November 2012
Green Infrastructure
Page 1
United States	Office of Research	National Health & Environmental
Environmental	and Development
Protection Agency	Washington, DC 20460
Environmental	and Development	Effects Research Laboratory
Western Ecology Division
The Problem with Pavement
Large paved surfaces keep rain from infiltrating the soil
and recharging groundwater supplies. Impervious
streets, parking lots, sidewalks, and rooftops transport
stormwater in volumes up to 16 times higher than natural
areas\ This stormwater runoff can deliver pollutants from
motor oil, lawn chemicals, sediments, and pet waste to
streams, rivers, and lakes untreated. Higher flows can
also cause erosion and flooding that can damage prop-
erty, infrastructure, and wildlife habitat.
In 2008, the EPA reported that the cost of wastewater
and conventional infrastructure in the United States to
If untreated, stormwater from urban areas delivers pol-
lutants to our streams, lakes, and rivers. High stormwa-
ter flows can also trigger gray infrastructure overflows
sending untreated sewage into our water supply sys-
tem. Picture copyright ©2008 WakeUP Wake County, Inc.
Left: an example of Downspout Disconnection rerout-
ing drainage pipes to permeable areas instead of the
sewer. Right: an example of a Green Roof, covered
with growing media and vegetation that enhances
Stormwater retention. Taken from: http://water.epa.gov/
infrastructure/greeninfrastructure/
be $298.1 billion2. Conventional stormwater infrastruc-
ture, or gray infrastructure, is largely designed to move
stormwater away from urban areas through pipes and
conduit. Alternatively, Green infrastructure uses natural
processes to reduce and treat stormwater in place by
soaking up and storing water. These systems provide
many environmental, social, and economic benefits that
promote urban livability and add to the bottom line.
What is Green Infrastructure?
Green infrastructure refers to systems that use vegeta-
tion, soils, and natural processes to manage stormwater
and generate healthier urban environments. Green infra-
structure based stormwater management systems mimic
natural hydrology to take advantage of interception,
evapotranspiration, and infiltration of stormwater runoff
at its source thus disconnecting impervious surfaces
from gray infrastructure. This provides flood protection,
cleaner air, and cleaner water.
Left:
Example of a
Bioswale that slows
runoff and filters
stormwater flows.
Taken from: http://
water.epa.gov/
infrastructure/
i
"...the City of Philadelphia found that
increased tree canopy would reduce
ozone and particulate pollution levels
enough to significantly reduce mortality,
hospital admissions, and work loss days."
http://water.epa.gov/infrastructure/greeninfrastructure/
gi_why.cfm#AirQuality

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November 2012
Green Infrastructure
Page 2
Green Roofs - roofs covered with growing media
and vegetation. They are cost effective in dense ur-
ban areas with high land values or where stormwa-
ter management costs are high.
Urban Tree Canopy- Trees intercept rain in their
leaves and branches thereby reducing and slowing
stormwater runoff.
Land Conservation - Open spaces and natural ar-
eas within and adjacent to cities can protect water
quality, mitigate flooding impacts, and provide rec-
reation.
Green Infrastructure Practices
Example of a Rain Garden that collects and absorbs runoff.
Taken from: http://water. epa.gov/infrastructure/greeninfrastructure/
United States Water Facts3
About 410 billion-gallons/day were withdrawn for
human use in 2005 (49% for thermoelectric power,
31% for irrigation, and 11% for public supply).
•	80% of this water was withdrawn from surface water.
•	An estimated 258 million people (86% of population)
relied on public water supply.
•	Two-thirds of public water supply was taken from sur-
face sources (lakes and streams) and the rest from
groundwater.
•	67% of fresh groundwater was used for irrigation.
Downspout Disconnection - the rerouting of rooftop
drainage pipes to permeable areas, rain barrels, or
cisterns. This allows stormwater to infiltrate into the
soil and/or stores stormwater for later use.
Rainwater Harvesting - systems that collect and
store rainfall for later use. These systems provide a
renewable water supply and can slow and reduce
runoff. Such systems can reduce demands on in-
creasingly limited water supplies in arid regions.
Rain Gardens - Also known as bioretention or bio-
infiltration cells, these are shallow, vegetated ba-
sins that collect and absorb runoff by infiltration and
evapotranspiration. They can be installed in nearly
any unpaved space.
Planter Boxes - structures with vertical walls and
open or closed bottoms filled with gravel, soil and
vegetation that collect and absorb runoff. Ideal for
space-limited sites in dense urban areas.
Bioswales - broad and shallow vegetated,
mulched, orxeriscaped channels that provide
stormwater treatment and retention. They slow wa-
ter flows and allow for infiltration, thereby filtering
stormwater flows. As linear features they are ap-
propriate along streets and parking lots.
Permeable Pavements - porous paved surfaces
that allow rain to infiltrate into soils. Permeable
pavements can be constructed from various materi-
als such as pervious concrete, porous asphalt, and
permeable interlocking pavers.
Green Streets and Alleys - integration of green in-
frastructure elements such as bioswales, planter
boxes, and trees into street and alley design.
Green streets and alleys are designed to store, in-
filtrate, and evaporate and transpire stormwater
while adding aesthetics of landscapes.
Green Parking - integration of green infrastructure
elements such as permeable pavements, and rain
gardens into parking lot design. Such structures
manage stormwater on site, mitigate urban heat
islands, and create a more pedestrian-accessible
environment.

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November 2012
Green Infrastructure
Page 3
Some Benefits of Green
Infrastructure
Water Quality: by soaking up and storing water in
place, green infrastructure reduces stormwater dis-
charges. Lower stormwater volumes mean reduced
gray infrastructure sewage overflows and lower pol-
lutant loads. Infiltration and storage of stormwater
can also help remove pollutants.
Flooding: Reducing stormwater discharges and
peak stream flows can mitigate flood risk.
Water supply: Rainwater harvesting and practices
that increase infiltration can provide a renewable,
water supply alternative. Harvested rainwater can be
used for outdoor irrigation and certain indoor uses
thereby significantly reducing municipal water use.
Water infiltration practices also recharge groundwa-
ter reservoirs.
Private and Public Cost Savings: Incorporation of
green infrastructure into stormwater management
systems can lower capital costs. Lower costs for site
grading, paving, and landscaping, and smaller or
eliminated piping and detention facilities provide
savings for developers. In cities with combined
waste and stormwater sewer systems, green infra-
structure control measures can cost less than con-
ventional controls, and their implementation can re-
duce stormwater infrastructure costs.
Table 1. Table of removal rate of pollutants using
Bioretention (Rain Garden)4.
Pollutant
Removal Rate
Total Phosphorus
70%-83%
Metals (Cu, Zn, Pb)
93%-98%
Total Nitrogen
68%-80%
Total Suspended Solids
90%
Organic Pollutants
90%
Bacteria
90%
Table 2. Adapted Summary of Cost Comparisons Between
Conventional and Green Infrastructure Approaches5
Project
Conven-
tional
Costs
Green
Infrastucture
Costs
Percent
Difference
Gap Creek
$4,620,600
$3,942,100
+15%
Garden
Valley
$324,400
$260,700
+20%
Kensington
Estates
$765,700
$1,502,900
-96%
Laurel
Springs
$1,654,000
$1,149,600
+30%
Somerset
$2,456,800
$1,671,500
+32%
Economic Benefits of Green
Infrastructure6
¦	Reduced flooding - a marginal reduction in
flooding can increase property values in flood-
plains by up to 5%.
¦	Improved water quality - can increase market
value by 15% for properties near lakes, rivers,
streams, or coastal areas.
¦	Reduced filtration costs - along the Anacostia
River in Washington, DC, bioretention instead
of piped stormwater and sand filters saved
$250,000.
¦	Infrastructure cost savings - replacing curb,
gutter, and storm sewers with roadside
bioswales saved one developer $70,000 per
mile.
¦	Increased property values - lots in green in-
frastructure neighborhoods sold for $3000
more than lots using conventional stormwater
infrastructure.
Example:
The Gap Creek subdivision in Sherwood, AR was
redesigned to include green infrastructure ele-
ments. Open space was increased from 1.5 acres
to 23.5 acres. Lots sold for $3000 more and cost
$4,800 less to develop, resulting in $2.2 million
additional profit for developer.

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November 2012
Green Infrastructure
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Table 3.Illustrative summary of the combination of potential benefits associated with five green infrastructure practices7. Used
by permission from "The Value of Green Infrastructure: a Guide to Recognizing Its Economic, Environmental and Social Benefits" CNT © 2010.
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Table 4. Table of Select Mid-range Costs in 2006 dollars for Select Gray and Green Infrastructure Components8.
Component
Construction Cost
Maintenance Cost
Component Lifespan
Curbs arid Gutters
$17.25/ft
SO. 15/ft
50 years
Parking Lot
$5.51/sq ft
$0.15/'sq ft
20 years
Standard Roof
$7.50/sq ft
$0.05/sq ft
23 years
Conventional Stormwater Storage
$11,55/cu ft
$0.03/cu ft
25 years
Bioswales (parking lot and roadside)
$15.00/sq ft
$0.12/sq ft
30 years
Rain Garden
$7.00/sq ft
$0.34/sq ft
30 years
Trees
$275.00/each
$20.00/each
32 years
Green Roof
$15.75/sq ft
$0.02/sq ft
40 years
Table 5. Table of Economic Values of Select Green Infrastructure.9
Green infrastructure Benefit
Economic Value of Benefit
Reduced Air Pollutants
$0.18/tree
C02 Sequestration
$0.12/tree/yr
Tree Value
$275.00/tree
Groundwater Recharge
$86.42/acre ft infiltrated
Reduced Runoff Treatment
$29.94/acre ft of runoff reduced
Reduced Energy Use
$0.18/sq ft green roof/year
Example of an Urban Tree Canopy. Taken from:
http://water.epa.gov/irifrastructure/greeninfrastructure/

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November 2012
Green Infrastructure
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REFERENCES AND RESOURCES
Green infrastructure information was adapted from:
"This website contains more information and resources.
1Schueler, T. 1995. The importance of imperviousness.
Watershed Protection Techniques 1 (3): 100-111.
2USEPA. 2008. Clean Watersheds Needs Survey 2008 -
Report to Congress. EPA-832-R-10-002W
3USGS. 2005. Estimated Use of Water in the United States
in 2005. Circular 1344:|e
4USEPA. 1990. Storm water Technology Fact Sheet Biore-
tention. EPA 832-F-99-012: S
5USEPA. 2007. Reducing Stormwater Costs through Low
Impact Development (LID) Strategies and Practices, EPA
841-F-07-006: fl
6NC State University, A&T State University Cooperative
Extension. (Viewed 2012, June 20). Low Impact Develop-
ment-an economic fact sheet: "
7 Center for Neighborhood Technology, www.cnt.org 2010.
The Value of Green Infrastructure: a guide to recognizing its
economic, environmental and social benefits, Chicago, IL:
8CNT.org. (Viewed 2012, June 20). Green Values National
Stormwater Management Calculator-cost sheet:
9CNT.org. (Viewed 2012, June 20). Green Values National
Stormwater Management Calculator-benefits sheet:
10 Pacific Institute. 2011. The Human Costs of Nitrate-
contaminated Drinking Water in the San Joaquin Valley:
Nitrogen Pollution
Issue: Run-off from impervious surfaces, leakage
from sewage infrastructure, septic systems, agricultural
ditches and tile drains creates excess nitrogen (N) in
groundwater, rivers, lakes, and coastal areas. Excess
N is detrimental for human and ecosystem health
causing blue baby syndrome, toxic algal blooms and
fish die-off via eutrophication and hypoxia.
FIVE YEAR CLEAN UP COSTS OF NITRATE CON-
TAMINATED DRINKING WATER IN SAN JOAQUIN
VALLEY, CA = $21 MILLION10
Opportunity: Many green infrastructure elements can
be optimized for N removal by sustaining conditions
necessary that promote biological N transformation
(e.g. denitrification).
COMMON KEY DESIGN PARAMETERS THAT
IMPROVE NITROGEN REMOVAL
Increasing groundwater residence time
Maintenance of riparian buffers and vegetation
Use of design elements that sustain anaerobic
soil conditions
Incorporation of organic matter into soils
Denitrification - microbial transformation of
mobile and available form of N (nitrate) to non-
reactive gaseous form (atmospheric N2gas).
NITROGEN POLLUTION REFERENCES
Passeport, E., P. Vidon, K. Forshay, L. Harris, S.S. Kaushal,
D.Q. Kellogg, J. Lazar, P.M. Mayer, E. Stander. 2013. Eco-
logical engineering practices for the reduction of excess N in
human influenced landscapes: A guide for watershed manag-
ers. Environmental Management 51:392-413
Kaushal, S., P.M. Groffman, P.M. Mayer, E. Striz, and A.
Gold. 2008. Effects of stream restoration on denitrification in
an urbanizing watershed. Ecological Applications 18:789-804
Mayer, P.M., S.K Reynolds, M.D. McCutchen, and T.J. Can-
field. 2007. Meta-analysis of nitrogen removal in riparian
buffers. Journal of Environmental Quality 36:1172-1180.
Contact for More Information:
Shannon Schechter, NRC, US EPA, GWERD, Ada, OK: 580-436-8987, schechter.shannon@epa.gov
Paul Mayer, US EPA, Western Ecology Division, Corvallis, OR: 541-754-4673, maver.paul@epa.gov

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