SITE INFORMATION AND CORRESPONDENCE_FILE 2

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PUBLIC AEALTH SERVICES 'oP IN co SAN JOAQUIN COUNTY Z. ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer - �- �� • 304 East Weber Avenue, Third Floor • Stockton, CA 9520 °ciFOR 209/468-3420 ' ALEX PEREZ JAN 0 6 08 SHELL OIL PRODUCTS COMPANY PO BOX 8080 MARTINEZ CA 94553 Re: Shell Service Station Site Code: 1223 6131 Pacific Avenue Stockton CA 95207 San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has completed review of the "Quarterly Monitoring Report- Third Quarter 1997" dated October 31, 1997 and prepared by Enviros and the "Site Investigation Report/Quarterly Monitoring Report Fourth Quarter 1997" dated November 11, 1997 and prepared by Cambria. PHS/EHD has the following comments for your consideration and response. On July 2, 1997,four soil borings,SB-1 through SB-4,were drilled and sampled to determine the vertical and horizontal extent of the soil contamination on site. Petroleum hydrocarbons were detected at the maximum depth of the soil investigation which was 71.5 feet below ground surface (bgs) in SB4. Significantly,high concentrations were detected at 56.5 feet bgs of up to 440 ppm TPH-gas, 6.4 ppm benzene, 24 ppm toluene, 6.4 ppm ethylbenzene, 38 ppm xylene and 4.6 ppm methyl tertiary butyl ether (MTBE). SB4 was located in the vicinity of the piping associated with the former underground storage tanks. The maximum depth of investigation in the vicinity of the former tanks occurred during the installation of vapor extraction well,VE2 on July 12, 1990. The sample collected at 45 feet bgs evidenced petroleum hydrocarbon contamination of up to 12,000 ppm TPH-gas, 110 ppm benzene, 570 ppm toluene, 200 ppm ethylbenzene,and 630 ppm xylene and was noted to be saturated with gasoline. The depth to water in 1990 through 1992 was approximately 56 feet bgs while the current depth to water is approximately 41 feet bgs. The vertical definition of contamination has not been completed. On September 16, 1997 the off site investigation to determine the extent of soil and groundwater contamination was initiated with the installation of MW4 through MW7. Double permit fees were assessed because drilling was initiated prior to the issuance of an off- site permit. The monitoring wells were drilled to a maximum depth of 55 feet bgs with the exception of MW4 (61 feet bgs) and were screened from 35 to 55 feet bgs. The field screening of the samples collected from MW4 at 56 and 61 feet bgs indicated contamination as documented with photoionization detection measurements of 629 and 578 ppm respectively.. The laboratory report documented significant contamination in samples collected from MW4 including 8.7 ppm TPH-gas and 1.9 ppm benzene at 56 feet bgs and 4.7 ppm TPH-gas and 0.63 ppm benzene at 61 feet bgs. Unfortunately,methyl tertiary butyl ether (MTBE) was not analyzed using EPA 8020,but only using EPA 8260 which had reported elevated detection limits. Also,the soil samples results obtained from MW4 through MW7 were not tabulated in Table 2: Soil Chemical Analytical Data. Please submit disposal documentation for the soil which was transported by Manley and Sons Trucking and disposed of at Forward Inc.'s. On October 9, 1997,Blaine Tech Services began purging and sampling the existing monitoring wells and developing the newly installed wells prior to sampling. The depth to A Division of San Joaquin County Health Care Services