Author(s)

J W Everett, L Kennedy & K Brozina

Abstract

Thousands of municipal solid waste landfills operate in the United States. Some, particularly older unlined ones, have released leachate to soil/ground water. Landfill leachate is typically high in labile organic constituents. Escaped leachate is a source of soil, ground water, and occasionally surface water pollution that may persist for decades. A redox series may occur, if a large quantity of a labile organic contaminant is spilled in the subsurface, where one type of electron acceptor is preferentially consumed before another. The common convention is that the order of electron acceptor utilization is O2 > NO3- > Mn > Fe3+> SO42- followed by methanogenesis. Significantly more Fe3+ and SO42-, compared to O2 and NO3- is often available in the subsurface. An approach to evaluating the natural attenuation of subsurface contaminants, Aqueous and Mineral Intrinsic Biodegradation Assessment (AMIBA) is described in this paper. The microbial reduction of Fe3+ and SO42-, forms reduced Fe and S mineral precipitates in amounts stoichiometrically equivalent to the contaminant mass oxidized by microbial processes. AMIBA involves measuring Fe3+ and reduced Fe and S minerals in affected sediments to assessment intrinsic bioremediation, both expressed and assimilative. The results from a number of studies are summarized here, including microcosm studies with simulated landfill leachate, fieldwork at an older unlined landfill, and studies conducted at fuel and chlorinated solvent contaminated sites. Results indicate that AMIBA can be used to assess natural attenuation at landfill sites.

Keywords