Historical Amendments and Revisions to the General Conformity Regulations
The “conformity” statute is found at § 176(c) of the Clean Air Act (CAA), where the EPA prohibits a federal agency from making a decision (taking an action) to implement a program, plan, project, or activity that would cause air emissions to interfere with the ability of a State or Tribe to achieve or maintain the National Ambient Air Quality Standards (NAAQS), which is required by law. Thus, federal agencies must assure their actions are designed and implemented in a manner consistent with and “conform” to the State or Tribal implementation plan intended to prevent and control air pollution.
Conformity was first established at 40 CFR 6.303 in 1979 and applied only to EPA actions. Today, conformity may apply to any federal action and any federal agency, as required under the 1990 CAA Amendments (pdf) (50.5 MB). The CAA amendments of 1990 tied conformity to attainment and maintenance of the NAAQS for the protection of the rights of States and Tribes that have authority and jurisdiction over such areas.
Under CAA § 176(c)(4), the EPA was directed to establish regulations to implement conformity, which subsequently prompted the EPA to supersede 40 CFR 6.303 and in its place established the new 40 CFR part 93 subpart A and subpart B. Under CAA § 176(c)(4)(B), the EPA established regulations under subpart A that apply only to federal highway and transit actions and are concerned with emissions of mobile sources such as cars, trucks, buses, etc. traveling on those federal roadways, referred to as the “Transportation Conformity” regulations. Under CAA § 176(c)(4)(A), the EPA established regulations under subpart B that apply to all other federal actions (referred to as "general" federal actions), where subpart B is referred to as the “General Conformity” regulations.” This means that general federal actions are defined by what they are not—they are not transportation programs, plans, or projects developed by a Metropolitan Planning Organization (MPO) or the Department of Transportation (DOT) according to 23 CFR part 450 “Planning Assistance and Standards,” or 49 CFR part 613 “Metropolitan and Statewide and Nonmetropolitan Planning.”
When the EPA created the subpart B General Conformity regulations, the agency also crated identical regulations under subpart W of 40 CFR part 51. Subpart W provided the regulations for States and Tribes to create their own General Conformity requirements unique to the needs of their own nonattainment and maintenance areas, while subpart B is to be followed by federal agencies. Subsequently, as a result of the federal 2005 SAFETEA-LU legislation, “Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users,” all except 40 CFR 51.851 was deleted. The SAFETEA-LU legislation changed the CAA, and the subpart B requirements were revised in 2010, to eliminate the requirement that States will submit their own General Conformity regulations to the EPA for approval.
In the time since the CAA 1990 Amendments, the EPA created subpart B and made subsequent revisions to subpart B as explained below, in order by year, in reverse order, from 2016 going back to 1993:
2016 Revisions—In the revisions to subpart B in 2016, the EPA removed the 2006 revision that added limitations for regulating emissions of NOx, VOC, and NH3 from the de minimis tables at § 93.153(b)(1) and (b)(2) but EPA did not remove the same limitations from the “Precursors of criteria pollutants” definition of PM2.5. The revision also listed carbon monoxide (CO) emissions as applicable within “All maintenance areas” instead of “All nonattainment areas,” as it is in the 1993 final rule, and in subsequent revisions in 2006 and 2010 to subpart B. The de minimis table § 93.153(b)(2) for maintenance areas included formatting errors making interpretation of the table difficult—
2010 Revisions—The revisions to subpart B in 2010 were the first, and the most recent, major revision. Every section of the 2006 version was revised and five new sections were added. The revisions added, among other things, § 93.150(e) for when there is “more than one nonattainment or maintenance area,” and paragraph 40 CFR 51.851(f), allowing a State or Tribe to develop for EPA approval, a list of their own unique presumed to conform activities, and added a definition for “Take or start an action.” The five added sections included § 93.161 for “facility-wide emission budgets,” § 93.162 for “emissions beyond the time period of the State implementation plan,” § 93.163 “timing of offsets and mitigation measures,” § 93.164, “provisions for inter-precursor mitigation measures,” and § 93.165, “Early emission reduction credit (EERC) program.” The revisions also removed the requirement for a “regional significance” analysis. The January 8, 2008, proposed rule is archived; search for the page number 1402—
Revisions to the General Conformity Regulations – Proposed Rule (73 FR 1402, 1/8/2008) (pdf) (5.9 MB)
2006 Revisions—The EPA proposed a draft and final rule to add de minimis rates for the PM2.5 in the tables at § 93.153(b)(1) and (b)(2) for nonattainment and maintenance areas, and added a definition for “Precursors of criteria pollutants” for the PM2.5 precursors. The revision also added limitations to the applicability of the precursor pollutants, NOx, VOC, and ammonia (NH3) to the tables and to the definition. The April 5, 2006, proposed rule is archived; search for the page number 17003—
1993 Original—The EPA proposed the first draft subpart B regulations, and the final version, in 1993. However, the final version was not effective until January 1994. As such the original subpart B may be referred to as the “1993” version or the “1993-1994” version. The links to these documents are archived in the Federal Register, and are available only as the entire day’s issue. Search for the page number for the beginning of each rulemaking—page 13836 for the proposal, and page 63214 for the final—
Determining Conformity of General Federal Actions to State or Federal Implementation Plans — Proposed Rule (58 FR 13836 3/15/1993)