Piney Branch Tunnel

DC Water’s Piney Branch Tunnel

CSO 049 Structure on Piney Branch Road NW

Piney Branch Tunnel overview

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 rainfall year when completed.

The Piney Branch Tunnel Project was first approved as part of DC Water’s Long Term Control Plan federal consent decree in 2005 and revised in 2020.  It will be constructed in the northwest part of Washington, DC, south of the existing CSO 049 and Piney Branch Parkway. The project’s pupose is to intercept the overflow before it reaches Piney Branch Stream, temporarily store the captured flow until the rain event subsides and then and send it to Blue Plains WWTP for treatment, as required by the revised consent decree. This will reduce the overflow frequency from 25 to one per average rainfall year and reduce the overflow volume from 39.7 million gallons to 1.4 million gallons – a reduction of 96 percent.  

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.


Environmental Assessment 2023 - early 2024
Request for Proposal Prepration 2024
Procurement 2025
Construction 2025-2029


DC Water and the National Park Service (NPS) are preparing  an Environmental Assessment (EA) to comply with the National Environmental Policy Act (NEPA). The EA analyzes 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


Project Location

Piney Branch Storage General Map


Just The Facts
Million-gallon storage Tunnel

Do you have a question or comment?

call customer

Call our          

  • call us



Upcoming Meeting

Board of Directors Meeting

April 24, 2023

Monday 9:00 AM

Latest Blog Post
Leveraging Green Infrastructure for the Triple Bottom Line
Leveraging Green Infrastructure for the Triple Bottom Line
Leveraging Green Infrastructure for the Triple Bottom Line
Upcoming Meeting
May 23, 2024
Thursday, 1:30 PM