Assessment of Bioenhanced Back Diffusion and Reductive Dehalogenase Gene Abundance in an Aquifer Cell Packed with Heterogenous Soils

Abstract

Remediation of chlorinated ethenes can be challenging at complex contaminated sites with low permeability soils acting as secondary source zones due to back diffusion of adsorbed contaminant mass. To better understand how bioremediation impacts back diffusion, a biotic aquifer cell packed with heterogenous porous media was established to monitor chlorinated ethene concentrations and Dehalococcoides mccartyi (Dhc) abundance during engineered remediation and after simulated source zone removal. Soils with high organic carbon content (greater than 0.27%) and low hydraulic conductivities (less than 0.05 m/day) measured the greatest increase in Dhc and reductive dehalogenase (RDase) gene abundances, greater bioenhanced back diffusion of stored contaminant mass (up to 72% near clay soil), and increased ethene production with Dhc abundance greater than 103 gene copies/mL. These findings assist in understanding the relationship between bioremediation and the removal of adsorbed contaminant mass and provide supporting information to help practitioners better implement remediation at complex sites.