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12 June 2012 AGE-NC Project No. 99-0682 Page 5 of 7 4.0. CONCLUSIONS Based upon the results of the ground water monitoring, AGE presents the following conclusions: • The average ground water elevation across the monitoring well network during the April 2012 monitoring event was 25.64 feet below NAVD88, indicating an average increase in ground water elevation of 1.29 feet from the October 2011 monitoring event. A graph depicting trends in ground water measurements is included in Appendix E. • The highest concentration of dissolved hydrocarbons continues to occur in the area of the former USTs. TPH-g, TPH-d, BTEX compounds and 1,2-DCA were reported at significant concentrations in the water sample collected from monitoring wells MW-1A(screened from 20-40 feet bsg)and MW-8 (screened from 59-69 feet bsg). Additionally, significant concentrations of dissolved hydrocarbons have been reported at well MW-11, northeast of the former UST area, indicating a historical ground water flow direction. • Historically, contaminants have generally increased in well MW-8, located in the source area, and contaminants have decreased in well MW-7 since the initial monitoring of the wells in April 2007. During the April 2012 monitoring event, concentrations of contaminants in wells MW-1 A, MW-1 C,and MW-8 decreased and concentrations of contaminants remained generally stable in wells MW-6, MW-7, MW-9, and MW-10; overall, natural attenuation does not appear to be producing a declining trend. Graphs depicting trends in contaminant concentrations in wells MW-1A, MW-6, MW-7 and MW-8 are included in Appendix D. • Currently,the lateral extent of petroleum hydrocarbon-impacted ground water in the upper water bearing units (HU1) appears to be defined to the southeast (MW-4) of the former UST area, north (MW-3 and MW-5), east of well MW-6 and south of the site by soil boring samples (Appendix A). • The lateral extent of hydrocarbon-impacted ground water within the 60 to 75 feet bsg water bearing zone (HU2-3) is defined to the west-northwest by well MW-9, to the south by boring CPT-5, to the east or southeast with samples from boring B-5, and to the northwest by boring CPT-6. The lateral extent of hydrocarbon-impacted ground water is undefined to the north and northeast of the site, as illustrated in Figure 6. • Concentrations of contaminants generally decline vertically in the source area (MW-1A and MW-8),with the exception of benzene and 1,2-DCA concentrations in well MW-8 (the benzene concentration in well MW-8 is over ten times higher than in the shallower well MW-1A). Higher concentrations observed in well MW-8 maybe Advanced GeoEnvironmental,Inc.