Administrative Rules of Montana › Department 17 - ENVIRONMENTAL QUALITY › Chapter 17.30 - WATER QUALITY › Subchapter 17.30.7 - Nondegradation of Water Quality › Rule 17.30.715 - CRITERIA FOR DETERMINING NONSIGNIFICANT CHANGES IN WATER QUALITY

Current through Register Vol. 13, July 5, 2024
(1) The following criteria will be used to
				determine whether certain activities or classes of activities will result in
				nonsignificant changes in existing water quality due to their low potential to
				affect human health or the environment. These criteria consider the quantity
				and strength of the pollutant, the length of time the changes will occur, and
				the character of the pollutant. Except as provided in (2), changes in existing
				surface or ground water quality resulting from the activities that meet all the
				criteria listed below are nonsignificant, and are not required to undergo
				review under  75-5-303, MCA:
(a) activities
				that would increase or decrease the mean monthly flow of a surface water by
				less than 15 percent or the seven-day ten-year low flow by less than 10
				percent;
(b) discharges containing
				carcinogenic parameters or parameters with a bioconcentration factor greater
				than 300 at concentrations less than or equal to the concentrations of those
				parameters in the receiving water;
(c) discharges containing toxic parameters,
				which will not cause changes that equal or exceed the trigger values in
				Department Circular DEQ-7. Whenever the change exceeds the trigger value, the
				change is not significant if the resulting concentration outside of a mixing
				zone designated by the department does not exceed 15 percent of the lowest
				applicable standard;
(d) changes in
				the concentration of nitrate in ground water which will not cause degradation
				of surface water if the sum of the predicted concentrations of nitrate at the
				boundary of any applicable mixing zone will not exceed the following values:
(i) 7.5 mg/L for nitrate sources other than
				domestic sewage;
(ii) 5.0 mg/L for
				domestic sewage effluent discharged from a conventional wastewater treatment
				system;
(iii) 7.5 mg/L for domestic
				sewage effluent discharged from a wastewater treatment system using level 2, as
				defined in ARM 17.30.702; or
(iv)
				7.5 mg/L for domestic sewage effluent discharged from a conventional wastewater
				treatment system in areas where the ground water nitrate level exceeds 5.0 mg/L
				primarily from sources other than human waste.
For purposes of this subsection (d), the word "nitrate" means
				  nitrate as nitrogen;
(e) changes in concentration of total
				inorganic phosphorus in ground water if water quality protection practices
				approved by the department have been fully implemented and if an evaluation of
				the phosphorus adsorptive capacity of the soils in the area of the activity
				indicates that phosphorus will be removed for a period of 50 years prior to a
				discharge to any surface waters;
(f) changes in the quality of water for any
				harmful parameter, nutrients listed at ARM 17.30.631, and parameters listed in
				Department Circular DEQ-12A, except as specified in (1)(g), for which water
				quality standards have been adopted other than carcinogenic, bioconcentrating,
				or toxic parameters, in either surface or ground water, if the changes outside
				of a mixing zone designated by the department are less than ten percent of the
				applicable standard and the existing water quality level is less than 40
				percent of the standard;
(g) for
				nutrients in domestic sewage effluent discharged from a wastewater treatment
				system that does not require an MPDES or MGWPCS permit, except as specified in
				(1)(d) and (e), which will not cause changes that equal or exceed the trigger
				values in Department Circular DEQ-7; and
(h) changes in the quality of water for any
				parameter for which there are only narrative water quality standards if the
				changes will not have a measurable effect on any existing or anticipated use or
				cause measurable changes in aquatic life or ecological integrity.