General Conformity Training Module 2.3: Demonstrating Conformity

Words that are shown in bold and italics are defined in the Glossary. 

2.3.1 Overview

Federal conformity. Conformity is a federal statute established by Congress within the Clean Air Act (CAA) for the prevention and control of pollutants the Environmental Protection Agency (EPA) finds to be harmful to public health and the environment, and for which the EPA has therefore established National Ambient Air Quality Standards (NAAQS). The NAAQS define the criteria that constitutes healthful outside ambient air relative to the concentration of EPA-defined criteria pollutant emissions and emissions of their precursor pollutants. 

Nonattainment and maintenance areas, and air quality implementation plans. States and Tribes have a legal obligation to attain and maintain these standards within nonattainment areas or re-designated attainment areas (i.e., maintenance areas), over which they have jurisdiction and authority, to the extent defined under CAA section 176(c)(5) and (c)(6). Such areas affected by emissions authorized by a federal agency are referred to as the "affected area." To this end, States and Tribes, and in certain circumstances, the EPA,  approves  air pollution prevention and control plans referred to as State, Tribal, or Federal implementation plans (SIP/TIP/FIP), hereafter referred to collectively as  a SIP. Occasionally, a SIP is updated and an implementation plan revision is adopted and approved. Some of these revisions apply to all the nonattainment and maintenance areas within the State or Tribe, and some are for specific nonattainment or maintenance areas. A SIP, together with its revisions, contains all the documents, regulations, procedures, and requirements to ensure timely attainment and maintenance of the NAAQS within the State or Tribe. All such plans and revisions that apply to a specific nonattainment or maintenance area is referred to as the applicable implementation plan (AIP) for that area. 

States and Tribes  having an area that is designated nonattainment have an obligation to attain the NAAQS by the statutory attainment date, and maintain the NAAQS for a period of no less than 20 years, according to the maintenance plan developed in accordance with CAA section 175A(a) and (b), during which the General Conformity regulations apply. Failure to meet or maintain the NAAQS can result in negative consequences including, but not limited to, loss of federal funding for some State or Tribal programs.

The federal conformity rule under CAA section 176(c) "Limitations on certain Federal assistance" is intended to assist State and Tribes in timely attainment and maintenance of the NAAQS by limiting the authorization of federal actions to only those that a federal agency can show will not interfere with the ability of a State of Tribe to attain and maintain the NAAQS within their nonattainment or maintenance areas, as those terms are defined under CAA section 176(c)(5) and (c)(6), and by requiring federal agencies to plan and design their actions in accordance with and with compliance to (i.e.,  conform to) to the purpose of the SIP  (42 U.S.C. Chapter 85, Subchapter I). 

CAA conformity categories and the conformity requirement. All federal actions are defined within just two categories and are subject to the CAA section 176 conformity statute accordingly. One category applies only to the emissions caused by transportation plans, programs, and projects (e.g., transit projects and emissions caused by motor vehicles operating on federal highways, etc.). As such, under CAA section 176(c)(4)(B), the EPA is directed to establish and maintain regulations to control such emissions under Transportation Conformity, which the EPA does under the Transportation Conformity program under 40 CFR part 93 subpart A.

The second category applies to activities that are not related to transportation plans, programs, and projects, hence "general" conformity, established under 40 CFR part 93 subpart B.  Establishment of the General Conformity regulations is directed under CAA section 176(c)(4)(A) and requires the EPA to periodically update the regulations. General Conformity, therefore, applies to all the activities not subject to Transportation Conformity and the EPA New Source Review (NSR) program, which includes the Prevention of Significant Deterioration (PSD) program requirements.  General Conformity, therefore, can apply to any criteria pollutant for which there is a NAAQS, and includes the criteria pollutant precursors. General Conformity can apply to point, area, volume, line, stationary, or mobile sources located on land, sea, or airborne. This includes, for example, emissions from construction activities (including nonroad engines) or operational activities, an aircraft during its landing and takeoff (LTO) cycle,  and emissions from vessels or equipment originating within the State Seaward Boundary. 

General Conformity requirement prohibits federal agencies from authorizing any activities unless or until the federal agency proposing the activities assures the emissions will not, within  affected area :

  1. Cause or contribute to a new violation of the NAAQS; 
  2. Increase the frequency or severity of an existing NAAQS violation; or,
  3. Delay timely attainment or maintenance of the NAAQS.  

2.3.2 Applicability Analysis. 

Activities that cause  emissions of criteria or precursor pollutants to originate within the affected area must be evaluated in the federal agency's applicability analysis, if the activities meet the applicability requirements under §§ 93.150 and 93.153(a) and (b). In the applicability analysis, the federal agency would examine each proposed activity and exclude from the analysis any emissions caused by activities that:

  1. The EPA describes as a category of activities that are presumed to conform (PTC) under § 93.153(i); or,
  2. The EPA describes as an exemption when the federal agency's activity is consistent with the specific scope of the exemption listed in § 93.153(c)(2) through (c)(4), (d), or (e); or, 
  3. The federal agency includes in its own list of PTC activities developed and published in the Federal Register, as required under § 93.153(f)-(h); or,
  4. The State or Tribe includes in its own list of PTC activities in their air quality implementation plan or revision allowed under § 93.151 and developed according to 40 CFR 51.851; or,
  5. The Metropolitan Planning Organization (MPO) determines are caused by transportation-related sources that would be subject to Transportation Conformity under 40 CFR part 93 subpart A, and the  federal agency should obtain documentation from the MPO to justify the excluded emissions.  

Total of direct and indirect emissions. Emissions caused by the activities that remain are included in the federal agency's net emissions increase analysis, where the federal agency would calculate the total of direct and indirect emissions for each year analyzed as specified under § 93.159(d) . In this analysis, the federal agency would calculate the annual emissions projected for future yeas caused by the proposed activities that would originate within the affected area, this is referred to as the "Build" scenario. This tabulated data is then compared to the annual emissions caused should the proposed activities never take place. This is referred to as the "No-Build "scenario. The difference between the two, year by year, pollutant by pollutant, reveals the annual net increases, year to year, and is referred to as the "total of direct and indirect emissions." The results of the comparison of the two scenarios will indicate whether there are any annual net increases, or annual net decreases, in the emissions of the relevant pollutants, specifically caused should the proposed activities be implemented; 

  1. If for all years analyzed and for emissions of all relevant pollutants the federal agency finds the annual net emissions would be less than the associated annual de minimis threshold rates given in the tables at § 93.153(b)(1) or (b)(2), the agency could prepare a De minimis finding. The federal agency should document in its files and  preserve all the materials and data upon which the agency relied on to reach this conclusion. No conformity determination is necessary. There are no reporting or public participation requirements that apply under §§​​​​​ 93.155 or 93.156 for a de minimis finding. The federal agency must not take or start its federal action until the General Conformity finding is complete.
  2.  If for one or more years analyzed the federal agency finds for one or more years an increase in emissions of a relevant pollutant that would meet or exceed the associated annual de minimis threshold rates given in the tables at § 93.153(b)(1) or (b)(2), the agency must prepare a conformity demonstration and determination. 

2.3.3 Conformity demonstration and determination. 

There are several methods for demonstrating conformity for net emissions that equal or exceed the associated de minimis threshold rates. The federal agency can, at its discretion, choose one or a combination of the criteria for demonstrating conformity under § 93.158, which include air quality modeling, if appropriate, and if necessary and applicable, any combination of the methods for meeting conformity under § 93.160 through 93.165 needed to meet conformity. The demonstration must be prepared in accordance with the procedures under § 93.159. Regardless of the criteria and methods used, the demonstration must support a positive conformity determination by offsetting, mitigating, or otherwise reducing the net increase in emissions to zero.

The federal agency must then prepare a conformity determination and note the determination in a decision document explaining and describing that, based on the results of the applicability analysis and the demonstration, how the emissions will meet conformity. The agency should stipulate that the emissions caused by the activities will meet the conformity requirements as defined under Clean Air Act (CAA) § 176(c)(1)(A) and (B) and therefore will not interfere with the State's or Tribe's ability to meet and maintain the NAAQS. In addition, the federal agency must meet all the requirements under § 93.150 and § 93.154, which includes that a federal agency must not take or start its federal action until the General Conformity determination is complete. 

The federal agency must retain all the information relied upon to prepare the demonstration and make their positive conformity determination and complete the reporting and public participation requirements under §§ 93.155 and 93.156. In this way, the federal agency will fulfill the affirmative responsibility under CAA section 176(c)(1) to assure conformity.  

2.3.4 Mitigation and emissions offsets

A federal agency can obtain emissions offsets or apply mitigation measures to reduce, avoid, compensate, or otherwise account for all of the net emissions increases indicated in the table of direct and indirect emissions for the purpose of demonstrating conformity.  Either way, the entire increase in net emissions for the one or more years where emissions of a relevant pollutant occur. Reducing or otherwise accounting for the emissions increases to a rate below de minimis is not sufficient to demonstrate conformity under CAA § 176(c)(1)(A) and (1)(B). For either mitigation or emissions offsets, the follow apply: 

  1. The federal agency must show that there are adequate resources to implement the mitigation measures or offset plans;
  2. The federal agency may use either, or both offsets or mitigation, for the purpose of meeting the conformity requirement ;
  3. After the application of mitigation or use of offsets, the net increase in emissions for the year must be zero;
  4. Emissions reductions or offsets must occur during the same calendar year in which the activities' emissions causing the need for mitigation or offsets occur, except as allowed under § 93.163 in an alternative year; For example --  If a project's activities would cause 150 tons of NOx emissions, per year, for 3 years, in a Serious ozone nonattainment area, that would be 450 tons of NOx emissions over the 3 years. For a Serious ozone nonattainment area, that would require 1.2 tons of reduced NOx emissions for every ton of new NOx caused by the project over the three years. The calculation is 450 tons NOx multiplied by 1.2 tons = 540 tons that need to be reduced. The mitigation or offsets must cause a reduction of 540 tons over a maximum of 6 years (3 x 2 = 6 years or twice the number of years needing the reduction to meet conformity.) Therefore, mitigation or offsets must provide 6 years of reductions of 90 tons of NOx per year to meet the requirements under section 93.163, because 540 tons / 6 years = 90 tons per year for 6 years.
  5. Agreements to apply mitigation measures and plans for obtaining emissions offsets must be in place before the federal agency can rely on them demonstrate conformity and make its positive conformity determination; and
  6. EPA, States, Tribes, and local agencies must be able to enforce the requirements of the mitigating emission reduction strategies or techniques used as an offset.
  7. Mitigation measures can be modified under § 93.160:
    1. Mitigation measures can be modified after the federal agency has completed its conformity demonstration by following the procedures under § 93.160(e); and,
    2. A written agreement to commit to mitigation measures, which are needed to demonstrate conformity, must be fulfilled by all parties that signed the agreement. Therefore, any written agreement must be signed and a copy included in the agency's conformity determination. All parties to the agreement must meet their obligations under the agreement.  If a third party fails to meet its commitment in implementing the measures, the enforcement will generally be against the third party and not the federal agency.
  8. Emissions offsets must be:
    1. Quantifiable – The federal agency must be able to quantify the emissions being offset using standard techniques or strategies;
    2. Surplus – The offsets must not be required by the AIP or other environmental laws or regulations;
    3. Enforceable – EPA or the State, Tribal, or local agency must have the ability to enforce the offsets. This can be done by including the measure in an operating permit or similar mechanism or by including the reductions in the AIP; and,
    4. Permanent – The offsets must be permanent within the timeframe the emission increases caused by the activities occur.

2.3.5 Demonstrating conformity in the absence of an approved AIP

A federal agency may propose activities within a nonattainment area or maintenance area where EPA has not approved an AIP for the area. In such case, the federal agency’s options for demonstrating conformity for its activities are limited. Since there is no AIP, the federal agency can secure a commitment from the State or Tribe to include the emissions in a future AIP revision, the federal agency may conduct modeling to demonstrate conformity, or the agency may secure emission reductions to mitigate or offset the emission increases.

A second case of a federal agency addressing conformity in the absence of an AIP occurs when the emissions from a federal activity will occur after the time period covered by the AIP. In this case, the federal agency can demonstrate conformity for the last budget included in the last EPA approved AIP and assume that the future AIP will allow at least that quantity of emissions. The State, Tribal or local air agency would be responsible for developing the AIP revision to account for the emissions from the activities. If the emissions from the activities are greater than the emissions allowed in the last budget in the AIP, then the federal agency can secure a commitment from the State or Tribe to include the emission in a future AIP.

General Conformity

Contact Us about General Conformity
Contact Us about General Conformity to ask a question, provide feedback, or report a problem.
Last updated on August 13, 2025