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��a� *a� UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br /> � A �QRegion 9 <br /> 75 Hawthorne Street <br /> P San Francisco CA 94105-3901 <br /> ;n <br /> 4D <br /> December 13, 1993 0 ,71 <br /> CDrn <br /> Marshall Cloud 3, <br /> Environmental Protection Office r <br /> DDRW-Tracy s. <br /> P.O. Box 960001 tv T J <br /> Stockton, CA 95296-0250 rn <br /> RE: DDRW-Tracy Human Health Risks in Selected Monitoring Wells <br /> Dear Marshall, <br /> This letter transmits EPA preliminary risk calculations with regard to human health affects <br /> associated with groundwater data collected during Montgomery Watson's (MW) quarterly well <br /> monitoring rounds for Defense Distribution Region West, (DDRW-Tracy). EPA is providing these <br /> calculations for consideration by DDRW-Tracy in the development of the Comprehensive risk <br /> assessment for DDRW-Tracy. <br /> EPA calculated preliminary carcinogenic health risks and non-carcinogenic health hazards <br /> using analytical data from groundwater samples taken from September 1992, January 1993, and April <br /> 1993. The attached table displays total carcinogenic risk and non-carcinogenic hazards for both <br /> average and reasonable maximum exposure (RME) concentration assuming a drinking water exposure <br /> from scenario designated monitoring wells at DDRW-Tracy, for selected chemicals only. These <br /> chemicals include, the volatile compounds, tetrachloroethene (tetrachloroethylene, perchloroethylene, <br /> or PCE), trichloro-ethene (trichloroethylene, or TCE); the organo-chlorine pesticides, chlordane, DDT, <br /> DDE, and dieldrin; and the metals, arsenic, chromium, and manganese. The human health effects data <br /> in the table were evaluated utilizing only an industrial drinking water scenario. It should be noted, <br /> health risks for a residential scenario would be approximately an order of magnitude higher than risks <br /> shown in this table. <br /> The highest RME carcinogenic and non-carcinogenic health risks are associated with wells <br /> LM3A, LM15A, LM25A, LM30A, LM101A, LM103A, and LM106A, which are all screened within <br /> the Upper Horizon or "above Upper Horizon" of the Upper Tulare Formation and are downgradient <br /> from the industrial wastepond or its sumps. Preliminary calculated carcinogenic risks for these wells <br /> are slightly less than one cancer per 10,000 population, or 10' risk. If a residential exposure scenario <br /> were utilized for these calculations, all would exhibit total carcinogenic risks greater than 10', and <br /> remediation of these compounds would be required by the National Contingency Plan (NCP). <br /> 1 <br />