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risk is calculated by dividing the long-term ingestion rate by the Rfd. If the result is less than one, <br /> the threshold limit above which health effects will occur should not be reached. <br /> TOXICITY ASSESSMENT <br /> Of the compounds currently found at the site, the primary driver of risk at this site is the benzene. <br /> Cancer Toxicity <br /> Benzene, a class A carcinogen, has been shown in work place studies to cause Leukemia in humans. <br /> The current EPA Cancer risk slope factor (SF) is 0.029 (1/(mg/kg-day)). <br /> Non-cancer Toxicity. <br /> Five compounds were considered for the non-cancer toxicity, Benzene, Ethlybenzene, Hexane, <br /> MTBE, Toluene, and Xylenes (which includes, meta, para and orto xylenes). See Appendix G, <br /> RBCA Spreadsheet, RBCA Chemical Data, and Toxicity Data for current EPA. <br /> Hexane was used to represent the alkane (non-aromatic) portion of gasoline. Hexane was chosen <br /> because its properties represent the light, faster moving, end of the alkanes and as such represents the <br /> worst case for alkane migration. <br /> EXPOSURE ASSESSMENT <br /> Three primary routes of exposure that must be considered at any site are: <br /> 1. Ingestion of compounds in soil. <br /> 2. Ingestion of compounds in groundwater. <br /> 3. Inhalation of compounds in vapor form. <br /> Of these three routes of exposure, only inhalation is a likely route of exposure to be encountered at <br /> this site. <br /> Ingestion of compounds in soil was not considered because there is no documented contamination in <br /> the upper three feet of soil and the site is paved over, limiting the probability of the ingestion of <br /> contaminated soil. <br /> On-site ingestion of compounds in groundwater was considered in order to determine the probability <br /> of adverse effects to off-site wells. Ingestion of groundwater at the site is unlikely, as it would <br /> require turning MW2 into a domestic well and proceeding to drink the water therefrom. <br /> Off-site ingestion was considered for the down gradient well (number 32) on the surrounding wells <br /> map, Appendix E. <br /> 14 R603 Update##52/CLOSURE RV 7198 <br />