Piney Branch Combined Sewer Overflow Remediation Environmental Assessment

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The National Park Service (NPS) and DC Water are undertaking a plan and environmental assessment to improve water quality in Piney Branch, a tributary of Rock Creek that flows through Piney Branch Parkway.

DC Water is proposing to build a 4.2-million-gallon underground storage facility to capture sewage, combined with stormwater, that would otherwise overflow into Piney Branch during heavy rains. The project would reduce the volume of untreated sewer discharges into Piney Branch by an estimated 96%, as well as reduce existing frequency of discharges from 25 events per year to one event, per average rainfall year.

DC Water seeks to control these overflows to improve water quality as part of the DC Clean Rivers Project. A diversion structure proposed at the Piney Branch Outfall, known as the Combined Sewer Outfall (CSO) 049, would redirect sewer flows to the storage facility and eventually convey the combined sewage to DC Water's Blue Plains Advanced Wastewater Treatment Plant for treatment when the pipes and system can handle the volume.

The Piney Branch CSO 049 Storage Project is needed to reduce sewage overflows that contribute to water quality impairment of Piney Branch and ultimately the Potomac River and the Chesapeake Bay; and to comply with the 2005 Federal Consent Decree entered into by DC Water, the District of Columbia, the US Environmental Protection Agency, and the US Department of Justice, as amended January 2016. More information on the Clean Rivers Project can be found at More information on this project can be found at

The public is encouraged to learn more about the project and provide input during the public scoping period, which lasts from 12:01 AM January 17, 2023 Eastern Standard Time (EST) until 11:59 PM February 16, 2023 EST. A virtual public meeting will be held on January 18, 2023 at 7:30 PM EST. See the "Meeting Notices" link on the left-hand side of this page for more information about the meeting.

We have uploaded a copy of the presentation DC Water will make during the virtual public meeting. We encourage the public to review the document and provide comment during the public scoping period. The presentation will be uploaded to the "Open for Comment" link on the left-hand corner of the screen.

Additional opportunities for public input will be available as the project continues.