The City of Minneapolis and the MWMO partnered to install an underground infiltration system in this heavily industrialized area near the University of Minnesota. The 10.3-acre area is covered with 92 percent impervious surfaces, with little space available for above-ground infiltration practices.
The project area historically drained to the city’s sanitary sewer. The city needed to divert the stormwater runoff to the Como Tunnel, a system that lacks capacity during larger storm events. As such, a main goal of the project was to capture and infiltrate stormwater runoff before diverting it into the tunnel.
Crews installed modified box culvert beneath the street. The system captures and contains stormwater runoff in a large, underground tank with gaps in the bottom that allow the water to slowly discharge into the soil. The project is projected to reduce the amount of runoff entering the sanitary sewer (and now the Como Tunnel) by almost 7 million gallons per year, providing both hydraulic and water quality benefits. It will also stop an estimated annual average of 19 pounds of total phosphorus and 10,300 pounds of total suspended solids from traveling to the Mississippi River.
In addition to reducing pollution in local waterbodies, the project will serve as a kind of pilot for the City of Minneapolis. Public works crews will learn more about the operation and maintenance of the infiltration system and will be monitoring its performance. If it performs as projected and proves to be cost-effective, the city may employ similar practices in the future.