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_ rte . A S S O C I A T E S I M C GROUNDWATER M®1$114TORIENG AND SAMPLING ATC performed quarterly groundwater monitoring and sampling on April 15, 2004 Field work included measuring the depth-to-water in wells MW1 through MM3 and purging and sampling the water from these wells and the site's domestic well The samples were analyzed for the presence of dissolved petroleum hydrocarbons Depth to water measurements were recorded on April 15, 2004 from monitoring wells MW1 through MW3 The water table elevation has increased an average of 2 69 feet in the monitoring wells since the last monitoring event in January 2004 Assuming horizontal isotropic conditions, groundwater flow in the uppermost aquifer beneath the site on April 15, 2004, was to the east- northeast The average hydraulic gradient was calculated to be 0 001 ft/ft or approximately 5 1 ft/mile Historically, groundwater beneath the site generally flows in a northeasterly direction Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the April 2004 monitoring event is shown on Figure 3 Groundwater samples were collected from wells MW I through MW3 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to ATC's Field Procedures on file with SJEHD Monitoring well purge logs are included in Attachment 1 Furthermore, ATC collected a water sample from the sampling port of the on-site Domestic Well Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Argon Laboratories, Inc , (DHS Certification No 2359) Samples were analyzed for BTEX by EPA method 802113, TPHg by EPA method modified 8015, and oxygenate fuel additives, including 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) by EPA method 8260B RESULTS Laboratory analyses detected petroleum hydrocarbon constituents in the sample collected from well MW 1 The constituent concentrations detected include TPHg (160 pbb), toluene (0 6 ppb), and xylenes (2 0 ppb) Groundwater samples collected from wells MW2, MW3, and the Domestic Well contained no detectable concentrations of TPHg and BTEX 1,2-DCA was detected in wells MWi and MW3 in concentrations of 37 ppb and 6 3 ppb, respectively No other detectable concentrations of fuel oxygenates were reported in any of the samples collected from the monitoring wells Analytical results are summanzed in Table 1 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 • w 1148851reportsl2gU2004 doc 3