Natural attenuation of volatile organic compounds (VOCs) in the leachate plume of a municipal landfill: Using alkylbenzenes as process probes

More than 70 individual VOCs were identified in the leachate plume of a clo sed municipal landfill. Concentrations: were low when compared with data pu blished for other landfills, and total VOCs accounted for less than 0.1% of the total dissolved organic carbon. The VOC concentrations in the core of the anoxic leachate plume are variable, but in all cases they were found to be near or below detection limits within 200 m of the landfill. In contras t to the VOCs, the distributions of chloride ion, a conservative tracer and nonvolatile dissolved organic carbon, indicate little dilution over the sa me distance, Thus, natural attentuation processes are effectively limiting migration of the VOC plume, The distribution of C2-3-benzenes, paired on th e basis of their octanol-water partition coefficients and Henry's law const ants, were systematically evaluated to assess the relative importance of vo latilization, sorption, and biodegradation as attenuation mechanisms. Based on our data, biodegradation appears to be the process primarily responsibl e for the observed attenuation of VOCs at this site. We believe that the al kylbenzenes are powerful process probes that can and should be exploited in studies of natural attenuation in contaminated ground water systems.