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February 11, 2013
Assessing vapor intrusion at Superfund sites

Factoring vapor intrusion (VI) into 5-year Superfund reviews is the topic of a guidance document released in late 2012 by EPA’s Office of Solid Waste and Emergency Response (OSWER).

The guidance, Assessing Protectiveness at Sites for Vapor Intrusion, is intended to supplement the Agency’s (Comprehensive Five-Year Review Guidance ), which was published in 2001 and does not discuss VI.

VI is the general term given to the migration of hazardous vapors from any subsurface contaminant source, such as contaminated soil or groundwater, through the vadose zone and into the indoor air, usually of overlying buildings through openings in the building foundation (e.g., cracks in the slab, gaps around utility lines, or elevator shafts).   Volatile organic compounds (VOCs) typically pose the most common VI concerns.

Five-year Superfund reviews are required when hazardous substances remain on-site above levels that permit unrestricted use and unlimited exposure.  The reviews are intended as an opportunity to evaluate the implementation and performance of a remedy to determine whether it remains protective of human health and the environment.  Five-year reviews can be performed by the EPA or the lead agency for a site, but the EPA retains the responsibility for determining the protectiveness of the remedy.

Was VI considered?

The guidance notes that VI may not have been considered when site-related decision documents were issued or that new information obtained since document issuance indicates that VI has become a potential pathway of concern.  In cases where VI was considered part of the site remedy, the assessment should attempt to determine whether the portion of the remedy designed to address VI is still protective of human health.  In the assessment, special attention should be given to sensitive populations such as the very young, the elderly, pregnant women, and the immunocompromised. 

The supplemental guidance recommends that reviewers use three technical questions to guide their assessments:

  • Is the remedy functioning as intended by the decision documents?  Factors to consider include the adequacy of existing data to assess the effectiveness of the VI remedy, whether concentrations of indoor air pollutants are below action levels, and whether physical changes in buildings have changed the effectiveness of the VI remedy.
  • Are the exposure assumptions, toxicity data, cleanup levels, and remedial action objectives (RAOs) used at the time of the remedy selection still valid?  Factors to consider include whether VI was evaluated in the baseline human health assessment, whether new contaminants or contaminant sources have been identified, and whether the cleanup levels included in the decision documents are still valid.
  • Has other information come to light that could call into question the protectiveness of the remedy?  Factors to consider include whether new homes or buildings have been built on the site, whether the groundwater plume migrated or the water table rose or changed substantially, and whether such natural disasters as floods or earthquakes have affected the integrity of the buildings or impacted the VI remedies.

Recommendations

The guidance indicates that the VI assessment should generally produce recommendations such as the following:

  • VI risks need to be assessed.
  • Additional evidence is needed to accurately assess VI risks.
  • Groundwater must be monitored to ensure migrating VOCs do not reach off-site buildings.
  • O&M and monitoring need to be improved to ensure VI remedies continue to operate as planned.
  • Institutional controls must be implemented to address risks to new construction in the area of a VOC plume. 

 

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