Alexandria Begins Testing Massive Tunnel Designed to Keep Sewage Out of the Potomac River
Part of the RiverRenew project, the system will capture 120 million gallons of sewage annually and prevent harmful overflows into local waterways.
ALEXANDRIA, VA – After years of planning and construction, Alexandria has reached a major milestone in its effort to protect local waterways: testing is now underway on a massive underground tunnel designed to keep sewage out of the Potomac River.
AlexRenew this week began accepting preliminary test flows into the new Waterfront Tunnel system, a key step that allows crews to test dewatering pumps and critical equipment ahead of the project’s anticipated operational deadline later this summer.
The tunnel is part of RiverRenew, the largest infrastructure project in Alexandria’s history. The effort began in July 2018, when the Virginia Department of Environmental Quality approved a joint Long-Term Control Plan developed by the City of Alexandria and AlexRenew. Following that approval, AlexRenew assumed responsibility for overhauling the city’s aging combined sewer system—some parts of which date back more than a century.
Those older pipes were designed to carry both sewage and stormwater in a single system. During heavy rains, they can become overwhelmed, causing combined sewer overflows that discharge untreated wastewater into the Potomac River and its tributaries.
RiverRenew is designed to fix that.
At the center of the solution is the 2.2-mile-long Waterfront Tunnel, completed in 2024. Built deep underground, the tunnel acts as a giant storage and conveyance system, capturing excess flow during storms and transporting it to AlexRenew’s treatment facility rather than allowing it to spill into the river. The project also includes a massive 12-story underground pumping station and the Hooffs Run Interceptor, completed in 2025, which helps redirect flows into the system.
Crews have spent the last four years advancing the design and construction of the tunnel and its supporting infrastructure. Once fully operational, RiverRenew will capture and convey an estimated 120 million gallons of combined sewage annually to be treated—dramatically reducing pollution and improving water quality in the Potomac River.
“This is a significant achievement for our team and a symbolic milestone on our journey to becoming operational,” said Matt Robertson. “Ultimately, RiverRenew will benefit our community, its waterways, and our region—that’s something we can all celebrate.”
While largely out of sight, the project’s impact is expected to be far-reaching. By preventing sewage overflows, RiverRenew will play a critical role in restoring and protecting one of the region’s most important natural resources.
AlexRenew, the public wastewater authority serving Alexandria and parts of Fairfax County, treats approximately 13 billion gallons of wastewater each year. With RiverRenew nearing completion, that work will soon expand in a major way—ensuring cleaner water for generations to come.
