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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

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.

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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

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CONTENTS

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

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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

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

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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

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.

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.

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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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

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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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.

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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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.

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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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

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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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.

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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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

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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

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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

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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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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.

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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

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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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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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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.

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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

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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

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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.

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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

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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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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

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.

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

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