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Rooftops to Rivers

  1. 1. ROOFTOPS TO RIVERSGreen Strategies for Controlling Stormwaterand Combined Sewer OverflowsProject Design and DirectionNancy Stoner, Natural Resources Defense CouncilAuthorsChristopher Kloss, Low Impact Development CenterCrystal Calarusse, University of Maryland School of Public PolicyNatural Resources Defense CouncilJune 2006
  2. 2. 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 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.
  3. 3. CONTENTSPeer Reviewers ivExecutive Summary vChapter 1: Introduction 1Chapter 2: The Growing Problem of Urban Stormwater 2Chapter 3: Controlling Stormwater in Urban Environments 6Chapter 4: Economic Benefits of Green Solutions 11Chapter 5: Policy Recommendations for Local Decision Makers 13Chapter 6: Conclusion 16Chapter 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. 37Appendix: Additional Online Resources 40Endnotes 43 iii
  4. 4. PEER REVIEWERSKatherine Baer Darla InglisAmerican Rivers Seattle Public UtilitiesTom Chapman Otto KauffmannMilwaukee Metropolitan Sewerage District City of VancouverMike Cox Jim MiddaughSeattle Public Utilities City of Portland Bureau of Environmental ServicesRobert Goo Steve ModdemeyerU.S. EPA Seattle Public UtilitiesBill Graffin Laurel O’SullivanMilwaukee Metropolitan Sewerage District Consultant to Natural Resources Defense CouncilJose Gutierrez Brad SewellCity of Los Angeles Environmental Affairs Natural Resources Defense CouncilDepartment Mike ShribergEmily Hauth Public Interest Research Group in MichiganCity of Portland Bureau of Environmental Services Heather WhitlowJonathan Helmus The Casey Trees Endowment FundCity of Vancouver David Yurkovich City of Vancouver iv
  5. 5. EXECUTIVE SUMMARYA s an environmental strategy, green infrastructure addresses the root cause of stormwater andcombined sewer overflow (CSO) pollution: the con- Each year, the rain and snow that falls on urban areas in the United States results in billions of gallons of stormwater runoff and CSOs. Reducing runoff withversion of rain and snow into runoff. This pollution green infrastructure decreases the amount of pollutionis responsible for health threats, beach closings, introduced into waterways and relieves the strain onswimming and fishing advisories, and habitat stormwater and wastewater infrastructure. Efforts indegradation. Water quality standards are unlikely many cities have shown that green infrastructure canto be met without effectively managing stormwater be used to reduce the amount of stormwater dischargedand CSO discharges. Green infrastructure—trees, or entering combined sewer systems and that it canvegetation, wetlands, and open space preserved or be cost-competitive with conventional stormwatercreated in developed and urban areas—is a strategy and CSO controls. Additional environmental benefitsfor stopping this water pollution at its source. include improved air quality, mitigation of the urban The urban landscape, with its large areas of heat island effect, and better urban aesthetics.impermeable roadways and buildings—known as Green infrastructure is also unique because it offersimpervious surfaces—has significantly altered the an alternative land development approach. New devel-movement of water through the environment. Over opments that use green infrastructure often cost less100 million acres of land have been developed in to build because of decreased site development andthe United States, and with development and sprawl conventional infrastructure costs, and such develop-increasing at a rate faster than population growth, ments are often more attractive to buyers because ofurbanization’s negative impact on water quality is environmental amenities. The flexible and decentral-a problem that won’t be going away. To counteract ized qualities of green infrastructure also allow it tothe effects of urbanization, green infrastructure is be retrofitted into developed areas to provide storm-beginning to be used to intercept precipitation and water control on a site-specific basis. Green infra-allow it to infiltrate rather than being collected on structure can be integrated into redevelopment effortsand conveyed from impervious surfaces. ranging from a single lot to an entire citywide plan.Case Study Program Elements and Green Infrastructure Techniques PROGRAM ELEMENTS TYPE OF GREEN INFRASTRUCTURE USED Wetlands/ Established Rain Gardens/ Downspout Riparian Used for Municipal Vegetated Disconnection/ Protection/ Direct CSO Programs & Swales & Permeable Rainwater UrbanCity Control Public Funding Green Roofs Landscape Pavement Collection ForestsChicagoMilwaukeePittsburghPortlandRouge River WatershedSeattleTorontoVancouverWashington v
  6. 6. Natural Resources Defense Council Rooftops to RiversThe 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 Nonetheless, wider adoption of green infra- new development plans and preserve existingstructure still faces obstacles. Among these is the vegetation.economic investment that is required across the 2. Incorporate green infrastructure into long-termcountry for adequate stormwater and CSO control. control plans for managing combined sewer overflows.Although green infrastructure is in many casesless costly than traditional methods of stormwater Green techniques can be incorporated into plans forand sewer overflow control, some municipalities infrastructure repairs and upgrades.persist in investing only in existing conventional 3. Revise state and local stormwater regulations tocontrols rather than trying an alternative approach. encourage green design. A policy emphasis should beLocal decision makers and organizations must placed on reducing impervious surfaces, preservingtake the lead in promoting a cleaner, more vegetation, and providing water quality improvements.environmentally attractive method of reducingthe water pollution that reaches their communities. The case studies that begin on page 17 offerNRDC recommends a number of policy steps nine examples of successful communities thatlocal decision makers can take to promote the use have reaped environmental, aesthetic, and eco-of green infrastructure: nomic benefits from a number of green infrastruc- ture initiatives.1. Develop with green infrastructure and pollution The table on page v provides a summarymanagement in mind. Build green space into of information contained within the case studies. vi
  7. 7. CHAPTER 1INTRODUCTIONW ater pollution problems in the United States have 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 sewer The green roof at Ford Motor Company’s Premier Automotivesystems through which contaminated stormwater North American Headquarters in Irvine, CA, was designed to visually mimic the natural landscape. PHOTO COURTESY OF ROOFSCAPES, INC.flows directly into waterways through undergroundpipes, causing streambank scouring and erosion anddumping pet waste, road runoff, pesticides, fertilizer, local levels, but fresh thinking is needed also. Someand other pollutants directly into waterways. In U.S. cities are already taking steps to successfullyolder cities, particularly in the Northeast and Great build green infrastructure into their communities.Lakes regions, stormwater flows into the same pipes Emerging green infrastructure techniquesas sewage and causes these combined pipes to over- present a new pollution-control philosophy basedflow—dumping untreated human, commercial, and on the known benefits of natural systems thatindustrial waste into waterways. Stormwater pollu- provide multimedia pollution reduction and usetion has been problematic to some extent for as long soil and vegetation to trap, filter, and infiltrateas there have been cities, but the volume of storm- stormwater. The cities already using green infra-water continues to grow as development replaces structure are finding that it is a viable alternativeporous surfaces with impervious blacktop, rooftop, to conventional stormwater management. Althoughand concrete. used widely overseas, particularly in Germany Contaminated stormwater and raw sewage and Japan, the use of green infrastructure in thedischarges from combined sewer overflows (CSOs) United States is still in its infancy; however, dataare required to be controlled under the Clean Water indicate that it can effectively reduce stormwaterAct, but progress is slow because the problems are runoff and remove stormwater pollutants, andlarge and multi-faceted and because the solutions cities that have implemented green design areare often expensive. A substantial influx of addi- already reaping the benefits (see the case studiestional resources is needed at the federal, state, and on page 17). 1
  8. 8. CHAPTER 2THE GROWING PROBLEMOF URBAN STORMWATERD evelopment as we have come to know it in the United States—large metropolitan centers sur-rounded by sprawling suburban regions—has con- landscape with impervious surfaces has significant environmental impacts. The level of imperviousness in a watershed has been shown to be directly relatedtributed greatly to the pollution of the nation’s waters. to the health of its rivers, lakes, and estuaries.As previously undeveloped land is paved over and Research indicates that water quality in receivingbuilt upon, the amount of stormwater running off roofs, water bodies is degraded when watershed impervi-streets, and other impervious surfaces into nearby ousness levels are at or above 10% and that aquaticwaterways increases. The increased volume of storm- species can be harmed at even lower levels.3water runoff and the pollutants carried within it Both the National Oceanic and Atmosphericcontinue to degrade the quality of local and regional Administration (NOAA) and Pennsylvania Statewater bodies. As development continues, nature’s University estimate that there are 25 million acres ofability to maintain a natural water balance is lost to impervious surfaces in the continental United States.4a changing landscape and new impervious surfaces. This quantity represents nearly one-quarter of the The trees, vegetation, and open space typical more than 107 million acres—almost 8% of non-of undeveloped land capture rain and snowmelt, federal land in the contiguous United States—thatallowing it to largely infiltrate where it falls. Under had been developed by 2002.5 In urban areas, it is notnatural conditions, the amount of rain that is uncommon for impervious surfaces to account forconverted to runoff is less than 10% of the rainfall 45% or more of the land cover.volume.1,2 Replacing natural vegetation and This combination of developed land and impervi- ous surfaces presents the primary challenge of storm-TABLE 1: Effects of Imperviousness on Local Water water mitigation. Existing stormwater and wastewaterBodiesa,b,c infrastructure is unable to manage stormwater in Watershed a manner adequate to protect and improve waterImpervious Level Effect quality. Standard infrastructure and controls fail to 10% • Degraded water quality reduce the amount of stormwater runoff from urban 25% • Inadequate fish and insect habitat environments or effectively remove pollutants. • Shoreline and stream channel erosion 35%–50% • Runoff equals 30% of rainfall volume >75% • Runoff equals 55% of rainfall volumea Environmental Science and Technology, Is Smart Growth Better for Water THE DEFICIENCIES OF CURRENT URBAN Quality?, August 25, 2004, STORMWATER INFRASTRUCTURE estjag-w/2004/policy/jp_smartgrowth.html (accessed December 6, 2004).b U.S. EPA, Protecting Water Quality from Urban Runoff, Nonpoint Source Stormwater management in urban areas primarily Control Branch, EPA 841-F-03-003, February 2003. consists of efficiently collecting and conveyingc Prince George’s County, Maryland Department of Environmental Resources, Low-Impact Development Design Strategies, January 2000. stormwater. Two systems are currently used: separate 2
  9. 9. Natural Resources Defense Council Rooftops to RiversBioswales on Portland’s Division Streetinfiltrate and treat stormwater runoff.PHOTO COURTESY OF THE PORTLAND BUREAU OF ENVIRONMENTALSERVICESstormwater sewer systems and combined sewer pollution from combined sewer systems tends to besystems. Separate stormwater sewer systems collect a more regional problem concentrated in the olderonly stormwater and transmit it with little or no treat- urban sections of the Northeast, the Great Lakesment to a receiving stream, where stormwater andits pollutants are released into the water. Combined TABLE 2: Urban Stormwater Pollutantssewer systems collect stormwater in the same setof pipes that are used to collect sewage, sending the Pollutant Sourcemixture to a municipal wastewater treatment plant. Bacteria Pet waste, wastewater collection systems Metals Automobiles, roof shingles Nutrients Lawns, gardens, atmospheric depositionSeparate Stormwater Sewer Systems Oil and grease AutomobilesThe large quantities of stormwater that wash across Oxygen-depleting Organic matter, trashurban surfaces and discharge from separate storm- substanceswater sewer systems contain a mix of pollutants, Pesticides Lawns, gardensshown in Table 2, deposited from a number of Sediment Construction sites, roadwayssources.6,7 Stormwater pollution from separate Toxic chemicals Automobiles, industrial facilitiessystems affects all types of water bodies in the Trash and debris Multiple sourcescountry and continues to pose a largely unaddressedthreat. In 2002, 21% of all swimming beach advisories TABLE 3: Urban Stormwater’s Impact on Water Qualityand closings were attributed to stormwater runoff.8Table 3 shows the percentage of assessed (monitored) Water Body Type Stormwater’s Rank % of Impaired as Pollution Source Waters Affectedwaters in the United States for which stormwater has Ocean shoreline 1st 55% (miles)been identified as a significant source of pollution.9 Estuaries 2nd 32% (sq. miles) Great Lakes 2nd 4% (miles)Combined Sewer Systems shorelineWhile pollution from separate sewer systems is a Lakes 3rd 18% (acres) Rivers 4th 13% (miles)problem affecting a large majority of the country, 3
  10. 10. Natural Resources Defense Council Rooftops to RiversTABLE 4: Pollutants in CSO DischargesaPollutant Median CSO Concentration Treated Wastewater ConcentrationPathogenic bacteria, viruses, parasites• Fecal coliform (indicator bacteria) 215,000 colonies/100 mL < 200 colonies/100mLOxygen depleting substances (BOD5) 43 mg/L 30 mg/LSuspended solids 127 mg/L 30 mg/LToxics• 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/LNutrients• Total Phosphorus 0.7 mg/L 1.7 mg/L• Total Kjeldahl Nitrogen 3.6 mg/L 4 mg/LTrash and debris Varies Nonea U.S. EPA, Report to Congress: Impacts and Control of CSOs and SSOs, Office of Water, EPA-833-R-04-001, August 2004.region, and the Pacific Northwest. Combined sewers, Because CSOs discharge a mix of stormwater andinstalled before the mid-twentieth century and prior sewage, they are a significant environmental andto the use of municipal wastewater treatment, are health concern. CSOs contain both expected storm-present in 746 municipalities in 31 states and the water pollutants and pollutants typical of untreatedDistrict of Columbia.10 They were originally used as sewage, like bacteria, viruses, nutrients, and oxygen-a cost-effective method of transporting sewage and depleting substances. CSOs pose a direct healthstormwater away from cities and delivering them to threat in the areas surrounding the CSO dischargereceiving streams. As municipal wastewater treat- location because of the potential exposure to bacteriament plants were installed to treat sewage and protect and viruses. Estimates indicate that CSO dischargeswater quality, the limited capacity of combined sewers are typically composed of 15–20% sewage andduring wet weather events became apparent.11 80–85% stormwater.13,14 An estimated 850 billion During dry periods or small wet weather events, gallons of untreated sewage and stormwater arecombined sewer systems carry untreated sewage discharged nationally each year as combined sewerand stormwater to a municipal wastewater treatment overflows.15 Table 4 shows the concentration ofplant where the combination is treated prior to being pollutants in CSO discharges.discharged. Larger wet weather events overwhelm acombined sewer system by introducing more storm-water than the collection system or wastewater POPULATION GROWTH AND NEW DEVELOPMENTtreatment plant is able to handle. In these situations, CREATE MORE IMPERVIOUS SURFACESrather than backing up sewage and stormwater into Current levels of development and imperviousnessbasements and onto streets, the system is designed to are a major, and largely unabated, source of waterdischarge untreated sewage and stormwater directly pollution. Projections of population growth and newto nearby water bodies through a system of com- development indicate that this problem will get worsebined sewer overflows (CSOs). In certain instances, over time and that mitigation efforts will become moredespite the presence of sewer overflow points, base- costly and difficult. Although the nation has collectivelyment and street overflows still occur. Even small failed to adequately address the current levels ofamounts of rainfall can trigger a CSO event; Wash- stormwater runoff and pollution, we have also failedington D.C.’s combined sewer system can overflow to implement emerging strategies that would minimizewith as little as 0.2 inch of rainfall.12 further pollution increases. Absent the use of state-of- 4
  11. 11. Natural Resources Defense Council Rooftops to Riversthe-art stormwater controls, each new acre of land footage of buildings—200 billion square feet—willdeveloped and each new parcel of impervious surface have been built after the year 2000.19will introduce new pollution into our waterways. Much of this population growth and new devel- Recent studies also indicate that stormwater opment will occur in coastal regions, a particularpollution may soon start to increase at a higher concern because urban stormwater runoff is alreadyrate than in the past. Over the past two decades, the largest source of ocean shoreline water pollution.the rate of land development has been two times Although coastal counties comprise only 17% ofgreater than the rate of population growth. Between the total acreage of the contiguous United States1982 and 1997, while the U.S. population grew 15%, they are home to more than 50% of the U.S. popu-the amount of developed land in the continental lation. Because of high population concentrationsUnited States grew 34%, an increase of 25 million on limited land areas, coastal counties contain aacres.16,17 The 25 million acres developed during higher percentage of development than interiorthis 15-year period represent nearly 25% of the total counties. In 1997, 27 million acres of coastal countiesamount of developed land in the contiguous states. had been developed, accounting for nearly 14% ofThis rapid development pattern is alarming not only the total land area. By contrast, 71 million acres,because of the conversion of a large and growing about 4% of the total land area of interior counties,percentage of the remaining undeveloped land, but had been developed.20 Based on these trends,also because of the increase in stormwater runoff that increased population and development in theseaccompanies development. coastal environments is likely to not only lead to If the relationship between land development and greater amounts of impervious surfaces in coastalpopulation growth continues, a significant amount of watersheds, but also higher percentages of impervi-land will be developed in the coming decades. The ousness. Conventional methods of stormwateranticipated 22% growth in U.S. population from 2000 control will not be able to adequately manage theto 2025 will add an additional 68 million acres of higher amount of stormwater pollution implied bydevelopment.18 By 2030, half of the total square this increased imperviousness. 5
  12. 12. CHAPTER 3CONTROLLING STORMWATERIN URBAN ENVIRONMENTST he foremost challenge of reducing stormwater pollution and CSO discharges is finding aneffective method of reducing the amount of storm- water quality. Municipalities that develop programs to actually reduce stormwater pollution are moti- vated to do so because of their proximity to uniquewater created in urban environments. Methods or valued water bodies or because of a need tocurrently used to manage stormwater largely fail to protect drinking water supplies. Some of the moreaddress the underlying problem of imperviousness. aggressive and innovative stormwater programs are Stormwater collected in separate systems typically located around sensitive or important water bodiesis not treated before being discharged. In instances like the Chesapeake Bay, the Great Lakes, or Pugetwhere treatment is provided, it usually consists of Sound. Federal regulations require states to identifyfiltration to remove suspended solids, debris, and quality-limited waterways and determine thefloatables. Because dissolved materials and nutrients reduction in the Total Maximum Daily Load (TMDL)are difficult to treat in urban stormwater and little of those pollutants necessary to meet water qualityhas been done to abate the scouring, erosion, and standards, but these pollutant load-reductionother physical impacts of stormwater discharges, requirements are not often translated into effectivetreatment efforts have been largely ineffective at stormwater management programs.2diminishing stormwater-related water pollution. Municipalities are required to implement short- Most municipal stormwater discharges are regu- term and long-term strategies to reduce overflowslated as point sources under the Clean Water Act from combined sewer systems, but significant(CWA) and require a National Pollutant Discharge numbers of overflows continue to occur. The CWAElimination System (NPDES) permit. However, end- prohibits the dry weather discharge of untreatedof-pipe treatment and control typical of other per- sewage and requires wet weather CSO dischargesmitted point-source discharges are often impractical for to be limited and to control discharges of solidsurban stormwater, because of the large volumes of and floatables. Federal regulations also require thatstormwater; generated and space constraints in urban municipalities develop long-term CSO control plansareas. Permits for urban stormwater require munici- that detail procedures and infrastructure modifica-palities to develop a stormwater management plan tions necessary to minimize wet weather overflowsand to implement best management practices.1 These and meet water quality standards.3 The long-termmanagement measures are typically used in lieu of control plans focus primarily on managing storm-specific pollutant removal requirements. “Performance- water impacts on combined sewer systems.based” standards are generally not required, and mini- Mitigating CSOs is costly. The 2000 Clean Water-mum control measures are sufficient for compliance. sheds Needs Survey (CWNS) estimated that $56 bil- As a result, compliance with urban stormwater lion (2005 dollars) in capital investment was neededpermits does not necessarily result in improved for CSO control.4 Separating combined sewer lines 6
  13. 13. Natural Resources Defense Council Rooftops to Riversand building deep storage tunnels are the two cur- imperviousness). Capturing, retaining, and tryingrently preferred methods of CSO control. The costs to improve the quality of vast quantities of urbanfor separating combined sewers, disconnecting storm- stormwater runoff is often more difficult andwater inlets from the combined sewer system, and expensive than reducing the amount of stormwaterdirecting them to a newly installed separate storm generated from the outset through strategies tosewer system range from $500 to $600 per foot of sewer reduce imperviousness and maximize infiltrationseparated, or $2.6 million to $3.2 million for each mile and filtration. On a municipal level, costs can beof combined sewer to be separated.5 While sewer sep- decreased when these techniques are incorporatedaration will eliminate CSO discharges and the release into redevelopment and ongoing infrastructureof untreated sewage, the trade-off is an increase in replacement efforts. Comprehensive stormwaterthe volume of untreated stormwater discharges. management programs can be used to minimize the Deep storage systems are large underground effect of impervious surfaces and manage precipi-tunnels with millions of gallons of storage capacity tation and stormwater with the use of naturalthat are built to hold the excess surge of combined processes. These “green” approaches are often lesssewer stormwater during wet weather events. These expensive and more effective than current storm-systems eventually direct the detained wastewater water and CSO the municipal treatment plant as combined sewerflow rates subside. If sized, constructed, and oper-ated properly, deep tunnels can significantly reduce GREEN ALTERNATIVESCSO discharges. However, deep tunnels take many Newer, flexible, and more effective urban storm-years to build and are very costly. Several cities have water and CSO strategies are being adopted inbegun or plan to begin deep tunnel projects costing North America. Cities are beginning to introducehundreds of millions or billions of dollars, as out- green infrastructure as a component of compre-lined in Table 5. hensive stormwater management plans aimed at Current stormwater management for separate reducing stormwater runoff, CSOs or both. Thisand combined sewer systems is ineffective because it approach is significant in that it can be used tofocuses on the symptoms (large stormwater volumes) address the stormwater problem “at the source”rather than the problem (development patterns and through efforts aimed at restoring some of theTABLE 5: Examples of Deep Storage Tunnel ProjectsCity Project Duration Completion Date Storage Capacity CostChicago, ILa,b 40+ years 2019 18 billion gallons $3.4 billionMilwaukee, WIc,d 17 years (Phase 1) 1994 405 million gallons $2.3 billion 8 years (Phase 2) 2005 88 million gallons $130 millionPortland, ORe 20 years 2011 123 million gallons $1.4 billionWashington, 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, (accessed February 16, 2005).b Metropolitan Water Reclamation District of Greater Chicago, Combined Sewer Overflow Public Notification Plan, (accessed December 15, 2005).c Milwaukee Metropolitan Sewerage District, Collection System: Deep Tunnel System, (accessed November 11, 2004).d Milwaukee Metropolitan Sewerage District, Overflow Reduction Plan, (accessed November 11, 2004).e Portland Bureau of Environmental Services, Working for Clean Rivers, (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. 7
  14. 14. Natural Resources Defense Council Rooftops to RiversStreet planters in Portland, OR, are used inhighly developed urban areas to introducegreen space and manage stormwater runoff.PHOTO COURTESY OF THE PORTLAND BUREAU OF ENVIRONMENTALSERVICESnatural hydrologic function of areas that have been system is able to infiltrate and retain a rainfallurbanized. Green infrastructure can also be used to volume greater than the 10-year storm withoutlimit development in sensitive headwaters regions discharging to the municipal storm sewer system.and groundwater recharge areas to avoid the seg- Green infrastructure can be used to restore vegeta-mentation and isolation of natural environmental tion and green space in highly impervious city areas.areas and resources. Planting street trees and other urban forestry initiatives Green infrastructure can be applied in many can reduce stormwater runoff because urban treeforms. It traditionally has been thought of as the canopies intercept rainfall before it hits the pavementinterconnected network of waterways, wetlands, and is converted to stormwater. Trees with maturewoodlands, wildlife habitats, and other natural canopies can absorb the first half-inch of rainfall.7areas that maintain natural ecological processes.6 Recently the concept of green infrastructure hasIn practice, installing green infrastructure means been broadened to include decentralized, engineeredpreserving, creating, or restoring vegetated areas stormwater controls. These green techniques areand natural corridors such as greenways, parks, con- designed to mimic the functions of the natural envi-servation easements, and riparian buffers. When ronment and are installed to offset the impacts oflinked together through an urban environment, urbanization and imperviousness. Green manage-these lands provide rain management benefits simi- ment techniques are used to minimize, capture, andlar to natural undeveloped systems, thereby reducing treat stormwater at the location at which it is createdthe volume of stormwater runoff. With green infra- and before it has the opportunity to reach the col-structure, stormwater management is accomplished lection system. Engineered systems commonly usedby letting the environment manage water naturally: in urban areas include green roofs, rain gardens, raincapturing and retaining rainfall, infiltrating runoff, barrels and cisterns, vegetated swales, pocket wet-and trapping and absorbing pollutants. For example, lands, and permeable pavements.the Village Homes community in Davis, California, Most green stormwater controls actually consistuses a system of vegetated swales and meandering of green growth, including vegetated systems likestreams to manage stormwater. The natural drainage green roofs and rain gardens, but other “green” 8
  15. 15. Natural Resources Defense Council Rooftops to RiversUrban trees intercept rainfall before it hits theground and is converted to stormwater runoff.PHOTO COURTESY OF THE LOW IMPACT DEVELOPMENT CENTERcontrols, like permeable pavements, are not vege- effective stormwater pollution control. This reducestated but designed to provide the water detention the amount of stormwater discharged from separateand retention capabilities of natural systems. Green stormwater sewer systems and aids combined sewerinfrastructure also encourages downspout discon- systems by decreasing the overall volume of waternection programs that redirect stormwater from entering the system, thus reducing the number andcollection systems to vegetated areas or that capture size of overflows. Another large benefit of greenand reuse stormwater, such as rain barrels. Down- infrastructure is that nearly every green techniquespout disconnection removes stormwater volume results in the removal of stormwater pollutants. Thefrom collection systems and allows green infra- natural processes employed by green infrastructurestructure components to manage the runoff. allow pollutants to be filtered or biologically or Green infrastructure offers numerous benefits when chemically degraded, which is especially advan-used to manage stormwater runoff. Many green tech- tageous for separate storm sewer systems that doniques reduce both stormwater volume and pollutant not provide additional treatment before dischargingconcentrations and, in contrast to conventional cen- stormwater. The combination of runoff reduction andtralized controls, provide flexibility in how and pollutant removal is an effective means of reducingwhere stormwater management is accomplished. The the total mass of pollution released to the environ-use of green infrastructure protects natural resources ment. Because of this, open areas and buffer zonesand lessens the environmental impacts of develop- are often designated around urban streams andment by not only addressing stormwater, but also by rivers to provide treatment and management ofimproving air quality and community aesthetics. overland flow before it reaches the waterway.1. Stormwater volume control and pollutant removal. 2. Decentralized, flexible, site-specific solution. GreenGreen infrastructure is effective for managing storm- infrastructure differs from other stormwater manage-water runoff because it is able to reduce the volume ment methods because it provides the opportunity toof stormwater and remove stormwater pollutants. manage and treat stormwater where it is generated.Reducing the amount of urban runoff is the most This decentralized approach allows green infrastructure 9
  16. 16. Natural Resources Defense Council Rooftops to Rivers aged and often inadequate infrastructure system by introducing new areas of imperviousness and addi- tional volumes of stormwater. Strategies will need to be adopted to manage urban growth and its impacts on water quality. The use of green infrastructure offers an alternative to existing development patterns and a new method of developing urban areas. Green infrastructure currently is being used to manage existing stormwater problems, but has the potential to significantly effect how future development contributes to stormwater and sewer overflow problems by preserving and incorporating green space into newly developed areas and by addressing the established connection between imperviousness and stormwater pollution. 4. Ancillary benefit. Green infrastructure is also attractive because it can be used to achieve multipleA RiverSafe RainBarrel installed at the Jane Holmes nursing environmental goals. Funds spent on conventionalresidence in Pittsburgh, PA, by the Nine Mile Run RainBarrel stormwater management are used only for waterInitiative. PHOTO COURTESY OF RIVERSIDES infrastructure. In addition to stormwater manage- ment benefits, green infrastructure improves airtechniques to be installed at numerous locations quality by filtering air pollution and helps to counter-throughout the city. Green infrastructure is flexible, act urban heat island effect by lowering surfaceallowing it to be applied in a wide range of locations temperatures. For example, many of the green infra-and circumstances, and can be tailored to newly structure projects in Chicago, while also providingdeveloped land or retrofitted to existing developed stormwater management, were initially installed toareas. This enables green infrastructure to be used mitigate urban temperature increases and improveon individual sites or in individual neighborhoods energy efficiency. Green infrastructure also improvesto address localized stormwater or CSO problems, urban aesthetics, has been shown to increase prop-or incorporated into a more widespread municipal erty values, and provides wildlife habitat and recrea-stormwater management program. tional space for urban residents. This multi-benefit environmental approach ultimately provides control3. Green design and the development problem. Projected programs that are more diverse and cost-effectivepopulation growth and development will strain an than projects aimed solely at stormwater control. 10
  17. 17. CHAPTER 4ECONOMIC BENEFITSOF GREEN SOLUTIONST he cost of stormwater control is a major factor in 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 from The Nine Mile Run RainBarrel Initiative used 500 RainBarrelsthe destruction of free, natural stormwater treatment to achieve CSO reduction for the ALCOSAN treatment plant in Pittsburgh. PHOTO COURTESY OF RIVERSIDESsystems—trees, meadows, wetlands, and other formsof soil and vegetation. For example, researchers atthe University of California at Davis have estimated developed world, protecting and enhancing thosethat for every 1,000 deciduous trees in California’s areas that have not yet been developed is often theCentral Valley, stormwater runoff is reduced nearly cheapest, most effective way to keep contaminated1 million gallons—a value of almost $7,000.4 Clearly, stormwater out of urban and suburban streams.preserving trees reduces polluted stormwater dis-charges and the need for engineered controls to replacethose lost functions. When those trees are cut down THE COSTS OF BUILDING GREEN IN NEWand their functions are lost, those costs are passed on DEVELOPMENTSto municipal governments, which then pass them on Green infrastructure in many instances is less costlyto their citizens. So, while the bulk of this report is than conventional stormwater management pro-about how to integrate green infrastructure into the grams or centralized CSO approaches and may 11
  18. 18. Natural Resources Defense Council Rooftops to Riversprovide an opportunity to decrease the economic TABLE 6: Cost of Conventional Urban Stormwater andburden of stormwater management. Studies in CSO ControlsaMaryland and Illinois show that new residential Cost to Managedevelopments using green infrastructure stormwater Control Cost Equationb 10 Million Gallonscontrols saved $3,500 to $4,500 per lot (quarter- to Surface storage C = 5.184V0.826 $35 millionhalf-acre lots) when compared to new developments Deep tunnels C= 7.103V0.795 $44 millionwith conventional stormwater controls.5,6 These Detention basins C = 62,728V0.69 $300,000developments were conceived and designed to Retention basins C = 69,572V0.75 $390,000reduce and manage stormwater runoff by preserving a James Heaney, et al., Costs of Urban Stormwater Control, National Risk Management Research Laboratory, Office of Research and Development,natural vegetation and landscaping, reducing overall EPA-600/R-02/021, January 2002. b Cost equations adjusted to 2005 dollars. Volume equals millions ofsite imperviousness, and installing green stormwater gallons. Cost for surface storage and deep tunnels is millions of dollars.controls. Cost savings for these developmentsresulted from less conventional stormwater infra-structure and paving and lower site preparation some instances, municipalities believe that the addi-costs. Importantly, in addition to lowering costs, tional benefits of green controls—including the crea-each of the sites discharges less stormwater than con- tion of more aesthetic city space and the significantventional developments. Adding to the cost savings, reduction in water pollution—justify the added cost.developments utilizing green infrastructure normally In addition, green infrastructure can be incrementallyyield more lots for sale by eliminating land-consuming introduced into urban environments, allowing theconventional stormwater controls, and lots in green costs to be incurred over a longer period of time.developments generally have a higher sale price The EPA has developed cost curves for conven-because of the premium that buyers place on tional urban stormwater controls relating stormwatervegetation and conservation development.7,8 storage capacity to control cost. The costs in Table 6 do not include any associated costs for construction and infrastructure. These costs represent the gener-OUTFITTING EXISTING DEVELOPMENTS WITH ally accepted costs of stormwater control and pro-GREEN INFRASTRUCTURE vide a baseline to which green infrastructure costsThe economics of retrofitting existing urban areas can be compared.with stormwater controls differ from new develop- In many instances, green infrastructure costsment. Urban stormwater retrofits can be expensive compare favorably with the costs of conventionaland complicated by space constraints, although this controls. However, cost comparisons for individual,is not always the case. Based upon the costs of their small-scale retrofit projects are not likely to favorpilot projects, city officials in Seattle and Vancouver green controls. In urban areas, green infrastructure(discussed in the case studies on pages 29 and 33), will be most cost-effective when it is incorporatedbelieve that the costs of future green infrastructure as part of an overall redevelopment effort or wheninstallations will be similar to or slightly more than large improvements to infrastructure are required.conventional stormwater controls.9,10 The analysis In these instances, the costs of green infrastructureconducted by the city of Vancouver indicates that are minimized relative to the scope and costs ofretrofitting green infrastructure into locations with the overall project. While green infrastructure mayexisting conventional stormwater controls will cost be more costly than conventional stormwater oronly marginally more than rehabilitating the conven- CSO controls in certain instances, the added coststional system, but introducing green infrastructure should be weighed against the enhanced stormwaterinto new development will cost less.11 However, control and other environmental benefits gainedwhile green infrastructure may be more expensive in from their use. 12
  19. 19. CHAPTER 5POLICY RECOMMENDATIONSFOR LOCAL DECISION MAKERSA lthough green infrastructure has been shown to reduce stormwater runoff and combined seweroverflows and improve water quality, its adoption integrated into such plans. Rather than relying solely on conventional, centralized storage projects to reduce CSO volumes, municipalities shouldacross the country has been slow. Cities that have considering using green techniques, which can beincorporated green infrastructure into their storm- integrated into redevelopment projects andwater management programs have often done so infrastructure repairs and upgrades. Each yearbecause of direct efforts to encourage alternative Portland, Oregon’s downspout disconnectionstormwater approaches. The following recommenda- program diverts 1 billion gallons of stormwater fromtions can be used to encourage the use of green the collection system and has been used to helpinfrastructure in municipalities. alleviate localized combined sewer system backups in city neighborhoods.41. Get development right the first time. Reducing orpreventing stormwater runoff is the most effective 3. Revise state and local stormwater regulations toway to minimize pollution because it prevents encourage green design. Most state and localpollutants from being transported to water bodies. stormwater regulations focus on peak flow rateIncorporating green infrastructure into the earliest control. To encourage more effective stormwaterstages of community development can negate or management, these regulations should be revised tolimit the need for larger-scale, more expensive require minimizing and reducing imperviousstormwater controls. Minimizing imperviousness, surfaces, protecting existing vegetation, maintainingpreserving existing vegetation, and incorporating predevelopment runoff volume and infiltrationgreen space into designs all decrease the impact that rates, and providing water quality improvements.urbanization has on water quality. Used in this way, These requirements encourage green infrastructuregreen infrastructure design is a more cost-effective because it can meet each of these objectives. Portland,strategy, often costing less to develop per lot while Oregon, requires on-site stormwater managementyielding more lots at an increased sale price.1,2 for new development and redevelopment in both CSO and separate sewer areas of the city and2. Incorporate green infrastructure into long-term encourages use of green infrastructure to complycontrol plans for managing combined sewer overflows. with the regulation (more details about Portland’sCities with combined sewer systems are required to development regulations can be found in the casedevelop long-term plans to reduce sewer overflows study on page 24).enough to meet water quality standards.3 Green New Jersey’s stormwater management standardsinfrastructure has proven to be valuable in reducing require 300-foot riparian buffers and stipulate ainflows into combined sewer systems and should be preference for nonstructural best management 13
  20. 20. Natural Resources Defense Council Rooftops to RiversThe vegetated infiltration basins in theBuckman Heights Apartments courtyardin Portland, OR, receive and infiltratestormwater from building roofs andsidewalks.PHOTO COURTESY OF PORTLAND BUREAU OF ENVIRONMENTALSERVICESpractices (BMPs). These standards also institute To date, the U.S. federal government has declinedwater quantity as well as quality regulations. The to set performance standards for stormwater dis-water quantity standards require no change in charges from development or to add specifics to thegroundwater recharge volume following construc- “maximum extent practicable” standard set by thetion and that infiltration be used to maintain pre- Clean Water Act for discharges from municipalities.7development runoff volumes and peak flow rates. Since the federal government has failed to showAny increase in runoff volume must be offset by a leadership in this area, state and local entities mustdecrease in post-construction peak flow rate. Water do so.quality standards require a reduction in stormwaternutrient loads to the “maximum extent feasible” 4. Establish dedicated funding for stormwaterand total suspended solids (TSS) reductions of 80%. management that rewards green design. AdequateIf the receiving water body is a high-quality water funding is critical for successful stormwateror tributary, the required TSS reduction is 95%.5 management programs. The billions of dollars Berlin, Germany, has incorporated the Green Area necessary to mitigate stormwater pollution andFactor (GAF) into its regulations. Based on land use combined sewer overflows require federal fundingand zoning, the GAF sets a greening target for each to augment state and municipal funding. Toproperty that provides the required ratio of vegetated encourage its use, dedicated stormwater fundingelements to impervious surface. Once property sources could identify a preference for green infra-owners apply for a building permit, they are required structure or establish a funding scale based uponto satisfy the green target goal. Property owners the relative use of green management green infrastructure practices from an approved Many jurisdictions are creating stormwater utili-list and determine compliance by calculating the ties similar in function to water and wastewater utili-proportion of the property dedicated to the greening ties. Stormwater utilities allow for the assessmenttarget. Selected green infrastructure practices are and collection of a user fee dedicated to a stormwaterweighted according to their effectiveness at meeting management program. Other jurisdictions dedicateenvironmental goals.6 a certain portion of collected local tax revenue to a 14
  21. 21. Natural Resources Defense Council Rooftops to Riversstormwater fund. Establishing a dedicated fund opportunity or incentive to use green infrastructure.removes stormwater management from general Jurisdictions should review their applicable storm-revenue funding, which is subject to variable funding water and wastewater ordinances and revise themand competes with other general taxation programs to remove barriers to green infrastructure use andfor money. Stormwater utilities, where allowed by encourage more environmentally friendly regulations.15enabling legislation, are popular because of theability to determine a user rate structure and as a 7. Preserve existing trees, open space, and streamcomplement to incentive programs.8,9 buffers. Too often, development removes nearly all existing natural features. Simply preserving trees,5. Provide incentives for residential and commercial open space, and stream buffers and incorporatinguse of green infrastructure. Various incentives are them into the community will help maintain wateralready in place to encourage green infrastructure quality and manage stormwater runoff while lessen-use in a number of cities. For example, Portland, ing the need for additional stormwater controls.Oregon, allows additional building square footage For example, New Jersey’s stormwater managementfor buildings with green roofs, and Chicago provides standards require 300-foot riparian buffers fora density bonus option for buildings with vegetative new developments and redevelopments to protectcover on the roof.10,11 The city of Chicago also pro- water quality.16vided 20 $5,000 grants to install small-scale com-mercial or residential green roofs in early 2006.12 Also 8. Encourage and use smart growth. Smart growth canbeginning in 2006, Portland will provide up to a 35% be used to limit sprawl and reduce the introductiondiscount in its stormwater utility fee for properties of impervious surfaces. Smart growth policies canwith on-site stormwater management.13 Maryland identify and protect sensitive environmental areasprovides credits for using green infrastructure when and direct development to locations with adequatedetermining compliance with its stormwater regu- infrastructure. By limiting sprawl and discouraginglatory requirements. Six different credits, all related development in sensitive areas, smart growth mayto green infrastructure design, are available.14 Several increase population densities and imperviousness incities fund or subsidize downspout disconnection previously urbanized areas. Smart growth strategiesprograms; Portland’s program pays homeowners should be coupled with green infrastructure to limit$53 per downspout disconnected or the city will the stormwater and infrastructure effects of a poten-disconnect the downspouts for free. tial increase in urbanization.6. Review and revise local development ordinances. 9. Get the community involved. Green infrastructureLocal zoning requirements and building codes often presents an opportunity for community outreach andinadvertently discourage the use of green infra- education. Downspout disconnections, rain barrels,structure. Provisions requiring downspouts to be rain gardens, and green roofs may individuallyconnected to the stormwater collection system manage a relatively small volume of stormwater butprohibit disconnection programs and the use of green collectively can have a significant impact. Portland’sspace for treatment of rooftop runoff. Mandatory downspout disconnection program, for example,street widths and building setbacks can unnecessarily now diverts 1 billion gallons of stormwater awayincrease imperviousness. Stormwater treatment from the combined sewer system each year. Greenrequirements that favor centralized collection and infrastructure can be introduced into a communitytreatment and prescribe treatment options offer little one lot at a time. 15
  22. 22. CHAPTER 6CONCLUSIONW hile development, imperviousness, and urban- ization have all taken their toll on downstreamwaterways, current stormwater and combined sewer of environmental commitments, including a consent decree to limit CSO discharges, Safe Drinking Water Act standards influencing the quality of infil-overflow (CSO) mitigation efforts have failed to trated stormwater, and emerging TMDL load andadequately address the problem or improve water waste load allocations.1 Other cities with combinedquality because they are focused on end-of-pipe sewer systems, or those that discharge stormwatersolutions. Current levels of development and to sensitive receiving waters, face similar require-imperviousness have degraded the nation’s water ments. Such regulations only increase the oppor-quality, and future population growth and develop- tunities for creativity and willingness on the partment will only exacerbate the problem. Additional of municipal decision makers to actively promotedevelopment will make stormwater and CSO control and introduce green infrastructure. City leaderssolutions even more difficult and costly. are finding that when faced with the simultaneous Green infrastructure offers the opportunity to not challenges of regulatory requirements, infrastructureonly develop new areas in a more environmentally limitations, and financial constraints, green infra-efficient manner, but also to rehabilitate existing devel- structure often emerges as an appropriate meansoped areas. Urbanization and development alter how of satisfying each.water is distributed throughout the environment. Much Another commonality among cities that havegreater volumes of stormwater are generated and dis- incorporated green infrastructure into theircharged to receiving water bodies in developed areas stormwater and CSO control plans is a commitmentthan would be in the natural environment. Green from city personnel. Whether elected officials orinfrastructure is providing measurable water quality professional staff, these city leaders have recognizedimprovements, most notably in stormwater volume the benefits of green infrastructure and havereduction and CSO mitigation. successfully communicated its value to the public. Some jurisdictions and cities have chosen green These cities have also been innovative with theirinfrastructure as a preferable method of stormwater regulations and environmental policies, looking foror CSO control based upon the specific needs and existing and alternative avenues to encouragegoals of the municipality. Others have installed green adoption of new stormwater and CSO controlinfrastructure to experiment with innovative storm- strategies. These efforts are often popular because ofwater or combined sewer overflow pilot projects. But the public’s positive response to the “greenscaping”all of these efforts demonstrate how it can be success- that has accompanied the programs. As many localfully integrated into urban communities. decision makers have already found, using green A common driver among the cities using green infrastructure in place of or in combination with lessinfrastructure is compliance with regulatory require- effective conventional methods of handlingments. The catalyst for Portland, Oregon’s active stormwater runoff can have benefits beyond justprogram, for example, is a need to satisfy a number economic cost savings and reduced pollution. 16
  23. 23. CHICAGOCHAPTER 7CASE STUDIEST he following nine case studies illustrate efforts in North America to incorporate green infrastructureinto urban stormwater and combined sewer overflow stormwater runoff but also to address other environmental issues, such as mitigating urban heat island effects and improving energy efficiency(CSO) control strategies, but this is not an exhaustive in buildings.list. Several factors were used to select case-study cities.Among them were extent and duration of program Stormwater Collection Through Expansion of theefforts, availability of information and quantifiable Combined Sewer Systemdata, geographic location, and the number and type While the city’s past environmental infrastructureof green infrastructure elements practiced. projects have had dubious goals, the water quality of Lake Michigan, the city’s drinking water source, has long been a concern. In the early 1900s, sewageChicago, Illinois and stockyard pollution from the Chicago RiverProgressive environmental change through creative prompted Chicago officials to reverse the courseuse of green infrastructure of the South Branch of the river away from LakePopulation: 2.9 million Michigan and to the Mississippi River in an effortType of green infrastructure used: green roofs; rain to improve the lake’s water quality.1 Water issuesgardens, vegetated swales, and landscape; perme- remain a concern for the city more than a centuryable pavement; downspout disconnection/rainwater later. The city manages one of the largest wastewatercollection collection and treatment systems in the world andProgram elements: used for direct CSO control; contends with flooding, surface water qualityestablished municipal programs and public funding impairment, and CSOs. Urban runoff challenges are Historically, Chicago has been known more exacerbated by the magnitude of infrastructurefor its industrial horsepower than for progressive needed to serve Chicago’s population. The city itselfenvironmental ideas. Rivers like Bubbly Creek still has over 4,400 miles of sewage infrastructure thatbear the names they earned from the pollution they cost about $50 million annually to maintain.2 Approx-once contained. Stories of the city’s sewage and imately 3 million people call Chicago home, andpollution problems from as early as the 1880s still the population of the entire six-county metro regionpersist as popular legends. However, recent initia- surrounding the city exceeds 8 million; the region’stives show that Chicago is emerging as a leader in population is projected to increase 20% by 2030.3green development, with an extensive green roof Impervious surfaces cover approximately 58% ofprogram, environmentally sensitive demonstration the city.4projects, and municipal policies that encourage Chicago has pursued a number of initiatives todecentralized stormwater management. The city improve stormwater collection, the most ambitioushas been particularly creative in its approach, using being a $3.4 billion project to collect and store storm-green infrastructure projects to not only manage water and sewage from the combined sewer system.5 17
  24. 24. CHICAGO Natural Resources Defense Council Rooftops to Rivers The green roof at Chicago’s City Hall introduces vegetation in the heart of downtown. Temperatures above the Chicago City Hall green roof average 10° to 15°F lower than a nearby black tar roof. During the month of August this temperature difference may be as great as 50°F. The associated energy savings are estimated to be $3,600 per year. PHOTO COURTESY OF ROOFSCAPES, INC. In the 1970s, the Metropolitan Water Reclamation And, unlike the past, the Chicago River is now seen District began construction of the primary control as a public amenity rather than a liability. solution for CSOs—the Tunnel and Reservoir Plan Chicago’s thriving green roof program began with (TARP). In 2003, with only part of the system opera- a 20,300 square foot demonstration roof on its own tional, more than 44 billion gallons of stormwater city hall. The green roof retains more than 75% of the were captured; 10 billion gallons, however, were volume from a one-inch storm, preventing this water released as CSOs.6 Approximately 2.5 billion gallons from reaching the combined sewer system.9 The pro- of storage are currently available in the TARP system. gram has led to more than 80 green roofs in the city, An additional 15.6 billion gallons of storage will be totaling over one million square feet.10 A 2003 Chicago available when two more reservoirs are added to the Department of the Environment study found that run- system; construction is scheduled for completion in off from green roof test plots was less than half of the 2019.7,8 When complete, the system will handle most runoff from conventional stone and black tar roof plots; of Chicago’s CSO discharges, storing combined runoff the difference was even larger for small storms. The and sewage until it can be sent for secondary treat- city encourages the use of green roofs by sponsoring ment at a wastewater treatment plant. installations and demonstration sites and by provid- ing incentives. A density bonus is offered to developers Chicago’s Green Roof Program who cover 50% or 2,000 square feet (whichever is Although the Metropolitan Water Reclamation greater) of a roof with vegetation. In early 2006, the city District has committed to this massive public works provided 20 $5,000 grants for green roof installations on project, the city has also pursued several initiatives small-scale commercial and residential properties.11 to install green infrastructure that promotes on-site stormwater management, including green roofs, Other Green Infrastructure Innovations: Chicago’s permeable paving projects, rain barrels, and green Citywide Commitment buildings. Much of this investment in green infra- Chicago has employed other green technologies to structure has paralleled the increase in population reduce urban runoff. To address localized flooding and building within the city over the last decade. caused by runoff from one alley, the city removed the 18
  25. 25. CHICAGONatural Resources Defense Council Rooftops to Riversasphalt from the 630 foot long, 16 foot wide alley and green renovations on a firehouse and police head-replaced it with a permeable paving system. Now, quarters; and the Green Bungalow Initiative, a pilotinstead of generating stormwater runoff, the alley project to affordably retrofit four of Chicago’s historicwill infiltrate and retain the volume of a three-inch, bungalows with green technologies and monitorone-hour rain event.12 The permeable pavement any corresponding energy savings. The program hasrequires little maintenance and has a life expectancy thus far shown average energy savings for the greenof 25 to 35 years.13 In this same ward, vegetated swales bungalows of 15% to 49%.17are also being used for stormwater management. The city has also pursued public outreach pro- In June 2004, Chicago has embarked on a city- grams, engaging homeowners through its recent rainwide green building effort. Chicago Mayor Richard barrel and rain garden programs. In the fall of 2004M. Daley presented The Chicago Standard, a set of city residents purchased more than 400 55-gallonconstruction principles designed for municipal rain barrels for $15 each.18 The program cost the citybuildings. The standards are based on the Leader- $40,000 excluding city labor. The Department ofship in Energy and Environmental Design (LEEDTM) Environment estimates the pilot project has theGreen Building Ration System14 and emphasize potential to divert 760,000 gallons annually from thesustainability, water efficiency, energy effects, and combined sewer system, a relatively small numberindoor air quality as well as stormwater manage- compared to the total amount of stormwater runoffment. For both the green roof and green building in the city. However, the program was targeted toefforts, Chicago has created municipal demonstration areas with a high frequency of basement flooding,projects to develop professional expertise in the city meaning the program may have a more significanton these technologies. impact in these localized areas. Since the water in rain barrels can be used for other purposes such asChicago Center for Green Technology. The centerpiece landscaping, this program has additional conserva-of the city’s green building efforts is the Chicago tion benefits as well. The city also began a comple-Center for Green Technology. The Chicago Depart- mentary rain garden program, planting four rainment of Environment transformed this property from gardens along with signage explaining benefits.a 17-acre brownfield full of construction debris to Chicago has also complemented its ground-levelthe first municipal building to receive the LEEDTM initiatives with two studies on the effectiveness ofplatinum rating.15 The 34,000 square foot center green infrastructure technologies. The first is theserves as an educational facility and rental space for monitoring study of the green roof box plots. Theorganizations and businesses with an environmental second is a 2004 Department of Environment Storm-commitment. Four 3,000 gallon cisterns capture water Reduction Practices Feasibility Study that usedstormwater that is used for watering the landscaping. hydraulic modeling to assess the effectiveness of bestThe site also features a green roof, bioswales, perme- management practices for the Norwood Park sewer-able paving, and a rain garden. Chicago Department shed. The study found that downspout disconnectionof Environment models indicate that Green Tech’s would achieve peak flow reductions in the 1,370-acrestormwater management technologies retain more area by 30% for a six-month or one-year storm if allthan 50% of stormwater on site—for a three-inch homes in the 80% residential area disconnected theirstorm, the site releases 85,000 gallons of stormwater downspouts from the sewer system.19,20 This wouldto the sewer system instead of the expected 175,000 potentially reduce peak flow in the CSO outfall pipegallons.16 The success of the Green Tech project by 20% and water levels in the sewer system by eightspurred several other green building projects, inches to two feet. The study also showed that three-including three new green libraries; a new police inch and six-inch-deep rain gardens installed at eachstation to be monitored for a national case study; home could reduce total runoff by approximately 4% 19
  26. 26. Natural Resources Defense Council Rooftops to Rivers and 7%, respectively, for the same six-month or one- operate combined sewers, which make up 5% of year storm events. MMSD’s total service area. Combined sewer over- flow points are located along rivers that flow intoMILWAUKEE For Additional Information Lake Michigan.23 The $2.3 billion Deep Tunnel Chicago Department of the Environment: System project, completed by MMSD in 1994, pro- vided 405 million gallons of underground sewer storage. Begun in 1986, the 19.4-mile-long system =Environment&entityNameEnumValue=05 collects and temporarily stores the large quantities of stormwater and wastewater that are conveyed through the sewers during wet weather events.24 Milwaukee, Wisconsin Prior to the system becoming operational, Investing in green infrastructure to improve water Milwaukee averaged 50 to 60 CSO events a year, quality which discharged 8 to 9 billion gallons of sewage Population: 587,000 and stormwater. The Deep Tunnel System was Type of green infrastructure used: green roofs; rain designed to limit CSOs to 1.4 events per year; in gardens, vegetated swales, and landscape; wetlands, the first 10 years of operation, from 1994 until 2003, riparian protection, or urban forests annual average CSO discharges were 1.2 billion Program elements: used for direct CSO control; gallons from 2.5 average annual events.25,26 Heavy established municipal programs and public funding rains in the spring of 2004 resulted in 1 billion gallons Like many municipalities with a combined sewer of CSO discharges during a two-week period.27 system, Milwaukee has a history of exposure to Although the Deep Tunnel System has substantially frequent CSO events and was faced with finding a reduced CSO events, excessive quantities of storm- viable overflow control strategy. To reduce the num- water can still trigger overflows, and MMSD has ber of CSOs and their impact on the water quality of committed an additional $900 million to an overflow Lake Michigan and its tributaries, the Milwaukee reduction plan.28 Metropolitan Sewerage District (MMSD), the regional wastewater treatment agency, built a deep Milwaukee’s Green Infrastructure Approach tunnel storage system in the 1980s and 1990s. MMSD As an additional strategy to limit CSO discharges, invested $3 billion during this period to reduce over- MMSD has begun to install green infrastructure flows. As a complement to this large capital invest- within the combined sewer area to decrease the ment, MMSD is investing in green infrastructure volume of stormwater entering the system. One projects to reduce stormwater inflow into the com- of the first initiatives was a disconnection program bined sewer system and mitigate stormwater runoff. that redirected building downspouts from the com- MMSD manages wastewater from 28 municipali- bined sewer system to rain barrels. Overflow from ties with a combined population of about 1.1 million the rain barrels is directed to pervious areas and rain people in a 420 square mile service area. All 28 com- gardens. In a cooperative cost-sharing arrangement munities own and operate their own sewer systems, with public entities and private businesses in the city, which drain into 300 miles of regional sewers owned MMSD partnered with others to install more than by MMSD. The district’s two wastewater treatment 60 rain gardens to receive and treat roof runoff. The plants each process about 80 to 100 million gallons total combined cost of these pilot projects was approx- of wastewater on a dry day.21 Treated wastewater imately $170,000.29 is discharged to Lake Michigan, which also serves as the city’s drinking water supply.22 The city of The Highland Gardens housing project. Seven green Milwaukee and the village of Shorewood own and roofs have been installed in the Milwaukee region. 20
  27. 27. Natural Resources Defense Council Rooftops to Rivers MILWAUKEEThe 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 MMSDOne of these is at the Highland Gardens housing Measuring the Effectiveness of Milwaukee’sproject, a 114-unit mid-rise for senior citizens and Green Infrastructurepeople with disabilities. A 20,000 square foot green The rain gardens and MMSD-financed green roofsroof was installed at a cost of $380,000. The roof were installed in 2003 and 2004. A monitoring programwill retain 85% of a two-inch rainfall. The remain- evaluating the effectiveness of the systems at managinging 15% of the water volume is directed to rain stormwater is being conducted with initial resultsgardens and a retention basin used for on-site expected in early 2006. To determine the potentialirrigation.30 These management strategies prevent impacts of the green infrastructure program, MMSDstormwater from being discharged to the collec- conducted a modeling analysis. The modeling efforttion system. showed that application of downspout disconnection, MMSD has installed or helped finance four other rain barrels, and rain gardens in residential areas wouldgreen roofs to reduce stormwater runoff. The first reduce each neighborhood’s contribution to the annualwas a 3,500 square foot structure on the roof of CSO volume 14% to 38%. Additional modeling resultsMMSD’s headquarters building in downtown showed the volume of stormwater sent to the treatmentMilwaukee. Native species of grasses and flowering plants from the neighborhoods was reduced 31% toplants were selected for the roof vegetation. The 37% and stormwater peak flow rates were reduced 5%cost of the green roof was just under $70,000.31 A to 36%, depending upon the size of the rain event.33second green roof was installed on the University (The model assumed a high participation rate for resi-of Wisconsin-Milwaukee’s Great Lakes Water Insti- dential areas. Volume and peak flow reductions wouldtute. MMSD contributed $110,000 of the $233,000 not be as great with a lower participation rate.)needed to install the 10,000 square foot unit. A third The effect of green infrastructure in commercialgreen roof was installed on the city’s Urban Ecology areas was also modeled. The use of green roofs, rainCenter, with MMSD contributing $40,000 of the gardens, and green parking lots is predicted to reducetotal project cost. The fourth green roof is at the commercial area contributions to CSO volume byMilwaukee County Zoo, to which MMSD con- 22% to 76%, but would not decrease—and couldtributed half of the $73,000 cost.32 even increase—the volume of stormwater sent to the 21