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The Washington, D.C., area has been struggling with CSOs for years. Under a 2005 Clean Water Act Consent Decree, the District of Columbia Water and Sewer Authority (DC Water) was required to implement its Long Term Control Plan (LTCP), which primarily consisted of the construction of a system of pumps and three underground storage tunnels to store excess flows pending treatment. A recently proposed amendment to that Consent Decree provides, in part, for the incorporation of Green Infrastructure (GI) in the Potomac River and Rock Creek sewersheds. (The Anacosta River is also a receiving water of D.C. discharges.)
Note: The extended comment period for the proposed amendment to the Consent Decree closes July 27.
In addition to the GI components, the proposed modification to the Consent Decree contains a financing structure that should keep costs down for ratepayers within the District and provide for stormwater mitigation in low-income areas. We’ll review both elements.
According to EPA Region 3 Administrator, Shawn Garvin, this modified Consent Decree could become a national model. If that is the case, you will most likely be seeing similar green infrastructure requirements when your permit is due or if you are subject to an enforcement action. We may also be seeing similar incentives in financing for green infrastructure projects around the country.
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Green Infrastructure
The green infrastructure (GI) components to the Consent Decree include:
- Using green infrastructure to retain the first 1.2 inches of rainwater on 365 acres (30 percent of the impervious area) in Piney Branch of the Rock Creek watershed, and 133 acres (also 30 percent of the impervious areas) in the Potomac watershed.
- Potentially eliminating the Rock Creek storage tunnel and significantly decreasing the size of the Potomac tunnel depending on the success demonstrated by green infrastructure.
- The District will provide the public space necessary for DC Water to construct the proposed green infrastructure projects and make changes to District regulations, codes, standards, guidelines, and policies needed for implementation.
The GI projects may include bioretention practices (bioretention cells, bioswales, vegetated filter strips, and tree box filters), rooftop collection practices (green roofs, blue roofs, downspout disconnection, rain barrels, and cisterns), permeable pavement, and large-volume underground storage. These facilities will be constructed in both public and privately-owned spaces.
The Consent Decree also calls for maintenance plans for the GI projects and a public outreach plan to engage property owners in the Potomac and Rock Creek sewersheds and interested stakeholders to promote the installation of GI projects on private property and to ensure public input into the site selection process and concept design for the control measures that DC Water proposes to install as part of the GI Program Plan.
GI controls will have to be inspected at least every 3 years.
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Financing Accounts for Low-Income Areas
As part of the Consent Decree, the District of Columbia will review its stormwater regulations and policies and, in particular, review the practicality of using its Stormwater Retention Credit program to maximize water quality benefits.
The program allows property owners and site developers to generate Stormwater Retention Credits (SRCs) by providing on-site stormwater retention beyond those required for respective sites. The credits can be purchased (in the open market run by the District Department of the Environment) by developers that are required to provide half of the requisite on-site retention volume with the option to meet the remaining retention volume through credits obtained through the SRC program. One aim of the program is to help to drive the implementation of green infrastructure in less affluent areas outside of the downtown core where opportunity costs related to land value are relatively low. This will lead to high amounts of retrofits in low-income and environmentally sensitive areas.
Beyond the SRC program, the District has established a stormwater fee with credits/rebates given to those who provide retention on-site.