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• Site Background Information K& S Gas & Grocery ' Page 2 of 5 ' detected at a depth of 45 feet bsg or in samples analyzed from the three other borings Soil probe boring installations were described in theAGE-prepared Preliminary Site Assessment Report in August 1997 ' One 20,000-gallon UST was installed at the site following the 1998 UST removals Approximately 341 tons of hydrocarbon-impacted soil were excavated during removal of the old USTs and over- excavation for the installation of the new UST and piping Soil was disposed of at Forward Landfill During the UST installation, two conductor casings were installed through the pea gravel adjacent to the UST in anticipation of future site assessment needs The UST removal, over-excavation, and ' UST installation were described in the AGE-prepared UST Removal Report, dated 26 May 1998 Three ground water monitoring wells (MW-1 through MW-3)were installed in December 1998 as ' part of site assessment activities Petroleum hydrocarbon-impacted soil was encountered in all well borings The maximum concentration of TPH-g was 4,200 mg/kg (MW-1) Benzene and MTBE were detected only in soil sample MW2-35 at 0 0058 mg/kg and 0 011 mg/kg,respectively TPH-g was detected in initial ground water samples collected from MW-1 through MW-3 at a maximum concentration of 330,000 micrograms/liter (µg/1) in the sample from MW-3 BTEX • compounds were detected at concentrations as high as 29,000 µg/1 benzene, 54,000 µg/1 toluene, 6,500 µg11 ethylbenzene, and 36,000 µg11 xylenes (MW-3) MTBE was detected in all three well samples at a maximum concentration of 510 µg/1(MW-1) In addition,TBA was detected in MW-1 and MW-2 at a maximum concentration of 830µg/l(MW-1) Monitoring well installation and initial monitoring activities were described in the AGE-prepared Monitoring Well Installation Report, dated 02 June 1999 Between February andNovember 2001,AGE advanced five paired cone penetrometer testing(CPT) soil borings(CPT-1 through CPT-5)at the site to depths between 100 feet and 150 feet bsg to assess the extent of petroleum hydrocarbon impact and to identify potential hydrologic units TPH-g was detected in grab ground water samples at concentrations as high as 14,000 µg/1 (CPT-4), BTEX compounds were detected at concentrations as high as 4,000 µg/1 (benzene, CPT-4), MTBE was I detected at concentrations as high as 13 µg11(CPT-4),TBA was detected at concentrations as high as 5 0 µg/l (CPT-2) I Based on CPT data,AGE developed a hydrogeologlc model for the site consisting of a vadose zone and six potential hydrologic units informally identified as Hydrologic Unit 1 (HU1), located between 30 feet and 70 feet bsg,Hydrologic Unit 2(HU2), located between 70 feet and 85 feet bsg, Hydrologic Unit 3 (HU3), located between 85 feet and 95 feet to 100 feet bsg, Hydrologic Unit 4 (HU4), located between 95 feet to 100 feet and 120 feet bsg, Hydrologic Unit 5 (HU5), located between 120 feet and approximately 135 feet bsg, and Hydrologic Unit 6(HU6), located between 135 feet and at least 150 feet bsg Geologic cross sections A A'and B-B'were generated from the CPT data, depicting the informal hydrologic units and petroleum hydrocarbon concentrations Advanced GeoEnvironmental,Inc.