The migration of contaminants from the subsurface into the indoor air environment, in a process described as soil vapor intrusion, is gaining attention as a potential pathway for exposure to contaminated soil and water. Indoor, outdoor and soil air samples were collected from forty homes in North Texas to investigate the attenuation of trichloroethylene (TCE) from contaminated groundwater into residential buildings. The mean and standard deviation of the soil and indoor air attenuation factors (ratio of indoor air concentration to soil vapor concentration) were 0.14 and 0.17, respectively. Five of the 40 values were greater than 0.1 which is the suggested upper-bound by the U.S. EPA (2002). Statistical tools were used to draw correlative relationships between contaminant groundwater, soil air and indoor air concentrations. The VolaSoil model described by Waitz et al. (1996), was modified for use as a screening tool for future investigations of indoor TCE concentration. Using measured soil vapor data, the model under predicted indoor air TCE concentrations likely due to heterogeneities in the unsaturated subsurface. Inputting groundwater TCE concentrations, the model was able to capture the contaminant migration processes and produce results consistent with measured indoor TCE concentrations. Therefore, the model described in this paper maybe appropriate to be use as a screening tool in future investigations in the contamination area. / text

Trichloroethylene (TCE) is one of the most common groundwater pollutants in the United States and is a suspected carcinogen. The United States Environmental Protection Agency (EPA) estimated that between 9% and 34% of the drinking water sources in the United States may contain TCE, and have set a maximum contaminant level of 5 ìg/L for drinking water. Traditional treatment technologies such as granular activated carbon and air stripping have only had marginal success at removing TCE from contaminated sites. Chemical oxidation processes have provided a promising alternative to traditional treatment methods. The objective of this research was to examine the conditions under which zero valent iron (Fe0) activates persulfate anions to produce sulfate free radicals, a powerful oxidant used for destroying organic contaminants in water. With batch experiments, it was found that persulfate activated by zero valent iron removed TCE more effectively than persulfate oxidation activated by ferrous iron. This laboratory study also investigated the influence of pH (from 2 to 10) on TCE removal. TCE was prepared in purified water and a fixed persulfate/TCE molar ratio was employed in all tests. The results indicated that this reaction occurred over a wide range of pH values. The production and destruction of daughter products cis 1,2 dichloroethylene and vinyl chloride were observed. The effect of persulfate dose on this reaction was also studied. Results showed that a molar ratio of 10/1/1 (persulfate/ZVI/TCE) yielded over 95 percent TCE destruction. Increasing the persulfate dose resulted in greater TCE destruction as well as destruction of the daughter products. Kinetic experiments at a molar ratio of 10/1/1 (persulfate/ZVI/TCE) show that approximately 90 percent of the TCE was destroyed in less than 15 minutes.

Trichloroethene (TCE) is the most frequently detected organic contaminant in groundwater, is classified as a probable human carcinogen, and exhibits toxicological effects on the human endocrine, immune, developmental, and reproductive systems. While significant research efforts have been devoted to the development of strategies for remediating TCE-contaminated groundwater, their advancement is currently hindered by limitations in current methodologies for measuring in situ reductive dechlorination rates, especially for sorbing solutes. This dissertation describes the development, evaluation, and demonstration of a method for measuring in situ reductive dechlorination rates that utilizes single-well, "push-pull" test technology. Initial field tests indicated that trichlorofluoroethene (TCFE) could be used as a surrogate for TCE in push-pull tests since (a) TCE and TCFE were transported similarly and (b) TCFE underwent reductive dechlorination by a pathway analogous to that of TCE while retaining the fluorine label. Because TCFE and TCE experienced sorption at the selected field site, a novel data analysis technique called "forced mass balance" (FMB) was developed to obtain in situ transformation rates of sorbing solutes from push-pull test data. The FMB technique was evaluated by quantifying errors in rates derived by applying FMB to push-pull test data generated by a numerical model. Results from simulated tests indicated that an example in situ rate for the reductive dechlorination of TCFE, which was obtained by applying FMB to field data, was underestimated relative to the true in situ rate by 10%. The utility of the rate-determination method presented in this dissertation was demonstrated by using it to evaluate the effectiveness of a chemical amendment, namely fumarate, at enhancing in situ reductive dechlorination rates in TCE-contaminated groundwater. Reductive dechlorination rates increased following three consecutive additions of fumarate in all five of the tested wells. The development of the rate-determination method described in this dissertation advances the state of bioremediation technology because methods for measuring in situ transformation rates are needed to both assess the potential for natural attenuation and to quantify the effects of bioremediation techniques in the field. / Graduation date: 2003

This microcosm study demonstrated the enhanced anaerobic transformation of vinyl chloride (VC) to ethylene. A previous microcosm study from Point Mugu site showed the accumulation of VC due to the slow transformation step of VC to ethylene. To overcome the rate-limiting step, two laboratory experiments tested the effect of trichloroethylene (TCE) additions on the rate enhancement, repeated low TCE additions and high TCE concentration additions. TCE (2 ��mol) was repeatedly added over a two week interval. In a parallel study, an equal amount of VC was added to another set of microcosms. TCE addition increased VC transformation to ethylene, with nearly 19% VC conversion to ethylene compared to 4% VC conversion in the VC added controls. However, the increased VC transformation rates were not sufficient enough to avoid VC accumulation. Rate of VC transformation decreased once TCE addition was stopped. This indicated the mixed culture required the transformation of TCE to maintain VC transformation rates. With TCE added at high concentrations (100 mg/L and 200 mg/L), nearly complete transformation of TCE to ethylene was observed. After the addition of high TCE concentrations, low concentration TCE (3 ��mol) was added and near 95% transformed to ethylene in 45 days. Two different low hydrogen yielding substrates, butyrate and propionate, were tested. Both were equally effective in promoting TCE dechlorination. Methanogenesis was inhibited at high TCE concentration with both substrates. Kinetic analysis of VC transformation data showed VC transformation followed the first order kinetics with respect to concentrations using a modified Monod equation. First-order kinetic constants increased after the addition of high ICE concentrations. After 200 mg/L of TCE addition, the first-order kinetic constant increased by factor of six compared to the rate obtained from the earlier low TCE concentration addition. However, reintroduction of TCE at low concentration maintained similar enhanced kinetic constants, as achieved at high concentration. This indicated the enhancement of VC transformation to ethylene was likely due to the growth of microorganisms using TCE as a terminal electron acceptor. These microorganisms were likely responsible for the transformation of VC to ethylene. / Graduation date: 2001

Chlorinated organic compounds are widely used in various industrial processes. Due to their high density and low water solubility, they are mainly utilized as cleaning solvents in dry cleaning operations, as well as semiconductor manufacturers. Many chlorinated organic compounds spilled sites contain residuals, which present in a pure liquid phase (dense non-aqueous phase liquids, DNAPLs). Trichloroethylene (TCE) is the most typical compound as a result. In situ bioremediation has been successfully used for the removal of TCE. This process has several advantages, such as relative simplicity, low cost, and potentially remarkable efficiency in contamination removal than others. By using the in situ bioremediation to remediate TCE contaminated groundwater, it must ensure (1) biodegradability of contaminants, and the presence of a competent biodegrading population of microorganisms, (2) presence of electron acceptors, and (3) environment condition and, nutrient sources. A field study for biodegradation TCE through molasses injection was conducted at the industrial trading estate in Kaohsiung City. The study included electronic products, semiconductor, nicety optical industry and so on. Molasses, nitrate and phosphate were introduced from injection well (BW1-1 and BW2-1) into aerobic and anaerobic groundwater contaminated site. In the aerobic zone, there were four wells being monitored: BW1-1, C029, BW1-2 and BW1-3. After 213 days of biostimulation treatment, TCE concentration detection results showed TCE concentrations in all wells monitored. BW1-1 and C029, there was a sharp decrease from 0.0853 mg/L to below the detection limit and from 0.1340 mg/L to 0.0038 mg/L. BW1-2 and BW1-3 showed a slight decrease from 0.0668 mg/L to 0.0211 mg/L and from 0.0323 mg/L to 0.0161 mg/L. After treatments, TCE concentrations in all wells monitored were dropped to 0.05 mg/L. In anaerobic zone, there were four wells being monitored: BW2-1, SW-4, BW2-2 and BW2-3. After 193 days of biostimulation treatment, TCE concentration detection results showed TCE concentrations in all wells monitored. BW2-1, SW-4, BW2-2 and BW2-3 all had a slight decrease from 0.0399 mg/L to 0.0043 mg/L, from 0.14603 mg/L to 0.0687 mg/L, from 0.1030 mg/L to 0.0365 mg/L and from 0.0492 mg/L to 0.0289 mg/L. According to the results from BIOCHLOR modeling, elevated aqueous concentration of chloroethenes with a classical reduction pathway for TCE leading to an accumulation of vinyl chloride and ethane. All the results revealed that bioremediation technology is one of the more feasible approaches to clean up TCE contaminated groundwater in this field.

REDUCTIVE DEHALOGENATION OF GAS-PHASE TRICHLOROETHYLENE USING HETEROGENEOUS CATALYTIC AND ELECTROCHEMICAL METHODSXiumin Ju, Ph.D.The University of Arizona, 2005Director: Dr. Robert G. ArnoldThe first part of this work investigates catalytic hydrodechlorination (HDC) of gas-phase trichloroethylene (TCE) using 0.5 wt.% Pt/g-Al2O3 and 0.0025 wt.% Pt/SiO2 in packed-bed reactors. TCE was efficiently transformed on the platinum surface using H2 as reducing agent. The main products of the reaction were ethane and chloroethane. In the case of Pt/Al2O3, more than 94% TCE conversion efficiency was maintained for over 700 hours of operation at 100ºC at a residence time of 0.37 seconds. At 22ºC, severe catalyst deactivation was observed. Catalyst deactivation was attributed to coking and chlorine poisoning. A series of treatments including (i) hydrogen gas addition at high temperature (oxygen free) to remove chlorine and (ii) oxygen addition at 500ºC to remove coke were attempted to regenerate the deactivated catalyst. Only hydrogen treatment partially restored catalyst activity. When using Pt/SiO2, catalyst deactivation was severe even at 100ºC, probably due to low surface area of Pt and the silica support. Adding KOH to the packed Pt/SiO2 catalyst during (otherwise) normal operation slowed catalyst deactivation. Adding O2 to the influent improved catalyst activity and slowed deactivation.The second part of this research involves the destruction of gas-phase TCE using an electrochemical reactor similar in design of a polymer electrolyte membrane (PEM) fuel cell. With a proton-conducting membrane in the middle, the anode and cathode comprised of carbon cloth and carbon-black-supported Pt were hotpressed together to form a membrane electrode assembly (MEA). TCE contaminated gas streams were fed to the cathode side of the fuel cell, where TCE was reduced to ethane and hydrochloric acid. The results suggest that TCE reduction occurs via a catalytic reaction with atomic hydrogen that is reformed on the cathode's surface rather than an electrochemical reduction via direct electron transfer. Substantial conversion of TCE was obtained, even in the presence of molecular oxygen in the cathode chamber. The process was modeled successfully by conceptualizing the cathode chamber as a plug flow reactor with a continuous source of H2(g) emanating from the boundary.

Thesis (Ph. D.)--University of Nevada, Reno, 2005. / "December, 2005." Includes bibliographical references. Online version available on the World Wide Web.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2002. / Härtill 5 uppsatser.

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