Representatives of the development team tasked with preparing the site were skeptical of the flood-relief plan when it was floated in September, citing the fact that the 27-acre McMillan site is a protected historic landmark. But city officials think converting the old filtration tanks to hold stormwater is compatible with its historic use.

“They will be used for their original purpose, except they won’t be cleaning the water, they’ll just be holding it,” Hawkins said.

Although the sewers in Bloomingdale and LeDroit Park generally carry combined sanitary and storm sewage, the McMillan tanks would hold only storm runoff, he added. Retrofitting the tanks would involve removing the filtering sand and installing a flexible plastic liner and pump facilities.

Aside from the new infrastructure, Hawkins said, his agency will be redoubling efforts to encourage homeowners in the affected area to install backflow preventers, devices meant to prevent sewer overflows that threaten basements even if flooding never reaches street level.