Could McMillan’s subterranean filtration cells again hold water? (Claire Bedat/ASLA)

But there was a novel medium-term solution discussed that could help alleviate drainage issues that led to three major flooding incidents over 10 days in July.

D.C. Water General Manager George S. Hawkins said his agency is exploring whether the historic McMillan Sand Filtration Site north of Bloomingdale could be used as a place to store storm runoff during major storms, easing the aging and overloaded sewers downhill.

Storing water at McMillan, which hasn’t filtered water since 1985, would be unlikely to prevent all flooding, Hawkins said. But in combination with other efforts, such as installing a “relief sewer” or transferring some flow to other “trunk” sewers, he said, “we’ll be able to get a dent.”

D.C. Water spokesman Alan Heymann said Wednesday that engineers are exploring whether the subterranean sand filtration facility is structurally sound enough for the job and whether it could hold the millions of gallons of storm runoff necessary to provide meaningful relief to the downhill neighborhoods.

The concept is that, during major storms, storm sewers upstream from Bloomingdale would dump runoff into McMillan’s filtration cells, where it would stay until the weather passes. Once downstream sewers were less taxed, the runoff would then be pumped though to be processed at Blue Plains.

Without endorsing the McMillan idea specifically, City Administrator Allen Y. Lew said Tuesday he would work up a medium-term relief plan within 30 days, with an eye toward implementing it in about a year. Hawkins indicated money shouldn’t be a problem: “I am confident that the financing element will not be as much a challenge as some of the other elements will be,” he said.

The McMillan-as-stormwater-impound idea has won fans among some area residents. Russell Kinner, who testified at the hearing, suggested that it would be using the site for “its original industrial purpose.” That is: “Keep it more or less the way it is, and store water there during storms.”

But keeping it more or less the way it is could mean tossing aside, or at least modifying or delaying, grand redevelopment plans for the site.

If D.C. Water and city officials decide they need to use McMillan’s underground filtration cells until the planned storage tunnel is complete in 2025, that stands to affect how redevelopment will proceed — perhaps it could be done in phases, or perhaps it would have to wait until the tunnel is fully in service. Jose Sousa, a spokesman for the city economic development office, said only that there have been “conversations” about using the McMillan site for stormwater impoundment.

D.C. Council member Kenyan McDuffie (D-Ward 5), who has both been intimately involved in the McMillan planning and has been crusading for storm-ravaged residents, said it’s “a little too early to get residents’ hopes up” about McMillan. But he said his first priority would be using the site for flood relief: “Given the devastation that the residents have experienced, the costs and the toll that been taken, then all options should be on the table.”

But McDuffie said he hasn’t given up on development, either. “The question I will have is, can we do both?” he said. “I haven’t heard that the two are mutually exclusive at this point.”