Revisions to Chapter 138, NO_x RACT
Frequently Asked Questions

The effective date of the revised rule is May 7, 2025. New standards in section 4 and 6 of the rule go into effect on May 1, 2026.

• Clarifying applicability;
• Establishing new NO_x standards for major sources located within the ozone transport region (OTR) due to promulgation of the 2015 8-hour ozone National Ambient Air Quality Standard;
• Replacing blanket exemptions for periods of startup, shutdown, and malfunction with alternative emission limits for periods of startup and shutdown; and
• Removing outdated and obsolete requirements.

Facilities located outside the OTR must continue to comply with the previously established standards for NO_x contained in section 3 of Chapter 138 or standards established through a previously implemented alternative NO_x RACT determination or standards established through a Best Available Control Technology (BACT) determination or Lowest Achievable Emission Rate (LAER) determination issued after August 3, 1994.

If an emissions unit must comply with a standard in section 3 of Chapter 138 (for major sources of NO_x located outside the OTR) and compliance is demonstrated through use of a Continuous Emissions Monitoring System (CEMS), then the emissions unit is also subject to the alternative emission limits in section 6 of the rule for periods of startup and shutdown. Such facilities should submit a Part 70 minor modification to address this new applicable requirement if the remaining term of their Part 70 license is three or more years.

Facilities may voluntarily choose to reevaluate BACT through a Chapter 115 minor modification to establish NO_x standards for normal operation or periods of startup and shutdown that supersede those of Chapter 138.

Pursuant to section 5 of Chapter 138, all major sources of NO_x located within the OTR must submit an application for a Chapter 115 minor modification to address NO_x RACT no later than October 28, 2025. NO_x RACT may be addressed by either acceptance of the applicable standards in sections 4 and 6 of the rule or the request of an alternative NO_x RACT determination. The Department will process this application and issue a NO_x RACT order.

An application for a Part 70 significant modification to incorporate the NO_x RACT order into the facility’s Title V license must be submitted no later than May 1, 2027. The two applications may be submitted concurrently.

As described in section 5 of Chapter 138, the application to address NO_x RACT must include an inventory of all affected units at the facility, proof of publication of a public notice of intent to file, and certification by a Responsible Official.

If there is no request for an alternative NO_x RACT determination, i.e., all units will comply with the standards in section 4 by May 1, 2026, the application should make such a statement. If control or operational changes are required for such compliance, the application should include a description of expected changes. The applicant should also acknowledge the applicability of the alternative emission limits for startup and shutdown in section 6 of the rule.

If there is a request for an alternative NO_x RACT determination for any emissions unit, the application must also include the information in section 4(H)(1) of Chapter 138 for each unit for which an alternative NO_x RACT determination is being submitted. This information includes, but is not limited to, the results of a site-specific alternative NO_x RACT analysis, methods proposed for demonstrating compliance, and a proposed schedule for implementation.

An alternative NO_x RACT analysis examines the technical and economic feasibility of available NOx control techniques for the specific unit being evaluated. A RACT analysis is very similar to a best available control technology (BACT) analysis in that it must consider all available control strategies and evaluate their technical and economic feasibility. NO_x RACT selects the control strategy with the highest level of control that is also both technically and economically feasible. The principal difference between a BACT analysis and a RACT analysis is that the threshold for economic feasibility (i.e., dollars per ton of pollutant removed) is typically lower for RACT.

An acceptable NO_x RACT analysis must:

• Consider all available NO_x control technologies;
• Describe each NO_x control technology considered;
• Explain why each NO_x control technology is or is not technically feasible and whether there are any adverse environmental trade-offs;
• Explain why each NO_x control technology that is technically feasible is or is not economically feasible, including showing how the dollars per ton of pollutant removed was calculated;
• Select and propose to use the highest level of control that is both technically and economically feasible;
• Propose a NO_x emission limit based on the control technology selected, including an appropriate averaging time; and
• Propose an alternative NO_x emission limit or work practice standards for periods of startup and shutdown.

The final alternative NO_x RACT analysis must be submitted with the Chapter 115 application due to the Department no later than October 28, 2025. It is strongly encouraged that facilities begin working with the Department well in advance of this date to ensure the analysis submitted is complete and acceptable.

The Department will process this application similar to a Chapter 115 minor modification and will issue a license that addresses NO_x RACT requirements for the facility. These requirements must then be incorporated into the facility’s Part 70 (Title V) license either through a Part 70 significant modification or as part of a pending Part 70 renewal.

The new standards for facilities located within the OTR and the alternative emission limits for startup and shutdown go into effect on May 1, 2026. These standards go into effect on that date regardless of whether the Department has completed processing of the facility’s NO_x RACT application.

If a facility has requested an alternative NO_x RACT determination, that determination does not supersede the requirements of sections 4 or 6 of Chapter 138 until a final order is issued by the Department. Therefore, facilities are strongly encouraged to work closely with the Department as they develop their alternative NO_x RACT analysis to ensure smooth processing of the application.

NO_x RACT requirements must be federally enforceable and part of Maine’s State Implementation Plan (SIP). Chapter 138 is included in Maine’s SIP.

After the Department issues a license that contains an alternative NO_x RACT determination, that license will be submitted to the Environmental Protection Agency (EPA) as a site-specific SIP submission. If approved by EPA, the license containing the alternative NO_x RACT determination will become part of Maine’s SIP. This makes the requirements of the order federally enforceable. It also means that the conditions of that license cannot be changed without EPA approval.

For questions regarding Chapter 138 and how these changes may affect your facility, please contact your Licensing project manager or Jane Gilbert, Licensing Supervisor, (207) 530-0554.