Rehabbing a Century-Old Interceptor Sewer Without Disturbing Bird Sanctuary and Peace Garden

What a difference a century makes. When the Southwest Minneapolis Interceptor Sewer was built in 1918, it was one of the first sanitary sewer lines in Minneapolis, Minn. The sewer main and manholes were made from hand-placed bricks and concrete.

Fast-forward 96 years later: Parts of the sewer main linking south Minneapolis and St. Louis Park to the Metropolitan Council Environmental Services (MCES) Treatment Plant in St. Paul have deteriorated to the point where officials said it needed to be repaired to ensure public safety.

The project was designed by Foth Infrastructure and Environment and MCES staff in close cooperation with the Minneapolis Park and Recreation Board staff. This involved wetland surveys, tree surveys, soil exploration and numerous meetings with agencies and since the site is in the heart of a dense urban area, there were many informational meetings open to the public.

Michels Pipe Services was awarded the contract and used a Premier Pipe USA cured-in-place pipe (CIPP) lining system to rehabilitate the sewer main and reconstruct the manholes, returning both to like-new conditions. Michels Pipe Services is a division of Michels Corp., one of the largest utility contractors in North America. Michels Pipe Services is an experienced installer of CIPP lining systems for sewer mains, water mains and other pressure pipes, and culverts around the country.

With the passage of time, the area above the sewer line had also changed. Minneapolis Chain of Lakes Regional Park — which the sewer main crosses — has become one of the most popular destinations in the City’s park system. It is home to a bird sanctuary, peace garden and environmentally sensitive wetlands. The surrounding area has experienced substantial residential growth, to the point where the sewer main serves more than 30,000 people.

Successfully rehabilitating more than 10,000 lf — or nearly 2 miles — of sanitary sewer main in this challenging environment took a significant amount of planning and construction management prior to work getting started in the spring 2014 and until it was completed in March 2015.

Project Staging

When possible, Michels prefers to start CIPP projects in gravity systems like this one at the highest elevation point and proceed down the line. In this case, this project consisted of three phases: 3,371 lf of 33-in. diameter main, followed by 3,474 lf of 39-in., followed by 3,605 lf of 60-in. The 33-in. main crossed under parkway roads, the 39-in. main crossed through the bird sanctuary and peace garden, and the 60-in. sewer was adjacent to a park and a residential neighborhood. To meet the requests of the customer, Minnesota Parks Board and representatives of the Thomas Sadler Roberts Bird Sanctuary, it was decided that the 39-in. main be completed last, from December to February 2015. This would minimize any disruption to bird nesting and breeding times.

The 33-in. and 39-in. liners were wet-out and transported by truck from Brownsville, Wis. Each was installed in six segments. Because the weight of the resin-impregnated liner would have been too great to ship to the project site, the 60-in. liner was wet-out over-the-hole in four segments.

Communication

Consistent, effective communication was essential to coordinate schedules between Michels and its subcontractors and to keep affected property owners abreast of the temporary inconveniences the work would necessitate. This included temporary parking and traffic restrictions, equipment parking, extended work hours, lights and the presence of diversion pumps, generators and other construction equipment.

There were 57 residents connected to these sewer mains. They were notified at the start of the project and again a month before the specific work started. The residents needed to relocate for two to five days, at the project’s expense, while the 60-in. liner was being installed.

Michels worked around the clock 24/7 to minimize all inconveniences to the fullest possible extent. For those construction zone inconveniences that could not be completely mitigated, it was Michels crew’s practice to clearly communicate the process and schedule of the work to develop a trusting and harmonious relationship with local residents.

Ground Conditions

The soil in the project area, particularly near the bird sanctuary and peace garden, is in a soft wetland that contains peat. The original pipe was built on pilings that were installed up to 20 ft deep to reach more stable sand. The benefit of winter construction was frozen soil beneath the trail. This allowed for a solid surface to handle the weight of the refrigerator truck used to haul the resin-impregnated pipe liner and other equipment to access manholes.

Helical piers were installed to stabilize the manholes Michels rebuilt in the bird sanctuary. The wet ground conditions along with the alignment had resulted in significant groundwater infiltration, which needed to be curbed before the liner was installed. In some instances, chemical grout was injected into the soils around the manhole and sewer main to reduce groundwater infiltration.
Weather



Throughout the year, Minneapolis’ weather can range from above 100 F to well below -10 F. Each season presents unique challenges. Groundwater infiltration was a particular issue during the spring thaw. Summer’s heat and direct sunlight required tents, tarps and refrigerated trucks to be used to prevent the liners from prematurely curing. Winter presented its own operational and safety issues. During installation in the bird sanctuary, the only accessible hydrant for use during water inversion was 2,000 ft away. Water supply lines periodically froze when temperatures dipped to below -10 F.

Additionally, all crewmembers were outfitted with boot cleats to improve traction. Working in frigid temperatures is common at Michels, and our crews and project managers know what precautions are necessary to maintain health and safety.

Bird Sanctuary

Successfully completing installation in the environmentally sensitive bird sanctuary required communication and cooperation with the Minneapolis Park and Recreation Board, which owns the 31-acre public parkland.

The sanctuary was established in 1936, nearly 20 years after the sewer main had been installed. The only point of access to the sanctuary and the sewer main was Bossen Lane. During planning, a decision was made to temporarily widen the path to accommodate the one-way passage of a refrigerator truck containing the liner, as well as other equipment needed during construction. At the end of the project, Bossen Lane was turned into a narrow limestone path that will be permanently maintained to allow access to the sewer line and for park users.

Although an over-the-hole wet-out method was considered for the heavy, 39-in. liner, that plan was not implemented because it would have required a larger jobsite footprint in the environmentally sensitive area.

Brady Sonnenberg is midwest operations manager with Michels Pipe Services. Willie Grams is project manager with Michels Pipe Services. Grams was the permanent, onsite project manager for this project.