SITE INFORMATION AND CORRESPONDENCE_1988-1991

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Ms. Barbara Marcotte • Page 3 above predicted ambient levels, but there is insuf icient information, both scientifically and practically, to dete ine if this may pose a health problem and is not considered in this risk assessment. Review of Applied Action Levels: Kleinfelder and ERS have used the DHS Decision Tree metho s for evaluating the health risks which SHAD may pose to Valley Haven residents. As such, the concept of an Applied Action Level is used to identify the environmental concentrations of VOC's which may present an unacceptable risk. Currently TOX has not developed AAL's for most of the compounds identified at SHAD. In lieu of DHS promulgated AAL' s, the risk assessment makes use of tha most current information available in the EPA IRIS database, as supplied to the contractor by TOX. The acronym "AAL" is used loosely by Kleinfelder in numerous places in the risk assessment to refer to health based criteria values developed by DHS, EPA and by Kleinfelder (for PCE) . Although the term "target concentration" is suggested by Kleinfelder, the use of these different terms is not consistent throughout the document. Furthermore, the report indicates that DHS has developed AALs in soil for 30 chemicals (p. 15) , but currently no soil AAL' have been formally promulgated by TOX. (This is not a major issue since the risk assessment is only concerned with volatilization and not ingestion or inhalation of wind eroded soil dust) . The toxic endpoint of five of the six VOC' s identified is cancer. As such, the concentrations used as criteria values for these five chemicals in this report are the ambient air concentrations which would result in an incremental increase of one excess cancer in a population of one million exposed over a lifetime of 70 years (de minimis risk) . The EPA IRIS values represent the most currently reviewed values for these numbers and are a suitable "action level" with respect to the DHS Decisior Tree methodology. IRIS numbers are presented for carbon tetrachloride, chloroform, 1, 2-dichloroethane, and trichloroethylene. Technically, it is the inhalation potency factors which are being used with an extrapolation to air concentrations representing a statistical upper bound risk of developing cancer at a specified concentration in air. The one noncarcinogen is the DHS applied action level for 1, 1, 1- trichloroethane. The air concentration value reported for carbon tetrachloride is incorrect. There is an error in the IRIS summary for this compound for the air levels shown for different risk levels. The potency value is correct but the calculated air value based on a 70kg person breathing 20 m3/day is incorrect. The correct value should be 0. 03 ug/m3 rather than 0. 07 ug/m3 . The difference does not significantly alter the conclusions though (Table 6. 1) .