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I <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 consists <br /> of a building and three pump islands with a covered canopy <br /> STRATIGRAPHY <br /> Light brown to brown,dry,sandy silt was encountered at 30 to 35 feet bsg Gray or tan,wet,coarse- <br /> sandy gravel was encountered from depths of 35 to 40 feet bsg An indurated clay generally <br /> 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 repair <br /> • procedures,hydrocarbon-impacted soil was discovered beneath the product line Subsequently,the <br /> EHD required an assessment of the vertical and lateral extent of the 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 vertical <br /> and lateral extent of hydrocarbon-impacted soil and ground water were delineated to the satisfaction <br /> of the San Joaquin County- Environmental Health Department (EHD) <br /> On 08 April 1994, six USTs were removed from the site Details of the USTs removal and soil <br /> I sampling were presented in a report prepared by GAS In May 1994, two 12,000-gallon USTs and <br /> associated piping were installed at the site to replace the removed tanks <br /> ISITE 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-impacted <br /> soil has been delineated,however,the lateral extent of hydrocarbon-impacted ground water has not <br /> been delineated to the satisfaction of the EHD Data collected from the site during the investigation <br /> of the former UST site indicated that hydrocarbon-impacted soil is present in the vadose zone from <br /> depths of approximately 5 to 55 feet bsg Rising ground water elevation has greatly exceeded the <br /> screened intervals of monitoring wells MW-1, MW-2 and MW-3, rendering data collected form <br /> these wells suspect Hydrocarbon-impacted ground water has been encountered north and east of the <br /> IAdvanced Geo Environmental Inc <br />