The overall objective of this project is to obtain a better understanding of the attenuation mechanisms and degradation kinetics of select chemicals, namely 1,4-dioxane (1,4-D), and targeted chlorinated volatile organic compounds (CVOCs) frequently found at Department of Defense (DoD) sites in dilute concentrations. Specifically, this project aims to elucidate how 1,4-D and these target chemicals degrade under different redox conditions and obtain information on kinetic parameters. In addition, this project aims to determine specific mechanisms (for example, biotic versus abiotic) and obtain insights into the microorganisms that are involved in the processes as well as potential substrates that may be added or naturally present in situ to facilitate biodegradation. 

This project will address the following objectives: 

1. The natural attenuation mechanisms and degradation kinetics of chemicals of interest in groundwater at environmentally relevant concentrations. 
2. The fate and transport of chemicals of interest during implementation of common groundwater treatment scenarios.

The specific objectives of the project are to: 

1. Collect soil and groundwater from representative DoD sites that contain 1,4-D and target chemicals of interest. Aquifer interfaces will be targeted due to their enhanced capacity for 1,4-D attenuation because of their potential for redox cycling and increased availability of dissolved oxygen, co-substrates, and/or nutrients. 
2. Determine the kinetic parameters of 1,4-D degrading microorganisms, including those for 1,4-D, oxygen, and inhibitory co-occurring chemicals. Variability in kinetic parameters and behaviors of these microbes will strongly influence their activity in plumes with dilute concentrations. 
3. Evaluate biodegradation of chemicals of interest under different redox conditions, and areas where enhanced capacity may be observed. Biodegradation of minor plume components such as 1,4-D and lesser CVOC are highly dependent on redox conditions, which will dictate the natural attenuation potential and the effectiveness of remedies of these compounds. This also includes abiotic degradation under iron cycling conditions. 
4. Integrate key kinetic parameters and information obtained to provide guidance to improve the monitored natural attenuation (MNA) evaluation process, and improve remedy selection and optimization for minor components within dilute plumes. Existing decision tools will be adapted to incorporate the findings from this research.

Despite significant advances in understanding the behavior of 1,4-D in the environment, there are still crucial information gaps that need to be addressed for better management of large dilute plumes. This project will fill several of the remaining gaps, including a better understanding of the kinetics that dictate degradation of 1,4-D at concentrations in the microgram per liter range, and in the presence of co-occurring chemicals that may have inhibitory or stimulatory interactions. This project will focus on sites where there is a potential for redox cycling due to a consistent influx of dissolved oxygen, where biotic and abiotic processes may be attenuating 1,4-D and co-occurring chemicals. The gathered information will be incorporated into a software tool that will assist site managers in a comprehensive evaluation of plume management using monitored natural or enhanced attenuation. (Anticipated Project Completion - 2026)

Cao, H., A.S. Pavitt, J.M. Hudson, P.G. Tratnyek, and W. Xu. 2023. Electron Exchange Capacity of Pyrogenic Dissolved Organic Matter (pDOM): Complementarity of Square-Wave Voltammetry in DMSO and Mediated Chronoamperometry in Water. Environmental Science: Processes & Impacts, 25:767-780. doi.org/10.1039/D3EM00009E. 

Cao, H., A.S. Pavitt, J.M. Hudson, P.G. Tratnyek, and W. Xu. 2023. Raw Data from Cao et al. (2023) Electron Exchange Capacity of Pyrogenic Dissolved Organic Matter (DOM): Complementarity of Square-Wave Voltammetry in DMSO and Mediated Chronoamperometry in Water. Zenodo. doi.org/10.5281/zenodo.7747019. 

Hudson, J.M., D. Latta, A.S. Pavitt, Y. Lan, M.M. Scherer, and P.G. Tratnyek. 2022. Thermodynamic Database and Calculator of Free Energies and Potentials for Redox Reactions Involving Iron Minerals in Aqueous Media (IMTD). Zenodo. doi.org/10.5281/zenodo.5151587.