Behind the project: Taggart Outfall Structural Rehabilitation

Wastewater systems are often the last thing on our minds. That was not the case for a group of over 4,000 Portland, OR schoolchildren in 1938.

Portland’s wastewater history starts in 1864 with a simple wooden trough that collected sewage and carried it directly to the river. Fifteen miles of 9 to 18-inch diameter terracotta pipe was installed by 1883, and 1,100 miles of concrete or brick pipe conveyed sewage directly into the river by 1933. At this time, public health concerns started to rise given the severe water pollution the current sewage system was causing. According to Environmental Services, “[p]ollution had robbed the river water of nearly all its oxygen,” and “…salmon fingerlings placed in the river died within 15 minutes.” The 4,000 schoolchildren held a rally, citizens acted, and the Water Purification and Prevention of Pollution Bill was passed in 1938.

Fast forward 82 years and the wastewater collection system now spans 2,500 miles of pipe ranging in size from 4-inches to 12-feet in diameter. There are now two wastewater treatment plants, over 90 sewage pump stations, and over 15,000 sumps that collect stormwater runoff from streets. The system serves more than 600,000 residents spread over 94,000 acres.

The Taggart Outfall was constructed in 1906 and is one of the longest-serving large diameter sewer pipes in the City. Spanning 7,600 linear feet, the 64 to 120-inch brick sewer is now in need of rehabilitation. James W. Fowler Co. (JWF) is working with the City of Portland Bureau of Environmental Services to rehabilitate portions of the Taggart Outfall. In order to minimize surface disruptions and maximize the use of existing resources, trenchless rehabilitation techniques will be used wherever feasible. JWF is also responsible for the repair of manholes and local hydraulic improvements.

The 114-year-old brick sewer tunnel is critical in serving Southeast Portland residents and visitors. While completion of this project will increase the sewer’s resiliency, extend service life for up to an additional 100 years, and help prevent sewage overflow in buildings and on streets, it doesn’t come without challenges. The tunnel is located close to high traffic areas including TriMet light rail tracks, Union Pacific Railroad tracks, as well as, Highway26/Powell Boulevard. Rainfall has also interrupted work as stormwater flows rapidly through the tunnel creating unsafe working conditions.

Even with the challenges presented, JWF crews have successfully continued with repairs. The main repair methods used are Slip Lining and Tunnel Liner Plate. Using a locomotive, crews work up to 75-feet below the surface to essentially construct a new sewer inside the old brick sewage system. Some sections will be completed by inserting 8-foot long fiberglass-reinforced pipe liner inside the tunnel; other sections will involve bolting new steel liner plates inside the tunnel. The gap between the new sewer and the old brick sewer will then be filled with grout. Working underground minimizes disruptions to the public and surrounding businesses.

The shaft looking down from ground level at the job site.
Photograph by: James W. Fowler Co.
Bolted new steel liner plates in comparison to old brick sewer tunnel.
Photograph by: James W. Fowler Co.
Photograph by: James W. Fowler Co.