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F� <br /> l' <br /> ii <br /> r 15 July 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 /> f: The relative elevation of ground water in each well was calculated b subtracting the round water <br /> � Y g g <br /> depth from the surveyed relative casing elevation (Table 1). Between February and May 1996, <br /> 1,1.= ground water rose approximately 0.3 feet in each well. In May 1996, ground water flow direction <br /> was divergent from the vicinity of the maintenance shop toward the southwest and the northeast. A <br /> northwest-southeast trending ground water"ridge"was apparent in the vicinity of the maintenance <br /> <9 shop. Relative ground water elevation contours are illustrated in Figure 3. <br /> _i <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 14,000 parts per <br /> billion (ppb, reported as micrograms per liter) and 870 ppb,. respectively. Volatile aromatic <br /> hydrocarbons were detected in the samples,from MW-2 and MW-3 at concentrations ranging from <br /> .: 4.8 ppb (ethyl benzene, MW-3) to 2,500 ppb (xylenes, MW-2). <br /> Detectable concentrations of benzene were present in sample collected from MW-4, however the <br /> I level is close to the method detection limit. Hydrocarbon were not detected in samples collected <br /> -1 from MW-1,MW-5 or MW-6. Analytical results of ground water samples are summarized in Table ' <br /> 2. The laboratory report (MAI Lab ID 65183 to 65188) and chain-of-custody are included as <br /> Appendix B. <br /> :,-A 4.0. CONCLUSIONS & RECOMMENDATIONS <br /> =� The ground water flow direction continues to shift at the site. During the past two consecutive <br /> quarters the flow direction has been divergent'from MW-3. Monitoring wells MW-5 has shown no <br /> impact from dissolved hydrocarbons, while MW-4 has contained low concentrations of benzene <br /> during the last two sampling events. <br /> Feasibility testing performed at the site, indicated that a cost-effective method of ground water <br /> 3 remediation will be in-situ air sparging(IAS), combined with soil vapor extraction. We recommend <br /> ==� the installation of the IAS/SVE system, after the remedial costs have been granted. <br /> ~� The next quarterly ground water sampling event should be conducted in August of 1996. <br /> : f <br />