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1 -• ran f.tyeka x - — � - "_ .. Gl 5 I r N- s r' sn I a,s -, y J .. i I I BACKGROUND INFORMATION Fernando's PIace ' 1201 South Center Street, Stockton, California PREVIOUS SITE ASSESSMENT 1 According to Work Plan -Phase 2 Site Investigation, 1201 S Center Street, Stockton, CA, dated 28 May 1999, prepared by Foothill Engineering (FE), two five-hundred gallon and one 8,500-gallon ' gasoline underground storage tanks (UST 1, UST 2 and UST 3, respectively) were removed from the site by Jim Thorpe Oil on 26 October 1994 Ten soil samples were analyzed from the excavation soil stockpile, the UST excavations and the product piping by GeoAnalytical Labs Each sample ' contained detectable concentrations of petroleum hydrocarbon contamination FE reported that the highest concentrations were located near the west end of UST 3 (Figure 2) The excavation was ' backfilled to surface grade following sample collection On 28 April 1998, soil boring PB 1 was advanced near UST 1 and UST 2 to a depth of 30 feet below surface grade (bsg) for the collection of soil samples Analyzed samples contained concentrations ' of total petroleum quantified as gasoline (TPH-g) as high as 14,100 milligrams per kilogram (mg/kg) Additionally, samples were collected from the soil boring for MW-1,installed on 28 April ' 1998 Analyzed samples from MW-1 contained high concentrations of TPH-g and benzene,toluene, ethylbeneze and total xylenes (BTEX) compounds to a depth of approximately fifty feet bsg ' Four additional ground water monitoring wells were installed by FE betwen 08 and 12 March 1999 iAnalyzed soil samples collected from monitoring well soil borings contained detectable concentrations of TPH-g to depths as great as 105 feet bsg and BTEX compounds to depths as great as 120 feet bsg Tables 1 and 2 summarize analytical results of soil and ground water samples collected during previous investigations Figure 2 illustrates monitoring well and former UST locations I Between 14 and 21 August 2001, six Cone Penetrometer Testing(CPT)borings were advanced on- and off-site to depths between 122 and 175 feet bsg Based on data collected from the CPT borings, AGE identified four potential hydrogeologic units (First Water Zone, Second Water Zone, Third Water Zone and Fourth Water Zone) Significant concentrations of TPH-g, BTEX and 1,2-DCA compounds were detected in grab ground water samples collected from each of the hydrogeologic units I ti L n REGIONAL GEOLOGIC SETTING ' According to the Geologic Map of California, published in 1977 by the State of California Department of Mines and Geology,the site area is within the Great Valley Geomorphic Province of California, a large, elongate, northwest trending structural trough The Great Valley Province has been filled'to its present elevation with thick sequences of sediment ranging in age from Jurassic to present day, creating a nearly flat lying alluvial plain extending from the Tehachapi Mountains in the south to the Klamath Mountains in the north The western and eastern boundaries of this I