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• • Site Background Information: Comfort Air, Inc. AGE-NC Project No. 95-0141 Page 2 of 5 PREVIOUS SUBSURFACE INVESTIGATIONS Monitoring Well Installations 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 (µg/1) and volatile aromatics (benzene, toluene, ethylbenzene and xylenes; BTEX) at concentrations as high as 17,000 µg/1. 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 at 40 and 45 feet bsg.Initial ground water samples detected TPH-g at concentrations as high as 6,800 µg/1 and BTEX at concentrations as high as 1,400 µg/1. 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 submitted for analysis.TPH-g and BTEX were reported in initial ground water samples collected from MW-5 at concentrations up to 93 µg/1 and 1.3 µg/l, respectively. On 25 and 26 October 2000, three additional ground water monitoring wells were installed at the site. 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 pilotboring forMW-6 contained concentrations ofTPH-g as high as 4,100 mg/kg, benzene as high as 17 mg/kg, 1,2-dibromoethane(EDB)as high as 460µg/kg and 1,2-dichloroethane (1,2-DCA) as high as 410 µg/kg. Contamination was detected in the deepest recovered sample from MW-6 at a depth of 65 feet bsg. One soil sample collected from the pilot boring for MW-8 contained 1,2-DCA at a concentration of 15 µg/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-DCA were detected in the initial ground water samples collected from MW-6, MW-7 and MW-8. Between 14 October and 23 October 2002, soil borings were advanced at the site to install monitoring wells MW-8B,MW-9A/B,MW-I OAB,MW-11AB and MW-12A/B)and one ground water monitoring/extraction well EX-1.No soil samples were analyzed. On 15 December 2004, a 118 foot soil boring was advanced at the site and completed as monitoring well MW-13 screened from 113 to 118 feet bsg. A total of 10 soil samples were analyzed for the Advanced GeoEnvironmental,Inc.