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1 12 April 2006 • AGE-NC Project No. 97-0301 ' Page 5 of 7 measurements or changes of recharge/discharge of the local ground water could greatly modify ground water flow direction. • The average ground water elevation at the site on 20 December 2005 was 22.17 feet below ' MSL. Generally, groundwater elevation at the site decreased an average 0.23 feet between the September 2005 and the December 2005 ground water monitoring events. The decrease in ground water elevation is probably due to seasonal fluctuation. ' Generally,a steep downward vertical gradient was observed from wells MW-8,MW-9,and MW-12 between the Second Water Zone,.Third Water Zone, and Fourth Water Zone; an upward vertical gradient was observed between the First Water Zone and the Second Water Zone in the northern portion, and a slight downward vertical gradient was observed in the southern portion of the site (Figure 3). ' Analysis of ground water sampl s collected from MW-1 and MW-7 suggest the dissolved plume is comprised of TPH-g,/BTEX, and 1,2-DCA. The core of the First Water Zone ' dissolved gasoline plume appears to be currently distributed near the location of wells MW-1 and MW-7; and predominantlX wtained within network of wells consisting of MW-2, MW-3, MW-4, MW-b,cV�IW 95 MW-11A, and MW-12'A (Figure 5). The detection ' . at MW-l0A renders the dissolved plume undefined towards the northeast(down-gradient). • Substantial concentrations of dissolved TPH-d and TPH-k have previously been detected in water samples collected from wells MW-1 and MW-7, indicating a limited distribution of ' TPH-d and TPH-k in the area assessed.For the tenth consecutive quarterly monitoring event, TPH-k,and TPH-mo were not detected from any of the twenty-three water samples analyzed. ' However, TPH-d was detected this quarter, in samples from wells MW-1 and MW-7 at concentrations of 9,800 pg/l and 24,000 µg/l, respectively. • BTEX concentrations in ground water samples MW-1 and MW-7 were above the Maximum Contaminant Levels (MCL's) in drinking water.Benzene concentrations from wells M-9A and MW-l0A were also above the MCL's. ' • A moderate concentration of TAME was detected at well MW-7 only, indicating that there is a minor and defined impact of this component. • This is the first quarter in the past 18 consecutive monitoring events that MTBE has not been ' detected in MW-1. • 1,2-DCA was not detected this quarter in the sample collected from wells MW-2, MW-4 through MW-6;MW-8,MW-11 and MW-12. 1,2-DCA does not appear to extend vertically beyond 40 feet bsg. The core of the First Water Zone dissolved 1,2-DCA plume appears to be currently distributed near the location of wells MW-7 and MW-9A and extending west to MW-1;and predominantly contained within network of wells consisting of MW-2,MW-3, MW-4, MW-6, MW-11A, and MW-12A (Figure 6). The First Water Zone dissolved 1,2- 1 . Advanced GeoEnvironmental,Inc. I