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A Glossary of Water-Related Terms A

A Glossary of Water-Related Terms A

publication 442-758 A Glossary of -Related Terms Brian Benham, Assistant Professor and Extension Specialist, Department of Biological Systems Engineering, Virginia Tech

The definitions and associated explanations of water-related terms presented here are intended to provide the reader with a working knowledge of terms that apply to Virginia’s . The list is designed to assist the user in understanding and interpreting water related information that may come from sources as varied as governmental agencies, environmental groups, or the news media. While terms and definitions are fairly consistent, some termi- nology presented here could be defined differently to describe water resources issues in other locations.

Advection – the process by which chemicals and heat A are transported along with the bulk motion of flowing Absorption –the process by which chemicals in - gas or liquid. For example, moves through eous, liquid or phases are incorporated into and and aquifer formations due predominantly to advection included within another gas, liquid, or solid chemical. (the bulk movement of water). For example, a sponge absorbs water. Algal bloom – large, visible masses of algae that develop in bodies of water during warm weather. Algal mine drainage –water draining from areas blooms are the result of excessive levels of nutrients that have been mined for coal or other ores. (generally or ) in water. The drainage water is acidic, sometimes having a pH less than 2.0, because of its contact with sulfur-bearing – Anion – a negatively charged . Nitrate (NO3 ) and . (Cl–) are examples of anions. Acid rain – precipitation that has a low pH (here, low Anion exchange – the chemical process where nega- pH is defined as anything less than 5.6). The precipi- tive of one chemical are preferentially replaced by tation becomes acidic when moisture in the air reacts negative ions of another chemical. In , with sulfur and nitrogen pollutants in the . the net effect is the removal of an unwanted ion from a . For example, some water treatment facili- Acre-foot – the of water required to cover an ties or homeowners install an anion exchange system to area of one acre of land with 12 inches (1 foot) of water – remove nitrate (NO3 ) from their water supplies. depth. One acre-foot equals 325,851 gallons of water. Aquifer – a geologic formation that holds and yields Activated – A material produced by heating usable amounts of water. The water in an aquifer is coal or in such a manner as to a porous struc- called groundwater. Aquifers may be categorized into ture, creating a very large internal surface area. Acti- confined aquifers and unconfined aquifers. vated carbon filters are widely used to adsorb organic compounds from water and wastewater and to remove Aquifer (confined) – an aquifer whose upper and and odors from drinking water. lower, boundary is defined by a layer of natural material that does not transmit water readily. Water is “confined” Adsorption – the attachment of gas , ions, under similar to water in a pipeline. Drilling a or to the surface of . For example, odors well into this type of aquifer is analogous to puncturing from freezers and refrigerators are adsorbed to baking a pressurized pipeline. In some areas confined aquifers soda. produce water without (flowing artesian well).

www.ext.vt.edu Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 2009 Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension , Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Rick D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg. Aquifer (unconfined) – an aquifer whose upper pollution by fecal material and the presence of patho- boundary consists of a relatively porous material that genic bacteria that can cause diseases such as intestinal transmits water readily from the ground surface. The infections, dysentery, hepatitis, typhoid fever and chol- water level in an unconfined aquifer is the water table. era. Generally reported as colonies or colony forming units (cfu) per 100 milliliters (ml) of sample. (see fecal coliform)

B Concentration – the amount of a given chemical or Bank – the margins of a stream or river channel. Banks pollutant in a particular volume or weight of air, water, are called right or left as viewed facing downstream, in , or other medium – often expressed as milligrams the direction of the flow. per liter (mg/l) or parts per million (ppm).

Baseflow – that part of streamflow derived from Cone of depression – the lowering in groundwater groundwater flowing into a stream or river. levels around a well in response to groundwater with- drawal (the pumping of water). The extent of the cone Biosolids – an organic material resulting from the of depression defines the area of influence of a well. treatment of wastewater, often applied to the land as an amendment. In Virginia, land application of biosol- Consumptive use – the total amount of water taken ids or sewage sludge is regulated through the “Nutrient up by vegetation for and/or building of Management Program” administered by the Virginia plant tissue, plus any associated, unavoidable evapora- Department of Conservation and Recreation. tion of .

Brook – a natural stream of water, smaller than a river Contaminant – an undesirable substance not normally or creek; especially a small stream that breaks directly present, or an usually high concentration of a naturally- out of the ground, as from a spring or seep. occurring substance, in water, soil, or other environ- mental medium. In more restricted usage, a substance C in water that may be harmful to human health. Creek – small stream of water which serves as the Capillary fringe – a zone of partially saturated soil just natural drainage course for a drainage basin; a flowing above the water table. The depth of the fringe depends stream normally smaller than a river and larger than a upon the size and distribution of the pore spaces within brook. The term is often relative according to size and the soil media. locality. Cation – a positively charged ion. For example, cal- Cubic feet per second (cfs) – a rate of the flow. cium (Ca+2) and (Mg+2) are cations. One cfs is equal to a volume of water one foot deep Cation exchange – a process where positively and one foot wide flowing a distance of one foot in one charged ions of one chemical are preferentially replaced second. One cfs is equal to approximately 450 gallons by positive ions of another chemical. For example, per minute (gpm). water softeners replace Ca+2 and Mg+2 ions with +2 (Na ) ions. D Channel (watercourse) – an open conduit either Depression storage – the volume of water con- naturally or artificially created that periodically or con- tained in natural depressions on the land surface, such tinuously contains moving water, or which forms a con- as puddles. necting link between two bodies of water. River, creek, stream, run, reach, branch, and tributary are some of the – a process where chemicals or heat move terms used to describe natural channels. in response to differences in chemical concentration or gradient. Movement is from high concen- Coliform bacteria – A group of nonpathogenic organ- tration (or temperature) to low concentration (or tem- isms (Colon bacilli) usually found in the digestive tract perature). This process could involve liquids, , of all warm-blooded animals and humans. The presence and solids. of coliform bacteria in water is an indicator of possible

2 Discharge area – an area or position where ground- water is delivered to the ground surface. Groundwater E can flow as springs or seeps, or contribute baseflow to Effluent – (1) something that flows out or forth, espe- streams or rivers. cially a stream flowing out of a body of water. (2) dis- charged wastewater such as the treated wastes from Discharge – the volume of water that passes a given animal production facilities, industrial facilities, or point during a given period. It is an all-inclusive out- plants. flow term, describing a variety of flows such as from a to a stream, or from a stream or river to a lake or Ephemeral stream – a stream that flows in response . to runoff producing precipitation events and thus dis- continuing its flow during dry seasons. Such flow is – the spreading and mixing of chemical usually of short duration. constituents in both surface and groundwaters caused by diffusion and mixing due to microscopic variations Estuarine – deepwater tidal habitats and in and velocities. tidal wetlands that are usually enclosed by land but have access to the ocean and are at least occasionally – the separation of different substances in diluted by freshwater runoff from the land (such as a by off those of a lower bays, mouths of rivers, marshes). first. For example, water can be distilled and the condensed back into a liquid that is almost pure water. Erosion – the detachment and transport of soil par- remain in the concentrated residue. Distilla- ticles by water and wind. Sediment resulting from soil tion can be used to remove inorganic chemicals, some erosion represents the single largest source of nonpoint nonvolatile organic chemicals, and bacteria. source pollution in the United States.

Doctrine of Prior Appropriation – system for allo- Eutrophication – the process of nutrient enrichment cating water to private individuals used in most western causing a water body to fill with aquatic plants and states. The prior appropriation doctrine is based on the algae. Eutrophic lakes often are undesirable for recre- concept of “First in Time, First in Right.” The first per- ation and may not support normal populations. son to take a quantity of water and put it to “beneficial use” has a higher priority of right than a subsequent user. – the process by which a liquid is trans- The right of appropriation is generally acquired by fil- formed to the gaseous state. ing a claim in accordance with state laws. Under drought Evapotranspiration (ET) – the process of transform- conditions, higher priority users are satisfied before ing soil water into water through the combination junior users receive water. Appropriative rights can be of evaporation from the soil surface and plant water use lost through nonuse; they can also be sold or transferred (transpiration). apart from the land. Contrast with Riparian Doctrine.

Domestic water use – water used for household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and water- F ing lawns and gardens. About 85% of domestic water is Fecal coliform – a portion of the coliform bacte- delivered to U.S. homes by a public-supply facility, such ria group originating in the intestinal tract of warm- as a county water department. About 15% of the nation’s blooded animals that passes into the environment in population obtains their domestic water from wells. feces. Fecal coliform often is used as an indicator of the bacteriological safety of a water supply. Generally Drawdown – the distance between the static water reported as colonies or colony forming units (cfu) per level in well and the surface of the cone of depression. 100 milliliters (ml) of sample. (see coliform bacteria)

Drainage – (1) the natural movement of surface water Field capacity – the amount of water a saturated over a land area to a river, lake or ocean (surface drain- soil contains after rapid internal drainage has ceased age), (2) removal of water from a soil using buried (approximately 2 days). pipelines that are spaced regularly and perforated (sub- surface drainage).

3 Flood – a temporary condition of partial or complete Health advisory level (HAL) – a nonregulatory, inundation of normally dry land areas from the over- health-based, chemical concentration in drinking water flow of inland or tidal waters or from the unusual and that results in no adverse health risks when ingested rapid accumulation of runoff, an overflow or inunda- over exposure periods ranging from one day to a tion that comes from a river or other body of water. lifetime.

Floodplain – land area adjacent to a river or stream Hydraulic conductivity – a term used to describe that can be covered by water when a river or stream the ease with which water moves through soil or a satu- overflows its banks. The extent of the flood plain rated geologic material. depends on topography and the magnitude of a given flood event. Hydraulic gradient – the slope of the water sur- face in an aquifer. The hydraulic gradient indicates the direction of groundwater flow. Water always flows from higher elevations to lower elevations. All other G factors being equal, flow is greater when the hydraulic Gaining stream – a stream or portion of a stream gradient is steeper. where flow increases because of discharge into the stream from groundwater. Hydrologic cycle – describes the constant move- ment of water above, on, and below the ’s surface. Groundwater (sometimes written as two words) Processes such as precipitation, evaporation, condensa- – water that fills voids, cracks, or other spaces between tion, infiltration, and runoff comprise the cycle. of clay, silt, sand, gravel or rock within a saturated zone or formation (aquifer) below the soil surface. I Groundwater mining – the removal of groundwater Infiltration – the downward entry of water through the from an aquifer in excess of the rate of natural or arti- soil surface. ficial recharge. Continued groundwater mining reduces the groundwater supply until it is no longer an econom- Infiltration rate – the quantity of water that enters the ical source of water. soil surface in a specified time interval. Often expressed as a volume per unit of soil surface per unit of time Groundwater recharge – the process where water (in3 per in2 per hour). Soil surface wetness, soil texture, enters the soil surface and eventually reaches the sat- residue cover, precipitation rate, irrigation application, urated zone. Recharge varies from place to place due topography, and other factors control the infiltration to the amount of rainfall, infiltration rate, and surface rate. vegetation. Irrigation – the controlled application of water to ara- ble lands to supply crop water requirements not satis- H fied by rainfall. Hardness (water) – a measure of the amount of dis- solved (Ca) and magnesium (Mg) in water. Hardness is often reported as ppm or milligrams per K Karst topography – a type of topography that is liter (mg/l) of CaCO3. If hardness is reported in grains per gallon, one grain per gallon of hardness equals 17.1 formed on limestone, gypsum, and other rocks by dis- solution, and is characterized by sinkholes, caves, and ppm of hardness as CaCO3. Hard water can produce scale deposits in pipes and water heaters. Additionally, underground drainage. compared to soft water, hard water requires that addi- tional and detergents be used to produce or lather. Hardness scale: Soft – 0-60 mg/l; Moderately L Hard – 61-120 mg/l; Hard – 121-180 mg/l; and Very Lake – A considerable body of inland water or an Hard – over 180 mg/l. expanded part of a river.

4 – the removal of dissolved chemicals from soil caused by the movement of a liquid (like water) N through the soil. Nitrate – an inorganic nitrogen compound. Nitrate may be naturally present in water, but high concentra- Limiting factor – any factor such as temperature, tions (greater than 2 or 3 ppm) are most likely due to light, water, or chemical that limits the existence, fertilizer runoff, livestock facilities, sanitary wastewa- growth, abundance, or distribution of an organism. For ter discharges, and/or atmospheric deposition (nitrate example, an increase in phosphorus loading to a lake, dissolved in precipitation). High levels of nitrate in stream, or river can trigger the growth of algae. drinking water (greater than 10 mg/l) are associated with methemoglobinemia and possibly an increased Losing stream – a stream or portion of a stream that risk for some cancers. discharges water into the groundwater, resulting in a smaller flow volume within the stream. Nonpoint source pollution (NPS) – pollution originating from diffuse sources on the landscape. Examples include runoff from fields receiving manure M applications, stormwater runoff from urban landscapes, or roadbed erosion in forestry. It has been estimated Maximum contaminant levels (MCLs) – high- that NPS pollution accounts for more than one-half of est level of a contaminant in drinking water that the the in the United States today. Environmental Protection Agency (EPA) has deter- mined will not endanger human health over a lifetime Nutrient – (1) an element or compound essential to of exposure. The EPA sets MCLs at levels that are eco- life, including carbon, , nitrogen, phosphorus, nomically and technologically feasible. People - and many others; (2) as a pollutant, any element or com- ing a typical amount of water per day (two liters for pound, such as phosphorus or nitrogen that in excessive adults, one for children) during their average lifetime amounts contributes to abnormally high organic growth (70 years) should not be endangered by ingesting a in aquatic ecosystems. contaminant at or below the MCL. For example, the

MCL for nitrate-nitrogen (NO3-N) is 10 milligrams per liter of water (mg/l). P Maximum Contaminant Level Goal (MCLG) – as Part per million (ppm) – a measure of concentration set by the EPA, the level of a contaminant in drinking of a dissolved material in terms of a mass ratio (mil- water at which there would be no risk to human health. ligrams per kilogram, µg/kg). For water analysis, part This goal is not always economically or technologi- per million often is presented as a mass per unit volume cally feasible, and the goal is not legally enforceable. (milligrams per liter, µg/l), 1 ppm = 1 mg/l.

Micrograms per liter (µg/l) – a measure of concen- Part per billion (ppb) – a measure of concentration tration. One thousand micrograms per liter is equiva- of a dissolved material in terms of a mass ratio (micro- lent to 1 milligram per liter. Micrograms per liter is grams per kilogram, mg/kg). For water analysis, part equivalent to parts per billion (ppb) per million often is presented as a mass per unit vol- ume (micrograms per liter, mg/l). There are one billion Milligrams per liter (mg/l) – a measure of concen- micrograms of water in one liter. tration. In very dilute solutions, 1 mg/l is equivalent to 1 part per million (ppm). Perched water table – water that occurs underground when a low permeability material, located above the Methemoglobinemia (blue baby syndrome) – a water table, blocks or intercepts the downward flow of condition that limits the oxygen-carrying capacity of water from the land surface. Water accumulates above red blood cells. The resulting oxygen starvation causes the impermeable material, creating a saturated zone. a bluish discoloration of the body. The condition is largely confined to infants less than 9 months old. To Percolation – the movement of water through sat- prevent methemoglobinemia, the EPA has set a nitrate- urated soil layers, often continuing downward to nitrogen (NO3-N) MCL of 10 part mg/l for public water groundwater. supplies.

5 Permeability – a measure of the ease with which liq- Porosity - the ratio of the volume of open spaces or uids or gases will move through soil or other porous voids to the total volume of a material. For example, a material. Permeability is a characteristic of the soil sand and gravel deposit may have 20 % porosity. Poros- media and does not depend on the type of being ity determines the amount of water that can be stored transmitted. in a saturated formation. A saturated formation 100 feet thick with a porosity of 20 % could store an equivalent pH – a numerical measure of acidity or alkalinity. The water depth of approximately 20 feet. pH scale ranges from 1 (acidic) to 14 (alkaline). A pH of 7 is neutral. Potable water supply – a source of water that is of adequate quality to be used for human consumption. Point-of-entry (POE) treatment – the treatment of Precipitate – a solid that has been deposited from an all water entering a house, farmstead or other facility. aqueous solution. For example, precipitates from Anion exchange is an example of POE treatment to groundwater to form a rust colored solid when exposed remove nitrate. to air.

Point-of-use (POU) treatment – treatment of water Precipitation – rain, sleet, snow, or hail that falls to at the point it is used. A common example would be the earth as the result of condensing in the water treatment at the kitchen sink for drinking and atmosphere. uses. , distillation and ozona- tion are examples of POU treatment methods. Pumping water level – The water level in a well when the is operating and water is being withdrawn. Point source pollution – pollutant loads discharged at a specific location from pipes, outfalls, and convey- ance channels. Point source discharges are generally regulated through the National Pollution Discharge R Elimination System (NPDES) permitting procedures Recharge area – the area where water predominantly established by the EPA. Point sources can also include flows downward through the unsaturated formation pollutant loads contributed by tributaries to the main (zone) to become groundwater. receiving stream or river. Reference dose (RFD) – the maximum daily expo- Pollutant – any substance of such character and in sure to a chemical that is judged to be without risk of such quantities that when it reaches a body of water adverse systemic health effects over a person’s lifetime; the effect is to degrade the receiving water perhaps to formerly called the Acceptable Daily Intake. a point rendering it unfit for some specified designated use. Reservoir – a pond, lake, tank, or basin (natural or human made) where water is collected and stored. Large Pollution – alteration of the physical, biological, bodies of groundwater are called groundwater reser- chemical, and radiological integrity of water due to voirs; water behind a dam is also called a reservoir. human activities – any unwanted contaminating prop- erty that renders a water supply unfit for its designated Return period – the average elapsed time between use. occurrences of a hydrologic event with a specified mag- nitude or greater. For example, a 100-year discharge Polychlorinated biphenyls (PCBs) – a group of measured on a given river is equaled or exceeded, on synthetic, toxic, industrial chemical compounds once average, once every 100 years. This does not mean that used in making and electrical transformers, which the 100-year discharge occurs once every 100 years, are chemically inert and not biodegradable. PCBs were but that the average time between events of that mag- frequently found in industrial wastes, and subsequently nitude or greater is 100 years. Stated another way, there found their way into surface and ground waters. As a is a 1% chance of a discharge equal to or greater than result of their persistence, they tend to accumulate in the 100-year flood event occurring in any given year. the environment. In streams and rivers, PCBs can attach to bottom sediment and can remain there indefinitely. Reverse osmosis (RO) – a water treatment pro- Although banned in 1979, PCBs continue to appear in cess used to remove dissolved inorganic chemicals the flesh of fish and other animals. and suspended particulate from a water supply.

6 Water, under pressure, is forced through a semiperme- able that removes molecules larger than the S pores of the membrane. Saturated formation – the portion of a soil profile or geologic formation where all voids, spaces or cracks Riparian – pertaining to the banks of a river, stream, or are filled with water. No air is present. (seeaquifer ) other typically, flowing body of water as well as to plant and animal communities along such bodies of water. This Saturated thickness – the total thickness of a satu- term is also commonly used for other bodies of water, rated formation. e.g., ponds, lakes. Sediment – in the context of , soil par- Riparian Doctrine – states that persons who own land ticles, sand, and dislodged from the land and adjacent to a stream have the right to make reasonable deposited into aquatic systems as a result of erosion. use of the stream’s flow on riparian lands, defined to be individual tracts in contact with the stream. Portions Shock chlorination – the addition of for of such tracts extending outside the watershed are gen- disinfecting a water supply system including the well erally considered nonriparian. Riparian rights, which and all distribution pipelines. Shock chlorination is rec- apply to lakes and streams alike, are similar from state ommended when coliform bacteria are detected, or after to state but differ in some of the details due to alterna- system repairs. Treated water, with a free chlorine con- tive interpretations by the state courts. Riparian users of centration of at least 200 ppm, is pumped throughout a stream share the streamflow among themselves, and the distribution system and allowed to set for at least 24 the concept of priority of use (Doctrine of Prior Appro- hours before flushing with nonchlorinated water. priation) is not applicable. Under drought conditions, Specific capacity – a measure of the productivity riparian rights users share shortages. Enforcement of of a well. Specific capacity is obtained by dividing the the riparian doctrine requires a lawsuit by a holder of well discharge rate (gallons per minute) by the well riparian rights who is injured by the water use of another drawdown (feet) while pumping. party. This fact, together with the absence of adminis- trative agency jurisdiction, means that nonriparian and Spring – a point of natural groundwater discharge to other water uses not recognized by the doctrine often the ground surface into a brook, stream, river, or lake. occur in riparian states through use of surplus water not needed to satisfy riparian rights, perhaps by means of Static water level – the water level in a well drilled reservoirs that impound water during periods of higher in an unconfined aquifer when the pump is not operat- flow. Although riparian rights can be severed from the ing. The static water level is the surface of the water- riparian land, rights with respect to transfer for use on bearing formation and typically is synonymous with nonriparian land have not been well defined in most the water table. states. Reliance on the doctrine of riparian rights for water allocation has declined substantially in recent Stream – a general term for a body of flowing water; decades as many of the eastern states have replaced natural water course containing water at least part of it with administration permitting programs based on the year. state-specific, water allocation legislation. Sublimation – the direct change of a solid to a vapor River – A natural stream of water of considerable vol- without the appearance of a liquid, as in the changing ume, larger than a brook or creek. of snow directly into water vapor without

River basin – the area drained by a river and its tribu- taries. (see watershed) T Runoff – that part of rainfall or snowmelt that does Transpiration – the physiological process by which not infiltrate the soil but flows over the land surface water vapor escapes from a living plant, principally toward a surface drain, eventually making its way to a through the leaves, and enters the atmosphere. stream, river, lake or an ocean. It can carry pollutants into receiving waters. Transmissivity – the capacity of an aquifer to transmit water. It is dependent on the water-transmitting charac- teristics of the saturated formation (hydraulic conduc-

7 tivity) and the saturated thickness. For example, sand Water table – the upper level of a saturated formation and gravel formations typically have greater hydraulic where the water is at . The water conductivities than sandstone formations. The sand and table is the upper surface of an unconfined aquifer. gravel will have a greater transmissivity if both forma- tions are the same thickness. Water quality standards – a group of statements that constitute a regulation describing specific water Total dissolved solids (TDS) – a measure of the quality requirements. In Virginia, water quality stan- concentration of dissolved inorganic chemicals in dards must have at least the following three compo- water. TDS can be measured indirectly by how water nents: designated uses, water quality criteria to protect conducts electricity. A water quality analysis will designated uses, and an antidegredation policy. Every sometimes report electrical conductivity (EC), usually state is required to develop water quality standards and in units of micromhos per centimeter (µmho/cm). To revise them periodically. estimate parts per million (ppm) of dissolved solids multiply the EC reading in µmho/cm by 0.64. Dis- Designated uses – those uses specified in water solved solids commonly found in Virginia are calcium, quality standards for each water body or seg- magnesium, sodium, , bicarbonate, , ment whether or not they are being attained. All chloride and silica. Virginia waters are designated for the following uses: recreational uses, e.g., swimming and boat- Turbidity – a measure of the cloudiness or opaque- ing; the propagation and growth of a balanced, ness of the water expressed in nephelometric turbidity indigenous population of aquatic life, including units (ntu). The turbidity is influenced by the amount game fish, which might reasonably be expected and nature of suspended organic and inorganic material to inhabit them; wildlife; and the production of in water. Typically, higher concentrations of the sus- edible and marketable natural resources, e.g., pended material equal greater turbidity. The source of fish and shellfish, generally stated as fishable turbidity could be sediment (fine sand, silt, and clay), and swimable. Through the protection of these organic material, particles of iron and manganese or minimum uses, other uses such as industrial other , rust from corroding , algae, water supply, irrigation and navigation also are precipitates, etc. protected.

Water quality criteria – include general narrative statements that describe good water quality and U specific numerical concentration limits that are Unsaturated zone – that part of the soil profile in known to protect aquatic life and human health. which the voids are not completely filled with water, These numerical and narrative criteria describe some air is present. water quality necessary to protect designated uses. V Antidegradation policy – Virginia’s antidegrada- tion policy protects water quality at three levels Vadose zone – zone of unsaturated soil that extends or “tiers.” Tier 1 specifies that existing instream from the soil surface to the groundwater table. water uses and the level of water quality to pro- tect the existing uses shall be maintained and pro- tected. This means that, as a minimum, all waters W should meet adopted water quality standards. Watershed – area that drains or contributes water to Tier 2 protects water that is better than specified a particular point, stream, river, lake or ocean. Water- water quality standards. Only in limited circum- sheds are also referred to as basins. Watersheds range in stances may water quality be lowered in these size from a few acres for a small stream basin, to large waters. Tier 3 are exceptional waters where no areas of the country like the Chesapeake Bay Basin that new, additional or increased discharge of sewage, includes parts of six states. (see river basin) industrial wastes or other pollution are allowed. These waters must be specifically listed in the regulation.

8 Well – (water) any artificial excavation constructed for the purpose of exploring for or producing groundwater

Water year – in U.S. Geological Survey (USGS) reports dealing with surface-water supply, the 12-month period, October 1 through September 30. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the year ended September 30, 1960, is called the “1960 water year.”

Wetlands – transitional lands between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is covered by shallow water. Wetlands are those areas where water saturation is the dominant factor determining the nature of soil development and the types of plant and animal com- munities living in the surrounding environment.

Acknowledgments The author would like to express appreciation for the review and comments provided by these Virginia Tech colleagues: Mary Leigh Wolfe, Associate Professor, Biological Systems Engineering; Lori Marsh Exten- sion Specialist and Associate Professor, Biological Systems Engineering; Kevin Brannan, Research Asso- ciate, Biological Systems Engineering; Tamim Younos, Associate Director, Virginia Water Resources Research Center; and Eric Bendfeldt, Extension Agent, Rocking- ham Co.

References ASAE. 1998. S526.1 soil and water terminology. ASAE Standards 1998. American Society of Agricultural Engineers, St. Joseph, MI, 49085. Driscoll, F.G., 1986. Groundwater and wells. Johnson Screens, St. Paul, Minnesota, 55112. Haan, C.T. 1991. Statistical methods in . Iowa State University Press, Ames, Iowa 50010. Horton, G.A, Water words dictionary, 1999, Nevada Division of Water Planning, Department of Con- servation and Natural Resources, Carson City, NV 89706-7921 Kranz, W., D.G. Gosselin, D. Hay, J. Goeke. 1993. Glossary of water-related terms, NebGuide – G93- 1191. University of Nebraska Cooperative Exten- sion, Lincoln, NE, 68588.

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