News Release

National Park Service approves DC Water’s Piney Branch Tunnel project to improve water quality

Date: March 6, 2025
Contact: Autumn Cook, 771-215-6954

WASHINGTON — The National Park Service (NPS) has completed an Environmental Assessment (EA) and approved DC Water’s proposal to construct the Piney Branch Tunnel. The project, on NPS land in Rock Creek Park, will improve water quality and reduce combined sewer overflows (CSOs) to the Piney Branch and Rock Creek. The Piney Branch Tunnel is part of DC Water’s Clean Rivers Project. 

Currently, around 40 million gallons of stormwater combined with untreated sewage overflow into Piney Branch each year. This harms local waterways and wildlife. The Piney Branch Tunnel will reduce the volume of CSOs by 96%, and the frequency from 25 overflows during a typical year to only one. The tunnel will capture and store sewer overflows and control the flow to DC Water’s Blue Plains Advanced Wastewater Treatment Plant until the system can handle the volume. 

The NPS completed an EA to evaluate the potential environmental impacts associated with the Piney Branch Tunnel project and considered two alternatives, a no-action alternative and a proposed action alternative. A Finding of No Significant Impact (FONSI) was signed on March 5, 2025, selecting the construction of the Piney Branch Tunnel as the alternative. The FONSI describes the rationale for the decision and outlines measures that will be taken to avoid, minimize and mitigate any impacts.  

The FONSI and other planning documents are available at: https://parkplanning.nps.gov/projectHome.cfm?ProjectID=111174 

Additional details about the Piney Branch Tunnel Project are available at dcwater.com/pbs. Learn more about the DC Clean Rivers Project by visiting dcwater.com/cleanrivers. 

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