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APPENDIX A - SITE BACKGROUND INFORMATION WEST CLAY PROPERTIES 639 West Clay Street, Stockton, California Two areas of concern related to former underground storage tanks (USTs) have been identified at the site The former UST No 3 area is located in the southern portion of the property and the former ' Cluster UST area is located in the north portion of the property Following is a brief history of environmental assessment and remediation UST No. 3 Location (South Area) 1990 to 1993 - It is AGE's understanding that one 1,000-gallon UST was removed from the site in May 1990,and the product line from the former UST to the dispenser was removed in October 1993 Subsequently,approximately 550 cubic yards of hydrocarbon-impacted soil was removed from the former UST area, the soil was excavated to a depth of approximately 38 feet below surface grade (bsg) Total petroleum hydrocarbons quantified as gasoline (TPH-g) was encountered in one excavation bottom sample at a concentration of 5,200 milligrams per kilogram(mg/kg) and in one sidewall sample at 2,100 mg/kg, however, the lateral and vertical extent of contamination was not assessed Following excavation, four soil borings (13-1 through 13-4) were advanced at the site as part of � . environmental assessment related to the former UST Three borings were completed as monitoring wells (MW-1 through MW-3) Ground water was determined to be impacted and additional assessment was required by the San Joaquin County Environmental Health Department(EHD) to define the lateral and vertical extent of impacted soil and ground water The excavation was not backfilled until April 1997 June 1996 - AGE begins working on project November 1996 - Four soil borings (13-5 through B-8) were advanced at the site Relatively low concentrations of BTEX constituents were detected In the soil sample collected at 30 feet bsg in soil boring B-7, analytes of concern were not detected in the soil samples collected and analyzed from borings B-5, B-6 and B-8 Xylenes and total petroleum hydrocarbons quantified as diesel(TPH-d) were detected in grab ground water samples collected from borings B-6 and B-8 May 1997-Monitoring wells MW-4 and MW-5 were installed at the site Target analytes were not detected above laboratory reporting limas in soil samples collected and analyzed from the pilot borings Relatively low concentrations of various target analytes were detected in ground water samples collected during the preliminary ground water monitoring and sampling event August 1998-Five monitoring wells(MW-6A/B,MW-7 and MW-SAB)were installed at the site Relatively low concentrations of benzene and xylenes were detected in the soil sample collected at 45 feet bsg from pilot boring MW-8 Analytes of concern were not detected in the soil samples • collected and analyzed from pilot bonngs MW-6 and MW-7 r Advanced GeoEnvironm ental,Inc I