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A S S O C I A T E S I N C and groundwater are impacted by petroleum hydrocarbons Site activities were summarized in ATC's Summary Report of Subsurface Investigation, dated January 15, 1999 SAMPLING ACTIVITIES On April 7, 1999, ATC personnel collected groundwater samples from monitoring wells MW1 through MW3 and the on-site groundwater supply well DW The locations of the 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 each monitoring well prior to sampling The wells were allowed to recover and samples were collected from each well using dedicated disposable bailers The surge tank from supply well DW was purged for five minutes prior to sampling The groundwater samples collected from each well were submitted to State-certified Sequoia Analytical (ELAP Cert No 12 10) for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA method 8015 modified, benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA method 8020, and oxygenate fuel additives utilizing EPA method 8260 Groundwater well purge and sample logs are contained in Attachment I • ANALYTICAL RESULTS Groundwater samples collected from wells MWi, MW2, and MW3 contained elevated concentrations of TPHg and BTEX Concentrations of TPHg ranged from 52,200 parts per billion (ppb) in well MW 1 to 272,000 ppb in well MW2 Concentrations of benzene ranged from 1,810 ppb in well MW1 to 38,700 ppb in well MW2 Groundwater samples collected from wells MW1, MW2, and MW3 contained no detectable concentrations of oxygenate fuel additives The groundwater sample collected from on-site supply well DW contained no detectable concentrations of TPHg, BTEX, or oxygenate fuel additives Analytical results of groundwater samples are summarized in Table 2 Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 GROUNDWATER FLOW DIRECTION Water level measurements were collected from wells MW 1 through MW3 on April 7, 1999 Water levels ranged from 59 10 to 59 98 feet below the tops of the well casing elevations, representing an average increase in the water table elevation of approximately 3 33 feet since November 1998 The water level data were used to develop the groundwater elevation contour map (Figure 3) Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed towards the northwest The average hydraulic gradient on April 7, 1999 was calculated to be 0 005 ft/ft or approximately 26 4 ft/mile A summary of groundwater monitoring data is presented in Table 1 w 1I63931quan1y12gr-1999 doc 2