Assessing Vapor Intrusion at a Superfund Site

Environmental Training Resource
March 15, 2013 — 922 views  
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A Superfund site is a site that has been designated for the dumping of toxic waste substances. The EPA (Environmental Protection Agency) then performs clean-ups at these sites, and pushes responsible companies to perform cleanups, or to recompense the EPA for the cleanups conducted. Vapor Intrusion (VI) is the migration process of hazardous chemical vapors from soil or groundwater to indoor air usually through gaps in the foundation of a building that lies near a superfund site.

Superfund site five-year reviews are necessary when hazardous chemicals on the site remain above permitted levels of use or exposure. These are performed by the EPA or the site's lead agency and is intended as an opportunity to evaluate the implementation and performance of a VI remedy.

The Vapor Intrusion Consideration

When the documents related to a site are issued, there may not have been a consideration of VI and maybe, new information that is obtained after document issuance shows that VI is a potential concern in that site. When a remedy is considered for VI, the vapor intrusion assessment may attempt to check if the remedy that was meant to tackle VI is still protecting human health. The assessment should give special importance to the parts of the population that are most sensitive to vapor intrusion, such as, the elderly, pregnant women, the immunocompromised, and the very young.

The Supplemental Guidance

The reviewers can use three questions as a guide for their assessments.

  •  Is the functioning of the remedy similar to the description in the decision documents? - It must be considered whether there is adequate existing data to evaluate the VI remedy's effectiveness, whether indoor air concentrations are lower than the action levels, and whether the VI remedy's effectiveness has been changed by physical changes to the building.

 

  •  Are the cleanup levels, toxicity data, remedial action objectives (RAOs), and exposure assumptions used when the remedy was selected, still accurate? - One has to consider whether there has been any identification of new sources of contaminants, new contaminants, and whether baseline assessment of human health was used when evaluating VI.

 

  •  Has any new information been discovered that could question the protective nature of the remedy? - It must also be considered whether any new buildings or homes have been constructed on-site, whether there was a rise or any substantial change in the water table, any migration of the groundwater plume, and whether natural disasters such as earthquakes or floods have affected the integrity of the construction or affected the VI remedies.

Recommendations of VI Assessments

Once the vapor intrusion assessment is completed; it identifies some issues, develops certain recommendations, and determines protection. A few common recommendations are as listed below.

  •  The risks of vapor intrusion need to be assessed accurately.
  •  More evidence needs to be identified, as it is required for accurate assessment of the VI risks.
  •  Groundwater should be monitored to make sure migrating VOCs do not enter buildings off-site
  •  Monitoring and O&M has to be improved to make sure that the remedies continue operating as planned.
  •  Institutional controls have to be implemented such that the risks that are present in the VOC plume area to new construction have been addressed.

The determined protectiveness levels can be stated as - Protective, protective on completion of remedial action, protective for short term, protectiveness deferred until more information is gathered, and not protective.

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