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u �s V � r 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 May 30, 2000, ATC personnel collected groundwater samples from monitoring wells MWI 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 Argon Laboratories (FLAP Cert No 2358) 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 1,200 parts per billion (ppb) in well DW to 480,000 ppb in well MW2 Concentrations of benzene ranged from 128 ppb in well MWI to 56,000 ppb in well MW2 Groundwater samples collected from wells MW1, MW2, MW3, and DW contained no detectable concentrations of oxygenate fuel additives although the detection limits were elevated due to dilution factors 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 MWI through MW3 on May 30, 2000 Water levels ranged from 58 42 to 59 33 feet below the tops of the well casing elevations, representing an average increase in the water table elevation of approximately 0 63 feet since April 1999 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 south-southwest The average hydraulic gradient on May 30, 2000 was calculated to be 0 003 ft/ft or approximately 15 8 ft/mile A summary of groundwater monitoring data is presented in Table 1 w\163931quart1yl2gr-2000 doc 2