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EXPOSURE ASSESSMENT Three primary routes of exposure that must be considered at any site are 1 Ingestion of compounds in soil 2 Ingestion of compounds in groundwater 3 Inhalation of compounds in vapor form Of these three routes of exposure, only inhalation is a likely route of exposure to be encountered at this site Ingestion of compounds in soil was not considered because there is no documented contamination in the upper three feet of soil and the site is paved over, limiting the probability of the ingestion of contaminated soil On-site ingestion of compounds in groundwater was considered in order to determine the probability of adverse effects to off-site wells Ingestion of groundwater at the site is unlikely, as it would require turning MW2 into a domestic well and proceeding to drink the water therefrom Off-site ingestion was considered for the down gradient well (number 32) on the surrounding wells map, Figure 9 RESULTS The results of a Tier 2 RBCA calculation are expressed as SSTLs This is the concentration at which, the calculated cancer risk will not exceed the 1/1,000,000 residential or 1/100,000 commercial cancer risk and the non-cancer threshold limit is less than one Vapor Inhalation None of the compounds exceeded the SSTLs for Volatilization to outside air (Appendix G Update Status Report 453, Worksheets 9 2 ) Ground Water Ingestion Only benzene would exceed the groundwater ingestion residentail model None of the compounds exceeded the SSTLs levels for on-site groundwater ingestion commercial (Appendix G, Update Status Report #53, Worksheet 9 3 ) The residual benzene level is not significant, as it would require the installation of a shallow groundwater well into the current plume and the continued drinking of that water Of greater risk is the Lincoln Village PCE/TCE/1,2 DCE plume 12 R603 Update#54/CLOSURE 3 12198