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PUBLIC AALTH SERVICOES <br /> SAN JOAQUIN COUNTY Q �z <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer • c .. P <br /> 9� FORN <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 C <br /> 209/468-3420 <br /> C u <br /> ED RALSTON <br /> TOSCO MARKETING COMPANY AUG 13 1997 <br /> ENVIRONMENTAL COMPLIANCE DEPARTMENT <br /> 2000 CROW CANYON PLACE STE 400 <br /> SAN RAMON CA 94583 <br /> Re: Unocal Station#6981 'Site Code: 1217123 <br /> 4707 Pacific Avenue <br /> Stockton CA 95207 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has reviewed <br /> the site's status. PHS/EHD has most recently received the following reports: <br /> "Quarterly Data Report"dated February 18, 1997 and prepared by MPDS <br /> "First Quarter 1997 VES Report"dated April 30, 1997 and prepared by GeoStrategies <br /> "Second Quarter 1997 VES Report"dated August 4, 1997 and prepared by GeoStrategies. <br /> PHS/EHD has the following comments for your consideration and response, now that the March <br /> Lane/Pacific Avenue Interchange Project is nearing completion. <br /> The most recent MPDS quarterly groundwater monitoring report submitted included the results of the <br /> January 1997 sampling event. At the time of sampling the depth to water was reported at approximately <br /> 36 feet below ground surface(bgs). As PHS/EHD has indicated in correspondence dated March 27, <br /> 1996, additional monitoring wells will be necessary to replace the four monitoring wells which have <br /> been destroyed(MW3, MW 10, MW 12 and MW 13) as part of the interchange project and to obtain <br /> representative groundwater samples. A summary of well construction details was also provided to <br /> compare the screened intervals of the wells with the then current depth to water. It must be noted that <br /> since that time, the water level which was at approximately 42 feet bgs has risen an additional 6 feet. <br /> PHS/EHD requested in writing on four occasions(March 27, 1996, June 24, 1996, September 18, 1996 <br /> and January 3, 1997) that a work plan be submitted to install additional monitoring wells. A work plan <br /> to install a minimum of four monitoring wells must be submitted by September 12, 1997. <br /> The 1996 annual remediation report which was included in the"Fourth Quarter 1996 VES Report'dated <br /> February 7, 1997,stated that it was not possible to prepare an accurate estimate of the radius of influence for <br /> the VES. The configuration of the operating system includes vapor extraction wells:V W2,VW4,and V W5. <br /> Based on a groundwater level of 36 feet bgs,V W2 and V W4(screened between 50.5 and 25.5 feet bgs)have <br /> only 10.5 feet of screened interval above the groundwater level,while VW5(screened between 31 and 6 feet <br /> bgs)has 25 feet of screened interval above the groundwater level. Prior to initiating vapor extraction, <br /> significant soil contamination of up to 4,300 ppm TPH-gasoline, 17.0 ppm benzene, 130 ppm toluene,42 ppm <br /> ethylbenzene,and 200 ppm xylene was evidenced at 50 feet bgs in the soil boring which was converted into <br /> V W2 on March 9, 1992. PHS/EHD suggests that the work plan that is due September 12, 1997 include soil <br /> borings to evaluate the remaining soil contamination and the installation of air sparge wells. The air sparge <br /> wells can be used to assess air sparging as a supplemental remedial method to address any soil contamination <br /> in the saturated zone and remaining groundwater contamination. <br /> .4 Division of San Joaquin Counh• Health Care Services <br />