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� 1 >I Ms Vicky McCartney May 23, 2005 Page 3 of 6 • Semi-Annual Groundwater Sampling Event On March 31, 2005 monitoring wells MW 1 through MW3 were monitored and sampled Groundwater elevations were calculated by measuring the depth to groundwater in each well and subtracting from the respective wellhead elevation Groundwater elevations at the site rose an average of 4 17 feet since last monitored on July 12, 2004 The average hydraulic gradient across the site was approximately 0 01 ft/ft (50 feet per mile) Groundwater flowed in a northeasterly direction A potentiometric surface map is depicted on Figure 3 Groundwater monitoring data are summarized in Table 1 Monitoring data sheets are included in Attachment C Prior to sampling, monitoring wells MW 1 through MW3 were purged of a minimum of three well casing volumes During the purging process, temperature, pH and electrical conductivity parameters were measured Samples were collected after parameter stabilization, and 100% water level recovery Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (ELAP #2359) for analysis of TPHg, BTEX, and gasoline oxygenate additives including 1,2-DCA Purge water was contained in a properly labeled DOT-approved 55-gallon drum The drum is currently being stored onsite Purge logs are included in Attachment C o RESULTS OF INVESTIGATION - 5 Subsurface Conditions _ Z, �J Soils encountered in the borings consisted primarily of silt and clay Two sand zones were also identified, one in the unsaturated zone and the second in the saturated zone The shallower sando was encountered in borings SBA, SBB and SBG This silty sand interval is approximately 5-10 feet thick and terminates at a depth between approximately 20-30 feet The deeper silty sand was present between the depths of approximately 43-48 feet in borings SBA and SBB and from approximately 48 feet to total depth of 52 feet in boring SBF Groundwater was encountered in the deeper sand No hydrocarbon odors or elevated PID readings were observed in soil borings SBB, SBC, SBD, SBE, SBF, and SBG In boring SBA, located down gradient of the former UST, slightly elevated PID readings were recorded from the 45 (35 3 parts per million [ppm]) and 50 (38 6 ppm) foot samples Hydrocarbon odors were not observed in soil samples collected in boring SBA Groundwater-saturated soils were first noted in the borings at depths between approximately 45 and 50 feet Water levels rose in the temporary well casings to depths between 33 feet and 41 feet bgs In borings SBC and SBD saturated soils were encountered at 5 feet bgs as a result of heavy precipitation Boring logs describing the hthology are included in Attachment B G\GROUNDZE\W E\SAR\2005\1SAR05bonngreportdoe