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T 08 December 1998 • AGE-NC Project No. 95-0109 Page 4 of 5 on Table S. Historical analytical results by EPA Method 602 are presented in Table 6. Tertiary butanol was detected in MW-8, MW-9 and MW-1 I at concentrations of 9.4 ppb, 8.4 ppb and i I ppb,respectively. Other oxygenated compounds were not detected in the samples collected during the September 1998 sampling event. 1,2-Dichloroethane (1,2-DCA) was detected in MW-7, MW-8, MW-9, and MW-14 at concentrations ranging from 1.7 ppb to 65 ppb. Nine additional analytes, detected by EPA Method 8260, are noted in Table 7. The laboratory report (MAI Laboratory I. D.Nos. 94788 through 94794)and chain-of-custody forms are included in Appendix B. 3.4. SITE GEOLOGY Medium to coarse sand is present beneath most of the site at depths of approximately 50 to 57 feet bsg. Silty clay lenses were encountered in several borings at a depth of approximately 30 to 35 feet. The remainder of the site consisted of interbedded silt and sand to the total depth explored (75 feet bsg). Lines of cross section are depicted on Figure 2. Geological cross sections are included as . Figures 4 through 6. 4.0. DISCUSSION AND CONCLUSIONS Based upon data collected from the site, AGE finds: • Ground water elevation decreased at the site during the third quarter of 1998. Ground water flow direction continues to be toward the south-southwest at the site. A ground water mound was observed near MW-9. Recharge may be occuring north of MW-9 on the former Lincoln School property. • Hydrocarbon concentrations increased significantly in MW-8 and MW-9 during the third quarter of 1998. The reason for this increase in not clear. Hydrocarbon concentrations have historically been higher in MW-9 during the September monitoring events, compared to other quarters. • The concentration of TPH-g in MW-14 returned to the previous range of concentrations. BTEX concentrations in MW-14 showed a more modest increase during the third quarter of 1998. • MTBE was not detected in any of the ground water samples collected during the September 1998 monitoring event. Tertiary butanol was detected in MW-8, MW-9 and MW-11 at concentrations as high as I 1 ppb. Other oxygenates were not detected during the September Advanced GeoEnvirosmcntal,Inc.