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Contaminated and Hazardous Waste Site Management

Glossary T

Talik: The permanent or temporary layer of unfrozen ground above, within, or below permafrost.

Target: The object at which a survey sighting is aimed.

Technical Assistance Grant (TAG) Program: A grant program that provides funds for qualified citizens' groups to hire independent technical advisors to help them understand and comment on technical decisions relating to Superfund cleanup actions.

Tedlar Bags: Gas-tight bags constructed of non-reactive material (Tedlar) for the collection and
transport of gas/vapor samples.

Tensiometer: A porous, permeable cup connected through a rigid tube to a pressure measuring device (e.g. manometer, vacuum gage) which records in situ soil water matric potential (or tension).

Tension: The condition whereby pore water rests at a pressure less than atmospheric.

Tensor: In three dimensions, there are nine components of hydraulic conductivity or dispersion and, in matrix form, they form a second-rank symmetric tensor. When the principal directions of anisotropy coincide with the x, y, and z coordinate axes, the nine components reduce to three. This is the usual approach for simplification in modelling.

Tentatively Identified Compounds (TIC): Compounds detected in samples that are not target compounds, internal standards, system monitoring compounds, or surrogates. Up to 30 peaks (those greater than 10% of peak areas or heights of nearest internal standards) are subjected to mass spectral library searches for tentative identification.

Terminal Electron Acceptor (TEA): A compound or molecule that accepts an electron (is reduced) during metabolism (oxidation) of a carbon source. Under aerobic conditions molecular oxygen is the terminal electron acceptor. Under anaerobic conditions a variety of terminal electron acceptors may be used. In order of decreasing redox potential, these TEAs include nitrate, manganic manganese, ferric iron, sulfate, and carbon dioxide. Microorganisms preferentially utilize electron acceptors that provide the maximum free energy during respiration. Of the common terminal electron acceptors listed above, oxygen has the highest redox potential and provides the most free energy during electron transfer.

Terrain Conductivity: Geophysical method in which EM methods measure directly the average electrical conductivity of the ground. Operates at low induction number.

Test Pit: A shallow pit, made by a backhoe, to characterize the subsurface.

Thermal Desorber: Describes the primary treatment unit that heats petroleum-contaminated materials and desorbs the organic materials into a purge gas or off-gas.

Thermal Desorption System: Refers to the thermal desorber and associated material handling, treated soil handling, off-gas treatment, and residuals treatment systems.

Thermal Treatment: The use of heat to remove or destroy contaminants from soil.

Thermistor: A circuit component with a high negative temperature coefficient of resistance; its resistance decreases as temperature increases.

Thermocouple: A device consisting of two dissimilar conductors joined together at their ends. Between the two junctions, a thermoelectric voltage is developed which is proportional to the temperature difference between them. It can be used to measure the temperature of one of the junctions when the other is held at a fixed, known temperature, or to convert radiant energy into electric energy.

Thermoplastics: Man-made materials used for well casing; composed of different formulations of plastics (e.g. PVC) which are softened by heating and hardened by cooling so that they are easily moulded and extruded.

Till: Consists of a generally unconsolidated, unsorted, unstratified heterogeneous mixture of clay, silt, sand, gravel and boulders of different sizes and shapes. Till is deposited directly by and underneath glacial ice without subsequent reworking by meltwater.
Unsorted, non-layered sediment carried by or deposited from a glacier.

Time Critical Removals: Including emergencies lasting longer than 30 calendar days, those releases requiring initiation of on-site activity within six months of the lead agency's determination, based on the site evaluation, that a removal action is appropriate.

Time Domain: In geophysics refers to measurements analyzed according to their behaviour in time. The usual alternative is frequency domain measurements.

Time Domain Reflectometry (TDR): A device which measures electrical characteristics of wideband transmission systems. Commonly used to measure soil moisture content.

Titration: A method for analyzing solution composition by adding known quantities of a standardized solution until a certain reaction (e.g. colour change, precipitation) is produced.

Tomography: A method for determining the distribution of physical properties within the earth by inverting the results of a large number of measurements made in three dimensions (e.g. seismic, radar, resistivity, EM) between different source and receiver locations.

Topography: The relief and form of the land.

Tortuosity, Tortuous: The relationship between the length of the flow channel followed by water and the length of the porous media in which the flow is occurring. Groundwater follows a tortuous path so, in this definition, tortuousity is always >1.

Total Dissolved Solids (TDS): Concentration of total dissolved solids (TDS) in groundwater expressed in milligrams per litre (mg/L), is found by evaporating a measured volume of filtered sample to dryness and weighing this dry solid residue.

Total Metals: Analyte elements which have been digested prior to analysis.

Total Petroleum Hydrocarbons (TPH): A measure of the mass or concentration of all the petroleum constituents present in a given amount of air, soil, or water.

Total Recoverable Petroleum Hydrocarbons (TRPH): An EPA method (418.1) for measuring petroleum hydrocarbons in samples of soil or water. Hydrocarbons are extracted from the sample using a chlorofluorocarbon solvent (typically Freon-113) and quantified by infrared spectrophotometry. The method specifies that the extract be passed through silica gel to removethe non-petroleum fraction of the hydrocarbons.

Trace (element): Any chemical (element) present in minute quantities in soil or water.

Traffic Report (TR): A sample identification form filled out by the sampler, which accompanies the sample during shipment to the laboratory and which documents sample condition and receipt by the laboratory. Also called Chain of Custody Report.

Transducer: A device or element that converts an input signal into an output signal of a different form. For example a pressure transducer converts pressure to an electric signal.

Transformation: A chemical or biological change in the structure of a chemical. For example, toluene may be transformed to toluic acid, or to H2O and CO2.

Transient: Occurring when the system is still changing with time; i.e., a steady state has not been attained. Most groundwater flow systems are transient, not steady state.

Transmissivity: The rate at which water of a certain density and viscosity is transmitted under a unit hydraulic gradient through a unit width of an aquifer (or confining bed). It is dependent on properties of the liquid and porous medium. Also known as the Coefficient of Transmissibility.

Transmitter: In resistivity and induced polarization (IP) surveys, where current is injected into the ground, it is a current waveform generator. In electromagnetic surveys, which induce currents in the ground, it is typically a loop or grounded wire.

Transpiration: Process by which water vapour is released through the leaves of plants. This water usually comes from the groundwater.

Travel Time: The time it takes (for example) a contaminant to travel from the source to a particular point downgradient.

Treatibility Studies: Testing a treatment method on contaminated groundwater, soil, etc., to determine whether and how well the method will work.

Trichloroethylene (TCE): A stable, colorless liquid with a low boiling point. TCE has many industrial applications, including use as a solvent and as a metal degreasing agent. TCE can be toxic to people when inhaled, ingested or through skin contact and can damage vital organs, especially the liver.

Turbine: A machine in which kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, blades, or paddles arrayed about the circumference of a wheel or cylinder.

Turbine Wheel: A rotor designed to convert fluid energy into rotational energy. Hydraulic turbines are used to extract energy from water as the water velocity increases due to a change in head or kinetic energy at the expense of potential energy as the water flows from a higher elevation to a lower elevation. The tangential component of the fluid velocity contributes to the rotation of the rotor in a turbo-machine.

Twelve-hour Time Period: The twelve (12) hour time period for GC/MS system instrument performance check, standards calibration (initial or continuing calibration), and method blank analysis begins at the moment of injection of the DBTPP or BFB analysis that the laboratory submits as documentation of instrument performance. The time period ends after 12 hours have elapsed according to the system clock. For pesticide/Arochlor analyses performed by GC/EC, the twelve hour time period in the analytical sequence begins at the moment of injection of the instrument blank that precedes sample analyses, and ends after twelve hours have elapsed according to the system clock.

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