Many of the Department of Defense’s (DoD's) remaining contaminated groundwater sites are candidates for remediation using technologies involving emplacement of particulate amendments. While the practice of utilizing some types of particulate amendments is well developed (e.g., hydraulic and pneumatic injection of micronsized zerovalent iron), other types of amendments are less-well proven. The main examples of the latter are activated carbon (AC)-based technologies, which have proliferated in recent years despite theoretical and practical reasons to be skeptical of their benefits. Of particular concern is the validity of the widespread assumption that adsorption of contaminants onto AC leads to enhanced degradation. Rigorously addressing this question will require better characterization methods than are currently available. The objective of this proof-of-concept project is to develop and validate a novel method for evaluating synergistic sorption/degradation effects in AC-amendments. Once demonstrated, the approach should be flexible enough to address many fundamental and practical questions regarding AC-amendment performance, either as a continuation of this study or through transfer of the methods to others working on AC-amendment-based remediation technologies.

This project will focus on laboratory experiments and numerical modeling designed to accomplish two major goals: develop a new electroanalytical tool for characterizing AC-amended systems and an improved quantitative conceptual understanding of AC-based sorption and degradation. Initially, laboratory electrochemical experiments will be used to probe well-characterized systems (e.g., AC alone, AC with internal and external addition of reactants, reactants alone). Next, probe contaminants will be added to these systems and chemical analyses (contaminant disappearance, product formation) will be performed to compliment the electrochemical measurements. Both types of data will be used to evaluate micro- and macro-scale numerical models of contaminant sorption and degradation on AC, resulting fundamental improvements in the conceptual understanding of AC-based amendments.

This project will provide a flexible, practical electroanalytical tool for probing the role(s) of AC in the subsurface transport and fate of contaminants. Perhaps more importantly, the combination of modeling and electroanalytical measurements proposed here will fundamentally improve the understanding of the processes leading to enhanced contaminant removal and sustained performance of the AC-amended systems. This combination of a new analytical tool and an improved conceptual understanding will benefit other SERDP-funded researchers in the near term and the user community in the longer-term. (Anticipated Project Completion - 2023)