DC Water Completes Major Repairs on Century Old Sewer Tunnel

Following a nearly year-long construction effort, DC Water has completed repairs on a 9-ft diameter, 140-year old sewer tunnel on 22nd Street Northwest, the authority reported on June 13. Construction was done in two phases, with the second phase completed one month ahead of schedule and under budget. The work zone in the area of 22nd and Q streets is being demobilized.

The tunnel section is part of the Northwest Boundary Trunk Sewer, built in the 1800s. Last year, an inspection revealed a large void in the soil above measuring 13 ft long and 10 ft wide and the tunnel in danger of collapse, necessitating the long-term closure of a section of 22nd Street.

Significant structural issues were also identified, as well as upstream and downstream from the emergency repair. These included longitudinal cracks, missing cobblestones and bricks, and root penetration prompting emergency repairs.

Construction, sometimes 24 hours a day, seven days a week, posed challenges with crews working two stories below ground in difficult conditions. At the same time the sewer pipe remained active with combined stormwater and sewer debris flowing through and prompting work stoppages when heavy rain inundated the system.

The work involved reinforcing the sewer tunnel and stabilizing the soil around the initial void. This required injecting grout into the soil, framing the walls with rebar, and using high-pressure spray-applied shotcrete and geopolymer, 4 in. to as much as 9 in. thick. This included:

• 139,000 lf of rebar
• 25,450 rebar anchors
• 28 tons of shotcrete
• 459 tons of geopolymer

Emergency repairs began in July 2024 as part of the first phase of the project which involved stabilizing the soil and reinforcing the tunnel around the initial void. Additional inspections identified more structural deficiencies requiring a second phase to repair more than 1,200 lf further upstream and downstream.

DC Water worked closely with the District Department of Transportation to minimize the disruption to traffic in the area and appreciates residents and commuters for their patience while repairs were made for the safety of the community.

DC Water operates approximately 2,000 miles of combined, separate, and stormwater sewers. Addressing aging water and sewer infrastructure throughout the District is a critical part of the 10-year, $9.6 billion Capital Improvement Program. This includes replacing or rehabilitating similar large diameter sewer lines that have reached the end of their useful life.

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