17.30.1006 CLASSIFICATIONS, BENEFICIAL USES, AND SPECIFIC STANDARDS FOR GROUND WATERS

(1) Class I ground waters are those ground waters with a natural specific conductance less than or equal to 1,000 microSiemens/cm at 25ºC.

(a) The quality of Class I ground water must be maintained so that these waters are suitable for the following beneficial uses with little or no treatment:

(i) public and private water supplies;

(ii) culinary and food processing purposes;

(iii) irrigation;

(iv) drinking water for livestock and wildlife; and

(v) commercial and industrial purposes.

(b) Except as provided in ARM 17.30.1005(2) , a person may not cause a violation of the following specific water quality standards in Class I ground water:

(i) the human health standards for ground water listed in DEQ-7;

(ii) for concentrations of parameters for which human health standards are not listed in DEQ-7, no increase of a parameter to a level that renders the waters harmful, detrimental, or injurious to the beneficial uses listed for Class I water. The department may use any pertinent credible information to determine these levels; and

(iii) no increase of a parameter that causes a violation of the nondegradation provisions of 75-5-303 , MCA.

(2) Class II ground waters are those ground waters with a natural specific conductance that is greater than 1,000 and less than or equal to 2,500 microSiemens/cm at 25ºC.

(a) The quality of Class II ground water must be maintained so that these waters are at least marginally suitable for the following beneficial uses:

(i) public and private water supplies;

(ii) culinary and food processing purposes;

(iii) irrigation of some agricultural crops;

(iv) drinking water for livestock and wildlife; and

(v) most commercial and industrial purposes.

(b) Except as provided in ARM 17.30.1005(2) , a person may not cause a violation of the following specific water quality standards for Class II ground water:

(i) the human health standards for ground water listed in DEQ-7;

(ii) for concentrations of parameters for which human health standards are not listed in DEQ-7, no increase of a parameter to a level that renders the waters harmful, detrimental, or injurious to the beneficial uses listed for Class II water. The department may use any pertinent credible information to determine these levels; and

(iii) no increase of a parameter that causes a violation of the nondegradation provisions of 75-5-303 , MCA.

(3) Class III ground waters are those ground waters with a natural specific conductance that is greater than 2,500 and less than or equal to 15,000 microSiemens/cm at 25ºC.

(a) The quality of Class III ground water must be maintained so that these waters are at least marginally suitable for the following beneficial uses:

(i) irrigation of some salt tolerant crops;

(ii) some commercial and industrial purposes;

(iii) drinking water for some livestock and wildlife; and

(iv) drinking, culinary, and food processing purposes where the specific conductance is less than 7,000 microSiemens/cm at 25ºC.

(b) Except as provided in ARM 17.30.1005(2) , a person may not cause a violation of the following specific water quality standards for Class III ground water:

(i) the human health standards listed in DEQ-7, except that the nitrate nitrogen and nitrate plus nitrite nitrogen standards listed in DEQ-7 do not apply to ground waters with a specific conductance equal to or greater than 7,000 microSiemens/cm at 25ºC. The nitrate nitrogen and nitrate plus nitrite nitrogen standards for these waters are each 50 mg/l; and

(ii) for concentrations of parameters for which human health standards for ground water are not listed in DEQ-7, no increase of a parameter to a level that renders the waters harmful, detrimental, or injurious to the beneficial uses listed for Class III water. The department may use any pertinent credible information to determine these levels.

(4) Class IV ground waters are those ground waters with a natural specific conductance greater than 15,000 microSiemens/cm at 25^oC.

(a) The quality of Class IV ground waters must be maintained so that they are suitable for some industrial and commercial uses.

(b) Except as provided in (5) and ARM 17.30.1005(2) , a person may not cause a violation of the following specific water quality standards for Class IV ground water:

(i) the human health standards for parameters categorized as carcinogens in DEQ-7;

(ii) for concentrations of parameters in DEQ-7 which are not listed as carcinogens, no increase of a parameter to a level that would adversely affect existing beneficial uses. The nitrate nitrogen and nitrate plus nitrite nitrogen standards are each 50 mg/l;

(iii) for concentrations of parameters for which human health standards are not listed in DEQ-7, no increase of a parameter to a level that would adversely affect existing beneficial uses. The department may use any pertinent credible information to determine these levels.

(5) For Class III or IV waters, where it can be demonstrated to the satisfaction of the department that the field hydraulic conductivity is less than 0.1 feet per day in an affected or potentially affected ground water zone, the nitrate nitrogen and nitrate plus nitrite nitrogen standards in (3) (b) (i) and (4) (b) (ii) do not apply, provided that all existing and anticipated uses of the ground waters are protected.

(6) The ground water quality standards for metal parameters are based on the dissolved portion (after filtration through a 0.45 micron filter) of the contaminant in the ground water. The ground water quality standards for other parameters in department Circular DEQ-7 are based upon unfiltered samples. For inorganic parameters, compliance with standards based on filtered samples must be assumed if analyses using the total recoverable method demonstrates compliance with the numerical standards.

History: 75-5-301, 80-15-105, 80-15-201, MCA; IMP, 75-5-301, 80-15-201, MCA; NEW, 1999 MAR p. 94, Eff. 1/15/99; AMD, 2002 MAR p. 387, Eff. 2/15/02; AMD, 2003 MAR p. 217, Eff. 2/14/03; AMD, 2004 MAR p. 1617, Eff. 4/9/04; AMD, 2006 MAR p. 528, Eff. 2/24/06.