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Contaminated Site Management

Glossary A

Abiotic: Not biotic; not formed by biologic processes.

Absolute Viscosity: A measure of a fluid's resistance to tangential or shear stress. Also referred to as dynamic viscosity; see also viscosity. Units are usually given in centipoise.

Absorbance: A measure of the decrease in incident light passing through a sample into the detector. It is defined mathematically as: I = radiation intensity

Absorption: The penetration of atoms, ions, or molecules into the bulk mass of a substance.

Accoustic impedence: Reflects the ability of a boundary to reflect seismic energy. It is the contrast of density times velocity across the boundary. A measure of the seismic inertia of the medium.

Accuracy: Refers to closeness of a measurement to the true value.

Actinomycetes: Any of numerous, generally filamentous, and often pathogenic, microorganisms resembling both bacteria and fungi.

Action Level: The concentration of a contaminant above which some action (monitoring, clean up, etc.) is required by regulation.

Active Layer/Zone: In permafrost terrains, the zone that undergoes cycles of freezing and thawing.

Adsorption: The retention of atoms, ions, or molecules onto the surface of another substance.

Advection: Process by which a solute is transported in groundwater, and moves at the same velocity.

Aeration: The process of bringing air into contact with a liquid (typically water), usually by bubbling air through the liquid, spraying the liquid into the air, allowing the liquid to cascade down a waterfall, or by mechanical agitation. Aeration serves to (1) strip dissolved gases from solution, and/or (2) oxygenate the liquid. The rate at which a gas transfers into solution can be described by Fick's First Law.

Aerobic: Refers to any process carried out in the presence of oxygen.

Afterburner: An off-gas post-treatment unit for control of organic compounds by thermal oxidation. A typical afterburner is a refractory-lined shell providing enough residence time at a sufficiently high temperature to destroy organic compounds in the off-gas stream.

Aggregate: Coarse mineral material (e.g., sand, gravel) that is mixed with either cement to form concrete or tarry hydrocarbons to form asphalt.

Air/Oil Table: The surface between the vadose zone and the oil; pressure of oil in the porous medium is equal to atmospheric pressure.

Air Stripping: A treatment system that removes, or "strips," volatile organic compounds from contaminated groundwater or surface water by forcing an airstream through the water and causing the compounds to evaporate.

Algae: Chiefly aquatic, eucaryotic one-celled or multicellular plants without true stems, roots and leaves, that are typically autotrophic, photosynthetic, and contain chlorophyll. Algae are not
typically found in groundwater.

Aliphatic: Of or pertaining to a broad category of carbon compounds distinguished by a straight, or branched, open chain arrangement of the constituent carbon atoms. The carbon-carbon bonds may be either saturated or unsaturated. Alkanes, alkenes, and alkynes are aliphatic hydrocarbons.

Aliquot: A measured portion of a sample taken for analysis. One or more aliquots make up a sample.

Alkanes: The homologous group of linear saturated aliphatic hydrocarbons having the general formula CnH2n+2. Alkanes can be straight chains, branched chains, or ring structures. Also referred to as paraffins.

Alkenes: The group of unsaturated hydrocarbons having the general formula CnH2n and characterized by being highly chemically reactive. Also referred to as olefins.

Alkynes: The group of unsaturated hydrocarbons with a triple Carbon-Carbon bond having the general formula CnH2n-2.

Alluvial Deposits: The general name for all sediments, including clay, (Alluvium) silt, sand, gravel or similar unconsolidated material deposited in a sorted or semi-sorted condition by a stream or other body of running water, in a stream bed, floodplain, delta or at the base of a mountain slope as a fan.

Alluvial Fans: A fan shaped deposit of detrital material deposited by a stream where it emerges from a steep mountain slope or from an upland onto a less steeply sloping terrain.

Alluvium: A general term for unconsolidated material (e.g. clay, silt, sand, gravel) deposited from running water. Often a sorted or semi-sorted sediment in the bed of a stream or on its floodplain or delta. The deposit may be in the form of an alluvial fan.

Ambient: Surrounding.

Ambient Groundwater Flow: The rate of flow and direction of flow of groundwater under unpumped, natural conditions.

Amplitude: The maximum departure of a wave from the average value.

Anaerobic: In the absence of oxygen.

Analog: In chemistry, a structural derivative of a parent compound.

Analysis Date/Time: The date and military time of the injection of the sample, standard, or blank into the GC/MS or GC system.

Analyte: The element or ion an analysis seeks to determine; the element of interest.

Analytical Sample: Any solution or media introduced into an instrument on which an analysis is performed excluding instrument calibration, initial calibration verification, initial calibration blank, continuing calibration verification and continuing calibration blank. Note the following are all defined as analytical samples: undiluted and diluted samples (EPA and non-EPA), predigestion spike samples, duplicate samples, serial dilution samples, analytical spike samples, post-digestion spike samples, interference check samples (ICS), CRDL standard for AA (CRA), CRDL standard for ICP (CRI), laboratory control sample (LCS), preparation blank (PB) and linear range analysis sample (LRS).

Analytical Spike: The furnace post-digestion spike. The addition of a known amount of standard after digestion.

Anion: A negatively charged atom or radical.

Anisotropic: The condition in which hydraulic properties of an aquifer are not equal when measured in all directions.

Anisotropy: The conditions under which one or more of the hydraulic properties of an aquifer vary with direction.

Annulus: The space between well casing or screen and the borehole wall, or between drill pipe and casing, or between separate sets of casing.

Anomaly: Refers to deviation from uniformity in a physical property.

Apparent Resistivity/Conductivity: The resistivity of a homogeneous isotropic ground that would give the same voltage/current or secondary/primary field ratios as observed in the field with resistivity or EM methods. The apparent conductivity is the reciprocal of the apparent resistivity.

Aqueous solubility: The extent to which a compound will dissolve in water. The log of solubility is generally inversely related to molecular weight.

Aquiclude: An outdated term for a geologic layer of very low permeability located so that it forms an upper or lower boundary to a groundwater flow system. Aquitard or Confining Layer are preferred terms.

Aquifer: Rocks or unconsolidated sediments that are capable of yielding a significant amount of water to a well or a spring.

Aquifer Depletion: Aquifer depletion occurs when groundwater is withdrawn from an aquifer at a rate greater than it can be replenished.

Aquifer Test: A test which involves adding to or discharging from a well, measured quantities of water, and recording the resulting changes in head in the aquifer (during and after addition/withdrawal). Examples are slug tests, bail tests, and pumping tests.

Aquifer Vulnerability: A measure of how vulnerable an aquifer is to contamination.

Aquifer Vulnerability Mapping: Mapping the vulnerability of an aquifer to contamination from sources. Vulnerability mapping does not consider the type of land use above an aquifer, only the intrinsic vulnerability of the aquifer, typically based on the type, thickness, and extent of geologic materials overlying an aquifer, depth to water, and type of aquifer materials.

Aquitard: A geologic formation that may contain groundwater but is not capable of transmitting significant quantities of groundwater under normal hydraulic gradients. In some situations aquitards may function as confining beds.

Archie's Law: An empirical relationship linking formation resistivity (rt), formation water resistivity (rw) and porosity q. The form of the relationship is: rt = arwq-m where a and m are experimentally determined constants.

Aromatic: Of or relating to organic compounds that resemble benzene in chemical behavior. These compounds are unsaturated and characterized by containing at least one 6-carbon benzene ring.

Artesian: The condition of water in a confined aquifer being under sufficient pressure that the potentiometric surface is above the bottom of the overlying confining bed. Water levels within wells screened in an artesian aquifer rise to a point above the bottom of the confining bed that overlies the aquifer (it is not necessary for the water to flow at land surface). If the water is under enough pressure so that the potentiometric surface is above land surface, water may actually flow from the well without pumping. Such a well is a flowing artesian well.

Asymptote: A line that is considered to be the limit to a curve. As the curve approaches the asymptote, the distance separating the curve and the asymptote continues to decrease, but the curve never actually intersects the asymptote.

Attenuation, Attenuate: The reduction or removal of groundwater constituents by the sum of all physical, chemical, and biological factors acting upon the groundwater. In geophysical terms, it refers to a reduction in energy or amplitude caused by the physical characteristics of a transmitting system.

Atterberg Limits: The moisture contents which define a soil's liquid limit, plastic limit, and sticky limit.

Auger: A tool for drilling/boring into unconsolidated earth materials (soil) consisting of a spiral blade wound around a central stem or shaft that is commonly hollow (hollow-stem auger). Augers commonly are available in flights (sections) that are connected together to advance the depth of the borehole.

Auger Flights: Winding metal strips welded to auger sections. They carry cuttings to the surface during drilling.

Autoignition Temperature: The temperature at which a substance will spontaneously ignite. Autoignition temperature is an indicator of thermal stability for petroleum hydrocarbons.

Autotrophic: Designating or typical of organisms that derive carbon for the manufacture of cell mass from inorganic carbon (carbon dioxide).

Autozero: Zeroing the instrument at the proper wavelength. It is equivalent to running a standard blank with the absorbance set at zero.

Average Linear Groundwater Velocity: The velocity of groundwater moving through porous rock or sediment. It is the time required for the water to move from A to B divided by the linear distance from A to B.

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