Read "PFAS Management at Airports: A Guide" at NAP.edu (2024)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

5 Assessment of Historical and Current Product Use and ActivitiesPFAS are a complex group of man-made chemicals widely manufactured since the 1940s (EPA 2021i). PFAS, as a group, are fluorinated carbon chain molecules with polar and nonpolar ends, which give PFAS-containing prod-ucts beneficial properties such as performance resiliency under extreme heat, cold, and vacuum or pressure as well as stain resistance and water repellence. This chapter’s overall goal is to assist airport operators in understanding the historical and current conditions relevant to AFFF use; nonaviation activities involving PFAS both on- and off-site; and PFAS migration mechanisms and pathways to potential sensitive receptors.2.1 PFAS Properties OverviewWhile it is estimated that there are more than 4,700 individual PFAS com-pounds, these compounds tend to have similar structures and perform as surfactants for a wide variety of uses. This section describes the basic chemical structure and properties of PFAS compounds and then describes how these properties contribute to AFFF’s overall effectiveness in combating aviation fuel fires.2.1.1 Basic PFAS Structure and CharacteristicsWhile PFAS include compounds from many distinct chemical classes containing various functional groups, they also display common traits such as having both hydrophilic, or polar, and hydrophobic, or nonpolar components. The hydrophilic and hydrophobic components create the capacity for PFAS to form micelles. Micelle formation is the critical element that creates the surfactant behavior of many PFAS-containing products, including the function of AFFF. Conversely, many of the challenges associated with developing a fluorine-free foam (F3) alternative product that performs with the same efficacy as AFFF derive from the difficulty in replicating the micellar surfactant properties without using fluorine or other halogens. The properties and function of AFFF relative to micelle formation are examined in the next section.Hydrophilic compounds, such as table salt, mix with or dissolve in water. Hydrophobic compounds, such as oil, are immiscible in, or fail to mix with, water. Similarly, polar compounds dissolve in other polar solutions, such as water, acids, or bases, while nonpolar compounds dissolve in nonpolar sub-stances, such as petroleum products or other organic compounds. PFAS are C H A P T E R 2ChapterÂ2 Topics• Overview of PFAS characteristics• Aviation and nonaviation activities involving products containing PFAS• How to investigate historical AFFF use, storage, and handling practices• PFAS behavior in the environment, including transformational processes and migration pathwaysFor Your Information• F3 transition planning is discussed in Section 3.3.4.• Regulatory progress toward F3 product authorization is covered in Section 3.3.4.1.

6 PFAS Management at Airports: A GuideToolkit on Assessing Current and Historical Product Use and ActivitiesAppendixÂA provides the following supporting materials that provide a starting point for assessing sources and determining exposure assessment strategies and controls for PFAS: AppendixÂA is available on the National Academies Press website (nap.nationalacademies.org) by searching for ACRP Research Report 262: PFAS Management at Airports: A Guide and looking under “Resources.”Tool 2.1: Guide to PFAS Fate and Transport in Subsurface EnvironmentsSummary of factors affecting PFAS fate and transport in subsurface environments.Tool 2.2: Guide to PFAS Fate and Transport in Surface and Groundwater EnvironmentsSummary of factors affecting PFAS fate and transport in surface and groundwater environments.Tool 2.3: Guide to PFAS Fate and Transport in AirSummary of factors affecting PFAS fate and transport in air.Tool 2.4: Tutorial for Conducting a Baseline Analysis• Step-by-step guide for finding airport-specific information and locating potential receptors.• Provides links to helpful government websites and shows how data can be accessed and utilized for a baseline review.Tool 2.5: Tutorial for Assessing Off-Site Source Areas• Step-by-step guide to assist with identifying historical and current industrial and commercial facilities near an airport.• Provides links to helpful government websites and shows how data can be accessed and utilized for assessing potential off-site sources or activities.Tool 2.6: Considerations for Selecting a Method of PFAS TestingChecklist for determining the appropriate laboratory analytical testing method on the basis of the environmental media containing the sample and the anticipated or predicted PFAS compounds.Tool 2.7: Tutorial for Conducting an AFFF Exposure Study• Step-by-step tutorial for assessing current and former AFFF use on-site.• Provides example interview questions for ARFF and airport staff about use, storage, disposal, and other facilities that use AFFF.

Assessment of Historical and Current Product Use and Activities 7 also known to display oleophobic (oil-repelling) and oleophilic (oil-mixing) properties. There-fore, PFAS fluorocarbon chains perform exceptionally well as either water-active or oil-active surfactants and therefore are highly effective in extinguishing Class B petroleum fires. However, these properties contribute to the ability of certain PFAS compounds to migrate through envi-ronmental media and persist in the environment for long periods of time.In their most basic form, PFAS are composed of a fluorinated carbon tail and a nonfluorinated head (FigureÂ2-1). The fluorinated carbon chain tail can be various lengths and have a linear or branched structure, depending on the compound. This tail also repels water and has affinity for organic matter and nonpolar compounds. The nonfluorinated head is hydrophilic, and often consists of a polar, water-soluble functional group that can interact with electrically charged, or ionized, particles, such as those found in some soils.PFAS may contain either negatively charged (anionic), or positively charged (cationic) polar groups. Anionic and cationic PFAS exhibit unique properties that reflect their utility in con-sumer end products. For example, anionic fluorinated surfactants are commonly used in metal plating, ultraviolet (UV) light–resistant coatings, and inks, while cationic fluorosurfactants are widely utilized in cleaning products and cosmetics. In addition, both groups have been used in AFFF formulations (Buck etÂal. 2012).Zwitterionic PFAS contain both negatively charged and positively charged polar groups in their molecular structures, and amphoteric PFAS can act as either an acid or a base, depending on the chemical mixture in which they are used. The hydrophilic and hydrophobic components of PFAS allows them to be highly effective surfactants that are used to lower the surface tension between two liquids, a gas and a liquid, or a liquid and a solid. The unique surfactant behavior of PFAS has key implications for their environmental fate and transport, which are discussed in greater detail in SectionÂ2.5.2.1.2 PFAS and Surfactant BehaviorSurfactant molecules dispersed in a liquid—for example, molecules of PFAS in water—can aggregate together to form a colloidal suspension. In this colloidal suspension, the hydrophilic heads, which are polar, or water soluble, interact with the water in the solution. The hydro-phobic tails, which are nonpolar, or water repelling, interact with each other. That is, the tails stick together. As a result, the PFAS micelle typically results in a spherical shape, like a soap bubble, with the hydrophilic heads forming the outside of the sphere in direct contact with the water in the solution. The hydrophobic tails, which are repelled by the water in solution, point in toward the center of the bubble, as shown in FigureÂ2-2. The outside of the micelle is soluble in water, but when it encounters oils or dirt, the nonpolar tails of the micelle bind to the oil or Toolkit TipTools 2.1, 2.2, and 2.3 also provide guides for assessing PFAS fate and transport in the environment.Figure 2-1. Example of PFAS structure showing fluorinated and nonfluorinated regions.

8 PFAS Management at Airports: A Guidedirt and encapsulate it within the micelle. A mixture or solution may form micelles when PFAS are present in sufficiently high concentrations, and the micelles are what gives the solution its foam-forming properties.The critical micelle concentration (CMC) is the concentration of PFAS in a solution in which the chemical creates a visible, separate phase liquid or film that floats on and completely coats the water or solution’s surface. The addition of PFAS changes the surface tension of the water or solution, especially if enough is added to achieve a CMC. Once the CMC has been reached, PFAS quantities added above the CMC threshold convert into micelles but have little to no effect on the surface tension of the solution. That is, PFAS form a film or sheet across the water surface until the surface is completely covered and the CMC is reached, at which point any further addition of PFAS forms micelles with the bubble shape.The competing tendencies of PFAS hydrophobic and hydrophilic components typically lead to uneven environmental distribution, with high accumulation at interfaces, such as soil and water, air and water, or water and nonaqueous phase liquid (NAPL) within the source areas (Guelfo and Higgins 2013, McKenzie etÂal. 2016, Brusseau 2018). Due to their surfactant behavior and tendency to accumulate at interfaces, the vertical migration of PFAS released in subsurface environments may be significantly delayed, and PFAS may persist within source areas and in subsurface environments for decades. In most cases, PFAS will partition to the interface, trans-form into precursors, and migrate via biotic and abiotic processes. A more-detailed discussion of how PFAS may be transported through a variety of environmental media is provided in Section 2.5.2.2 Aviation ActivitiesMany formulations of PFAS, including some PFAS in AFFF products, are listed as proprietary or were historically considered inert ingredients, and therefore are often not listed in product Safety Data Sheets (SDSs). While other products and applications have been identified as potentially containing at least one PFAS compound, the research conducted to develop this guide determined that AFFF remains the primary concern for airports. The following discussion generally summarizes where and how AFFF is more commonly used or stored in an airport setting. For the purposes of this section, aviation activities refers to aircraft rescue and firefighting (ARFF) facilities and activities, structures that use fixed AFFF fire suppression systems, and military joint-use facilities on or adjacent to the airport property.Figure 2-2. Conceptual drawing of PFAS micelle structure.

Assessment of Historical and Current Product Use and Activities 9 2.2.1 ARFF Activities and VehiclesARFF facilities store AFFF, and ARFF crews train with and use AFFF. AFFF can be released to the environment under various scenarios. It may be accidentally released during delivery, transfer, or storage. It can also be deployed intentionally for training, testing, operational require-ments, or emergency response. ARFF staff are no longer required to flow foam during training exercises or for maintenance purposes or equipment testing, due to the approval of no-flow equipment. However, past required AFFF deployment may have resulted in PFAS-exposed materials and media (FAA 2021a, 117th Congress of the United States of America 2019).As F3 products become more readily available, operators will transition ARFF vehicles from AFFF to F3. Processes and procedures for transitioning are not yet defined, nor are requirements associated with AFFF residuals established. FAA’s latest guidance on F3 and related information is available on its web page “Fluorine-Free Foam (F3) Transition for Aircraft Firefighting” (FAA n.d.-c).2.2.2 Fixed AFFF SystemsHangars, bulk fuel storage facilities, and multilevel quick turnaround rental car facilities may use a fixed AFFF system for fire suppression. Historical testing of systems, accidental releases, or fires may have resulted in the discharge of AFFF from the fire suppression system. Releases may have historically been directed to sanitary sewer systems, but, in some cases, AFFF could be released to the environment. Additionally, if the fire suppression systems are upgraded or replaced, inclusion of procedures for characterization and proper disposal of AFFF-containing materials and equipment may be considered.2.2.2.1 Hangar Fire Suppression SystemsHigh-expansion foam (HEF) and AFFF are the two main types of foam used in hangar fire suppression systems, but only AFFF contains PFAS. While HEF does not contain PFAS, typical HEF installations require hose lines for manual fire-extinguishing systems, which may utilize AFFF. HEF systems use foam generators to entrain air into foam and water solutions. The HEF generators have expansion ratios typically in the range of 100:1 to 1000:1 which creates a foam resembling foamy shaving cream that spreads as it levels out. While HEF systems generally only discharge quantities to the minimum foam depth necessary to extinguish a fire, these depths are generally measured in terms of feet rather than inches. However, HEF does not produce significant amounts of liquid runoff. On the other hand, AFFF produces a thin film layer of foam, typically only a few inches thick. Different AFFF delivery systems produce different foam thicknesses based on the agitation of the foam and water solution. As a result, AFFF discharges are mostly liquid and generate significant volumes of liquid runoff.The most common elements of hangar foam fire suppression systems are foam concentrate storage tanks. Most tanks are either vertical or horizontal bladder tanks, often painted red, typically ranging from 500 to 1,500 gallons in size, although similarly sized atmospheric storage tanks may also be used with foam concentrate pump systems (FigureÂ2-3).HEF systems use foam generators, which are located at the roof level of the hangar, and each foam generator can cover several thousand square feet of floor area. Many older systems have outside air ducted from roof vents, and may also have many louvers to relieve the pressure from the outside air. Older systems typically have two tanks—one primary and one reserve. HEF sys-tems may also have a smaller AFFF concentrate tank, typically less than 100 gallons, for supply-ing hand lines. Some hose stations will have integral tanks at each station instead of a centralized foam and water distribution system.

10 PFAS Management at Airports: A GuideMultiple discharge devices are used for AFFF deployment in hangars. The most common method delivers AFFF through standard sprinklers, although sprinklers are typically present with all foam systems, whether delivering AFFF solutions or providing overhead protection for other AFFF or HEF systems. Foam monitor nozzles are also used to deliver foam, and monitor nozzles are required in larger hangars for underwing protection. Specially designed trench drain nozzles are another method that distributes foam at the floor level.2.2.2.2 Inadvertent Discharges from Suppression SystemsFire protection regulatory codes and suppression system designs focus on the system’s reli-ability and verifying that the systems will function as designed during a fire event. While AFFF is a proven firefighting medium that offers significant advantages, potential releases of AFFF during inadvertent discharges may be a challenge. Both the type of AFFF delivery method and type of fire detection system can affect the potential for false system activation and inadvertent discharges.Closed-Head Sprinkler Systems. Closed-head foam and water sprinkler systems are the simplest, and these utilize the same basic type of sprinklers used in commercial and residential applications. Each individual sprinkler has a fusible link or glass bulb that activates only the associated individual sprinkler head when heated. Closed-head sprinklers are used in hangars where the link or bulb is intact. Sprinklers rarely have inadvertent activations, so most leaks involve some form of physical damage to the sprinklers or piping. Closed systems refer to the following three main types of sprinkler systems:• Wet-pipe systems are the most common and deliver foam or water within seconds of sprinkler activation.• Dry-pipe systems are installed when hangars may be subject to freezing. They use pressurized air to keep valves closed. – Sprinkler activation releases the air pressure, which opens the valve and allows foam or water to flow through activated sprinklers. – A time delay results from the delay in pressure drop and the delivery time to flow water to an activated sprinkler, thereby requiring calculation for a larger discharge area. These systems typically have larger pipe sizes.Figure 2-3. AFFF fire suppression system with AFFF concentrate storage tank.

Assessment of Historical and Current Product Use and Activities 11 • Preaction systems eliminate the delay in water delivery time by using detection systems that open valves and charge pipes with water before the sprinkler activates. The size of the pipes in preaction systems are generally the same as those in wet-pipe systems,While closed-head foam and water systems are the most reliable for avoiding inadvertent discharges, they are limited by fire codes to Class II and Class III hangars, which are less than 40,000 square feet (ft2) and are only used for AFFF. Hose valve stations used for manual firefighting are typically activated by manually opening a valve; thus, the risk of inadvertent discharge is relatively low.Deluge Systems. Larger hangars require foam to be discharged simultaneously over large areas of the hangar and may require foam to be discharged over the entire hangar surface area. To meet this need, large hangars often use deluge systems. Deluge system discharge devices are opened, and a deluge valve activates to flow the foam and water solution through all discharge devices downstream of each valve. Discharge devices include open sprinklers, which are sprinklers with the fusible link or glass bulb removed. Other discharge devices include monitor nozzles, trench drain nozzles, and HEF generators.Detection Systems. The detection system is the primary source for inadvertent AFFF discharges from deluge systems. The numerous types of detection systems utilized in hangars are based on three main categories: heat detection, smoke detection, and flame detection. These systems have different advantages and disadvantages regarding reaction time and the potential for false activation. False activation may not necessarily imply malfunctioning equipment, as it also includes activation from nonfire conditions that the detector picks up as a fire scenario. For example, a flame detector may activate because of a gas grill located outside of the facility. While the detector is accurately detecting an actual fire condition, this scenario does not warrant foam system activation.Heat detection systems often have slower response times than smoke or flame detection systems but are less likely to have false activations. Hangar fire codes do not usually dictate the type of detection system that must be used, so these are normally chosen by the owner and system’s design engineer.2.2.3 Tenant FacilitiesTenants may operate facilities with AFFF fixed fire suppression systems, and these may include some or all of the types of systems and associated fire detectors discussed in the previous section. Tenants may also conduct industrial activities involving PFAS-containing chemicals that are not necessarily aviation related. Lease agreements often provide tenants with a degree of autonomy and privacy, and airport tenants are typically responsible for their handling and storage of chemicals and fire suppression systems within their leasehold. For these reasons, coordination and collaboration with tenants is important to understand the potential for chemical use, storage, and disposal.2.2.4 Joint-Use Military FacilitiesFAA defines the term “joint-use airport” as an airport owned by the Department of Defense (DoD) at which both military and civilian aircraft make shared use of the airfield. Airports may also have DoD entities as tenants with shared roles (ARFF, airport traffic control towers, airfield operations). Joint-use facilities with military operations may use AFFF in either fixed fire suppression systems or during ARFF-related activities. DoD has been investigating facili-ties around the United States, including shared commercial airports, for releases of PFAS to the Fuel farms and fuel storage facilities may use AFFF fire suppression systems, and these facilities may store AFFF concentrates on-site.

12 PFAS Management at Airports: A Guideenvironment and potential contamination of soils, groundwater, surface water, or sediments. Airports should coordinate with DoD personnel about the fate and transport of PFAS nearby or on airport property and seek to understand the potential for adverse effects on airport opera-tions or property.2.3 Off-Airport ActivitiesAirport operators may want to understand off-airport activities involving PFAS in the vicinity of their airports, even though these activities are not directly related to airport operations. Airport operators should be aware of adjacent land uses and their potential for releasing PFAS to the environment. Although the following discussion does not address every activity, industry, or scenario in which PFAS environmental exposure could occur adjacent to an airport, it does identify potential activities that could affect an airport, depending on setting.2.3.1 Solid Waste Management FacilitiesProducts in landfills that could contain PFAS include cosmetics, food packaging and containers, cleaning products, paints or sealants, waterproof apparel, coated paper products, pharmaceuticals, and other products containing fluorinated surfactants (Glüge etÂal. 2020).Airport operators may want to determine their proximity to nearby landfills and, if appli-cable, assess the probability of PFAS migrating onto airport property should landfill leachate escape containment. Federal regulations impose statutory limitations on the construction of new landfills within 5Âmiles of a public airport; however, these restrictions were not applicable before AprilÂ5, 2000 (FAA 2006). Some states, such as North Carolina and Texas, host websites with geographic information systems (GIS)-enabled tools that show landfill locations (TCEQ 2022, NCDEQ 2022), but identifying closed and capped former landfills may be more challeng-ing. While redevel opment of appropriately closed and capped landfills is a commonly accepted land reuse procedure, the widespread use of PFAS in consumer products means these sites may be introducing PFAS to surround-ing environmental media if leachate containment was insufficient or has been compromised.2.3.2 Industrial FacilitiesIndustrial activities that may involve PFAS-containing products include aerospace; building and construction; dry cleaning; pharmaceuticals; plas-tics production; printing and inks; tanneries; textiles manufacturing; metals fabrication and electroplating; electronics fabrication; chemical manufac-turing of products such as soaps and cleaning products, paints and sealants, cosmetics, and treated paper products; and many others (Glüge etÂal. 2020). Many airports across the United States are contained within a commercial or industrial district, which may include manufacturing plants, factories, and other heavy industrial activity. These facilities may process, produce, or use PFAS-containing chemicals, and releases to the air, stormwater systems, or groundwater may have occurred through normal operations. Depending on the location and geophysical conditions in the area, migration to airport property could occur.Common off-site source areas of PFAS are landfill sites, industrial sites, fueling facilities, wastewater treat-ment plants, groundwater recharge and injection wells, and agricultural fields.For Your InformationNonaviation industrial PFAS activities include• Aerospace• Building and construction• Dry cleaning• Pharmaceuticals manufacturing• Plastics production• Printing and inks• Tanneries• Textiles manufacturing• Metals fabrication and electroplating• Electronics fabrication• Chemical manufacturing of products such as soaps and cleaning products• Paints and sealants• Cosmetics• Treated paper products• Enhanced oil and gas recovery with fracking

Assessment of Historical and Current Product Use and Activities 13 2.3.3 Oil and Gas Exploration and Refining FacilitiesFluorosurfactants have applications in the oil and gas industry, and petroleum extraction, transmission, or refining facilities near the airport may be off-site sources of PFAS migration onto airport property. Fluorosurfactants, including PFAS surfactants, are used for pipeline and other gas transportation clearing, condensate unloading, hydrocarbon removal, and paraffin solubilizing (Glüge etÂal. 2020). They can also function as a hydrocarbon foaming agent, which has a comparatively lesser density and aides in bringing condensate to the surface in gas wells with low gas rates (Buck etÂal. 2012). Fluorosurfactants can also increase the tension between the hydrocarbon and salt solution interface, which is effective for desalting and demulsifying applications (ICT 2021). PFAS and petroleum hydrocarbon fuels in the form of NAPLs may commingle at locations where fuels were used or disposed of (Brusseau 2018).2.3.4 Wastewater Treatment Plants, Biosolids Applications, and Septic SystemsIf there are wastewater treatment plants nearby, airport operators should consider whether PFAS have a reasonable probability of migrating onto airport property from affected environmental media such as soils, storm-water, or groundwater. PFAS may not be destroyed or removed by current municipal wastewater treatment methods for effluent or sludge, which means these chemicals may be conveyed to other areas in biosolids generated from the water treatment process (Sepulvado etÂal. 2011, Venkatesan and Halden 2013). Biosolids may be applied directly to land as fertilizers or allowed to reincorporate into soils through biodegradation. Biosolids containing PFAS can contaminate environmental media if they are applied directly to soils, or if, when dry, they become airborne as dust and deposit on other nearby properties. Septic systems are used to treat wastewater on-site. If septic systems are located on or near the airport property, PFAS derived from consumer products or industrial facilities could be introduced to the environment. Streams that receive wastewater treatment discharges may be adversely affected by PFAS.2.3.5 Groundwater RechargeDry wells are underground structures that may be used to artificially recharge groundwater supplies (USGS 2019). Often, surface water runoff, stormwater, and greywater are channeled into these wells, where the water moves underground. The porous-walled chambers allow the water to gradually infiltrate into the soil and recharge groundwater supply volumes. Surface water or stormwater affected by PFAS can contaminate aquifers or potable groundwater supplies. Groundwater near an airport property could then be affected by these adjacent land uses.2.3.6 Agricultural AreasPesticides, fungicides, and herbicides that contain PFAS may be applied to agricultural areas on properties adjacent to the airport and could then migrate onto airport property through aerial deposition by dust or overspray, surface water or stormwater flows, or groundwater trans-port (Ogawa etÂal. 2020, OECD 2013, Glüge etÂal. 2020). Fluorinated chemicals can be found in pyrethroid control products and pesticides used to control mosquitoes, termites, wasps, and other agricultural pests (OECD 2013, BCPC 2021). Several fungicides containing fluorinated Toolkit TipTool 2.5: Tutorial for Assessing Off-Site Source Areas• Step-by-step guide for deter-mining historical and current industrial and commercial facilities near airport properties.• Provides links to helpful government websites.• Shows how to access and utilize data for assessing potential off-site sources of PFAS.

14 PFAS Management at Airports: A Guidefunctional groups may also be applied to ornamental or landscape vegeta-tion. Many PFAS-containing commercially available herbicides may be used for controlling noxious weeds and landscaping. Pesticides, fungicides, and herbicides may be applied as emulsions by sprays, broadcast as dissolving pellets over soils, or as coatings or safeners on grass seed. One study assessed 10 insecticide formulations used in the United States and found perfluoro-octane sulfonic acid (PFOS) in six of the products in concentrations ranging from 3.92 to 19.2 milligrams per kilogram (mg/kg) [3,920,000 to 19,200,000 parts per trillion (ppt)] (Lasee etÂal. 2022, PEER 2022).In 2022, EPA announced a proposal to remove 12 PFAS chemicals from the current list of inert ingredients approved for use in pesticide products (EPA 2022g). Removal from the inert ingredients list would restrict the use of these chemicals in pesticide products in the future, if a request was made by a manufacturer.2.4 Assessing the Presence of PFAS and Associated ActivitiesThis section summarizes an approach to gathering information and understanding how AFFF-related activities and off-site activities may affect an airport’s environmental condition.2.4.1 Establish a BaselineA baseline analysis of past and present on-site AFFF activities and other potential off-site sources of PFAS will help an airport operator understand, plan, and mitigate possible adverse effects to ongoing operations or development activities. Airport operators should direct atten-tion to former and current firefighting training areas as well as any release sites or disposal areas of PFAS-affected soil. Records reviews and desktop analyses can provide a guide for future site assessments by indicating locations of possible contamination and factors that may warrant fur-ther verification studies.2.4.1.1 Records ReviewThe first step in establishing a baseline is to review available records. A records review may find evidence about historical releases, including what was released, where, the duration, whether or how it was contained or remediated, where any waste materials were placed, and any other rel-evant information. Purchase orders; ARFF operational records, including emergency events and training; documentation of construction activity; equipment inspection sheets; spill documentation; disposal records; and chain-of-custody documentation are examples of possible information sources for conducting a baseline analysis of AFFF use. Airport personnel who have worked on-site for a long time may offer insight on finding infor-mation on emergency events, ARFF training, or other activities in which AFFF may have been used. While anecdotal evidence will need to be substantiated by a records review or other assessment method, senior personnel can help start a project by sharing their institutional knowledge.Purchase Orders. In the past, market alternatives to traditional AFFF concentrate formula-tions with long-chain PFAS surfactant additives were limited to short-chain PFAS formulations that met MIL-SPEC criteria and were approved in the Qualified Products Database (QPD) For Your Information• Consider reviewing SDS documentation for pesticides, fungicides, and herbicides routinely used on airport property.• A desktop evaluation would show adjacent agricultural land uses where these products may also have been applied.• While these products may be used outdoors in accordance with the manufacturer’s instructions, they may contain PFAS.For Your InformationWhen conducting a baseline analysis to evaluate PFAS risk, airport operators should verify that AFFF usage complies with FAA requirements and other applicable laws.Conducting a baseline analysis and site assessment are helpful first steps for airports in determining their exposure risk.

Assessment of Historical and Current Product Use and Activities 15 (DoD 2020). “Long-chain PFAS” is the shorthand terminology for PFAS molecules with eight or more carbon atoms in the alkyl chain and is often shortened in the context of AFFF to “C8” or “C8 foam.” Certain long-chain PFAS AFFF formulations in the past may have included perfluorooctanoic acid (PFOA) or PFOS surfactants, which are the chemicals currently under the greatest regulatory scrutiny. Similarly, “short-chain PFAS” commonly refers to compounds with six or fewer carbons in the alkyl chain and may be referred to as “C6” or “C6 foam.” While short-chain PFAS chemicals have not received the same degree of regulatory attention in the past, some may be regulated in the future. C8 foams were prevalent in the market from the beginning of AFFF’s commercial production and use in the early 1960s through the mid-2010s. C6 foams emerged in response to EPA’s voluntary PFOA stewardship program around the same time; however, C8 foams may still be present in facility inventories.Consider reviewing historical purchase orders, invoices, and other procurement records to understand the quantities of AFFF ordered, stored, and used on-site in the past and the types of AFFF involved—that is, C6 or C8 foams. It may be possible to develop a rough time frame for how long and how frequently various types of AFFF were used on-site from these records. Often an Internet search for a specific product by brand name will reveal necessary information if there is uncertainty over whether a product contained C6 or C8 PFAS. With this information, it may be possible to determine the chemical compositions AFFF products used in the past and then to ascertain the various factors potentially affecting fate and transport on-site. These records, considered in conjunction with SDS documentation, should create a more comprehen-sive understanding of potential AFFF issues on-site.ARFF Operational Records. Another way to identify the amount of AFFF historically used is to review ARFF operational and training records. Emergency records from crashes and fires may identify dates and locations where AFFF may have been used. ARFF training records could include• Frequency of training,• Type of equipment used,• Frequency of equipment inspection, and• Secondary containment measures.Documentation of Construction Activity. An airport may also consider reviewing documentation of construction activity and municipal agreements such as records of soil or other fill materials received from off-site and soil movement. If soil or fill materials are suspected to contain PFAS, a construction record review might lend insight into whether soil was moved to another location at the facility or if it was moved off-site. If soil was moved off-site, the review should consider where it was moved. More discussion on this is provided in ChapterÂ3, Section 3.4.Equipment Inspection Sheets. Airports should consider reviewing equipment inspection sheets to determine what ARFF equipment has been stored on-site. The records may serve to corroborate inventory records or incomplete purchase order or invoice documentation. Equipment inspection sheets may also be able to confirm the presence of fire suppression systems in hangars, transfer equipment, and other equipment that may contain or be used to move AFFF. Inspection sheets might also indicate whether any of the equipment was damaged, which could mean that there had been leaks or spills of AFFF.Toolkit TipTool 2.4: Tutorial for Conducting a Baseline AnalysisStep-by-step guide for determining historical weather data, identifying nearby water sources and wetlands, and locating wells.This tool provides links to helpful government websites and shows how data can be accessed and utilized for a baseline review of AFFF exposure.

16 PFAS Management at Airports: A GuideSpill Documentation. Airports should review spill documentation for mentions of AFFF or areas of suspected AFFF storage or use. If reviews indicate that spills occurred in areas that likely contained AFFF equipment or were used for transferring, testing, or training, then it is possible that AFFF was used in these areas. In the case of fuel spills, AFFF may have been deployed as a precautionary measure.Disposal Records. Disposal records may provide insight into AFFF use and disposal methods. Airports may be able to determine prior AFFF use if there are records of contaminated environmental media, ARFF equipment use, or decontamination or disposal of spent AFFF following an emergency response. Disposal records can also show how the materials were desig-nated and whether they were treated and disposed of as hazardous waste or discarded through municipal waste streams.Chain-of-Custody Documentation. Chain-of-custody documentation may be one of the most useful resources for determining AFFF use and movement from sourcing to disposal. If chain-of-custody documentation is available, there may be records of procurement, use and transfer, and disposal. These records may provide insight into the extent of AFFF use on the property.2.4.1.2 Data AnalysisAfter identifying AFFF application sites, the frequency of releases, the chemical signatures of AFFF used, and other factors listed above, airports may consider conducting a desktop analysis, which could provide insight into potential AFFF migration patterns. If the dates of AFFF accidental or intentional releases are known, airports may be able to research weather conditions to determine whether AFFF was likely to reach stormwater con-veyances. Sensitive receptors that could be affected by PFAS contamination can be identified through a desktop analysis.After locations of AFFF storage; use in training, emergency activities, testing, and maintenance; and disposal practices have been determined, the potential of release is assessed. The assessment considers the proximity of potential receptors, including water supply wells and surface waters such as reservoirs, rivers, and canals. A data analysis should assess whether potable water supply wells are downgradient of AFFF application areas. Stormwater can convey PFAS off-site or connect areas to other conveyances, such as groundwater, that could transport toward potential receptors. Therefore, locations of storm drains, drainage swales, and other areas where stormwater is stored, conveyed, or discharged should be identified.More information on how to conduct a baseline analysis, including step-by-step guidance in how to navigate websites and retrieve data, is provided in Tool 2.4. Tool 2.7 provides a tutorial for conducting an AFFF exposure study. The fate and transport processes and factors that affect PFAS migration in environmental media are discussed in Section 2.5: Evaluating Fate and Transport.2.4.2 Investigating Potential ReleasesAirport operators may find embarking on an investigation of PFAS to be a formidable task, given the unpredictability of what may be found and the scientific and regulatory uncer-tainty that exists. However, obtaining knowledge about the extent of an airport’s past PFAS releases allows an airport operator to make more-informed decisions regarding PFAS risk. What Is a Receptor?A receptor is a natural or human-constructed feature that could be adversely affected by a substance such as PFAS.Examples of receptors:• Public or potable water supplies, such as groundwater and groundwater wells;• Surface waters, such as reservoirs or rivers;• Agricultural crops or fields where food for human consumption is grown; and• Public utilities, such as sanitary sewer systems.

Assessment of Historical and Current Product Use and Activities 17 Key principles for PFAS investigations include expert guidance, a conceptual site model (CSM), and goal orientation.• Expert guidance. PFAS investigations should be directed and performed with input from qualified environmental professionals. A well-designed investigation will yield the most useful results and form the foundation for a plan to respond to what is discovered.• Conceptual site model. Development of a CSM can aid an airport operator’s risk management efforts by identifying how PFAS from the airport could affect humans or the environment and using that information to address the risk. A CSM identifies physical, chemical, and biological processes that cause contaminant migration and determines possible locations of groundwater and surface water affected by PFAS, such as pathways to drinking water wells or intakes in proximity to the airport. The CSM should consider surrounding industry and land uses as potential nonairport-related sources of PFAS. If PFAS data are available, they will make the CSM more useful in identifying and con-trolling pathways.• Goal orientation. Airport operators should verify that their investigation, testing, and analysis has a specific goal. In a preliminary investigation, the goal should be to conduct a baseline assessment. Later, the goal may be characterizing PFAS impacts in the soil around a specific planned construction activity zone, characterizing PFAS impacts in groundwater sitewide, or determining whether known PFAS contamination in groundwater is moving off-site. Each scenario would require a slightly different investigation. Focusing on the specific goal and the steps to achieve that goal reduces project time and lowers project costs.Involving legal counsel in PFAS assessments is worth considering. Some states recognize an environmental audit privilege—an evidentiary privilege that protects the results of an organiza-tion’s internal environmental audit from disclosure during litigation. However, state laws on the topic vary, and understanding when and how to incorporate legal support will be location specific.In nonlitigation contexts, because most airports are public or semipublic entities, state open records laws may compel disclosure of documents to a requesting third party, for example, the media, potential plaintiffs, or concerned citizens, unless a privilege or exception applies. The precise strategy will depend on applicable state law, the PFAS issue at hand, and the policy of the airport with respect to public disclosure. An airport can maximize protection of this information by having its attorney complete the following actions:• Directing the environmental audit throughout the process from start to completion;• Retaining and supervising necessary consultants;• Attending relevant interviews;• Taking part in communications, email exchanges, and creation of documents; and• Labeling any documents created as confidential so that protections of the attorney-client privilege and attorney work product doctrine may fully apply.Finally, the results of consultants’ investigation and analysis should be added to an airport’s risk management plan and distributed to the airport leadership team for their input and review. Airport leadership may also want to consider the investigation’s findings in the context of wider airport planning development.2.4.3 Assessment of Nonairport ActivitiesAirports may consider assessing PFAS exposure from nonairport sources, including tenants, fixed-base operators (FBOs), and joint-use facilities. Off-site sources from commercial or industrial facilities should also be considered if migration onto airport property through aerial deposition, groundwater transport, or surface water movement is possible given an airport’s location.

18 PFAS Management at Airports: A Guide2.4.3.1 Assessment of Tenant, FBO, and Joint-Use Facility SourcesDuring a PFAS exposure assessment, airports may also consider contacting tenants, FBOs, or the joint-use facility directly. They may have their own documentation regarding the chemicals used on-site, any training they perform, construction activities, and emergency events as well as other documentation relevant to determining the extent of PFAS used at their facility. Lease agreement documents may provide some insight into the activities associated with a facility’s use. Reviewing this information could help investigators determine which facilities might warrant attention as part of the overall study effort.2.4.3.2 Assessment of Off-Site Activities or LocationsTo determine potential off-site sources of exposure, airports may consider identifying nearby industrial or commercial facilities. Reviewing current and historical imagery available through Google Earth (https://earth.google.com) and topoView (https://ngmdb.usgs.gov/topoview/) may be a good starting point. Airports can follow up this review by researching information on the business, industrial site, or owner of the nearby property; this information is typically available on the county tax assessor’s website.Once the airport has narrowed down a list of potential off-site sources, information can be purchased through third-party environmental data-bases. Alternatively, the airport can utilize the Freedom of Information Act to acquire data from regulatory agencies about another business’s activities. Chemical data reporting under the Toxic Substances Control Act provides information on the industries that regularly use PFAS chemicals and the relative quantities by industry, although some data are confidential and not reported (EPA 2021g). EPA also provides a tool called InertFinder that enables searches for inert ingredients in a variety of products by product use or trade name (EPA n.d.-d), as well as the Safer Choice program, which helps consumers identify PFAS-free product alternatives (EPA n.d.-h). These resources may prove useful when off-site activities or locations are being evaluated. More information on how to assess off-site sources, including step-by-step guidance on navigating the websites and resources described above, is provided in Tool 2.5.2.4.4 Investigation Sampling ConsiderationsAfter a baseline analysis and site investigation, airports should consider whether sampling is appropriate for their situation. Airports should evaluate airport staff health and safety, the potential for receptor exposure, regulatory requirements, and future development plans as part of the decision-making process regarding sampling. The airport may find it prudent to sample in certain areas that may host future project sites to reduce the likelihood of delays and unexpected costs during development. Sampling mandates from state regulatory agencies may also require airports to sample for PFAS in environmental media or infrastructure materials. The following sections provide a high-level overview of what to include in sampling plans, how to incorporate environmental fingerprinting and forensic techniques, and how to evaluate available laboratory analytical testing methods.2.4.5 Sampling Plan Development and ImplementationSampling plans are used to document the reason for sampling, the type of media, the testing methods, and other details associated with sampling and analyses of environmental media. When Toolkit TipTool 2.5: Tutorial for Assessing Off-Site Sources• Step-by-step guide for deter-mining historical and current industrial and commercial facilities near airport properties.• Provides links to helpful government websites.• Shows how to access and utilize data for assessing potential off-site sources of PFAS.

Assessment of Historical and Current Product Use and Activities 19 prioritizing sampling areas, the airport may want to consider locations where the releases are suspected to have occurred on the property or on upgradient off-site or nonairport sources.The airport should keep in mind that PFAS can migrate on and off the property and through different environmental media, meaning that the site of initial release may not be the site where PFAS accumulation occurs. Airport operators should consider contracting with independent service providers with experience in soil, surface water, and groundwater sampling for field collection of samples.In developing a sampling plan, there are different approaches based on the media being sampled and the method of sampling. Regardless of the media sampled and the method chosen, airports should always consider the potential for cross contamination. Generally, analytical laboratories have very low detection thresholds for PFAS, so any PFAS-containing items used during sampling could easily contaminate a sample and produce a false positive. If the airport is sampling for other contaminants of concern, it should consider sampling for PFAS before anything else, as used sampling containers may be composed of or contain PFAS and lead to cross contamination. Airports should also avoid using items that contain fluoropolymers during sampling collection or transport, including the following (Michigan EGLE 2018):• Polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP),• Polyvinylidene fluoride (PVDF),• Polychlorotrifluoroethylene (PCTFE), and• Ethylene-tetrafluoro-ethylene (ETFE).Many types of equipment and supplies used for environmental sampling may contain PFAS chemicals that could contaminate samples (ITRC 2018). TableÂ2-1 lists equipment used for PFAS sampling by category and general industry practices to avoid contamination (MassDEP 2021, Michigan EGLE 2018).In addition, staff who are conducting sampling should also consider taking the following precautions to avoid the potential for cross-contamination of PFAS:• Washing hands and putting on new nitrile gloves after each sample has been retrieved.• Using chemical-free, or “natural,” sunscreens and insect repellents.• Avoiding cosmetics, moisturizers, creams, and other hand products that are more likely to come into contact with samples.• Wearing synthetic or cotton fabrics that have been washed more than six times and avoiding any clothing or boots that are water or stain resistant.• Bringing food in resealable plastic storage bags and aluminum foil, as opposed to prepackaging, and avoiding contact with fast-food wrappers.• Utilizing ice instead of chemical frozen packs wherever possible.A project health and safety plan should also be developed in accordance with appropriate Occupational Safety and Health Administration requirements as a part of the sampling plan to promote the safety and health of field staff.2.4.5.1 Decontamination ProceduresSampling and measurement equipment should be decontaminated before and after each use, and the clean hands/dirty hands method should be employed. Team members should put on a new pair of disposable, powderless nitrile gloves before decontaminating each piece of equipment. The equipment for sampling use should be placed into new, clean, clear plastic bags, and once these bags have been used, they should not be reused. No piece of decontaminated For Your InformationConsider adding sampling results to an existing airport GIS database.

20 PFAS Management at Airports: A Guideequipment should be placed directly onto the ground, and equipment should be handled as minimally as possible.If heavy equipment is required where the above process is impractical, the equipment should be cleaned with potable water by using a high-pressure washer or steam. This process should take place at a facility with secondary containment, to prevent the release of PFAS, and the potable water to be used should be tested in advance for PFAS. Rinsates, purge waters, and wash waters used to decontaminate equipment should be treated as PFAS-contaminated water. Soils and nonreusable equipment should also be treated as PFAS contaminated waste material and dis-posed of via an approved waste disposal facility.2.4.5.2 General Quality Assurance and Quality Control for SamplingQuality assurance (QA) and quality control (QC) procedures may vary according to the types of media sampled and site conditions, but sampling plan protocols should follow these general QA/QC standard operating procedures during the sampling effort:• One blind duplicate sample collected per 20 samples, or a 5% QA/QC sample rate;• One blind duplicate sample per sampling round for laboratory analysis check;• One rinsate blank per day collected from each type of field-sampling equipment;• One equipment blank per day collected for each piece of sampling equipment;• One field blank collected per day; and• One trip blank collected per sample storage container.Suggested for Use Avoid Use High-density polyethylene (HDPE) or low-density polyethylene (LDPE) bladders PTFE tape or other consumables Silicone tubing and silicone lubricants Fluorinated lubricants, such as perfluoropolyether (PFPE) Peristaltic pump or stainless-steel submersible pump Waterproof coatings containing PFAS, such as GORE-TEX or Tyvek Potable water followed by deionized rinse for decontamination and equipment washing Municipal water for washing or decontamination A clean, new pair of nitrile gloves for handling each sample Chemically treated or recycled paper towels Laboratory-provided sample containers that remain sealed until use LDPE bottles or other unsealed plastic bottles Polypropylene bottles or glass containers for samples and rinse water PTFE-lined caps for sample containers or PTFE consumables of any kind HDPE sheeting, regular ice, bubble wrap, and passive diffusion bags Chemical ice packs (e.g., blue ice packs) and waterproof labels Regular loose paper and paper products Waterproof or treated paper or field books, including spiral-bound notebooks Aluminum, polypropylene, or Masonite clipboards Plastic clipboards, binders, or notepads Regular ballpoint pens Permanent markers Plastic bags and aluminum foil Nonplastic bags or food containers while on-site Table 2-1. PFAS sampling equipment considerations to avoid potential cross-contamination.

Assessment of Historical and Current Product Use and Activities 21 PFAS-free water, preferably deionized, should be ordered from the laboratory or obtained from a known, chemically clean source. Samples should be kept at or below 4oC by packing with frozen water ice only. To prevent contamination from melted ice within the cooler, extra sample bottles should be filled with PFAS-free water, sealed, and then frozen. These bottles of PFAS-free ice can then be used in sample coolers to maintain sample temperatures of 4oC or less. Standard Methods for the Examination of Water and Wastewater provides more-detailed instructions on general sampling procedures and QA/QC protocols see (APHA, AWWA, and WEF 2023).Control Samples: Blanks. Field blanks should be collected by pouring PFAS-free water from the containment vessel into a sample container provided by the analyzing laboratory while on-site in the field. The sample bottle is then labeled in the same fashion as sample bottles and submitted to the laboratory for analysis. A trip blank should be ordered from the laboratory conducting the sample analysis and supplying the sample containers. It must arrive in the same packaging as the sample containers, and the trip blank should be inspected on arrival for breakage, leaks, or air bubbles. The trip blank must not be opened, and it should be returned to the laboratory within the same packaging as the samples. A rinsate blank should be collected immediately before equipment is used for sampling. PFAS-free water is poured over the equip-ment and collected in a laboratory-supplied water sample container. An equipment blank should be collected immediately after an item has been decontaminated, in the same fashion as the rinsate blank.Control Samples: Duplicates. Blind duplicate samples should be collected by using the same methodology used to collect the original sample. The duplicate sample containers should be filled from the sample location, so that the chemistry is as close to identical as possible. It is important to label the blind duplicate sample, so that the laboratory cannot identify the sample as a duplicate. The two sample containers—the test sample and the duplicate sample should be opened simultaneously and each sample container filled to approximately 20% of the volume of the given container before the discharge of the sampling equipment is switched to the other sampling container. This process is then replicated, alternating back and forth between sample and duplicate sample containers until both containers are full.2.4.5.3 Chain of Custody and Data ManagementEach sample container should be labeled in ink in the field. Due to the potential for contami-nation from permanent markers, ballpoint pens should be used. Labels may be printed ahead of time and affixed to sample bottles, but confirm the labels or the adhesives do not contain PFAS chemicals. Each bottle should clearly show the sample date and time; incorporating the date and time into the sample identification number is suggested to avoid sample misidentification. Recording dates as year, month, and day and times according to the 24-hour system is preferred, but whatever method is chosen, the party responsible for directing the sampling effort should verify that the methods chosen for recording the date and time are used consistently on all labels and documentation.Depending on the duration of the sampling effort and number of samples to be collected, this person should also be responsible for routinely checking or auditing containers and main-taining audit records, as appropriate. Each sample’s identification number should be unique and reflect the sample’s identity. For example, a subsurface soil sample collected from 2Âft below the ground surface at Borehole 1 within Site A on JuneÂ15, 2019, at 1:17 p.m. could read as follows: 2.0BH1SASubSurf201906151317. Since no two boreholes will be sampled in the same location at the exact same time, this labeling convention allows all team members to decipher when and where a sample was collected, even if they themselves were not part of that particular sampling

22 PFAS Management at Airports: A Guideteam. Using this method will expedite sample data analysis when reports return from the labo-ratory as well.Chain of custody (CoC) forms must be kept by field personnel—preferably with one person designated as the responsible party—to document the possession of all samples collected from the moment of collection until the sample is disposed of. At a minimum, the CoC form must include the following information:• Project name;• Location, date, and time of collection;• Name(s) of samplers;• The unique sample identification number for each sample documented on the form;• Sample type and any preservation measures used;• Laboratory analyses required; and• Date, time, and signatures for each transaction in which there is a change in sample custody.Following is an example of a change in sample custody: The person who collected the sample hands the sample over to the laboratory, recording the date and time when the sample was sub-mitted on the CoC form and signing it. Then the laboratory staff member receiving the sample puts the date and time received on the form and signs it; that person is now responsible for the sample until it is transferred to another responsible party and the CoC process is repeated.Original CoC forms should be kept in sealable LDPE bags taped to the inside of the cooler or sample storage container or to the shipping container lid. Filled coolers with CoC forms affixed to the lids should be sealed with tape, and the responsible party should put her or his initials over the tape in pen. Copies of the CoC forms are kept by a designated member of the sampling team for the project’s records.2.4.6 Laboratory Analytical Testing MethodsThere are currently multiple methods for laboratory analytical testing based on the environmental media containing the sample. In 2021, EPA published Method 1633, the first validated draft, for testing for 40 different types of PFAS (EPA 2021a). In June of 2022, EPA released the second draft method (EPA 2022g). DoD has compiled rigorous QA criteria for PFAS testing under the Quality Systems Manual (DoD and DOE 2019), and these criteria were used in validation studies for Method 1633. Once this testing method becomes a part of Clean Water Act compliance monitoring requirements through rulemaking, airports will have a way to monitor PFAS in wastewater, sur-face water, groundwater, soils, biosolids, sediment, landfill leachate, and fish tissue.Several methods have been published for PFAS in drinking water, non-drinking water, and solid matrices, including EPA and ASTM methods, but validation studies for these methods have not yet been published. When determining the appropriate laboratory analytical testing method to use, airports should consider reviewing state regulatory requirements for PFAS analytical method compliance and target lists of compounds. More information about the methods used for testing, the specific PFAS types detectable by each method, and each method’s applicability to different types of environmental media can be found in Tool 2.6, ASTM D7968-17a and ASTM D7979-20, and the EPA website (EPA 2020a, 2021c, 2022b, n.d.-b, n.d.-f).Environmental fingerprinting and forensic techniques involve evaluating the source or age of environmental contaminants at exposed sites to establish who is responsible for paying For Your InformationA reliable PFAS fingerprinting program should• Target the types and amount of individual PFAS compounds that can be measured in a sample.• Identify the potential changes in the measured individual PFAS compounds in the sample due to environmental transformations.

Assessment of Historical and Current Product Use and Activities 23ÂÂ remediation costs, predict accurate fate and transport, and implement effi-cient remediation strategies. A large array of forensic techniques has been developed, and these are available for common environmental contami-nants. These techniques include chemical fingerprinting, signature chemicals, isotopic fingerprinting, mineralogical fingerprinting, atmospheric tracers, DNA fingerprinting, tree-ring fingerprinting, and contaminant transport modeling. Typically, specific fingerprints are generated that may be compared between samples and with suspected sources. To date, very few of the methods listed have been applied to PFAS. However, as of SeptemberÂ2023, there were four techniques available that are based on chemical analyses and statistical evaluations and include environmental fingerprinting: chemical fingerprinting via targeted analysis, total oxidizable precursors, total organic fluorine, and nontarget analysis.2.4.6.1 Targeted AnalysisTargeted analysis is used to identify and analyze the targeted PFAS compounds, including the type and amount of individual PFAS, in a sample. The chemical fingerprint of the sample is then compared with published source signatures in the scientific literature. Researchers may also use known fate and transport properties to aid in targeted analysis.2.4.6.2 Total Oxidizable PrecursorsTotal oxidizable precursors are determined by oxidizing environmental samples in the labo-ratory and analyzing the number of individual PFAS before and after oxidation. This method can help predict the changes in PFAS signatures due to environmental transformations. Therefore, samples can be matched to source materials even if their fingerprints have changed.2.4.6.3 Total Organic FluorineCollection of total organic fluorine data does not require sample prepa-ration. This technique requires direct injection of an aqueous sample into a combustion ion chromatograph system. Similar methods used to test the concentrations of organic fluorine in a sample include adsorbable organic fluorine (AOF) and extractable organic fluorine (EOF). However, for AOF and EOF, the samples must undergo a preparation process before being analyzed by the combustion ion chromatograph system. In AOF testing, a 100-milliliter (mL) sample is passed through activated charcoal beds and is washed with a nitrate solution to remove inorganic fluorine. For EOF testing, a 100-mL sample is passed through a wax solid-phase extraction column. Then, PFAS are eluted with methanol from the column and concentrated to 1 mL. These three methods provide additional chemical signatures for source evaluation.2.4.6.4 Nontarget AnalysisThis technique involves the determination of unidentified PFAS profiles, that is, PFAS compounds without a known chemical structure or analytical reference standards, in a sample. Nontarget analysis can be used to obtain unique PFAS signatures on the basis of peaks of uniden-tified PFAS compounds present in the sample. This process may be used to report new PFAS, including the identification of novel structures and chemical formulas. While currently there are only nonstandard, or user-defined, methodologies for identifying PFAS compounds, increased interest from regulatory agencies could lead to the development of standardized methods for nontarget analysis.For Your InformationACRP Research Report 255 (Anderson etÂal. 2023) includes more information on source identification and differentiation techniques.Toolkit TipTool 2.6: Considerations for Selecting a Method of PFAS TestingGuide for determining the appropriate laboratory analytical testing method based on the environmental media containing the sample and the anticipated or predicted PFAS compounds.

24 PFAS Management at Airports: A GuideBefore the techniques described above are applied, the forensic investigation can help support the validity of sample data results by• Collecting samples from representative locations;• Avoiding cross-contamination during sampling, handling, and shipping; and• Utilizing reliable and comparable analytical techniques for PFAS analyses across sets of samples.Additional information on each forensic technique and specific considerations are provided in Tool 2.6. For more information on sampling, several guidance documents are available (DoD 2017, Michigan DEQ 2018, Government of Western Australia 2017). These sources pro-vide information on materials and equipment used in PFAS-focused investigations as well as materials to avoid because of known or suspected PFAS constituents in those products.2.5 Evaluating Fate and TransportPrevious sections in this chapter reviewed general PFAS characteristics, on-site and off-site activities potentially involving PFAS, and methods for establishing a basic understanding of possible exposure areas. This section covers how PFAS may migrate from or onto an airport property given how PFAS move in and through environmental media. Evaluating fate and transport depends on the type of environmental media involved, site characteristics, and poten-tial exposure pathways. This section outlines PFAS transformation mechanisms and migratory pathways in soils and subsurface environments, groundwater, surface water, and air. Following are some of the factors affecting fate and transport:• Local environmental characteristics;• Physical and chemical parameters of the exposed media;• Weather patterns and climatology at the release site;• Type, structure, and surfactant properties of the released PFAS;• Presence of other non-PFAS co-contaminants; and• Circ*mstances surrounding the rate and duration of a release.Each fate and transport process results in a variety of outcomes, some of which may result in chemical transformations, a change in the concentration of PFAS, or uptake by biotic or abiotic processes.2.5.1 Transport in Soils and Subsurface EnvironmentsPFAS may be released to soils and subsurface environments in the following representative scenarios:• Surface applications;• Leaks and spills during transport, handling, or storage;• Exfiltration from sewer lines or leaching from storm drains;• Waste storage, such as potential leaching from waste storage ponds; and• Atmospheric deposition, including both wet and dry deposition.If released to soils, PFAS tend to concentrate within or near the source area and are subjected to downward leaching by precipitation, flooding, or irrigation events through the dissolution of the soil-bound contaminant mass (Sepulvado etÂal. 2011, Ahrens and Bundschuh 2014) or via colloidal transport (ITRC n.d.-c). The result is a gradual vertical migration of PFAS toward groundwater. PFAS may disproportionately accumulate at interfaces, such as the soil–groundwater, air–groundwater, or NAPL–groundwater interfaces. For example, PFAS may be found within soil pores at the capillary fringe, which is the subsurface layer in which groundwater seeps up

Assessment of Historical and Current Product Use and Activities 25 from the water table by capillary action to fill pores. PFAS may also be contained within a smear zone, which occurs when the water table fluctuates between historical high and low elevations, smearing PFAS across the soil. This situation could take place when AFFF is used to respond to petroleum fires, so that PFAS becomes mixed with light NAPL. The vertical migration through soil of PFAS partitioned at interfaces is slower, and these interfaces may be considered secondary PFAS sources. FigureÂ2-4 describes the process by which PFAS may move through soil and sub-surface environments.Both biotic and abiotic PFAS transformation processes may occur in subsurface zones. Often, polyfluorinated compounds, or precursors, transform into perfluorinated compounds with shorter chain lengths. Basically, while the carbon–fluorine bond is very strong and not readily destroyed naturally, other bonds, such as the carbon–carbon bond, may break more easily. The result is a precursor transformation in which the area no longer contains the original PFAS compound but is now contaminated with several smaller fluorinated organic compounds. PFAS contamination in the environment at concentrations below the CMC may form hemimi-celles or bilayer structures, which may result in increased PFAS persistence in subsurface areas exposed to AFFF or other PFAS (Yu etÂal. 2009, Du etÂal. 2014, Brusseau 2018). PFAS may persist in soil-bound source areas longer than other contaminants without this surfactant behavior, leading to contamination lasting for years to decades (Baduel etÂal. 2015, Guo etÂal. 2020).Due to PFAS transformation in subsurface zones, the extent of contamination with fluorinated organic compounds at source areas could be substantially greater than the PFAS concentrations measured in samples, since most of the precursor compounds could not yet be identified with the methods available as of SeptemberÂ2023. In effect, PFAS subsurface transformation processes may alter the original signature of the released PFAS; therefore, the extent of PFAS contamina-tion may be more difficult to measure with currently available technologies.Soil characteristics, such as clay and organic matter content, affect how quickly PFAS will migrate through soils or where PFAS may accumulate. Vertical migration toward groundwater may be slowed, depending on the charge of the PFAS lipophilic head versus the charge of adsorbent subsurface substrates such as soils or other organic chemicals present in soils or ground-water. When PFAS are released to soils, the hydrophobic tails have an affinity for soil organic material, which increases retention in soils. At the same time, the negatively charged hydrophilic heads display electrostatic repulsion to the negatively charged soil particles, decreasing the soil retention of the released PFAS. That is, when PFAS lipophilic heads and adsorbent oil particles have opposing charges, PFAS micelles, hemimicelles, and bilayers may accumu-late and persist in subsurface soils for a long time.Studies are underway to determine whether perfluorinated compounds can undergo biodegradation, but the data are inconclusive. PFAS may be removed from subsurface soils by plant uptake and biological sequestration, leading to decreased PFAS concentrations in soil. Additional information on PFAS released to soils and subsurface environments can be found in Tool 2.1.2.5.2 Transport in Groundwater and Surface WaterPFAS may migrate from source areas into groundwater by gradual vertical migration in unsaturated soils through a series of mechanisms, including leaching and colloidal transport. PFAS typically dissolve in groundwater and may travel long distances by advection, generating long contamination plumes that may extend over several miles. PFAS transport in groundwater may be affected by adsorption to LEACHINGBIOTIC UPTAKEPARTITIONING TOSOILPARTITIONING TOINTERFACESTRANSFORMATION(BIOTIC ANDABIOTIC)Figure 2-4. Fate and transport pathway for PFAS in subsurface environments.For Your InformationSurface applications over less permeable surfaces such as concrete may still result in PFAS migration into subsurface soils through absorption or diffusion.For Your InformationPFAS subsurface transformation processes may alter the original signature of released PFAS; therefore, the extent of PFAS contamination may be more difficult to measure with currently available technologies.

26 PFAS Management at Airports: A Guidethe organic fraction of soils in the saturated zone as well as by diffusion in and out of lower-permeability soils or bedrock. With partitioning to soil, PFAS lateral migration in groundwater slows, leading to decreased PFAS concentration in groundwater. However, back-diffusion out of these low-permeability materials may result in the long-term persistence of PFAS in groundwater even after source removal and remediation (ITRC n.d.-c). Due to matrix diffusion, the interface of low-permeability layers and groundwater could be considered a secondary PFAS source. FigureÂ2-5 describes the pro-cess by which PFAS may move through groundwater and surface water. PFAS also dissolve in surface water, where they may be sequestered in sediments by processes influenced by the organic matter content of the sediment, may partition to air–water interfaces, or may form foams at higher concentrations and under certain conditions. In still bodies of water, or lentic systems, PFAS may gradually increase in concentration, while in flowing water, or lotic systems, concentrations of PFAS may remain constant or gradually decrease away from the source. Uptake by fish, aquatic organisms, and plants may also occur in surface water, and long-chain PFAS containing eight or more carbons are known to bioconcentrate in aquatic organisms (ITRC n.d.-b).PFAS may be subjected to biotic and abiotic transformation in water. As for PFAS in soil, these processes typically involve precursor transformations that potentially result in significant increases in total PFAS concentrations and distinct signatures away from the source zone. PFAS signatures in surface water generally do not change significantly over long distances, which would suggest precursor transformations may be less significant in this medium. However, more research is needed to better understand the factors governing PFAS transformations in GROUNDWATERDISSOLUTION ANDADVECTIVETRANSPORTSOIL PARTITIONINGMATRIX DIFFUSIONTRANSFORMATION(BIOTIC AND ABIOTIC)SURFACE WATERDISSOLUTION ANDADVECTIVETRANSPORTPARTITIONING TOWATER INTERFACES; FOAM FORMATIONTRANSFORMATION(BIOTIC AND ABIOTIC)BIOTIC UPTAKESEDIMENTS AND AIR–Figure 2-5. Fate and transport processes for PFAS in groundwater and surface water.Toolkit TipTool 2.2: Guide to PFAS Fate and Transport in Surface and Groundwater EnvironmentsConsiderations and factors affecting fate and transport in surface and groundwater environments.

Assessment of Historical and Current Product Use and Activities 27 surface versus groundwater. Additional information on PFAS transport and processes in water can be found in Tool 2.2.2.5.3 Release to AirPFAS may become airborne when in contact with air or when inadvertently aerosolized during use. PFAS products or materials may be released to air through the following uses:• Surface applications of products;• Handling;• Construction and demolition activities; and• Waste storage, treatment, or disposal activities.Most classes of PFAS may partition to particles suspended in air or to liquid droplets dis-persed in air. Partitioning to air occurs when concentrated PFAS in contaminated surface water or soil are picked up by wind and aerosolized as airborne dust particles. PFAS are typically transported short distances in air. However, once airborne, volatile PFAS may occur in a gaseous state (e.g., fluorotelomer alcohols) or may be incorporated within aerosols and other particulate matter in the air and then potentially travel long distances. Wet and dry depositions are the major mechanisms of removal of PFAS from the atmosphere and can occur from the scavenging of particle-bound PFAS or partitioning of gaseous PFAS to water droplets (Dreyer etÂal. 2010, Barton etÂal. 2007, Hurley etÂal. 2003). FigureÂ2-6 summarizes the process by which PFAS may move through air.PFAS may also transform in air due to photooxidation processes (ITRC n.d.-b). While direct photolysis of PFAS has not been observed, indirect photolysis of some precursors was shown to occur in the atmosphere, resulting in significant contributions to the deposition of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) (Armitage etÂal. 2009, Yarwood etÂal. 2007, Ellis etÂal. 2004). Some precursor compounds may transform into more stable carboxylic perfluorinated acids, such as PFOA. Additional information on PFAS released to air can be found in Tool 2.3.Toolkit TipTool 2.3: Guide to PFAS Fate and Transport in AirProvides considerations and factors affecting fate and transport in air.PARTITIONING INTOGASEOUS PHASEPARTITIONING INTOAEROSOLS ANDPARTICULATE MATTERFROM AIRWET AND DRYDEPOSITIONTRANSFORMATIONFigure 2-6. Fate and transport processes for PFAS in air.