Air Quality Improvement Planning (AQIP) Section

State Plans

Revised On: May. 1st, 2025 - 10:24 am

What are State Plans?

When the U.S. Environmental Protection Agency (EPA) issues guidelines for controlling emissions from existing sources of certain air pollutants, Section 111(d) of the Clean Air Act (CAA) requires states to create a State Plan. This plan must set standards for these sources that are at least as strict as the EPA's published guidelines, and it must explain how the state will enforce and ensure compliance with these standards. State Plans then get submitted to the EPA for approval.

For more information about implementing regulations for the adoption and submission of State Plans under CAA § 111(d), please refer to the EPA’s webpage | Learn More >

How are State Plans different from a State Implementation Plan?

A State Implementation Plan (SIP) is required under Section 110 of the CAA and serves a different purpose than a State Plan under Section 111(d). A SIP outlines how a state will attain and maintain the National Ambient Air Quality Standards (NAAQS) for specific air pollutants, known as "criteria pollutants." These include carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter (PM₁₀ and PM_2.5), and sulfur dioxide | Learn More >

While SIPs focus on meeting ambient air quality standards across the state, State Plans under Section 111(d) apply to specific categories of existing sources and are based on EPA set emission guidelines for pollutants not covered by the NAAQS.

Completed State Plans

State Plan for Existing Municipal Solid Waste Landfills

On Aug. 29, 2016, the EPA finalized a rulemaking updating the standards of performance and emission guidelines for Municipal Solid Waste (MSW) landfills. Under CAA § 111(d), ADEQ developed a State Plan that updated ADEQ’s rules with the current emission guidelines for MSW landfills under ADEQ’s jurisdiction through incorporation by reference of 40 Code of Federal Regulations (C.F.R.) Part 60, Subpart Cf | View Plan >

The EPA finalized its approval of ADEQ's State Plan on July 28, 2020 | View >

State Plan Negative Declaration for Hospital/Medical/Infections Waste Incinerators

In 1997, the EPA finalized a rulemaking promulgating emission guidelines and compliance times for Hospital/Medical/Infections Waste Incinerators (HMIWI), that was codified at 40 C.F.R. Part 60, Subpart Ce. 62 FR 48379 (Sept. 15, 1997). On Nov. 16, 1999, ADEQ submitted a negative declaration letter to the EPA asserting that the State of Arizona contained no HMIWIs subject to the EPA’s final rule and therefore a State Plan would not be required. On June 22, 2000, the EPA approved ADEQ’s negative declaration referenced in 65 FR 38740 | View >

State Plans Under Development

ADEQ is currently in the process of developing two State Plans as required by Section 111(d) of the CAA:

State Plan for Existing Oil and Natural Gas Operations

On March 8, 2024, the EPA issued its final emission guidelines for regulating methane emissions from existing oil and natural gas operations, which includes, but is not limited to, well sites, compressor stations, storage vessel/tanks batteries, and other operations related specifically to existing crude oil and natural gas operations. Federal Rule: 40 C.F.R. Part 60, Subpart OOOOc | View >

States have until March 9, 2026, to submit State Plans to the EPA for this rule. For more information about any ADEQ rulemaking(s) related to this State Plan and opportunities for involvement in the rulemaking process, please visit ADEQ’s active rulemaking webpage | View Page >

Public Notices and Meetings: ADEQ will update this page with additional information regarding outreach and participation opportunities as they become available.

State Plan for Existing Fossil Fuel-Fired Power Plants

On May 9, 2024, the EPA published final carbon pollution standards for power plants that set carbon dioxide (CO₂) emission guidelines for existing coal-, oil- and gas-fired steam generating units. In this action, the EPA also repealed the Affordable Clean Energy (ACE) Rule. Federal Rule: 40 C.F.R. Part 60, Subpart UUUUb | View >

Under this rule, States have until May 11, 2026, to submit State Plans addressing the EPA’s emission guidelines for these sources.

ADEQ held a public information session regarding the Power Sector State Plan on March 20, 2025 | View Presentation >

ADEQ will update this page with additional information regarding outreach and participation opportunities as they become available.

Regulatory Background for Fossil Fuel-Fired Power Plants

Before the State Plan currently under development, ADEQ worked on two prior State Plans for fossil fuel-fired power plants under CAA § 111(d): the Clean Power Plan and the Affordable Clean Energy Rule:

The Clean Power Plan (CPP)

On Aug.3, 2015, the EPA announced the CPP, a rule that required states to develop and implement a plan to reduce CO₂ emissions from existing fossil fuel-fired power plants. The CPP was part of a comprehensive federal program to mitigate climate change.

The CPP required states to adopt standards to meet CO₂ emission reduction goals established by the EPA. States had until Sept. 6, 2016, to transmit a final plan or an “initial submittal” to the EPA. If the EPA approved the initial submittal, the deadline for submitting a final plan would have been extended to Sept. 6, 2018.

The proposed CPP would have required Arizona to achieve a 52 percent reduction in the CO₂ emissions rate for affected power plants and to achieve about 90 percent of that reduction by 2020. The reduction for Arizona was much more stringent than the reductions proposed for our neighbors in the West and was among the most severe imposed on any state. As a result, at least in part, of extensive comments and technical data submitted by ADEQ and Arizona stakeholders, the EPA lowered the CO₂ emission rate to 34 percent, and established a much more gradual timeline for achieving that reduction.

In response to the EPA’s CPP, ADEQ’s Air Quality Division initiated the State Plan development process. However, on Oct. 10, 2017, the EPA proposed to repeal the CPP. As a result, Arizona’s State Plan for the CPP was never submitted to the EPA.

The Clean Power Plan’s Replacement: Affordable Clean Energy (ACE) Rule

On Dec. 28, 2017, the EPA published an Advanced Notice of Proposed Rulemaking, seeking information from the public and stakeholders regarding certain components of the CPP.¹ Comments were due to the EPA by Feb. 26, 2018 | View Comments >

On July 8, 2019, the EPA published a Notice of Final Rulemaking promulgating its ACE Rule.² In this same rulemaking, the EPA also rescinded the CPP and established new regulations for CAA § 111(d) State Plans.

On Nov. 8, 2019, ADEQ held an initial stakeholder meeting to discuss the ACE Rule planning processes.

On April 23, 2020, ADEQ and representatives from the affected coal-fired electric generation units commenced a technical working group. This group met on a monthly basis to address technical issues regarding the Heat Rate Improvement (HRI) analysis of the EPA’s identified Best System of Emissions Reduction (BSER) as mandated by the ACE Rule.

On Dec. 19, 2021, the Federal D.C. Circuit Court of Appeals struck down the ACE rule and remanded it to the EPA.

On June 30, 2022, the U.S. Supreme Court held that the EPA lacked authority under CAA § 111(d) to set a cap on greenhouse gas emissions from power plants based on generation shifting. Following the Supreme Court’s decision, the EPA began development of a new rule for greenhouse gas standards and guidelines for fossil fuel-fired power plants.

The ACE Rule was repealed on May 9, 2024, and Arizona’s State Plan for the ACE Rule was never submitted to the EPA.

¹82 FR 61,507
²84 FR 32,520

AQD | AQIP | State Plans