Recent research and advancements in detection have led the Minnesota Pollution Control Agency to investigate contaminated sites that have the potential for vapor intrusion into nearby structures. Vapor intrusion happens when chemical vapors from contaminated groundwater or contaminated soil move through the soil into the basements or through the foundations of buildings.
In the past, contaminated sites were viewed in terms of their effects on groundwater, not their ability to contaminate indoor air. Environmental scientists and health officials have only recently begun to understand the potential connections between contaminated groundwater or soil and soil vapors.
What we've found so far
Currently, the MPCA Site Remediation and Redevelopment Program oversees the investigation and cleanup of 881 active sites. The MPCA has determined that the potential for vapor intrusion exists at 631 sites where releases of hazardous substances have contaminated soil and groundwater.
The status of these 631 sites is depicted in the figure below. At 298 of these sites, investigations are completed and work has been done to the resolve any vapor issue. At 152 sites, the MPCA found a clear risk for vapor problems and is taking steps to protect the health of people in affected buildings. At the majority of sites where vapor investigation has been completed and actions are being taken, the vapor risks were at commercial and industrial buildings. Investigation is continuing at 181 sites to determine if they pose a risk.
How many soil vapor sites in Minnesota? (actual and suspected)
When a vapor-intrusion risk is identified at a site, the MPCA’s first priority is to evaluate and if necessary mitigate vapor-intrusion risks to nearby buildings. Then we will turn our efforts to seeing that the underlying cause of the vapor intrusion — the contaminated groundwater and/or soil — is cleaned up to eliminate the vapor-intrusion threat.
Reopening closed case files of contaminated site
In recent years new scientific understanding that contamination in soil or groundwater can result in the possibility of vapor intrusion has developed. In the past sites with the type of contamination that is more likely to result in vapor intrusion risk did not receive evaluation for vapor intrusion investigation as is standard practice today. The MPCA is beginning the process of re-evaluation closed sites for potential vapor intrusion risks. The work is being prioritized starting at sites with the highest potential risk for vapor intrusion. If a potential vapor intrusion risk is identified during the re-evaluation process, the file will be re-opened. Re-opened sites will be added to the "Where are the sites with identified or potential vapor risks?" interactive map above.
There are more than 4,300 closed sites in the VIC, Superfund, Site Assessment and RCRA programs. Approximately 1,430 closed sites were identified as having volatile organic compounds (VOCs) as contaminants of potential concern. The MPCA prioritized approximately 150 of the 1,430 closed sites based on the presence of VOCs and the proximity of the site to sensitive receptors, including schools and day care facilities.
The MPCA has conducted detailed file reviews on 37 of the closed sites and selected four sites for follow-up field investigation due to potential vapor concerns. Of the four sites investigated, three are being re-opened based on vapor intrusion risks identified in the follow-up investigation work.