Natural Attenuation Assessment Using Mineral Data.

Aqueous and mineral intrinsic biodegradation assessment (AMIBA) relies on the measurement of iron and sulfur mineral species, in addition to standard water analyses, to evaluate the intrinsic bioremediation component of natural attenuation. AMIBA can be used to: (1) assess the contribution of various biodegradation processes; (2) quantify the efficiency of biodegradation; (3) determine an overall depletion rate for hydrocarbon plume and source; (4) estimate future capacity for biodegradation; and (5) indirectly demonstrate plume contraction. The purpose of this paper is to introduce AMIBA to practitioners, focusing on sample collection and data interpretation. Results from three sites are also presented, illustrating different conditions and outcomes. At each site multiple soil borings were installed and sampled at multiple depths. Contaminants, mineral Fe(II) and Fe(III), mineral sulfide (as FeS and FeS₂), nitrate, oxygen, and sulfate analyses were conducted on sediment and/or groundwater. AMIBA was used to estimate as much as 96% contaminant destruction and estimates of depletion rates could also be determined. Oxygen was never the principle electron acceptor linked to contaminant degradation. Iron and sulfate are consistently dominant electron acceptors except at one site where nitrate was present due to human activities. [ABSTRACT FROM AUTHOR]