Page 17 of the PAERAB's Spring 2011 Community Update Newsletter

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Text Box: chemicals that are of potential concern may be more extensive than just the compounds released at the site”. “...Regulatory agencies have different ways to define volatile chemicals for the VI pathway. The USEPA (2002b) defines volatiles as chemicals with a Henry’s law constant greater than 10-5 atm m3 mol-1 at room temperature. NJDEP (2005b) considers a chemical to be volatile if its Henry’s law constant is greater than 10-5 atm m3 mol-1 and its vapor pressure is greater than 1 mm Hg at room temperature”. .”… Often, significant contaminant concentrations are found only in relatively close proximity to the original source. USEPA guidance establishes an area within 100 feet vertically or laterally from a volatile concentration of regulatory concern as a potential impact area (USEPA 2002b). Some states have established buffers of 30 feet. Others states, such as New Jersey (NJDEP 2005b), established different distance criteria based on the contaminant type (petroleum versus chlorinated hydrocarbons). Recent work (Lowell and Eklund 2004) suggests that even for sites with the presence of pure petroleum product and contamination a couple of meters below the surface, VOC emissions will tend to be insignificant at lateral distances of about 100 feet transgradient to groundwater flow from a source. Hydrocarbons

Text Box: probably will not migrate as far laterally if oxygen is present”. On page 27… “The length of time between the release date and the time of soil gas collection will affect the magnitude of the contaminant concentrations at a location away from a release point. The time required for soil gas to reach near-steady concentrations at any point increases with the square of the distance from the source. Soil gas concentrations measured near a source will in most cases be representative of near-steady conditions”. “An evaluation of the vapor intrusion pathway requires consideration of the use of the buildings in proximity of contaminated media (e.g., groundwater, soil, soil gas). For sites that have measurable sources of volatile chemicals and a viable migration route to the building, the ultimate risk decisions may depend on the use of the buildings under current conditions. Future use of current buildings and undeveloped parcels may also need to be considered in light of the probable future exposure patterns”. On Pages 27—28… ‘It is important to note that exposure to the “general public” in public buildings is usually not the most significant risk driver if there are any full-time workers in the building. USEPA’s draft VI guidance may be interpreted to recommend that people exposed in occupational settings should be evaluated under Occupational Safety and Health Administration (OSHA) using occupational standards rather than by

Text Box: current risk-based screening approaches. This position appears to be going through a reconsideration based on recent draft revisions to the USEPA VI guidance. Many state agencies now require that occupational exposure be based on risk-based screening values and not OSHA standards when the COCs are not used in the building being investigated. Again, check with your state agency for guidance in this area. In all cases, consider the potential future use of the building, not just the current function’. On Page 29… “If there is enough information to confirm VI at a concentration that adversely impacts human health (possible acute exposure), the investigator moves onto the Mitigation Phase ... Otherwise, further characterization is required as part of the Site Investigation Phase ... Of course, the investigator may elect to be proactive and move directly to the mitigation phase at any point in the process, irrespective of the information collected to date”. On Page 30… “Many investigators and state agencies prefer to begin the investigation process outdoors (i.e., exterior groundwater or soil gas measurements) in the hope that vapor intrusion can be ruled out without having to test indoors (subslab and/or indoor air samples). An exterior assessment also allows the properties most likely affected

ITRC Vapor intrusion intro - continued

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