Environmental Laboratory - Focus on PFAS Analysis 39 more mobile PFAS.


A series of remedial technologies that separate and destroy PFAS are being developed, with Tetra Tech leading the way in scaling up destructive approaches such as sonolysis, electron beams and use of supercritical water oxidation.


Summary Figure 2 Generic Conceptual Site Model Considering PFAS Fate and Transport [13].


remaining at the source (e.g. fi re training areas), associated with surfi cial soils, concrete and the capillary fringe (or smear zone) where the water table fl uctuates. The presence of high levels of undetectable PFAA-precursors in soils can have signifi cant implications when selecting remedial technologies as the “Dark Matter” can mean certain remedial approaches are potentially ineffective unless their performance on the PFAA-precursors is proven. A generic conceptual site model (CSM) describing PFAS fate and transport is presented below in Figure 2. Tetra tech is applying a specialist cleaning agent termed PFAScrub® to remove PFAS from soils and this has been demonstrated to remove an order of magnitude more PFAS than using water alone.


Chemical Analyses


Analytical methods to assess the presence of the polyfl uorinated precursors and PFAAs, such as the total oxidisable precursor (TOP) assay have been commercially available since 2015. This method can detect a wide range of PFAA precursors indirectly, by converting them into PFAAs using a chemical oxidant, so the resulting PFAAs can then be detected, as their chemical analysis is often possible. For the TOP assay to be applied to detect PFAA-precursors in soils some additional extraction methods are required which focus on removing cations and zwitterions, so that they can then be quantifi ed. Recent research has shown that 97% of the PFAS in soil sources remain undetected [14]. The TOP assay could be described as the PFAS uncloaking tool, but care needs to be taken ensuring that the published data quality objectives are met [15] and that interpretation is accurate.


PFAS Water Treatment


When considering treatment of PFAS impacted waters such as groundwater and surface water, charactering the water using TOP assay can be essential to allow design of the treatment solution. Estimation of the sorptive capacity of a water treatment system


may be fl awed if only a fraction of the PFAS in the water has been assessed. This can be more important when considering water that is being extracted from an area close to a PFAS source, as there will have been less time for the PFAA-precursors to have been transformed via biological activity. Activated carbon is more effective for treatment of the longer chain (more hydrophobic) PFAAs such as PFOS and PFOA, as opposed to the shorter chains such as PFHxA. For shorter chain anionic PFAS, ion exchange resins are generally more successful, as electrostatic interactions can be used to remove them from water. Characterising the water that needs treating for natural organic matter and common anions, such as sulphate, can be very important to determine the likelihood of successful treatment. Running small scale column studies and water treatment laboratory scale or fi eld pilots can be used to design treatment systems.


Other technologies that are developing to remove PFAS from water include multiple proprietary sorbent media and foam fractionation, to remove PFAS from solution and concentrate it. Treatment methods that apply oxidants, such as ozofractionation, which applies ozone in foam fractionation, will convert PFAA precursors into PFAAs, meaning that some of the amphiphilic PFAA precursor that could readily be separated by the foam fractionation process are instead oxidised into a short chain PFAAs that are not as easily removed [16]. Application of oxidants, such as ozone, or biological attack on common PFAA-precursors, known as fl uorotelomers, leads to the generation of a series of short chain PFAAs, including some termed ultrashort PFAAs (with 1 to 3 carbon atoms in their chain), that are not detected using commercially available analyses. The generation of a third of the mass of precursors as ultrashort chains has been reported when oxidants are applied [17]. Transformation of a fl uorosurfactant found in certain AFFFs, through 6:2FTS (6:2fl uorotelomer sulphonate) is shown in Figure 3. This process will occur if oxidants or aerobic biological treatment processes are applied to treat PFAS which often includes PFAA-precursors. So, application of water treatment technologies using aerobic biological processes and chemical oxidants may lead to the formation of


Management of PFAS impacts to ground requires a detailed understanding of the unique behaviours of this class of compounds, where physical, chemical, and biological processes can act to retain or mobilise PFAS from soils into groundwater or surface waters which can impact drinking water supplies. As regulations become increasingly comprehensive and stringent, the risks posed by a wide range of PFAS will need to be considered. When considering remediation of soils impacted by PFAS, there are signifi cant uncertainties characterising PFAS, which is an essential step before embarking on a remedial approach. Tetra Tech can assist with characterising and treating PFAS, as a result of experience characterising, risk assessing and treating this class of contaminants since 2005.


1. Salvidge, R. High levels of toxic chemicals found in Cambridgeshire drinking water. 2022; Available from: https:// www.theguardian.com/environment/2022/feb/08/high-levels- of-toxic-chemicals-found-in-cambridgeshire-drinking-water.


2. S.Pepper. Has SFFF Come of Age? 2021; Available from: https:// www.industrialfi reworld.com/613420/has-sff-come-of-age.


3. Ramsden, N., Foam Testing, in Pertroleum Review. 2018, Energy Institute. p. 32-33.


4. ACAF, S. DFW Fire Testing. Available from: https://www. youtube.com/watch?v=uXyGlYHw_ZM&t=33s.


5. Health, I.D.o.P. PFAS in Drinking Water. 2021; Available from: https://dph.illinois.gov/topics-services/environmental-health- protection/private-water/fact-sheets/pfas-drinking-water.html.


6. DHI. Danish EPA more tough on PFAS in drinking water. 2021; Available from: https://tox.dhi.dk/en/news/news/article/danish- epa-more-tough-on-pfas-in-drinking-water/.


7. USEPA. PFAS Strategic Roadmap: EPA’s Commitments to Action 2021-2024. 2021; Available from: https://www.epa.gov/ system/fi les/documents/2021-10/pfas-roadmap_fi nal-508.pdf.


8. DWI. Requirements for Poly and Perfl uorinated Alkyl Substances (PFAS) monitoring by water companies in England and Wales. 2021; Available from: https://www.epa.gov/ system/fi les/documents/2021-10/pfas-roadmap_fi nal-508.pdf.


9. DWI. Guidance on the Water Supply (Water Quality) Regulations 2016 specifi c to PFOS (perfl uorooctane sulphonate) and PFOA (perfl uorooctanoic acid) concentrations in drinking water. 2021; Available from: https://cdn.dwi.gov. uk/wp-content/uploads/2021/01/12110137/PFOS-PFOA- guidance-2021.pdf.


10. Commission, E. COMMISSION STAFF WORKING DOCUMENT Poly- and perfl uoroalkyl substances (PFAS) 2020; Available from: https://ec.europa.eu/environment/pdf/ chemicals/2020/10/SWD_PFAS.pdf.


11. Suthan S. Suthersan , J.H., Ian Ross , Erica Kalve , Joseph Quinnan , Erika Houtz , Jeff Burdick, Responding to Emerging Contaminant Impacts: Situational Management. Groundwater Monitoring & Remediation, 2016. 36: p. 22.


12. Brusseau, M.L. and B. Guo, Air-water interfacial areas relevant for transport of per and poly-fl uoroalkyl substances. Water Res, 2021. 207: p. 117785.


13. Ross, I., et al., Per- and Polyfl uoroalkyl Substances. 2018.


14. Nickerson, A., et al., Enhanced Extraction of AFFF-Associated PFASs from Source Zone Soils. Environmental Science & Technology, 2020. 54(8): p. 4952-4962.


15. Ross, I., Hurst, J., . Managing Risks and Liabilities associated with Per- and Polyfl uoroalkyl Substances (PFASs). CL:AIRE Technical Bulletin TB19 2019; Available from: https://www. claire.co.uk/component/phocadownload/category/17- technical-bulletins?download=668:tb-19-managing-risks-and- liabilities-associated-with-per-and-polyfl uoroalkyl-substances- pfass-2019.


16. McDonough, J. FIRST TIME USE OF OZOFRACTIONATION TO TREAT AFFF RELEASE AND VALIDATION BY TOP ASSAY. 2019; Available from: http://www.newea.org/wp-content/ uploads/2019/02/AC19_JMcDonough_26.pdf.


17. Kempisty, D.M., Xing, Y., Racz, L., Perfl uoroalkyl Substances in the Environment: Theory, Practice, and Innovation. 2019, Boca Raton, FL: CRC Press.


Figure 3 Conversion of PFAA precursors to a range of PFAAs via chemical oxidation or biotransformation.


Author Contact Details Ian Ross Ph.D. PFAS Global Lead Tetra Tech • Quay West at MediaCityUK, Trafford Wharf Rd, Trafford Park, Manchester, M17 1HH, UK • Tel: +44 7855 745531 • Email: ian.ross1@tetratech.com • Web: www.tetratech.com


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