Bencor designed and constructed reinforced slurry diaphragm walls for CSO Shafts along the tunnel alignment.

The Project

DC Water is in the process of implementing its Long Term Control Plan (LTCP) to meet requirements established by the US Environmental Protection Agency for pollution control and reduction of combined sewer overflows into nearby waterways. The DC Clean Rivers Project Division H - Anacostia River Tunnel is one of several contracts that comprise the overall LTCP, which consists of a network of new tunnels, sewers and diversion structures designed to capture overflows to Rock Creek, and the Anacostia and Potomac rivers for treatment at the Blue Plains Advanced Waste Water Treatment Plant.

The Solution

Bencor was contracted to design and construct 6 reinforced concrete slurry diaphragm wall shafts along the tunnel alignment. The slurry walls provided initial support during shaft excavation and also formed part of the permanent structure. These shafts also served as the main access point for the tunnel construction and ultimately will assist in discharging CSOs to the Anacostia River (shaft diameters vary from approximately 22 feet up to 70 feet). The walls ranged in depth from approximately 126 feet to 140 feet, and a thickness of 2.5 to 3 feet. Anticipated soil conditions included fill, alluvium, and very stiff to hard silt and clays. A combined total of approximately 138,900 square feet of wall was installed, using hydromill technology.

Project Facts


DC Water

Main Contractor(s)

Impregilo Healy Parsons, JV

Keller Business Unit(s)



Parsons Corporation