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State Implementation Plan

As required in Section 110 of the federal Clean Air Act (CAA), each state must submit a plan, a State Implementation Plan (SIP), to the United States Environmental Protection Agency (U.S. EPA) detailing what they will do to accomplish implementation, maintenance and enforcement of National Ambient Air Quality Standards (NAAQS). There is one SIP per state, but each state’s SIP includes numerous documents approved by U.S. EPA since the adoption of the federal CAA. Therefore, a SIP is an ever-evolving dynamic document.

A SIP details how the state plans to limit air pollution from industrial, mobile, and any other “source” of pollution in order to protect human health and the environment. SIPs generally contain:

  • A monitoring program to collect air pollutant measurements.
  • Air quality calculations and modeling to predict trends, as well as explore different emission reduction strategies.
  • An emissions inventory, which includes lists of the amount of air pollution released by sources.
  • Control strategies to reduce emissions.
  • Formal adoption of measures (enforceable by U.S. EPA, states, and citizens) to be sure necessary emission reductions are achieved.
  • Periodic review to evaluate whether those reductions were achieved and whether the NAAQS are still sufficient to protect human health and the environment.

SIP Types

Infrastructure SIPs:

An infrastructure SIP shows that Indiana has the legal authority, regulatory structure, and resources to implement the NAAQS in all areas of the state. An infrastructure SIP must be developed when U.S. EPA establishes a new NAAQS or revises an existing NAAQS.

Attainment Plans:

An attainment plan describes the measures Indiana is taking to improve air quality and bring a nonattainment area into attainment with the NAAQS. An attainment plan must be prepared when U.S. EPA designates an area “nonattainment” for not meeting a NAAQS.

Maintenance Plans:

After a nonattainment area meets the NAAQS, Indiana can request that U.S. EPA redesignate the area from nonattainment to attainment. The maintenance plan describes the actions that will be taken for a period of 10 years to ensure that the area will meet the NAAQS after U.S. EPA approves redesignation.

Program SIPs:

A program SIP implements programs or parts of programs required by the federal CAA. One example of a program SIP in Indiana is the Motor Vehicle Inspection & Maintenance Plan, which U.S. EPA required for carbon monoxide and ozone nonattainment areas.

SIP Related Documents listed by Pollutant

The IDEM offers detailed information on Indiana's SIP-related documents listed under the criteria pollutants.

Nonattainment Area Designation

What does it mean and how does it happen?

The federal Clean Air Act, which was passed in 1970 and last amended in 1990, requires U.S. EPA to set NAAQS for pollutants that cause adverse effects to public health and the environment. Monitors, placed strategically across the nation, provide air samples that are tested for information about what is contained in the air we breathe.

Nonattainment areas are regions within the country where the concentration of one or more criteria pollutants exceeds the NAAQS. Once U.S. EPA announces that an area does not meet NAAQS that area is considered to be “designated as nonattainment”. After such a designation determination is made, the state works with businesses, local governments, and the public to reduce emissions from pollution sources contributing to the nonattainment status of the area.

Setting the standards: How does the process work?

U.S. EPA technical staff draft NAAQS, based on extensive study of scientific and technical data and input from experts, in order to determine the level of pollutants in ambient air below which human health effects are unlikely. Before U.S. EPA announces a final decision on NAAQS, the proposed standards are published in the Federal Register for public review and comment. Once NAAQS are announced as final, a basic schedule (set by the federal CAA) is in effect for achieving the standards. The states have primary responsibility for selecting programs most likely to improve air quality in their state.

How is an area designated as nonattainment?

IDEM provides detailed information on NAAQS that addresses this question.

What steps are required to move an area from nonattainment to attainment?

States may ask U.S. EPA to redesignate an area “attainment” if:

  • the area has monitored attainment of the air quality standard;
  • the area has a fully approved State Implementation Plan;
  • U.S. EPA has determined that the improvement in air quality is due to permanent and enforceable reductions in emissions;
  • the state has submitted, and U.S. EPA has approved, a maintenance plan for the area; and,
  • the area has met all other applicable federal CAA requirements.

U.S. EPA may approve or deny a redesignation request based on air monitoring information, activities listed in the SIP, and comments submitted by the public.

How do areas redesignated “attainment” keep their air clean?

Nonattainment areas that later are designated to attainment are considered maintenance areas. The steps to maintain air quality are defined in a maintenance plan. Generally, the control measures used to improve air quality will remain in place.

The maintenance plan must demonstrate continued compliance, considering projected growth, for a period of ten years. If outdoor air monitors record a violation of the standard, the maintenance plan includes a commitment to determine appropriate measures to address the cause of the violation.