District of Columbia Water and Sewer Authority - DC Water Clean Rivers Project

DC Water Clean Rivers Project

The District of Columbia is one of 772 older cities in the country with a combined sewer system. The combined sewer system covers about a third of the city, and was built in the late 19th century to carry both sanitary sewage and storm water in the same pipe. The system operates well in dry weather. However, during rainstorms, the flow can exceed the capacity of the pipe. To prevent sewer backups and flooded streets, these combined sewers may discharge into the Anacostia and Potomac Rivers and Rock Creek, a phenomenon known as combined sewer overflows (CSOs).

To date, DC Water has significantly reduced CSOs by eliminating approximately 40 percent of the overflows through a $140 million program. This investment included inflatable dams to catch and store overflows during rain storms; tide gates to keep river water from flowing into the sewer system; sewer separation to eliminate CSO outfalls; and pumping station construction and rehabilitation to increase flow capacity. A deep underground tunnel system is employed in a $2.4 billion, 20-year DC Water Clean Rivers Project to reduce CSOs by 96 percent overall and 98 percent in the Anacostia River.

This tunnel system will store the combined sewage during wet weather and release it for treatment at Blue Plains once there is capacity in the system.