In this subchapter the following terms have the meanings indicated below and are supplemental to the definitions given in 75-5-103 , MCA:

(1) "Acutely toxic conditions" means conditions lethal to aquatic organisms passing through the mixing zone. Lethality is a function of the magnitude of pollutant concentrations and the duration of organism exposure to those concentrations.

(2) "Bioconcentrating parameters" means the parameters listed in department Circular DEQ-7 which have a bioconcentration factor greater than 300.

(3) "Carcinogenic parameters" means the parameters categorized as carcinogens in department Circular DEQ-7.

(4) "Chlorophyll a" means the mass of chlorophyll a pigment after correction for phaeophytins.

(5) "Chronic toxicity" means that death or functional impairment occurs or can be expected to occur to organisms exposed for periods of time exceeding 96 hours.

(6) "Conduit" means any artificial or natural duct, either open or closed, capable of conveying liquids or pollutants.

(7) "Conventional water treatment" means in order of application the processes of coagulation, sedimentation, filtration, and disinfection. If determined necessary by the department it also includes taste and odor control and lime softening.

(8) "Dewatered stream" means a perennial or intermittent stream from which water has been removed for one or more beneficial uses.

(9) "Electrical conductivity (EC) " means the ability of water to conduct an electrical current at 25ºC. The electrical conductivity of water represents the amount of total dissolved solids in the water and is expressed as microSiemens/centimeter (µS/cm) or micromhos/centimeter (µmhos/cm) or equivalent units and is corrected to 25ºC.

(10) "Discharge" means the injection, deposit, dumping, spilling, leaking, placing, or failing to remove any pollutant so that it or any constituent thereof may enter into state waters, including ground water.

(11) "EPA" means the US Environmental Protection Agency.

(12) "Ephemeral stream" means a stream or part of a stream which flows only in direct response to precipitation in the immediate watershed or in response to the melting of a cover of snow and ice and whose channel bottom is always above the local water table.

(13) "Geometric mean" means the value obtained by taking the Nth root of the product of the measured values where zero values for measured values are taken to be the detection limit.

(14) "Harmful parameters" means parameters listed as harmful in department Circular DEQ-7.

(15) "Intermittent stream" means a stream or reach of a stream that is below the local water table for at least some part of the year, and obtains its flow from both surface run-off and ground water discharge.

(16) "Mixing zone" means the area of a water body contiguous to an effluent with characteristics qualitatively or quantitatively different from those of the receiving water. The mixing zone is a place where effluent and receiving water mix and not a place where effluents are treated. Certain water quality standards may not apply in the mixing zone for those parameters regulated by a MPDES or NPDES permit. An effluent, in its mixing zone, may not block passage of aquatic organisms nor may it cause acutely toxic conditions, except that ammonia, chlorine, and dissolved oxygen may be present at concentrations so as to cause potentially toxic conditions in no more than 10% of the mixing zone provided that there is no lethality to aquatic organisms passing through the mixing zone. The area in which these exceedences may be allowed shall be as small as practicable. Provisions for specific mixing zones will be determined on a case-by-case basis by application of the department's surface water mixing zone rules in ARM 17.30.501 through 17.30.518.

(17) "MPDES" means the Montana pollutant discharge elimination system.

(18) "NPDES" means the national pollutant discharge elimination system.

(19) "Naturally occurring" means conditions or material present from runoff or percolation over which man has no control or from developed land where all reasonable land, soil and water conservation practices have been applied. Conditions resulting from the reasonable operation of dams in existence as of July 1, 1971, are natural.

(20) "Nonpoint source" means the source of pollutants which originates from diffuse runoff, seepage, drainage, or infiltration.

(21) "Outstanding resource water" or "ORW" has the meaning set out in 75-5-103 , MCA.

(22) "Pesticide" means insecticides, herbicides, rodenticides, fungicides, or any substance or mixture of substances intended for preventing, destroying, controlling, repelling, altering life processes, or mitigating any insects, rodents, nematodes, fungi, weeds, and other forms of plant or animal life.

(23) "Phaeophytins" means the degradation products of chlorophyll.

(24) "Pollutants" means sewage, industrial wastes and other wastes as those terms are defined in 75-5-103 (12) , (19) , (26) , MCA.

(25) "Reasonable land, soil, and water conservation practices" means methods, measures, or practices that protect present and reasonably anticipated beneficial uses. These practices include, but are not limited to, structural and nonstructural controls and operation and maintenance procedures. Appropriate practices may be applied before, during, or after pollution-producing activities.

(26) "Seasonal lake or pond" means a natural depression in the land surface that periodically holds water from precipitation or snow and ice melt in the immediate watershed.

(27) "Sodium adsorption ratio (SAR) " means a value representing the relative amount of sodium ions to the combined amount of calcium and magnesium ions in water using the following formula: SAR = [Na]/(([Ca]+[Mg]) /2) ^½, where all concentrations are expressed as milliequivalents of charge per liter.

(28) "Secondary contact recreation" means activities in or on the water where the potential for immersion or ingestion of water is low, such as wading or boating.

(29) "Sediment" means solid material settled from suspension in a liquid; mineral or organic solid material that is being transported or has been moved from its site of origin by air, water, or ice and has come to rest on the earth's surface, either above or below sea level; or inorganic or organic particles originating from weathering, chemical precipitation, or biological activity.

(30) "Semi-permanent lake or pond" means a natural depression in the land surface, not including reservoirs, that receives ground water in addition to precipitation runoff from the immediate watershed, and occasionally goes dry.

(31) "Settleable solids" means inorganic or organic particles that are being transported or have been transported by water from the site or sites of origin and are settled or are capable of being settled from suspension.

(32) "Sewer" means a pipe or conduit that carries wastewater or drainage water.

(33) "Surface waters" means any waters on the earth's surface including, but not limited to, streams, lakes, ponds, and reservoirs; and irrigation and drainage systems discharging directly into a stream, lake, pond, reservoir, or other surface water. Water bodies used solely for treating, transporting, or impounding pollutants shall not be considered surface water.

(34) "Storm sewer" or "storm drain" means a pipe or conduit that carries storm water and surface water and street washings.

(35) "Total nitrogen" means the total nitrogen concentration (as N) of unfiltered water. This may be determined by direct methods, or derived as the sum of the soluble (as N) and non-soluble (as N) nitrogen fractions. The filter used to separate the soluble and non-soluble fractions must be 0.45 µm.

(36) "Total phosphorus" means the total phosphorus concentration (as P) of unfiltered water.

(37) "Toxic parameters" means those parameters listed as toxins in department Circular DEQ-7.

(38) "True color" means the color of water from which the turbidity has been removed.

(39) "Turbidity" means a condition in water or wastewater caused by the presence of suspended matter resulting in the scattering and absorption of light rays.

(40) "Use attainability analysis" means a scientific assessment and analysis of the factors affecting the attainment of a use(s) . Information that may be used include chemical, physical and biological data, as well as photo documentation and comparison to reference conditions, that are of sufficient detail to accurately portray the level and potential level of use support of a waterbody. The use attainability analysis is required by the US EPA according to 40 CFR 131.10(g) , (h) and (j) .

(41) "DEQ-7" means the department circular that is adopted and incorporated by reference in ARM 17.30.619 and is entitled "Montana Numeric Water Quality Standards." This circular establishes water quality standards for toxic, carcinogenic, bioconcentration, nutrient, radioactive, and harmful parameters.