Pipe Reaming, Restrained-Joint PVC Pipe Helps Colorado Municipality Complete Challenging Sewer Line Replacement

By John Coogan, North American Specialty Products | July 2013, Vol. 68, No. 7

A few years ago, the city of Fort Collins, CO, decided to replace 4,000 feet of aging vitrified clay, sanitary sewer line that had caused many headaches for the municipality.

The sewer line was often in need of maintenance, as the pipe had several cracks and offset joints, and its old brick manholes were deteriorating. The line was also undersized for accommodating the growing needs of the part of town it served. To make matters worse, the redevelopment of this district over the years had made maintenance access very difficult. A portion of the sewer line now had six commercial buildings and 10 mobile homes directly above it and is located within 10-feet of eight other homes.

“The original sewer main’s accessibility was just awful -- most of the manholes were in places that you just couldn’t get to,” says Dean Saye, project manager for the city of Fort Collins Utilities. “To improve access during the pipe replacement, we had the option of rerouting the line or keeping it in place and making improvements to it.”

The utilities department first huddled with its design team, which included Stantec Consulting Engineers of Fort Collins, to form its plan of action. Stantec Consulting began designing a rehabilitated sewer line that would adequately convey current and future flow rates. The engineer also made attempts to find the best route for relaying the sewer to a corridor that would allow better access for city maintenance workers.

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The existing sewer had relatively minimum grades of .20 percent and .40 percent. With these minimal slopes and the need to extend existing sanitary sewer services and purchase a new permanent easement, the design team determined it was cost-prohibitive and not feasible to reroute the sewer line to a more accessible alignment. The new line would need to follow the old route.

Design team
Through its Alternative Project Delivery Service (APDS) -- a design-build-style operation that allows contractors to serve on the design team and contribute constructability knowledge -- the city brought Connell Resources Inc., of Fort Collins, on as general contractor. Together, the team worked to figure out the least disruptive way to replace the failing sewer line. The majority of the 4,000 feet could be replaced through an open trench, but the 1,600-foot portion running under the business district required a trenchless method that would allow the new line to follow the same path as the existing line.