Per- and polyfluoroalkyl substances (PFAS) comprise a large group of several thousand xenobiotics, with varying fate and transport characteristics. Many PFAS can exhibit long-range transport in water bodies, but some are significantly less mobile and may constitute a long term, more localised ongoing source. The differing sources of PFAS, such as from coatings or firefighting foams can play a very significant role in their fate and transport characteristics. The widespread use of PFAS has led to background concentrations in soils, surface waters, groundwater, rainwater, snow and thus biota. Confirming that the PFAS detected in multiple matrices do not comprise background will be essential. To develop an effective conceptual site model (CSM) to evaluate the risks PFAS may pose to identified site-specific receptors, an understanding of the nature, location, and fate and transport characteristics of differing polyfluorinated precursors and perfluoroalkyl acids (PFAAs) seems essential.

Site-specific examples of long and short chain PFAS partitioning to sediments from surface waters will be presented. The detection of high concentrations of polyfluorinated precursors to short chain PFAAs in surficial soils using advanced analytical tools, will also be described.

A review of background concentrations of PFAS in multiple matrices will provide some pragmatism for assessment of PFAS. An overview of the biotransformation characteristics of the two main classes of PFAA precursors will aim to assess their relative importance when developing site-specific conceptual models, with examples of precursor concentrations in surface waters from recent spills of firefighting foams versus more weathered and attenuated sources and plumes.

Some PFAS are commonly detected in surface waters as a result of their mobility and extreme persistence, but low-level detections may sometimes be considered as a background concentrations and may not originate at the local site under investigation. Atmospheric long-range transport of PFAS needs to be considered when investigating sites impacted with PFAS. From some site investigations, it is clear that the “long chain” amphiphilic PFAAs demonstrate far greater sorption to sediments and natural organic matter (NOM) than their shorter chain analogs. Some PFAA precursors are suggested to be more mobile than the PFAAs they form, but they may also suffer biotransformation to PFAAs whilst moving through aerobic surface and groundwater. Results from recent site investigations will show how some classes of precursors are less mobile and constitute a long-term source of PFAAs.

Ian Ross, Senior Technical Director and Global In-situ Remediation Technical Lead / Global PFAS Lead, Arcadis
Ian Ross, Ph.D., is a Senior Technical Director and Global In-situ Remediation Technical Lead / Global PFAS Lead at Arcadis from Leeds, West Yorkshire, UK.

His focus for the last four years has been on solely on PFAS after initially working on options for perfluorooctane sulfonate (PFOS) management in 2005 after the Buncefield Fire in the UK. He has was part of the team authoring and reviewing the CONCAWE PFAS guidance document and has published several articles on PFAS analysis, site investigation and remediation, including a recent book chapter on PFAS management.

He has been focussed on the bioremediation of xenobiotics for over 26 years as a result of three applied industrially sponsored academic research projects. At Arcadis he has worked designing and implementing innovative chemical, physical and biological remediation technologies.

He has evaluated the fate and transport, biodegradation potential and treatment options for contaminants including hydrocarbons, chlorinated solvents, nitroaromatics, PFAS, lindane (hexachlorocyclohexane), polychlorinated biphneyls (PCBs), Aldrin, Dieldrin and DDT.

He has experience with multiple physical, chemical and biological treatment technologies and has won several national and international remediation awards for designing their application.

Effective in-situ remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) is the ongoing goal of many laboratory-scale studies. An investigation was made to determine the potential removal of aqueous PFOA and PFOS in groundwater using thermally-activated persulfate. The facets of this project were to (1) evaluate the performance of a fluoride-selective electrode (FSE) in different matrix combinations that were representative of in-situ groundwater remediation activities; (2) investigate the removal of PFOA and PFOS with the addition of permanganate to thermally-activated or ambient persulfate; and, (3) compare the removal of PFOA by thermally-activated or ambient persulfate in different sediment-slurry experiments.

A systematic investigation of the impacts of oxidant-based reagents and a quenching agent, aqueous geochemistry, and the presence of sediments was conducted for the FSE, in order to provide guidance on the use of this analytical tool. Matrix spike recovery was within the acceptable bounds defined by the United States Environmental Protection Agency (USEPA), and the electrode slopes were consistent with the slope of the calibration curve, in the presence of persulfate and in different geochemical aqueous phases. The FSE can be used with caution as a tool to track the production of fluoride during degradation processes used for PFAS.

The impact of adding permanganate to both thermally-activated (60 °C) and ambient (20 °C) persulfate treatment systems for the removal of PFOA and PFOS was investigated using a 1:100 molar ratio of permanganate: persulfate. PFOA was successfully removed (> 99 %) in the thermally-activated persulfate with permanganate (dual-oxidant) and thermally-activated persulfate systems in both ultrapure and sodium bicarbonate simulated groundwater after seven days. Both short-chain PFCAs and aqueous F- were generated and indicated that PFOA was degraded in these experiments. The removal of PFOA was not evident in the ambient dual-oxidant and heated permanganate systems and there was no indication of removal of PFOS by any combination of oxidants. Removal of PFOA or PFOS was not improved in the thermally-activated or ambient persulfate systems with the addition of permanganate at the tested ratio.

The challenges for the implementation of thermally-activated persulfate for the removal of PFOA in groundwater settings include the interaction of persulfate and PFOA with the aquifer sediments. Removal of PFOA was compared using three different sediments in sacrificial sediment-slurry batch reactors. At least 60 % of the initial PFOA was removed after seven days in all three sediment slurries using thermally-activated persulfate. Short-chain PFCAs remained present in the systems longer, and less PFOA was removed when sediments were present in the reactors. Sorbed PFOA was extracted from each of the three sediments and was found at the highest concentrations in the sediment with the largest organic carbon content under acidic pH conditions. Thermally-activated persulfate was still effective for the removal of PFOA from soil-slurry reactors, but at decreased removal efficiency.

Funding for this research project was provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (C. Ptacek PI), a NSERC Collaborative Research and Development Grant (N. Thomson PI), and the American Petroleum Institute (N. Thomson PI), in addition to scholarships awarded to J. Cooper, including the Ontario Graduate Scholarship and NSERC Graduate Scholarship – Master’s Program.

Janice Cooper, Environmental Scientist, Stantec Consulting
Janice Cooper completed her Master's of Science at the University of Waterloo and conducted research on the treatment of PFOA and PFOS using thermally-activated persulfate. She is now working as an environmental scientist at Stantec Consulting in Waterloo, Ontario.

The U.S. Department of Defense (US DoD) Strategic Environmental Research and Development Program (SERDP) funded a project using the self-sustaining treatment for active remediation (STAR) smouldering combustion process to treat per- and polyfluoroalkyl substances (PFAS) compounds in soils or investigation derived wastes (IDW). IDW includes drill soil cuttings, as well as spent activated carbon (GAC) waste streams generated from treating water from well development and sampling.

STAR is a smouldering combustion process for the treatment of contaminated soils and liquid organic wastes. The process is self-sustaining following a short duration, low energy input ‘ignition event’ for low volatility, high-energy compounds such as petroleum hydrocarbons. The energy released from the reacting contaminants is used to pre-heat and combust contaminants in the adjacent area. A self-sustaining combustion front propagates through the contaminated porous media provided that a sufficient flux of air is supplied. STAR can destroy a variety of recalcitrant organic compounds with removal efficiencies typically in excess of 99%. STAR has been recently demonstrated at Waterfront Toronto to treat hydrocarbons below ground and beneath the water table using down well heaters inserted at target locations, and in soils that are placed on a low profile above ground modular engineered base systems called STARx HottPads™.

Due to the high thermal stability of PFAS, temperatures greater than 900°C are required to destroy these compounds and temperatures at or above 1000°C are necessary to minimize production of short-chained volatile organic fluorines (VOFs) and fluorinated dioxins and furans (PFDD/F). Hydrofluoric acid (HF) will be produced in greater abundance, and VOF and PFDD/F in lesser abundance, with increasing completeness of PFAS combustion. As the PFAS are not contaminants that can support smouldering combustion in and of themselves like petroleum hydrocarbons, a surrogate fuel is required. For this study, GAC was used as a surrogate fuel.

Tests were conducted to establish the amount of GAC needed to create smoulderable mixtures that produced temperatures greater than 900°C. Subsequent tests examined the fate of PFAS adsorbed to GAC and then combined with sand, or a soil contaminated with PFAS and mixed with uncontaminated GAC under smoldering conditions. Results reveal that the smouldering front propagated in a self-sustained manner through the PFAS-impacted mixtures, destroying all the GAC and organic carbon and generating temperatures in excess of 900°C. Post-treatment concentrations of PFAS in the remaining sand, soil, and ash were below detection limits (0.05 µg/kg). Initial emission analysis indicated that over 82% of the available fluorine was captured as HF with only small amounts of PFAS emitted which could be subsequently captured by activated carbon and treated. Results to date are promising, suggesting STAR may provide an effective remediation technique for PFAS-impacted soils and IDW at field scale at Canadian federal sites.

David Major, Managing Director, Savron (a division of Geosyntec Consultants, Inc.), and Associate Editor, Ground Water Monitoring and Remediation
Dr. David Major, Ph.D., BCES, has helped develop and commercialize remediation technologies such as zero-valent iron (ZVI) permeable reactive barriers, molecular biomarkers, bioaugmentation cultures, and currently Savron’s smouldering-based combustion technology (STAR). David has served on various national scientific advisory boards including the U.S. EPA Expert Panel on dense non-aqueous phase liquids (DNAPL) Remediation (The DNAPL Remediation Challenge: Is There a Case for Source Depletion), and the U.S. National Research Council Committee on Geological and Geotechnical Engineering in the New Millennium. He has co-developed and taught Interstate Technology & Regulatory Council (ITRC) course on monitored natural attenuation, accelerated bioremediation, and bioremediation of DNAPLs. He has received several awards including: University of Waterloo Faculty of Science Alumni of Honour Award (2007) in recognition of his professional accomplishments; Space Hall of Fame®(2007) for helping NASA commercialize “Products from Space Benefiting Planet Earth”; ASTM C.A. Hogentogler Award (2015); and, ICE Telford Premium (2016) awards for papers on ground improvement technology.

Adsorptive media such as granular activated carbon (GAC) and ionic resins are common separation methods to remove per- and polyfluoroalkyl substances (PFAS) from water. However, other materials, such as biochar, may be a more suitable and cost-effective alternative for in-situ applications to remove PFAS from groundwater. The objective of this study was to demonstrate and evaluate the removal of PFAS from groundwater by different mixtures of media containing soil, wood shavings, and biochar.

Removal of perfluorooctnoic acid (PFOA) and perfluorooctanoic sulfonic acid (PFOS), among other PFAS compounds, was the target of a two-phase bench-scale treatability study conducted to demonstrate PFAS removal from groundwater. Phase 1 was focused on batch experiments to screen for different media mixtures based on their adsorptive properties. The first experiment determined the removal of PFAS at four initial concentrations using media mixtures consisting of 100% soil; 50% soil and 50% wood shavings; 50% soil and 50% biochar type A (medium particle size); and, 50% soil and 50% biochar type B (large particle size). A more fine-tuned optimization of the media composition was done in a second batch experiment by determining the extent of PFAS removal using different proportions of wood and biochar amendments. Phase 2 consisted of a column experiment to determine the retention of PFAS under flow-through conditions by the following media compositions: 1) 14% wood shavings, 1% biochar and 85% soil; 2) 10% wood shavings, 5% biochar and 85% soil; 3) 5% biochar and 95% soil; and, 4) 100 % soil (control).

Results from the first batch experiment from Phase 1 indicate that 100% removal of PFOS and PFOA was achieved in mixtures containing biochar. Removals between 69% and 79% for PFOS and removals between 14% and 28% for PFOA were obtained for the soil control. The mixture containing soil and wood shavings achieved removals between 66% and 73% for PFOS and removals between 16% and 23% for PFOA. Results from the second batch experiment indicated that the best media composition had 15% of wood shavings, 5% of biochar, and 80% of soil with removals of PFOA and PFOS at 98.5% and 96.5%, respectively. Phase 2 experimental results showed the highest retention of PFAS in media containing 5% biochar and 95% soil, with breakthrough for PFOA and PFOS occurring after 6.7 pore volumes of groundwater. This mixture had the highest adsorption capacity of PFOA and PFOS, at 2.23 g/m3 and 0.22 g/m3.

Based on these results, biochar is demonstrated as an amendment that increases the removal of PFAS compounds significantly when added to soil. These findings can aid in permeable barrier design if the total mass of PFAS to be removed and the percentage of biochar amended to the mixed media are known. Depending on the material source, biochar may be a more sustainable and cost-effective amendment than other adsorbents for the implementation of permeable barriers to achieve in-situ treatment of shallow PFAS-impacted groundwater and/or prevent off-site migration.

Mahsa Shayan, Environmental Engineer, Remediation – Ontario, AECOM
Dr. Mahsa Shayan, Ph.D., EIT, has eleven years of professional and research and development (R&D) experience in environmental site characterization and remediation, specialized in contaminant fate and transport studies and remedial option analysis for sites impacted by a wide range of emerging and conventional contaminants. Mahsa’s experience includes subsurface contaminant fate and transport analyses and remediation of soil and groundwater systems through the use of field investigations, laboratory experiments, and numerical models. Her primary interests are directed toward design and assessment of in-situ treatment technologies including in-situ chemical oxidation (ISCO) and enhanced bioremediation (EBR) and combined remedies. She also has expertise in the smart and targeted use of environmental molecular diagnostic tools, including compound specific isotope analysis (CSIA) and molecular biology techniques, for enhanced conceptual site model (CSM) development and remediation performance assessment.

The prolonged application of aqueous film-forming foams (AFFF) containing per- and polyfluoroalkyl substances (PFAS) at firefighting training areas (FTAs) has resulted in long-term sources of PFAS leaching into soil and groundwater. The leachability risk of PFAS from resultant soil source zones to groundwater can be mitigated by reducing their mobility in the subsurface via fixation. Treatability tests were conducted to explore the in-situ soil stabilization (ISS) of PFAS in FTA source zones using commercially-available adsorption media (i.e., “fixants”). ISS presents a potential PFAS source zone management alternative that eliminates ex-situ management of PFAS wastes while protecting groundwater from future leaching. ISS consists of the use of heavy-construction equipment, augers, and/or cutting tools to mix soil, water, and fixants in place in the vadose and saturated zones. ISS reduces leachability through stabilization with the fixants and minimizes vertical infiltration and variability in lateral hydraulic conductivity by homogenizing preferential pathways with low-permeability strata. Laboratory tests were conducted with four objectives: 1) establish basic adsorption performance of selected fixants for PFAS; 2) test performance as a function of pH; 3) compare performance with and without Portland cement; and, 4) obtain leachability data to demonstrate potential long-term stability of in-situ treatment.

Bulk soil and groundwater samples were collected from an Australian airport site known to be impacted with PFAS from AFFF use. Three commercially-available fixants were selected for the test program based on their potential for adsorption of anionic PFAS: aluminum hydroxide (AlOH)/carbon blend (AHCB); pyrolyzed cellulose (PC); and, modified clay (MC). The program consisted of batch contact tests of impacted soil and groundwater mixed in a liquid/solid ratio of 2:1. The batches were mixed on a linear mixing table for 18 hours. Control and duplicate batches were run and pH was monitored at points along the process. After mixing, samples were separated and filtrate samples were analyzed for a PFAS suite of 28 compounds using liquid chromatography-tandem mass spectrometry (LC/MS/MS). Larger batch contacts were run with soil and groundwater to simulate in-situ soil mixing. Leachability tests were then conducted on treated batches with and without Portland cement.

All three reagents tested demonstrated effective adsorption of PFAS. MC demonstrated the best removal of perfluorinated sulfonates, which were the main contaminants. The result at the lowest dose of 5-percent by weight represents better than 99.9% reduction in dissolved-phase concentration. The AHCB demonstrated the best overall removal of perfluorinated carboxylate (PFCAs) compounds, particularly for short-chain PFCAs. Adsorption capacities measured for AHCB, PC, and MC of the 28 PFAS standard suite in were 25.6, 15.3, and 38.3 microgram PFAS per gram fixant, respectively. The PC showed a significantly less removal capacity of short-chain PFAS compared to the AHCB and the MC. The sequential leaching test of the MC exhibited up to two order-of-magnitude decrease in leachability over the control sample. The overall mass of PFAS leached was approximately 1% of the total PFAS mass after an estimated 50 pore volumes of leaching. The tests demonstrate the strong potential of this technology as an effective tool for mitigating migration of PFAS through soil and groundwater.

Stephanie Joyce, Project Manager, Arcadis Canada Inc.
Stephanie Joyce has over 14 years of experience in environmental consulting, specializing in environmental site assessments, long term monitoring and regulatory applications. Stephanie has completed over 60 Phase I, II and III ESAs, in the Northwest Territories, Nunavut and Ontario. Her clients have included primarily federal, territorial and municipal government departments. Recent project responsibilities have included project manager for the preparation of guidance documents for conducting assessments of former fire-fighting training areas for PFAS impacts and the evaluation and demonstration of PFAS remediation technologies. She is currently managing a bench scale study evaluating soil stabilization technologies.