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• A. Very low rates of oxygen exchange from the <br /> atmosphere to the aquifer. This slows the action <br /> of aerobic biodegradation which is much faster <br /> than anaerobic biodegradation. <br /> B. Very low rates of carbon dioxide exchange from the <br /> aquifer to the atmosphere, thereby causing a build <br /> up of carbon dioxide in the aquifer inhibiting the <br /> aerobic bacteria. <br /> C. Very low rate of hydrocarbon exchange from the <br /> aquifer to the atmosphere, causing a significant <br /> slowing of gasoline dissipation to the atmosphere. <br /> 2 . Confined aquifer, with gasoline trapped under the <br /> confining clay layer: <br /> A. No permeable vadose zone (dry soil) . This <br /> makes straight vapor extraction impractical <br /> because of the lack of a dry permeable <br /> section of the aquifer from which to extract <br /> the hydrocarbons. Air flow is nearly <br /> impossible through the confining clay. <br /> B. Uneven nature of base of confining clay layer <br /> trapping floating free product. The floating <br /> product trapped in high spots in the aquifer <br /> will not flow towards a pumping well until <br /> the aquifer has been dewatered to below the <br /> base of the clay. <br /> RECOMMENDATIONS <br /> Due to the confined nature of the aquifer at this site and the <br /> clayey nature of the aquifer itself, the most effective way to <br /> remediate this site would be to excavate the highest levels of soil <br /> contamination. Also we suggest that the ground water which does <br /> and will contain product be pumped and treated after excavating. <br /> DISPOSAL OF CUTTINGS AND WASTE WATER <br /> Tri-Valley Growers agreed to handle to disposal of the cuttings and <br /> waste water from SBA and the soil and water were combined with the <br /> Tri-Valley soil and water. <br /> 5 <br />