Vapor Intrusion: Just the Facts

Mar 17, 2020

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By now we have all heard of the term “Vapor Intrusion”, but there is a lot of confusion over the implications of vapor when doing an environmental assessment. While much information is still emerging, here is what we do know:

“Vapor Intrusion (VI) is the migration of volatile chemicals from the subsurface

into overlying buildings.” – Environmental Protection Agency (2002)

Below are some common sources which cause a Vapor Intrusion issue:

  • Dry Cleaners
  • Service Stations/Body Shops
  • Metal Works
  • Landfills
  • Large Industrial Sites
  • Wood Treaters

Common VI contaminants Include:

  • Chlorinated Volatile Organic Compounds (PCE, TCE, Vinyl Chloride)
  • Benzene (Petroleum)
  • Methane (Landfills)
  • Semi-volatile Organic Compounds and others: Naphthalene, Pesticides, Polycyclic aromatic hydrocarbons (PAHs), PCBs, Mercury

Often, these chemicals get into the soil and groundwater after a spill or leak from a tank, but not all these spills lead to vapor intrusion. The conditions have to be right – the chemical must be volatile, the building foundation and subsurface conditions must allow for the migration and intrusion, and often weather conditions must be favorable. Many of these chemicals are linked to negative health effects, including cancer.

While the U.S. EPA has provided guidance related to VI under remediation requirements of RCRA and CERCLA, it is not yet regulated under federal law and is inconsistently enforced. While the USEPA has issued guidance documents since 2002, the application of the guidance and enforcement has been left up to the individual states to regulate either through laws, guidance, or not at all.

In a growing nationwide trend, Michigan’s Department of Environment, Great Lakes, and Energy (EGLE) is re-assessing vapor intrusion issues at known contaminated sites and possibly re-opening properties EGLE considered “closed” with residual contamination. In response to new technologies that can detect much lower levels of the problem compounds, Michigan officials estimate there are as many as 4,000 sites of interest to be investigated for VI and possibly further investigated or reopened.

In the meantime, just EGLE rescinded the VI screening values that were released in 2013 and used to determine whether soil, groundwater, soil gas or indoor air were present at concentrations unacceptable for vapor inhalation. Together with the Michigan Department of Public Health (MDPH), EGLE concluded the screening values issued in 2013 were not protective enough of the indoor inhalation (VI) exposure pathway for select compounds. Until EGLE releases new screening levels, evaluating vapor intrusion should be site specific and information should be submitted to EGLE for evaluation and approval.


EGLE/MDHHS: What is Vapor Intrustion and How is it Investigated?