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1 <br /> 1 <br /> Appendix A - Historical Background <br />' PACIFIC MINI-MART <br /> 4511 Pacific Avenue, Stockton, California <br />' SITE USAGE <br />' The site is located at the northwest corner of Pacific Avenue and Rose Marie Lane in Stockton, <br /> California and currently operates as a gasoline dispensing station and mini-mart The facility <br /> consists of a building and three pump islands with a covered canopy <br /> 1 <br /> STRATIGRAPHY <br /> 1 Light brown to brown, dry, sandy silt was encountered at 30 to 35 feet bsg Gray or tan, wet, <br /> coarse-sandy gravel was encountered from depths of 35 to 40 feet bsg An indurated clay <br />' generally underlaid the sandy gravel at depths of 40 to 60 feet bsg <br /> UNDERGROUND STORAGE TANK REMOVAL <br /> In February 1991, a broken coupling in a product line was discovered and repaired During <br />' repair procedures, hydrocarbon-impacted soil was discovered beneath the product line <br /> Subsequently, the EHD required an assessment of the vertical and lateral extent of the <br /> hydrocarbon impact <br />' Between 1991 and 1993 three soil borings, one vapor extraction well and three ground water <br /> monitoring wells were installed at the site by Geological Audit Services, Inc (GAS) The <br /> vertical and lateral extent of hydrocarbon-impacted soil and ground water were delineated to the <br /> satisfaction of the San Joaquin County - Environmental Health Department (EHD) <br /> IOn 08 April 1994, six USTs were removed from the site Details of the USTs removal and soil <br /> sampling were presented in a report prepared by GAS In May 1994, two 12,000-gallon USTs <br /> and associated piping were installed at the site to replace the removed tanks <br /> SITE ASSESSMENT <br /> Between 1991 and 1997, four soil borings, one vapor extraction well and seven ground water <br /> monitoring wells were installed at the site The vertical and lateral extent of hydrocarbon- <br /> impacted soil has been delineated, however, the lateral extent of hydrocarbon-impacted ground <br /> water has not been delineated to the satisfaction of the EHD Data collected from the site during <br /> the investigation of the former UST site indicated that hydrocarbon-impacted soil is present in <br /> the vadose zone from depths of approximately 5 to 55 feet bsg Rising ground water elevation <br /> has greatly exceeded the screened intervals of monitoring wells MW-1, MW-2 and MW-3, <br /> rendering data collected form these wells suspect Hydrocarbon-impacted ground water has been <br />