Minneapolis: Superior Plating site

Investigation and cleanup of contaminated soil and groundwater is under way at and near the Superior Plating Superfund Site in northeast Minneapolis. The work is being done by a voluntary party, First and University Investor LLC, through the Minnesota Pollution Control Agency’s Voluntary Investigation and Cleanup (VIC) Program under the oversight and partnership of the MPCA’s state Superfund Program.

What's the problem?

Superior Plating and the MPCA identified three issues:

  • An area of groundwater — called a "plume" — is contaminated with chlorinated solvents, including trichloroethylene (TCE), a common industrial solvent. This contamination is moving slowly with shallow groundwater away from the building toward the southeast. Action is being taken to capture the contamination and pump it back to the Superior Plating site for treatment.
  • Several areas of soil beneath and immediately adjacent to the building are contaminated with solvents and heavy metals, primarily chromium.
  • Occasionally, chromium-contaminated liquid seeps from the ground behind the northwest side of the building and collects in a ditch along nearby railroad tracks. This liquid contains high levels of metals and VOCs. The seepage is most likely caused by soil contamination under the building and seems to appear only at times of high soil moisture (i.e., spring runoff or rain).

The Superior Plating Company was located at University and First avenues Northeast in Minneapolis. Built in the 1890s, the building originally was used as a streetcar barn and repair facility. Superior Plating began using part of the building in 1956, expanding to the rest of it in the early 1960s. The building was used for the company's metal-plating operations, in which metal parts were brought to the plant and plated with various other metals.

At first, the plating lines were set up on the building's original wood plank floor. Drips, spills and leaks from the lines passed through the floor and were caught by a system of concrete-lined troughs in the subfloor. Liquid in this system flowed to several sumps and ultimately to the sanitary sewer. It's thought that leaks from these troughs let chemicals seep into the soil and bedrock beneath the building.

The company later had better pollution-prevention methods, but contamination remains in the soil and groundwater below and near the building. This contamination has been known about since the early 1980s, when the Minneapolis Community Development Agency conducted an investigation of the site that revealed the presence of volatile organic compounds (VOCs) and metals in the groundwater.

Soil sampling through the floor of the building showed similar contaminants. Superior Plating worked cooperatively with the MPCA since the 1980s to address these problems. The site was placed on the state Superfund list (the Permanent List of Priorities) in 1985, with a federal Hazard Ranking Scoring system score of 6. This system assigns a number from 1 to 100, indicating the relative risk a site poses, with 1 representing lowest risk and 100 highest.

If you have questions or would like more information about the Superior Plating site, please contact:

Walker Smith
651-757-2559
walker.smith@state.mn.us