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ROOFTOPS TO RIVERS
Green Strategies for Controlling Stormwaterand Combined Sewer
Overflows
Project Design and DirectionNancy Stoner, Natural Resources
Defense Council
AuthorsChristopher Kloss, Low Impact Development CenterCrystal
Calarusse, University of Maryland School of Public Policy
Natural Resources Defense CouncilJune 2006
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ABOUT NRDCThe Natural Resources Defense Council is a national
nonprofit environmental organization with more than 1.2million
members and online activists. Since 1970, our lawyers, scientists,
and other environmental specialists haveworked to protect the
world’s natural resources, public health, and the environment. NRDC
has offices in NewYorkCity, Washington, D.C., Los Angeles, San
Francisco, and Beijing. Visit us at www.nrdc.org.
ACKNOWLEDGMENTSNRDC wishes to acknowledge the support of The
McKnight Foundation; The Charles Stewart Mott Foundation;The Joyce
Foundation; The Geraldine R. Dodge Foundation, Inc.; The Marpat
Foundation; The Morris and GwendolynCafritz Foundation; Prince
Charitable Trusts; The Mary Jean Smeal Family Fund; The Brico Fund,
Inc.; The SummitFund of Washington; The Naomi and Nehemiah Cohen
Foundation; and The Jelks Family Foundation, Inc.
NRDC Director of Communications: Phil GutisNRDC Publications
Manager: Alexandra KennaughNRDC Publications Editor: Lisa
GoffrediProduction: Bonnie GreenfieldCover Photo: ©2006 Corbis.
View of Arlington, Virginia, seen from across the Potomac River in
Washington, D.C.
Copyright 2006 by the Natural Resources Defense Council.
For additional copies of this report, send $5.00 plus $3.95
shipping and handling to NRDC Reports Department, 40 West 20th
Street, New York, NY 10011. Californiaresidents must add 7.5% sales
tax. Please make checks payable to NRDC in U.S. dollars.
This report is printed on paper that is 100 percent
post-consumer recycled fiber, processed chlorine free.
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Peer Reviewers iv
Executive Summary v
Chapter 1: Introduction 1
Chapter 2: The Growing Problem of Urban Stormwater 2
Chapter 3: Controlling Stormwater in Urban Environments 6
Chapter 4: Economic Benefits of Green Solutions 11
Chapter 5: Policy Recommendations for Local Decision Makers
13
Chapter 6: Conclusion 16
Chapter 7: Case Studies 17Chicago, Illinois 17Milwaukee,
Wisconsin 20Pittsburgh, Pennsylvania 22Portland, Oregon 24Rouge
River Watershed, Michigan 27Seattle, Washington 29Toronto, Ontario,
Canada 31Vancouver, B.C., Canada 33Washington, D.C. 37
Appendix: Additional Online Resources 40
Endnotes 43
iii
CONTENTS
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Katherine BaerAmerican Rivers
Tom ChapmanMilwaukee Metropolitan Sewerage District
Mike CoxSeattle Public Utilities
Robert GooU.S. EPA
Bill GraffinMilwaukee Metropolitan Sewerage District
Jose GutierrezCity of Los Angeles Environmental
AffairsDepartment
Emily HauthCity of Portland Bureau of Environmental Services
Jonathan HelmusCity of Vancouver
iv
PEER REVIEWERS
Darla InglisSeattle Public Utilities
Otto KauffmannCity of Vancouver
Jim MiddaughCity of Portland Bureau of Environmental
Services
Steve ModdemeyerSeattle Public Utilities
Laurel O’SullivanConsultant to Natural Resources Defense
Council
Brad SewellNatural Resources Defense Council
Mike ShribergPublic Interest Research Group in Michigan
Heather WhitlowThe Casey Trees Endowment Fund
David YurkovichCity of Vancouver
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As an environmental strategy, green infrastructureaddresses the
root cause of stormwater andcombined sewer overflow (CSO)
pollution: the con-version of rain and snow into runoff. This
pollutionis responsible for health threats, beach closings,swimming
and fishing advisories, and habitatdegradation. Water quality
standards are unlikelyto be met without effectively managing
stormwaterand CSO discharges. Green
infrastructure—trees,vegetation, wetlands, and open space preserved
orcreated in developed and urban areas—is a strategyfor stopping
this water pollution at its source.
The urban landscape, with its large areas ofimpermeable roadways
and buildings—known asimpervious surfaces—has significantly altered
themovement of water through the environment. Over100 million acres
of land have been developed inthe United States, and with
development and sprawlincreasing at a rate faster than population
growth,urbanization’s negative impact on water quality isa problem
that won’t be going away. To counteractthe effects of urbanization,
green infrastructure isbeginning to be used to intercept
precipitation andallow it to infiltrate rather than being collected
onand conveyed from impervious surfaces.
EXECUTIVE SUMMARY
Each year, the rain and snow that falls on urbanareas in the
United States results in billions of gallonsof stormwater runoff
and CSOs. Reducing runoff withgreen infrastructure decreases the
amount of pollutionintroduced into waterways and relieves the
strain onstormwater and wastewater infrastructure. Efforts inmany
cities have shown that green infrastructure canbe used to reduce
the amount of stormwater dischargedor entering combined sewer
systems and that it canbe cost-competitive with conventional
stormwaterand CSO controls. Additional environmental
benefitsinclude improved air quality, mitigation of the urbanheat
island effect, and better urban aesthetics.
Green infrastructure is also unique because it offersan
alternative land development approach. New devel-opments that use
green infrastructure often cost lessto build because of decreased
site development andconventional infrastructure costs, and such
develop-ments are often more attractive to buyers because
ofenvironmental amenities. The flexible and decentral-ized
qualities of green infrastructure also allow it tobe retrofitted
into developed areas to provide storm-water control on a
site-specific basis. Green infra-structure can be integrated into
redevelopment effortsranging from a single lot to an entire
citywide plan.
Case Study Program Elements and Green Infrastructure
Techniques
Wetlands/Established Rain Gardens/ Downspout Riparian
Used for Municipal Vegetated Disconnection/ Protection/Direct
CSO Programs & Swales & Permeable Rainwater Urban
City Control Public Funding Green Roofs Landscape Pavement
Collection Forests
Chicago � � � � � �
Milwaukee � � � � �
Pittsburgh � � � � �
Portland � � � � �
Rouge River Watershed � � � �
Seattle � � � � �
Toronto � � � �
Vancouver � � � � �
Washington � � �
P R O G R A M E L E M E N T S T Y P E O F G R E E N I N F R A S
T R U C T U R E U S E D
v
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Natural Resources Defense Council Rooftops to Rivers
Nonetheless, wider adoption of green infra-structure still faces
obstacles. Among these is theeconomic investment that is required
across thecountry for adequate stormwater and CSO control.Although
green infrastructure is in many casesless costly than traditional
methods of stormwaterand sewer overflow control, some
municipalitiespersist in investing only in existing
conventionalcontrols rather than trying an alternative
approach.Local decision makers and organizations musttake the lead
in promoting a cleaner, moreenvironmentally attractive method of
reducingthe water pollution that reaches their communities.NRDC
recommends a number of policy stepslocal decision makers can take
to promote the useof green infrastructure:
1. Develop with green infrastructure and pollution
management in mind. Build green space into
new development plans and preserve existingvegetation.
2. Incorporate green infrastructure into long-term
control plans for managing combined sewer overflows.
Green techniques can be incorporated into plans
forinfrastructure repairs and upgrades.
3. Revise state and local stormwater regulations to
encourage green design. A policy emphasis should beplaced on
reducing impervious surfaces, preservingvegetation, and providing
water quality improvements.
The case studies that begin on page 17 offernine examples of
successful communities thathave reaped environmental, aesthetic,
and eco-nomic benefits from a number of green infrastruc-ture
initiatives.
The table on page v provides a summaryof information contained
within the case studies.
The aerial photograph at left of Washington, DC, shows the
amount of green space and vegetation present in 2002. The photo
atright shows how this same area would look in 2025 after a
proposed 20-year program to install green roofs on 20% of city
buildingsover 10,000 square feet. PHOTOS COURTESY OF THE CASEY
TREES ENDOWMENT FUND
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Water pollution problems in the United Stateshave evolved since
the days when Ohio’sCuyahoga River was on fire. Increasingly, water
pol-lution from discrete sources such as factory pipes isbeing
overshadowed by overland flows from streets,rooftops, and parking
lots, which engorge down-stream waterways every time it rains. This
storm-water has nowhere to go because the naturalvegetation and
soils that could absorb it have beenpaved over. Instead, it becomes
a high-speed, high-velocity conduit for pollution into rivers,
lakes, andcoastal waters.
Most U.S. cities have separate stormwater sewersystems through
which contaminated stormwaterflows directly into waterways through
undergroundpipes, causing streambank scouring and erosion
anddumping pet waste, road runoff, pesticides, fertilizer,and other
pollutants directly into waterways. Inolder cities, particularly in
the Northeast and GreatLakes regions, stormwater flows into the
same pipesas sewage and causes these combined pipes to
over-flow—dumping untreated human, commercial, andindustrial waste
into waterways. Stormwater pollu-tion has been problematic to some
extent for as longas there have been cities, but the volume of
storm-water continues to grow as development replacesporous
surfaces with impervious blacktop, rooftop,and concrete.
Contaminated stormwater and raw sewagedischarges from combined
sewer overflows (CSOs)are required to be controlled under the Clean
WaterAct, but progress is slow because the problems arelarge and
multi-faceted and because the solutionsare often expensive. A
substantial influx of addi-tional resources is needed at the
federal, state, and
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CHAPTER 1
local levels, but fresh thinking is needed also. SomeU.S. cities
are already taking steps to successfullybuild green infrastructure
into their communities.
Emerging green infrastructure techniquespresent a new
pollution-control philosophy basedon the known benefits of natural
systems thatprovide multimedia pollution reduction and usesoil and
vegetation to trap, filter, and infiltratestormwater. The cities
already using green infra-structure are finding that it is a viable
alternativeto conventional stormwater management. Althoughused
widely overseas, particularly in Germanyand Japan, the use of green
infrastructure in theUnited States is still in its infancy;
however, dataindicate that it can effectively reduce
stormwaterrunoff and remove stormwater pollutants, andcities that
have implemented green design arealready reaping the benefits (see
the case studieson page 17).
INTRODUCTION
The green roof at Ford Motor Company’s Premier AutomotiveNorth
American Headquarters in Irvine, CA, was designed tovisually mimic
the natural landscape. PHOTO COURTESY OF ROOFSCAPES, INC.
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Development as we have come to know it in theUnited States—large
metropolitan centers sur-rounded by sprawling suburban regions—has
con-tributed greatly to the pollution of the nation’s waters.As
previously undeveloped land is paved over andbuilt upon, the amount
of stormwater running off roofs,streets, and other impervious
surfaces into nearbywaterways increases. The increased volume of
storm-water runoff and the pollutants carried within itcontinue to
degrade the quality of local and regionalwater bodies. As
development continues, nature’sability to maintain a natural water
balance is lost toa changing landscape and new impervious
surfaces.
The trees, vegetation, and open space typicalof undeveloped land
capture rain and snowmelt,allowing it to largely infiltrate where
it falls. Undernatural conditions, the amount of rain that
isconverted to runoff is less than 10% of the rainfallvolume.1,2
Replacing natural vegetation and
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CHAPTER 2
landscape with impervious surfaces has significantenvironmental
impacts. The level of imperviousnessin a watershed has been shown
to be directly relatedto the health of its rivers, lakes, and
estuaries.Research indicates that water quality in receivingwater
bodies is degraded when watershed impervi-ousness levels are at or
above 10% and that aquaticspecies can be harmed at even lower
levels.3
Both the National Oceanic and AtmosphericAdministration (NOAA)
and Pennsylvania StateUniversity estimate that there are 25 million
acres ofimpervious surfaces in the continental United States.4
This quantity represents nearly one-quarter of themore than 107
million acres—almost 8% of non-federal land in the contiguous
United States—thathad been developed by 2002.5 In urban areas, it
is notuncommon for impervious surfaces to account for45% or more of
the land cover.
This combination of developed land and impervi-ous surfaces
presents the primary challenge of storm-water mitigation. Existing
stormwater and wastewaterinfrastructure is unable to manage
stormwater ina manner adequate to protect and improve waterquality.
Standard infrastructure and controls fail toreduce the amount of
stormwater runoff from urbanenvironments or effectively remove
pollutants.
THE DEFICIENCIES OF CURRENT URBANSTORMWATER
INFRASTRUCTUREStormwater management in urban areas
primarilyconsists of efficiently collecting and
conveyingstormwater. Two systems are currently used: separate
THE GROWING PROBLEMOF URBAN STORMWATER
TABLE 1: Effects of Imperviousness on Local WaterBodiesa,b,c
WatershedImpervious Level Effect
10% • Degraded water quality
25% • Inadequate fish and insect habitat• Shoreline and stream
channel erosion
35%–50% • Runoff equals 30% of rainfall volume
>75% • Runoff equals 55% of rainfall volume
a Environmental Science and Technology, Is Smart Growth Better
for WaterQuality?, August 25, 2004,
http://pubs.acs.org/subscribe/journals/estjag-w/2004/policy/jp_smartgrowth.html
(accessed December 6, 2004).
b U.S. EPA, Protecting Water Quality from Urban Runoff, Nonpoint
SourceControl Branch, EPA 841-F-03-003, February 2003.
c Prince George’s County, Maryland Department of
EnvironmentalResources, Low-Impact Development Design Strategies,
January 2000.
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stormwater sewer systems and combined sewersystems. Separate
stormwater sewer systems collectonly stormwater and transmit it
with little or no treat-ment to a receiving stream, where
stormwater andits pollutants are released into the water.
Combinedsewer systems collect stormwater in the same setof pipes
that are used to collect sewage, sending themixture to a municipal
wastewater treatment plant.
Separate Stormwater Sewer SystemsThe large quantities of
stormwater that wash acrossurban surfaces and discharge from
separate storm-water sewer systems contain a mix of
pollutants,shown in Table 2, deposited from a number ofsources.6,7
Stormwater pollution from separatesystems affects all types of
water bodies in thecountry and continues to pose a largely
unaddressedthreat. In 2002, 21% of all swimming beach advisoriesand
closings were attributed to stormwater runoff.8
Table 3 shows the percentage of assessed (monitored)waters in
the United States for which stormwater hasbeen identified as a
significant source of pollution.9
Combined Sewer SystemsWhile pollution from separate sewer
systems is aproblem affecting a large majority of the country,
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Natural Resources Defense Council Rooftops to Rivers
pollution from combined sewer systems tends to bea more regional
problem concentrated in the olderurban sections of the Northeast,
the Great Lakes
TABLE 2: Urban Stormwater Pollutants
Pollutant Source
Bacteria Pet waste, wastewater collection systems
Metals Automobiles, roof shingles
Nutrients Lawns, gardens, atmospheric deposition
Oil and grease Automobiles
Oxygen-depleting Organic matter, trashsubstances
Pesticides Lawns, gardens
Sediment Construction sites, roadways
Toxic chemicals Automobiles, industrial facilities
Trash and debris Multiple sources
TABLE 3: Urban Stormwater’s Impact on Water Quality
Water Body Type Stormwater’s Rank % of Impairedas Pollution
Source Waters Affected
Ocean shoreline 1st 55% (miles)
Estuaries 2nd 32% (sq. miles)
Great Lakes 2nd 4% (miles)shoreline
Lakes 3rd 18% (acres)
Rivers 4th 13% (miles)
Bioswales on Portland’s Division Streetinfiltrate and treat
stormwater runoff.PHOTO COURTESY OF THE PORTLAND BUREAU OF
ENVIRONMENTALSERVICES
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region, and the Pacific Northwest. Combined sewers,installed
before the mid-twentieth century and priorto the use of municipal
wastewater treatment, arepresent in 746 municipalities in 31 states
and theDistrict of Columbia.10 They were originally used asa
cost-effective method of transporting sewage andstormwater away
from cities and delivering them toreceiving streams. As municipal
wastewater treat-ment plants were installed to treat sewage and
protectwater quality, the limited capacity of combined sewersduring
wet weather events became apparent.11
During dry periods or small wet weather events,combined sewer
systems carry untreated sewageand stormwater to a municipal
wastewater treatmentplant where the combination is treated prior to
beingdischarged. Larger wet weather events overwhelm acombined
sewer system by introducing more storm-water than the collection
system or wastewatertreatment plant is able to handle. In these
situations,rather than backing up sewage and stormwater
intobasements and onto streets, the system is designed todischarge
untreated sewage and stormwater directlyto nearby water bodies
through a system of com-bined sewer overflows (CSOs). In certain
instances,despite the presence of sewer overflow points, base-ment
and street overflows still occur. Even smallamounts of rainfall can
trigger a CSO event; Wash-ington D.C.’s combined sewer system can
overflowwith as little as 0.2 inch of rainfall.12
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Natural Resources Defense Council Rooftops to Rivers
Because CSOs discharge a mix of stormwater andsewage, they are a
significant environmental andhealth concern. CSOs contain both
expected storm-water pollutants and pollutants typical of
untreatedsewage, like bacteria, viruses, nutrients, and
oxygen-depleting substances. CSOs pose a direct healththreat in the
areas surrounding the CSO dischargelocation because of the
potential exposure to bacteriaand viruses. Estimates indicate that
CSO dischargesare typically composed of 15–20% sewage and80–85%
stormwater.13,14 An estimated 850 billiongallons of untreated
sewage and stormwater aredischarged nationally each year as
combined seweroverflows.15 Table 4 shows the concentration
ofpollutants in CSO discharges.
POPULATION GROWTH AND NEW DEVELOPMENTCREATE MORE IMPERVIOUS
SURFACESCurrent levels of development and imperviousnessare a
major, and largely unabated, source of waterpollution. Projections
of population growth and newdevelopment indicate that this problem
will get worseover time and that mitigation efforts will become
morecostly and difficult. Although the nation has
collectivelyfailed to adequately address the current levels
ofstormwater runoff and pollution, we have also failedto implement
emerging strategies that would minimizefurther pollution increases.
Absent the use of state-of-
TABLE 4: Pollutants in CSO Dischargesa
Pollutant Median CSO Concentration Treated Wastewater
Concentration
Pathogenic bacteria, viruses, parasites• Fecal coliform
(indicator bacteria) 215,000 colonies/100 mL < 200
colonies/100mL
Oxygen depleting substances (BOD5) 43 mg/L 30 mg/L
Suspended solids 127 mg/L 30 mg/L
Toxics• Cadmium 2 µg/L 0.04 µg/L• Copper 40 µg/L 5.2 µg/L• Lead
48 µg/L 0.6 µg/L• Zinc 156 µg/L 51.9 µg/L
Nutrients• Total Phosphorus 0.7 mg/L 1.7 mg/L• Total Kjeldahl
Nitrogen 3.6 mg/L 4 mg/L
Trash and debris Varies None
a U.S. EPA, Report to Congress: Impacts and Control of CSOs and
SSOs, Office of Water, EPA-833-R-04-001, August 2004.
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the-art stormwater controls, each new acre of landdeveloped and
each new parcel of impervious surfacewill introduce new pollution
into our waterways.
Recent studies also indicate that stormwaterpollution may soon
start to increase at a higherrate than in the past. Over the past
two decades,the rate of land development has been two timesgreater
than the rate of population growth. Between1982 and 1997, while the
U.S. population grew 15%,the amount of developed land in the
continentalUnited States grew 34%, an increase of 25
millionacres.16,17 The 25 million acres developed duringthis
15-year period represent nearly 25% of the totalamount of developed
land in the contiguous states.This rapid development pattern is
alarming not onlybecause of the conversion of a large and
growingpercentage of the remaining undeveloped land, butalso
because of the increase in stormwater runoff thataccompanies
development.
If the relationship between land development andpopulation
growth continues, a significant amount ofland will be developed in
the coming decades. Theanticipated 22% growth in U.S. population
from 2000to 2025 will add an additional 68 million acres
ofdevelopment.18 By 2030, half of the total square
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Natural Resources Defense Council Rooftops to Rivers
footage of buildings—200 billion square feet—willhave been built
after the year 2000.19
Much of this population growth and new devel-opment will occur
in coastal regions, a particularconcern because urban stormwater
runoff is alreadythe largest source of ocean shoreline water
pollution.Although coastal counties comprise only 17% ofthe total
acreage of the contiguous United Statesthey are home to more than
50% of the U.S. popu-lation. Because of high population
concentrationson limited land areas, coastal counties contain
ahigher percentage of development than interiorcounties. In 1997,
27 million acres of coastal countieshad been developed, accounting
for nearly 14% ofthe total land area. By contrast, 71 million
acres,about 4% of the total land area of interior counties,had been
developed.20 Based on these trends,increased population and
development in thesecoastal environments is likely to not only lead
togreater amounts of impervious surfaces in coastalwatersheds, but
also higher percentages of impervi-ousness. Conventional methods of
stormwatercontrol will not be able to adequately manage thehigher
amount of stormwater pollution implied bythis increased
imperviousness.
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The foremost challenge of reducing stormwaterpollution and CSO
discharges is finding aneffective method of reducing the amount of
storm-water created in urban environments. Methodscurrently used to
manage stormwater largely fail toaddress the underlying problem of
imperviousness.
Stormwater collected in separate systems typicallyis not treated
before being discharged. In instanceswhere treatment is provided,
it usually consists offiltration to remove suspended solids,
debris, andfloatables. Because dissolved materials and nutrientsare
difficult to treat in urban stormwater and littlehas been done to
abate the scouring, erosion, andother physical impacts of
stormwater discharges,treatment efforts have been largely
ineffective atdiminishing stormwater-related water pollution.
Most municipal stormwater discharges are regu-lated as point
sources under the Clean Water Act(CWA) and require a National
Pollutant DischargeElimination System (NPDES) permit. However,
end-of-pipe treatment and control typical of other per-mitted
point-source discharges are often impractical forurban stormwater,
because of the large volumes ofstormwater; generated and space
constraints in urbanareas. Permits for urban stormwater require
munici-palities to develop a stormwater management planand to
implement best management practices.1 Thesemanagement measures are
typically used in lieu ofspecific pollutant removal requirements.
“Performance-based” standards are generally not required, and
mini-mum control measures are sufficient for compliance.
As a result, compliance with urban stormwaterpermits does not
necessarily result in improved
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CHAPTER 3
water quality. Municipalities that develop programsto actually
reduce stormwater pollution are moti-vated to do so because of
their proximity to uniqueor valued water bodies or because of a
need toprotect drinking water supplies. Some of the moreaggressive
and innovative stormwater programs arelocated around sensitive or
important water bodieslike the Chesapeake Bay, the Great Lakes, or
PugetSound. Federal regulations require states to
identifyquality-limited waterways and determine thereduction in the
Total Maximum Daily Load (TMDL)of those pollutants necessary to
meet water qualitystandards, but these pollutant
load-reductionrequirements are not often translated into
effectivestormwater management programs.2
Municipalities are required to implement short-term and
long-term strategies to reduce overflowsfrom combined sewer
systems, but significantnumbers of overflows continue to occur. The
CWAprohibits the dry weather discharge of untreatedsewage and
requires wet weather CSO dischargesto be limited and to control
discharges of solidsand floatables. Federal regulations also
require thatmunicipalities develop long-term CSO control plansthat
detail procedures and infrastructure modifica-tions necessary to
minimize wet weather overflowsand meet water quality standards.3
The long-termcontrol plans focus primarily on managing storm-water
impacts on combined sewer systems.
Mitigating CSOs is costly. The 2000 Clean Water-sheds Needs
Survey (CWNS) estimated that $56 bil-lion (2005 dollars) in capital
investment was neededfor CSO control.4 Separating combined sewer
lines
CONTROLLING STORMWATERIN URBAN ENVIRONMENTS
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and building deep storage tunnels are the two cur-rently
preferred methods of CSO control. The costsfor separating combined
sewers, disconnecting storm-water inlets from the combined sewer
system, anddirecting them to a newly installed separate stormsewer
system range from $500 to $600 per foot of sewerseparated, or $2.6
million to $3.2 million for each mileof combined sewer to be
separated.5 While sewer sep-aration will eliminate CSO discharges
and the releaseof untreated sewage, the trade-off is an increase
inthe volume of untreated stormwater discharges.
Deep storage systems are large undergroundtunnels with millions
of gallons of storage capacitythat are built to hold the excess
surge of combinedsewer stormwater during wet weather events.
Thesesystems eventually direct the detained wastewaterto the
municipal treatment plant as combined sewerflow rates subside. If
sized, constructed, and oper-ated properly, deep tunnels can
significantly reduceCSO discharges. However, deep tunnels take
manyyears to build and are very costly. Several cities havebegun or
plan to begin deep tunnel projects costinghundreds of millions or
billions of dollars, as out-lined in Table 5.
Current stormwater management for separateand combined sewer
systems is ineffective because itfocuses on the symptoms (large
stormwater volumes)rather than the problem (development patterns
and
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Natural Resources Defense Council Rooftops to Rivers
imperviousness). Capturing, retaining, and tryingto improve the
quality of vast quantities of urbanstormwater runoff is often more
difficult andexpensive than reducing the amount of
stormwatergenerated from the outset through strategies toreduce
imperviousness and maximize infiltrationand filtration. On a
municipal level, costs can bedecreased when these techniques are
incorporatedinto redevelopment and ongoing
infrastructurereplacement efforts. Comprehensive
stormwatermanagement programs can be used to minimize theeffect of
impervious surfaces and manage precipi-tation and stormwater with
the use of naturalprocesses. These “green” approaches are often
lessexpensive and more effective than current storm-water and CSO
controls.
GREEN ALTERNATIVESNewer, flexible, and more effective urban
storm-water and CSO strategies are being adopted inNorth America.
Cities are beginning to introducegreen infrastructure as a
component of compre-hensive stormwater management plans aimed
atreducing stormwater runoff, CSOs or both. Thisapproach is
significant in that it can be used toaddress the stormwater problem
“at the source”through efforts aimed at restoring some of the
TABLE 5: Examples of Deep Storage Tunnel Projects
City Project Duration Completion Date Storage Capacity Cost
Chicago, ILa,b 40+ years 2019 18 billion gallons $3.4
billion
Milwaukee, WIc,d 17 years (Phase 1) 1994 405 million gallons
$2.3 billion
8 years (Phase 2) 2005 88 million gallons $130 million
Portland, ORe 20 years 2011 123 million gallons $1.4 billion
Washington, DCf 20 years after construction begins n/a 193.5
million gallons (proposed) $1.9 billion (projected)
a Tudor Hampton, “Chicago Engineers Move Fast to Finish Epic
Tunneling Feat,” Engineering News-Record, August 18,
2003,http://www.enr.com/news/environment/archives/030818a.asp
(accessed February 16, 2005).
b Metropolitan Water Reclamation District of Greater Chicago,
Combined Sewer Overflow Public Notification
Plan,http://www.mwrd.org/mo/csoapp/CSO/cso.htm (accessed December
15, 2005).
c Milwaukee Metropolitan Sewerage District, Collection System:
Deep Tunnel System, http://www.mmsd.com/projects/collection8.cfm
(accessedNovember 11, 2004).
d Milwaukee Metropolitan Sewerage District, Overflow Reduction
Plan, http://www.mmsd.com/overflows/reduction.cfm (accessed
November 11, 2004).e Portland Bureau of Environmental Services,
Working for Clean Rivers,
http://www.portlandonline.com/bes/index.cfm?c=32123 (accessed
November 15,
2004).f D.C. Water and Sewer Authority, “WASA Proposes Plan to
Control Combined Sewer Overflows to Local Waterways: Combined Sewer
Long Term Control
Plan,” The Reporter, Summer 2001.
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natural hydrologic function of areas that have beenurbanized.
Green infrastructure can also be used tolimit development in
sensitive headwaters regionsand groundwater recharge areas to avoid
the seg-mentation and isolation of natural environmentalareas and
resources.
Green infrastructure can be applied in manyforms. It
traditionally has been thought of as theinterconnected network of
waterways, wetlands,woodlands, wildlife habitats, and other
naturalareas that maintain natural ecological processes.6
In practice, installing green infrastructure meanspreserving,
creating, or restoring vegetated areasand natural corridors such as
greenways, parks, con-servation easements, and riparian buffers.
Whenlinked together through an urban environment,these lands
provide rain management benefits simi-lar to natural undeveloped
systems, thereby reducingthe volume of stormwater runoff. With
green infra-structure, stormwater management is accomplishedby
letting the environment manage water naturally:capturing and
retaining rainfall, infiltrating runoff,and trapping and absorbing
pollutants. For example,the Village Homes community in Davis,
California,uses a system of vegetated swales and meanderingstreams
to manage stormwater. The natural drainage
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Natural Resources Defense Council Rooftops to Rivers
system is able to infiltrate and retain a rainfallvolume greater
than the 10-year storm withoutdischarging to the municipal storm
sewer system.
Green infrastructure can be used to restore vegeta-tion and
green space in highly impervious city areas.Planting street trees
and other urban forestry initiativescan reduce stormwater runoff
because urban treecanopies intercept rainfall before it hits the
pavementand is converted to stormwater. Trees with maturecanopies
can absorb the first half-inch of rainfall.7
Recently the concept of green infrastructure hasbeen broadened
to include decentralized, engineeredstormwater controls. These
green techniques aredesigned to mimic the functions of the natural
envi-ronment and are installed to offset the impacts ofurbanization
and imperviousness. Green manage-ment techniques are used to
minimize, capture, andtreat stormwater at the location at which it
is createdand before it has the opportunity to reach the
col-lection system. Engineered systems commonly usedin urban areas
include green roofs, rain gardens, rainbarrels and cisterns,
vegetated swales, pocket wet-lands, and permeable pavements.
Most green stormwater controls actually consistof green growth,
including vegetated systems likegreen roofs and rain gardens, but
other “green”
Street planters in Portland, OR, are used inhighly developed
urban areas to introducegreen space and manage stormwater
runoff.PHOTO COURTESY OF THE PORTLAND BUREAU OF
ENVIRONMENTALSERVICES
-
controls, like permeable pavements, are not vege-tated but
designed to provide the water detentionand retention capabilities
of natural systems. Greeninfrastructure also encourages downspout
discon-nection programs that redirect stormwater fromcollection
systems to vegetated areas or that captureand reuse stormwater,
such as rain barrels. Down-spout disconnection removes stormwater
volumefrom collection systems and allows green infra-structure
components to manage the runoff.
Green infrastructure offers numerous benefits whenused to manage
stormwater runoff. Many green tech-niques reduce both stormwater
volume and pollutantconcentrations and, in contrast to conventional
cen-tralized controls, provide flexibility in how andwhere
stormwater management is accomplished. Theuse of green
infrastructure protects natural resourcesand lessens the
environmental impacts of develop-ment by not only addressing
stormwater, but also byimproving air quality and community
aesthetics.
1. Stormwater volume control and pollutant removal.
Green infrastructure is effective for managing storm-water
runoff because it is able to reduce the volumeof stormwater and
remove stormwater pollutants.Reducing the amount of urban runoff is
the most
9
Natural Resources Defense Council Rooftops to Rivers
effective stormwater pollution control. This reducesthe amount
of stormwater discharged from separatestormwater sewer systems and
aids combined sewersystems by decreasing the overall volume of
waterentering the system, thus reducing the number andsize of
overflows. Another large benefit of greeninfrastructure is that
nearly every green techniqueresults in the removal of stormwater
pollutants. Thenatural processes employed by green
infrastructureallow pollutants to be filtered or biologically
orchemically degraded, which is especially advan-tageous for
separate storm sewer systems that donot provide additional
treatment before dischargingstormwater. The combination of runoff
reduction andpollutant removal is an effective means of reducingthe
total mass of pollution released to the environ-ment. Because of
this, open areas and buffer zonesare often designated around urban
streams andrivers to provide treatment and management ofoverland
flow before it reaches the waterway.
2. Decentralized, flexible, site-specific solution.
Greeninfrastructure differs from other stormwater manage-ment
methods because it provides the opportunity tomanage and treat
stormwater where it is generated.This decentralized approach allows
green infrastructure
Urban trees intercept rainfall before it hits theground and is
converted to stormwater runoff.PHOTO COURTESY OF THE LOW IMPACT
DEVELOPMENT CENTER
-
techniques to be installed at numerous locationsthroughout the
city. Green infrastructure is flexible,allowing it to be applied in
a wide range of locationsand circumstances, and can be tailored to
newlydeveloped land or retrofitted to existing developedareas. This
enables green infrastructure to be usedon individual sites or in
individual neighborhoodsto address localized stormwater or CSO
problems,or incorporated into a more widespread municipalstormwater
management program.
3. Green design and the development problem. Projectedpopulation
growth and development will strain an
10
Natural Resources Defense Council Rooftops to Rivers
aged and often inadequate infrastructure system byintroducing
new areas of imperviousness and addi-tional volumes of stormwater.
Strategies will need tobe adopted to manage urban growth and its
impactson water quality. The use of green infrastructureoffers an
alternative to existing development patternsand a new method of
developing urban areas. Greeninfrastructure currently is being used
to manageexisting stormwater problems, but has the potentialto
significantly effect how future developmentcontributes to
stormwater and sewer overflowproblems by preserving and
incorporating greenspace into newly developed areas and by
addressingthe established connection between imperviousnessand
stormwater pollution.
4. Ancillary benefit. Green infrastructure is alsoattractive
because it can be used to achieve multipleenvironmental goals.
Funds spent on conventionalstormwater management are used only for
waterinfrastructure. In addition to stormwater manage-ment
benefits, green infrastructure improves airquality by filtering air
pollution and helps to counter-act urban heat island effect by
lowering surfacetemperatures. For example, many of the green
infra-structure projects in Chicago, while also providingstormwater
management, were initially installed tomitigate urban temperature
increases and improveenergy efficiency. Green infrastructure also
improvesurban aesthetics, has been shown to increase prop-erty
values, and provides wildlife habitat and recrea-tional space for
urban residents. This multi-benefitenvironmental approach
ultimately provides controlprograms that are more diverse and
cost-effectivethan projects aimed solely at stormwater control.
A RiverSafe RainBarrel installed at the Jane Holmes
nursingresidence in Pittsburgh, PA, by the Nine Mile Run
RainBarrelInitiative. PHOTO COURTESY OF RIVERSIDES
-
11
The cost of stormwater control is a major factorin the
successful implementation of pollutioncontrol programs. A large
investment is required toadequately address CSOs and stormwater
runoff. Inaddition to the $56 billion necessary to control CSOs,the
Environmental Protection Agency (EPA) hasidentified $6 billion of
documented needs for munici-palities to develop and implement
stormwater man-agement programs required by the Phase I and
IIstormwater regulations, as well as $5 billion in docu-mented
needs for urban runoff control.1,2 However,the EPA estimates that
while $5 billion has beendocumented, up to $16 billion may be
needed forurban runoff control.3 These costs present a signifi-cant
burden to municipal governments challengedwith funding these
programs.
Of course, natural stormwater retention and filtra-tion is
provided by Mother Nature for free. The highcosts associated with
urban stormwater result fromthe destruction of free, natural
stormwater treatmentsystems—trees, meadows, wetlands, and other
formsof soil and vegetation. For example, researchers atthe
University of California at Davis have estimatedthat for every
1,000 deciduous trees in California’sCentral Valley, stormwater
runoff is reduced nearly1 million gallons—a value of almost
$7,000.4 Clearly,preserving trees reduces polluted stormwater
dis-charges and the need for engineered controls to replacethose
lost functions. When those trees are cut downand their functions
are lost, those costs are passed onto municipal governments, which
then pass them onto their citizens. So, while the bulk of this
report isabout how to integrate green infrastructure into the
CHAPTER 4
developed world, protecting and enhancing thoseareas that have
not yet been developed is often thecheapest, most effective way to
keep contaminatedstormwater out of urban and suburban streams.
THE COSTS OF BUILDING GREEN IN NEWDEVELOPMENTSGreen
infrastructure in many instances is less costlythan conventional
stormwater management pro-grams or centralized CSO approaches and
may
ECONOMIC BENEFITSOF GREEN SOLUTIONS
The Nine Mile Run RainBarrel Initiative used 500 RainBarrelsto
achieve CSO reduction for the ALCOSAN treatment plant inPittsburgh.
PHOTO COURTESY OF RIVERSIDES
-
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Natural Resources Defense Council Rooftops to Rivers
provide an opportunity to decrease the economicburden of
stormwater management. Studies inMaryland and Illinois show that
new residentialdevelopments using green infrastructure
stormwatercontrols saved $3,500 to $4,500 per lot (quarter-
tohalf-acre lots) when compared to new developmentswith
conventional stormwater controls.5,6 Thesedevelopments were
conceived and designed toreduce and manage stormwater runoff by
preservingnatural vegetation and landscaping, reducing overallsite
imperviousness, and installing green stormwatercontrols. Cost
savings for these developmentsresulted from less conventional
stormwater infra-structure and paving and lower site
preparationcosts. Importantly, in addition to lowering costs,each
of the sites discharges less stormwater than con-ventional
developments. Adding to the cost savings,developments utilizing
green infrastructure normallyyield more lots for sale by
eliminating land-consumingconventional stormwater controls, and
lots in greendevelopments generally have a higher sale pricebecause
of the premium that buyers place onvegetation and conservation
development.7,8
OUTFITTING EXISTING DEVELOPMENTS WITHGREEN INFRASTRUCTUREThe
economics of retrofitting existing urban areaswith stormwater
controls differ from new develop-ment. Urban stormwater retrofits
can be expensiveand complicated by space constraints, although
thisis not always the case. Based upon the costs of theirpilot
projects, city officials in Seattle and Vancouver(discussed in the
case studies on pages 29 and 33),believe that the costs of future
green infrastructureinstallations will be similar to or slightly
more thanconventional stormwater controls.9,10 The
analysisconducted by the city of Vancouver indicates
thatretrofitting green infrastructure into locations withexisting
conventional stormwater controls will costonly marginally more than
rehabilitating the conven-tional system, but introducing green
infrastructureinto new development will cost less.11 However,while
green infrastructure may be more expensive in
some instances, municipalities believe that the addi-tional
benefits of green controls—including the crea-tion of more
aesthetic city space and the significantreduction in water
pollution—justify the added cost.In addition, green infrastructure
can be incrementallyintroduced into urban environments, allowing
thecosts to be incurred over a longer period of time.
The EPA has developed cost curves for conven-tional urban
stormwater controls relating stormwaterstorage capacity to control
cost. The costs in Table 6do not include any associated costs for
constructionand infrastructure. These costs represent the
gener-ally accepted costs of stormwater control and pro-vide a
baseline to which green infrastructure costscan be compared.
In many instances, green infrastructure costscompare favorably
with the costs of conventionalcontrols. However, cost comparisons
for individual,small-scale retrofit projects are not likely to
favorgreen controls. In urban areas, green infrastructurewill be
most cost-effective when it is incorporatedas part of an overall
redevelopment effort or whenlarge improvements to infrastructure
are required.In these instances, the costs of green
infrastructureare minimized relative to the scope and costs ofthe
overall project. While green infrastructure maybe more costly than
conventional stormwater orCSO controls in certain instances, the
added costsshould be weighed against the enhanced stormwatercontrol
and other environmental benefits gainedfrom their use.
TABLE 6: Cost of Conventional Urban Stormwater andCSO
Controlsa
Cost to ManageControl Cost Equationb 10 Million Gallons
Surface storage C = 5.184V0.826 $35 million
Deep tunnels C = 7.103V0.795 $44 million
Detention basins C = 62,728V0.69 $300,000
Retention basins C = 69,572V0.75 $390,000
a James Heaney, et al., Costs of Urban Stormwater Control,
National RiskManagement Research Laboratory, Office of Research and
Development,EPA-600/R-02/021, January 2002.
b Cost equations adjusted to 2005 dollars. Volume equals
millions ofgallons. Cost for surface storage and deep tunnels is
millions of dollars.
-
13
Although green infrastructure has been shown toreduce stormwater
runoff and combined seweroverflows and improve water quality, its
adoptionacross the country has been slow. Cities that
haveincorporated green infrastructure into their storm-water
management programs have often done sobecause of direct efforts to
encourage alternativestormwater approaches. The following
recommenda-tions can be used to encourage the use of
greeninfrastructure in municipalities.
1. Get development right the first time. Reducing orpreventing
stormwater runoff is the most effectiveway to minimize pollution
because it preventspollutants from being transported to water
bodies.Incorporating green infrastructure into the earlieststages
of community development can negate orlimit the need for
larger-scale, more expensivestormwater controls. Minimizing
imperviousness,preserving existing vegetation, and
incorporatinggreen space into designs all decrease the impact
thaturbanization has on water quality. Used in this way,green
infrastructure design is a more cost-effectivestrategy, often
costing less to develop per lot whileyielding more lots at an
increased sale price.1,2
2. Incorporate green infrastructure into long-term
control plans for managing combined sewer overflows.
Cities with combined sewer systems are required todevelop
long-term plans to reduce sewer overflowsenough to meet water
quality standards.3 Greeninfrastructure has proven to be valuable
in reducinginflows into combined sewer systems and should be
CHAPTER 5
integrated into such plans. Rather than relying solelyon
conventional, centralized storage projects toreduce CSO volumes,
municipalities shouldconsidering using green techniques, which can
beintegrated into redevelopment projects andinfrastructure repairs
and upgrades. Each yearPortland, Oregon’s downspout
disconnectionprogram diverts 1 billion gallons of stormwater
fromthe collection system and has been used to helpalleviate
localized combined sewer system backupsin city neighborhoods.4
3. Revise state and local stormwater regulations to
encourage green design. Most state and localstormwater
regulations focus on peak flow ratecontrol. To encourage more
effective stormwatermanagement, these regulations should be revised
torequire minimizing and reducing impervioussurfaces, protecting
existing vegetation, maintainingpredevelopment runoff volume and
infiltrationrates, and providing water quality improvements.These
requirements encourage green infrastructurebecause it can meet each
of these objectives. Portland,Oregon, requires on-site stormwater
managementfor new development and redevelopment in bothCSO and
separate sewer areas of the city andencourages use of green
infrastructure to complywith the regulation (more details about
Portland’sdevelopment regulations can be found in the casestudy on
page 24).
New Jersey’s stormwater management standardsrequire 300-foot
riparian buffers and stipulate apreference for nonstructural best
management
POLICY RECOMMENDATIONSFOR LOCAL DECISION MAKERS
-
practices (BMPs). These standards also institutewater quantity
as well as quality regulations. Thewater quantity standards require
no change ingroundwater recharge volume following construc-tion and
that infiltration be used to maintain pre-development runoff
volumes and peak flow rates.Any increase in runoff volume must be
offset by adecrease in post-construction peak flow rate.
Waterquality standards require a reduction in stormwaternutrient
loads to the “maximum extent feasible”and total suspended solids
(TSS) reductions of 80%.If the receiving water body is a
high-quality wateror tributary, the required TSS reduction is
95%.5
Berlin, Germany, has incorporated the Green AreaFactor (GAF)
into its regulations. Based on land useand zoning, the GAF sets a
greening target for eachproperty that provides the required ratio
of vegetatedelements to impervious surface. Once propertyowners
apply for a building permit, they are requiredto satisfy the green
target goal. Property ownersselect green infrastructure practices
from an approvedlist and determine compliance by calculating
theproportion of the property dedicated to the greeningtarget.
Selected green infrastructure practices areweighted according to
their effectiveness at meetingenvironmental goals.6
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Natural Resources Defense Council Rooftops to Rivers
To date, the U.S. federal government has declinedto set
performance standards for stormwater dis-charges from development
or to add specifics to the“maximum extent practicable” standard set
by theClean Water Act for discharges from municipalities.7
Since the federal government has failed to showleadership in
this area, state and local entities mustdo so.
4. Establish dedicated funding for stormwater
management that rewards green design. Adequatefunding is
critical for successful stormwatermanagement programs. The billions
of dollarsnecessary to mitigate stormwater pollution andcombined
sewer overflows require federal fundingto augment state and
municipal funding. Toencourage its use, dedicated stormwater
fundingsources could identify a preference for green
infra-structure or establish a funding scale based uponthe relative
use of green management techniques.
Many jurisdictions are creating stormwater utili-ties similar in
function to water and wastewater utili-ties. Stormwater utilities
allow for the assessmentand collection of a user fee dedicated to a
stormwatermanagement program. Other jurisdictions dedicatea certain
portion of collected local tax revenue to a
The vegetated infiltration basins in theBuckman Heights
Apartments courtyardin Portland, OR, receive and
infiltratestormwater from building roofs andsidewalks.PHOTO
COURTESY OF PORTLAND BUREAU OF ENVIRONMENTALSERVICES
-
stormwater fund. Establishing a dedicated fundremoves stormwater
management from generalrevenue funding, which is subject to
variable fundingand competes with other general taxation
programsfor money. Stormwater utilities, where allowed byenabling
legislation, are popular because of theability to determine a user
rate structure and as acomplement to incentive programs.8,9
5. Provide incentives for residential and commercial
use of green infrastructure. Various incentives arealready in
place to encourage green infrastructureuse in a number of cities.
For example, Portland,Oregon, allows additional building square
footagefor buildings with green roofs, and Chicago providesa
density bonus option for buildings with vegetativecover on the
roof.10,11 The city of Chicago also pro-vided 20 $5,000 grants to
install small-scale com-mercial or residential green roofs in early
2006.12 Alsobeginning in 2006, Portland will provide up to a
35%discount in its stormwater utility fee for propertieswith
on-site stormwater management.13 Marylandprovides credits for using
green infrastructure whendetermining compliance with its stormwater
regu-latory requirements. Six different credits, all relatedto
green infrastructure design, are available.14 Severalcities fund or
subsidize downspout disconnectionprograms; Portland’s program pays
homeowners$53 per downspout disconnected or the city willdisconnect
the downspouts for free.
6. Review and revise local development ordinances.
Local zoning requirements and building codes ofteninadvertently
discourage the use of green infra-structure. Provisions requiring
downspouts to beconnected to the stormwater collection
systemprohibit disconnection programs and the use of greenspace for
treatment of rooftop runoff. Mandatorystreet widths and building
setbacks can unnecessarilyincrease imperviousness. Stormwater
treatmentrequirements that favor centralized collection
andtreatment and prescribe treatment options offer little
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Natural Resources Defense Council Rooftops to Rivers
opportunity or incentive to use green
infrastructure.Jurisdictions should review their applicable
storm-water and wastewater ordinances and revise themto remove
barriers to green infrastructure use andencourage more
environmentally friendly regulations.15
7. Preserve existing trees, open space, and stream
buffers. Too often, development removes nearly allexisting
natural features. Simply preserving trees,open space, and stream
buffers and incorporatingthem into the community will help maintain
waterquality and manage stormwater runoff while lessen-ing the need
for additional stormwater controls.For example, New Jersey’s
stormwater managementstandards require 300-foot riparian buffers
fornew developments and redevelopments to protectwater
quality.16
8. Encourage and use smart growth. Smart growth canbe used to
limit sprawl and reduce the introductionof impervious surfaces.
Smart growth policies canidentify and protect sensitive
environmental areasand direct development to locations with
adequateinfrastructure. By limiting sprawl and
discouragingdevelopment in sensitive areas, smart growth
mayincrease population densities and imperviousness inpreviously
urbanized areas. Smart growth strategiesshould be coupled with
green infrastructure to limitthe stormwater and infrastructure
effects of a poten-tial increase in urbanization.
9. Get the community involved. Green infrastructurepresents an
opportunity for community outreach andeducation. Downspout
disconnections, rain barrels,rain gardens, and green roofs may
individuallymanage a relatively small volume of stormwater
butcollectively can have a significant impact. Portland’sdownspout
disconnection program, for example,now diverts 1 billion gallons of
stormwater awayfrom the combined sewer system each year.
Greeninfrastructure can be introduced into a communityone lot at a
time.
-
16
CHAPTER
While development, imperviousness, and urban-ization have all
taken their toll on downstreamwaterways, current stormwater and
combined seweroverflow (CSO) mitigation efforts have failed
toadequately address the problem or improve waterquality because
they are focused on end-of-pipesolutions. Current levels of
development andimperviousness have degraded the nation’s
waterquality, and future population growth and develop-ment will
only exacerbate the problem. Additionaldevelopment will make
stormwater and CSO controlsolutions even more difficult and
costly.
Green infrastructure offers the opportunity to notonly develop
new areas in a more environmentallyefficient manner, but also to
rehabilitate existing devel-oped areas. Urbanization and
development alter howwater is distributed throughout the
environment. Muchgreater volumes of stormwater are generated and
dis-charged to receiving water bodies in developed areasthan would
be in the natural environment. Greeninfrastructure is providing
measurable water qualityimprovements, most notably in stormwater
volumereduction and CSO mitigation.
Some jurisdictions and cities have chosen greeninfrastructure as
a preferable method of stormwateror CSO control based upon the
specific needs andgoals of the municipality. Others have installed
greeninfrastructure to experiment with innovative storm-water or
combined sewer overflow pilot projects. Butall of these efforts
demonstrate how it can be success-fully integrated into urban
communities.
A common driver among the cities using greeninfrastructure is
compliance with regulatory require-ments. The catalyst for
Portland, Oregon’s activeprogram, for example, is a need to satisfy
a number
CHAPTER 6
of environmental commitments, including a consentdecree to limit
CSO discharges, Safe DrinkingWater Act standards influencing the
quality of infil-trated stormwater, and emerging TMDL load andwaste
load allocations.1 Other cities with combinedsewer systems, or
those that discharge stormwaterto sensitive receiving waters, face
similar require-ments. Such regulations only increase the
oppor-tunities for creativity and willingness on the partof
municipal decision makers to actively promoteand introduce green
infrastructure. City leadersare finding that when faced with the
simultaneouschallenges of regulatory requirements,
infrastructurelimitations, and financial constraints, green
infra-structure often emerges as an appropriate meansof satisfying
each.
Another commonality among cities that haveincorporated green
infrastructure into theirstormwater and CSO control plans is a
commitmentfrom city personnel. Whether elected officials
orprofessional staff, these city leaders have recognizedthe
benefits of green infrastructure and havesuccessfully communicated
its value to the public.These cities have also been innovative with
theirregulations and environmental policies, looking forexisting
and alternative avenues to encourageadoption of new stormwater and
CSO controlstrategies. These efforts are often popular because
ofthe public’s positive response to the “greenscaping”that has
accompanied the programs. As many localdecision makers have already
found, using greeninfrastructure in place of or in combination with
lesseffective conventional methods of handlingstormwater runoff can
have benefits beyond justeconomic cost savings and reduced
pollution.
CONCLUSION
-
CH
ICA
GO
The following nine case studies illustrate efforts inNorth
America to incorporate green infrastructureinto urban stormwater
and combined sewer overflow(CSO) control strategies, but this is
not an exhaustivelist. Several factors were used to select
case-study cities.Among them were extent and duration of
programefforts, availability of information and quantifiabledata,
geographic location, and the number and typeof green infrastructure
elements practiced.
Chicago, IllinoisProgressive environmental change through
creativeuse of green infrastructurePopulation: 2.9 millionType of
green infrastructure used: green roofs; raingardens, vegetated
swales, and landscape; perme-able pavement; downspout
disconnection/rainwatercollectionProgram elements: used for direct
CSO control;established municipal programs and public funding
Historically, Chicago has been known morefor its industrial
horsepower than for progressiveenvironmental ideas. Rivers like
Bubbly Creek stillbear the names they earned from the pollution
theyonce contained. Stories of the city’s sewage andpollution
problems from as early as the 1880s stillpersist as popular
legends. However, recent initia-tives show that Chicago is emerging
as a leader ingreen development, with an extensive green
roofprogram, environmentally sensitive demonstrationprojects, and
municipal policies that encouragedecentralized stormwater
management. The cityhas been particularly creative in its approach,
usinggreen infrastructure projects to not only manage
CHAPTER 7
stormwater runoff but also to address otherenvironmental issues,
such as mitigating urbanheat island effects and improving energy
efficiencyin buildings.
Stormwater Collection Through Expansion of theCombined Sewer
SystemWhile the city’s past environmental infrastructureprojects
have had dubious goals, the water qualityof Lake Michigan, the
city’s drinking water source,has long been a concern. In the early
1900s, sewageand stockyard pollution from the Chicago Riverprompted
Chicago officials to reverse the courseof the South Branch of the
river away from LakeMichigan and to the Mississippi River in an
effortto improve the lake’s water quality.1 Water issuesremain a
concern for the city more than a centurylater. The city manages one
of the largest wastewatercollection and treatment systems in the
world andcontends with flooding, surface water qualityimpairment,
and CSOs. Urban runoff challenges areexacerbated by the magnitude
of infrastructureneeded to serve Chicago’s population. The city
itselfhas over 4,400 miles of sewage infrastructure thatcost about
$50 million annually to maintain.2 Approx-imately 3 million people
call Chicago home, andthe population of the entire six-county metro
regionsurrounding the city exceeds 8 million; the
region’spopulation is projected to increase 20% by 2030.3
Impervious surfaces cover approximately 58% ofthe city.4
Chicago has pursued a number of initiatives toimprove stormwater
collection, the most ambitiousbeing a $3.4 billion project to
collect and store storm-water and sewage from the combined sewer
system.5
CASE STUDIES
17
CHAPTER
-
In the 1970s, the Metropolitan Water ReclamationDistrict began
construction of the primary controlsolution for CSOs—the Tunnel and
Reservoir Plan(TARP). In 2003, with only part of the system
opera-tional, more than 44 billion gallons of stormwaterwere
captured; 10 billion gallons, however, werereleased as CSOs.6
Approximately 2.5 billion gallonsof storage are currently available
in the TARP system.An additional 15.6 billion gallons of storage
will beavailable when two more reservoirs are added to thesystem;
construction is scheduled for completion in2019.7,8 When complete,
the system will handle mostof Chicago’s CSO discharges, storing
combined runoffand sewage until it can be sent for secondary
treat-ment at a wastewater treatment plant.
Chicago’s Green Roof ProgramAlthough the Metropolitan Water
ReclamationDistrict has committed to this massive public
worksproject, the city has also pursued several initiativesto
install green infrastructure that promotes on-sitestormwater
management, including green roofs,permeable paving projects, rain
barrels, and greenbuildings. Much of this investment in green
infra-structure has paralleled the increase in populationand
building within the city over the last decade.
18
Natural Resources Defense Council Rooftops to Rivers
And, unlike the past, the Chicago River is now seenas a public
amenity rather than a liability.
Chicago’s thriving green roof program began witha 20,300 square
foot demonstration roof on its owncity hall. The green roof retains
more than 75% of thevolume from a one-inch storm, preventing this
waterfrom reaching the combined sewer system.9 The pro-gram has led
to more than 80 green roofs in the city,totaling over one million
square feet.10 A 2003 ChicagoDepartment of the Environment study
found that run-off from green roof test plots was less than half of
therunoff from conventional stone and black tar roof plots;the
difference was even larger for small storms. Thecity encourages the
use of green roofs by sponsoringinstallations and demonstration
sites and by provid-ing incentives. A density bonus is offered to
developerswho cover 50% or 2,000 square feet (whichever isgreater)
of a roof with vegetation. In early 2006, the cityprovided 20
$5,000 grants for green roof installations onsmall-scale commercial
and residential properties.11
Other Green Infrastructure Innovations: Chicago’sCitywide
CommitmentChicago has employed other green technologies toreduce
urban runoff. To address localized floodingcaused by runoff from
one alley, the city removed the
CH
ICA
GO
The green roof at Chicago’s City Hallintroduces vegetation in
the heart ofdowntown. Temperatures above theChicago City Hall green
roof average 10°to 15°F lower than a nearby black tarroof. During
the month of August thistemperature difference may be as greatas
50°F. The associated energy savingsare estimated to be $3,600 per
year.PHOTO COURTESY OF ROOFSCAPES, INC.
-
asphalt from the 630 foot long, 16 foot wide alley andreplaced
it with a permeable paving system. Now,instead of generating
stormwater runoff, the alleywill infiltrate and retain the volume
of a three-inch,one-hour rain event.12 The permeable
pavementrequires little maintenance and has a life expectancyof 25
to 35 years.13 In this same ward, vegetated swalesare also being
used for stormwater management.
In June 2004, Chicago has embarked on a city-wide green building
effort. Chicago Mayor RichardM. Daley presented The Chicago
Standard, a set ofconstruction principles designed for
municipalbuildings. The standards are based on the Leader-ship in
Energy and Environmental Design (LEEDTM)Green Building Ration
System14 and emphasizesustainability, water efficiency, energy
effects, andindoor air quality as well as stormwater manage-ment.
For both the green roof and green buildingefforts, Chicago has
created municipal demonstrationprojects to develop professional
expertise in the cityon these technologies.
Chicago Center for Green Technology. The centerpieceof the
city’s green building efforts is the ChicagoCenter for Green
Technology. The Chicago Depart-ment of Environment transformed this
property froma 17-acre brownfield full of construction debris tothe
first municipal building to receive the LEEDTM
platinum rating.15 The 34,000 square foot centerserves as an
educational facility and rental space fororganizations and
businesses with an environmentalcommitment. Four 3,000 gallon
cisterns capturestormwater that is used for watering the
landscaping.The site also features a green roof, bioswales,
perme-able paving, and a rain garden. Chicago Departmentof
Environment models indicate that Green Tech’sstormwater management
technologies retain morethan 50% of stormwater on site—for a
three-inchstorm, the site releases 85,000 gallons of stormwaterto
the sewer system instead of the expected 175,000gallons.16 The
success of the Green Tech projectspurred several other green
building projects,including three new green libraries; a new
policestation to be monitored for a national case study;
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Natural Resources Defense Council Rooftops to Rivers
green renovations on a firehouse and police head-quarters; and
the Green Bungalow Initiative, a pilotproject to affordably
retrofit four of Chicago’s historicbungalows with green
technologies and monitorany corresponding energy savings. The
program hasthus far shown average energy savings for the
greenbungalows of 15% to 49%.17
The city has also pursued public outreach pro-grams, engaging
homeowners through its recent rainbarrel and rain garden programs.
In the fall of 2004city residents purchased more than 400
55-gallonrain barrels for $15 each.18 The program cost the
city$40,000 excluding city labor. The Department ofEnvironment
estimates the pilot project has thepotential to divert 760,000
gallons annually from thecombined sewer system, a relatively small
numbercompared to the total amount of stormwater runoffin the city.
However, the program was targeted toareas with a high frequency of
basement flooding,meaning the program may have a more
significantimpact in these localized areas. Since the water inrain
barrels can be used for other purposes such aslandscaping, this
program has additional conserva-tion benefits as well. The city
also began a comple-mentary rain garden program, planting four
raingardens along with signage explaining benefits.
Chicago has also complemented its ground-levelinitiatives with
two studies on the effectiveness ofgreen infrastructure
technologies. The first is themonitoring study of the green roof
box plots. Thesecond is a 2004 Department of Environment
Storm-water Reduction Practices Feasibility Study that
usedhydraulic modeling to assess the effectiveness of
bestmanagement practices for the Norwood Park sewer-shed. The study
found that downspout disconnectionwould achieve peak flow
reductions in the 1,370-acrearea by 30% for a six-month or one-year
storm if allhomes in the 80% residential area disconnected
theirdownspouts from the sewer system.19,20 This wouldpotentially
reduce peak flow in the CSO outfall pipeby 20% and water levels in
the sewer system by eightinches to two feet. The study also showed
that three-inch and six-inch-deep rain gardens installed at
eachhome could reduce total runoff by approximately 4%
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and 7%, respectively, for the same six-month or one-year storm
events.
For Additional InformationChicago Department of the
Environment:http://egov.cityofchicago.org/city/webportal/portalEntityHomeAction.do?entityName=Environment&entityNameEnumValue=05
Milwaukee, WisconsinInvesting in green infrastructure to improve
waterqualityPopulation: 587,000Type of green infrastructure used:
green roofs; raingardens, vegetated swales, and landscape;
wetlands,riparian protection, or urban forestsProgram elements:
used for direct CSO control;established municipal programs and
public funding
Like many municipalities with a combined sewersystem, Milwaukee
has a history of exposure tofrequent CSO events and was faced with
finding aviable overflow control strategy. To reduce the num-ber of
CSOs and their impact on the water quality ofLake Michigan and its
tributaries, the MilwaukeeMetropolitan Sewerage District (MMSD),
theregional wastewater treatment agency, built a deeptunnel storage
system in the 1980s and 1990s. MMSDinvested $3 billion during this
period to reduce over-flows. As a complement to this large capital
invest-ment, MMSD is investing in green infrastructureprojects to
reduce stormwater inflow into the com-bined sewer system and
mitigate stormwater runoff.
MMSD manages wastewater from 28 municipali-ties with a combined
population of about 1.1 millionpeople in a 420 square mile service
area. All 28 com-munities own and operate their own sewer
systems,which drain into 300 miles of regional sewers ownedby MMSD.
The district’s two wastewater treatmentplants each process about 80
to 100 million gallonsof wastewater on a dry day.21 Treated
wastewateris discharged to Lake Michigan, which also servesas the
city’s drinking water supply.22 The city ofMilwaukee and the
village of Shorewood own and
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operate combined sewers, which make up 5% ofMMSD’s total service
area. Combined sewer over-flow points are located along rivers that
flow intoLake Michigan.23 The $2.3 billion Deep TunnelSystem
project, completed by MMSD in 1994, pro-vided 405 million gallons
of underground sewerstorage. Begun in 1986, the 19.4-mile-long
systemcollects and temporarily stores the large quantitiesof
stormwater and wastewater that are conveyedthrough the sewers
during wet weather events.24
Prior to the system becoming operational,Milwaukee averaged 50
to 60 CSO events a year,which discharged 8 to 9 billion gallons of
sewageand stormwater. The Deep Tunnel System wasdesigned to limit
CSOs to 1.4 events per year; inthe first 10 years of operation,
from 1994 until 2003,annual average CSO discharges were 1.2
billiongallons from 2.5 average annual events.25,26 Heavyrains in
the spring of 2004 resulted in 1 billion gallonsof CSO discharges
during a two-week period.27
Although the Deep Tunnel System has substantiallyreduced CSO
events, excessive quantities of storm-water can still trigger
overflows, and MMSD hascommitted an additional $900 million to an
overflowreduction plan.28
Milwaukee’s Green Infrastructure ApproachAs an additional
strategy to limit CSO discharges,MMSD has begun to install green
infrastructurewithin the combined sewer area to decrease thevolume
of stormwater entering the system. Oneof the first initiatives was
a disconnection programthat redirected building downspouts from the
com-bined sewer system to rain barrels. Overflow fromthe rain
barrels is directed to pervious areas and raingardens. In a
cooperative cost-sharing arrangementwith public entities and
private businesses in the city,MMSD partnered with others to
install more than60 rain gardens to receive and treat roof runoff.
Thetotal combined cost of these pilot projects was approx-imately
$170,000.29
The Highland Gardens housing project. Seven greenroofs have been
installed in the Milwaukee region.
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One of these is at the Highland Gardens housingproject, a
114-unit mid-rise for senior citizens andpeople with disabilities.
A 20,000 square foot greenroof was installed at a cost of $380,000.
The roofwill retain 85% of a two-inch rainfall. The remain-ing 15%
of the water volume is directed to raingardens and a retention
basin used for on-siteirrigation.30 These management strategies
preventstormwater from being discharged to the collec-tion
system.
MMSD has installed or helped finance four othergreen roofs to
reduce stormwater runoff. The firstwas a 3,500 square foot
structure on the roof ofMMSD’s headquarters building in
downtownMilwaukee. Native species of grasses and floweringplants
were selected for the roof vegetation. Thecost of the green roof
was just under $70,000.31 Asecond green roof was installed on the
Universityof Wisconsin-Milwaukee’s Great Lakes Water Insti-tute.
MMSD contributed $110,000 of the $233,000needed to install the
10,000 square foot unit. A thirdgreen roof was installed on the
city’s Urban EcologyCenter, with MMSD contributing $40,000 of
thetotal project cost. The fourth green roof is at theMilwaukee
County Zoo, to which MMSD con-tributed half of the $73,000
cost.32
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Measuring the Effectiveness of Milwaukee’sGreen
InfrastructureThe rain gardens and MMSD-financed green roofswere
installed in 2003 and 2004. A monitoring programevaluating the
effectiveness of the systems at managingstormwater is being
conducted with initial resultsexpected in early 2006. To determine
the potentialimpacts of the green infrastructure program,
MMSDconducted a modeling analysis. The modeling effortshowed that
application of downspout disconnection,rain barrels, and rain
gardens in residential areas wouldreduce each neighborhood’s
contribution to the annualCSO volume 14% to 38%. Additional
modeling resultsshowed the volume of stormwater sent to the
treatmentplants from the neighborhoods was reduced 31% to37% and
stormwater peak flow rates were reduced 5%to 36%, depending upon
the size of the rain event.33
(The model assumed a high participation rate for resi-dential
areas. Volume and peak flow reductions wouldnot be as great with a
lower participation rate.)
The effect of green infrastructure in commercialareas was also
modeled. The use of green roofs, raingardens, and green parking
lots is predicted to reducecommercial area contributions to CSO
volume by22% to 76%, but would not decrease—and couldeven
increase—the volume of stormwater sent to the
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The green roof atop MMSD’s head-quarters, shown just after
installation,demonstrates how stormwater flow intothe city’s sewer
system could be reduced.PHOTO COURTESY OF MMSD
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treatment plants. Stormwater peak flow rates fromcommercial
areas are predicted to be reduced 13% to69% with the introduction
of green infrastructure.34
MMSD has allocated more than $5.5 million forfiscal years 2002
through 2014 for rain water rerout-ing programs intended to prevent
stormwater fromentering the combined sewer system. An
additional$4.5 million has been allocated for fiscal years
2003through 2009 to promote, install, and monitor
greeninfrastructure practices aimed at reducing stormwater.35
MMSD is also purchasing and protecting open spaceto reduce
stormwater runoff and improve water qualityin its urban waterways.
The capital budget designatesfunds to purchase privately owned
wetlands to pre-vent development and establish conservation
ease-ments. More than $27 million has been allocated forfiscal
years 2000 through 2011. As of fiscal year 2005,775 acres had been
purchased in three watersheds forjust under $5.8 million.36 A
greenways initiative willidentify lands that compose greenway
connections,linkages between sites, delineated
environmentalcorridors, isolated natural wetlands, open space,
andriparian wetlands. Linkages between these areas willbe acquired
to protect and establish greenways alongjurisdictional waterways or
their tributaries. Prefer-ential consideration is given to land
that providesstormwater or flood management benefit.37
For Additional InformationMilwaukee Metropolitan Sewerage
District:http://www.mmsd.com/home/index.cfm
Pittsburgh, Pennsylvania“Restorative development” beautifies
land andcleans waterPopulation: 325,000Type of green infrastructure
used: green roofs; raingardens, vegetated swales, and landscape;
down-spout disconnection/rainwater collection; wetlands,riparian
protection, or urban forestsProgram elements: used for direct CSO
control
Pittsburgh is a postindustrial city struggling torepair the
environmental degradation wrought by
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its manufacturing past. The city’s development as asteel
powerhouse and mining center is intrinsicallytied to its geographic
and hydrologic setting. Thecity has developed around the confluence
of threerivers—the Allegheny, the Monongahela, and theOhio. Over
the past two decades Pittsburgh’s metro-politan population has
declined, partly due to thecollapse of the steel industry. The
city’s populationdecreased by 9.5% in the 1990s and the entire
metro-politan area saw a decline of 1.5%, trends that
weresignificantly greater than other same-size cities inthe
northeastern central area.38 The “steel city” is leftwith pollution
nuisances like brownfields and slagheaps, as well as a shrinking
urban center and aconsiderable sewage overflow problem.
It is precisely because of this industrial reputationand
declining urban center that Pittsburgh has hadthe opportunity and
the incentive to redevelop andreclaim large land parcels and turn
them into green-ways and parks. The restoration, described
as“restorative redevelopment,” is motivated by a desireto restore
habitat, beautify land, increase parkland,and raise property
values—in all, generally makingPittsburgh a more attractive city.39
Pittsburgh’s effortsin alternative stormwater management have been
acombination of government-sponsored restorationof green space and
privately funded demonstrationsites. The impetus for Pittsburgh’s
green restorationcomes largely from the private sector,
charitablefoundations, and citizens’ groups.
Water Pollution from Pittsburgh’s Sewer SystemPittsburgh clearly
has a need for supplementalstormwater management projects. The
city’s storm-water runoff contributes to frequent CSOs. In
2003,red-flag advisories for impaired water quality wereissued on
111 out of 139 summer recreation days(from May 15 to October 1). In
2004, 125 red-flagadvisories were issued.40 The metropolitan
areacontains more than 300 combined sewer outfallsand over 4,000
miles of underground pipes. Manyof these outfalls are upstream of
drinking waterintakes. Solving Pittsburgh’s wet weather
sewageproblems is a complicated problem that is
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exacerbated by the fragmented nature of the collec-tion and
treatment system. While there is one treat-ment plant operated by
the Allegheny CountySanitary Authority (ALCOSAN) in the metro
area,there are 83 separate municipalities, each responsiblefor
maintaining their own collection system. Manypipes are in a state
of disrepair, and ALCOSAN esti-mates that repairing the system
using traditionalsewage infrastructure strategies will cost more
than$3 billion. This investment includes an expansionof the
wastewater treatment plant capacity over thenext 20 years from 225
million gallons per day (mgd)to 875 mgd to reduce CSOs. However,
565 mgdof this increased capacity would only provideprimary
treatment.41
Against this troubled environmental background,the private
sector and citizens’ groups in Pittsburghhave taken an active role
to design and implementgreen infrastructure projects. Several
demonstrationprojects have focused specifically on
stormwatercapture or treatment.
Pittsburgh’s Green Infrastructure CommitmentPittsburgh’s Phipps
Conservatory and BotanicalGardens is undergoing a major expansion
and, whencomplete, will boast over 15,000 square feet of green
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roofs.42 The conservatory will capture rainwater fromits glass
roofs and store it in a cistern to be used laterto regulate water
levels in ornamental ponds. Thefacility will feature a green roof
test garden and a30-by-100-foot rain garden in a low-lying site
nearthe impervious parking areas.43
The McGowan Institute for Regenerative Medicine,built on a
brownfield site, collects rainwater from theroof for gray water
needs and irrigation. The facilityreuses 57% of rainwater falling
on the site, retaining168,000 gallons of stormwater annually.44
As a LEEDTM Gold certified building, Pittsburgh’sDavid L.
Lawrence Center is the world’s first certi-fied green convention
center. Through stormwaterreclamation, the facility reduces its
potable wateruse by approximately 60%. It has an in-house
watertreatment plant to recycle black water and featuresa stainless
steel roof that reduces total suspendedsolids in stormwater
runoff.45 By capturing andreusing rainwater on-site, each of these
projectsdecreases the amount of stormwater that would haveotherwise
entered the combined sewer system.
Nine Mile Run and Frick Park. One of Pittsburgh’skey restoration
efforts is the $7.7 million projectcurrently under way at Nine Mile
Run, one of the
The green roof surrounding the executiveoffices on the Heinz 57
Center in Pittsburghnot only provides environmental benefits,but
also creates green space for outdoormeetings and employee enjoyment
14stories above the ground.PHOTO COURTESY OF ROOFSCAPES, INC.
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last remaining daylit streams in the city. 46 The streamflows
underground through several neighborhoodsand daylights in Frick
Park, a 455-acre natural andrecreation area. Before its confluence
with theMonongahela River, Nine Mile Run collects storm-water
runoff from a seven-mile watershed with 43%impervious surfaces.47 A
number of environmentalproblems contribute to the stream’s
impairment. Toaccommodate development, Nine Mile Run wasculverted
and no longer flows in its natural meander-ing pattern, inhibiting
its function as a wildlife habitat.In wet weather conditions,
stormwater dischargesincreased stream flow in Nine Mile Run,
erodingmuch of the stream bank. The altered hydrology inthe
watershed leaves little water in the stream duringdry weather
conditions, making it unable to supportaquatic life. The stream
also borders a 238-acremountain of slag; runoff from the slag
increased thenatural pH of the stream. As with most
Pittsburghwaterways, Nine Mile Run is also the conduit formany
combined sewer overflows.
The Army Corps of Engineers is undertaking themain portion of
the project to clean up Nine MileRun under authority of Section 206
of the WaterResources Development Act of 1996. The project is
alarge-scale effort that will include the construction ofwoody and
herbaceous wetlands to provide bothwildlife habitat and stormwater
filtration. Thestormwater management component of the projecttakes
advantage of Pittsburgh’s porous and perme-able soils to capture
recharge and attempts to preventpollutants in stormwater from
reaching the stream.In an effort to repair the stream and re-create
morenatural conditions, the new river design addsmeanders and pool
and riffle sequences, undoingchannelization. The project also fits
into the city ofPittsburgh’s larger Riverfront Development
Plan,which includes land conservation along streambanks to prevent
runoff and erosion and increasedset-asides for recreational trails
along Nine MileRun.48 The restoration effort will add an
estimated100 acres to Frick Park.
The restoration would not be as effective withoutcorresponding
attempts to reduce sources of wet
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weather pollution to Nine Mile Run. The municipalcontribution to
the project, $2.7 million, is designatedto repair sewer lines,
preventing leakages due to old,failing pipes. The city has also
partnered with a devel-oper to transform the slag heap, a
brownfield site, into a710-home residential development. Aiding in
this effortare groups like 3 Rivers Wet Weather
DemonstrationProgram and the Nine Mile Run Watershed Associa-tion.
The community groups commissioned an engin-eering study to
determine where rain barrels would bemost effective in reducing the
stormwater runoff thatcontributes to CSOs. The organizations
installed 500large rain barrels (132 gallons each) in critical
neighbor-hoods.49 The groups focused on the educational com-ponent
of the project to make homeowners aware oflot-level solutions to
stormwater management.
For Additional InformationNine Mile Run Watershed
Association:http://www.ninemilerun.org/
Portland, OregonMaking green infrastructure a policy
priorityPopulation: 539,000Type of green infrastructure used: green
roofs; raingardens, vegetated swales, and landscape; down-spout
disconnection/rainwater collectionProgram elements: used for direct
CSO control;established municipal programs and public funding
Portland has actively promoted funding and edu-cation for
innovative stormwater management since1998 and boasts numerous
green applications through-out the city. These projects feature
many types of greeninfrastructure technologies, including
bioswales, greenroofs, infiltration planters, and sustainable
streetdesign. The city has been at the leading edge of thegreen
infrastructure movement and is beginning toaccumulate significant
data on the effectiveness ofdecentralized stormwater management
technologies.
As with many cities, part of the motivation toachieve more
successful stormwater strategies comesfrom a history of pollution
and a desire to repairnearby ecosystems. One of Portland’s
primary
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ecological concerns is the Willamette River, whichin the course
of its flow takes with it a considerablevolume of combined sewer
overflow. In 2004,Portland experienced 50 overflow events
anddischarged 2.8 billion gallons of combined overflowinto local
waterways.50 In some areas, undersizecombined sewers cause basement
sewer backups,requiring homeowners to sanitize their basementsafter
sewage backs up into their homes. Stormwaterhas also transported
toxic pollution into area waterbodies. Portland Harbor, the
industrialized lowerportion of the Willamette, was designated an
EPAsuperfund site for contaminated sediments. Investi-gations into
the contribution of overland stormwaterflow and other sources of
this heavy-metal pollutionare under way.
Portland’s Dual Approach to Managing CSOsTo alleviate these
pressing CSO managementproblems, Portland has pursued a dual
approach,expanding its public infrastructure and pursuing lot-level
strategies to manage stormwater.51 The “BigPipe” is Portland’s
primary combined sewage controlsolution, adding capacity to the
overloaded sewersystem. In recent years, the city has made
consider-able progress toward reducing overflows. The
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constructed capacity, along with other projects, hasvirtually
eliminated CSOs to the Columbia Slough,which discharges into the
Willamette River, and haseliminated or controlled eight Willamette
River CSOoutfalls. When the projects are completed in 2011,CSOs to
the Willamette will be reduced by 94%.52
These strategies are