The Basics on Vapor Intrusion

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By Steve Barnett

Vapor intrusion (VI) refers to migration of volatile chemicals from contaminated groundwater or soil into an overlying building.  USEPA and NJDEP are updating regulations and guidance.  NJDEP issued a guidance document in March 2013, http://www.nj.gov/dep/srp/guidance/vaporintrusion/vig_main.pdf

USEPA issued a draft guidance document in April 2013. http://www.epa.gov/oswer/vaporintrusion/documents/vaporIntrusion-final-guidance-20130411-reviewdraft.pdf

NJDEP regulations require a VI investigation if VI groundwater screening levels are exceeded within 30 feet of a building for petroleum products or 100 feet for other compounds or if other specified conditions are present.  Action must be taken within specified timeframes, including possibly indoor air sampling, from the time a VI investigation is known to be needed.  Indoor air sampling results must be provided to NJDEP within 14 days if exceedances are detected and within 30 days if there are no exceedances.  Securing site access is often the critical path or the “long pole in the tent” task that holds up a VI investigation.

Updates to USEPA and NJDEP guidance and regulations favor indoor air sampling, rather than modeling, as the primary investigation method.  And they reach further into areas that are historically and currently subject to OSHA regulation of air concentrations, i.e., commercial and industrial buildings.

OSHA Permissible Exposure Limits (PEL’s) are orders of magnitude higher than VI screening levels.  For example, the OSHA PEL for benzene is 1 ppm (parts per million), whereas the VI indoor air screening level is 2 ppb (parts per billion); for perchloroethylene (a/k/a tetrachloroethylene, a/k/a “perc” or drycleaning fluid), the OSHA PEL is 100 ppm, and the NJDEP indoor air screening level is 9 ppb for residential and 47 ppb for nonresidential.

Some points when considering VI indoor air sampling:

  • VI screening levels are essentially set at limits of detection of sampling and analytical instruments, because as a policy matter, all things being equal, it is thought the goal should be no detectable chemicals off-gassing from groundwater or soils into a building.  That does not necessarily mean that such levels present a health hazard. 
  • Part per billion levels can result from use or even mere storage of chemicals - and  not even industrial grade or industrial amounts.  Common household cleaning chemicals such as floor, glass or wood cleaners; chemicals used to service air conditioning or heating equipment; new or even not-so-new carpet, furniture or office equipment; and outside sources, can cause very low indoor air levels being sampled for in VI analysis. 
  • NJDEP VI instructions require removing all materials at least 48 hours before any indoor air sampling.  However, in many cases, 48 hours may not be enough, such as if there have been historic use or spills inside the building of the materials.  VI sampling in a liquor store, pharmacy or grocery store, for example, may be problematic or not possible due not only to the business interruption costs of removing all materials but also the likelihood of residual amounts of products from spills or off-gassing remaining in the building or building materials.
  • Especially in urban areas, outside sources such as vehicle traffic emissions can interfere with VI indoor air sampling. NJDEP’s March 2013 VI Guidance Appendix G, “Background Levels of Volatile Organic Chemicals in Homes: A Review of Recent Literature” includes summaries and tables of published values. For example, benzene levels in homes ranged from 1.6 ppb to 3.06 ppb. Given the VI indoor air screening level of benzene being 2 ppb, it is easy to see how it may be difficult or even impossible to determine whether a VI issue is present for benzene in an urban building.
  • Often Material Safety Data Sheets (MSDS’s) are not available or are not reviewed and reliance is placed on the sampling technician’s understanding or the label.  Further, MSDS’s are only required to list substances if they are >1% for non-carcinogens and >0.1% for carcinogens, and substances present below those concentrations in liquid or solid materials can give airborne readings in the ppb range.  Therefore, it may be necessary to obtain manufacturer specifications or ingredient listings to be certain a product does not contain a substance.  The best practice is simply to remove everything.
  • There is a tendency to sample in hidden or confined locations to avoid employee inquiries or concerns.  VI sampling should never be done in a garage, equipment maintenance area, boiler room, janitor’s closet, chemical storage room, industrial area, or any other area where chemicals have been or are routinely used or stored.  Even removing the known containers cannot account for possible historic use, spills or residues. Sampling may also be done on weekends to avoid employee inquiries.