About 98 times a year, the District gets enough rain that its aging combined sewer system overflows, dumping roughly 2.5 billion gallons of wastewater in the Anacostia and Potomac rivers, as well as into Rock Creek. But today, D.C. Water broke ground on a $2.6 billion project that will all but eliminate the overflow, making area rivers and the Chesapeake Bay significantly cleaner in the process.

Known as the Clean Rivers Project, the first phase of the infrastructure initiative will see the construction of a massive tunnel — 23 feet in diameter and 100 feet below the Anacostia River — where combined sewer overflow will pool during heavy storms. The tunnel, which will be dug out by an enormous German-made tunnel boring machine that is as long as a football field, is expected to open in 2018. Two other tunnels will follow in 2025.

D.C. Water General Manager George Hawkins noted at the groundbreaking that the “mammoth underground tunnel” represented the single largest infrastructure project undertaken by the District since Metro was built. He said that the need for the tunnels came as a consequence of a sewer system that mixes storm runoff and sewage during periods of heavy rain. Some 770 other cities have similar systems, and a number of them have started building tunnels to collect the overflow.

The project’s cost is being borne overwhelmingly by the District, primarily through the imposition of an Impervious Area Charge, a fee is applied to impervious surfaces such as rooftops and parking lots.

Dignitaries such as Sen. Benjamin Cardin (D-MD), D.C. Del. Eleanor Holmes Norton and Mayor Vince Gray also attended the ground-breaking, and spoke of the environmental impact that the tunnel would have once it’s completed.