Use and Potential Impacts of AFFF Containing PFASs at Airports (2017)

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47 5.1 Overview As indicated in Chapter 2 of this report, AFFF has been used for decades at airports in the United States and Canada to extinguish fires. PFASs, principal active ingredients in AFFF, are considered an emerging contaminant in the environmental industry. Some PFASs are ubiq- uitous in the environment and exhibit properties that could pose a potential human health or ecological risk to sensitive receptors at low concentrations. Historical use, training, testing, maintenance, and disposal practices may have resulted in a release of PFASs into the envi- ronment. This chapter discusses how to address environmental impacts associated with past releases or applications of AFFF into the environment. Specifically, this chapter describes the following: • Best practices for sampling environmental media for PFASs so that representative samples are obtained. Key information for evaluating whether there is a potential unacceptable human health or ecological risk involves identifying whether PFASs are present in environmental media (i.e., soil, sediment, groundwater, and surface water) and at what concentration. • Current, commercially available laboratory analytical methods for PFASs that are necessary to achieve analytical detection limits appropriate for comparing concentrations to stringent regulatory criteria. Analytical approaches under development and not yet commercially available in the United States or Canada are also identified. • Risk management considerations specific to the impacts of PFASs, including key factors in developing the conceptual site model (CSM) and strategies to manage potentially unacceptable risks. • State-of-the-practice remediation technologies and approaches that have demonstrated some success (or are generally believed to hold promise) in field-scale remediation of PFASs in soil and groundwater. Emerging technologies and approaches under review and development are also identified. 5.2 Sampling of PFASs 5.2.1 General Challenges with Sampling of PFASs Traditional, standardized environmental sampling protocols provide effective means to collect representative samples from various environmental media for most contaminants. However, as described in Chapter 2, the chemical and physical properties of some PFASs offer unique challenges in obtaining concentrations of PFASs representative of field conditions. For example, the fact that compounds containing PFASs stratify in water as they migrate to the air-water inter- face means that groundwater samples need to be taken from the surface of the water table and laboratory analytical methods must involve vigorous shaking of water samples before a subsample C h a p t e r 5 Addressing Legacy Environmental Impacts

48 Use and potential Impacts of aFFF Containing pFaSs at airports is removed and injected into laboratory instrumentation. PFASs are also likely to “stick” to suspended particles in water or to a filter if samples are filtered to retain the “dissolved” fraction of the water sample. In addition, the ubiquity of PFASs in the environment from sources such as clothing (e.g., Gore-Tex™) or sampling equipment (e.g., PTFE or Teflon™) could contaminate samples, resulting in measured concentrations that are greater than the actual concentrations in the environmental media being evaluated. In order to obtain representative samples, specific sample collection protocols are recommended when a site is to be investigated for PFASs. These protocols include avoiding the use of glass or metals, as some PFASs bind to these materials. Contact with materials that may contain PFASs such as PTFE (i.e., Teflon™) should also be avoided, and samples should be collected using polyethylene or polypropylene containers and equipment. Additional guidance on conducting sampling programs for PFASs can be found in the following: • U.S. EPA Method 537. Determination of Selected Perfluorinated Alkyl Acids in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC-MS/MS). • Transport Canada’s Perfluorochemical Sampling and Analysis Guidance. • United Nations Environment Programme (UNEP) Chemicals Branch’s PFAS Analysis in Water for the Global Monitoring Plan of the Stockholm Convention: Set-Up and Guidelines for Monitoring. The following sections discuss best practices for sampling soil, sediment, groundwater, and surface water for PFASs and reducing the likelihood for cross-contamination. Also discussed are quality assurance and quality control considerations and innovative approaches to sampling for PFASs. 5.2.2 PFASs—Sampling Challenges and Mitigation 5.2.2.1 Cross-Contamination Cross-contamination occurs when samples collected in the field are impacted by chemicals from sources other than the media being sampled. Cross-contamination can result in a detectable concentration where no PFASs are present or a concentration that is biased high relative to what is present in the environment. The potential for cross-contamination is significant given the ubiquity and environmental persistence of some PFASs and the very low detection limits and regulatory criteria associated with many PFASs. General practices recommended to eliminate the likelihood of cross-contamination regardless of media are presented below. Sampling Equipment and Sample Containers The use of glass or metals should be avoided because compounds containing PFASs bind to these materials. Samples should be collected using polyethylene or polypropylene containers and equipment. Contact with materials that may contain PFASs such as PTFE should also be avoided (e.g., Teflon™ tubing, Teflon™ bailers, and sticky labels and adhesive tape used during sample collection and storage). Use of aluminum foil should also be avoided, as some PFAAs could be transferred from the aluminum foil to the sample. Drilling Water/Hydroexcavation Potential sources of PFASs (other than what is in the environmental media being investigated) should be considered and removed during sampling field programs to avoid cross-contamination. For example, if water is necessary to obtain a soil sample (e.g., drilling or hydroexcavation), it is important to confirm that the water does not contain PFASs that could impact the samples or, worse, impact the study area.

addressing Legacy environmental Impacts 49 Field Equipment Decontamination Field equipment that is used at multiple sampling locations (e.g., flow-through cells, field meters, and interface probes) requires proper decontamination between uses at different sampling loca- tions. Decontamination should be conducted with rinsate that is free of PFASs (i.e., water that is free of PFASs) and detergents. Water that is free of PFASs can be obtained from a laboratory. Where impacts of PFASs are known to be present, field decontamination of each piece of field equipment should be conducted prior to use, at least twice between sampling locations, and before leaving the site. Personal Protective Equipment and Field Clothing Personal protective equipment and field clothing commonly worn during field investigations may represent potential sources of PFASs that could cross-contaminate samples collected in the field. The following practices are recommended: • Field clothing to be worn on-site should be restricted to clothing made of natural fibers (e.g., cotton). Synthetic fibers and/or clothing that is water resistant, waterproof, or stain- treated should not be worn during the field program. • Field personnel should avoid documenting field notes on waterproof field books/paper as the coated paper may contain PFASs. Acceptable field documentation alternatives include field tablets, other electronic data entry interfaces, or uncoated paper. • Most safety footwear is made from leather and synthetic fibers that have been treated to provide some degree of waterproofing/increased durability and may represent a trace source of some PFASs. For the health and safety of field personnel, the protection afforded by the footwear must be maintained. Field staff should avoid directly contacting samples after touching their footwear (e.g., tying shoelaces). • Field personnel should frequently replace gloves (using disposable single-use gloves and having multiple changes per location) to mitigate the potential for cross-contamination. At a minimum, sampling gloves should be replaced after contact with equipment and prior to contact with sample bottles or containers of water that are free of PFASs. Gloves should be nitrile or latex; regular canvas or leather work gloves should not be used for sample collection or for personal protection when handling AFFF or media impacted by PFASs. Food Packaging For health and safety reasons, food and beverages should not be consumed during field activities except during a designated break in a designated clean area. However, due to the historical use of some PFASs in food packaging, field personnel must be particularly careful when sampling for PFASs. The following practices are recommended for field personnel (and visitors to the area): • Do not bring food on-site in any paper packaging (i.e., do not bring any fast food to the site that uses any form of paper wrapping like sandwiches with paper wrap or coffee in paper cups). • Avoid products such as aluminum foil, coated papers, and coated textiles. • Wash hands after eating and prior to engaging in sample collection, and wear appropriate gloves (e.g., nitrile) for sample collection. Specific Best Practices for Sampling Aqueous Media In order to alleviate the potential for cross-contamination, the following practices, specific to aqueous media sampling, are recommended: • A well condition survey should be completed after groundwater purging and sampling has been completed to help mitigate the possibility of cross-contamination of groundwater samples. (Please note that this practice is atypical for groundwater sampling programs, which usually have static water levels, and which include monitoring well depths as one of the first steps.)

50 Use and potential Impacts of aFFF Containing pFaSs at airports • Aqueous samples should be collected directly into bottles prepared by a laboratory to be free of PFASs. High-density polyethylene (HDPE) tubing connected to a peristaltic pump (where feasible) with silicon tubing should be used for the groundwater sampling program. 5.2.2.2 Suspended Particulate Matter in Aqueous Samples The adsorptive properties of some PFASs relative to field filtration and their ability to “stick” to particles in the water column can make quantifying PFASs in aqueous matrices challenging. To avoid suspended particulate matter and solids during groundwater sampling, procedures for compounds with PFASs in groundwater should follow the field procedures established for low-flow purging and sampling, as described in the two documents listed below, with adaptations to address the sampling concerns specific to PFASs (e.g., cross-contamination and no materials containing PTFE): • Low Stress (low flow) Purging and Sampling Procedure for the Collection of Groundwater Samples from Monitoring Wells, EQASOP-GW 001 US EPA (2010). • ASTM D4448-01 (Reapproved 2013)—Standard Guide for Sampling Ground-Water Moni- toring Wells. As with groundwater, surface water samples should be collected in accordance with standard methodologies, avoiding suspended and/or particulate matter in retrieved water samples. As men- tioned earlier, the presence of particulate matter in water samples can contribute to measured concentrations that are greater than the actual environmental concentrations and, therefore, not representative of the media (i.e., water) sampled. Filtration is not recommended before laboratory extraction, as the filter may absorb PFASs or may be a source of contamination. 5.2.2.3 Sampling Frequency AFFF formulations may contain precursors that transform or degrade into other, more stable and recalcitrant PFASs such as PFOS and PFOA. Changes in the concentrations of precursors and these more stable PFASs may occur over time. Consequently, in addition to assessing seasonal considerations, sampling more than once may help to better assess sites where PFASs are transforming and/or identify whether migration is occurring. 5.2.3 Quality Assurance and Quality Control A quality assurance/quality control (QA/QC) program appropriate for achieving the project’s data quality objectives should be adopted for any type of environmental program. Typically, an appropriate QA/QC field sample collection program for field investigations involving PFASs includes (at a minimum) field duplicates and equipment blanks. Brief descriptions of each type of field QA/QC sample important to investigations involving PFASs (as recommended by U.S. EPA Method 537) follow: • Field duplicate: a duplicate sample taken in the field from the same location as the original sample to ascertain sampling precision. The sample is given another name so it is not identified with any field duplicate, to further test precision. • Equipment blank: rinsate from the equipment used to take the sample. The purpose of the equipment blank is to assess the effectiveness of the implemented decontamination process and the potential of cross-contamination of samples due to insufficient decontamination of sampling equipment. • Field reagent blank (FRB): An analyte-free water in a sample bottle that is provided by a laboratory. The FRB is shipped to the sampling site along with the sampling bottles. At the

addressing Legacy environmental Impacts 51 sampling site, the sampler opens the shipped FRB and pours the preserved reagent water into an empty shipped sample bottle, then seals it and labels it as the FRB. The FRB is shipped back to the laboratory along with the samples and is analyzed to ensure that PFASs were not introduced into the sample during sample collection/handling. Given the ubiquity of some PFASs, modifications to these standard QA/QC samples should use laboratory-supplied water and sample containers that are free from PFASs and suitable for sampling PFASs. 5.2.4 Innovative Approaches to Sampling PFASs in Water Innovative sampling approaches are being developed by researchers to address or alleviate concerns associated with cross-contamination, biases, and extraction concerns associated with programs sampling PFASs in water and the lack of real-time characterization tools for PFASs. Two of these approaches, passive sampling and ion-selective electrodes (ISEs), are summarized below. Neither method has been standardized or adopted by the U.S. EPA. 5.2.4.1 Passive Sampling in Water Passive sampling is an efficient and cost-effective way of measuring contaminants in the environment over a measured period of time and with limited field time. Passive, or diffusive, sampling relies on the unassisted molecular diffusion of gaseous agents (analytes) through a diffusive surface onto an adsorbent. Passive sampling in water for PFOS has been implemented in environmental field assessments in Sweden by the Swedish Environmental Protection Agency. In-situ calibration with the use of reference compounds has not been observed to be successful (75); however, certain types of passive sampler (e.g., polar organic chemical integrative sampler or POCIS) may be a suitable tool for biomonitoring of PFASs (76). 5.2.4.2 Ion-Selective Electrodes An ISE is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solu- tion into an electric potential. ISEs fabricated from fluorous materials are used to measure PFOS in drinking and groundwater down to the part-per-trillion level with no sample preparation. Research to evaluate the applicability of this technology for measuring PFOS in soil is ongoing. This would be a rapid screening tool that could provide field results in real time (rather than waiting for laboratory analysis). A universal PFOS anion soil extraction methodology that is broadly applicable to different soil types has not been developed. Research to develop a method to categorize different soil types and develop suitable extraction methods for each soil sample type is ongoing (77). 5.3 Analysis of PFASs Analytical procedures are required to identify concentrations of PFASs that are representative of the environmental media being assessed and consistent with levels of potential concern. As research provides new information on human health and ecotoxicological impacts associated with PFASs and their fate and transformation in the environment, regulations and corre- sponding analytical methodologies are targeting lower detection limits. Laboratory analytical methods are being developed as the working understanding of the chemicals themselves is growing (78). Commercially available analytical methodologies (e.g., the types of analyses that are undertaken by commercial analytical laboratories) are currently not capable of quantify- ing the full suite of PFASs that exist in soil and groundwater; this is partially due to the lack of available reference standards. Stratification in water samples requires that samples are shaken

52 Use and potential Impacts of aFFF Containing pFaSs at airports vigorously in the laboratory prior to analysis. Additionally, significant challenges arise due to the propensity of precursor PFASs to transform into daughter compounds in the environment (e.g., do the laboratory results adequately account for the full mass of PFASs and the associ- ated potential risks, at the site?). Airport managers and operators should be aware of these limitations and identify laboratories that understand these challenges and have procedures in place to address them so that the analytical results are representative and reproducible. The following sections discuss • Commercially available analytical methods used for analyses of PFASs. • Key considerations associated with analyses of PFASs. • Laboratory accreditation for analyses of PFASs. • Promising analytical methods in development. 5.3.1 Commercially Available Analytical Methodology The commercially available analytical method for PFASs in drinking water is U.S. EPA Method 537: Determination of Selected Perfluorinated Alkyl Acids in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC-MS/MS), which analyzes a suite of 14 PFAAs (including PFOA and PFOS, shown in Table 5-1) following published N-ethyl perfluorooctane sulfonamido acetic acid N-Et-PFOSA- AcOH 2991-50-6 Y N N-methyl perfluorooctane sulfonamido acetic acid N-Me- PFOSA-AcOH 2355-31-9 Y N Perfluorobutanoic acid PFBA/PFBTA 375-22-4 N N Perfluoropentanoic acid PFPeA 2706-90-3 N N Perfluorohexanoic acid PFHxA 307-24-4 Y N Perfluoroheptanoic acid PFHpA 375-85-9 Y Y Perfluorooctanoic acid PFOA 335-67-1 Y Y Perfluorononanoic acid PFNA 375-95-1 Y Y Perfluorodecanoic acid PFDA 335-76-2 Y N Perfluoroundecanoic acid PFUnA 2058-94-8 Y N Perfluorododecanoic acid PFDoA 307-55-1 Y N Perfluorotetradecanoic acid PFTA 376-06-7 Y N Perfluorotridecanoic acid PFTrDA 72629-94-8 Y N Perfluorobutane sulfonic acid PFBS 375-73-5 Y Y Perfluorohexane sulfonic acid PFHxS 355-46-4 Y Y Perfluorooctane sulfonamide PFOSA 754-91-6 N N Perfluorooctane sulfonic acid PFOS 1763-23-1 Y Y Analyte Acronym Chemical Abstract Services Registry Number (CASRN) Included in US EPA 537 Rev. 1.1 Included in UCMR 3 Table 5-1. Common PFASs included in commercial laboratory analysis.

addressing Legacy environmental Impacts 53 methodology. Reporting limits for this methodology range from 0.005 to 0.020 µg/L, i.e., below U.S. EPA’s health advisory of 0.07 µg/L for PFOS and PFOA. A drawback to U.S. EPA Method 537 is that it includes a limited range of analytes; this method does not currently report the results for the full range of short-chain PFAAs, many fluorotelomers, or the many other precursor PFASs. Additionally, U.S. EPA Method 537 was developed for the analysis of PFASs in drinking water, which is a relatively clean matrix compared to groundwater and one which will have different extraction requirements than solid matrices (e.g., soil and sediment). In order to fully under- stand the potential extent of contamination by PFASs in the environment, additional laboratory techniques are being developed to increase the range of analytes for U.S. EPA Method 537 (and similar LC-MS/MS methods) to include up to 39 PFASs (i.e., Modified U.S. EPA Method 537). U.S. EPA Method 537 outlines areas where deviation from the prescribed procedure is allow- able and where the described methodology must be followed (e.g., sample collection and quality control requirements). U.S. EPA Method 537 also describes possible sources of interference and standards to be utilized. The International Organization for Standardization (ISO) has also developed a method to analyze PFASs based on the same basic principles as U.S. EPA Method 537. The ISO method developed for evaluating PFASs, specifically PFOS and PFOA in unfiltered samples, is ISO 25101:2009—Water Quality—Determination of Perfluorooctanesulfonate (PFOS) and Perfluo- rooctanoate (PFOA)—Method for Unfiltered Samples Using Solid Phase Extraction and Liquid Chromatography/Mass Spectrometry. Similar to U.S. EPA Method 537, ISO 25101:2009 uses solid phase extraction and solvent elution with analyte determination by LC-MS/MS. The focus of this methodology is linear isomers of PFOS and PFOA, but other isomers (i.e., branch isomers) can be reported separately as non-linear isomers. Further limitations to the ISO method include the following: • The ISO method may result in unrepresentative results as the materials used in the method may result in contamination of the sample being analyzed (e.g., seals, O-rings, and tubing), ultimately biasing the results high. Likewise results may indicate lower concentrations than what is in the sample due to sorption to glassware or filters (79). • Solid phase extraction methods generate significant amounts of liquid and solid waste, are laborious, and are predisposed to negative and positive artifacts (1). A standardized method has not yet been developed for extracting and analyzing PFASs in soils and sediments. Four methods for the extraction of PFASs from sediments have been described in the scientific literature: • A wrist-action shaker operated at maximum deflection, extraction by methanol, followed by a graphitized carbon adsorbent clean up (80). • An acetic acid wash, followed by repeated extraction with methanol/1 percent acetic acid in water (90:10, v/v) in a heated sonication bath and subsequent clean up using C18 cartridges (81). • Pressurized fluid extraction with acetone/methanol (25:75, v/v) at 100°C followed by head- space solid-phase microextraction (82). • Sonication with acetonitrile/water (60:40, v/v) and ion pairing clean up (83). Different extract clean-up methods can be used, either separately or in combination, depending on the characteristics of the sediment, the extraction solvent, and the concentration level. Commercial laboratories typically homogenize soil or sediment samples in water that is free of PFASs, conduct a liquid/liquid extraction, and analyze the extraction by isotope dilution LC-MS/MS. Extraction of PFASs from soil and sediment requires the use of a solvent. The resulting extraction liquid (i.e., eluent) is then homogenized by centrifugation prior to LC-MS/MS analysis, as would be done for an aqueous sample. The lack of an available standardized methodology for

54 Use and potential Impacts of aFFF Containing pFaSs at airports extracting and analyzing PFASs in soil reinforces the need to use a reliable, accredited analytical laboratory. The following sections describe key considerations in laboratory analysis for airports or site custodians when discussing an analytical program for PFASs with an analytical laboratory and what to look for in methodology and accreditation. 5.3.2 Key Considerations in Laboratory Analysis 5.3.2.1 Laboratory Standards Standard reference chemicals have not yet been developed for each of the PFASs in AFFF; therefore, identification, let alone quantitative analysis, is limited to the known and quantifiable PFASs in AFFF. Additionally, even with available reference standards, these results may vary according to the laboratory methods used. Some PFASs (such as PFOS) are observed in AFFF as a mixture of linear and branched isomers. Depending on the calibration method used by the analytical laboratory, there may be bias in instrumental responses between linear and branched PFOS isomers using LC-MS/MS analysis, which is discussed further below. It is important that a commercial laboratory is using suitable standard methodology to carry out analyses of PFASs. Where no suitable standard methodology exists (e.g., PFASs in soils/sediments), an accredited laboratory facility should be used (as discussed in Section 5.3.3). 5.3.2.2 Branched and Linear Isomers PFASs exist as both branched and linear isomers. Both versions, together, make up the total concentration of individual PFASs. This analytical concern has come to attention most recently for PFOS, but the problem exists for other PFASs, including PFOA. The analytical laboratory results should include data that addresses both “versions” so that the total concentration reported is representative. If the concentration of only one isomer is reported, the reported value may underrepresent actual concentrations in the field (and potential risk). Reference standards (other than mixed linear/branched standards) are available separately for linear PFOS and PFOA, but not for the branched isomers (84). This calibration is important to evaluating whether the total amount of PFOS reported is an accurate representation of a sample. If a laboratory is quantitating using linear standards, this may result in a systematic high bias for PFOS analysis on real samples containing any branched PFOS. This calibration concern is an issue that has been acknowledged by commercial laboratories competent in analysis of PFASs and underlies the need for selecting a reputable laboratory with the appropriate accreditations. Stable isotope dilution methods have been developed for analyzing PFASs and are an alternate to using standard calibration solutions that run into branched/linear isomer issues, as described above. Stable isotope dilution methods use relative ratios of natural to enriched isotopes to directly evaluate concentration of the target analyte, providing a more usable PFOS value. It is important to confirm that a commercial laboratory reports PFOS values that include both the branched and linear types. 5.3.2.3 Precursors Both past and current AFFF formulations contain “precursor compounds,” or parent com- pounds that can degrade to more persistent daughter products. Older formulations of AFFF contained long chains (e.g., C8 or greater), which could break down to PFOA and PFOS. Newer formations contain short-chain PFASs (e.g., C6 and below), which can still degrade to persistent daughter products (PFHxA and PFBA); however, these daughter products are thought to pose fewer ecotoxicological risks since the daughter products have lower potential for bioaccumulation

addressing Legacy environmental Impacts 55 than the long-chain compounds. A site investigation for PFOS without an analysis for precursor PFASs may not result in a fully representative CSM or accurate understanding of the potential risk posed by PFASs at an airport. Analysis for precursor PFASs is imperative to have a comprehensive understanding of the impact of PFASs. If a site has levels of PFOS and PFOA below the levels recommended by guidelines in the region, it is possible that precursor compounds could degrade to resilient and regulated PFOS and PFOA and cause an exceedance of the level recommended by guidelines and a human health or environmental ecotoxicological risk. While many precursors are not regulated at this time, airports should be aware of the potential future liability associated with these compounds, i.e., they may become future sources of PFOS or PFOA and/or potentially other (currently) regulated compounds or become regulated themselves. There is no commercially available method for precursor analyses; however, new, commercialized, standardized methods are in development as a response to regulatory drivers and the need to effectively meet new regulations. 5.3.2.4 Quality Assurance and Quality Control QA/QC programs come from the methodology being used (e.g., prescribed by U.S. EPA Method 537) and from overall laboratory accreditation (discussed further in Section 5.3.3). The laboratory-provided QA/QC information should be carefully reviewed due to the many potential contamination sources. Laboratory-provided information to review can include method and/or matrix interferences notes, recovery of internal and surrogate analyte standards used, adequate calibration, and laboratory duplicate/blank values meeting internal criteria. Other data to evaluate include laboratory-blinded field duplicate sample results, equipment blank results, and field blank results. Values should comply with the pre-ordained QA/QC program that meets the data quality objectives of the field sampling program. QA/QC flags should be reviewed with the commercial laboratory prior to accepting or rejecting the results. 5.3.3 Laboratory Accreditation In addition to conducting sample analysis for PFASs using standardized methods (where available and applicable), laboratories should be accredited for analyses of PFASs by a reputable accreditation agency. Accreditation implies that a laboratory has established the technical com- petence to perform specific types of testing and analysis and that their equipment and methods will provide results that are reliable, reproducible, and representative of actual concentrations. Laboratory accreditation is for the testing and calibration for laboratories to “ISO/IEC 17025— General requirements for the competence of testing and calibration laboratories,” which is a generic standard applicable to many different analyses. Accreditation/recognition for specialty analyses such as PFOA/PFOA is distinct from laboratory accreditation. It is recommended that an accredited analytical laboratory be used and that the analytical laboratory be contacted prior to sample submission to confirm that PFASs are included in their standard analysis and to confirm the sampling requirements. Accreditation bodies, methodologies, and laboratories are described for the United States and Canada in the following subsections. 5.3.3.1 United States of America In the United States, the following organizations provide accreditation for analyses of PFASs. Links are provided to their webpages, which list accredited laboratories and can be used to find an accredited laboratory across jurisdictions: • U.S. Department of Defense Environmental Laboratory Accreditation Program (DoD ELAP) (http://www.denix.osd.mil/edqw/Accreditation/AccreditedLabs.cfm)

56 Use and potential Impacts of aFFF Containing pFaSs at airports • American Association for Laboratory Accreditation (A2LA) (https://www.a2la.org/dirsearch new/newsearch.cfm) • Perry Johnson Laboratory Accreditation, Inc. (PJLA) (http://www.pjlabs.com/search- accredited-labs) • ANSI-ASQ National Accreditation Board (ANAB) (http://search.anab.org/search-accredited- companies.aspx) • Laboratory Accreditation Bureau (L-A-B) (http://search.l-a-b.com/) 5.3.3.2 Canada In Canada, methodologies to analyze PFASs are accredited under CAN-P-1585: Require- ments for the Accreditation of Environmental Testing Laboratories, Program Specialty Area— Environmental Testing (PSA-ET)—December 2008. The organizations listed below provide accreditation for analyses of PFASs. Links are provided to their webpages, which list accredited laboratories and can be used to find an accredited laboratory across jurisdictions: • Standards Council of Canada (SCC) (https://www.scc.ca/en/accreditation/product-process- and-service-certification/directory-of-accredited-clients) • Canadian Association for Laboratory Accreditation Inc. (CALA) (http://www.caladirectory.ca/) 5.3.4 Analytical Method Development As consumer needs and regulatory drivers change, industry continues to modify and develop analytical methods. Changes in laboratory methods have resulted in more PFASs being able to be analyzed (e.g., short-chain PFASs), lower detection limits (i.e., allowing lower concentrations of PFASs to be detected), and better management of potential biases in the analytical procedures (e.g., sample-ware and filter composition). The following sections discuss analytical methods that are under development in academic and research communities. 5.3.4.1 Total Organic Fluorine There are two methods in development for quantifying total organic fluorine (similar to using total petroleum hydrocarbon analysis). These methods are particle-induced gamma-ray emission (PIGE) and adsorbable organo-fluorine via combustion ion chromatography. These values over- come the analytical challenges posed by the limited availability of reference standards. Further, these methods enable airports and their environmental professionals to evaluate the extent of the impacts of PFASs at a site because organic fluorine is anthropogenic. At a site impacted by AFFF, this is likely to be related directly to the presence of AFFF. The limitation of these methods (similar to the limitation of total petroleum hydrocarbon analysis) is that specific compounds (such as PFOS) are not identified. The PIGE method is currently being commercially developed and is available in the United States, although it is not standardized by the U.S. EPA. 5.3.4.2 Increasing the Number of Identifiable PFASs Methods are in development to analyze a more comprehensive range of PFASs (79). Two promising methods include liquid chromatography/quadrupole time of flight/tandem mass spectrometry (LC-QTOF-MS/MS) and total oxidizable precursor (TOP) assay. LC-QTOF-MS/MS is a semi-quantitative method revealing the empirical formula of multiple PFASs by assessing the accurate mass of the molecular ions of PFASs (69). The TOP assay involves a reaction with hydroxyl radicals that reveals precursors with the potential to degrade into more stable fluorochemicals (e.g., PFAAs such as PFOS and PFOA). Concentrations before and after oxidation are compared to determine the concentrations of chain-length-specific PFAA precursors. The TOP assay

addressing Legacy environmental Impacts 57 approach quantifies the sum of PFASs that could be converted to PFAAs in the environment by simulating accelerated environmental degradation, with a slightly expanded range of PFSA and PFCAs quantified. Performing this analysis before and after the sample containing PFASs is partially digested reveals the “hidden mass” of PFAAs that were previously not detectable. The TOP methodology has revealed that for AFFF-impacted sites the existing analytical LC-MS/MS methods are only detecting some 30 percent of the total PFAA mass hidden in PFASs. The TOP assay is now commercially available in the UK, but is not yet commercially available in the United States or Canada. Commercial analytical methods are under development in Canada. 5.4 Risk Management For airports with a history of AFFF use (and the associated release to the environment of PFASs), potential human health and ecological risks may exist. Airports are challenged to understand whether they have an unacceptable risk and, if so, how to manage that risk. Risk management is employed when unacceptable risks are determined to be present via a human health or ecological risk assessment. Risk management integrates the site’s remedial strategy with technical, political, legal, social, and economic considerations to develop risk reduction and prevention strategies. Risk manage- ment effectively manages one or more of the three risk components (i.e., source/contaminants, receptors, and exposure pathways) alleviating or eliminating potential risks to human health and/or the environment. Generally, risk management consists of one or more of the following: • Administrative controls that limit access or exposure to potential contamination. • Engineering controls that render potential exposure pathways “inoperable” (or otherwise cuts off the pathway between contamination and receptors). • Remediation that removes or reduces the mass of contaminant at the site. The following sections describe how risk management approaches can be applied specifically to sites impacted by PFASs. 5.4.1 Defining Risk In order for a human health or ecological risk to be present, three conditions must be fulfilled (see Figure 5-1). There must be the following: • A source/contaminant: A chemical (or group of chemicals) found at a concentration that represents a potential concern to human health or the environment. Figure 5-1. Principles of risk model.

58 Use and potential Impacts of aFFF Containing pFaSs at airports • A receptor: A human or ecological receptor that would be exposed to the source. • An exposure pathway: At least one complete exposure pathway through which the receptor(s) would be exposed to the source/contaminant. As shown in the principles of risk model presented in Figure 5-1, risk management aims to remove one or more of these conditions, eliminating potential risk. As described in the following section, a conceptual site model (CSM) is developed to identify source, pathways, and receptors; better understand the relationship among these elements; and develop a risk management strategy. 5.4.2 Conceptual Site Model The CSM discussed here is a general representation of the nature and fate and transport of PFASs at an airport facility. A site-specific CSM should be developed as necessary to assess potential and/or actual exposure to PFASs and be reviewed to identify whether data gaps exist. Aligning with the risk model, the CSM consists of three main components: source/contamination, receptors, and pathways (i.e., exposure and migration). Figure 5-2 provides an example of a CSM for an airport, grapahically presenting sources, potential receptors, and exposure pathways. 5.4.2.1 Source/Contamination AFFF manufactured and imported into the United States and Canada prior to the voluntary phase-out in production in 2002 contained PFASs, including—predominantly—PFOS. While manufacturers have since modified their formulations to eliminate PFOS, AFFF formulations continue to include short-chain PFASs, the toxicological properties of which are not well known. Historical application of AFFF (i.e., via emergency response, testing, and training) to the envi- ronment (e.g., soil or surface water) and incidental releases (e.g., spills, leaks, and disposal), therefore, represent a potential source of contamination by PFASs. Specifically, potential sources of contamination by PFASs associated with AFFF may include the following: • AFFF storage areas (i.e., where the potential for leaks and spills existed). • Areas where AFFF was applied as part of an emergency response. • Firefighting training areas, burn pits, or other areas where AFFF may have been discharged as part of training. • Areas where AFFF was discharged as part of foam testing. • Areas where AFFF was loaded or removed from ARFF vehicles during vehicle maintenance. • Historical disposal areas (e.g., where expired or contaminated AFFF concentrate was disposed to the environment or where AFFF foam was directed following release, including lagoons and retention ponds). As indicated in Chapter 2 of this report, other sources of PFASs may be present at an airport or on adjacent property. Obtaining good quality information about the source/contamination should follow the best management practices for sampling and analysis of PFASs as described Sections 5.2 and 5.3. 5.4.2.2 Pathways For CSMs, pathways can be categorized as exposure pathways or migration pathways. As described previously, exposure pathways are how contamination moves through the envi- ronment from a source to a receptor. Migration pathways are how contamination moves off-site, independent of whether a receptor is present. Table 5-2 identifies exposure pathways and migration pathways for each type of environmental media (i.e., soil, groundwater, surface water, sediment, and air).

Figure 5-2. Sources, pathways, and receptors in airport firefighting.

60 Use and potential Impacts of aFFF Containing pFaSs at airports 5.4.2.3 Receptors Receptors can be either humans or ecological flora and fauna (i.e., plant and/or animal) that could be exposed to contamination. Receptors known to be potentially sensitive to PFASs include the following: • Fish • Birds • Terrestrial animals • Invertebrates • Humans (exposure to drinking water, dermal contact pathways, consumption of fish) Some PFASs are known to bioaccumulate and biomagnify in the food chain. This affects recep- tors at different points along the food chain, e.g., humans consuming fish. Field measurements of PFOS, PFOA, PFHxS, and PFOSA in the Great Lakes food web have suggested that precursors to PFASs metabolize to PFASs that have known ecotoxicological properties (e.g., PFOS, PFOA, PFHxS, PFOSA) (85). These results indicate that the risks to some receptors are difficult to quantity without knowledge about the precursors. Soil Human Health—dermal contact Yes Human Health—ingestion Yes Human Health—soil inhalation No Human Health—vapor inhalation pathway No Ecological Soil Contact Yes Ecological—nutrient and energy cycling Unknown Lateral Migration—surface runoff Yes Vertical Migration—infiltration/percolation Yes Groundwater Human Health—potable/drinking water Yes Human Health—agricultural use—irrigation Unknown Human Health—agricultural use—livestock Unknown Human Health Contact Yes Ecological—protection of aquatic life receptors Yes Lateral Migration—advective/diffusive transport Yes Surface Water Human Health—protection of aquatic life (fish ingestion) Yes Ecological—protection of aquatic life Yes Lateral Migration—advective/diffusive transport Yes Sediment Ecological—aquatic life receptors Yes Migration—sediment transport Yes Air Migration—long-range transport, atmospheric deposition Yes (on a global scale) Environmental Media Exposure Pathway Potential Risk Driver for PFASs? Table 5-2. Exposure and migration pathways for AFFF.

addressing Legacy environmental Impacts 61 5.4.3 Managing Risk Associated with the Impacts of PFASs The scientific and regulatory communities’ understanding of the chemistry, fate, transport, and toxicology of PFASs continues to evolve rapidly. In the midst of this changing regulatory climate, airports are currently challenged to understand what unacceptable risks may be pres- ent and what to do about these risks if they are present. Airports need to proactively manage the potential risks associated with current operations (i.e., with respect to AFFF management through the life cycle stages, as detailed in Chapter 4) while considering how best to address potential risks associated with legacy environmental impacts, understanding that historical use of AFFF at airports likely resulted in releases of PFASs to the environment. Risk management strategies for legacy impacts of PFASs in the environment need to consider the CSM, whether there is a current unacceptable risk, whether there is a potential for a future unacceptable risk, and how to eliminate unacceptable risk. Given the recalcitrant nature of some PFASs to remedia- tion, proactively cutting off the exposure pathway between contamination by PFASs and poten- tial receptors may provide a cost-effective means for managing unacceptable or, preemptively, potentially unacceptable risks, where permissible. Some examples are as follows: • Eliminating direct contact to soil impacted by PFASs and limiting infiltration (and potential groundwater migration) by covering a portion of the site with pavement. • Eliminating surface water runoff to prevent surface water from being impacted by sediment containing PFASs. • Requiring workers to don appropriate personal protective equipment (PPE) when working with AFFF or media impacted by PFASs. • Prohibiting potable groundwater or surface water use by providing an alternate water supply should a potable source be suspected of being impacted by PFASs. • Installation of erosion and sediment controls in areas where soils that may be impacted by PFASs are planned to be disturbed. If unacceptable risks cannot be managed by means of cutting off the exposure pathway, reme- diation may be required. Section 5.5 discusses remediation options that remove or reduce the mass of contamination by PFASs to acceptable levels as defined by regulatory standards. Finally, airports also need to consider and plan for the potential implications of contamina- tion by PFASs on capital projects. Should soil or groundwater impacted by PFASs be encoun- tered during construction of capital infrastructure projects, the cost to manage the impacted media could be significant and delays to the capital project could be substantial. 5.5 Remediation Options Remediation of PFASs in environmental media is required if unacceptable risks are present and cannot be appropriately managed without remediation. PFASs, however, have unique prop- erties that are problematic when environmental remediation is required. Those properties that have made many PFASs very useful in a wide range of commercial and industrial applications (e.g., high degrees of chemical and thermal stability) result in challenges relative to remediation. Many PFASs do not readily degrade in the environment (86) and are resistant to many forms of remediation. For example, a strong fluorine-carbon bond and low vapor pressure mean that some PFASs (e.g., PFOA and PFOS) are resistant to a number of conventional water treatment technologies, including direct oxidation, biodegradation, air stripping and vapor extraction, and direct photolysis (ultraviolet radiation). Additionally, PFASs in AFFF are a mixture of compounds, each with variable properties. Different remedial approaches will be successful at varying degrees with each compound and, like environmental remediation in general, a multitude of site-specific factors will greatly

62 Use and potential Impacts of aFFF Containing pFaSs at airports affect the effectiveness of any given remedial approach. Moreover, with PFASs, degradation of select precursors if present (or had been historically present) within AFFF can compound the issue by generating additional persistent PFASs (e.g., PFOA and PFOS). Finally, the selec- tion and ultimate effectiveness of remedial approaches may be significantly influenced by co-mingled contaminants as would be the case with the application of AFFF for extinguishing Class B fires. Given the challenges identified above, development of proven remedial technologies for PFASs has been elusive. Recent publications have discussed some bench-scale success with degradation or destruction using advanced oxidation (87), enhanced photochemical (88), and irradiation meth- ods (89); however, these technologies are often not practical for field-scale implementation (90). Traditional methods such as “excavation and disposal” and “pump and treat” have been success- fully applied in the field, but maintain the limitations that are typically associated with these meth- ods (and would likely be exasperated by the nature of some PFASs). With excavation and disposal, contamination is just being transferred to another site; with groundwater treatment via “pump and treat,” high costs of operation and maintenance are ongoing for long periods of time. Known available and emerging technologies are summarized in Table 5-3. Like remediation of other recalcitrant and persistent compounds, remediation of PFASs is not likely to be achieved with a single remedial technology; rather, a successful remedial strategy will likely consist of a combination of remedial approaches applied appropriately. Any treatment technology that uses oxidants may release more mobile forms of PFASs that will be subsequently more difficult to remove. Airport operators and their contractors should consider fully the limitations and implications of using degradatory technologies. Further, given that remediation technologies for PFASs are under development, a remediation strategy may involve short-term solutions (e.g., pump and treat or administrative measures) to address known unacceptable risks until appropriate remedial approaches have been developed. In order to develop appropriate approaches for successful remediation, consideration should be given to developing decision support models to support the choice of short- and long-term remediation strategies for PFASs at sites where AFFF has been applied or otherwise released into the environment (98). One such example decision tree, developed by Avinor, considers the following (98): • Which PFASs are present and their physicochemical properties. • Hydrogeological conditions. • Off-site and on-site risks at present and in the future. • Acceptable time frames for remediation. • Technology acceptance and stakeholder involvement. • Costs for remediation. • Acceptable disturbance of day–to-day operations. The following sections discuss the current state of practice of remedial technologies and approaches that have demonstrated some success (or are generally believed to hold promise) in field-scale remediation of PFASs in soil and groundwater. In addition, Section 5.5.3 identifies limitations that an airport should consider in the disposal of released AFFF and water impacted by AFFF. 5.5.1 Soil Soil remediation may be required if current concentrations of PFASs pose a potential risk to human and/or ecological health. Remediation may be required to limit contaminant migration (e.g., vertical infiltration to groundwater pathway) and/or remove the impacts from the site (e.g.,

addressing Legacy environmental Impacts 63 concentrations of PFASs in soil need to be brought into compliance with applicable guidelines and/or regulations). The following sections describe remediation methodologies that address impacts of PFASs in soil. 5.5.1.1 Excavation Excavation may be appropriate for removal of PFASs when the substances have not signifi- cantly migrated vertically and the objective is contaminant mass removal. Unfortunately, some of the more mobile PFASs can, depending on site conditions, migrate to depths that make excavation cost prohibitive. Upon excavation, there are two main options for disposal of soils impacted by PFASs: incineration and landfill disposal. Incineration Off-site, high-temperature incineration (> 1100°C) has proven to be a viable (yet expensive) method for destruction of PFASs. However, incineration facilities must limit the volume of soil So ur ce T re at m en t In-situ chemical oxidation Emerging Lab scale (ScisoR for PFOS/PFOA) (91) *It should be noted that this approach can generate short-chain PFASs that are more mobile and are difficult to remove by more traditional remediation approaches (e.g., granulated activated carbon) In-situ enhanced bioremediation N/A __ In-situ thermal N/A __ Stabilization Commercial Carbon and other commercially available additives (RemBindTM and MatCARETM) Soil Removal Commercial __ Gr ou nd w at er T re at m en t Sorptive media (granulated activated carbon) Commercial High-temperature thermal regeneration required to reuse carbon Sorption to carbon is low/ineffective for short- chain PFASs Sorptive media (synthetic media) Commercial Commercially available additives include RemBindTM and MatCareTM. PerfluorAd—coagulant (emerging) Sorptive media (ion exchange resin) Commercial Ion exchange media (92 , 93 ) Ultrafiltration Commercial Reverse osmosis and nanofiltration Sonochemical Emerging Investigated at the bench scale for landfill leachate and groundwater (94 , 95 ) Air stripping Commercial Spray stripper system as part of Pump and Treat for volatile organic compounds. Mobilized volatile PFASs (aerosols, volatilization), moved less volatile PFASs deeper within the soil column (96). Found to be ineffective in removing PFASs from landfill leachate adequately prior to land application (97) Remedy Status Technology Details Table 5-3. Summary of available and emerging technologies for PFASs.

64 Use and potential Impacts of aFFF Containing pFaSs at airports and groundwater impacted by PFASs that is introduced into their operations at a given time to avoid operational efficiency issues. This circumstance adds additional complexity to large-scale remediation projects for PFASs. Landfill Disposal Given the cost of incineration, off-site disposal at an appropriately engineered landfill may provide a more viable disposal alternative. An appropriate facility must be selected for the dis- posal of soils containing PFASs, since several PFASs (e.g., PFOS and PFOA) are water soluble and have limited biodegradation potential and, as a result, end up in landfill leachate (30). More- over, biodegradation of precursor PFASs will produce a number of persistent and toxic PFASs (e.g., PFOS and PFOA). Landfills must be designed to prevent migration of PFASs via land- fill leachate into the environment. This may require the leachate to be treated with advanced water treatment methods (29, 30). Airports disposing of soil impacted by PFASs should verify that the receiving facility is engineered with double liners and leachate collection systems and is appropriately certified to receive soil impacted by PFASs. Airports should also verify that the receiving wastewater treatment plant used to treat leachate is capable of treating PFASs, as many landfills send their leachate off-site for treatment (99). Transferring soils (and leachate) impacted by PFASs from a site to a facility that is not designed to contain PFASs (or manage the leachate) could be considered as simply relocating the problem, and, therefore, the best practice is to ensure that the receiving facility is appropriately designed to treat and handle soils impacted by PFASs. 5.5.1.2 Immobilization/Stabilization Adsorbents (also called sorbents) are materials that have an ability to adsorb substances, resulting in their immobilization and stabilization. Adsorbents that have the potential to treat PFOS and PFOA include organo-clays, clay minerals, and carbon nanotubes. Commercial sorbents containing activated carbon, aluminum hydroxide (amorphous), and other proprietary additives have been explored for their sorbent properties with PFASs. Bench-scale studies have shown that sorbent technology holds promise for field application; however, site-specific conditions would need to be evaluated in order to assess the applicability for implementation. At the field scale, use of amine-modified clay sorbents, as opposed to activated carbon, for treatment of sites impacted by PFASs (82, 83) has shown some promise. 5.5.2 Groundwater Numerous studies have evaluated the suitability of treatment technologies for PFASs in waste- water and drinking water. Unfortunately, these technologies are not always directly applicable to the treatment of contaminated groundwater in-situ. This section describes those technolo- gies that have demonstrated success in field-scale applications and should be considered for the remediation of groundwater and surface water impacted by PFASs, depending on site conditions and project objectives. 5.5.2.1 Pump and Treat Pump and treat is a common method for cleaning up groundwater impacts where groundwater is pumped from wells to an above-ground treatment facility that removes the contaminants prior to disposal or reuse. Because of the length of time required to “treat” the contaminant mass in groundwater, pump and treat remedial technologies should be viewed as “control” technologies, rather than source removal remedial technologies. Much of the current literature on the success- ful application of treatment technologies has been shown for water treatment plants. While the principles remain the same (e.g., inlet flow of PFASs in water, PFASs sorb to granulated activated

addressing Legacy environmental Impacts 65 carbon [GAC]/removed by membrane, “treated” effluent), the inlet concentrations, quantity of reactive media required, and time frame to treat groundwater impacted by PFASs may be very different. The following sections discuss pump and treat systems that have been applied for the remediation of PFASs in groundwater. Activated Carbon Pumping and ex-situ treatment of groundwater with activated carbon filters has proven to be viable and an appropriate treatment technology, although the efficiency of activated carbon filters has been observed to be variable (102). Use of activated carbon has also been shown to be less effective at removing short-chain PFASs (65, 66), which must be considered given the overall uncertainty associated with the ecotoxicity, synergistic effects, and environmental fate and transport of PFASs. Activated carbon is commonly used to adsorb contaminants found in water. Activated carbon, which is used in a granulated or powdered form, is an effective adsor- bent because it is highly porous and provides a large surface area on which contaminants may adsorb. Several case studies have indicated that GAC is a common and effective (>90 percent removal) treatment for contamination with long-chain PFASs. However, short-chain PFASs have been observed to break through. The efficiency of this method varies based on several factors: • Target effluent contaminant concentration • pH • Water temperature • Contact time • Properties of the selected carbon • Concentration of inorganic substances in the water • Ambient natural organic matter • Chlorine concentrations in the water Dudley et al. (103) evaluated powdered activated carbon (PAC) and found that >90 percent removal of PFNA and PFOS was possible but only with unreasonably high adsorbent dosages, unless contact times could be extended to approach adsorption equilibrium. Use of PAC has also been shown to be less effective at removing short-chain PFASs. Modified sorbents other than activated carbon (e.g., amine-treated clays) have also been evaluated at the bench-scale for applications to groundwater. Coagulation and Activated Carbon Coagulation-flocculation is a chemical water treatment technique typically applied prior to sedimentation and filtration (e.g., rapid sand filtration) to enhance the ability of a treatment process to remove particles prior to subsequent polishing treatments, such as PAC or GAC. The coagulation process works with chemicals that exhibit a charge (zwitterionic, cationic, and/or anionic), such as PFASs. A recent study found that a combination of coagulation and adsorption by PAC was effective (>90 percent removal) at removing both PFOS and PFOA from water (104). Coagulation alone is not an effective means of removal for long-chain PFASs (e.g., PFNA, PFOS and PFOA) (65, 105). Removal of PFOS and PFOA by coagulation works by adsorption of the contaminants onto the surface of the coagulants; anions absorb onto the positive surface of coagulants and flocs and are then removed with sedimentation and filtration. Subsequent to coagulation-flocculation treatments, PAC was shown to have a significantly higher absorption rate and capacity than GAC and higher absorption efficiency for PFOA than PFOS (104). The removal ratios for PAC increased with decreasing pH and with increasing coagulant dose, which was consistent with other research results evaluating pH on PAC efficacy for removal of PFASs (103).

66 Use and potential Impacts of aFFF Containing pFaSs at airports Ion Exchange Resin Ion exchange (IX) involves the use of resins (i.e., very small plastic porous beads with a fixed charge) to exchange undesirable ions with hydrogen or hydroxyl. The removal rate is dependent upon a number of factors: • Initial contaminant concentration • Competing ion concentration • Treatment design (e.g., flow rate, resin bead size) • Resin ion properties One significant advantage of IX over activated carbon is that IX resins can be regenerated and reused, whereas activated carbon is difficult to regenerate and is typically discarded after a single use. IX resins, specifically anion exchange treatments, have been investigated in pilot studies for application in pump and treat systems for removing PFASs. The removal of PFOA and PFOS has been reported at a New Jersey drinking water treatment plant using porous anion exchange resin impregnated with iron oxide (105). Researchers have noted that the short-chain PFASs were not removed through the documented IX treatment processes (65). A possible alternative for removal of PFASs could be a hybrid adsorption/anion exchange treatment approach, in which more strongly adsorbing PFASs are initially removed by activated carbon and the more weakly adsorbing PFASs subsequently removed by anion exchange. The hybrid approach may facilitate resin regeneration, which is more readily accomplished if only PFASs that interact more weakly with the resin need to be removed. The management of the spent resin (e.g., incineration, landfill, and regeneration) and of the brine (e.g., chemical/biological processes or disposal) must be considered with this technology. Membranes (Reverse Osmosis, Nanofiltration) Reverse osmosis (RO) can remove many types of molecules and ions from solutions and is used in both industrial processes and the production of potable water. RO systems have been used for the treatment of PFASs in drinking water. The solute (a compound of PFASs) is retained on the pressurized side of the membrane, and the pure solvent (water) passes through to the other side. Pretreatment is required prior to implementing an RO system to reduce membrane fouling (biological, chemical, and/or physical). RO is effective at remov- ing both long and short-chain compounds, filtering out both precursor materials and short- chain by-products. Nanofiltration is another form of membrane technology that is pressure-driven and has been shown to be effective in removing PFASs in water treatment systems (106). The method is easy to operate and reliable for pollutant removal. High PFOS removal rates have been observed in nanofiltration systems. RO is thought to provide more desirable performance than nanofiltration. Both systems result in reject water (20 to 25 percent), which must be managed properly to avoid further contamination of surrounding water and ensure compliance with applicable regulations. Additional waste to be considered is membrane disposal. Given anticipated low total dissolved solids in groundwater, the cost of RO systems may be reasonable for groundwater systems. Low-pressure RO could be applied (operating at <250 psi) for treatment. The use of centralized reject processing/management facilities to serve several local satellite water treatment plants could be considered to minimize capital and operating costs. RO and nanofiltration treatment systems have not yet been implemented at the field scale for remediation of groundwater contaminated by PFASs.

addressing Legacy environmental Impacts 67 5.5.2.2 Permeable Reactive Barrier Permeable reactive barriers (PRBs), which essentially are vertical walls (or trenches) created below ground to clean up contaminated groundwater, have been investigated for use in treating groundwater impacted by PFASs. The wall is “permeable,” which means that groundwater can flow through it. As the water flows through the wall, the water reacts with the material in the wall and is thereby treated. Concerns with GAC and other reactive media for use in PRBs mirror those mentioned above for pump and treat systems. Concerns with observed breakthrough in column experiments (41, 107, 108) have slowed application of PRBs in the field for groundwater impacted by PFASs. 5.5.3 Disposal of Discharged Foam AFFF containing PFASs that is released (e.g., from incidents, training, and foam tests) requires treatment and should be captured and disposed of carefully. Municipal wastewater treatment systems that receive captured AFFF/AFFF wastewater may not have the appropriate, advanced methods to treat some of the PFASs that would likely be present. Pretreatment (with a viable technology applicable for PFASs in aqueous solutions, as identified in Section 5.5.2) may be required for acceptance at a wastewater treatment facility.