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, LMC, a Lennar Company, through the Minnesota Pollution Control Agency’s Brownfields Program under the oversight and partnership of the MPCA’s state Superfund Program.
Redevelopment of the eastern portion of the site into the Nordhaus apartments was completed in 2016 by LMC. Redevelopment of the western portion of the site into another apartment building is currently underway by LMC. LMC and their environmental consultant, Terracon, plan to begin soil cleanup work in March 2019.
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 and per- and polyfluoroalkyl substances (PFAS). This contamination is moving slowly with shallow groundwater away from the former plating building toward the southeast. Action is being taken to delineate the plume and submit recommendations for cleanup of the plume.
- Several areas of soil beneath and immediately adjacent to the former building were contaminated with solvents and heavy metals, primarily chromium. These soils were cleaned up during the redevelopment of the eastern portion of the Site in 2015-2016. The new Nordhaus apartment building now occupies the area of the former plating building.
- Occasionally, chromium-contaminated liquid used to seep from the ground behind the northwest side of the former plating building and collected in a ditch along the adjacent railroad tracks. This liquid contained high levels of metals and VOCs. The seepage was primarily caused by soil contamination under the former plating building and mostly appeared at times of high soil moisture (i.e., spring runoff or heavy rain). The MPCA installed a new leachate collection system during the redevelopment of eastern portion of the Site. Since the new leachate collection system was activated in 2017, there has not been seepage of contaminated groundwater into the railroad ditch. The leachate collection system has been operating as intended and the MPCA has observed a decrease in the concentrations of contaminants.
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.
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