This multi-year project is getting started. Here’s what you need to know.

Potomac River near georgetown waterfront. Photo Credit: canva

The health of the Potomac River has been improving, as noted in our 2023 Report Card. This is due to the hard work of many community partners and volunteers to reduce pollution and restore water quality.

There’s still plenty of work to do, though. Potomac Conservancy noted some of the biggest concerns in the report card, such as rising urban runoff due to pollution from fertilizers, street oils, trash, sediment, and diluted sewage. This threatens to hamper the impressive strides the river has made.

Did they start construction?

Inside the Northeast Boundary Tunnel. Photo credit: DC Water

DC Water began work on the Potomac River Tunnel Project earlier this year. The next major phase of the Clean Rivers Project will focus on mitigating the district’s combined sewer overflow (CSO). This system, built around 1900, carries both sewage and stormwater in one pipe.

Sewer systems can be easily overwhelmed during heavy storms, sending diluted sewage straight into streams. Last September, DC Water completed the Northeast Boundary Tunnel, which takes overflow away from the Anacostia River.

The largest part of the project, the tunnel, is five miles long, 23 feet in diameter, and 100 feet deep (that is four feet taller than the statue in the Thomas Jefferson Memorial). The promise of the new span is that it will prevent overflows of sewage and help alleviate flooding in neighborhoods in Washington, D.C.

“The Potomac River Tunnel will control the overflow along the Potomac River from the Lincoln Memorial to Georgetown,” said Hadiah Jordan, senior public outreach coordinator for DC Water.

“Diversion structures and drop shafts will be constructed to divert CSO flows to a deep underground storage and conveyance tunnel.” Thanks to gravity, the captured flows divert to Blue Plains Wastewater Treatment Plant. According to Jordan, the Potomac CSO reduction would be 93%; in comparison, the Anacostia’s is 98%. - Jordan

DC Water stressed it will comply with federal and district environmental regulations during construction. “This includes water, air, solid waste, hazardous substances, oil, and noise pollution,” Jordan added. After the tunnel is constructed, DC Water will conduct post-construction monitoring in the Potomac to assess the efficacy of the overflow controls. Construction will take time, though: The tunnel is not expected to be completed until 2030.

Map of potomac river tunnel project. photo credit: dc water

The Clean Rivers Project is mandated by a 2005 federal consent decree with the U.S. Environmental Protection Agency to reduce CSOs that hinder water quality. It was modified in 2015 to include more green infrastructure, like rain gardens and pavement, that captures and stores rainwater.

In April, DC Water began the first steps for the Potomac tunnel by identifying underground utilities along Independence Ave. SW. Much of the work will be around West Potomac Park; there will also be seven other site locations for the tunnel project.

As the Potomac River Tunnel takes shape, Potomac Conservancy will continue to tunnel through the project to ensure the Potomac River's water is cleaner and safer for fishing, swimming, and drinking.