17.30.618 NATURAL AND NONANTHROPOGENIC WATER QUALITY STANDARDS
(1) Named waterbodies, waterbody segments, or waterbodies within geographic regions listed below have natural or nonanthropogenic concentrations for one or more parameters that exceed the applicable standards. For these waterbodies, the standards specified in (2) supersede the otherwise applicable water quality standards found elsewhere in state law.
(2) No person may violate the numeric water quality standards identified below:
(a) Mainstem Yellowstone River Nonanthropogenic Standards. Water quality standards for human health for total recoverable arsenic (CASRN number 7440-38-2). Average arsenic concentrations during a calendar year may not exceed the standards, and downstream water quality and applicable beneficial uses shall continue to be maintained. The standards, specified by segment, are as follows:
(i) From the Montana/Wyoming border (44.9925, -110.5172) to the mouth of Mill Creek (45.4165, -110.6548): 28 µg/L;
(ii) From the mouth of Mill Creek (45.4165, -110.6548) to the mouth of the Boulder River (45.8530, -109.9247): 22 µg/L;
(iii) From the mouth of the Boulder River (45.8530, -109.9247) to the mouth of the Stillwater River (45.6399, -109.2829): 16 µg/L; and
(iv) From the mouth of the Stillwater River (45.6399, -109.2829) to the mouth of the Clarks Fork of the Yellowstone River (45.6510, -108.7145): 13 µg/L.
(3) Named waterbodies, waterbody segments, or waterbodies within geographic regions specified in (2) have no assimilative capacity for the applicable natural or nonanthropogenic standards. Therefore, the department may not grant a mixing zone under ARM Title 17, chapter 30, subchapter 5 for these waterbodies and the specified standards.
History: 75-5-201, 75-5-301, MCA; IMP, 75-5-222, 75-5-306, MCA; NEW, 2020 MAR p. 1618, Eff. 8/29/20.