Superior Plating Superfund Site
Update to amended decision documentSuperior Plating Superfund Site Amended Minnesota Decision Document, March 20, 2014
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).
Is the site a hazard to public health or the environment?
The TCE plume could be a health concern if it were to get into drinking water wells. Fortunately, everyone in the area is connected to city water, and there are no known private wells in the area. Nonetheless, the TCE plume is considered a threat to groundwater in the area. A down-gradient remediation system is in place to control the spread of the plume by capturing the polluted water and pumping it back to the Superior Plating site for treatment before discharging it to the sanitary sewer.
Most of the soil contamination at the site is under the building's concrete floor, so there is no direct exposure to people. There is some potential for exposure if contaminated soil in a small area at the back (north) of the building becomes airborne as dust. The seepage on the northwest side of the building is a concern as it could come in contact with people or animals. The seepage is classified as hazardous waste because of its relatively high concentration of contaminants.
The MPCA has investigated the potential for soil vapor in the soils above the plume and determined that the levels are low and not considered a health risk.
What's being done?
Before it went bankrupt, Superior Plating Company worked with the MPCA to define the extent and magnitude of the groundwater contamination.
To address the TCE plume, in 1992 the company installed a state-of-the-art system to extract and treat contaminated groundwater. This system uses an extraction well to pull two to five gallons a minute from the plume. The water is sent through a clear tube, where it is exposed to strong ultraviolet light. This breaks down the contaminants to levels acceptable for sanitary sewer disposal, and the water is then discharged to the sanitary sewer system for final treatment. The system, which is designed to both treat the water and prevent it from moving further away from the plant, is working well.
The seepage at the northwest side of the building has been an issue. In December 2011 and again in February 2012, environmental contractors, working under the direction of MPCA emergency responders and city officials, cleaned up the seepage. During normal soil moisture conditions, a sump pump under the gravel collected any liquid and conveyed it back, into the plant, where was treated in the company's on-site wastewater-treatment system. This system is no longer operative, and seepage is now manually pumped and collected in a holding tank on site.
While it occupied the building, Superior Plating tried to remediate as much of the contaminated soils as it could. However, because of operations it was difficult to deal with this problem effectively, mostly because of the heavy concentration of contamainated soils beneath the building. Any plan for complete removal of the contaminated soils must involve removing the building also. Excavation is not an option as long as the building exists on site.
What happens next?
Since the bankruptcy of Superior Plating Company in 2012, a new owner has purchased the site. The new owner, First and University Investor LLC (FUI), has entered into an agreement with the MPCA to address the remediation of the soils and the operation and maintenance of the groundwater-treatment systems.
FUI entered the VIC Program before it purchased the site. After much collaboration and negotiation, FUI and the MPCA have agreed that FUI will be responsible for:
- demolition of the building, ensuring that any contaminated media in and beneath the building are disposed of at properly regulated facilities;
- removal of contaminated soils beneath the building according to the MPCA-approved Response Action Plan dated November 7, 2013;
- continue the operation and maintenance of the groundwater systems; and
- leave the site excavated with exposed bedrock for no longer than six months while working on a development plan.
For its part, the MPCA has agreed to take responsibility for any contaminated media outside the property boundaries, and to continue to maintain and operate the groundwater systems, if necessary, after five years post remediation of the site.
In December 2013, the MPCA collected soil vapor samples from representative probes placed throughout the groundwater plume area. The results found no detections exceeded 10 times the intrusion screening value (a number developed by the MPCA to determine the potential for soil vapors to be a public health risk).
Since late December 2013, the MPCA has also overseen FUI’s activities to clean up the interior of the building. This work has been extensive and time consuming. Once the building is totally clean, demolition may proceed under the oversight of the MPCA and the city of Minneapolis.
To assist MPCA staff, the agency has contracted with Bay West, a state contractor, to provide oversight and monitoring for two and one-half days a week (but potentially less frequently if warranted by results of the monitoring) for the duration of the demolition and remediation project. This oversight will include observations, air monitoring, and filing of a daily electronic report with the MPCA. For more details, see the following document.
The MPCA has worked diligently to assist Superior Plating through its closing and FUI through its new ownership and responsibilities. Human health and the environment will always be the MPCA’s priority and the agency will continue to oversee the remediation of the Superior Plating Superfund Site with those priorities in mind.
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.
For more information
If you have questions or would like more information about the Superior Plating site, please contact:
MPCA Public Information Office
520 Lafayette Road
Saint Paul, MN 55155