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C" T 1 A S S O C I A T E S I N C Additionally, in December 2001, an ATC geologist supervised the advancement of five Geoprobe borings, SB12 to S1316 to a depth of approximately 25 feet bgs Three additional ' offsite borings were advanced to depths of approximately 42 feet bgs and completed as groundwater monitoring wells MW8 through MW 10 Field activities and analytical results were detailed in ATC's Offiste Subsurface Investigation Report, dated April 24, 2003 1 QUARTERLY GROUNDWATER MONITORING ACTIVITIES 1 On March 18, 2004, ATC personnel collected groundwater samples from monitoring wells MW2 through MW10 and CW Well MW1 was not sampled because it was converted to a dual extraction well in February 2004 The locations of the monitoring wells are shown on Figure 2 ' Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring wells and recorded A minimum of three well casing volumes was purged from each well prior to sampling The wells were allowed to recover ' and samples were collected from each well using dedicated disposable bailers Groundwater well purge and sample logs are contained in Attachment 1 ' The groundwater samples collected from each well were submitted to State-certified Argon Laboratories, Inc (ELAP Cert No 2359) for chemical analyses of TPHg by EPA method 801513, benzene, toluene, ethylbenzene, xylenes (BTEX) by EPA method 8021B, and methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), tertiary butyl alcohol (TBA), tertiary amyl ether (TAME), di-isopropyl ether (DIPE), 1,2-dichloroethane (1,2-DCA), and ethyl dibromide ' (EDB) by EPA method 8260B Groundwater Analytical Results TPHg and/or BTEX constituents were detected at or above laboratory reported detection limits in groundwater samples collected from wells MW5, MW6, and MW7 The groundwater samples collected from wells MW2, MW4, MW5, MW6, MW7, MW9, and CW contained low concentrations of MTBE ranging from 0 8 parts per billion (ppb) to 5 3 ppb None of the groundwater samples collected contained detectable concentrations of ETBE, TBA, TAME, DIPS, or EDB, however groundwater samples collected from Canepa's well contained 10 ppb of 1,2-DCA The samples collected from MW3, MW8 and MW10 contained no detectable concentrations of any of the constituents analyzed ' Theg roundwater sample collected in March 2004 from MW2, located near the vapor extraction wells, contained a slightly higher concentration of MTBE than the sample collected in December 2003 Groundwater samples collected from MW4 and MW9 contained slightly decreased concentrations of MTBE with respect to the samples collected from these wells in December 2003, but are all below the Maximum Contamination Limit (MCL) and within historical ranges Concentrations in the remaining wells generally were slightly lower than those detected in December 2003 A summary of analytical results is presented in Table 1 Groundwater laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 s\env iro1625961quart1y\1gr 2004 doc 3 1