Water Quality in the Las Vegas Valley Area and Carson and Truckee River Basins, Nevada and California, 1992-96

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The terms in this glossary were compiled from numerous resources. Some definitions have been modified and may not be the only valid ones for these terms.

The dissolving or blending of a metal (commonly gold and silver) in mercury to separate it from its parent material. As related to fish, externally visible skin or subcutaneous disorders, including deformities, eroded fins, lesions, and tumors.

Aquatic-life criteria
Water-quality guidelines for protection of aquatic life. Often refers to U.S. Environmental Protection Agency water-quality criteria for protection of aquatic organisms.

A water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to a well.

Artificial recharge
Augmentation of natural replenishment of ground-water storage by some method of construction, spreading of water, or by pumping water directly into an aquifer.

Background concentration
A concentration of a substance in a particular environment that is indicative of minimal influence by human (anthropogenic) sources.

Basic Fixed Sites
Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and trace elements, nutrients, and organic carbon to assess the broad-scale spatial and temporal character and transport of inorganic constituents of streamwater in relation to hydrologic conditions and environmental settings.

Basin area
Areas that do not receive adequate precipitation for ground-water recharge and streamflow. These areas can receive recharge and streamflow from upstream headwater areas.

Basin and Range physiography
A region characterized by a series of generally north-trending mountain ranges separated by alluvial valleys.

General term for consolidated (solid) rock that underlies soils or other unconsolidated material.

Benthic invertebrates
Insects, mollusks, crustaceans, worms, and other organisms without a backbone that live in, on, or near the bottom of lakes, streams, or oceans.

Bottom (bed) sediment
The material that temporarily is stationary in the bottom of a stream or other watercourse.

Bottom sediment and tissue studies
Assessment of concentrations and distributions of trace elements and hydrophobic organic contaminants in streambed sediment and tissues of aquatic organisms to identify potential sources and to assess spatial distribution.

Carbonate rocks
Rocks (such as limestone or dolostone) that are composed primarily of minerals (such as calcite and dolomite) containing the carbonate ion (CO32-).

Modification of a stream, typically by straightening the channel, to provide more uniform flow; often done for flood control or for improved agricultural drainage or irrigation.

Chlorinated solvent
A volatile organic compound containing chlorine. Some common solvents are trichloroethylene, tetrachloroethylene, and carbon tetrachloride.

Confining layer
A layer of sediment or lithologic unit of low permeability that bounds an aquifer.

The flowing together of two or more streams; the place where a tributary joins the main stream.

Consolidated rock
Metamorphic, sedimentary, or igneous (granitic or volcanic) rock that typically form mountainous uplands and underlie unconsolidated deposits in valleys.

A chemical or biological substance in water, sediment, or biota that can be measured by an analytical method.

Degradation of water quality compared to original or natural conditions due to human activity.

Degradation products
Compounds resulting from transformation of an organic substance through chemical, photochemical, and (or) biochemical reactions.

Dissolved solids
Amount of minerals, such as salt, that are dissolved in water; amount of dissolved solids is an indicator of salinity.

Drainage basin
The portion of the surface of the Earth that contributes water to a stream through overland runoff, including tributaries and impoundments.

Drinking water advisory
A non-regulatory document that analyzes the available cancer and non-cancer data on a contaminant and recommends acceptable levels.

Endocrine system
The collection of ductless glands in animals that secrete hormones, which influence growth, gender, and sexual maturity.

The addition of an element or chemical compound so that its total concentration is at least 10 percent greater than the concentration at a background site.

Evaporite minerals (deposits)
Minerals or deposits of minerals formed by evaporation of water containing salts. These deposits are common in arid climates.

A collective term that includes water lost through evaporation from the soil and surface-water bodies and by plant transpiration.

Any of a large number of natural or synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its fertility.

Fish community
Fish species that interact in a common area.

Relating to the Earth's internal heat; commonly applied to springs or vents discharging hot water or steam.

Granitic rocks
Coarse-grained igneous rock.

Headwater area
Mountains and adjacent areas where precipitation is adequate to provide ground-water recharge and streamflow.

Human health advisory (HA)
Nonregulatory levels of contaminants in drinking water that may be used as guidance in the absence of regulatory limits. Advisories consist of estimates of concentrations that would result in no known or anticipated health effects (for carcinogens, a specified cancer risk) determined for a child or for an adult for various exposure periods.

Graph showing variation of water elevation, velocity, streamflow, or other property of water with respect to time.

Intensive Fixed Sites
Basic Fixed Sites with increased sampling frequency during selected seasonal periods and analysis of dissolved pesticides for 1 year. Most NAWQA Study Units have one to two integrator Intensive Fixed Sites and one to four indicator Intensive Fixed Sites.

Irrigation drainage
The part of irrigation applied to the surface that is not consumed by evapotranspiration or uptake by plants and that migrates to an aquifer or surface-water body.

A material or constituent in solution, in suspension, or in transport; usually expressed in terms of mass or volume.

Main stem
The principal course of a river or a stream.

Maximum contaminant level (MCL)
Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency.

The average of a set of observations, unless otherwise specified.

The middle or central value in a distribution of data ranked in order of magnitude. The median is known also as the 50th percentile.

Metamorphic rocks
Rocks that have formed in the solid state in response to pronounced changes of temperature, pressure, and chemical environment.

Element or compound essential for animal and plant growth including nitrogen and phosphorus.

Occurrence and distribution assessment
Characterization of the broad-scale spatial and temporal distributions of water-quality conditions in relation to major contaminant sources and background conditions for surface water and ground water.

Organic material
Natural material derived from plants and animals.

Organochlorine compound
Synthetic organic compounds containing chlorine. As generally used, refers to compounds containing mostly or exclusively carbon, hydrogen, and chlorine. Examples include organochlorine insecticides and polychlorinated biphenyls.

Soil or rock overlying a valuable mineral deposit.

A chemical applied to crops, rights of way, lawns, or residences to control weeds, insects, fungi, nematodes, rodents or other "pests."

A class of organic compounds containing an aromatic ring and hydroxyl groups. Phenols are used in the production of phenolic resins, germicides, herbicides, fungicides, pharmaceuticals, dyes, plastics, and explosives.

Phthalate esters
A class of organic compounds containing an aromatic ring, oxygen, and other organic groups. Pthtalates are used as plasticizers, to manufacture products from polymers of vinyl chloride, propylene, ethylene, and styrene.

Polychlorinated biphenyls (PCBs)
A mixture of chlorinated derivatives of biphenyl, marketed under the trade name Aroclor with a number designating the chlorine content (such as Aroclor 1260). PCBs were used in transformers and capacitors for insulating purposes and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979.

Polycyclic aromatic hydrocarbon (PAH)
A class of organic compounds with a fused-ring aromatic structure. PAHs result from incomplete combustion of organic carbon (including wood), municipal solid waste, fossil fuels, and natural or anthropogenic introduction of uncombusted coal and oil. PAHs include benzo(a)pyrene, fluoranthene, and pyrene.

Principal aquifer
Unconsolidated deposits with more than 100 feet of saturated thickness and dissolved solids less than 1,000 mg/L. The primary sources of ground water for public supply and irrigation.

Secondary maximum contaminant level (SMCL)
The maximum contamination level in public water systems that, in the judgment of the U.S. Environmental Protection Agency (USEPA), are required to protect the public welfare. SMCLs are secondary (nonenforceable) drinking- water regulations established by the USEPA for contaminants that may adversely affect the odor or appearance of such water.

Particles, derived from rocks or biological materials, that have been transported by a fluid or other natural process, and are suspended or settled in water.

Sedimentary rocks
Rocks formed by the accumulation of sediment in water or from air.

Sediment quality guideline
Threshold concentration above which there is a high probability of adverse effects on aquatic life from sediment contamination, determined using modified USEPA [44] procedures.

Semipermeable membrane device
Passive sampling devices for organochlorine and semivolatile organic compounds. They are low-density polyethylene tubes filled with fish lipid. The fish lipid sequesters dissolved compounds from water.

Semivolatile organic compound (SVOC)
Operationally defined as a group of synthetic organic compounds that are solvent-extractable and can be determined by gas chromatography/mass spectrometry. SVOCs include phenols, phthalate esters, and polycyclic aromatic hydrocarbons (PAHs).

Shallow water-table aquifer
Unconsolidated deposits containing water whose surface is at atmospheric pressure. In the Study Unit, these aquifers are not typically used as public supply.

Populations of organisms that may interbreed and produce fertile offspring having similar structure, habits, and functions.

Stream reach
A continuous part of a stream between two specified points.

Study-Unit Survey
Broad assessment of the water-quality conditions of the major aquifer systems of each Study Unit. The Study-Unit Survey relies primarily on sampling existing wells and, wherever possible, on existing data collected by other agencies and programs. Typically, 20 to 30 wells are sampled in each of three to five aquifer subunits.

Compression of soft aquifer materials in a confined aquifer due to pumping of water from the aquifer. Subsidence has occurred in Las Vegas Valley within the Study Unit.

Sulfide mineral
A mineral with reduced forms of sulfur usually combined with another element such as iron (pyrite, FeS2). Sulfide minerals often produce sulfuric acid when exposed to the atmosphere and water.

Synoptic study
A short-term investigation of specific water-chemistry or ecological conditions during selected seasonal or hydrologic conditions to provide improved resolution for critical water-quality conditions.

Synthetic organic compounds
Compounds that are manmade and contain carbon. Common synthetic organic compounds are pesticides, volatile organic compounds such as solvents, gasoline components, and trihalomethanes, phenols, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and pthtalate esters.

Rock that remains after processing ore to remove the valuable minerals.

Tertiary-treated sewage
The third phase of treating sewage that removes nitrogen and phosphorus before it is discharged.

Tolerant species
Those species that are adaptable to (tolerant of) human effects on the environment.

Trace element
An element found in only minor amounts (concentrations less than 1.0 microgram per liter) in water or sediment; includes arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.

Triazine herbicide
A class of herbicides containing a symmetrical triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an alternating sequence). Examples include atrazine, prometon, and simazine.

A river or stream flowing into a larger river, stream, or lake.

Trihalomethanes (THM)
A group of volatile organic compounds containing one carbon atom, one hydrogen atom, and three halide (fluorine, chlorine, bromine, and iodine) atoms. Common THMs include chloroform, bromoform, and dichlorofluoromethane. These compounds can be a result of chlorination processes in water-supply wells.

Unconsolidated deposit
Deposit of loosely bound sediment that typically fills topographically low areas. These deposits are common in valleys throughout the Study Unit and typically form principal aquifers when saturated.

Un-ionized ammonia
The neutral form of ammonia in water. The un-ionized ammonia is present as NH4OH in an amount dependent on ammonia concentration, temperature, and pH. As water temperature and pH are increased, the proportion of un-ionized ammonia increases.

Urban drainage
Water derived from runoff or shallow ground-water discharge from urban areas.

Volatile organic compounds (VOCs)
Organic chemicals that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, and some by-products of chlorine disinfection.

Water table
The point below the land surface where ground water is first found and below which the earth is saturated. Depth to the water table varies widely across the country.

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Suggested citation:
Bevans, H.E., Lico, M.S., and Lawrence, S.J., 1998, Water Quality in the Las Vegas Valley Area and the Carson and Truckee River Basins, Nevada and California, 1992-96, on line at <URL:>, updated 19 March 1998

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Last modified: Tue Mar 17 17:53:42 1998