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C. \TATC A S S O C I A T E S I N C groundwater was first encountered Groundwater samples indicated the presence of petroleum hydrocarbons Results are summarized in ATC's Summary Report of Additional Subsurface Investigation, dated September 9, 1998 On February 18, 1999, a geologist from ATC Associates supervised the installation of three groundwater monitoring wells from 39 to 41 feet bgs Soil bonngs MW1, MM2, and MW3 were completed as two-inch monitoring wells One soil sample from each boring was collected and after the groundwater monitoring wells were developed on groundwater sample was collected from each well Soil and groundwater samples contained detectable concentrations of petroleum hydrocarbons Results are summarized in ATC's Summary Report of Additional Subsurface Investigation, dated June 1, 1999 SAMPLING ACTIVITIES On June 12, 2000, groundwater samples were collected by ATC Associates personnel from monitoring wells MW 1 through MW3 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 rrvnimum of three well casing volumes were purged from each well prior to sampling The wells were allowed to recover and samples were collected from each well using dedicated disposable bailers s The groundwater samples collected from each well were submitted to State-certified Sequoia Analytical (FLAP Cert No 1624) for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA methods 8015 modified, and benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA methods 8020 Groundwater well purge and sample logs are contained in Attachment 1 ANALYTICAL RESULTS The groundwater sample collected from well MWl contained detectable concentrations of benzene, ethyl benzene, xylenes, and TPHg, and the chromatogram pattern indicated a weathered gasoline result The TPHg concentration was 4,590 parts per billion (ppb) The BTEX concentrations ranged from <5 0 to 221 ppb Only benzene, detected at a concentration of 23 8 ppb, exceeded the California Maximum Contaminant Level (MCL) of 10 ppb for drinking water The groundwater sample collected from well MW2 contained detectable concentrations of only xylenes at 0 904 ppb TPHg, benzene, toluene, and ethylbenzene were nondetect in tins groundwater sample The groundwater collected from well MW3 contained TPHg at a concentration of 769 ppb and the chromatogram pattern indicated a weathered gasoline result The BTEX concentrations • ranged from <5 0 to 14 2 ppb Analytical results of groundwater samples are summarized in Table 2 w\149811gw►rUyl2gr--2000 doc 2