Key Fate and Transport Processes Impacting the Mass Discharge, Attenuation, and Treatment of Poly- and Perfluoroalkyl Substances and Comingled Chlorinated Solvents or Aromatic Hydrocarbons

Dr. Christopher Higgins | Colorado School of Mines

ER-2720

Objective

The overall goal of this research is to attain improved insight into the fundamental fate and transport processes that control per- and polyfluoroalkyl substance (PFAS) fate and transport as well as comingled chlorinated solvents and/or fuel hydrocarbons in groundwater at aqueous film forming foam (AFFF)-impacted sites. This research will particularly focus on the release and transformation of polyfluorinated PFASs to the more problematic perfluoroalkyl acids (PFAAs) in source zones as well as the impact of commonly employed remediation technologies for co-contaminants on PFAS fate. Specific objectives include:

  1. Investigation of the fundamental mechanisms controlling the release of PFASs from complex source-zone phases;
  2. Examination of the coupled diffusion and potential abiotic reactions of PFASs and comingled contaminants in low permeability materials;
  3. Assessment of the biotic transformation of the wide range of PFASs and co-contaminants (chlorinated solvents and BTEX) present in the dissolved plume and the impacts of PFASs on co-contaminant bioremediation; and
  4. Quantification of the impacts of remedial activities targeting co-contaminants (i.e., BTEX, chlorinated solvents) on the PFAS plume.

The ultimate goal of improved insight into the fundamental fate and transport processes in these mixed contaminant systems will facilitate the development and optimization of treatment strategies for management of PFAS sites comingled with co-contaminants.

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Technical Approach

The hypothesis is that the complex nature of PFASs present in AFFF results in complex and long-term release from both primary sources (which may contain non-aqueous phase liquids [NAPLs]) and low permeability zones. Further, coupled biotic and abiotic transformation of polyfluorinated PFASs to the problematic PFAAs are impacted by site mineral and geochemical conditions as well as the application of conventional treatment technologies. The application of enhanced aerobic transformation of aromatic hydrocarbons (biosparging), biostimulated reductive dechlorination of chlorinated ethenes, and application of in situ chemical oxidation (ISCO) have unknown impacts on the release and transformation of polyfluorinated PFASs to the more problematic PFAAs.

This three-year project will examine these impacts and interactions through carefully controlled batch and column laboratory experiments. However, to represent the true complexity of PFAS chemistry and co-contaminant interactions, field-collected groundwater and soil/aquifer samples will be employed to serve as the primary source of these constituent compounds. When appropriate, AFFF formulations or mixtures thereof also will be tested. Comprehensive analytical methodologies will be employed, targeting not only the ~200 PFASs relevant to these sites, but also the potential for yet unidentified PFASs and volatile intermediates. Of particular interest are interactions of polyfluorinated PFASs with NAPLs, the diffusive transport and transformation of PFASs in clays, the biological transformation of PFAS present in AFFF, and the advective release and transformation of PFASs from field-collected materials under simulated remediation conditions. These topics will be addressed through four integrated experimental tasks designed to address the objectives above.

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Benefits

Comingled PFAS and hydrocarbon and/or chlorinated solvent plumes have become a concern of growing urgency for the DoD. Adverse PFAS impacts on groundwater are widespread at DoD facilities, and these mixed contaminant systems may pose a significant barrier to site closure. This work will significantly enhance our understanding of the role of polyfluorinated PFASs and the role of source zones and low permeability materials in PFAS release. These data will enable the DoD to appropriately apply synergistic remediation technologies for these mixed contaminant plumes and source zones. (Anticipated Project Completion - 2020)

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Points of Contact

Principal Investigator

Dr. Christopher Higgins

Colorado School of Mines

Phone: 303-384-2002

Fax: 303-273-3413

Program Manager

Environmental Restoration

SERDP and ESTCP

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