Rules & Regulations of the State of Tennessee
Title 0400 - Environment and Conservation
Subtitle 0400-40 - Water Resources (WPC)
Chapter 0400-40-03 - General Water Quality Criteria
Section 0400-40-03-.04 - DEFINITIONS

(1) Atypical consumers - Those persons in the vicinity of a stream or lake who due to physiological factors or previous exposure are more sensitive to specific pollutants than is the population in general. Examples of atypical consumers may include, but are not limited to: children; pregnant or nursing women; subsistence fishermen; frequent purchasers of commercially harvested fish; and agricultural, industrial, or military personnel who may have had previous occupational exposure to the contaminant of concern.

(2) Conventional water treatment - Conventional water treatment as referred to in the criteria denotes coagulation, sedimentation, filtration, and chlorination or disinfection.

(3) Degradation - The alteration of the properties of waters by the addition of pollutants, withdrawal of water, or removal of habitat, except those alterations of a short duration.

(4) De Minimis degradation - Degradation of a small magnitude, as provided in this paragraph.

(5) Domestic wastewater discharge - A discharge of sanitary and other non-process wastewater from a treatment facility other than a publicly-owned treatment works (POTW) treating municipal sewage and/or industrial waste. Examples of domestic wastewater discharges include, but are not limited to, homes, subdivisions, campgrounds, hotels, travel centers, parks, and schools.

(6) Ecoregion - A relatively homogeneous area defined by similarity of climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant variables.

(7) Epilimnion - The upper layer of water in a thermally stratified lake or reservoir. This layer consists of the warmest water and has a fairly uniform (constant) temperature.

(8) Groundwater - Water beneath the surface of the ground within the zone of saturation, whether or not flowing through known and definite channels.

(9) Groundwater table - The upper surface of the zone of saturation by ground water.

(10) Hypolimnion - The lowest layer in a thermally stratified lake or reservoir. This layer consists of colder, more dense water, has a constant temperature and no mixing occurs. The hypolimnion of a eutrophic lake is usually low or lacking in oxygen.

(11) Interflow - The runoff infiltrating into the surface soil and moving toward streams as shallow, perched water above the main groundwater level.

(12) In-system mitigation - Mitigation for habitat alterations sufficient to result in no overall net loss of resource values, if provided in the same eight-digit hydrologic unit code as the alteration, or in another area proximate to the alteration as approved by the Division to offset the loss of resource values in the area. In-system mitigation may not occur within a different major river drainage basin as the alteration (i.e., Tennessee River, Cumberland River, Mississippi River).

(13) Lentic - Still water aquatic ecosystems such as ponds, lakes, or reservoirs.

(14) Lotic - Flowing water aquatic ecosystems such as streams and rivers.

(15) Measurable degradation, as used in the context of discharges or withdrawals - Changes in parameters of waters that are of sufficient magnitude to be detectable by the best available instrumentation or laboratory analyses.

(Note: Because analytical techniques change, the Department may consider either the most sensitive detection method needed to comply with State standards or any biological, chemical, physical, or analytical method, conducted in accordance with EPA approved methods as identified in 40 C.F.R. part 136 (2022). Consistent with T.C.A. § 69-3-108, for scenarios involving cumulative, non-measurable activities or parameters that are managed by a narrative criterion, the Department will use mathematical models and ecological indices to ensure no degradation will result from the authorization of such activities, consistent with the State's mixing zone policy.)

(16) Minimum Level (ML) - A term referring to the lowest sample concentration at which reliable quantitative measurements can be made as defined in Appendix A of 40 C.F.R. part 136 (2022).

(17) Mixing zone - That section of a flowing stream or impounded waters in the immediate vicinity of an outfall where an effluent becomes dispersed and mixed.

(18) Multiple populations - Two or more individuals from each of two or more distinct taxa, in the context of obligate lotic aquatic organisms.

(19) New or increased discharge - A new discharge of pollutants to waters of the state or an increase in the authorized loading of a pollutant above either (1) numeric effluent limitations established in a National Pollutant Discharge Elimination System permit for that discharge, or (2) if no such limitations exist, the actual discharges of that pollutant.

(20) Normal weather conditions - Those within one standard deviation of the cumulative monthly precipitation means for at least the three months prior to the hydrologic determination investigation, based on a 30-year average computed at the end of each decade. Precipitation data shall come from National Oceanographic and Atmospheric Agency's National Climatic Data Center, National Resources Conservation Service's National Climatic Data Center, Natural Resources Conservation Service's National Water and Climate Center, or other well-established weather station.

(21) Obligate lotic aquatic organisms - Organisms that require flowing water for all or almost all of the aquatic phase of their life cycles.

(22) Parameter - A biological, chemical, radiological, bacteriological, or physical property of water that can be directly measured. Some criteria are expressed in terms of a single parameter; others, such as habitat, nutrients, and biological integrity are not directly measured, but are derived from measurements of parameters.

(23) Perched water - Water that accumulates above an aquitard that limits downward migration where there is an unsaturated interval below it, between the aquitard and the zone of saturation.

(24) Photic zone - The region of water through which light penetrates and where photosynthetic organisms live.

(25) Reference condition - A parameter-specific set of data from regional reference sites that establish the statistical range of values for that particular substance at least-impacted streams.

(26) Reference site - Least impacted waters within an ecoregion that have been monitored to establish a baseline to which alterations of other waters can be compared.

(27) Resource values - The physical, chemical, and biological properties of the water resource that help maintain classified uses. These properties may include, but are not limited to, the ability of the water resource to:

(28) Response variable - A characteristic of water quality that can be measured and changes as a result of an alteration of habitat, water withdrawal, or discharge of pollutants, as distinguished from agents that cause changes in aquatic systems.

(29) Significant degradation - An appreciable permanent loss of resource values resulting from a habitat alteration in a waterbody with unavailable parameters for habitat, unless mitigation sufficient to ensure no overall net loss of resource values is provided.

(30) Stratification - The tendency in lakes and reservoirs for distinct layers of water to form as a result of vertical change in temperature and, therefore, in the density of water. During stratification, dissolved oxygen, nutrients, and other parameters of water chemistry do not mix well between layers, establishing chemical as well as thermal gradients.

(31) Stream - A surface water that is not a wet weather conveyance.

(32) Subecoregion - A smaller, more homogenous area that has been delineated within an ecoregion.

(33) Thermocline - The middle layer in a thermally stratified lake or reservoir. In this layer there is a rapid decrease in temperature with depth. Also called the metalimnion.

(34) Wadeable streams - Streams that can be sampled using a hand held, one meter square or smaller kick net without water and materials escaping over the top of the net.

(35) Watercourse - A man-made or natural hydrologic feature with a defined linear channel which discretely conveys flowing water, as opposed to sheet-flow.

(36) Wet weather conveyance - Man-made or natural watercourses, including natural watercourses that have been modified by channelization:

(37) Wet weather conveyance determination - The decision based on site specific information of whether a particular watercourse is a stream or a wet weather conveyance. It is synonymous with "stream determination" and "hydrologic determination."

(38) Zone of saturation - A subsurface zone below the groundwater table in which all of the interconnected voids and pore spaces are filled with water.