McMillan Stormwater Storage and Green Infrastructure (Washington, D.C.)


DC Water developed this emergency fast-track, design-build project to alleviate flooding in two Washington, D.C. neighborhoods that was caused by heavy rain events. The technical solution for this project used a combination of new infrastructure, existing structures, and new green infrastructure to reduce, capture, and store more than three million gallons of stormwater.


• Conversion of one below-grade catacomb-like sand filter cell (approximately one acre in area) into an underground storage basin for three million gallons of stormwater during a wet-weather event

• Temporary flume bypass of live sewers to enable construction of two underground diversion structures under heavily traveled city streets

• Installation of eighty 65-foot-deep secant piles to support a 50-foot-deep diversion structure excavation

• Construction of a 25-foot-deep diversion structure and installation of a 48-inch-diameter pipe under North Capitol Street to divert flow into the storage basin

• Construction of a 65-foot-long × 20-foot-wide × 60-foot-deep steel/reinforced concrete “hybrid” diversion structure under First Street NW to route flow to a future tunnel drop shaft

• Fourteen green infrastructure retention basins to assist in the collection of stormwater and free capacity within the conveyance system

Work included extensive night work and maintenance of traffic plans required to minimize disruptions on the surrounding areas. This project went on to receive a 2015 Engineering News-Record Best Project Award in the Water/Environment category for the Mid-Atlantic Region.