Evidence for Natural Attenuation of Volatile Organic Compounds in the Leachate Plume of a Municipal Landfill near Norman, Oklahoma

By Robert P. Eganhouse, Lara L. Matthews, Isabelle M. Cozzarelli and Martha A. Scholl

ABSTRACT

Samples of ground water collected downgradient from the Norman Landfill in 1995 and 1996 were analyzed for volatile organic compounds (VOCs) by purge-and-trap gas chromatography/mass spectrometry. More than 70 individual compounds were identified. The VOCs originate from a wide variety of natural and anthropogenic sources. This is consistent with the heterogeneous mixture of materials likely to have been buried at the site. Concentrations of VOCs are low when compared with published data for other landfills, and the dominant class (monoaromatic hydrocarbons) accounts for less than 0.1% of the total dissolved organic carbon. The low concentrations likely reflect the age of the landfill and the character of the wastes. Spatial distributions of the VOCs in ground water are variable, but concentrations of all compounds are near or below detection limits within 200 meters of the landfill. Meanwhile, the distribution of chloride ion, a putative conservative tracer, shows little dilution over the same distance. Thus, natural attentuation processes are effectively limiting migration of the VOC plume. Large differences in the spatial distribution of isomeric alkylbenzenes suggest that biodegradation is a significant, if not dominant, process contributing to the observed attenuation.