Aging sewer pipe in South St. Paul will be replaced

New pipes to be installed under Mississippi River

Work is scheduled to begin in July to replace an aging regional sanitary sewer that runs through South St. Paul and under the Mississippi River en route to the Metropolitan Wastewater Treatment Plant in St. Paul.

The existing 48-inch-diameter sewer, operated by the Metropolitan Council Environmental Services Division (MCES), was built in 1973. Each day about 7 million gallons of wastewater from South St. Paul, Inver Grove Heights, Newport and St. Paul Park are pumped through the sewer, also referred to as a forcemain.

People on a barge extracting soil borings from the Mississippi River bed.

The new sewer will cross the Mississippi River about 1.5 miles north of the Interstate 494 (Wakota) Bridge in South St. Paul. Crews are shown doing soil borings in 2007. Engineers used information from the borings to help design the project.

MCES determined it would be difficult and more costly to repair the approximately 4-mile-long sewer, and opted instead to replace it with two side-by-side 30-inch pipes. This option also will provide MCES more flexibility in operating and maintaining the sewer and ensure better service for the cities.

First phase: Through the stockyards

The first phase of the approximately $37 million project will be in a commercial and industrial area of South St. Paul, north of Interstate 494 between Concord Blvd. and the Mississippi River – a large portion of which once included the stockyards and meat packing plants. Ames Construction, with a bid of approximately $13.8 million, has been awarded the contract for this phase of the project.

Navigating sensitive river areas

The next two phases will involve installing the new pipes under the river, then along a peninsula between the river and Pig’s Eye Lake. “We’re working with several local, state and federal agencies and commercial entities to minimize the project’s impact on river navigation and environmentally sensitive areas in and along the river,” said Bill Moeller, MCES’s assistant general manager in charge of the Interceptor Services Department.

Among issues being addressed are minimizing disruption of barge traffic, surveying and relocating an endangered species of mussels in the river, scheduling work around the winter roosting season for bald eagles, and steering clear of a nearby heron rookery. MCES anticipates resolving the issues and bidding these two phases of the work in the next several months.

The river crossing will involve digging a 10-foot-deep, 68-foot-wide trench in the river bed to install a 1,300-foot stretch of pipe. Concrete collars and riprap will keep the pipe submerged in the trench, then it will be backfilled to return the river bed to its original condition.

Total project completion expected in 2012

Completion of the first three phases is anticipated in mid-2011. The final two phases of work involve connecting the new sewer pipes to the wastewater treatment plant, and installing a short section of pipes near the MCES wastewater pumping station at the south end of the project area. The latter will be coordinated with MnDOT’s I-494/Wakota Bridge construction. Completion is expected in 2012.