Soil Vapor Poses New Challenges

Soil vapor has changed environmental and real estate due diligence practice. Minnesota has followed the national trend in focusing on addressing public health concerns about potential vapor intrusion. Releases of hazardous substances, such as trichloroethylene (TCE) and tetrachloroethylene also known as perchloroethylene (PCE), often impact structures where occupants may be exposed to potentially harmful vapors.

Minneapolis Como Case Triggers New Approach.

Vapor intrusion rose to prominence in Minnesota after impacts were discovered in residences located near a former Superfund site in the Como neighborhood in Minneapolis. Thereafter, the Minnesota Pollution Control Agency (MPCA) required the responsible party to test and pay for mitigation in over 163 homes. A federal court initially certified a class action brought by neighbors in the area,  but that decision was reversed on appeal.

Extensive testing was conducted in the area where TCE was disposed.  Evidence of additional vapor sources was found in a nearby upgradient area. The MPCA conducted an investigation into new potential sources in an adjacent multi-block industrial area named the SE Hennepin Area Groundwater and Vapor State Superfund Site. The MPCA asked businesses located in this area to test their buildings for soil vapor. When elevated levels of TCE and PCE were found, the MPCA required commercial and industrial building owners to conduct mitigation.

MPCA Referral to US EPA for Listing as a Superfund Site.

MPCA staff have collected soil vapor data from property owners and in the right of way and referred the Como and SE Hennepin Area sites to the U.S. Environmental Protection Agency (EPA) for inclusion on the Superfund’s National Priority List (NPL).  The Como/SE Hennepin Area site will be the first site in EPA Region 5 to be scored based solely on soil vapor impacts.  It is expected that the site will be listed on the NPL, which will free up federal money to expand the investigation including into properties where owners have not permitted soil vapor testing.

Concerns about vapor intrusion have had ripple effects in the Twin Cities and across Minnesota.

  • New Vapor Superfund Sites.
    • Within the past few years, the MPCA added fifteen sites to the State Superfund list. Most of these sites were in the Twin Cities metropolitan area.  Vapor impacts often affect surrounding neighborhoods. The Superfund listing permits the State to use funds to conduct investigations and to pursue responsible parties for cost recovery.
  • Reopening Closed MPCA Files/Brownfields Program.
    • The MPCA is reviewing closed files and reopening sites to study vapor. Although groundwater contamination (including TCE and PCE) was noted at these sites, tests for soil vapor impacts were never completed. Regulators are now requiring owners and responsible parties to test for vapor releases on-site. If vapors are found, the MPCA requires tests on neighboring properties.
    • Parties seeking liability assurances from the MPCA’s Brownfields Program, including a No Association Determination (NAD) and Retroactive No Association Determination (RNAD), must test under building slabs and at the perimeter of the property for soil vapor impacts. If soil vapor impacts exceeding standards are detected, mitigation systems are required to protect building occupants.
  • Vapor, Vapor, Vapor – Everywhere.
    • The two contaminants of concern – TCE and PCE – were used over time in the Twin Cities and across the state by many businesses. TCE was used widely to clean parts and in many manufacturing operations. PCE was used by dry cleaners. Whenever the chemicals are used in normal operations there can be small spills and incidental releases. When PCE and TCE are spilled, soil and groundwater become contaminated. As a result, vapors are released from impacted groundwater.  
  • Where is the source of the vapors?
    • Finding the source of soil vapors can be challenging. In many cases multiple sources may contribute to a vapor plume. Releases of TCE and PCE in groundwater result in releases of soil vapor. Vapors migrate through porous soils and accumulate under building slabs.  Small cracks and seams in structures create pathways for harmful vapor to enter buildings. The Minnesota Department of Health (MDH) has found that exposure to low levels of vapors over time poses health risks.
  • Guidance Over Rules.
    • The MPCA has issued guidance to address how sites are to be assessed for vapor impacts. The guidance requires sampling in both heating and cooling seasons. The number of samples depends on the size of the building footprint. When elevated levels are found that are deemed to pose a risk to public health, building mitigation is now required. Mitigation systems need to be tailored to ensure proper removal of the vapors. The guidance provides regulators with flexibility. However, there is uncertainty and risk as to how the issues will be handled in the future.
  • Environmental Covenants.
    • The MPCA now requires that an environmental covenant must be recorded to notify future owners of the presence of vapors and the ongoing obligation to operate and maintain mitigation systems. Because the source of the vapors cannot be removed, the vapor condition and mitigation obligations run with the land into perpetuity. Mitigation systems typically are active systems.  Fans, blowers and other components will need replacement.  The environmental covenant provides that an owner who fails to operate and maintain an active system may be subject to civil penalties.  A copy of the recorded covenant needs to be provided to the MPCA, county and municipal authorities.
  • Fixes Can Be Costly.
    • When residences are affected by vapors and no responsible party can be located, the MPCA or EPA generally will foot the bill to address the soil vapor impacts. Responsible parties are tapped to pay for vapor mitigation on property they own and on off-site property until the end of the vapor plume is found. If a commercial or industrial business or building owner discovers it has a vapor issue but there is no known responsible party, the MPCA looks to the owner to investigate and mitigate its building at its cost.
  • Potential Claims.
    • With the vapor issue there are potential concerns and claims from many parties – homeowners, tenants and neighboring property owners. Once a vapor impact is found, there is arguably a duty to notify persons – employees, tenants and neighbors – who may be impacted. The cleanup standards are more protective for vulnerable individuals, including infants and young children, women who are pregnant or may become pregnant, elderly persons and those living with chronic disease or a compromised immune system.

Please see the disclaimer at the bottom of this page that relates to limitations on this blog and to legal advice. For information on limiting liability for soil vapor, vapor intrusion or for counsel in responding to government or third-party requests related to soil vapor and vapor intrusion issues please contact:

Joseph G. Maternowski

Hessian & McKasy, PA

Work:  612-746-5754


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