Indiana’s state implementation plan (SIP) is a collection of documents describing the goals and procedures that Indiana has adopted, with United States Environmental Protection Agency (U.S. EPA) approval, to protect the state’s air quality in accordance with the federal Clean Air Act (CAA) and the National Ambient Air Quality Standards (NAAQS) for six common and widespread “criteria” air pollutants, including carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2). The term “SIP” refers to the entire collection of documents or any single document within the collection. Indiana’s SIP includes details including but not limited to:
- Information about Indiana’s ambient air quality monitoring program to collect air pollutant data.
- Air quality calculations and modeling data to predict trends and explore different emission reduction strategies.
- Emission inventories, which list the amount of pollutants estimated to be released by different anthropogenic (caused by human activities) sources. These include:
- point sources (stationary facilities),
- nonpoint sources (dispersed “area” sources too small and numerous to count),
- onroad sources (such as gasoline and diesel passenger cars and heavy duty vehicles on roads) and
- nonroad sources (certain heavy duty engines, vehicles, and equipment used for a wide range of applications).
- Control strategies selected to reduce emissions.
- Formal adoption of measures, such as federally-approved state rules to achieve necessary emission reductions.
- Periodic review and evaluations of planned reductions.
U.S. EPA periodically reviews and may revise the NAAQS. When a NAAQS revision occurs, IDEM generally needs to amend one or more of the components in Indiana’s SIP. IDEM provides opportunities for the public to participate before submitting proposed revisions to U.S. EPA for approval. IDEM provides draft and approved SIP documents online, including:
- Recommendations for Air Quality Designations
- Within two years of issuing a new or revised NAAQS, U.S. EPA must designate air quality for all areas of the country according to these standards. States make recommendations to U.S. EPA within one year of a new or revised NAAQS. These recommendations are not SIPs, but are SIP-related.
- Infrastructure SIPs
- Indiana’s Infrastructure SIPs demonstrate Indiana’s legal authority, regulatory structure, and resources to implement, maintain, and enforce the NAAQS in all areas of the state. Section 110 of the federal CAA requires states to submit infrastructure SIPs within three years of a new or revised NAAQS.
- Attainment Demonstrations
- IDEM develops attainment demonstrations, as required, for certain areas that U.S. EPA designates as “nonattainment.” A nonattainment area is an area that does not meet the NAAQS for one or more of the criteria pollutants or is determined to be contributing to nearby violations. An attainment demonstration describes the measures Indiana is taking to improve air quality and bring a nonattainment area into attainment with the NAAQS. IDEM’s Nonattainment Status for Indiana Counties page includes a map of Indiana’s nonattainment areas and Indiana’s attainment history for each NAAQS.
- Requests for Redesignation and Maintenance Plans
- When ambient air quality monitoring data shows that a nonattainment area has achieved the NAAQS, Indiana develops and submits a Request for Redesignation and Maintenance Plan to U.S. EPA for review and approval. A request for redesignation is a request to change an area’s designation status from “nonattainment” to “attainment” of the NAAQS. A maintenance plan describes how Indiana will ensure the area continues to maintain compliance with the NAAQS.
- Program SIPs
- Indiana’s SIP includes documents to implement certain federally-required programs. Examples include Indiana’s Transportation Conformity SIP (to ensure that transportation activities will not cause new air quality violations, worsen existing violations, or delay timely attainment of the NAAQS), Regional Haze SIP (for the remedy and prevention of visibility impairments in federally-protected parks and wildlife areas), and Motor Vehicle Inspection and Maintenance Plan (I/M testing program) for the implementation of federal requirements for carbon monoxide and ozone.
IDEM uses public notices to announce opportunities for the public to view and submit comments on draft documents and request a public hearing. Generally, the timeframe for written comments or submitting a request for a public hearing on a draft submittal is 30 days. If a public hearing is requested, IDEM may extend the public comment period. The public can subscribe to receive email updates.
U.S. EPA’s Role
U.S. EPA is responsible for approving SIPs. U.S. EPA publishes notices in the Federal Register concerning proposed and final federal actions on Indiana’s SIP submittals, including opportunities for submitting public comments to U.S. EPA.
The United States Code of Federal Regulations contains each state’s SIP at Title 40 Part 52 (40 CFR Part 52). When U.S. EPA approves a SIP or a SIP revision, it amends 40 CFR Part 52 to add the approved SIP. The federally enforceable SIP for Indiana is compiled at 40 CFR Part 52, Subpart P [PDF]. U.S. EPA’s Air Implementation Plan site includes SIP status updates and federally approved plans.
Once a SIP is approved by U.S. EPA, both IDEM and U.S. EPA can enforce it.
IDEM’s Criteria Pollutant page provides links to Indiana’s SIP submittals by pollutant.