SITE INFORMATION AND CORRESPONDENCE_1993-2003

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w ',oi uyso4 i OEMORANDUM , Cal/BPA s' CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD V„ CENTRAL VALLEY REGION 3443 Routier Road,Suite A,Sacramento,CA 95827-3098 Pete Wilson,Governor (916)255-3000 • CALNET 8-494-3000 • FAX(916)255-3015 TO: Cori L. Condon FROM: Jon B. Marshack, D.Env. Associate Engineering Geologist Senior Environmental Specialist Federal Facilities Unit Environm Tec tical Support DATE: 29 August 1997 SIGNATURE: SUBJECT: DRAFT PUBLIC HEAL THASSESSMENT FOR DEFENSE DISTRIBUTION REGION WEST(DDR if9 SHARPE ARMY DEPOT—VOCs IN WELLS Request: The volatile organic chemicals (VOCs)trichloroethylene(TCE),tetrachloroethylene (perchloroethylene or PCE), and 1,2-dichloroethane (1,2-DCA)have been detected in on-site wells and in private domestic wells located north and northwest of the subject site. The Agency for Toxic Substances and Disease Registry (ATSDR)was asked to evaluate the health significance of the exposure to these contaminants in drinking water. You requested that I review and comment on that portion of the subject document, prepared by ATSDR and dated 2 July 1997,that discusses health risks from chemicals detected in off- site domestic wells. Response: In the subject document, "ATSDR concludes that consumption of water from private wells is not expected to result in adverse health problems" [p. 13, ¶ I] and that"future exposure potential is likely to be minimal" [p. 13,¶2]. These conclusions are based on cancer risk calculations and comparison of the resulting risk estimates with the 10-4 to 10-6 (I added cancer case in 10,000 to 1,000,000 persons exposed)risk range. This range is considered by USEPA to represent"acceptable"residual risk associated with chemicals that remain after remediation of federal Superfund sites. ATSDR's conclusions are inconsistent with Regional Board's position regarding pollution of groundwater that is or is likely to be beneficially used. In recent decisions regarding an off-site VOC plume from Mather Air Force Base,the Board has taken the position that replacement water supply must be provided when the level of carcinogenic chemicals is detected and confirmed at or above concentrations that represent 10-6 lifetime cancer risk levels in individual wells. This decision implements the narrative toxicity objective for groundwater from the Basin Plan for the Sacramento and San Joaquin River Basins. Lifetime cancer risk estimates ranging from 1.3 x 10-6 to 4 x 10-5 were calculated using 1)maximum detected concentrations of individual pollutants in the domestic wells near Sharpe, 2) Cal/EPA and USEPA cancer potency factors, and 3) exposure assumptions consistent with regulations developed by Cal/EPA's Office of Environmental Health Hazard Assessment (OEHHA) under Proposition 65 and with assumptions used by USEPA to derive lifetime health advisories. The report also contains several errors and omissions that could significantly affect the assessment of health risks from pollutants in groundwater. Recycled Paper Our mission is to preserve and enhance the quality of California's water resources,and ensure their proper allocation and efficient use for the benefit ofpresent andfuture generations.