In July 2018, SERDP and ESTCP held a Workshop addressing management of chlorinated solvents in groundwater. Approximately 60 personnel representing DoD remedial program managers (RPMs), federal and state regulators, engineers, researchers, industry representatives, and consultants attended. Workshop participants identified several research needs that, if addressed, would improve the DoD’s ability to safely and cost-effectively manage chlorinated solvent-contaminated groundwater sites. A more detailed description of identified research needs can be found in the report from the workshop. Proposers are strongly encouraged to review the Workshop Report for additional detail.
Existing CSMs often fail to account for the range of possible mechanisms and processes that sustain and control the persistence of dilute chlorinated solvent plumes. This failure is typically due to several factors, including the inability to verify that all suspected degradation processes are occurring, the inability to sufficiently quantify the significance of the process, and/or the lack of appropriate modeling tools to incorporate these processes into fate and transport models. Examples of mechanisms and processes that are often neglected or poorly characterized and quantified in CSMs include (but are not limited to):
- Persistent low-intensity source areas. Often, source areas persist even after the bulk of the contaminant mass has been removed, and after the contaminant flux has been substantially reduced.
- Naturally occurring long-term biotic and abiotic transformation processes. Even very slow dechlorination processes can have a substantial impact on plume attenuation when considering timescales of decades. However, it is difficult to incorporate these processes in CSMs because of a lack of reliable kinetic data and an inadequate understanding of when these mechanisms and their relative degradation rates are and are not likely to be appropriate for inclusion in a CSM.
- Interactions with low permeability materials. Quantifying the processes that occur within LPZs, and characterizing the interactions between LPZs and hydraulically conductive zones, remains difficult. Proper descriptions of contaminant release and uptake into such zones can require more characterization data than is usually available, and in fact it is often impractical to collect sufficient data with current tools.
Overall, there is an absence of tools and techniques to validate the contribution of these processes on plume persistence. A quantitative assessment of these processes would also allow for better assessment of the maximum concentration of a contaminant that can be allowed in groundwater leaving a source of contamination such that the concentration of the contaminant will not exceed groundwater cleanup levels, and consequently, when it is appropriate to stop pumping groundwater or to transition from active treatment of a source or plume to a more passive treatment strategy.
SERDP and ESTCP have funded several projects in an effort to understand processes that impact contaminants in groundwater. Proposers should be familiar with these past projects, which can be found at https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration. Proposed efforts should be complementary and not duplicative of previously funded projects.