The McMillan storage tanks could be finished as soon as spring 2014, said George S. Hawkins, the D.C. Water and Sewer Authority’s general manager, and the First Street tunnel could be completed two years later. Engineers estimate the projects could reduce flooding depths by 20 inches.
Under previous time lines, the affected neighborhoods would not have seen significant relief until 2025.
Hawkins presented an outline of the plans to D.C. Water’s board of directors during a Thursday morning meeting. More details were discussed at an afternoon meeting of a flooding task force appointed by Mayor Vincent C. Gray (D).
“It looks like we’re getting there, like we’re almost there,” City Administrator Allen Y. Lew said before briefing task force members. “Not 100 percent, but a substantial, significant portion of the problem this area has experienced going back years.”
The area affected by the flash floods is an anomaly of geography and infrastructure. Low-lying to begin with, it is also a place where three major storm sewers’ draining points to the north and west converge into a single line that runs south under First Street to a trunk sewer running along Florida Avenue.
Floods have plagued the area intermittently for generations, but this year’s deluges were unprecedented. Four times, brief but intense storms caused significant flooding in the blocks surrounding Rhode Island Avenue and First Street. Sewage backed up into the basements or flowed from street level into about 200 households. Standing water approached two feet deep on some streets.
Storing runoff at the McMillan site, where much of the city’s drinking water was filtered and treated until 1985, is expected to relieve pressure on the First Street line during intense rains. The tunnel will provide additional relief — enough that the water from last summer’s most severe storm would have barely lapped the top of street curbs. But a full solution is not expected until the completion of a 23-foot-wide, east-west trunk sewer that would drain the First Street bore.
The proposal, in part, represents an acceleration of existing plans to build relief sewers, previously expected to be completed in 2025. Rather than wait to build the First Street tunnel, D.C. Water wants to start tunneling immediately, using the 19-foot bore to store runoff while the trunk line is built from the east.