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10 June 1998 <br /> AGE-NC Project No 95-0101 <br /> Page 7 of 8 <br /> 43 RELATIVE GROUND WATER ELEVATION AND GRADIENT <br /> The relative elevation of ground water in each well was calculated by subtracting the depth to water <br /> from the surveyed relative casing elevation (Table 3) Ground water elevation increased an average <br /> of 2 94 feet between July 1996 and May 1998 Relative ground water elevation contours are depicted <br /> on Figure 5 As in previous monitoring events, the relative elevation of ground water in MW-5 was <br /> lower would be expected, based on the ground water elevation in surrounding wells The inferred <br /> ground water gradient, as calculated using data from MW-1, MW-2 and MW-3 was 0 005 ft/ft <br /> directed S 31° E <br /> 44 ANALYTICAL RESUL I'S OF GROUND WATER SAMPLES <br /> Petioleum hydrocarbons and oxygenated compounds were not detected in samples collected at the <br /> site during the May 1998 sampling event The analytical results are summarized on Table 4 The <br /> laboratory report (MAI sample Nos 89700-89705) and chain-of-custody fora: ate included in <br /> Appendix C <br /> 5.0. SUIV MARY & CONCLUSIONS <br /> Based upon data collected from the site, AGE concludes the following <br /> • The vertical extent of impacted soil does not appear to be very great, with most of the <br /> impacted soil occurring between 35 feet and 45 feet bsg in the area of B9 and MW-2 Soil <br /> below 45 feet bsg in MW-2 has minor TPH-g concentrations <br /> a The impacted soil in the narrow vertical zone between 35 and 45 feet bsg near 139 (VW-1) <br /> and MW-2 consists of relatively impermeable silt and clay <br /> o The impacted soil remaining at the site near B9 (VW-1) does not appear to have resulted in <br /> significant degradation of ground water <br /> o Petroleum hydrocarbons were not detected at the site in ground water samples collected from <br /> monitoring wells during the most recent monitoring event <br /> • Ground water has been "cleaning up" since monitoring began in 1987, when the TPH-g <br /> concentration in MW-2 was 2,749 ppb Since 1991, TPH-g has been present at detectable <br /> concentrations in MW-2 during only 3 out of 10 ground water monitoring events, with the <br /> maximum detected concentration of TPH-g at 230 ppb during the last seven years of <br /> monitoring <br /> • It is unlikely that remediation of remaining impacted soil at the site would be cost effective <br /> Atli aercedGeoEmiron mental,Inc <br />