South St. Paul Interceptor Improvements
Metropolitan Council Environmental Services (MCES) provides wastewater conveyance and treatment service to the greater Twin Cities metro area. One important project identiﬁed in recent MCES planning was a much-needed replacement of a major forcemain interceptor. Wastewater from the Cities of South St. Paul, Inver Grove Heights, St. Paul Park and Newport is pumped through the forcemain to the Metropolitan Wastewater Treatment Plant (MWWTP), a distance of approximately four miles. The 40-year-old, 48-inch diameter pre-stressed concrete cylinder pipe forcemain was showing signs that could lead to failure. A leak in this pipeline would be highly problematic; it crosses the Mississippi River and carries all wastewater from four Cities along a levee that protects the City of South St. Paul.
The South St. Paul Interceptor Improvements project replaced the aging forcemain with a dual 30-inch diameter forcemain. This dual forcemain pipeline passes through the former S. St. Paul Stockyards site, three railroad tracks, a Mississippi River ﬂood control levee, the Mississippi River, a wooded wetland and the MWWTP’s efﬂuent channel. Finally, the alignment was close to the location of an archaeological site and bald eagle nesting areas.
These obstacles lent considerable complexity to the project and required creative thinking from the design team and construction contractor to keep the project on time and within budget. The project involved tunneling through a levee with compressed air techniques and an open-trench excavation across the Mississippi River that used sonar to guide the excavation process. The project was completed on time and within budget during summer of 2012 at a construction cost of approximately $33 million.