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I09 April 2002 • AGE-NC Project No 95-0141 IPage 2 of 13 22 PREVIOUS SITE ASSESSMENT In February 1992, three groundwater monitoring wells (MW-1, MW-2 and MW-3) were installed near the former UST area by RESNA Industries of Escalon, California Evidence of petroleum hydrocarbon-impacted soil was detected in all borings at depths between 20 and 35 feet below surface grade (bsg) Initial ground water samples contained TPH-g at concentrations as high as 300,000 micrograms per liter (µg11) and volatile aromatics (benzene, toluene, ethylbenzene and xylenes, BTEX) at concentrations as high as 17,000 µg11 A fourth groundwater monitoring well was installed northeast of the former UST area in October 1993 Evidence of petroleum hydrocarbon soil contamination was detected in soil samples collected I at 40 and 45 feet bsg Initial ground water samples detected TPH-g at concentrations as high as 6,800 µg/l and BTEX at concentrations as high as 1,400 µg/l In May 1994, a fifth ground water monitoring well(MW-5)was advanced near the northeast corner of the site Petroleum hydrocarbons were not reported in soil samples subinitted for analysis TPH-g and BTEX were reported in initial ground water samples collected from MW-5 at concentrations up �• to 93 µg/l and 1 3 µg/1, respectively Three additional groundwater monitoring wells were installed at the site on 25 and 26 October 2000 Two of the wells (MW-7 and MW-8) were installed in first encountered ground water and one well (MW-6) was advanced to a depth of 65 feet bsg to monitor deeper ground water Soil samples collected from the pilot boring for MW-6 contained concentrations of TPH-g as high as 4,100 mg/kg, benzene as high as 17 mg/kg, ethyldibromide (EDB) as high as 460 mg/kg and 1,2-dichloroethane (1,2-DCA) as high as 410 mg/kg Contamination was detected in the deepest recovered sample from MW-6 at a depth of 65 feet bsg One soil sample collected fromthe pilot boring for MW-8 contained 1,2-DCA at a concentration of 15 mg/kg Soil samples from the pilot boring for MW-7 did not contain detectable concentrations of analytes of concern TPH-g,BTEX and 1,2-DCAwere detected in the initial ground water samples collected from MW-6, MW-7 and MW-8 Details of the procedures and results of the monitoring well installation were presented in Monitoring Well Installation Report - Fourth Quarter 2000, dated 16 January 2001, prepared by AGE Between March 1992 and October 1999, seven ground water monitoring events were performed at the site, ground water monitoring has been conducted quarterly since November 2000 During the most recent sampling event(February 2002), TPH-g was detected in ground water samples collected from seven of the eight monitoring wells at concentrations as high as 150,000 µg/1 BTEX constituents were detected in six of the eight groundwater monitoring wells at concentrations as high as 8,600 /l benzene, 25,000 1 toluene 3 200 1 eth lbenzene and 15 000 /l total xylenes µg µlb � µPQ Y � µg • Advanced GeoEnvironmentai,Inc I i I