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This SERDP and ESTCP webinar focuses on DoD-funded research to better understand and quantify the abiotic degradation of chlorinated solvents. Specifically, the investigators will discuss the development of a laboratory carbon-14 isotope assay to quantify degradation rates in aquifer sediments and a field-deployable kit to measure the oxidation-reduction potential of aquifer sediments in situ.
 

“Development of Protocols to Quantify Abiotic Transformation Rates and Mechanisms for Chlorinated Ethenes in Water Supply Aquifers” by Dr. David Freedman (SERDP Project ER20-1368)

The Department of Defense (DoD) has responsibility for many large plumes with dilute concentrations of tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene isomers (cDCE, tDCE, 1,1-DCE) and vinyl chloride (VC) in groundwater. The objective of this project was to develop a deeper understanding for the role of magnetic materials in the abiotic degradation of chlorinated ethenes in aquifers. This presentation described the development of a protocol using a carbon-14 (¹⁴C) assay to quantify the degradation rate constants based on accumulation of ¹⁴C-labeled products. Dual element compound specific isotopic analysis is also being used in microcosms without addition of labeled compounds. The ¹⁴C assay has been used to evaluate abiotic TCE degradation in sediment samples from one site to date. The results were consistent with the hypothesis that higher levels of magnetic materials result in higher abiotic rate constants.  Furthermore, the results were consistent with the importance of a hydroxyl radical in the abiotic degradation of TCE.
 

“Field Deployable Oxidation-Reduction Potential Kits for Quantitative Assessment of Abiotic Monitored Natural Attenuation Rates” by Dr. Dimin Fan (SERDP Project ER20-1374)

This research project supported SERDP’s effort to improve quantitative understanding of naturally occurring long-term abiotic contaminant transformation processes to better assist DoD with assessing the transition of contaminated sites from active remediation to passive management. Given the challenges to measure slow abiotic attenuation rates by conventional means, the project aimed to develop an alternative approach that uses the oxidation-reduction potential (ORP) of reactive solids to estimate the potential for contaminant transformation. Traditional ORP measurement cannot accurately measure the ORP of reactive solids because of poor communication between solid and electrode. This research evaluated the feasibility of adding electron shuttles during ORP measurement to improve the electrochemical response of electrode to reactive solids and further correlated the improved ORP values with abiotic contaminant transformation rates. This presentation described the development of an improved ORP measurement approach that has evolved from a simple model system to a more complex field-like conditions with the goal to develop a working kit and protocol that can be reliably used to measure ORP of redox active solids collected from the field.

Dr. David Freedman is a professor and department chair in the Department of Environmental Engineering and Earth Sciences at Clemson University. He started his academic career at the University of Illinois and moved to Clemson University in 1996. The main focus of Dr. Freedman’s research has been the biotic and abiotic degradation of groundwater contaminants, including many halogenated organics, and more recently, 1,4-dioxane. He has received research support from SERDP, ESTCP, EPA, DOE, U.S. Army Construction Engineering Research Laboratory, U.S. Air Force Office of Scientific Research, Westinghouse Savannah River Corporation, and numerous consulting firms. He received a bachelor’s degree in science and environmental change from the University of Wisconsin (Green Bay), and master’s and doctoral degrees in environmental engineering from the University of Cincinnati and Cornell, respectively.

Dr. Dimin Fan is an environmental scientist at Geosyntec Consultants in San Diego, California. Dimin’s areas of research focus on developing and characterizing abiotic iron-based remediation technologiesfor active and passive management of contaminant plumes and the use of carbonaceous materials for the in situ remediation of organic contaminants. Dimin has served as the principal investigator or key performer for several research projects on quantitative characterizations of abiotic natural attenuation processes mediated by reactive iron minerals. He has authored more than 20 peer-reviewed research papers, including several recent ones on novel tools to characterize abiotic natural attenuation process. He earned a bachelor’s degree in environmental chemistry from Nanjing University in China, a master’s degree in soil physics from University of Delaware, and a doctoral degree in environmental science and engineering from Oregon Health and Science University.