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A S S O 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 October 7, 1998, groundwater samples were collected by ATC personnel from monitoring wells MW-3 and MW-6 The locations of the monitonng 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 Sequoia Analytical (ELAP cert no 1210) for analysis of total petroleum hydrocarbons as gasoline (TPHg), and benzene, toluene, ethylbenzene, total xylenes (BTEX), methyl tertiary butyl ether (MTBE) utilizing EPA methods 8015/8020 Groundwater well purge and sample logs are contained in Attachment 1 ANALYTICAL RESULTS Petroleum hydrocarbon constituents were detected above laboratory method detection limits in the sample collected from well MW-3 The sample from MW-6 contained no detectable concentrations of TPHg, BTEX, or MTBE TPHg and toluene, ethylbenzene, and xylenes were detected in the sample from well MW-3 The method detection limits for benzene and MTBE were elevated due to dilution factors 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 October 7, 1998 Water levels ranged from 22 27 to 23 08 feet below the tops of the well casings, representing an average decrease in the water table elevation of approximately 1 33 feet since July 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 east-northeast The average hydraulic gradient on October 7, 1998 was calculated to be 0 001 ft/ft or approximately 5 ft/mile A summary of groundwater monitoring data is presented in Table 1 • w 1626051quarl1yl4gr-1998 doe 2