SITE INFORMATION AND CORRESPONDENCE_FILE 1

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A PUBLIC #1EALTH SERVICES SAN JOAQUIN COUNTY ENVIRONMENTAL HEALTH DIVISION y , Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer 304 East Weber Avenue, Third Floor • Stockton CA 9520 209/468-3420 rnIF 7 Ra L BOB BOOST JUN 2 5 1997 UNOCAL 2000 CROW CANYON PL STE 400 SAN RAMON CA 94583 RE: 437 East Miner Ave., Stockton CA 95202 SITE CODE: 1181 San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has completed review of the Unocal correspondence dated June 11, 1997. PHS/EHD has prepared the following comments for your clarification and response. Your correspondence included a copy of the San Francisco Bay Regional Water Quality Control Board's (Region 2), Low Risk Criteria. PHS/EHD has reviewed Region 2's interpretation of their basin plan. The above referenced site is located in San Joaquin County which is situated within the San Joaquin River Basin of the Central Valley Region. The Central Valley Regional Water Quality Control Board adopted the "Third Edition of the Water Quality Control Plan (Basin Plan) for the Sacramento River and San Joaquin River Basins" on December 9, 1994 which was approved by the State Water Resources Control Board on February 16, 1995. The Basin Plan has designated all ground waters in San Joaquin County as suitable or potentially suitable (at minimum) for municipal and domestic water supply, agricultural supply, industrial service supply and industrial process supply. At a minimum, water designated for use as domestic or municipal supply shall not contain concentrations of chemical constituents in excess of the maximum contaminant levels as specified in Title 22 of the California Code of Regulation. The groundwater monitoring data, that has been collected since the unauthorized release was documented, clearly indicates that the operation of underground storage tanks has degraded water quality beneath the site. The State Water Resources Control Board Policy 92-49 states that the Regional r Water Quality Control Board is to ensure that dischargers are required to clean up and abate the effects of discharges in a manner that promotes attainment of either background water quality, or the best water quality which is reasonable. If background levels of water quality cannot be restored 92-49 allows for the approval of alternative cleanup levels. The alternate cleanup levels that may be approved that are less stringent than background must be consistent with §2725 of the Underground Storage Tank Regulations which refers to the Basin Plan which in turn references the maximum contaminant levels that are specified in Title 22. Also alternative cleanup levels shall be consistent with the maximum benefit to the people of the state; not unreasonably affect present and anticipated beneficial use of such water and not result in water quality less than that prescribed in the Water Quality Control Plan and Policies adopted by the State and Regional Water Boards. PHS/EHD has reviewed the soil contamination evidenced and has determined that the contamination summarized below is in contact with groundwater. The most recent reported depth to groundwater (February 3, 1997) was approximately 33 feet below ground surface while groundwater as low as 47.91 feet has been reported (November 17, 1994). PHS/EHD has also indicated that the vertical extent of the adsorbed and dissolved petroleum hydrocarbon contamination has not been determined. Sample ID TPH- as Benzene Toluene Eth (benzene Xylene UL@ 45 feet 19,000 mg/kg 140 mq/kq m /k900 mg/kq mg/k370 mg/kq mg/k1,600 m /k UV7@ 35 feet 20,000 mq/kq m /k99 mg/kg 670 mg/kg 340 mg/kg 1,500 m /k A Division of San Joaquin County Health Cam Services