For the purpose of this subchapter:

1. (1) The definitions contained in ARM 17.8.901 shall be applicable.
2. (2) "Cause or contribute" means, in regard to an ambient air quality impact caused by emissions from a major source or modification, an ambient air quality impact that exceeds the significance level as defined in (3) , for any pollutant at any location.

3. (3) "Significance level" means, for any of the following pollutants, an ambient air quality impact greater than any of the averages cited below:

   1. (a) for sulfur dioxide:

      1. (i) an annual average of 1.0 micrograms per cubic meter (µg/m 3 ) ;
      2. (ii) a 24-hour average of 5.0 µg/m 3 ; or
      3. (iii) a three-hour average of 25.0 µg/m 3 .

   2. (b) for PM-10:

      1. (i) an annual average of 1.0 µg/m 3 ; or
      2. (ii) a 24-hour average of 5.0 µg/m 3 .
   3. (c) for nitrogen dioxide, an annual average of 1.0 µg/m 3 .

   4. (d) for carbon monoxide:

      1. (i) an eight-hour average of 0.5 milligrams per cubic meter (mg/m 3 ) ; or
      2. (ii) a one-hour average of 2.0 mg/m 3 .

Authorizing statute(s): 75-2-111, 75-2-203, MCA

Implementing statute(s): 75-2-202, 75-2-203, 75-2-204, MCA

History: NEW, 1993 MAR p. 2919, Eff. 12/10/93; TRANS, from DHES, 1996 MAR p. 2285.