Developing Groundwater Clean-Up Levels Based on the Vapor Intrusion Pathway

Additional Info

  • Practice Areas: Groundwater Assessment and Remediation, Subsurface Vapor Intrusion to Indoor Air, Risk Assessment and Applied Toxicology
  • Event or Publication: AWMA Vapor Intrusion 2012
  • Title: Developing Groundwater Clean-Up Levels Based on the Vapor Intrusion Pathway
  • All Authors: Susan Welt, Franklyn Legall, Miguel Singer
  • Geosyntec Authors: Susan Welt
  • Date: 2013
  • Location: Chicago, Illinios
  • Type: Presentation

Groundwater clean-up levels that would be protective of indoor air via the vapor intrusion (VI) pathway were developed for a former warehouse facility located in an industrial area in Sao Paulo, Brazil.

The Site is about 3,300 m2and located downgradient and adjacent to the former manufacturing facility where chlorinated solvent degreasing operations were performed. Tetrachloroethene (PCE), trichloroethene (TCE) and breakdown products cis-1,2 dichloroethene (cis-DCE), and vinyl chloride (VC) are present in the overburden aquifer beneath the Site. As residential development encroaches upon the current industrial land use in the area, the local regulatory agency is concerned with the potential for VI as an exposure pathway and has required shallow groundwater restoration to levels that would prevent indoor air impacts from VI. The agency used a modified Johnson & Ettinger (JE) model to develop default groundwater clean-up levels that are protective of each exposure pathway. However, the agency agreed that VI-related samples could be collected to develop Site-specific groundwater clean-up levels based on the VI pathway only since no one was drinking or would routinely come into contact with the shallow groundwater. Although the VI-related sample results indicated elevated volatile organic compound (VOC) levels in the sub-slab environment with the building in its current natural ventilation state (no HVAC modification), only low levels (below the acceptable indoor air concentrations for a worker) were detected in the indoor air. Thus, under current conditions, the building can be occupied with acceptable impacts to human health. These data were used to develop Site-specific shallow groundwater clean-up goals, which were at least an order of magnitude greater than the agency default levels. Furthermore, since on-Site remedial efforts would further reduce VOC concentrations in shallow groundwater within the plume footprint, the need for groundwater remediation under adjacent (off-Site) building structures to achieve VOC concentrations protective of human health (via the VI pathway) was unlikely.

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