5 Colo. Code Regs. § 1001-14-VII
The Commission's review of the large volume of scientific data presented at the hearings led to several conclusions relevant to the establishment of appropriate ambient air quality standards for the State of Colorado. Sulfur dioxide is a colorless, irritating gas with a taste threshold on the order of 600 to 800 micrograms per cubic meter and an odor threshold approximately twice that value. It is converted in the atmosphere (at a presently undetermined rate) into particulate sulfuric acid droplets, and solid metallic sulfates. The hazards to human health of such sulfates are presently under extensive investigation by EPA and a broad section of the scientific community.
This Commission has not considered the question of health impacts of particulate surfaces in its adoption of ambient air standards for Colorado except to note that the information available is often conflicting and confusing. The same remarks are applicable to the effect of particulate sulfates on visibility. The Commission is very much aware that many have questioned the validity of EPA primary and secondary sulfur dioxide standards to protect humans, and animals, and vegetation with regard to (a) long term exposure to low concentrations of sulfur dioxide, (b) effects of altitude on atmospheric conversion of sulfur dioxide and attendant sulfate hazards, and (c) synergistic action of sulfur dioxide with other pollutants on vegetation.
The concerns of this Commission with regard to such considerations has led to the adoption of ambient air standards more restrictive than the EPA primary and secondary standards because:
Under the Prevention of Significant Deterioration doctrine, EPA has adopted sulfur dioxide ambient air quality standards in three classes. Class I preserves the pristine quality of pristine air. Class II permits moderate deterioration, and Class III sets an absolute limit at the Federal secondary standard (that ambient air standard designed to protect human welfare). The evidence received by this Commission was overwhelming in its support of the preservation of pristine conditions in National Parks, National Monuments, Wilderness and Primitive Areas, and the Gunnison Gorge Recreation area. It is logical to apply the EPA Prevention of Significant Deterioration Class I standards to these regions, to protect the air quality for intrusion by external sources, and no submission by any industrial representative in these public hearings opposed the use of the Federal Class I standards for the areas noted above.
The Commission has discovered no adequate rationale for adoption of the (EPA) PSD Class III standard for sulfur dioxide. This Commission questions the need for authorization of such concentrations of sulfur dioxide in the State of Colorado. Existing conditions in Colorado do not appear to even approach the Class in levels, and no proposal for development, as described by industrial representatives at the hearings, would be at all restricted by a standard more stringent than the Federal Class II standard. Therefore, Federal PSD Class II standards have been adopted as the Colorado Category III standards: proposed development of sulfur dioxide sources as presented to the Commission by a variety of industrial representatives, can proceed with much less impact than the Federal Class II for sulfur dioxide would allow. The Commission has thereby maintained consistency with Federal PSD requirements and feels that the State will be in a position in the near future to request delegation of authority from the Environmental Protection Agency for enforcement of PSD requirements.
The Colorado Category I standards for sulfur dioxide effective December 18, 1975 are very stringent ones, and because the bulk of the state is now designated as a Colorado Category I, certain proposed industrial development, as presented before this Commission and including energy conversion, might thereby be restricted. One proposed solution to this problem was redesignation to the Federal (PSD) Class II for the entire state. This concentration of sulfur dioxide. As noted above, the Commission simply does not feel that such extreme degradation in existing air quality for sulfur dioxide throughout the entire state is necessary. It is not necessary, according to evidence presented to the Commission, to go to the Colorado Category II standards set forth under the 1975 regulation to permit projected new industrial development.
The Commission has therefore adopted a standard, which are essentially at the halfway mark between PSD Class I and PSD Class II. This standard does allow for all the proposed development of sulfur dioxide sources described in hearings before this Commission and is an acceptable one to the Commission because it will not prohibit development, with careful siting considerations, yet avoids the necessity for redesignation involving substantial deterioration of existing air quality for sulfur dioxide. It should be noted that, at the PSD Class II levels, many Colorado citizens might actually be physically affected by the unpleasant and irritating taste of sulfur dioxide in the ambient air.
All of the above-described ambient standards to be established by this Commission for sulfur dioxide, are incremental standards. However, the Commission also feels strongly that an absolute standard, and "under lid," should be placed on sulfur dioxide levels as well. It is the absolute concentration, rather than the increment, which affects human health, welfare, and the "quality of life" which our Colorado Air Pollution Control Act so clearly seeks to protect. In order to assure compliance with the policy of this state, this Commission has adopted a three-hour average concentration of sulfur dioxide, of 700 micrograms per cubic meter, as an absolute standard not to be exceeded more than once per year. This absolute standard is again related to that level of sulfur dioxide in the ambient air, which may cause obvious physical irritation for certain Colorado citizens. This Commission intends to protect those citizens and all other residents of our State from impairment of their general welfare, convenience, and enjoyment of the beauty of life, which Colorado has to offer.
Ambient air quality standards will play an important role in the permitting process, and since that process involves the application of predictive modeling all incremental standards should be considered significant only to one significant figure.
As noted above, Colorado Category I for sulfur dioxide has been designated for certain areas based on the evidence received at public hearing. The Commission has also provided for designation of any National Parks, Monuments, Wilderness or Primitive Areas or Wild and Scenic River Corridors, which may be established in Colorado in the future. Such designation will be made after Commission evaluation of the comments of members of the public at hearing.
The Commission, on the basis of broad support from industry and the general public, decided not to permit redesignation of the Category I areas. The Commission found that sufficient documentation should accompany a redesignation request to show that the request is serious, well thought out in its various implications, and has some public support. On the basis of considerable testimony, it also developed a set of criteria by which the redesignation request will be judged. The Commission thus concluded that all of these elements in the redesignation process must be met before the designation is granted.
This action brings the State of Colorado regulations into conformity with the Federal regulations for (a) the methods for measurements of ambient concentrations of sulfur dioxide and (b) the manner in which these concentrations are reported:
This question as to whether these concentrations should be expressed in (a) micrograms per actual cubic meter or (b) micrograms per standard cubic meter (at 25 degrees Celsius and one atmosphere) is not resolved. If the hazard is related to the ratio of sulfur dioxide to oxygen the standard cubic meter concentration is preferable. If the concentrations are expressed in micrograms per standard cubic meter, the equivalent expression in parts per million is independent of altitude and temperature; this is not true if the concentrations are given in micrograms per actual cubic meter. The deciding issue in the decision was conformity with Federal Standards.
This action brings the State of Colorado Ambient Air Quality Standards for Total Suspended Particulates into conformity with the existing Federal Ambient Air Quality Standards for Total Suspended Particulates, and are the same standards, which are required to be met by 1982 by the Clean Air Act (1977 Amendments) and the Colorado State Implementation Plan.
Ambient Air Quality Standards play an important role in determining various aspects of the State air pollution permitting process and thus the adoption of State Ambient Air Quality Standards for Total Suspended Particulates identical to the Federal standards subject's applicants for an emission permit to only one standard, rather than different State and Federal Standard
The deciding issues in the decision were conformity with Federal standards and great public understanding.
* Rationale/TSP - Repeal and Readoption: Adopted 4/12/79
5 CCR 1001-14-VII