PFAS and AFFF: How Firefighting Foam Contamination Affects Hangar Value

Abstract

1. Introduction

Aqueous film-forming foam, universally abbreviated AFFF, was developed for hydrocarbon fuel fires and became standard at airports and in some aircraft hangars. Its effectiveness derives in part from fluorinated surfactants, which are per- and polyfluoroalkyl substances. PFAS do not break down on any practical timescale, which is why the compounds acquired their popular name. A facility that last discharged fluorinated foam decades ago can sit above a plume today.

For an appraiser, a lender, or an acquirer, this creates a valuation problem with an unusual shape. The contamination is frequently invisible, frequently undocumented, and frequently present at facilities where no fire ever occurred, because testing and maintenance discharges were routine. The liability regime attaching to it changed materially in 2024 and has continued to move since. And the evidence base for quantifying the effect on value is thin, recent, and inconsistent across studies.

The U.S. Airport PFAS and AFFF Exposure Map is a searchable screening tool covering airports with documented or presumed exposure, and is a starting point for the record described in Section 7.

This paper addresses each of those. Section 2 identifies which hangars actually carry the exposure, and corrects a technical conflation that is common in the practitioner discussion and that matters because it misallocates the risk. Section 3 states the regulatory position as of September 2026, which is not the position most published commentary describes. Section 4 sets out the four channels through which PFAS reaches value. Section 5 assembles the quantitative evidence that exists and confronts a federal decision excluding expert testimony that relied on part of it. Section 6 places the analysis within the recognized appraisal framework for contaminated property. Section 7 addresses the change in due diligence scope that occurred on 8 July 2024. Section 8 gives the verifiable scale of the problem and states plainly where no authoritative figure exists. Section 9 sets out limitations.

2. Which Hangars Carry the Exposure

2.1 The Standard and Its Groups

Aircraft hangar fire protection in the United States is governed by NFPA 409, the Standard on Aircraft Hangars, currently in its 2026 edition. The standard classifies hangars into four groups, and the classification drives what suppression is required.

Under the 2011 edition, which is the edition that governed when most of the systems now at issue were designed and installed, Group I is any hangar with an aircraft access door exceeding 28 feet in height, a single fire area exceeding 40,000 square feet, or provision for aircraft with a tail height exceeding 28 feet. Groups II and III are defined by door height at or below 28 feet combined with fire area limits that vary by construction type. Group IV covers membrane-covered rigid steel frame structures.

Group I required foam suppression, with three permitted configurations. Group II also required foam under the 2011 edition, with four permitted configurations. Groups III and IV did not require foam suppression. That last point should be treated as well supported rather than as a categorical rule, since the relevant chapter text is not reproduced in full in the publicly accessible copy consulted for this paper.

The 2022 edition changed this materially. It removed the blanket Group II foam mandate, created a performance-based design pathway permitting alternative schemes with or without foam, exempted Group II hangars from foam requirements where hazardous activities are prohibited, and approved ignitable-liquid floor drainage systems in place of foam systems. The 2026 edition adds requirements governing synthetic fluorine-free foam when used in accordance with the manufacturer's listing, and raises the aircraft access door height threshold from 28 feet to 35 feet across Groups I, II and III, which the publisher attributes to current aircraft design and hangar usage. Any analysis still using a 28-foot Group I trigger is working from a superseded edition.

2.2 Two Foam Pathways, One PFAS Source

The practitioner discussion frequently treats hangar foam systems as a single category and describes them as AFFF systems. The standard does not, and the distinction determines which hangars carry PFAS exposure.

NFPA 409 has permitted two chemically distinct pathways. Low-expansion systems, including foam-water deluge and supplementary low-level systems, employ AFFF, protein, or fluoroprotein foam liquid concentrates. High-expansion systems utilize surfactants as the foaming ingredient and are designed to fill the protected area to a depth of at least three feet within one minute, with generators delivering expansion ratios of roughly 200:1 to 1000:1. AFFF sits at the opposite end of that range. The application rate provisions confirm the classification: the standard specifies minimum rates for protein, fluoroprotein, and AFFF solutions within the low-expansion provisions, and treats high-expansion as a separate design alternative.

This matters because fire protection engineers report that most commercial hangars were designed with high-expansion systems, chosen precisely because AFFF systems require costly trenching, larger water storage, and containment infrastructure. The same source states that high-expansion formulations available today do not contain compounds classified as PFOS or PFOA.

Two caveats are necessary and the paper states both rather than resolving the question in either direction. That engineering statement is specific to PFOS and PFOA and to formulations available currently, so it is not a historical warranty that every high-expansion concentrate ever manufactured was fluorine-free. Published inventories of firefighting foam product categories list high-expansion foams without stating whether they contain fluorosurfactants. The correct position is therefore that the PFAS exposure attaches to the low-expansion pathway, that the high-expansion pathway is probably not a PFAS source but has not been shown to be categorically free of them, and that the analysis in any given assignment turns on identifying which system the hangar actually had and what concentrate was actually used in it.

2.3 AFFF Hangar Systems Existed and Were a Source

None of the above suggests the problem is theoretical. AFFF-based hangar suppression systems were installed and were a documented PFAS source.

The clearest confirmation comes from the Air Force. In March 2023 Air Force Materiel Command announced the elimination of PFAS-containing foam from hangar fire suppression systems, describing a program that closed and locked the AFFF supply valves at hangar systems, with all AFFF tanks locked and tagged by 1 March. Most affected facilities converted to water-only sprinkler systems; four hangars were designated mission-critical exceptions. An organization does not lock out and drain hangar foam tanks across its inventory unless those tanks contained the compound at issue.

Beyond the hangar itself, an airport carries loading from other sources that reaches hangar parcels: apparatus testing and training discharges at the fire station and training area, equipment washdown, and response to actual incidents. At a certificated airport these were required activities under federal regulation, discussed in Section 3.5. A hangar with no foam system of its own can still sit on contaminated ground.

3. The Regulatory Position

The regulatory position moved substantially between 2024 and the present, and it moved in opposite directions on the two authorities that matter most. Commentary written to a 2024 snapshot is now wrong on one of them and incomplete on the other.

3.1 CERCLA Designation, and Its Survival on Appeal

On 8 May 2024 the Environmental Protection Agency designated perfluorooctanoic acid and perfluorooctanesulfonic acid, including their salts and structural isomers, as hazardous substances under section 102(a) of the federal cleanup statute. The rule took effect on 8 July 2024 and set a reportable quantity of one pound in any twenty-four hour period, triggering notification obligations.

The designation was challenged and upheld. In August 2026 the Court of Appeals for the District of Columbia Circuit unanimously rejected all three challenges, holding that the statutory standard requires only a possibility of serious harm rather than certainty, and finding that the agency reasonably estimated costs and properly accounted for the statute's multistep enforcement framework. The designation is in effect, has not been stayed, and has now survived appellate review.

The consequence for a property owner is direct. Liability under the cleanup statute attaches to current owners and operators without regard to fault. An acquirer of hangar property with foam history is acquiring a contingent liability, not merely a physical condition.

3.2 Drinking Water Standards, and Their Uncertain Future

On 26 April 2024 the agency promulgated the first national primary drinking water regulation for PFAS, effective 25 June 2024. It set enforceable limits of 4.0 nanograms per liter for PFOA and for PFOS; 10 nanograms per liter for PFHxS, PFNA, and HFPO-DA; and a hazard index of 1 for mixtures of two or more of PFHxS, PFNA, HFPO-DA, and PFBS. Initial monitoring was required by 26 April 2027 and compliance with the limits by 26 April 2029.

In May 2025 the agency announced it would keep the limits for PFOA and PFOS, rescind the regulations and reconsider the regulatory determinations for the other four, and extend the compliance date to 2031. Two proposed rules published on 20 May 2026 would implement that: one rescinding the four standards, one moving the PFOA and PFOS compliance date from 2029 to 2031. Both comment periods closed on 20 July 2026. Neither has been finalized.

The rule is also in litigation. In January 2026 the reviewing panel unanimously denied the agency's motion for summary vacatur of the hazard index provisions, holding that the merits were not so clear as to warrant summary action, notwithstanding the agency's concession of a procedural violation in how those provisions were proposed. Argument on the merits is scheduled for 18 September 2026.

The position as of the date of this paper is therefore that all six standards remain in effect, with the 2029 compliance date intact, and that two separate processes could change that. An analysis that assumes either the 2024 position or the announced 2025 position will be wrong in one direction or the other. The valuation-relevant point is that regulatory uncertainty of this kind is itself a risk factor a market participant prices, independently of where the rules land.

3.3 What Has Not Happened

Two common assumptions are wrong, and the distinctions matter for how liability is framed.

No PFAS compound is a hazardous waste under the federal waste statute. The agency proposed listing nine PFAS as hazardous constituents in early 2024, which is a preliminary step and does not carry cradle-to-grave generator liability. That proposal has not been finalized, and in May 2026 the agency withdrew a related proposed rule on the corrective action definition of hazardous waste, stating it would not pursue regulatory clarification extending corrective action authority to substances that are not listed hazardous wastes or constituents.

The federal chemical reporting rule requiring manufacturers and importers to report PFAS back to 2011 has been delayed three times. The current position, set out at 91 Fed. Reg. 18786 on 13 April 2026, opens the submission period on 31 January 2027 or sixty days after the effective date of a forthcoming substantive requirements rule, whichever is earlier. The window is six months generally and twelve months for small manufacturers reporting solely as article importers.

3.4 The Enforcement Discretion Policy and Its Three Limits

The agency issued an enforcement discretion and settlement policy for PFAS under the cleanup statute in April 2024, and it names airports explicitly. The policy identifies five categories of parties the agency does not intend to pursue: community water systems and publicly owned treatment works, municipal separate storm sewer systems, publicly owned or operated municipal solid waste landfills, publicly owned airports and local fire departments, and farms where biosolids have been land-applied. For airports the policy conditions the forbearance on following the regulations governing foam use, exercising a high standard of care to limit and contain releases, and forgoing the use of AFFF where possible.

Three limits determine how much weight this carries in a valuation, and all three cut against relying on it.

It is a policy, not a rule. It creates no rights, binds no court, and can be revised.

It covers publicly owned airports. A private hangar owner, a fixed-base operator, a maintenance organization, or a private airport receives nothing from it.

It constrains the agency. It does not constrain private third-party claims, state enforcement, or contribution actions between private parties. For a property value analysis the third limit is the operative one, because the diminution mechanism does not run through federal enforcement in the first place.

There is a further point worth stating plainly. A policy of declining to pursue publicly owned airports is only necessary because those airports are otherwise within the statute's reach. The policy is evidence that airports are potentially responsible parties, not evidence that they are not.

3.5 The FAA Transition, and What the Regulation Still Says

Section 332 of the FAA Reauthorization Act of 2018 directed that, not later than three years after enactment, the Administrator shall not require the use of fluorinated chemicals to meet the applicable performance standards. The deadline was 5 October 2021.

Two features of that provision are commonly misstated. It is a prohibition on the agency requiring fluorinated foam. It is not a ban on airports using it, and it does not itself phase anything out. And it addresses section 139.319(l) of the certification regulation, which governs extinguishing agent standards and whose substance sits in chapter 6 of the advisory circular, not the section specifying vehicle and agent quantities.

The regulation specifying agents and quantities at certificated airports has not been amended since 2004, and it does not reach every airport equally. At Index A it offers a compliance path with no foam at all: one vehicle carrying at least 500 pounds of sodium-based dry chemical, halon 1211 or a clean agent satisfies the rule. AFFF is specified only at Indexes B through E.

The defensible statement is therefore narrower and stronger than the one commonly made. Five hundred seventeen airports held certificates as of 3 September 2026; at 323 of them the regulation specified AFFF, and at the 194 Index A airports a compliance path without it existed. It requires each vehicle carrying AFFF to carry enough to mix with twice the water the vehicle carries. What has changed is that fluorine-free foams on the Department of Defense qualified products list are accepted as satisfying the requirement. The accurate statement is that the agency no longer requires fluorinated foam in practice while the regulatory text still specifies it, and a paper or an appraisal should say both rather than either.

The military specification for fluorine-free concentrate was published in January 2023. The statutory prohibition on military AFFF use carried an original deadline of 1 October 2024, which has been extended twice by waiver, most recently in July 2025, to 1 October 2026.

The agency continues to issue guidance on testing. The current alert, issued 5 August 2026, recommends vehicle system testing within the six-month period before an airport's periodic inspection and accepts four input-based testing systems in place of discharge testing. Airport Improvement Program funds are available to purchase a qualified input-based testing system, currently with no local match. Whether those funds reach foam disposal or transition costs generally is answered in Section 3.7, and the answer is that a separate statute does the work.

3.6 State Law

State regulation is where the practical constraints frequently bind, and it varies enough that a general treatment is of limited use.

More than thirty states have enacted statutes addressing firefighting foam, typically banning discharge in training and testing, restricting manufacturer sales, or establishing take-back programs. Connecticut, Illinois, New Hampshire, Michigan, and Washington have take-back or collection programs, with Washington launching a state disposal program in September 2025. North Carolina established an inventory program.

Cleanup standards vary and are not uniformly stricter than federal. Michigan's residential groundwater cleanup criteria under its Part 201 program, in effect since December 2020, set 8 parts per trillion for PFOA, 16 for PFOS, 6 for PFNA, 51 for PFHxS, 370 for HFPO-DA, and 420 for PFBS. Note that Michigan's PFNA criterion is stricter than the federal limit while its PFOA and PFOS criteria are less strict. A blanket statement that state standards exceed federal standards would be wrong; the comparison is compound by compound.

One state requires PFAS notice on transfer of real property. New Hampshire added PFAS to its statutory transfer notification in 2024, effective 1 January 2025. The required text is a generic awareness notice rather than a property-specific disclosure of contamination, and should not be characterized as a disclosure duty. General seller disclosure obligations in most states would reach known PFAS contamination as a known material defect, but that is an existing duty rather than a PFAS-specific mandate.

3.7 The Federal Money, and Who Is Excluded From It

One federal funding mechanism is aimed squarely at airport PFAS, and its eligibility rule decides most of what this paper is about.

Section 767 of the FAA Reauthorization Act of 2024, enacted 16 May 2024, established a PFAS Replacement Program for Airports. It authorises not more than $350,000,000 over five fiscal years at a 100 percent federal share, reimbursing costs incurred after 12 September 2023. Eligible costs are the one-time initial acquisition of fluorine-free foam meeting the military specification at the capacity of all required rescue and firefighting equipment plus twice the quantity carried on each required truck; disposal of PFAS products including the old foam and the wastewater from cleaning equipment; cleaning or disposal of existing equipment; acquisition of equipment necessary to transition; and replacement of firefighting equipment the Secretary determines must be replaced. Up to $30,000,000 is reserved for Index A airports without existing fluorine-free production capability, for vehicle replacement, capped at $2,000,000 per grant. The balance is distributed pro rata by each airport’s required foam concentrate gallonage.

Two features of the statute matter more than the money.

It funds transition, not remediation. Nothing in section 767 reimburses site investigation, groundwater treatment or cleanup. A certificated airport gets its foam swapped out at full federal expense and still owns the plume.

General aviation airports get nothing. Section 767(e)(1) defines an eligible airport as “an airport holding an Airport Operating Certificate issued under part 139.” Five hundred seventeen airports hold one. Most hangars do not sit at those airports. The single federal funding mechanism aimed at airport PFAS structurally excludes the properties this paper is about.

The other door is closed as well, which resolves a question earlier editions of this paper left open. FAA Program Guidance Letter 26-03, dated 6 January 2026, confirms that stand-alone environmental remediation is not eligible for Airport Improvement Program funding: “Stand-alone environmental remediation and removal of fuel farms, underground fuel tanks, hazardous waste, or contaminated soil” is not independently fundable, and only the discrete part of a project dedicated to mitigating contamination needed to permit an otherwise eligible project may be included.

So the federal position as of this writing is precise and unfavourable to the general aviation hangar. Transition is fully funded at certificated airports and not funded at all elsewhere. Remediation is funded nowhere. A hangar owner at a non-certificated field facing a PFAS finding has no federal programme to apply to, and the cost sits on the property.

4. The Four Value Channels

PFAS reaches property value through four distinct channels. An analysis capturing only one of them will overstate value, and the fourth is the one most often omitted.

Remediation cost. Treatment of soil and groundwater for PFAS is expensive and the applicable standards are unsettled, as Section 3.2 describes. A cost estimate prepared against one set of criteria may be inadequate against another. Where a remedy has not been designed, the cost is an estimate of an estimate.

Contingent liability. Since July 2024 a release of two PFAS compounds is a release of a hazardous substance under the federal cleanup statute, and that designation survived appeal in August 2026. Liability attaches to owners and operators without regard to fault, and the enforcement discretion policy does not reach private parties at all. A lender evaluating a loan secured by hangar improvements is evaluating a balance sheet exposure, not only a collateral condition.

Marketability and stigma. A documented contamination history narrows the buyer pool and lengthens marketing time even where a remedy is complete. This appears in a valuation as a yield adjustment and a holding period adjustment rather than only as a deduction, and Section 5 sets out evidence that the effect persists after remediation.

Insurance and financing friction. This channel is now documented rather than anecdotal. The standard-form liability exclusion promulgated by the industry advisory organization, form CG 40 32 05 23, dated May 2023, excludes bodily injury or property damage that would not have occurred but for the inhalation, ingestion, absorption, consumption, discharge, dispersal, seepage, migration, release or escape of, contact with, exposure to, existence of, or presence of any PFAS. The breadth is the point: the exclusion reaches threatened or suspected presence and does not require a proven release. A companion form applies to businessowners policies. Major brokers report that PFAS restrictions are now common across most property and casualty lines, that dedicated pollution coverage without a PFAS exclusion has become difficult to obtain, and that where coverage is available it may carry a sublimit well below the exposure.

An asset that cannot be insured against a known exposure is worth less than one that can, for reasons that have nothing to do with whether the exposure materializes. That is a financing and marketability effect operating independently of remediation cost, and it should be analyzed separately rather than folded into stigma.

5. What the Evidence Shows

5.1 The Strongest Study

Marcus and Mueller (2024) is the strongest peer-reviewed quantification available. Using residential transaction data and a difference-in-differences design around the community water system in Paulsboro, New Jersey, they find that housing prices decreased by approximately 31 to 42 percent after information about PFAS contamination in the local drinking water supply was released, with estimates within the affected system reaching 42 to 48 percent. Against a pre-discovery mean home value of roughly $95,000, a 42 percent decline is roughly $40,000 per property.

Two features of that result matter more than the headline number.

The authors attribute the magnitude to more than avoidance cost, noting that the effect is far larger than the cost of a home filtration system and therefore captures perceived risk and stigma along with willingness to pay to avoid exposure. That is the mechanism this paper argues for, measured rather than asserted.

And they observe no rebound after remediation, attributing the persistence partly to the four-year interval between discovery and public notification. A contaminated property that is cleaned up does not, on this evidence, return to its prior value.

5.2 The Other Study, and the Spread

Islam and Heintzelman, in a working paper that has not been peer reviewed and should be cited as such, examined more than 157,000 single-family sales in two Pennsylvania counties from 2010 to 2022 using hedonic and difference-in-differences methods. They find average property value within a contaminated water system service area drops by 2.8 percent relative to homes outside it, with effects extending beyond the contaminated area because public announcements and media coverage affected the market regardless of local testing results.

A third study, published in August 2026, sits between them and was not available when the spread was first described. Wang examined Japanese residential land prices from 2015 to 2024 using a staggered difference-in-differences design with an event-study estimator, comparing municipalities named in a 2020 national survey against controls at five to fifteen kilometres. It reports an overall decline of 1.3 to 6.4 percent, deepening to 4.4 to 6.4 percent by the fourth year.

Two of its findings bear on the mechanism rather than the magnitude. The declines emerged only after media coverage intensified around 2023, three years after the disclosure itself, which is direct evidence for salience rather than information as the driver. And the effect was larger at higher-value properties, 6.4 to 6.5 percent in the top quartile, which is the opposite of what a pure avoidance-cost model predicts and further evidence for the stigma channel.

The gap between 2.8 percent and 31 to 42 percent is not reconcilable as a single PFAS effect, and a paper that quotes one figure without the others invites a straightforward attack. The plausible explanations are severity, salience, and concealment: Paulsboro was a high-profile case involving a multi-year delay in notification.

The defensible finding is that PFAS diminution is severely context-dependent, that the contextual variables include the salience of the disclosure as much as the concentration of the contaminant, and that a practitioner importing a percentage from any of these studies into an unrelated market is doing something the studies themselves do not support. Three peer-reviewed or working-paper estimates now span 1.3 percent to 42 percent, and two of the three attribute the timing of the effect to media attention rather than to the disclosure that preceded it.

5.3 The Adverse Authority

A federal court has excluded damages testimony that relied on the general environmental contamination meta-analysis literature to establish diminution. In Alexander v. Halliburton Energy Services (W.D. Okla. 2015), the plaintiffs' damages expert relied on a published meta-analysis to opine on diminution from groundwater contamination. The court excluded the opinions, finding that the model did not give the value of the properties immediately after the injuries as state law required, and that the opinions were not relevant to the damages issues.

The underlying objection is methodological and applies directly here. A meta-analysis aggregating disparate locations, timeframes, and contaminant types is not tied to the specific real estate market at issue, and an expert who substitutes a published average for market evidence has not performed a market analysis.

This paper cites that case rather than omitting it, for two reasons. An analysis intended to support testimony should confront adverse authority on its own central method. And the practical implication is the correct one: the published studies establish that the effect exists, that it can be large, and that it can persist after remediation. They do not establish a percentage that can be applied to a subject property. The percentage has to come from the subject market.

5.4 The Broader Contamination Literature

The general literature on environmental contamination and non-residential property provides useful structure even where it cannot supply a number. Saginor, Simons, and Throupe (2011) conducted a meta-analysis of 106 contaminated non-residential observations, drawn from peer-reviewed articles and appraiser case studies, regressing percentage and dollar losses on contamination type, region, land use, distance from source, elapsed time, market conditions, litigation, and indemnification. Model adjusted R-squared values range from 37 to 66 percent. Approximately a third of cases showed no loss at all. Creosote and polychlorinated biphenyl contamination, rural location, and under-remediation status were statistically significant, and properties in the remediation phase showed smaller losses than those where remediation had not begun.

The finding that a third of cases showed no loss is the useful one for practice. It establishes that contamination does not mechanically reduce value, that the variance is wide, and that the question in any assignment is empirical rather than presumptive. A mean drawn across a distribution containing many zeros is a different quantity from a typical impairment, and it should not be presented as one.

Bell and Tachovsky (2022) address PFAS valuation methodology directly, treating regression analysis, sale and resale analysis, and case study approaches for properties with contaminated water supplies. The contribution is methodological rather than quantitative.

No peer-reviewed study quantifying PFAS effects on airport, hangar, or aviation property has been published. That absence is stated here as a finding.

6. The Appraisal Framework

Contaminated property valuation has an established vocabulary and structure, and using it correctly keeps an analysis reviewable.

Advisory Opinion 9, which addresses the appraisal of real property that may be impacted by environmental contamination, defines the operative terms. Unimpaired value is the market value of a contaminated property developed under the hypothetical condition that the property is not contaminated. Impaired value is the market value with full consideration of the effects of its environmental condition. Environmental risk is the additional or incremental risk of investing in, financing, buying, or owning property attributable to its environmental condition. Environmental stigma is an adverse effect on property value produced by the market's perception of increased environmental risk due to contamination. Diminution in value is the difference between the unimpaired and impaired values. Remediation cost is the cost to clean up a contaminated property to appropriate regulatory standards.

Appraisal Institute Guide Note 6, on consideration of hazardous substances in the appraisal process, carries the same definitions and states the relation: impaired value equals unimpaired value less property value diminution. It also frames the scope of work decision, noting that an appraisal may be prepared so that the value opinion reflects no known or suspected contamination, or so that it does reflect known contamination. That choice is a scope decision to be made and documented at the outset, not a conclusion.

Two points of usage. The framework's term is remediation cost, not cost to cure; cost to cure is general appraisal vocabulary and is not defined in the advisory opinion, so an analysis attributing it to that source is inaccurate. And the Advisory Opinions were removed from the standards themselves beginning with the 2024 edition and are now published in a separate guidance and reference manual that can be updated independently. Practitioners should confirm the current status and text of any Advisory Opinion in the current manual rather than relying on an older printing.

Applied to a hangar, the structure gives the analysis its order. Establish the unimpaired value. Establish the remediation cost if a remedy has been designed, or disclose that it has not. Analyze stigma and environmental risk separately and from market evidence rather than from a published percentage. And test whether contamination changes the highest and best use, which on airport land it can, because a use the sponsor or the regulator will not permit on a contaminated parcel is not a legally permissible use.

Where the record is silent, the absence of testing is a finding to disclose, not a clean bill of health. An appraisal that reports no known contamination at a hangar with foam system history and no environmental assessment has reported the absence of a document rather than the absence of a condition.

7. What Changed in the Phase I

This section addresses the single item with the most immediate practical consequence, and it turns on a date.

The standard practice for a Phase I environmental site assessment is ASTM E1527-21, recognized by the federal all appropriate inquiries rule as satisfying the statutory inquiry required to establish the landowner liability defenses. That recognition took effect in February 2023, and the prior edition ceased to satisfy the rule in February 2024. E1527-21 is the sole compliant standard.

As drafted, E1527-21 placed PFAS among emerging contaminants, alongside asbestos, radon, lead paint, and mold, in the appendix addressing non-scope considerations. The standard limits hazardous substances to substances designated under the federal cleanup statute. Because no PFAS compound was then designated, PFAS fell outside mandatory scope and could be addressed only where a user specifically requested it or where the assessment was performed to satisfy state requirements as well. State PFAS regulation, however strict, did not pull PFAS into federal scope.

That is what nearly all published commentary says, and it is now out of date, because the standard contains its own conditional trigger. Emerging contaminants come within scope if and when they are defined as hazardous substances under the cleanup statute. PFOA and PFOS were so defined effective 8 July 2024.

The operative position is therefore precise and narrow. PFAS as a class remains a non-scope consideration under E1527-21. PFOA and PFOS specifically came within the standard's scope on 8 July 2024 by operation of the standard's own language, and can constitute recognized environmental conditions. Other PFAS compounds remain outside scope. A statement that PFAS is a non-scope consideration, without that carve-out, is no longer correct.

This reading is the plain application of the standard's conditional language and reflects practitioner consensus rather than a pronouncement by the standards body, which has issued none. It has two consequences worth stating for an audience of lenders and acquirers. A Phase I performed to E1527-21 after July 2024 should screen PFAS regulatory databases and document PFOA and PFOS presence at the subject and adjoining properties in order to support the liability defenses. And a report prepared before that date, or prepared after it by a consultant working from older guidance, may not have done so, which means a file containing a clean Phase I is not necessarily a file containing a PFAS screen.

For a hangar with foam history, that gap is the difference between a diligence file that supports a defense and one that does not.

8. Scale and Cost

8.1 How Many Facilities

There is no authoritative count of airports with confirmed PFAS contamination, and figures circulating in trade and advocacy material should not be used as one.

Two verifiable figures anchor the scale. The federal certification status list effective 3 September 2026 shows 517 certificated airports, each assigned an aircraft rescue and firefighting index from A through E. The regulation specifying agents and quantities names AFFF at every one of those index levels. So 517 is a defensible figure for airports that were subject to a federal regulation specifying AFFF, which is a statement about regulatory exposure rather than about confirmed contamination, and should be presented as such.

On the military side, the Government Accountability Office reported in February 2025 that as of June 2024 the Department of Defense had identified 718 military installations where PFAS was used or may have been released.

Advocacy compilations report much larger site counts across all categories. Those compilations draw on government testing data and are not fabricated, but they do not break out airports and cannot support an airport-specific count.

8.2 What Remediation Costs

No government agency, court filing, or peer-reviewed source has published a documented per-airport PFAS remediation cost for civilian airports. That is stated here as a finding rather than filled with an estimate. Section 8.4 assembles what has been disclosed, which is a different and narrower thing.

The only authoritative cost data is department-wide on the military side. The Government Accountability Office reported in February 2025 that the department has spent $2.6 billion since 2017, that estimated future investigation and cleanup costs exceed $9.3 billion in fiscal year 2025 and beyond, and that those estimates have more than tripled since 2022. The report's own thesis is that those figures are incomplete, so they function as a floor rather than an estimate, and the report provides no per-installation average.

Figures of the form "tens of millions per airport" or "millions to hundreds of millions per site" appear in trade and plaintiff-side material without methodology or source. They should not be carried into an appraisal.

8.3 The Litigation, and What It Does Not Do

The consolidated firefighting foam litigation is among the largest in the federal system, with 15,264 actions pending as of 1 September 2026 out of 19,840 filed historically, which places it third by pending actions nationally.

Two settlements have received final approval. One manufacturer announced a settlement with public water systems in June 2023, approved by the court on 29 March 2024, for a pre-tax present value commitment of up to $10.3 billion payable over thirteen years, with a nominal cap of $12.5 billion; those are the same settlement stated on two bases and should not be treated as separate figures. A second group of defendants settled with public water systems for $1.185 billion, allocated among three companies, with final approval in December 2023. A state natural resource damage settlement of up to $450 million was announced in May 2025.

The limitation matters more than the totals. Both principal settlements resolve claims of public water systems for PFAS in drinking water. Neither is a property damage settlement, and neither compensates a hangar or airport property owner for diminution.

Airports occupy both positions simultaneously. They appear as plaintiffs against foam manufacturers seeking to recover cleanup costs, and they are exposed as potentially responsible parties under a statute whose liability attaches to owners and operators without regard to fault. That dual posture is itself a valuation fact. An acquirer of hangar property is acquiring a contingent liability and, at most, an unliquidated claim. No documented airport-specific recovery could be confirmed.

8.4 What Airports Have Actually Spent

The finding in Section 8.2 stands: no authoritative total remediation cost has been published for any civilian airport. What can now be assembled is something narrower and still useful, a record of disclosed PFAS investigation, response and transition spending at named airports, drawn from state grant announcements and airport disclosures.

Michigan is the only state that has published airport-by-airport figures. Its third round of PFAS response grants, awarded 16 January 2026, distributed $9,000,000 among nineteen airports for testing and monitoring, source control and cleanup strategy for groundwater and stormwater, cleaning of firefighting equipment, and replacement turnout gear. Four airports received $1,000,000 each: Cherry Capital, the former Marquette County Airport, Houghton County Memorial and Pellston Regional. The smallest awards were $150,000. Across three rounds from 2020 the state has awarded roughly $18,500,000 to nineteen commercial service airports, with cumulative per-airport totals reaching about $1.6 million at Cherry Capital.

Two readings of that table are available and only one is defensible.

It does not establish what remediating an airport costs. Every line is a grant, a contract or a pilot, and none is a completed cleanup. Fairbanks has sampled 194 private wells, found 106 above the state action level, connected 99 properties to a utility, capped its fire training pit and run two pilot studies, and has published no total.

What it does establish is the order of magnitude of disclosed activity, and that order of magnitude is lower than the trade discussion implies. Individual line items run from $150,000 to $5,000,000. The largest disclosed civilian airport PFAS expenditure located anywhere is $5.23 million. Figures in the tens of millions per airport circulate in trade material and none of them could be traced to a source.

One consent order and one federal settlement notice are worth recording because they show the enforcement path without supplying a number. Westchester County Airport operates under a New York consent order executed 6 June 2019 requiring site characterisation and interim remedial measures for groundwater; no cost is disclosed. And on 16 April 2026 the agency noticed a proposed settlement at the Tucson International Airport Area Superfund site requiring the city to construct a treatment system for influent to the area remediation plant; no dollar amount appears in the notice. That is the only federal settlement notice involving PFAS at a named United States airport site located in this search.

9. Limitations

Five limitations bear on how this paper should be used.

The regulatory position is unstable. Two proposed rules affecting the drinking water standards were pending as of the date of this paper, and argument in the challenge to those standards was scheduled for days after it. The chemical reporting deadline has moved three times. Anything in Section 3 that turns on a pending proceeding should be checked against the current record before it is relied on.

The foam pathway question is not fully resolved. This paper establishes that the standard permitted two distinct pathways and that the low-expansion pathway is the AFFF source. It does not establish that high-expansion concentrates were categorically free of fluorosurfactants across their history, and the sources consulted do not support that claim. In an assignment, the system type and the concentrate actually used are questions of fact to be established from the record, not assumed from the building's group classification.

The quantitative evidence is residential and it is inconsistent. The three studies with usable magnitudes measure residential prices in three markets and span an order of magnitude. None addresses commercial aviation property. Applying any of those figures to a hangar would repeat the error a federal court excluded testimony for in the case discussed in Section 5.3.

The transfer problem is narrower and more serious than property type. Every one of those studies keys on drinking water exposure, through a public water system service area or through private wells. That is the mechanism producing the effect. A hangar is not occupied residentially, is typically not served by a private well, and the exposure pathway that drives a residential price response is largely absent. What remains at a hangar is the four channels this paper sets out: liability under the cleanup statute, remediation cost, insurance unavailability, and contraction of the buyer pool. Residential magnitudes do not transfer because the exposure pathway does not transfer, and that is the limitation a practitioner should state rather than the weaker one about property type.

Several figures a practitioner needs do not exist. There is no authoritative count of contaminated airports, no published per-airport civilian remediation cost, and no aviation-specific diminution study. Where this paper would otherwise supply a range, it says that no source exists.

Nothing here decides a legal question. Liability allocation between sponsor and tenant, the availability of statutory defenses, notification obligations, and insurance coverage are matters for counsel, and several of them carry deadlines a party can lose by inaction.

10. Conclusion

The exposure is real, it is unevenly distributed, and the analysis of it has been imprecise in ways that matter.

It is unevenly distributed because hangar fire protection permitted two foam pathways and only the low-expansion one used AFFF. Identifying which system a hangar had, and what concentrate went into it, is the first question in the analysis rather than an afterthought, and it is a question of fact with a documentary answer.

It is real because AFFF hangar systems were installed and were a documented source, as the Air Force confirmed when it locked out its own hangar foam tanks, and because airport-wide loading from apparatus testing, training, and response reaches parcels that never had a system of their own.

The liability position tightened and has held. The designation of PFOA and PFOS as hazardous substances took effect in July 2024 and survived appellate review in August 2026. Liability attaches to owners and operators without fault, the federal enforcement policy sheltering publicly owned airports reaches neither private owners nor private claims, and the standard-form insurance exclusion is broad enough to reach suspected presence.

Value moves through four channels, and the insurance and financing channel is the one most often omitted and the easiest to document. The quantitative evidence establishes that the effect exists, that it can be very large, and that it can persist after remediation, while also establishing that it varies by an order of magnitude across markets. That variance is the honest finding, and it means the percentage in any given assignment has to come from that market rather than from a published study.

For a lender or an acquirer, one date does more work than any other. Guidance written before 8 July 2024 says PFAS is outside the scope of the standard Phase I. Since that date, two PFAS compounds are inside it. A clean Phase I in the file is not, by itself, evidence that anyone looked.

References

Air Force Materiel Command. 2023. "Air Force to Eliminate PFAS-Containing Foam from Hangar Fire Suppression Systems." March 3, 2023.

Alexander v. Halliburton Energy Services, Inc., No. CIV-11-1343-M (W.D. Okla., July 22, 2015).

American Society for Testing and Materials. 2021. Standard Practice for Environmental Site Assessments: Phase I Environmental Site Assessment Process. ASTM E1527-21. West Conshohocken, PA: ASTM International.

Appraisal Institute. 2013. Guide Note 6: Consideration of Hazardous Substances in the Appraisal Process. Effective July 26, 2013, with minor revisions 2020. Chicago: Appraisal Institute.

Appraisal Standards Board. Advisory Opinion 9: The Appraisal of Real Property That May Be Impacted by Environmental Contamination. Washington, DC: The Appraisal Foundation. Advisory Opinions were relocated from USPAP to the USPAP Guidance and Reference Manual beginning with the 2024 edition.

Bell, R., and M. Tachovsky. 2022. "Real Estate Damage Economics: The Impact of PFAS 'Forever Chemicals' on Real Estate Valuation." Environmental Claims Journal 34 (2): 136-155. https://doi.org/10.1080/10406026.2021.1923926

Chalmers, J. A., and T. O. Jackson. 1996. "Risk Factors in the Appraisal of Contaminated Property." The Appraisal Journal 64 (1): 44-58.

Chamber of Commerce of the United States of America v. Environmental Protection Agency, No. 24-1193 (D.C. Cir., decided August 18, 2026).

Environmental Protection Agency, Office of Enforcement and Compliance Assurance. 2024c. PFAS Enforcement Discretion and Settlement Policy Under CERCLA. April 19, 2024.

Environmental Protection Agency. 2022. "Standards and Practices for All Appropriate Inquiries." 87 Federal Register 76578 (December 15, 2022).

Environmental Protection Agency. 2024a. "PFAS National Primary Drinking Water Regulation." 89 Federal Register 32532 (April 26, 2024).

Environmental Protection Agency. 2024b. "Designation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) as CERCLA Hazardous Substances." 89 Federal Register 39124 (May 8, 2024).

Environmental Protection Agency. 2026. "Extending the Compliance Deadline for the PFOA and PFOS Maximum Contaminant Levels." 91 Federal Register 29425 (May 20, 2026). Proposed rule.

FAA Reauthorization Act of 2018, Public Law 115-254, section 332, 132 Stat. 3273 (October 5, 2018).

FAA Reauthorization Act of 2024, Pub. L. No. 118-63, section 767, 138 Stat. 1291-1293 (May 16, 2024), codified as a note to 49 U.S.C. section 44706. https://www.congress.gov/118/plaws/publ63/PLAW-118publ63.htm

Federal Aviation Administration. 2023. Aircraft Firefighting Foam Transition Plan, May 8, 2023. https://www.faa.gov/sites/faa.gov/files/FAA_Aircraft_F3_Transition_Plan_2023.pdf

Federal Aviation Administration. 2023. Aircraft Firefighting Foam Transition Plan. Washington, DC: U.S. Department of Transportation.

Federal Aviation Administration. 2026. Airport Improvement Program Program Guidance Letter 26-03, January 6, 2026. https://www.faa.gov/airports/aip/guidance_letters/aip_pgl_26_03

Federal Aviation Administration. 2026. Part 139 Airport Certification Status List, effective September 3, 2026.

Federal Aviation Administration. 2026a. "AFFF and Synthetic Fluorine Free Foam (F3) Testing at Certificated Part 139 Airports." CertAlert 26-03, August 5, 2026.

Federal Aviation Administration. 2026b. Part 139 Airport Certification Status List. Effective September 3, 2026.

Government Accountability Office. 2025. Persistent Chemicals: DOD Needs to Provide Congress More Information on Costs Associated with Addressing PFAS. GAO-25-107401. February 24, 2025.

Insurance Services Office. 2023. Exclusion: Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS). Form CG 40 32 05 23.

Islam, M., and M. D. Heintzelman. 2023. "Perceptions of Risk: The Impacts of PFAS Contamination on Local Property Values." Working Paper, SSRN 4547307. Not peer reviewed.

Jackson, T. O. 2001. "The Effect of Previous Environmental Contamination on Industrial Real Estate Prices." The Appraisal Journal 69 (2): 200-210.

Jackson, T. O. 2003. "Methods and Techniques for Contaminated Property Valuation." The Appraisal Journal 71 (4): 311-320.

Jackson, T. O. 2004. "Surveys, Market Interviews and Environmental Stigma." The Appraisal Journal 72 (4): 300-310.

Jackson, T. O. 2005. "Evaluating Environmental Stigma with Multiple Regression Analysis." The Appraisal Journal 73 (4): 363-369.

Jackson, T. O., and M. Sowinski. 2006. "Institutional Controls and Contaminated Property Valuation." The Appraisal Journal 74 (4): 328-332.

Marcus, M. M., and R. Mueller. 2024. "Unregulated Contaminants in Drinking Water: Evidence from PFAS and Housing Prices." Journal of Environmental Economics and Management 125: 102987. https://doi.org/10.1016/j.jeem.2024.102987

Michigan Department of Environment, Great Lakes, and Energy. 2022. Part 201 Generic Residential Groundwater Cleanup Criteria, rule set 2020-130 EQ, Rule 44. In effect since December 2020.

Michigan Department of Environment, Great Lakes, and Energy. 2026. "EGLE Awards $9 Million in PFAS Response Grants to Airports," January 16, 2026. https://www.michigan.gov/egle/newsroom/press-releases/2026/01/16/egle-awards-9-million-in-pfas

National Fire Protection Association. 2011, 2022, 2026. NFPA 409: Standard on Aircraft Hangars. Quincy, MA: NFPA.

New Hampshire Revised Statutes Annotated 477:4-a, Notification Required: Radon, Arsenic, Lead, PFAS and Flood. PFAS provision added 2024, chapter 98:1, effective January 1, 2025.

PFAS Reporting and Recordkeeping Requirements, 91 Fed. Reg. 18786 (Apr. 13, 2026).

Saginor, J., R. Simons, and R. Throupe. 2011. "A Meta-Analysis of the Effect of Environmental Contamination on Non-Residential Real Estate Values." Journal of Property Investment and Finance 29 (4/5): 460-478. https://doi.org/10.1108/14635781111150349

Simons, R. A., and J. D. Saginor. 2006. "A Meta-Analysis of the Effect of Environmental Contamination and Positive Amenities on Residential Real Estate Values." Journal of Real Estate Research 28 (1): 71-104.

United States Judicial Panel on Multidistrict Litigation. 2026. Pending MDL Dockets by Actions Pending. September 1, 2026. In re Aqueous Film-Forming Foams Products Liability Litigation, MDL No. 2873 (D.S.C.).

Wang, M. 2026. "PFAS contamination disclosures and declining residential land prices in polluted areas of Japan." Journal of Environmental Economics and Management 139: 103391. https://doi.org/10.1016/j.jeem.2026.103391

14 C.F.R. section 139.317, Aircraft rescue and firefighting: Equipment and agents. Last amended 69 Federal Register 31523 (June 4, 2004).

This paper is research and general information for professionals evaluating aviation real estate. It is not appraisal, legal, or tax advice, and it does not create an engagement. Environmental liability and disclosure obligations vary by jurisdiction and are questions for counsel.