As used in this part:

1. (1) “304(a) guidance” refers to Section 304(a) of the Clean Water Act, 33 U.S.C. § 1314(a), which requires the United States Environmental Protection Agency to publish and periodically update ambient water quality criteria which will be protective of human health and the environment;
2. (2) “Abatement” means the reduction in degree or intensity of pollution;
3. (3) “Acute toxicity” means a statistically significant difference (at the ninety-fifth percent (95%) confidence level) in mortality or immobilization between test organisms and a control measured during a specified period of time which is normally less than ninety-six (96) hours;
4. (4) “Algae” means simple plants (without roots, stems, or leaves) that contain chlorophyll and are capable of photosynthesis;
5. (5) “Aquatic biota” means all those life forms which inhabit the aquatic environment;
6. (6) “Aquatic life” means the designated use of a waterbody determined by the fish community and other associated aquatic biota;
7. (7) “Base flows” means that portion of the stream discharge that is derived from natural storage (i.e., outflow from groundwater or swamps), or sources other than recent rainfall that creates surface runoff. Also called sustaining, normal, dry weather, ordinary, or groundwater flow;
8. (8) “Bioaccumulation” means the process by which a compound is taken up by an aquatic organism, both from water and through food;
9. (9) “Chronic toxicity” means a statistically significant difference (at the ninety-fifth percent (95%) confidence level) in mortality or immobilization, reduced reproduction or limited growth between test organisms and a control measured during a substantial segment of the life span of the test organism;
10. (10) “Commission” means the Arkansas Pollution Control and Ecology Commission;
11. (11) “Conventional pollutants”, pursuant to section 304(a)(4) of the Clean Water Act, 33 U.S.C. § 1314(a)(4), includes biochemical oxygen demand (BOD), total suspended solids (nonfilterable) (TSS), pH, fecal coliform, and oil and grease;
12. (12) “Criterion continuous concentration (CCC)” means an estimate of the highest concentration of a material in ambient water to which an aquatic community can be exposed indefinitely without resulting in an unacceptable adverse effect. This is the chronic criterion;
13. (13) “Criterion maximum concentration (CMC)” means an estimate of the highest concentration of a material in ambient water to which an aquatic community can be exposed briefly without resulting in an unacceptable adverse effect. This is the acute criterion;

14. (14) “Critical flows” means the flow volume used as background dilution flows in calculating concentrations of pollutants from permitted discharges. These flows may be adjusted for mixing zones. The following critical flows are applicable:

    1. (A) For a seasonal aquatic life - one cubic foot per second (1 ft³/sec) minus the design flow of any point source discharge (may not be less than zero (0));
    2. (B) For human health - harmonic mean flow or long-term average flow;

    3. (C) For minerals - harmonic mean flow, except as follows:

       1. (i) 8 CAR § 21-511(a) Site Specific Mineral Criteria listed with an asterisk- 4 cubic feet per second; and
       2. (ii) 8 CAR § 21-511(c) Domestic Water Supply: Q7-10; and
    4. (D) For metals and conventional pollutants - Q7-10;

15. (15)

    1. (A) “Critical season” means that period of the year when water temperatures exceed twenty-two degrees Celsius (>22°C (71.6°F)).
    2. (B) This is normally the hot, dry season and after the majority of the fish spawning activities have ceased.
    3. (C) This season occurs during a different time frame in different parts of the state, but normally exists from about mid-May to mid-September;
16. (16) “Cumulative” means increasing by successive additions;
17. (17) “Degradation” means the act or process of causing any decrease in quality;
18. (18) “Design flow” means a facility discharge flow of process wastewater that is authorized in a NPDES permit;
19. (19) “Designated uses” means those uses specified in the water quality standards for each waterbody or assessment unit whether or not they are being attained;
20. (20) “Discharge” means a discrete point source of waste or wastewater entering into waters of the state;
21. (21) “Dissolved oxygen” (DO) means a measure of the concentration of oxygen in solution in a liquid;
22. (22) “Division” means the Division of Environmental Quality of the Department of Energy and Environment, or its successor;
23. (23) “Ecoregion” means a large area of landscape with relatively homogenous physical, chemical, and biological characteristics;
24. (24) “Effluent” means water that is not reused after flowing out of any wastewater treatment facility or other works used for the purpose of treating, stabilizing, or holding wastes;
25. (25) “Escherichia coli” means a rod-shaped gram-negative bacillus abundant in the large intestines of mammals;
26. (26) “Endemic” means native to and confined to a specific region;
27. (27) “Existing uses” means those uses listed in Section 303(c)(2) of the Clean Water Act, 33 U.S.C. § 1313(c)(2) (i.e., public water supplies, propagation of fish and wildlife, recreational uses, agricultural and industrial water supplies, and navigation), which were actually attained in the waterbody on or after November 28, 1975, whether or not they are included in the water quality standards;
28. (28) “Fishable/swimmable” refers to one of the national goals stated in Section 101(a)(2) of the Clean Water Act, 33 U.S.C. § 1251(a)(2), “...provides for the protection and propagation of fish, shellfish and wildlife and provides for recreation in and on the water.”;
29. (29) “Groundwater” means water below the land surface in a zone of saturation;
30. (30) “Hardness” means a measure of the sum of multivalent metallic cations expressed as calcium carbonate (CaCO3);
31. (31) “Harmonic mean flow” means the reciprocal of the mean of the reciprocals of daily flow measurements;
32. (32) “Headwater” means the upper watershed area where streams generally begin; headwater typically consists of 1st- and 2nd-order streams;
33. (33) “Heavy metals” means a general name given to the ions of metallic elements heavier than iron, such as cadmium, lead, mercury, copper, zinc, and chromium;
34. (34) “Human health criteria” means levels of toxicants in ambient water which will not manifest adverse health effects in humans;
35. (35) “Hypolimnion” means that portion of a thermally stratified lake or reservoir below the zone in which the rate of temperature change is greatest. An area of minimal circulation and mixing;
36. (36) “Impairment” means exceedances of the water quality standards by a frequency and/or magnitude which results in any designated use of a waterbody to fail to be met as a result of physical, chemical, or biological conditions;

37. (37)

    1. (A) “Indicator species” means species of fish which may not be dominant within a species group and may not be limited to one (1) area of the state, but which, because of their presence, are readily associated with a specific ecoregion.
    2. (B) All indicator species need not be present to establish a normal or representative fishery;
38. (38) “Indigenous” means produced, growing, or living naturally in a particular region or environment;
39. (39) “Interstate” means of, connecting, or existing between two (2) or more states;
40. (40) “Intrastate” means existing or occurring within a state;
41. (41) “Ionizing radiation” means gamma rays and x-rays; alpha and beta particles, high speed electrons, neutrons, protons, and other nuclear particles; but not sound or radio waves, or visible, infrared, or ultraviolet light;

42. (42)

    1. (A) “Key species” means fishes which are normally the dominant species (except for some ubiquitous species) within the important groups such as fish families or trophic feeding levels.
    2. (B) All specified key species need not be present to establish a normal or representative fishery;
43. (43) “Long term average flow” means an average annual stream flow based on a period of record which reflects the typical annual variability;
44. (44) “Milligrams per liter (mg/L)” means the concentration at which one milligram (1mg) is contained in a volume of one liter (1 L); one milligram per liter (1 mg/L) is equivalent to one part per million (1 ppm) at unit density;

45. (45)

    1. (A) “Mixing zone” means an area where an effluent discharge undergoes mixing with the receiving waterbody.
    2. (B) For toxic discharges a zone of initial dilution may be allowed within the mixing zone;
46. (46) “Most probable number (MPN)” is used to estimate the concentration of viable microorganisms in a sample by means of replicating liquid broth growth in ten-fold dilutions;
47. (47) “Mouth” means the point of confluence where a stream enters a larger body of water;
48. (48) “Natural background” means ambient conditions or concentrations of a parameter due to nonanthropogenic sources; natural background does not typically interfere with support of designated uses nor the level of aquatic biota expected to occur naturally at the site;
49. (49) “Naturally occurring excursions” means temporary deviation from natural background due to natural events such as severe storm events, drought, temperature extremes, etc.;
50. (50) “Nephelometric turbidity unit (NTU)” means a measure of turbidity based upon a comparison of the intensity of light scattered by a sample of water under defined conditions with the intensity of light scattered by a standard reference suspension; NTU are considered comparable to the previously reported Jackson Turbidity Units (JTU). May also be reported as Formazin Turbidity Units (FTU) in equivalent units;

51. (51)

    1. (A) “Noncritical season” means that period of the year when water temperatures are twenty- two degrees Celsius or below (≤22°C (71.5°F)).
    2. (B) This includes the major part of the year from fall through spring, including the spawning season of most fishes.
    3. (C) It normally occurs from about mid-September to mid-May;
52. (52) “Nonpoint source” means a contributing factor to water pollution that is not confined to an end-of-the-pipe discharge, i.e., stormwater runoff not regulated under Clean Water Act § 402(p)(1), 33 U.S.C. § 1342(p), agricultural or silvicultural runoff, irrigation return flows, etc.;
53. (53) “Nuisance species” means those organisms capable of interfering with the beneficial use of water;
54. (54) “Nutrient” means any substance assimilated by an organism which promotes growth and replacement of cellular constituents. The usual nutrient components of water pollution are nitrogen, phosphorus, and carbon;
55. (55) “Objectionable algal densities” means numbers of total algae which would interfere with a beneficial use;
56. (56) “Persistent” means degraded only slowly by the environment;
57. (57) “pH” means the negative logarithm of the effective hydrogen-ion concentration in gram equivalents per liter;
58. (58) “Picocurie” means one trillionth (10^-12) of a curie which is a unit of quantity of any radioactive nuclide in which 3.7 X 10¹⁰ disintegrations occur per second;
59. (59) “Point source” means a discharge from a discrete point;
60. (60) “Q7-10” means a flow volume equal to or less than the lowest mean discharge during seven (7) consecutive days of a year which, on the average, occurs once every ten (10) years;
61. (61) “Regulated-flow stream” means those streams restricted by structures which have the ability to control stream flow;

62. (62)

    1. (A) “Seasonal aquatic life” means the designated aquatic life use that occurs in some waterbodies only during the period when stream flows increase substantially and water temperatures are cooler.
    2. (B) This is normally during the months of December through May;

63. (63)

    1. (A) “State of Arkansas Continuing Planning Process (CPP)” is a document setting forth the principal procedures of the state’s water quality management programs, developed pursuant to Section 303(e) of the Clean Water Act, 33 U.S.C. § 1313(e), and 40 C.F.R. § 130.5.
    2. (B) The CPP is not a rule;
64. (64) “Storm flows” takes into account all flows and data collected throughout the year, including elevated flows due to rainfall events;
65. (65) “Surface water” means the water contained on the exterior or upper portion of the earth's surface as opposed to groundwater;
66. (66) “Synergism” means cooperative action of discrete agents such that the total effect is greater than the sum of the effects taken independently;
67. (67) “Total dissolved solids (TDS)” means the total soluble organic and inorganic material contained in water; includes those materials, both liquid and solid, in solution and otherwise, which pass through a standard glass fiber filter disk and are not volatilized during drying at one hundred eighty degrees Celsius (180°C);
68. (68) “Trout fishery” means water that is suitable for the growth and survival of trout, usually characterized as high-quality water having a maximum summer temperature of sixty-eight degrees Fahrenheit (68°F) or less;
69. (69) “Use attainability analysis” means a structured scientific assessment of the factors affecting the attainment of the fishable/swimmable use which may include physical, chemical, biological, and economic factors;
70. (70) “Waterbodies, waterways, waters”, in this part, refers to surface waters of the state as described in the Arkansas Water and Air Pollution Control Act, Arkansas Code § 8-4-101 et seq.;
71. (71) “Water effects ratio (WER)” means a specific pollutant’s acute or chronic value measured from a specific site ambient water, divided by the respective acute or chronic toxicity of the same pollutant in laboratory water; and

72. (72)

    1. (A) “Zone of initial dilution (ZID)” means an area within the mixing zone where a toxic effluent discharge initiates mixing in the receiving waterbody.
    2. (B) This is an area where acute water quality criteria may be exceeded, but acute toxicity may not occur.