In February 2007, the MPCA received the results of an investigation in St. Louis Park that found elevated levels of PCE and TCE in the soil vapor. Based on this information, MPCA staff determined that additional testing was needed, and St. Louis Park officials were notified.
Due to the size, complexity and expense of the additional study needed, the MPCA requested assistance from the U.S. Environmental Protection Agency (EPA). The two agencies developed a plan for additional sampling to evaluate the risk to people living and working in the area. Public meetings were held in December 2007 and testing began in early 2008.
With the owners’ permission, the EPA first conducted air and soil sampling at target properties to determine whether VOC vapors were entering indoor air. This involved drilling a small hole in the floor of the slab, basement or crawl space of the building to collect a sub-slab vapor sample.
If analysis of the sample results indicated elevated VOC vapor levels, the EPA double-checked slabs, basements, crawl spaces, and outdoor and indoor air. Staff performed another round of indoor air sampling after removing all household cleaners and paints, which can be a source of VOCs in indoor air.
If VOC concentrations exceeded screening levels, the EPA took all steps necessary to fix any problems found and to protect the health and safety of residents. Sub-slab depressurization systems (soil vapor intrusion mitigation systems) were installed in about 40 homes. Remediation was free of charge to homeowners.
The EPA’s work was completed in June 2008.
Since then, the MPCA has undertaken additional studies to identify chemical release source areas and the parties responsible for the releases. Follow-up work has been done also to assure that the vapor mitigation systems continue to be effective and determine whether the VOC vapors had traveled to other areas.