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' APPENDIX A - HISTORICAL SUMMARY <br /> WEST CLAY PROPERTIES <br />' 639 West Clay Street, Stockton, California <br />' Two areas of concern related to former underground storage tanks (USTs) have been identified at <br /> the site The former UST No 3 area is located at the southern portion of the property and the former <br /> Cluster UST area is located at the north portion of the property Following is a brief history of <br />' environmental assessment and remediation <br />' UST No. 3 Location (South Area) <br /> 1990 to 1993 - It is AGE's understanding that one 1,000-gallon UST was removed from the site in <br />' May 1990, and the product line from the former UST to the dispenser was removed in October 1993 <br /> Subsequently,approximately 550 cubic yards of hydrocarbon-impacted soil were removed from the <br /> former UST area, the soil was excavated to a depth of approximately 38 feet below surface grade <br />' (bsg) Total petroleum hydrocarbons quantified as gasoline (TPH-g) was encountered in one <br /> excavation bottom sample at a concentration of 5,200 milligrams per kilogram (mg/kg) and in one <br />' sidewall sample at 2,100 mg/kg, however, the lateral and vertical extent of contamination was not <br /> assessed <br />' Following excavation, four soil borings (B-1 through B-4) were advanced at the site as part of <br /> environmental assessment related to the former UST Three borings were completed as monitoring <br /> wells (MW-1 through MW-3) Ground water was determined to be impacted and additional <br /> assessment was required by the San Joaquin County Environmental Health Department (EHD) to <br /> define the lateral and vertical extent of impacted soil and ground water The excavation was not <br /> backfilled until April 1997 <br />' June 1996 - AGE begins working on project <br />' November 1996 - Four soil borings (B-5 through B-8) were advanced at the site Relatively low <br /> concentrations of BTEX constituents were detected in the soil sample collected at 30 feet bsg from <br /> soil boring B-7, analytes of concern were not detected in the soil samples collected and analyzed <br /> from bonngs B-5, B-6 and B-8 Xylenes and total petroleum hydrocarbons quantified as diesel <br /> (TPH-d) were detected in grab ground water samples collected from borings B-6 and B-8 <br /> May 1997- Monitoring wells MW-4 and MW-5 were installed at the site Target analytes were not <br /> detected above laboratory reporting limits in soil samples collected and analyzed from the pilot <br /> borings Relatively low concentrations of various target analytes were detected in ground water <br />' samples collected during the preliminary ground water monitoring and sampling event <br />' August 1998-Five monitoring wells (MW-6A/B,MW-7 and MW-8A/B)were installed at the site <br /> Relatively low concentrations of benzene and xylenes were detected in the soil sample collected at <br />