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Two Ozone Classifications, One Plant: The 25 Ton Threshold Houston and Dallas Fort Worth Sources Are Permitting Against Right Now
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Two Ozone Classifications, One Plant: The 25 Ton Threshold Houston and Dallas Fort Worth Sources Are Permitting Against Right Now

Houston and Dallas Fort Worth sit in two ozone nonattainment classifications at once, so the binding air permitting threshold is 25 tpy of VOC or NOx, not 50.

by iSi Environmental

A plant in Harris County and a plant in Bexar County both sit inside ozone nonattainment areas, and they screen a new project against different numbers. Texas carries four ozone nonattainment areas today, counting the El Paso portion of the El Paso-Las Cruces area, and two of them, Houston-Galveston-Brazoria and Dallas-Fort Worth, carry obligations under two separate ozone standards at the same time. That double classification is what decides a facility’s real air permitting thresholds. It is also the fact most self-audits and most vendor summaries get wrong. In HGB and DFW the binding major source threshold is 25 tons per year of VOC or NOx, and screening against 50 tpy produces the wrong answer.

The failure mode is specific and expensive. A facility runs its potential to emit against the newer 2015 Serious numbers, lands at 40 tpy of NOx, files as a minor source, and builds. Under the 2008 Severe classification that same facility was major, the project was a major modification, and it needed a nonattainment NSR permit with LAER and offsets at 1.3 to 1. The error does not surface during construction. It surfaces during a Title V renewal, an inspection, or a due diligence review two years later, priced at up to $124,426 per day per violation under CAA Section 113(b) (40 CFR 19.4 Table 1).

On September 29, 2026, EPA announced it is reconsidering the classification determinations for all three Texas metros. Nothing about the paragraph above changed. There is no proposed rule, no Federal Register document, no docket, and no comment period. Every threshold, offset ratio, RACT duty and attainment deadline below is in force and enforceable today.

The Status Box: What Applies as of September 30, 2026

Houston-Galveston-BrazoriaDallas-Fort WorthSan Antonio
2008 NAAQS classificationSevere, effective 2022-11-07Severe, effective 2022-11-07None
2015 NAAQS classificationSerious, effective 2024-07-22Serious, effective 2024-07-22Serious, effective 2024-07-22
Counties, 2008 Severe area8, including Liberty10, including RockwallNot applicable
Counties, 2015 Serious area6, excludes Liberty and Waller9, excludes RockwallBexar only
Major source threshold in practice25 tpy VOC or NOx25 tpy VOC or NOx50 tpy VOC or NOx
NNSR offset ratio in practice1.3 to 11.3 to 11.2 to 1
Attainment date driving the math2027-07-20 (2008), 2027-08-03 (2015)2027-07-20 (2008)2027-09-24 (2015)
CAA Section 185 fee exposureYes, Severe areaYes, Severe areaNo
Effect of the 2026-09-29 announcementNone. No proposed rule exists.None. No proposed rule exists.None. No proposed rule exists.

Two manufacturers with identical emissions inventories, one in Fort Bend County and one in Bexar County, run different applicability math and buy different amounts of offset. The Fort Bend site crosses into major source status at half the tonnage and pays 8 percent more in offsets per ton once it does.

What Is the Current Ozone Nonattainment Classification for Houston, Dallas-Fort Worth and San Antonio?

HGB and DFW are classified Severe for the 2008 8-hour ozone NAAQS, effective November 7, 2022 (87 FR 60926), and Serious for the 2015 NAAQS, effective July 22, 2024 (89 FR 51829). San Antonio is Serious for the 2015 standard only. HGB and DFW therefore carry two overlapping classifications, and the more stringent one governs.

The 2008 standard has not been revoked. It remains in force at 40 CFR 50.15, so its Severe classification still applies alongside the 2015 classification, which is why it keeps producing the controlling number. Where two classifications sit on the same facility, the stricter requirement applies. In HGB and DFW that is Severe-15 under the 2008 standard, not Serious under 2015.

San Antonio is the simpler case. Bexar County carries one classification under one standard, so the applicability analysis has one branch instead of two (EPA, Designations for the San Antonio Metropolitan Area).

What Is the Major Source Threshold for Air Permitting in Houston or Dallas-Fort Worth?

25 tons per year of VOC or NOx, set by the Severe classification under the 2008 ozone NAAQS at 42 USC 7511a(d). The 50 tpy figure implied by the 2015 Serious classification does not control in these two areas. A facility screening against 50 tpy can wrongly conclude it is a minor source.

The band between 25 and 50 tpy is where the exposure concentrates. Mid-market coatings operations, tank farms, printing plants, fabrication shops with solvent cleaning, and any combustion-heavy site with permitted but lightly loaded boilers routinely land there. Facilities in that band are major sources in HGB and DFW and minor sources in San Antonio on identical numbers.

Note what the threshold does not depend on. It is not driven by county population, by SIC code, by whether TCEQ has ever inspected the site, or by whether the facility holds a Title V permit. It is driven by area classification and facility-wide potential to emit.

Which Counties Are Covered by Each Texas Ozone Nonattainment Area?

The HGB 2008 Severe area covers 8 counties: Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery and Waller. The DFW 2008 Severe area covers 10: Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, Tarrant and Wise. The 2015 Serious footprints are narrower. Liberty and Waller are excluded on the HGB side and Rockwall on the DFW side (40 CFR 81.344). San Antonio is Bexar County only.

Those two exclusions are the county-level wrinkle worth reading twice. Liberty and Waller Counties sit in the 2008 Severe area but not the 2015 Serious area, so a Liberty or Waller County facility’s entire ozone nonattainment obligation flows from the 2008 standard. If that classification is ever revisited, it is the whole ballgame for that site rather than one of two overlapping regimes. Rockwall County is the same case on the DFW side, in the 2008 Severe list and absent from the 2015 Serious list per TCEQ (TCEQ, Dallas-Fort Worth ozone history and current status).

Screen against both county lists, in that order, every time. A single-list screen against the 2015 footprint is how a Liberty, Waller or Rockwall County site ends up treated as outside nonattainment when it is a 25 tpy Severe area site. Cross-check the county against the EPA Green Book Texas listing and save the page in the compliance file with the date.

How Is Potential to Emit Calculated for Major Source Screening?

Potential to emit is maximum capacity to emit under a facility’s physical and operational design, counting only federally enforceable limits. Sources under common control in a contiguous area aggregate into one facility. Actual historical emissions do not control the test, which is why lightly loaded plants holding unrestricted permits are frequently major sources without knowing it.

Three practical consequences follow. First, an emissions inventory reporting actuals is not an applicability test, and using it as one is the most common shortcut in facility self-audits. Pull PTE from the Title V application or the most recent construction permit instead. Second, VOC and NOx are tested separately. A facility at 18 tpy VOC and 31 tpy NOx in Harris County is a major source on the NOx side alone. Third, a voluntary operating practice does not reduce PTE. Only a federally enforceable limit does, which is what makes a synthetic minor limit a deliberate permitting decision rather than a paperwork step.

Run the aggregation question before the arithmetic. Two permitted units under common control on adjoining tracts are one source for this purpose, and splitting them across two spreadsheets is how a 25 tpy threshold gets missed by design.

What Is the Emission Offset Ratio for a New Project in a Texas Ozone Nonattainment Area?

1.3 to 1 in HGB and DFW under the Severe classification (42 USC 7511a(d)(2)), and 1.2 to 1 in San Antonio under Serious (42 USC 7511a(c)(10)). Offsets must be surplus, quantifiable, permanent, federally enforceable, and located in the same nonattainment area as the project, or, where the state allows it, in a contributing nonattainment area of equal or higher classification (42 USC 7503(c)(1)), before a facility can rely on them.

Each of those five qualifiers has killed a project schedule somewhere. Credits generated by a shutdown already counted in a SIP demonstration are not surplus. Credits from a facility in a neighboring attainment county do not help a Harris County project. Credits documented only by a corporate memo are not federally enforceable. The time to test a credit package is before the application is filed, because a credit failing review during technical review restarts the offset search with a clock running.

At 1.3 to 1, a project adding 30 tpy of NOx needs 39 tpy of verified reductions. Budget the acquisition and the review, not just the tonnage.

Does LAER or BACT Apply to a Project in a Texas Ozone Nonattainment Area?

LAER applies to new and modified emission units permitted through nonattainment NSR. LAER is the most stringent emission limitation achieved in practice or contained in any SIP, whichever is more stringent, and unlike BACT its definition contains no cost-effectiveness step (42 USC 7501(3)). Cost is not a basis for choosing a less stringent limit than one already achieved in practice.

BACT attaches to PSD permitting in attainment areas and includes an economic feasibility step. Applicants who have only ever permitted under PSD tend to carry that step into an NNSR application and build a cost analysis into the control selection. That analysis has no effect on the outcome. The RACT determinations sitting elsewhere in an ozone SIP do include cost feasibility, which is a further reason the three acronyms get conflated.

The practical sequencing point: identify the LAER comparator early, because the emission limit it produces drives equipment selection, and equipment selection drives the schedule.

When Are the Attainment Deadlines for Texas Ozone Nonattainment Areas?

HGB and DFW must attain the 2008 ozone NAAQS by July 20, 2027, and HGB must attain the 2015 NAAQS by August 3, 2027 (TCEQ HGB status). San Antonio must attain the 2015 NAAQS by September 24, 2027 (TCEQ San Antonio status). The 2026 ozone season is an attainment year, so much of the controlling data is fixed.

That last point governs how a facility should read the next twelve months. Design values run on three years of monitored data. Whatever the 2026 season produced is in the books. Any classification relief argued in 2027 is being argued against a data record that already exists, which is why “wait and see” is a weaker position here than it looks.

What Is the Clean Air Act Section 185 Fee and Does It Apply to My Houston Facility?

The CY2025 Section 185 rate is $12,850.67 per ton of VOC and NOx, assessed on major sources in Severe and Extreme ozone areas that miss their attainment date (EPA memorandum, October 2, 2025). TCEQ has estimated the HGB-wide obligation could be as much as $154 million in 2028, the earliest year the fee could be imposed if the July 20, 2027 deadline is missed (TCEQ HGB 185 fee program).

This is the item most worth modeling now, for one reason: it is not an enforcement action. Section 185 attaches by operation of statute when a Severe area misses its attainment date, and it is assessed on major sources whether or not any individual source violated anything. A facility with a clean compliance record, current permits and no open notices of violation can still owe the fee. It is calculated on emissions above 80 percent of a baseline.

HGB is the live case. TCEQ previously sought to cease its Section 185 fee program for the revoked 1979 1-hour ozone standard, and in December 2024 EPA proposed to disapprove that cessation (89 FR 103734, FR Doc 2024-29935). No final action on that proposal has been published. The 2008-standard fee obligation is separate and attaches by statute. For the mechanics of how these programs are built and assessed, see EPA’s Section 185 fee program guidance.

Build the number into the 2028 budget as a scenario line now. A major source in HGB can compute its own exposure today from its baseline and its projected emissions, and the calculation takes an afternoon.

What Is the Penalty for a Clean Air Act Violation in Texas in 2026?

Up to $124,426 per day per violation under CAA Section 113(b), per 40 CFR 19.4 Table 1 for penalties assessed on or after January 8, 2025. Permitting violations accrue daily rather than per event, so one unpermitted modification discovered eighteen months after startup produces a very large calculated exposure before any negotiation begins.

The daily-accrual mechanic is what makes a threshold error compound. The exposure is not the cost of the permit that should have been obtained. It is the number of days between construction and discovery, multiplied by the daily maximum, as the opening position in a settlement discussion.

One honest limit on this section. A search of EPA’s published material found no enforcement initiative, National Enforcement Priority, or inspection-targeting document specific to Texas ozone nonattainment NSR. The penalty ceiling is sourced and the Section 185 mechanism is sourced. Any claim that inspections in these metros are rising is not, and this post will not make one.

Does the September 2026 EPA Reconsideration Announcement Change My Permitting Obligations?

No. On September 29, 2026 EPA announced it will reconsider the Texas ozone classifications and the 2022 disapproval of Texas’s Section 179B demonstration, stating it “plans to propose reconsideration actions by the end of this year and finalize all actions next year” (EPA news release). No proposed rule, docket or comment period exists. Every threshold and deadline remains enforceable.

An announcement of intent to propose is not a proposal, and a proposal is not a final rule. Each step carries its own Federal Register document, its own docket and its own effective date, and obligations change at the last of those steps rather than the first. Until then a permit writer at TCEQ applies the current classification, and an EPA enforcement officer evaluates conduct against the current classification.

The operational instruction follows directly. Do not relax a control, a permit limit, a monitoring requirement or a recordkeeping obligation on the strength of this announcement. There is nothing yet to comply with and nothing yet to cite. What a facility should do is track the docket when it opens, expected by the end of 2026, and preserve the emissions and modeling data needed to file a useful comment.

What Is Clean Air Act Section 179B and What Is Texas Claiming Under It?

Section 179B lets a state demonstrate that an area would have attained the ozone standard but for emissions transported into it from outside the United States. EPA disapproved Texas’s 179B demonstration in 2022 and announced on September 29, 2026 that it is reconsidering that disapproval. A granted demonstration could affect classification outcomes.

Texas has continued to build the technical record. TCEQ published a Section 179B(b) demonstration for Bexar County under the 2015 ozone NAAQS in June 2026, and El Paso has its own long-running international transport demonstration as part of the El Paso-Las Cruces TX-NM area. El Paso is a separate matter from the three metros here and deserves its own treatment.

What 179B does not do is worth stating plainly, because the headline invites the wrong inference. A successful demonstration addresses an attainment determination. It does not automatically retire RACT obligations already written into an approved SIP, and it does not unwind permits already issued with offsets and LAER attached.

Should I Delay a Permit Application to Wait for the Reconsideration to Finalize?

Waiting carries real risk. EPA’s own stated timeline puts final action sometime in 2027, possibly after the July 20, 2027 attainment date, and reconsideration may narrow obligations rather than remove them. A permit issued under current rules stays valid. A project stalled for a year loses a construction season in exchange for a legal outcome nobody can cite yet.

Three things a facility gives up by waiting. Offset availability, which tightens as other applicants in the same area buy the same credits. Schedule, because the technical review clock does not start until the application is filed. And optionality, because a permit in hand can be amended, while a project held at the concept stage has nothing to amend.

There is a narrow case for timing. A project in Liberty, Waller or Rockwall County, whose only ozone obligation flows from the 2008 standard, has more riding on the reconsideration than a Harris County project with obligations under both standards. Even there, the decision should be made against a modeled schedule and a priced offset package rather than against a news release.

What Cuts Against the Relief Story

The one-sided version of this news is that EPA is granting Texas relief. Five things cut against it, and they belong in the same document as the exposure.

The announcement has no legal effect, and EPA’s own timeline outruns the deadline. EPA says it will propose by the end of 2026 and finalize in 2027. The 2008-standard attainment date is July 20, 2027. A final action landing in mid or late 2027 may arrive after the date whose consequences it would relieve, including the Section 185 fee trigger.

Litigation pressure runs in both directions. In Sierra Club v. EPA, No. 23-3581 (6th Cir., Dec. 5, 2025), the Sixth Circuit vacated EPA’s redesignation of the Detroit area to attainment for the 2015 ozone standard and put the metro back into nonattainment NSR. A reconsideration that loosens classifications becomes a target for challenge the day it is final, so “finalized in 2027” does not mean “settled in 2027.”

Reconsideration is not redesignation. Even a successful 179B demonstration goes to the attainment determination. Obligations already embedded in an approved SIP are stickier than the classification headline suggests, and permits already issued with offsets and LAER attached do not unwind themselves.

One recent Fifth Circuit ruling against an EPA Texas designation exists, and it is not an ozone case. Texas v. EPA, No. 17-60088 c/w No. 21-60673 (5th Cir., May 16, 2025, on rehearing) granted the petitions for review and remanded EPA’s sulfur dioxide nonattainment designation for Rusk and Panola Counties, holding that EPA’s reliance on a single disputed model violated the APA. It shows the court will rule against an EPA Texas designation. It says nothing about ozone, it involves different counties, and it does not govern HGB, DFW or San Antonio. It is flagged here because it is the case most likely to be miscited into an ozone discussion.

The monitoring record is largely written. Design values run on three years of data, and the 2026 ozone season is an attainment year for the 2027 deadlines. A reconsideration argued in 2027 argues against a data record that already exists.

No counter-signal was found indicating any other state is moving the opposite direction on ozone classification in response to the Texas action. It is too recent for that to have shown up.

What to Do in the Next 30 Days

  1. Establish area status in writing for every Texas site, against both county lists. Save the Green Book page and the Federal Register citation with the date checked. A Liberty, Waller or Rockwall County site needs the distinction documented explicitly.
  2. Recalculate facility-wide potential to emit for VOC and for NOx separately, from design capacity and federally enforceable limits, not from the emissions inventory. Run the result against 25 tpy in HGB and DFW and against 50 tpy in Bexar County.
  3. Re-screen every in-flight and planned project against the number that came out of step 2. Any project screened against 50 tpy in HGB or DFW gets redone.
  4. Price the offset package at 1.3 to 1 in HGB and DFW and at 1.2 to 1 in San Antonio, and test each credit against all five qualifying criteria before relying on it.
  5. Identify the LAER comparator for any new or modified unit before locking equipment selection, and drop the cost-effectiveness analysis from the control decision.
  6. Verify RACT posture for existing sources under the applicable TCEQ rules for each area and standard. RACT is a standing obligation and does not wait for a project to trigger it.
  7. Model Section 185 fee exposure at $12,850.67 per ton for every major source in HGB and DFW, on emissions above 80 percent of baseline, and carry it as a 2028 budget scenario.
  8. Change nothing on the strength of the September 29 announcement. Calendar the docket instead, expected to open by the end of 2026, and preserve the emissions and modeling data a comment would need.

Where iSi Fits

The work above is a two-list boundary check, a potential-to-emit recalculation, an offset package review and a Section 185 model. For a plant manager doing it between production issues, it stretches across a quarter. The cost of getting it wrong is not the permit fee. It is a construction hold on a line expansion, or a major modification discovered in year three at a daily penalty rate.

iSi handles potential-to-emit calculations, air permit applicability determinations and nonattainment NSR permitting support for manufacturers across 40 states, including the Texas metros covered here. If you want the applicability question answered in writing before the reconsideration docket opens, call (316) 264-7050 or request a quote.

Sources

iSi’s environmental, safety, and industrial hygiene consultants work across 40 states, with fixed pricing and quotes back the same day. Request a quote.

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