Laserfiche WebLink
EPA Comments on the DDJC-Tracy <br /> Hypothetical Risk and Hazard Exposure Scenario for Dieldrin <br /> March 1,2007 <br /> GENERAL COMMENT <br /> 1. Consistent with previous requests from EPA, the California Department of Toxic <br /> Substances Control, and the Central Valley Regional Water Quality Control Board (i.e., <br /> email from Ms. Xuan-Mai Tran dated January 30, 2007), risk and hazard estimates <br /> associated with dieldrin exposure should be predicated on the current maximum detected <br /> concentration(MDC) of dieldrin in groundwater(i.e., 0.19 micrograms per liter [ug/L]). <br /> This topic was discussed by EPA in a meeting held January 11, 2007, and reiterated in an <br /> email from Ms. Xuan-Mai Tran dated January 30, 2007. Please recalculate the estimates <br /> using the MDC as the exposure point concentration (EPC). <br /> 2. Based on our current understanding of the risks due to dieldrin, it would appear that <br /> dieldrin needs to be retained as a COC. <br /> 3. A cumulative risk analysis was not performed, assuming that aquifer cleanup levels were <br /> met for trichloroethene (TCE) and tetrachloroethene (PCE), as outlined by Mr. John <br /> Chesnutt in the January 11 meeting. <br /> 4. Also, as currently calculated, it should be noted that dermal risk appears to be driving the <br /> cumulative risk and is approximately four times greater than risk associated with <br /> ingestion. The predominant reason underlying this exaggerated dermal risk is DDJC's <br /> decision to adjust for absorption efficiency(i.e., to represent the oral slope factor [SFo] in <br /> terms of absorbed dose). However, since the EPA has not promulgated a gastrointestinal <br /> absorption(ABSGO value for dieldrin(and in the absence of a compelling discussion to <br /> adjust for administered versus absorbed dose), DDJC may be considerably inflating the <br /> risk corresponding to dermal absorption. <br /> MINOR COMMENTS <br /> 1. Table 2: Risk and Hazard Estimates—Ingestion of Groundwater, Residential Use of <br /> Groundwater: In the denominator of the non-cancer equation for an adult receptor <br /> exposed to dieldrin via ingestion of tap water, the non-cancer averaging time (AT„.) <br /> indicates an AT for a child receptor. However, the AT should correspond to an adult. <br /> Please revise the AT parameter in the denominator of the non-cancer equation to reflect <br /> an adult receptor AT and verify that this is merely a typographical error and that the <br /> calculation is correct. <br /> 1 <br />