1. (a) Definitions. The following words and terms, when used in this chapter, shall have the defined meanings, unless the context clearly indicates otherwise.

   1. (1) Acute toxicity--Toxicity which exerts a stimulus severe enough to rapidly induce an effect. The duration of exposure applicable to acute toxicity is typically 96 hours or less. Tests of total toxicity normally use lethality as the measure of acute impacts. (Direct thermal impacts are excluded from definitions of toxicity.)
   2. (2) Ambient--Refers to the existing water quality in a particular water body.
   3. (3) Attainable use--A use which can be reasonably achieved by a water body in accordance with its physical, biological, and chemical characteristics whether it is currently meeting that use or not. Guidelines for the determination and review of attainable uses are provided in the standards implementation procedures. The designated use, existing use, or presumed use of a water body may not necessarily be the attainable use.
   4. (4) Background--Refers to the water quality in a particular water body that would occur if that water body were relatively unaffected by human activities.
   5. (5) Bedslope--Stream gradient, or the extent of the drop in elevation encountered as the stream flows downhill. One measure of bedslope is the elevation decline in meters over the stream distance in kilometers.
   6. (6) Best management practices--Schedules of activities, maintenance procedures, and other management practices to prevent or reduce the pollution of water in the state from point and nonpoint sources, to the maximum extent practicable. Best management practices also include treatment requirements, operating procedures, and practices to control plant site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.
   7. (7) Bioaccumulative toxic--A chemical which is taken up by aquatic organisms from water directly or through the consumption of food containing the chemicals.
   8. (8) Bioconcentration factor--A unitless value describing the degree to which a chemical can be concentrated in the tissues of an organism in the aquatic environment and which is absorbed directly from the water. The bioconcentration factor is the ratio of a chemical's concentration in the tissue of an organism compared to that chemical's average concentration in the surrounding water.
   9. (9) Biological integrity--The species composition, diversity, and functional organization of a community of organisms in an environment relatively unaffected by pollution.
   10. (10) Chronic toxicity--Toxicity which continues for a long-term period after exposure to toxic substances. Chronic exposure produces sub-lethal effects, such as growth impairment and reduced reproductive success, but it may also produce lethality. The duration of exposure applicable to the most common chronic toxicity test is seven days or more.
   11. (11) Classified--Refers to a water body that is listed and described in Appendix A or Appendix C in §307.10 of this title (relating to Appendices A - E). Site-specific uses and criteria for classified water bodies are listed in Appendix A.
   12. (12) Contact recreation--Recreational activities involving a significant risk of ingestion of water, including wading by children, swimming, water skiing, diving, and surfing.
   13. (13) Criteria--Water quality conditions which are to be met in order to support and protect desired uses.
   14. (14) Critical low-flow--Low-flow condition (e.g., 7Q2 flow) below which some standards do not apply. The impacts of permitted discharges are analyzed at critical low-flow.
   15. (15) Designated use--A use which is assigned to specific water bodies in Appendix A or in Appendix D in §307.10 of this title. Typical uses which may be designated for specific water bodies include domestic water supply, categories of aquatic life use, recreation categories, and aquifer protection.
   16. (16) Discharge permit--A permit issued by the state or a federal agency to discharge treated effluent or cooling water into waters of the state.
   17. (17) EC₅₀--The concentration of a toxicant that produces an adverse effect on 50% of the organisms tested in a specified time period.
   18. (18) E. coli--Escherichia coli, a subgroup of fecal coliform bacteria that is present in the intestinal tracts and feces of warm-blooded animals. It is used as an indicator of the potential presence of pathogens.
   19. (19) Effluent--Wastewater discharged from any point source prior to entering a water body.
   20. (20) Enterococci--A subgroup of fecal streptococci bacteria (mainly Streptococcus faecalis and Streptococcus faecium) that is present in the intestinal tracts and feces of warm-blooded animals. It is used as an indicator of the potential presence of pathogens.
   21. (21) Epilimnion--The upper mixed layer of a lake (including impoundments, ponds, and reservoirs).
   22. (22) Existing use--A use which is currently being supported by a specific water body or which was attained on or after November 28, 1975.
   23. (23) Fecal coliform--A portion of the coliform bacteria group which is present in the intestinal tracts and feces of warm-blooded animals; heat tolerant bacteria from other sources can sometimes be included. It is used as an indicator of the potential presence of pathogens.
   24. (24) Freshwaters--Inland waters which exhibit no measurable elevation changes due to normal tides.
   25. (25) Halocline--A vertical gradient in salinity under conditions of density stratification that is usually recognized as the point where salinity exhibits the greatest difference in the vertical direction.
   26. (26) Harmonic mean flow--A measure of mean flow in a water course which is calculated by summing the reciprocals of the individual flow measurements, dividing this sum by the number of measurements, and then calculating the reciprocal of the resulting number.
   27. (27) Incidental fishery--A level of fishery which applies to water bodies that are not considered to have a sustainable fishery but which have an aquatic life use of limited, intermediate, high, or exceptional.
   28. (28) Industrial cooling impoundment--An impoundment which is owned or operated by, or in conjunction with, the water rights permittee, and which is designed and constructed for the primary purpose of reducing the temperature and removing heat from an industrial effluent.
   29. (29) Intermittent stream--A stream which has a period of zero flow for at least one week during most years. Where flow records are available, a stream with a 7Q2 flow of less than 0.1 ft³/s is considered intermittent.
   30. (30) Intermittent stream with perennial pools--An intermittent stream which maintains persistent pools even when flow in the stream is less than 0.1 ft³/s.
   31. (31) LC₅₀--The concentration of a toxicant that is lethal (fatal) to 50% of the organisms tested in a specified time period.
   32. (32) Method detection limit--The minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte. The method detection limit (MDL) is estimated in accordance with 40 CFR 136, Appendix B.
   33. (33) Minimum analytical level--The lowest concentration at which a particular substance can be quantitatively measured with a defined accuracy and precision level, using approved analytical methods. The minimum analytical level is not the published method detection limit for an EPA-approved analytical method, which is based on laboratory analysis of the substance in reagent (distilled) water. The minimum analytical level is based on analyses of the analyte in the matrix of concern (i.e., wastewater effluents). The executive director will establish general minimum analytical levels that will be applicable when information on matrix-specific minimum analytical levels is unavailable.
   34. (34) Mixing zone--The area contiguous to a discharge where mixing with receiving waters takes place and where specified criteria, as listed in §307.8(b)(1) of this title (relating to Application of Standards), can be exceeded. Acute toxicity to aquatic organisms is not allowed in a mixing zone, and chronic toxicity to aquatic organisms is not allowed beyond a mixing zone.
   35. (35) Noncontact recreation--Aquatic recreational pursuits not involving a significant risk of water ingestion; including fishing, commercial and recreational boating, and limited body contact incidental to shoreline activity.
   36. (36) Nonpersistent toxic--A toxic substance that readily degrades in the aquatic environment, exhibits a half-life of less than 96 hours, and does not have a tendency to accumulate in organisms.
   37. (37) Oyster waters--Waters producing edible species of clams, oysters, or mussels.
   38. (38) Persistent toxic--A toxic substance that is not readily degraded and exhibits a half-life of 96 hours or more in an aquatic environment.
   39. (39) Pollution--The alteration of the physical, thermal, chemical, or biological quality of, or the contamination of, any water in the state that renders the water harmful, detrimental, or injurious to humans, animal life, vegetation, or property or to the public health, safety, or welfare, or impairs the usefulness or the public enjoyment of the water for any lawful or reasonable purpose.
   40. (40) Point source--Any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants or wastes are or may be discharged into or adjacent to any water in the state.
   41. (41) Presumed use--A use which is assigned to generic categories of water bodies (such as perennial streams). Presumed uses are superceded by designated uses for individual water bodies in Appendix A or Appendix D of §307.10 of this title.
   42. (42) Public drinking water supply--A water body designated to provide water to a public water system as defined in Chapter 290 of this title (relating to Public Drinking Water).
   43. (43) Saltwater--A coastal water which has a measurable elevation change due to normal tides. In the absence of tidal information, saltwater is generally considered to be a coastal water which typically has a salinity of two parts per thousand or greater in a significant portion of the water column.
   44. (44) Salinity--The total dissolved solids in water after all carbonates have been converted to oxides, all bromide and iodide have been replaced by chloride, and all organic matter has been oxidized. For most purposes, salinity is considered equivalent to total dissolved salt content. Salinity is normally expressed in parts per thousand.
   45. (45) Seagrass propagation--A water-quality-related existing use which applies to saltwater with significant stands of submerged seagrass.
   46. (46) Segment--A water body or portion of a water body which is individually defined and classified in the Texas Surface Water Quality Standards. A segment is intended to have relatively homogeneous chemical, physical, and hydrological characteristics. A segment provides a basic unit for assigning site-specific standards and for applying water quality management programs of the agency. Classified segments may include streams, rivers, bays, estuaries, wetlands, lakes, or reservoirs.
   47. (47) Settleable solids--The volume or weight of material which will settle out of a water sample in a specified period of time.
   48. (48) Seven-day, two-year low-flow (7Q2)--The lowest average stream flow for seven consecutive days with a recurrence interval of two years, as statistically determined from historical data. As specified in §307.8 of this title, some water quality standards do not apply at stream flows which are less than the 7Q2 flow.
   49. (49) Shellfish--Clams, oysters, mussels, crabs, crayfish, lobsters, and shrimp.
   50. (50) Significant aquatic life use--A broad characterization of aquatic life which indicates that a subcategory of aquatic life use (limited, intermediate, high, or exceptional) is applicable. Some aquatic life is expected to be present even in water bodies which are not designated for specific categories of aquatic life use. Some provisions to protect aquatic life applies to any water body in the state whether an aquatic life use is assigned or not. These provisions include the general criteria in §307.4 of this title (relating to General Criteria), the numerical acute aquatic life criteria in §307.6(c) of this title (relating to Toxic Materials), and the whole effluent toxicity requirements to preclude acute toxicity to aquatic life in §307.6(e) of this title.
   51. (51) Standard Methods for the Examination of Water and Wastewater--A document describing sampling and analytical procedures, which is published by the American Public Health Association, American Water Works Association, and Water Environment Federation. The most recent edition of this document is to be followed whenever its use is specified by these rules.
   52. (52) Standards--The designation of water bodies for desirable uses and the narrative and numerical criteria deemed necessary to protect those uses.
   53. (53) Standards implementation procedures--Procedures entitled Procedures to Implement the Texas Surface Water Quality Standards, which are adopted by the commission and approved by EPA as part of the State Continuing Planning Process.
   54. (54) Storm water--Rainfall runoff, snow melt runoff, surface runoff, and drainage.
   55. (55) Storm water discharge--A point source discharge that is composed entirely of storm water associated with an industrial activity, a construction activity, a discharge from a municipal separate storm sewer system, or other discharge designated by the agency.
   56. (56) Stream order--A classification of stream size, where the smallest, unbranched tributaries of a drainage basin are designated first order streams. Where two first order streams join, a second order stream is formed; and where two second order streams join, a third order stream is formed, etc. For purposes of water quality standards application, stream order is determined from USGS topographic maps with a scale of 1:24,000.
   57. (57) Surface water in the state--Lakes, bays, ponds, impounding reservoirs, springs, rivers, streams, creeks, estuaries, wetlands, marshes, inlets, canals, the Gulf of Mexico inside the territorial limits of the state (from the mean high water mark (MHWM) out 10.36 miles into the Gulf), and all other bodies of surface water, natural or artificial, inland or coastal, fresh or salt, navigable or nonnavigable, and including the beds and banks of all water-courses and bodies of surface water, that are wholly or partially inside or bordering the state or subject to the jurisdiction of the state; except that waters in treatment systems which are authorized by state or federal law, regulation, or permit, and which are created for the purpose of waste treatment are not considered to be water in the state.
   58. (58) Sustainable Fisheries--Descriptive of water bodies which potentially have sufficient fish production or fishing activity to create significant long-term human consumption of fish. Sustainable fisheries include perennial streams and rivers with a stream order of three or greater; lakes and reservoirs greater than or equal to 150 acre-feet and/or 50 surface acres; all bays, estuaries, and tidal rivers. Water bodies which are presumed to have sustainable fisheries include all designated segments listed in Appendix A unless specifically exempted.
   59. (59) Tidal--Descriptive of coastal waters which are subject to the ebb and flow of tides. For purposes of standards applicability, tidal waters are considered to be saltwater. Classified tidal waters include all bays and estuaries with a segment number that begins with 24xx, all streams with the word tidal in the segment name, and the Gulf of Mexico.
   60. (60) To discharge--Includes to deposit, conduct, drain, emit, throw, run, allow to seep, or otherwise release or dispose of, or to allow, permit, or suffer any of these acts or omissions.
   61. (61) Total Maximum Daily Load (TMDL)--The total amount of a substance that a water body can assimilate and still meet the Texas Surface Water Quality Standards.
   62. (62) Total dissolved solids--The amount of material (inorganic salts and small amounts of organic material) dissolved in water and commonly expressed as a concentration in terms of milligrams per liter. The term is equivalent to the term filterable residue, as used in the publication entitled, Standard Methods for the Examination of Water and Wastewater.
   63. (63) Total suspended solids--Total suspended matter in water, which is commonly expressed as a concentration in terms of milligrams per liter. The term is equivalent to nonfilterable residue, as used in the publication entitled, Standard Methods for the Examination of Water and Wastewater.
   64. (64) Total toxicity--Toxicity as determined by exposing aquatic organisms to samples or dilutions of instream water or treated effluent. Also referred to as whole effluent toxicity or biomonitoring.
   65. (65) Toxicity--The occurrence of adverse effects to living organisms due to exposure to toxic materials. Adverse effects caused by conditions of temperature and dissolved oxygen are excluded from the definition of toxicity. With respect to the provisions of §307.6(e) of this title, which concerns total toxicity and biomonitoring requirements, adverse effects caused by concentrations of dissolved salts (such as sodium, potassium, calcium, chloride, carbonate) in source waters are excluded from the definition of toxicity. Source water is defined as surface water or groundwater that is used as a public water supply or industrial water supply (including a cooling-water supply). Source water does not include brine water that is produced during the extraction of oil and gas, or other sources of brine water that are substantially uncharacteristic of surface waters in the area of discharge. In addition, adverse effects caused by concentrations of dissolved salts which are added to source water by industrial processes are not excluded from the requirements of §307.6(e) of this title, except as specifically noted in §307.6(e)(2)(B) of this title, which concerns requirements for toxicity testing of 100% effluent. This definition of toxicity does not affect the standards for dissolved salts in this chapter other than §307.6(e) of this title. The standards implementation procedures contain provisions to protect surface waters from adverse effects of dissolved salts and methods to address the effects of dissolved salts on total toxicity tests.
   66. (66) Toxicity biomonitoring--The process or act of determining total toxicity. Documents which describe procedures for toxicity biomonitoring are cited in §307.6 of this title. Also referred to simply as biomonitoring.
   67. (67) Water-effects ratio--The water-effects ratio is calculated as the toxic concentration (LC₅₀) of a substance in water at a particular site, divided by the toxic concentration of that substance as reported in laboratory dilution water. The water-effects ratio can be used to establish site-specific acute and chronic criteria to protect aquatic life. The site-specific criterion is equal to the water-effects ratio times the statewide aquatic life criterion in §307.6(c) of this title.
   68. (68) Water quality management program--The agency's overall program for attaining and maintaining water quality consistent with state standards, as authorized under the Texas Water Code, the Texas Administrative Code, and the Clean Water Act, §§106, 205(j), 208, 303(e) and 314 (33 United States Code, §§1251 et seq.).
   69. (69) Wetland--An area (including a swamp, marsh, bog, prairie pothole, or similar area) having a predominance of hydric soils that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support and that under normal circumstances supports the growth and regeneration of hydrophytic vegetation. The term "hydric soil" means soil that, in its undrained condition, is saturated, flooded, or ponded long enough during a growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation. The term "hydrophytic vegetation" means a plant growing in: water or a substrate that is at least periodically deficient in oxygen during a growing season as a result of excessive water content. The term "wetland" does not include irrigated acreage used as farmland; a man-made wetland of less than one acre; or a man-made wetland for which construction or creation commenced on or after August 28, 1989, and which was not constructed with wetland creation as a stated objective, including but not limited to an impoundment made for the purpose of soil and water conservation which has been approved or requested by soil and water conservation districts. If this definition of wetland conflicts with the federal definition in any manner, the federal definition prevails.
   70. (70) Wetland water quality functions--Attributes of wetlands that protect and maintain the quality of water in the state, which include storm water storage and retention and the moderation of extreme water level fluctuations; shoreline protection against erosion through the dissipation of wave energy and water velocity, and anchoring of sediments; habitat for aquatic life; and removal, transformation, and retention of nutrients and toxic substances.
   71. (71) Zone of initial dilution--The small area at the immediate point of discharge where initial dilution with receiving waters occurs, and which may not meet certain criteria applicable to the receiving water. A zone of initial dilution is substantially smaller than a mixing zone.

2. (b) Abbreviations. The following abbreviations apply to this chapter:

   1. (1) AP--aquifer protection.
   2. (2) BMP--best management practices.
   3. (3) AS--agricultural water supply.
   4. (4) CASRN--Chemical Abstracts Service Registry number.
   5. (5) CFR--Code of Federal Regulations.
   6. (6) Cl^-1--chloride.
   7. (7) CR--contact recreation.
   8. (8) DO--dissolved oxygen.
   9. (9) E--exceptional aquatic life use.
   10. (10) EPA--United States Environmental Protection Agency.
   11. (11) degrees F--Degree(s) Fahrenheit.
   12. (12) ft³/s--cubic feet per second.
   13. (13) H--high aquatic life use.
   14. (14) I--intermediate aquatic life use.
   15. (15) IS--industrial water supply.
   16. (16) L--limited aquatic life use.
   17. (17) MCL--maximum contaminant level (for public drinking water supplies).
   18. (18) mg/L--milligrams per liter.
   19. (19) ml--milliliter.
   20. (20) MS4--municipal separate storm sewer system.
   21. (21) N--navigation.
   22. (22) NCR--noncontact recreation.
   23. (23) NPDES--National Pollutant Discharge Elimination System, as set out in the Clean Water Act, §402 (33 United States Code 1342).
   24. (24) O--oyster waters.
   25. (25) PS--public water supply.
   26. (26) 7Q2--seven-day, two-year low-flow.
   27. (27) SO₄^-2--sulfate.
   28. (28) TDS--total dissolved solids.
   29. (29) TMDL--total maximum daily load.
   30. (30) TPDES--Texas Pollutant Discharge Elimination System.
   31. (31) TSS--total suspended solids.
   32. (32) USFDA--United States Food and Drug Administration.
   33. (33) USGS--United States Geological Survey.
   34. (34) WF--waterfowl habitat.
   35. (35) WQM--water quality management.
   36. (36) µg/L--micrograms per liter.
   37. (37) ZID--zone of initial dilution.

Source Note:The provisions of this §307.3 adopted to be effective July 10, 1991, 16 TexReg 3400; amended to be effective July 13, 1995, 20 TexReg 4701; amended to be effective August 17, 2000, 25 TexReg 7722.