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7 I j J • TC A S S O C I A T E S I N C L?0 jtLr ';t „ iI 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 borings MW 1, MW2, 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 March 16, 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 minimum of three well casing volumes were purged from eachrWell prior to sampling The wells'were . allowed to recover and samples were collected from each well using dedicated disposable bailers The groundwater samples collected from each well were submitted to State-certified Sequoia Analytical (FLAP Cert No 1210) 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 MW 1 contained detectable concentrations of TPHg, benzene, ethyl benzene and toluene The TPHg concentration was 1,150 parts per billion (ppb) The BTEX concentrations ranged from <1 0 to 29 1 ppb Only benzene exceeded the California Maximum Contaminant Level (MCL) of 10 ppb for drinking water The groundwater sample collected from well MW2 contained detectable concentrations of TPHg and BTEX The TPHg concentration was 277 ppb and BTEX concentrations ranged from 0 636 to 2 23 ppb Benzene was detected at a concentration barely above the MCL The groundwater collected from well MW3 contained TPHg at a concentration of 1,510 ppb and the chromatogram pattern indicated a weathered gasoline result The BTEX concentrations ranged from <5 0 to 21 10 ppb Analytical results of groundwater samples are summarized in • Table 2 w\149811quartiyl4gr-1999&C 2