A Perfect Storm(water)

The City of Seattle is revising its Stormwater Code to require all single-family residential development projects and certain other development projects to implement “green infrastructure technologies” for stormwater control.[1] Such technologies include porous pavement, green roofs, and cisterns. Seattle and other communities are in the vanguard of a national trend toward “Low-Impact Development” or “LID,” which incorporates green infrastructure.

A recent EPA report, Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices, argues that – as compared to conventional stormwater management practices – LID stormwater practices produce capital cost savings ranging from 15 to 80 percent. EPA’s report, released earlier this year, summarized 17 case studies of developments nationwide. It concluded that applying LID techniques can reduce project costs and improve environmental performance by reducing runoff volumes and pollutant loadings to downstream waters, and can reduce incidences of combined sewer overflows.

Background

Most stormwater runoff is the result of man-made hydrologic modifications that normally accompany development. The EPA has identified stormwater discharges as a major source of pollution for all waterbody types in the United States.[2] The impacts of stormwater discharges are not static; they usually increase with land development and urbanization.[3] Additional impervious surfaces, soil compaction, and tree and vegetation removal may alter the movement of water through the environment, preventing stormwater from evaporating and infiltrating into the ground, and converting precipitation into overland non-point source flows.[4] These modifications can affect both the characteristics of the developed site and also the watershed in which the development is located.[5]

Green infrastructure and LID are stormwater management strategies that seek to mitigate the impacts of increased runoff and stormwater pollution.[6] According to EPA, LID’s goal is to use design techniques that infiltrate and reuse stormwater close to its source to mimic the way water moved through the landscape before it was developed. Traditional approaches to stormwater management typically involve hard infrastructure, such as curbs, gutters, and piping. LID-based designs, in contrast, comprise a set of site design approaches and small-scale stormwater management practices that use natural drainage features or engineered swales and vegetated contours to infiltrate, convey, and treat stormwater runoff.[7] The EPA has found that these practices can effectively remove nutrients, pathogens, and metals from stormwater, and reduce the volume and intensity of stormwater flows.[8]

Seattle’s Revised Stormwater Code to Require Green Infrastructure

In January 2007, The Washington Department of Ecology (“Ecology”) issued Seattle a Phase I Municipal Stormwater Discharge Permit under the National Pollution Discharge Elimination System (“NPDES”) provisions of the federal Clean Water Act (“CWA”)[9] and Washington’s Water Pollution Control Act (“WPCA”)[10]. At the same time, Ecology issued new Phase II Municipal Stormwater General Permits that, for the first time, require 100 cities, 13 counties, and other entities across Washington to regulate discharges from their stormwater systems. Effective February 16, 2007, the new Municipal Stormwater permits require Seattle, the newly regulated municipalities, and other public entities to adopt ordinances or otherwise develop and implement stormwater management systems that include, at minimum: public education and outreach; public participation; illicit discharge detection and elimination; stormwater runoff control from new development, redevelopment, and construction sites; and pollution prevention. For more on Washington’s Municipal Stormwater permits see J. Kray, Washington State Issues New Stormwater Permit Rules Affecting 100 Cities, 13 Counties, Marten Law Group Environmental News (February 21, 2007).

On February 15, 2008 the City of Seattle submitted a final draft of proposed revisions to its Stormwater Code to Ecology for review.[11] Seattle’s revised Code defines “green infrastructure technologies” to mean “a drainage control facility that uses infiltration, evapotranspiration, or stormwater reuse.”[12] Examples include porous pavement, bioretention facilities, infiltration trenches, dry wells, green roofs, cisterns, and bioretention planters with underdrains. The Code will require all single-family residential projects to “implement green infrastructure technologies to infiltrate, disperse, and retain drainage water onsite to the maximum extent feasible without causing flooding, landslide, or erosion impacts.”[13] The Code will also require projects that discharge stormwater into certain flow-critical creeks, the public combined sewer, or a capacity-constrained system to implement green infrastructure technologies.[14]

Ecology is now reviewing Seattle’s proposed revisions to its Stormwater Code to determine if the proposals are consistent with the Phase I Municipal Stormwater General Permit. Ecology has not set a deadline for providing its comments on Seattle’s revised Code. Once Ecology completes its review of the proposed Code, Seattle will begin a formal public comment and rulemaking process for the Code revisions.[15]

EPA’s LID Report

In its Report, EPA evaluated 17 case studies from around the nation, including four case studies from Washington and one each from Oregon and British Columbia. The LID Report compared the projected or known costs of LID practices with those of conventional development approaches. In general, the case studies demonstrated that LID practices can reduce project costs and improve environmental performance. Although not all the benefits of the projects highlighted in the case studies were monetized, the report showed, with one exception, that LID practices were both fiscally and environmentally beneficial to communities. In a few case studies, EPA found that initial project costs were higher than those for conventional designs; in most cases, however, significant savings were realized due to reduced costs for site grading and preparation, stormwater infrastructure, site paving, and landscaping. As the following table shows, total capital cost savings typically ranged from 15 to 80 percent when LID methods were used.

Cost Comparisons Between Conventional and LID Approaches

The LID Report examined projects that highlight LID practices such as rain gardens, grassy swales, cisterns, rain barrels, cluster building, permeable pavements, and green or vegetated roofs as tools to capture stormwater. For developers and planners interested in implementing or promoting LID projects in the community, the LID Report provides a breakdown of site development costs for both traditional and low impact scenarios, which can be useful when presenting new designs to groups who are not familiar with LID’s costs and benefits. Developers using LID practices can potentially increase developable land by reducing size requirements for stormwater retention basins.[19] This is especially important where, as in Washington, stormwater management requires larger ponds to manage stormwater flows.[20] For example, the LID Report shows that Bellingham, Washington saved $62,000 by retrofitting two parking lots—one at City Hall and the other at Bloedel Donovan Park—with rain gardens instead of installing underground vaults to manage stormwater.

In April 2007, EPA, the National Association of Clean Water Agencies, the Association of State and Interstate Water Pollution Control Administrators, Low Impact Development, and the Natural Resources Defense Council signed a statement of intent to formalize the use of LID strategies. Benjamin Grumbles, EPA’s assistant administrator for water, recently stated that early this year EPA will issue a strategy showing how LID and green infrastructure should be implemented.[21] You can find more information at EPA’s Green Infrastructure website and at EPA’s LID website.

Conclusion

Developers, municipalities, regulators, and others involved in stormwater management should take note of Seattle’s proposals to require green stormwater practices for residential and other development and follow the City’s proposals as they move through the rulemaking process. They should also familiarize themselves with LID strategies and EPA’s LID Report. The Report provides valuable guidance on lower cost stormwater management options that can potentially save costs, deliver environmental benefits, and reduce exposure to regulatory and citizen suit enforcement under the federal, state, and local water quality laws.[22]

For more information about Marten Law Group’s water quality and water resources practices, please contact Jeff Kray.