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' 30 May 2001 ' AGE-NC Project No 95-0143 Page 7of8 ' Ground water elevation decreased approximately 0 54 feet between November 2000 and February2001 Groundwater elevation was within the screened interval of MW-17,MW-22, MW-23, MW-24 and the five vapor extraction wells, but above the screened interval of the ' other eight monitoring wells The exposed portion of the screened interval in the five vapor extraction wells was within a silty layer and dust above a sandy layer The inferred ground ' water flow direction remains variably toward the north to northeast at the site • Petroleum hydrocarbons were detected in water samples from four of the nine wells sampled at concentrations ranging from. 100 gg/l (MW-6) to 160,000 gg/l (MW-3) MTBE was not ' detected in ground water samples collected during the February 2001 monitoring event Only minor concentrations (less than 7 gg/1) of DIPE and TBA have been detected since monitoiing began in 1997 ' • TPH-g, BTEX and MTBE were not detected above laboratory reporting limits in the soil vapor sample collected on 15 February 2001 from the influent vapor stream of the SVE unit ' Significant decreases in soil vapor concentrations have occurred since early April 2000 As discussed in AGE's Quarterly Report-Fourth Quarter 2000, dated 11 April 2000, the drop in soil vapor concentrations coincides with an increase in ground water elevation Elevated '• ground water levels appear to degrade the effectiveness of the horizontal vapor extraction system Additionally, the exposed screened intervals of the vertical extraction wells were within a sandy to clayey silt layer, the characteristics of which, combined with the high I ground water elevation, may limit the effectiveness of the vertical vapor extraction wells Furthermore, vertical vapor extraction well VW-3 was found to be filled with clean sand to approximately 15 feet bsg during the February 2001 monitoring event It appears that the ' well screen may have collapsed, allowing the filter pack to infiltrate the well VW-3 is located in the area most impacted by the petroleum hydrocarbon release ' TPH-g and BTEX compounds were detected in two analyzed soil samples collected from boi ing EW-3 The average concentrations of TPH-g and BTEX detected in samples analyzed from EW-3 during the March 2001 soil investigation were lower than the average concentrations detected in soil samples collected at similar depths from vapor extraction well VW-5, aistalled during the first quarter of 1999 VW-5 and EW-3 are approximately 5 feet apart Considering the proximity of the two sampling locations and the laboratory data, it appears that a degree of attenuation has occurred in soil since installation of the remediation system Analytical results of soil samples are summarized in Table 7, soil analysis for VW-5 is also included for comparison 5.0 RECOMMENDATIONS . Based upon data collected during the February2001 and previous sampling events and SVE system Imonitoring results, AGE recommends ,Advanced GeoEnvironmentul,Int,