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4 PUBLIC HEALTH SERVIOLS <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION ` <br /> Karen Furst, M.D., M.P.H., Health Officer �. <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 aL' oR � <br /> 2091468-3420 <br /> August 12. 1999 <br /> EDWARD C ANTON, CHIEF <br /> DIVISION OF CLEAN WATER PROGRAMS <br /> STATE WATER RESOURCES CONTROL BOARD <br /> P 0 BOX 944212 <br /> SACRAMENTO CA 94244-2120 <br /> RE: PETITION OF UNOCAL CORPORATION FOR REVIEW OF DENIAL OF <br /> PETROLEUM UNDERGROUND STORAGE TAINK SITE CLOSURE AT <br /> 1665 PACIFIC AVENUE, STOCKTON, CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> reviewed your correspondence dated July 221 1999, regarding the above referenced site. Our <br /> comments are as fallow: <br /> • PHS/EHD does not agree that there would be no water quality benefit gained by further <br /> investigation and definition of the contaminant plume at this site. Pump tests and other <br /> studies performed during site investigations in our area generally support the conclusion that <br /> the groundwater aquifers are hydraulically connected. This is further supported by the fact <br /> that groundwater direction of flow at most sites is towards the nearest water production wells <br /> and changes occur when production well usage is modified. <br /> • PHS/EHD does not agree that the site information gathered to date supports the conclusion <br /> that biodegradation has reduced the levels of hydrocarbon contamination. Natural'attenuation <br /> through dispersion/dilution caused by the increased amount of water in the aquifer, as shown <br /> by the change in depth to groundwater over the years, has reduced the levels of hydrocarbon <br /> contamination. However, the existing down gradient monitoring wells do not extend to the <br /> depth where the highest groundwater contaminant concentrations have been documented on "` 1 <br /> site. The site information does support the fact that vapor extraction may be effectively used <br /> to reduce the hydrocarbon contamination at this site. <br /> • PHS/EHD is aware that saline intrusion has contributed to water quality problems in the <br /> Stockton area. However, groundwater continues to be the principal source of drinking, <br /> industrial, and agricultural water in San Joaquin County. Even though surface water from the <br /> Stockton East Water District is used to supplement municipal water supplies in the City of <br /> Stockton during periods of availability, water purveyors within the City of Stockton <br /> primarily rely on groundwater wells to meet overall water supply demands. Therefore the <br /> protection of groundwater in the area of this site for future beneficial uses should not be <br /> discounted. <br /> • PHS/EHD has requested and continues to request that UNOCAL define the extent of the <br /> contamination and perform a feasibility study to evaluate at least two viable remedial <br /> alternatives for this sits, so that a Corrective Action Plan (CAP) may be prepared. Due to the <br /> i <br /> i <br /> i <br /> A Division of San joaciuin Counry:fealth Care Services <br />