Over the past decade federal and state authorities have expressed growing concern about the effects of soil vapor intrusion on public health and the environment. Vapor intrusion occurs when chemical vapors seep from an underground source of contamination, through the soil and groundwater, and ultimately migrate through basements, sub-ground spaces or the foundations of buildings. Environmental and public health authorities express anxiety about the potential for these chemical vapors to pose a material risk to human health especially when the structures that are impacted are residences.
Two common chemical contaminants that were used by many industries and that can cause vapor intrusion are trichloroethylene (TCE) and perchloroethyene (PCE). TCE was used to clean parts and equipment in various industrial settings. PCE was also used in industrial settings especially at dry cleaning operations. Because TCE and PCE were widely used for decades, there are many potential sources of releases. A release of TCE or PCE in even small amounts may result in significant and widespread contamination. In large metropolitan areas, such as the Twin Cities, there are hundreds of sources of TCE and PCE. The map below identifies sites across the Twin Cities metropolitan area where the Minnesota Pollution Control Agency (MPCA) has documented that vapor intrusion concerns are present.
The source of contamination that creates a vapor intrusion issue may be a considerable distance away from the basement or subspace that is affected. Typically, the contamination leaches from a source on the polluted site (a tank, sump, trench or spilled or buried waste) and into the groundwater. The contaminant then flows laterally with the ground water polluting a broader area at some distance away. Then, contaminated vapor travels vertically through the soil and into basements or foundations through cracks or seams in the floor and walls. Vapor intrusion may impact indoor air quality and, depending on the contaminant, serious public health risks especially in the residential setting. For a visual depiction of how soil intrusion may affect nearby properties see the graphic below.
In some cases, when soil vapors are found under a home or business the MPCA or the U.S. Environmental Protection Agency (EPA) will offer to install a mitigation system, a series of fans and filters, to remove the vapors from beneath the foundation. The vapors are then pumped into the outside air. In cases where the MPCA or the EPA have identified responsible parties, the agencies may ask or order those private parties to install vapor mitigation systems in affected residences or businesses.
Ten years ago the MPCA did not view contaminated sites in terms of their ability to contaminate indoor air. Polluted sites were primarily viewed as a concern based on their impairment of soil and groundwater. With emerging concerns of the potential for vapor intrusion to impact public health, the MPCA is now more focused on identifying vapor intrusion sites and adding those sites to the Minnesota’s Superfund Permanent List of Priorities. Once a site is added to this list, the MPCA may spend State monies or direct responsible parties to investigate and remediate those sites. In late August 2016 the MPCA added 10 new sites to the Minnesota Superfund list. Most of those 10 news Superfund sites are vapor intrusion sites.
One such site is known as the 55th and Lyndale Avenue South Site. This site includes two properties in Minneapolis, one of which housed a former dry-cleaning operation. According to the MPCA, the 55th and Lyndale Avenue South site is contaminated with PCE in the groundwater. However, the MPCA has preliminarily determined that it is likely that the contamination is coming from more than one source.
A 2013 and 2014 MPCA investigation revealed that there was possible vapor intrusion caused by the PCE in the groundwater. The vapor was intruding into several nearby homes and businesses. After testing nearby structures, the soil vapors exceeded 100 times the industrial indoor air standard under the foundation of select buildings. The MPCA responded to the release and installed mitigation systems to alleviate the potential health effects on the buildings’ occupants. To date, the MPCA has installed mitigation systems on five homes, with four additional installations are planned to be made.
Detailed information about the 10 sites which have been added by the MPCA to the Superfund Permanent List of Priorities can be found at: https://www.pca.state.mn.us/sites/default/files/p-ac16-05c.pdf
Please see the disclaimer at the bottom of this page that relates to limitations on this blog and to legal advice. For advice on limiting liability for vapor intrusions or for counsel on navigating the Superfund process please contact:
Hessian & McKasy, P.A.
Note: The map is current as of October 2015, but does not include sites with petroleum contamination.
** Graphics were produced by the Minnesota Pollution Control Agency**