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Scientific-Investigations Report 2012–5032

Prepared in cooperation with the Strategic Environmental Research and Development Program

Microbial Mineralization of cis-Dichloroethene and Vinyl Chloride as a Component of Natural Attenuation of Chloroethene Contaminants under Conditions Identified in the Field as Anoxic

By Paul M. Bradley

Thumbnail of report coverAbstract

Chlororespiration is a key component of remediation at many chloroethene-contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products may suggest that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene-contaminated shallow aquifer systems, however, non-conservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms, and is consistent with contaminant degradation to non-diagnostic mineralization products. An ongoing technical debate over the potential for mineralization of dichloroethene (DCE) and vinyl chloride (VC) to CO2 in the complete absence of diatomic oxygen has largely obscured the importance of microbial DCE/VC mineralization at dissolved oxygen (DO) concentrations below the current field standard (DO < 0.1-0.5 milligrams per liter) for nominally anoxic conditions. This study demonstrates that oxygen-based microbial mineralization of DCE and VC can be substantial under field conditions that are frequently characterized as "anoxic." Because mischaracterization of operant contaminant biodegradation processes can lead to expensive and ineffective remedial actions, a modified framework for assessing the potential importance of oxygen during chloroethene biodegradation was developed.

First posted May 1, 2012

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Suggested citation:

Bradley, P.M., 2012, Microbial mineralization of cis-dichloroethene and vinyl chloride as a component of natural attenuation of chloroethene contaminants under conditions identified in the field as anoxic: U.S. Geological Survey Scientific Investigations Report 2012–5032, 30 p.



Contents

Abstract

Introduction

Purpose and Scope

Selected References

Chapter 1. Strategic Environmental Research and Development Program Project Summary

Chapter 2. Anoxic Mineralization: Environmental Reality or Experimental Artifact?

Chapter 3. Microbial Mineralization of Dichloroethene and Vinyl Chloride under Hypoxic Conditions

Chapter 4. Reinterpreting the Importance of Oxygen-Based Biodegredation in Chloroethene-Contaminated Groundwater

Appendix 1: Project Publications


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