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OokTc • A S S 0 C I A T E S I N C In August 1995, Smith Technology conducted a subsurface site investigation to further define the extent of contamination in groundwater at the site Smith Technology supervised the installation of monitoring wells MW-4, MW-5 and MW-6 These three new wells were developed and sampled along with monitoring wells MW-1, MW-2, and MW-3 Analytical results of groundwater samples from the six monitoring wells indicated the presence of elevated concentrations of petroleum hydrocarbons in the vicinity of wells MW-3 and MW-6, on the northeast corner of the site SAMPLING ACTIVITIES On April 14, 1998, groundwater samples were collected by ATC personnel from monitoring wells MW-3 and MW-6 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 each well 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 American Environmental Network laboratory (ELAP cert no 1172) for analysis of total petroleum hydrocarbons as gasoline (TPHg), and benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA methods 8015/8020, and oxygenate fuel additives utilizing EPA method 8260 Groundwater well purge and sample logs are contained in Attachment i ANALYTICAL RESULTS Petroleum hydrocarbon constituents were detected above laboratory method detection limits in the sample collected from well MW-3 MTBE was detected in well MW-3 at 200 parts per billion (ppb), although the sample was diluted due to matrix interference A summary of analytical results is presented in Table 1 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 MW-6 on April 14, 1998 Water levels ranged from 20 18 to 20 99 feet below the tops of the well casing elevations, representing an average increase in the water table elevation of approximately 5 26 feet since January 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 generally towards the northeast The average hydraulic gradient on April 14, 1998 was calculated to be 0 0008 ft/ft or approximately 4 ft/mile A summary of . groundwater monitoring data is presented in Table 1 w 1626051quart1y12gr-1998 doc 2