SITE INFORMATION AND CORRESPONDENCE FILE 2

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PUBLIC,.H- EALTH SERVICES �. . �o SAM JOAQUIN COUNTY r' i ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer 304 East Weber Avenue, Third Floor • Stockton, CA 95202 6F0 He 209/468-3420 ALEX PEREZ AUG 2 7 1%7 SHELL OIL COMPANY PO BOX 4023 CONCORD CA 94524 Re; Shell Service Station Site Code: 1070 2575 Country Club Stockton CA 95204 San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has reviewed the Enviros "Work Plan Addendum"dated August 13, 1997. PHS/EHD has prepared the following comments for your consideration and response. The addendum was prepared to respond to PHS/EHD's April 7, 1997 directive to install a deeper monitoring well and to consider installing the well during the same mobilization as the monitoring well proposed southwest of MWS is installed. The addendum proposed the drilling and sampling of two additional borings to a maximum depth of 35 feet below ground surface (bgs) rather than the installation of a deeper monitoring well. The first of the two additional borings was proposed to be located northeast of the station building. During the initial phase of investigation, following the catastrophic release of 8,500 gallons of gasoline product, a CPT boring was placed northeast of the station building, CPT4. Unfortunately, no soil samples were submitted from this boring; however, the groundwater sample which was collected on December 28, 1994 evidenced 240 ppm TPH-gasoline, 35 ppm benzene, 40 ppm toluene, 2.9 ppm ethylbenzene, and 15 ppm xylene. The suite of analytes did not include methyl tertiary butyl ether. It would appear that the soil boring proposed northeast of the station building will provide valuable information to further define the extent of soil contamination. Since the distance between MW5 and MW4 is 160 feet, and this proposed boring is approximately midway between the two,you should consider completing the proposed boring located northeast of the station building into a monitoring/remediation well. The second of the two additional borings was proposed to be located southwest of the newly installed underground storage tanks. During the latter phase of the investigation, MW8 was installed adjacent to the proposed boring. Unfortunately, there were no soil samples submitted below a depth of 20 feet bgs. The 20 foot sample collected during the installation of MW8 evidenced soil contamination of 960 ppm TPH-gas, 5.2 ppm benzene, 15 ppm toluene, 16 ppm ethylbenzene, 75 ppm xylene and 10 ppm methyl tertiary butyl ether. It would appear that the soil boring proposed southwest of the newly installed underground storage tanks will provide valuable information to further define the vertical extent of soil contamination. A Division of San Joaquin County Health Care Services