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State Implementation Plan (SIP)

The State Implementation Plan (SIP) is developed to show how a state will meet the National Ambient Air Quality Standards (NAAQS) for six common pollutants, called "criteria pollutants," as set forth by the Clean Air Act.

A SIP is the accumulated record of many documents that form a blueprint and timeline for the state's plans to assure compliance with the NAAQS for criteria pollutants (carbon monoxide, sulfur dioxide, ozone, nitrogen dioxide, lead, and particulate matter), as outlined in the Clean Air Act. SIPs include, among other things, control plans, regulations, inventories of emissions within the state, and transcripts of public involvement in the SIP-development process. Once approved, the SIP is enforceable by the state and EPA. Elements of South Carolina's SIP have been in place since 1972. Though there have been many amendments, there is only one South Carolina SIP. For more information, see EPA's SIP webpage.

What's in the SIP?

Several individual elements can make up the state's complete "SIP." There are many different components of the SIP, including:

  • Infrastructure SIP elements
  • Non-attainment SIP elements
  • Attainment Demonstrations
  • Maintenance Plans
  • Section 111(d)/129 Plans

Infrastructure State Implementation Plan (SIP)

Sections 110(a)(1) and (2) of the Clean Air Act require all states to submit plan elements to provide for the implementation, maintenance, and enforcement of the NAAQS. Sections 110(a)(1) and (2) further require states to address basic SIP requirements, including but not limited to the following elements: emissions limits and other control measures, ambient air quality monitoring, a program for the enforcement of control measures, adequate resources to implement the SIP, and public notification and government consultation. These elements are commonly called "infrastructure" elements of the SIP. Section 110(a) requires states to submit SIP revisions within three (3) years after promulgation of a new or revised NAAQS. These SIP amendments essentially certify to EPA that the state has the elements in place to allow it to continue to maintain the NAAQS.

The first NAAQS for which EPA required an infrastructure SIP certification was the 1997 Ozone NAAQS. EPA has since required infrastructure SIPs for NAAQS that have been revised.

For more information on Infrastructure SIP certifications, see EPA's Infrastructure SIP webpage.

Nonattainment SIP elements

A nonattainment plan is the specific SIP plan element designed to address a particular area in the state that has been designated as nonattainment for a standard. Once nonattainment designations take effect, the state has three years to develop a nonattainment SIP revision outlining how a particular area will attain and maintain the standards by reducing air pollutant emissions in that area.


The only nonattainment plans in South Carolina are for the York County part of the Charlotte-Gastonia-Rock Hill NC-SC nonattainment area for the 2008 Ozone NAAQS.
On May 23, 2014, the Department published a Notice of Intent to Revise the SIP and submitted a proposed Marginal Nonattainment Area SIP to meet the requirements for the York County portion of the Charlotte-Rock Hill NC-SC 8-hour Ozone Nonattainment Area, for the 2008 NAAQS ozone standards. This SIP certifies that each Clean Air Act 182(a) marginal area requirement has been met, to include an emissions inventory.

The Clean Air Act also requires states with areas designated as nonattainment areas for Ozone(O3), carbon monoxide (CO), particulate matter (PM10 and PM2.5), or nitrogen dioxide (NO2) to demonstrate that any transportation plans, programs, and projects planned for the area are consistent with the state's air quality goals - attaining and maintaining the standards. South Carolina incorporated a Memorandum of Agreement into the SIP to satisfy the Interagency Consultation Requirements of the Federal Transportation Conformity Rule.

Attainment Demonstrations

The Clean Air Act requires that states submit attainment demonstrations for nonattainment areas to show that the area will attain and can continue to attain the NAAQS for which it was in nonattainment. For more information on the attainment demonstration for the York County portion of the Charlotte-Gastonia-Rock Hill NC-SC (Metrolina) nonattainment area for the 1997 Ozone NAAQS, see our Metrolina Attainment Demonstration website.

Maintenance Plans

An area that was once designated as nonattainment, but has been redesignated as attainment, must submit a maintenance plan, as required by section 175A of the Clean Air Act. South Carolina has submitted maintenance plans for two areas of the state, Cherokee County and the York County portion of the Charlotte-Gastonia-Rock Hill NC-SC nonattainment area.

Section 111(d)/129 Plans

Section 129 of the Clean Air Act (CAA) regulates solid waste combustion sources, such as incinerators. Section 111 of the CAA requires the U.S. Environmental Protection Agency (EPA) to issue "Standards of Performance for New Stationary Sources" (NSPS). Within one year of when EPA issues NSPS rules for solid waste combustion sources, Section 111(d)/129 requires plans from states, commonly called "Section 129 plans," that detail how the state will implement and enforce those standards. Section  111(d)/129 plans consist of regulations, a list of affected sources, and permits and emissions inventories for these sources. DHEC has adopt-by-reference authority to enforce NSPS regulations, which means when DHEC adopts an EPA-issued NSPS rule, DHEC has the authority to enforce it. We adopt these regulations by reference in our End of Year Revisions. CAA Section 129(b)(2) requires that if a state fails to submit an approvable Section 111(d)/129 plan within two years of the date that EPA issues an NSPS rule for a group of solid waste combustion sources, then the EPA is required to develop a federal plan.

The requirements for these plans are distinct from State Implementation Plan (SIP) revisions that are based on Sections 110, 111, 172, or 175A of the Clean Air Act. Provisions for sanctions, the content of the plans, and timing differ in the various types of plans.

DHEC has submitted four (4) Section 111(d)/129 plans to the EPA for five NSPS rules:

  • CISWI Rule: Commercial and industrial solid waste incineration units
  • HMIWI Rule: Hospital, medical, and infectious waste incinerators
  • LMWC Rule: Large municipal waste combustors
  • OSWI Rule: Other solid waste incineration units
  • SSI Rule: Sewage sludge incineration units

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