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THRIFTY OIL CO . <br /> June 19, 1998 <br /> Mr. Mike Infurna <br /> County of San Joaquin <br /> Public Health Services/Environmental Health Division <br /> 304 East Weber Avenue, 3rd Floor <br /> Stockton, Ca 95202 <br /> RE: Thrifty Oil Co. Station. #172 <br /> 7647 Pacific Avenue <br /> Stockton, Ca 95207 <br /> Supplement to Work Plan for Corrective Action <br /> Dear Mr. Infurna: <br /> Presented herein is a letter supplement to the Work Plan for Corrective Action, dated September 8, <br /> 1997, prepared for Thrifty Oil Co. Station#172. This letter supplement was prepared in response <br /> to your request to include groundwater remediation as part of our proposed remedial efforts. <br /> CORRECTIVE ACTION <br /> Site Conditions <br /> Groundwater beneath this site is present under water table conditions and has been steadily rising <br /> for the past several years from approximately 50 feet below surface grade to 42 feet below surface <br /> grade. Hydrocarbon impacted groundwater appears to be localized in the vicinity of groundwater <br /> monitoring well MW-11. This well contains a maximum benzene concentration of 20,000 ug/L, as <br /> sampled on February 18, 1998. The next highest benzene concentration was reported in well MW- <br /> 10 at a concentration of 2.8 ug/L,all other wells contained concentrations below laboratory detection <br /> limits. <br /> Thrifty proposes to operate a groundwater remediation system inconjuction with a soil vapor <br /> extraction system(proposed in the Work plan for Corrective Action, dated September 8, 1997). The <br /> purpose of the groundwater remediation system is to control and reduce the migration of dissolved <br /> hydrocarbons in groundwater and lower groundwater elevations in order to expose hydrocarbon <br /> impacted soil to vapor extraction. <br /> Groundwater Remediation System <br /> Thrifty proposes to extract groundwater from monitoring well MW-11 utilizing a pneumatically <br /> operated pump. Based upon the soil types present in the saturated zone, Thrifty anticipates a flow <br /> 13539 E. Foster Rd., Santa Fe Springs, CA 90670-0138•(562)923-9876 <br />