One Airshed, Two Thresholds: What Ozone RACT Actually Requires of St. Louis Missouri Sources Right Now
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One Airshed, Two Thresholds: What Ozone RACT Actually Requires of St. Louis Missouri Sources Right Now

The Eighth Circuit stay keeps Missouri St. Louis sources at 100 tpy RACT and NNSR thresholds today, while the Illinois side of the same airshed sits at 50 tpy.

by iSi Environmental

If you run a permitted plant in St. Louis City, St. Louis County, St. Charles County, Jefferson County, or Boles Township in Franklin County, you are inside an ozone nonattainment area for the 2015 8-hour standard of 0.070 ppm, and reasonably available control technology applies to you today. What most operators in that footprint have wrong is the number. Headlines and vendor summaries say Missouri sources are now at a 50 tons-per-year major-source threshold. They are not. A federal court stay put that change on hold, and the Moderate-area numbers are what MoDNR is permitting against right now.

The result is a split nobody expected: one airshed, one design value, one attainment date, and two different major-source thresholds depending on which side of the Mississippi your plant sits on.

The Status Box: What Actually Applies as of August 19, 2026

Missouri portionIllinois portion
CountiesSt. Louis City, St. Louis Co., St. Charles Co., Jefferson Co., Boles Township only in Franklin Co.Madison, Monroe, St. Clair
Classification on paperSerious, effective 2024-12-31Serious, effective 2025-01-16
Effectiveness statusStayed by the Eighth Circuit 2025-06-06, case in abeyanceNo stay has been reported
Major source threshold in practice100 tpy VOC or NOx (Moderate)50 tpy VOC or NOx
NNSR offset ratio in practice1.15:11.20:1
Clean Data DeterminationFinal 2026-08-13, effective 2026-09-14Final 2026-08-13, effective 2026-09-14

Two manufacturers 15 miles apart, one in St. Charles County and one in Madison County, run different applicability math on the same corporate emissions inventory. That is the current state of the bi-state corridor, and it is the fact that gets missed because it lives in a footnote.

Is the St. Louis Missouri Area Actually Classified Serious Right Now?

The Missouri portion was reclassified from Moderate to Serious effective December 31, 2024 (89 FR 92816), but on June 6, 2025 the Eighth Circuit stayed the effectiveness of that rule pending judicial review. MoDNR states the operational result plainly: “While the stay is in effect, the moderate nonattainment area permitting requirements will remain in place” (MoDNR).

This distinction matters and it is easy to get backwards. The reclassification happened. It was not vacated and it was not withdrawn. What is suspended is its effectiveness, which is why EPA’s Green Book still lists the five Missouri areas as Serious while MoDNR permits at Moderate. Both statements are accurate; they describe different things. EPA itself acknowledges the stay in footnote 1 of its August 13, 2026 Clean Data Determination (91 FR 52243).

One caveat worth stating directly: EPA’s confirmation of the stay reflects the posture as of its signature on that rulemaking. The Eighth Circuit docket should be checked before any permitting decision that turns on it. If the stay is lifted, the Serious numbers switch on.

What Is RACT, and How Is It Different From BACT and LAER?

RACT is “the lowest emissions limitation that a particular source is capable of meeting by the application of control technology that is reasonably available considering technological and economic feasibility” (44 FR 53762). It applies to existing sources in nonattainment areas and it is a standing obligation, not a project trigger.

BACT and LAER are the other two. BACT attaches to new or modified major sources under PSD in attainment areas. LAER attaches to new major sources and major modifications under nonattainment NSR. Both are more stringent than RACT, and both fire only when you build or modify. RACT sits on your plant whether or not you touch anything.

The practical consequence: RACT is the one you can be out of compliance with quietly, for years, without a project ever putting it in front of a permit writer.

Does RACT Apply to My Plant in St. Louis?

Two independent tests, and either one alone triggers RACT. First, facility-wide potential to emit at or above 100 tpy VOC or 100 tpy NOx today, or 50 tpy if the Serious reclassification takes effect. Second, with no tonnage floor at all, whether any operation falls in a Control Techniques Guideline category covered by Missouri’s 10 CSR 10-5 series rules (91 FR 52617).

Work through it in four questions. You do not need to call anyone to answer these.

1. Are you inside the boundary? The Missouri portion is St. Louis City, St. Louis County, St. Charles County, Jefferson County, and Boles Township only in Franklin County. This is a part-county designation, not a whole-county one. If your plant is in Franklin County outside Boles Township, you are in an attainment or unclassifiable area and none of this applies to you. That carve-out was litigated and upheld in Clean Wisconsin v. EPA, 964 F.3d 1145 (D.C. Cir. 2020), and describing Franklin County as wholly nonattainment is the single most common error in vendor summaries.

2. What is your potential to emit, not your actual emissions? Major-source status runs on PTE: maximum capacity to emit under your physical and operational design, counting federally enforceable limits and ignoring voluntary practice. Add up facility-wide VOC and, separately, facility-wide NOx. Your Emissions Inventory Questionnaire under 10 CSR 10-6.110 reports actuals. Do not use it as your applicability test. Pull the PTE calculations from your Title V application or your most recent construction permit instead, and run the number against both 100 tpy and 50 tpy.

3. Do you fall under a CTG source category? This is the trap. Major-source RACT has a tonnage threshold. CTG RACT does not. If your operation is covered by a Control Techniques Guideline category, RACT applies through Missouri’s rule regardless of your size. In the St. Louis area the operative rules include 10 CSR 10-5.220 (petroleum liquid storage, loading and transfer), 10-5.300 (solvent metal cleaning), 10-5.330 (industrial surface coating), 10-5.340 (rotogravure and flexographic printing), 10-5.442 (offset lithographic printing), 10-5.500 (volatile organic liquid storage), 10-5.520 (VOC from existing major sources), and 10-5.530 (wood furniture coating) (Missouri CSR Title 10 Division 10 Chapter 5). If you run a paint line, a parts washer, a press, or a solvent tank in the five-county area, start here and not with the tonnage math.

4. Are you planning a project? NNSR under 10 CSR 10-6.060 is triggered by a new major source or a major modification of an existing major source. Exempt and insignificant activities are listed at 10 CSR 10-6.061; de minimis modeling thresholds sit at 10 CSR 10-6.020(3)(A) Table 1.

What Is the Major Source Threshold for a Serious Ozone Nonattainment Area?

50 tons per year of VOC or NOx, down from 100 tpy at Moderate, with the nonattainment NSR offset ratio rising from 1.15:1 to 1.20:1 (EPA, Required SIP Elements by Nonattainment Classification; CAA 182(c) and 182(c)(10)). The ladder continues to 25 tpy and 1.3:1 at Severe, and 10 tpy and 1.5:1 at Extreme.

Read those Serious figures as contingent for Missouri sources. They are the numbers that apply on the Missouri side if the Eighth Circuit lifts the stay. They are the numbers that apply on the Illinois side today. Any facility with facility-wide PTE between 50 and 100 tpy of either pollutant is a synthetic minor today and a major source the day the stay lifts, with LAER and offsets attaching to any modification that follows.

How Do Missouri and Illinois Requirements Differ for the Same St. Louis Metro?

The Illinois portion, Madison, Monroe, and St. Clair Counties, was reclassified Serious by a rule published December 17, 2024 and effective January 16, 2025, and operates at 50 tpy and 1.20:1. The Missouri portion is stayed and operates at 100 tpy and 1.15:1. One airshed, one design value, one attainment date of August 3, 2027, and two thresholds.

The bi-state split runs deeper than the numbers. Missouri sits in EPA Region 7 and the Eighth Circuit; Illinois sits in EPA Region 5 and the Seventh Circuit. The Illinois challenge is in abeyance and no stay has been reported there, which is why the Illinois side proceeded at Serious while the Missouri side did not. If you operate on both sides, you maintain two applicability analyses, two permitting postures, and two offset budgets against the same corporate inventory. A companion piece covering the Illinois NOx RACT side of this corridor is in progress.

Which Missouri Regulation Actually Contains the NOx RACT Requirement?

10 CSR 10-5.510, “Control of Emissions of Nitrogen Oxides,” SIP-approved May 18, 2000 at 65 FR 31482. It applies at potential to emit of 100 tpy or more of NOx in Franklin, Jefferson, St. Charles, and St. Louis Counties and St. Louis City.

The rule title does not contain the word RACT. That is why it gets missed in facility self-audits: a keyword search of the Missouri code for “RACT” does not return the rule that imposes NOx RACT on you. EPA has also acted recently on two adjacent Missouri rules that carry St. Louis-area obligations, covering large stationary internal combustion engines (FR Doc 2026-14260) and petroleum liquid storage, loading and transfer (FR Doc 2026-14880).

When Does a Newly Reclassified Serious Area Have to Submit Its RACT SIP, and When Must Sources Comply?

Under 40 CFR 51.1402(b)(1)(i), the SIP is due 18 months after the reclassification effective date or January 1 of the attainment year, whichever is earlier. RACT implementation follows at 18 months after the SIP deadline or the start of the attainment-year ozone season, whichever is earlier. For St. Louis Missouri those compute to January 1, 2026 and March 1, 2026. Both dates are already behind us.

Both are complicated by the stay, which is exactly why sequencing matters more than the calendar here. Do not assume a passed deadline is a resolved deadline.

What Is the Deadline to Comment on EPA’s Proposed Approval of Missouri’s RACT Determinations?

September 14, 2026. EPA published the proposal on August 14, 2026 at 91 FR 52617, docket EPA-R07-OAR-2026-5842, proposing to approve Missouri’s inspection and maintenance program, NNSR program, and VOC and NOx RACT determinations from the state’s September 6, 2023 SIP submittal (FR Doc 2026-16571). Comment through regulations.gov.

The technical support document in that docket contains Tables 5 and 6, which list every major VOC and NOx source in the area with unit-level emissions data and the state’s RACT determination for each unit. Most plant managers in the five-county area do not know their facility is named in an open federal docket right now. If your facility is in those tables, read your own row. If the RACT determination for one of your units rests on stale control assumptions or a unit configuration you no longer run, this comment period is the cheapest correction opportunity you will get.

Does a Clean Data Determination Get My Facility Out of RACT?

No. The August 13, 2026 Clean Data Determination, effective September 14, 2026, suspends only the state’s obligation to submit attainment demonstrations, reasonably available control measures, reasonable further progress plans, and contingency measures under 40 CFR 51.1318. EPA states the area “will remain designated nonattainment … until such time as the EPA determines that the [area] meets CAA requirements for redesignation” (91 FR 52243).

Count what it suspends: four state planning obligations. Count what it suspends for you: zero. RACT stands. NNSR permitting stands. Every permit condition, monitoring requirement, recordkeeping obligation, emissions statement, and reporting deadline you have today survives September 14 unchanged. A parallel determination issued the same day for the Illinois portion (91 FR 52246) does the same thing on that side.

This is the item most likely to be misread across the market over the next 90 days, and misreading it in the direction of relief is expensive.

It becomes federally enforceable. EPA can enforce it directly under CAA 113, any citizen can sue on it under CAA 304, and any future change requires a formal SIP revision, meaning a state submittal plus EPA approval, rather than a negotiation with MoDNR. Five St. Louis-area agreements are in the current proposal: Anheuser-Busch, Ameren Labadie, Ameren Sioux, Ameren Meramec, and Elementis Specialties (91 FR 52617).

The specific limits in the proposal give you a sense of what RACT looks like when it lands: 0.12 lb/mmBTU NOx on a 30-day average at Ameren Labadie, 0.18 lb/mmBTU ozone-season at Ameren Sioux, a 1,500 degree F setpoint with 95% minimum destruction efficiency on the Elementis regenerative thermal oxidizer, and an 8% monthly and 6% 12-month rolling process-loss cap at Anheuser-Busch.

The loss of informal amendment is the point to weigh before September 14. If you are negotiating a consent agreement with MoDNR right now, negotiate it as though it will be federal law, because that is the trajectory.

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

$124,426 per day per violation for civil judicial penalties under CAA 113(b), and $59,114 per day with a $472,901 total cap for administrative penalties under CAA 113(d)(1) (40 CFR 19.4 Table 1). Field citations under CAA 113(d)(3) run $11,823 per day per violation.

These figures did not go up this year. OMB memorandum M-26-11 cancelled the 2026 civil penalty inflation adjustment, so 2025 levels carry forward unchanged (91 FR 25936). Any content citing a higher 2026 number is fabricating it.

What EPA Region 7 has actually charged in Missouri air cases recently is instructive, and it is not exotic. Continental Cement in Hannibal settled in January 2025 for a $74,440 civil penalty plus at least $282,000 to replace two school district diesel buses with propane, on findings that leak detection systems on emission controls were not adequately operated. BCP Ingredients in Verona settled in December 2024 for a $300,000 civil penalty, $350,000 in community projects, and scrubber installation, after unrepaired alarms contributed to a seven-hour ethylene oxide release. The pattern in both: unmaintained monitoring and detection equipment, unrepaired alarms, and recordkeeping gaps, with the true cost running several times the headline penalty once the supplemental project or capital obligation is counted.

Is Kansas City Subject to Ozone RACT or NNSR?

No. Kansas City MO-KS has no 2015 ozone nonattainment or maintenance designation. Its only Green Book ozone listing is under the revoked 1979 1-hour standard, in maintenance since July 23, 1992 for Clay, Jackson, and Platte Counties. Kansas City sources are subject to ordinary Missouri minor NSR and federal PSD, not NNSR offsets or LAER (EPA Green Book, Missouri).

Kansas, Nebraska, and Oklahoma have zero 2015 ozone nonattainment areas (EPA Green Book county listing). St. Louis is the exception in this region, not the template.

The Case Against Panic

Several signals cut against reading any of this as an emergency, and they deserve to be stated as plainly as the exposure does.

The design value is improving. The 2023 to 2025 value is 0.070 ppm, exactly at the standard, down from 0.074 ppm for 2021 to 2023. That improvement is what produced the Clean Data Determinations for both portions of the area, and it makes a redesignation request a plausible 2027 development.

The stay is real and it is holding. Missouri sources are not at 50 tpy, and nobody should be re-permitting a project on the assumption that they are.

RACT is a cost-effectiveness test, not a technology mandate. Missouri’s own analysis concluded additional NOx controls were not economically feasible at several major sources, and EPA is proposing to accept that. For Anheuser-Busch, RACT landed on good operating practice, proper maintenance, pollution prevention, and a process-loss cap, with no add-on control device. For Elementis, EPA found no more stringent comparator in RBLC or WebFIRE, so the existing limits stand.

And EPA’s proposed consent-agreement approvals include force majeure clauses treated as complete affirmative defenses, relying on SSM Litigation Group v. EPA, 150 F.4th 593 (D.C. Cir. 2025). Sources gain a defense they did not clearly have before.

Two counterweights on the other side. The 0.070 ppm design value depends on EPA excluding wildfire-influenced days under the Exceptional Events Rule, and that concurrence was contested during the comment period; petitions for judicial review of the Clean Data Determination are due by October 13, 2026 under CAA 307(b)(1). And EPA’s proposed Ozone Reclassification SIP Rule (91 FR 35639, comments closed July 13, 2026, no final rule as of today) does not relax Serious RACT or Serious NNSR. EPA states it “would not relieve a State of substantive planning obligations upon reclassification.” Do not budget against it as pending relief.

What to Do in the Next 30 Days

  1. Establish boundary status in writing, including township for any Franklin County site. Save the Green Book page and the Federal Register citation in the compliance file. Do not rely on a mailing address or a metro map.
  2. Recalculate facility-wide PTE for VOC and NOx separately, from design capacity and permit limits. Document the result against both 100 tpy and 50 tpy.
  3. Screen every emission unit against the CTG category list independent of the tonnage outcome. Map each unit to a specific 10 CSR 10-5.xxx rule or document why none applies.
  4. Verify NOx RACT posture under 10 CSR 10-5.510 specifically, by rule number rather than by keyword.
  5. Read the August 14 proposal and comment by September 14 if you are named in Tables 5 or 6 of the technical support document.
  6. Build the 50 tpy sensitivity case into any project you are permitting in the next 24 months, and decide now whether netting or a synthetic minor limit is worth taking.
  7. Budget the current fee schedule. Effective January 1, 2026, an NSR, PSD, or HAP construction permit application in Missouri carries a $6,000 filing fee plus $100 per hour of review; minor permits run $300 plus $100 per hour (MoDNR).

Where iSi Fits

The work above is a PTE recalculation, a CTG screen, and a 50 tpy sensitivity case. That is two to four weeks of focused effort for someone who does it regularly and considerably longer for a plant manager doing it between production issues. An unexpected permit hold can delay a line expansion by 60 to 90 days, and at typical mid-market production values that delay costs more than a decade of compliance support.

iSi handles potential-to-emit calculations, air permit applicability determinations, and nonattainment NSR permitting support for manufacturers across 40 states, including on both sides of this particular river. If you want the applicability question answered in writing before the September 14 comment window closes, call (316) 264-7050.

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