Assessing Project Impacts - Ambient Air Standards

1. National Ambient Air Quality Standards - The 1970 Clean Air Act was enacted by Congress to protect the health and welfare of the public from the adverse effects of air pollution. Subsequently, the EPA established National Ambient Air Quality Standards for six criteria pollutants sulfur dioxide or SO₂, particulate matter less then 10 microns or PM₁₀, nitrogen dioxide or NO₂, carbon monoxide or CO, ozone or O2, and lead or Pb , and Prevention of Significant Deterioration increments for three pollutants SO₂, PM₁₀, and NO₂. The NAAQS specify maximum concentrations for various averaging times below which the air quality is considered acceptable with an adequate margin of safety and they include both primary and secondary standards.

   The primary standards are intended to protect human health; whereas, the secondary standards are intended to protect public welfare (e.g., damage to vegetation) from any known or anticipated adverse effects associated with the presence of air pollutants. The more stringent of the primary or secondary standards is applicable to the modeling evaluation. The NAAQS have been developed for various averaging periods. The NAAQS for short-term periods (24 hours or less) are not to be exceeded more than once per year. Long-term NAAQS refer to limits that cannot be exceeded for averaging periods over three months or longer.

2. Increment - A PSD increment, on the other hand, is the maximum allowable increase in concentration above a baseline concentration for a pollutant. The baseline concentration is generally defined as the concentration existing at the time that the first complete PSD permit application affecting the area is submitted. It is important to note that the air quality cannot deteriorate beyond the concentration allowed by the applicable NAAQS, even if not all of the PSD increment is consumed. The PSD increments and the NAAQS are in the following table.

3. Significant Ambient Air Concentration - In addition to the six criteria pollutants, the DEQ regulates specific toxic pollutants. Toxic pollutants are designated in Air Toxics Program Priority Implementation Policy and the toxicity values of these are found in the 1991-1992 ACGIH Handbook (not including the six criteria pollutants). Each pollutant has an hourly or a combination of an hourly and an annual Significant Ambient Air Concentration. Compliance must be shown for both, if both exist. For specifics on toxic pollutants, refer to the Virginia regulations for control and abatement of air pollution, 9 VAC 5 Chapter 50, Part II, Article 3 for New and Modified Stationary Sources.

Modeling

An air quality modeling analysis for a PSD proposed facility, such as a base load power plant, is required to demonstrate that its emissions of specific pollutants will not cause or significantly contribute to a violation of any ambient air quality standard or PSD increment. The modeling analysis must be done in conformance with the EPA and DEQ guidance and procedures. In the case of a Class I (defined in the following section on assessments) analysis, direct consultation with the specific federal land manager is required to adequately determine the air quality impacts of this proposed facility.

The basic goals of an air quality analysis are:

1. To ensure that economic growth will occur in harmony with the preservation of existing natural resources.
2. To protect the public health and welfare from any adverse effect which might occur even at air pollution levels less than the NAAQS.
3. To preserve, protect, and enhance the air quality in areas of special, natural, recreational, scenic, or historic value such as national parks and wilderness areas.
4. To require that major new stationary sources and major modifications be carefully reviewed prior to construction to ensure compliance with the NAAQS and applicable air quality increments.

For a proposed peak demand power plant that does not normally require an air quality analysis, DEQ has decided to require one to determine if it will have a significant impact upon air quality on the surrounding area. If the results are insignificant, no further analysis is required. Otherwise, a PSD type analysis will be required.

Protecting Exceptional Resources

The third purpose of the PSD program is more explicitly defined to 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. These are mandatory Class I areas include the following areas that were in existence as of August 7, 1977:

1. International parks
2. National wilderness areas and national memorial parks in excess of 5,000 acres
3. National parks in excess of 6,000 acres

These Class I areas are managed by the USDA Forest Service, National Park Service and the Fish and Wildlife Service. These federal land managers have the affirmative responsibility to protect these areas unique attributes and air quality.

The first level of protection is estimating the proposed facility's impact on the Class I PSD increments. These were small amounts of additional pollution that Congress dictated. These values are in the previously referenced table.

In addition, the Clean Air Act referenced air quality-related values, which could not be adversely impacted by the proposed facility. These air quality-related values include visibility, odor, flora, fauna, and geological resources: archeological, historical, and other cultural resources; and soil and water resources. The values for various Class I areas differ, depending on the purpose and characteristics of a particular area and the assessment by an area's federal land manager. The thresholds of each Air Quality Related Values for compliance assessment are determined by the specific federal land manager. The two Class I areas in Virginia are the Shenandoah National Park (managed by the National Park Service) and James River Face Wilderness Area (managed by the USDA Forest Service).