Assessing and Enhancing Naturally-Occurring Abiotic Dechlorination in Aquifer Solids
Charles Schaefer, PhD
Director, CDM Smith Remediation Laboratory
The potential role of natural attenuation mechanisms for mitigating chlorinated solvent impacted groundwater plumes is receiving increased attention. Of particular interest are PCE and TCE dechlorination reactions that occur in low permeability (e.g., rock matrices, clays) materials, as even very slow dechlorination reactions can have a beneficial impact on dissolved plume longevity and contaminant mass discharge. Abiotic dechlorination reactions facilitated by the presence of ferrous minerals has been shown to be an important process, but there remain many unknowns regarding the kinetics of these reactions in natural systems.
Abiotic dechlorination of PCE and TCE in several natural rock and clay systems was evaluated in a series of laboratory experiments. Reaction rates were evaluated as a function of ferrous mineral content, as determined by both the 1,10-phenanthroline method and magnetic susceptibility. In addition, dechlorination was evaluated under both aerobic and anaerobic conditions. Methods to enhance these naturally occurring reactions, via heat and applied current, also were assessed.
Initial results showed that ferrous mineral content measured via the 1,10-phenanthroline method, not magnetic susceptibility, served as a reasonable screening tool for abiotic dechlorination potential in low permeability aquifer solids. Higher coupling products, such as propane, were often observed as transformation products in anaerobic systems. Under aerobic conditions, an oxidative abiotic dechlorination mechanism was observed, yielding volatile fatty acid transformation products. Both heat and applied current were shown to substantially enhance these naturally occurring reactions.
Charles Schaefer is a senior engineer for CDM Smith, and is the Director of the CDM Smith’s Remediation Laboratory in Bellevue, WA. His areas of research include pore-scale diffusion and mass transfer processes, in situ bioremediation, treatment of emerging contaminants, and electrochemical treatment of drinking water. Charles has served as a Principal Investigator on several SERDP and ESTCP research grants, many of which have focused on chlorinated solvents in bedrock systems. He has authored over 40 peer-reviewed papers and is a member of ITRC. In addition to research, Charles also serves as a technical consultant on several federal and commercial projects for CDM Smith, many of which are addressing chlorinated solvents in complex geological settings. Charles earned his bachelor’s, master’s, doctorate degrees in chemical and biochemical engineering from Rutgers University in New Brunswick, NJ, and has over 15 years of consulting experience.
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