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Air Quality

Prevention of Significant Deterioration (PSD)

DHEC's Prevention of Significant Deterioration (PSD) regulations (S.C. Regulation 61-62.5, Standard No. 7) apply to new major sources or major modifications at sources located in areas that are attaining the National Ambient Air Quality Standards (NAAQS) or are unclassifiable under 40 CFR 81.341. The PSD regulations require the sources to:

  • install the "Best Available Control Technology" (BACT);
  • conduct an air quality analysis;
  • conduct an additional impacts analysis; and
  • Opportunity for public involvement

The main purpose of the PSD air quality analysis is to demonstrate that new emissions emitted from a proposed major stationary source or major modification, in conjunction with other applicable emissions increases and decreases from existing sources, will not cause or contribute to a violation of any applicable NAAQS or PSD increment. Generally, the analysis will use ambient air monitoring data and air quality dispersion modeling results to assess the existing air quality and predict ambient concentration levels that would result from the proposed project and future growth associated with the project.

Additional impacts analysis assesses the impacts of air, ground and water pollution on soils, vegetation, and visibility caused by any increase in emissions from the source or modification under review, and its associated growth. Associated growth is industrial, commercial, and residential growth that will occur in the area due to the source.

The PSD regulations do not prevent sources from increasing emissions. Instead, they are designed to:

  • protect public health and welfare;
  • preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreational, scenic, or historic value;
  • insure that economic growth will occur in a manner consistent with the preservation of existing clean air resources; and
  • assure that any decision to permit increased air pollution in any area to which this section applies is made only after careful evaluation of all the consequences of such a decision and after adequate procedural opportunities for informed public participation in the decision making process.

The NAAQS is a maximum allowable concentration "ceiling." A PSD increment, on the other hand, is the maximum concentration increase that is allowed to occur above a baseline concentration for a specific pollutant. The baseline concentration is defined for each pollutant and, in general, is equal to the ambient concentration existing at the time that the first complete PSD permit application affecting the area is submitted. PSD increments prevent the air quality in clean areas from deteriorating to the level set by the NAAQS. Significant deterioration is said to occur when the amount of new pollution would exceed the applicable PSD increment. It is important to note, however, that the air quality cannot deteriorate beyond the applicable NAAQS level, even if not all of the PSD increment is consumed.

The PSD review is lengthy and complicated. The permit could take up to 270 days (upon receipt of a complete application) to be issued, including a required public notice and 30-day comment period. It is recommended that an applicant schedule a premeeting with the appropriate BAQ Permitting Staff prior to submitting any PSD Applications. For a facility locating within 300 km of a Class 1 Area it is recommended to involve early on Federal Land Managers.


For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.