Piney Branch Tunnel Groundbreaking, Final Phase of Clean Rivers Project

On July 9 2026, DC Water broke ground on the Piney Branch Tunnel, the final major tunnel in our Clean Rivers Project. This work will help keep sewage and trash out of local waterways and make Rock Creek, the Potomac River, and the Chesapeake Bay cleaner for our community.

When we finish the Piney Branch Tunnel, it will hold at least 4.2 million gallons of rainwater and wastewater during heavy storms. Instead of overflowing into Piney Branch, that water will go to the Blue Plains Water Resource Recovery Facility, where it will be treated.

"We have already seen how the Clean Rivers Project can make a real difference for the Anacostia River, and this project will bring those same benefits to Rock Creek and the Potomac River,” said DC Water Interim Chief Executive Officer and General Manager Matt Brown. “The Piney Branch Tunnel is one more way we are protecting our waterways and building a cleaner, healthier future for everyone who lives, works and enjoys the outdoors in DC.”

Much of DC’s sewer system is more than 100 years old. During heavy rain, it can take in more water than it can handle. When that happens, rainwater mixed with wastewater is released into creeks and rivers. That adds pollution and trash to our waterways and can harm fish and other wildlife.

Right now, this happens in Piney Branch about 25 times a year. With the tunnel, we expect it to happen about once a year and cut the amount of overflow by 96%.

This summer, our crews will prepare the site before tunneling starts. In the fall, we expect crews to begin digging through rock, which will include planned blasting. The tunnel is scheduled to be finished by the end of 2029. 

Piney Branch Tunnel Project

DC Water’s Clean Rivers Project is constructing the Piney Branch Tunnel Project within Rock Creek Park in northwest Washington, DC.  The tunnel will capture and store a minimum of 4.2-million gallons of sewage combined with stormwater, known as combined sewer overflow (CSO), that will otherwise overflow into Piney Branch when the capacity of the existing combined sewer system is exceeded during storms. The United States Environmental Protection Agency (USEPA) currently lists Piney Branch as an impaired waterbody under the Clean Water Act.

The Piney Branch Tunnel Project will comply with the 2005 Federal Consent Decree entered into by DC Water, the District, the USEPA, and the US Department of Justice, as amended January 2016, and modified December 2020. The project is designed to improve water quality in Piney Branch, Rock Creek, and ultimately the Potomac River and Chesapeake Bay by reducing untreated discharges to the sewer system and increasing sewer overflow storage and conveyance capacity.

Currently, an estimated 40 million gallons of untreated combined sewer discharge overflows into Piney Branch in a year of average rainfall during heavy storm events. This harms local waterways and wildlife. Once completed, the Piney Branch Tunnel will capture and store most of this overflow during storms, reducing these overflows by 96% and limit the frequency of overflow events from 25 to one in a year of average rainfall.