GLOSSARY

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.

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

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

Bed sediment— The material that temporarily is stationary in the bottom of a stream or other watercourse.

Benthic— Of, related to, or occurring on the bottom of a water body.

Community— In ecology, the species that interact in a common area.

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

Criterion— A standard rule or test on which a judgment or decision can be based. Plural, Criteria.

Cubic foot per second (ft³/s, or cfs)— Rate of water discharge representing a volume of 1 cubic foot passing a given point during 1 second, equivalent to approximately 7.48 gallons per second, or 448.8 gallons per minute, or 0.02832 cubic meter per second.

Detection limit— The minimum concentration of a substance that can be identified, measured, and reported within 99 percent confidence that the analyte concentration is greater than zero; determined from analysis of a sample in a given matrix containing the analyte.

Dissolved constituent— Operationally defined as a constituent that passes through a 0.45-micrometer filter.

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

Downgradient— At or toward a location farther from the source of ground-water flow.

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 standard or guideline— A threshold concentration in a public drinking-water supply, designed to protect human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contaminate levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.

Escherichia coli—A common species of intestinal or fecal bacteria.

Fecal bacteria— Microscopic single-celled organisms (primarily fecal coliforms and fecal streptococci) found in the wastes of warm-blooded animals. Their presence in water is used to assess the sanitary quality of water for body-contact recreation or for consumption. Their presence indicates contamination by the wastes of warm-blooded animals and the possible presence of pathogenic (disease producing) organisms.

Intolerant organisms— Organisms that are not adaptable to human alterations to the environment and thus decline in numbers where human alterations occur. See also Tolerant species.

Major ions— Constituents commonly present in concentrations exceeding 1.0 milligram per liter. Dissolved cations generally are calcium, magnesium, sodium, and potassium; the major anions are sulfate, chloride, fluoride, nitrate, and those contributing to alkalinity, most generally bicarbonate and carbonate.

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.

Micrograms per liter (µg/L)— A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter) of water; equivalent to one part per billion in most streamwater and ground water. One thousand micrograms per liter equals 1 milligram per liter.

Milligrams per liter (mg/L)— A unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water; equivalent to one part per million in most streamwater and ground water.

Minimum reporting level (MRL)— The smallest measured concentration of a constituent that may be reliably reported using a given analytical method. In many cases, the MRL is used when documentation for the detection limit is not available.

Modified Hilsenhoff Biotic Index (MHBI)— The Hilsenhoff Biotic Index (HBI) is a benthic invertebrate community index developed by W.L. Hilsenhoff. The HBI is determined by assigning a pollution tolerance value for each family of benthic invertebrates, then computing the average tolerance for a sample. In a modification of the HBI developed by R.W. Bode and M.A. Novak, pollution tolerance values are assigned by genus, which provides greater resolution in the average tolerance.

Nutrient— In aquatic systems, a substance that contributes to algal growth. Nutrients of concern include nitrogen and phosphorus compounds, but not elemental nitrogen.

Picocurie (pCi)— One trillionth (10¹²) of the amount of radioactivity represented by a curie (Ci). A curie is the amount of radioactivity that yields 3.7 x 10¹⁰ radioactive disintegrations per second (dps). A picocurie yields 2.22 disintegrations per minute (dpm), or 0.037 dps.

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

Recharge— Water that infiltrates the ground and reaches the saturated zone.

Babcock Mill at Babcock State Park, WV. Photograph by Douglas B. Chambers, USGS.

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), is 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.

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

Specific conductance— A measure of the ability of a liquid to conduct an electrical current.

Suspended (as used in tables of chemical analyses)— The amount (concentration) of undissolved material in a water-sediment mixture. It is associated with the material retained on a 0.45-micrometer filter.

Suspended sediment— Particles of rock, sand, soil, and organic detritus carried in suspension in the water column, in contrast to sediment that moves on or near the streambed.

Taxon— Any identifiable group of taxonomically related organisms, such as a species or family. Plural, Taxa.

Tolerant species— Those species that are adaptable to (tolerant of) human alterations to the environment and often increase in number when human alterations occur.

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

Upgradient— At or toward a location nearer to the source of ground-water flow.

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-quality standards— State-adopted and U.S. Environmental Protection Agency-approved ambient standards for water bodies. Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.

Watershed— See Drainage basin.