Power Plants: Air Pollution Emissions

For permitting purposes, air pollution sources are grouped based on size and location into major and minor attainment area sources, and major and minor non-attainment area sources. A large new power plant using a combustion technology is likely to be a "major source" (as defined in clean air laws), so minor sources will not be discussed in this summary. This discussion includes power plants that burn fuels including coal, natural gas, industrial residues, or wood.

An attainment area is an area where the national ambient air quality standard for a particular pollutant is being met. A non-attainment area for a particular pollutant is an area where the ambient air quality standard for the pollutant is not being met.

The air quality impacts of any proposed major new source must be thoroughly reviewed before it is issued permits to construct or operate. A major new source proposed in a non-attainment area must meet stringent conditions (specified below) so that it does not further degrade air quality in the non-attainment area. A major new source locating in an attainment area must undergo a PSD (prevention of significant deterioration) review to ensure that it will not significantly diminish air quality in the attainment area, and leaves room for other emission sources.

Emissions of the following air pollutants require air permits: total suspended particulates, particulate matter less than ten microns (PM₁₀), lead, sulfur dioxide, nitrogen oxides, carbon monoxide, volatile organic compounds, and any of the hazardous compounds listed in Chapter NR 445 [exit DNR] of the Wisconsin Administrative Code.

The processing of an air permit application for a large power plant follows these steps:

1. Submittal of a Complete Application
   The applicant must submit a complete application before the review process begins. The application must include all pertinent information, including site location, facility configuration and design, fuel composition and burning rates, air pollutant emission rates, air pollution control equipment design and efficiency, and an analysis of the impact the source will have on air quality. A permit application is complete only when all of the required information has been received.
2. Department Review and Preliminary Determination
   The Department has 120 days to review the permit application and make a preliminary determination as to whether it may be approved. A permit application may be approved if the proposed source meets certain conditions such as:
   1. It will meet all applicable emissions limitations.
   2. It will not cause or exacerbate a violation of an ambient air quality standard or an ambient air increment. Ambient air increments (or PSD increments) represent a margin of air quality that may not be used by any new source that locates in an attainment area. Increments are applied to preserve air quality in attainment areas.
   3. It will not degrade the air quality in an area enough to prevent the construction or operation of another source for which an application has already been filed.

In addition, attainment and non-attainment area major sources must meet other conditions including:

1. Attainment Area Sources (PSD Review)
   1. The source must use the best available control technology (BACT) to control emissions of each applicable air contaminant. BACT is determined by comparing the performance of similar units permitted recently.
   2. The source must not adversely affect air quality related values of any National Park, wilderness area, etc. These values may include visibility or other characteristics.
   3. The permitee must carry out air quality monitoring to measure its’ effects on air quality.
2. Non-attainment Area Sources
   1. The source must offset any increases in emissions by obtaining emission decreases from other sources that are in, or significantly affect, the air quality in the non-attainment area. The total for the area of emissions of the non-attainment pollutant(s) after the offsets must be less than the total emissions allowed in the area before the permit application.
   2. The air pollutants from the source will be emitted at the lowest achievable emission rate (LAER) [a technical determination] for each non-attainment air contaminant.
   3. All other sources in Wisconsin controlled by the permit applicant must meet all applicable air pollution control requirements.
   4. For major sources proposed to be located in carbon monoxide or volatile organic compound non-attainment areas, the benefits of the construction of the source must outweigh the environmental costs imposed by the source's location.

Public Comment and Final Determination

The Department publishes a legal notice describing the preliminary determination in a newspaper widely circulated in the project area. The public has thirty days from the publication date to comment on the proposed permit. If requested, the Department may hold a hearing on the proposed air permit at which verbal comments will be accepted. It can be combined with a hearing on an EIS, if one is prepared.

Based on the preliminary determination, and on any information received during the public comment period or at the public hearing, the Department determines whether the criteria for issuing the permit will be met. Then the Department either issues or denies the permit, or sets conditions in the permit to ensure that all criteria will be met.

For more information on DNR's role in power plant permitting and air emissions please visit the Air Management Program.