xvEPA
United States
Environmental Protection
Agency
2012 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
Pittsburgh UNITED
Pittsburgh, Pennsylvania
Addressing Green Infrastructure Design Challenges
in the Pittsburgh Region
Space Constraints
Photo: Tree Box Facility using Silva Cell at the
August Wilson Center for African American Culture
January 2014
EPA 800-R-14-001
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, the water is absorbed and filtered by soil and plants. When rain falls on our roofs, streets, and
parking lots, however, the water cannot soak into the ground. In most urban areas, stormwater is
drained through engineered collection systems and discharged into nearby waterbodies. The
stormwater carries trash, bacteria, heavy metals, and other pollutants from the urban landscape,
polluting the receiving waters. Higher flows also can cause erosion and flooding in urban streams,
damaging habitat, property, and infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. 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 and storing water. These neighborhood or site-scale green infrastructure
approaches are often referred to as low impact development.
EPA encourages the use of green infrastructure to help manage stormwater runoff. In April 2011, EPA
renewed its commitment to green infrastructure with the release of the Strategic Agenda to Protect
Waters and Build More Livable Communities through Green Infrastructure. The agenda identifies
technical assistance as a key activity that EPA will pursue to accelerate the implementation of green
infrastructure.
In February 2012, EPA announced the availability of $950,000 in technical assistance to communities
working to overcome common barriers to green infrastructure. EPA received letters of interest from
over 150 communities across the country, and selected 17 of these communities to receive technical
assistance. Selected communities received assistance with a range of projects aimed at addressing
common barriers to green infrastructure, including code review, green infrastructure design, and cost-
benefit assessments. Pittsburgh UNITED was selected to receive assistance developing fact sheets and
technical papers to provide solutions for site conditions that are perceived to limit green infrastructure
applicability.
For more information, visit http://water.epa.gov/infrastructure/greeninfrastructure/gi support.cfm.
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Acknowledgements
Principal EPA Staff
Kenneth Hendrickson, USEPA Region 3
Dominique Lueckenhoff, USEPA Region 3
Christopher Kloss, USEPA
Tamara Mittman, USEPA
Community Team
Jennifer Rafanan Kennedy, Clean Rivers Campaign
Sara Powell, Nine Mile Run Watershed Association
Consultant Team
Dan Christian, Tetra Tech
Valerie Novaes, Tetra Tech
Anne Thomas, Tetra Tech
Technical Review Team
Beth Dutton, 3 Rivers Wet Weather
Kari Mackenbach, URS Corporation
Jim Pillsbury, Westmoreland Conservation District
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2012 EPA Green
Infrastructure Technical Assistance Program.
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Contents
Introduction 1
Space Constraints and Stormwater Management Overview 1
Characterization of Development in the Greater Pittsburgh Area 2
Methods to Address Space Constraints 4
General Considerations 4
1. Reducing Impervious Cover 4
2. Adding Subsurface Storage 5
3. Working around Buried Utilities 6
4. Protecting Existing Structures 7
5. Providing Support of Adjacent Structures 7
6. Working around Healthy Trees 8
Right-of-Way Projects 10
1. Right-of-Way Widths and Roadside Parking 10
2. Building Access 12
Urban Site Development 13
Examples of Implemented Projects 18
Market Street Rain Gardens, Lemoyne, Pennsylvania 18
Design Summary 18
Albert M. Greenfield Elementary School, Philadelphia, PA 19
1. Design Summary 19
2. Lessons Learned 19
References 21
Manuals, Articles, and Books 21
Websites 21
IV
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Table
Table 1. Green Infrastructure Practices for Urban Site Development 14
Figures
Figure 1. Future Land Use 3
Figure 2. Removal of Unused Impervious Cover 4
Figure 3. Subsurface Storage 5
Figure 4. Retaining Walls 7
Figure 5. Permeable Pavement within a Depressed Centerline 9
Figure 6. Curb Extension Bioretention 10
Figure 7. Street and Lane Widths 11
Figure 8. Behind-the-Curb Bioretention Practices 12
Figure 9. Behind-the-Curb Bioretention with Subgrade Aggregate Storage - Toledo, OH 12
Figure 10. Bioretention Practices within Pedestrian Corridors 13
Figure 11. Vegetated Roofs 14
Figure 12. Dry Well or Seepage Pit 15
Figure 13. Cisterns 15
Figure 14. Planter Boxes 16
Figure 15. Bioretention 17
Figure 16. Lemoyne, PA Market Street Rain Gardens 18
Figure 17. Albert M. Greenfield Elementary School "Green" Playground 19
Figure 18. Permeable Play Surface (left) and Rain Garden (right) 20
Figure 19. Pennsylvania Woodland Forest Garden and Agricultural Zone 20
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Introduction
Future development in the Pittsburgh area is expected to involve significant development on space-
constrained sites, including redevelopment and infill sites in dense urban environments. Integrating
green infrastructure into these development sites can minimize urban stormwater impacts and provide
many other environmental benefits, including improved air quality and reduced urban heat island
impacts. Although the design of green infrastructure practices on space-constrained sites must be
considered early in the planning and design process, many effective design practices are available for
this development context.
Green infrastructure is an important design strategy for protecting water quality while also providing
multiple community benefits. EPA defines green infrastructure as structural or non-structural practices
that mimic or restore natural hydrologic processes within the built environment. Common green
infrastructure practices include permeable pavement, bioretention facilities, and green roofs. These
practices complement conventional stormwater management practices by enhancing infiltration,
storage, and evapotranspiration throughout the built environment and managing runoff at its source.
This paper describes strategies to implement green infrastructure on space-constrained sites, defines
the extent and nature of space-constrained sites in and around Pittsburgh, and provides examples of
projects successfully implemented on space-constrained sites. The goal of this paper is to provide
recommendations for design that are based on facts, research, and engineering in order to help
practitioners make informed decisions regarding the use of green infrastructure on space-constrained
sites.
Space Constraints and Stormwater Management Overview
Future development in the Pittsburgh area is expected to involve significant development on infill and
redevelopment sites. Several characteristics of these sites may limit the space available for stormwater
management. First, redevelopment and infill sites often have high percentages of impervious cover and
low percentages of open space. This lack of open space may limit the ability to apply soil and vegetation-
based practices. Second, redevelopment and infill sites may include many existing features that must be
protected from construction or infiltration. These include buried utilities, existing structures such as
basements and sewers, and mature trees. Finally, redevelopment and infill sites must accommodate
multiple uses in a limited area. Care must be taken to maintain all the required uses, such as building
access and required moving lane widths.
One of the challenges to the use of green infrastructure in the greater Pittsburgh area is the perception
that green infrastructure is incompatible with space-constrained sites. This perception is based on the
concern that green infrastructure will require significant open space that is unavailable on infill and
redevelopment sites. Experience demonstrates, however, that green infrastructure can effectively be
integrated into space-constrained sites. Different strategies are available for different development
contexts - with some strategies more appropriate for street rights-of-way and some strategies more
appropriate for larger urban development sites. The following sections provide a more detailed
discussion of the extent of space-constrained sites in the Pittsburgh area, as well as methods to design
green infrastructure to address space constraints.
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Characterization of Development in the Greater Pittsburgh Area
The Allegheny County Comprehensive Plan contains
extensive information on future planned development
within the county, emphasizing redevelopment and infill
development as opposed to low-density greenfield
development. The plan discusses the importance of infill
development and reuse of existing buildings in downtown
Pittsburgh and Oakland, urban neighborhoods, community
downtowns, and transit-oriented development areas. As
shown in Figure 1, infill development makes up an
extensive portion of the future planned development for
the Pittsburgh area.
The plan also addresses the importance of 'Complete
Streets' and recommends that limited-access highways be
upgraded according to the concepts of 'Complete Streets.'
While complete streets do not necessarily address
stormwater, enhancing stormwater management is often
one of the elements considered.
For additional information refer to the Allegheny Places
web site and the complete comprehensive plan:
http://www.alleghenyplaces.com/comprehensive plan/co
mprehensive plan.aspx.
Development Definitions
Infill - Refers to development in urban
areas with existing streets,
infrastructure and development.
(USEPA, 1999)
Greenfield- Refers to development on
previously undeveloped ("green")
parcels in suburban or non-urban
locations with limited existing
infrastructure and development.
(USEPA, 1999)
Redevelopment- Development that
occurs on previously developed land.
(Website: USEPA-NPDES, 2013.)
Stormwater Retrofit - Provides
stormwater treatment in locations
where practices did not exist or were
ineffective. They are often incorporated
around existing development and
infrastructure. (Center for Watershed
Protection, 2007).
Complete Street - The concept of
making streets comfortable, safe and
convenient for travel by auto, foot,
bicycle and transit. (Allegheny County
Comprehensive Plan)
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Figure 1. Future Land Use
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Methods to Address Space Constraints
This section describes methods to safely and effectively retain runoff on sites with limited open space.
The first subsection discusses general considerations for space-constrained sites. This subsection
describes general planning and design approaches appropriate for dense urban environments, and
reviews methods for protecting existing site features. The following subsections discuss tailored
planning and design approaches for the road right-of-way and for other urban development sites.
General Considerations
I. Reducing Impervious Cover
Runoff is generated when rain falling on impervious
surfaces, including streets, sidewalks, and parking
areas, cannot soak into the ground. Even in dense
urban environments, opportunities should be
identified to reduce stormwater runoff by reducing
these impervious surfaces.
One approach to reducing impervious surfaces is to
remove impervious cover that is not used (Figure
2). Examples include the "no parking" zone areas
1) near fire hydrants, 2) between driveway
approaches, or 3) near intersections based on
intersection setback requirements. These areas could
be converted to or planned as bioretention areas.
Volunteers could be involved in identifying unused
shopping center parking spots and driving aisles on
the busiest days. Neighborhood residents could
identify unused neighborhood parking spots. This
knowledge can help justify incorporating green
infrastructure or pervious cover in these areas. In
cooperation with local or state authorities, unused
sidewalk, traffic lanes, traffic islands, and curbside
parking may be identified and removed.
Another approach is to reduce the demand for
impervious surfaces by organizing shared parking
spaces. Parking spaces could be shared between
neighboring businesses or between developments
that have different hours of operation. Examples
include sharing parking between a bank and a bar or
between a day care and a housing complex.
NE Sandy and 15 Avenue, Portland, OR
Before
After
Source: Kevin Perry,
Nevue Ngan Associates
Figure 2. Removal of Unused Impervious Cover
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Concrete Pavers
Source: Clean Water Services, 2009
Evapotranspiration
2. Adding Subsurface Storage
Many practices can provide subsurface detention
or retention of stormwater while requiring
minimal surface space. Some of these practices
allow infiltration through paved surfaces, while
others collect runoff from paved drainage areas
and direct the runoff into a storage system.
Permeable Pavements: Permeable pavements can
be installed in place of traditional pavements to
allow infiltration through paved surfaces. These
systems allow stormwater to infiltrate through the
pavement into an aggregate subgrade. Depending
on the system design, stormwater will then
infiltrate into the soil or drain through an
underdrain to an outlet. Types of permeable
pavement include: interlocking concrete pavers
(Figure 3), cellular reinforced paving filled with
topsoil and grass or gravel, pervious concrete, or
pervious asphalt. For roadway applications,
interlocking concrete pavers, pervious concrete, or
pervious asphalt are typically used. Cellular
reinforced paving is normally used in parking lots
and utility access drives.
Permeable pavement does not require additional
space on a project site, but rather is an alternative
to traditional pavement. Permeable pavement can
be installed across the entire width of road or
parking lot or just within the parking lanes or
stalls. The wider the installation of permeable
pavement, the less pollutant load per unit of
permeable pavement from the drainage area.
Permeable sidewalk and driveway approaches are
others options for reducing runoff.
Suspended Pavement Systems: Suspended
pavement systems can be combined with
permeable pavement to support tree growth and
provide additional storage, while also providing
structural support for cars and trucks. An example
of a suspended pavement system is the Silva Cell
(Figure 3). The Silva Cell uses a system of crates to
hold lightly compacted soil while supporting traffic
loads. The lightly compacted soil will store more
water than a compacted soil, allow tree roots to
access a greater soil volume, and enhance evapotranspiration rates. While the rooting soil will not
provide enough storage to retain large storms, it can retain the smaller storms that comprise 80 to 90
Suspended Pavement
Source: www.deeproot.com
Underground Pipe Storage
Source: www.cenews.com
Figure 3. Subsurface Storage
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percent of the annual rainfall in Pittsburgh. ASilva Cell system is installed along Liberty Avenue at the
August Wilson Center for African American Culture in Pittsburgh (see cover image).
Structural Soils: Structural soils can also be combined with permeable pavement to support tree growth
while meeting load bearing requirements. Structural soil is a mixture of crushed aggregate and soil that
can be compacted to bear the load of a pavement. At the same time, structural soil allows tree roots to
grow freely, supporting tree growth and enhancing evapotranspiration rates.
Vault and Pipe Storage: Vault and Pipe storage systems drain runoff from a paved drainage area into a
subsurface storage unit. . Curb inlets or surface drains direct stormwater into underground storage
vaults or into a system of large-diameter interconnected storage pipes. The stormwater is then released
directly through an outlet pipe into the stormwater drainage system, or allowed to infiltrate into the
ground. Systems that allow infiltration provide some retention of stormwater, while systems that do
not, provide only temporary storage. Because large storage volumes can be installed, these systems are
particularly suitable if detention of large storm events is required. Note, however, that these systems
should not be expected to substantially improve water quality unless preceded by a pretreatment
practice such as a swale or prefabricated device.
3. Working around Buried Utilities
When installing green infrastructure on redevelopment or infill sites, care must be taken to protect
existing site features, including utilities, structures, and mature trees. Many different utilities may be
buried within the street right-of-way in the greater Pittsburgh area. These utilities include sewer, water,
electrical, gas, fiber optic, cable, and telephone. While some rights-of-way will not include all of these
utilities, others located in busier urban corridors will have multiples of these utilities. Utilities may be
buried at shallow depths, within 18 inches of grade, or at greater depths, more than 5 feet below grade.
Public utilities in the Pittsburgh area are often not well marked and are sometimes unexpectedly shallow
because they were installed one hundred years ago. Making conservative assumptions and building
flexibility into green infrastructure designs will help alleviate problems during construction.
All work near utility lines should be coordinated with the respective utility company. When working
with the utility company, collaborative decisions can be made regarding potentially moving the utility,
adding waterproofing measures, and evaluating structural support requirements. Whatever the
configuration of utilities, the following are a few guidelines for working around utilities:
• Call 8-1-1 (Pennsylvania One Call) before digging to have buried utilities located on the site.
• Combined sewer - The combined sewer is often buried well below the bottom of a green
infrastructure practice, but in Pittsburgh the older pipes are sometimes shallow. The age and
condition of a nearby sewer should be considered when placing and designing a green
infrastructure practice. If a green infrastructure practice is installed above an older pipe,
grouting the joints of the pipe may be desired to diminish the possibility of water entering the
pipe.
• Water main - Water main is buried approximately 4 feet from grade to the crown of the pipe,
which would locate it just beneath a typical practice. As long as careful excavation of the
practice is conducted, there should be no problem with a water main in the vicinity of a green
infrastructure practice. In Pittsburgh, old water main may not be buried this deep. Green
infrastructure practices should be located away from old water mains as much as possible.
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• Gas mains - High pressure gas mains should definitely be avoided. Low pressure shallow mains
are usually not a problem. Many times, the project is an opportunity for the gas company to
update their line.
• Single conduit utilities - Single conduit utilities, including electrical, telephone, fiber optic, and
cable, are typically buried approximately 18 inches below grade in a watertight conduit. As
long as careful excavation of the practice is conducted, there should be no problem with single
conduit utilities placed within the vicinity of a green infrastructure practice.
• Concrete support structures - Generally, utilities such as duct banks, steam, chilled water, etc.,
that use concrete support structures should be avoided due to the expense of moving them.
4. Protecting Existing Structures
When installing green infrastructure in dense urban
environments, existing structures such as basements and
sewers must be protected. Because these structures are
often older, they may be susceptible to leaks or damage from
nearby construction. Care must therefore be taken to guard
against basement flooding or infiltration into the sewer. For
buildings, one waterproofing strategy is to include an
impermeable barrier between the water infiltrating from the
practice and the adjacent basement. Another strategy is to
waterproof the outside of the adjacent basement. For
sewers, engineers should determine what the impact of
infiltration would be on the sewer system. Waterproofing
strategies include trenchless pipe lining, as well as providing
a full concrete or plastic containment system for the green
infrastructure practice. Investigations into groundwater
movement in the area may be warranted to determine
potential impacts. If groundwater mounding is a concern,
underdrains can be incorporated into the green
infrastructure practice.
5. Providing Support of Adjacent Structures
It may be necessary to provide structural support within
green infrastructure practices that are installed near
buildings and roads. Depending on the practice placement,
there is often concern that nearby compacted soils will
migrate into the less compacted soils used in green
infrastructure practices. To guard against this, retaining walls
can be constructed. Examples of green infrastructure
practices with retaining walls include 1) the Lansing, Ml
planter boxes, which have about 5.5-foot deep reinforced
masonry block retaining walls with footings, and 2) the
Portland, OR planter boxes, which have about 13-inch deep poured concrete retaining walls (Figure 4).
Different situations require different designs. A geotechnical engineer should be consulted.
SW 12 Avenue, Portland ,OR
Source: Kevin Perry, Nevue Ngan
Associates
Michigan Avenue, Lansing, Ml
Source: Anne Thomas, Tetra Tech
Figure 4. Retaining Walls
7
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Tree Definitions
Mature Tree - For purposes of
stormwater management, a
"mature tree" means that the tree
has a well-developed canopy. This
is usually a 20 to 25 year old tree.
(American Public Power
Association, 2013)
Interception -The process through
which plants capture and store
precipitation on their leaves and
branches.
Evapotranspiration - Includes
evaporation of water to the air
from the tree canopy as well as
transpiration of water to the air
from the movement of water
within a plant.
6. Working around Healthy Trees
The sections above discussed several existing features
that must be considered when developing a previously
developed site, including utilities and structures. Another
feature that must be considered is the presence of
healthy, mature trees. While existing utilities and
buildings pose obstacles to incorporating green
infrastructure into a site, existing trees represent an
opportunity that should be taken advantage of,
particularly in the Pittsburgh area. Pittsburgh's tree
canopy covers 42 percent of the city and is highly valued
by city residents and leaders. The 2012 Pittsburgh Urban
Forest Master Plan outlines the city's strategy for
managing and growing the urban tree canopy.
Stormwater Benefits of Trees: Mature trees provide
significant stormwater quantity and rate control benefits
through soil storage, interception, and
evapotranspiration. A tree with a 25-foot diameter
canopy can hold the 1-inch 24-hour storm event from
2,400 square feet of impervious surface. Interception and
evapotranspiration also decrease runoff volume with
larger trees providing exponentially more benefit than
smaller trees (MacDonagh, Smiley, and Bloniarz, 2012). In
addition to stormwater quantity benefits, trees provide numerous ancillary benefits including water
quality treatment, a reduction in urban heat island effect, an improvement in air quality, a reduction in
combined sewer treatment needs, an increase in aesthetics and recreational opportunities, a reduction
in noise pollution, and a decrease in flooding (Center for Neighborhood Technology, 2010).
Because of the inherent stormwater benefits of trees, it is advantageous to plan to protect mature trees
during the site planning process. Protecting trees along a right-of-way corridor or site development
does not preclude the use of other green infrastructure practices along the corridor, but it will help
determine placement and type of practices.
Tree Preservation and Planting: Following the identification of mature trees on a site and the decision
to preserve them, it is recommended to get advice from a professional urban forester or arborist with
experience in protecting trees from construction damage. Damage to the root system causes the most
harm to the overall health of a tree. Different species of trees react differently to root damage, which is
what a tree-care specialist can help assess during the planning phase. Most healthy trees can tolerate
one-sided root cutting and recover with long-term care including watering, dead branch removal, and
replacement of turf with mulch, shrubs or perennials. Construction equipment and materials should not
be stored over a tree's soil to avoid compaction (Johnson, G. R., 2013).
In addition, it is helpful to incorporate trees as much as possible into a development site or right-of-way
for the many long-term benefits they provide. A helpful guide for preserving and planting urban trees is
the Urban Watershed Forestry Manual, Part 2: Conserving and Planting Trees at Development Sites
(Center for Watershed Protection, 2006).
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Green Infrastructure Placement: Bioretention and permeable pavement are common candidates for
green infrastructure proposed to be installed around or in conjunction with mature trees. Depending on
the results of a tree-care specialist's assessment and the density of the trees, it is likely either one of
these practices can be retrofitted into a right-of-way or development site including mature trees.
Many times, curb extension bioretention can be located in open spaces away from trees or near smaller
trees. The depth of these practices is usually 3 to 4 feet below grade, which would impact adjacent tree
roots, but perhaps not detrimentally.
Similarly, permeable pavement within a parking lane or a parking row as opposed to across the entire
road or parking lot may be a possibility depending on the tree assessment. A permeable pavement
system including a storage layer typically extends an additional one to two feet below the existing
pavement. If extensive tree damage seems likely with permeable pavement installation, consider 1)
crowning the road along the curb line and including permeable pavement within the depressed
centerline (Figure 5) or 2) eliminating just the storage layer along the curb line.
1 Permeable
pavement material
(permeable
asphalt, permeable
concrete, or
permeable pavers)
2 High albedo
concrete paving
with recycled
aggregate and slag
3 Optional pipe
under drain
4 Energy efficient
dark sky compliant
light fixture
Source: Chicago Department of Transportation, 2010
Figure 5. Permeable Pavement within a Depressed Centerline
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Right-of-Way Projects
Challenges to incorporating green infrastructure within the right-of-way often include maintaining
essential moving lane and pedestrian pathway widths, keeping necessary roadside parking spots, and
providing access to businesses or residences. The use of permeable pavement is often a practical option
within the right-of-way, but more thought must be given to incorporating bioretention practices. This
section offers guidance on retrofitting bioretention within the right-of-way.
I. Right-of-Way Widths and Roadside Parking
Right-of-way widths and the location of roadside parking will vary from street to street throughout the
Pittsburgh area. There are different concerns regarding space availability for different green
infrastructure practices. This section will discuss curb extension bioretention and "behind-the-curb"
bioretention/bioswales as related to right-of-way width and roadside parking. Specific design guidance
on these practices can be found in the Pennsylvania Stormwater Best Management Practices Manual.
Curb Extension Bioretention: Curb extension bioretention is the practice of capturing road runoff
within a vegetated shallow depressed area which extends out from the curb into the street, typically
into a parking lane (Figure 6). Curb extension bioretention also results in traffic calming and can be used
to shorten pedestrian crossing distances. An important concern when evaluating for retrofit of curb
extension bioretention within the right-of-way is maintaining the appropriate moving lane widths,
pedestrian pathway widths, and parking spots.
Source: Washington Square, Lansing, Michigan
Figure 6. Curb Extension Bioretention
Maintaining a 10-to 14-foot moving lane is recommended in most situations, which should also allow
access by emergency vehicles. Refer to Figure 7 for recommendations on moving lane widths for three
variations of residential streets. According to Americans with Disabilities Act (ADA) regulations,
pedestrian pathways should be at least 48 inches in width.
The location and utilization of roadside parking (one side or both sides) must also be considered. If
there is a high demand for roadside parking, loss of parking spots due to curb extension bioretention
may not be a good option. In such situations, permeable pavement or bioretention/bioswale located
behind the curb may be considered as they do not result in changes to moving lane widths.
10
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ir-121
Moving
Lane
I 10'
1 Moving
Lane
S4--36-
Local
(Parking not expected or
restricted to ona side)
Local
(Parking on botti sides)
Residential Collector
(Parking on both sides)
Source: Kulash, 2001
Figure 7. Street and Lane Widths
Behind-the-Curb Bioretention: Behind-the-curb bioretention provides the same function as a curb
extension bioretention but is located behind the curb and is sometimes installed along a lengthy portion
of the road (Figure 8). It is not dependent on the road width but is dependent on the available right-of-
way area behind the curb. At a minimum, a 5-foot width is needed without subtracting from the
minimum ADA sidewalk width of 48 inches.
To accommodate roadside parking, a minimum 18-inch wide flat surface (e.g. grass, concrete, mulch)
should be provided directly behind the curb at the level of the curb to allow people to safely step out of
a car (Figure 8).
With both curb extension bioretention and behind-the-curb bioretention, it is possible to increase
storage in the system by utilizing one of the subgrade storage options discussed in Section 'Adding
Subsurface Storage/The subgrade storage can be provided beneath the area behind the curb or even
the road. Refer to Figure 9 for a design detail of subgrade storage.
11
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Behind-the-Curb Bioretention
Source: SvR Design Company Green
Factor Workshop
Roadside Parking Safety Bench
Source: Maywood Avenue, Toledo,
Ohio
Figures. Behind-the-Curb Bioretention Practices
1200'
TYPE B
CURB & GUTTER
PLANTING MIX
3M" DOUBLE WASHED
ODOT *7 AGGREGATE
DOUBLE WASHED ODO1
#57 AGGREGATE
6" PERFORATED SCHEDULE 40 PVC TO BE
FIELD VERIFIED BY ENGINEER TO ENSURE
PROPER DRAINAGE TO STORM CB'S
BIOSWALE CELL SECTION (TYP.)
SCALE r = Z
Figure 9. Behind-the-Curb Bioretention with Subgrade Aggregate Storage - Toledo, OH
2. Building Access
When installing green infrastructure practices within the right-of-way, it is essential to consider access
to businesses and residences. This can be done by incorporating pedestrian "bridges" across practices
or placing the practices so that access is not inhibited. For example, movable metal plates placed over
behind-the-curb bioretention in Lansing, Ml serve to provide pedestrian access to businesses as well as
outdoor seating (Figure 10).
12
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'am
Moveable metal plates over bioretention providing for
outdoor seating.
Source: Michigan Avenue, Lansing, Michigan
Metal plates allowing pedestrian access from roadside
parking.
Source: Market Street, Lemoyne, Pennsylvania
Figure 10. Bioretention Practices within Pedestrian Corridors
Urban Site Development
While bioretention and permeable pavement are the most appropriate practices for urban right-of-way
projects, many different green infrastructure practices can be integrated into other urban development
sites. The suite of green infrastructure practices appropriate for larger infill or redevelopment sites
includes permeable pavement, bioretention, vegetated roofs, dry wells, and rainwater harvesting. Table
1 describes the practices not discussed in previous sections.
All of these practices share one feature in common - they can be integrated into existing or planned
land uses while requiring minimal additional surface space. For example, vegetated roofs can be
integrated into the building design, providing storage and evapotranspiration on the roof surface.
Similarly, bioretention can be integrated into planned landscaped areas, while permeable pavement can
be integrated into planned paved areas. Instead of requiring additional space, these green infrastructure
practices enhance the hydrologic function of planned land uses. Figure 11 through Figure 15 below
illustrate how many of these green infrastructure practices can be integrated into the building or
landscape design.
13
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Table 1. Green Infrastructure Practices for Urban Site Development
Green Infrastructure
Practice
Description
Vegetated Roof
Dry Well or Seepage
Pit
Rain barrels and
Cisterns
Captures the rain that falls directly onto the roof. Soil storage and evapotranspiration
help reduce peak flow and volume. Stormwater is treated by the many processes
within the soil layer. It is often the first step of a treatment train. Refer to BMP 6.5.1
from the PA Stormwater BMP Manual for design guidance.
Captures roof drainage. Infiltration reduces peak flow and volume. Can be useful on
sites where no surface storage is available. Refer to BMP 6.4.6 from the PA
Stormwater BMP Manual for design guidance. This is regulated as a Class V well and
is overseen by EPA Region 3.
Captures roof drainage. Storage reduces peak flow and volume. Can be used as part
of a gray water reuse system or for irrigation. Refer to BMP 6.5.2 from the PA
Stormwater BMP Manual for design guidance.
Source: PA Stormwater BMP Manual Source: Friends Center, Philadelphia, PA
Figure 11. Vegetated Roofs
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Source: PAStormwater BMP Manual
Figure 12. Dry Well or Seepage Pit
Source: Sustainable Urban Science Center, Philadelphia, PA
Figure 13. Cisterns
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Structural wall
(with waterproofing)
Downspout
Hooded overflow
Gravel or splash
block
6" Ponding Depth
Filter fabric
Perforated pipe
(to run length of planter)
Foundation drain
Structural footing
18" Growing Medium
Source: Clean Water Services, 2009
Source: SvR Green Factor Workshop
Source: Clean Water Services, 2009
Figure 14. Planter Boxes
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Source: Clean Water Services, 2009
Source: SvR Green Factor Workshop
Source: SvR Green Factor Workshop Source: SvR Green Factor Workshop
Figure 15. Bioretention
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Examples of Implemented Projects
Market Street Rain Gardens, Lemoyne, Pennsylvania
Source: Kairos Design Group, LLC
The Lemoyne Borough in Cumberland County, PA completed Phase I of their downtown revitalization
project in 2010. The revitalization project calls for several phases of streetscape improvements within
the Market Street corridor based on a "Complete Street" design. A Complete Street is designed to create
a comfortable, safe, attractive, and easily accessible travel route for pedestrians, bicyclists, motorists,
and public transport. The Market Street Complete Street also includes bioretention to provide
stormwater management (Figure 16). This project is an example of a right-of-way project with space
constraints typical of an urban area. Available space in the Market Street corridor is constrained by
underground utilities, the need to provide pedestrian access to businesses, and the need to provide
roadside parking.
Figure 16. Lemoyne, PA Market Street Rain Gardens
Design Summary
The Market Street design uses a combination of green infrastructure practices along the corridor
including bioretention planter boxes, bioretention curb extensions, and interlocking concrete pavers to
capture and infiltrate the "first flush" of rainfall. An underdrain was not utilized in the designs. Within
the bioretention areas, a variety of salt/drought tolerant native plant species were used with an
engineered soil mix to support the plants and promote infiltration into the in situ soils. Not only do the
green infrastructure practices provide stormwater treatment, but also green space. The overall design
accommodates buried utilities, roadside parking, pedestrian traffic, and gutter flow for the larger storm
events. Utilities located beneath the green infrastructure practices include the water, telephone, gas,
and sanitary sewer lines.
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Albert M. Greenfield Elementary School, Philadelphia, PA
Source: Michele Adams, President, Meliora Design, LLC; American Society of Landscape Architects;
Schuylkill Action Network
As part of the Philadelphia Water Department's
"Green City, Clean Waters" plan, the Albert M.
Greenfield Elementary School became a pilot site
for using green infrastructure to reduce the volume
and rate of stormwater discharges into the
combined sewer system within Philadelphia. The
school is located in center city Philadelphia, which is
a highly urbanized area. The project was a
collaborative effort between the Philadelphia
Water Department, PA Dept. of Environmental
Protection, the Albert M. Greenfield Foundation,
the Philadelphia School District, and many others.
This project serves as an example of an urban site
development which transformed impervious
surfaces into a green drainage network while
maintaining the intended school playground use.
Source: http://phillywatersheds.org/categorv/blog-
tags/stream-restoration
Figure 17. Albert M. Greenfield Elementary School
"Green" Playground
I. Design Summary
In 2009 and 2010, the first two phases of this retrofit project were completed installing an indigenous
Pennsylvania woodland forest garden and agricultural zone, removing impervious cover, adding a
permeable play surface, and installing two rain gardens (Figure 17 through Figure 19). The
improvements capture and treat 97 percent of the rainfall from the school yard or 1 inch of rainfall
depth as required by the water department. The existing soil was a compacted urban fill not conducive
to supporting plant growth or storing water, so up to three feet of engineered soil was brought in to
support the system. A perforated underdrain was used beneath the rain gardens and permeable play
surface, not as an outlet to the combined sewer system, but only as a means to distribute the water to
promote infiltration. An overflow system was installed to drain runoff from events larger than the 1-
inch event. Future phases include adding a vegetated roof to the building.
2. Lessons Learned
Located in a constrained urban setting in center city Philadelphia, the Albert M. Greenfield Elementary
School did not have additional open space in which to install green infrastructure. The pilot project
therefore focused on creating shared usage of the playground area. Significant concerns and ideas were
identified in design charrettes and included the importance of maintaining the system integrity while
understanding that this is a functioning school playground. Rather than fencing off the rain gardens,
these areas were incorporated into the curriculum of the school such that the students understand their
significance and are engaged in the plant and animal life of the gardens. Innovative design features
were also used to protect the gardens such as installing strategically placed nets/climbing structures
near the basketball courts (Figure 17); an idea courtesy of a student involved in the charrettes.
From a stormwater design perspective, this project shows the ability of an urban site to infiltrate a
significant amount of water. From a comprehensive design perspective, the overall lesson learned is the
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importance of involving all stakeholders in the design process to successfully share space in a
constrained urban setting.
.- ".I
Source: www.viridianls.com
Figure 18. Permeable Play Surface (left) and Rain Garden (right)
Photo Credit: Paul Rider
Figure 19. Pennsylvania Woodland Forest Garden and Agricultural Zone
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References
Manuals, Articles, and Books
Brown, R., Hunt, W. and Kennedy, S. 2009. Urban Waterways: Designing Bioretention with an Internal
Water Storage Layer. NC Cooperative Extension.
Cappiella, K., Schueler, T., Tomlinson, J. and Wright, T. September 2006. Urban Watershed Forestry
Manual: Part 3 Urban Tree Planting Guide. United States Department of Agriculture Forest Service.
Center for Neighborhood Technology and American Rivers. 2010. The Value of Green Infrastructure: A
Guide to Recognizing Its Economic, Environmental and Social Benefits.
Center for Watershed Protection. 2006. Urban Watershed Forestry Manual Part 2: Conserving and
Planting Trees at Development Sites. United States Department of Agriculture, Forest Service.
Center for Watershed Protection. 2007. Urban Subwatershed Restoration Manual Series, Manual 3:
Urban Stormwater Retrofit Practices Version 1.0.
Chicago Department of Transportation. 2010. The Chicago Green Alley Handbook.
Clean Water Services. July 2009. Low Impact Development Approaches Handbook.
Davey Resource Group. 2012. Pittsburgh Urban Forest Master Plan. Tree Pittsburgh.
Kulash, W. M. 2001. National Association of Home Builders, American Society of Civil Engineers, Institute
of Transportation Engineers, and Urban Land Institute. Residential Streets. Third Edition. Washington
D.C.: ULI-the Urban Land Institute.
MacDonagh, P., Smiley, T., and Bloniarz, D. 2012. The Urban Forest is Broken: Rethinking Street Trees as
Urban Infrastructure. 2012 Stormwater Symposium, Session 19.
Ontario Ministry of the Environment. 2003. Stormwater Management Planning and Design Manual.
Queen's Printer for Ontario.
Pennsylvania Department of Environmental Protection. 2006. Pennsylvania Stormwater Best
Management Practices Manual.
United States EPA. 1999. The Transportation and Environmental Impacts of Infill versus Greenfield
Development: A Comparative Case Study Analysis. EPA publication number 231-R-99-005.
Websites
Allegheny Places: The Allegheny County Comprehensive Plan. December 2008.
http://www.alleghenyplaces.com/comprehensive_plan/comprehensive_plan.aspx
American Society of Landscape Architects
http://www.asla.org/uploadedFiles/CMS/Advocacy/Federal_Government_Affairs/Stormwater_Case_Stu
dies/Stormwater%20Case%20467%20Greenfield%20Elementary%20School,%20Philadelphia,%20PA.pdf.
Last accessed April 15, 2013.
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American Public Power Association
http://www.publicpower.org/treeben/faq.asp. Last accessed April 4, 2013.
Deep Root
http://www.deeproot.com/blog/blog-entries/greenbuild-2010-presentation-recap-is-the-urban-forest-
broken. Last accessed April 4, 2013
Johnson, G. R. 2013. Protecting Trees from Construction Damage: A Homeowner's Guide. University of
Minnesota Extension
http://www.extension.umn.edu/distribution/housingandclothing/dk6135.html. Last accessed April 4,
2013.
City of Portland, Oregon
http://www.portlandoregon.gov/bes/article/167503. Last accessed April 22, 2013.
Schuylkill Action Network
http://www.schuylkillwaters.org/project_files/Greening%20Greenfieldv2.pdf. Last accessed April 15,
2013.
United States EPA- National Pollutant Discharge Elimination System
http://cf pub. epa.gov/npdes/stormwater/menuof bmps/index.cfm?action=browse&Rbutton=detail&bmp
=127. Last accessed April 15, 2013.
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