Overcoming Barriers to the Remediation of Carbon Tetrachloride through Manipulation of Competing Reaction Mechanisms

Abstract

Most approaches that have been proposed for the remediation of groundwater contaminated with carbon tetrachloride (CCl4) produce chloroform (CHCl3) as the major product and methylene chloride (CH2Cl2) as a minor product. Both of these products are nearly as persistent and problematic as the parent compound, but competing reaction pathways produce the more desirable products carbon monoxide (CO) and/or formate (HCOO-). Results scattered throughout the chemical and environmental engineering literature show that the branching between these reaction pathways is highly variable, but the controlling factors have not been identified. If we understood the fundamental chemistry that controls the branching among these, and related, product-formation pathways, we could improve the applicability of a host of remediation technologies (both chemical and biological) to the large plumes of CCl4 that contaminate DOE sites across the country. This project will provide the first complete characterization of the mechanisms and kinetics of competing degradation reactions of CCl4 through laboratory experiments in simple model systems closely coordinated with theoretical modeling studies. The results provide strategies for maximizing the yield of desirable products from CCl4 degradation, and the most promising of these will be tested in column model systems using real site waters and matrix materials.