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23 August 1996 <br /> AGE Project No. 95-0118 <br /> Page 2 of 3 <br /> 3.0. FINDINGS <br /> 3.1. RELATIVE GROUND WATER ELEVATION AND GRADIENT <br /> -"' The relative ground water elevation in each well was calculated by subtracting the ground water <br /> depth from the surveyed relative casing elevation(Table 1). Between May and August 1996, ground <br /> water elevation decreased an average 0.81 feet in each well. <br /> In August 1996, ground water flow direction was again divergent from the vicinity of the <br /> { maintenance shop toward the southwest and the northeast. A northwest-southeast trending ground <br /> water "mound" was apparent in the vicinity of the maintenance shop. Relative ground water <br /> •J elevation contours are illustrated in Figure 3. <br /> 3.2. ANALYTICAL RESULTS OF GROUND WATER SAMPLES <br /> TPH-g was detected in water samples from. MW-2 and MW-3 at concentrations of 1,400 parts per <br /> billion (ppb, reported.as micrograms per liter) and 300 ppb, respectively. Volatile aromatic <br /> hydrocarbons were detected in the samples from MW-2 and MW-3 at concentrations ranging from <br /> 4.2 ppb (toluene, MW-2) to 290 ppb (xylenes, MW-3): <br /> Hydrocarbon were not detected in samples collected from. MW-1, MW-4, MW-5 or MW-6. <br /> _ Analytical results of groundwater samples are summarized in Table 2. The laboratory report (MAI <br /> Lab ID 67869 to 67874) and chain-of-custody are included as Appendix B. <br /> 4.0. CONCLUSIONS & RECOMMENDATIONS <br /> The relative ground water elevation during the last quarter has declined an average 4.81 feet. Data <br /> collected from monitoring wells MW-1, MW-4, MW-5 and MW-6 have demonstrated that the <br /> hydrocarbon plume is located within these boundaries. The dissolved hydrocarbon plume is <br /> delineated at the site, yet the concentrations of hydrocarbons have been highly varied between <br /> '. quarterly sampling events. The changing hydrocarbon concentrations suggests that the hydrocarbons <br /> :may not be stable and may not have the tendency to remain in place'. <br /> --- Feasibility testing performed at the site, indicated that a cost-effective method of ground water <br /> remediation will be in-situ air sparging(IAS), combined with soil vapor extraction. We recommend <br /> the installation of the IASISVE system, after the remedial costs have been granted. <br /> The next quarterly ground water sampling event should be conducted in November of 1996. <br /> I <br />