Aqueous and mineral intrinsic bioremediation assessment: Natural attenuation

An approach to evaluating intrinsic bioremediation, aqueous and mineral intrinsic biodegradation assessment (AMIBA) is described. AMIBA is based on the microbial reduction of Fe³⁺ and SO^2-₄, forming reduced Fe and S mineral species in amounts stoichiometrically equivalent to the contaminant mass oxidized by microbial processes. Mineral data from sediment cores are emphasized rather than the aqueous data used in existing protocols. AMIBA was demonstrated at Westover Air Force Base, Chicopee, Massachusetts. Over 300 times more reduced Fe²⁺ was in mineral form, compared to aqueous. The distribution of mineral Fe³⁺ and Fe²⁺ marked the historic extent of the plume, confirming plume retreat. Aqueous SO^2-₄ reduction resulted in the deposition of equivalent amounts of iron sulfide minerals near the source area. The total mass of fuel degraded by intrinsic bioremediation and the rate of source depletion was estimated. Thus, the past and future performance of intrinsic bioremediation was assessed using one sampling event rather than relying on protracted monitoring, as is the current practice.