Indiana NOX Monitoring Rules: What Non-EGUs Must Do Now

Here's the compliance lesson worth pulling from this rulemaking: many Indiana industrial facilities are operating under monitoring and recordkeeping frameworks that don't yet reflect what EPA and IDEM now formally require. The EPA's May 14, 2026 approval of Indiana's revised State Implementation Plan — Federal Register document 2026-09612 — isn't a future obligation. It's a present one, and the first hard reporting deadline under the updated framework falls July 30, 2026.

If your facility operates a large combustion unit that isn't an electric power plant, this update applies to you. Understanding what changed, who it covers, and what your compliance program must do about it right now is the right place to start.

What the EPA Just Approved

On May 14, 2026, EPA published its final approval of a SIP revision submitted by the Indiana Department of Environmental Management (IDEM). The action falls under Clean Air Act (CAA) Section 110(k), which governs EPA's review of state implementation plans.

The revision addresses nitrogen oxides (NOX) emissions monitoring, reporting, and recordkeeping requirements for new and existing large non-Electric Generating Units (non-EGUs) subject to Indiana's NOX SIP Call obligations. The NOX SIP Call — codified at 40 CFR Part 51, Subpart AA — was originally promulgated in October 1998 and covers 22 states, including Indiana. It requires substantial NOX reductions from large combustion sources to address the interstate transport of ozone-forming pollutants. Indiana has carried these obligations for over 25 years. What changed with this SIP revision is the monitoring framework Indiana will use to enforce and verify them.

Indiana's previous SIP provisions didn't fully reflect current EPA policy on alternative monitoring approaches for non-EGU source categories. The approved revision brings Indiana into alignment — and gives IDEM explicit, formally EPA-approved authority over which monitoring systems affected facilities may use.

That last point matters more than it might appear. It means that operating under an unapproved or outdated monitoring methodology isn't just a technical discrepancy. It's a compliance gap with a now-enforceable state-level consequence.

Who the NOX SIP Call Covers

The term "large non-EGU" carries a specific regulatory meaning under 40 CFR Part 51, Appendix Y: a stationary combustion unit with a maximum rated heat input capacity of 250 mmBtu/hr or more that is not used primarily to generate electricity for sale. Affected source categories in Indiana typically include:

• Industrial and commercial boilers serving manufacturing, refining, or processing operations
• Cement kilns
• Glass furnaces
• Lime kilns
• Iron and steel reheat furnaces
• Paper and pulp combustion units
• Other large industrial combustion sources

If your facility operates units in these categories at or above the 250 mmBtu/hr threshold, the monitoring and recordkeeping requirements in Indiana's updated SIP are not discretionary.

One number worth holding onto: the NOX SIP Call collectively covers facilities responsible for millions of tons of NOX reductions annually across those 22 states. Indiana's industrial base — particularly its steel, cement, and glass sectors — puts a significant portion of in-state NOX emissions squarely within non-EGU source categories. That's the policy context behind why IDEM pursued this SIP revision and why EPA approved it.

The Monitoring Requirements

This is where facilities most often have compliance gaps, and the reason is usually operational rather than intentional. Systems that were correctly configured years ago have drifted. Staff turnover has erased institutional memory about why certain monitoring decisions were made. The audit that should have happened last year didn't.

The primary monitoring pathway for large non-EGUs under the NOX SIP Call is 40 CFR Part 75, Subpart H — continuous emissions monitoring system (CEMS) requirements. Part 75 CEMS produce hourly NOX mass emissions data with rigorous quality assurance protocols. They are expensive to install and maintain, which is why EPA allows alternative approaches for certain non-EGU source categories.

Indiana's SIP revision updates those alternative monitoring provisions. Under the revised framework, a facility may use:

• Low-mass emissions (LME) exemptions — available if the unit emits below defined threshold levels, with documentation to support the determination
• Approved alternative monitoring systems (AMS) — periodic testing or mass balance approaches in place of continuous monitoring, requiring a formal AMS petition and approval from IDEM and EPA
• Fuel flow monitoring combined with emission factors — available for certain unit types under specific conditions

The critical point is that whatever monitoring approach your facility uses must be formally approved and consistently applied. Switching between monitoring methodologies without documented approval from IDEM and EPA is itself a violation — not a technicality, but a substantive compliance failure.

Reporting and Recordkeeping Obligations

Reporting: Facilities using Part 75 CEMS submit NOX emissions data through EPA's Electronic Data Reporting (EDR) system within 30 days after the end of each calendar quarter. Quarterly reports include hourly emissions data, operating hours, heat input data, and quality assurance results. Some alternative monitoring approaches allow annual reporting, but the quarterly cadence is the default for CEMS-equipped facilities.

Recordkeeping: All monitoring data, QA/QC records, calibration documentation, and supporting calculations must be retained for a minimum of five years. Certain compliance demonstration records carry a 10-year retention requirement. These records must be available for inspection by IDEM or EPA on request — "available" meaning organized, retrievable, and complete. Boxes of unsorted printouts in a storage room do not meet that standard.

Certification: The Designated Representative — typically the facility's responsible official — certifies the accuracy of all emissions data submissions. False certification carries serious legal exposure under the CAA. If your DR has changed and the updated certification isn't on file with EPA's Clean Air Markets Division (CAMD), address that before the next reporting deadline.

Deviation reporting: Any exceedances of emission standards or CEMS failures must be reported to IDEM according to Indiana's SIP deviation reporting requirements. This is where a well-known regulatory provision tends to surprise facilities: under 40 CFR 75.68, missing CEMS data during operating hours defaults to the 90th percentile emission rate from the most recent quality-assured operating period. In other words, unexplained data gaps are treated as high-emission hours for compliance calculations. A monitor that goes down for three days without proper documentation doesn't produce a gap — it produces a compliance liability.

Effective Dates and Deadlines

Federal Register rules under the CAA typically take effect 30 days after publication. With the May 14, 2026 publication date for this rule, the effective date is approximately June 13, 2026.

That date is not a start date for action. If your monitoring systems, QA/QC protocols, and recordkeeping practices aren't already aligned with Indiana's updated SIP requirements, you have a gap that's open right now.

The first reporting deadline that falls squarely under the updated framework is the Q2 2026 quarterly emissions report, due July 30, 2026. Any monitoring deficiencies in Q2 need to be identified and addressed before that submission window closes.

CEMS vs. Alternative Monitoring: What the Difference Costs You

Facilities consistently underestimate the compliance burden difference between these approaches. Here's a direct comparison across the dimensions that matter for an Indiana non-EGU operating under the updated SIP:

The pattern I see consistently in practice: facilities with CEMS spend more upfront but face far fewer enforcement surprises. Facilities using AMS approaches can run into problems when operating conditions change — a new fuel type, a process modification, a significant increase in operating hours — and the original AMS approval no longer reflects actual conditions. When that happens, the facility is often running without a valid monitoring methodology and doesn't know it.

Practical Steps for Affected Indiana Facilities

In my view, most compliance failures under emissions monitoring rules come from operational drift rather than intentional noncompliance. The monitoring system that worked correctly five years ago may have calibration records that are two quarters stale. The AMS approval that was current when your environmental manager left may not have been updated when the unit configuration changed. These are fixable problems — but only if you audit for them before an inspector does.

Here's where to focus given the updated Indiana SIP framework:

Verify your monitoring approval status. If your facility uses an AMS rather than Part 75 CEMS, confirm in writing that your petition was approved and that you're operating within its approved parameters. A verbal assurance from a former consultant isn't documented approval.

Pull your QA/QC records for the last four quarters. Look specifically for data gaps, late RATA tests, calibration drift assessments that weren't filed, and any deviation events that weren't formally reported. Incomplete records in one quarter create exposure in the next.

Check your deviation reporting history. Prior quarters with monitoring failures that weren't properly reported to IDEM create ongoing liability. A proactive disclosure is treated far better by regulators than a discovered violation — and that gap between discovery and disclosure is real.

Confirm your recordkeeping is retrievable. Five-year retention is the rule, not an aspiration. If records from 2021 aren't organized and available for inspection, fix that before your next IDEM contact.

For multi-unit facilities: map each unit individually. Applicability and monitoring approach can differ unit by unit within the same facility. A blanket assumption that the whole site is compliant because one unit is compliant is exactly the kind of oversight that produces findings.

What ISO 14001 Facilities Should Know

If your Indiana facility holds or is pursuing ISO 14001:2015 certification, this SIP revision creates a direct update obligation under clause 6.1.3, which requires your Environmental Management System to track and respond to applicable legal and regulatory requirements.

Indiana's updated SIP is a new legal requirement. It belongs in your legal register. The monitoring, reporting, and recordkeeping obligations described above should be mapped to your EMS procedures and included in your next annual legal compliance evaluation. If your facility undergoes an ISO 14001 surveillance audit and your legal register doesn't reflect the current state of Indiana's SIP, that's an audit finding — and in my experience, it's a finding that tends to pull several related gaps into view.

The SIP update is also a reasonable prompt to verify that your EMS documentation reflects your actual current monitoring approach, especially if the facility has changed unit configurations, fuel types, or operating schedules since the last compliance review. Learn more about ISO 14001 certification consulting or schedule a compliance consultation to discuss how this rule affects your facility.

Getting Your Compliance Program Current

At Certify Consulting, I've worked with 200+ clients on environmental compliance reviews, monitoring system audits, and regulatory submissions — with a 100% first-time audit pass rate across eight-plus years. Facilities that proactively conduct internal monitoring audits before EPA or state inspections consistently achieve better outcomes. The reason isn't that the audit changes the underlying facts. It's that the audit gives the facility time to characterize and address issues on its own terms rather than under enforcement pressure.

The July 30, 2026 Q2 reporting deadline is the first concrete accountability moment under Indiana's updated NOX SIP framework. That's six weeks from the effective date of this rule. It's enough time to get current — but not enough time to start slow.

If you're an Indiana industrial facility navigating these requirements and want a clear picture of where your compliance program stands, reach out at certify.consulting.

Last updated: 2026-06-12