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I06 October 2005 . AGE-NC ProjectNo 01-0827 IPage 6 of 7 ' 4.0. SUMMARY AND CONCLUSIONS Based on the data collected from the site, AGE finds • On 12 September 2005, ground water was encountered at a depth of approximately 23 feet btoc, indicating a decrease of approximately 0 65 feet since the June 2005 sampling event ' • The ground water flow direction was inferred to be toward the east, at a gradient of approximately 0 01 ftJfl on-site,which is consistent with the historical ground flow direction ' • The detections of TPH-g compounds in the ground water sample collected from deep vapor well VW-2d demonstrate a contamination trend decrease to the lowest concentration detected (Appendix F) The lack of detections of TPH-g in the deepest well (MW-6) confirms the ' vertical extent of the dissolved hydrocarbons Decreased TPH-g and BTEX concentrations during the remediation period may suggest decreased sources for the desorption of hydrocarbons from soil into ground water and the likely destruction of hydrocarbon mass by ' the ozone contact oxidation • Fuel additive MTBE was again detected in the well VW-2d sample collected • Low ORP values detected in the source area demonstrate the presence of a generally reduced environment in the saturated zone near the source area Ideally,the introduction of oxygen- rich air (ozone air spargmg) in the source area should produce an oxidizing environment, which will lead to a reduction in contaminant levels Since operation of the ozone air sparge system commenced,dissolved oxygen concentrations in samples collected from wells at the ' site indicate an adequate migration of ozone-rich sparged air Into the subsurface I5.0. RECOMMENDATIONS Based on the findings of the remediation activities recounted in this report, AGE recommends ' • Continued quarterly ground water monitoring, the next monitoring event is scheduled for ' December 2005 • Limit the quarterly monitoring schedule sampling to impacted ground water wells,eliminate the non-impacted wells, located more distal to the UST area, from the sampling program ' • Continue operation of the ozone air spargmg system until the September sampling event Advanced GeoEnvironmental,Inc