General Conformity Training Module 1.3: Background

• Module I The Basics
• 1.1 What and Where
• 1.2 Who and How
• 1.3 Background
• 1.4 More Information

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

The information provided in this tutorial is not sufficient for completing a thorough and comprehensive General Conformity evaluation. The federal agency must consult the requirements at 40 CFR part 93 subpart B.

1.3.1 Why did Congress add conformity to the CAA? 

The federal conformity requirement as we know it today, at § 176 of the Clean Air Act (CAA), is largely the result of the passage of the 1990 Clean Air Act Amendments. Congress recognized that a federal agency's decision to take or start a federal action to implement certain federal projects could interfere with a State's or Tribe's ability, and legal obligation, to attain and maintain the National Ambient Air Quality Standards (NAAQS) within the nonattainment areas and maintenance areas over which States and Tribes have authority and jurisdiction. For example, emissions caused by construction and operation of an airport improvement project, or projects to dredge a harbor channel to allow passage of larger or additional ships, could, if implemented, cause new emissions or modify existing sources of emissions to a degree that might delay or interfere with attainment or maintenance of the NAAQS. Because it is the sole responsibility of a federal agency to assure the State, Tribe, and the public, that its projects' emissions will not interfere with the NAAQS attainment or maintenance planning process, Congress established and maintains CAA § 176 for the protection of the NAAQS and the rights of States and Tribes to attain and maintain those standards without delay.

The CAA conformity requirement prohibits federal agencies from taking or starting any action to engage in, fund, permit or license, approve, or support or otherwise authorize a program, plan, project, or activity that does not conform to the purpose of the implementation plan designed to protect the NAAQS within a nonattainment or maintenance area affected by a federal project.

1.3.2 Legal requirement for the General Conformity program requirements

The legal requirement for conformity program requirements is found in CAA § 176(c)(4) “Criteria and procedures for determining conformity,” where the EPA is directed to promulgate and maintain two sets of regulations. Thus, the Transportation Conformity regulations implement CAA § 176(c)(4)(B) for plans, programs, and projects funded by the Federal Highway Administration or Federal Transit Administration programs under 40 CFR part 93 subpart A, and all other activities are considered "general federal activities" and are evaluated under the General Conformity regulations that implement CAA § 176(c)(4)(A) and are codified under 40 CFR part 93 subpart B.

1.3.3 Air Quality Management

1.3.3.1 National Ambient Air Quality Standards (NAAQS)[1]

In order to protect public health and the environment, EPA establishes NAAQS for six of the most common air pollutants emitted throughout the United States that can cause serious health problems, as well as cause damage to the environment and to property. They include ozone (O₃), carbon monoxide (CO), sulfur dioxide (SO₂), particulate matter pollution (PM₁₀ and fine particulates, PM₂.₅), lead (pb), and  nitrogen dioxide (NO₂), which is an indicator for controlling the more harmful pollutant within that family of nitrogen oxides (NOx).

There are four basic elements, or “criteria” of a NAAQS that together serve to define each standard—(1) the indicator (e.g., CO, SO₂, etc), meaning the chemical species or mixture that is to be measured in determining whether an area attains the standard, (2) the form of the standard (e.g., “not to be exceeded more than once per year, or “annual mean,” etc.), (3) the averaging time (e.g., concentration measured over a period of time, such as annual average, 24-hour average, etc.) for each of the two types of standards, the primary standard[2] and the secondary standard,[3] and (4) the maximum allowable concentration level for each of the primary and secondary standards, indicated in units of micrograms per cubic meter (mg/m³), parts per million (ppm), or parts per billion (ppb), where a concentration level is a measure of the air quality impact (mass of pollutant existing within a volume of otherwise clean air) and are not the same as tons per year, which is the mass flow rate (e.g., emitted from a vehicle exhaust). Such standards are established for each of the six aforementioned pollutants. Thus, they are referred to as the “criteria” pollutants. The CAA does not require EPA to establish primary NAAQS at a zero-risk level, but rather at a level that reduces risk sufficiently so as to protect public health with an adequate margin of safety.

1.3.3.1.1 Designations and Classifications 

The CAA directs the EPA to designate areas as nonattainment, attainment, or unclassified based on ambient air quality monitored data and other information depending on whether the area is violating the standard, attaining the standard, or whether the EPA is unable to designate the area due to incomplete data (unclassifiable).

In addition, the CAA also requires the EPA to classify nonattainment areas based upon the severity of the pollution problem for O₃, PM₁₀, PM_2.5, or CO, e.g., an ozone nonattainment area may be classified as marginal, moderate, serious, severe, or extreme, in order of increasing potential harm. The stringency of the State's or Tribe's control measures are tied to reflect the area’s nonattainment classification. For example, an area with a higher classification, such as a severe or extreme O₃ nonattainment area, has more stringent requirements for prevention and control than for a moderate ozone nonattainment area. The designation and classification for each nonattainment area, by State, county, by U.S. territory, and sometimes, by Tribe, is codified in subpart C of 40 CFR part 81. Additional information on which areas are designated and their date of classification is available on EPA’s Green Book website.

1.3.3.1.2 Nonattainment and Maintenance Areas 

The EPA designates an area as nonattainment generally based upon air quality monitoring data or modeling studies that show the degree to which the area is currently violating, or contributes to the violation of a NAAQS. Where the data do not make such a showing, EPA designates the area as attainment or unclassifiable. When a nonattainment area subsequently attains the NAAQS and is no longer violating or contributing to violations of the NAAQS, the State or Tribe may ask the EPA to redesignate the area as attainment by submitting a request for EPA approval, which includes a plan to maintain the NAAQS (e.g., a maintenance plan)  under CAA § 175A. Such areas are known as maintenance areas.

Maintenance areas, though retaining the attainment designation, are subject to the requirements of the CAA § 175A maintenance plan for 20 years following the effective date the area is designated attainment. Such plans are included as revisions to the State or Tribal air quality implementation plan, which imposes certain requirements to help improve and maintain the air quality of maintenance areas.

1.3.3.2 State, Tribal, and Federal Implementation Plans

The air quality implementation plan, and its revisions, are developed by States (SIPs) and Tribes (TIPs), and sometimes by the EPA as Federal Implementation Plans (FIPs). The SIPs, TIPs, or FIPs, as appropriate, are developed for each nonattainment and maintenance area and may include a variety of documents and regulations such as regional haze plans, annual emissions for an inventory of emission sources,[4] projected community growth data, a strategy to improve the air quality laws and regulations needed to implement the strategy to attain or maintain, and a demonstration that the area will attain the standard. The plan together with all its revisions that are applicable to a single nonattainment area or maintenance area are referred to, collectively, as that area’s applicable implementation plan (AIP).

Applicable Implementation Plans are developed and adopted by States and Tribes and are designed to improve air quality within nonattainment and maintenance areas. State air agencies and Tribal governments are responsible for developing and implementing the AIPs, which are submitted to EPA and, upon approval, become federally enforceable. On Tribal lands, federally recognized Indian tribes can develop their own TIPs similar to SIPs. However, if the State or Tribe fails to submit a required plan, EPA can promulgate a Federal Implementation Plan known as a FIP.

1.3.3.3 Federal Compliance

Section 176(c)(4)A) of the CAA requires federal agencies to design and implement their projects to be consistent with, and the emissions caused by the project must conform to, the purpose of the AIP as determined by the agency’s applicability analysis under 40 CFR part 93 subpart B (hereinafter subpart B). In such an applicability analysis, if the annual net increases in emissions of relevant pollutants from all the activities for all the years evaluated for a project are below the associated de minimis rates associated with the affected nonattainment or maintenance area, the federal agency can make its de minimis finding and no other analysis is required. The EPA suggests that the federal agency preserve all the data and analysis it relied on to make their de  minimis finding.

When preparing the net emissions increases, also referred to as the “total of direct and indirect emissions,” the net increase in annual emissions may be reduced by excluding from the applicability analysis any emissions from activities that are presumed to conform or exempt.

1.3.3.3.1 Presumptions of conformity

A federal agency can exclude from their applicability analysis, and reduce the annual net emissions, by identifying activities included in their project that are (1) listed as presumed to conform by the EPA under § 93.153(i), (2) listed in an agency’s own list of presumed to conform activities developed and published according to § 93.153(f)-(h), or (3) listed in the State or Tribal General Conformity implementation plan revision as a presumption, also subject to the analysis under § 93.153(f) and (g). Presumptions of conformity are rebuttable under § 93.153(j) and if the EPA or any third party can show the emissions do not meet the requirements to be presumed to conform, the federal agency must prepare a General Conformity Determination under 1.3.3.3.3 of this section if the annual net emissions increase, without the presumptions, would equal or exceed de minimis rates associated with the affected nonattainment or maintenance area.

1.3.3.3.2 Exemptions

A federal agency can exclude from their applicability analysis, and reduce the annual net emissions, by identifying activities included in their project that are emissions from activities that the EPA has already identified as exempt under § 93.153(c)(2), (d),[5] or (e).  Exemptions are not rebuttable; however, the project’s activities that the agency claims are exempt must be consistent with the EPA’s scope, size, and description of the exemption. No federal agency other than the EPA, and no State air agency or Tribal government has the authority to declare emissions from certain other activities are exempt under General Conformity. Only the EPA has the authority to declare exemptions to General Conformity. The federal agency should make note in its files of the activities it is claiming are exempt. While not rebuttable in terms of size, scope, or description, the EPA or a third party could disagree that the federal agency’s claim of an exemption is not consistent with the EPA’s exemption as given in subpart B.

1.3.3.3.3 General Conformity Determination

If for any year analysed for the General Conformity evaluation the federal agency finds the annual net increase in emissions is equal to or greater than the de minimis rates associated with the affected nonattainment or maintenance area, the agency must prepare a demonstration of conformity according to the criteria and procedures in subpart B and make their statement of conformity (their determination) public.

A federal agency must make a determination, or if applicable a de minimis finding,  before the agency can take or start the action. Otherwise, the activities cannot be approved or implemented. If a federal agency is required to prepare a General Conformity Determination, the agency is required to act according to the public participation and public office reporting requirements under subpart B.

The DRAFT General Conformity demonstration and determination requires the publication of a notice for public review and comment for 30 days. These notifications are also required when the federal agency makes its final conformity determination. The federal agency must respond the public comments, in writing, and make these responses available to any person who asked for them.

1.3.4 How is General Conformity related to other air pollution control programs?

1.3.4.1 Transportation Conformity

Transportation Conformity ensures that transportation plans, projects, and programs meet air quality goals and must be approved by the Department of Transportation or other federal agency or rules under 40 CFR part 93 subpart A.

Transportation Conformity applies to transportation plans (TPs), transportation improvement programs (TIPs), or Federal Highway Administration or Federal Transit Administration projects proposed within certain nonattainment areas or maintenance areas. Project emissions subject to Transportation Conformity are not also subject to the provisions of the General Conformity program.

1.3.4.2 Nonattainment New Source Review (NNSR) and Prevention of Significant Deterioration (PSD) program requirements

The EPA considers the NNSR and PSD program requirements to be similar to the controls applied under the General Conformity program requirements. Therefore, if emissions from a part or portion of an activity otherwise subject under subpart B requires a permit under EPA’s NNSR or PSD program requirements, those emissions are exempt under General Conformity and the emissions can be excluded from the applicability analysis of the total of direct and indirect emissions.

1.3.4.3 National Environmental Policy Act

The National Environmental Policy Act (NEPA), passed in 1969, requires federal agencies to consider how “major” federal actions, including the use of federal funds, lands, or permits, may impact human health and the environment. The human environment includes natural, cultural, and socioeconomic resources. NEPA also requires that decisions include public input and involvement. Additional information on NEPA can be found at https://www.epa.gov/nepa.

The NEPA process and procedures, which were last updated effective on July 1, 2024, and the General Conformity process, are inextricably connected. If a NEPA project includes a proposed action or alternatives that include activities that meet the requirements under the General Conformity provisions, the federal agency must consider a General Conformity evaluation, but only for the proposed action alternative or other feasible alternative the federal agency decides will be ultimately implemented. For convenience and efficiency, the General Conformity process may be integrated with the NEPA process, particularly for the public reporting and participation process required for each program. However, this coordination is not required. The General Conformity evaluation and the NEPA assessment are two separate and unique processes where General Conformity supports only the NEPA project the federal agency ultimately intends to implement, approve, or otherwise authorize.  However, the two may be prepared separately. The federal agency determines the most appropriate way, case by case, given the individual situation, to integrate the conformity and NEPA processes.

There are certain requirements for NEPA, such as the development of alternative actions, that are not required under General Conformity. Therefore, it may not make sense to perform a General Conformity evaluation for all NEPA alternatives, but only for the proposed action, another alternative, combination of alternatives, or other derivative project the federal agency intends to approve or implement. At a minimum, at the point in the NEPA process when the preferred alternative is recommended, the air quality evaluation of General Conformity can proceed for that alternative.