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4.2 Groundwater Contamination Elevated petroleum hydrocarbon analytes were detected in the water samples collected from wells MW 1 through MW3 TPHg concentrations ranged from 3,200 parts per billion (ppb) to 130,000 ppb BTEX concentrations ranged from 31 ppb to 28,000 ppb The samples collected from wells MW1 through MW3 did not contain detectable concentrations of MTBE, but detection limits were elevated due the presence of elevated concentrations of petroleum hydrocarbons The groundwater sample collected from well CW contained no detectable concentrations of BTEX or tMTBE, but did contain TPHg at 60 ppb The horizontal extent of groundwater contamination at the site can not be determined based upon present available data Well MW2, which is located upgradient from the former tanks locations, contains TPHg and benzene at concentrations one order of magnitude less than the TPHg and benzene concentrations in well MW3 and two orders of magnitude less than the TPHg and benzene concentrations in well MW 1 Wells MW 1 and MW3 are located adjacent to and downgradient from the former tank locations, respectively 5.0 RECOMMENDATIONS ' Smith Technology recommends that additional soil borings be advanced and completed as groundwater monitoring wells to define the horizontal extent of soil and groundwater contamination It is estimated that four soil boring/monitoring wells will be required to define the horizontal extent of contamination One boring should be advanced approximately 60 feet southwest of well MW2, one boring should be advanced approximately 50 feet east of well MW 1, Ione boring should be advanced 60 feet northeast of well MW3, and one boring should be advanced approximately 50 feet north of boring SB6 Soil samples should be collected from the soil borings and analyzed for TPHg, BTEX, and MTBE at a State-certified laboratory Based on initial findings summarized in this report, it is probable that active remediation will be required at the site It is recommended that an air sparge well be installed for future pilot testing This site is a good candidate for air sparge and vapor extraction remediation techniques Upon ' approval of these recommendations by PHS/EffD, Smith Technology will prepare a workplan for this additional investigation After field activities have been completed and analytical data received from the laboratory, a Problem Assessment Report (PAR) should be prepared which summarizes field activities, contains boring and well construction logs, shows the horizontal and vertical extent of soil and groundwater contamination, and proposes remedial options to cleanup the site w\9773 Breportslpst doe 6 • SMTN