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' 11•August 1999 AGE-NC Project No. 95-0109 Page 7 of 10 Data collected as,early as February 1994 was'included in the calculations of the remaining mass of hydrocarbons at the:site. Additional remediation is.likely to, have occurred in these areas, which , would further reduce the total mass of hydrocarbons remaining'at the site. . ; ' AGE notes that the hydrocarbon masses calculated are not intended'to be precise, but are only .estimates;based on the assumptions listed above for•use io evaluate`the'effectiveness of the remedial i. effort. The mass calculations and formulas are:presented in.Appendix E. 3.5. GROUND WATER GRADIENT AND DIRECTION The depth io ground water'ranged from 49.72 feet-bsg north bf the site to 52.39 feet bsg south of the site during the March 1999 monitoring event. The data indicates an average 1.23 feet increase of. ground water elevation between December 1998 and March 1999.'Grourid water elevation contours, based upon data collected on 17.March 1999, are depicted in Figure 3. The inferred ground water ' flow.direction is toward the south. Ground water elevations for MW-1 through MW-5 were.higher than the surrounding wells: These wells exhibit poor recharge and do not appear to be in equilibrium with the surrounding ground water, therefore data from these wells was not used to determine the ground water flow direction. ' 'Ground water elevation decreased an average of 0.24 feet between March and June 1999,•and decreased and average of 0.74 feet between June and July 1999. Ground water contours, based upon data collected on 30 July,1999 are depicted in,Figure 4.•A depression appears to be.located west of _ MW-14, while a localized high is located near,MW-9: Data,fro'm the,.June 1999.monitoring eyent51"s was.not plotted, but appears to be similar to the July 1999-data. Ground water elevations are-, summarized on Table 3. 3.6.' MICROBIOLOGICAL ACTIVITY'1N GROUNDWATER. Concentrations of-dissolved oxygen•variably increased and'decreased between-theDecember 1998 and March 1999 monitoring events and between'the Marchand-June 1999�'moriitoring &vents.in ' water samples collected from the wells.Only low general, microbiological activity was detected-in 'samples from both MW-9 and MW- `the "March •1999 sampling ^event. Selective 1 , • . , n...,.. - s'ubpopulations were not detected in the March 1999 samples: The laboratory report (.A. Keith Kaufman,March 30, 1999) and chain-of-custody form�are.included in Appendix D. Advanced GeoEnvironmental,Inc.'