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05 April 1996 ' AGE -NC Project No 95-0142' ,Page 4 of 5 - 43 DISSOLVED METALS IN GROUND WATER The presence of dissolved metals in ground water can reduce the permeability of the saturated zone soils during in-situ _air sparging Total dissolved iron and manganese were detected at 80 and 510 mg/l (milligrams per liter or parts per million ppm), respectively The concentrations of dissolved iron in the ground water sample exceeds the_ concentration of 20 ppm or less for effective in-situ air sparging The long term effectiveness of each air-sparging well may be diminished if concentrations of dissolved iron remain above 20 ppm The laboratory report (FGL Lab No 631269-1) and chain -of - custody are included in Appendix C 44 ANALYTICAL RESULTS OF PURGED WATER SAMPLES TPH-g and BTE&X were not detected in samples collected from either drum at the site The laboratory report (MAI Laboratory I D Nos 62337 and -62338) and chain -of -custody are included in Appendix B 5.0. CONCLUSIONS AND RECOMMENDATIONS 5 1 HYDROCARBON -IMPACTED GROUND WATER Ground water gradient calculations based upon data collected during the March 1996 sampling indicates that flow direction at the eastern edge of the site has rotated approximately 10° to the east The greatest concentrations of hydrocarbons present during the March 1996 sampling event were present in VE -3, immediately east of the former UST excavation ' Between December 1995 and March 1996, concentrations of petroleum hydrocarbons decreased in MW -3 and MW -4 Based upon the most recent ground water data, the ground water surface lies above the tops of the screened casings of MW -1, MW -2 and MW -3, and therefore, samples collected from these wells may not be representative of actual aquifer conditions We do not recommend the installation of additional ground water monitoring wells at this time However, additional wells may be required in the future, if the local and regional ground water elevation continues to remain at the current level or if the dissolved hydrocarbon plume migrates south of MW -2 or northeast of MW -4 Y The next quarterly ground water monitonng should be scheduled for June 1996, if ground water elevations are within the screened intervals, wells MW -1 through MW -4 should be sampled Vapor well VE -1 and VE -3 should be sampled to determine the dissolved hydrocarbon concentrations in the vicinity of the former UST