By Mike DeBonis, Thursday, December 6, 2:56 PM
D.C. Water and city government officials are proposing to divert runoff from severe storms into holding facilities before it threatens to inundate the Bloomingdale and LeDroit Park neighborhoods of Northwest Washington in response to a spate of flash floods last summer.
The work, estimated to cost as much as $40 million more than previous flood-relief plans, would involve converting facilities on the former McMillan sand filtration site into storage tanks capable of holding 3 million gallons of runoff each. Meanwhile, D.C. Water crews would immediately begin digging a six-block-long, Metro-size tunnel under First Street, which could store 6 million gallons of stormwater and sewage.
The McMillan storage tanks could be finished as soon as spring 2014, said George S. Hawkins, D.C. Water`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.
[Allew Lew quote here....]
[Stuff that Bloomingdale residents already know in these removed paragraphs.]
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.
Under the new plan, the entire project would be completed by 2022, three years earlier than previously contemplated.
[Two removed paragraphs about money.]
Complicating the relief plans is an effort to redevelop the McMillan site into a new neighborhood of residences, shops and offices. Recently, Gray issued an economic development plan that proposed a medical hub for the site, tying into the three hospitals immediately to the north.
Officials believe that the flood relief plan will not significantly alter the development plans. One filtration cell on the site`s northeast corner would capture flow from a storm sewer running down North Capitol Street; on the site`s western edge, another cell will be used to capture flow headed straight down First Street. Three acres at the southwest corner would be used for the tunnel-boring operation.
Representatives of the development team tasked with preparing the site were skeptical of the flood relief plan when it was initially floated in September, citing the fact that the 27-acre McMillan site is a protected historic landmark. But city officials believe converting the old filtration tanks to hold stormwater is compatible with its historic use.
[some noncritical paragraphs removed.]
[These three paragraphs are on backflow preventers.]
[Teri Janine Quinn is quoted in the last two paragraphs.]