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' 17 August 2004 AGE-NC Project No 01-0827 ' Page 5 of 6 ' 4.0. SUMMARY AND CONCLUSIONS Based on the data collected from the site, AGE finds ' • On 10 May and 10 June, ground water was encountered at a depth of approximately 23 feet btoc The ground water flow direction was inferred to be towards the east to southeast on- site, at gradients of approximately 0 01 ft/ft to 0 009 ft/ft on-site • With the exception of wells MW-5,VW-I and VW-3,all wells are"drowned"and analytical data from these wells may not be representative of the shallow ground water conditions • With the exception of benzene,the maximum concentrations of petroleum hydrocarbon and BTEX compounds were detected in the ground water sample collected from deep vapor well ' VW-2d on 10 May 2004, however, the highest MTBE concentration was detected in the sample collected from VW-2d on 12 July 2004 ' • 1,2-DCA was not detected in the ground water samples this quarter • The concentrations of benzene in sample VW-2d and MTBE in sample VW-2d were above the DHS's Primary Maximum Contaminant Levels (MCL) for drinking water However, ' there are no immediate plans to use the shallow and deeper ground water in the region for domestic purposes ' • Oxidation is a process in which a molecule or ion loses electrons Reduction is a process by which electrons are gained A measurement of the potential for these processes to occur is called ORP (Oxidation Reduction Potential) Low ORP values, detected in the source area, demonstrate the presence of generally reduced environment in the saturated zone near the source area This reduced environment is likely due to the high saline and sulfur enriched shallow water at the site Ideally, the introduction of oxygen rich air(ozone air sparging) in ' the source area should produce an oxidizing environment which will lead to a reduction in contaminant levels Dissolved oxygen concentrations collected from wells at the site, since operation of the ozone air sparge system commenced, indicate an adequate migration of ' ozone-rich sparged air into the subsurface • Generally, since the initiation of operation of the ozone-sparging system, dissolved ' concentrations of TPH and BTEX compounds have decreased,however, TPH-g and BTEX concentrations increased during the second quarter of sampling, suggesting continued desorption of hydrocarbons from soil into ground water 1 1 ' Advanced GeoEnvironmental,Inc