The potential for landfill gas to impact ground water quality
Morris, Harry H.
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The investigation of ground water contamination at a solid waste disposal site is typically focused on aqueous phase contaminant migration. For some compounds, vapor phase contaminant migration may occur through the vadose zone followed by dissolution of the gas phase into the ground water. If this mechanism were overlooked, the appropriate remediation technique of installing or upgrading the landfill gas extraction system would not be considered. Instead, a more costly remediation effort focused on aqueous contaminant transport, which would not correct the problem, would likely be recommended. Data collected from this investigation, along with the results from other published and unpublished reports, indicate that dissolution of landfill gas was the source of low level concentrations of several priority pollutant volatile organic compounds (VOC’s) found in the ground water at a number of solid waste disposal sites. Evidence that supported the conclusion that landfill gas was the source of VOC’s detected in the ground water at several waste disposal sites included the lack of detecting a significant increase in leachate "indicator" parameters associated with the VOC’s. The VOC’s were detected, in some cases, in upgradient monitoring wells; carbon, oxygen, and hydrogen isotopes indicated the lack of a relationship between landfill leachate and the ground water samples from the impacted well, and a direct relationship between the landfill gas and gases observed in the headspace of the monitoring well. In some cases, the VOC detected in the ground water was either the same compound, or a degradation product of a compound found in the landfill gas. To gain a better understanding of the importance of this phenomenon in ground water contamination, the potential mechanisms involved in the transfer of contaminants from the vapor to aqueous phase were identified, the compounds of concern (COC’s) (those which readily transfer to the vapor phase, and therefore, are the most likely to be detected in the ground water as a result of vapor phase migration) were determined, and the average and maximum COC concentrations in ground water that can be attributed to vapor phase migration were calculated.