The FENCES Act amends section 179B of the Clean Air Act and adds a new section (179C) to clarify when emissions originating outside the United States — including those the bill says may be natural — may be treated as beyond U.S. control for purposes of nonattainment designations and federal sanctions. The bill inserts the phrase “(regardless of whether such emissions result from human activity)” into 179B, adds an explicit bar to designating areas as nonattainment where a State can show the area would be in attainment but for foreign emissions, and creates a statutory exemption from certain sanctions and fee provisions when a State makes specified demonstrations.
This matters because it changes the legal test for nonattainment and sanctions from purely domestic responsibility to a but-for causation framework tied to demonstrable foreign or otherwise uncontrollable sources. The bill shifts evidentiary burdens onto states and the EPA and creates recurring procedural obligations (including a five-year renewal requirement) that will shape modeling, monitoring, permitting, and enforcement strategy in border and downwind regions.
At a Glance
What It Does
The bill amends section 179B to treat emissions from outside the U.S.—including natural sources—as potentially making an area nonattainment “but for” those emissions. It adds a new 179B(e) preventing nonattainment designations when a State demonstrates to EPA that foreign emissions are the but-for cause, and creates section 179C to make sanctions or fees under sections 179 or 185 inapplicable for certain severe ozone and serious particulate nonattainment areas if similar demonstrations succeed.
Who It Affects
State air agencies (especially in border and downwind states), EPA regional offices that review demonstrations, stationary sources and developers in areas that would otherwise be designated nonattainment, and entities responsible for air quality monitoring and regional emissions modeling. Transportation planners and port authorities also face implications through a mobile-source carve-out.
Why It Matters
It establishes a statutory pathway for states to avoid designations and sanctions based on foreign or natural emissions, changing the practical stakes of attainment demonstrations and compliance planning. The law creates recurring evidentiary demands (including 5‑year renewals) that will concentrate technical and legal resources at state agencies and at EPA.
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What This Bill Actually Does
The bill changes the Clean Air Act in two distinct ways. First, it amends section 179B to make clear that emissions “emanating from outside of the United States” count as emissions beyond U.S. control whether or not those emissions arise from human activity.
Practically, that means natural phenomena—such as wildfires or long-range transport of dust—that cross the border are explicitly treated as potential reasons an area could fail to meet an ambient air standard without holding the State responsible.
Second, the bill adds two linked legal protections for states. It inserts a new subsection into 179B that bars the federal government from designating an area as nonattainment for a new or revised national ambient air quality standard if the State demonstrates to EPA that the area would be in attainment but for emissions from outside the United States (again, regardless of human causation).
Separately, the bill creates a new section 179C establishing that sanctions or fee provisions under sections 179 and 185 do not apply to certain high-classification nonattainment areas (Severe/Extreme ozone or Serious particulate) where the State shows the failure to attain or the specific deficiency resulted from foreign emissions, an exceptional event, or mobile-source emissions beyond the State’s control and where the State is fully implementing measures within its authority.Operationally, the statute places the burden on States to build “but-for” demonstrations to EPA’s satisfaction and requires those demonstrations to be renewed at least once every five years. The statute preserves the underlying obligation to pursue attainment measures: non‑applicability of sanctions does not relieve states of their duty to establish and implement plans.
The mobile-source carve-out is conditional — a State must show both that the mobile emissions are beyond its ability to reduce and that it has implemented all measures it can under its jurisdiction.Taken together, the bill doesn’t eliminate federal oversight; it creates a repeatable, evidence-driven escape hatch for states that can document cross‑border or uncontrollable sources are the critical cause of nonattainment. That reshapes where the technical work will sit (modeling, source-apportionment, and monitoring) and how EPA evaluates compliance threats and enforcement priorities.
The Five Things You Need to Know
The bill inserts the phrase “(regardless of whether such emissions result from human activity)” into section 179B, explicitly covering natural as well as anthropogenic foreign emissions.
It adds 179B(e), which prohibits a federal nonattainment designation for a new or revised NAAQS if a State demonstrates to EPA that the area would be in attainment but for emissions originating outside the United States.
The bill creates a new section 179C that makes sanctions and fees under sections 179 and 185 inapplicable for Severe/Extreme ozone areas and Serious particulate areas when the State shows the deficiency was due to foreign emissions, an exceptional event, or mobile-source emissions beyond State control.
Section 179C requires States to renew their demonstrations at least once every five years for the sanctions/fees inapplicability to continue.
The mobile-source exemption in 179C is two-pronged: the State must show (A) the mobile emissions are beyond the State’s ability to control or eliminate and (B) the State is fully implementing measures within its legal authority to control those mobile emissions.
Section-by-Section Breakdown
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Clarifies 179B to include non‑anthropogenic foreign emissions
This amendment introduces the parenthetical “(regardless of whether such emissions result from human activity)” into existing 179B language wherever the statute refers to emissions emanating from outside the United States. Mechanically, the change expands the class of emissions that can be treated as beyond U.S. control to include natural events (for example, wildland fire smoke or dust storms transported across borders), not just foreign industrial or mobile sources. Practically, enforcement and designation decisions must now treat naturally originating transboundary pollution as presumptively relevant to but‑for causation analyses.
Bars nonattainment designation where State proves but‑for foreign emissions
The new subsection creates a statutory bar: EPA may not designate an area as nonattainment for a new or revised primary or secondary NAAQS if the State demonstrates to the Administrator that the area would be in attainment but for emissions from outside the United States (again, including natural sources). This places a legal checkpoint before a designation can issue, requiring EPA to accept a State’s technically supported showing that foreign emissions are the decisive factor. The provision will require clear procedural work—what form demonstrations must take, how EPA evaluates modeling, and how robust uncertainty treatment must be—because it effectively removes several areas from the universe of potential designations if the State carries its burden.
Creates sanctions/fee inapplicability for certain high‑classification areas
Section 179C prevents sanctions under section 179 and fees under section 185 from applying to Severe/Extreme ozone areas (section 181 classifications) and Serious particulate areas (section 188) when a State demonstrates the nonattainment or deficiency was caused by: (1) foreign emissions, (2) an exceptional event as already defined in the Act, or (3) mobile-source emissions that are beyond the State’s control while the State is fully implementing its available measures. The section preserves the substantive duty to pursue attainment measures, so it is a procedural and sanction‑relief tool rather than a substantive rollback of attainment obligations. The five‑year renewal requirement creates a recurring compliance and modeling schedule.
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Who Benefits
- State air agencies in border or downwind regions: They gain a statutory path to avoid nonattainment designations and associated sanctions if they can document cross‑border or natural but‑for causes, reducing immediate regulatory pressure on state plans.
- Industrial sources and developers in affected areas: Facilities that would otherwise face permitting constraints and offset requirements tied to a new nonattainment designation may avoid those costs where a successful State demonstration prevents designation.
- Ports, freight operators, and transportation planners: The statute’s explicit mobile‑source carve‑out offers a potential defense for regions where international shipping or interstate mobile emissions substantially drive exceedances, lowering near‑term regulatory risk for transportation infrastructure projects.
Who Bears the Cost
- State environmental agencies: States must assemble technically robust but‑for demonstrations (modeling, monitoring, legal submissions) and redo this work every five years, creating recurring budgetary and staffing costs.
- EPA regional offices and Headquarters: EPA must review, adjudicate, and potentially litigate complex source‑apportionment demonstrations and decide when sanctions and designations apply, increasing administrative workload and technical review demands.
- Local communities and public‑health advocates: If cross‑border or natural emissions are accepted as the decisive cause of nonattainment, local stakeholders could face delayed or reduced domestic emission controls, potentially prolonging exposure to unhealthy air while states await or perform recurrent demonstrations.
Key Issues
The Core Tension
The central dilemma is fairness versus accountability: the bill aims to avoid penalizing states for pollution they cannot control, including natural transboundary sources, but by reducing the immediate threat of designations and sanctions it risks weakening incentives for domestic emissions reductions and creates technical and administrative burdens that may produce uneven outcomes across states.
The bill delegates intense technical and legal work to states and EPA without specifying procedural standards for how ‘‘but‑for’’ demonstrations must be prepared or evaluated. Source apportionment across international boundaries is scientifically complex: atmospheric modeling, background concentration estimation, and attribution of episodic events contain inherent uncertainty.
The statute’s insistence that foreign emissions count “regardless of whether” they are natural places wildfires and other natural phenomena squarely into regulatory calculus, but the bill does not define thresholds for when natural background levels are sufficient to defeat a designation. That gap invites litigation, divergent EPA regional practices, and uneven outcomes between well‑resourced and under‑resourced states.
The new sanctions carve‑out narrows the immediate enforcement toolbox for EPA where a State prevails, but the bill explicitly preserves the obligation to continue pursuing attainment measures. That tension—removing punitive consequences while keeping the obligation intact—could produce compliance plans that focus on documentation rather than accelerated emissions reductions.
The mobile‑source exception is operationally ambiguous: the phrases “beyond the control of the State” and “fully implementing such measures as are within the authority of the State” are fact‑intensive and likely to be contested, particularly where federal or regional transportation policy intersects with state authority. Lastly, the five‑year renewal requirement creates recurring uncertainty for regulated entities and communities: relief is temporary and contingent, not permanent, which will complicate long‑term planning for permits and infrastructure.
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