DC Water’s Clean Rivers Project is planning a 4.2-million-gallon underground storage tunnel to capture sewage combined with stormwater, known as combined sewer overflow (CSO), that would otherwise overflow into Piney Branch and ultimately Rock Creek during heavy rains. This project will reduce overflow volume from CSO 049 by 96 percent in an average year when completed. 

The Piney Branch Storage Project was first approved as part of DC Water’s Long Term Control Plan under the 2005 Federal Consent Decree and refined in 2020.  It will be constructed in the northwest part of Washington, DC, south of the existing CSO outfall structure (CSO 049) along Piney Branch Parkway. The project’s purpose is to temporarily store combined flows that would otherwise overflow into Piney Branch and redirect the captured flow into the existing sewer system for treatment at the Blue Plains Advanced Wastewater Treatment Plant.

The project includes construction of a diversion structure at the Piney Branch outfall, known as CSO 049, to redirect sewer flows to the storage tunnel 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.  This project is needed to reduce CSOs to improve water quality in Piney Branch, Rock Creek, and ultimately the Potomac River and the Chesapeake Bay; and to comply with the terms of the Federal Consent Decree. This project will reduce the overflow frequency at CSO 049 from 25 events per average year to one event per average year and reduce the overflow volume in an average year from 39.7 million gallons to 1.4 million gallons – a reduction of 96 percent.


Environmental Assessment (EA) Date

Data Collection


Impact Assessment

Public Scoping Period January 18-February 16, 2023
EA Released to Public TBD
Public Meeting TBD
Finalize Decision Document TBD
Future Consent Decree Deadlines  
Award Contract for Design May 2024
Award Contract for Construction May 2026
Place in Operation November 2029











DC Water and the National Park Service (NPS) are beginning a planning process that includes the preparation of an Environmental Assessment (EA) to comply with the National Environmental Policy Act (NEPA). The EA will analyze potential environmental impacts that would result from implementing the Project. As the coordinating agencies in the preparation of the EA, DC Water and NPS are working closely with multiple stakeholders including residents, Advisory Neighborhood Commissions, District Department of Transportation, District Department of Public Works, District Fire and Emergency Medical Services, District Department of Energy and Environment, District Office of the Deputy Mayor for Planning and Economic Development, District Department of General Services, National Park Service, and the Washington Metropolitan Area Transit Authority. In addition, DC Water is coordinating with multiple federal and local agencies and other organizations through the National Environmental Protection Act and the National Historic Preservation Act compliance procedures.  

Public Participation

Public participation is vital to the NEPA planning process. The NEPA process started with a public scoping meeting on January 18, 2023 and a 30-day public scoping period from January 18 to February 16, 2023, in which the NPS and DC Water gathered public input regarding issues or concerns associated with implementing the proposed project. The webinar from the January 18, 2023 public scoping meeting is posted in the Documents List online at https://parkplanning.nps.gov/dcPineyBranch.

The EA is anticipated to be released for public comment in late-2023. The public comment period will be advertised as it approaches.

Project Location

Piney Branch Storage General Map