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02 March 2005 AGE-NC Project No 97-0333 ' Page9of10 _ ' monitoring event, the overall trend of decreasing MTBE concentrations is evident The results from the ground water monitoring and sampling event performed on 30-31 December ' 2004 are as follows • Generally,depth to ground water at the site varied between 21 and 23 feet bsg,ground water ' elevations ranged between 10 3 8 feet and 11 99 feet above MSL The ground water elevation increased approximately 5 09 feet between the October and December 2004 ground water monitoring events, the increase in elevation may be due to seasonal fluctuation • First Zone ground water flow was inferred to be toward a ground water depression in the area of wells EW-1,MW-6,and MW-7A under a hydraulic gradient of approximately 0 005 ft/ft ' On the southeast-half of the site, ground water was inferred to be flowing toward the northwest under a gradient of approximately 0 02 ft/ft (Figure 4) ' • Second Zone,Third Zone,and Primary Aquifer ground water flow was inferred to be toward the northwest at approximate gradients of 0 001 ft/ft or less (Figures 5, 6, and 7, respectively) - f Due to the low ground water gradient at the site, small variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly ' modify the inferred ground water flow direction • Historically,the highest on-site concentrations of dissolved MTBE have been detected in the samples collected in the area of First Zone monitoring wells MW-2, MW-3, and MW-6, ' however,during the fourth quarter 2004,the highest MTBE concentration was detected from the Primary Aquifer Zone at 4,300 lig/1(MW-7E) ' • Minor to significant PCE and/or TCE concentrations were detected in ground water monitoring wells located in First Zone, Second Zone,Third Zone,and Primary Aquifer Zone aquifers(Figure 10,Table 4) The highest concentrations of dissolved PCE were detected in ' the samples collected from First Zone wells MW-2,MW-3,and MW-6 at concentrations as high as 2,600 gg/l (MW-3) s • PCE and TCE are chlorinated solvents often associated with dry cleaning operations Based on the December 2004 PCE iso-concentration map in First Zone water (Figure 10), AGE interprets the PCE/TCE plume to have originated from the dry cleaner's facility located ' immediately cast of the Rainwater Car Wash • Based on a trend of increasing PCE concentrations observed at the pump-and-treat influent since July 2004 and from increasing PCE concentrations reported from monitoring wells MW-2, MW-3, MW-6 and MW-7A, it would appear as though the core-area of the PCE -plume has migrated west towards the northwest section of the Rainwater Car-Wash site,and , ' Advanced GeoEnvi ron mental,Inc tt