On December 17th, 2024, the United States Environmental Protection Agency (EPA) redesignated the existing moderate ozone attainment areas in Northwest Indiana as serious nonattainment, effective January 16th, 2025. The affected areas in Indiana include the following townships located in Lake County and Porter County: Calumet, Hobart, North, Ross, St. John, Center, Jackson, Liberty, Pine, Portage, Union, Washington, and Westchester Townships. This article will discuss the background that determines nonattainment, the path towards attainment, and the permitting impacts on facilities located inside of the nonattainment area.
Nonattainment Overview
The Clean Air Act (CAA) Amendments of 1990 set forth the national ambient air quality standards (NAAQS) covering six criteria pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM2.5 and PM10), and sulfur dioxide (SO2). The NAAQS standards are separated into two categories: primary and secondary standards. The primary standards are set to protect human health, specifically the health of “sensitive” populations, such as asthmatics, children, and the elderly. Secondary standards are set to protect public welfare, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. Not every pollutant has a primary and secondary standard, and some, like ozone, have a combined primary and secondary standard. The EPA regulatory reviews the existing standards and periodically revises standards, for example, ozone standards were updated in 1997, 2008, and most recently in 2015. The 2015 ozone standard was published as a primary and secondary standard of 0.070 ppm (70 ppb) with an 8-hour averaging period, specifically based on the annual fourth-highest daily maximum 8-hour concentration, averaged over three years. As part of a newly published NAAQS, states are required to submit attainment designations to the EPA based on local ambient air sampling. Once the nonattainment designations are in place, the EPA requires states to prepare and submit a State Implementation Plan (SIP) that outlines the states compliance with the new NAAQS as well as plans to bring each nonattainment area into compliance with the NAAQS.
Permitting Impacts in Indiana
Nonattainment construction permitting in Indiana is governed by nonattainment new source review (NA-NSR) as laid out in 326 IAC 2-3. Indiana’s Department of Environmental Protection (IDEM) follows the EPA’s guidelines for NA-NSR of new major sources and existing sources undergoing major modifications. As shown in Table 1, the shift from “moderate’ nonattainment to “serious” nonattainment has lowered the major source permitting thresholds for the affected portions of Lake and Porter Counties.
Table 1: Major Source Thresholds and Ozone Attainment Status
| Ozone Attainment Status | Major Source Threshold |
| Attainment | 100 tpy VOC or NOx |
| Marginal Nonattainment | 100 tpy VOC or NOx |
| Moderate Nonattainment | 100 tpy VOC or NOx |
| Serious Nonattainment | 50 tpy VOC or NOx |
| Severe Nonattainment | 25 tpy VOC or NOx |
| Extreme Nonattainment | 10 tpy VOC or NOx |
The decrease in the major source threshold will also affect Indiana facilities by requiring any minor or synthetic minor sources with the potential to emit (PTE) greater than 50 tpy for either NOx or VOC to submit an application to either become a major source and subject to Title V permitting, or to submit an application to limit the source-wide PTE below 50 tpy for NOx and VOC.
For major sources that plan a modification, emissions increases from the modification should be compared against the de minimis emission rates for VOC and NOX to evaluate NA-SNR applicability. Per 326 IAC 2-3-1(p), the de minimis emission increase should not exceed twenty-five (25) tons per year when the net emissions increases from the modification are aggregated on a pollutant specific basis with all other net emissions increases from the source over the last five years. If a facility triggers NA-NSR in a serious ozone nonattainment area, facilities will be required to offset the emissions increase of the modification at a ratio of 1.2 to 1 tons of offset credits to every one (1) ton of emissions increases [326 IAC 2-3-3(a)(5)(B)]. In addition, the modification much achieve and implement the Lowest Achievable Emission Rate (LAER) for each applicable pollutant. LAER is similar to Best Available Control Technology (BACT), with the exception that LAER cannot take into account economic or cost considerations and are non-negotiable case-by-case determinations.
Conclusion
The reclassification from moderate to serious nonattainment for ozone will require existing facilities in the impacted areas to determine which permitting option fits the facility. Although IDEM has not published an official deadline for compliance with the ozone bump-up, it is important that facilities take necessary actions to maintain compliance with the new nonattainment category. These necessary actions, such as reviewing facility-wide PTE, preparing and submitting a permit modification application as needed, taking new emission limits as needed, and understanding future permitting requirements will be key for maintaining compliance with the serious nonattainment status of Lake and Porter counties.
Trinity is Available to Help
If you have additional questions, contact Trinity Consultants directly or email local experts Emily Stewart or Katie Zuercher.
