In a mixed retail/residential area near the intersection of Diamond Lake Road and Nicollet Avenue in Minneapolis, the MPCA is working on the presence of perchloroethylene (PCE, also called “perc” or tetrachloroethylene) in the soil and groundwater.
The MPCA is investigating the extent of the PCE contamination, which is related to the use of perc solvent at one or more dry cleaning businesses that have operated in the neighborhood.
The initial investigation included testing five commercial buildings. To limit the further spread of PCE vapor in the soil, the MPCA has installed a mitigation system at a dry cleaning business on Nicollet Avenue. It has also installed a mitigation system at a nearby apartment building to ensure residents are not exposed to PCE.
The issue: Vapor intrusion
The PCE-contaminated groundwater could release PCE vapor that can rise through the soil and seep through basement and foundation cracks into homes and other buildings, where it could be inhaled by people. This is known as “vapor intrusion.” If vapor intrusion is occurring, it is likely that PCE vapors are higher in basements than on upper floors.
One remedy for such a situation is to install a soil vapor mitigation system, which operates like a radon mitigation system. If a building already has a radon mitigation system that was installed by a certified contractor and the system is functioning properly, it is likely that the problem of PCE vapor in the building’s indoor air is being addressed.
If a person breathes in low levels of contaminants in indoor air for a long time, there is an increased chance that person’s health could be affected. The risk to health depends on several factors, such as how much and what kind of contamination is present and how long a person has breathed it. The Minnesota Department of Health (MDH) has a fact sheet about PCE and health: Tetrachloroethylene (PCE, Perc) in Air. The MPCA wants to identify vapor intrusion and take steps to reduce or eliminate it where possible.
Map: Diamond Lake Road and Nicollet Avenue Site
The map below shows which buildings are in the mitigation area.
|October – December 2013||During a real estate screening assessment, PCE was detected in soil vapor samples from a neighboring commercial property. The consultant reported the suspected contamination to the State Duty Officer, who notified the MPCA. MPCA responders tested soil vapor at 15 locations around 5417 Nicollet Ave. The testing confirmed PCE contamination in soil vapor that exceeded the screening level at 5421 Nicollet Ave., a dry cleaning business. A vapor intrusion mitigation system was installed at the dry cleaning business to reduce the amount of PCE getting into the building.|
|January – December 2014||Soil vapor testing was conducted at three more nearby buildings: the hardware store at 5425 Nicollet Ave., an apartment building at 24 E. Diamond Lake Road, and Mayflower United Church and its school building at 106 E. Diamond Lake Road. The MPCA began preliminary work to install a vapor intrusion mitigation system at the apartment building and to conduct additional testing at the church and school building.|
|January – June 2015||The MPCA held question and answer sessions for residents of the apartment building at 24 E. Diamond Lake Road, for members of the Mayflower United Church of Christ, and for those who teach or have children attending the Mayflower Early Childhood Education Center and Kinderstube German Immersion Preschool. Air quality testing on the ground floor of the school building established that PCE and its breakdown products were not in the air. Installation of a soil vapor intrusion mitigation system at 24 E. Diamond Lake Road was completed in June. The system has been checked and it operating as it should.|
|July 2015||More soil vapor assessment was conducted to further define the area of concern. Mitigation systems were installed in residential buildings that have PCE sub-slab soil vapor test results above the level set by the MDH.|
|Fall 2015||Conducted a review of properties in the area to identify potential sources of the PCE contamination.|
Collected soil and groundwater samples from seven borings, and soil vapor samples from seven temporary probes to help identify potential source areas.
Also conducted a second round of sub-slab and indoor air sampling at the Mayflower Church located at 106 East Diamond Lake Road.
|February 2016||Conducted a second round of post-mitigation confirmation sampling, in a different season than the first round, at the apartment building located at 24 East Diamond Lake Road.|
|April – June 2016||Installed a vapor mitigation system and conducted one round of post-mitigation confirmation sampling at the Mayflower School located at 106 East Diamond Lake Road.|
|Winter/Spring 2017||Plan to collect one more round of vapor and indoor air samples at the church and school buildings.|