Pittsburgh lines 75-foot-deep sewer near Pittsburgh Zoo

The Pittsburgh Water and Sewer Authority (PWSA) recently rehabilitated one of the largest sewers in its system — a 78-inch sewer, buried 75 feet underground — with lining as part of its Large Diameter Sewer Rehab Program.

The 78-inch sewer, located near the Pittsburgh Zoo, was selected for rehab work due to the degraded condition of the pipe, observed during camera inspections. Carrying approximately 16 million gallons of wastewater per day, the sewer is important to the health of the overall system. The lining is expected to prolong the site’s life by approximately 50 years.

Crews worked their way down the interior of the pipe, using utility maintenance holes as access points, installing the liner and completing inspections of their work as they moved along. Lining sewers avoids costly excavations, especially on large-diameter sewers like this one, which is buried 75 feet underground.

Sewer rehabilitation of this scale requires specialty expertise as well as a tolerance for small spaces and depths. Crew members are lowered into the pipe via utility maintenance hole or other access point to apply the liner, with temporary retaining walls and bypasses located upstream of the work to stop any wastewater flows from interfering with their progress.

PWSA documented the contractor team and their progress in this short video:

The Large Diameter Sewer Rehab Program involves trenchless rehabilitation of 36" diameter or greater sewer mains to restore structural integrity, reduce root intrusion, infiltration, and document the status of the pipe with camera and visual inspection. The pipe located near the Pittsburgh Zoo was one of three sites that received rehab work as part of this $1.4 million contract.

Large diameter sewers are very difficult to repair if they fail as they are typically much deeper than the upstream pipes and often run under critical infrastructure and environmental features, like busways, railroads, or streams.