Rock dam blockage inside ruptured 72-in. Potomac Interceptor sewage line has added new complication to repair the system serving Washington, D.C. and suburbs.
Snowmelt and flow debris continue to complicate the District of Columbia Water and Sewer Authority’s efforts to advance repair of the ruptured 72-in. Potomac Interceptor sanitary sewer line, which on Jan. 19 released what observers say could be up to 300-million gallons of raw sewage into the Potomac River just outside Washington, D.C.
The event is being considered by experts to be the largest wastewater spill in U.S. history.
The agency, known as DC Water, has largely managed to prevent additional releases through a temporary pumping system that uses a dry section of the adjacent C&O Canal as a temporary bypass channel around the damaged section while a repair plan is formulated.
The agency has not responded to requests by ENR to identify the contractors involved in the cleanup and containment effort, or elaborate on information in public statements.
In a Feb. 11 "open letter" published on its website, DC Water CEO and General Manager David L. Gadis said the agency’s “immediate priorities have been containment, environmental monitoring and stabilization - working closely with federal, state, and local partners to assess water quality, ecological impacts and necessary remediation.”
Complicating the effort is the unexpected disovery of a large rock dam blockage inside the damaged sewer line that has been difficult to remove with existing DC Water pumping and machinery capacity.
Work was set to expedite with the Feb. 13 site arrival from out of state, of five 13-million-gallon-per-day pumps, which will provide capacity to more fully isolate the damaged section of pipe and allow workers to remove the large rock dam about 30 ft away from the break and formulate and implement a repair strategy. At least two are expected to operate by Feb. 15, as rain and snowmelt will cause higher flows.
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DC Water crews also are excavating two new access pits to support full installation of the enhanced bypass pumping system. "These additional pumps will increase system redundancy and capacity as work progresses," it said. "It’s expected to take an estimated 4-6 weeks of additional time to get a system in place that will add more, larger bypass pumps in a new location and stabilize the site for heavy machinery to safely begin removing the large rocks and boulders inside the sewer line."