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In cooperation with the Southern Division Naval Facilities Engineering Command

Oxidation-Reduction Processes in Ground Water at Naval Weapons Industrial Reserve Plant, Dallas, Texas

By S.A. Jones, Christopher L. Braun, and Roger W. Lee

U.S. Geological Survey
Water-Resources Investigations Report 03–4046


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Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Hydrogeology

Sampling and Analytical Methods and Results

Volatile Organic Compounds

Dissolved Oxygen

Nitrate and Nitrite

Ferrous Iron and Total Iron

Sulfate and Sulfide

Dissolved Hydrogen

Total Organic Carbon

Oxidation-Reduction Processes

Volatile Organic Compounds

Dissolved Oxygen

Nitrate and Nitrite

Ferrous Iron and Total Iron

Sulfate and Sulfide

Dissolved Hydrogen

Total Organic Carbon

Screening Results

Summary

References Cited

Appendix—Data

Figures

1.   Map showing location of study area, wells sampled, and lithologic cross section 1–1' at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
2.   Lithologic section 1–1' at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
3.   Map showing water-level altitudes in shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, March 1998
4.   Graph showing dissolved hydrogen concentrations associated with oxidation-reduction processes in ground water
5–16.   Maps showing:
  5.   Trichloroethene concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  6.   cis-1,2-Dichloroethene concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  7.   Vinyl chloride concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  8.   Dissolved oxygen concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  9.   Dissolved oxygen concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, March 1998
  10.   Nitrite concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  11.   Ferrous iron concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  12.   Ferrous iron concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, March 1998
  13.   Sulfide concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  14.   Sulfide concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, March 1998
  15.   Dissolved hydrogen concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits and indicated oxidation-reduction processes at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, September 1997
  16.   Dissolved hydrogen concentrations from wells screened in the upper or in the upper and middle parts of the shallow alluvial deposits and indicated oxidation-reduction processes at the Naval Weapons Industrial Reserve Plant, Dallas, Texas, March 1998

Tables

1.   Well information and sampling dates for wells sampled at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
2.   Selected constituents, methods, and procedures used to evaluate oxidation-reduction processes in ground water at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
3.   Chemical results for selected volatile organic compounds from wells sampled at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
4.   Selected field and laboratory data from wells sampled at the Naval Weapons Industrial Reserve Plant, Dallas, Texas
5.   Mean first-order decay rates and computed half-lives for trichloroethene, dichloroethene, and vinyl chloride under five oxidation-reduction conditions

Abstract

Concentrations of trichloroethene in ground water at the Naval Weapons Industrial Reserve Plant in Dallas, Texas, indicate three source areas of chlorinated solvents—building 1, building 6, and an off-site source west of the facility. The presence of daughter products of reductive dechlorination of trichloroethene, which were not used at the facility, south and southwest of the source areas are evidence that reductive dechlorination is occurring. In places south of the source areas, dissolved oxygen concentrations indicated that reduction of oxygen could be the dominant process, particularly south of building 6; but elevated dissolved oxygen concentrations south of building 6 might be caused by a leaking water or sewer pipe. The nitrite data indicate that denitrification is occurring in places; however, dissolved hydrogen concentrations indicate that iron reduction is the dominant process south of building 6. The distributions of ferrous iron indicate that iron reduction is occurring in places south-southwest of buildings 6 and 1; dissolved hydrogen concentrations generally support the interpretation that iron reduction is the dominant process in those places. The generally low concentrations of sulfide indicate that sulfate reduction is not a key process in most sampled areas, an interpretation that is supported by dissolved hydrogen concentrations. Ferrous iron and dissolved hydrogen concentrations indicate that ferric iron reduction is the primary oxidation-reduction process. Application of mean first-order decay rates in iron-reducing conditions for trichloroethene, dichloroethene, and vinyl chloride yielded half-lives for those solvents of 231, 347, and 2.67 days, respectively. Decay rates, and thus half-lives, at the facility are expected to be similar to those computed. A weighted scoring method to indicate sites where reductive dechlorination might be likely to occur indicated strong evidence for anaerobic biodegradation of chlorinated solvents at six sites. In general, scores were highest for samples collected on the northeast side of the facility.

 


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