occur.
Site features that should be protected include riparian areas, floodplains, stream buffers, wetlands, and
soils with infiltration potential. Using the information collected in the Step 2 soil evaluation, more specific
locations of soils with greater infiltration rates that are near or on hydrologic flow paths should be
protected to avoid or limit hydrologic impacts. As an example, Figure B-5 indicates the key hydrologic areas
that should be considered for protection. The blue area identified as an area for possible infiltration should
be separated from other site features by surrounding it with construction fencing to prevent access and
avoid compaction. In addition, the areas having a natural hydrologic function either through storage or
conveyance should be protected. (Also see Figure B-5 in setting site clearing and grading limits.)
With the conclusion of Phase I, the initial site assessment has been completed. The decisions made
regarding green infrastructure practices during the site assessment process should be documented to
ensure that if changes are required in future Phases II and III, the original design ideas are available for
reference. That helps ensure that green infrastructure concepts are considered during every component
of project site planning. Phase II of site planning, described below, results in a preliminary design plan.
To Complete Step 3:
• Protect areas of natural hydrologic
function.
• Protect possible areas for infiltration.
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Source: Tetra Tech
Figure B-5. Identify and protect key hydrologic areas, such as infiltrating soils (blue area) and
wetlands (orange areas).
B.1.2 Phase II - Preliminary Design
The result of the second phase of site planning is a completed preliminary design done by conducting
Steps 4 through 7, below. Working through those steps is an iterative process for designing a preliminary
plan that implements green infrastructure concepts as fully as possible.
B.1.2.1 Step 4: Use Drainage and Hydrology as a Design Element
Natural hydrologic functions (e.g., flow paths)
should be included as a fundamental component of
the preliminary design. Naturally present functions
should be retained, or if that is not an option,
replicate natural functions with appropriate BMP
placement.
Spatial site layout options
Natural hydrologic functions, including interception
depression storage, and infiltration, should be distributed throughout the site to the extent possible. In
conserving predevelopment and retrofit hydrology, runoff volume, peak runoff rate, flow frequency and
duration, and water quality control must be considered. Rainfall abstractions are the physical processes
of interception, evaporation, transpiration, infiltration, and storage of precipitation.
To Complete Step 4:
• Identify the spatial layout of the site
using hydrologic flow paths and natural
drainage as a feature.
• Determine approximate locations for
infiltration and conveyance BMPs.
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Runoff flow frequency and duration should try to mimic predevelopment conditions by implementing
practices to minimize runoff volume and rate. Green infrastructure practices also provide pollutant
removal processes that enhance water quality treatment for the designed treatment volume.
By setting the development envelope back from natural drainage features, the drainage can retain its
hydrologic functions and its water quality benefit to the watershed as shown in the example in Figure B-
6, assuming that runoff from the contributing watershed is mitigated to predevelopment conditions.
Source: Tetra Tech
Figure B-6. Identify idea! locations for green infrastructure implementation according to site
conditions.
Spatial layout should use the natural landforms and hydrologic flow paths identified in Step 2 as a major
design element of the site. Common elements using that premise include designing open drainage
systems to function as both treatment and conveyance devices. Impervious elements such as parking
lots, roadways, and sidewalks can be designed on the existing contour to minimize effects on the natural
hydrologic flow path.
Determine potential BMP locations
Stormwater management practices can be designed to achieve water quality and flood protection goals
by applying four basic elements, alone or in combination: infiltration, retention/detention, biofiltration,
and evapotranspiration.
Infiltration systems should be designed to match predevelopment hydrology and to infiltrate the
majority of runoff from small storm events, when applicable and to the extent possible. Existing site soil
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conditions generally determine whether infiltration is feasible without soil amendments or underdrains.
Other site conditions that preclude infiltration are high ground water tables, steep slopes, or shallow
bedrock. Infiltration systems can also help control peak flow rates by providing retention and volume
control.
Retention/detention systems are intended to store runoff for gradual release or reuse.
Retention/detention basins also allow for evaporation of runoff and evapotranspiration by plants. They
are most appropriate where soil percolation rates are low or where longer retention times are designed
into the system. They are also appropriate when designing to control peak flow rates for downstream
flood and channel protection.
Biofiltration devices are designed using vegetation to achieve low-velocity flows, to allow settling of
particulates and filtering of pollutants by vegetation, rock, or media. Pollutant degradation can also
occur through biological activity and sunlight exposure. Biofilters can be designed to be linear features
that are especially useful in treating runoff from parking lots and along highways.
Evapotranspiration is inherent in all BMP systems. Evaporation is maximized in systems that retain or
detain runoff, and vegetated systems maximize transpiration as plants use the stored water for growth.
Selecting the appropriate structural BMPs for a project area should be on the basis of site-specific
conditions (e.g., land availability, slope, soil characteristics, climate condition, and utilities) and
stormwater control targets (e.g., peak discharge, runoff volume, or water quality targets).
In the example shown in Figure B-6, areas are identified that
will be developed for parking and building footprints. The figure
also indicates ideal locations where green infrastructure BMPs
can be placed (such as a biofiltration swale and bioretention)
and can be incorporated into the natural drainage paths to
function as conveyance and treatment green infrastructure
BMPs. The infiltration opportunities identified in Figure B-5
suggest that the blue oval near the road, which is on HSG C,
would be more suitable for a biofiltration BMP, while much of the rest of the potential BMP area is on
HSG B, indicating that this area would be better for infiltration systems (Figure B-6). Note that both
biofiltration and infiltration BMPs can also meet landscaping requirements and create features that
enhance and beautify the site.
B.l.2.2 Step 5: Establish Clearing and Grading Limits
Limits of clearing and grading refer to the total site area that is to be developed, including all impervious
and pervious areas. The area of development ideally should be in less sensitive locations with respect to
hydrologic function and should be outside protected areas and areas containing setback regulations,
easements, and utilities.
Stormwater management
practices can be designed to
achieve water quality and flood
protection goals by applying
four basic elements: infiltration,
retention/detention, filtration,
and evapotranspiration.
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Site fingerprinting refers to site clearing and
development with minimal disturbance of existing
vegetation and soils. Such techniques include
reducing paving and compaction of highly
permeable soils, minimizing the size of
construction easements and material storage
areas, site clearing and grading to avoid tree
removal, delineating and flagging the smallest site disturbance area possible, and maintaining existing
topography to the extent possible. Figure B-7 illustrates the use of orange construction fencing to
preserve the natural features and drainage pathways, and maintain infiltration on suitable soils at the
example site as identified in previous steps.
To Complete Step 5:
• Define the limits of clearing and grading.
• Minimize disturbance to areas outside the
limits of clearing and grading.
proposed
parking lot
footprint
proposed building
footprint
potential BMP locations
Source: Tetra Tech
Figure B-7. Establish grading envelope to protect natural areas and infiltrating soils.
B. 1.2.3 Step 6: Reduce/Minimize Total and Effective Impervious Area
Rainfall that does not infiltrate or pool where it falls results in runoff. As the imperviousness of the site
increases, runoff also increases with each acre of impervious cover producing approximately 27,150
gallons of stormwater for each inch of rainfall. Predevelopment runoff, measured as a runoff coefficient
or the ratio of runoff volume to the total amount of rainfall, can be maintained by compensating for
increases in impervious areas, soil compaction, and the loss of abstraction through planning and design.
Such tools can be used to also manage the peak runoff rate and volume and protect water quality.
construction fence to establish
| clearing and grading limits
flow direction
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Disconnect impervious area
Diverting stormwater runoff from impervious areas such as
rooftops and pavement to adjacent pervious areas can be
used to infiltrate stormwater runoff and to reduce flow
rates (shown in Figure B-7). Proper design can align pervious
surfaces with building drainage. Such a technique is also
referred to as impervious area disconnect.
To reduce the storage and conveyance requirements, the
directly connected impervious area of the site should be minimized to the extent practicable. That can
be accomplished through increasing the building density by increasing the vertical extent and minimizing
the horizontal extent. Impervious area disconnect can also include using permeable features instead of
impermeable including permeable pavement for walkways, trails, patios, parking lots, and alleys; and
constructing streets, sidewalks, and parking lot aisles to the minimum width necessary.
Possible locations for impervious area disconnect techniques are shown in Figure B-8 below in yellow. As
shown in the figure, the medians along either side and in the middle of the roadway provide vegetated
pervious areas for minimizing or reducing the impacts associated with the total impervious area and for
infiltration and filtration processes to take place. The figure also demonstrates the use of pervious
pavement in the parking lot and along the roadway (in red).
To Complete Step 6:
• Investigate the potential for
impervious area disconnection.
• Evaluate the conceptual design to
reduce impervious surfaces.
Source: Tetra Tech
Figure B-8. Site example demonstrating placement of pervious material (red) and opportunities to
minimize connected impervious area (yellow).
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Minimize impervious area
Street layouts often can be designed to reduce the extent of paved areas, and street widths can be
narrowed to decrease the total impervious area as long as applicable street design criteria are satisfied.
Eliminating curbs and gutters along streets and including curb cuts around parking areas, where
consistent with city standards and where appropriate, can promote drainage to on-site pervious areas
and decrease directly connected area considerably. Other options include replacing curbs and gutters
with roadside vegetated swales and directing runoff from the paved street or parking areas to adjacent
green infrastructure facilities. Such an approach for alternative design can reduce the overall capital cost
of the site development while addressing stormwater quantity and quality issues and improving the
site's aesthetic values. Figure B-8 illustrates the inclusion of pervious paving and bioretention systems
with curb cuts along the street ROW to demonstrate locations where that can be achieved.
Specific examples of alternative transportation options include narrow paved travel lanes, consolidated
travel lanes, increased green parking areas, and horizontal deflectors (chicanes) or intersection pop-
outs. Such options can be included for other multi-beneficial purposes such as traffic calming and
pedestrian safety (Ewing 1999), increased parking spaces, and improved aesthetics. Four examples of
transportation alternatives are described below.
Narrowed travel lanes: Narrow travel lanes can help reduce impervious area and infrastructure costs,
calm traffic in pedestrian-oriented areas, and create room for stormwater facilities. Existing roadways
can be narrowed to minimum widths in accordance with established roadway standards. Residential
street crossings are often combined with traffic-calming measures, which reduce street width and are
designed to maintain low vehicle speeds, such as raised crosswalks, chicanes, and gateway narrowing.
Consolidated travel lanes: Consolidating travel lanes or converting unused pavement next to travel
lanes into landscape areas can result in reduced imperviousness. The increased landscape space could
be used for stormwater facilities and create space for bike lanes, wider sidewalks, and a more balanced
and vibrant streetscape. Parking lanes can also be converted to permeable paving that can be used for
stormwater management.
Increased green parking: Techniques used to reduce the total impervious coverage and consequential
runoff from parking lots are broadly referred to as green parking. Green parking techniques include
minimizing the number and dimension of parking stalls; using alternative pervious pavers wherever
suitable; incorporating stormwater BMPs such as depressed bioretention islands into parking lot
designs; and encouraging shared parking and incentivizing structured parking (Figure B-8). When
implemented together, green parking alternatives reduce volume and the mass of pollutants generated
from parking lots, reduce the urban heat island effect, and enhance a site's aesthetics.
Intersection deflectors (chicane): A chicane is a series of deflections involving the narrowing of one side
of the street by an amount that requires the through traffic to deflect from its previously straight path
(MassHighway 2006). The combination of narrowed street width and the serpentine path of travel slow
traffic (Figure B-9). On new streets, chicanes narrow the street by widening the sidewalk or landscaped
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areas between the curb and sidewalk. On streets considered for retrofit, raised islands can be installed
to narrow the street. Advantages of chicanes include reduced traffic speeds, opportunities for
landscaping, and created spaces for stormwater management facilities. Chicanes are inappropriate for
use on streets classified as collector or higher, bus routes, emergency response routes, where there is a
grade that exceeds 5 percent, or where stopping sight distance is limited such as at the crest of a hill
Source: Tetra Tech
Figure B-9. Bioretention incorporated into a pop-out (Kansas City, Missouri).
Intersection pop-outs, Intersection pop-outs are curb extensions that narrow the street at intersections
by widening the sidewalks at the point of crossing. They are used to make pedestrian crossings shorter
and reduce the visual width of long, straight streets (Figure B-10). Where intersection pop-outs are
constructed by widening the landscaped planting strip, they can improve the aesthetics of the
neighborhood and provide more opportunities for stormwater controls at the site by facilitating
interception, storage, and infiltration. Intersection pop-outs should be designed to properly
accommodate bicyclists, transit vehicles, and emergency response vehicles. Intersection pop-outs can
be installed on local streets; however, pop-outs are inappropriate on major streets and primary
arterials.
Reduced width of road sections can also reduce total site imperviousness. Streets, sidewalks, and
parking lot aisles should be constructed to the minimum width possible without compromising public
safety and access. In addition, sidewalks and parking lanes can be limited to one side of the road.
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Source'. Tetra Tech
Figure B-10. Example of an intersection pop-out.
Traffic or road layout can significantly influence the total imperviousness of a site plan. Selecting an
alternative road layout can result in a sizeable reduction in total site imperviousness. Alternative road
layout options that can reduce imperviousness from the traditional layout pattern use queuing lanes,
parking on only one side of the street, incorporating islands in cul-de-sacs, and using alternative turn
areas that require less pavement (CWP 1998).
Other transportation opportunities for reducing impervious area include using shared driveways,
limiting driveway widths to 9 feet, and using driveway and parking area materials that reduce runoff and
increase the time of concentration (e.g., grid systems and paver stones).
Several iterations of manipulating site imperviousness can be done to consider natural features, areas of
infiltration, and hydrologic pathways to best achieve a balance between necessary imperviousness with
disconnected and pervious site features. Once the total area of imperviousness has been minimized, the
impervious areas can be incorporated into the site plan or capital improvement roadway project.
In Figure B-8 opportunities for imperviousness reduction and runoff disconnection were identified for
both the building site and for alternative transportation options. The sidewalk surrounding the building
was disconnected by routing runoff to the pervious landscaped areas surrounding the building (shown in
yellow), and pervious paving was identified in the low-traffic areas of the parking lot to reduce site
imperviousness. Pervious paving was also identified as an opportunity for reduction in impervious area
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for on-street parking (shown in red), and a median bioswale along with ROW bioretention were
identified as methods for runoff disconnection (shown in yellow).
B.1.2.4 Step 7: Determine Green Infrastructure BMPs
Green infrastructure BMPs employ a number of
processes, including settling/sedimentation;
filtration; sorption; photolysis; biological
processes (bioaccumulation and
biotransformation/phytoremediation); and
chemical processes (for complete descriptions,
see Section 5) for pollutant removal. In addition
to pollutant removal, green infrastructure BMPs
provide hydrologic controls by reducing peak
flows and volume through processes of infiltration,
predevelopment hydrologic functions.
During BMP selection, it is important to consider a BMP's unit processes to ensure that the management
practice will provide the necessary benefits and avoid potential complications.
Hydrologic controls dictate how incoming stormwater is partitioned into the various components of the
hydrologic budget. Stormwater volume can be detained, infiltrated, evapotranspired, drained, or
bypassed depending on the design of hydrologic controls and features such as impermeable liners,
underdrains, inlet and outlet structures, soil media permeability, and storage capacity.
Settling/sedimentation is the physical process of particle separation as a result of a difference in density
between the solids and water. Most BMPs use settling to some degree, especially through detention or
retention practices such as bioretention. Settling is enhanced by slowing down or spreading out runoff
to create low-velocity flow conditions.
Filtration is the physical process of separating solids from a liquid media. Particles are filtered from
water by the smaller interstitial space the water flows through in the porous medium. Sedimentation
and sorption can also occur as water passes through a filtering practice. Sorption refers to the processes
of absorption (an incorporation of a pollutant into a substance of a different state) and adsorption (the
adherence of a pollutant to the surface of another molecule). Sorption is also referred to under chemical
treatment processes. Filtration is a common unit process in a number of BMPs such as bioretention and
planter boxes.
Floatation is a treatment unit process where the mechanism for pollutant removal is opposite to that in
settling and sedimentation. In floatation, the density of pollutants, such as trash and petroleum, is less
than that of water. Oil/water separators and trash guards are the primary BMP practices that use
floatation.
To Complete Step 7:
• Determine potential BMPs according to
hydrologic and pollutant removal process
needs and cost estimates (see Section 5).
• Repeat Steps 4 through 7 as necessary to
ensure that all stormwater management
requirements are met
evaporation, and storage and reproducing
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Biological treatment processes (bioaccumulation, biotransformation, phytoremediation) are processes
that occur in practices that incorporate soils and plants for pollutant removal via biological
transformation or mineralization, pollutant uptake and storage, or microbial transformation. It can also
include organisms that consume bacteria. BMPs that can be designed to use such unit processes are
bioretention, bioswales, and planter boxes.
Chemical treatment processes include sorption, coagulation/flocculation, and disinfection. Chemical
characteristics of stormwater such as pH, alkalinity, and reduction-oxidation (redox) potential determine
which chemical process is appropriate. Sorptive BMPs generally include engineered media for removing
pollutants of concern. Precipitation and disinfection processes require actively adding chemicals to
encourage coagulation/flocculation and precipitation or chemicals such as chlorine to mitigate
pathogenic microbes in stormwater. Chemical treatment processes are usually employed as end-of-pipe
solutions where no other BMP can effectively treat an existing storm drain system. In these cases, low
flow might be more effectively treated by pumping into a sanitary sewer.
Using multiple treatment processes either in individual or multiple BMPs is called a treatment train.
Meeting targeted treatment objectives can usually be achieved using a series of green infrastructure
BMPs in a treatment train. Treatment trains can often be designed along ROWs, in parking lots,
underground, or incorporated into landscaped areas. Green infrastructure site planning should result in
a treatment train of green infrastructure strategies and BMPs
to meet treatment and water quality goals.
A number of factors should be considered for choosing
appropriate BMPs for a site. For example, the presence of
group C or D soils on a site might preclude the use of an
infiltration BMP or require the use of an underdrain into the design of infiltration BMPs. Native
vegetation, which is adapted to the local climate and soils, should be used for vegetated BMPs when
soils allow. If native soils are replaced with imported soils to improve infiltration, non-native noninvasive
but drought-tolerant plants might be a desired choice. Other geotechnical, site-specific considerations
include the level of the underlying water table and bedrock, any existing infrastructure in retrofit
designs, and the presence of areas of concern that exhibit soil and ground water contamination.
¦ Greenscapes Massachusetts is partially funded by MassBays and provides information on low-
impact landscaping practices including irrigation and chemical use: http://greenscapes.org/
The information gathered and organized during Steps 1-6 provide the foundation for selecting BMP
types that are most appropriate to meet the site's stormwater management needs. Section 5 of this
handbook summarizes information about specific green infrastructure BMPs and provides guidance on
selecting appropriate green infrastructure BMPs for a site. Table 5-1 (BMP Selection Matrix) summarizes
the selection criteria and should be consulted to assist in the process.
At the completion of Phase II, the site planning for the project is complete. At that point in the site
planning process, the development area should be delineated and the approximate type and potential
locations for appropriate BMPs should be identified. The preliminary plan should be documented in
Using multiple treatment
processes either in individual or
multiple BMPs is called a
treatment train.
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addition to the decisions that were made in developing the preliminary plan for future reference and to
ensure that the green infrastructure planning concepts are carried through to project construction. After
the preliminary design is completed, the final design is achieved through identifying the appropriate
green infrastructure facility type and size for meeting stormwater management needs and
requirements.
The example shown in Figure B-ll indicates the approximate type and locations of potential stormwater
management practices. The type, size, or location could change according to site construction or other
site design changes and requirements.
Source: Tetra Tech
Figure B-ll. Site plan indicating all possible BMP locations (blue areas) and types (annotated).
Results of Phase II
The analyses in Phase II should produce a preliminary site plan that includes:
• Hydrologic flow paths and natural drainage features (Step 4)
• Locations where infiltration and conveyance features could be located (Step 4)
• Limits of clearing and grading (Step 5)
• Results of an impervious area reduction analysis (e.g., parking area reduction,
permeable pavement options) (Step 6)
• Candidate BMPs (see Section 5) and their approximate locations (Step 7)
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B.1.3 Phase III - Determine Final Design
B.l.3.1 Step 8: Determine Approximate Size of Green Infrastructure BMPs
The level of control that is required for a site to
achieve stormwater management goals can be
determined through a site-specific hydrologic
evaluation. The hydrologic evaluation is performed
using hydrologic modeling and analysis techniques. A
stepwise process is followed to conduct a hydrologic evaluation:
1. Delineate the watershed and subwatershed areas.
2. Define the design storm (MassDEP 1997).
3. Determine the type of model to be used.
4. Collect data for predevelopment conditions.
5. Using hydrologic models, evaluate predevelopment, baseline conditions.
6. Using hydrologic models, evaluate the hydrologic benefits from decreasing and disconnecting
impervious areas, and compare the benefits to baseline conditions.
7. Using hydrologic models, evaluate the hydrologic control from implementation of one or more
green infrastructure BMPs.
The Stormwater Management Standards require stormwater management systems to be designed so
that the post-development peak discharge rates do not exceed predevelopment peak discharge rates.
To prevent storm damage and downstream and off-site flooding, Standard 2 requires that the post-
development peak discharge rate is equal to or less than the predevelopment rate from the 2-year and
the 10-year 24-hour storms. BMPs that slow runoff rates through storage and gradual release, such as
green infrastructure techniques, extended dry detention basins, and wet basins must be provided to
meet Standard 2. Where an area is within the 100-year coastal floodplain or land subject to coastal
storm flowage, the control of peak discharge rates is usually unnecessary and may be waived.
The Standards note that an evaluation of the impact of
peak discharges from the 100-year 24-hour storm
must also be performed. If this evaluation shows that
increased off-site flooding will result from peak
discharges from the 100-year 24-hour storms, BMPs
must also be provided to attenuate these discharges.
The evaluation might show that retaining the 100-year
24-hour storm event is not needed. In some cases,
retaining stormwater from the 100-year 24-hour storm
event on-site might aggravate downstream impacts,
because of the project's location within the watershed
and the timing of the release of stormwater.
To Complete Step 8:
• Determine the approximate BMP size.
To Complete Step 9:
• Integrate conventional stormwater
management needs.
• Verify that geotechnical and drainage
requirements have been met.
• Complete BMP designs such as finish
details and notes.
• Complete the site plans.
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B.1.3.2 Step 9: Green Infrastructure Final Design
Following iterations of Steps 4-7 and BMP sizing in Step 8, additional conventional stormwater control
techniques can be added to the site as necessary to meet site drainage and other requirements (Figure
B-12). Review of the earlier documentation of decisions made during planning phases should also be
conducted to ensure that the intent of the green infrastructure planning principles were carried through
to the final design. The iterative review process can result in more or less area required for stormwater
management. Notice that in Figure B-12, the iterative process resulted in the elimination of planter
boxes at the base of the building as the other green infrastructure BMPs provided the required volume
of capture. The example shown in Figure B-12 illustrates the final site layout, including the properly sited
and sized BMP locations.
Source: Tetra Tech
Figure B-12. Completed site plan including iterations of Steps 4-7 and BMP sizing completed.
Completing Step 9 concludes Phase III of the design process. Section 5 provides important
considerations for the design, construction, and operation of the chosen BMPs, including BMP
construction, inspection, and operation and maintenance.
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B.2 References
CWP (Center for Watershed Protection). 1998. Better Site Design: A Handbook for Changing
Development Rules in Your Community. Prepared for the Site Planning Roundtable by the Center
for Watershed Protection, Ellicott City, MD.
http://www.cwp.org/online-watershed-librarv/doc download/92-better-site-design-a-
handbook-for-changing-development-rules-in-your-community-part-l and
http://www.cwp.org/online-watershed-library/doc download/93-better-site-design-a-
handbook-for-changing-development-rules-in-vour-communitv-part-2
Ewing, R.H. 1999. Traffic Calming: State of the Practice. Publication: no. IR-098. Prepared for the U.S.
Department of Transportation, Federal Highway Administration, Office of Safety Research and
Development, McLean, VA, and Office of Human Environment, Washington, DC, by the Institute
of Transportation Engineers, Washington, DC. http://www.ite.org/traffic/tcstate.asp
MassDEP (Massachusetts Department of Environmental Protection). 1997. Massachusetts Stormwater
Handbook. Revised February 2008.
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-
handbook.html.
MassHighway (Massachusetts Department of Transportation Highway Division). 2006. Glossary.
http://www.massdot.state.ma. us/Portals/8/docs/designGuide/Glossarv.pdf.
Prince George's County. 1999. Low Impact Development Design Strategies: An Integrated Approach.
EPA-841-B-00-003. Prepared for the U.S. Environmental Protection Agency, Washington, DC, by
Prince George's County, MD, Department of Environmental Resources, Programs and Planning
Division, http://water.epa.gov/polwaste/green/upload/lidnatl.pdf
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Appendix C
Green Infrastructure BMP
Operation, Maintenance, and Monitoring
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C. BMP Maintenance and Monitoring - Supplemental Information
C.l BMP Operation and Maintenance
The major goal of BMP operation and maintenance is to ensure that the BMP is meeting the specified
design criteria for stormwater flow rate, volume, and water quality control functions. If structural green
infrastructure systems are not properly maintained, BMP effectiveness can be reduced, resulting in
water quality impacts. Routine maintenance and any need-based repairs for a structural BMP must be
completed according to schedule or as soon as practical after a problem is discovered. Deferred BMP
maintenance could result in detrimental effects on the landscape and increased potential for water
pollution and local flooding.
Training should be included in program development to ensure that maintenance staff has the proper
knowledge and skills. Most structural BMP maintenance work—such as mowing, removing trash and
debris, and removing sediment—is nontechnical and is already performed by property maintenance
personnel. More specialized maintenance training might be needed for more sophisticated systems.
Typical BMP maintenance activities include periodic inspection of surface drainage systems to ensure
clear flow lines, repair of eroded surfaces, adjustment or repair of drainage structures, soil cultivation or
aeration, care of plant materials, replacement of dead plants, replenishment of mulch cover, irrigation,
fertilizing, pruning, and mowing. Landscape maintenance can have a significant impact on soil
permeability and its ability to support plant growth. Most plants concentrate the majority of their small
absorbing roots in the upper 6 inches of the soil surface if the surface is protected by a mulch or forest
litter. If the soil is exposed or bare, it can become so hot that surface roots will not grow in the upper 8
to 10 inches. The common practice of removing all leaf litter and detritus with leaf blowers creates a
hard-crusted soil surface of low permeability and high heat conduction. Proper mulching of the soil
surface improves water retention and infiltration, while protecting the surface root zone from
temperature extremes (Hinman 2005).
In addition to influencing permeability, landscape maintenance practices can adversely affect water
quality. Because commonly used fertilizers and herbicides are a source of toxic compounds, use of these
substances should be kept to a minimum. Overwatering, which can be a significant contributor to runoff
and dry-weather flows, should be prevented. Watering should only occur to accommodate plant health
and should be adjusted at least four times a year. Whenever practical, use weather-based irrigation
controllers and follow real-time evapotranspiration (plant water use) data using local meteorological
information sources. In addition, organic methods for fertilizers and pest control (including Integrated
Pest Management) should be used.
General maintenance activities for the two major categories of structural facilities (infiltration and
biofiltration/filtration) are as follows:
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Infiltration BMPs
~ Mowing and maintaining upland vegetated areas if applicable
~ Cleaning and removing debris after major storm events
~ Cleaning out accumulated sediment
~ Repairing or replacing stone aggregate
~ Maintaining inlets and outlets
~ Removing accumulated sediment from forebays or sediment storage areas when 50 percent of
the original volume has been lost
Biofiltration and Filtration BMPs
~ Removing trash and debris from control openings
~ Watering and mowing vegetated areas
~ Removing and replacing all dead and diseased vegetation
~ Stabilizing eroded side slopes and bottom
~ Repairing erosion areas
~ Mulching void areas if needed
~ Maintaining inlets and outlets
~ Repairing leaks from the sedimentation chamber or from deteriorating structural components
~ Removing the top few inches of media and cultivating the surface when the filter bed is clogged
~ Cleaning out accumulated sediment from the filter bed once depth exceeds approximately one-
half inch or when the filter layer no longer draws down within 24 hours
Detailed descriptions of operation and maintenance for specific types of green infrastructure BMPs are
included in the Massachusetts Stormwater Handbook (MassDEP 1997) and general maintenance issues
are presented in the following sections.
C.l.l Bioretention
Maintenance activities for bioretention units should be focused on the major system components,
especially landscaped areas. Bioretention landscape components should blend over time through plant
and root growth, organic decomposition, and natural soil horizon development. Those biological and
physical processes over time will lengthen the facility's life span and reduce the need for extensive
maintenance. Refer to the Massachusetts Stormwater Handbook (MassDEP 1997) for design guidance
on soil media and plant selection.
Irrigation of vegetated areas might be needed during the plant establishment period but fertilizer and
pesticide application should be minimized. In periods of extended drought, temporary supplemental
irrigation could be used to maintain plant vitality. Irrigation frequency will depend on the season and
type of vegetation. Properly selected vegetation will go dormant during dry periods but will revitalize
when rainfall occurs. Native plants generally require less irrigation than non-native plants and should be
incorporated into site designs where feasible. Native plants are also less susceptible to disease and
require fewer pesticides. Controlled drainage can also be used to manage soil moisture by selectively
elevating the underdrain outlet in dry periods; this will result in greater soil moisture retention between
rainfall events. The underdrain outlet should always be no less than 18 inches below the soil surface to
prevent saturation of the plant rooting zone.
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Routine maintenance should include a twice-yearly evaluation of the trees and shrubs and subsequent
removal of any dead or diseased vegetation (USEPA 1999). Corrective actions should be taken to remove
areas with standing water for more than 24 hours in the BMP to restore proper infiltration rates and
prevent mosquito and other vector habitat formation. An Integrated Pest Management Plan should be
developed to minimize the use of broad-spectrum pesticides that could kill beneficial insects that feed
and pollinate the native vegetation. To maintain the treatment area's appearance, it might be necessary
to prune and weed. Replace muich for aesthetics or when erosion is evident. Depending on pollutant
loads, soil media might need to be replaced within 5 to 10 years of construction (USEPA 2000).
Stabilizing the area around the bioretention area can reduce maintenance by reducing the sediment
flowing into the BMP. Figure C-l shows an example of how a bioretention area can clog with sediment if
the surrounding area is not properly stabilized. Proper design of inlet systems can also reduce
maintenance requirements by removing trash and other gross solids keeping floatables out of the
bioretention area and, in some cases, in the street for easy collection and removal by a street sweeper
or maintenance crew as shown in Figure C-2.
Source: NCSU-BAE
Figure C-l. Bioretention area clogged with sediment.
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Source: Tetra Tech
Figure C-2. Inlet sump to remove gross solids.
C.1.2 Water Quality Swale
The maintenance objectives for water quality swale systems consist of retaining stormwater conveyance
capacity, runoff volume control, and pollutant removal efficiency. To meet those objectives, it is
important to maintain a consistent ground cover in the water quality swale. Maintenance activities
involve replacing or redistributing mulch, mowing (where appropriate), weed control, irrigating during
drought conditions, reseeding or sodding bare areas, and clearing debris and blockages.
Manage vegetation on a regular schedule during the growth season to maintain adequate coverage.
Accumulated sediment should also be removed manually to avoid concentrated flow. During the plant
establishment period, minimize fertilizer and pesticide application. Irrigation might be needed to
maintain plant vitality, especially during plant establishment or in periods of extended drought.
Irrigation frequency will depend on the season and type of vegetation. Properly selected vegetation wili
go dormant during dry periods but wiii revitalize when rainfall occurs. Native plants require less
irrigation than non-native plants and should be incorporated into site designs where feasible. Native
plants are also less susceptible to disease and require fewer pesticides. An Integrated Pest Management
Plan should be developed to minimize the use of broad-spectrum pesticides that could kill beneficial
insects that feed and pollinate the native vegetation. Water quality swales should be designed to
minimize flow velocity and prevent the type of erosion shown in Figure C-3. If excessive flows are
identified as the cause of the problem, they should be diverted to prevent erosion and minimize
maintenance.
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Source: Tetra Tech
Figure C-3. Erosion caused by excessive flows in a bioswale.
C.1.3 Tree Box Filter
General maintenance requirements for tree box filters are the same as the routine periodic
maintenance of other landscaped areas or bioretention BMPs. The primary maintenance requirement
for tree box filters is to inspect the vegetation and soil media. Regularly remove any accumulated trash
and sediment in the device, especially after large storms, or as needed during periods where
overhanging vegetation is dropping leaves. Inspect soils to evaluate root growth and mitigate channel
formation or uneven distribution in the soil media.
C.1.4 Sand Filter
The primary maintenance requirement for sand filters is to remove trash, accumulated sediment, and
media contaminated with hydrocarbons. If the filter does not drain within 48 hours, or if sediment has
accumulated to a depth of 6 inches, the top layer (1-3 inches) of sand (media) must be replaced.
C.1.5 Permeable Pavement
The primary maintenance requirement for permeable pavement consists of regular inspection for
clogging (Figure C-4). The main goal of the maintenance program is to prevent clogging by fine sediment
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particles, which should be accomplished through a combination of preventative tasks including timely
removal of debris (leaf litter, acorns, grass clippings, mulch, and such) and stabilizing surrounding areas.
To maintain the infiltrative capacity of permeable pavements, vacuum sweeping should be performed a
minimum of twice a year. Frequency of vacuum sweeping should be adjusted according to the intensity
of use and deposition rate on the permeable pavement surface. Settled paver block systems might
require resetting. When modular pavements incorporate turf into their void area, normal turf
maintenance practices, including watering, fertilization, and mowing might be required (FHWA 2002).
Source: Tetra Tech
Figure C-4. Plant growth, debris buildup, and puddles indicate
that permeable pavement is clogging. Prompt maintenance
should be performed to prevent joints from fully sealing.
For proper performance, maintenance staff must ensure that stormwater is infiltrating properly and is
not standing or pooling on the surface of the permeable pavement for extend periods of time. Standing
water can indicate clogging of the pavement void space and vacuuming is necessary to restore
infiltration. If ponding still occurs, inspect and replace the media sublayer, and check the underdrain for
blockage.
C.1.6 Cisterns and Rain Barrels
General maintenance activities for cisterns and rain barrels are easily performed by maintenance
personnel or homeowners. The Texas A&M Agrilife Extension Service's Rainwater Harvesting (2008)
guide provides maintenance recommendations to homeowners. The primary maintenance requirement
is to inspect the tank and distribution system and test any backflow prevention devices. Rain barrels
require minimal maintenance several times a year and after major storms to prevent clogging. Cisterns
require inspections for clogging and structural soundness twice a year, including inspection of all debris
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and vector control screens. If a first-flush diverter is used, it should be dewatered and cleaned between
each storm event that fills the diverted storage pipe. Self-cleaning filters and screens, such as the ones
shown in Figure C-5, can help prevent debris from entering the cistern and reduce maintenance.
Accumulated sediment in the tank must be removed at least once a year. The Texas Manual on
Rainwater Harvesting (TWDB 2005) provides additional measures for systems designed for potable
water supply or drip irrigation applications.
Source: Tetra Tech
Figure C-5. Self-cleaning inlet filters.
C.1.7 Constructed Stormwater Wetlands
Maintenance activities for wetlands involve removing accumulated sediments and ensuring that plant
distribution and flow paths remain as designed. Constructed wetlands built for the purpose of
stormwater treatment are not considered jurisdictional wetlands in most regions of the country, but
designers should check with their wetland regulatory authorities (U.S. Army Corps of Engineers, Region
6) to ensure this is the case (Virginia 2011).
Bedload sediment tends to be concentrated in pretreatment areas and forebays. It is important that this
sediment not enter the rest of the wetland, because accumulated coarse sediments can affect the
growing conditions of the wetland plants or change flow paths and design depths. Sediment removal
should be performed more frequently, or pretreatment and forebay areas should be resized, if excessive
sediment is found outside designated areas. Sediment removal in vegetated areas should be performed
carefully to prevent damage to plants. Depending on the land use of contributing areas, sediment
testing might be necessary to determine if accumulated pollutants require special disposal.
Wetlands should be inspected regularly or as needed after storm events. Inspectors should refer to a
map of the wetland as designed to determine if the types and distribution of plants are as intended.
Undesirable species should be identified and removed as needed. If plant die-off has occurred,
reevaluate growing conditions and select replacement plants adapted to those conditions. Ensure that
design depths and flow paths are maintained, and remove trash and debris that has accumulated in or
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around the wetland. Outlets should be designed such that the water level in the wetland can be varied
for establishment periods and maintenance using a variable outlet control similar to that shown in
Figure C-6. A minimum orifice size should be considered and a trash rack, similar to the one shown in
Figure C-7, can be used to minimize and limit clogging.
Source: Tetra Tech
Figure C-6. Outlet varied with weir boards.
Source: NCSU-BAE
Figure C-7. Outlet with a trash rack.
C.1.8 Green Roofs
Operation and maintenance of stormwater management (green, blue, brown, biodiverse) roofs
primarily involves maintaining drainage structures and vegetation. Roof drains, gutters, and downspouts
should be routinely inspected for clogging. If excess material tends to build up around drainage
structures, the source of the problem should be remediated, To prevent vegetation from growing too
close to roof drains and to identify roof drains for maintenance personnel, a circle of white gravel can be
placed around the drain to designate a no plant zone as shown in Figure C-8. Vegetation should be
inspected periodically, especially during prolonged dry weather, to determine irrigation needs and
general health. Properly selected vegetation will go dormant during dry periods, but will revitalize when
rainfall occurs. Periodic inspection of growing media and underlying drainage layers might also be
necessary for extensive green roofs to ensure that reservoir layers are not filling with sediment deposits
or extensive root networks. Intensive green roofs could require pruning and mowing at the end of the
growing season, depending on vegetation type.
' ' > ... .¦ "T5.
l Jf
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Roofs require appropriate health and safety protocols for fall protection. Maintenance staff and
designers should consult their office safety officer or Occupational Safety and Health Administration
guidance for proper equipment and safety plans. Foot traffic should be limited, to the extent
practicable, to reduce plant damage and preserve aesthetic design goals. Additional guidance on roof
design, maintenance, and leak detection is available from Design Guidelines and Maintenance Manual
for Green Roofs in the Semi-Arid and Arid West (Tolderlund 2010).
Source: Amy Hathaway
Figure C-8. White gravel indicates a no plant zone for a green roof.
C.2 BMP Monitoring
Performance monitoring of stormwater BMPs is an important component of green infrastructure
implementation programs. Monitoring provides the BMP designer and regulator with a mechanism to
validate certain design assumptions and to quantify compliance with pollutant-removal performance
objectives. Specific monitoring objectives should be considered early in the design process to ensure
that green infrastructure practices are adequately configured for monitoring. Detailed monitoring
guidance provided by EPA is listed in this section's references list (USEPA 2012). The MassDEP also
provides a total suspended solids (TSS) removal calculation worksheet to automatically compute TSS
removal efficiency by various BMPs
(www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-handbook.html).
The instrumentation and monitoring configuration will vary from site to site, but the following general
principles should be considered.
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C.2.1 Monitoring Hydrology
An inlet/outlet sampling setup is suggested as the most effective monitoring approach to quantify flow
and volume in stormwater BMPs. The runoff source and type of BMP will dictate the configuration of
inflow monitoring. A weir or flume is typically installed at the inlet of BMPs that receive concentrated,
open-channel flow (i.e., from a pipe, curb cut, or a swale as shown in Figure C-9, Figure C-10, and Figure
C-ll). Often a baffle or weir box is used in conjunction with weirs to still flows for more precise readings,
as shown in Figure C-12. The height of water flowing over the structure is automatically recorded
(typically with a pressure transducer, such as a bubbler), which is used to calculate the inflow rate. By
integrating the flow rate over each monitored time step, total runoff volume for each storm event can
be calculated.
When runoff enters a BMP via conduit, weirs or weir boxes can still be used for monitoring, but acoustic
Doppler velocimeters (ADVs) might be preferred. ADVs measure flow by recording the velocity and
depth of water and will provide more accurate results if inflow conduits are expected to flow full
(pressure flow), although some models require heavy turbidity to attain accurate readings. Outflow can
be monitored using similar techniques as inflow by installing a weir or ADV at the point of
overflow/outfall.
Source: Tetra Tech
Figure C-9. Inflow pipe to bioretention area equipped with compound weir and bubbler for flow
measurement. Water quality sampling tube and strainer are visible inside pipe.
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Source: Tetra Tech
Figure C-10. Iniet curb cut with a v-notch weir,
Source: Tetra Tech
Figure C-ll. Outlet of a roadside bioretention pop-out equipped with a
V-notch weir for flow monitoring.
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Source: Tetra Tech
Figure C-12. Uriderdrains from permeable pavement equipped with
30-degree V-notch weir boxes and samplers for flow and water quality monitoring.
It is critical during hydrologic monitoring that no downstream tailwater interfere with the monitoring
device, or false readings will be generated. To prevent tailwater effects at the inlet, the invert of the
inflow pipe should be well above the expected temporary ponding depth of the BMP (Figure C-13). This
is typically not possible with offline BMPs because the weir elevation controlling the bypass is at the
maximum elevation in the BMP. Additional freeboard between the inlet and the maximum expected
water depth should be provided to prevent the inlet monitoring device from being inundated by
tailwater from the BMP (Figure C-14). The same considerations should be addressed when monitoring
outflow by ensuring that the receiving storm drain network has sufficient capacity to convey high flows
such that no tailwater inundates the outflow monitoring device. Figure C-15 shows an example of
potential monitoring points.
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MM
Source: Tetra Tech
Figure C-13. Example of a bioretention underdrain outlet with sufficient drop to install a flow
monitoring weir without encountering tailwater.
Invert of weir is too low and H-flume is
PS h 9 • 9 1 if I
inundated when bioretention fills with runoff
Source: Tetra Tech
Figure C-14. Poorly installed H-flume at the inlet to a bioretention area in which the invert of the
weir is too low, and tailwater from the bioretention will interfere with measurement.
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Inflow from
Catchment
Figure C-15. Monitoring points.
In addition to monitoring inflow and outflow, rainfall should be
recorded on-site. Rainfall data can also be used to estimate inflow
to BMPs that receive runoff only by sheet flow or direct rainfall (i.e.,
permeable pavement or green roofs). The type of rain gauge
depends on monitoring goals and frequency of site visits (USEPA
2012). An automatic recording rain gauge (i.e., tipping bucket rain
gauge), used to measure rainfall intensity and depth, is often paired
with a manual rain gauge for data validation (Figure C-16). For more
advanced monitoring, weather stations can be installed to
simultaneously monitor relative humidity, air temperature, solar
radiation, and wind speed. These parameters can be used to
estimate evapotranspiration.
Source: Tetra Tech
Figure C-16. Example of manual
(left) and tipping bucket (right)
rain gauges.
Water level (and drawdown rate) is another useful hydrologic
parameter. Depending on project goals, perforated wells or
piezometers can be installed to measure infiltration rate and
drainage. Care should be taken when installing wells to ensure that
runoff cannot enter the well at the surface and short circuit directly to subsurface layers. Short circuiting
can result in the discharge of untreated runoff that has bypassed the intended treatment mechanisms. It
might be useful to pair soil moisture sensors with water-level loggers in instances where highly detailed
monitoring performance data are required (such as for calibration and validation of models).
Outlet Monitoring Point
(Drainage + Overflow)
Inlet Monitoring Point
• = Monitoring Point
Water Level / Draw Dowi.
Monitoring Point
Drainage Monitoring Point
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C.2.2 Monitoring Water Quality
Although hydrologic monitoring can occur as a standalone practice, water quality data must be paired
with flow data to calculate meaningful results of constituent loading. Flow-weighted automatic sampling
is the recommended method for collecting samples that are representative of the runoff event and can
be used to calculate pollutant loads (total mass of pollutants entering and leaving the system). Simply
measuring the reduction in constituent concentrations (mass per unit volume of water) from inlet to
outlet can provide misleading results because it does not account for load reductions associated with
infiltration, evapotranspiration, and storage.
Influent water quality samples are typically collected just upstream of the inlet monitoring device (weir
box, flume, and such) just before the runoff enters the BMP. The downstream sampler should be at the
outlet control device just before the overflow entering the existing storm drain infrastructure. A strainer
is usually installed at collecting end of the sampler tubing to prevent large debris and solids from
entering and clogging the sampler. Automatic samplers should be programmed to collect single-event,
composite samples according to the expected range of storm flows. Depending on the power
requirements, a solar panel or backup power supply might be needed.
In addition to collecting composite samples, some water quality constituents can be monitored in real
time. Parameter testing applies to stormwater quality control BMPs. Municipal and construction site
parameters are generally the contaminants in runoff studies, such as total dissolved solids, TSS,
suspended sediment concentration, or total petroleum hydrocarbons, total Kjeldahl nitrogen, total
nitrogen, total phosphorus, chemical oxygen demand, biological oxygen demand, Escherichia coli, total
coliform, enterococci, pH, conductivity, temperature, and the following metals: lead, copper, zinc, and
nickel (TARP 2001).
C.2.3 Sample Collection and Handling
Programmable automatic flow samplers with continuous flow measurements should be used unless it is
demonstrated that alternate methods are superior or that automatic sampling is infeasible. Grab
samples should only be used for certain constituents, in accordance with accepted standard sampling
protocols, unless it is demonstrated that alternate methods are superior. Constituents that typically
require grab sampling include pH, temperature, cyanide, total phenols, residual chlorine, oil and grease,
total petroleum hydrocarbons, Escherichia coli, total coliform, fecal coliform, fecal streptococci, and
enterococci. Collection and flow-weighted composite sampling also should follow the NPDES guidance
(TARP 2001).
Quality assurance and quality control protocols for sample collection are necessary to ensure that
samples are representative and reliable. The entire sample collection and delivery procedure should be
well documented in the quality assurance project plan (QAPP), including chain of custody (list of
personnel handling water quality samples) and notes regarding site condition, time of sampling, and
rainfall depth in the manual rain gauge. Holding times for water quality samples vary by constituent, but
all samples should be collected and delivered to the laboratory on ice as soon as possible (typically 6 to
24 hours) after a rainfall event. Some water quality constituents require special treatment upon
collection, such as acidification, to preserve the sample for delivery. Appropriate health and safety
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protocol should always be followed when on-site, including, for example, using personal protective
equipment such as safety vests, nitrile gloves, and goggles.
C.3 References
FHWA (Federal Highway Administration). 2002. Storm Water Best Management Practices in an Ultra-
Urban Setting: Selection and Monitoring. Federal Highway Administration, Washington, DC.
Accessed February 25, 2013. http://environment.fhwa.dot.gov/ecosystems/ultraurb/index.asp.
Hinman, C. 2005. Low Impact Development Technical Guidance for Puget Sound. Report No. PSAT 05-03.
Puget Sound Action Team, Washington State University, Olympia, WA.
MassDEP (Massachusetts Department of Environmental Protection). 1997. Massachusetts Stormwater
Handbook. Revised February 2008.
http://www.mass.gov/eea/agencies/massdep/water/regulations/massachusetts-stormwater-
handbook.html.
TARP (Technology Acceptance Reciprocity Partnership). 2001. The TARP Protocol for Stormwater Best
Management Practice Demonstrations. Final Protocol 08/01, Updated 07/03. Endorsed by
California, Massachusetts, Maryland, New Jersey, Pennsylvania, and Virginia.
http://www.mass.gov/eea/docs/dep/water/laws/i-thru-z/swprotoc.pdf.
Texas A&M Agrilife Extension Service. 2008. Rainwater Harvesting. Texas A&M Agrilife Extension
Service, College Station, TX.
http://rainwaterharvesting.tamu.edu/rainwater-basics/.
Tolderlund, L, 2010 Design Guidelines and Maintenance Manual for Green Roofs in the Semi-Arid and
Arid West. University of Colorado, Denver, CO.
TWDB (Texas Water Development Board). 2005. The Texas Manual on Rainwater Harvesting. 3rd ed.
Texas Water Development Board, Austin, TX.
USEPA (U.S. Environmental Protection Agency). 1999. Stormwater Technology Fact Sheet: Bioretention.
EPA 832-F-99-012. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Accessed February 25, 2013.
http://water.epa.gov/scitech/wastetech/upload/2002 06 28 mtb biortn.pdf.
USEPA (U.S. Environmental Protection Agency). 2000. Low Impact Development: A Literature Review.
EPA-841-B-00-005. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
Accessed February 25, 2013. http://www.lowimpactdevelopment.org/pubs/LID litreview.pdf.
USEPA (U.S. Environmental Protection Agency). 2012. Urban Stormwater BMP Performance Monitoring.
U.S. Environmental Protection Agency, Office of Water, Washington, DC. Accessed February 27,
2013. http://water.epa.gov/scitech/wastetech/guide/stormwater/monitor.cfm.
Virginia. 2011. Virginia Department of Conservation and Recreation Stormwater Design Specification No.
13. State of Virginia. Accessed June 21, 2013.
http://vwrrc.vt.edu/swc/NonPBMPSpecsMarchll/VASWMBMPSpecl3CONSTRUCTEDWETLAND.
html.
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