DC Water’s Piney Branch Tunnel Project is moving ahead with construction, the next phase of the Authority’s Clean Rivers initiative to improve the water quality in the Anacostia River, Potomac River, and Chesapeake Bay watershed. The project received approval from the National Park Service (NPS) following completion of the Environmental Assessment, including rigorous public review.  

The analysis and approval by NPS are required by federal law to move forward with construction. The 4.2-million-gallon underground storage facility will capture stormwater and untreated sewage during heavy rains, holding it until the overflow can be released back into the system during low flow periods and treated at the Blue Plains Advanced Wastewater Treatment Facility.  

“We appreciate the work of the National Park Service on this important infrastructure project to improve water quality and quality of life,” said DC Water Chief Executive Officer and GM David Gadis. “The Piney Branch Tunnel will keep nearly 40 million gallons of stormwater and untreated sewage from our waterways and restore this natural resource for the public to enjoy.”  

The project is expected to reduce the volume of sewage overflows by 96%, reducing pollution in Piney Branch, Rock Creek, and downstream areas including the Potomac River and Chesapeake Bay. The tunnel will also cut down on the frequency of sewer overflow events, from 25 in a year of average rainfall to just once a year.  

The NPS carefully reviewed the project’s potential effects on the environment and community. This included water quality, wetlands, plants, wildlife— including threatened and endangered species— historic sites and public spaces. The review compared the environmental impact of building the tunnel versus the impact of taking no action. 

Design work is underway for the tunnel project, with construction expected to break ground in 2026. The tunnel is scheduled to be operational by 2029, with completion of all restoration work and other project related improvements by 2030.  

DC Water’s Clean Rivers initiative is a $2.7 billion project to construct 18-miles of tunnels to divert sewage overflows and improve water quality 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.  

To learn more, go to the Piney Branch Tunnel Project  and Clean Rivers Initiative pages on our website dcwater.com.