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1 <br />' 02 December 1998 <br /> AGE-NC Protect No 95-0130 <br /> Page 4 of 5 <br />' • Ground water was inferred to be flowing toward the northeast at a calculated gradient of <br /> 0 006 ft/ft, or approximately 30 feet per mile (Figure 3) Due to the low gradient at the site, <br /> slight variations in ground water measurements or changes of recharge/discharge of the local <br />' ground water could greatly modify ground water flow direction <br /> • The ground water surface elevation at the site is above the slotted screen intervals in wells <br />' MW-1 through MW-5 and VW-I C, VW-2A and VW-3A, therefore samples collected from <br /> these wells may not be representative of dissolved petroleum hydrocarbon concentrations in <br /> shallow ground water <br /> • From June to September 1998, substantial dissolved hydrocarbon-concentration Increases <br /> were observed from wells MW-2 through MW-4 (Appendix C) A relationship appears to <br /> exist between the Increased concentrations reported from MW-2 and MW-4 and ongoing <br /> remediation activities at 102 South Wilson Way, which could be causing an eastward shift <br /> in the dissolved petroleum hydrocarbon plume <br />' • From June 1998 to September 1998, a substantial decrease in dissolved hydrocarbon- <br /> concentrations were observed from well VW-2A (Appendix C) A relationship appears to <br /> exist between the decrease of petroleum hydrocarbon concentrations and drowning of the <br /> screen interval <br /> • A plot of TPH-g and benzene concentrations and ground water elevation versus time <br /> (Appendix C) suggests a trend of decreasing petroleum hydrocarbon concentrations and <br /> increasing ground water elevations at MW-5 <br /> I • TBA was detected in water samples collected from MW-2 and MW-3 at concentrations of <br /> 13 µg/1 and 64 µg11, respectively <br /> • DIPE was detected in a water sample collected from MW-2 at a concentration of 1 6 µg/1 <br /> • Concentrations of benzene detected in samples collected from wells MW-2 through MW-5, <br /> VW-1C, VW-2A and VW-3A were above the State of California Maximum Contaminant <br /> ILevel (MCL) for drinking water of 1 0 ppb <br /> • Concentrations of toluene were above the MCL of 150 ppb in samples collected from wells <br /> IVW-1C, VW-2A and VW-3A <br /> • Concentrations of ethylbenzene were above its MCL of 700 ppb in samples collected from <br /> wells VW-I C, VW-2A and VW-3A <br /> • Concentrations of xylenes were above the MCL of 1,750 ppb in samples collected from wells <br /> VW-1C, VW-2A and VW-3A <br /> • Concentrations of MTBE were confirmed in water samples collected from wells MW-2, <br /> MW-3, VW-I C, VW-2A and VW-3A at concentrations ranging between 2 1 4g/1 and 4,100 <br /> Advanced GeoEnvironmental,Inc <br />