Office of Research and Development

National Risk Management Research Laboratory, Ada, Oklahoma 74820

Effects of Thermal Treatments 

on the Chemical Reactivity of 

Trichloroethylene

EPA 600/R-07/091 | August 2007 | www.epa.gov/ada

Office of Research and Development

National Risk Management Research Laboratory, Ada, Oklahoma 74820

Effects of Thermal Treatments 

on the Chemical Reactivity of 

Trichloroethylene

Jed Costanza, James Mulholland, and 

Kurt Pennell

Georgia Tech University

Eva Davis

Project Officer, Robert S. Kerr Environmental 

Research Center
ii

Notice

The U.S. Environmental Protection Agency through its Office of Research 

and Development managed the research described here under EPA Cooperative agreement Contract No. R-82947401 to Georgia Institue of Technology, 

Atlanta, Georgia, through funds provided by the U.S. Environmental Protection 

Agency’s Office of Research and Development, National Risk Management 

Research Laboratory, Ada, Oklahoma. It has been subjected to the Agency’s 

peer and administrative review and has been approved for publication as an 

EPA document. Mention of trade names or commercial products does not 

constitute endorsement or recommendation for use.

All research projects making conclusions or recommendations based on 

environmental data and funded by the U.S. Environmental Protection Agency 

are required to participate in the Agency Quality Assurance Program. This 

project was conducted under an approved Quality Assurance Plan. Information 

on the plan and documentation of the quality assurance activities and results 

are available from the lead author.
iii

Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation’s land, air, and water 

resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions 

leading to a compatible balance between human activities and the ability of natural systems to support and nurture 

life. To meet this mandate, EPA’s research program is providing data and technical support for solving environmental 

problems today and building a science knowledge base necessary to manage our ecological resources wisely, 

understand how pollutants affect our health, and prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory is the Agency’s center for investigation of technological 

and management approaches for preventing and reducing risks from pollution that threatens human health and the 

environment. The focus of the Laboratory’s research program is on methods and their cost-effectiveness for prevention 

and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water 

systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; 

and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies 

that reduce the cost of compliance and to anticipate emerging problems. NRMRL’s research provides solutions 

to environmental problems by: developing and promoting technologies that protect and improve the environment; 

advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical 

support and information transfer to ensure implementation of environmental regulations and strategies at the national, 

state, and community levels.

This report describes laboratory experiments conducted to determine the reactivity of trichloroethylene (TCE), a 

commonly-used industrial solvent and a groundwater contaminant at many Superfund sites, under the conditions used 

for in situ thermal remediation. It was found that at temperatures below 420°C, TCE is essentially unreactive without 

the presence of some type of catalyst, such as a base or mineral. Thus, during in situ thermal remediation at these 

temperatures, TCE is recovered by volatilization and vapor extraction. At higher temperatures, significant reaction of 

TCE may occur; however, the products of these reactions may include larger molecular weight chlorinated compounds 

as well as carbon dioxide and hydrochloric acid, which would be the expected products when TCE is completely 

mineralized.

Stephen G. Schmelling, Director

 Ground Water and Ecosystems Restoration Division

National Risk Management Research Laboratory
iv

Acknowledgment

EPA would like to thank the peer reviewers, Dr. Bill Mabey, Dr. Gorm Heron, and Dr. Rick Wilken, for their insightful 

and useful comments.
v

Contents

Project Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.3 Experimental Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4 Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4.1 Quartz Tube Reactor Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4.2 Sealed Ampule Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.3 Implications to Field Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.5 Report Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Background Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 Trichloroethylene Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 TCE-Water Phase Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Selected Experiments on the Stability of TCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3.1 TCE-NAPL Degradation by Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3.2 Hydrolysis of TCE-NAPL Degradation Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.3.3 Degradation of TCE Dissolved in Water at Elevated Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3.4 Thermal Degradation of TCE in a Water-Filled Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3.5 Degradation of Gas-Phase TCE within Heated Quartz Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3.6 TCE Degradation Products as a Function of the Cl:H Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4 Operational Conditions of In Situ Thermal Treatment Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.4.1 Steam Flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.4.2 Thermal Conductive Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.4.3 Electrical Resistive Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.4.4 Hybrid Thermal Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

TCE Degradation in Flow-Through Quartz Tube Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.2 Experimental Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.2 Quartz Tube Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.2.3 Experimental Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.3.1 Experimental Series 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.3.2 Experimental Series 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.3.3 Experimental Series 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.2.3.4 Experimental Series 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.2.3.5 Experimental Series 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.2.4 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3.1 Results of Experimental Series 1-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3.2 Results of Experimental Series 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.3.2.1 TCE Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.3.2.2 Compounds in the DCM Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.3.2.3 Compounds Detected in Tedlar® Bags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.3.2.4 Compounds Detected in the Water Rinse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.3.2.5 Compounds Detected in the Iso-Octane Rinse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3.2.6 Mass Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.4.1 Nitrogen as the Carrier Gas at 420°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.4.2 Air as the Carrier Gas at 420°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.4.3 Experiments Conducted at 120 and 240°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
vi

3.6 Quality Assurance Summary for the Flow-Through Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

TCE Degradation in Heated Ampules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.2 Experimental Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.2.1 Preparation of Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.2.2 Preparation of Aqueous Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4.2.3 Preparation of Ampules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

4.2.4 Description of Ampule Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.2.4.1 Ampule Experiment 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.2.4.2 Ampule Experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4.2.4.3 Ampule Experiment 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.2.3.4 Ampule Experiment 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

4.2.4 Ampule Sampling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.2.5 Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

4.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

4.3.1 Results of Ampule Experiment 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

4.3.2 Results of Ampule Experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

4.3.3 Results of Ampule Experiment 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

4.3.2 Results of Ampule Experiment 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.3.2.1 Change in TCE Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.3.2.2 Change in pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

4.3.2.3 CO and CO2 in the Gas Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

4.3.2.4 Other Gas Phase Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4.3.2.5 Aqueous Phase Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4.3.2.6 Mass Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.4.1 Oxygen Initiated TCE Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.4.2 Hydrogen Elimination Initiated TCE Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

4.4.3 Oven Explosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

4.4.4 Comparison to Knauss et al. (1999) Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.6 Quality Assurance Summary for the Ampule Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

APPENDIX A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Detailed Experimental Methods for Flow-Through Quartz Tube Reactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

A.1 Quartz Tube Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

A.2 Quartz Tube Temperature Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

A.3 Modified TCE Introduction Method: Experimental Series 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

A.4 Effluent Trapping Procedures and Analytical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

A.5 Quartz Tube Rinse Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

APPENDIX B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Change in Dissolved Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

APPENDIX C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

C.1 Rates of TCE Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

C.2 Methods used to Determine TCE Dedradation Rate Parameters in Ampule Experiments . . . . . . . . . . . . . . 94
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Figures

Figure 2.1 Water and TCE-NAPL vapor pressure as a function of solution temperature at 1 bar or 

1.02 atm of total gas phase pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 2.2 Measured concentration of TCE vs. time along with the zero-order reaction model fit. . . . . . . . . . 14

Figure 2.3 Natural log of the measured TCE concentration normalized by the initial TCE 

concentration vs. time along with the first-order reaction model fit. . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 2.4 Reciprocal of the measured concentration of TCE vs. time along with the second-order 

reaction model fit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 2.5 Measured concentration of TCE vs. time for Experiment TCE-40 and radical chain 

reaction model fit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 3.1 Quartz tube experimental apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 3.2 Amounts of TCE, PCE and carbon tetrachloride (CCl4) recovered during the first 

experimental series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 3.3 Amounts of TCE, tetrachloroethylene (PCE) and carbon tetrachloride (CCl4) recovered

 during the second experimental series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 3.4 Recovery of TCE with nitrogen or air as the carrier gas, averaged over three relative 

humidities (inlet temperatures). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 3.5 Amount of chloride detected in the post experiment water rinse. . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 3.6 Amount of dichloroacetate detected in the post experiment water rinse. . . . . . . . . . . . . . . . . . . . . . 37

Figure 4.1 Picture of the 50 mL funnel-top ampule before and after sealing. . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Figure 4.2 Explosion-resistant ampule incubation apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figure 4.3 Illustration of the ampule gas sample collection method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Figure 4.4 Amount of TCE in the 100 mg/L anoxic (Batch 4) and oxic (Batch 3) ampules stored 

at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 4.5 Amount of TCE in anoxic 100 mg/L ampules with Ottawa sand (Batch 6) and Ottawa 

sand+1% goethite (Batch 7) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . 63

Figure 4.6 Amount of TCE in 100 mg/L anoxic ampules amended with NaOH (0.26 mM) to 

pH 10 (Batch 5) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Figure 4.7 The pH of anoxic (Batch 1) and oxic (Batch 2) ampules with 1,000 mg/L of TCE and 

TCE-free controls stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Figure 4.8 The pH of anoxic (Batch 4) and oxic (Batch 3) ampules with 100 mg/L of TCE and 

TCE-free controls stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Figure 4.9 The pH of anoxic ampules that contained acid-washed Ottawa sand with 100 mg/L 

of TCE (Batch 6) and TCE-free controls stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . 65

Figure 4.10 The pH of anoxic ampules that contained acid-washed Ottawa sand+1%goethite with 

100 mg/L of TCE (Batch 7) and TCE-free controls stored at 22°C and incubated at 

120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Figure 4.11 The pH of anoxic ampules amended with NaOH (0.26 mM) to pH 10 and 100 mg/L

of TCE (Batch 5) along with TCE-free controls stored at 22°C and incubated at 120°C. . . . . . . . . 67

Figure 4.12 Amounts of CO and CO2 in anoxic (Batch 1) and oxic (Batch 2) ampules with 

1,000 mg/L of TCE and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Figure 4.13 Amounts of CO and CO2 in anoxic (Batch 4) and oxic (Batch 3) ampules with 

100 mg/L of TCE and incubated at 120°C. No CO or CO2 was detected in ampules 

stored at 22°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Figure 4.14 Amounts of CO and CO2 in anoxic ampules with Ottawa sand and 100 mg/L of 

TCE (Batch 6) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Figure 4.15 Amounts of CO and CO2 in anoxic ampules with Ottawa sand+1%goethite and 

100 mg/L of TCE (Batch 7) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . 69

Figure 4.16 Amounts of CO and CO2 in anoxic ampules amended with NaOH (0.26 mM) to pH 10 

(Batch 5) and 100 mg/L of TCE incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Figure 4.17 Mass spectrum of the 2.05 min chromatogram peak from the analysis of 1 mL of gas

from Ampule 83. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
viii

Figure 4.18 Amount of chloride in anoxic (Batch 1) and oxic (Batch 2) ampules with 1,000 mg/L 

of TCE stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Figure 4.19 Amount of chloride in anoxic (Batch 4) and oxic (Batch 3) ampules with 100 mg/L of 

TCE stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Figure 4.20 Amount of chloride in anoxic ampules with Ottawa sand and 100 mg/L of TCE (Batch 6) 

stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Figure 4.21 Amount of chloride in anoxic ampules with Ottawa sand+1%goethite and 100 mg/L 

TCE (Batch 7) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Figure 4.22 Amount of chloride in anoxic ampules amended with NaOH (0.26 mM) to pH 10 with 

100 mg/L of TCE (Batch 5) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . 71

Figure 4.23 Concentration of dichloroacetate (DCAA) in the anoxic (Batch 1) and oxic (Batch 2) 

ampules with 1,000 mg/L of TCE stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . 71

Figure 4.24 Concentration of chloroacetate in ampules amended with NaOH (0.26 mM) to pH 10 

and 100 mg/L TCE (Batch 5) incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Figure 4.25 Amount of glycolate and formate in anoxic (Batch 1) and oxic (Batch 2) ampules with 

1,000 mg/L of TCE incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Figure 4.26 Amount of glycolate and formate in anoxic (Batch 4) and oxic (Batch 3) ampules with 

100 mg/L of TCE incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Figure 4.27 Amount of glycolate and formate in anoxic ampules with Ottawa sand and 100 mg/L of 

TCE (Batch 6) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Figure 4.28 Amount of formate in anoxic ampules with Ottawa sand+1%goethite and 100 mg/L of 

TCE (Batch 7) stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Figure 4.29 Amount of sulfate in anoxic ampules with Ottawa sand and 100 mg/L of TCE (Batch 6) 

stored at 22°C and incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Figure 4.30 Amount of glycolate in anoxic ampules amended with NaOH (0.26 mM) to pH 10 and 

with 100 mg/L of TCE (Batch 5) incubated at 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Figure A.1 Temperature profile within the quartz tube heated to 120°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Figure A.2 Quartz tube apparatus for the fifth quartz tube experimental series. . . . . . . . . . . . . . . . . . . . . . . . . 88

Figure C.1 The change in anoxic ampule TCE content as a function of incubation time. . . . . . . . . . . . . . . . . . 95

Figure C.2 The change in oxic ampule TCE content as a function of incubation time. . . . . . . . . . . . . . . . . . . . 95

Figure C.3 The change in anoxic ampule TCE content, ampules with Ottawa sand, as a function of 

incubation time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Figure C.4 The change in anoxic ampule TCE content, ampules with Ottawa sand and 1% 

Goethite, as a function of incubation time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Figure C.5 The change in anoxic ampule TCE content as a function of incubation time. . . . . . . . . . . . . . . . . . 95

Figure C.6 The change in oxic ampule TCE content as a function of incubation time. . . . . . . . . . . . . . . . . . . . 95

Figure C.7 The change in anoxic ampule TCE content, ampules with Ottawa sand, as a function of 

incubation time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Figure C.8 The change in anoxic ampule TCE content, ampules with Ottawa sand and 1% 

Goethite, as a function of incubation time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Figure C.9 The change in anoxic ampule TCE content based on detected reaction products. . . . . . . . . . . . . . . 96

Figure C.10 The change in oxic ampule TCE content based on detected reaction products. . . . . . . . . . . . . . . . . 96

Figure C.11 The change in anoxic ampule TCE content, ampules with Ottawa sand, based on 

detected reaction products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Figure C.12 The change in anoxic ampule TCE content, ampules with Ottawa sand and 1% 

Goethite, based on detected reaction products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
ix

Tables

Table 2.1 Selected Properties of TCE (McNeill, 1978) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 2.2 Selected Properties of Water (Gebhart et al., 1988) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 2.3 Selected TCE Stability Test Results 24 hour test (Carlisle and Levine, 1932) . . . . . . . . . . . . . . . . . 9

Table 2.4 Oxygen and TCE Gas-Phase and NAPL Degradation Products (McKinney et al., 1955) . . . . . . . . 10

Table 2.5 Hydrolysis of TCE NAPL Degradation Products (McKinney et al., 1955) . . . . . . . . . . . . . . . . . . . 10

Table 2.6 Rate of Dichloroacetic Acid (DCAA) Disappearance from Heated Water (Prager et al., 2001) . . . 11

Table 2.7 Summary of Knauss et al. (1999) Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 2.8 Amount of TCE Degraded after Passing Through a Heated Quartz Tube Residence 

Time of 2 Seconds (Graham et al., 1986) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 2.9 Selected Degradation Products after Passing TCE through a Heated Quartz Tube

(Yasuhara and Morita, 1990) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 2.10 Selected Degradation Products after Passing TCE through a Heated Quartz Tube 

Containing Fly Ash, 0.9 to 1.5 second Residence Time (Froese and Hutzinger, 1994) . . . . . . . . . . 17

Table 2.11 Selected Degradation Products at 600°C as a Function of Quartz Tube Solids Content, 

0.9 to 1.5 second Residence Time (Froese and Hutzinger, 1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 2.12 Selected Compounds in a TCE Flame with Cl:H Ratio of 3 (Chang and Senkan, 1989) . . . . . . . . . 19

Table 2.13 Selected Compounds after Passing TCE through a Flame with Cl:H Ratio of 0.09 

(Werner and Cool, 2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 3.1 Summary of Flow Through Quartz Tube Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table 3.2 Fifth Experimental Series Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Table 3.3 Amounts of TCE, PCE, and CCl4 from the Sand Filled Quartz Tube at 420°C . . . . . . . . . . . . . . . . 31

Table 3.4 Amount of TCE, PCE, CCl4, and CO2 from an Empty Quartz Tube at 420°C . . . . . . . . . . . . . . . . . 31

Table 3.5 Experiments Completed for the Fifth Experimental Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 3.6 TCE Recovery with Nitrogen as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 3.7 TCE Recovery with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 3.8 Concentration (ppmv) of Compounds Detected in the DCM Trap for the 420°C 

Experiments with Nitrogen as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Table 3.9 Concentration (ppmv) of Compounds Detected in the DCM Trap for the 420°C 

Experiments with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 3.10 Concentration of Compounds Detected in the Tedlar® Bag and Phosgene Trap for 

the 420°C Experiments with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Table 3.11 Change in the Amount of CO2 and Phosgene Detected with Increase in Water Content 

for the 420°C Experiments with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Table 3.12 Amount of Haloacetic Acids in the Water Rinse from 240°C and 420°C Experiments 

with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 3.13 Estimated Amounts (umol) of Compounds in Water Rinse from 420°C Experiment 

with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 3.14 Amounts (umol) of Compounds in the Iso-Octane Rinse from the 420°C Experiments 

with Nitrogen as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 3.15 Amounts (umol) of Compounds in the Iso-Octane Rinse from the 420°C Experiments 

with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Table 3.16 Distribution of Carbon and Chlorine for the 420°C Experiments with Nitrogen as the 

Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Table 3.17 Distribution of Carbon and Chlorine for the 420°C Experiments with Air as the Carrier 

Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Table 3.18 Carbon in the DCM Trap and Iso-Octane Rinse, and Chloride in the Water Rinse for

the 420°C Experiments with Nitrogen as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Table 3.19 Carbon in the DCM Trap and Iso-Octane Rinse, and Chloride in the Water Rinse for 

the 420°C Experiments with Air as the Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Table 3.20 Amount of Chloride and DCAA in the Water Rinse from the 120°C Experiments . . . . . . . . . . . . . 44
x

Table 3.21 Amount of Chloride, DCAA, and TCAA in the Water Rinse from the 240°C 

Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Table 4.1 Ampule Experimental Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Table 4.2 Experimental Matrix Used for the Fourth Ampule Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Table 4.3 Summary of Ampules Prepared for the Fourth Ampule Experiment . . . . . . . . . . . . . . . . . . . . . . . . 51

Table 4.4 Schedule for Convection Oven Ampule Incubation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Table 4.5 Schedule for Room Temperature Ampule Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Table 4.6 Schedule for Explosion-Resistant Apparatus Ampule Incubation . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Table 4.7 Results of the First Ampule Experiment After 6 Days at 120°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Table 4.8 Results of Second Ampule Experiment After 10 Days at 120°C . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Table 4.9 Initial and Final TCE Concentrations in the Second Ampule Experiment. . . . . . . . . . . . . . . . . . . . . 58

Table 4.10 Initial and Final TCE Concentration in Anoxic Ampules from the Third Ampule 

Experiment (1.4 uL of TCE added to each ampule, Initial DO = 0.79 mg/L) . . . . . . . . . . . . . . . . . 58

Table 4.11 Initial and Final TCE Concentration in Oxic Ampules from the Third Ampule 

Experiment (TCE mixed into 250 mL of water prior to addition to each ampule, 

Initial DO = 8.22 mg/L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Table 4.12 Third Ampule Experiment Results for Anoxic Ampules (1.4 uL of TCE added to 

each ampule, Initial DO = 0.79 mg/L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Table 4.13 Third Ampule Experiment Results for Oxic Ampules (TCE mixed into 250 mL of 

water prior to addition to each ampule, Initial DO = 8.22 mg/L) . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Table 4.14 Amount (Aqueous and Gas Phases) of TCE in 1,000 mg/L (nominal) Anoxic (Batch 1) 

and Oxic (Batch 2) Ampules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Table 4.15 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic (Batch 4) 

and Oxic (Batch 3) Ampules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Table 4.16 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic Ampules 

with Sand (Batch 6) and Sand+1% Goethite (Batch 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Table 4.17 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic Ampules 

Amended with NaOH (0.26 mM) to pH 10 (Batch 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Table 4.18 Elements Present in Ottawa Sand and Ottawa sand+1% Goethite . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Table 4.19 Mass Balance Between Carbon and Chloride Lost as TCE and Detected as Degradation 

Products in Ampules Incubated at 120°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Table 4.20 Amount of Carbon and Chloride Detected as Degradation Products and the Cl:C Ratio 

for Ampules Incubated at 120°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Table B.1 Dissolved Oxygen (DO) Concentration Range for Anoxic and Oxic Ampules with 

1,000 and 100 mg/L of TCE (Batches 1-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Table B.2 Dissolved Oxygen (DO) Concentration Range for Anoxic Ampules that Contained 

Solids (Ottawa sand and Ottawa Sand+1% Goethite) or NaOH (pH 10) (Batches 5-7) . . . . . . . . . 92

Table C.1 Rate of TCE Disappearance from the 100 mg/L Ampules at 120°C . . . . . . . . . . . . . . . . . . . . . . . . 93
xi

List of Abbreviations

A, B, C constants in equations

ACS American Chemical Society

AIBN Azo-bis-isobutyronitrile

ASTM American Society of Testing and 

Materials

ATSDR Agency for Toxic Substances and 

Disease Registry

atm atmosphere

C Celsius

Cg Gas phase concentration of 

trichloroethylene

Co Initial concentration of 

trichloroethylene

Cw Aqueous phase concentration of 

trichloroethylene

CTCE Concentration of trichloroethylene

cfm cubic feet per minute

cis-1,2-DCE cis-1,2-Dichloroethylene

cm centimeter

cP centiPoise

DCA Dichloroacetylene

DCAA Dichloroacetic acid

DCM Dichloromethane

DI Deionized

DNAPL Dense, non-aqueous phase liquid

DO Dissolved oxygen

d day

Ea Activation Energy

ECD Electron Capture Detector

EGDY East Gate Disposal Yard

EPA Environmental Protection Agency

ERH Electrical Resistance Heating

e

- Electron

FID Flame Ionization Detector

FTIR Fourier-Transform Infrared

ft feet

ft3 cubic feet

ft/min feet per minute

GC Gas Chromatography

GC/MS Gas Chromatography/Mass 

Spectrometry

g grams

g/mL grams per milliliter

g/mol grams per mole

H Henry’s Law constant

HCB Hexachlorobenzene

HCDD Hexachlorodibenzo-p-dioxin

HP Hewlett-Packard

HPO Hydrous pyrolysis/oxidation

HPLC High Performance Liquid 

Chromatography

hrs hours

IC Ion chromatography

ICP-MS Inductively Coupled Plasma – Mass 

Spectrometry

ID Inner diameter

ISE Ion Selective Electrode

IR Infrared

J Joule

k or k rate constant

ko Zero-order rate constant

k1 First-order rate constant

k2 Second-order rate constant

k1*, k2*, k3* Rate constants for radical-initiated 

reactions

kg kilograms

kJ/mol kilojoules per mole

L liter

LLNL Lawrence Livermore National 

Laboratory

lbs/day pounds per day

M Molarity

M* Radical initiator

MCL Maximum Contaminant Level

MDL Method Detection Limit

MPa Million Pascals

MS Mass Spectrometry

MSD Mass Select Detector

MTBE Methyl-tert-butyl ether

MΩ-cm Mega ohms per centimeters

m meter

mg milligrams

mg/kg milligrams per kilogram

mg/L milligrams per liter

min minute

mol/kg moles per kilogram

mL milliliter

mL/g milliliters per gram

mL/hr milliliters per hour

mL/min milliliters per minute

mM millimolar

mm millimeter

mm micrometer

mmol millimoles

mmolal millimolality

N Normality

NA or na Not analyzed

NAPL Non-aqueous phase liquid

NM not measured

NPL National Priorities List

No. Number
xii

n number of ampule results used to 

calculate statistics

nd amount not evident in graph or below 

analysis detection limit

nm nanometers

nmol nanomoles

nr not reported

OD Outer diameter

Patm Atmospheric pressure

Pt Total pressure

Po Pure phase vapor pressure

Po

water Water vapor pressure

Po

TCE Trichloroethylene vapor pressure

PEEK Poly ether-ether ketone

PCE Tetrachloroethylene

pH Hydroxide ion content

ppmv parts per million volume

psi pounds per square inch

R Universal Gas Constant

R2 correlation coefficient

RH Relative Humidity

RSD Relative standard deviation

SEE Steam Enhanced Extraction

S.D. standard deviation

s second

T Temperature, Kelvin

TCAA Trichloroacetate

TCE Trichloroethylene

TCE0 Trichloroethylene, initial moles

TCE* Trichloroethylene radical

TCE-O2* Trichloroethylene-oxygen radical

TCD Thermal Conductivity Detector

TCH Thermal Conduction Heating

t Time

trans-1,2-DCE trans-1,2-Dichloroethylene

U.S. United States

UV ultraviolet

UZA Ultra zero grade air

ug/L micrograms per liter

uL microliter

uL/L microliter per liter

uM micromolarity

umol micromoles

VOCs Volatile Organic Compounds

Vol volume

vs. versus

wt weight

XRD X-ray Diffraction

(g) gas phase

(aq) aqueous phase

t

1/2 half life

< less than

< greater than

% percent

~ approximately
xiii

Al Aluminum

Al2O3 Aluminum oxide

Ar Argon

C Carbon atom

CHOO- Formate

CH2O Formaldehyde

CH3

· Methyl radical

CH4 Methane

C2H2O Ketene

C2H4 Ethylene

C2H6O Dimethyl ether

CHCl3 Chloroform

CH2Cl2 Dichloromethane

C2HCl Chloroacetylene

C2H4 Ethene

C2H6 Ethane

C2HCl3

(also Cl2

C=CHCl) Trichloroethylene

C2HClO Chloroketene

C2H2Cl2 Dichloroethylene

C2H3Cl Vinyl Chloride

C2H4Cl2 Dichloroethane

C3H8 Propane

C3HCl5 Pentachlorocyclopropane

C3H2Cl4 Tetrachloropropene

C4HCl5 Pentachlorobutadiene

C4H2Cl4 Tetrachlorobutadiene

C4H2Cl6 Hexachlorobutene

C6HCl5 Pentachlorobenzene

C6H5Cl7 Heptachlorocyclohexane

:CCl2 Dichlorocarbene

CCl4 Carbon Tetrachloride

:C2Cl2 Dichlorovinylidene

C2Cl2

(also ClC≡ CCl) Dichloroacetylene

C2Cl3 Trichloroethylene hydrolysis 

product

C2

Cl3· Trichloroethylene radical

C2Cl4 Tetrachloroethylene

C2Cl4H2 1,1,2,2-Tetrachloroethane

C2Cl6 Hexachloroethane

C3Cl5 Pentachloro-1-propene

C3Cl6 Hexachloropropene

C4Cl2OH4 3,4-Dichloro-3-butene-2-one

C4Cl4O Perchlorocyclobutenone

C4Cl6 Hexachlorobutadiene

C6Cl5OH Pentachlorophenol

C6Cl6 Hexachlorobenzene

C6Cl6 Tetrachloro-1,3-cyclopentadiene-5-

dichloromethylene

C8

Cl6 Hexachlorophenylacetylene

C8Cl8 Octachlorostyrene

C10Cl8 Octachloronaphthalene

CO Carbon monoxide

CO2 Carbon dioxide

CO3

2- Carbonate ion

COCl2 Phosgene

CaSO4 Calcium sulfate

Cl Chlorine atom

Cl- Chloride ion

Cl· Chlorine radical

ClHO-. radical formed by the reaction of a 

chlorine radical with water

ClH2

C2OCl Chloroacetyl chloride

ClH2C2OO- Chloroacetate

Cl2 Chlorine gas

Cl2

-. Dichlorine radical anions

Cl2COCHCl Trichloroethylene epoxide

Cl2C2HOH Dichloroethenol

Cl2C2O Dichloroketene

Cl2HC2Cl2

· Tetrachloroethyl radical

Cl2HC2OO- Dichloroacetate

Cl2HC2Cl2OO· Peroxy radical

Cl2HC2OCl Dichloroacetyl chloride

Cl3C2

-

(also Cl2C=CCl-) Trichlorovinyl anion

Cl3C2HCl· 1,1,1,2-Tetrachloroethyl radical

Cl3C2OCl Trichloroacetyl chloride

Cl3C2OO- Trichloroacetate

Cl3C2O2CH3 Trichloroacetic acid methyl ester

ClO· Chlorine-oxygen radical

CoCl2 Cobalt dichloride

Cu Copper

Chemical Formulas
xiv

CuO Copper oxide

Fe (also Fe0) Iron, zero valent

Fe2+ Ferous iron ion

Fe3+ (also Fe(III)) Ferric iron ion

FeOOH Goethite

FeNH4(SO4)2 Ferric ammonium disulfate

FeS2 Pyrite

FeS2 Marcasite (polymorph of pyrite)

Fe(SCN)2+ Iron-thiocyanate complex

Fe2O3 Hematite

H Hydrogen atom

H· Hydrogen radical

H+ Hydronum ion

HCO3

- Bicarbonate ion

HCOOH Formic acid

HC2Cl Chloroacetylene

HC2Cl2 TCE hydrolysis product

HClC2Cl· Vinyl radicals

HCl2C2OOH Dichloroacetic acid

HOCH2COOH Glycolic acid

HOC2OOH Oxoacetic acid

HOC2OO- Oxoacetate

HOH2C2OO- Glycolate

HOOC2OO- Oxalate

HCl Hydrochloric acid

HNO3 Nitric acid

HS- Hydrogen bisulfide ion

H2 Hydrogen gas

H2CO3 Carbonic acid

H2ClC2OOH Monochloroacetic acid

H2O Water

H2PO4

- Phosphate ion

H2SO4 Sulfuric acid

H4SiO4 Silicic acid

H3O+ Water, protonated

H3SiO4

- Silicic acid, dissociated

HgCl2 Mercuric chloride

Hg(SCN)2 Mercuric thiochanate

N2 Nitrogen

NO3

- Nitrate ion

NaHCO3 Sodium bicarbonate

NaOH Sodium hydroxide

Na2CO3 Sodium carbonate

O2 Oxygen

OH- Hydroxide ion

SiO2 Silica

SO4

2- Sulfate ion

TiCl4 Titanium tetrachloride
xv

Abstract

A series of experiments were completed to investigate abiotic degradation and reaction product formation of 

trichloroethylene (TCE) when heated to temperatures ranging from 60 to 480°C. The experimental systems were 

designed to simulate conditions anticipated during the thermal treatment of subsurface environments, most notably 

the inclusion of a gas phase which is essential because of the strong dependence of TCE vapor pressure and Henry’s 

Law constant on temperature. The two experimental systems, a 0.5 L quartz tube flow-though reactor and 50 mL 

borosilicate glass ampules, provided for the quantification of TCE degradation in the presence of three phases (solid, 

liquid, gas). The quartz-tube apparatus was used to study short residence time (<10 minutes) conditions that are 

thought to occur during thermal conductive heating and during the recovery of contaminants by vapor phase extraction. 

The glass ampules were used to study longer residence time conditions (>1 day) that are thought to occur during steam 

flushing and electrical resistive heating. No electrical potential was applied during the experiments, and hence, these 

experiments do not directly simulate electrical resistive heating. 

The quartz tube experiments were conducted at the temperatures of 120, 240 and 420°C, in the presence of water 

vapor, and with either nitrogen or air as the carrier gas. Free chloride ions were detected at all three temperatures 

considered, which was interpreted as evidence of gas-phase TCE degradation. The amount of chloride formed in the 

120°C experiments was small, representing less than 0.01% of the TCE that passed through the quartz tube. Passing 

TCE through the quartz tube heated to 420°C with nitrogen as the carrier gas resulted in substantially greater amounts 

of chloride (up to 6.5% of TCE). Chlorinated compounds (up to 7% as TCE) with 4 and 6 carbon atoms and at least 

5 chlorine atoms were also detected at 420°C. Introducing air containing 21% oxygen into the quartz tube heated 

to 240°C resulted in the detection of chloride representing up to 0.4% of TCE introduced, as well as the detection 

of dichloroacetate and trichloroacetate. At 420°C, the presence of oxygen in the carrier gas resulted in significant 

increases in the number and amount of reaction products detected. Under these conditions, more than 20% of the 

carbon introduced as TCE was transformed into carbon monoxide and carbon dioxide, while up to 22% of the chlorine 

introduced as TCE was detected in the form of chlorinated carbon compounds. Increasing the quartz tube water content 

resulted in an increase in TCE recovery concurrent with a decrease in TCE degradation products with nitrogen as the 

carrier gas. With air as the carrier gas, increasing the quartz tube water content in the 420°C experiments may have 

served to hydrolyze phosgene and remove reactive chlorine from the gas phase while not impacting the amount of TCE 

degraded. 

The ampule experiments were conducted in borosilicate glass ampules that were filled to approximately three-quarters 

capacity with aqueous solutions containing TCE at initial concentrations of 100 and 1,000 mg/L. The rate of TCE 

degradation and products formed was determined as function of dissolved oxygen concentration, hydroxide ion 

concentration, and solids content. There was no significant reduction (>10%) in TCE content of the ampules with initial 

concentration of 1,000 mg/L of TCE that were incubated over a 20-day period at 120°C. However, significant changes 

in solution pH were observed along with the detection of chloride ions and organic compounds other than TCE. The 

concentration of TCE decreased in ampules that initially contained 100 mg/L of TCE and were incubated at 120°C. The 

decrease in TCE content was matched with a decrease in ampule pH, an increase in the chloride, formate, and glycolate 

content of the aqueous phase, and an increase in the carbon monoxide and carbon dioxide content of the gas phase. 

Dichloroacetylene (DCA) was detected in ampules and may represent an intermediate formed during TCE degradation. 

DCA is a reactive compound that can interact with the variety of compounds present in soil such as organic carbon. 

Thus, the degradation products formed during the in-situ thermal treatment TCE may not be limited to those found in 

the ampule experiments since the ampules did not contain organic carbon other than TCE. The rates of TCE degradation 

in ampules with anoxic water, both with and without sand, and in oxic water were similar at 120°C. The degradation 

rate in ampules with anoxic water and sand was increased by adding 1% (wt) goethite.

The experimental results presented herein represent a first step toward understanding TCE chemical reactivity and 

reaction product formation during thermal treatment. Additional experimentation, both at the laboratory and field 

scale, is recommended to further elucidate TCE reaction pathways and rates, and to more accurately represent the 

complexities inherent in natural subsurface materials and field-scale application of thermal treatment technologies. 

1

1.0

Project Summary

1.1 Introduction

Laboratory studies on the hydrolysis of environmentally 

significant halogenated compounds have shown that 

trichloroethylene (C2HCl3) is extremely recalcitrant in 

aqueous environments, with a measured half-life as large 

as approximately 100,000 years under neutral conditions 

at 25°C (Jeffers and Wolfe, 1996). Other researchers 

found TCE to resist hydrolysis at 100°C (Dilling et al., 

1975). However, in-situ aqueous phase degradation of 

trichloroethylene (TCE) into carbon dioxide (CO2) and 

chloride (Cl-) is claimed to occur during the thermal 

treatment of contaminated subsurface environments 

(Knauss et al., 2000). This claim is based on 

experimental results obtained from a completely waterfilled, constant pressure, gold-walled reactor operated in 

the temperature range from 70 to 100°C (Knauss et al., 

1999). The only degradation products reported in these 

experiments were dissolved carbon dioxide and chloride. 

However, no quantitative evaluation of the amounts 

of carbon dioxide and chloride recovered with respect 

to the initial mass of trichloroethylene was performed. 

While limited quantitative data are available on chemical 

reaction as a means of destroying contaminants in 

thermal remediation (Stegemeier and Vinegar, 2001), insitu degradation of TCE into carbon dioxide and chloride 

has been observed during thermal conductive heating 

at temperatures ranging from 500 to 700°C (Baker and 

Kuhlman, 2002). 

Subsurface environments are extremely complex 

systems, comprised of three phases including mixtures 

of solids, liquids, and gases. Subsurface solids are 

composed of minerals and organic matter, which may 

facilitate the abiotic degradation of TCE into products 

other than those found in pure water or gas reaction 

environments (Lee and Batchelor, 2003; 2004; Haderlein 

and Pecher, 1998). A comprehensive review of TCE 

degradation and the degradation products formed in 

heated environments in the presence of three phases 

(solid, liquid-water, and gas) does not currently exist. 

The potential TCE degradation products are not limited 

to carbon dioxide and chloride alone, but also include 

acutely toxic products such as dichloroacetyl chloride 

(Cl2HC2OCl) and phosgene (COCl2) that have been 

detected during the gas phase photocatalytic treatment of 

TCE (Haag et al., 1996; Amama et al., 2001). 

As the use of thermal technologies, including steam 

flushing, electrical resistive heating and thermal 

conductive heating, to remediate chlorinated solvent 

source zones becomes more common, there is a need to 

not only determine rates of TCE degradation and thus 

how much degradatation can be expected to occur in 

situ, but also to elucidate thermal reaction pathways and 

degradation products. Because of the strong dependence 

of TCE vapor pressure and Henry’s Law constant 

on temperature, it is essential that such experiments 

include a gas phase. For this reason, the experimental 

systems used in this work, a quartz tube reactor and 

sealed ampules, were specifically selected to provide for 

quantification of TCE degradation in presence of three 

phases (solid, liquid, gas). Although these experimental 

systems do not replicate field conditions, they represent 

a significant step forward from previous work, which 

considered TCE degradation in single-phase water (e.g., 

Knauss et al., 1999) or gas (e.g., Zhang and Kennedy, 

2002) systems. 

1.2 Research Objectives

The primary objective of this work was to determine if 

significant TCE transformation occurs in three-phase 

systems (gas, liquid-water, solid) at temperatures and 

conditions typically used for thermal remediation. 

Transformation of TCE was confirmed through the 

identification of reaction products. Identification of 

reaction products also allows some understanding 

of the likely dominant reaction mechanisms for the 

conditions studied. The research involved a series of 

laboratory experiments performed in either a flowthrough quartz tube or sealed glass ampules that were 

designed to simulate conditions anticipated to occur 

during thermal treatment of porous media contaminated 

with TCE. Experimental conditions were varied in order 

to systematically evaluate the effects of temperature, 

oxygen concentration, hydroxide ion concentration, 

water content, and solids content on the rate of TCE 

degradation and degradation products formed. The 

following conditions (i.e., experimental variables) are 

anticipated in the subsurface during thermal treatment: 

• The temperature of the subsurface can range from 

approximately 50 to 600°C or greater depending 

upon the thermal treatment technology employed.

• The subsurface can remain at an elevated 

temperature for a period of one month to more than 

one year.

• The concentration of oxygen in the gas phase can 

range from less than 1 up to 21%. The concentration 

of oxygen in the liquid phase can range from less 

than 0.1 up to 8 mg/L.
2

• Within soil pore spaces water and TCE will be 

converted from the condensed to vapor phase as the 

subsurface temperature increases.

• There may be significant changes in the 

concentration of dissolved ionic species as the 

subsurface temperature increases.

In addition to changes that occur as a result of heating, 

the initial subsurface conditions prior to thermal 

treatment can vary depending upon: 

• The type and amount of mineral and organic matter 

present in the solid phase.

• The initial amount of TCE present in the aqueous 

phase, solid phase, and gas phase, and existing as a 

separate non-aqueous phase liquid (NAPL).

 Based on a detailed review of previous experimental 

results described in Chapter 2.3 (see Table 2.4), the 

anticipated TCE degradation products under oxidative 

conditions include carbon monoxide (CO) and 

carbon dioxide (CO2) in the gas phase, and chloride, 

dichloroacetic acid, oxoacetic acid, and formic acid 

in the aqueous phase when the subsurface is heated to 

temperatures of less than 120°C (e.g., steam flushing, 

electrical resistive heating) and there are no other 

reactive species present. At temperatures greater than 

300°C (e.g., thermal conductive heating), the expected 

gas phase TCE transformation products include CO, 

CO2, phosgene (COCl2), and chlorinated hydrocarbons 

(see Tables 2.8, 2.11, and 2.12) when there are no other 

reactive species present. Therefore, the experimental 

systems and analytical methods must be carefully 

designed and tested in order to collect and detect a wide 

range of degradation products that may occur in the gas, 

solid and aqueous phases. 

1.3 Experimental Systems

While laboratory-scale apparatus are useful for 

investigating simulated subsurface conditions, the 

experimental materials must be relatively inert. In 

general, borosilicate glass provides thermal stability 

(softening point of 820°C), and is primarily composed 

of silica (SiO2) which is more similar to subsurface 

materials than metal based materials such as stainlesssteel. The collection and analysis of samples from each 

phase within a dynamic or closed apparatus is required 

to quantify the TCE degradation and reaction product 

formation. Calculating the difference between the 

amount of carbon and chlorine atoms present before and 

after each experiment (i.e., mass balance) allows for 

an assessment of whether or not all possible reactants 

and products have been measured. The selectivity and 

sensitivity of each analytical method must be appropriate 

for the expected degradation products. Infrared 

spectroscopy is applicable for the analysis of dissolved 

carbon dioxide, but requires concentrations of greater 

than 0.24 mM (Burt and Rau, 1994) for quantification. 

However, most of the carbon dioxide is expected to be 

present in the gas phase of three-phase systems, meaning 

that the collection and analysis of gas samples will be 

more sensitive to the amount of carbon dioxide formed. 

Sample preparation methods must also be appropriate. 

For example, the presence of haloacetic acids (i.e., 

dichloroacetic acid) may not be detected by traditional 

analytical techniques if the proper sample preparation 

methods are not used. Determining the presence of 

haloacetic acids requires addition of a strong acid to 

reach at least pH 2 for spectroscopic detection, and an 

additional derivitization step for gas chromatographic 

separation. 

For the experiments conducted in this project, subsurface 

conditions were simulated using two experimental 

systems: 1) a 0.5 L flow-though quartz tube apparatus 

and 2) 25 and 50 mL borosilicate glass ampules. The 

quartz tube was used to study the high temperature 

(>120°C), short residence time (<10 minutes) reactions 

that are thought to occur within approximately 1 to 3 

feet of heater wells used in thermal conductive heating. 

The gas-phase effluent from the flow-through tubes 

was passed through liquid traps and then captured in 

a Tedlar® bag. The liquid-trap fluids, Tedlar®-bag 

contents, and solid extracts were analyzed using gas 

chromatography (GC), ion chromatography (IC), and 

ion selective electrodes. The borosilicate glass ampules 

were used to study low temperature range (60 to 120°C) 

over longer residence times (>1 day), conditions that 

are likely to occur during steam flushing and electrical 

resistive heating. No electrical potential was applied to 

the ampules, and hence, the system does not directly 

simulate electrical resistive heating. The ampules were 

destructively sampled at specified time intervals and 

samples from each phase were collected for analysis 

using gas chromatography (GC), ion chromatography 

(IC), and ion selective electrodes. In addition, GC 

mass spectrometry (GC/MS) was employed to identify 

unknown compounds detected in the aqueous and gas 

phase effluent sample and solid phase rinses. 

1.4 Conclusions and 

Recommendations

1.4.1 Quartz Tube Reactor Experiments

A series of five quartz tube reactor experiments were 

completed over a temperature range of 22 to 480°C 

(Chapter 3). Specific experiments were conducted 

to investigate the effects of temperature, water vapor 

content, solids (Ottawa sand), and oxygen content on 

TCE degradation and reaction product formation. In 

all of the quartz tube experiments, some degree of 

TCE degradation was observed, however, the greatest 

amount of TCE was transformed (up to 48% of the TCE 

introduced) at temperature of 420°C in the presence 
3

of oxygen (air as the carrier gas). The amount of TCE 

degraded was dependent on the temperature of the 

quartz tube, with more being degraded in the 420°C 

experiments than in the 120 or 240°C experiments. 

The amount of TCE degraded was also dependent on 

the amount of oxygen present in the 240 and 420°C 

experiments, with more TCE degraded when air (i.e., 

21% O2) was used as the carrier gas. With nitrogen as the 

carrier gas, up to four TCE degradation products were 

identified in the liquid-trap fluids and quartz tube rinses, 

with no CO or CO2 detected for experiments completed 

at 420°C. The amount of TCE recovered for the 420°C 

experiments with nitrogen as the carrier gas was greater 

than 97%, with up to 3.4% detected as chlorinated 

hydrocarbon degradation products. The amount of TCE 

recovered as chlorine was greater than 100%, with up to 

7% as chlorinated degradation products. The degradation 

products detected contained 4 and 6 carbon atoms 

with greater than 5 chlorine atoms per molecule. TCE 

degradation was proposed to be initiated by thermal 

induced unimolecular dissociation of TCE but was also 

influenced by chlorine induced degradation. Increasing 

the quartz tube water content resulted in an increase 

in TCE recovery concurrent with a decrease in TCE 

degradation products that was suggested to indicate a 

decrease in chlorine induced TCE degradation.

With air as the carrier gas, there was an increase in the 

amount of TCE degraded and an increase in the number 

of degradation products detected as compared with 

experiments completed with nitrogen as the carrier gas. 

The average recovery of TCE was greater than 94% with 

air as the carrier gas for the 120 and 240°C experiments, 

but decreased to approximately 53% in the 420°C 

experiments. Carbon-based TCE degradation products 

were detected in the 240 and 420°C experiments with 

air as the carrier gas. Three degradation products were 

identified in the quartz tube rinse from the 240°C 

experiments, and up to 13 degradation products were 

detected in the liquid-trap fluids and quartz tube rinses in 

the 420°C experiments. The degradation products ranged 

from single carbon compounds with 3 chlorine atoms 

(i.e., chloroform) to compounds with up to 6 carbons 

and 6 chlorine atoms (i.e., hexachlorobenzene). Carbon 

monoxide (CO), CO2

, and phosgene were detected in 

the gas phase of the 420°C experiments only with air as 

the carrier gas. The amount of TCE recovered as carbon 

for the 420°C experiments with air as the carrier gas 

ranged from 79.1 to 91.5%, and the amount of chlorine 

recovered ranged from 74.6 to 88.8%. TCE degradation 

was proposed to be initiated by thermal induced 

unimolecular dissociation but was also influenced by 

the formation of peroxyl radicals due to the presence 

of oxygen. Increasing the quartz tube water content in 

the 420°C experiments with air as the carrier gas may 

have served to hydrolyze phosgene and remove reactive 

chlorine from the gas phase, while not impacting the 

amount of TCE degraded.

1.4.2 Sealed Ampule Experiments

Four series of ampule experiments were completed to 

investigate the effects of oxygen content, hydroxide 

ion content (pH), and solids (Ottawa sand and goethite) 

on TCE degradation at temperature ranging from 22 to 

120°C for periods of up to 41 days (Chapter 4). The 

results of the ampule experiments demonstrate that 

TCE was degraded within sealed glass ampules that 

contained gas, water, and solids. The rates of TCE 

degradation in ampules with anoxic water, both with and 

without sand, and in oxic water were similar at 120°C. 

The degradation rate in ampules with anoxic water and 

sand was increased by adding 1% (wt) goethite, with 

a first order half-life on the order of 10 days at 120°C. 

The primary TCE degradation products included CO 

and CO2 in the gas phase and chloride, hydronium ions, 

formate, glycolate in the aqueous phase. Minor amounts 

(<1 mg/L) of dichloroacetic acid (DCAA) were detected 

in select ampules, most consistently in ampules that that 

were stored at 22°C and initially contained 1,000 mg/L 

TCE along with oxygen. Dichloroacetylene (DCA) was 

detected in minor amounts (i.e., DCA < 1% of TCE) 

in ampules that contained TCE and were incubated at 

120°C. 

Dichlororacetylene, in addition to being a TCE 

degradation product, was also thought to represent a 

key intermediate. The presence of DCA was proposed 

to indicate that the lone hydrogen atom in TCE was 

being eliminated by nucleophiles, such as sodium 

hydroxide (NaOH), which increased the rate of TCE 

degradation and amount of DCA when added to the 

ampules as NaOH. Dichloroacetylene was proposed to 

be hydrolyzed to form chlorinated organic acids, such as 

DCAA, which were then hydrolyzed at 120°C to form 

the non-chlorinated organic acids, glycolate and formate. 

1.4.3 Implications to Field Applications

The results in this report are important for demonstrating 

that transformation reactions can occur during thermal 

remediaton. However, extending these laboratory results 

toward predicting the rate of TCE degradation during 

the in-situ thermal treatment of TCE contaminated 

subsurface regions involves a significant degree of 

speculation. Laboratory experiments are performed 

on simplified systems or with materials that have, in 

some way, been altered from their natural state in the 

subsurface environment. Most thermal remediation 

projects for TCE are focused on physical recovery 

through vaporization and vacuum extraction. The 

transformation reactions demonstrated here will occur 

simultaneously with vaporization, and the relative 

rates of the two processes will be controlled by site 

specific conditions. A remediation system could not be 
4

designed or operated for one of the processes without the 

other process also occurring. In most cases, however, 

vaporization rates are likely to be much faster than the 

transformation reactions demonstrated here, as thermal 

treatment of TCE contaminated sites are often completed 

in much shorter times (less than one year) than would 

be required to reduce TCE concentrations to a similar 

degree by the in situ transformation processes found 

here. Thus, in situ thermal remediation systems for TCE 

require robust extraction and treatment systems that can 

recover and treat the transformation products as well as 

the unreacted TCE. 

Ampules such as those used in the aqueous phase 

experiments here have been used successfully by other 

researchers to study transformation rates of volatile 

organic compounds. The ampule experiments reported 

here extend that work by the addition of Ottawa sand or 

1% (wt) goethite, materials collected from the subsurface 

and commonly found in soil environments. However, 

the Ottawa sand was acid-washed, which could remove 

surface coatings, while the goethite was ground prior to 

use, potentially creating fresh active surfaces (Papirer et 

al., 1993). 

The water used in all experiments was deionized, 

whereas natural groundwater contains ions. For 

example, sodium hydroxide (an anion) was used in the 

ampule experiments to simulate a strong nucleophile 

and was shown to increase the rate of TCE degradation 

at 120°C by an order-of-magnitude compared to the 

rate determined for deionized water. The primary 

nucleophiles expected in the subsurface environment 

include hydrogen bisulfide (HS-

), hydroxide (OH-), 

phosphate (H2PO4

2-), bicarbonate (HCO3-

), sulfate 

(SO4

2-), and nitrate (NO3-

) in order of decreasing 

nucleophilicity with hydrogen bisulfide as the strongest 

nucleophile and nitrate as the weakest. Thus the anionic 

content of natural groundwater, in addition to the iron 

containing minerals present, may strongly influence 

the rate of TCE degradation. Therefore, predicting the 

potential rate of TCE degradation during in-situ thermal 

treatment requires specific information regarding the 

geochemistry of the site being treated, keeping in 

mind that the increase in temperature can affect the 

geochemistry. For example, significant levels of sulfate 

(> 1 mM) were formed in ampules incubated at 120°C 

from the dissolution of pyrite and marcasite found in the 

Ottawa sand.

Free radical reactions may contribute to contaminant 

transformation during thermal remedation. Under 

ambient conditions free radicals may be created in the 

subsurface by the reaction of chlorinated compounds 

with naturally occurring iron-containing materials 

(Kriegman-King and Reinhard, 1992; 1994). However, 

a significant variation from natural conditions in these 

laboratory experimental systems is the absence of 

naturally occurring organic matter. Although naturally 

occurring organic matter has not been found to have an 

effect on reactions such as hydrolysis (Haag and Mill, 

1988), it has been found to have significant effects on 

free radical reactions. Haag and Hoigne (1985) found 

that fast consumption of hydroxyl radicals by natural 

dissolved organic solutes and bicarbonate ions decreased 

the amount of organic pollutants oxidized. 

With regard to free radical reactions, TCE has been 

found to be virtually unreactive in oxidation reactions 

without a radical initiator (Kucher et al., 1990). 

Radical-mediated reactions are important for TCE 

decomposition in both the aqueous and vapor phase, and 

TCE is known to react with hydroxyl radicals (Buxton 

et al., 1988). As discussed in Section 2.3.4, the kinetic 

data reported by Knauss et al. (1999) are consistent 

with a radical chain reaction, but this is essentially an 

experimental observation, and the details of the reaction 

mechanism are unknown. It is not possible to assess 

the importance of this reaction in situ during thermal 

remediation. According to Buxton et al. (1988), radicals 

can be generated in the laboratory in aqueous solution 

by radiolysis of water, photolysis, high frequency 

electric discharge, sonolysis, and Fenton-type reactions. 

However, none of these types of radical-generating 

processes may be present in the subsurface during 

thermal remediation.

High temperatures such as that found in an incinerator 

flame may generate free radicals in the vapor state 

(Taylor et al., 1990), and the possibility exists for this to 

occur in the subsurface near heaters or electrodes. The 

species of radicals formed depends on the temperature 

of the system, the compounds present, and the fuel 

to oxygen ratio. At temperatures below 750 - 800°C, 

diatomic radicals are sufficiently stable to contribute 

to organic reactions, which may form larger molecules 

rather than break down chemicals, while at higher 

temperatures atomic radicals are prevalent and more 

likely lead to the breakdown of compounds (Taylor 

et al., 1990). Naturally occurring organic matter is 

likely to play a significant role in reaction rates and 

products formed in free radical reactions occurring in 

the subsurface, but natural organic matter (particularly 

humic substances) can be both a source (radical initiator) 

and sink (inhibitor, radical termination step) for free 

radicals. 

Steam flushing and electrical resistive heating are 

expected to heat TCE contaminated subsurface regions 

to temperatures between 70 to 120°C. Based on the 

results for the ampule experiments, the rate of thermally 

induced TCE degradation in the 70 to 120°C range could 

be significant depending on the mineral species present 

in the soil (e.g., goethite) and the anion concentration 
5

of the soil water (e.g., HS-). However, in situ changes 

in the phase distribution of TCE as the temperature is 

increased must be considered. Prior to heating, the 

contaminant (i.e., TCE) will be distributed between the 

organic liquid (NAPL) (if present), aqueous, solid, and 

gas phases. As the temperature increases, the aqueous 

solubility of TCE-NAPL has been shown to increase, 

which is likely to result in somewhat higher groundwater 

concentrations. However, gas-phase concentration of 

TCE would be expected to increase substantially due to 

the increase in vapor pressure and Henry’s law constant 

(Heron et al., 1998). In addition, the gas-phase content 

of a soil will increase as water evaporates, increasing 

the fraction of contaminant mass in the gas-phase. The 

application of a vacuum to the thermally-treated zone is 

used to enhance the removal of gas-phase constituents 

from the subsurface, but requires continuity of gas flow 

pathways to be effective. 

Although in some steam injection systems air is 

injected with steam to enhance the movement of vapor 

phase contaminants to recovery wells or in an effort 

to increase oxidation reactions, many contaminated 

subsurface environments, such as those found at Cape 

Canaveral (Interagency DNAPL Consortium, 2002) 

or Fort Lewis’s East Gate Disposal Yard (Truex et. 

al, 2007) appear to have reductive conditions rather 

than oxidative conditions. This may be advantageous, 

because despite the known recalcitrance of TCE under 

oxidative conditions, laboratory experiments on the 

abiotic degradation of TCE have shown reduction may 

occur under some anaerobic conditions. Bulter and 

Hayes (2001) found TCE transformation to occur with 

freshly prepared iron sulfide, but not with an ‘aged’ iron 

sulfide with a slightly more crystalline structure. Su and 

Puls (1999) detected TCE degradation with several types 

of zero valent iron; however, the reaction rate constant 

and activation energy varied significantly. Nevertheless, 

at least a one order-of-magnitude increase in reaction 

rate was found with each of the zero valent irons as 

the temperature was increased from 10 to 55°C. This 

process could contribute to TCE degradation in some 

ERH remediation systems where iron is used as backfill 

around electrodes.

During thermal conductive heating three broad 

temperature regimes can be envisioned to emanate 

radially from the heater wells: a 700 to 900°C region 

located in the immediate vicinity of and within the heater 

well, a 500 to 700°C region within a 1 to 3 foot radius 

of the heater well, and a 100 to 250°C region located 10 

to 20 feet from or between heater wells. Temperatures 

at the heating wells for thermal conductive heating are 

often in the range that can generate radicals, thus it may 

be possible to form free radicals in these systems in the 

immediate area around the heater wells. Some of the 

free radicals formed could react with naturally occurring 

organic matter rather than TCE, forming unknown 

products, and effectively quenching the free radical 

chain reaction. Thus, the amount of TCE transformed 

during actual remediation may be less than what was 

found in laboratory experiments. Based on the results 

of the quartz tube experiments, TCE is expected to be 

transformed at temperature above 400°C into other 

chlorinated hydrocarbons, and if sufficient oxygen is 

present, into CO and CO2

. Carbon monoxide (CO) and 

CO2 were only detected when oxygen was present, while 

no CO or CO2 was detected in experiments completed 

without oxygen. Phosgene (COCl2), a toxic gas, will 

also form with oxygen present. Phosgene is a gas at 

ambient temperature; thus, it would be recovered by 

the vacuum extraction system. Phosgene is relatively 

stable in incineration environments (Taylor et al., 1990), 

and thus may pass through the reaction chamber of a 

thermal oxidizer and into the scrubber, where it readily 

hydrolyzes to nontoxic products with water and thus 

would be anticipated to be removed (Haag et al., 1996). 

The more volatile chlorinated-hydrocarbon degradation 

products (e.g., chloroform, carbon tetrachloride) can 

be recovered by a properly designed and operated 

vacuum extraction system. Less volatile degradation 

products such as hexachlorobenzene are also likely to 

be sufficiently vaporized to be recovered in the vapor 

extraction system at the temperatures commonly used 

in these systems, although some mass may condense or 

be sorbed by soil particles. Chlorinated organic acids 

such as dichloroacetic and trichloroacetic acid may 

also be formed in the subsurface, although their yields 

would be expected to be only a very small percentage 

of the TCE (less than 0.1% combined). These organic 

acids are water soluble (trichloroacetic acid is a solid 

at ambient temperatures), with low vapor pressures and 

moderate boiling points (194 and 197°C, respectively; 

Verschueren, 2001). A small fraction of their mass 

may be recovered by a gas-phase vacuum extraction 

system, while mass remaining in the water phase could 

hydrolyze in the heated water (see Table 2.6).

The complete transformation of TCE to CO2

, CO, 

hydrocloric acid (HCl) and water, without the formation 

of chlorinated degradation products, has been shown 

to require temperatures on the order of 900 to 1,000°C 

(Chang and Senkan, 1989; Werner and Cool, 2000). 

Since the heater wells normally reach temperatures of 

up to 800°C, a fraction of the TCE contaminant mass 

may undergo complete oxidation to nontoxic products 

within the heater wells prior to extraction to the above 

ground treatment system. In the lower temperature 

zones outside of the heater wells, the formation of 

higher molecular weight chlorinated organic compounds 

will be favored if high concentrations of chlorinated 

chemicals are present, and some of these, such as 

tetrachloroethylene and hexachlorobenzene, are more 
6

difficult to degrade than TCE (Dilling et al., 1975; 

Taylor et al., 1990). Thus, a robust vapor extraction 

system must be employed as well as an off-gas treatment 

system to ensure destruction or removal of chlorinated 

hydrocarbons that may exist in the effluent gas stream. 

Clearly, the experimental results presented herein 

represent only a first step toward understanding TCE 

chemical reactivity and reaction product formation 

during thermal treatment. Additional experimentation, 

both at the laboratory and field scale, is recommended to 

further elucidate TCE reaction pathways and rates, and 

to more accurately represent the complexities inherent in 

natural subsurface materials and field-scale application 

of thermal treatment technologies. 

1.5 Report Organization

Following this project summary (Chapter 1), background 

information (Chapter 2) related to the stability of TCE in 

heated systems is presented, followed by a description 

of operational conditions for steam flushing, thermal 

conductive heating, and electrical resistive heating. 

Experimental methods and results for the quartz tube 

studies are presented in Chapter 3, followed by the 

experimental methods and results for the ampule studies 

in Chapter 4, with cited references listed in Chapter 5. 

Appendix A describes detailed experimental methods 

used for the quartz tube reactor studies, Appendix B 

contains dissolved oxygen data from some of the ampule 

experiments, and Appendix C contains rate constants 

calculated for TCE degradation assuming a first order 

reaction rate and a description of the methods used 

to compute these rates from the ampule experimental 

results. 
7

2.0

Background Information

Trichloroethylene (TCE) is a contaminant commonly 

found in the subsurface at industrial and military 

installations in the United States and abroad. Improper 

disposal or release of liquid or “neat” TCE to the 

environment frequently results in the presence of 

a separate organic phase contaminant, commonly 

referred to as a non-aqueous phase liquid (NAPL), 

that can become entrapped within soil pore spaces as 

individual droplets and ganglia (Hunt et al., 1988). 

These entrapped NAPL droplets and ganglia are 

immobile under normal groundwater flow regimes. 

If sufficient NAPL is released to the subsurface, the 

organic liquid is likely to accumulate in “pools” above 

layers of lower permeability media. In general, NAPLs 

will not enter a lower permeability layer unless the 

entry pressure is exceeded, that is, the pressure exerted 

by a continuous NAPL pool must be sufficient to 

displace water from the pore space. The presence of 

TCE-NAPL in the subsurface often represents a longterm source of contamination as TCE slowly dissolves 

into the groundwater flowing through the “source 

zone.” Pumping of groundwater and soil gas from 

the subsurface followed by above ground treatment is 

often used to control the migration of dissolved-phase 

TCE plumes, and in some limited cases, to restore the 

subsurface. Increasing the subsurface temperature has 

been shown to increase the transfer of TCE mass from 

the NAPL to the water and gas phases, which increases 

the rate and amount of TCE that can be removed from 

the subsurface by extraction methods. Thus, subsurface 

heating can be employed to dramatically enhance TCE 

mass recovery (Davis, 1997) and holds the potential to 

transform TCE into nontoxic products via thermallyinduced chemical reactions (e.g., Knauss et al., 1999). 

The following sections describe relevant physical and 

chemical properties of TCE, selected results from 

experiments on the thermal stability of TCE reported in 

the literature, and the operational conditions associated 

with commonly used in-situ thermal treatment 

technologies. 

2.1 Trichloroethylene Properties

TCE is an important solvent used for cleaning metal 

parts and electrical components, and in the manufacture 

of hydrofluorocarbon refrigerants (HSIA, 2001). TCE 

is a colorless, sweet smelling, volatile liquid that is 

acutely toxic to humans when ingested (Mertens, 1999). 

Even though TCE is referred to as a non-flammable 

liquid, it should be kept away from open flames and 

metal surfaces with temperatures greater than 176°C 

due to the flammability of its vapors (Mertens, 1999). 

If TCE is exposed to a temperature greater than 420°C 

when oxygen is present, it will spontaneously ignite 

(Mallinckrodt and Baker, 2003a). 

Even though TCE has low solubility in water, TCE 

is one of the most commonly found groundwater 

contaminants in the United States, and is present at 

305 of the 1,236 National Priority List (NPL) sites 

(U.S. EPA, 2003). While the long-term health effects of 

drinking water contaminated with small amounts of TCE 

are not yet known, the U.S. EPA has set the maximum 

contaminant level (MCL) for drinking water at 5 μg/L 

(ATSDR, 1997). If TCE is found in groundwater 

at concentrations greater than 5 μg/L, treatment or 

control of the groundwater is usually required. Selected 

properties of TCE and water as a function of temperature 

are given in Tables 2.1 and 2.2. 

Table 2.1 Selected Properties of TCE (McNeill, 

1978)

Molecular Weight

(g/mol) 131.39

Melting Point (°C) -87.1

Boiling Point (°C) 86.7

Critical Temperature 

(°C) 271.0

Critical Pressure 

(MPa) 5.02

Koc†

 (mL/g) 160

Log Kow† 2.38

Properties at 

Temperature (°C) 20 60 100

TCE Explosive Limit 

in Air (Vol%) 8 to 10.5 no data 8 to 52

TCE Viscosity

(cP = 100×g/cm s) 0.58 0.42 no data

TCE Liquid Density 

(g/mL) 1.465 no 

data 1.325

Solubility in Water 

(mg/L) 1,068 1,219 no data

Henry’s Law 

Constant* 

(dimensionless)

0.3 1.5 5.3 

(95°C)

Vapor Pressure of 

TCE (MPa) 0.008 0.042 0.148

MPa = 1.00 bar = 1.02 atm

* Heron et al., 1998; † LaGrega et al., 2001
8

Table 2.2 Selected Properties of Water (Gebhart 

et al., 1988)

Properties at 

Temperature (°C) 20 60 100

Water Viscosity

(cP = 100×g/cm s) 0.99 0.46 0.28

Water Density (g/mL) 0.998 0.983 0.958

Water Solubility in TCE 

(mg/L) 330 1,090 no data

Vapor Pressure of Water 

(MPa) 0.002 0.020 0.101

MPa = 1.00 bar = 1.02 atm

2.2 TCE-Water Phase Behavior

Boiling of a water and TCE-NAPL mixture occurs 

at 73.4°C, which is below the boiling point of either 

water (100°C) or TCE-NAPL (86.7°C). Boiling occurs 

when the vapor pressure of a liquid mixture exceeds 

the surrounding gas phase pressure. For a mixture 

consisting of two immiscible liquids, such as water 

and TCE-NAPL, the total vapor pressure is equal to 

the sum of the vapor pressures of each pure constituent 

(Dalton’s Law: Pt = Po

water + PoTCE), and the mixture will 

boil when the total vapor pressure is equal to the local 

gas phase pressure (Pt = Patm) (Atkins, 1998). As long 

as TCE-NAPL is present, the mixture will boil at the 

lower temperature (73.4°C), and since TCE-NAPL has 

a greater vapor pressure than water, the composition of 

the boiling vapor is 93% TCE and 7% water by weight 

(Horvath, 1982). This phenomenon serves as the basis 

for steam distillation, in which TCE is separated from 

water at temperatures below its normal (pure) boiling 

point. 

The diagram in Figure 2.1 shows the pure phase 

vapor pressures calculated using the Antoine equation 

[Po

 = 10(A-(B/(T+C))] and parameters measured for TCENAPL (McDonald, 1944) and water (Bridgeman and 

Aldrich, 1964) along with the total vapor pressure which 

is the sum of the pure phase vapor-pressures. Figure 2.1 

also contains the weight percent of TCE based on the 

fraction of TCE vapor pressure relative to the total vapor 

pressure. Boiling of the TCE-NAPL and water mixture 

would occur at 73.4°C, assuming that the surrounding 

gas phase pressure was at 1 bar, with 93% of the vapor 

consisting of TCE by weight.

Figure 2.1 Water and TCE-NAPL vapor pressure as a 

function of solution temperature at 1 bar or 

1.02 atm of total gas phase pressure.

2.3 Selected Experiments on the 

Stability of TCE

The following sections provide information on the 

methods and results of laboratory experiments performed 

to investigate the thermal stability of TCE. The first four 

sections (2.3.1 through 2.3.4) focus on the stability of 

TCE-NAPL and the products formed after exposing TCE 

to oxygen and water. The subsequent two sections (2.3.5 

and 2.3.6) address the stability of gas-phase TCE and 

the products formed after introducing TCE into heated 

quartz tubes along with the importance of the chlorine 

to hydrogen ratio on the distribution of degradation 

products.

2.3.1 TCE-NAPL Degradation by Oxygen

The stability of TCE-NAPL in industrial process 

equipment has been a research topic since at least 1932. 

Experiments were initially performed to determine the 

conditions that caused the degradation of TCE and the 

formation of corrosive degradation products, which 

could damage industrial equipment. Carlisle and Levine 

(1932) studied TCE degradation by placing TCE-NAPL 

and pure oxygen, or air, into 85 mL glass vials and 

heating the sealed vials to a temperature between 24 and 

130°C. The vials were opened after 24 hours and 25 mL 

of the NAPL contents were equilibrated with 25 mL 

of water to determine the amount of chloride that had 

formed. The water contained phenolphthalein indicator 

and the resulting solution was titrated with a 0.01 N 

sodium hydroxide (NaOH) solution until a pink color 

appeared. The amount of NaOH required to neutralize 

the indicator solution was reported as the amount of free 

acid formed within the TCE-NAPL, and represented the 

water soluble TCE degradation products. No analysis of 

gas-phase constituents present in the head space of glass 

vials was performed. 
9

In the presence of pure oxygen, the amount of TCE 

degraded increased with increasing temperature 

(Table 2.3) as indicated by the increase in the amount of 

NaOH required to titrate the phenolphthalein indicator 

to pink. The minimum amount of TCE degraded in 

24 hours was 0.001% (mole basis) at 24°C, while 

the maximum of 2.52% (mole basis) occurred at 

a temperature of 130°C. The maximum first-order 

half-life for the disappearance of TCE with pure oxygen 

present was 475 years at 24°C, and 99 days at 130°C 

based on the %TCE degraded in 24 hours. A lower 

TCE degradation rate was observed with air present, 

presumably due to the decrease in oxygen content. The 

trend of increasing TCE degradation with temperature, 

as observed with pure oxygen, was not observed above 

90°C with air present. Carlisle and Levine (1932) 

suggested that a shift to non-acid degradation products 

occurred above 90°C when air was present since the 

acid titration analysis method was only sensitive to 

hydronium ions. 

Mugdan and Wimmer (1934) quantified the degradation 

products in the gas phase and NAPL after passing 

oxygen gas through TCE-NAPL heated to temperatures 

between 50 and 70°C. The gas-phase products included 

hydrochloric acid (HCl), carbon monoxide (CO), and 

phosgene (COCl2), while the only product found in 

the NAPL was dichloroacetyl chloride (Cl2HC2OCl). 

After passing oxygen gas through TCE-NAPL heated 

to 60°C, Kirkbride (1942) observed the formation of 

additional products in the NAPL, including TCE epoxide 

(Cl2COCHCl) and hexachlorobutene (C4H2Cl6).

McKinney et al. (1955) found that TCE-NAPL was 

completely degraded to 15% gas-phase products and 

85% NAPL products, on a molar basis, after passing 

oxygen through TCE-NAPL at 70°C. The gas-phase 

products included HCl, CO, and phosgene (COCl2), 

while the NAPL reaction product was water-soluble, had 

a density of 1.545 g/mL at 20°C, and was a nearly equal 

mixture of dichloroacetyl chloride (Cl2HC2OCl) and 

TCE epoxide (Cl2COCHCl) (Table 2.4). McKinney et al. 

(1955) completed experiments using 1) TCE stabilized 

with triethylamine, 2) unstabilized TCE, and 3) TCE 

that had been used for extracting oil from soybeans. The 

triethylamine stabilizer was removed from TCE-NAPL 

by the soybean oil extraction process meaning that this 

used, or waste TCE, which was historically released 

into the environment, was no longer stabilized against 

reacting with oxygen. The complete degradation of 

TCE-NAPL was reported after 193 hours of bubbling 

oxygen through TCE-NAPL at 70°C. However, the 

Table 2.3 Selected TCE Stability Test Results 24 hour test (Carlisle and Levine, 1932)

Temperature (°C) 24 40 50 70 90 110 130

TCE NAPL and Pure Oxygen (100% O2

)

mL of NaOH added to 25 

mL of water 0.4 416 440 500 520 590 700

H+

 formed (mole)* 4.0x10-6 4.2 x10-3 4.4 x10-3 5.0 x10-3 5.2 x10-3 5.9 x10-3 7.0 x10-3

%TCE degraded (mole 

basis)† 0.00 1.50 1.59 1.80 1.87 2.13 2.52

TCE NAPL and Air (21% O2

, 79% N2)

mL of NaOH added to 25 

mL of water 2.2 -- 2.5 192 191 119 130

H+

 formed (mole)* 2.2x10-5 2.5 x10-5 1.9 x10-3 1.9 x10-3 1.2 x10-3 1.3 x10-3

%TCE degraded (mole 

basis)† 0.01 0.01 0.69 0.69 0.43 0.47

* Calculated based on the results of Carlisle and Levine assuming 1 mole of OH- was equal to 1 mole H+.

† Assuming one Cl atom lost per TCE molecule (HC2Cl2 hydrolysis product).
10

reaction rate was determined after addition of benzoyl 

peroxide to TCE, where benzoyl peroxide is known to 

generate peroxyl radical initiator compounds above 70°C 

(Fossey et al., 1995). McKinney et al. (1955) also found 

that partially-oxidized TCE influenced the rate of TCE 

degradation. 

Table 2.4 Oxygen and TCE Gas-Phase and NAPL 

Degradation Products (McKinney et al., 

1955)

Reaction Product Phase

Approximate 

Amount 

(% mole basis)

hydrochloric acid (HCl) gas 5

carbon monoxide (CO) gas 5

phosgene (COCl2

) gas 5

dichloroacetyl chloride 

(Cl2

HC2OCl) NAPL 47

TCE epoxide 

(Cl2

COCHCl) NAPL 38

The reaction between oxygen and TCE-NAPL is 

thought to involve a radical chain reaction mechanism 

(Kaberdin and Potkin, 1994). Kucher et al. (1990) used 

azo-bis-isobutyronitrile, a known temperature induced 

radical chain initiator, to study the oxidation of TCE 

in acetonitrile at 75°C. The reaction products included 

TCE epoxide (Cl2

COCHCl) and dichloroacetyl chloride 

(Cl2HC2OCl) in a ratio of 3:1 after 1 hour of reaction 

time. 

In summary, exposing TCE-NAPL to oxygen in the 

temperature range from 50 to 75°C, in the absence of 

water, resulted in the formation of gas-phase and NAPL 

reaction products that were thought to result from a 

radical chain reaction mechanism. The next section 

covers past experiments performed to examine the 

compounds formed after exposing the TCE-NAPL and 

oxygen degradation products to water.

2.3.2 Hydrolysis of TCE-NAPL Degradation 

Products

Placing the TCE-NAPL degradation products 

dichloroacetyl chloride and TCE epoxide in water 

at 27 and 75°C resulted in the formation of gas- and 

aqueous-phase products (Table 2.5). The gas-phase 

products included CO and CO2, and the aqueous-phase 

products included chloride ions, dicholoroacetic acid 

(HCl2

C2OOH) along with oxoacetic (HOC2OOH) 

and formic acid (HCOOH). The temperature of the 

reaction (27 or 75°C) appeared to have little effect on 

the distribution of hydrolysis products. Similar reaction 

product distributions were also noted in water that 

contained NaOH at 10 and 30°C. McKinney et al. (1955) 

speculated that dichloroacetic acid (DCAA) was the 

hydrolysis product of dichloroacetyl chloride, while 

the non-chlorinate organic acids were formed from the 

hydrolysis of TCE epoxide.

Table 2.5 Hydrolysis of TCE NAPL Degradation 

Products (McKinney et al., 1955)

Reactor Temperature (°C) 27 75

Reaction Product Phase

moles formed per 

147.4 g of liquid 

reaction products

carbon monoxide 

(CO) gas 0.087 0.100

carbon dioxide (CO2

) gas 0.005 na

chloride ion (Cl-

) aqueous 1.410 1.200

dichloroacetic acid 

(HCl2

C2OOH) aqueous 0.740 0.850

oxoacetic acid 

(HOC2

OOH) aqueous 0.180 0.057

formic acid 

(HCOOH) aqueous 0.033 0.060

na – not analyzed

The degradation of TCE epoxide was determined in a 

separate experiment by Kline et al. (1978) that involved 

injecting TCE epoxide into a solution of acetone 

(0.2 mL) which contained 1.5 mL of 0.5 M sodium 

phosphate buffer. Dichloroacetic acid (DCAA) was 

the only reported degradation product after 4 minutes 

at 37°C. Cai and Guengerich (1999) prepared TCE 

epoxide from TCE using m-chloroperbenzoic acid, a 

known radical initiator compound, and then placed TCE 

epoxide in water at 0°C, and the degradation products 

were measured as a function of pH. The products formed 

included CO in the gas phase, formic acid, oxoacetic 

acid, and DCAA in the aqueous phase over a pH range 

from 0 to 14. The amount of CO and formic acid 

formed increased with pH, the amount of oxoacetic acid 

decreased with pH, and the amount of DCAA formed 

was independent of pH. 

Based on the work described above, TCE can be 

transformed into dichloroacetyl chloride and TCE 

epoxide after exposure to oxygen with TCE epoxide, 

and potentially dichloroacetyl chloride, transformed 

into DCAA upon exposure to water. Thus, DCAA is 

one of the TCE degradation products anticipated to 
11

form during the thermal treatment of TCE contaminated 

subsurface environments. DCAA is a colorless liquid at 

room temperature (25°C) with a density of 1.57 g/mL, 

a melting point of between 9 and 11°C, and a boiling 

point of 197°C (Mallinckrodt and Baker, 2003b). DCAA 

has been classified as a probable human carcinogen with 

the maximum contaminant level goal of 0 ug/L (U.S. 

EPA, 1998). DCAA is soluble in water with a practical 

drinking water treatment level of 6 ug/L. 

Haag et al. (1996) measured the rate of DCAA 

disappearance from water heated to between 88 and 

180°C as a function of NaOH concentration. The authors 

obtained a half-life of 1.71 days for the hydrolysis of 

DCAA at 103°C and pH 7, and a half-life of 1.27 hours 

with 0.96 M of NaOH present. Prager et al. (2001) 

showed that DCAA was hydrolyzed to chloride and 

oxoacetic acid in heated water and that a temperature of 

180°C was required to achieve complete degradation of 

DCAA in 8 minutes. 

The expected half-life for DCAA in water at pH 7 

calculated from the Arrhenius parameters determined 

by Prager et al. (2001) are given in Table 2.6. Thus 

DCAA is expected to accumulate in water during the 

degradation of TCE at temperatures less that 70°C while 

DCAA is expected to be degraded into oxoacetic acid 

within a few days at temperatures greater than 90°C 

based on the half-lives given in Table 2.6.

Table 2.6 Rate of Dichloroacetic Acid (DCAA) 

Disappearance from Heated Water 

(Prager et al., 2001)

Temperature (°C)

First Order 

Disappearance 

Rate (1/day)

Half-Life 

(day)

60 9.3x10-4 742

70 4.8x10-3 143

80 2.3x10-2 30.5

90 9.8x10-2 7.0

100 39.3x10-2 1.8

120 5.1 0.14

2.3.3 Degradation of TCE Dissolved in Water at 

Elevated Temperatures

Carlisle and Levine (1932) placed approximately 25 mL 

of TCE-NAPL and 25 mL of water into 80 mL glass 

vials with nitrogen gas in the headspace to determine if 

TCE was degraded by water at elevated temperatures. 

The vials were sealed and heated to fixed temperatures 

between 50 and 150°C for 24 hours. After cooling the 

vials to room temperature, the acid content of the water, 

an indicator of TCE degradation via the formation of 

acidic compounds, was determined by titrating with 

a 0.01 M NaOH solution until the phenolphthalein 

indicator turned pink. Less than 0.35% by weight of the 

TCE-NAPL was lost assuming that one chlorine atom 

was removed per TCE molecule, which led Carlisle and 

Levine (1932) to conclude that TCE does not readily 

hydrolyze in water. The observed reduction in TCE 

content was attributed to the small amount of oxygen 

within the vials at the beginning of each experiment. 

Assuming that oxygen-saturated water (8 mg/L O2) 

was present at the start of each experiment, then 

approximately 6.25x10-5 moles of oxygen were available 

to react with TCE. Although this is a sufficient amount 

of oxygen to account for the acid formed in vials heated 

to 50°C, it is insufficient by 2 to 15 times to account 

for the acid formed at temperatures greater than 50°C. 

Carlisle and Levine (1932) stated that the thermal 

decomposition of TCE at higher temperatures had 

probably occurred, although no reaction mechanism or 

reaction products were proposed or measured.

Dilling et al. (1975) completed a year-long experiment 

at ambient conditions to measure the persistence of TCE 

dissolved in water. Oxygen-saturated water (8 mg/L 

O2) containing 1.0 mg/L of TCE was loaded into each 

of three ice-cooled Pyrex tubes so that approximately 

one-half of the tube volume was filled with solution 

(i.e., gas phase was present) and then the tubes were 

flame sealed. The sealed tubes were placed in a dark 

container and stored at approximately 25°C. One tube 

was destructively sampled after 6 months (182 days), 

and the remaining two tubes were destructively sampled 

after one year (365 days). Only aqueous samples 

were collected and they were only analyzed for TCE 

content. The reported first-order disappearance rate was 

2.1x10-3 day-1, corresponding to a first-order half-life 

of 326 days at 25°C. In a separate experiment, Pearson 

and McConnell (1975) measured the persistence of 

TCE in water using sealed glass bottles and reported 

an estimated half-life of 2.5 years (912 days) for the 

disappearance of TCE from water at 25°C.

Jeffers and Wolfe (1996) studied the disappearance 

of TCE dissolved in water by placing approximately 

0.3 mL of TCE contaminated water in glass tubes 

and flame sealing both ends to create a sealed bulb 

with approximately 0.02 mL of headspace. The TCE 

contaminated water was prepared by mixing water 

with TCE-NAPL for 2 minutes at room temperature to 

yield an initial concentration estimated to be 10% of the 

solubility limit for TCE (i.e., 110 mg/L for TCE) (Jeffers 

et al., 1989). Experiments were completed in water with 

0.01 M HCl adjusted to pH 7 (Jeffers and Wolfe, 1996) 

and in alkaline water containing from 0.1 to 0.001 M 

NaOH (Jeffers et al., 1989; Jeffers and Wolfe, 1996). 
12

The water used was deionized, distilled, and boiled prior 

to use, which probably resulted in low dissolved oxygen 

content, however, no dissolved oxygen measurements 

were reported. The bulbs were heated to temperatures 

between 60 and 190°C for an unspecified period of time. 

The bulbs were then cooled to room temperature and 

the liquid content was analyzed by gas chromatography 

for TCE content only. The only data reported were the 

activation energy (120 kJ/mol) and pre-exponential 

factor (5.0×109 1/minute) for the Arrhenius equation 

[k = A×exp(-Ea/RT)] which was used to estimate a 

first-order rate constant of 4.5×10-12 (1/mintues) along 

with an estimated half-life of greater than 100,000 years 

for the disappearance of TCE from water at ambient 

temperature (25°C). The calculated first-order rate 

constant at 90°C was 2.7×10-8 (1/mintues) with a halflife of approximately 49 years based on the Arrhenius 

parameters reported by Jeffers and Wolfe (1996).

Gu and Siegrist (1997) increased the rate of TCE 

disappearance from water by adding sodium hydroxide 

(NaOH). They reported the complete disappearance of 

TCE after 300 minutes from an aqueous solution that 

had an initial TCE concentration of 630 mg/L after 

amending with 2 M of NaOH and heating to greater than 

60°C. The primary reaction products included chloride 

and glycolic acid (HOCH2COOH), with intermediate 

products including DCAA and monochloroacetic acid 

(H2ClC2OOH). Nearly all the chlorine atoms originally 

present as TCE were recovered as chloride in the reactor 

effluent at 80°C, however, only 60% of the carbon 

atoms introduced were recovered as organic acids. Gu 

and Siegrist (1997) suggest that the unaccounted for 

carbon may have been lost to gas phase degradation 

products (i.e., CO2) that were not captured for analysis, 

however, the alkaline solution would be expected to 

serve as a trap for CO2. The authors also acknowledged 

that the organic-acid detection limit (50 mg/L) for the 

high pressure liquid chromatography (HPLC) analysis 

method made it difficult to account for all the organic 

acid degradation products.

Atwater et al. (1996) demonstrated the removal of TCE 

from water using a flow-through reactor that contained 

ruthenium and platinum on activated carbon granular 

solids heated to between 90 and 120°C. The water 

contained TCE at 15 mg/L and dissolved oxygen in 

stoichiometric excess. When operated at 120°C, the 

reactor was capable of removing 91% of the influent 

TCE with a residence time of 12 seconds. However, the 

appearance of chloroform (CHCl3

) in the reactor effluent 

led Atwater et al. (1996) to increase the residence time to 

5 minutes in order to achieve the complete degradation 

of TCE without forming the unwanted chloroform 

degradation product.

In summary, TCE dissolved in water is degraded with 

a half-life ranging from approximately 1 year (Dilling 

et al., 1975) to greater than 100,000 years (Jeffers and 

Wolfe, 1996) at room temperature (25°C). The rate of 

TCE degradation can be increased by heating with the 

half-life reduced to 49 years at 90°C based on results by 

Jeffers and Wolfe (1996). The rate of TCE degradation 

can be further increased by adding sodium hydroxide or 

solid catalysts with the completed degradation of TCE 

after 300 minutes at 60°C when amended with 2 M 

NaOH and after 5 minutes at 120°C with the ruthenium 

catalyst.

2.3.4 Thermal Degradation of TCE in a WaterFilled Reactor

Knauss et al. (1999) measured the disappearance of TCE 

from a water-filled reactor in an effort to demonstrate 

that dissolved-phase TCE could be degraded in-situ 

during thermal treatment of TCE contaminated aquifers. 

The reactor consisted of a gold-walled cylinder with 

a wall thickness of 0.01 inch and an outside diameter 

of 1.75 inches by 7 inches long for a total volume of 

approximately 250 mL (Seyfried et al., 1979). The 

gold cylinder was sealed with a titanium head piece 

that contained a single gold capillary tube for sample 

collection. The gold cylinder and titanium seal were held 

within a steel housing that was pressurized to between 

0.1 to 3.4 mPa (1 to 340 bar) and heated to between 

70 and 100°C. Pressurizing the gold cylinder caused 

all reaction products to remain dissolved in water and 

allowed small liquid samples to be forced from the 

reactor through the gold capillary tube. Seyfried et al. 

(1987) recommended rinsing the titanium head with 

dilute HCl solution followed by concentrated nitric acid 

(HNO3

) solution to remove any potential sources of 

contamination. They also recommended heat treating the 

titanium head at 300°C in air to develop an inert surface 

oxide layer. For example, McCollom and Seewald 

(2003) reported heating their titanium fittings in air 

for 24 hours at 400°C prior to use in experiments on 

the hydrothermal stability of formic acid. Knauss et al. 

(1999) did not discuss procedures used to prepare their 

reactor. 

Knauss et al. (1999) reported results obtained for nine 

separate experimental runs (Table 2.7). Each experiment 

was completed with air-saturated water (8 mg/L O2

) that 

contained 150 mg/L of phosphate buffer (pH 7.2). Water 

solutions with initial TCE concentrations between 0.3 

and 21 mg/L were placed into the gold-walled reactor 

with no headspace and heated to a fixed temperature 

between 70 and 100°C at a constant pressure of 1 MPa 

(10 bar) for an extended time period. Aqueous samples 

were collected from the reactor periodically through 

the gold capillary tube into 1 mL gas tight syringes. 

Analysis for inorganic ions, including chloride, was 

completed using a HPLC (HP 1090) connected to a 
13

conductivity detector. The aqueous phase TCE content 

was determined using purge and trap separation with 

analysis by a gas chromatograph connected to a flame 

ionization detector. 

Knauss et al. (1999) reported that chloride, hydronum 

ions (H+), and dissolved CO2 were the only degradation 

products detected during preliminary experiments 

designed to look for intermediates. However, no analysis 

of the experimental results was provided to demonstrate 

that the initial amount of TCE in the reactor was 

accounted for by the degradation products detected at the 

end of the experiment (i.e., mass balance). Based on the 

data presented by Knauss et al. (1999) for the amount of 

chloride and CO2 detected, the carbon and chloride mass 

balances were calculated and are provided in Table 2.7. 

The final amount of chloride was within 11% of the 

initial amount introduced as TCE (moles Cl- = 3×moles 

TCE) for experiments TCE-35 through -41 but was 

greater than the initial amount for experiments TCE-42 

through -53. For example, the amount of chloride 

reported in experiment TCE-42 was 244% of the initial 

amount of TCE present in the reactor. The amount of 

chlorine formed during experiments TCE-51 and -53 

must have been reported incorrectly since these values 

are orders-of-magnitude in excess of the amount of 

chlorine initially present in the reactor as TCE. 

There was greater variability in the carbon mass balance 

shown in Table 2.7 as compared to the chloride balance, 

which may have been due to the difficulty in measuring 

dissolved phase CO2

 at these low concentrations. Knauss 

et al. (1999) determined the amount of dissolved total 

CO2 formed, stated as the sum of carbonic acid (H2CO3), 

bicarbonate (HCO3

-

), and carbonate (CO3

-2), using 

direct infrared (IR) spectroscopy. No description of the 

IR analysis method (e.g., sorption bands used or scan 

time) was provided, although the reported detection 

limit was 0.068 mM. Falk and Miller (1992) studied 

fourier-transform infrared (FTIR) spectroscopy as an 

analytical method for determining the aqueous phase 

concentration of total CO2 using the co-added signals 

from 400 interferograms (5-minute scan time) with 4 

cm-1 band resolution. Falk and Miller (1992) concluded 

that this was not a feasible analysis technique for HCO3

-

or CO3

-2 because the adsorption bands (1385 and 1360 

cm-1, respectively) overlapped and were within the water 

vapor region. Analysis of dissolved CO2 was found to 

be feasible at the 2342.9 cm-1 adsorption band, with an 

estimated detection limit of 0.4 mM. Falk and Miller 

(1992) stated that increasing the scan time could have 

decreased the detection limit. Burt and Rau (1994) 

reported a dissolved CO2

 detection limit of 0.24 mM. 

Hence, the detection limit reported by Knauss et al. 

(1999) is 3.5 to 6 times lower than those reported by 

Burt and Rau (1994) and Falk and Miller (1992). The 

ratio of the CO2 found to CO2 (as TCE) in the feed, 

as reported in Table 2.7, was consistently greater than 

one, which may indicate that the IR analysis method 

employed by Knauss et al. (1999) was not sensitive to 

the low CO2 concentrations because the signal to noise 

ratio was too small to accurately resolve the 2342.9 cm-1

adsorption band.

Knauss et al. (1999) provided the following expression 

for the rate of TCE disappearance based on the 

experiments completed at 90°C when dissolved oxygen 

Table 2.7 Summary of Knauss et al. (1999) Experimental Results

Experiment Duration 

(days)

Temperature 

(°C)

Initial TCE 

(mg/L)

Final Cl-

(mM)

Cl found/ 

Cl feed (%)

Final CO2

(mM)

CO2 found/ 

CO2 feed (%)

TCE-35 6.11 100 5.96 0.151 111 0.157 173

TCE-37 19.2 81 5.87 0.114 100 0.116 152

TCE-39 11.1 90 21.30 0.400 92 0.310 107

TCE-40 43.3 70 5.50 0.145 118 0.182 224

TCE-41 4.24 90 1.45 0.035 105 0.070 315

TCE-42 7.28 90 2.87 0.016 244 N/A N/A

TCE-43 2.23 90 1.62 0.049 143 0.056 246

TCE-51 7.2 90 6.09 5.563* 4012 0.120 130

TCE-53 3.31 90 5.15 3.809* 3517 0.104 144

* Data presented by Knauss et al. (1999) Table 1, but appears to be incorrectly reported. 

Reported analytical detection limits: TCE = 0.0002 mM, Cl- = 0.003 mM, CO2 = 0.068 mM.
14

was in excess:

7 1 0.85 0.03 5.77 1.06 10 TCE

o

dC s C

dt

−− ± =− ± × (2.1)

where Co is the initial TCE concentration (mol/kg ~ 

molality). Although Equation 2.1 fit the experimental 

data, analyzing the data reported by Knauss et al. (1999) 

using traditional kinetic reaction modeling techniques 

provides additional detail regarding the mechanism 

of TCE disappearance. Figure 2.2 contains the 

concentration of TCE with time, as measured by Knauss 

et al. (1999), for four of the experiments completed at 

90°C. Also shown in Figure 2.2 is the predicted TCE 

concentration with time assuming a zero-order reaction 

model described by:

0 0 0

TCE

TCE

dC k or C C k t

dt = − = − (2.2)

Figure 2.2 Measured concentration of TCE vs. time 

along with the zero-order reaction model 

fit.

The disappearance of TCE appears to follow the zeroorder reaction model over the initial two days, however, 

the rate of TCE disappearance increased relative to 

the zero-order rate after two days for Experiment 

TCE-39 and decreased relative to the zero-order rate for 

Experiments TCE-51, -41, and -43.

Figure 2.3 contains the same data shown in Figure 2.2 

plotted as the natural log of the TCE concentration 

normalized by the initial TCE concentration. Also 

shown in Figure 2.3 is the change in normalized TCE 

concentration as predicted according to a first-order 

reaction model described by: 

1 1

0

ln TCE TCE

TCE

dC C k C or k t

dt C

  = − = −    

(2.3)

Figure 2.3 Natural log of the measured TCE 

concentration normalized by the initial 

TCE concentration vs. time along with the 

first-order reaction model fit.

The disappearance of TCE from the gold-walled reactor 

did not follow the first-order reaction model in that the 

rate of TCE disappearance was less than predicted by 

the first-order model during the initial two days of each 

experiment followed by an increase in the rate of TCE 

disappearance relative to that predicted by the first-order 

model. The rate of TCE disappearance also appears 

to depend on the initial concentration of TCE with a 

decrease in the rate of TCE disappearance corresponding 

to an increase in the initial TCE concentration 

(Figure 2.3). 

Figure 2.4 contains the same data shown in Figures 2.2 

and 2.3 but plotted as the reciprocal of the TCE 

concentration vs. time, consistent with a second-order 

reaction model describe by:

2

2 2

0

TCE 1 1 TCE

TCE

dC k C or k t

dt C C = − = +

(2.4)

The disappearance of TCE during Experiment TCE-39 

appears to follow the second-order reaction model 

(Equation 2.4) over a period of four days but then the 

rate of TCE disappearance deviates from that predicted 

by the second-order model.

While the disappearance of TCE from the goldwalled reactor operated at 90°C followed the zeroorder reaction model over the initial two days of each 

experiment (Figure 2.2), the disappearance of TCE 

was not described by the zero-, first-, or second-order 

reaction models over the entire experimental period. 

An alternative reaction model involves a radical chain 

reaction mechanism which incorporates the following 

reaction steps:
15

Figure 2.4 Reciprocal of the measured concentration 

of TCE vs. time along with the secondorder reaction model fit.

Initiation: TCE + M* → TCE* k1* (2.5)

Peroxyl Radical: TCE* + O2 → TCE-O2* k2* (2.6)

Propagation:TCE + TCE-O2* → TCE epoxide +

dichloroacetyl chloride k3* (2.7)

The symbol M* represents some radical initiator such 

as the gold or titanium surface within the reactor or 

chlorine radicals which transfer a single electron to TCE 

and results in the formation of the TCE radical species 

(TCE*). This three step TCE disappearance mechanism 

was based on work by Kucher et al. (1990) and was used 

to fit the results for the Knauss et al. (1999) experiment 

completed at 70°C (TCE-40). The 70°C experiment 

was chosen because the rate of TCE disappearance was 

slower as compared to the 90°C experiments and thus 

the features that indicate a radical chain mechanism, 

including a delayed reaction rate during the initial three 

days (reactor heat-up was less than one day) as the 

concentration of the peroxyl radicals increased followed 

by an increase in the TCE disappearance rate between 

day 10 and 40 (Figure 2.5), were more pronounced. 

Figure 2.5 shows the concentration of TCE vs. time data 

as reported by Knauss et al. (1999), along with the best 

fit using the reaction model described by Equations 2.5 

through 2.7 determined using finite difference analysis 

with time steps of 0.1 days. The disappearance of 

TCE followed the radical chain model over the 43 day 

experimental period with the reaction rate coefficients 

for the initiation and peroxyl radical formation (k1* and 

k2*) equal to 1.62 and 1.80 mmolal-1 day-1 respectively, 

while the rate coefficient for the peroxyl radical attack 

on TCE (k3*) was equal to 132.6 mmolal-1 day-1.

The close agreement between the radical chain model 

and the measured TCE disappearance for Experiment 

TCE-40 does not necessarily validate this model. 

Figure 2.5 Measured concentration of TCE vs. time 

for Experiment TCE-40 and radical chain 

reaction model fit.

However, the radical chain model is consistent with 

two of the key observations made by Knauss et al. 

(1999), namely that the rate of TCE disappearance 

was dependent on the initial TCE concentration and 

that the rate of TCE disappearance was independent of 

the dissolved oxygen concentration as long as it was 

in excess of the initial amount of TCE present. The 

dependence on the initial TCE concentration is due to 

the slow rate of radical initiation (k1

* and k2*) compared 

to the fast rate of the peroxyl-radical TCE reaction (k3*). 

That is, the formation of peroxyl radicals is the rate 

limiting step (k2*/k3* = 0.01). 

Knauss et al. (1999) found that dissolved-phase TCE 

could be degraded in a heated reactor with CO2 and 

chloride as the only detected degradation products. 

The time for one-half of the initial amount of TCE 

to be degraded at 90°C ranged from approximately 1 

to 5 days depending on the initial TCE concentration 

(Figure 2.2). Knauss et al. (1999) reported that the rate 

of TCE disappearance from the heated reactor was best 

described using a pseudo first-order reaction model 

(Equation 2.1). Analysis of the Knauss et al. (1999) data 

provided herein suggests that a radical chain reaction 

mechanism provided the best fit for the disappearance of 

TCE over the entire experimental period.

2.3.5 Degradation of Gas-Phase TCE within 

Heated Quartz Tubes

One method of treating unwanted waste TCE is 

by feeding the waste into incinerators operated at 

temperatures greater than 1,000°C. The degradation of 

TCE and the products formed during the incineration 

process have been studied by passing gas-phase TCE 

through heated quartz tubes, trapping the effluent leaving 

the quartz tubes, and analyzing the traps to determine 

the TCE degradation products formed. The following 

section provides details of past quartz tube experimental 
16

results with the goal of anticipating the degradation 

products that might form during the high-temperature 

treatment of subsurface environments contaminated with 

TCE.

Pyrolysis is a general term used to describe organic 

chemical reactions that occur at elevated temperatures 

(Brown, 1980; Moss, 1994). Pyrolysis has also been 

used to indicate high temperature gas-phase reactions 

that occur in the absence of oxygen (Mulholland et 

al., 1992), whereas pyrolysis has been used by others 

to describe high temperature gas-phase reactions that 

occur with oxygen present (Yasuhara and Morita, 1990). 

The term pyrolysis is avoided in the following sections 

because of the ambiguity with regard to the presence of 

oxygen, instead of using this terminology, the oxygen 

content of the gas phase will be stated when appropriate.

Graham et al. (1986) measured the amount of TCE 

degraded after injecting TCE-NAPL into a heated quartz 

tube (2 second residence time) as a function of quartz 

tube temperature and oxygen concentration (Table 2.8). 

The amount of TCE degraded increased with quartz tube 

temperature and oxygen content. TCE degradation was 

initiated at 600°C when the amount of oxygen present 

was equal to the stoichiometric amount required for 

the complete combustion of TCE (2.5 moles of O2

 per 

mole TCE) and decreased to 500°C when the amount 

of oxygen present was in excess to the stoichiometric 

amount. Temperatures greater than 800°C were required 

to degrade 99% of the TCE introduced into the quartz 

tube, independent of oxygen content. Graham et al. 

(1986) detected the greatest number of TCE degradation 

products at 750°C with some products detected at 

1000°C after 99.9% of the parent TCE had been 

degraded; however, the exact identity and distribution of 

products was not reported.

Increasing the residence time within a quartz tube has 

been shown to decrease the temperature at which TCE 

degradation is initiated. Yasuhara and Morita (1990) 

passed air (80% N2 and 20% O2) at 50 mL/min through 

chilled TCE and into a quartz tube that was maintained 

at a temperature between 300 and 800°C. The amount 

of oxygen present, approximately 1.6 moles O2 per mole 

TCE, was less than the stoichiometric amount required 

for complete combustion. The residence time within the 

quartz tube ranged from 23 to 43 seconds (Table 2.9), 

and the degradation of TCE was initiated at a 

temperature of less than 300°C with approximately 99% 

of the TCE degraded at 500°C. Therefore, an increase in 

the quartz tube residence time to greater than 20 seconds 

resulted in 200 and 300°C reduction in the temperature 

required for the initiation of TCE degradation and 

for 99% destruction of TCE, respectively. Zhang 

and Kennedy (2002) found that TCE degradation 

within a surface boundary layer with residence time 

of approximately 0.04 seconds did not occur until the 

temperature reached 1000°C. 

Yasuhara and Morita (1990) also quantified 

condensable TCE degradation products by passing the 

effluent gas stream leaving the quartz tube through 

a dichloromethane (CH2Cl2) filled trap. The greatest 

number of reaction products (23 compounds) was 

identified in the dichloromethane trap fluid after 1 

hour of feeding TCE into a quartz tube maintained 

at 400°C. The most prevalent compounds found at 

400°C included TCE, tetrachloroethylene (C2Cl4), 

carbon tetrachloride (CCl4), hexachloroethane (C2Cl6), 

hexachlorobutadiene (C4Cl6), and hexachlorobenzene 

(C6Cl6). TCE was not present (i.e., > 99% destruction) in 

the dichloromethane trap fluid when the quartz tube was 

maintained at temperatures greater than 600°C, while 

tetrachloroethylene (C2Cl4) and carbon tetrachloride 

(CCl4) were detected at all temperatures between 300 

and 800°C (Table 2.9).

Froese and Hutziner (1994) determined the amount of 

chlorinated benzenes and phenols formed after passing 

TCE and air (0.9 to 1.5 second residence time) through 

a heated quartz tube that contained 0.5 grams of solids. 

Table 2.8 Amount of TCE Degraded after Passing Through a Heated Quartz Tube 

Residence Time of 2 Seconds (Graham et al., 1986)

Quartz Tube Temperature (°C) 500 600 650 700 800 950 1000

Oxygen Content Amount TCE degraded (wt%)

None* NM 0 10 40 75 99.9 NM

Stoichiometric NM 0 NM 85 98.5 NM NM

Excess 0 20 70 90 98.5 NM NM

* Measurements completed by injecting a mixture of chlorobenzene, carbon tetrachloride, TCE, trichloro-trifluoroethane 

and toluene. Pure TCE-NAPL was only used in the Stoichiometric and Excess experiments.

NM – not measured
17

The solids included fly ash collected from an incinerator 

and a series of silica gel (SiO2) solids that were amended 

with aluminum oxide (Al2O3) (10 wt% Al), hematite 

(Fe2O3) (10 wt% Fe), and copper oxide (CuO) (1 wt% 

Cu) (Table 2.10). The effluent from the quartz tube 

reactor was passed through a tube filled with activated 

carbon (Carbotrap) to collect condensable degradation 

products. The Carbotrap and quartz tube reactor 

were extracted with dichloromethane, toluene, and a 

1:1 hexane/dichloromethane mixture to determine the 

amount of chlorinated benzenes and phenols formed. 

The quartz tube and solids was extracted with toluene, 

methanol, and the 1:1 hexane/dichloromethane mixture. 

Lower molecular weight compounds such as carbon 

tetrachloride (CCl4

) or tetrachloroethylene (C2Cl4) were 

not analyzed. 

The amount of chlorinated benzenes and phenols formed 

as a function of temperature at 400, 500, and 600°C 

was determined only with fly ash as the solid phase 

(Table 2.10). A number of di-, tri-, tetra-, penta-, and 

hexa- chlorinated benzene and phenol compounds were 

detected, primarily condensed within the quartz tube and 

on the solids. However, the penta- and hexachlorinated 

compounds were formed in the greatest abundance. The 

greatest amount of chlorinated compounds was formed 

at 600°C, with hexachlorobenzene reported as the 

predominant TCE degradation product (Table 2.10).

Table 2.10 Selected Degradation Products after 

Passing TCE through a Heated Quartz 

Tube Containing Fly Ash, 0.9 to 

1.5 second Residence Time (Froese and 

Hutzinger, 1994)

Quartz Tube 

Temperature (°C) 400 500 600

Selected Reaction 

Products wt% of TCE in feed

pentachlorobenzene

(C6

HCl5) nd 1x10-2 40.0x10-3

hexachlorobenzene 

(C6Cl6) nd 1x10-2 300.0x10-3

pentachlorophenol 

(C6Cl5OH) 5x10-6 3x10-5 1.3x10-3

Values estimated from graphs found in Froese and 

Hutzinger (1994).

nd – amount not evident in graph

Table 2.9 Selected Degradation Products after Passing TCE through a Heated Quartz Tube (Yasuhara and 

Morita, 1990)

Quartz Tube Temperature (°C) 300 400 500 600 700 800

Residence Time (seconds) 43 36 32 28 25 23

Selected Reaction Products Amount present in liquid trap after 1 hour (% of Carbon in Feed)

trichloroethylene (C2

HCl3) 65.51 31.02 0.17 0.00 0.00 0.00

tetrachloroethylene (C2

Cl4) 0.30 6.95 11.78 13.92 4.68 0.03

carbon tetrachloride (CCl4

) 0.02 0.76 3.58 6.81 4.48 2.87

hexachloroethane (C2

Cl6) 0.18 1.94 0.27 0.06 0.04 0.00

hexachlorobutadiene (C4

Cl6) 0.21 0.94 0.91 0.18 0.00 0.00

hexachlorobenzene (C6

Cl6) 0.00 0.24 0.43 0.09 0.01 0.00

Total 66.21 41.84 17.13 21.06 9.21 2.90
18

The effect of solids on the amount of chlorinated 

benzenes and phenols formed in the quartz tube was 

evaluated at 600°C (Table 2.11). Only 11% of the quartz 

tube volume was filled with solids, which were located 

near the effluent end of the tube. The presence of the 

silica gel (SiO2

) was shown to have no impact on the 

formation of chlorinated benzenes and phenols, while 

the presence of fly ash and aluminum oxide increased the 

formation of these products and the presence of hematite 

(Fe2O3) and copper oxide (CuO) resulted in a decrease in 

the amount of chlorinated benzenes and phenols formed.

Mulholland et al. (1992) determined the condensedphase products formed after passing TCE and nitrogen 

(no oxygen present) through a heated quartz tube 

(1.5 second residence time) at temperatures ranging 

from 800 and 1200°C. The solids produced by the 

degradation of TCE were collected on a filter, which 

was subsequently rinsed with dichloromethane 

(CH2

Cl2) to determine the tar and soot fractions, 

where soot was defined as the fraction that is 

insoluble in dichloromethane. The chemical species 

present in the tar fraction were identified using mass 

spectrometry (MS), liquid chromatography, and IR 

analysis. Approximately 10% (wt) of the TCE that 

passed through the quartz tube heated to 800°C 

was converted into tar. Hexachlorobenzene (C6Cl6), 

hexachlorophenylacetylene (C8Cl6), octachlorostyrene 

(C8Cl8), and octachloronaphthalene (C10Cl8) were the 

most abundant compounds found in the tar based on MS 

response. 

Mulholland et al. (1992) suggested that 

dichloroacetylene (C2Cl2) was a key intermediate 

that led to the formation of the higher molecular 

weight compounds. Wu and Lin (2004) detected 

dichloroacetylene (C2Cl2) as one of the primary 

TCE degradation products after passing TCE and a 

stoichiometric amount of oxygen through a quartz tube 

(residence time between 0. to 1.5 seconds) heated to 

between 575 to 850°C. 

Chang and Senkan (1989) measured the intermediates 

and products that formed after burning a mixture of 

TCE (22.6%), oxygen (33.1%), and argon (Ar; 44.3%), 

where oxygen was in excess of the stoichiometric 

requirement for complete combustion. The mixture 

burned as a two-stage flame, with the initial stage at 

approximately 1,000°C and the final stage at 1,500°C. 

The final degradation products included (in order of 

abundance) CO, HCl, chlorine gas (Cl2), and CO2. 

Intermediates identified in the initial flame stage 

included phosgene (COCl2), tetrachloroethylene (C2Cl4), 

carbon tetrachloride (CCl4), dichloroacetylene (C2Cl2), 

dichloroacetyl chloride (Cl2HC2OCl), and trichloroacetyl 

chloride (Cl3C2OCl) among others (Table 2.12). 

The data reported by Chang and Senkan (1989) 

demonstrate that passing TCE through a temperature 

gradient from 600 to 1,000°C, with oxygen present, 

produced a variety of chlorinated compounds. These 

chlorinated compounds were then transformed into nonchlorinated carbon compounds (e.g., CO2

), but only at 

temperatures in excess of 1,000°C in the final stage of 

the flame.

In summary, passing gas-phase TCE through quartz 

tubes heated between 300 and 800°C resulted in the 

formation of a wide variety of compounds from carbon 

tetrachloride (CCl4) and tetrachloroethylene (C2Cl4) to 

hexachlorobenzene (C6Cl6). Thus, the possibility exists 

that these compounds could be formed during the in-situ 

thermal treatment of regions contaminated with TCE 

where temperatures exceed 300°C. Based on the work 

by Chang and Senkan (1989), temperatures in excess of 

1,000°C would be required to destroy these compounds. 

Reducing the amount of chlorinated degradation 

Table 2.11 Selected Degradation Products at 600°C as a Function of Quartz Tube Solids Content, 0.9 to 1.5 

second Residence Time (Froese and Hutzinger, 1994)

Quartz Tube Contents 

(solids were 11% of 

tube volume)

Empty SiO2 SiO2

/Al2O3 SiO2/Fe2O3 SiO2/CuO SiO2/Flyash

Products Formed wt% of TCE in feed

pentachlorobenzene 0.0058 0.0035 0.012 1.2x10-4 3x10-4 0.04

hexachlorobenzene 0.0025 0.0058 0.080 2.2x10-4 5x10-4 0.30

pentachlorophenol nr 1.4x10-4 8.2x10-4 3.0x10-4 0.4x10-4 1.3x10-3

Values estimated from graphs found in Froese and Hutzinger (1994).

nr – not reported
19

products and increasing the non-chlorinated products is 

thought to be dependent on the amount of chlorine and 

hydrogen in the high-temperature region. The following 

section provides a discussion of experiments performed 

to investigate changes in TCE degradation product 

distribution as a function of the chlorine to hydrogen 

(Cl:H) ratio. 

2.3.6 TCE Degradation Products as a Function 

of the Cl:H Ratio

Mulholland et al. (1992) suggested that the ratio of the 

chlorine to hydrogen (Cl:H) present in the quartz tube 

would affect the type of degradation products formed. 

With a Cl:H ratio of less than one (Cl:H < 1), chlorine 

would preferentially react with hydrogen to form 

HCl, and with a Cl:H ratio of greater than 1 (Cl:H>1), 

chlorine was predicted to react with carbon to form 

chlorinated hydrocarbons. The experiments completed 

by Chang and Senkan (1989) and Mulholland et al. 

(1992) represent results for TCE degradation with a Cl:H 

ratio of 3, thus the observed chlorinated hydrocarbons 

were the expected TCE degradation products. 

In contrast, Werner and Cool (2000) measured the 

products formed during combustion of TCE using a 

chlorine to hydrogen ratio of less than 1 (Table 2.13). 

Here, the authors introduced TCE into a methane 

(CH4

) flame that consisted of 17% CH4, 35% O2, 

46% Ar, and 2% TCE by volume for a Cl:H ratio of 

approximately 0.09. A two-stage flame was not observed 

in contrast to the high Cl:H ratio experiment by Chang 

and Senkan (1989). The final combustion products 

included (in order of abundance) H2

O, CO2, CO, HCl, 

methane (CH4), and O2. Intermediates identified in the 

flame adjacent to the burner surface (200 to 1000°C) 

included dichloroethylene (C2H2Cl2), vinyl chloride 

(C2H3Cl), ethylene (C2H4), dichloroethenol (Cl2C2HOH), 

dichloroketene (Cl2C2O), chloroketene (C2HClO), and 

ketene (C2H2O), indicating that the oxidation state of the 

TCE carbon atoms was being reduced within the flame 

with Cl:H ratio of less than one. The observation that 

the TCE carbons were reduced in low Cl:H ratio flames 

is also supported by the results of Yang and Kennedy 

(1993) who found acetylene, ethylene, and ethane were 

the primary intermediates after introducing TCE into a 

methane flame with Cl:H ratio of 0.14.

Table 2.12 Selected Compounds in a TCE Flame with Cl:H Ratio of 3 (Chang and Senkan, 1989)

Species in Flame

Initial Stage 

(600-1000°C) 

(% mole basis)

Final Stage (1500°C) 

(% mole basis)

carbon monoxide (CO) 15.00 1

carbon dioxide (CO2

) 4.00 20

hydrochloric acid gas (HCl) 10.00 10

chlorine gas (Cl2

) 9.00 9

tetrachloroethylene (C2

Cl4) 2.00 nd

phosgene (COCl2

) 1.80 nd

carbon tetrachloride (CCl4

) 1.50 nd

dichloroacetyl chloride (Cl2

HC2OCl) 1.00 nd

trichloroacetyl chloride (Cl3

C2OCl) 0.80 nd

dichloroacetylene (C2

Cl2) 0.80 nd

hexachloropropene (C3

Cl6) 0.50 nd

hexachlorobutadiene (C4

Cl6) 0.35 nd

hexachloroethane (C2

Cl6) 0.15 nd

Maximum measured values estimated from graphs found in Chang and Senkan (1989).

nd – below analysis detection limit
20

Table 2.13 Selected Compounds after Passing TCE 

through a Flame with Cl:H Ratio of 0.09 

(Werner and Cool, 2000)

Species in Flame

Initial Flame 

(200-1000°C)

(% mole basis)

Final Flame 

(1500°C)

(% mole 

basis)

carbon monoxide 

(CO) 6.00 6

carbon dioxide 

(CO2

) 3.00 11

hydrochloric acid 

gas (HCl) 2.50 2.5

water (H2

O) 17.00 19

methane (CH4)* 3.00 0.5

oxygen (O2

)* 12.00 0.5

dichloroehtylene 

(C2

H2Cl2) 0.50 nd

ethylene (C2

H4) 0.40 nd

vinyl chloride 

(C2

H3Cl) 0.07 nd

ketene 0.05 nd

dichloroethenol 0.01 nd

dichloroketene 0.01 nd

chloroketene 0.01 nd

Maximum measured values estimated from graphs found 

in Werner and Cool (2000).

* Present in feed

nd – below analysis detection limit

Zhang and Kennedy (2002) used methane (CH4), 

dimethyl ether (C2H6O), and propane (C3H8) to study 

the effect of decreasing the Cl:H ratio on the destruction 

of TCE flowing over a heated ceramic surface. There 

was no change in the amount of TCE (0.5% TCE 

and 99.5% N2

) between the influent and effluent after 

passing TCE past (residence time of 0.04 seconds) a 

heated ceramic surface up to the temperature of 1000°C. 

Adding methane (4% CH4, 0.5% TCE, and 95.5% N2) 

to the TCE gas stream flowing past the heated ceramic 

surface did not yield any measurable TCE destruction. 

The addition of propane (4.4% C3H8, 0.5% TCE, and 

95.1% N2

) did cause some TCE degradation (the exact 

amount was unspecified) whereas adding dimethyl ether 

(4% CH4, 7 % C2H6O, 0.5% TCE, 88.5% N2) resulted in 

the complete destruction of TCE. Zhang and Kennedy 

(2002) speculated that the methyl radical (CH3

 ̇) was 

the primary species and the hydrogen radical (H ̇) 

the secondary species involved in the destruction of 

TCE based on the calculated concentrations of these 

constituents at 1000°C.

Chuang and Bozzelli (1986) performed an experiment 

using hydrogen gas (H2) and water as the hydrogen 

sources for the transformation of chloroform (CHCl3) 

to HCl within a heated quartz tube operated over a 

temperature range of 550 to 1000°C. The residence times 

were between 0.02 and 2 seconds, and the Cl:H ratio 

was approximately 0.14. Several intermediate products 

were formed in the presence of hydrogen gas, including 

dichloromethane, monochloromethane, and methane, 

which indicated that the chloroform carbon oxidation 

state had been reduced. The products formed when water 

was used as the hydrogen source at temperatures below 

950°C included PCE and TCE, indicating an increase 

in the number of chlorine atoms per carbon or that the 

chloroform carbon had been oxidized. Although the 

complete destruction of chloroform was observed in the 

presence of both hydrogen and water, hydrogen was able 

to reduce chloroform beginning at 600°C, consistent 

with the fact that water is more stable at elevated 

temperatures than hydrogen. The ratio of chlorine 

to hydrogen may affect the type of TCE degradation 

products formed. With a Cl:H ratio of greater than one, 

chlorine produced from the degradation of TCE may 

react with the remaining TCE and TCE degradation 

products to form chlorinated compounds. With a Cl:H 

ratio of less than one, chlorine may react with hydrogen 

atoms to yield HCl and prevent the formation of 

unwanted chlorinated hydrocarbons.

Taylor et. al (1990) developed a Thermal Stability 

Ranking under fuel-rich, low-Cl conditions for the 

hazardous organic compounds listed in Appendix VIII 

of 40 CFR Part 261.3. Of the 320 compounds on this 

list, TCE is classified as one of the 77 compounds most 

resistant to decomposition. The decomposition of 

these resistant compounds is believed to be dominated 

by bimolecular decomposition processes. At high 

temperatures (800 – 1000°C), decomposition is 

mainly affected by H atom methathesis and Cl atom 

displacement reactions, while at lower temperatures 

reactive organic and inorganic radicals may be present, 

creating increased molecular weight compounds. 

Chang and Senkan (1989) found that the major reaction 

pathway for TCE in a flame (greater than 750°C) was 

by chlorine radical (Cl·

) attack, with the formation of 

C2Cl3

·

 and HCl. In cooler parts of the flame, addition 

of C2Cl3

·

 and ClO· to TCE is also important, with the 

formation of higher molecular weight species such as 

hexachlorobenzene. 
21

2.4 Operational Conditions of In Situ 

Thermal Treatment Technologies

The following sections provide a brief review of 

steam flushing, thermal conductive heating, and 

electrical resistive heating, three thermal remediation 

techniques commonly used to treat chlorinated solvent 

contaminated aquifers (U.S. EPA, 2004). The purpose 

of these sections is to discuss subsurface conditions 

(e.g., temperature, residence time) that might exist 

during application of these thermal technologies. The 

increase in subsurface temperature resulting from 

thermal treatments will lead to substantial changes in the 

distribution of volatile organic contaminants between 

the solid, liquid, and gas phases. For example, the 

vapor pressures and Henry’s Law constants of TCE and 

PCE increase markedly with temperature (Heron et al., 

1998; Sleep and Ma, 1997), indicating that a substantial 

fraction of the contaminant mass will exist in the gas 

phase during thermal remediation. As a result, thermal 

treatment systems incorporate a vacuum extraction 

system to recover gas-phase contaminants from the 

subsurface. The following sections are not intended to 

provide a comprehensive review of thermal treatment 

methods or their application, but rather to provide the 

reader with a brief summary of the basic approaches and 

principles. 

2.4.1 Steam Flushing

Injecting steam into the subsurface through wells has 

been shown to be effective for mobilizing fluids, heating 

the subsurface, and removing TCE (Udell, 1997). 

When steam is injected into the subsurface, it initially 

condenses, releasing the latent heat of vaporization 

which heats the soil and interstitial fluids. With 

continued injection, three distinct zones develop: a 

nearly isothermal steam zone at steam temperature 

surrounding the injection point, a relatively narrow 

variable temperature zone, and an isothermal zone at 

ambient temperature. The temperature of the injected 

steam is limited by the injection depth, as the injection 

pressure must remain below the overburden pressure 

to avoid steam breakthrough at the ground surface, 

and specifying the steam pressure fixes the steam 

temperature. In general, pressures of less than 0.5 psi 

ft of overburden are employed in unconsolidated media 

to avoid breakthrough of the steam front at the surface 

(Davis, 1997; Udell, 1997). Thus, steam temperatures 

are normally in the range of 120 to 140°C for injection 

depths between 40 and 120 feet below ground surface. 

Interstital fluids are displaced in front of the steam 

zone, and residual liquids held in the pore space and 

adsorbed contaminants are vaporized when the steam 

zone reaches them, and are then transported to the 

steam front. Within the ambient temperature zone, 

these vapors can condense, forming a contaminant 

bank. When the contaminant is a dense, non-aqueous 

phase liquid (DNAPL) such as TCE, this can lead to 

downward mobilization of the DNAPL (Schmidt et 

al., 1998; Kaslusky and Udell, 2002). Thus, when 

treating DNAPLs such as TCE, air co-injection is now 

commonly used. Co-injecting air with the steam has the 

effect of carrying part of the heat as well as contaminant 

vapors to the extraction wells more quickly, creating a 

much wider variable temperature zone and somewhat 

reducing the temperatures within the steam zone 

(Kaslusky and Udell, 2002).

The depth of steam injection sets a maximum injection 

pressure that can be used, but some field applications of 

steam injection have chosen to employ lower pressures 

and temperatures. Thus, a wide range of temperatures 

have been used in field applications of steam injection 

remediation. The following two case studies describe 

steam injection demonstration projects where the 

purpose of the demonstration was to document in situ 

oxidation of TCE during steam injection.

Steam-air coinjection was used for the steam injection 

demonstrataion at Launch Complex 34, Cape Canaveral, 

Florida to recover TCE from the surficial aquifer. The 

vendor claimed that hydrous pyrolysis/oxidation (HPO) 

of TCE would occur during the demonstration. Air 

was injected into the deep wells at rates ranging from 

approximately 3,000 – 8,000 lbs/day. Steam was 

injected at rates generally in the range of 15,000 – 

80,000 lbs/day, which lead to subsurface temperatures 

in the steam zone ranging from about 90 to 150°C 

(Integrated Water Resources, 2003). Groundwater 

dissolved oxygen concentrations prior to steam 

injection were less than 1 mg/l, the redox potential 

was negative, and cis-1,2-DCE was detected in most 

groundwater samples with concentrations as high as 

260 mg/l. Vinyl chloride was not detected prior to steam 

injection (detection limits were as high as 83 mg/l). 

After steam and air co-injection, dissolved oxygen 

remained low (oxygen is not readily soluble in hot 

water), redox potential ranged from negative to positive 

values, cis-1,2-DCE was detected at concentrations as 

high as 52 mg/l, and vinyl chloride was now detected 

at concentrations as high as 0.128 mg/l. Chloride 

concentrations and alkalinity, which would have been 

expected to increase if significant TCE oxidation 

had occurred, instead showed decreases (Interagency 

DNAPL Consortium, 2002). However, the inside-out 

design of this remediation system caused groundwater 

from outside the steam treatment area to be continuously 

pulled towards the treatment area, and this may have 

masked changes in groundwater concentrations that 

occurred within the heated zone.

A steam enhanced extraction demonstration using a 

single injection and extraction well was carried out 

at Beale Air Force Base (Carroll et al., 2004). The 

purpose of the demonstration was to produce conditions 

in the subsurface for HPO of TCE to be optimized, 
22

thereby minimizing the need to extract volatilized 

contaminants. Oxygen was co-injected with the steam 

into a single well for 48 hours, then the well was 

shut in to allow reaction to occur before dual phase 

extraction was initiated and a volume of water in 

excess of the amount injected as steam was extracted. 

Measured temperatures reached as high as 113°C. Prior 

to the demonstration the groundwater was essentially 

anoxic and dechlorination of the TCE was occurring; 

however, during the demonstration dissolved oxygen 

levels increased to 4 – 5.5 mg/l within the heated 

zone. Thus it appears that some groundwater samples 

during steam and air injection were supersaturated with 

oxygen. Trends in dissolved oxygen, alkalinity and ion 

concentrations suggest that HPO occurred; however, the 

authors acknowledge that, “Distinguishing between the 

relative importance of HPO, Steam Enhanced Extraction 

(SEE) and other potential mechanisms for destruction 

or removal of chlorinated VOCs has proved to be 

problematic with the available data.” 

Thus, during steam injection remediation, volatile 

contaminants are found dissolved in the aqueous 

phase, as a separate phase (NAPL), and in the gas 

phase. Contaminants are exposed to soil at elevated 

temperatures, oxygen, and steam during their migration 

toward vacuum extraction wells. Steam injection 

systems are normally designed to allow for a couple 

weeks to a month for the steam zone to reach the 

extraction wells. Establishing steam zones throughout 

the area to be heated, allowing heat conduction into 

low permeability zones that do not readily take steam, 

and pressure cycling to aid in contaminant recovery 

usually requires several months of time for a full scale 

steam remediation. Residence times for vapors in the 

subsurface will depend on the air and steam injection 

rates and the vacuum pressure at the recovery wells, 

but can be expected to be relatively short, on the order 

of a day. However, dissolved and adsorbed phase 

contaminants may be exposed to high temperatures 

for considerably longer time periods, on the order of 

months.

The residence time of gas-phase contaminants in the 

heated subsurface is difficult to anticipate since each 

steam drive application is tailored to specific subsurface 

conditions. The residence time at the Visalia Superfund 

site was determined by measuring the time to recover 

xenon and helium gas tracers. The initial displacement 

stage residence time was 10 hours between an injection 

and extraction well that were 24 meters apart based 

on the xenon tracer (Newmark et al., 1998). For most 

steam flushing applications, the residence time of gasphase contaminants flowing through heated soil during 

transport to vapor recovery wells is expected to be less 

than one day. 

2.4.2 Thermal Conductive Heating

Steel wells containing resistive heating elements can be 

used to heat subsurface regions contaminated with TCE 

via thermal conduction heating (TCH) with recovery of 

the volatilized TCE accomplished by applying vacuum 

extraction through the heated steel well screens. Heating 

elements within the heater wells typically operate at 

temperatures between 650 and 800°C, and the heat 

is conducted radially into the soil. Vapors that are 

generated move countercurrent to the direction of the 

heat as they are extracted at the heater wells. When 

volatile organic compunds (VOCs) are to be remediated 

using thermal conductive heating, the target treatment 

temperature for the midpoint between wells is generally 

100°C. Steep temperature gradients are formed, drying 

out the soil nearest the heater wells. If there is a water 

table present and the soil has sufficient permeability, 

much of the area between heater wells will remain 

saturated and thus at temperatures below 100°C. For 

treatment zones above the water table, greater drying 

of the soil will occur, and the high temperature zones 

will extend further from the heater wells. Heater well 

spacings on the order of 12 to 18 feet are commonly 

used when treating VOCs, with treatment times on the 

order of 4 to 6 months.

In one of the earliest applications of TCH for the 

remediation of VOCs, Vinegar et al. (1999) reported 

using heater well temperatures between 745 and 900°C 

to remediate a site located in Portland, Indiana, that was 

contaminated with TCE and PCE. The heater wells were 

located every 7.5 feet resulting in one heater well every 

50 square feet with the soil temperatures between heater 

wells ranging from 100 up to 250°C after heating for 5 

months. Stegemeier and Vinegar (2001) speculate that 

the high temperature soil region (500 to 700°C) extends 

approximately 1 foot radially from each heater well. 

The residence time of TCE within this 1-foot region is 

controlled by the rate of gas extraction. The treatment 

zone area was 7,500 square feet to a depth of 18 feet, 

which represents a treatment volume of approximately 

40,500 cubic feet, assuming a gas filled porosity of 

0.3. A single 1,800 cfm blower was used to extract gas 

from 130 heater/vacuum wells. Using the reported 

blower capacity and the estimated treatment volume 

yields an estimate for the overall gas residence time of 

22.5 minutes (40,500 ft3 ÷ 1,800 ft3/min = 22.5 min). 

A first-cut estimate of the gas residence time within the 

1-foot high-temperature zone that is adjacent to each 

heater well is 0.5 minutes according to:

π 12 ft2 18 ft 130 wells 0.3 ft3 void min

 = 0.5 min

ft3

 soil 4,669 ft3

(2.8)
23

which represents the circular area around the well, the 

length of well screen, the number of wells, and the 

porosity of soil divided by flow rate. Here, the gas flow 

rate was corrected to 500°C using the ideal gas law 

according to:

1,800 ft3 773 K

= 4,669 ft3

/min at 500°C min 298 K

(2.9)

A second application of thermal conductive heating 

used a 3,000 cfm blower to extract gas from 761 heater/

vacuum wells at a TCE-contaminated site in Eugene, OR 

(Stegemeier and Vinegar, 2001). The estimated residence 

time in the 1-foot high temperature zone for this case 

was 1.1 minutes, calculated following the approach 

described above. These residence time estimates assume 

that gas is uniformly removed from each well and that 

no preferential flow channels exist. In reality, the gas 

flow through each 1-foot high temperature zone could 

range from seconds to days depending on the soil gas 

permeability and pressure distribution within the vacuum 

manifold system. 

In conductive heating remedial systems, gas from 

uncontaminated subsurface regions flows into the 

contaminated treatment zone that have been heated 

to temperatures between 100 to 250°C, and becomes 

saturated with the volatile contaminants (e.g., TCE). 

Vapors entering the heated treatment zone are not 

likely to be atmospheric air with 21% oxygen as vapor 

barriers are commonly used if the treatment area is close 

to the ground surface. Thus, the vapors more likely 

come from other subsurface regions that have lower 

oxygen content due to microbiologic consumption. The 

contaminant-saturated gas then travels through a high 

temperature region located adjacent to each heater/

vacuum extraction well. Baker and Kuhlman (2002) 

suggest that TCE degradation occurs as vapors migrate 

through the soil region adjacent to the heater/vacuum 

well, which may reach temperatures of 500 to 700°C. 

This high temperature zone is claimed to function as a 

“packed-bed reactor that is hot enough to accomplish 

rapid decomposition by either pyrolysis, if oxygen is 

deficient, or by oxidation, if oxygen is available” (Baker 

and Kuhlman, 2002).

According to data from Kim and Choo (1983) on 

pyrolysis of TCE via a dehydrochlorination reaction 

pathway which forms dichloroacetylene (presented by 

Baker and Kuhlman, 2002), the destruction of 99% 

of the TCE entering the 500 to 700°C region would 

require a residence time of approximately 7 days at 

500°C and 7 seconds at 700°C. The thought is that TCE 

enters into the high temperature zone at 500°C and is 

transformed into intermediate products. The intermediate 

products formed from TCE degradation at 500°C then 

undergo further transformations as they encounter 

temperatures near 700°C closer to the heater/vacuum 

wells. As discussed in Section 2.3.5, dichloroacetylene 

is thought to lead to the formation of higher molecular 

weight compounds. To date, there is no data available to 

determine the amount of TCE destruction or the reaction 

byproducts that may be expected from conductive 

heating remediation of TCE.

Based on the examples discussed above, thermal 

conductive heating may result in gas phase TCE being 

exposed to temperatures ranging from 100 to 250°C for a 

period of time greater than a month, and to temperatures 

ranging from 500 to 700°C for a period from days to 

seconds. Vapors in the treatment area are likely to be 

low in oxygen content. Water vapor may or may not be 

present depending on whether the target treatment area is 

above or below the water table. To date, well-controlled 

experiments have not been conducted to confirm or 

refute TCE reactivity and byproduct formation under 

these conditions. 

2.4.3 Electrical Resistive Heating

Electrical resistance heating (ERH) passes an electrical 

current through the subsurface zone targeted for 

treatment. The current is actually conducted by water 

within the pores of the soil, and the resistance of soils 

to carrying current results in resistive heating (Beyke 

and Fleming, 2005). The electrical current is delivered 

through steel rods (electrodes) installed into the 

contaminated soil. If the system is above the water table 

or in low permeability soils, water is injected into the 

annular space between the soil and electrodes during 

heating to prevent the soil adjacent to the electrodes 

from drying out. The temperature of the subsurface 

increases relatively slowly, and reaches 100 to 120°C, 

the boiling point of water at the local pressure, generally 

after about two to three months of heating time. Because 

water is needed in the pore spaces to carry current 

between electrodes, the temperature cannot go higher 

than the boiling point of water at the local pressure, 

and the soil cannot be allowed to dry out. Volatile 

organic compounds and water within the heated soil are 

subsequently recovered by vacuum extraction through 

the electrodes or through extraction wells located within 

the heated soil region. For example, a TCE-contaminated 

aquifer was heated to a temperature of 100°C for 6 

months using ERH (Beyke and Fleming, 2005), and 

approximately 30,000 pounds of TCE was recovered 

through vapor extraction wells located within the heated 

aquifer formation. Heron et al. (1998) demonstrated 

electrical resistive heating in a controlled laboratoryscale box filled with TCE-contaminated water. An 

average temperature of 90°C was maintained within 

the box for a period of 25 days, and a single centrallylocated extraction well was used to recover gas-phase 

TCE. 
24

Between 2003 and 2007, three areas containing spent 

chlorinated solvent NAPL at the Fort Lewis Army 

Logistics Center’s East Gate Disposal Yard (EGDY) near 

Tacoma, Washington, were remediated using ERH. The 

main objective of the remediation was to recover TCE 

DNAPL, which was the source for a plume more than 

a mile long downgradient of the site. Pre-remediation 

site characterization activities showed that there were 

considerable petroleum hydrocarbons present as well 

as cis-1,2-DCE from the reductive dechlorination of 

TCE. During the remediation of the third NAPL area, 

groundwater and vapor samples were collected and 

analyzed to determine if dechlorination (either biotic 

or abiotic) continued as the temperature of the site was 

increased. Vapor and dissolved phase consitutents that 

were analyzed for included methane, ethane, ethene, and 

acetylene, as well as cis- and trans-1,2-DCE, and vinyl 

chloride. Although cis-1,2-DCE concentrations were 

high in some areas of EGDY prior to the remediation, 

very little vinyl chloride was found. Baseline samples 

for gases analyzed prior to the initiation of heating 

showed significant methane concentrations, but ethane, 

ethene, and acetylene were below detection limits. 

Within a week after the initiation of heating, at which 

time two small areas of the site had reached temperatures 

as high as 70°C while most of the site was between 

10 and 15°C, the ethene concentration in the effluent 

vapors was 30 percent of the TCE concentration. During 

the second week of operations, ethane concentrations 

also reached approximately 30 percent of the TCE 

concentration. However, as heating of the site 

continued, the concentrations of ethane and ethene both 

dropped significantly in the effluent vapors. Acetylene 

also appeared in the effluent stream soon after heating 

began, but its concentration remained low. Methane 

concentrations ranged from 100 percent to 2 percent 

of the TCE concentrations, with an average of about 

20 percent. Once the average temperatures of the 

site reached approximately 90°C, ethane, ethene, and 

acetylene concentrations again fell to below detection 

limits, while methane concentrations remained as 

significant portion of the effluent vapors (Davis, 2007).

In summary, electrical resistive heating will result in the 

exposure of liquid contaminants to slowly increasing 

temperatures, which eventually can reach up to 120°C. 

Once a volatile contaminant is vaporized, it likely will 

not remain in the heated subsurface for a period of time 

greater than one day. There will always be water vapor 

present in the effluent stream, however, the vapors are 

likely to be low in oxygen content. Ambient air will 

not likely enter the heated subsurface region; if the 

treatment zone is near the ground surface a vapor barrier 

is commonly used to prevent atmospheric air from 

being pulled into the system. The residence time of gas 

phase contaminants that pass through heated soil during 

transport to vapor recovery wells is expected to be less 

than one day.

2.4.4 Hybrid Thermal Technologies

Steam flushing and electrical resistive heating may 

be implemented simultaneously. For example, the 

thermal treatment design for the Young-Rainey Science, 

Technology, and Research Center located in Largo, 

Florida, involved a combination of electrical resistance 

heating to initially heat surrounding and underlying soils, 

followed by steam drive to flush contaminants from soils 

within the preheated region to extraction wells (U.S. 

DOE, 2003). In practice, this would mean potentially 

exposing TCE to temperatures approaching 120°C 

for more than a day before driving the TCE from high 

permeability soils via steam flushing.
25

3.0

TCE Degradation in Flow-Through Quartz 

Tube Reactors

3.1 Introduction

A series of controlled experiments were conducted to 

investigate TCE reactivity and degradation product 

formation when passing gas-phase TCE through a quartz 

tube reactor that was heated to temperatures ranging 

from 60 and 480°C. The experiments were intended 

to approximate conditions that could occur during the 

extraction of gas-phase TCE either from or through a 

heated subsurface region, and to explore the potential 

effects of oxygen content, water content and solids 

(Ottawa sand) on TCE reactivity under these conditions. 

However, these experiments were not intended to 

precisely replicate all of the conditions and variables that 

could be encountered in the field. The first experimental 

series was performed to determine the minimum 

temperature at which TCE degradation products could be 

detected when the quartz tube reactor was partially filled 

with Ottawa sand. The second set of experiments was 

performed with the reactor tube empty at temperatures 

up to 480°C in order to obtain experimental data that 

could be directly compared to results reported by 

Yasuhara and Morita (1990) for a similar empty reactor 

system. The third experimental series focused on 

determining TCE degradation products from quartz 

tube reactors that were either partially- or completelyfilled with Ottawa sand, and operated at 420°C. The 

fourth experimental series was designed to investigate 

the effect of water, introduced as vapor into the TCE 

saturated carrier gas, on the degradation products formed 

within an empty quartz tube reactor operated at 420°C. 

Results obtained from the first four experiments were 

used to refine methods and design the fifth experimental 

series, which was conducted to determine the amounts 

of TCE degradation products formed as a function of 

three experimental variables; 1) quartz tube temperature, 

2) oxygen content, and 3) water vapor content. A 

summary of the quartz tube reactor experiments is 

presented in Table 3.1.

A description of the quartz tube reactor apparatus and 

the methods used to collect and measure chemical 

compounds found in the gas-phase effluent exiting the 

quartz tube are presented in Section 3.2. Experimental 

methods specific to each of the five experimental 

series are given in Section 3.2.3. Results of all five 

experimental series are presented in Section 3.3. 

Detailed experimental procedures related to quartz tube 

preparation, temperature profile, TCE introduction, 

and effluent trapping are provided in Appendix A. The 

final two sections of the chapter provide a discussion 

(Section 3.4) of the quartz tube results in terms of 

potential chemical reaction mechanisms and a summary 

(Section 3.5) of quartz tube experimental results and 

conclusions. 

Table 3.1 Summary of Flow Through Quartz Tube Experiments 

Experimental 

Series Quartz Tube Contents Temperature Range (°C) Purpose

1 100 grams sand 24 to 420 Identify degradation products

2 Empty 22 to 480 Compare with literature results

3 100 grams sand and 

completely sand filled 420 Partially vs. completely sand filled quartz 

tube

4 Empty 420 Evaluate effect of water 

5 Empty 120 to 420 Degradation products as a function of oxygen 

and water vapor content
26

3.2 Experimental Materials and 

Methods

3.2.1 Materials

Ottawa sand (ASTM 20-30 mesh) was obtained from 

U.S. Silica Co. (Berkeley Springs, WV). Prior to use, 

2,000 grams of sand was placed into a 3 L capacity 

Pyrex glass drying tray and a 1 N solution of nitric acid 

was added to completely cover the sand. The sand 

was then allowed to soak in the nitric acid solution for 

30 minutes before draining the excess liquid. The 1 N 

nitric acid soaking process was repeated, and then the 

sand was rinsed in DI water. The wet sand was placed 

into a drying oven and heated to 130°C for 3 hours to 

remove excess moisture, and then heated to 200°C for 

and additional 2 hours to complete the drying process. 

A 2 L bottle of 99.5% American Chemical Society 

(ACS) reagent-grade TCE was obtained from SigmaAldrich, Inc. (Milwaukee, WI). The TCE was not 

stabilized with an anti-oxidant. TCE from the 2 L bottle 

was used in all experiments described herein, and for the 

preparation of calibration solutions. A dedicated 40 mL 

vial with Teflon lined septum affixed with a screw cap 

was periodically filled with TCE from the 2 L bottle. 

TCE used in each experiment was dispensed directly 

from the 40 mL vial. The 40 mL vial and 2 L bottle of 

TCE were stored in the flammable storage locker at 

room temperature.

3.2.2 Quartz Tube Apparatus

The quartz tube experimental system consisted of a 

quartz-glass tube, a quartz-glass pre-mix chamber, 

and a quartz-glass effluent transition (Figure 3.1). The 

quartz tube was General Electric Type 124 fused quartz 

(Technical Glass Products, Mentor, OH), with an outer 

diameter (OD) of 38 mm, wall thickness of 2 mm, and 

a length of 53 cm. Two quartz tubes were used in the 

experiments: the first was customized (Lillie Glassware, 

Marietta, GA) by installing a slotted quartz-glass shelf 

located at the midpoint of the quartz tube (quartz tube 

#1) to hold sand, and the second section of quartz 

tube was completely open (quartz tube #2). The premix chamber was manufactured by Lillie Glassware 

(Marietta, GA) to provide an approximate 70 mL 

chamber in which influent gas and TCE could mix 

before entering the quartz tube. The effluent connection 

was custom made by Lillie Glassware (Marietta, GA) 

from quartz glass to transition the gas flow from the 38 

mm OD tube down to an 8 mm OD tube. The pre-mix 

chamber and effluent transition were connected to the 

quartz tube using custom made 38 mm ID, 316 grade 

stainless steel (316-SS) adapters (Swagelok Co., Salon, 

OH) fitted with Viton® o-rings. 

Figure 3.1 Quartz tube experimental apparatus.

The flow rate of the TCE-free carrier gas at 22°C 

entering into the experimental apparatus was determined 

using a mass flow meter (Model 179A, MKS 

Instruments, Andover, MA). The mass flow meter was 

calibrated using an ADM 2000 gas flow meter (J&W 

Scientific, Folsom, CA) that had been calibrated by 

California Integrated Coordinators (Placerville, CA). 

The pressure within the reaction system was determined 

using a pressure transducer (Honeywell, Freeport, IL), 

which was calibrated using water- (0.02 to 0.05 bar) 

and mercury- (0.07 to 0.7 bar) filled manometers. Both 

the mass flow meter and pressure transducer were 

connected to a data logger (CR23X, Campbell Scientific, 

Logan UT) to automatically record the gas flow rate and 

pressure within the quartz tube system at one second 

intervals during each isothermal experiment.

The effluent end of the quartz tube was connected to 

a 40 mL screw-thread vial via a 10 cm long section of 

1/16 inch OD poly ether-ether ketone (PEEK) tubing. 

The PEEK tubing was affixed to the 38 to 8 mm effluent 

transition by a 316-SS Swagelok (Solon, OH) union with 

Teflon ferules and was inserted through a pre-drilled 

hole in a Teflon lined septum affixed to the 40 mL vial 

with an open-hole screw cap. The 40 mL vial contained 

approximately 30 mL of dichloromethane (DCM) and 
27

was located in a 500 mL beaker filled with crushed ice. 

The purpose of the DCM filled 40 mL vial was to trap 

all compounds with greater than two carbons (e.g., PCE) 

exiting the quartz tube. After passing the TCE saturated 

carrier gas through the heated quartz tube, the DCM 

trap was removed, sealed with a Teflon lined septum 

without holes, and weighed using an analytical balance 

(Model# AG245, Mettler-Toledo, Columbus, OH). The 

weight of the DCM filled trap was used to estimate the 

volume of DCM in the 40 mL vial assuming a DCM 

density of 1.325 g/mL. 

Post-experiment sand samples (5 grams each) were 

collected and placed into separate 25 mL test tubes along 

with 2 mL of DI water. Each test tube was sealed with a 

Teflon lined septum affixed with an aluminum crimp and 

then placed in a freezer. The frozen sand samples were 

then processed using a hot solvent extraction method 

that involved incubating the 5 gram soil samples in a 1:1 

(volume) iso-octane and methanol mixture at 85°C for 

24 hours. Previous studies performed at Georgia Tech 

have shown that the hot solvent extraction procedure, 

which is based on the methods of Sawhney et al. (1988) 

and Huang and Pignatello (1990), is equivalent to 

Soxhlet extraction for chlorinated benzenes (Prytula, 

1998).

3.2.3 Experimental Procedures

3.2.3.1 Experimental Series 1

Nine (9) experiments were completed with one quartztube apparatus assembly for tube oven temperatures of 

24, 40, 60, 120, 180, 240, 300, 360, and 420°C at 1 atm 

of carrier gas pressure during the first experimental 

series. These experiments were conducted to determine 

if TCE could be degraded within the quartz tube, and 

if the quartz tube could withstand operating in the 

temperature range from ambient to 600°C. The first 

experimental series involved passing dry air (AirgasSouth, Inc., Marietta, GA) through a gas-washing bottle 

(250 mL Pyrex) filled with TCE-NAPL at 22°C. The 

TCE saturated air flowed through the quartz tube that 

contained 100 grams of acid washed 20-30 mesh Ottawa 

sand positioned on quartz-glass wool (Technical Glass 

Products, Mentor, OH) and held at the midpoint of 

the quartz tube by a slotted quartz-glass shelf (quartz 

tube #1). The TCE-saturated air was passed through 

the reactor system for a period of approximately 

16 minutes, which represented 3 pore volumes (320 mL 

total quartz tube pore volume assuming sand porosity 

of 0.3), and resulted in approximately 450 mg of TCE 

being transferred into the quartz tube. The mass of TCE 

delivered to the tube was determined gravimetrically by 

measuring the weight (PG503-S, Mettler-Toledo, Inc., 

Columbus, OH) of the TCE-filled gas washing bottle 

before and after each 16 minute run period. The airflow 

rate was approximately 60 mL/min, which resulted in 

a residence time of approximately 5 minutes at 25°C. 

The effluent from the heated quartz tube passed through 

a vial containing dichloromethane (DCM) to trap all 

condensable products; no gas samples were collected. 

At the end of 16 minutes, the airflow was stopped and 

the gas pressure within the quartz tube apparatus was 

monitored for a period of 5 minutes to test for gas 

leaks. No additional volume of air was passed through 

the quartz tube after each 16 minute TCE introduction 

period meaning that at least 1 pore volume of TCE 

saturated air remained in the tube at the end of each 

16 minute trial. The temperature of the quartz tube 

was increased, allowed to stabilize for 30 minutes, and 

the 16 minute TCE introduction period was repeated. 

The apparatus was not disassembled between each 

isothermal run. 

3.2.3.2 Experimental Series 2

The second experimental series involved passing dry 

air that was saturated with TCE through the quartz 

tube used in the first experimental series (quartz tube 

#1), but without sand present (empty). The empty 

reactor experiments were performed to replicate 

results reported by Yasuhara and Morita (1990), who 

passed TCE-saturated air through an empty quartz tube 

over a temperature range of 300 to 800°C. Nine (9) 

experiments were completed (including 2 replicates at 

120 and 240°C) at temperatures of 24, 120, 240, 300, 

360, 420, and 480°C at 1 atm of carrier gas pressure. 

The quartz tube apparatus was disassembled and 

decontaminated between each isothermal trial completed 

above 300°C due to the presence of degradation 

products observed during the first experimental series. 

The airflow rate was approximately 60 mL/min, which 

resulted in a residence time of approximately 5 minutes 

at 25°C. The TCE-saturated air flowed through the 

empty tube reactor for a period of 20 minutes, which 

represented 3 pore volumes (400 mL total quartz tube 

pore volume) and resulted in approximately 700 mg of 

TCE being transferred into the quartz tube. Although 

these experiments were intended to include temperatures 

up to 600°C, experiments were only completed up to 

480°C because the quartz tube shattered into many 

small pieces while heating to 540°C. The destruction 

of the quartz tube at 540°C was unexpected as these 

tubes were rated to 1,200°C (Technical Glass Products, 

Mentor, OH). Repeated attempts to operate the reactor at 

temperatures above 500°C resulted in destruction of the 

quartz tubes. 

3.2.3.3 Experimental Series 3

The third experimental series involved passing dry 

air saturated with TCE through a quartz tube that was 

partially or completely filled with Ottawa sand. The 

purpose of this experiment was to determine if filling 

the empty volume of the tube with sand had any effect 
28

on the amount of TCE degraded and the degradation 

products formed. These experiments were completed 

at a single temperature of 420°C, since operation of the 

reactor at this temperature in the second experimental 

series was found to degrade a significant amount of TCE 

and produce detectable amounts of degradation products. 

The partially sand-filled quartz tube experiment was 

completed with 100 g of acid treated 20-30 mesh Ottawa 

sand located on a quartz shelf (quartz tube #1), and was 

operated under the same flow conditions (16 minute TCE 

introduction period) as in the first experimental series. 

The completely sand-filled experiment was conducted 

with 700 grams of acid treated 20-30 mesh Ottawa sand 

located in the quartz without the glass shelf (quartz 

tube #2). TCE-saturated air was passed through the 

completely filled quartz tube operated at a temperature 

of 420°C and 1 atm carrier gas pressure for a period 

of approximately 16 minutes. This time represents 

5.4 tube pore volumes (177 mL pore volume assuming 

a porosity of 0.3) and resulted in 551 mg of TCE 

being introduced into the tube. The airflow rate was 

approximately 60 mL/min, which resulted in a residence 

time of approximately 3 minutes at 25°C. At the end 

of each 16 minute run, airflow was stopped and the 

system pressure was monitored for a period of 3 minutes 

to test for gas leaks. Hence, at least 1 pore volume of 

TCE saturated air remained in the apparatus. A second 

trapping sequence was then completed by passing dry 

air without TCE through the apparatus for a period of 

20 minutes to flush any residual gas-phase TCE from 

the tube. After effluent trapping was completed, the tube 

was capped and allowed to cool to room temperature 

overnight. The apparatus was disassembled the following 

day and 5 gram sand samples were collected from near 

the entrance, at the mid-point, and exit of the sand-filled 

quartz tube. A sample of the glass wool located at the 

exit of the quartz tube was also collected. The sand and 

glass wool samples were processed using a hot solvent 

extraction method described above (Section 3.2.2). 

3.2.3.4 Experimental Series 4

The fourth experimental series involved passing 

humidified air and gas-phase TCE through an empty 

quartz tube operated at 420°C. The experiments were 

completed using three different carrier gas humidity 

levels; 0, 25, and 100% relative humidity (RH). The 25% 

RH experiment used a 1:3 ratio of air that had passed 

through a water-filled gas washing bottle at 22°C and air 

saturated with TCE at 22°C. The 100% RH experiment 

involved passing air through a gas washing bottle that 

contained an approximate 1:1 (volume) mixture of 

TCE-NAPL and water at 22°C. A 1.6 L Tedlar® bag 

was used to capture all of the gas leaving the DCM trap. 

The gas within the Tedlar® bag was analyzed for CO2

content using a gas chromatograph (GC) equipped with a 

thermal conductivity detector (TCD). 

3.2.3.5 Experimental Series 5

The fifth experimental series was designed based 

on the results of the initial four experimental series 

with the goal of accounting for all TCE degradation 

products in an effort to close the mass balance. The 

experiments were planned so that the amount of each 

TCE degradation product could be determined as a 

function of three experimental variables; 1) quartz tube 

temperature, 2) oxygen content, and 3) water vapor 

content (Table 3.2). The quartz tube temperatures were 

fixed at 120, 240, and 420°C to reduce the number of 

individual experiments in the series. 

For the fifth experimental series, TCE was introduced 

into the pre-mix chamber as neat liquid TCE at a fixed 

rate of 0.68 mL/hr using a syringe pump (Model 11, 

Harvard Apparatus, Holliston, MA). This allowed the 

rate of TCE introduction to be fixed while adjusting the 

amount of water entering the quartz tube to vary the 

chlorine to hydrogen ratio inside the apparatus. Ultra 

zero grade air (Airgas-South, Inc., Marietta, GA) or 

nitrogen (Airgas-South, Inc., Marietta, GA) was used as 

the carrier gases. Ultra zero grade air (UZA) was used 

as received, while the nitrogen was passed through an 

oxygen trap (Alltech Associates, Inc., Deerfield, IL) 

before entering the quartz tube. 

The residence time through the quartz tube was fixed at 

approximately 4.3 minutes for all isothermal trials during 

the fifth experimental series. This represented a gas 

flow rate of approximately 85 mL/min (at 22°C) with 

the empty quartz tube at 120°C, which was the upper 

measurement limit of the mass flow meter and thus 

Table 3.2 Fifth Experimental Series Matrix

Tube (°C) Inlet (°C) Reactor 

Contents Carrier Gas Runs Variable

120, 240, 420 20, 80, 100 Empty N2 3x3x1x1 = 9 baseline

120, 240, 420 20, 80, 100 Empty Zero air 3x3x1x1 = 9 oxygen

Sum 9x2 = 18
29

fixed the residence time for all subsequent experiments 

completed at temperatures greater than 120°C. The 

gas flow rates to achieve a 4.3 minute residence time 

were calculated using the ideal gas law to correct for 

the gas expansion within the quartz tube at elevated 

temperatures. The gas flow rate used with the empty 

quartz tube at 240°C was approximately 65 mL/min (at 

22°C), and approximately 48 mL/min (at 22°C) with the 

quartz tube at 420°C. 

3.2.4 Analytical Methods

The concentration of TCE in the DCM trap fluid was 

determined by collecting three, 2 mL DCM samples, 

which were placed in separate autosampler vials. An 

internal standard, 1,1,1-trichloroethane, was added to 

each vial, which was then capped with Teflon®-lined 

septa affixed by a crimp seal. The analysis of DCM 

fluids consisted of using an automatic liquid sampler 

(HP6890) to inject 1 uL of DCM into a GC (Hewlett 

Packard 6890) equipped with a 30 m by 0.32 mm OD 

DB-5 column (Agilent Technologies, Palo Alto, CA) 

that was connected to a Flame Ionization Detector 

(FID). The GC inlet was operated at 9.45 psi in the split 

mode (10:1) at 200°C with helium as the carrier gas 

and a constant column flow rate of 2 mL/min. The GC 

oven temperature was isothermal at 50°C for 8 minutes 

followed by a 20°C/min ramp to 150°C. The FID was 

operated at 300°C with 400 mL/min of air, 30 mL/min 

hydrogen, and 40 mL/min of nitrogen as the makeup 

gas. 

TCE calibration standards in the concentration range 

from 8,000 to 20,000 mg/L were analyzed by GC/FID 

to determine the amount of TCE in the DCM trap 

fluid. The calibration standards were prepared by first 

adding approximately 30 mL of DCM to 50 mL glass 

volumetric flasks (50±0.05mL at 20°C), which were 

sealed with ground-glass stoppers. The initial weight of 

the flasks and DCM was determined using an analytical 

balance (Model# AG245, Mettler-Toledo, Columbus, 

OH) after allowing the flasks to stand for a period of 

30 minutes. Neat TCE was then introduced into each 

flask using a gas tight syringe, the stopper inserted into 

each flask, and then the weight of each 50 mL flask with 

TCE was recorded. Each flask was filled to the indicator 

mark with DCM, sealed and inverted several times to 

mix the solution. The concentration of each calibration 

solution was calculated using the weight of TCE added 

and the volume of DCM. GC/FID analysis of an EPA 

8240B/8260A Matrix Spike Mix (Sigma-Aldrich 

#47412) spiked into DCM was performed to verify TCE 

retention time and concentration.

The identity of compounds associated with unidentified 

chromatographic peaks from the GC/FID analysis of 

DCM trap fluids was determined using a GC (Varian 

Star 3600CX) equipped with a 30 m by 0.25 mm OD 

CP-Sil 8 CB Low Bleed/MS capillary column (Varian) 

connected to a Varian Saturn 2000 Ion Trap Mass 

Spectrometer (MS). Compounds were identified using 

software (SaturnView ver. 5.41, Varian, Inc., Palo Alto, 

CA) that matched their mass spectra with reference mass 

spectra in the NIST/EPA/NIH Mass Spectral Library 

(NIST98). Compounds were identified when their mass 

spectrum fit with a matching NIST98 library spectrum 

with purity of greater than 700. The mass spectrometer 

was tuned to optimize the detector voltage (EM-Voltage) 

and mass axis calibrated using perflurorotributylamine 

(FC-43) prior to each use.

3.3 Experimental Results

3.3.1 Results of Experimental Series 1-4

The amount of TCE recovered in the DCM trap fluid 

of the first experimental series is shown in Figure 3.2 

as function of temperature. At temperatures less than 

240°C, the amount of TCE recovered in the DCM trap 

fluid was less than the amount delivered to the quartz 

tube. The missing mass of TCE was attributed, in part, 

to the residual gas-phase TCE that remained within the 

quartz tube as no attempt was made to flush TCE from 

the apparatus after the 16 minute introduction period. 

At temperatures of 300°C and above, PCE and carbon 

tetrachloride (CCl4) were detected in the DCM trap fluid, 

and the amounts of PCE and CCl4 detected continued to 

increase as the tube temperature was raised to 420°C. 

The experimental series was terminated prior to reaching 

600°C due to repeated failure of the quartz tube at 

temperatures of 480°C and above. These data indicate 

that TCE underwent thermally induced degradation 

when flowing through a quartz tube containing 100 g 

of Ottawa sand and heated to temperatures greater than 

300°C. PCE and CCl4 were the degradation products 

detected in the DCM trap and represent chlorinated 

oxidation products that were expected during TCE 

degradation because the Cl:H ratio was equal to 3 and 

TCE was the only source of chlorine and hydrogen 

(Mulholland et al., 1992, see also Section 2.3.6) 

Results of the second experimental series, in which 

gas-phase TCE was passed through an empty quartz 

tube reactor at temperatures up to 480°C, are shown in 

Figure 3.3. The lower mass recoveries at 22 and 120°C

occurred prior to implementation of flushing step to 

capture residual gas phase mass in the reactor. Dry air 

without TCE was passed through the quartz tube for 

15 minutes following the 20 minute TCE introduction 

period in all experiments completed above 240°C. 

Consequently, the amount of TCE collected in the DCM 

trap for the 240°C yielded a mass recovery of ~98%, 

indicating that TCE was not degraded at temperatures 

less than 240°C for these experimental conditions. 
30

Starting at temperatures of 300 to 360°C, TCE, PCE and 

carbon tetrachloride (CCl4) were detected in the effluent 

DCM trap. The extent of TCE degradation increased as 

the temperature was raised to 480°C, with no measurable 

amounts of TCE observed at 480°C. These findings are 

consistent with data presented by Yasuhara and Morita 

(1990), which followed similar trends; a sharp decline 

in TCE coincident with the appearance of PCE and CCl4

between 300 and 500°C, and no detectable amounts of 

TCE at temperatures of 500°C and above. 

Results of the second experimental series indicate 

that TCE degradation products in addition to PCE 

and CCl4 are likely to have formed at 420°C as the 

amount of TCE, PCE, and CCl4 detected in the DCM 

trap accounted for less than 35% of the amount of TCE 

introduced into the quartz tube reactor. The missing 

degradation products are hypothesized to be CO and 

CO2 based on the experimental work described in 

Section 2.3.5 (Chang and Senkan, 1989). Experimental 

procedures were modified in experimental series five to 

collect and measure CO and CO2

. 

The results of the third experimental series, in which 

TCE was introduced into quartz tube reactors that were 

either partially- or completely-filled with Ottawa sand 

at 420°C, are summarized in Table 3.3. The completely 

sand-filled tube produced more PCE and had lower 

TCE recovery than the tube containing 100 grams of 

sand (Table 3.3). No CCl4 was detected in the DCM 

trap during the third experimental series as compared 

to the significant amount detected during the initial 

experimental series. However, the first and third 

experimental series results are not directly comparable 

since a decontamination step was not completed between 

each isothermal experiment during the first experimental 

series. PCE was the only compound detected in the isooctane extracts and only from the sand sample collected 

at the tube exit. An initial sand-filled experiment was 

completed for tube temperatures of 120 and 240°C, 

however, the sand-filled quartz tube shattered at 400°C

while heating to 420°C. Based on this experience and 

the quartz tube failures during preliminary experiments, 

it was concluded that sand-filled quartz tubes are not 

capable of consistently withstanding temperatures 

greater than 400°C.

In the fourth experimental series, gas containing both 

water and TCE passed through empty quartz tube 

reactors at 420°C. Results from these experiments 

indicate that increasing the quartz tube water-vapor 

content led to an increase in the amount of CO2

 and 

CCl4 detected (Table 3.4). However, the amount of 

CO2 represented less than 5% of the total amount of 

carbon introduced into the quartz tube as TCE. Thus, 

we hypothesize that additional degradation products 

formed during the fourth experimental series. This 

observation led to the development of a method to detect 

carbon monoxide (CO) and CO2

 along with the use of an 

additional liquid filled trap to determine the amount of 

phosgene (COCl2) formed. 

The ratio of chlorine to hydrogen in the fourth 

experimental series was greater than one. Based on the 

prior experimental results described in Section 2.3.6 

(Mulholland et al., 1992; Werner and Cool, 2000), a 

Cl:H of less than 1.0 provides an insufficient amount 

of hydrogen to reduce the amount of chlorinated 

degradation products. This line of reasoning provides 

justification to conduct experiments with chlorine to 

hydrogen ratios of less than one (i.e., more water vapor) 

to determine if TCE could be degraded without forming 

chlorinated degradation products. 

Figure 3.2 Amounts of TCE, PCE and carbon 

tetrachloride (CCl4) recovered during the 

first experimental series.

Figure 3.3 Amounts of TCE, tetrachloroethylene 

(PCE) and carbon tetrachloride (CCl4) 

recovered during the second experimental 

series.
31

3.3.2 Results of Experimental Series 5

Empty quartz-tube experiments were completed for 

tube temperatures of 120, 240, and 420°C at carrier 

gas pressures of 1 atm. Separate experiments were 

completed with the inlet at 22, 60, and 100°C for each 

tube temperature to evaluate the effect of increasing the 

quartz-tube water content on TCE degradation and the 

degradation products formed. Separate experiments were 

completed with nitrogen and air (UZA) as the carrier 

gas to evaluate the effect of oxygen on TCE degradation 

(Table 3.5). The following sections describe the recovery 

of TCE after being introduced into the empty heated 

quartz-tube, along with the identity and quantity of TCE 

degradation products detected in the DCM trap, water 

rinse, iso-octane rinse, and Tedlar® bag. The latter 

sample devices were installed in an attempt to collect 

and identify a wider range of potential degradation 

products and to improve mass balance closure. 

Table 3.3 Amounts of TCE, PCE, and CCl4 from the Sand Filled Quartz Tube at 420°C

Amount of Sand Amount TCE 

Introduced (mg)

Amount TCE 

Recovered (mg)

TCE 

Recovered (%)

Amount PCE 

(mg)

Amount 

CCl4

 (mg)

100 grams

partially filled

(Exp. Series 1)

456 273 60 63 28.5

100 grams

partially filled

(Exp. Series 3)

503 226 45 156 None*

700 grams completely 

filled

(Exp. Series 3)

551 172 31 250 None†

* Other degredation products detected included hexachloroethane, penta- and hexachloro-propene, and penta- and hexachlorobutadiene.

† Other degredation products detected included penta- and hexachloroethane.

Table 3.4 Amount of TCE, PCE, CCl4, and CO2 from an Empty Quartz Tube at 420°C

% RH TCE Introduced 

(mmol)

TCE Recovered 

(mmol) PCE (mmol) CCl4

 (mmol) CO2 (mmol)

0 9.51 4.23 0.29 0.18 0.08

25 5.96 2.64 0.19 0.38 0.11

100 8.69 4.69 0.34 0.39 0.38

Table 3.5 Experiments Completed for the Fifth Experimental Series

Tube (°C) Inlet (°C) Tube Contents Carrier Gas Variable

120, 240, 420 20, 80, 100 Empty N2 baseline

120, 240, 420 20, 80, 100 Empty Zero air oxygen
32

3.3.2.1 TCE Recovery

The amount of TCE detected in the DCM trap with 

respect to the amount introduced into the quartz tube as 

a function of quartz tube temperature and carrier gas is 

shown in Figure 3.4. The average recovery of TCE with 

nitrogen as the carrier gas was greater than 94% at all the 

reactor temperatures and inlet stream relative humidities. 

With air as the carrier gas, the average recovery of TCE 

was greater than 94% for tube temperatures of 120 

and 240°C but dropped to approximately 53% for the 

tube at 420°C. The amount of TCE recovered at each 

tube temperature shown in Figure 3.4 represents the 

average for the three experiments completed at different 

quartz-tube water contents (inlet temperatures). Table 

3.6 contains the average amount of TCE recovered as 

a function of quartz-tube water content with nitrogen 

as the carrier gas. The low TCE recovery observed for 

the 60°C inlet temperature and 120°C tube temperature 

was due to a leak in the experimental apparatus, and this 

value was not used to calculate the average recovery 

at 120°C shown in Figure 3.4. The amount of TCE 

recovered as a function of quartz-tube water content 

with air as the carrier gas is shown in Table 3.7. The 

average values reported in Tables 3.6 and 3.7 are shown 

graphically in Figure 3.4.

Figure 3.4 Recovery of TCE with nitrogen or air as 

the carrier gas, averaged over three relative 

humidities (inlet temperatures). 

Tables 3.6 and 3.7 also contain the Pearson correlation 

coefficient (R2) that describes the variability in TCE 

recovery as a function of quartz tube water content along 

with the P-Value, which indicates the significance of 

the correlation between the quartz-tube water content 

and TCE recovery. The statistical calculations were 

performed using MINITAB software (Release 14, 

Minitab Inc., State College, PA). A linear relationship 

between the quartz tube water content and the amount 

of TCE recovered was not obtained (R2

<0.3 and 

P-Value>0.5) for the 240°C experiment with nitrogen 

as the carrier gas (Table 3.6). In contrast, the increase 

in TCE recovery was linearly related (R2

=0.994 and 

P-Value=0.05) to the increase in water content for the 

420°C experiment. With air as the carrier gas, there was 

no linear relationship (R2<0.2 and P-Value>0.5) between 

the quartz tube water content and the amount of TCE 

recovered for the 120°C and 420°C experiments. The 

decrease in TCE recovery was linearly related (R2=0.998 

and P-Value=0.03) to the increase in water content 

for the 240°C experiment with air as the carrier gas 

(Table 3.7).

Table 3.6 TCE Recovery with Nitrogen as the 

Carrier Gas 

(%Recovery = TCE in DCM Trap ÷ TCE injected × 100)

Inlet 

Temperature 

(°C)

(Relative 

Humidity, %)

Quartz Tube Temperature (°C)

120 240 420

22 (2) 91.2±6.0 98.7±1.3 93.1±1.9

60 (20) *68.0±4.6 101.7±2.9 95.5±1.5

100 (95) 96.9±4.5 96.2±1.0 99.1±1.9

Average ± 

Standard 

Deviation

94.0±7.6 98.8±3.3 95.9±3.1

Correlation 

Coefficient 

(R2

)

NA

0.227

(P-Value 

=0.68)

0.994

(P-Value 

=0.05)

* Leak in experimental system, average based on 22 and 

100°C inlet temperatures.

Table 3.7 TCE Recovery with Air as the Carrier Gas

(%Recovery = TCE in DCM Trap ÷ TCE injected × 100)

Inlet 

Temperature 

(°C)

(Relative 

Humidity, %)

Quartz Tube Temperature (°C)

120 240 420

22 (2) 95.3±1.2 96.2±1.2 52.4±1.2

60 (20) 97.7±2.1 94.1±0.6 54.6±0.2

100 (95) 96.3±1.7 92.0±1.5 51.7±0.9

Average ±

Standard 

Deviation

96.4±3.0 94.1±2.0 52.9±1.5

Correlation 

Coefficient 

(R2

)

0.144 

(P-Value 

=0.75)

0.998 

(P-Value 

=0.03)

0.052 

(P-Value 

=0.85)
33

TCE recovery of less than 100% is one indication that 

TCE degradation had occurred within the experimental 

apparatus. However, accounting for the amount of 

missing TCE with the amount of degradation products 

detected (i.e., mass balance) provides a greater level 

of confidence to conclude that TCE was degraded as 

opposed to experimental loss which could result from a 

gas leak. The amount of each TCE degradation product 

detected is presented in Sections 3.3.2.2 through 3.3.2.5, 

and the mass balance between the missing amount of 

TCE from each isothermal experiment and the amount 

of degradation products detected are provided in 

Section 3.3.2.6. 

3.3.2.2 Compounds in the DCM Trap

The effluent carrier gas leaving the quartz tube reactor 

passed through an ice cooled, 40 mL vial filled 

with DCM to trap condensable TCE degradation 

products that were soluble in DCM. These anticipated 

TCE degradation products included PCE, CCl4, 

hexachlorobutadiene, and hexachlorobenzene based 

on the results of the first four experimental series and 

work by Yasuhara and Morita (1990) presented in 

Section 2.3.5. Samples from the DCM trap for each isothermal trial were initially analyzed by GC/FID. TCE 

was the only compound detected in the DCM trap for the 

120 and 240°C experiments regardless of carrier gas or 

quartz tube water content. Thus, at temperatures below 

240°C no TCE degradation products were detected 

in the DCM trap, consistent with results obtained in 

experimental series 2.

Chromatograms obtained from the analysis of DCM 

trap samples from each 420°C experiment with nitrogen 

as the carrier gas contained up to four unidentified 

peaks in addition to the TCE peak. Subsequent GC/MS 

analysis of the DCM samples showed that the four 

other compounds were titanium tetrachloride (TiCl4), 

pentachlorobutadiene (C4HCl5), hexachlorobutadiene 

(C4Cl6), and pentachlorobenzene (C6HCl5). These 

compounds are thought to represent the primary TCE 

degradation products since no other organic compounds 

were detected in the DCM rinse of the quartz tube 

apparatus. Titanium tetrachloride was detected in all 

three experiments performed at 420°C without oxygen 

present. Titanium tetrachloride was thought to form due 

to a reaction between the gas phase chlorine from the 

degradation of TCE and titanium in the 316-SS Cajon 

connectors. The amount of titanium tetrachloride was 

estimated using the response factor that was determined 

for CCl4.

The gas phase concentrations (ppmv or uL/L gas) 

of each detected compound are reported in 

Table 3.8. The amounts of pentachlorobutadiene and 

pentachlorobenzene shown in Table 3.8 were estimated 

using a GC/FID response factor of 3.0 (concentration 

of compound/chromatogram area). This response factor 

was based on the average response factor (3.01±0.41) 

determined from calibration solutions of TCE, PCE, 

hexachloroethane, and hexachlorobutadiene. The 

actual concentration values were calculated using the 

ideal gas law to convert the moles of each compound 

detected into a gas phase volume at 25°C and 1 atm. 

The calculated volume of gas for each compound 

was normalized to the duration of TCE injection 

(30 minutes) and the gas residence time (4.3 minutes) 

in the quartz tube (500 mL). These data are intended 

to represent the concentration of each compound that 

would be present in a gas sample collected from the 

quartz tube during TCE injection. The purpose of 

Table 3.8 Concentration (ppmv) of Compounds Detected in the DCM Trap for the 420°C Experiments with 

Nitrogen as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity %)

22

(2)

60

(20)

100

(95)

TCE* 24,010±491 24,517±397 25,992±501

titanium tetrachloride (TiCl4

) 864±37 524±30 186±26

pentachlorobutadiene (C4HCl5) 395±7.0 305±5.0 175±3.0

hexachlorobutadiene (C4Cl6) * 14±0.0 5±0.3 1<

pentachlorobenzene (C6

HCl5) 22±0.4 1< 1<

Total 24,571 24,905 26,192

Values reported as ppmv in the quartz tube (mL gas phase compound÷30 min×4.3 min÷500 mL).

* Amount determined using calibration solutions. Amount of other compounds was estimated.
34

expressing these results as gas phase concentrations 

is to gain insight into conditions during thermal 

remediation where these compounds are anticipated to 

be present in the gas phase. Thus, TCE would be the 

dominant compound present (>97% by volume) with 

relatively minor amounts (<1% by volume) of pentaand hexachlorobutadiene, and pentachlorobenzene in a 

representative volume containing TCE that was heated 

to 420°C and was absent of oxygen. 

The relative humidity of the injected gas stream was 

varying the inlet temperature from 22 to 100°C to 

evaluate the effects of water on TCE degradation 

product formation. It was hypothesized that a reduction 

in the Cl:H ratio would result in the formation of less 

chlorinated TCE degradation products. Increasing the 

quartz tube water content led to a decrease in the number 

and amount of degradation products detected (Table 3.8), 

similar to the trend noted with the increase in TCE 

recovery (Table 3.6, R2=0.994 and P-Value=0.05). 

Thus, increasing the amount of water in the apparatus 

at 420°C with nitrogen as the carrier gas did not shift 

the TCE degradation products toward less chlorinated 

compounds, but had the effect of decreasing the amount 

of TCE degraded based on the DCM trap results.

With air as the carrier gas, up to 14 peaks, in addition 

to TCE, were observed in the GC/FID chromatograms 

of DCM trap samples for the reactor experiments 

conducted at 420°C. The identities of the compounds 

associated with the unknown GC/FID peaks were 

determined by GC/MS analysis (Table 3.9), with 

the exception of the peak with retention time of 

2.05 minutes, which could not be identified due to 

interference from DCM co-elution. The compound 

with retention time of 2.05 minutes may have been 

dichloroethane (C2H4Cl2) based on the elution order 

for a test mix of chlorinated solvents available in the 

Table 3.9 Concentration (ppmv) of Compounds Detected in the DCM Trap for the 420°C Experiments with Air 

as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity %)

22 I

(2)

22 II

(2)

60

(20)

100

(95)

*TCE 15,339±1,395 13,709±1,722 14,474±1,450 13,568±1,442

Unknown (reported as C2

H4Cl2) 675±128 854±54 683±45 95±25

*chloroform (CHCl3) 276±12 257±3 209±9 205±5

*carbon tetrachloride (CCl4) 1,639±52 1,145±54 984±41 281±34

*tetrachloroethylene (C2Cl4) 822±26 829±35 863±17 365±18

trichloroacetic acid methyl ester 

(Cl3

C2O2CH3) 34±2 37±1 1< 1<

tetrachloropropene (C3

H2Cl4) 19±1 18±1 19±0 21±1

pentachlorocyclopropane (C3

HCl5) 93±5 109±3 110±0 27±1

perchlorocyclobutenone (C4Cl4O) 30±2 39±5 52±2 24±1

*hexachloroethane (C2Cl6) 226±8 288±5 261±1 81±1

tetrachlorobutadiene (C4

H2Cl4) 92±5 97±3 102±1 44±1

titanium tetrachloride (TiCl4) 1< 1< 1< 1<

pentachlorobutadiene (C4HCl5) 38±2 33±1 35±0 42±2

hexachloropropene (C3Cl6) 30±0 28±1 24±1 6±0

*hexachlorobutadiene (C4Cl6) 65±4 69±3 57±0 18±1

hexachlorobutene (C4H2Cl6) 7±0 11±0 12±0 1<

pentachlorobenzene (C6

HCl5) 1< 1< 1< 1<

Total 19,386 17,523 17,883 14,777

Values reported as ppmv in the quartz tube (mL gas phase compound÷30 min×4.3 min÷500 mL)

* Amount determined using calibration solutions. Amount of other compounds was estimated.
35

chromatogram library. The concentrations of chloroform, 

CCl4, PCE, hexachloroethane, hexachlorobutadiene, and 

hexachlorobenzene were determined using calibration 

solutions prepared from ACS grade, high purity 

reagents (Sigma-Aldrich, Inc., Milwaukee, WI). The 

concentrations of other compounds were estimated using 

a response factor of 3 as discussed above.

Two experiments were completed with the inlet at 22°C

(22I and 22II) (Relative Humidity of 0.02%) with air as 

the carrier gas and the quartz tube operated at 420°C. 

The 22 II experiment was completed with the addition 

of an aniline trap located in-line after the effluent DCM 

trap to determine the amount of phosgene exiting the 

quartz tube. Although the two experiments (22I and 

22II) could be considered replicates, the addition of 

the aniline trap resulted in a pressure increase within 

the quartz tube from 1.058±0.001 to 1.072±0.013 bar. 

Based on the results shown in Table 3.9, a gas sample 

collected from the quartz tube at 420°C with air as the 

carrier gas would primarily contain TCE (>80% by 

volume). The gas sample would also contain significant 

amounts of CCl4

 (2 to 8% by volume), PCE (2.5 to 5% 

by volume), hexachloroethane (0.5 to 2% by volume), 

and chloroform (~1.5% by volume). 

Increasing the water content (Relative Humidity from 

0.02 to 0.95) in the quartz tube reactors operated at 

420°C with air as the carrier gas did not affect the 

amount of TCE degraded (Table 3.9, R2<0.5 and 

P-Value>0.5), in contrast to the results obtained with 

nitrogen as the carrier gas (Table 3.8). However, 

there was a decrease in some of the chlorinated TCE 

degradation products with increasing water content 

(Table 3.9), most notably CCl4 and hexachloroethane. 

Non-chlorinated TCE degradation products such as 

ethane (C2H6) were not detected in the DCM trap, 

which were anticipated due to the decrease in Cl:H ratio 

with the addition of water. Thus, increasing the water 

content of the quartz reactor did not result in a shift from 

chlorinated to non-chlorinated TCE degradation products 

as originally hypothesized. Water did, however, affect 

the amounts of other TCE degradation products formed 

as discussed in the following sections.

3.3.2.3 Compounds Detected in Tedlar® Bags

The entire volume of carrier gas that passed through the 

experimental apparatus during each isothermal run was 

collected in Tedlar® bags to determine TCE degradation 

products that were not retained within the DCM trap. 

The anticipated degradation products included CO, CO2, 

and phosgene (COCl2) based on prior experimental 

results as described in Section 2.3.5. The amount of CO 

and CO2 formed was determined by GC/TCD analysis 

of a 60 mL gas sample from each 1.6 L Tedlar® bag. 

Carbon monoxide (CO) and CO2 were detected only 

when passing TCE through the quartz tube heated to 

420°C with air as the carrier gas (Table 3.10). 

A 250 uL gas sample from the Teldar® bag was collected 

during the 420°C experiment with inlet temperature 

of 22°C (i.e., 22 I) and was analyzed by GC/MS. The 

presence of phosgene (COCl2) was identified by mass 

spectrum match with the NIST98 library. An aniline 

trap was added to determine the amount of phosgene 

formed as per EPA method TO-6 (U.S. EPA, 1999) and 

the experiment was repeated (i.e., 22 II). The amount of 

phosgene formed was determined gravimetrically and 

by determining the concentration of carbanilide formed. 

The concentration of phosgene reported in Table 3.10 

was calculated using the ideal gas law from the moles of 

phosgene detected in the 1.6 L volume Tedlar® bag at 

25°C and 1 atm. 

The aniline trap was used for experiments completed at 

420°C with air as the carrier gas to evaluate the effect 

of increasing water content on the amount of phosgene 

produced. Phosgene concentrations were found to 

decrease with increasing quartz-tube water content 

Table 3.10 Concentration of Compounds Detected in the Tedlar® Bag and Phosgene Trap for the 420°C 

Experiments with Air as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

CO (uL/L)

(% of TCE-C)

CO2 (uL/L)

(% of TCE-C)

Phosgene (uL/L)

(% of TCE-C)

gravimetric UV 254

22 I (2) 8640 (15.4) 2120 (3.8) NA NA

22 II (2) 8712 (15.3) 1755 (3.1) 7964 (7.0) 1067 (0.9)

60 (20) 9410 (16.3) 2285 (4.0) 929 (0.8) 836 (0.7) 

100 (95) 8846 (15.5) 4395 (7.7) 15 (0.3) 345 (0.3)

Correlation Coefficient

R2

0.16 

(P-Value=0.61)

0.85 

(P-Value=0.08)

0.84

(P-Value=0.26)

0.96

(P-Value=0.13)
36

(Table 3.10). However, the compound formed after 

passing the quartz tube effluent through the aniline trap 

may not have been due to phosgene alone. For example, 

O’Mara et al. (1971) found that gas phase HCl formed 

during the combustion of vinyl chloride caused aniline 

to polymerize in a liquid trap and form a compound 

that had a UV absorbance of 254 nm which interfered 

with the detection of phosgene. While the concentration 

of HCl in the quartz tube effluent was not determined, 

the amount of chloride found in the water rinse (see 

Section 3.3.2.4 and Figure 3.5) suggests that gas phase 

HCl was present in the quartz tube effluent. Thus, the 

decrease in phosgene concentration with increase in 

quartz tube water content shown in Table 3.10 may have 

been due to phosgene hydrolysis alone, or may represent 

a reduction in effluent HCl concentration along with 

phosgene hydrolysis. Hydrolysis of phosgene can occur 

in the gas- and aqueous phases, and is reported to yield 

CO2 according to (Ryan et al., 1996):

COCl2 + H2O → CO2 + 2HCl (3.2)

An increase in the amount of CO2 produced with 

increasing in quartz tube water content was apparent. 

In contrast, the concentration of CO in the effluent 

(8,902±349 ppmv) and TCE recovery remained 

consistent (Table 3.7), implying a shift in degradation 

product distribution with phosgene being converted to 

CO2 as expected based on Equation 3.2. The amounts 

(moles) of CO2 and phosgene formed along with the 

difference between the amount of CO2 found with the 

inlet at 22°C (22 II), at 60°C, and at 100°C are shown in 

Table 3.11. The increase in CO2 production with increase 

in quartz tube water content (i.e., CO2 Gain, Table 3.11) 

was approximately 33% of the amount of phosgene 

lost between the inlet temperatures of 22°C and 100°C

based on the phosgene gravimetric analysis, but was 

6 times greater than the amount of phosgene lost based 

on the UV 254 analysis. The gravimetric results suggest 

that the increase in CO2 was primarily due to phosgene 

hydrolysis. However, the UV 254 analysis results 

suggest that not all the solids formed in the aniline trap 

represented carbanilide. 

3.3.2.4 Compounds Detected in the Water Rinse

After each isothermal run, approximately 30 mL of 

freshly dispensed DI water were used to rinse the quartz 

tubes once they had cooled to room temperature (22°C). 

The water rinse was performed to determine the watersoluble TCE degradation products formed after passing 

TCE through the heated quartz tube. The anticipated 

degradation products included chloride, due to the loss 

of chlorine atoms from TCE (i.e., dechlorination), and 

haloacetic acids such as dichlororacetate, based on the 

past experimental work described in Section 2.3.2 (e.g., 

McKinney et al., 1995). 

The amounts of chloride in the water rinse as a function 

of quartz tube temperature, carrier gas, and inlet 

temperature (water content) is shown in Figure 3.5. 

Chloride was detected in the water rinse from each 

isothermal experiment regardless of carrier gas used. 

This result suggests that TCE was degraded, to some 

extent, in all of the quartz tube experiments performed 

in the fifth experimental series. The amount of chloride 

in the 120°C experiment with the inlet temperature at 

22°C and nitrogen as the carrier gas was 0.06 umol, 

which was below the method detection limit (MDL) of 

0.07 umol, and the concentration of chloride with air as 

the carrier gas was 0.10 mg/L with a MDL of 0.05 mg/L; 

all other chloride concentrations were at least an orderof-magnitude above their MDL. The amount of chloride 

increased with increasing quartz tube water content (i.e., 

inlet temperature), even for experiments completed at 

the lowest quartz tube temperature of 120°C where TCE 

recovery was greater than 94% (Figure 3.4), and no TCE 

degradation products were detected in the DCM trap. 

The amount of chloride measured in the 240 and 420°C

experiments with air as the carrier gas was greater than 

the amount of chloride detected in experiments with 

nitrogen as the carrier gas, which was consistent with 

the lower TCE recovery noted in Figure 3.4 with air as 

the carrier gas. The amount of chloride was greatest in 

the water rinse after the 420°C experiments where TCE 

degradation products were detected in the DCM trap.

Table 3.11 Change in the Amount of CO2 and Phosgene Detected with Increase in Water Content for the 420°C 

Experiments with Air as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %) CO2 (mmol) CO2

 Gain

CO2 – CO2 (22II)

Phosgene (mmol)

gravimetrically UV 254

22 I (2) 0.28 -0.05 NA NA

22 II (2) 0.23 0.00 0.52 0.07

60 (20) 0.30 0.07 0.06 0.05

100 (95) 0.58 0.35 0.00 0.02

NA – not analyzed
37

Figure 3.5 Amount of chloride detected in the post 

experiment water rinse.

The amount of dichloroacetate (Cl2HC2OO-) as a 

function of quartz tube temperature, carrier gas, and inlet 

temperature (water content) is shown in Figure 3.6. As 

mentioned in Section 2.3.2, DCAA has been classified 

as a probable human carcinogen (US EPA, 1998). No 

haloacetic acids (e.g., dichloroacetate) were detected 

in the water used to rinse the quartz tube operated at 

120°C with nitrogen as the carrier gas and the minimum 

concentration of DCAA detected with air as the carrier 

gas was 0.006 mg/L which was near the MDL of 

0.005 mg/L. The amount of dichloroacetate (DCAA) 

detected in the water rinse with air as the carrier gas 

was greater than the amount of DCAA detected in 

experiments completed with nitrogen as the carrier gas. 

Figure 3.6 Amount of dichloroacetate detected in the 

post experiment water rinse.

Trichloroacetate (Cl3C2OO-) was also detected in the 

water rinse from the quartz tube operated at 240 and 

420°C with air as the carrier gas (Table 3.12), whereas 

no trichloroacetate (TCAA) was detected in experiments 

with nitrogen as the carrier gas. TCAA was identified 

by mass spectrum match with the NIST02 library after 

GC/MSD analysis and the concentration of TCAA 

was estimated based on the ratio of chromatogram 

peak areas between DCAA and TCAA along with the 

concentration of DCAA that was determined using 

calibration solutions. The amounts of TCAA and DCAA 

were similar for the 240°C experiments, whereas the 

amount of TCAA exceeded that of DCAA for the 420°C

experiments with inlet temperature of 22 and 100°C. The 

water rinse from each 420°C experiment with air as the 

carrier gas had a pale yellow color and a strong solvent 

odor, whereas the water rinse with nitrogen as the carrier 

gas was clear.

After processing the water rinse solutions for haloacetic 

acid analysis, the MTBE extract was analyzed by 

GC/MSD, which revealed the presence of additional 

chlorinated compounds (Table 3.13). Each compound 

was identified by mass spectrum match with the NIST02 

library and the mass of each compound was estimated 

based on the ratio of chromatogram peak area to the 

peak area for DCAA. Based on the results shown in 

Figure 3.5 and Table 3.12, a water sample collected 

from the quartz tube experiment operated at 240°C and 

420°C with nitrogen as the carrier gas would contain 

chloride and dichloroacetric acid (DCAA). With air as 

the carrier gas, a water sample collected from the quartz 

tube operated at 240°C would contain DCAA and TCAA 

(Table 3.12) and a water sample from the quartz tube 

at 420°C would contain the chlorinated hydrocarbons 

3,4-dichloro-3-butene-2-one, pentachlorobutadiene, 

hexachlorobutene, and pentachlorobenzene (Table 3.13), 

in addition to DCAA and TCAA. 

3.3.2.5 Compounds Detected in the Iso-Octane Rinse

The DI water rinse was immediately followed by a 

30 mL iso-octane rinse for period of 5 minutes. The 

iso-octane rinse was performed to determine organic 

TCE degradation products that had condensed within the 

experimental apparatus while passing TCE through the 

heated quartz tube. The anticipated degradation products 

included hexachlorobutadiene and hexachlorobenzene 

based on the past experimental work described in 

Section 2.3.5 (e.g., Froese and Hutziner, 1994). The isooctane rinse samples were initially analyzed by GC/MS 

to identify the TCE degradation products present, while 

the mass of each product in each iso-octane rinse was 

determined by GC/FID analysis. No TCE degradation 

products were detected in the iso-octane rinse for the 

120 and 240°C experiments regardless of carrier gas or 

water content. 

Up to three products were detected in the 420°C

experiment with nitrogen as the carrier gas (Table 3.14). 

Increasing the quartz tube water content (i.e., inlet 

temperature) led to a decrease in the number and amount 

of degradation products detected with nitrogen as the 

carrier gas, similar to the increase in TCE recovery noted 
38

Table 3.12 Amount of Haloacetic Acids in the Water Rinse from 240°C and 420°C Experiments with Air as the 

Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

Quartz Tube Temperature (°C) – Air as Carrier Gas

240 420

DCAA (umol) TCAA (umol)* DCAA (umol) TCAA (umol)*

20 (2) 0.53±0.00 0.30 0.53±0.00 1.92

60 (20) 1.48±0.01 0.66 8.12±0.02 6.02

100 (95) 0.78±0.01 0.30 1.08±0.04 3.42

*TCAA concentration estimated based on ratio of TCAA to DCAA chromatogram peak area.

Table 3.13 Estimated Amounts (umol) of Compounds in Water Rinse from 420°C Experiment with Air as the 

Carrier Gas

Compound

Inlet Temperature (°C)

(Relative Humidity, %)

22 I (2) 22 II (2) 60 (20) 100 (95)

tetachloroethylene (C2

Cl4) nd nd 0.25 0.49

1,1,2,2-tetrachloroethane (C2

Cl4H2) nd nd nd 0.09

hexachloroethane (C2

Cl6) nd nd 0.07 nd

3,4-dichloro-3-butene-2-one (C4

Cl2OH4) 0.36 0.11 1.40 11.63

pentachlorobutadiene (C4

HCl5) 0.09 0.11 0.08 0.08

hexachlorobutadiene (C4

Cl6) nd nd 0.03 nd

pentachloro-1-propene (C3

Cl5) 0.46 nd 0.14 nd

hexachlorobutene (C4

H2Cl6) nd 0.54 0.76 0.10

pentachlorobenzene (C6

HCl5) 0.08 0.11 0.23 0.14

hexachlorobenzene (C6

Cl6) nd 0.02 0.08 0.01

tetrachloro-1,3-cyclopentadiene-5-

dichloromethylene (C6

Cl6) nd 0.16 0.04 nd

nd – not detected in the chromatogram

Table 3.14 Amounts (umol) of Compounds in the Iso-Octane Rinse from the 420°C 

Experiments with Nitrogen as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

22

(2)

60

(20)

100

(95)

hexachlorobutadiene (C4

Cl6) 0.01< 0.01< 0.01<

hexachlorobutene (C4

H2Cl6) 0.01< 0.01< 0.01<

pentachlorobenzene (C6

HCl5) 0.75±0.02 0.01< 0.01<

heptachlorocyclohexane (C6

H5Cl7) 0.55±0.01 0.01< 0.01<

hexachlorobenzene (C6

Cl6) 5.03±0.02 1.58±0.02 0.01<
39

in Table 3.6 (R2=0.994). There were no degradation 

products detected by GC/FID analysis in the iso-octane 

rinse of the 420°C experiment with the inlet temperature 

at 100°C which represented the maximum water content 

(relative humidity of 95%) for the fifth experimental 

series. 

There were up to five compounds detected in the 420°C

experiments with air as the carrier gas (Table 3.15). 

Hexachlorobutadiene and hexachlorobutene were 

detected in addition to penta- and hexachlorobenzne in 

the iso-octane rinse for the inlet temperature of 22°C. 

Penta- and hexachlorobenzene were detected in the isooctane rinse with the inlet at 100°C. These compounds 

were also detected in the MTBE extract of the water 

rinse (Table 3.13) that was completed prior to the isooctane rinse for the 420°C experiment with air as the 

carrier gas. Based on the results presented in Tables 

3.14 and 3.15, hexachlorobenzene is likely to be the 

most prominent degradation product formed under these 

experimental conditions, and increasing the amount of 

water vapor entering the reactor would decrease the 

amount of TCE degradation products formed.

Table 3.15 Amounts (umol) of Compounds in 

the Iso-Octane Rinse from the 420°C 

Experiments with Air as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

22 I

(2)

22 II

(2)

60

(20)

100

(95)

hexachlorobutadiene 

(C4

Cl6) 0.66 0.47 NA 0.01<

hexachlorobutene 

(C4

H2Cl6) 1.55 1.26 NA 0.01<

pentachlorobenzene 

(C6

HCl5) 0.95 0.75 NA 0.65

heptachlorocyclohexane 

(C6

H5Cl7) 0.01< 0.01< NA 0.01<

hexachlorobenzene 

(C6

Cl6) 4.29 4.23 NA 1.56

NA – not analyzed, sample broken during storage

3.3.2.6 Mass Balance

The amount of TCE as moles of carbon (moles carbon = 

2 × moles TCE) detected in the DCM trap with respect 

to the moles of TCE as carbon that were injected into the 

experimental apparatus operated at 420°C with nitrogen 

as the carrier gas is provided in Table 3.16 as “%Carbon 

in Feed.” Similarly, the amount of TCE recovered as 

moles of chlorine (moles chlorine = 3 × moles TCE) 

with respect to the moles of TCE as chlorine that were 

injected into the apparatus is also provided in Table 

3.16 as “%Chlorine in Feed.” These measures of TCE 

recovery are analogous to those presented for TCE in 

Section 3.3.2.1, and in Figure 3.4 and Table 3.6.

The amount of TCE degradation products detected in 

the DCM trap and quartz tube rinses are also reported in 

Table 3.16 as moles of carbon and chlorine with respect 

to the amount of carbon and chlorine delivered to the 

quartz tube apparatus as TCE. The purpose of reporting 

the amount of carbon or chlorine detected is to show 

the distribution of each TCE degradation product in the 

apparatus and to determine if all the carbon and chlorine 

atoms were accounted for (i.e., mass balance). For 

example, while 93.1% of the carbon delivered during 

the experiment with the inlet at 22°C was detected 

in the DCM trap as TCE (Table 3.16), 3.4% of the 

carbon delivered was detected in the DCM trap as TCE 

degradation products that were presented in Table 3.8, 

and 0.5% of the carbon delivered was detected in the 

quartz tube rinses as TCE degradation products as listed 

in Table 3.14. Thus, the net recovery of the TCE injected 

with the inlet at 22°C increased from 93.1% when TCE 

recovery alone was considered to 97.1% on a carbon 

basis, and increased to 101.2% on a chlorine basis when 

the TCE degradation products were included.

TCE was the predominant (>93%) compound detected 

in the DCM trap, and there were more chlorinated TCE 

degradation products condensed within the DCM trap 

than found in the water or iso-octane rinses of the 420°C

experiments with nitrogen as the carrier gas. Increasing 

the quartz-tube water content resulted in a decrease in 

the amount of TCE degradation products in the DCM 

trap while the amount of chloride found in the water 

rinse increased. Overall, very good mass recovery of 

TCE on a carbon (>97%) and chlorine (>100%) basis 

was obtained in the 420°C experiment with nitrogen as 

the carrier gas.

The distribution of carbon and chlorine in the 

experimental apparatus operated at 420°C with air as 

the carrier gas is provided in Table 3.17. Approximately 

18-23% of the carbon introduced as TCE was converted 

to CO and CO2

, while the other half consisted of 

chlorinated hydrocarbons detected in the DCM trap and 

as phosgene for the experiment with inlet temperature of 

22°C. Increasing the quartz tube water content resulted 

in a decrease in the amount of chlorinated carbon 

compounds in the DCM trap and in the water and isooctane rinses of the quartz tube, along with an increase 

in the amount of chloride found in the water rinse.

The amount of carbon and chlorine recovered in the 

DCM trap, water and iso-octane rinses, and in the 

Tedlar® bag decreased with increasing quartz tube 

water content for the 420°C experiments with air as the 

carrier gas (Table 3.17). The amounts of missing carbon 

and chlorine were nearly equal, suggesting that the 

missing compounds could have consisted of chlorinated 
40

hydrocarbons. It is possible that the unaccounted for 

chlorinated hydrocarbons were present in the Tedlar® 

bag and went undetected during the GC/TCD analysis 

for CO/CO2

 content due to adsorption on the Carboxen 

1010 capillary column.

3.4 Discussion

The goal of the quartz tube experiments was to 

determine the identity and amount of TCE degradation 

products formed after exposing gas phase TCE to 

temperatures from 60 to 480°C. The following sections 

present potential TCE degradation mechanisms based on 

the quartz tube experimental results.

3.4.1 Nitrogen as the Carrier Gas at 420°C

The 420°C experiment with nitrogen as the carrier gas 

involved passing TCE and water vapor through the 

quartz tube heated to 420°C. Nitrogen and water are inert 

relative to oxygen and are not thought to have caused 

TCE degradation under the experimental conditions. 

Therefore, the degradation of TCE, as indicated by the 

detection of carbon compounds and chloride ions in the 

DCM trap and quartz tube rinses is hypothesized to have 

occurred via unimolecular dissociation of TCE rather 

than a bimolecular reaction with nitrogen or water. 

The compounds formed after passing gas-phase 

TCE at 320°C through a laser beam include HCl, 

dichlorovinylidene (:C2

Cl2), dichloroacetylene (C2Cl2), 

vinyl radicals (HClC2Cl ̇), and chlorine atoms (Cl) 

according to (Yokoyama et al., 1995): 

Table 3.16 Distribution of Carbon and Chlorine for the 420°C Experiments with Nitrogen as the Carrier Gas

Inlet Temperature (°C) 

(Relative Humidity, %)

22

(2)

60

(20)

100

(95)

22

(2)

60

(20)

100

(95)

Phase Compound %Carbon in Feed %Chlorine in Feed

Compounds in 

DCM Trap

TCE 93.1±1.9 95.5±1.5 99.1±1.9 93.1±1.9 95.5±1.5 99.1±1.9

All Other 3.4±0.1 2.4±0.0 1.3±0.0 7.3±0.2 4.7±0.2 1.1±0.0

Compounds in 

Gas Phase CO/CO2 <1.4 <1.4 <1.4 <1.4 <1.4 <1.4

Condensed in 

Quartz Tube

Water + IsoOctane Rinses 0.5±0.0 0.1±0.0 0.0±0.0 0.8±0.1 0.9±0.1 2.2±0.3

Net Recovery 97.1±1.9 98.1±1.5 100.4±1.9 101.2±1.9 101.1±1.6 102.4±1.9

Table 3.17 Distribution of Carbon and Chlorine for the 420°C Experiments with Air as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

22 II

(2)

60

(20)

100

(95)

22 II

(2)

60

(20)

100

(95)

Phase Compound % Carbon in Feed % Chlorine in Feed

Compounds in 

DCM Trap

TCE 52.4±1.2 54.6±0.2 51.7±0.9 52.4±1.2 54.6±0.2 51.7±0.9

All Other 13.2±0.3 11.9±0.2 3.2±0.1 20.3±0.4 18.0±0.3 4.9±0.1

Compounds in 

Gas Phase

CO/CO2 18.4 20.3 23.2 0.0 0.0 0.0

Phosgene 7.0 0.8 0.0 14.0 1.1 0.0

Condensed in 

Quartz Tube

Water + IsoOctane Rinses 0.6±0.0 0.6±0.0 1.0±0.0 2.0±0.0 6.7±0.4 17.8±1.8

Net Recovery 91.5±1.2 88.1±0.3 79.1±0.9 88.8±1.3 80.5±0.5 74.6±2.0
41

 

(3.3)

While Yokoyama et al. (1995) found spectroscopic 

evidence to suggest that dichlorovinyl radicals (3.3c) 

had formed after passing TCE through the laser beam, 

the branching ratio for the Cl (3.3c) to HCl elimination 

(3.3a and 3.3b) reactions was 0.17, which indicates that 

the HCl elimination pathway produced approximated 

5 times more TCE degradation products than the Cl 

elimination reaction pathway under these experimental 

conditions. The predominance of the HCl elimination 

pathway (3.3a and 3.3b) is supported by the results 

of Reiser et al. (1979) which indicate that HCl and 

dichloroacetylene were the primary products from the 

photolysis of TCE at 25°C. 

The elimination of HCl from TCE (Equations 3.3a and 

3.3b) was proposed to occur at elevated temperatures 

after passing TCE through a flame (Chang and Senkan, 

1989) and after passing gas-phase TCE through a heated 

quartz tube (Wu and Lin, 2004) based on the detection 

of dichloroacetylene. Passing TCE through the quartz 

tube apparatus used herein at 420°C with nitrogen as the 

carrier gas is proposed to have caused the unimolecular 

dissociation of TCE described by Equation 3.3. The 

products in Equation 3.3 are reactive compounds 

thought to have rapidly transformed into the chlorinated, 

4 and 6 carbon compounds that were detected in 

experiments completed herein using the empty quartz 

tube with nitrogen as the carrier gas (Tables 3.8 and 

3.14). Goodall and Howlett (1954) also found HCl and 

hexachlorobenzene as the primary TCE degradation 

products after passing gas phase TCE through a Pyrex 

tube heated between 385 and 445°C with nitrogen as the 

carrier gas.

Increasing the water content of the quartz tube at 420°C

with nitrogen as the carrier gas resulted in an increase 

in TCE recovery, an increase in the amount of chloride 

detected in the water rinse, and a decrease in the amount 

of degradation products detected in the DCM trap and in 

the iso-octane rinse (Table 3.18). These results indicated 

that increasing the amount of water in the quartz tube 

at 420°C resulted in a decrease in the amount of TCE 

degraded. 

The role that water played in reducing TCE degradation 

is not known. Water may have reacted with the 

unimolecular degradation products shown in Equation 

3.3 and prevented them from reacting with TCE, thereby 

decreasing the amount of TCE degraded. For example, 

chlorine initiated TCE degradation has been shown to 

occur at 25°C and is thought to proceed by forming 

tetrachloroethyl radicals (Cl2

HC2Cl2 ̇) according to 

(Catoire et al., 1997): 

(3.4)

Increasing the quartz-tube water content in the 

experiments completed at 420°C with nitrogen as the 

carrier gas could have prevented the chlorine radicals 

produced by the unimolecular dissociation of TCE 

(Equation 3.3c) from reacting with TCE. However, 

chlorine radicals are not thought to react with water 

based on the equilibrium coefficient for the aqueous 

phase reaction as shown in Equation 3.5 which is 

1.4×10-7 at 24°C (Yu et al., 2004).

Cl• + H2O → ClHO–• + H+ (3.5)

Table 3.18 Carbon in the DCM Trap and Iso-Octane Rinse, and Chloride in the Water Rinse for the 420°C 

Experiments with Nitrogen as the Carrier Gas

Inlet Temperature (°C) 22 60 100

(Relative Humidity, %) (2) (20) (95)

TCE Recovery (%) 93.1±1.9 95.5±1.5 99.1±1.9

Carbon in DCM trap other than TCE (umol) 251.6 176.7 99.7

Carbon in iso-octane rinse (umol) 38.0 9.4 0.0

Carbon in water rinse (umol) 0.01 0.01 0.84

Chloride in water rinse (umol) 52.0 83.9 242.7

Note: No CO or CO2 was detected in the experiments with nitrogen as the carrier gas.
42

While chlorine radicals are not expected to react with 

water, they are known to react with chloride-ions 

dissolved in water to form dichlorine radical anions 

(Cl2

-

 ̇) (Yu and Barker, 2003).

Cl• + Cl– → Cl2

–• (3.6)

Since the amount of chloride increased with quartz tube 

water content, water may have reduced the amount 

of gas-phase chlorine radicals and thus reduced the 

amount of TCE degraded. The source of the chloride 

ions is thought to be from the HCl produced during 

the unimolecular dissociation of TCE according to 

Equations 3.3a and 3.3b since HCl readily ionizes in 

water. For example, the presence of water molecules in 

a gas stream with HCl molecules at 25°C was shown 

to cause an increase in the hydrogen to chlorine bond 

length at the water to HCl molar ratio of 1:1 and the 

complete ionization of HCl with the water to HCl molar 

ratio at 5:1 (Farnik et al., 2003).

HCl has been proposed as a source of chlorine radicals 

in the post-flame zone of combustion chambers 

(Procaccini et al., 2003). However, the experimental 

work completed to date suggests that HCl is stable at 

420°C, with an estimated dissociation half-life of 3×109

years (Baulch et al., 1981). Thus, HCl is not expected 

to yield chlorine radicals at 420°C with nitrogen as 

the carrier gas. Even though HCl is not expected to 

dissociate to yield chlorine radicals at 420°C there is 

experimental evidence to suggest that HCl reacts with 

organic compounds at elevated temperatures. The 

presence of HCl caused the chlorination of gas phase 

hexachlorodibenzo-p-dioxin (HCDD) at 248°C with the 

formation of hepta- and octachlorodibenzo-p-dioxins 

whereas less chlorinated dibenzo-p-dioxins were found 

in experiments completed without HCl (Addink et 

al., 1996). Procaccini et al. (2003) found that adding 

gas-phase HCl and benzene to a post ethene (C2H4) 

combustion zone at 640°C resulted in the formation of 

chlorobenzene and chlorophenols, demonstrating that 

HCl could react with benzene. The reaction between 

HCl and benzene was proposed to involve chlorine 

radicals based on the similarity in product distribution 

after using Cl2

 gas and HCl in combination with benzene 

(Procaccini et al., 2003). Thus, HCl may be reacting 

with TCE in the experiments completed herein at 420°C

with nitrogen as the carrier gas. Increasing the water 

content of the 420°C experiment with nitrogen as the 

carrier gas is proposed to have decreased the amount of 

HCl and chlorine radicals available to react with TCE. 

An alternative explanation is that the increase in water 

content could cause an increase in the HCl elimination 

pathways (Equations 3.3a and 3.3b) and a decrease in the 

chlorine radical pathway (Equation 3.3c).

3.4.2 Air as the Carrier Gas at 420°C

The 420°C experiment conducted with air (21% oxygen) 

as the carrier gas involved passing TCE and water vapor 

through the quartz tube heated to 420°C. The presence 

of molecular oxygen in the 420°C experiments resulted 

in a decrease in TCE recovery and an increase in the 

number and amount of TCE degradation products 

detected as compared to the experiments completed 

with nitrogen as the carrier gas. Thus, the presence of 

oxygen in the 420°C experiments resulted in an increase 

in the amount of TCE degraded in excess of the amount 

of TCE degraded by unimolecular dissociation alone 

(Equation 3.3). The increase in TCE degradation with 

oxygen present is thought to involve the formation of 

peroxyl radical species. Molecular oxygen is suspected 

to have reacted with tetrachloroethyl radicals produced 

from the reaction between chlorine and TCE as shown in 

Equation 3.4 to form peroxyl radicals (Cl2HC2Cl2OO ̇) 

according to (Catoire et al., 1997; Nimlos et al., 1993):

(3.7)

The peroxyl radicals are suspected to react with TCE in 

a radical chain mechanism resulting in an increase in the 

amount of TCE degraded at 420°C as compared to the 

amount degraded with nitrogen as the carrier gas. 

The TCE degradation products detected in the DCM trap 

(Table 3.9), water rinse (Table 3.13), and iso-octane rinse 

(Table 3.15) are thought to have formed by reactions 

involving radicals such as the tetrachloroethyl radical, 

by reactions involving non-radical compounds such 

as dichlorocarbene, or a combination of radical and 

non-radical interactions. For example, trichloroacetate 

(TCAA) was detected in the DCM trap and in the water 

rinse (Table 3.12) of the quartz tube after the 420°C

experiments with air as the carrier gas. The formation 

of 1,1,1,2-tetrachloroethyl radicals (Cl3C2HCl ̇) from 

the chlorine initiated TCE degradation (Equation 3.8) 

is suspected as the key intermediate that reacted with 

molecular oxygen to yield TCAA. 

(3.8)

The formation of tetrachloroethyl radical isomers 

may have been due to the additional chlorine radicals 

produced during the peroxyl induced degradation of 

TCE. TCAA is known to yield dichlorocarbene (:CCl2

) 

and CO2 upon heating (Kaberdin and Potkin, 1994; 

p. 250, Smith and March, 2001). Dichlorocarbene is a 

reactive compound that is known to combine with TCE 

to yield pentachlorocyclopropane (Sepiol and Soulen, 
43

1975), which was detected in the DCM trap (Table 3.9). 

Dichlorocarbene has been suggested to dimerize to form 

PCE, to react with chlorine to form CCl4, and with HCl 

to form chloroform (CHCl3) (Zhu and Bozzelli, 2003), 

all compounds that were detected in the DCM trap 

(Table 3.9). 

Dichloroacetylene (DCA) is another intermediate 

compound that may have contributed to the formation 

of the TCE degradation products observed in the DCM 

trap and rinses. Reichert et al. (1980) synthesized DCA 

(C2Cl2) from TCE and then exposed DCA to air at room 

temperature (22°C). DCA decomposed on contact with 

air and formed phosgene, PCE, hexachlorobutadiene, 

trichloroacryloyl chloride, trichloroacetyl chloride, CCl4, 

and chloroform. Several of these products including 

PCE, hexachlorobutadiene, CCl4, and chloroform were 

also detected in the 420°C experiment with air as the 

carrier gas, suggesting that DCA may have been present.

Increasing the amount of water entering the quartz tube 

by increasing the inlet temperature from 22°C to 60°C

resulted in a decrease in TCE recovery for the 22I to 

60 experiments, whereas there was an increase in TCE 

recovery for the 22II to 60 experiments (Table 3.19). 

The lowest TCE recovery occurred when the inlet was 

operated at 100°C (relative humidity of 95%). While 

there was no clear trend in TCE recovery with increasing 

water content (R2=0.052, see Table 3.7), increasing the 

quartz tube water content led to a decrease in the amount 

of degradation products in the DCM trap and iso-octane 

rinse, with an increase in the products detected in the 

gas phase and an increase in the amount of chloride 

in the water rinse (Table 3.19). The increase in CO2

coupled with the decrease in phosgene may have been 

related to the increase in quartz tube water content as 

described in Section 3.3.2.4. However, the amount of 

chloride detected in the water rinse for the 100°C inlet 

experiment (1954 umol) was approximately twice the 

amount expected if all the phosgene had reacted with 

water (2×521=1042 umol). The amount of chloride 

detected above the amount expected from phosgene 

hydrolysis (1954 – 1042 = 912 umol) might represent 

chlorine that was prevented from reacting with TCE due 

to the presence of water in the quartz tube. Thus, water 

may have hydrolyzed phosgene and served to remove 

reactive chlorine radicals and HCl from the gas phase 

while not impacting the amount of TCE degraded.

3.4.3 Experiments Conducted at 120 and 240°C

The small amount of chloride (<0.02% of TCE in 

the feed) detected in the water rinse from the 120°C

experiments completed with nitrogen and air as the 

carrier gas (Table 3.20) was initially thought to represent 

background chloride from the laboratory air. However, 

the detection of DCAA in water rinses from the 120°C

experiment with air as the carrier gas indicated that 

TCE degradation was occurring. Table 3.20 contains 

the amount of chloride (umol) and DCAA detected 

(nmol) in the water rinse from the 120°C experiments. 

The detection limit for chloride was 0.07 umol, and 

was determined using the standard deviation of 12 

measurements of a 2 uM calibration standard collected 

over a one month period and the student’s t value of 

2.718 (n=11, alpha=0.01). The detection limit for the 

DCAA was determined using the standard deviation 

of 12 measurements of a 12 ug/L calibration standard 

analyzed over a 15 day period. 

Table 3.19 Carbon in the DCM Trap and Iso-Octane Rinse, and Chloride in the Water Rinse for the 420°C 

Experiments with Air as the Carrier Gas

Inlet Temperature (°C)

(Relative Humidity, %)

22 I

(2)

22 II

(2)

60

(20)

100

(95)

TCE Recovery (%) 59.5±0.9 52.4±1.2 54.6±0.2 51.7±0.9

Carbon in DCM trap other than TCE (umol) 967.4 981.0 897.4 240.8

Carbon in iso-octane rinse (umol) 40.3 36.8 NA 13.3

Carbon as CO (umol) 1130.7 1140.2 1231.6 1157.8

Carbon as CO2

 (umol) 277.5 228.4 299.1 575.1

Carbon as Phosgene (umol) gravimetrically NA 521.1 60.8 1.0

Carbon as DCAA (umol) 0.6 0.5 8.1 1.1

Carbon as TCAA (umol) 0.7 1.9 6.0 3.4

Total Carbon other than TCE (umol) 2417.2 2909.9 2503.0 1992.5

Chloride in water rinse (umol) 104.7 105.1 725.1 1953.9
44

Table 3.20 Amount of Chloride and DCAA in the 

Water Rinse from the 120°C Experiments

Inlet 

Temperature 

(°C)

(Relative 

Humidity, %)

Nitrogen as 

Carrier Gas Air as Carrier Gas

Cl-

(umol)

DCAA 

(nmol)

Cl-

(umol)

DCAA 

(nmol)

22 (2) <0.07 <0.5 0.11 2.70±0.03

60 (20) 0.74 <0.5 0.45 1.89±0.06

100 (95) 0.94 0.8 0.48 2.08±0.05

No estimate of uncertainty, only one Cl- measurement 

performed.

If the chloride detected in the 120°C experiments 

represents the degradation of TCE, then carbon 

degradation products in addition to DCAA should 

have been detected. Dichloroacetylene (C2

Cl2) is the 

expected product after elimination of HCl from TCE 

(Equations 3.3a and 3.3b). With nitrogen as the carrier 

gas, dichloroacetylene should have been collected in 

the Tedlar® bag; however, the bag was only analyzed 

for CO and CO2 content and none was detected. With 

air as the carrier gas, dichloroacetylene was expected 

to react with oxygen to form CO and CO2 and, based 

on the amount of chloride detected, there should have 

been from 2 to 30 ppmv of CO2 in the Tedlar® bag. The 

CO2 content of the Tedlar® bag for the experiment at 

120°C with air as the carrier gas was determined using 

a GC/TCD method; however, the detection limit for this 

method was 500 ppmv, and no CO or CO2 was detected. 

Increasing the tube temperature to 240°C did not 

significantly increase the amount of chloride detected 

with nitrogen as the carrier gas (Table 3.21) as compared 

to the amount detected in the 120°C experiments 

(Table 3.20). The presence of oxygen in the 240°C

experiments resulted in an increase in the amount 

of DCAA, TCAA, and chloride detected relative 

to the experiments completed with nitrogen as the 

carrier gas (Figures 3.7 and 3.8). This suggests that 

chlorine initiated TCE degradation occurred to yield 

the 1,1,1,2-tetrachloroethyl radical, which reacted 

with oxygen to yield TCAA. No other chlorinated 

hydrocarbon compounds were detected indicating that 

there was insufficient thermal energy for the radical 

chain reaction to propagate.

Increasing the water content of the quartz tube in the 

240°C experiment with air as the carrier gas resulted in a 

decrease in TCE recovery (R2

=0.998 and P-Value=0.03, 

see Table 3.7), while no trend in TCE recovery was 

apparent for the 240°C experiment completed with 

nitrogen as the carrier gas (R2=0.227 and P-Value=0.68, 

see Table 3.6). Thus, water did have an effect on the 

recovery of TCE when combined with oxygen, which 

may have been to induce TCE degradation. However, the 

amount of chloride, DCAA, and TCAA detected in the 

water rinse did not significantly increase with quartz tube 

water content. Additional carbon degradation products 

should have been detected to confirm that water was 

causing TCE degradation since the amount of DCAA 

and TCAA detected in the 240°C experiment with air as 

the carrier gas represented less than 1% of the missing 

TCE as carbon. The range of CO2 concentrations, 

assuming the missing TCE was completely converted 

to CO2, would have been from 2170 to 4596 ppmv, well 

above the GC/TCD method detection limit; however, 

no CO or CO2 was detected. The two explanations for 

the decrease in TCE recovery with increasing water 

content for the 240°C experiments with air as the carrier 

gas are: 1) there were additional chlorinated carbon 

reaction products, such as dichloroacetylene, that went 

undetected or 2) more TCE partitioned into the water 

in the quartz tube with air as the carrier gas than with 

nitrogen as the carrier gas. 

Table 3.21 Amount of Chloride, DCAA, and TCAA in the Water Rinse from the 240°C Experiments

Inlet Temperature (°C)

Nitrogen as Carrier Gas Air as Carrier Gas

Cl-

 (umol) DCAA (nmol) Cl- (umol) DCAA (nmol) TCAA (nmol)

22 0.27 2.9±0.1 11.2±0.9 528±4 299

60 0.36 2.5±0.1 15.5±2.2 1481±8 662

100 0.34 2.9±0.1 14.9±0.2 711±13 305
45

3.5 Summary

The average recovery of TCE with nitrogen as the 

carrier gas was greater than 94% at all the experimental 

temperatures. Carbon-based TCE degradation products 

were only detected in the experiments completed at 

420°C with nitrogen as the carrier gas. Up to four 

degradation products were identified in the DCM trap, 

two in the water rinse, three in the iso-octane rinse, and 

no CO or CO2 was detected for experiments completed 

at 420°C with nitrogen as the carrier gas. The amount 

of TCE recovered as carbon for the 420°C experiments 

with nitrogen as the carrier gas was greater than 97%, 

with 93% as TCE. The amount recovered as chlorine 

was greater than 100% with up to 7% as chlorinated 

degradation products. The degradation products detected 

contained 4 and 6 carbon atoms, with greater than 

5 chlorine atoms per molecule. TCE degradation was 

proposed to be initiated by thermal induced unimolecular 

dissociation but was also influenced by chlorine induced 

degradation. Increasing the quartz tube water content 

resulted in an increase in TCE recovery which was 

suggested to indicate a decrease in chlorine induced TCE 

degradation.

The average recovery of TCE was greater than 94% 

with air as the carrier gas for the 120 and 240°C

experiments, but dropped to approximately 53% in 

the 420°C experiments. The small amount (<0.02% 

TCE) of chloride detected in experiments completed 

at 120°C and at 240°C was thought to represent TCE 

degradation. However, no carbon degradation products 

were identified that could account for the missing TCE. 

Carbon based TCE degradation products were detected 

in the 240 and 420°C experiments with air as the carrier 

gas. There were three degradation products identified in 

the water rinse from the 240°C experiments. Up to 13 

degradation products were detected in the DCM trap, 

13 in the water rinse, and five in the iso-octane rinse 

in the 420°C experiments. The degradation products 

ranged from single carbon compounds with 3 chlorine 

atoms (i.e., chloroform) to compounds with 6 carbons 

and 6 chlorine atoms (i.e., hexachlorobenzene). Carbon 

monoxide (CO), CO2

, and phosgene were detected in 

the gas phase of the 420°C experiments. The amount 

of carbon recovered for the 420°C experiments with 

air as the carrier gas was 91.5% for the 22°C inlet 

experiment but decreased to 79.1% for the experiment 

completed with the inlet at 100°C. The amount of 

chlorine recovered followed a similar trend with 88.8% 

recovered for the 22°C inlet experiment and just 74.6% 

recovered with the inlet at 100°C. TCE degradation 

was proposed to be initiated by thermal induced 

unimolecular dissociation but was also influenced by 

the formation of peroxyl radicals due to the presence of 

oxygen. Increasing the quartz tube water content in the 

420°C experiments with air as the carrier gas may have 

hydrolyzed phosgene and served to remove reactive 

chlorine radicals and HCl from the gas phase while not 

impacting the amount of TCE degraded. 

The experiments reported herein represent one 

of only a few efforts to quantify gas-phase TCE 

degradation and reaction product formation under 

well-controlled thermal treatment conditions. Several 

of the important results of this work are: (1) little, if 

any, TCE degradation occurred at temperatures below 

240°C; (2) at 420°C, up to 34 degradation products 

were detected in the effluent solvent trap (e.g., CCl4

, 

PCE, hexachloroethane), solvent and water rinses of 

the reactor (DCAA, TCAA), and effluent gas (e.g., CO, 

CO2, and phosgene); (3) at 420°C, with nitrogen as the 

carrier gas degradation products accounted for 1 to 4% 

of the TCE-carbon feed, and with air (22% oxygen) 

as the carrier gas degradation products accounted for 

28 to 38% of the TCE-carbon feed, with 18 to 23% of 

the carbon attributed to the formation of CO and CO2. 

Here, it is important to recognize that these results are 

specific to the experimental conditions employed in 

these laboratory studies, and do not precisely replicate 

the field conditions. For example, the following 

differences between the reported laboratory studies and 

thermal treatment conditions in the field could alter TCE 

degradation and product formation: (1) natural minerals 

and organic matter present in subsurface soils could 

either facilitate or quench specific reaction pathways, 

(2) temperatures near thermal wells can be much higher 

(e.g., 600-800°C) than those studied here (22 to 420°C), 

which could lead to complete oxidation of reaction 

products, (3) oxygen may be depleted in the thermal 

treatment swept zone which could alter reaction product 

distributions. Nevertheless, the experimental results 

reported here provide quantitative measurements of gasphase TCE degradation and reaction product formation 

in heated, flow-through reactors, and provide important 

insight into the reaction products and pathways that 

could potentially occur during thermal treatment of 

TCE-contaminated soil. 

3.6 Quality Assurance Summary for the 

Flow-Through Experiments

These experiments involved passing a carrier gas that 

contained TCE through a quartz tube heated to between 

25 and 480°C. The quality assurance efforts for these 

experiments focused on:

1. Assessing system cleanliness prior to each 

experiment (pre-rinse/pre-trap) 

2. Estimating the variability in sample collection and 

analyses (replicates)

3. Demonstrating analysis method performance 

relative to methylene chloride (matrix spike)
46

4. Determining if contaminants were introduced during 

sample storage (storage blanks)

System Cleanliness. The apparatus was assembled and 

rinsed with freshly dispensed dichloromethane (DCM) 

prior to each experimental run. Then carrier gas was 

passed through the apparatus followed by a DCM 

filled vial prior to TCE introduction. Samples from the 

DCM rinse and trap were then analyzed to determine 

if the decontamination methods were adequate. During 

preliminary experiments it was discovered that rinsing 

the apparatus with iso-octane was inadequate for 

removing all the products formed after passing TCE 

through the apparatus operated at 300°C; the results 

of this experimental trial were discarded and not used. 

Consequently, the decontamination method was modified 

so that the apparatus was disassembled, washed in 45°C

soapy water, rinsed with deionized water, and heated in a 

drying oven at 240°C for at least an hour. No compounds 

were detected in samples from either the DCM rinse 

or carrier gas trap collected prior to each subsequent 

experiment. 

Sample Collection and Analyses Variability. At least 

two samples were collected from the DCM trap, isooctane rinse, and methyl-tert-butyl ether (MTBE) used to 

extract compounds from a water rinse of the apparatus. 

These replicates samples were used to assess the range of 

compounds in the samples and any variability introduced 

during sample collection and analysis. Variability was 

low, less than 10% relative standard deviation (RSD) 

for all replicates, and less than 5% RSD for select 

experiments. Given that analytical grade solvents were 

used in these experiments, the low variability was 

expected.

Method Performance. Assessing method performance 

involved adding 1 mL of EPA 8240B/8260A Matrix 

Spike Mix (Sigma-Aldrich #47412) to the solvent 

being analyzed (i.e., DCM, iso-octane, or MTBE) and 

analyzing the matrix spike. The resulting analyses were 

within 10% of the expected concentrations. This was 

not unexpected as the matrix used for these experiments 

were analytical grade solvents.

Storage Blanks. Vials filled with freshly dispensed 

solvent were stored with each batch. No compounds 

were detected in any of the storage blanks.
47

4.0

TCE Degradation in Heated Ampules

4.1 Introduction

Four experimental series were performed to determine 

the rate of TCE degradation and degradation products 

formed after heating dissolved phase TCE to 120°C 

over periods of up to 40 days. The experiments were 

completed using glass ampules filled with TCE 

contaminated water and sealed by melting the ampule 

neck with a propane-oxygen torch (flame sealed). 

Approximately three-quarters of the ampule volume was 

filled with TCE contaminated water with the remaining 

one-quarter volume contained gas, thus TCE was present 

in both the dissolved- and gas-phase within the ampules 

during the experiments. The first ampule experiment 

was performed to demonstrate that dissolved oxygen 

levels could be maintained in flame-sealed ampules by 

measuring the dissolved oxygen concentration before 

and after heating water-filled ampules to 120°C over 

a period of 6 days (Table 4.1). The second ampule 

experiment involved demonstrating analytical methods 

to determine the aqueous phase concentrations of TCE 

and dichloroacetic acid (DCAA), one of the anticipated 

TCE degradation products. The third ampule experiment 

introduced room temperature control ampules and 

solids into the ampules along with an evaluation of the 

method used to introduce TCE into the ampules. The 

fourth ampule experiment was designed to determine the 

rate of TCE disappearance along with the identity and 

amount of each TCE degradation product as a function 

of 1) dissolved oxygen concentration, 2) hydroxide ion 

concentration, and 3) ampule solids content. 

The following section (Section 4.2) describes the ampule 

experimental system along with the methods used to 

prepare the ampules. Experimental methods and results 

specific to each of the experimental series are given in 

Section 4.3. The final two sections provide a discussion 

of the ampule results in terms of potential TCE 

degradation mechanisms (Section 4.4) and a summary of 

the ampule experiment results (Section 4.5). 

4.2 Experimental Materials and 

Methods

4.2.1 Preparation of Solids

Two solids compositions were used in the fourth ampule 

experiment including 20-30 mesh Ottawa sand and a 

mixture of 20-30 mesh Ottawa sand and 1% goethite. 

The solids were prepared by soaking approximately 

2,000 g of sand from Ottawa, IL (ASTM 20-30 Sand, 

U.S. Silica Co., Berkeley Springs, WV) in 1 N nitric 

acid solution as described in Section 3.1.3. However, 

the DI rinse method employed was improved to remove 

residual nitric acid from the sand. The DI rinse consisted 

of placing small volumes of sand into the top of a 

20-30-100 mesh ASTM sieve stack and running DI 

water over the sand. The sand was then placed back into 

a drying tray and DI-Nanopure water was added to cover 

the sand. The pH of the DI-Nanopure water covering the 

sand was measured with a pH probe (Accumet Model 

50, Fisher Scientific, Fair Lawn, NJ) and the water rinse 

was repeated until the pH of the standing DI-Nanopure 

water was 7. The sand was then placed into a drying 

Table 4.1 Ampule Experimental Matrix

Experimental 

Series Variables Purpose

1 Dissolved Oxygen, Hydroxide Ions Demonstrate that ampules can retain oxygen

Identify reaction products

2 Dissolved Oxygen Demonstrate sample analysis techniques

3 Dissolved Oxygen

Solids

Room temperature controls, solids, evaluation of TCE 

introduction method

4 Dissolved Oxygen, Hydroxide Ions

Solids

Determine rate of TCE disappearance and degradation products 

as function of oxygen, hydroxide ion, and solids
48

oven and heated to 130°C for 3 hours to remove excess 

moisture and then baked at 200°C for 2 hours. The oven 

temperature was lowered to 100°C and the sand was 

allowed to cool for 3 hours. 

Approximately 1,000 g of the acid-washed sand was 

placed into a second glass drying tray to which 10 grams 

of goethite powder was added to create a uniform 

1% (wt) mixture. Research grade goethite chips, 

approximately 1 gram each, were obtained from Ward’s 

Natural Science (Rochester, NY), and were reported to 

have been collected from Grants County, New Mexico. 

The goethite chips were ground into a fine powder (silt 

to clay size particles) using a mortar and pestle prior 

to mixing with the sand. The drying trays were then 

autoclaved with steam at 17 psi (121°C) for 25 minutes 

and the water from the autoclave process was allowed 

to vent from the trays for a period of approximately 

30 minutes. Ampules that had been autoclaved and 

cooled in a desiccator according to procedures outlined 

in Section 4.1.1 were loaded with approximately 

20 grams of either Ottawa sand or Ottawa sand+1% 

goethite and then sealed with aluminum foil. 

4.2.2 Preparation of Aqueous Solutions

All aqueous solutions were prepared with deionized 

(DI) water that was freshly dispensed from a Nanopure®

analytical deionization system (model D4741, Barnstead 

International, Dubuque, IA). The Nanopure® system has 

four inline purification cartridges that produce organic 

free, Type I reagent grade water in accordance with 

the specifications provided in the ASTM D1193-99e1, 

“Standard Specification for Reagent Water.” The DI 

water was dispensed only after the electrical resistance 

of the water was greater than 18 MΩ-cm at room 

temperature (22°C) and through a 0.2 μm pore size filter.

Aqueous solutions with low dissolved oxygen content 

(<0.3 mg/L), referred to as anoxic water, were prepared 

prior to each experiment by sparging freshly dispensed 

DI-Nanopure water with argon gas (Airgas-South, Inc., 

Marietta, GA) after passing through an oxygen trap 

(part# 4001, Alltech Associates, Inc., Deerfield, IL). The 

anoxic water was sparged with argon for at least 1 hour 

and had a dissolved oxygen concentration between 0.2 

and 0.3 mg/L as indicated by the Rhodazine D method 

(part# K7501, CHEMetrics, Inc., Calverton, VA). 

Oxygen-saturated water, referred to as oxic water, was 

prepared by sparging DI-Nanopure water with ultra zero 

grade air (UZA) (Airgas-South, Inc., Marietta, GA). The 

oxic water was sparged with UZA for at least 1 hour 

and had a dissolved oxygen concentration between 8 

and 10 mg/L as indicated by the Indigo Carmine method 

(part# K7512, CHEMetrics, Inc., Calverton, VA). Gas 

sparging was accomplished by passing the carrier gas 

through a glass tube fitted with a fritted glass disk 

that generated small bubbles to enhance gas transfer. 

Sparging was completed within a 4 L aspiration carboy 

that had been autoclaved with 17 psi of steam (121°C) 

for 25 minutes prior to each use. 

Stock solutions of TCE were prepared by transferring 

either argon- or UZA-sparged DI-Nanopure water from 

a 4 L carboy (Section 4.1.2) via gravity drainage into 

2 L volumetric flasks. The 2 L flasks were prepared 

prior to use by autoclaving with steam at 17 psi 

(121°C) for 25 minutes, rinsing with DI-Nanopure 

water (>18 MΩ/cm), and drying at 200°C for 2 hours. 

The flasks were allowed to cool to room temperature 

within the drying oven and were then flushed with argon 

gas prior to filling with sparged DI-Nanopure water. 

Argon was used instead of nitrogen due to the greater 

density of argon, 0.98 g/mL for argon vs. 0.68 g/mL for 

nitrogen at 25°C (calculated using the ideal gas law), 

which was thought to minimize the introduction of 

atmospheric oxygen during anoxic ampule preparation. 

A Teflon-coated stir bar was placed into each water-filled 

flask, to which neat TCE was added using a gas-tight 

syringe. Approximately 1.37 mL of TCE was added 

to create 1,000 mg/L solutions (1.37 mL×1.46 g/mL÷ 

2 L = 1000 mg/L), and 0.14 mL of TCE was added to 

create 100 mg/L solutions (0.14 ml×1.46 g/mL÷2 L = 

102 mg/L). The 2 L flasks were then sealed with glass 

stoppers and then the stoppers were wrapped with 

parafilm. The 2 L flasks were wrapped in aluminum foil 

to minimize exposure to light, and placed on a magnetic 

stir plate where the contents of each flask were mixed 

at room temperature for at least 24 hours. The pH 

10 stock solution was prepared by adding 10 mL of a 

NaOH solution (901.4 mg/L) to the 2 L flask containing 

100 mg/L of TCE just prior to ampule loading. The 

resulting NaOH concentration was 0.26 mM in the 2 L 

volume with 100 mg/L of TCE. American Chemical 

Society (ACS) certified NaOH obtained from Fisher 

Scientific (Fair Lawn, NJ) was used to prepare the stock 

solution.

4.2.3 Preparation of Ampules

The ampule experiments were conducted in clear, 25 mL 

(Kimble-Kontes, Vineland, NJ) or 50 mL (Wheaton 

Science Products, Millville, NJ) borosilicate glass 

ampules (Figure 4.1). The 25 mL ampules were used 

for the initial three experimental series and the 50 mL 

funnel-top ampules were used for the fourth experiment 

to minimize the amount of carbon monoxide and 

carbon dioxide (CO/CO2) introduced during the flame 

sealing process. The ampules were autoclaved with 

17 psi of steam (121°C) for 25 minutes, then rinsed 

with deionized (DI) water (>18 MΩ/cm), and dried in 

an oven at 200°C for 2 hours. The ampules were then 

removed from the oven and placed in a glass desiccator 

that contained approximately 100 grams of indicator 

drierite (97 % CaSO4 and 3% CoCl2) to maintain water 
49

free conditions. For the anoxic and oxic experiments, 

the desiccator was evacuated to 750 mm Hg of vacuum 

and then backfilled with either argon gas or ultra 

zero grade air (UZA), respectively. Each ampule was 

then flushed with argon or UZA just prior to filling 

with aqueous solution. Each water-filled ampule was 

temporarily sealed with aluminum foil until a complete 

batch of ampules was prepared (~10 minutes). Ampules 

containing solids were prepared in an identical fashion, 

but filled with either sand or sand+1% goethite as they 

were removed from the desiccator. 

The ampules were flame sealed using a propane-oxygen 

torch (BernzOMatic, Medina, NY) that has a maximum 

flame temperature of approximately 2,500°C. The flame 

sealing process consisted of heating the ampule neck 

using the outer portion of the torch flame to vaporize 

any water droplets present within the neck followed by 

melting the glass using the inner portion of the torch 

flame. The flame seal location was approximately 3 cm 

above the gold band (Figure 4.1) in accordance with 

Wheaton Science instructions. The vaporization of water 

required approximately 10 seconds, while melting the 

glass to form the seal required less than 5 seconds. The 

sealed ampule was then placed in a rack and allowed to 

cool to room temperature.

Figure 4.1 Picture of the 50 mL funnel-top ampule 

before and after sealing.

Each ampule was labeled with a permanent marker to 

indicate the sequential ampule number, preparation 

date, and ampule contents. The ampules were then 

weighed using an analytical balance (Model# AG245, 

Mettler-Toledo, Columbus, OH) after checking the 

balance accuracy with an ASTM E617 class 2 certified 

traceable 20±0.0001 gram weight (Cat. # 820000.2, 

Denver Instruments, Denver, CO). 

4.2.4 Description of Ampule Experiments

4.2.4.1 Ampule Experiment 1

The first ampule experiment consisted of filling each 

of 4, 25 mL ampules with 20 mL of DI-Nanopure 

water (>18 MΩ-cm), leaving approximately 5 mL of 

gas headspace in each ampule. Two (2) ampules were 

filled with nitrogen sparged water with initial dissolved 

oxygen (DO) concentration of less than 0.5 mg/L 

(anoxic water) and 2 ampules were filled with ultra 

zero grade air (UZA) sparged water with initial DO 

concentration of 8.17 mg/L (oxic water). Approximately 

1.4 uL of neat TCE was then injected into each of the 

4 ampules through a temporary aluminum film seal 

to create aqueous solutions containing approximately 

100 mg/L of TCE. The ampule with anoxic water and 

TCE represented the control since Knauss et al. (1999) 

had found that dissolved oxygen affected the rate of 

TCE disappearance. Two (2) of the 4 ampules were 

amended with solid sodium hydroxide (NaOH) chips to 

adjust the solution pH to approximately 11. No duplicate 

ampules were prepared in this first ampule experiment. 

All 4 ampules were flame-sealed and placed in an oven 

maintained at 120°C for a period of 6 days. 

At the end of 6 days the oven was turned off and allowed 

to cool for 12 hours to room temperature (22°C). The 

ampules were destructively sampled and the gas-phase 

CO2 concentrations was determined using a GC (HP 

6890) equipped with a gas sampling valve, a Supel-Q 

PLOT capillary column (Supelco, Bellefonte, PA), and 

a thermal conductivity detector (TCD). The Supel-Q 

PLOT column was only capable of separating CO2

from the ampule gas and using this column resulted 

in a detection limit of 200 ppmv for CO2. The DO 

concentration of each sample was determined using 

a membrane-covered voltammetric sensor (YSI 5010 

BOD Probe, YSI, Inc. Yellow Springs, OH). Aqueous 

samples were collected from each ampule and injected 

into a GC (Varian 3600CX) equipped with a Varian 

Saturn 2000 mass spectrometer (MS) to analyze for TCE 

degradation products.

4.2.4.2 Ampule Experiment 2

The second ampule experiment consisted of filling 

each of 8, 25 mL ampules with 20 mL of DI-Nanopure 

water, leaving approximately 5 mL of gas headspace 

in each ampule. Four (4) ampules were filled with 

nitrogen sparged water with initial DO concentration 

of 0.68 mg/L (anoxic water) as measured using the YSI 

voltammetric sensor, and 4 ampules were filled with 

UZA sparged water with initial DO of 9.8 mg/L (oxic 

water). Approximately 1.4 uL of neat TCE was added to 
50

7 of the 8 ampules to achieve an initial aqueous phase 

TCE concentration of approximately 100 mg/L, while 

one ampule with oxic water was TCE-free to serve as 

a control. All of the ampules were flamed sealed and 

placed in an oven at 120°C for a period of 10 days. 

One ampule with anoxic water and TCE was broken 

during the flame sealing process, leaving 7 ampules for 

incubation. 

4.2.4.3 Ampule Experiment 3

The third ampule experiment was designed to 

incorporate a set of room temperature controls, introduce 

solids (20-30 mesh Ottawa sand) into the ampules, 

and evaluate the method of introducing TCE into the 

ampules. The experiment involved 25 mL ampules 

that contained 20 mL of DI-Nanopure water and 

approximately 5 mL of gas headspace. Twelve (12) 

ampules contained anoxic water and nitrogen gas, and 

a matching set of 12 ampules contained oxic water and 

UZA gas for a total of 24 ampules in all. Approximately 

10 grams of 20-30 mesh Ottawa sand were added to 

8 ampules, 4 with anoxic water and 4 with oxic water. 

Approximately 1.4 uL of neat TCE was introduced 

into 10 of the 12 ampules with anoxic water, while 

the remaining 2 ampules were TCE free. TCE was 

introduced into 10 of the 12 oxic ampules as a 100 mg/L 

aqueous solution that was prepared by adding neat TCE 

to a 250 mL volumetric flask filled with UZA-sparged 

DI-Nanopure water and a Teflon-coated stir bar. The 

250 mL flask was sealed, placed on a magnetic stir plate, 

and the contents mixed for 12 hours at room temperature 

(22°C) before filling each ampule with 20 mL of the 

solution via glass pipette. 

After filling the ampules with aqueous solution, a 

100 uL aqueous sample was collected from each ampule 

in an effort to determine the initial concentration 

of TCE. The samples were analyzed using a mass 

spectrometer (ITS40, Thermo-Finnegan, Waltham, 

MA) equipped with a vial sparge module that allowed 

TCE to be purged from water in a 40 mL vial directly 

into the mass spectrometer (MS) per EPA method 

8265 (U.S. EPA, 2002). The vial sparge method was 

being evaluated as an alternative to the direct GC 

injection method for determining aqueous-phase TCE 

concentration. After collecting a sample to determine 

the initial TCE concentration, each ampule was flame 

sealed using a propane torch and 19 of the ampules 

were placed in an oven maintained at 120°C. The 

remaining 5 ampules were wrapped with aluminum 

foil and stored in a vented hood at room temperature 

(22°C). The 19 ampules were removed from the oven 

after 10 days and allowed to cool to room temperature 

and then all 24 ampules were destructively sampled on 

the same day in numerical order. The gas phase from 

each ampule was initially analyzed for CO2 content 

followed by the analysis of aqueous phase samples to 

determine the concentration of TCE, DO, DCAA, and 

chloride ions. The concentration of TCE in each ampule 

after the 10 day period was determined using the vial 

sparge method and a headspace method that involved 

collecting a 1 mL aqueous sample from each ampule and 

injecting the sample into a previously sealed headspace 

vial for analysis by a GC equipped with a headspace 

autosampler.

4.2.3.4 Ampule Experiment 4

The fourth ampule experiment was undertaken to 

determine the rate of TCE degradation and the TCE 

degradation products formed after incubating dissolvedphase TCE at 120°C for up to 40 days. The experimental 

matrix was expanded compared to the initial three 

experiments and included the following experimental 

variables: 1) dissolved oxygen concentration, 

2) hydroxide ion concentration, and 3) solids content 

(Table 4.2). 

Table 4.2 Experimental Matrix Used for the Fourth Ampule Experiment

Liquid Content 

(~50 mL) 

Solids Content 

(20 g total solids)

Headspace Gas 

(~20 mL)

Experimental 

Variable

Anoxic water, pH 7 None Argon Control

Oxic water, pH 7 None UZA Oxygen

Anoxic water, pH 10 None Argon Hydroxide Ion

Anoxic water, pH 7 ASTM 20-30 Sand Argon Solids

Anoxic water, pH 7 20-30 Sand + 

1% Goethite Argon Goethite
51

Of particular note, the solids were expanded to include 

goethite, a common Fe-containing soil mineral which 

is known to be chemically reactive. The experimental 

methods were refined or modified based on the results 

of the initial three ampule experiments. Several batches 

of ampules were prepared over a period of two weeks to 

evaluate the experimental variables listed in Table 4.2. 

The ampules prepared with TCE were designed to 

evaluate the rate of TCE degradation and the degradation 

products formed. Ampules prepared without TCE or 

solids were intended to determine if CO and CO2 were 

being introduced during the flame sealing process. 

Ampules without TCE but with solids were intended to 

determine the amount of CO2 that could be attributed to 

the presence of solids. The number of ampules prepared 

for each experimental batch are listed in Table 4.3. 

An initial TCE concentration of 100 mg/L was intended 

for all experiments, however, a miscalculation led to the 

preparation of a 1,000 mg/L TCE solution used for the 

initial 2 batches of ampules (Ampules 1-61), which were 

added to the experimental matrix. Three (3) additional 

ampules (Nos. 3a, 6a, and 10a) were prepared in the first 

batch to replace ampules that had to be re-sealed. These 

3 re-sealed ampules were retained to evaluate the effect 

of exposing the ampule contents to the propane-oxygen 

flame. Only 6 TCE-free ampules were prepared in the 

second batch instead of the 18 that were planned since 

the 1,000 mg/L TCE concentration was in addition to 

the planned 100 mg/L concentration. In Batch 6 and 7, 

one of the TCE-free sand and one of goethite-containing 

ampules cracked open during preparation and were 

not replaced. In all, 242 ampules were prepared for the 

fourth ampule experiment.

The initial concentration of TCE in the ampules was 

determined by analyzing aqueous samples from 3 of 

the ampules in each batch just prior to flame sealing 

(Section 4.5.2). The average initial TCE concentration 

for Batch 1 was 893±21 mg/L, 878±44 mg/L for Batch 

2, 95.2±3.5 mg/L for Batch 3, 85.3±2.5 mg/L for Batch 

5, and 77.0±6.4 mg/L for Batch 4 based on the direct 

GC analysis method as the headspace GC equipment 

was unavailable. The solids-containing ampules had an 

average initial TCE concentration of 87.5±3.6 mg/L, 

as both the Ottawa sand and Ottawa sand+1%goethite 

ampules (Batches 6 and 7) were prepared using the 

same anoxic TCE solution. The average initial TCE 

concentration for the 1,000 mg/L solutions prepared for 

Batch 1 and 2 was less than 1,000 mg/L, as was the TCE 

concentration in the 100 mg/L solutions prepared for 

Batches 3 through 7 (Table 4.4). Thus the 1,000 mg/L 

and 100 mg/L ampules are in name only (i.e., nominal), 

with the actual initial concentrations provided in 

Table 4.4.

Table 4.3 Summary of Ampules Prepared for the Fourth Ampule Experiment

Ampule 

Batch No.

Number of Ampules 

Prepared

Nominal

Initial TCE 

Concentration 

(mg/L) 

Oxygen 

Content Solids Content Ampule Number with 

TCE

without 

TCE

1 21 18 1,000 Anoxic None 1 – 36

2 18 6 1,000 Oxic None 37 – 61

3 18 18 100 Oxic None 62 – 97

4 18 18 100 Anoxic None 98 – 133

5 18 18 100 Anoxic None (pH 10) 134 – 170

6 18 17 100 Anoxic Sand+

1% Goethite

171 – 188

209 – 225

7 18 18 100 Anoxic Sand 189 – 207

226 – 243
52

After flame-sealing the ampules in each batch, the 

ampules were divided in half so that 18 ampules (9 

with TCE and 9 without TCE) were incubated at 

120°C in a convection oven (VWR Model 1320, VWR 

International, West Chester, PA), while the remaining 

18 ampules (9 with TCE and 9 without TCE) were stored 

at room temperature (22°C) in the dark. The ampules 

for oven incubation were contained in a 3 L Pyrex glass 

drying tray that was placed in the convection oven at 

120°C where the temperature was measured using a 

certified traceable thermometer (part# 15-060-223, 

Fisher Scientific, Fair Lawn, NJ) located within the 

oven enclosure. The ampules stored at room temperature 

were placed in a storage rack located inside an insulated 

container (ice chest) to minimize exposure to light.

Ampules with TCE and without TCE were removed 

from the oven and room temperature storage at 10 and 

20 day intervals for destructive sampling according to 

the schedule listed in Table 4.4 and 4.5. Four days after 

placing the solids filled ampules in the convection oven, 

an explosion occurred that destroyed the 82 ampules 

being incubated within the oven. The 82 ampules that 

were stored at room temperature (Table 4.5) were 

moved to a 4°C chamber to minimize the formation of 

potentially explosive TCE degradation products.

Following the explosion, the remaining 1,000 mg/L 

ampules that had been stored at room temperature 

(Table 4.5) along with the 20-day, 100 mg/L oxic 

ampules that had been removed from the oven just 

prior to the explosion were destructively sampled to 

determine if dichloroacetylene (C2Cl2) had formed. 

Dichloroacetylene (DCA) is reportedly a spontaneously 

explosive compound (Urben et al., 1999) and was 

suspected to have caused the oven explosion. DCA was 

one of the TCE degradation products detected during 

the high temperature degradation of TCE in quartz tubes 

(Wu and Lin, 2004; Kim and Choo, 1983) but was not 

anticipated to form in the ampules at 120°C with water 

present. DCA was detected in the gas phase from the 

100 mg/L oxic ampules that had been incubated at 120°C 

in the convection oven and thus the ampule experiment 

was considered to be an explosion hazard. Butler and 

Hayes (2001) warn of the possibility of ampules popping 

or exploding as a result of the buildup of gases such as 

hydrogen when metals are present in the ampules. As a 

consequence, an explosion-resistant incubation apparatus 

was constructed to incubate the 72, 100 mg/L ampules 

that were being stored in the 4°C chamber. 

The explosion-resistant apparatus consisted of a block 

of aluminum into which 2 inch diameter holes were 

drilled to accommodate the ampules. The aluminum 

Table 4.4 Schedule for Convection Oven Ampule Incubation

Initial TCE 

Concentration 

(mg/L)

Oxygen 

Content

Batch No.

No. of Ampules 

10 day

No. of Ampules

20 day

No. of Ampules

30 day

No. of Ampules

893±21 Anoxic

1 oven exploded

18 [9] 6 [3] 6 [3] 6 [3] Lost

878±44 Oxic

2 oven exploded

12 [9] 4 [3] 4 [3] 4 [3] Lost

95.2±3.5 Oxic

3 oven exploded

18 [9] 6 [3] 6 [3] 6 [3] Lost

77.0±6.4* Anoxic

4 oven exploded oven exploded

18 [9] 6 [3] 6 [3] Lost 6 [3] Lost

85.3±2.5 Anoxic

5 oven exploded oven exploded oven exploded

18 [9] 6 [3] Lost 6 [3] Lost 6 [3] Lost

87.5±3.6 Anoxic

6 oven exploded oven exploded oven exploded

18 [9] 6 [3] Lost 6 [3] Lost 6 [3] Lost

87.5±3.6 Anoxic

7 oven exploded oven exploded oven exploded

18 [9] 6 [3] Lost 6 [3] Lost 6 [3] Lost

*Analyzed using the direct GC injection method, all other ampules by headspace analysis.

(#) – Batch number corresponds to Table 4.10.

[#] – Number of ampules that contained TCE.
53

Table 4.5 Schedule for Room Temperature Ampule Storage

Initial TCE 

Concentration 

(mg/L)

Oxygen 

Content

Batch No.

No. of Ampules 

10 day

No. of Ampules

20 day

No. of Ampules

30 day

No. of Ampules

893±21 Anoxic 1

21 [12] 8 [5] 7 [4] 6 [3]

878±44 Oxic 2

12 [9] 4 [3] 4 [3] 4 [3]

95.2±3.5 Oxic 3

18 [9] 6 [3] 6 [3] 6 [3]

77.0±6.4 Anoxic 4

18 [9] 6 [3] 6 [3] 6 [3]

85.3±2.5 Anoxic 5

18 [9] 6 [3] 6 [3] 6 [3]

87.5±3.6 Anoxic 6

17 [9] 6 [3] 6 [3] 5 [3]

87.5±3.6 Anoxic 7

18 [9] 6 [3] 6 [3] 6 [3]

(#) – Batch number corresponds to Table 4.3.

[#] – Number of ampules that contained TCE.

block was heated using a standard bench top hot plate 

(Fisher Scientific, Fair Lawn, NJ) and the temperature of 

the block was determined using a K-type thermocouple 

connected to a data logger (Model# CR23X, Campbell 

Scientific, Inc., Logan, UT), which automatically 

recorded the temperature at 15-minute intervals. As 

shown in Figure 4.2, the hot plate and aluminum block 

were located behind a 2 by 2 foot, 1/2 inch thick sheet 

of polycarbonate (Part# 8574K57, McMaster-Carr, 

Atlanta, GA) that served to shield laboratory personnel 

from exploding ampules. The ampules were manipulated 

behind the polycarbonate sheet using an 18-inch long 

pair of metal tongs. In addition, laboratory personnel 

wore a polycarbonate face shield (Fisher Scientific, Fair 

Lawn, NJ) when manipulating ampules.

Figure 4.2 Explosion-resistant ampule incubation apparatus.
54

Incubation of the ampules that were stored in the 4°C 

chamber was done according to the schedule given 

in Table 4.6. The ampules had been stored in the 4°C 

chamber for approximately 5 months prior to incubating 

in the explosion-resistant apparatus. The ampules that 

contained Ottawa sand+1% goethite (Batch 6) were 

incubated first with the duration of incubation at 120°C 

limited to 4 days since the oven explosion occurred 

4 days after placing the solids-filled ampules in the oven. 

The ampules containing pH 10 water (Batch 5) were 

then incubated over a 4-day period. The ampules with 

sand (Batch 7) were incubated for 40 days at 120°C 

after significant levels of DCA had been detected in the 

pH 10 ampules. The remaining oxic ampules (Batch 3) 

were then incubated at 120°C for 30 days and the 

anoxic ampules (Batch 4) for 30 and 41 days. A limited 

number of ampules from each batch were stored at room 

temperature including: 4 of the sand+goethite, 4 of the 

pH 10, 4 of the sand, 2 of the oxic, and 4 of the anoxic 

ampules.

4.2.4 Ampule Sampling Methods

The ampule sampling process was initiated by removing 

the ampules from the oven and placing them in a 

darkened vent hood to allow the hot ampules to cool 

to room temperature. The ampules were then weighed 

using the same analytical balance used to determine 

the initial ampule weight. The ampule opening method 

consisted of inverting the ampule and measuring the 

distance of the gas-filled space to estimate the volume 

of gas in each ampule (Step 1, Figure 4.3). The ampule 

neck was then broken by hand along the pre-scored line 

(Step 2, Figure 4.3). The water within the ampule body 

did not drain out since gas could not flow past the water 

that blocked the ampule opening which was smaller in 

diameter than the ampule body. The opened ampule was 

then placed into a custom made sampling collection 

apparatus that was filled with a stream of argon gas 

flowing at 100 mL/min to minimize the introduction of 

oxygen and carbon dioxide during sample collection 

(Step 4, Figure 4.3). The sample collection apparatus 

consisted of a 60 mL plastic syringe body that was cut in 

half with an 18-gauge, 30 cm long stainless steel needle 

affixed to the syringe body. A 10 mL syringe (Becton 

Dickinson and Co., Franklin Lakes, NJ) was attached to 

the 30 cm long needle via a Luer lock connection in an 

effort to collect a gas sample from the inverted ampule. 

Table 4.6 Schedule for Explosion-Resistant Apparatus Ampule Incubation

Ampule Content No. of Ampules Time (days)

No. Ampules

Time (days)

No. Ampules

Time (days)

No. Ampules

Batch 4

No. Ampules

Sand+Goethite

(6)

1 2 3 --

12 [6] 4 [2] 4 [2] 4 [2]

pH 10

(5)

1 2 3 4

14 [7] 4 [2] 4 [2] 4 [2] 2 [1]

Sand

(7)

10 30 40 --

14 [7] 4 [2] 4 [2] 6 [3]

Oxic

(3)

30 -- -- --

3 [2] 3 [2]

Anoxic

(4)

30 41 -- --

8 [4] 4 [2] 4 [2]

(#) – Batch number corresponds to Table 4.10.

[#] – Number of ampules that contained TCE.
55

4.2.5 Analytical Methods

The dissolved oxygen (DO) concentration was 

determined using a membrane-covered voltammetric 

sensor (YSI 5010 BOD Probe, YSI, Inc. Yellow Springs, 

OH) during the initial three experiments. This method 

required transferring the aqueous phase from each 

ampule into a second vial that could accommodate the 

YSI probe body. The dissolved oxygen concentration of 

ampules in the fourth experiment was determined using 

the Rhodazine D method (part# K7501, CHEMetrics, 

Inc., Calverton, VA) for DO between 0 and 1 mg/L or 

the Indigo Carmine method (part# K7512, CHEMetrics, 

Inc., Calverton, VA) for DO between 1 and 10 mg/L. 

The CHEMets method was contained within a selffilling ampule that was inserted into the ampule neck 

(Step 3, Figure 4.3) to determine the DO concentration 

while waiting for argon to flush ambient air from the 

60 mL syringe body. A 10 mL sample of the gas within 

the ampule was then collected by slowly retracting the 

syringe plunger (10 mL in 30 seconds) and allowing 

the argon gas to bubble through the liquid-filled portion 

of the ampule and backfill the gas-filled space as the 

gas sample was being removed. The 10 mL gas sample 

was analyzed within 60 seconds of collection using a 

gas chromatograph (HP 6890) equipped with a thermal 

conductivity detector (TCD). The ampule was then 

removed from the 60 mL syringe body and placed 

upright to allow for collection of liquid samples. The 

water within the ampule was then transferred into a 

pre-washed 50 mL borosilicate glass vial and sealed 

with a Teflon® lined septum affixed with an open-top 

screw cap. The pH of the ampule water was measured 

in the 50 mL glass vial by placing a DI water rinsed pH 

probe (Fisher Scientific, Fair Lawn, NJ) into the vial and 

waiting approximately 5 minutes before recording the 

pH value. The vial was then labeled using a permanent 

marker and stored in a 4°C chamber.

Aqueous phase concentrations of TCE were determined 

by gas chromatography (GC) using a headspace method 

and a direct GC injection method. The headspace 

method consisted of transferring a 1 mL aqueous sample 

into a 20 mL vial that was sealed with a Teflon-lined, 

butyl rubber stopper (West Pharmaceutical Services, 

Inc., Lionville, PA) affixed with an aluminum crimp 

cap. The headspace vials were placed in an autosampler 

(HP 7694) that was programmed to heat each sample to 

70°C for a period of 15 minutes prior to transferring the 

headspace gas into an HP 6890 GC for analysis. The GC 

was equipped with a 30 m x 0.32 mm DB-624 column 

(Agilent Technologies, Palo Alto, CA) connected to a 

flame ionization detector (FID). Calibration standards 

containing 60, 80, and 100 mg/L TCE were analyzed 

with each experimental sample batch. The calibration 

standards were prepared by injecting small volumes of 

10,000 mg/L TCE methanol stock solution into 100 mL 

flasks that contained DI-Nanopure water cooled to 4°C. 

The direct GC injection method involved introducing 

1 uL of aqueous solution into a HP 6890 GC equipped 

with a 990 uL inlet liner, a 30 m x 0.32 mm OD DB-5 

column (Agilent Technologies, Palo Alto, CA), and a 

FID. The inlet was operated at 200°C with a constant 

helium pressure of 20 psi and a 2:1 split ratio: these inlet 

parameters served to minimize water vapor back-flash 

after injecting the 1 uL aqueous sample. 

Immediately prior to flame sealing, the initial aqueousphase concentration of TCE in the ampules was 

determined by collecting a 1 mL water sample from 

Figure 4.3 Illustration of the ampule gas sample collection method.
56

three randomly-selected ampules in each experimental 

batch of 18 ampules. The TCE concentration measured 

immediately prior to sealing the ampules was 

considered to be representative of the initial aqueous 

phase TCE concentration. Following incubation, the 

aqueous phase TCE concentrations were determined 

by collecting 3, 1 mL water samples from each ampule 

immediately after collecting a 10 mL gas sample. Two 

(2) of the 3, 1 mL water samples, which contained 

1,1,1-trichloroethane as an internal spike, were analyzed 

by the direct GC injection method and the third 1 mL 

water sample was analyzed by the headspace method. 

The concentrations of formate (CHOO-), glycolate 

(HOH2C2OO-), sulfate (SO4

2-), and chloride (Cl-

) 

in aqueous phase samples from the ampules were 

determined using a Dionex DX-100 Ion Chromotograph 

(IC) equipped with an AS14A IonPac column with 8 mM 

Na2CO3/1 mM NaHCO3 eluent concentrate flowing 

at 1 mL/min. Organic acid calibration standards were 

prepared from 1 M stock solutions in the concentration 

range from 0.02 to 0.50 mM. Formate and glycolate 

solutions were prepared from 99% grade solids (glycolic 

acid and sodium formate, ACROS Organics, Morris 

Plains, NJ). One limitation of IC analysis is the relatively 

high detection limit: the average method detection 

limits for glycolate and formate were 0.86 mg/L and 

0.31 mg/L, respectively. The chloride ion content of 

aqueous samples was determined by IC analysis to allow 

for comparisons with chloride concentrations measured 

using the titration method of Bergmann and Sanik 

(1957). The DO content of water held within the ampule 

neck was measured immediately after opening using the 

CHEMets ampules (Step 3, Figure 4.2). The aqueous 

phase concentration of DCAA was determined using the 

modified EPA method 552.2.

4.3 Experimental Results

4.3.1 Results of Ampule Experiment 1

Carbon dioxide (CO2) was detected in the 2 ampules 

without NaOH, regardless of the initial dissolved oxygen 

content (Table 4.7). No TCE was detected in water 

samples collected from the NaOH amended ampules 

while TCE was present in the ampules without NaOH. 

The concentration of TCE was not determined. The 

absence of CO2 and TCE in the NaOH amended ampules 

indicated that other TCE degradation products had 

formed, which was suspected to be dichloroacetic acid 

(DCAA) based on the past experimental work presented 

in Section 2.3.2. Additional aqueous phase samples were 

collected from the NaOH amended ampules and the pH 

of the samples were adjusted to less than 1 by adding 

concentrated sulfuric acid. The pH adjustment was 

performed to convert any organic ions that may have 

been present from the anionic to the acid form because 

organic acids can be detected using an ultraviolet (UV) 

light spectrophotometer. After adjusting the pH of each 

sample to less than 1, the water samples from the NaOH 

amended ampules absorbed light at 270 nm in a Varian 

UV-visible spectrophotometer, which, based on the 

similarity to work by Mertens and von Sonntag (1994), 

suggested that DCAA was present.

The first ampule experiment demonstrated that DO 

levels in the ampules could be maintained with greater 

than 95% of the initial amount of the DO detected 

after incubating the sealed ampules for 6 days at 

120°C. In addition, the importance of NaOH on the 

rate of TCE disappearance was demonstrated in that 

no TCE was detected in NaOH amended ampules 

after 6 days at 120°C, while TCE was detected in the 

ampules without NaOH. It was evident that a method to 

determine the DCAA content of water solutions needed 

to be developed based on the observation of UV light 

absorbance in water samples from the NaOH amended 

ampules. A method to determine the concentration of 

TCE in water was also found to be necessary in effort to 

determine if small changes in TCE content were equal to 

the amount of CO2

 detected.

4.3.2 Results of Ampule Experiment 2

After cooling to room temperature, the ampules were 

destructively sampled to determine the amount of CO2

in the gas phase and the concentration of DO, TCE, 

and DCAA in the aqueous phase. Gas samples from 

Table 4.7 Results of the First Ampule Experiment After 6 Days at 120°C

Ampule Contents Initial DO (mg/L) Final DO (mg/L) Final pH CO2

 in Gas Phase 

(uL/L)

Water and TCE <0.5 <0.5 6.74 1032

Water and TCE 8.17 7.8 6.60 1000

Water, TCE, and NaOH <0.5 <0.5 11.24 nd

Water, TCE, and NaOH 8.17 7.9 10.75 nd

nd – below detection limit (~200 uL/L)
57

3 of the 7 ampules were not analyzed because these 

ampules were damaged during the opening process 

which resulted in the ampule contents being exposed to 

ambient air (~500 uL/L CO2) and potentially biasing the 

amount of CO2 in those samples. The TCE content of 

the ampule aqueous phase was determined by injecting a 

1 uL water sample from each ampule directly into a gas 

chromatograph (GC) equipped with a flame ionization 

detector (FID). The DCAA concentration of the 

ampule water was determined using the modified EPA 

method 552.2.

The ampules with oxic water had DO at concentrations 

ranging from approximately 7.5 to 8.6 mg/L after 

10 days at 120°C (Table 4.8) as determined using the 

YSI voltammetric sensor. The similarity between initial 

and final DO concentrations of the control ampule 

(9.08 vs. 8.52 mg/L), and minimal changes in ampule 

weights (≤ 0.0006%) were taken to indicate that the 

flame-sealed ampules provided a gas-tight environment 

over the 10-day, 120°C incubation period. For ampules 

that contained TCE, the pH decreased from 7 to 

approximately 6.2, and CO2 was detected in the ampules 

with both anoxic and oxic water. As anticipated, CO2

was not detected in the gas headspace of the TCE-free 

control ampule. Dichloroacetic acid (DCAA) was 

detected at concentrations near the method detection 

limit (~5 ug/L) in 3 of the 7 ampules.

The pH of the TCE-free control ampule increased 

from 7.15 to 8.19, which was attributed to the 

thermal enhanced dissolution of silica (SiO2) from the 

borosilicate glass ampule walls. As SiO2 dissolves into 

water it forms silicic acid (H4SiO4), which is a weak 

acid with an initial dissociation constant of pKa = 9.5 

(H4SiO4→H3SiO4

-

 + H+) (Stumm and Morgan, 1996). 

Thus the dissociation of silicic acid would cause the pH 

of the solution to increase as SiO2 was dissolved from 

the ampule walls. 

The initial concentration of TCE was not determined 

using the direct GC injection technique but was in 

the 95 to 115 mg/L range as estimated based on the 

mass of TCE added to each ampule and the volume of 

water in each ampule (Table 4.9). The concentration 

after incubating the ampules at 120°C for 10 days was 

determined using the direct GC injection technique and 

was less than the initial, calculated TCE concentration. 

The relative standard deviation (%RSD= standard 

deviation ÷ average × 100) is one measure of the 

precision associated with an analysis method. A %RSD 

of less than 15% is considered adequate for determining 

the concentration of TCE in aqueous samples (U.S. 

EPA, 1996). The %RSD values shown in Table 4.4 were 

determined by analyzing three separate water samples 

collected from each ampule and shows that the direct GC 

injection method was capable of determining aqueous 

phase TCE concentration with adequate precision.

There appeared to be a significant reduction in the 

amount of TCE after 10 days at 120°C based on the 

results shown in Table 4.9; however, the small amount 

of CO2

 detected and DCAA indicated that the apparent 

reduction in TCE was due to an overestimation in the 

initial concentration of TCE. This led to the conclusion 

that the initial concentration of TCE should be measured 

rather than estimated and an additional set of ampules 

should be maintained at room temperature to help in 

quantifying any temperature induced changes in TCE 

content.

Table 4.8 Results of Second Ampule Experiment After 10 Days at 120°C 

Ampule Contents Initial DO 

(mg/L)

Final DO 

(mg/L)

Initial 

pH Final pH Weight Change (%) CO2

 (uL/L)

Water and TCE* 0.68 na 7.34 na 0.0006 1007

Water and TCE* 0.68 na 7.34 6.1 0.0006 na

Water and TCE 0.68 na 7.34 na 0.0006 na

Water and TCE 9.08 7.5 7.15 6.3 0.0003 na

Water and TCE* 9.08 8.55 7.15 6.47 0.0006 879

Water and TCE 9.08 8.43 7.15 6.16 0.0000 739

Water 9.08 8.52 7.15 8.19 0.0006 nd

DO – dissolved oxygen

* DCAA detected in water samples near detection limit of 5 ug/L.

na – not analyzed, contents lost after breaking ampule neck

nd – not detected, below detection limit of ~200 uL/L
58

4.3.3 Results of Ampule Experiment 3

The initial concentration estimated by the mass of TCE 

added was greater than the concentration determined 

by the vial sparge method (Table 4.10). The difference 

between the estimated and measured TCE concentration 

was thought to be due to non-equilibrium between 

the neat TCE droplet that was added to each ampule 

and the ampule water because the sample used to 

determine the initial TCE concentration was collected 

within 30 minutes of injecting the neat TCE. The nonequilibrium condition between the neat TCE droplet and 

ampule water was indicated by the significant difference 

(P-value=0.01, alpha=0.05) between the initial TCE 

concentration determined for Ampule 1 (46.9±1.0 mg/L) 

and for the other identically prepared ampules 

(69.4±3.8 mg/L for Ampule 2 and 69.4±3.8 mg/L for 

Ampule 3) even though a similar amount of neat TCE 

was added to each ampule (2.1, 2.3, and 2.2 mg TCE, 

respectively). The difference in the initial concentration 

between ampules indicated that the neat TCE in Ampule 

1 was not completely dissolved into the ampule water 

at the time when the water sample was collected in an 

effort to estimate the initial TCE concentration. The 

concentration of TCE in Ampule 1 measured after 

10 days at 120°C increased from 46.9 mg/L to 66.7 mg/L 

which supports the conclusion that a portion of the 

neat TCE was not dissolved when the sample used to 

establish the initial TCE concentration was collected. 

In addition to the non-equilibrium condition, there must 

have been a loss of TCE mass after injecting the neat 

TCE droplet into each ampule since the concentration, 

as determined by the vial sparge method, was less than 

the concentration estimated from the mass of TCE added 

to each ampule. Thus it was concluded that injecting 

neat TCE to establish an initial mass of TCE was not 

desirable since estimating the initial concentration of 

TCE was complicated by the non-equilibrium condition 

and loss of TCE mass during the loading process.

Table 4.9 Initial and Final TCE Concentrations in the Second Ampule Experiment

Ampule Contents Initial TCE (mg/L)* Final TCE (mg/L)† Relative Standard Deviation 

(%RSD)

Water and TCE* 110.0 57.9 3.4

Water and TCE* 95.0 66.5 0.5

Water and TCE 105.0 42.9 5.2

Water and TCE 100.0 49.5 0.6

Water and TCE* 100.0 60.2 3.2

Water and TCE 115.0 65.3 4.7

Water not added nd not determined

* Calculated based on the mass of TCE added to each ampule and volume of water in each ampule.

† Determined using direct GC injection technique.

nd – not detected

Table 4.10 Initial and Final TCE Concentration in Anoxic Ampules from the Third Ampule Experiment (1.4 uL of 

TCE added to each ampule, Initial DO = 0.79 mg/L)

Contents Temperature 

(°C)

Initial TCE (mg/L) Final TCE (mg/L)

Estimated Vial Sparge Vial Sparge Headspace

TCE, water

120 110±7.1 58.2±15.9 62.4±6.2 61.5±3.7

22 110 77.8 80.6 69.9

TCE, water, sand

120 107±7.6 87.9±12.2 62.5±5.1 63.2±5.7

22 110 84.8 80.6 81.2

Error represents one standard deviation calculated from duplicate ampule results.
59

Table 4.11 contains the initial and final concentration 

of TCE in the ampules filled with oxic water. Here, 

instead of amending each ampule with 1.4 uL of neat 

TCE, as done with the ampules filled with anoxic water 

(Table 4.10), the ampules with oxic water were filled 

with an aqueous mixture that had been prepared by 

mixing neat TCE with water at room temperature for a 

period of 12 hours. The average concentration of TCE 

in the mixture was 71.7±4.1 with a %RSD of 5.7. This 

average was calculated based on the analysis of a 100 uL 

sample collected from each of the 10 ampules after 

filling with the aqueous TCE mixture, which shows the 

adequate precision of the vial sparge analysis method 

and degree of TCE homogeneity in the mixture. The vial 

sparge method was not used in subsequent experiments 

since there was no substantial improvement in analysis 

precision over the direct GC injection or headspace 

methods and because the vial sparge method was timeconsuming due to the manual sample-injection step. 

TCE was introduced into each ampule in the subsequent 

experiment as an aqueous solution that was prepared 

by mixing neat TCE with a 2 L volume of water for 

24 hours at room temperature.

The concentration of TCE increased in the ampules 

with anoxic water from 58.2 to 62.4 mg/L after 10 days 

at 120°C while it decreased from 87.9 to 62.5 mg/L in 

ampules that contained Ottawa sand and anoxic water 

(Table 4.10); however, these changes are in comparison 

to the initial TCE concentration which, as described 

above, did not represent the true initial condition due 

to non-equilibrium between neat TCE and water. In 

ampules with oxic water (Table 4.11), there was a 

significant decrease in TCE concentration (P-value= 

0.01, alpha=0.05) from 72.5 to 57.2 mg/L after 10 days 

at 120°C and from 69.9 to 58.3 mg/L in ampules with 

sand and oxic water, which may have indicated that 

TCE was being degraded. However, there was also a 

decrease in TCE concentration in the matching ampules 

stored at 22°C where TCE was not expected to degrade 

over 10 days. No statistical comparison between the 

22°C and 120°C results was possible as only one ampule 

was stored at 22°C for each experimental variable. 

Thus the variability (the basis for statistical tests) of the 

TCE concentration in the ampules stored at 22°C was 

unknown. A matching number of 22°C control ampules 

were prepared in the subsequent experiment to allow for 

statistical comparisons between 22°C and 120°C results. 

If TCE was being degraded in the ampules incubated at 

120°C, the rate of disappearance, based on the results 

shown in Table 4.11, was approximately 1.5 mg/L·day, 

which meant that 24 days would have been required to 

degrade 50% of the initial amount of TCE, assuming a 

zero-order reaction model. The subsequent experiment 

was extended up to 40 days in effort to observe a greater 

change in TCE concentration potentially caused by the 

degradation of TCE.

Table 4.11 Initial and Final TCE Concentration in Oxic Ampules from the Third Ampule Experiment (TCE 

mixed into 250 mL of water prior to addition to each ampule, Initial DO = 8.22 mg/L)

Contents Temperature

(°C)

Initial TCE (mg/L) Final TCE (mg/L)

Vial Sparge Vial Sparge Headspace

TCE, water

120 72.5±6.0 57.2±3.6 59.9±1.2

22 73.3 69.1 65.7

TCE, water, 

sand

120 69.9±3.5 58.3±3.2 64.7±1.3

22 71.4 58.0 66.8

Error represents one standard deviation calculated from duplicate ampule results.
60

The final CO2 content of the gas phase, and the aqueous 

phase concentration of DO and DCAA along with the 

final pH for the ampules with anoxic water are shown 

in Table 4.12 and in Table 4.13 for the ampules with 

oxic water. The pH of the aqueous solution decreased 

from 7.73 to 6.46 in ampules with anoxic water that 

contained TCE and where incubated at 120°C, while 

the pH decrease was less than 0.3 pH units in the TCEfree ampule with anoxic water (Table 4.12). A similar 

decrease in the pH of ampules with oxic water was 

observed with the pH decreasing from 7.80 to 6.55 for 

ampules incubated at 120°C (Table 4.13). The pH also 

decreased in ampules that contained both anoxic and 

oxic water along with TCE and were stored at 22°C, the 

pH decreased to values lower than expected based on the 

results from ampules incubated at 120°C.

The decrease in pH was matched with the detection of 

CO2 in the gas phase. This could either indicate that TCE 

was being degraded or that CO2 was introduced during 

the flame sealing process from the torch combustion 

products; CO2 can dissolve in water to form carbonic 

acid and thus decrease the pH. Since TCE was not 

expected to degrade in the ampules stored at 22°C where 

the pH decreased and CO2 was detected, it was suspected 

that the ampule contents were being exposed to the torch 

flame combustion-products during the flame sealing 

process. To test this hypothesis, several empty 25 mL 

ampules were flame sealed and CO2 was subsequently 

Table 4.12 Third Ampule Experiment Results for Anoxic Ampules (1.4 uL of TCE added to each ampule, Initial 

DO = 0.79 mg/L)

Contents Temperature 

(°C)

Final pH

(Initial pH=7.73)

Final DO 

(mg/L)

CO2

(uL/L) DCAA (ug/L)

water 120 7.46 4.5 na nd

TCE, water 120 6.46±0.18 6.7±0.5 838±104 0.7±0.6

TCE, water 22 4.85 na 2,320 5.4

sand, water 120 3.17 na 2,783 nd

TCE, water, sand 120 3.86 3 (n=1) 3,493±144 6.0±1.6

TCE, water, sand 22 3.14±0.06 na 646 10.3

na – not analyzed

nd – below detection limit (~0.2 ug/L)

Table 4.13 Third Ampule Experiment Results for Oxic Ampules (TCE mixed into 250 mL of water prior to 

addition to each ampule, Initial DO = 8.22 mg/L)

Contents Temperature 

(°C)

Final pH

(Initial pH=7.80)

Final DO 

(mg/L)

CO2

(uL/L)

DCAA

(ug/L)

water 120 7.63 7.7 nd nd

TCE, water 120 6.55±0.07 6.7±0.6 847±369 nd

TCE, water 22 6.45 6.9 1,103 nd

water, sand 120 3.09 na 2,845 nd

TCE, water, sand 120 3.25±0.03 2.8±0.2 2,187±392 nd

TCE, water, sand 22 3.94 6.0 1,733 nd

na – not analyzed

nd – below detection limit (~0.2 ug/L)
61

detected in the ampules after destructive sampling. 

Thus the CO2 detected in the ampules may have been 

introduced during the flame sealing process and not from 

the degradation of TCE. This finding prompted the use 

of “funnel top” ampules in all subsequent experiments, 

which can be flame sealed without exposing the ampule 

contents directly to the torch flame.

The pH of the water in the ampules that contained 

sand decreased from approximately 7.7 to less than 4.0 

regardless of TCE content, initial DO concentration, 

or incubation temperature. It was suspected that the 

20-30 mesh Ottawa sand, which had been treated by 

soaking in a 0.5 N nitric acid solution and then rinsed 

with DI water, contained residual nitric acid due to an 

inadequate DI rinse. A separate test was performed 

by placing 100 grams of the acid treated Ottawa sand 

in a beaker and adding enough freshly dispensed 

DI-Nanopure water to cover the sand. The pH of the 

DI water decreased from 7.7 to 4.2 indicating that 

the DI rinse after the 0.5 N nitric acid treatment was 

not sufficient to remove the residual nitric acid. This 

result prompted additional rinsing procedures for the 

subsequent experiment that included rinsing the sand 

until the rinse water was at pH 7.

The chloride content of the water samples was 

determined using an ion selective electrode (ISE). 

However, the ISE failed to yield consistent values for the 

1 mM chloride solution used to check probe response 

during measurements. As a result, chloride data are 

not reported here, and alternative analytical methods 

that included a colorimetric technique by Bergmann 

and Sanik (1957) and use of Ion Chromatography 

as described in Section A.5 were employed in the 

subsequent experiment. The DO concentration in 

ampules filled with anoxic water increased from 0.79 to 

greater than 4.5 (Table 4.12). The DO concentration was 

determined using the YSI voltammetric sensor that was 

used in the first and second ampule experiments, which 

required exposing the sample to air followed by vigorous 

stirring thus potentially introducing oxygen into the 

samples. To minimize exposure to oxygen during the 

measurement process, a colorimetric method (Chemets) 

for measuring dissolved oxygen was adopted for the 

subsequent ampule experiment.

4.3.2 Results of Ampule Experiment 4

The following sections describe results obtained 

from 38 ampules that were incubated at 120°C in the 

convection oven prior to the oven explosion (Table 4.4), 

51 ampules incubated at 120°C in the explosion resistant 

apparatus (Table 4.6), and 67 ampules that were stored 

at 22°C (Table 4.5). No results were obtained from the 

convection oven incubation of the pH 10 or the solidsfilled ampules (Batch 5, 6 and 7) because these ampules 

were destroyed in the oven explosion.

The dissolved oxygen data collected from these ampules 

showed evidence of problems with the analysis. 

The data could not be used to draw conclusions on 

TCE reactions, but is presented in Appendix B for 

completeness.

4.3.2.1 Change in TCE Content

The average amount of TCE in the 1,000 mg/L 

(nominal) ampules with time is shown in Table 4.14. 

The amount of TCE in each ampule was calculated 

based on the aqueous phase TCE concentration and 

the estimated gas phase TCE concentration. The gas 

phase TCE concentration was estimated using Henry’s 

law (Cg = HCw), assuming equilibrium conditions, 

with Cw equal to the TCE aqueous phase concentration 

as determined by GC analysis, and the dimensionless 

Henry’s Law constant (H) equal to 0.318 at 25°C 

(Staudinger and Roberts, 1996). The inclusion of TCE 

in the gas phase accounts for differences in gas phase 

volume between ampules, which typically represented 

less than 15% of the total TCE content. These estimates 

were performed to correct for the differences in the 

volume of gas (headspace) between ampules that were 

due to slight differences in the volume of water initially 

added to each ampule. The amount of TCE (i.e., micro 

moles or umol) in each ampule was then calculated 

based on the concentration of TCE and the volume of 

water and volume of gas in each ampule. The volume of 

water in each ampule was determined by the difference 

between the weight of the sealed ampule and the weight 

of the empty ampule and neck after destructive sampling 

along with a density of water equal to 0.997 g/mL. The 

volume of gas in each ampule was estimated based on 

the length of gas filled space and the ampule diameter 

that was equal to 3 cm. The amount of TCE in the 

ampules shown in Table 4.14 is the average along with 

the standard deviation (i.e., average±S.D.) calculated 

from the number (n) ampules at each time period. 

There was more TCE in the 1,000 mg/L ampules 

incubated at 120°C than stored at 22°C (Table 4.14), 

with the exception of the oxic 20-day ampules. However, 

a paired t-test performed on these data suggest that the 

difference between the average amount of TCE in the 

1,000 mg/L ampules incubated at 120°C and stored at 

22°C was not significant (P-Values>0.22, alpha=0.05). 

Thus there was no apparent change in the TCE content 

for the 1,000 mg/L ampules. The one exception was 

Ampule 58 from Batch 2, which had a 50.9% reduction 

in the amount of TCE after 20 days at 120°C. The result 

from Ampule 58 was not used in calculating the 20 day 

average shown in Table 4.14.

The average amount of TCE in the 100 mg/L (nominal) 

anoxic (Batch 4) and oxic (Batch 3) ampules, based 

on the amount detected in the aqueous phase and that 

estimated in the gas phase, is shown in Figure 4.4 as a 
62

function of time. There was little change in the amount 

of TCE in the anoxic ampules (Batch 4) incubated at 

120°C or stored at 22°C over the 41 day period. There 

was no statistical difference (P-Values>0.05, Table 4.15) 

between the amount of TCE in the anoxic ampules 

incubated at 120°C and stored at 22°C over 41 days, 

which supports the claim that there was little change in 

the amount of TCE in the anoxic ampules.

Figure 4.4 Amount of TCE in the 100 mg/L anoxic 

(Batch 4) and oxic (Batch 3) ampules 

stored at 22°C and incubated at 120°C.

In contrast, there was a decrease in the amount of TCE in 

the oxic ampules that contained 100 mg/L of TCE after 

10, 20, and 30 days at 22°C and 120°C (P-Value<0.05) 

as compared to the initial amount of TCE in Batch 3. 

There was less TCE in the oxic ampules incubated at 

120°C than was present in the ampules stored at room 

temperature after 10 and 20 days (P-Values<0.05, 

Table 4.15). These results suggest that the presence 

of oxygen affected the amount of TCE found in the 

ampules incubated at 120°C and stored at 22°C.

The average amount of TCE decreased in the anoxic 

ampules that contained solids (Batches 6 and 7) as a 

function of time as shown in Figure 4.5. The amount 

of TCE detected in the ampules that contained either 

Ottawa sand alone or Ottawa sand+1% goethite and were 

incubated at 120°C was significantly less (P-Value>0.05) 

than the amount in the corresponding ampules stored 

at 22°C (Table 4.16). There was 22.8% less TCE in the 

ampules with sand after 30 days at 120°C with 20.8% 

less TCE in the ampules with sand+1%goethite after 

4 days at 120°C as compared to the amount in the 

ampules stored at 22°C. This result indicated that the 

rate of TCE disappearance was greater in the ampules 

that contained Ottawa sand+1% goethite as compared to 

ampules with Ottawa sand alone. 

Table 4.14 Amount (Aqueous and Gas Phases) of TCE in 1,000 mg/L (nominal) Anoxic (Batch 1) and Oxic 

(Batch 2) Ampules

Content Day

Total TCE (umol) P-Value 

120°C n 22°C n (120 vs. 22°C) 

Anoxic

Initial TCE (umol) = 

368±8

10 202±49* 3 175±49* 3 0.22

20 337±22 2† 276±55 3 0.09

30 Lost 317±12 3 --

Oxic

Initial TCE (umol) = 

350±17

10 355±14 3 338±2 3 0.09

20 337±26 2‡ 343±22 3 0.40

30 Lost 342±11 3 --

n – Number of ampules used to calculate average and standard deviation.

* TCE by direct GC injection.

Lost – Ampules destroyed in oven explosion.

† Ampule 7 contents lost during opening.

‡ Ampule 58 results excluded due to significant difference in TCE content.
63

Figure 4.5 Amount of TCE in anoxic 100 mg/L 

ampules with Ottawa sand (Batch 6) and 

Ottawa sand+1% goethite (Batch 7) stored 

at 22°C and incubated at 120°C.

The average amount of TCE in the anoxic ampules that 

contained water amended with NaOH to achieve a pH of 

10 (Batch 5) decreased as a function of time as shown 

in Figure 4.6. There was 10.8% less TCE in the pH 10 

ampules after 4 days at 120°C compared to the amount 

of TCE in the 22°C ampules (Table 4.17). 

Table 4.15 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic (Batch 4) and Oxic 

(Batch 3) Ampules 

Content Day Total TCE (umol) P-Value

120°C n 22°C n (120 vs. 22°C)

Anoxic

Initial TCE (umol) = 

31.4±2.6*

10 30.5±2.3 3 32.8±1.6 3 0.12

30† 31.3±2.8 2 33.2 1 0.34

41† 30.9±1.7 2 32.5 1 0.29

Oxic

Initial TCE (umol) = 

39.0±1.0

10 34.8±2.5 3 37.3±1.0 3 0.06

20 32.5±0.3 3 35.9±0.6 3 0.01

30† 31.3±2.5 2 35.3 1 0.21

n – Number of ampules used to calculate average and standard deviation.

* TCE by direct GC injection.

† Incubated using the explosion resistant apparatus, all other ampules incubated in convection oven.

Table 4.16 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic Ampules with Sand (Batch 

6) and Sand+1% Goethite (Batch 7) 

Content Day

Total TCE (umol) P-Value 

120°C n 22°C n (120 vs. 22°C)

Sand

Initial TCE (umol) 

= 30.6±0.9

10 22.5±0.4 2 0.04

20 17.3±0.5 2 0.04

30 19.6±2.2 3 25.4±1.0 2 0.01

Sand + 1% 

Goethite

Initial TCE (umol) 

= 30.6±0.9

1 25.4±1.7 2 0.35

2 20.6±1.9 2 0.07

3 25.0±0.5 2 --

4 19.8±2.3 2 0.07

n – Number of ampules used to calculate average and standard deviation.
64

Figure 4.6 Amount of TCE in 100 mg/L anoxic 

ampules amended with NaOH (0.26 mM) 

to pH 10 (Batch 5) stored at 22°C and 

incubated at 120°C.

4.3.2.2 Change in pH

The pH of ampules was expected to decrease with 

the degradation of TCE. Assuming that all the TCE 

initially present was transformed into CO2 and chloride, 

then the pH in ampules would have decreased from 

7 to approximately 2 based on the initial amount of 

TCE present in the 1,000 mg/L ampules and from 7 to 

3 in ampules with 100 mg/L. The aqueous phase pH 

of anoxic (Batch 1) and oxic (Batch 2) ampules with 

1,000 mg/L (nominal) of TCE are shown in Figure 4.7. 

The pH decreased in both the anoxic and oxic ampules 

from 7.0 to 4.34±0.08 (n=2) and 3.65±0.19 (n=2), 

respectively, after 20 days at 120°C. The pH of the oxic 

1,000 mg/L ampules stored at 22°C also decreased, 

from 7.0 to 4.74±0.35 (n=3) after 20 days but did not 

substantially decrease after an additional 10 day period. 

In contrast, the pH of the anoxic 1,000 mg/L ampules 

stored at 22°C increased from 7.0 to 7.43±0.82 (n=3) 

after 20 days (Figure 4.7). The pH of the TCE-free 

anoxic and oxic ampules (controls) increased from 7.0 

to 8.45±0.16 (n=12), this average was calculated from 

the pH of TCE-free ampules after 10, 20, and 30 days at 

22°C and 120°C. The pH measurements for the TCE-free 

controls were from 12 of the 24 ampules that were 

initially prepared in Batch 1 and 2 (Table 4.4). The pH 

increase in TCE-free ampules was thought to represent 

the dissolution of SiO2 from the ampule glass walls as 

discussed in Section 4.3, whereas the pH decrease in 

TCE containing ampules was thought to represent the 

release of hydrogen atoms from TCE molecules due to 

the degradation of TCE.

Figure 4.7 The pH of anoxic (Batch 1) and oxic 

(Batch 2) ampules with 1,000 mg/L of TCE 

and TCE-free controls stored at 22°C and 

incubated at 120°C.

The aqueous phase pH of anoxic (Batch 4) and oxic 

(Batch 3) ampules with 100 mg/L (nominal) of TCE are 

shown in Figure 4.8. The pH of the anoxic (Batch 4) 

ampules incubated at 120°C decreased from 7.0 to 

4.69±0.04 (n=3) after 10 days, to 6.60±0.04 (n=2) 

after 30 days, and to 6.36±0.08 (n=2) after 40 days. 

It should be noted that the 30 and 41 day results for 

Table 4.17 Amount (Aqueous and Gas Phases) of TCE in 100 mg/L (nominal) Anoxic Ampules Amended with 

NaOH (0.26 mM) to pH 10 (Batch 5)

Content Day

Total TCE (umol) P-Value

(120 vs. 22°C) 120°C n 22°C n

NaOH

Initial TCE (umol) = 

35.3±1.0

1 28.5±0.7 2 0.09

2 26.8±1.7 2 0.01

3 24.4±4.1 2 0.07

4 28.0 1 31.4±1.9 2 --

n – Number of ampules used to calculate average and standard deviation.
65

the anoxic 100 mg/L ampules were obtained using the 

explosion resistant incubation apparatus, while the 10 

day results were obtained from the convection oven prior 

to the explosion. There was a difference in the ampule 

temperature profile between heating methods with the 

ampule necks exposed to ambient temperature (22°C) 

in the explosion resistant apparatus (see Figure 4.2) 

while the entire ampule was exposed to 120°C in the 

convection oven. 

Figure 4.8 The pH of anoxic (Batch 4) and oxic 

(Batch 3) ampules with 100 mg/L of TCE 

and TCE-free controls stored at 22°C and 

incubated at 120°C. 

In the oxic 100 mg/L ampules (Batch 3), the pH 

decreased from 7.0 to 5.42±0.28 (n=3) after 10 days, to 

4.95±0.04 (n=3) after 20 days, and to 6.66±0.40 (n=2) 

after 30 days, with the 10 and 20 day results obtained 

from the convection oven and the 30 day results 

obtained from the explosion resistant apparatus. The 

pH of the 100 mg/L anoxic and oxic ampules stored 

at room temperature (22°C) increased to 8.0±0.32 

(n=3) and 7.75±0.23 (n=3), respectively, after 10 days 

but then decreased to 6.36 (n=1) and 7.34 (n=1), 

respectively, after 30 days at 22°C. The average pH of 

the anoxic and oxic TCE-free control ampules that were 

stored at 22°C and incubated at 120°C was 8.00±0.70 

(n=26) over 41 days which shows that the pH did not 

substantially change in ampules without TCE. The pH 

measurements for the TCE-free controls were from 26 of 

the 36 ampules that were initially prepared in Batches 3 

and 4 (Table 4.4).

The pH of anoxic ampules that contained acid washed, 

20-30 mesh Ottawa sand (Batch 6) are shown in 

Figure 4.9. After 40 days at 120°C, the pH decreased 

in ampules with TCE and TCE-free ampules, from 

an initial value of 7.00 down to 2.96±0.05 (n=3) 

and 3.21±0.13 (n=3), respectively. The lower pH in 

the ampules with TCE was significantly different 

(P-Value=0.01, alpha=0.05) than the pH in the TCEfree ampules indicating that TCE was being degraded. 

However, the Ottawa sand also served as a source of 

hydrogen atoms since the pH of the TCE-free control 

ampules was less than 4 after 10, 20, and 40 days. The 

pH decrease was not believed to be from the nitric acid 

used during sand pre-treatment since the sand was rinsed 

with DI-Nanopure water after the acid wash until the 

rinse water in contact with sand yielded a pH of 7.

Figure 4.9 The pH of anoxic ampules that contained 

acid-washed Ottawa sand with 100 mg/L 

of TCE (Batch 6) and TCE-free controls 

stored at 22°C and incubated at 120°C.

One explanation for the pH decrease in the ampules with 

sand is related to the detection of sulfate ions (SO4

2-) in 

the ampule aqueous phase, which led to the hypothesis 

that the Ottawa sand contained pyrite (FeS2). Pyrite 

is known to dissolve in water and form sulfate and 

increase water acidity with 16 H+ produced for every 

molecule of pyrite (Stumm and Morgan, 1996, p. 691), 

which could have caused the observed decrease in pH. 

A sample of the acid treated Ottawa sand was sent to 

the U.S. Silica Co. Corporate Laboratory in Berkeley 

Springs, West Virginia, where the sand was analyzed by 

X-ray diffraction analysis (XRD). The mineral phases 

identified in the sand included pyrite, marcasite (FeS2 

- polymorph of pyrite), and hematite (Fe2O3), however, 

no estimate of the relative amount of the minerals (i.e., 

mg/kg) was provided. Ottawa sand was analyzed for 

20 elements using ICP-MS (Thermo Jarrell-Ash, Enviro 

36) after a double acid digest using a dilute HCl and 

H2SO4 solution by the Chemical Analysis Laboratory, 

The University of Georgia, Athens, GA. Silica was the 

predominant element in Ottawa sand and iron was the 

major component in Ottawa sand amended with 1% 

goethite (Table 4.18).
66

Table 4.18 Elements Present in Ottawa Sand and 

Ottawa sand+1% Goethite

Element

Ottawa 

Sand

(mg/kg)

Ottawa 

Sand+1%Goethite 

(mg/kg)

Silica 4.54 11.31

Calcium 3.96 32.25

Iron 3.23 119.4

Zinc 2.33 4.51

Sodium 2.27 4.64

Aluminum 2.10 3.61

Nickel 1.75 0.14

Magnesium 1.10 2.40

Potassium 0.89 2.46

Assuming all the iron in the Ottawa sand represented 

FeS2

 and that all pyrite present was oxidized to sulfate, 

then the pH in the ampules would be expected to 

decrease from 7 to 3.34 in ampules with Ottawa sand 

based on the following calculations.

3.23 mg 

Fe

20 g 

sand kg mmol Fe ampule 1,000 mL =0.029 

mM Fe kg ampule 1,000 g 55.84 

mg

40 mL 

water

L

16 H+ 0.029 mM 

Fe = 0.46 mM H+

Fe ampule

pH = -log[0.46×10-3 M + 1×10-7 M] = 3.34

Transformation of the sulfur in pyrite and marcasite 

into sulfate requires a source of dissolved oxygen or 

ferric iron (Fe3+) (Stumm and Morgan, 1996). While no 

measurement for ferric iron was performed, the hematite 

identified in the Ottawa sand may have served as a 

source of ferric iron and thus accounts for the detection 

of sulfate in the anoxic ampules.

Another source of acidity was the CO2 found after 

incubating ampules amended with Ottawa sand 

(Section 4.3.2.4). Assuming that gas phase CO2

 was in 

equilibrium with the ampule water at 25°C and using 

a value of 0.0339 M/atm for the Henry’s coefficient 

between CO2

(g) and dissolved phase CO2(aq), which 

is assumed to transform into carbonic acid (H2CO3), 

results in a decrease from pH 7 to approximately 4 in the 

ampules with Ottawa sand. Thus there are at least two 

potential sources of acidity in the Ottawa sand that could 

account for the observed decrease in ampule pH.

The pH of anoxic ampules that contained acid-washed 

Ottawa sand+1% goethite (Batch 7) is shown in 

Figure 4.10. The pH decreased from 7.00 to 3.64±0.05 

(n=2) in ampules with 100 mg/L of TCE after 4 days 

at 120°C and to 4.44±0.18 after 3 days at 22°C. The 

pH in TCE-free ampules stored at 22°C and incubated 

at 120°C decreased to 4.79±0.35 (n=8). The pH of the 

anoxic ampules that contained water amended with 

NaOH to achieve an initial pH of 10 (Batch 5) is shown 

in Figure 4.11. At 120°C, the pH of NaOH-amended 

ampules that contained 100 mg/L of TCE decreased from 

10.0 to 7.06 (n=1) after 4 days. In contrast, the pH of the 

TCE-free control ampules remained at 9.03±0.11 (n=9) 

and the ampules with 100 mg/L TCE were at pH of 

9.37±0.04 (n=2) after 4 days at 22°C (Figure 4.11).

Figure 4.10 The pH of anoxic ampules that contained 

acid-washed Ottawa sand+1%goethite with 

100 mg/L of TCE (Batch 7) and TCE-free 

controls stored at 22°C and incubated at 

120°C.
67

Figure 4.11 The pH of anoxic ampules amended with 

NaOH (0.26 mM) to pH 10 and 100 mg/L 

of TCE (Batch 5) along with TCE-free 

controls stored at 22°C and incubated at 

120°C.

4.3.2.3 CO and CO2 in the Gas Phase

A 10 mL gas sample was collected from each ampule 

using a gas-tight syringe and approximately 6 mL of 

the gas sample was analyzed by a GC/TCD equipped 

with a Carboxen 1010 capillary column capable of 

separating CO and CO2 from the ampule gas samples. 

Carbon monoxide (CO) and CO2 were anticipated TCE 

degradation products based on the past experimental 

work presented in Section 2.3.2. The amount (umol) 

of CO and CO2 in each ampule was calculated based 

on the gas-phase concentration determined for CO and 

CO2, and the estimated volume of headspace gas in each 

flame-sealed ampule. The amount of CO2 reported does 

not include the amount of CO2 dissolved in the aqueous 

phase, which was expected to be substantial given the 

Henry’s law coefficient of 0.83 M(aq)/M(g) for 25°C 

(Stumm and Morgan, 1996, p. 214). Using the average 

gas volume of 20 mL and liquid volume of 45 mL for 

the ampules shows that the amount of dissolved CO2

is expected to be 1.7 times greater than the amount 

in the gas phase. The additional amount of dissolved 

CO2 was incorporated in calculating the rate of TCE 

degradation based on the rate of carbon products formed 

(Table 4.22). 

The amounts of CO and CO2 in ampules that initially 

contained 1,000 mg/L of TCE (Batch 1 and 2) and 

were incubated at 120°C are shown in Figure 4.12. 

The CO and CO2 content of the ampules increased 

during the 120°C incubation period, with nearly 

identical amounts of CO and CO2

 detected in all of the 

ampules after 10 days regardless of the initial oxygen 

content (anoxic or oxic). After 20 days of incubation at 

120°C, the amount of CO and CO2 detected in the oxic 

ampules nearly doubled, while the amount detected 

in the anoxic ampules remained similar to the 10-day 

incubation values. The average amount of CO and CO2

shown in Figure 4.12 excludes the amount detected 

in Ampules 9, 55, and 58, which were incubated at 

120°C. In the case of Ampule 9, an anoxic ampule with 

1,000 mg/L of TCE from Batch 1, there was a significant 

difference (P-Value=0.02, alpha=0.05) between 

the amount of CO and CO2 detected after 20 days 

(CO+CO2 = 12,386 ppmv) compared to the amount 

detected in the companion replicate ampules, Ampules 

7 and 8 (2,057±387 ppmv). There was a significant 

difference (P-Value=0.06, alpha=0.05) between the 

amount of CO and CO2 detected after 10 days in Ampule 

55 (4,250 ppmv) and in replicate Ampules 53 and 54 

(1,983±419 ppmv), oxic ampules with 1,000 mg/L of 

TCE from Batch 2. In this case, Ampule 55 had to be 

flame sealed a second time during preparation thus 

the ampule contents may have been exposed to the 

propane-oxygen flame. The greatest difference between 

replicate Batch 2 ampules was obtained after 20 days 

for Ampule 58 (123,143 ppmv) and Ampules 56 and 57 

(4,515±304 ppmv).

Figure 4.12 Amounts of CO and CO2 in anoxic 

(Batch 1) and oxic (Batch 2) ampules 

with 1,000 mg/L of TCE and incubated at 

120°C.

The amounts of CO and CO2 detected in anoxic 

(Batch 4) and oxic (Batch 3) ampules that initially 

contained 100 mg/L of TCE and were incubated at 

120°C for up to 41 days are shown in Figure 4.13. 

Carbon monoxide (CO) and CO2 were not detected 

in ampules stored at 22°C that contained 100 mg/L 

of TCE and were without TCE (TCE-free). Carbon 
68

monoxide (CO) was detected in ampules that contained 

TCE and were incubated at 120°C using the convection 

oven, whereas CO wasn’t detected in ampules using 

the explosion resistant apparatus until 41 days at 

120°C. This result may indicate that the difference in 

temperature profile between the two incubation systems 

led to differences in TCE degradation rate.

Figure 4.13 Amounts of CO and CO2 in anoxic 

(Batch 4) and oxic (Batch 3) ampules with 

100 mg/L of TCE and incubated at 120°C. 

No CO or CO2 was detected in ampules 

stored at 22°C.

The amounts of CO and CO2 detected in anoxic ampules 

that contained 20-30 mesh Ottawa sand (Batch 6) are 

shown in Figure 4.14. The average amount of CO 

detected (0.97±0.08 umol) in ampules that contained 

TCE and were incubated at 120°C over a 40-day period 

was approximately twice the amount detected in the 

ampules stored at 22°C for 40 days. Carbon monoxide 

(CO) was not detected in ampules without TCE that were 

stored at 22°C and incubated at 120°C. For the ampules 

incubated at 120°C, the amount of CO2 increased with 

incubation time, with amount of CO2 detected in ampules 

with TCE in excess of the amount of CO2 detected in 

ampules without TCE.

Figure 4.14 Amounts of CO and CO2 in anoxic ampules 

with Ottawa sand and 100 mg/L of TCE 

(Batch 6) stored at 22°C and incubated at 

120°C.

The amounts of CO and CO2

 detected in anoxic ampules 

that contained 20-30 mesh Ottawa sand + 1% goethite 

(Batch 7) are shown in Figure 4.15. The amount of 

CO increased during incubation over 4 days at 120°C. 

In contrast, no CO was detected in TCE-free ampules 

that were stored at 22°C. At 120°C, the amount of CO2

increased with incubation time in excess of the amount 

of CO2 detected in the TCE-free ampules. Relative the 

data shown in Figure 4.14, the amount of CO2 generated 

in the presence of 1% goethite was greater than 

detected in ampules that contained Ottawa sand alone. 

Figure 4.16 shows the amount of CO and CO2 detected 

in the ampules that contained 0.26 mM of NaOH. The 

amount of CO increased over the initial 2 days of the 

incubation period at 120°C and then decreased over the 

last 2 days. No CO was detected in the ampules without 

TCE at 120°C and with TCE that were stored at 22°C. 

The amount of CO2 increased with incubation time until 

reaching a plateau of approximately 0.8 umol on day 3 

and 4.
69

Figure 4.15 Amounts of CO and CO2 in anoxic 

ampules with Ottawa sand+1%goethite and 

100 mg/L of TCE (Batch 7) stored at 22°C 

and incubated at 120°C.

Figure 4.16 Amounts of CO and CO2 in anoxic 

ampules amended with NaOH (0.26 mM) 

to pH 10 (Batch 5) and 100 mg/L of TCE 

incubated at 120°C.

4.3.2.4 Other Gas Phase Compounds

After analyzing 6 mL of the 10 mL gas sample for 

CO/CO2 content, the 10 mL syringe with 4 mL of gas 

sample was removed from the GC/TCD injection loop 

and the syringe needle tip was sealed with a rubber 

septum. Approximately 1 mL of the gas sample was 

then injected directly into the inlet of a Varian 3600CX 

GC equipped with a 30 m long by 0.32 mm OD Varian 

CP-Sil 8MS column connected to a Varian Saturn 2000 

mass spectrometer (MS). The purpose of injecting the 

gas sample directly into the GC/MS was to screen for the 

presence of compounds other than CO, CO2

, and TCE. 

This analysis step was added after the oven explosion 

had occurred to determine if potentially explosive TCE 

degradation products were present in the ampule gas 

phase. The first gas samples analyzed by GC/MS were 

from Ampules 83, 84, and 85 (Batch 3), oxic ampules 

that contained 100 mg/L of TCE and had been incubated 

at 120°C for 20 days in the convection oven. The gas 

samples were found to contain dichloroacetylene (DCA), 

CO2

, and TCE. Dichloroacetylene was identified by mass 

spectrum match with the NIST98 library (Figure 4.17). 

Figure 4.17 Mass spectrum of the 2.05 min 

chromatogram peak from the analysis of 

1 mL of gas from Ampule 83.

The concentration of DCA was not determined, 

as this compound is unstable and difficult to 

prepare for calibration purposes. The abundance of 

dichloroacetylene was less than 1% of the TCE present 

(base peak). Dichloroacetylene (DCA) was not present 

in the gas samples from Ampules 95, 96, and 97, the 

matching 100 mg/L oxic ampules that were stored 

at 22°C. Dichloroacetlylene (DCA) was consistently 

identified in gas samples from ampules that were 

incubated at 120°C for Batch 3 through 7, no gas 

samples from Batch 1 or 2 ampules were analyzed by 

GC/MS. The greatest amount of DCA was detected 

in the gas phase of the pH 10 ampules (Batch 5) by 

GC/MS analysis. An unidentified peak was present in the 

headspace GC/FID chromatogram from the analysis of 

1 mL water samples collected from the pH 10 ampules. 

The identity of the GC/FID peak was assigned to DCA 

based on the GC/MS results and the estimated dissolved 

phase DCA concentration was 1.8±0.5 mg/L for the 

pH 10 ampules incubated at 120°C, estimated using the 

headspace response factor for TCE. 

4.3.2.5 Aqueous Phase Compounds

The amount of chloride detected in both anoxic and 

oxic ampules incubated at 120°C increased for all 
70

experimental conditions considered and in excess 

of the amount measured in paired ampules stored at 

22°C (Figures 4.18 through 4.22). Thus increasing 

the temperature of ampules resulted in an increase in 

the rate of TCE degradation since TCE was the only 

source of chloride within the ampules. The presence 

of oxygen appeared to have an affect on the amount of 

TCE degraded in the 1,000 mg/L ampules (Batches 1 

and 2) as there was a greater amount of chloride 

(P-Value=0.001, alpha=0.05) in the 1,000 mg/L ampules 

with oxygen after 10 and 20 days at 120°C (Figure 4.18). 

However, there was no discernable difference 

(P-Value=0.66, alpha=0.05) between the amount of 

chloride in the anoxic (Batch 4) and oxic (Batch 3) 

ampules with 100 mg/L of TCE after 10 and 30 days at 

120°C (Figure 4.19). The amount of chloride detected 

in the 100 mg/L oxic (Batch 3) ampules increased from 

7.6±1.3 umol after 10 days to 9.9±0.6 umol after 20 days 

at 120°C using the convection oven incubation but was 

6.0±0.1 umol after 30 days using the explosion resistant 

apparatus. There was a similar trend for chloride in the 

anoxic 100 mg/L ampules with more chloride detected 

after 10 days in the convection oven that after 30 and 41 

days in the explosion resistant apparatus.

Figure 4.18 Amount of chloride in anoxic (Batch 1) and 

oxic (Batch 2) ampules with 1,000 mg/L 

of TCE stored at 22°C and incubated at 

120°C.

Figure 4.19 Amount of chloride in anoxic (Batch 4) 

and oxic (Batch 3) ampules with 100 mg/L 

of TCE stored at 22°C and incubated at 

120°C.

The presence of 20-30 mesh Ottawa sand (Batch 6) 

caused an increase in the amount of chloride 

(Figure 4.20) in ampules incubated at 120°C compared 

to the amount of chloride in the anoxic (Batch 4) 

ampules that were without sand (Figure 4.19); both 

batches were incubated in the explosion resistant 

apparatus. There was 13.8±1.9 umol of chloride detected 

in the anoxic ampules that contained 20-30 mesh Ottawa 

sand after 30 days at 120°C as compared to 6.3±0.0 umol 

of chloride in the ampules with anoxic water alone.

Figure 4.20 Amount of chloride in anoxic ampules 

with Ottawa sand and 100 mg/L of TCE 

(Batch 6) stored at 22°C and incubated at 

120°C.
71

The addition of goethite to the Ottawa sand resulted 

in 6.8±1.7 umol of chloride (Figure 4.21) after 4 days 

at 120°C while the amount of chloride in the pH 10 

ampules was 13.8 umol (n=1) after 4 days at 120°C 

(Figure 4.22).

Aqueous samples collected from the ampules were 

analyzed for haloacetic acids content, including 

chloroacetate (ClH2C2OO-), dichloroacetate 

(Cl2HC2OO-), and trichloroacetate (Cl3C2OO-). While 

dichloroacetate (DCAA) was not detected (>2 ug/L) 

in any of the ampules containing 100 mg/L of TCE 

(Batches 3-7), DCAA was detected in several of the 

ampules containing 1,000 mg/L of TCE (Batch 1 and 2). 

In 3 of the anoxic ampules, DCAA was detected at the 

following concentrations: 16 ug/L after 10 days at 22°C, 

7 ug/L after 20 days at 120°C, and 6.1 ug/L after 30 days 

at 22°C. The one exception was the 125 ug/L of DCAA 

detected in Ampule 9, the 1,000 mg/L anoxic ampule 

that also had more CO and CO2 than in its companion 

replicate ampules. DCAA was detected in all of the oxic 

ampules with 1,000 mg/L of TCE (Batch 2), with the 

largest DCAA concentration detected in ampules that 

were stored at 22°C (Figure 4.23). DCAA was detected 

in the ampules that contained solids (Batch 6 and 7), 

but at relatively low concentrations (i.e., < 5 ug/L). 

Chloroacetate was detected in pH 10 ampules that 

were incubated at 120°C (Figure 4.24), whereas the 

chloroacetate concentration in the pH 10 ampules stored 

at 22°C were less that 5 ug/L.

Figure 4.21 Amount of chloride in anoxic ampules with 

Ottawa sand+1%goethite and 100 mg/L 

TCE (Batch 7) stored at 22°C and 

incubated at 120°C.

Figure 4.22 Amount of chloride in anoxic ampules 

amended with NaOH (0.26 mM) to pH 10 

with 100 mg/L of TCE (Batch 5) stored at 

22°C and incubated at 120°C.

Figure 4.23 Concentration of dichloroacetate (DCAA) 

in the anoxic (Batch 1) and oxic (Batch 2) 

ampules with 1,000 mg/L of TCE stored at 

22°C and incubated at 120°C.

Figure 4.24 Concentration of chloroacetate in ampules 

amended with NaOH (0.26 mM) to pH 10 

and 100 mg/L TCE (Batch 5) incubated at 

120°C.
72

The aqueous solution that remained after the haloacetic 

acid and chloride analysis (~5 mL) was analyzed by 

Ion Chromatography (IC) to determine if other anionic 

species were present. The IC chromatogram contained 

three elution peaks with retention times of 3.35, 3.73, 

and 4.75 minutes. The 4.75 minute peak was attributed 

to chloride based on comparison with the elution time 

for a 1 mM chloride standard solution. The 3.35 and 

3.73 minute peaks were attributed to formate (CHOO-) 

and to glycolate (HOH2C2OO-), respectively, based on 

comparison with elution times for a solution containing 

1 mM of glycolate, acetate, and formate. Glycolate and 

formate were detected in all ampules that contained 

1,000 mg/L of TCE (Batch 1 and 2) and were incubated 

at 120°C (Figure 4.25). The average values shown in 

Figure 4.25 do not include the results from Ampules 

9, 55, and 58 as the results from these ampules were 

significantly different from the other ampules as 

discussed in Section 4.6.4. The amount of formate 

increased with time at 120°C in the oxic and anoxic 

ampules that contained 1,000 mg/L of TCE while the 

amount of glycolate decreased with incubation time. 

There was more glycolate than formate after 10 days 

in all the 1,000 mg/L ampules, while there was more 

formate than glycolate after 20 days. Glycolate and 

formate were not detected in ampules stored at 22°C that 

contained 1,000 mg/L of TCE or in the TCE-free control 

ampules.

Figure 4.25 Amount of glycolate and formate in anoxic 

(Batch 1) and oxic (Batch 2) ampules with 

1,000 mg/L of TCE incubated at 120°C.

Glycolate and formate were detected in both the anoxic 

(Batch 4) and oxic (Batch 3) ampules that contained 

100 mg/L of TCE and were incubated at 120°C 

(Figure 4.26). Formate was not detected in either the 

anoxic or oxic ampules with 100 mg/L of TCE after 

30 days at 120°C. However, it should be noted that 

the 30 and 40 day results for the anoxic ampules were 

obtained using the explosion resistant incubation 

apparatus, whereas the 10 and 20 day results for the 

oxic ampules were obtained using the convection oven. 

Glycolate and formate were not detected in the anoxic 

and oxic ampules that contained 100 mg/L of TCE and 

were stored at 22°C or in the TCE-free control ampules. 

The amount of formate detected in the anoxic ampules 

that contained 20-30 mesh Ottawa sand and 100 mg/L 

of TCE (Batch 6) decreased with time at 120°C, while 

the amount of glycolate increased over the 40-day 

incubation period (Figure 4.27). Formate was the only 

organic acid detected in the ampules that contained 

Ottawa sand + 1% goethite (Batch 7) and the amount of 

formate increased over the 4-day incubation period at 

120°C (Figure 4.28).

Figure 4.26 Amount of glycolate and formate in anoxic 

(Batch 4) and oxic (Batch 3) ampules with 

100 mg/L of TCE incubated at 120°C.

Figure 4.27 Amount of glycolate and formate in anoxic 

ampules with Ottawa sand and 100 mg/L 

of TCE (Batch 6) stored at 22°C and 

incubated at 120°C.
73

Figure 4.28 Amount of formate in anoxic ampules with 

Ottawa sand+1%goethite and 100 mg/L 

of TCE (Batch 7) stored at 22°C and 

incubated at 120°C.

Sulfate (SO4

2-) was an additional anion detected in 

ampules that contained solids. The amount of sulfate 

detected in anoxic ampules with 20-30 mesh Ottawa 

sand that were stored at 22°C and incubated at 120°C 

is shown in Figure 4.29. Sulfate was present at aqueous 

phase concentrations of greater than 1 mM and is 

hypothesized to have been formed from the thermal 

decomposition of pyrite and marcasite (FeS2), which 

were found to be present in the 20-30 mesh Ottawa sand 

(Dr. Matt Paige, facsimile communication, 30 August 

2004) as discussed in Section 4.6.2. Similar amounts of 

sulfate were detected in ampules that contained goethite 

in addition to 20-30 mesh Ottawa sand (data not shown). 

Glycolate was the only organic acid detected in the 

100 mg/L ampules with NaOH (Batch 5) that were 

incubated at 120°C as shown in Figure 4.30.

Figure 4.29 Amount of sulfate in anoxic ampules 

with Ottawa sand and 100 mg/L of TCE 

(Batch 6) stored at 22°C and incubated at 

120°C.

Figure 4.30 Amount of glycolate in anoxic ampules 

amended with NaOH (0.26 mM) to pH 10 

and with 100 mg/L of TCE (Batch 5) 

incubated at 120°C.
74

4.3.2.6 Mass Balance

A balance between the loss of TCE and the moles of 

carbon and chloride detected in ampules incubated at 

120°C is provided in Table 4.19. The moles of TCE 

lost were determined by subtracting the moles of TCE 

detected after each 120°C incubation period from the 

initial moles of TCE as determined immediately prior to 

flame sealing the ampules. The moles of carbon lost were 

calculated as twice the moles of TCE lost (2×TCE lost) 

and the moles of chlorine lost as three times the moles 

of TCE lost (3×TCE lost). The mass balance is a unitless 

ratio of the moles of TCE lost divided by the moles 

of degradation products detected with a value of 1 

indicating an ideal balance between what was lost and 

what was found. A value of less than zero corresponds to 

a gain in the moles of TCE present in the ampule. 

The results shown in Table 4.19 indicate that more TCE 

was lost than could be accounted for by the moles of 

carbon detected in the gas phase as CO and CO2

, and in 

the aqueous phase as formate, glycolate, and haloacetic 

acids (i.e., mass balance > 1). There was also more 

TCE lost than could be accounted for by the moles of 

chlorine detected in the aqueous phase as chloride. The 

failure to achieve mass balance could be attributed to 

the following explanations: 1) more organic compounds 

were present than were detected, 2) experimental error 

occurred during the analysis of TCE, and/or degradation 

products, or 3) losses occurred during the sample 

collection process, in particular volatile degradation 

products.

Table 4.19 Mass Balance Between Carbon and Chloride Lost as TCE and Detected as Degradation Products in 

Ampules Incubated at 120°C

Ampule Content

(Batch No.)

Incubation 

Time (days) C lost/C detected Cl lost/Cl detected

Anoxic 

1000 mg/L TCE

(1)

10 6.4±13.0 6.9±14.4

20 3.7±2.7 2.9±0.6

Oxic 

1000 mg/L TCE

(2)

10 -2.5±5.2 -1.0±4.1

20 2.7±4.4 2.4±3.1

Oxic 

100 mg/L TCE

(3)

10 1.9±1.1 1.8±1.2

20 1.8±0.0 2.0±0.2

30 2.5±0.7 3.9±1.2

Anoxic 

100 mg/L TCE

(4)

10 0.4±1.0 0.3±0.8

30 0.1±0.9 0.1±1.3

41 0.2±0.5 0.2±0.8

Ottawa Sand

100 mg/L TCE

(6)

10 1.2±1.6 1.0±1.2

30 2.3±1.4 1.9±2.2

40 1.6±2.5 1.4±2.4

Ottawa Sand +

1% Goethite

100 mg/L TCE

(7)

1 -0.2±1.8 -0.4±2.0

2 2.0±2.2 3.2±2.0

4 1.8±2.5 2.7±2.4

pH 10

100 mg/L TCE

(5)

1 2.5±0.2 3.5±0.3

2 1.7±0.2 1.9±0.3

3 2.1±1.2 2.6±1.8

4 1.4 (n=1) 1.4 (n=1)
75

The ratio of the TCE degradation products—moles of 

chloride divided by the moles of carbon as CO, CO2, 

formate and glycolate—provides another measure to 

determine if all degradation products were detected 

and has the advantage of being independent of the 

TCE analysis. The ideal ratio of chlorine to carbon 

(Cl:C), assuming TCE is the only parent compound, is 

1.5 (3Cl:2C). The values for Cl:C shown in Table 4.20 

are all close to 1.5, suggesting that the compounds 

detected represent the majority of the TCE degradation 

products. Therefore, the poor overall mass balance 

results shown in Table 4.19 most likely reflect losses in 

TCE during sample collection and analysis.

Table 4.20 Amount of Carbon and Chloride Detected as Degradation Products and the Cl:C Ratio for Ampules 

Incubated at 120°C 

Ampule Content

(Batch No.)

Incubation Time 

(days) C detected (umol) Cl detected (umol) Cl:C

Anoxic 

1000 mg/L TCE

(1)

10 6.5±0.3 5.6±0.3 0.9±0.1

20 6.0±0.7 13.0±1.5 2.2±0.3

Oxic 

1000 mg/L TCE

(2)

10 5.3±1.7 9.5±0.3 1.8±0.6

20 9.0±2.0 21.1±6.3 2.3±0.9

Oxic 

100 mg/L TCE

(3)

10 4.5±0.5 7.7±1.3 1.7±0.2

20 7.3±1.0 9.9±0.6 1.4±0.1

30 6.1±0.2 6.0±0.1 1.0±0.0

Anoxic 

100 mg/L TCE

(4)

10 4.7±0.6 8.3±1.1 1.8±0.2

30 6.6±1.0 6.3±0.0 1.0±0.1

41 7.1±0.1 6.6±0.4 0.9±0.1

Ottawa Sand

100 mg/L TCE

(6)

10 5.2±1.2 8.8±0.4 1.7±0.4

30 7.1±0.8 13.1±1.9 1.8±0.3

40 7.3±0.8 12.7±0.6 1.7±0.2

Ottawa Sand +

1% Goethite

100 mg/L TCE

(7)

1 3.3±0.5 2.7±0.9 0.8±0.3

2 4.5±1.1 4.3±0.6 1.0±0.3

4 5.9±0.8 6.0±0.3 1.0±0.1

pH 10

100 mg/L TCE

(5)

1 5.5±0.1 5.8±0.1 1.1±0.0

2 9.8±0.7 13.6±0.7 1.4±0.1

3 11.1±2.0 14.2±4.8 1.3±0.5

4 10.1 (n=1) 16.2 (n=1) 1.6

* Corrected for the moles of carbon found in paired ampules without TCE
76

4.4 Discussion

The primary objectives of the ampule experiments 

were to determine the rate of TCE degradation and 

the TCE degradation products formed after exposing 

dissolved-phase TCE to temperatures of 22 and 120°C 

for periods of up to 40 days. The primary gas phase 

degradation products observed in these experiments 

were CO and CO2 (>99%), while the primary aqueous 

phase products included chloride, hydronium ions, 

glycolate, and formate (>99%). The following sections 

provide a discussion of possible TCE degradation 

initiation mechanisms, including oxygen addition to 

TCE and hydrogen elimination from TCE. A reaction 

sequence is presented to explain the oven explosion, and 

a separate section provides comparisons between the 

ampule experimental results obtained herein and those of 

Knauss et al. (1999).

4.4.1 Oxygen Initiated TCE Degradation

Based on the review of thermal reaction experiments 

presented in Sections 2.3.1, passing pure oxygen through 

liquid TCE-NAPL heated to 70°C is known to yield 

hydrochloric acid (HCl), carbon monoxide (CO), and 

phosgene (COCl2) as gas phase products, and TCE 

epoxide (Cl2COCHCl) and dichloroacetyl chloride 

(Cl2HC2OCl) as NAPL products. This reaction can be 

stated as (McKinney et al., 1955): 

Cl2C=CHCl + O2(g) → 70 C HCl(g) + CO(g) +

COCl2(g) + Cl2COCHCl + Cl2HC2OCl (4.1)

McKinney et al. (1955) obtained these results after 

adding benzoyl peroxide or partially-oxidized TCE to 

liquid TCE-NAPL and Kucher et al. (1990) observed 

the same reaction products after adding azo-bisisobutyronitrile (AIBN) to liquid TCE-NAPL. Benzoyl 

peroxide and AIBN are known to produce radical 

initiator compounds upon heating to temperatures 

greater than 70°C (Fossey et al., 1995). The reaction 

between TCE and oxygen is thought to involve a radical 

chain reaction mechanism (Kaberdin and Potkin, 

1994). No radical initiator compounds were added to 

the ampule experiments. However, it is possible that 

partially-oxidized TCE was generated during the flame 

sealing process. The radical initiation mechanism for 

the aqueous oxidation of TCE is unknown and was not 

determined in the experiments herein.

If the reaction products including HCl, phosgene, 

dichloroacetyl chloride, and TCE epoxide shown in 

Equation 4.1 were to form in the presence of an aqueous 

phase, they would likely undergo subsequent degradation 

reactions as discussed in Section 2.3.2. Hydrochloric 

acid gas would generate hydronium and chloride 

ions in the aqueous phase. Phosgene would undergo 

hydrolysis to form CO2

 according to Mertens and von 

Sonntag (1994):

COCl2(g) → H O,25 C 2  CO2 + 2HCl (4.2)

k = 6 (s-1) at 25°C

Dichloroacetyl chloride would be expected to undergo 

hydrolysis to form dichloroacetate (Cl2HC2OO-) 

(Kivinen, 1972). TCE epoxide has been synthesized 

and the hydrolysis products included CO in the gas 

phase, and formate, dichloroacetate, and oxoacetate 

(HOC2OO-) in the aqueous phase (Cai and Guengerich, 

1999). Dichloroacetate (DCAA) is a stable end-product 

at room temperature, as indicated by its detection in the 

oxic ampules that contained 1,000 mg/L of TCE and 

were stored at 22°C (see Figure 4.24). As discussed in 

Section 2.3.2, Prager et al. (2001) demonstrated that 

DCAA is rapidly (t1/2 = 0.14 day or 3.4 hrs) hydrolyzed 

to oxoacetate (HOC2OO-) at 120°C according to:

Cl2HC2OO- → H O,120 C 2  HOC2OO- + 2HCl (4.3)

Oxoacetate was not detected in any of the ampules 

incubated at 120°C. Prager et al. (2001) suggest that 

glycolate (HOH2C2OO-) and oxalate (HOOC2OO-) 

were likely products from the aqueous phase thermal 

degradation of oxoactetate. While oxalate was not 

detected, glycolate and formate (CHOO-), two closely 

related organic acids, were found in the ampule aqueous 

phase and are thought to be the products of DCAA 

degradation in the ampule experiments reported herein. 

Decarboxylation of glycolate (HOH2C2OO-) is thought to 

form CO2 and formaldehyde (CH2O) according to Belsky 

et al. (1999):

HOH2C2OO- + H+→ CH2O + CO2 + H2 (4.4)

Formaldehyde would then be hydrolyzed to formate 

(CHOO-) and hydroxide ions (OH-) according to:

CH2O + H2O → CHOO- + OH- + 2H+ (4.5)

Formate was suggested as a stable end-product below 

temperatures of 150°C by Shende and Mahajani 

(1997). However, any one of these organic acids could 

be present during the thermal remediation process as 

they have been cited as the end products after thermal 

treatment of organic compounds by wet air oxidation 

(Mishra et al., 1995) and supercritical water oxidation 

(Buhler et al. 2002). 

Dichloroacetyl chloride, TCE epoxide, and phosgene 

were not detected in the aqueous or gas phase samples 

collected from the ampules incubated at 120°C in 

the experiments reported herein. While the exact 

mechanism of oxygen initiated TCE degradation is not 

known (Kaberdin and Potkin, 1994), phosgene, TCE 

epoxide, and dichloroacetyl chloride are proposed as 

intermediates that were hydrolyzed to form HCl, CO, 
77

CO2, dichloroacetate, glycolate, and formate within the 

ampule reaction environment. 

4.4.2 Hydrogen Elimination Initiated TCE 

Degradation

An alternative to the oxygen-initiated TCE degradation 

mechanism presented above is based on the belief that 

the lone hydrogen atom in TCE has an acid character 

and is susceptible to elimination by strong nucleophiles 

such as hydroxide ions (OH-) (Smith and March, 2001). 

For example, passing gas-phase TCE over potassium 

or sodium hydroxide (NaOH) at 130°C has long been 

known to degrade TCE to yield dichloroacetylene 

(DCA) (Delavarenne and Viehe, 1969). Pielichowski 

and Popielarz (1984) reported a 70% yield of DCA 

after adding TCE to a NaOH solution heated to 70°C. 

The elimination of the acidic hydrogen from TCE has 

been proposed to form an unstable intermediate, a 

trichlorovinyl anion (Cl3C2

-

), which reacts spontaneously 

to form DCA (C2Cl2) after loss of a chlorine atom 

(Pielichowski and Popielarz, 1984) according to:

Cl2C=CHCl + OH- → 120 C [Cl2C=CCl-] → 120 C

 ClC≡CCl + Cl- + H2O (4.6)

DCA was identified in all gas phase samples collected 

from ampules that contained TCE and were incubated at 

120°C, whereas DCA was not detected in ampules with 

TCE that were stored at 22°C. Thus the TCE degradation 

observed in the ampules was suspected to have involved 

hydrogen elimination based on the presence of DCA.

The addition of NaOH to the ampules resulted in an 

increase in the rate of TCE degraded along with an 

increase in the amount of DCA detected, as compared 

to the results from the deionized water ampules, which 

was consistent with the proposed hydrogen-elimination 

initiation mechanism. In ampules with deionized water, 

the elimination of the lone TCE hydrogen atom may 

have been initiated by water or hydroxide ions (10-7 M). 

Increasing the ampule temperature from 22°C to 120°C 

would have increased the hydroxide ion concentration 

from 10-7 to 10-6 M (Marshall and Frank, 1981) and 

increased the interaction between TCE and water 

molecules by lowering the water dielectric strength. 

An increase in hydroxide ion concentration would be 

expected to increase the rate of hydrogen elimination 

from TCE and the increase in TCE and water interaction 

may have allowed the electrophilic oxygen atom in 

water to act as a nucleophile and eliminate the TCE 

hydrogen. However, the mode of hydrogen elimination 

from TCE in deionized water is not currently known.

The addition of goethite to the ampules that contained 

anoxic water and sand increased the rate of TCE 

degradation. While the TCE degradation mechanism 

with goethite is unknown, chloroacetylene (HC2

Cl), a 

compound closely related to DCA, has been detected 

during the degradation of chloroethenes by zero valent 

iron (Arnold and Roberts, 2000). Where zero valent 

iron (Fe0

) is thought to serve as an electron donor 

(Fe0 → Fe2+ + 2e-) during the reductive dechlorination 

of TCE, goethite is not expected to serve as an electron 

source since the iron in goethite is oxidized (Fe3+). 

Instead, goethite may serve as a source of hydroxide ions 

through a dissolution reaction:

FeOOH + H2O → Fe3+ + 3OH- (4.7)

The dissolution of goethite would be expected to 

increase the ampule pH with the formation of hydroxide 

ions, however, the pH in ampules with goethite 

decreased over the 4 day incubation period (Figure 4.10). 

Using pH to indicate the presence of hydroxide ions 

may not be accurate since pH is the hydronium ion 

concentration in the bulk ampule solution rather than 

at the goethite-water interface and because the pH 

measurement was performed after cooling the ampules 

to room temperature (22°C). 

Chloroacetylene has also been detected during 

TCE degradation by zero valent zinc (Arnold and 

Roberts, 1998) and vitamin B12 (Burris et al., 1996). 

Dichloroacetylene, in addition to chloroacetylene, have 

been detected during the sonolysis of TCE contaminated 

water (Drijvers et al., 1996). The presence of 

chloroacetylenes under this range of reaction conditions 

suggests that the elimination of hydrogen is an important 

reaction pathway for the degradation of TCE. The 

degradation of the chloroacetylenes intermediates is 

equally important because acetylenes can engage in a 

wide variety of reactions (Hopf and Witulski, 1995).

Dichloroacetylene (DCA) is known to react explosively 

with oxygen to form CO, CO2

, and phosgene (COCl2) 

(Ott et al., 1930), but is also stabilized against oxygen 

in the presence of excess TCE (Williams, 1972; 

Reichert et al., 1975). Aqueous solutions of DCA 

have been prepared at concentrations up to 70 mg/L 

and are reported to be stable over a period of 24 hours 

at room temperature (Reichert et al., 1983; Arnold 

and Roberts, 1998). There are also reports of DCA 

spontaneously igniting upon mixing with water (Ott and 

Packendroff, 1931; Riemschneider and Klaus, 1961). 

While DCA is known to react with oxygen, the amount 

of oxygen present in the ampules did not decline over 

the experimental period (see Table 4.18, excluding 

Ampule 58). DCA was detected in the oxic ampules 

with 100 mg/L of TCE and was most likely stabilized 

by the excess amount of TCE present. Therefore, DCA 

is hypothesized to have been stabilized against reacting 

with the oxygen in the oxic ampules. 

Acetylene is known to react with water in both the 

aqueous and gas phase to form acetaldehyde, which 
78

hydrolyzes to form acetate (Nieuwland and Vogt, 

1945). The addition of water to acetylene is rate limited 

and requires acidic conditions along with elevated 

temperature (Lucchini and Modena, 1990). The pH 

decrease in ampules that were incubated at 120°C 

(Section 4.6.2) may have provided the acidic and 

temperature conditions necessary to cause the hydrolysis 

of DCA and produce chloroacetyl chloride (ClH2C2OCl), 

the analog of acetaldehyde, according to:

 ClC≡CCl + H3O+ → 120 C ClH2C2OCl + H+ (4.8)

Chloroacetyl chloride could then have reacted with 

water to form chloroacetate (ClH2C2OO-). For example, 

chloroacetate is the reaction product formed when 

passing TCE through heated concentrated sulfuric acid 

(Kaberdin and Potkin, 1994). Chloroacetate was detected 

in the pH 10 ampules which also had the greatest 

concentration of DCA. Chloroacetate is known to react 

with water (i.e., hydrolyze) to form glycolate (Prager 

et al., 2001), and glycolate was detected in the pH 10 

ampules. Therefore, DCA could have been hydrolyzed 

to DCAA, which was then degraded at 120°C 

(Equation 4.3) to the non-chlorinated organic acids, 

glycolate and formate, observed in the ampules that 

were not amended with NaOH. However, since DCA is 

reactive and could potentially interact or react with soil 

constituents such as organic carbon, DCA formed during 

the in-situ thermal treatment of TCE could degrade to 

form non-chlorinated organic acids. 

4.4.3 Oven Explosion

The oven explosion is hypothesized to have been 

caused by the detonation of DCA in at least one ampule. 

Reichert et al. (1975) showed that DCA is stable in the 

presence of excess TCE, however, once the ratio of DCA 

to TCE exceeds 1:2, a spontaneous reaction occurs with 

oxygen. The explosion occurred 4 days after introducing 

the sand, sand+1% goethite, and pH 10 ampules into 

the oven, and 20 days after incubation of the 1,000 

and 100 mg/L ampules began. The explosion scenario 

involves the formation of DCA in many ampules and 

in excess of TCE in at least one ampule. Some event 

then occurred to initiate the rapid DCA decomposition 

resulting in the detonation of at least one ampule and 

the force from that one ampule exploding is thought to 

have caused the other ampules to break open and release 

additional DCA into the air resulting in an explosion that 

destroyed the oven.

Goethite was initially suspected of having caused the 

formation of DCA in an amount in excess of TCE. 

However, the goethite ampules contained argon sparged 

water and argon gas, meaning that the oxygen content 

was limited to approximately 3 umol. The reaction of 

3 umol of DCA with oxygen to yield CO, CO2

, and 

phosgene would have released approximately 1.4 J of 

energy based on the heats of reaction (Zhu and Bozzelli, 

2002) which is estimated to result in a 1 bar pressure 

increase within an ampule. The ampules have a rated 

pressure capacity of approximately 14 bar, thus the 

estimated 1 bar pressure increase in the ampules with 

goethite would be insufficient to cause an ampule to 

break open. In addition to the goethite ampules, there 

were ampules with 1,000 mg/L of TCE that contained 

air sparged water with air in the headspace and had 

been in the oven for 24 days. There was approximately 

100 umol of oxygen in these oxic ampules and a reaction 

with DCA would have released approximately 48 J of 

energy or an estimated pressure increase of 47 bar, about 

three times greater than the rated pressure capacity of the 

ampules. 

A significant amount of DCA could have been generated 

in the sand+1% goethite or pH 10 ampules, rendering 

these ampules potentially explosive. However, the 

amount of oxygen present in these ampules was limited 

to less than 3 umol making it unlikely that they initiated 

the oven explosion. The 1,000 mg/L oxic ampules that 

had been incubating for a period of 24 days at 120°C 

are more likely to have initiated the explosion due to the 

presence of approximately 100 umol of oxygen.

4.4.4 Comparison to Knauss et al. (1999) 

Results

The in-situ transformation of TCE to CO2 and chloride 

ions has been claimed to occur during the thermal 

treatment of subsurface environments contaminated 

with TCE according to researchers working in the 

Applied Geology and Geophysics Group at the U.S. 

Department of Energy, Lawrence Livermore National 

Laboratory (LLNL). The LLNL group based their 

claim on experimental results obtained by measuring 

the disappearance of dissolved-phase TCE along with 

the appearance of dissolved phase CO2 and chloride 

ions. The experiments were completed over a period of 

up to 43 days within a heated, constant pressure, goldwalled reactor that was completely water filled (Knauss 

et al., 1999). The ampule experiment reported herein 

was conducted, in part, to independently evaluate the 

conclusions reached by the LLNL group. 

The results of the gold-walled experiments conducted 

by Knauss et al. (1999) were significantly different than 

those reported herein. TCE concentrations decreased 

to 50% of the initial concentration within 2 days in 

the gold-walled reactor operated at 90°C. In contrast, 

approximately 80.2% of the initial amount of TCE 

(Table 4.15) remained after 30 days of incubation 

at 120°C in the oxic ampules. Knauss et al. (1999) 

stated that chloride and carbonate were the only TCE 

degradation products detected in the gold-walled 

experiment. The primary compounds detected in the 
79

ampule experiments included CO and CO2 in the gas 

phase, chloride, hydronium, glycolate, and formate in 

the aqueous phase. Knauss et al. (1999) analyzed the 

aqueous phase from their gold-walled reactors using 

a direct infrared spectroscopic method and a high 

pressure liquid chromatograph (HP 1090) connected 

to a conductivity detector. Details regarding operation 

conditions for these methods were not provided, but 

if chloride were detected then organic acids, such as 

glycolate and formate, should have been detected if 

present. However, Gu and Siegrist (1997) reported 

that the liquid chromatography method had a detection 

limit of 50 mg/L for glycolate, which is at least twice 

the initial concentration of TCE used by Knauss et al. 

(1999). Therefore, organic acids may have formed in the 

Knauss et al., (1999) experiments, but may have been 

well below detection limit of the analytical method.

The difference in experimental results between these 

two studies may also be associated with the differences 

in reactor wall materials. While the gold-walled reactor 

is supposedly chemically “inert” (Seyfried et al., 1979), 

gold powder has also been used as a catalyst to increase 

the rate of reactions. The glass ampules used herein may 

not be entirely chemically “inert” either. The use of the 

2,500°C flame to seal the ampule may have generated 

radical species that caused an increase in the rate of 

TCE degradation. For example, there was a 50.9% 

reduction in the amount of TCE in Ampule 58 along 

with a consumption of dissolved oxygen and a reduction 

in the amount of gas phase oxygen by an estimated 50%. 

The half-life for TCE degradation in Ampule 58 was 

approximately 20 days, similar to the disappearance 

rate reported by Knauss et al. (1999) for an initial TCE 

concentration of 1,000 mg/L.

There were other significant differences between the 

Knauss et al. (1999) gold-walled experiment and the 

ampule experiment reported herein. The gold-walled 

experiment used a completely water-filled reactor under 

a pressure of 10 bar. The ampule experiments were 

completed in glass ampules that were partially filled with 

water at a pressure of approximately 1.4 bar at 120°C. 

The gold-walled experiment involved measuring the 

concentration of TCE in a single gold-walled vessel 

every day over a period of days. The ampule experiment 

used destructive sampling of individually prepared 

ampules after incubation periods to determine the TCE 

degradation products. 

Due to these differences, a direct comparison regarding 

the rate of TCE degradation determined by Knauss et 

al. (1999) and the results reported herein is not possible. 

However, the results of both studies can be used to 

conclude that TCE can be degraded in sealed containers 

incubated at elevated temperatures for up to 40 days.

4.5 Summary

The results obtained from the four ampule experiments 

demonstrate that TCE was degraded within sealed glass 

ampules that contained gas, water, and solids. The rates 

of TCE degradation in ampules with anoxic water, both 

with and without sand, and in oxic water were similar 

at 120°C. The degradation rate in ampules with anoxic 

water and sand was increased by adding goethite at 

120°C. The primary TCE degradation products included 

CO and CO2 in the gas phase and chloride, hydronium 

ions, formate, glycolate in the aqueous phase, which 

represented less than 15% of the initial amount of TCE 

initially present when incubated at 22 and 120°C for 

periods of up to 40 days. Minor amounts (<1 mg/L) 

of dichloroacetic acid (DCAA) were detected in select 

ampules, most consistently in ampules that were stored 

at 22°C and initially contained 1,000 mg/L TCE along 

with oxygen. Dichloroacetylene (DCA) was detected in 

minor amounts (i.e., DCA < 1% of TCE) in ampules that 

contained TCE and were incubated at 120°C. 

Dichlororacetylene, in addition to being a TCE 

degradation product, was also thought to represent a 

key intermediate. The presence of DCA is proposed to 

indicate that the lone hydrogen atom in TCE was being 

eliminated by nucleophiles, such as sodium hydroxide, 

which increased the rate of TCE degradation and 

amount of DCA when added to the ampules as NaOH. 

Dichloroacetylene was proposed to be hydrolyzed 

to form chlorinated organic acids, such as DCAA, 

which were then hydrolyzed at 120°C to form the 

non-chlorinated organic acids, glycolate and formate. 

However, DCA is a reactive compound that can interact 

with the variety of compounds present in soil such as 

organic carbon. Therefore, the degradation products 

formed during the in-situ treatment of TCE may not 

be limited to those found in the ampule experiments 

reported herein.

From a practical perspective, these findings suggest 

that abiotic TCE degradation during thermal treatment 

may vary considerably depending on site conditions 

and operational variables, but it is likely that gas phase 

recovery of TCE will be the most important process 

in thermal remediation at temperatures up to 120°C. 

Additional laboratory-scale studies and treatability 

tests with a range of soils and soil constituents are 

warranted to further elucidate factors controlling abiotic 

TCE reaction pathways, byproduct formation, and 

reaction rates. Field samples should also be analyzed to 

determine if significant concentrations of byproducts are 

formed during in situ thermal remediation. 
80

4.6 Quality Assurance Summary for the 

Ampule Experiments

These experiments involved placing water with dissolved 

phase TCE into glass ampules that were flame sealed and 

incubated at 22 and 120°C for up to 40 days. The quality 

assurance efforts for these experiments focused on:

1. Assessing system cleanliness (clean controls) 

2. Estimating the variability between ampules 

(replicate ampules)

3. Demonstrating analysis method performance 

relative to water (matrix spike)

4. Determining if contaminants were introduced during 

sample storage (storage blanks)

Ampule Cleanliness. Immediately before use, ampules 

were rinsed with Nanopure deionized (DI) water, 

autoclaved at 121°C for 20 minutes followed by DI 

water rinse before being dried in an oven at 240°C for 

at least 2 hours. Ampules with DI water and gas alone 

were prepared to evaluate the compounds formed in 

ampules without TCE. These clean controls also served 

to determine if compounds (e.g., O2 and CO2) were 

being introduced during sample collection and analysis. 

No compounds were detected in the ampules filled with 

DI water and gas alone. Therefore, the ampules were 

initially clean and no compounds were introduced during 

sample collection or analyses.

Variability. Replicate samples were not collected due 

to the limited volume of gas and DI water within each 

ampule. Instead, variability was assessed by preparing 3 

replicate ampules and collecting one sample from each 

ampule phase. This approach provided a measure of the 

experimental variability which was thought to be more 

important than the analytical variability measured by 

replicate samples. Experimental variability was low for 

these experiments, less than 15% RSD in all cases and 

less than 5% RSD for most results. This was expected 

as efforts were employed to mix solutions and solids 

before loading into ampules. Also, care was taken to 

collect and analyze samples using consistent methods 

and procedures. 

An explosion occurred during the incubation of ampules 

which limited the number of replicate ampules to 2 and 

eliminated replicates in one case (NaOH ampules, day 

4 incubation). While this limited the ability to assess 

experimental variability, it did not preclude an estimate 

of variability and thus had limited impact on the overall 

experimental objectives. 

Method Performance. Analytical method performance 

was determined using solutions spiked with compounds 

obtained from commercial sources. For example, 

chloride standards were prepared from a certified 

reference solution with the same DI water source used 

to fill the ampules. Method performance during analysis 

of each sample batch was evaluated using the spiked 

solutions and solutions that were free of compounds 

(blanks). In all cases, method performance was within 

5% of the expected response for spiked solutions and no 

compounds were detected in method blanks.

Storage Blanks. Vials with DI water were prepared and 

stored with each sample batch. No compounds were 

detected in any storage blanks. No storage blanks were 

prepared for the gas samples as they were analyzed 

immediately after collection.
81

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87

Detailed Experimental Methods 

for Flow-Through Quartz Tube 

Reactors

A.1 Quartz Tube Preparation

The quartz tube and associated connectors were prepared 

prior to each isothermal experiment by washing in hot 

(45°C) tap water with detergent (Versa-Clean, Fisher 

Scientific). The tube and connectors were then rinsed 

with deionized (DI) water and placed in a drying oven at 

200°C for a period of 2 hours. The tube and connectors 

were allowed to cool to room temperature and the 

experimental apparatus was assembled and rinsed with 

approximately 20 mL of dichloromethane (DCM) for 

a period of 5 minutes. A 2 mL sample of the DCM 

rinse was collected and stored at 4°C until analyzed 

to demonstrate the organic-free initial experimental 

condition. After collecting the DCM rinse, the 

experimental apparatus was disassembled and remained 

in the vent hood for a period of 5 minutes to remove the 

residual DCM. The apparatus was then re-assembled 

after placing the quartz tube within piece of a 1.5 inch 

ID galvanized steel pipe that was located in the tube 

oven (Model 21100, Barnstead-Thermolyne, Dubuque, 

IA). The steel pipe served to minimize heat transfer 

between the tube oven lining and quartz tube. 

A.2 Quartz Tube Temperature Profile

The temperature profile within the empty quartz tube 

from the gas inlet to outlet was determined while the 

tube oven was operated at 120°C (Figure A.1). The 

temperature within the quartz tube was measured by 

inserting a certified traceable oven thermometer encased 

in a vermiculite filled enclosure (Fisher Scientific, 

Fair Lawn, NJ) into the heated quartz tube. The oven 

thermometer was held at a specific location within 

the quartz tube for 5 minutes and removed to read the 

temperature value. This temperature measurement 

procedure was repeated over the entire length of the 

quartz tube from inlet to outlet in approximately 

5 cm increments. There was no gas flow during the 

temperature profile measurement procedure. 

The temperature profile in the quartz tube was 

determined after 30, 60, 90 and 120 minutes of heating 

with the temperature profiles after heating the tube 

for 90 and 120 minutes nearly identical. As shown 

in Figure A.1, the quartz tube is not at a uniform 

temperature. TCE entering the quartz tube experiences 

increasing temperatures (temperature gradient) with the 

tube inlet at 70°C and the maximum tube temperature 

(130°C) located approximately 25 cm or about 10 inches 

from the tube inlet. This temperature gradient is 

similar in length to the one foot wide, 500 to 700°C

high-temperature zone claimed to cause the in-situ 

destruction of TCE during thermal conductive heating 

(Section 2.4.2). An attempt was made to measure the 

temperature profile of the quartz tube with the oven 

at 240°C, however, the thermometer enclosure began 

to smoke after being inserted into the tube and the 

enclosure was not advanced further to avoid causing the 

enclosure to catch fire. No attempt was made to measure 

the temperature profile of the quartz tube at 420°C; the 

high temperature profile is thought to be similar to that 

shown in Figure A.1 with the region approximately 

25 cm from the inlet at 420°C and the tube inlet near 

ambient temperature since it is located outside the oven.

Figure A.1 Temperature profile within the quartz tube 

heated to 120°C.

A.3 Modified TCE Introduction Method: 

Experimental Series 5

The process of introducing TCE into the pre-mix 

chamber consisted of initially recording the weight of 

a 1 mL gas-tight syringe that contained approximately 

0.34 mL (~0.5 g) of neat TCE using an analytical 

balance (Model# AG245, Mettler-Toledo, Columbus, 

OH) with 0.001 gram readability. The analytical balance 

had been checked using an ASTM E617 class 2 certified 

traceable 20±0.0001 gram weight (Cat. # 820000.2, 

Denver Instruments, Denver, CO) prior to determining 

the syringe weight. The syringe needle was the inserted 

through a Teflon lined septum affixed with a crimp seal 

6.0

APPENDIX A
88

to a port located on the pre-mix chamber and TCE was 

injected at the slow rate of 0.68 mL/hr for a period of 

30 minutes. There were no drops of neat TCE visible 

at the syringe needle tip, which was located inside the 

premix chamber, when using this TCE injection rate so 

that TCE entered the quartz tube in the gas phase. The 

syringe was removed from the pre-mix chamber and 

the final weight recorded using the analytical balance 

and the amount of TCE introduced into the apparatus 

was determined by the difference in weight between the 

initial TCE-filled syringe and the final syringe weight 

after the 30 minute TCE injection period. The apparatus 

was flushed with TCE-free humidified carrier gas for 

45 minutes after removing the syringe to recover as 

much of the TCE introduced into the experimental 

apparatus as possible.

The carrier gas was humidified by passing through a 

mini-bubbler (ACE Glass, Vineland, NJ) filled with 

approximately 30 mL of deionized (DI) water prior 

to entering the quartz tube (Figure A.2). The DI water 

was freshly dispensed from a Nanopure® analytical 

deionization system (model D4741, Barnstead 

International, Dubuque, IA) with a conductance of 

greater than 18 MΩ-cm. The amount of water vapor 

entering the quartz tube was adjusted by increasing the 

temperature of the mini-bubbler and pre-mix chamber 

using a resistant-wire based heat tape (McMaster-Carr, 

Atlanta, GA) that was wrapped around the mini-bubbler 

and pre-mix chamber and connected to a feedback 

voltage controller equipped with a K-type thermocouple. 

Three inlet temperatures were used including room 

temperature (22), 60 and 100°C. The temperatures were 

chosen to explore a range of chloride to hydrogen (Cl:H) 

ratios based on the work presented in Section 2.3.6. 

The room temperature inlet condition had a calculated 

Cl:H ratio of 1 at a carrier-gas flow rate of 85 mL/min 

with the TCE liquid influent rate fixed at 0.68 mL/hr. 

The 60°C inlet temperature had a calculated Cl:H ratio 

of 0.28 and the 100°C inlet temperature had a Cl:H 

ratio of 0.07. The 100°C inlet temperature represented a 

condition where the number of hydrogen atoms in water 

was approximately 15 times greater than the number of 

chlorine atoms in TCE.

A.4 Effluent Trapping Procedures and 

Analytical Methods

The gas stream leaving the ice-cooled, DCM filled 

trap (Section 3.1.5) was collected in 1.6 L Tedlar® 

bags to retain all single-carbon, non-condensable 

degradation products (e.g., carbon dioxide). Each bag 

was flushed three times with nitrogen gas prior to use. 

The Tedlar® bag was removed from the quartz tube 

Figure A.2 Quartz tube apparatus for the fifth quartz tube experimental series. 
89

effluent stream when full and a gas sample from the bag 

was immediately analyzed to determine the amount of 

CO and CO2 formed by the degradation of TCE in the 

heated quartz tube. The gas sample from the Tedlar® 

bag was collected by pulling approximately 60 mL of the 

Tedlar® bag contents through a 250 uL gas sample loop 

attached to a gas sampling valve heated to 120°C and 

located within an insulated box on a Hewlett-Packard 

(HP) 6890 Gas Chromatograph (GC). The gas sample 

in the 250 uL sample loop was then injected into the 

GC inlet that was operated at 8.90 psi in the splitless 

mode for 0.75 minutes at 200°C and was connected 

to a 30 m by 0.32 mm OD Carboxen-1010 column 

(Part# 24246, Supleco, Bellefonte, PA) attached to a 

thermal conductivity detector (TCD). Helium was used 

as the capillary column carrier-gas at a constant flow 

of 2 mL/min and the GC oven was operated at 35°C

for 7 minutes followed by a 40°C/min temperature 

ramp to 130°C for 5 minutes. The TCD was operated at 

210°C with a helium reference flow of 15 mL/min and 

helium makeup flow at 5 mL/min. The Carboxen-1010 

column is capable of separating O2, N2, CO, CO2, and 

water. However, TCE and other organic compounds 

are retained within the carbon molecular sieve based 

column; the column was periodically conditioned at 

200°C to remove organic compounds. The GC/TCD 

was calibrated using serial dilution of an initial 100 mL 

volume of certified carbon dioxide (15%), carbon 

monoxide (7%), oxygen (5%), and nitrogen (73%) 

gas mixture (Cat. No. 23442, Scotty Specialty Gases, 

Plumsteadville, PA). The serial dilution was performed 

in a 500 mL syringe (Model S-500, Hamilton Company, 

Reno, NV) with nitrogen as the dilution gas. At least 

three CO/CO2 concentrations were used to calibrate the 

GC/TCD response. This technique had a detection limit 

of approximately 300 uL/L (ppmv) for CO and 500 uL/L 

(ppmv) CO2.

In addition to the DCM trap, a second 40 mL vial filled 

with approximately 30 mL of toluene that contained 2% 

(wt) aniline was added to the 420°C UZA experiments 

to determine the amount of phosgene formed during 

the degradation of TCE. Any phosgene present in the 

effluent reacted with the aniline to form carbanilide 

(1,3-diphenylurea), a stable compound. The toluene/

aniline traps were analyzed by first removing all the 

tolulene from the trap by passing nitrogen at 20 mL/min 

through the trap while heating the trap to 60°C. The 

trap was taken to complete dryness and weighed to 

determine the mass of carbanilide formed. A 10 mL 

volume of acetonitrile was then added to dissolve the 

dry carbanilide and the concentration of carbanilide 

was determined by measuring the ultraviolet (UV) 

light absorbance at 254 nm. Calibration solutions 

were prepared using carbanilide (Sigma-Aldrich, 

Milwaukee, WI) in acetonitrile. This second trap and 

analysis methods was based on U.S. EPA method TO-6 

(U.S. EPA, 1999).

The GC/MS analysis of the DCM trap fluids from 

the 420°C experiments identified a number of TCE 

degradation products. However, the amounts of 

chloroform (CHCl3), carbon tetrachloride (CCl4), 

tetrachloroethylene (PCE), hexachloroethane (C2Cl6), 

hexachlorobutadiene (C4Cl6), and hexachlorobenzene 

(C6Cl6) were determined by GC/FID analysis. Master 

stock solutions (10,000 mg/L) for each of the previous 

compounds were prepared in DCM using ACS 

grade reagents (Sigma-Aldrich, Milwaukee, WI). 

Hexachlorobenzene (HCB) master stock was prepared 

by adding HCB solids to iso-octane. The GC/FID 

response was determined for each compound using at 

least four calibration standards prepared by volumetric 

dilution of the master stock at concentrations in the 

expected range.

A.5 Quartz Tube Rinse Procedure

The quartz tube was removed from the tube oven after 

cooling to room temperature and the interior of the 

apparatus was rinsed with DI water and iso-octane 

to determine the TCE degradation products that had 

formed and condensed or adsorbed onto the quartz 

glass surfaces. The apparatus was initially rinsed 

with approximately 30 mL of DI water for a period of 

5 minutes to collect the water-soluble compounds (i.e., 

chloride) that formed during each isothermal experiment. 

The second rinse used 30 mL of iso-octane for a period 

of 5 minutes to collect the non-polar TCE degradation 

products (i.e., hexachlorobenzene) from the experimental 

apparatus.

The chloride content of all water solutions was measured 

using a colorimetric method described by Bergmann and 

Sanik (1957). The method involved a selective chemical 

reaction between free chloride, mercuric thiocyanate 

[Hg(SCN)2], and iron (III) ions from ferric ammonium 

disulfate [FeNH4(SO4)2] as shown in Equation A.1:

 2Cl-

 + Hg(SCN)2 + 2FeNH4(SO4)2 →

HgCl2 + 2Fe(SCN)2+ + 2NH4(SO4)2

3- (A.1)

The resulting iron-thiocyanate complex [Fe(SCN)2+] 

forms a yellow color that is directly related to the 

amount of chloride present in water samples. The 

method consisted of placing 2 mL of a water sample 

into a 3 mL capacity Suprasil quartz cuvette (Fisher 

Scientific, Fair Lawn, NJ). Next, 200 uL of a 9 M nitric 

acid solution with 250 mM of ferric ammonium sulfate 

was added to the cuvette followed by 200 uL of ethanol 

saturated with mercuric thiocyanate. The cuvette was 

capped with a Teflon lid, inverted 4 times to mix the 

contents, and then placed in a Varian spectrometer 
90

(Model Cary 3E). The light absorption at 460 nm was 

measured after 10 minutes with reference to DI water 

contained in a second transmission matched cuvette. 

Calibration solutions at concentrations of 2, 20, 50, 100, 

200, 400, 600, and 1000 uM were prepared in 100 mL 

volumetric flasks using a certified 1,000 mg/L chloride 

master stock (SPEX CertiPrep, Metuchen, NJ). The 

detection limit for this technique was approximately 

0.1 mg/L.

The haloacetic acid content of water samples was 

determined using procedures based on EPA method 

552.2 (U.S. EPA, 1995). This procedure involved 1) pH 

adjustment, 2) liquid-liquid extraction, 3) derivatization, 

and 4) neutralization followed by GC analysis. The 

water-rinse samples were contained in 40 mL glass vials 

sealed with Teflon lined septa affixed with a screw caps. 

The pH of each water rinse sample was adjusted to less 

than 0.5 by adding 1.5 mL of concentrated sulfuric acid 

(H2SO4) to convert any carboxylates present into the acid 

form. The pH adjustment was followed by adding 5 mL 

of methyl-tert butyl ether (MTBE) to the 40 mL vials 

which were then resealed and hand-shaken for 2 minutes 

to extract the haloacetic acids. Approximately 3 mL of 

the MTBE was then transferred from each 40 mL vial 

to 14 mL glass vials using a Pasteur pipette. One mL of 

acidic methanol (10% H2SO4) was added to each 14 mL 

vial, which were sealed with a Teflon lined septa affixed 

with a screw cap and then placed in an oven at 50°C for 

a period of 2 hours to convert the carboxylic acids to 

their derivatized, methyl ester form. After cooling the 

14 mL vials to room temperature, the MTBE extract and 

acid methanol mixture was neutralized by adding 2 mL 

of saturated sodium bicarbonate solution. Two 1 mL 

samples of the MTBE extracts were transferred from the 

14 mL vials into 2 mL autosampler vials and the internal 

standard, 1,2,3-trichloropropane, was added to each 

2 mL vial. The vials were then sealed with Teflon lined 

septa affixed with aluminum crimps. 

The analysis of the MTBE extracts consisted of using 

an automatic liquid sampler (HP7683) to inject 1 uL 

of sample into a GC (HP6890) equipped with a 30 m 

by 0.32 mm OD HP-1 capillary column connected 

to an electron capture detector (ECD). The GC inlet 

was operated at 7.00 psi in the splitless mode for 

0.5 minutes at 200°C with helium as the column carrier 

gas at a constant flowrate of 2 mL/min. The GC oven 

was operated at 35°C for 21 minutes followed by an 

11°C/min temperature ramp to 136°C for 3 minutes, 

and a final temperature ramp of 20°C/min to 230°C

for 3 minutes. The ECD was operated at 250°C with a 

nitrogen gas makeup flow of 60 mL/min. Dichloroacetic 

acid calibration standards at concentrations of 12, 

50, 100, and 400 ug/L were prepared from a 60 mg/L 

primary dilution standard made from ACS grade 

dichloroacetic acid (Sigma-Aldrich, Milwaukee, WI). 

The calibration samples were processed with each 

sample batch along with at least two uncontaminated 

water samples including freshly dispensed DI water and 

a storage blank.

The GC/ECD chromatograms from the analysis of 

the MTBE extracts collected from the 420°C UZA 

experiments contained peaks that eluted at times 

different than dichloroacetic acid. A GC (HP 6890) 

equipped with a 30 m by 0.32 mm DB-5ms column 

connected to a mass select detector (MSD, HP5973) 

was used to identify the compounds associated with 

the unknown peaks. The GC operating conditions 

were identical to the GC/ECD method given above. 

Compounds were identified using software (ChemStation 

ver. D.00.00.38, Agilent Technologies, Palo Alto, CA) 

that matched their mass spectra with reference mass 

spectra in the NIST/EPA/NIH Mass Spectral Library 

(NIST02). The unknown compound was identified 

when the mass spectrum fit with a matching NIST02 

library spectrum with quality of greater than 70. The 

ChemStation software rated the mass spectrum match 

on a scale of 0 to 100 whereas the Varian software used 

a scale of from 0 to 1,000. The iso-octane rinse was 

initially analyzed using the Varian GC/MS to determine 

the identity of TCE degradation products. The amount 

of each degradation product was then determined using 

GC/FID analysis. 
91

Change in Dissolved Oxygen

Dissolved oxygen (DO) was determined using a 

colorimetric method that reports DO concentration 

(mg/L) in a range between two values (e.g., 6 to 

8 mg/L). An estimate of the average DO concentration 

range for each set of ampules, as a function of time, 

was made based on the colorimetric analysis result for 

each vial (Table B.1). The DO concentration in the oxic 

ampules (Batches 2 and 3) remained constant (6-8 mg/L) 

or increased by one increment (8-10 mg/L) over the 

30-day incubation period, with the exception of Ampule 

58 (1,000 mg/L TCE). The DO concentration in Ampule 

58 decreased from 6-8 mg/L to 0.6-0.8 mg/L after 

incubation at 120°C for 20 days. This result suggests that 

oxygen was not consumed during ampule incubation at 

120°C, with the exception of Ampule 58 where oxygen 

was consumed in conjunction with a greater than 50% 

decrease in TCE content after 20 days at 120°C. 

7.0

APPENDIX B

Table B.1 Dissolved Oxygen (DO) Concentration Range for Anoxic and Oxic Ampules with 1,000 and 100 mg/L 

of TCE (Batches 1-4)

Ampule Temperature 

(°C) Time (days) 1,000 mg/L anoxic (1)

1,000 mg/L 

oxic (2)

100 mg/L anoxic 

(4)

100 mg/L 

oxic (3)

Initial 0 0.2 to 0.3 6 to 8 0.2 to 0.3 6 to 8

120

10

4 to 5 6 to 8 2 to 3 6 to 8

22 3 to 5 6 to 8 2 to 3 6 to 8

120 and 22 (Controls) 1 to 3 6 to 8 2 to 3 6 to 8

120

20

1 to 3 8 to 10*

NA

8 to 10

22 2 to 3 8 to 10 8 to 10

120 and 22 (Controls) 3 to 4 8 to 10 8 to 10

120

30

Lost Lost 0.8 to 1.0 6 to 8

22 4 to 5 8 to 10 0.8 to 1.0 6 to 8

120 and 22 (Controls) 5 to 6 8 to 10 0.8 to 1.0 6 to 8

120

41 NA NA

0.8 to 1.0

22 0.8 to 1.0 NA

120 and 22 (Controls) 0.8 to 1.0

(#) – Batch number

Controls – TCE-free ampules

* Excludes Ampule 58 results, DO between 0.6 and 0.8 mg/L after 20 days at 120°C.

Lost – Ampules destroyed in oven explosion

NA – No ampules analyzed for DO at time interval
92

The DO concentration tended to increase in anoxic 

ampules with TCE and without TCE (TCE-free). The 

DO concentration increased in anoxic ampules that 

contained 1,000 mg/L of TCE (Batch 1) from an initial 

value of 0.2-0.3 mg/L to final values up to 4-5 mg/L after 

30 days at 22°C and 120°C. The DO concentration also 

increased in TCE-free controls for the Batch 1 ampules 

from 0.2-0.3 mg/L to 5-6 mg/L over the course of the 

incubation period. Anoxic ampules with 100 mg/L 

of TCE and without TCE (Batch 4) exhibited slight 

increases in oxygen content on day 10 (2-3 mg/L), 

followed by declines on day 30 (0.8-1.0 mg/L). 

The DO concentrations of ampules that contained 

Ottawa sand (Batch 6), Ottawa sand+1% goethite 

(Batch 7), and amended with NaOH (Batch 5) are 

provided in Table B.2. All of the sampled ampules 

exhibited a slight increase in dissolved oxygen 

concentration, ranging from the initial anoxic condition 

(0.2-0.3 mg/L) up to 1-2 mg/L for the TCE-free control 

ampules containing Ottawa sand+1% goethite (Batch 6). 

However, the observed increases in dissolved oxygen 

concentration in ampules containing solids and NaOH 

(Batches 5-7) were less than in the anoxic ampules 

containing 1,000 mg/L TCE (Batch 1, Table B.1). For 

Batch 6 and 7 ampules, solids filled the ampule neck 

thus preventing the measurement of dissolved oxygen 

using the procedures illustrated in Figure 4.2. Hence, 

the DO concentration for these ampules had to be made 

within the main ampule body to gain access to sand-free 

water, and for this reason, DO was measured in ampules 

that contained solids but not TCE where the CHEMets 

reagents may have led to interferences during subsequent 

analyses for TCE degradation products.

Table B.2 Dissolved Oxygen (DO) Concentration Range for Anoxic Ampules that Contained Solids (Ottawa 

sand and Ottawa Sand+1% Goethite) or NaOH (pH 10) (Batches 5-7)

Ampule 

Temperature (°C) Time (days)

Batch 6

Sand

DO (mg/L)

Time 

(days)

Batch 7

Sand+1%Goethite

DO (mg/L)

Batch 5

pH 10

DO (mg/L)

Initial 0 0.2 to 0.3 0 0.2 to 0.3 0.2 to 0.3

120 

10

NA

1

NA 0.8 to 1.0

120 (Controls) 0.8 to 1.0 1 to 2 0.4 to 0.6

120 

30

NA

2

NA 0.8 to 1.0

120 (Controls) 0.6 to 0.8 1 to 2 0.4 to 0.5

22

40

NA

3

NA 0.8 to 1.0

120 (Controls)

22 (Controls)

0.3 to 0.4

0.8 to 1.0

1 to 2

1 to 2

0.4 to 0.6

0.8 to 1.0

(#) – Batch number

Controls – TCE-free ampules

NA – Did not measure DO in solids filled ampules that contained TCE
93

C.1 Rates of TCE Degradation

Previous studies performed by Knauss et al. (1999) 

and Jeffers and Wolfe (1996) reported the rate of TCE 

disappearance based on the first-order reaction rate 

model. Thus, for comparison purposes, the rate of TCE 

disappearance is reported in Table C.1 based on a fit of 

the natural log of TCE concentration vs. incubation time, 

and a fit of the natural log of total carbon and chlorine 

degradation products versus incubation time. The rate 

for ampules with 1,000 mg/L of TCE (Batches 1 and 2) 

are not presented as these results were from only 2 time 

periods. 

 While the rate of TCE disappearance from the anoxic 

(Batch 4) ampules could not be determined using the 

TCE concentration results, there was a measurable 

increase in the amount of carbon with incubation time 

whereas the rate of chlorine production did not fit a firstorder rate model. The rates of TCE disappearance from 

the oxic (Batch 3) ampules, based on the decrease in the 

amount of TCE and the increase in carbon degradation 

products were similar; however, the uncertainty in the 

first order fit based on the carbon degradation products 

makes this similarity statistically insignificant. The rate 

of chlorine production in the oxic ampules did not fit a 

8.0

APPENDIX C

Table C.1 Rate of TCE Disappearance from the 100 mg/L Ampules at 120°C

Basis Decrease in TCE Increase in Carbon Increase in Chloride

Rate Rate (1/day) 

×1000

Half-Life 

(days)

Rate (1/day) 

×1000

Half-Life 

(days)

Rate (1/day) 

×1000

Half-Life 

(days)

Anoxic (4) No Change -- 2.6±0.8

R2 = 0.83 262 1.2±1.3R2 = 0.30 591

Oxic (3) 3.4±0.8

R2

 = 0.89 201 2.8±1.2R2 = 0.72 248 1.8±1.6R2 = 0.37 393

Sand (6) 6.2±2.6

R2

 = 0.74 111 2.8±1.0R2 = 0.80 244 3.5±1.2R2 = 0.81 200

Sand+ 

1%Goethite (7)

53.4±20.1

R2

 = 0.78 13 23.3±6.3R2 = 0.87 30 15.8±3.2R2 = 0.92 44

NaOH (5) 34.0±21.9

R2

 = 0.45 20 39.9±11.9R2 = 0.79 17 42.0±8.1R2 = 0.90 17

Knauss et al. 

(1999) -606 1.1 Not Reported -- Not Reported --

Jeffers and Wolfe 

(1996) -0.8 858 Not Reported -- Not Reported --
94

first-order rate model, similar to the results for the anoxic 

ampules. Note that the anoxic and oxic ampule results 

span different incubation systems, necessitated by the 

convection oven explosion, thus the results for these 

two series are not strictly comparable for all incubation 

times.

The rate of degradation based on carbon detected as 

degradation products was similar within an order-ofmagnitude between the anoxic (Batch 4), oxic (Batch 3), 

and anoxic ampules that contained sand (Batch 6) 

suggesting that oxygen and sand had no influence 

on the rate of TCE disappearance from the ampules. 

The addition of goethite increased the rate of TCE 

disappearance by an order of magnitude, demonstrating 

that a commonly found mineral could have a significant 

impact on the rate of TCE disappearance during thermal 

treatment. The rate of TCE disappearance reported by 

Knauss et al. (1999), reported in Table C.1 assuming an 

initial TCE concentration of 100 mg/L and a temperature 

of 120°C, was an order-of-magnitude greater than the 

rate measured using the ampules with goethite and two 

orders-of-magnitude greater than ampules with oxic and 

anoxic water. The rate of TCE disappearance reported 

by Jeffers and Wolfe (1996), assuming a temperature of 

120°C, was approximately an order-of-magnitude less 

than that determined for the anoxic and oxic ampules, 

and approximately 3 orders-of-magnitude less than the 

rate reported by Knauss et al. (1999). 

These rates are not necessarily comparable since they 

were obtained using different experimental systems. The 

most significant difference between the experimental 

systems was that Knauss et al. (1999) used a gold 

walled reactor that was completely water filled (no gas 

phase present) while Jeffers and Wolfe (1996) used 

Pyrex tubing (0.3 mL) with gas phase present, and the 

work completed herein used borosilicate glass ampules 

(50 mL) with a gas phase present.

C.2 Methods used to Determine TCE 

Dedradation Rate Parameters in 

Ampule Experiments 

Three methods were evaluated for determining the 

rate of TCE degradation. The first method consisted 

of plotting the natural log of the average number of 

moles of TCE (Tables 4.15 and 41.6) normalized by the 

average initial moles of TCE as a function of incubation 

time as described by the following equation:

0

ln or ln molesTCE TCE

initial molesTCE TCE

   

       

(C.1)

Figures C.1 through C.4 show plots of Equation C.1 for 

all four ampule experiments along with the first order 

decay coefficient as determined from the slope of a linear 

regression analysis. There was no significant change in 

the amount of TCE in the anoxic ampules (Figure C.1) 

and thus no rate of TCE loss was determined for the 

anoxic ampules based on TCE content. There was an 

apparent loss of TCE from the other ampules at 22°C

and 120°C based on the data shown in Figures C.2 

through C.4. However, the apparent loss of TCE from 

the ampules incubated at 120°C may not have been 

entirely attributable to degradation alone. No reaction 

products were detected (i.e., chloride or organic acids) 

in the companion ampules stored at 22°C while a rate 

of TCE loss was apparent in these ampules. Thus, a 

second method for interpreting the rate of TCE loss 

from ampules incubated at 120°C involved adding 

the apparent amount of TCE lost from the ampules, 

based on the amount of TCE detected in the ampules 

stored at 22°C, to the amount of TCE detected in the 

120°C ampules. Non-degradative loss of TCE was 

thought to occur after cooling the 120°C ampules to 

room temperature (22°C), which was potentially due 

to sorption to ampule walls or solids, when present. 

Equation C.2 corrects for the loss of TCE from the 22°C

ampules:

0

0

25 120 C

ln

TCE

  TCE TCE TCE − −        

 

(C.2)

The loss of TCE after correcting for the apparent loss 

from the 22°C ampules is shown in Figures C.5 through 

C.8. The first order rates shown in these figures are 

reported in Table C.1.

The final method used to determine the rate of TCE 

degradation was based on the amount of reaction 

products detected. The sum of carbon represented by 

CO, CO2, formate, and glycolate were subtracted from 

the average initial amount of TCE according to the 

following equation:

[ ] 0

0

2 ln

Carbon

TCE

TCE

  Σ −  

 

(C.3)

The rate of TCE degradation was also determined based 

on the amount of chloride detected using Equation C.4:

[ ] 0

0

3 ln

Chloride

TCE

TCE

  Σ −  

 

(C.4)

Figures C.9 through C.12 show plots of Equations C.2, 

C.3, and C.4 for the ampule results.
95

Figure C.1 The change in anoxic ampule TCE content 

as a function of incubation time.

Figure C.2 The change in oxic ampule TCE content as 

a function of incubation time.

Figure C.3 The change in anoxic ampule TCE content, 

ampules with Ottawa sand, as a function of 

incubation time.

Figure C.4 The change in anoxic ampule TCE 

content, ampules with Ottawa sand and 1% 

Goethite, as a function of incubation time.

Figure C.5 The change in anoxic ampule TCE content 

as a function of incubation time.

Figure C.6 The change in oxic ampule TCE content as 

a function of incubation time.
96

Figure C.7 The change in anoxic ampule TCE content, 

ampules with Ottawa sand, as a function of 

incubation time.

Figure C.8 The change in anoxic ampule TCE 

content, ampules with Ottawa sand and 1% 

Goethite, as a function of incubation time.

Figure C.9 The change in anoxic ampule TCE content 

based on detected reaction products.

Figure C.10 The change in oxic ampule TCE content 

based on detected reaction products.

Figure C.11 The change in anoxic ampule TCE content, 

ampules with Ottawa sand, based on 

detected reaction products.

Figure C.12 The change in anoxic ampule TCE 

content, ampules with Ottawa sand and 

1% Goethite, based on detected reaction 

products.

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