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the highest ingestion rate of the inceptor, and 100 percent bioaccumulation of the chemicals. The <br /> WQA analyzed soil samples. Fate and transport modeling was done to see if the chemicals <br /> identified in the WQA can be detected in the groundwater. <br /> Results showed that the aerial extent of the landfill cells decreased and additional ERAS were <br /> necessary to determine the actual threats to ecological receptors. The human health threats were <br /> minimal, and the WQA and Fate and Transfport modeling did not indicate that chemicals would <br /> be detected in the groundwater. <br /> Because excess gas buildup could degrade the cap and release into the atmosphere or create an <br /> explosive environment, it was necessary to determine whether a gas collection system was <br /> needed. An air sample was collected through a steel probe that was driven three feet below <br /> ground surface (bgs). This probe penetrated through the existing soil cover and reached the top of <br /> the landfill content. Sample concentrations from these point measurements were compared <br /> against the ambient air preliminary remediation goals (DRGs). <br /> Flux measurements were taken from locations that showed the highest concentrations, according <br /> to the point measurements. The flux measurements would determine the mass of chemicals <br /> released from the landfill over time. Federal regulations indicate that a gas collection system is <br /> required when non-methane organic compounds (NMOC) exceed 50 megagrams per year <br /> (Mg/yr). The results of gas sampling indicated that the methane and carbon dioxide levels were <br /> minimal; the maximum NMOC concentration was less than one Mg/yr at any location; and <br /> hydrogen sulfide (H2S)was the only chemical detected above the PRGs(IAS-11). Although H2S <br /> was detected in the point sample(3 feet bgs), it is assumed that this would also be detected at <br /> ground surface. The gas collection system was not deemed necessary according to federal <br /> regulations. <br /> Landfill regulations indicate that the permeability of the existing soil cover should be less than 1 <br /> X 10"6 centimeters per second (cm/s). As the permeability of each cell was found to be greater <br /> than this, an engineered cap was deemed necessary. Compaction tests, surface soil sampling, <br /> density tests, and other physical property tests were conducted to determine the bearing capacity <br /> of the cells. The maximum compaction was about one foot at any cell. The compaction of most <br /> of the cells was within 0.2 feet; minimal compaction is expected. <br /> The typical municipal waste landfill requires a cover to have the bearing capacity of 20 to 40 <br /> kilonewtons per meter squared(kN/m2). The bearing capacities ranged from 22 to 300 kN/m2 <br /> with a safety factor of 10. The conclusion is that an engineering cap is needed with a <br /> permeability of less than 1 x 10-6, and that the current soil could support a cap. <br /> Two large groundwater plumes were found at IAS-07/IAS-16/Site 39 and IAS-11. They are <br /> assumed to have originated from some type of release from the landfills. Chlorinated solvents, <br /> such as trichloroethene, dichloroethene, and vinyl chloride (VC), were detected. The WQA was <br /> used to determine if the existing soil can attenuate the detected chemicals before they reached the <br /> groundwaterl. No attenuation was assumed for samples collected below the water table; these <br /> 3 <br />