&EPA
United States
Environmental Protection
Agency
2012 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
Pittsburgh UNITED
Pittsburgh, Pennsylvania
Addressing Green Infrastructure Design Challenges
in the Pittsburgh Region
Fact Sheet Series
Photo: Roadside bioretention facility
January 2014
EPA 800-R-14-005
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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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Contents
Space Constraints Fact Sheet 1
Steep Slopes Fact Sheet 3
Abundant and Frequent Rainfall Fact Sheet 5
Clay Soil Fact Sheet 7
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
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2012 EPA Green
Infrastructure Technical Assistance Program.
IV
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Space Constraints
Fact Sheet Series Addressing Green Infrastructure
Design Challenges in the Pittsburgh Region
The roofs, roads, and parking lots in our urban areas prevent rainfall from
soaking into the ground, overwhelming sewers and leading to flooding
and polluted rivers. Green infrastructure helps solve flooding and prevent
water pollution by using soil, vegetation, and natural processes to restore
natural drainage patterns in our communities. Green infrastructure can
also clean our air, revitalize our neighborhoods, create jobs, save our
communities money, and provide other lasting community benefits.
The Challenge
Future development in the Pittsburgh region is expected to require
development of previously developed sites (redevelopment) or available
sites nestled within urban areas (infill). Planned construction activities on
redevelopment or infill sites and the road right-of-way present the
opportunity to incorporate green infrastructure into urban areas. When
incorporating green infrastructure into these areas however, limited
space may pose a challenge because the existence of buried utilities,
mature trees, basements, buildings, and roads pose obstacles.
Fortunately, designers have developed strategies for overcoming this
challenge, for example, by using green features that serve multiple
purposes or fit into small spaces. With care, the right green infrastructure
practices can work well in the Pittsburgh region.
Opportunities
Green Infrastructure practices such as bioretention, permeable pavement,
green roofs, and rain barrels are all practices that are successful in urban
space-constrained sites.
• Bioretention practices can be designed next to buildings and roads to
absorb stormwater. Planted with trees, they become even more
efficient at absorbing water.
• Permeable pavement can be substituted for traditional pavement,
thereby not taking up additional space. Reducing the overall area of
pavement also
helps.
Green roofs
absorb rainfall
while protecting
the roof at the
same time.
Draining a roof
to a rain barrel
to water a
garden helps r
reduce
stormwater and
saves drinking
water.
Precipitation
Canopy Interception
and Evaporation
Dots Take Up Soil
Moisture. Increasing
Runoff Storage
Potential
Green Infrastructure
Practices that Work in
Constrained Spaces
This bioretention planter box was designed
into a pedestrian corridor.
Source: Tetra Tech
" -' • -*
Stormwater from a rooftop drains into this
terraced bioretention facility.
Source: SvR Design Company Green Factor
Workshop
I I I \
This large parking lot helps to infiltrate
stormwater through a permeable pavement
system.
Source: Clean Water Services
This diagram shows the many natural routes
rain water may take when it falls on a tree as
opposed to merely running off of an impervious
surface.
Source: Xiao, Q.; McPherson, E. G.; Ustin, S. L;
Grismer, M. E. 2000. A new approach to
modeling tree rainfall interception. Journal of
Geographical Research Atmospheres 105: 29173-
29188.
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Case Studies
Albert M. Greenfield Elementary School, built 2010, Philadelphia, PA
Albert M. Greenfield Elementary School is a pilot site for using green
infrastructure to reduce the number and volume of combined sewer
overflows within Philadelphia. The school is located within an urban
corridor and is bordered on all sides by busy streets. As a
collaborative effort, a plan was created to transform the existing
impervious school yard into a green space complete with green
infrastructure.
The installed green infrastructure includes a woodland garden and
rain gardens, which are installed along the perimeter of the
playground, and permeable pavement, which doubles as a forgiving
play surface. Combined, these practices capture and infiltrate 97
percent of the annual runoff from the school yard.
Green infrastructure is incorporated into this school
yard as permeable play surface and garden areas.
Source: http://phillywatersheds.org/category/blog-
tags/stream-restoration
Results
• This project shows the ability of an urban site to infiltrate a
significant amount of water.
• Innovative design features were used to protect the gardens, such as installing strategically placed nets/climbing
structures (pictured) near the basketball courts; an idea courtesy of a student involved in the design process.
• The overall lesson learned is the importance of involving all interested parties in the design process to successfully
share space in a constrained urban setting.
Source: Michele Adams, President, Meliora Design, LLC; American Society of Landscape Architects; Schuylkill Action Network
Market Street Bioretention, built 2010, Lemoyne, PA
The Lemoyne Borough in Cumberland County, PA has a downtown
revitalization project underway. The overall multi-phase streetscape
improvements project uses green infrastructure as part of the
stormwater management system.
Bioretention and permeable pavers were used within the Market
Street right-of-way to capture and infiltrate the "first flush" of
rainfall. Stormwater runs off of the street and into the bioretention
areas through cuts in the curb. The stormwater is treated through
an engineered soil mixture before infiltrating through the underlying
soil.
Results
• The green infrastructure practices provide green space as well as
stormwater treatment and volume reduction.
• Because of the use of road salt in the winter and lack of rain in
the summer, a variety of salt- and drought-tolerant native
plant species were planted in the bioretention areas.
• The design accommodates typical roadside challenges
including buried utilities, roadside parking, pedestrian traffic, and gutter flow for the larger storm events.
Source: Kairos Design Group, LLC
With innovation and collaboration, green infrastructure practices can be
effectively incorporated into constrained urban areas
This roadside bioretention captures stormwater from
the road. The paved shoulder and metal grates provide
roadside parking access.
Source: Kairos Design Group, LLC
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Steep Slopes
Fact Sheet Series Addressing Green Infrastructure
Design Challenges in the Pittsburgh Region
The roofs, roads, and parking lots in our urban areas prevent rainfall from
soaking into the ground, overwhelming sewers and leading to flooding and
polluted rivers. Green infrastructure helps solve flooding and prevent
water pollution by using soil, vegetation, and natural processes to restore
natural drainage patterns in our communities. Green infrastructure can
also clean our air, revitalize our neighborhoods, create jobs, save our
communities money, and provide other lasting community benefits.
The Challenge
Soil erosion and landslides are concerns whenever construction occurs on
or near slopes, but become even more of a concern when slopes are
saturated with water. The Pittsburgh area has a dramatic landscape
dominated by steep hills and valleys. Since many green infrastructure
practices enhance infiltration of water into the soil, care must be taken
when designing green infrastructure for the Pittsburgh area.
Fortunately, development is restricted on steep slopes, so this challenge is
not as daunting as the landscape might suggest. Most ordinances state
that a slope greater than 25 percent should be left undisturbed, while
roads are typically built with slopes of less than 5 percent. Many strategies
are available to manage stormwater at its source for slopes of up to 25
percent.
Opportunities
Green Infrastructure practices appropriate for steep slopes include slope
protection, tree planting, use of diversion berms, and use of check dams
within bioretention practices.
Protecting natural slopes reduces
erosion and enhances infiltration.
Planting trees and other vegetation
on a disturbed slope stabilizes soil and
absorbs water.
Diversion berms are constructed
across slopes to reduce erosion
caused by rapidly flowing water and
to promote plant growth.
Check dams can be incorporated into
bioretention practices on slopes to
encourage infiltration and reduce
erosion.
Slope Ranges in the
Pittsburgh Area
Source: Tetra Tech, 2013
! 0-5 percent
5-25 percent
25+ percent
Green Infrastructure
Practices that Work on
Steep Slopes
This diversion berm is constructed across a
steep slope (max. 25% slope) to slow
stormwater.
Source: Tetra Tech
The rock check dams placed along this grassy
swale help slow stormwater and prevent
erosion in the swale (max. 6% slope).
Source: Pennsylvania SW BMP Manual - BMP
6.4.8
Permeable Pavement
Aggregate Storage
Baffle
When permeable pavement is installed on a
slope (max. 5% slope), baffles can be
constructed beneath the pavement to increase
water storage and promote infiltration.
Source: Adapted from
http://perviouspavement.org/design/hydrologic
aldesign.html
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Case Studies
110th Street Cascade, built 2002, Seattle, WA
In Seattle, a series of cascading bioretention cells was installed on a sloped (6% grade),
residential road to reduce the flow rate and volume of stormwater and to help reduce
sediment and pollutant loads from a 2-acre drainage area. The design uses concrete
walls, vegetation, and rock to slow down and infiltrate the water.
Results
• Monitoring results showed that the system was able to completely absorb 186 (79
percent) of the 235 precipitation events recorded from 2004 to 2006.
• In very dry conditions, storms with rainfall depths of up to 1 inch were completely
absorbed by the system.
• Sediment, a pollutant harmful to aquatic life, was reduced by approximately 86
percent.
• Pollutant reductions occurred for sediment, lead and motor oil, nitrogen,
phosphorus, copper, and zinc.
Source: Horner, R. R. and Chapman, C. (September 2007). NW 110th Street Natural Drainage System
Performance Monitoring. Civil and Environmental Engineering, University of Washington.
Cascading bioretention cells in
Seattle help treat and infiltrate
stormwater from roads.
Source: Seattle Public Utilities;
www.seattle.gov
Permeable Pavement Road, built 2006,
Auckland, New Zealand
A 2,100 square foot permeable pavement test site was constructed
on an active roadway with a slope of 6-7.4% and underlying existing
clay soils. Flow monitoring was conducted to assess the
effectiveness of the site in reducing stormwater volume and peak
flow rate. The peak flow rate of a storm is the maximum measured
volume of water that moves past a point in a given amount of time.
£_ermeable Pavement Underdrain
rge Monitoring Point (Subsurface) > \
This monitoring site in Auckland, New Zealand tested
the effectiveness of permeable pavement on slopes.
Source: Passman and Blackbourn, 2010
Results
• Monitoring results showed that the stormwater volume and
peak flow rate passing through the permeable pavement was
reduced.
• The permeable pavement was able to slow the flow of stormwater so that it resembled the flow from a natural
area.
• The permeable pavement was able to effectively handle stormwater from frequent storms and large storms even
on steep slopes.
• Typical of sites in the Pittsburgh area, the Auckland project site was challenged with a moderate slope, soil allowing
little infiltration, and frequent rainfall.
Source: Passman, E. A., and Blackbourn, S. June 2010. Urban Runoff Mitigation by a Permeable Pavement System over Impermeable Soils. Journal
of Hydrologic Engineering, ASCE. 15:475-485.
A variety of green infrastructure designs are suitable for handling
stormwater on moderate to steep slopes including berms, swales,
permeable pavement, and cascading bioretention cells.
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Abundant and Frequent Rainfall
Fact Sheet Series Addressing Green Infrastructure
Design Challenges in the Pittsburgh Region
The roofs, roads, and parking lots in our urban areas prevent rainfall from
soaking into the ground, overwhelming sewers and leading to flooding and
polluted rivers. Green infrastructure helps solve flooding and prevent
water pollution by using soil, vegetation, and natural processes to restore
natural drainage patterns in our communities. Green infrastructure can
also clean our air, revitalize our neighborhoods, create jobs, save our
communities money, and provide other lasting community benefits.
The Challenge
The Pittsburgh area
receives 37 to 45 inches
of rainfall per year,
which is typical for the
region. With the area's
humid climate and
frequent rain events,
some practitioners may
view green
infrastructure as
inappropriate for the
Pittsburgh area.
Analyzing the area's
rainfall pattern,
however, shows that
green infrastructure
works very well with
Pittsburgh's climate. As shown in the figure above, the Pittsburgh area
receives most of its annual precipitation as small rain events of one inch or
less. Green infrastructure can effectively manage these small events.
Opportunities
Green Infrastructure practices such as rain gardens, permeable pavement,
and green roofs are all practices that can succeed in Pittsburgh's climate.
• Rain gardens capture stormwater draining from roofs. When the
garden is full of water, extra water is channeled downhill away from
the building.
• Permeable pavement is used for sidewalks, parking lots, and roads. It
allows water to drain through it to a stone storage reservoir and then
infiltrate into the soil. Underdrains laid in the storage reservoir help
the practice drain between rainfall events.
• Green roofs introduce vegetation and soil onto roofs to absorb and
filter rainfall. When the soil is saturated, the extra water overflows
through a roof drain to a vegetated area, such as a rain garden.
Southwest Pennsylvania Annual
Rainfall Grouped by Storm Depth
Source: Westmoreland Conservation
District www.wcdpa.com
Green Infrastructure
Practices that Work with
Frequent Rainfall
A storm inlet is used in this bioretention area to
drain overflowing stormwater.
Source: Pennsylvania Stormwater BMP Manual
A stone channel is used in this residential rain
garden to direct overflowing stormwater to the
street.
Source: Stewardship Partners/Flickr
When this bioretention planter box is full of
stormwater, the extra water "backs up" into the
street to drain into a storm inlet.
Source: ASIA HQs, Washington, DC
This underdrain pipe system will help to drain
the bioretention area above it.
Source: Brisbane City Hall, San Mateo County
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Case Studies
Michigan Avenue Bioretention Planter Boxes, built 2006, Lansing, MI
In 2006, bioretention planter boxes were installed along four
blocks of Michigan Avenue, a busy 5-lane street in Lansing, Ml.
The planters can treat the runoff from 1 to 4 inches of rain
falling on the adjacent street and sidewalk.
If the planter reaches its maximum capacity, the extra
stormwater "backs up" into the street and drains to a curb
storm inlet. Water held in the soil is used by the plants,
infiltrates to groundwater, or is released through an underdrain.
Results
• Flow meters were used to monitor the system, and model
results show that about 90% of the total annual stormwater
volume was treated by the planter box.
• While only 16% of the stormwater volume is kept within
the planters, the peak flow rate of the water released
through the underdrain is reduced by 87%.
Bioretention planter boxes in Lansing help treat stormwater
from roads and sidewalk.
Source: Christian and Novaes, 2011
Source: Christian, D. and Novaes, V. 2011. Michigan Avenue Bioretention: Monitoring the Results Three Years Later. MWEA 86 Annual
Conference.
Sterncrest Drive Bioswale and Rain Gardens, built 2007, Cuyahoga
County, OH
In 2007, the Chagrin River Watershed Partners with a grant
from the U.S. EPA replaced 1,400 feet of roadside ditch with
grassed bioswale and nine rain gardens to conduct a study. The
U. S. Geological Survey (USGS) then monitored the site from
2008-2010 to better define the effect of green infrastructure on
stormwater runoff. The bioswales and rain gardens were
designed to handle a 0.75-inch rainfall falling on the adjacent
roadway. Rainfall and runoff data were collected along with
overflow data to determine how well the system performed.
Results
• Numerous rainfall events greater than 0.75-inch were
absorbed by the bioswales and rain gardens.
• Over the three years of monitoring, the system only
overflowed 22 times.
• The bioswales and rain gardens performed better than
expected in that there were more rainfall events greater
than 0.75-inch that did not cause an overflow than events
that caused an overflow.
Roadside rain garden in Cuyahoga County is monitored for its
effectiveness in absorbing stormwater.
Source: USGS, 2011.
Source: Darner, R.A., and Dumouchelle, D. H. 2011. Hydraulic characteristics of low-impact development practices in northeastern Ohio, 2008-
2010: U.S. Geological Survey Scientific Investigations Report 2011-5165,19 p.
Green infrastructure practices can be designed to effectively manage the
frequent small rainfall events in the Pittsburgh area.
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Clay Soil
Fact Sheet Series Addressing Green Infrastructure
Design Challenges in the Pittsburgh Region
The roofs, roads, and parking lots in our urban areas prevent rainfall from
soaking into the ground, overwhelming sewers and leading to flooding and
polluted rivers. Green infrastructure helps solve flooding and prevent
water pollution by using soil, vegetation, and natural processes to restore
natural drainage patterns in our communities. Green infrastructure can
also clean our air, revitalize our neighborhoods, create jobs, save our
communities money, and provide many other lasting community benefits.
The Challenge
The Pittsburgh region's clay soil is sometimes perceived as a challenge to
green infrastructure practices. Clay soil is often thought to allow little to no
infiltration of water to the groundwater table.
In actuality, undisturbed clay soil can infiltrate water quite well. The real
challenge is when soil has been disturbed and compacted by construction.
Compacted soil often results in very little infiltration and ponding is often
observed.
While the design of green infrastructure practices for sites with clay soils
may require greater care, the right green infrastructure practices can work
well in Pittsburgh's clay soil.
Opportunities
Green Infrastructure practices such as rain gardens, permeable pavement,
and bioretention are all practices that are successful in clay soils.
• Rain Gardens capture Stormwater draining from roofs. Even in clay
soils, infiltration can be expected if the soil is protected from
compaction or restored through deep plowing.
• Permeable pavement is used for sidewalks, parking lots, and roads. It
allows water to drain through it to a stone storage layer. Underdrains
can be laid in the storage layer to help the practice drain in clay soils.
• Bioretention is similar to a rain garden but is typically more
engineered. In clay soil, an underdrain is generally installed to ensure
drainage.
J^
Sandy Fill —
I I
Drainage
Upturned Elbow
This diagram shows a bioretention system. Underdrains drain the system in clay soils.
Source: Brown, R., Hunt, W. and Kennedy, S. 2009. Urban Waterways: Designing
Bioretention with an Internal Water Storage Layer. NC Coop. Ext.
Green Infrastructure
Practices that Work with
Clay Soils
This rain garden collects roof water through a
downspout.
Source: Tetra Tech
Stormwater drains through this permeable
paver drive to a stone storage layer.
Source: Tetra Tech
This roadside bioretention collects and treats
roadway Stormwater.
Source: Tetra Tech
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Case Studies
Rain Gardens, built 2004, Madison,
WI
In 2003, the US Geological Survey installed four rain
gardens next to municipal buildings in Madison, Wisconsin
to test the effect of soil type and plant type on the rain
garden's ability to absorb stormwater. Two rain gardens
were installed in sandy soils and two rain gardens were
installed in clay soils. For each soil type, one rain garden
was planted with turf, and the other with native prairie
grasses. The rain gardens were 100 to 400 square feet in
area and 0.5 feet in depth, and were not equipped with
underdrains. The USGS monitored the rain gardens for 4
years, observing inflows, outflows, rainfall amounts, and
evapotranspiration amounts.
Roof stormwater drains to these monitored rain gardens in
Madison, Wisconsin.
Source: Selbig and Balster, 2010.
Results
• The rain gardens were able to infiltrate nearly 100% of the stormwater they received over four years of operation
in both clay soil and sandy soil!
• The rain garden planted with the prairie species infiltrated stormwater better than the rain garden planted with
turf grass.
• Roots in the rain garden planted with native prairie grass species extended 4.7 feet deep compared with 0.46 feet
in the rain garden planted with turf grass.
Source: Selbig, W.R., and Balster, Nicholas. 2010. Evaluation of turf-grass and prairie-vegetated rain gardens in a clay and sand soil, Madison,
Wisconsin, water years 2004-08: U.S. Geological Survey Scientific Investigations
Roadside Bioretention, built 2009, Toledo,
OH
Nearly 800 feet of residential roadside bioretention and permeable
sidewalk were constructed in Toledo, Ohio to help reduce the
occurrence of sewer overflows during heavy rainfall events. The project
was constructed in clay soils and included underdrains to help drain the
system if needed. Underground water storage was provided beneath
the permeable sidewalk. Flow monitors were installed before and after
construction to assess the effectiveness of the system at absorbing
stormwater.
Results
• Long-term modeling shows an annual average stormwater volume
reduction of about 64 percent.
• Peak flow rates are reduced by 60 percent to 70 percent. The peak
flow rate of a storm is the maximum measured volume of water that
moves past a point in a given amount of time.
• Reducing peak flow can help to reduce flooding.
Source: Tetra Tech. 2009. City of Toledo, OH, Maywood Avenue Storm Water Volume
Reduction Project Construction Plan Set.
v
Roadway and sidewalk stormwater drains to this
roadside bioretention system on Maywood
Avenue in Toledo, Ohio.
Source: Tetra Tech, 2009.
Studies have shown that green infrastructure can be very effective when
installed on clay soils.
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