Accuracy - The degree of agreement of a measured value with the true or expected value of the quantity of concern (Taylor, 1987). The concept of accuracy includes both bias and precision.

Analyte (target analyte) - "Substances being determined in an analysis" (Bennett, 1986). The term "target analyte" is used in this report to refer to any chemical or biological substance for which concentrations in a sample will be determined. Target analyte does not include field-measured parameters such as temperature, pH, DO, or conductivity.

Alkalinity - The acid-neutralizing capacity of a solution. Alkalinity indicates how much change in pH will occur with the addition of moderate amounts of acid. Because alkalinity of most natural waters is composed almost entirely of bicarbonate and carbonate ions, determinations of alkalinity can provide accurate estimates of concentrations of these ions. Bicarbonate and carbonate ions are among the dominant anions present in natural waters thus alkalinity measurements provide information about major ion relations and evolution of water chemistry.

Ambient - The natural conditions that would be expected to occur in waters unaffected or not influenced by human activities.

Bias - Systematic error inherent in a method or caused by some artifact or idiosyncrasy of the measurement system. The error can be positive (indicating contamination) or negative (indicating loss of analyte concentration) (Taylor, 1987).

Biochemical oxygen demand (BOD) - A measure of the amount of oxygen consumed by biological processes breaking down organic matter.

Centroid (as used to designate a special case of stream-sampling location for the EDI method) - The vertical in the increment at which the discharge is equal on both sides.

Centroid (of entire cross section) of flow - The vertical in the stream cross section at which the discharge is equal on both sides.

Chemical oxygen demand (COD) - A measure of the oxygen required to oxidize all compounds in water, both organic and inorganic.

Chloride (Cl) - One of seven major ions in most natural waters; element that dissolves from rock materials. The following contribute to an increase in chloride levels: aridity, return drainage from irrigation, sewage, drainage from oil wells, salt springs, and industrial waste. Increased levels of chloride will heighten the corrosive effects of water; combined with sodium, causes a salty taste.

Clean hands/dirty hands (CH/DH) - A field practice that requires two people to obtain and process water-quality samples to reduce contamination at the parts-per-billion level. One sampling person is designated as clean hands (CH) and the other is designated as dirty hands (DH). CH handles only equipment that touches the water sample, and DH handles all the equipment that could be a source of contamination. Both personnel are outfitted with multiple layers of powderless, latex gloves that can be removed at various stages in sampling and sample processing.

Clean sampling procedures - Sampling protocols used when analyzing samples at the parts-per-billion level.

Composite sample - Water sample collected from different locations of a stream cross section.

Conductivity - See specific conductance.

Constituent - An essential part: component, element. Serving to form, compose, or make up a unit or whole.

Contact recreation - Recreational activities that involve a substantial risk of ingesting water, including wading by children, swimming, water skiing, diving, and surfing.

Contamination (of water) - Change of ambient water composition by the addition of biological or chemical substances as a result of human activity or natural processes. Addition of such substances can be detrimental to the quality of the water resource.

Data quality - Refers to the properties of the measurement such as precision, bias, detection limit, and other relevant measures.

Data-quality requirements - The subset of data-quality objectives (DQOs) that pertains specifically to the analytical detection level for concentrations of target analytes and the variability or error brackets allowable to fulfill the scientific objectives of the study.

Depth integration - A method of sampling at every point throughout a given depth (the sampled depth) whereby the water-sediment mixture is collected isokinetically so that the contribution from each point is proportional to the stream velocity at the point. This process yields a sample that has properties that are discharge weighted over the sampled depth (American Society for Testing and Materials, 1990).

Dissolved (D) - Refers to constituents that exist in true chemical solution in a water sample; as a convenient operational definition used by agencies that collect water data, the term "dissolved" commonly is used to refer to constituents in a representative water sample passed through a 0.45-µm filter membrane for inorganic analysis or a 0.7-µm glass fiber filter for organic analysis.

Dissolved oxygen (DO) - The oxygen freely available in water. Adequate DO is necessary for the life of fish and other aquatic organisms. About 3 to 5 mg/L or ppm is the lowest limit for support of fish life over a long period of time.

Effluent - Something that flows out or waste material (such as smoke, liquid industrial refuse, or sewage) that is discharged into the environment, especially as a pollutant.

Estuary - Regions of interaction between rivers and near-shore ocean waters where tidal action and river flow create a mixing of freshwater and saltwater. These areas can include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife.

Filtered - Pertains to constituents in a water sample passed through a filter membrane of specified pore diameter, most commonly 0.45 µm or less for inorganic analytes and 0.7 µm for organic analytes.

Ion - An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

Isokinetic sampling - Collecting a sample in such a way that the water-sediment mixture moves with no change in velocity as it leaves the ambient flow and enters the sampler intake (American Society for Testing and Materials, 1990).

Load - The mass of a material entering a system over a certain time period (pounds per day or kilograms per day).

Maximum contaminant level (MCL) - The maximum permissible level of a contaminant in water delivered to any user of a public water system. Maximum contaminant levels are enforceable standards.

Metals - Any of a class of chemical elements that have a luster and can conduct heat and electricity. In water quality, these elements (in high enough concentrations) can be considered toxic. Common examples include copper, chromium, lead, mercury, and zinc.

Method detection limit (MDL) - The minimum concentration of a substance that can be identified, measured, and reported with 99-percent confidence that the analyte concentration is greater than zero; determined from analysis of a sample in a given matrix containing the analyte.

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

Nutrients - Elements or compounds that are essential for animal and plant growth. The term generally is applied to nitrogen and phosphorus in wastewater but also is applied to other essential and trace elements.

Normality, N (equivalents/L) - The number of equivalents of acid, base, or redox-active species per liter of solution. Example: a solution that is 0.01 F in HCl is 0.01 N in H+.

Organics - Shortened term used to refer to manmade organic chemicals made up primarily of carbon, hydrogen, and oxygen. Common examples include pesticides, solvents such as methanol and acetone, and polychlorinated biphenyls (PCB). PCBs are chemical compounds often used as coolants or insulators in electrical transformers.

Organochlorines - Synthetic organic compounds that contain chlorine. A generally used term referring to compounds that contain mostly or exclusively carbon, hydrogen, and chlorine. Examples are DDT, chlordane, and lindane; PCBs; and some solvents that contain chlorine.

pH - Represents the negative base-10 logarithm of hydrogen ion activity of a solution in moles per liter; a measure of the acidity (pH less than 7) or alkalinity (pH greater than 7) of a solution.

Precision - The degree of mutual agreement characteristic of independent measurements as the result of repeated application of the process under specified conditions (Taylor, 1987).

Secchi disk transparency - A method of measuring (in meters) the turbidity of a water body by averaging the depths below the surface that a Secchi disk disappears from view when lowered and reappears when raised.

Sediment - Solid material that originates mostly from disintegrated rocks and is transported by, suspended in, or deposited from water. Solid material includes chemical and biochemical precipitates and decomposed organic sediment that are influenced by such environmental factors as degree of slope of basin, length of slope, soil characteristics, land use, and quantity and intensity of rainfall.

Semivolatile organic compounds (SVOC) - A group of synthetic organic compounds that are solvent-extractable and can be determined by gas chromatography/mass spectrometry. SVOCs include phenols, phthalates, and polycyclic aromatic hydrocarbons (PAH).

Specific conductance - A measure of the ability of water to conduct an electrical current. The measure is used as a surrogate for the amount of dissolved solids or salt content in the water.

Sulfate (SO4) - A form of sulfur; one of seven major ions in most natural waters.

Total - Pertains to the constituents in an unfiltered, representative water-suspended-sediment sample. This term is used only when the analytical procedure ensures measurement of at least 95 percent of the constituent present in both dissolved and suspended phases of the sample. Knowledge of the expected form of the constituent in the sample, as well as the analytical methodology used, is required to judge when the results should be reported as "total."

Total dissolved solids (TDS) - A measure of dissolved materials in water that indicates salinity. For many purposes, TDS concentration is a major limitation on the use of water.

Toxicity - The degree of health risk (causing death, disease, or birth defects) posed to living organisms.

Transit - The movement of the sampler from the water surface to the streambed or from the streambed to the water surface.

Turbidity - The measure of the scattering effect that suspended solids have on light; the higher the intensity of scattered light, the higher the turbidity.

Quality assurance (QA) - A system of protocols and procedures (such as sampling at the right place and (or) time using the correct equipment and techniques) implemented to meet expected standards of quality needed to fulfill study objectives and control unmeasurable components of a study.

Quality control (QC) - A system of activities (such as collection of blank or replicate samples) whose purpose is to control the quality of environmental data by generating a set of data that will be used to estimate the magnitude of the bias and variability that result from the procedures used to obtain the data.

Variability - Random error in independent measurements as the result of repeated application of the process under specific conditions.

Vertical - A vertical line of observation within an increment from the water surface to the streambed.

Volatile organic compounds (VOC) - A compound that has high vapor pressure and low water solubility. VOCs typically are industrial solvents, constituents in petroleum fuel products, or by-products produced by chlorination in water treatment.

Whole water (W) - Pertains to the constituents in solution after an unfiltered representative water-suspended-sediment sample is digested (usually using a dilute acid solution). Complete dissolution of particulate matter often is not achieved by the digestion treatment, and thus, the determination represents something less than the "total" amount (that is, less than 95 percent) of the constituent present in the dissolved and suspended phases of the sample. For inorganic determinations, digestions are performed in the original sample container to ensure digestion of material absorbed on the container walls. To achieve comparability of analytical data, equivalent digestion procedures would be required of all laboratories performing such analyses because different digestion procedures are likely to produce different analytical results.

| IFM home page | USGS | EPA |
| Back to Table of Contents | |

Contact Dee Lurry for more information