17.30.518    SOURCE SPECIFIC MIXING ZONES

(1) If adequate information regarding stream flow or ground water flow is not available or if a standard mixing zone is not applicable or desired by the applicant, an applicant may request a source specific mixing zone.

(2) A source specific surface or ground water mixing zone will only be granted after the applicant demonstrates to the department that the requested mixing zone will comply with the requirements of ARM 17.30.506 and 17.30.507 and the provisions of 75-5-303 , MCA.

(3) For lakes, the area of a mixing zone must not exceed 5% of the area of the lake or extend more than a 200 foot radius from the discharge, whichever is more restrictive.

(4) For source specific mixing zones in other surface water, the applicant shall provide information adequate to demonstrate to the department that the requirements of 75-5-301 (4) , MCA, are satisfied. In addition, the applicant shall present a discussion of the mixing zone in the context of the restrictions and general considerations specified in ARM 17.30.506, and information addressing the following items, as applicable:

(a) quantity, toxicity, and persistence of the pollutant;

(b) rate of flow;

(c) volume of flow;

(d) concentration of pollutants within the mixing zone;

(e) length of time pollutants will be present;

(f) proposed boundaries of the mixing zone;

(g) potential impacts to water uses;

(h) potential compliance monitoring;

(i) contingency plan if pollutants migrate beyond the mixing zone at concentrations greater than the allowed limits; and

(j) specific explanation as to why the proposed mixing zone is the smallest practicable size and why it will have a minimum practicable effect on water users.

(5) For source specific mixing zones in ground water the applicant shall provide information adequate to demonstrate to the department that the requirements of 75-5-301 (4) , MCA, are satisfied. In addition, the applicant shall present a discussion of the mixing zone in the context of the restrictions and general considerations specified in ARM 17.30.506, and information addressing the following items, as applicable:

(a) quantity, toxicity, and persistence of the pollutant;

(b) water-bearing characteristics of subsurface materials;

(c) rate and direction of ground water flow;

(d) pollutant migration;

(e) volume of ground water and area available for mixing;

(f) concentration of pollutants within the mixing zone;

(g) length of time pollutants will be present;

(h) proposed boundaries of the mixing zone;

(i) potential impacts to water uses;

(j) compliance monitoring;

(k) contingency plan if pollutants migrate beyond the mixing zone at concentrations greater than the allowed limits; and

(l) specific explanation as to why the proposed mixing zone is the smallest practicable size and why it will have a minimum practicable effect on water users.

History: 75-5-301, MCA; IMP, 75-5-301, MCA; NEW, 1994 MAR p. 2136, Eff. 8/12/94; TRANS, from DHES, 1996 MAR p. 1499.