Trichloroethylene and perchloroethylene in the groundwater at this site has contaminated groundwater and caused vapor intrusion issues. In March 2022, the Environmental Protection Agency added this site to the National Priorities List.
Health and environmental concerns
The primary contaminant of concern is trichloroethylene (TCE). Perchloroethylene (PCE) has also been detected but at lower levels of concern. TCE and PCE are solvents used for metal cleaning, plating, vehicle repair, and other industrial processes. PCE is also a commonly used solvent in the dry cleaning industry. TCE can have short-term health risks, and both TCE and PCE have the potential to cause long-term human health risks.
Location
The Southeast Hennepin Area Groundwater and Vapor Site (Minneapolis, Minn.) is bounded to the north by Broadway Street NE, to the east by Industrial Boulevard NE, to the south by Hennepin Avenue, and to the west by Taft Street NE.
Project information
In 2001, TCE was detected in the groundwater at the property located at 359 Hoover Street NE. TCE was reported at a concentration of 3,500 micrograms per liter (µg/l). It was determined that the contamination was coming from off site. There were no groundwater receptors at the time of the investigation and soil vapor intrusion had not yet been identified as a potential problem.
In 2009, TCE was detected in the groundwater at an auto repair shop located at 2314 East Hennepin Ave. at a concentration of 1,620 µg/l. The shop is located southwest (down-gradient) from property at 359 Hoover St. Soil vapor samples were not collected during the investigation.
In 2013 and 2014, TCE was found in soil vapor samples collected below residential basement floors — also referred to as sub-slab samples — at properties east (up-gradient) of the General Mills Superfund site testing area. As a result, the MPCA has collected additional sub-slab samples from residential and commercial properties around both the SE Hennepin Superfund site and the General Mills Superfund site to identify properties with elevated sub-slab soil vapor concentrations. Properties with elevated sub-slab soil vapors have the potential for chemical vapor intrusion into the buildings and may require building mitigation to address vapor intrusion risk.
Next steps and timeline
National Priorities List
In March 2022, the Environmental Protection Agency added the SE Hennepin site to the National Priorities List. We support this listing, as it will provide additional resources, funding, and technical expertise to support long-term clean-up efforts, protecting the surrounding community from exposure to site contamination. For additional information on EPA’s decision, visit National Priorities List (EPA).
Groundwater contamination investigation
During fall and winter 2014, General Mills completed a groundwater investigation at the request of the MPCA. Monitoring wells were installed both northeast (up-gradient) and southwest (down-gradient) of the General Mills site.
Results for the groundwater samples collected from monitoring wells located northeast of the General Mills site indicated that TCE was detected at a concentration of 3,290 µg/l in a monitoring well located northeast of the former General Mills property. The Health Risk Limit (HRL), established by the MDH, is 0.4 µg/l for TCE. No drinking water wells have been affected.
The MPCA completed several groundwater investigations from 2015-2019 to evaluate the extent of the TCE contamination in the groundwater and to identify potential sources of the contamination. TCE was detected in the groundwater at concentrations as high as 5,300 µg/l. Additional groundwater investigation is necessary to determine the full extent and magnitude of the groundwater contamination.
Soil vapor
TCE concentrations were greater than the action levels at three of the sampled residences and 21 of the sampled commercial properties. Three residential properties have vapor mitigation systems installed. Sub-slab mitigation systems have been installed at 12 commercial properties; 9 commercial properties need mitigation systems to be installed, and 17 commercial properties either need initial or additional vapor sampling.
