Protecting Public Health and the Environment.

Glossary of Environmental Terms

Refers to section 303 subsection "d" of the Clean Water Act, which requires states to develop a list of water bodies that do not meet water quality standards (a "§303(d) list").  This section also requires TMDLs be prepared for listed waters.  Both the list and the TMDLs are subject to EPA approval.
Refers to section 305 subsection "b" of the Clean Water Act, which requires that each state prepare a report every two years that describes the quality of that state's surface water (referred to as a "§305(b) report") and submit that report to EPA.  Also see Integrated Report.
§319 Subgrants
Refers to grants authorized under section 319 of the Clean Water Act. This section established a grant program under which states, territories, and tribes may receive funds to support a wide variety of nonpoint source pollution management activities, such as technical assistance, training, and demonstration projects. The grant money is supplied by EPA to DEQ;  DEQ oversees "subgrants" for specific projects.
§401 Certification
Clean Water Act Section 401 certification allows each state to have input into projects that may affect its waters. It is required for any permit or license issued by a federal agency for any activity that may result in a discharge into waters of the state to ensure that the proposed project will not violate state water quality standards. DEQ is responsible for issuing §401 certifications in Idaho.


Abate (Abatement)
To reduce the degree or intensity of, or eliminate, pollution.
A volume of water that would cover one acre to a depth of one foot.  Often used to quantify reservoir storage and the annual discharge of large rivers.
Acutely Hazardous Waste
A listed hazardous waste that is so dangerous that it can be fatal to humans in small doses (e.g., certain pesticides). 
Fish whose life history involves seasonal migration from lakes to streams for spawning.
Administrative Record
All documents that are considered or relied on in making technical or policy decisions.
The attachment of one substance to the surface of another.  Clays, for example, can adsorb phosphorus, meaning that phosphorus can attach itself to clay.
A process by which water becomes charged with air directly from the atmosphere.  Dissolved gases, such as oxygen, are then available for reactions in water.
Describes life, processes, or conditions that require the presence of oxygen.
Agricultural Burning
A method of removing crop residue to control disease, weeds, and pests; to reduce the need for herbicides and pesticides; and to reduce fire hazards. It is also a method of clearing irrigation ditches and canals.
Air Pollutant
Any substance in air that could, in high enough concentration, harm humans, other animals, vegetation, or material. Also see pollutant.
Air Quality Index (AQI)
A guide for reporting daily air quality. It indicates how clean or polluted the air is in a particular area and identifies potential health impacts.
Air Toxics
A group of air pollutants that are known or suspected to cause serious health problems such as cancer, birth defects, and lung damage. Examples of air toxics include asbestos, lead, and mercury.
A newly hatched, incompletely developed fish (usually a salmonid) still in a nest or inactive on the bottom of a water body, living off stored yolk.
Non-vascular (without water-conducting tissue or tubes) aquatic plants that occur as single cells, colonies, or filaments.
Sediment deposited by flowing water.
Relating to material deposited by flowing water. Also see alluvium.
General conditions in the environment. 
Fish, such as salmon and sea-run trout, that live part or the majority of their lives in the salt water but return to fresh water to spawn.
Describes the processes that occur in the absence of molecular oxygen and describes the condition of water that is devoid of molecular oxygen.
The condition of oxygen absence or deficiency.
Relating to, or resulting from, the influence of human beings on nature.
Refers to EPA's interpretation of the Clean Water Act goal that states and tribes maintain, as well as restore, water quality.
The cultivation of fish under controlled conditions for commercial, conservation, and recreation purposes.
Pertaining to water.  Usually refers to plants or animals occurring, growing, or living in water.
Acquatic Assemblage
See Assemblage.
A natural underground area where large quantities of ground water fill the spaces between rocks and sediment. According to Idaho's Ground Water Quality Rule (pdf on Department of Administration Web site), to be considered an aquifer in Idaho, the area must produce "economically significant quantities of water to wells and springs."
Area-Wide Optimization Program (AWOP)
An effort to improve performance of facilities that treat surface water to provide drinking water by optimizing technologies already in place. AWOP emphasizes particle removal and disinfection.
A naturally occurring element found in the earth's crust and in rocks and soil, water, air, and plants and animals. There are trace amounts of it in all living matter.
The name given to a number of naturally occurring minerals mined for properties such as thermal insulation and high tensile strength. In the past, asbestos fibers were added to products to strengthen them and to provide heat insulation and fire resistance.  It is now known that inhaling these fibers can cause asbestosis or lung cancer.
Assemblage (Aquatic)
An association of interacting populations of organisms in a given water body (e.g., a fish assemblage encompasses all of the fish species in a water body).  Also see community.
Assessment Database (ADB)
A relational database application for tracking water quality assessment data, such as beneficial use attainment and causes and sources of impairment. 
Assimilative Capacity
The maximum amount of pollutants an environment can absorb without ill effect to beneficial uses. 
Attainable Use
A beneficial use that, with improvement, a water body could support in the future.
Attainment Area
A geographic area that meets or has pollutant levels below the National Ambient Air Quality Standards. Also see nonattainment area.
An organism that uses carbon dioxide as its main source of carbon.  This most commonly happens through photosynthesis.


Backyard Burning (Residential Burning)
A form of open, outdoor burning where the smoke does not pass through a stack, duct, or chimney. Backyard burning includes fires in burn barrels.
Bank Stability
The resistance of a stream bank to erosion.
Bankfull Depth
The depth of water in a stream measured from the surface to the channel bottom when the water surface is even with the top of the stream bank.
Basin (River Basin)
See River Basin.
Basin Advisory Group (BAG)
A group of individuals whose role is to advise DEQ on water quality objectives in a specific river basin. The role of BAGs is outlined in Idaho Statute (39-3613 through 39-3616). Also see Watershed Advisory Group.
Basin Enviromental Improvement Commission
A commission charged with overseeing a system for environmental remediation, natural resource restoration, and related measures to address heavy metal contamination in the Coeur d'Alene Basin.  The commission was created by the Idaho legislature under the Basin Environmental Improvement Act of 2001 (Idaho Code Title 39, Chapter 81).
A large body of intrusive igneous rock that has more than 40 square miles of surface exposure and no known floor.  A batholith usually consists of coarse-grained rocks such as granite.
Material (generally sand-sized or larger sediment) that is carried along a streambed by rolling or bouncing.
Beneficial Use
Any of the various uses of water that are recognized in water quality standards, including, but not limited to, aquatic life, recreation, water supply, wildlife habitat, and aesthetics.
Beneficial Use Reconnaissance Program (BURP)
A program for conducting systematic biological and physical habitat surveys of water bodies in Idaho.  BURP protocols address lakes, reservoirs, and small (wadeable) streams and rivers.
Pertaining to or living on or in the bottom sediments of a water body.
Benthic Organic Matter
The organic matter on the bottom of a water body.
Organisms living in and on the bottom sediments of lakes and streams. 
Best Management Pracites (BMPs)
Recommended techniques designed to assist industries and individuals in complying with environmental regulations.
Best Professional Judgment
A conclusion or interpretation derived by a trained and technically competent individual by interpreting and synthesizing information.
Biochemical Oxygen Demand (BOD)
The amount of dissolved oxygen used by organisms during the decomposition of organic matter, expressed as mass of oxygen per volume of water, over some specified period of time.
Biological Integrity
The ability of an aquatic ecosystem to support and maintain a balanced, integrated, adaptive community of organisms having a species composition, diversity, and functional organization comparable to the natural habitats of a region.
The weight of biological matter. 
The nutrient-rich organic materials resulting from the treatment of sewage sludge.  Biosolids can be safely recycled and applied as fertilizer.
The animal and plant life of a given region.
A term applied to the living components of an area.
Abandoned, idled, or underused industrial or commercial facilities or sites where expansion or redevelopment is complicated by environmental contamination. The Brownfields program helps communities mitigate potential health risks and restore the economic viability of such areas or properties.
Burn Ban
A voluntary or mandatory order that restricts outdoor (open) burning and the use of wood stoves and fireplaces when an area's air quality is degraded and human health may be adversely impacted.


Canopy Closure
The percentage of ground or water covered by shade from the foliage of plants.
Carbon Monoxide (CO)
A colorless, odorless, poisonous gas and one of six "criteria [air] pollutants" for which EPA has established protective standards. Carbon monoxide forms when the carbon in fuels does not completely burn.
A section of a stream with a highly turbulent series of short falls, small scour basins or plunge pools, and very rapid water movement.  The gradient of the channel exceeds 8%.
Cathode Ray Tube (CRT)
A component of many electronic devices (such as TVs and computer monitors) that converts an electronic signal into a visual image (also called a "picture tube").  Much of the focus on managing e-waste revolves around CRTs.
Central (Community) Septic System
A type of decentralized wastewater treatment system that serves two or more homes or more than 2,500 gallons of wastewater per day.  Typically used for subdivisions, schools, and the like that are not connected to municipal wastewater systems.
Centralized Wastewater Treatment System (Municipal Wastewater Treatment Plant, Publicly Owned Treatment Works, City Sewer System)
A type of wastewater treatment system that connects homes, businesses, and industry directly to a wastewater treatment plant where it is treated before being discharged into the environment.
In a stream, a narrow, confined channel through which water flows rapidly and smoothly.
Clean Air Act (CAA)
A federal law that established nationwide standards for various air pollutants and provided for the regulation of polluting emissions via state implementation plans. The original Clean Air Act was passed in 1963, but the national air pollution control program is actually based on the 1970 version of the law. The 1990 Clean Air Act Amendments are the most far-reaching revisions of the 1970 law.
Clean Water Act (CWA)
The Federal Water Pollution Control Act, as last reauthorized by the Water Quality Act of 1987.  It establishes a process for states to use to develop information on, and control the quality of, the nation’s water resources.
Cold Water Aquatic Life
A beneficial use as defined in Idaho's water quality standards.  Water quality appropriate for the protection and maintenance of a viable aquatic life community for coldwater species.
Coliform Bacteria
A group of bacteria predominantly inhabiting the intestines of humans and animals but also found in soil.  Coliform bacteria are commonly used as indicators of the possible presence of pathogenic (disease-causing) organisms (also see fecal coliform bacteria).
Material transported to a site by gravity.
A group of interacting organisms living together in a given place.
Community (Central)Septic System
See central septic system.
Community Water System
A public water system that serves at least 15 connections used by year-round residents or at least 25 individual year-round residents.  That is, a system that serves people at their homes.
A mixture of decaying organic matter, such as from grass clippings, leaves, and kitchen waste, used to improve soil structure and provide nutrients.
Comprehensive Environmental Response, Compensation and Liability Act (CERCLA or Superfund)
A law that created a tax on the chemical and petroleum industries and provided broad federal authority to respond directly to releases or threatened releases of hazardous substances that may endanger public health or the environment.  The tax went to a trust fund for cleaning up abandoned or uncontrolled hazardous waste sites.
Concentrated (Confined) Animal Feeding Operation (CAFO)
A confined area for the controlled feeding of animals; also called a "feedlot."
Conditionally Exempt Small Quantity Generator (of Hazardous Waste) (CESQG)
A hazardous waste generator that generates 220 pounds or less of hazardous wastes per calendar month and 2.2 pounds or less of acutely hazardous wastes per calendar month. 
The ability of an aqueous (watery) solution to carry an electric current.
Confined Aquifer
An aquifer overlain by one or more layers of impermeable rock or soil that restrict water to within the aquifer.
Consumer Confidence Report (CCR)
An annual report prepared by each community water system in Idaho telling its customers where their drinking water comes from and what’s in it.
Continuing Planning Process
A document or series of documents describing present and planned water quality management programs and the strategy used by the state in implementing these programs.  Required by section 303(e) of the Clean Water Act.
See Water Quality Criteria.
Criteria Pollutants
Six air pollutants for which EPA has established standards to protect the health and welfare of people, plants, and animals, as well as to prevent damage to buildings, monuments, water resources, and natural areas.  The six pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide.
Cubic Feet per Second (cfs)
A unit of measure for the rate of flow (discharge) of water.  One cubic foot per second is the rate of flow of a stream with a cross-section of one square foot flowing at a average velocity of one foot per second.  At a steady rate, one cubic foot per second is equal to 448.8 gallons per minute and 10,984 acre-feet per day.
Cultural Eutrophication
The process of eutrophication that has been accelerated by human-caused influences. 
Culturally Induced Erosion
Erosion caused by increased runoff or wind action due to the work of humans.
A method of extracting metals from ores by treatment with a cyanide solution.


Decentralized Water Treatment System
A septic system that serves homes and other buildings not served by public sewer systems.  Most decentralized systems are on-site systems. Decentralized systems can be individual systems or central (community) systems.
The breakdown of organic molecules (e.g., sugar) to inorganic molecules (e.g., carbon dioxide and water) through biological and non-biological processes.
Deferred Source
Certain "minor" sources of air pollution for which EPA has not determined whether they will be required to obtain Tier I operating permits.  EPA is allowing states to defer permitting of these sources until June 1, 2006. These deferred sources include, but are not limited to, perchloroethylene dry cleaners, petroleum dry cleaners, hot-mix asphalt plants, and rock-crushing plants.
Depth Fines
Percent by weight of small particles within a vertical core of volume of a streambed or lake bottom sediment. 
Designated Use
A beneficial use for a water body as identified in state water quality standards.
The amount of water flowing in a stream channel at the time of measurement (flow).  Usually expressed as cubic feet per second.
Dissolved Oxygen (DO)
The oxygen dissolved in water.  Adequate DO is vital to fish and other aquatic life. 
Any event or series of events that disrupts ecosystem, community, or population structure and alters the physical environment.
A part of an on-site septic system.  The area of ground and the system of subsurface pipes or chambers into which partially treated wastewater from the septic tank is discharged for final treatment and absorption by soil. Also called a "leachfield" or "absorption field."
Drinking Water Planning Grant Program
A program that provides assistance to eligible public drinking water systems for facility planning projects designed to ensure safe and adequate supplies of drinking water.
Drinking Water Protection
A voluntary program a community can implement to help prevent the water that supplies its public water system from becoming contaminated. The program may involve creating a drinking water protection plan and implementing management practices.
Drinking Water Revolving Loan Fund
A fund that provides below-market-rate interest loans to help repair or build new drinking water facilities. 


E. coli (Escherichia coli)
A group of bacteria found in the normal intestinal flora of warm-blooded animals. Their presence in water often indicates that the water has been in contact with or contaminated by fecal material.
The scientific study of relationships between organisms and their environment.
Ecological Indicator
A characteristic of an ecosystem that can provide quantitative information on ecological structure and function.  An indicator can contribute to a measure of integrity and sustainability. 
Ecological Integrity
The condition of an unimpaired ecosystem as measured by combined chemical, physical (including habitat), and biological attributes.
The interacting system of a biological community and its non-living (abiotic) environmental surroundings.
A discharge of untreated, partially treated, or treated wastewater into a receiving water body.
The use of electricity to provide a sufficient electrical stimulus in fish to permit easy capture by netting.
Electronic Waste (e-waste)
Unwanted, obsolete, or unusable electronic products such as computers, TVs, stereo equipment, and cell phones.
Emergency Response
A response effort by designated responders (e.g., local fire departments) to an occurrence that results, or is likely to result, in an uncontrolled release of a hazardous substance.
Emission (Air Emission)
A substance discharged into the air.
Emissions Unit
An identifiable piece of process equipment or other part of a facility that emits or may emit any air pollutant.
Endangered Species
Animals, birds, fish, plants, or other living organisms threatened with imminent extinction and officially declared as "endangered" under the Endangered Species Act. 
The complete range of external conditions, physical and biological, that affect a particular organism or community.
U.S. Environmental Protection Agency. The federal agency whose mission is to protect human health and the environment.
Windblown. Referring to the process of erosion, transport, and deposition of material by the wind.
EPA Identification Number
A unique number assigned to facilities that generate specified amounts of hazardous waste. It is used by states and EPA to track hazardous waste activities.
Ephemeral Stream
A stream or portion of a stream that flows only in direct response to precipitation.  It receives little or no water from springs and no long continued supply from melting snow or other sources.
The wearing away of areas of the earth's surface by water, wind, ice, and other forces.
Describes a highly productive body of water in which nutrients do not limit algal growth.  It is typified by high algal densities and low clarity. Also see mesotrophic and oligotrophic.
The process of nutrient enrichment in aquatic systems, such that the productivity of the system is no longer limited by the availability of nutrients. This is a natural process but may be accelerated by human activities.
A violation (according to DEQ policy) of the pollutant levels permitted by water quality criteria.
Existing Beneficial Use or Existing Use
A beneficial use actually attained in waters on or after November 28, 1975.
Exotic Species
A species that is not native (indigenous) to a region.


Animal life, especially the animals characteristic of a region, period, or special environment.
Fecal Coliform Bacteria
Bacteria found in the intestinal tracts of all  mammals.  Their presence in water is an indicator of pollution and possible contamination by pathogens (also see coliform bacteria).
Fecal Streptococci
A species of bacteria including disease-causing (pathogenic) strains found in the intestines of warm-blooded animals.
Feedback Loop
A process for tracking progress toward goals and revising actions according to that progress.
 A long thin series of cells attached one to another, or a very long thin cylindrical single cell.
Fixed-Location Monitoring
Sampling or measuring environmental conditions continuously or repeatedly at the same location.
Land beyond a stream channel that forms the perimeter for the maximum probability flood.
See Discharge.
1.  Fish whose life history takes place entirely in streams; they migrate to smaller streams for spawning.  2.  Pertaining to or living in streams or rivers or produced by the action of flowing water.
Fractured Rock Aquifer
An aquifer where water fills spaces produced by broken or shattered rock that would otherwise be impervious, such as basalt or granite. Fractured basalt aquifers are found in southern Idaho, the Lewiston-Moscow basin, and the Weiser area.
Water that is not salty.
Fugitive Dust
Particulate matter suspended in the air by the wind and human activities. It originates primarily from the soil and is not emitted from vents, chimneys, or stacks.
Fully Supporting (Water Quality Standards)
A water body that is in compliance with water quality standards and within the range of biological reference conditions for all designated and exiting beneficial uses as determined through the Water Body Assessment Guidance.
Fully Supporting but Threatened
A water body that fully supports beneficial uses, but that is declining in quality. If this decline is not addressed, the water body may not support beneficial uses in the future.


General Resource Aquifer
One of three categories of aquifers defined in Idaho's Ground Water Quality Rule (pdf on Department of Administration Web site).  All aquifers in Idaho other than the Spokane Valley-Rathdrum Prairie Aquifer are general resource aquifers.  The other two categories are "sensitive resource aquifer" and "other resource aquifer."
A facility or mobile source that emits pollutants into the air or releases hazardous waste into water or soil.
Geographical Information Systems (GIS)
A computer system for capturing, storing, querying, analyzing, and displaying geographic data.  
A portion of a stream with slow-moving, relatively shallow water.
Grab Sample
A single sample collected at a particular time and place.  Usually refers to collecting samples of or in water. 
The slope of a land, water, or streambed surface.
Ground Water
Water beneath the earth's surface; the water that fills the natural open spaces in soil and rocks underground in much the same way as water fills a sponge.
Ground Water Quality Management Plan
A set of strategies that focus on understanding the dynamics of ground water and contaminants, preventing contamination, protecting current quality, and remediating contaminated water to maintain or improve water quality.  Plans are written by ground water quality advisory groups with assistance from DEQ for areas with contaminated ground water. 
Growth Rate
A measure of how quickly something living will develop and grow.


The living place of an organism or community.
Hazardous Air Pollutants
Air pollutants that cause or may cause cancer or other serious health problems (e.g., birth defects) or adverse environmental and ecological effects.
Hazardous Waste
A waste that can pose a substantial or potential hazard to human health or the environment. There are two types of hazardous waste: characteristic (hazardous wastes that exhibit certain characteristics, such as flammability) and listed (hazardous wastes that appear on any of four specific lists issued by EPA). 
Atmospheric moisture, dust, smoke, and vapor that diminishes visibility.
The origin or beginning of a stream.
Hydrogen Sulfide
A colorless, extremely toxic, irritating gas with a rotten-egg odor at low concentrations and no detectable odor at high concentrations. 
Hydrologic Basin
The area of land drained by a river system, a reach of a river and its tributaries in that reach, a closed basin, or a group of streams forming a drainage area (also see watershed).
Hydrologic (Water) Cycle
The cycling of water from the atmosphere to the earth (precipitation) and back to the atmosphere (evaporation and plant transpiration).  Atmospheric moisture, clouds, rainfall, runoff, surface water, ground water, and water in soil are all part of the hydrologic cycle.
Hydrologic Unit
One of a nested series of numbered and named watersheds arising from a national standardization of watershed delineation (definition/description).  DEQ frequently uses the fourth level of this delineation, commonly called subbasins, when writing TMDLs. 
Hydrologic Unit Code (HUC)
The number assigned to a hydrologic unit.  Often used to refer to fourth field hydrologic units (subbasins).
The science dealing with the properties, distribution, and circulation of water.


Idaho OnePlan
A multi-agency project that combines government regulations and current best management practices for agriculture into a single plan, integrating federal, state, and local regulations.  The program aids farmers by providing data and software to help them develop a single conservation farm plan that can be pre-endorsed by the various agencies, thereby streamlining and simplifying the regulatory process that farmers face.
Igneous Rock
Rock formed by the solidification of molten (melted) rock material (magma) from under the earth's crust.
A surface, such as pavement, that water cannot penetrate.
Implementation Plan (TMDL Implementation Plan)
A document guided by an approved TMDL that provides a framework for local stakeholders to use to reach the goals established in the TMDL.
Incinerate (Incineration, Incinerator)
To burn.  Incinerators burn solid waste and are regulated according to the volume and type of waste managed. Incineration is one alternative to placing solid waste in a landfill.
Individual Septic System
A system for treating wastewater from one or two homes not connected to a municipal wastewater treatment system.  The wastewater is treated underground, on-site.  This is one type of decentralized system. Also see on-site wastewater treatment system.
A tributary stream.
Materials not derived from biological sources.
A condition or measurement at a moment (instant) in time.
Integrated Report
A report that summarizes a biennial analysis of the quality of Idaho's water bodies.  The report is required under the Clean Water Act and must be submitted to EPA for approval. The report serves as a guide for developing TMDLs and is a combination of what used to be two different documents:  §305(b) report and §303(d) list.
The extent to which all parts or elements of a system (e.g., an aquatic ecosystem) are present and functioning.
Intergravel Dissolved Oxygen
The concentration of dissolved oxygen within gravel in water bodies used by fish for spawning. 
Intermittent Stream
A stream that flows only part of the year. 
Interstate Waters
Waters that flow across or form part of state or international boundaries, including boundaries with Indian nations.
Intrusive Rock
Rock that has been forced, while in a plastic or melted (molten) state, into cavities or between cracks or layers of other rocks.
An atmospheric condition in which the air temperature rises with increasing altitude, trapping cold surface air and air pollutants in lower elevation areas. 
Irrigation Return Flow
Water (above and below ground) that leaves a field following the application of irrigation water and eventually flows into streams.  Also see runoff.


Key Watershed
A watershed that was designated in the State of Idaho Bull Trout Conservation Plan (1996) as critical to the long-term persistence of regionally important trout populations.


Land Application
A process or activity involving application of wastewater, surface water, or semi-liquid material to the land surface for the purpose of treatment, pollutant removal, or ground water recharge.  Also see wastewater-land application.
An area of land or an excavation in which wastes are placed for permanent disposal.
Large Quantity Generator (LGQ) (of Hazardous Waste)
A generator of hazardous waste that generates 2,200 pounds or more of hazardous waste per calendar month or more than 2.2 pounds of acutely hazardous waste per calendar month.
Large Soil Absorption System (LSAS)
A type of decentralized, central (community) septic system that receives more than 2,500 gallons of wastewater per day.  Wastewater is treated on-site and underground. Developments and facilities such as resorts, schools, subdivisions, and rest areas that are not connected to centralized systems (e.g., municipal wastewater treatment systems) often use LSASs to treat their wastewater.
A toxic metal found naturally in the environment that was commonly used in consumer products such as gasoline and paint before it was discovered that it is harmful to human health.  If inhaled or swallowed, lead can build up in the body over time and cause serious damage to the brain, kidneys, nervous system, and red blood cells.
Leaking Underground Storage Tank
A leaking tank located at least partially underground and designed to hold gasoline or other petroleum products or chemicals.  Also see underground storage tank.
The scientific study of fresh water, especially the history, geology, biology, physics, and chemistry of lakes.
Load Allocation (LA)
A portion of a water body's load capacity for a specific pollutant that is given to a particular nonpoint source. Also see wasteload allocation.
The quantity of a substance entering a receiving stream, usually expressed in pounds or kilograms per day or tons per year.  Loading is the product of flow (discharge) and concentration.
Load(ing) Capacity (LC)
A determination of how much of a pollutant a water body can receive over a given period without causing violations of state water quality standards.  Upon allocation to various sources, and a margin of safety, it becomes a TMDL.
Soil with a relative balance of sand, silt, and clay.  Loam is highly desirable for agriculture.
A uniform wind-blown deposit of silty soil.  Silty soils are among the most highly erodible.
Relating to flowing water such as a stream or river.


An invertebrate animal (an animal without a backbone) large enough to be seen without magnification.
An aquatic plant. Most have roots in soil, but some are free-floating.
Maximum Achievable Control Technology (MACT)
The emission standard for sources of air pollution requiring the maximum reduction of hazardous emissions, taking cost and feasibility into account. Under the Clean Air Act Amendments of 1990, the MACT must not be less than the average emission level achieved by controls on the best performing 12 percent of existing sources, by category of industrial and utility sources.  Also see National Emission Standards for Hazardous Air Pollutants.
MACT Hammer
The Clean Air Act required EPA to issue MACT standards for categories of sources that emit hazardous air pollutants according a set schedule, beginning in 1992 and continuing through November 15, 2000. If EPA missed the promulgation deadline for any given source category by more than 18 months, the "hammer" falls, meaning facilities that are major sources and operate emissions units in a category for which a MACT standard has not yet been developed must submit a permit application to obtain a case-by-case determination of required emission limitations.
Major Source (of Air Pollution) (Title V)
Facilities that emit 100 tons per year or more of any regulated air pollutant, or 10 tons per year or more of any single hazardous air pollutant (specifically listed in the Clean Air Act), or 25 tons per year or more of a combination of hazardous air pollutants. A Tier I operating permit is required by the Clean Air Act for most major sources of air pollution.  Note: Different sets of air regulations have different requirements for "major source" designation.  The requirements listed above apply to Title V of the Clean Air Act.
Margin of Safety (MOS)
A portion of a water body's loading capacity set aside to acknowledge uncertainly about the relationship between pollutant loads and the quality of a receiving water body.  This is a required component of a TMDL and is often incorporated into conservative assumptions used to develop the TMDL.  The MOS is not allocated to any source of pollution.
Mass Wasting
A general term for the down slope movement of soil and rock material under the direct influence of gravity.
Describes the central tendency of a set of numbers.  The arithmetic mean (calculated by adding all items in a list, then dividing by the number of items) is the statistic most familiar to most people.  Also referred to as the "average."
A curve in a stream.
Meander Pool
A pool in a stream resulting from a shift in channel direction (meander) and found along the outer curves of the channel, where scouring (localized erosion) occurs.
The middle number in a sequence of numbers (e.g., 4 is the median of 1, 2, 4, 14, 16).  If there are an even number of numbers, the median is the average of the two middle numbers (e.g., 6 is the median of 1, 2, 5, 7, 9, 11).
A naturally occurring element present throughout the environment. Human activity can release mercury into the air, water, and soil.  When mercury enters water, biological processes transform it to a highly toxic form that builds up in fish and animals that eat fish. People are exposed to mercury primarily by eating fish.
A moderately productive water body.  Also see eutrophic and oligotrophic.
1. A discrete measure of something, such as an ecological indicator (e.g., number of distinct taxon). 2. The metric system of measurement.
Mill Yard Debris Facility (Wood Debris Facility)
A facility that manages exclusively solid wood, bark, or wood fiber generated from wood product manufacturing.
Milligrams per Liter (mg/L)
A unit of measure for concentration. In water, essentially equivalent to parts per million (ppm).
Million Gallons per Day (MGD)
A unit of measure for the rate of discharge of water, often used to measure flow at wastewater treatment plants.  One MGD is equal to 1.547 cubic feet per second.
Minor Source (of Air Pollution)
In Idaho, any source of air pollution that is not a major source.
Mixing Zone
A place where wastewater is discharged into a "receiving water" (e.g., a stream).  The wastewater mixes with the receiving water and is diluted.  In this defined area or volume of receiving water, the receiving water may not meet all applicable water quality standards.
A system of assumptions, data, and inferences used with mathematics to predict outcomes.  For example, meteorologists use models to predict the weather.
A periodic or continuous measurement of the properties or conditions of something, such as a water body or air quality. 
The location where flowing water enters a larger water body.
Municipal Wastewate Treatment Plant (Centralized Wastewater Treatment System, Publicly Owned Treatment Works, City Sewer System)
A type of centralized wastewater treatment system that connects homes, businesses, and industry directly to a central facility where wastewater is treated before being discharged into the environment. 
Municipal Solid Waste Landfill
A landfill that receives solid waste generated by households, hotels, campgrounds, and other similar facilities.  It may also receive other types of solid waste, such as from commercial and industrial facilities.


Narrative Criteria
Part of Idaho's water quality standards that addresses pollutants, such as color and odor, that can’t be measured with numeric criteria.  Narrative criteria are statements that describe a desired water quality goal, such as Idaho's waters being "free from" pollutants such as oil and scum, color and odor, and other substances that can harm people and fish.
National Ambient Air Quality Standards (NAAQS)
Air quality standards that list the maximum concentration above which adverse effects on human health may occur for six air "criteria pollutants."
National Emission Standard for Hazardous Air Pollutants (NESHAP)
Air quality standards that regulate 188 hazardous air pollutants from particular industrial sources. These industry-based NESHAPs are also called Maximum Achievable Control Technology (MACT).
National Pollutant Discharge Elimination System (NPDES)
A national program established by the Clean Water Act for permitting point sources of pollution.  Discharge of pollution from point sources is not allowed without a permit.  EPA administers the NPDES program in Idaho.  
Natural Background (Natural Condition)
A condition indistinguishable from that without human-caused disruptions. Usually used to refer to water quality.  Since human-caused changes don't always affect all aspects of water quality, it is possible for water to be considered natural for one parameter but not another.
New Source Performance Standards (NSPS)
Uniform national air emission standards that limit the amount of pollution that may be emitted from stationary sources built or modified after regulations prescribing a certain standard of performance had been implemented.
A form of nitrogen, an element whose compounds are vital components of foods and fertilizers. It is a natural and essential nutrient, but too much can result in water pollution.
Nitrate Priority Area
An area of ground water polluted by nitrate. DEQ has developed a list of the top 25 nitrate priority areas in Idaho.  These areas are the focus of ground water remediation.
An element essential to plant growth, and thus is considered a nutrient. 
Nitrogen Dioxide (NO2)
A brownish, highly reactive gas present in all urban atmospheres. Nitrogen dioxide is a "criteria pollutant" that can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections.
Nonattainment Area
An EPA classification for a geographic area that has violated federal health-based standards for outdoor air pollution. Each nonattainment area is declared for a specific pollutant. Also see attainment area.
Non-Community, Non-Transient Water System
A public water system that serves at least 25 of the same people, four or more hours per day, for four or more days per week, for 26 or more weeks.  That is, a system that always serves the same people, but not at their homes, such as a system for a school or business. 
Non-Community, Transient Water System
A public water system that does not serve at least 25 of the same people, four or more hours per day, for four or more days per week, for 26 or more weeks.  That is, a system that serves different people all the time, such as a system for a campground.
Nonmetallic Mineral Processing Plant
A rock crushing facility.
Non-Municipal Solid Waste Landfill
A landfill that only accepts solid waste that is not mixed with waste generated by households or is not specifically excluded from regulation under Idaho's Solid Waste Management Rules (pdf on Department of Administration Web site). Non-municipal solid waste may include such materials as glass, plastic, wood, roofing materials, sheet rock, and certain quantities of hazardous or pathogenic waste.
Nonpoint (Source)
Pollution originating over a wide geographical area; not discharged from a specific location or "point."  Nonpoint sources of pollution include roads and agricultural fields. Generally used when referring to pollutants of water.
Not Assessed
Describes a water body that has been studied, but is missing critical information needed to complete a water body assessment.
Not Attainable
Describes a water body that has characteristics that make it unlikely that a beneficial use can be attained (e.g., a stream that is dry but designated for salmonid spawning).
Not Fully Supporting
Not in compliance with water quality standards or not within the range of biological reference conditions for a beneficial use as determined through the Water Body Assessment Guidance.
Notice of Violation (NOV)
A formal legal means of informing responsible parties that violations of environmental rules or permits have occurred. An NOV includes a listing of the violations at a facility, an assessed penalty amount for each violation, and a description of the procedure for negotiating an agreement designed to return the facility to compliance in a timely manner.
Anything which is injurious to the public health or an obstruction to the free use of any waters of the state.
Numeric Criteria
Values in water quality standards that should rarely be exceeded if beneficial uses are to be supported. Individual criteria are based on specific data and scientific assessment of adverse effects. Numeric guidelines assign numbers that represent limits and/or ranges of chemical concentrations, like oxygen, or physical conditions, like water temperature. Also see narrative criteria.
Any substance required by living things to grow (e.g., nitrogen and phosphorus).
Nutrient Cycling
The flow of nutrients from one component of an ecosystem to another, such as when a plant or animal dies and releases nutrients that become available to other plants and animals.
Nutrient-Pathogen Evaluation
A scientific evaluation of the water quality impacts of on-site subsurface sewage disposal (septic systems). The evaluation predicts whether the effluent from sewage disposal systems will be diluted enough to prevent ground water contamination.


Describes a body of water in which productivity is low and nutrients are limiting to algal growth.  These water bodies are unusually clear. Also see mesotrophic and eutrophic.
On-Site Wastewater Treatment System (Septic System)
A system for treating wastewater from individual homes and businesses not connected to municipal systems.  Wastewater is discharged into an underground tank where solids and water are separated. Solids settle to the bottom of the tank. Bacteria in the tank break down organic matter. Water flows from the tank and into a drainfield of underground pipes surrounded by gravel and soil.
The measure of how much something is impenetrable by light (the measure of how opaque something is.)
Open Burning
Any burning outdoors that does not pass through a stack, duct, or chimney. This includes outdoor residential, agricultural, and prescribed burning and burning that occurs in burn barrels and similar devices.
Organic Matter
Compounds manufactured by plants and animals that contain principally carbon. 
Any living thing composed of one or more cells.
Other Resource Aquifer
One of three categories of aquifers defined in Idaho's Ground Water Quality Rule (pdf on Department of Administration Web site).  These aquifers require the lowest level of protection and may have standards that are less strict than those in the Ground Water Quality Rule. There are currently no aquifers in Idaho designated as "other resource aquifers."  The other two aquifer categories are "sensitive resource aquifer" and "general resource aquifer."
Oxygen-Demanding Materials
Materials, mainly organic matter, in a water body that consume oxygen during decomposition. 
A gas that forms in the atmosphere when three atoms of oxygen are combined. It is created at ground level by a chemical reaction between oxides of nitrogen (e.g., nitrogen dioxide) and volatile organic compounds. Ozone can be "good" or "bad," depending on its location in the atmosphere (high in the atmosphere is "good"; close to ground level is "bad").


A measurable property whose value provides information about the characteristics of something.  For example, temperature and dissolved oxygen are parameters of a stream or lake.
Particulate Matter (PM)
The term for small particles in the air including dust, dirt, soot, smoke, and liquid droplets. 
Disease-producing organisms (e.g., bacteria, viruses, parasites).
Perched Aquifer
A small aquifer that is separated from a main aquifer below it by an impermeable layer of rock or soil and an unsaturated zone.
Perennial Stream
A stream that flows year-around in most years.
Organisms, such as algae and small crustaceans, that live attached to surfaces projecting from the bottom of a freshwater aquatic environment.
Permit to Construct (PTC)
An air quality permit issued by DEQ that is required prior to construction or modification of buildings, structures, or installations that emit, or may emit, pollutants into the air.
Permit by Rule (PBR)
A provision of the Rules for the Control of Air Pollution in Idaho (pdf on Department of Administration Web Site) under which a facility or source registers with DEQ and meets specific requirements for that type of source. Once registered, the facility is deemed to have a permit to construct (PTC), thereby authorizing construction without the need to first obtain a PTC.  Currently, the opportunity to obtain a PBR is available only to nonmetallic mineral processing plants. Participation is entirely voluntary.
A substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest. 
The negative log10 of the concentration of hydrogen ions.  Water ranges from very acid (pH=1) to very alkaline (pH=14).  A pH of 7 is neutral.  Surface waters such as streams and lakes usually measure between pH 6 and 9. 
Phased TMDL
A TMDL that identifies interim load allocations and details further monitoring to gauge the success of management actions in achieving goals.  Under a phased TMDL, a refinement of load allocations, wasteload allocations, and the margin of safety is planned at the outset.
An element essential to plant growth. It is considered to be a plant nutrient and is often in limited supply.
The process in green plants and some other organisms by which carbohydrates are made from carbon dioxide and water using light as an energy source.
A plant whose roots generally extend downward to the water table; common in riparian habitats.
Physiochemical (Physical/Chemical, Physicochemical)
The physical and chemical factors of the water column (e.g., temperature or pH) that relate to aquatic biota.
Microscopic algae (phytoplankton) and animals (zooplankton) that float freely in the open water of lakes and oceans.
Plunge Pool
A pool created by water passing over or through an obstruction in the stream channel, then dropping steeply into the streambed below, scouring out a basin or pool.
Particles in the air less than 2.5 micrometers in diameter. Often referred to as "fine" particles.  Also see PM10.
Particles in the air less than 10 micrometers in diameter.  Particles this size (PM10, including PM tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse."
Point (Source)
A source of pollutants with a discrete conveyance, such as a pipe, ditch, or other identifiable "point" of discharge.  Also see nonpoint.
Any substance introduced into the environment that adversely affects the usefulness of a resource or the health of humans, animals, or ecosystems. Also see air pollutant.
Pollutant Trading
A voluntary, business-like way of helping to improve water quality by controlling wastewater discharges to surface waters in a cost-effective manner. It involves one facility facing relatively high pollution reduction costs paying another facility with lower pollution reduction costs to reduce its pollution to allow the first facility to discharge more than its share. Thus, the level of pollutants discharged to a specific body of water stays the same (or is reduced) and both businesses are better off, financially, as a result of the trade.
The undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities.
Pollution Prevention (P2)
Practices that reduce or eliminate the creation of pollutants or waste through increased efficiency in the use of raw materials, energy, water, or other resources, or protecting resources through conservation. P2 goes beyond recycling and reusing and involves using resources efficiently and not creating waste in the first place.
The number of humans or other living creatures in a designated area.
Poultry (and Swine) Facility
Any place, site, location, or part thereof where swine or poultry are kept, handled, housed, or otherwise maintained.
Preliminary Assessment (Program)
A program to evaluate and prioritize assessment of potentially contaminated sites, such as abandoned mines, old landfills, illegal dumps, and abandoned industrial facilities.
Presumed Use
One type of beneficial use described in Idaho's water quality standards.  Idaho presumes most undesignated waters (waters that do not have a specific designated use) will support cold water aquatic life and either primary or secondary contact recreation. Presumed uses must be fully protected.
The reduction in the amount of pollutants, elimination of certain pollutants, or alteration of the nature of pollutant properties in wastewater prior to, or instead of, discharging it into a wastewater treatment plant.
Having the primary responsibility for administering and enforcing regulations. States are encouraged by EPA to obtain primacy for federal environmental programs.
Primary Contact Recreation
A beneficial use as defined in Idaho's water quality standards. Applies to waters where people engage in activities that involve immersion in, and likely ingestion of, water, such as swimming and water skiing. Also see secondary contact recreation.
A collection of methods for accomplishing a task.
Public (Drinking) Water System
A water system that supplies water to at least 25 people or has at least 15 service connections.
Publicly Owned Treatment Works (Municipal Wastewater Treatment Plant, Centralized Wastewater Treatment System, City Sewer System)
A type of wastewater treatment system that connects homes, businesses, and industry directly to a wastewater treatment plant where it is treated before being discharged into the environment.


Descriptive of kind, type, or direction. 
Quality Assurance (QA)
A program organized and designed to provide accurate and precise results. The goal of QA is to assure data are of the quality needed and claimed.
Quality Control (QC)
A series of inspections and checks to verify that an item complies or conforms with specified requirements.
Descriptive of size, magnitude, or degree.


A stream section with fairly homogenous physical characteristics.
An exploratory or preliminary survey of an area.
Transforming waste materials into usable resources.
Not using a product in the first place, so that no waste is generated.
A physical or chemical quantity whose value is known, and thus is used to calibrate or standardize instruments.
Reference Condition
A stream condition that fully supports applicable beneficial uses with little affect from human activity and represents the highest level of use support attainable. 
Reference Site
A specific location on a water body that is minimally impaired and is representative of reference conditions for similar water bodies. 
Cleanup or other methods used to remove or contain toxic or hazardous materials.
Representative Sample
A portion of material or water that is as similar in content and consistency as possible to that in the larger body of material or water being sampled.
In water quality, refers to fish that do not migrate.
Residential Burning (Backyard Burning)
A form of open, outdoor burning where the smoke does not pass through a stack, duct, or chimney. Residential burning includes fires in burn barrels.
Resource Conservation and Recovery Act (RCRA)
A federal law to protect human health and the environment from the potential hazards of waste disposal; to conserve energy and natural resources; to reduce the amount of waste generated; and to ensure that wastes are managed in an environmentally sound manner.  RCRA is comprised of three interrelated parts: hazardous waste, solid waste, and underground storage tanks.
A process by which organic matter is converted to energy, carbon dioxide, water, and other things by organisms such as plants, animals, and bacteria. 
Using something again to avoid generating the waste that is created by throwing something away and replacing it with something new.
A relatively shallow, gravelly area of a streambed with a locally fast current, recognized by surface choppiness. Also an area of higher streambed gradient and roughness.
Associated with aquatic (stream, river, lake) habitats. Living or located on the bank of a water body.
Riparian Area (Zone)
A thin strip of land bordering a stream or river.
A large, natural, or human-modified stream that flows in a defined course or channel or a series of diverging and converging channels. 
River Basin
The land area drained by a river and its tributaries. Idaho is divided into six major river basins: Panhandle, Clearwater, Salmon, Southwest, Upper Snake, and Bear River.
The portion of rainfall, melted snow, or irrigation water that flows across the land surface, through shallow underground zones, and through ground water to create streams. 
A statement of general applicability that has been promulgated in compliance the Idaho Administrative Procedure Act, Idaho Code §§67-5201 et seq (pdf on Department of Administration Web site). A rule implements, interprets, or prescribes law or policy or the procedure or practice requirements of an agency.
The process for formulation, adoption, amendment, or repeal of a rule.


Soft-finned fishes of cold and temperate waters, such as salmon, trout, and whitefish.  These fish belong to, or are characteristic of, the family Salmonidae.
Scour Basin
A depression in a streambed caused by localized erosion.
Secondary Contact Recreation
A beneficial use as defined in Idaho's water quality standards.  Applies to waters where people engage in activities where ingestion of water may occasionally occur, such as fishing, boating, wading, and infrequent swimming. Also see primary contact recreation.
Fine materials from weathered rocks and organic material that are suspended in, transported by, and eventually deposited by water or air.
Sedimentary Aquifer
An aquifer located in sedimentary materials, such as loose gravels and sands.  In Idaho, sedimentary aquifers are typically found in the south.  The Boise Valley Aquifer is one example. 
Sensitive Resource Aquifer
One of three categories of aquifers defined in Idaho's Ground Water Quality Rule (pdf on Department of Administration Web site).  Sensitive resource aquifers require the strongest level of protection. The Spokane Valley-Rathdrum Prairie Aquifer is the only sensitive resource aquifer in Idaho. The other two categories of aquifers are "general resource aquifer" and "other resource aquifer."
The contents of a septic tank. 
Sewage Sludge
The solid, semisolid, or liquid untreated residue generated during the treatment of domestic wastewater (sewage).
A measure of the straightness of a stream channel.  It is the ratio of channel length between two points in a channel to the straight line distance between the same two points.
Site Specific Criteria
Water quality criteria (in Idaho's water quality standards) that reflect the toxicity of a pollutant in a specific water body.
Small Quantity Generator (of Hazardous Waste) (SQG)
A generator of hazardous waste that generates more than 220 but less than 2,200 pounds of hazardous wastes per calendar month and 2.2 pounds or less of acutely hazardous wastes per calendar month.
Sole Source Aquifer
An aquifer that has been designated by EPA as the sole or principal source of drinking water for an area. A designated sole source aquifer receives special protection.  Three Idaho aquifers—the Eastern Snake River Plain Aquifer, the Spokane Valley-Rathdrum Prairie Aquifer, and the Lewiston Basin Aquifer—are sole source aquifers.
Solid Waste
Non-liquid, non-soluble materials ranging from municipal garbage to industrial wastes that contain complex and sometimes hazardous substances. Solid wastes include sewage sludge, agricultural refuse, demolition wastes, mining residues, and liquids and gases in containers.
Source Water Assessment
A study (and the resulting report) that provides information on the potential contaminant threats to public drinking water sources. 
Describes something that can be dissolved, especially easily dissolved.
A liquid or gas used to dissolve another substance.
To deposit eggs and produce offspring.  Used when referring to fish.
Spent Solvent
Any material that has been used as a solvent and as a result of contamination can no longer serve the purpose for which it was produced without processing. Spent solvent is considered solid waste and may be hazardous.
A category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding. Also refers to an organism belonging to such a category.
Ground water seeping out of the earth where the water table intersects the ground surface.
The absence of mixing in a water body.
State Implementation Plan (SIP)
A compilation of rules and plans that together  demonstrate how a state will achieve, maintain, and enforce federal air quality standards.
Stationary Source
Any building, structure, emissions unit, or installation that emits or may emit any air pollutant.
Unable to tolerate a wide temperature range.
Storm Water
Water from rain or melting snow that does not immediately soak into the ground.
A natural water course containing flowing water for at least part of the year. 
Stream Bank
The ground bordering a stream channel above the streambed and below the level of rooted vegetation.
Stream Order
The hierarchical ordering of streams based on the degree of branching.  A first-order stream is an unbranched stream (hence, a very small stream).  Higher order streams (larger numbers/bigger streams) result from the joining of two streams of the same order (e.g., two first order streams flow together to form a second order stream).
The channel through which a natural stream of water runs or used to run.
Physical, chemical, or biological entities that can cause adverse effects on ecosystems or human health.
A large watershed of several hundred thousand acres.  This is the name commonly given to 4th field hydrologic units. 
Subbasin Assessment (SBA)
A watershed-based problem assessment that is the first step in developing a TMDL in Idaho.
A small watershed delineated within a larger watershed, often for purposes of describing and managing local conditions. 
Sulfur Dioxide (SO2)
A colorless, reactive gas produced during the burning of sulfur-containing fuels such as coal and oil, during metal smelting, and during other industrial processes. Generally, the highest concentrations are found near large industrial sources, such as power plants and industrial boilers. Sulfur dioxide is one of six "criteria [air] pollutants" as defined by EPA.
A low-lying place, such as a pit, that receives drainage.
Sump Waste
The mixture of dirt, grime, and grit that accumulates in a sump. Sump waste is considered solid waste and may be hazardous.
The program operated under the legislative authority of CERCLA and SARA that funds and carries out EPA solid waste emergency and long-term removal and remedial activities.
Superfund Amendments and Reauthorization Act (SARA)
A law that amended CERCLA and, among other things, stressed the importance of permanent remedies and innovative treatment technologies in cleaning up hazardous waste sites. 
Supplemental Environment Project (SEP)
An environmentally beneficial project that DEQ may allow a facility to implement in lieu of or to reduce a cash penalty when that facility has been found in violation of an environmental regulation. The SEP must go beyond what is required to ensure compliance with environmental regulations.
Surface Fines
Sediments of small size deposited on the surface of a streambed or lake bottom. 
Surface Runoff (Overland Flow)
Precipitation, snow melt, or irrigation water in excess of what can infiltrate into the soil and be stored in small surface depressions; a major transporter of nonpoint source pollution.
Surface Water
The collection of all bodies of water, such as streams, lakes, rivers, and wetlands, evident on the surface of the land.
Surface Water Ambient Monitoring Plan
A document that outlines DEQ's approach to collecting and integrating ambient water quality monitoring data from a variety of monitoring programs.
Suspended Sediments
Fine sediments (usually sand size or smaller) that remain suspended by turbulence in the water column until deposited in areas of weaker current. 
Swine (and Poultry) Facility
Any place, site, location, or part thereof where swine or poultry are kept, handled, housed, or otherwise maintained.
Synthetic Minor
A facility that potentially could emit air pollution above the level that requires a Tier I air permit, but that volunteers to limit production and/or hours of operation to lower its potential to emit pollutants below Tier I permit thresholds. This allows the facility to obtain a Tier II permit instead.  Since the facility would otherwise be a "major" source of air pollution, it is called a "synthetic" minor source.


Any formal taxonomic unit or category of organisms (e.g., species, genus, family, order). 
The classification of organisms in an ordered system that indicates natural relationships.
Technical Advisory Group (TAG)
A group of knowledgeable citizens and experts that assist watershed advisory groups in evaluating water quality issues.
The center of a stream's current, where most of the water flows.
Threatened Species
Species, determined by the U.S. Fish and Wildlife Service, that are likely to become endangered within the foreseeable future throughout all or a significant portion of their range.
Tier I (Title V) Operating Permit (Air)
An operating permit for a facility that emits air pollution.  In general, "major" sources of air pollution need Tier I permits. A Tier I permit establishes operational, monitoring, recordkeeping, and reporting requirements to demonstrate compliance with air emissions standards. 
Tier II Operating Permit (Air)
An operating permit for a facility that emits air pollution.  Tier II permits are issued to facilities that have voluntarily opted to set emissions limits to become "synthetic minor" sources of air pollution.  Occasionally, a Tier II permit may be issued for a facility when DEQ has determined that it may impact human health or the environment.  The fees for Tier II permits are lower and the reporting requirements less complex than those required for Tier I operating permits.
Tier II Facility (Waste)
An incinerator that has a cumulative volume of 600 cubic yards or more.  The facility must comply with basic Tier II waste regulations and deadlines and meet certain specific additional design, operating, and closure requirements. 
Title V (Tier I) Operating Permit (Air)
See Tier I Operating Permit.
Total Dissolved Solids
The dry weight of all material in solution in a water sample. 
Total Maximum Daily Load (TMDL)
A water quality improvement plan.  A TMDL is a water body's loading capacity after it has been allocated among pollutant sources.  TMDL = Load Capacity = Load Allocation + Wasteload Allocation + Margin of Safety.  In common usage, a TMDL also refers to the written document that contains the statement of loads and supporting analyses, often incorporating TMDLs for several water bodies and/or pollutants within a given watershed.
Total Suspended Solids (TSS)
The dry weight of material from a water sample retained on a filter after filtration. 
Toxics (Air Toxics)
A group of air pollutants that are known or suspected to cause serious health problems such as cancer, birth defects, and lung damage. Examples of air toxics include asbestos, lead, and mercury.
Toxic Pollutants
Materials that cause death, disease, or birth defects in organisms that ingest or absorb them.  The quantities and exposures necessary to cause these effects can vary widely.
Trade Waste
Any solid, liquid or gaseous material resulting from the construction or demolition of any structure or the operation of any business, trade, or industry.
Transfer Station
A facility where solid wastes are transferred from a vehicle or container and then transported off-site to another facility. Rural drop-boxes and other storage facilities where individual wastes are stored are not considered transfer stations, although waste tire collection sites are.
Treatment, Storage, and Disposal Facility (TSD)
A facility that treats, stores, or disposes of hazardous waste. A treatment facility chemically or physically treats hazardous waste to make it less hazardous. A storage facility stores large amounts of hazardous waste. A disposal facility provides permanent containment or destruction of waste materials.
A stream feeding into a larger stream or lake.
Triennial Review
A review of state water quality standards required at least once every three years. 
Trophic State
The level of growth or productivity of a lake as measured by phosphorus content, chlorophyll a concentrations, amount (biomass) of aquatic vegetation, algal abundance, and water clarity.  Also see eutrophic and oligotrophic.
The "cloudiness" of water; the reduction in transparency in water due to the presence of suspended particles (sediments).


Unconfined Aquifer
An aquifer that is not overlain by a layer of impermeable rock or soil. Water in a well will naturally stay at the level of the water table.
Underground Storage Tank (UST)
A tank located at least partially underground and designed to hold gasoline or other petroleum products or chemicals. Also see leaking underground storage tank.
Universal Waste
The general term for certain common hazardous wastes, such as batteries, some pesticides, thermostats, and spent fluorescent lamps.  The Universal Waste Rule allows these wastes to be managed under streamlined requirements. The rule encourages recycling and proper disposal to reduce the regulatory burden on businesses that generate these wastes.
Unsaturated Zone
The underground area above the water table where air fills most of the spaces in the soil and rock, although some water may be present. Also see vadose zone.
Use Attainability Analysis (UAA)
A tool used to potentially change the designated use of a water body if it is shown that the use is not attainable.  It is a structured scientific assessment of the beneficial uses a water body could support, given application of required effluent limits and implementation of cost-effective and reasonable best management practices.
Used Oil
Any oil that has been refined from crude or synthetic oil and has been used as a lubricant, electrical insulation oil, hydraulic fluid, heat transfer oil, brake fluid, refrigeration oil, grease, or machine cutting oil.  Used oil does not include used oil mixed with hazardous waste except for in specific instances, petroleum and synthetic based-products used as solvents, antifreeze, wastewater from which the oil has been removed, or oil-contaminated media or debris.


Vadose Zone
An underground unsaturated region between the soil surface and the water table. 
Valley Fill Aquifer
An aquifer generally found in intermountain valleys where sediments and rocks were loosely deposited a long time ago by air, water, or glacial activity on the earth's surface. As more material was deposited on top, these sediments and rocks generally remained loosely packed with many spaces to hold water. One example of a valley fill aquifer is the Spokane Valley-Rathdrum Prairie Aquifer located in north Idaho.
Visible Emissions
Particulate air emissions from a facility (e.g., smoke, dust, fumes) ranging in size from 0.1 micrometer to 200 micrometers in diameter (for reference, the average human hair is 70 micrometers in diameter).
Volatile Organic Compounds (VOCs)
Organic compounds in the air that combine with other pollutants to form ozone and fine particulate matter. They are common in household and industrial products, such as paints and varnishes, solvents, and fuels.


Warning Letter
An informal tool for gaining compliance with environmental regulations without resorting to a more formal method such as a notice of violation. A warning letter informs the responsible party of apparent deficiencies or violations and requests corrective actions within a certain time.
Any material (solid, liquid, or contained gas) that is discarded, recycled, reused, or considered inherently waste-like.
Wasteload Allocation (WLA)
The portion of receiving water's loading capacity that is allocated to one of its existing or future point sources of pollution.  Wasteload allocations specify how much pollutant each point source may release to a water body.  Also see load allocation.
Spent or used water, such as from households and businesses, that contains enough harmful material to damage the water's quality. Every building with running water generates some sort of wastewater.
Wastewater-Land Application
One option for treating and disposing of wastewater. Wastewater is applied to land for irrigation and is absorbed by the crop or assimilated into the soil.  It is a natural way of recycling the water.  Anyone wishing to land-apply wastewater must obtain a wastewater-land application permit.  Also see land application.
Wastewater Planning Grant Program
A program that provides financial assistance to entities in Idaho planning to upgrade public wastewater facilities.
Wastewater Treatment Plant
A facility containing a series of tanks, screens, filters and other processes by which pollutants are removed from water.
Wastewater Treatment System
A system for disposing of wastewater.  There are generally two types of systems: centralized and decentralized. Centralized systems are "public sewer systems" and usually serve established towns and transport wastewater to a central location for treatment. Decentralized systems are systems that do not connect to a public sewer system. They may treat wastewater on-site or may discharge to a private treatment plant.
Water Body
A stream, river, lake, estuary, coastline, or other water feature, or portion thereof.
Water Body Assessment
An appraisal of a water body's support of beneficial uses.
Water Body Assessment Guidance (WBAG)
A document that describes DEQ's methods for evaluating data and determining beneficial use support of Idaho water bodies.
Water Body Identification Number (WBID)
A number that uniquely identifies a water body in Idaho and ties in to Idaho's water quality standards and GIS information.
Water Column
The entire depth of a water body, from its surface to the bottom.
Water Pollution
Any alteration of the properties of water or the discharge of any pollutant into water which will or is likely to create a nuisance or to render the water harmful to public health, safety, or welfare; to fish and wildlife; or to domestic, commercial, industrial, recreational, aesthetic, or other beneficial uses.
Water Pollution Control State Revolving Loan Fund
A fund to provide below-market-rate interest loans to help build new or repair existing wastewater treatment facilities. Eligible facilities include treatment plants, interceptor sewers, and collector sewers.
Water Quality
A term for the combined biological, chemical, and physical characteristics of water with respect to its suitability for a beneficial use.
Water Quality Criteria (Criteria)
In the context of water quality, a narrative or numeric statement of water quality on which to base judgment of suitability of a beneficial use.
Water Quality Limited
A label that describes water bodies for which one or more water quality criteria are not met or beneficial uses are not fully supported. 
Water Quality Limited Segment (WQLS)
Any segment placed on a state's §303(d) list for failure to meet applicable water quality standards, and/or is not expected to meet applicable water quality standards in the period prior to the next list.  These segments are also referred to as "§303(d) listed."
Water Quality Management Plan
A compilation of the guidance and programs DEQ uses to implement the Clean Water Act and developed in accordance with act. 
Water Quality Modeling
The prediction of the response of some characteristics of lake or stream water based on mathematical relations of input variables such as climate, stream flow, and inflow water quality. Also see model. 
Water Quality Standards
State-adopted and EPA-approved ambient standards for water bodies.  The standards prescribe the use of the water body and establish the water quality criteria that must be met to protect designated uses.
Water Table
The upper surface of ground water; below this point, the soil is saturated with water.
A region or area drained by surface or ground water flows.  Watersheds are infinitely nested, and any large watershed is composed of smaller subwatersheds.
Watershed Adivisory Group (WAG)
A group of citizens that provides local input and guidance on a specific watershed, mainly during the development and implementation of a TMDL.
Wellhead Protection
A program established under the 1986 amendments to the Safe Drinking Water Act, with the goal of minimizing the likelihood of contamination to public water systems supplied by ground water. In general, wellhead protection has been replaced by drinking water protection. 
An area that at least some of the time is saturated by surface or ground water.  Examples include swamps, bogs, and marshes. 
Wetted Width
The width of a water surface measured perpendicular to the direction of flow.
Width: Depth Ratio
An index of the cross section shape of a stream channel at bankfull level.
Wood Debris Facility (Mill Yard Debris Facility)
A facility that manages exclusively solid wood, bark, or wood fiber generated from wood product manufacturing.


Young of the Year
Young fish born the year captured; seen as evidence of spawning activity.