Toxic substancesA chemical or mixture of chemicals that presents a high risk of injury to human health or to the environment.
Toxic Substances Control Act (TSCA)(TSCA)The Toxic Substances Control Act (TSCA), passed in 1976, requires tests of chemicals that may harm human health or the environment; reviews of new…
toxicity(tok-SIH-sih-tee) The extent to which something is poisonous or harmful.
toxicsAs defined in the 1990 Clean Air Act Amendments, toxics include benzene, 1,3 butadiene, formaldehyde, acetaldehyde, and polycyclic organic matter.
Tracking arrayA PV panel array that follows the path of the sun to maximize the solar radiation incident on the PV surface.
Traditional cultural propertyA property that is eligible for inclusion in the National Register of Historic Places because of its association with cultural practices or beliefs of a…
transesterificationA chemical process which reacts an alcohol with the triglycerides contained in vegetable oils and animal fats to produce biodiesel and glycerin.
Transmission corridorAn electric or pipeline transmission corridor is a route approved on public lands, in a BLM or other federal agency land use plan, as a location that may…
Transmission lineA set of electrical current conductors, insulators, supporting structures, and associated equipment used to move large quantities of power at high…
TransmissivityThe rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit hydraulic gradient.
Traveling GrateA furnace grate that moves fuel through the combustion chamber.
TravertineA sedimentary rock formed by the precipitation of carbonate minerals from solution in ground and surface waters, and/or geothermal hot-springs.
Tree measurement saleA type of timber sale contract in which the buyer and seller agree upon the volume at the time of the sale.
Tribal landIn NAGPRA, tribal land is defined as: (a) all lands within the exterior boundaries of any Indian reservation; (b) all dependent Indian communities; (c)…
TribeTerm used to designate a federally recognized group of American Indians and their governing body. Tribes may be composed of more than one band.
TributaryA creek, stream, or river that feeds a larger stream or river, or lake.
triglycerideA triglyceride is an ester of glycerol and three fatty acids. Most animal fats are composed primarily of triglycerides.
TroposphereThe layer of the atmosphere closest to the Earth's surface.
TsunamiOcean wave produced by earthquakes or underwater landslides.
TuffVolcanic rock made up of rock and mineral fragments in volcanic ash matrix. Tuffs commonly are composed of much shattered volcanic rock glass—chilled…
TurbidityThe relative clarity of water, which may be affected by material in suspension in the water.
TurbineA device for converting the flow of a fluid (air, steam, water, or hot gases) into mechanical motion.
Turn Down RatioThe ratio of a boiler's or gasifier's maximum output to its minimum output.
Turn of logsA group of logs yarded at the same time by the same machine.
Turnkey systemA system which is built, engineered, and installed to the point of readiness for operation by the owner.
U.S. Environmental Protection AgencyThe independent federal agency, established in 1970, that regulates federal environmental matters and oversees the implementation of federal environmental…
Ultimate AnalysisA procedure for determining the primary elements in a substance (carbon, hydrogen, oxygen, nitrogen, sulfur, and ash).
Unconsolidated shore wetlandsIncludes all wetland habitats having three characteristics: (1) unconsolidated substrates with less than 75% areal cover of stones, boulders, or bedrock…
UnderflowThe movement of groundwater through the soil or a subsurface stratum, or under a structure; specifically, the water flowing beneath the bed of a stream…
UnderstoryThe trees and other woody species growing under a relatively continuous cover of branches and foliage formed by the overstory trees.
Uniform Building Code (UBC)(UBC)A building code published by the International Conference of Building Officials, adopted and amended by Oregon Department of Commerce.
Uniform Mechanical Code (UMC)(UMC)A code sponsored by the International Association of Plumbing and Mechanical Officials and the International Conference of Building Officials, adopted and…
Unit (fuel or pulp)A bulk measure of hog fuel or pulp chips containing 200 cubic feet. A unit contains varying amounts of solid material depending on the amount of…
Unit (timber)A timber harvest area with defined boundaries. The area is managed as a unit for harvest and subsequent management activities.
United States Code (USC)(USC)A compilation of the general and permanent federal laws of the United States. It is divided into 51 titles that represent broad areas subject to federal…
Unmerchantable woodMaterial which is unsuitable for conversion to wood products due to poor size, form, or quality.
Unrest (episode)Usually non-eruptive volcanic activity (e.g., ground deformation, steam plumes, degassing) that may be interpreted as a precursor to an eruption.
Unstable slopesSlopes considered unstable due to their incline (or critical angle of repose), applied to slopes made of unconsolidated material.
Unsuitable areasAreas not appropriate for timber harvest due to fragile or shallow soils, scenic values, special wildlife habitat areas, and riparian or wetland values…
UplandThe portion of the landscape above the valley floor or stream.
UplightingLight directed upward at greater than 90° above nadir, generally upward into the sky.
Upper-air soundingAn upper-air observation of the vertical profile of an atmospheric variable such as temperature or wind.
UpwarpA broad anticline with gently sloping limbs formed as a result of differential uplift.
Urban Growth BoundaryA line drawn around a city that prohibits development outside that boundary. Designed to slow or prevent sprawl, UGBs are designed to accommodate growth…
uronic acidA simple sugar whose terminal -CH2OH group has been oxidized to an acid, COOH group.
Utility scale facilitiesFacilities that generate large amounts of electricity that is delivered to many users through transmission and distribution systems.
vacuum distillationThe separation of two or more liquids under reduced vapor pressure; reduces the boiling points of the liquids being separated.
Valley floorThe gently sloping to nearly level bottom surface of a valley.
Valley segmentThat portion of a stream network with similar morphologies and governing geomorphic processes identified by valley bottom and sideslope geomorphic…
VentA component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vernal poolSeasonally-flooded depressions found on soils with an impermeable layer such as a hardpan, claypan, or volcanic basalt.
VertebrateAny species having a backbone or spinal column including fish, amphibians, reptiles, birds, and mammals.
Vertical angle of viewElevation of viewer relative to the elevation of the proposed action, and the resulting angle of difference.
View durationLength of time a proposed action is in view. Impacts that are viewed for a long period of time are generally judged to be more severe than those viewed…
Viewer distanceThe distance from a viewpoint to a seen object or landscape element.
ViewpointA point from which a landscape view is analyzed and/or evaluated.
ViewshedThe total landscape seen or potentially seen from all or a logical part of a travel route, use area, or water body.
Visibility factorsConditions or other phenomena that affect the visibility or appearance of an object or a landscape.
Visual absorption capabilityThe physical capacity of a landscape to accept human alterations without loss of its inherent visual character or scenic quality.
Visual attentionNoticing and focusing of vision on a particular object or landscape element.
Visual clutterThe complex visual interplay of numerous disharmonious landscape characteristics and features resulting in a displeasing view.
Visual contrastOpposition or unlikeness of different forms, lines, colors, or textures in a landscape.
Visual disharmonyA state of disagreement, incongruity, or disproportionate arrangement of forms, lines, colors, and textures in the visual elements of a seen landscape.
Visual featureAn element, such as a land or water form, vegetation, or structure in the seen landscape.
Visual harmonyA pleasing array of visual elements in a landscape, usually as a result of a sense of visual order, compatibility, and completeness between and among the…
Visual impactAny modification in land forms, water bodies, or vegetation, or any introduction of structures, which negatively or positively affect the visual character…
Visual intrusionAny human-caused change in the land form, water form, vegetation, or the addition of a structure which creates a visual contrast in the basic elements…
Visual mitigationActions taken to avoid, eliminate, or reduce potential adverse impacts on scenic resources.
Visual Resource Management (VRM) Class Designations(VRM)Class I objective is to preserve the existing character of the landscape. The level of change to the characteristic landscape should be very low and must…
Visual Resource Management (VRM) Classes(VRM)Categories assigned to BLM lands, utilizing the Visual Resource Inventory Classes in the RMP process, with an objective which prescribes the amount of…
Visual Resource Management (VRM) System(VRM)BLM's system for minimizing the visual impacts of surface-disturbing activities and maintaining scenic values for the future.
Visual resourcesRefers to all objects (man-made and natural, moving and stationary) and features such as landforms and water bodies that are visible on a landscape.
Visual sensitivityPublic concern for the maintenance of scenic quality in a particular landscape setting.
Visual unityThe quality or state of appearing to be united in principles and relationships or to be logically and aesthetically connected because of the visual…
volatileA solid or liquid material that easily vaporizes.
volatile matterThose products, exclusive of moisture, given off by a material as a gas or vapor, determined by definite prescribed methods that may vary according to the…
Volatile organic compound (VOC)(VOC)Any organic compound that participates in atmospheric photochemical reactions except those designated by the EPA as having negligible photochemical…
VolatilityThe term volatility indicates how much and how quickly the value of an investment, market, or market sector changes.
Volcanic AshConsists of rock, mineral, and volcanic glass fragments smaller than 2 millimeters (mm) (0.
Volcanic chainA linear sequence of volcanoes that occurs within a tectonic plate. As the plate moves over a stationary hot spot, new volcanoes are created.
Volcanic coneA landform built by the material ejected from a volcanic vent and piled up around the vent in the shape of a cone with a central crater.
Volcanic ventThe opening at the Earth's surface through which volcanic materials issue forth.
VolcanismThe process by which magma and associated gases rise to the Earth's crust and are extruded, or expelled, onto the surface and into the atmosphere.
VolcanoA vent (opening) in the surface of the Earth through which magma erupts. It is also the landform that is constructed by the erupted material.