Environmental Engineering Reference
In-Depth Information
Toxicity:
the degree to which a substance or agent can cause harm to an organism when
exposed. Also referred to as potency.
Trace fossil:
preserved evidence in rock or sediment that a living organism was present
(i.e., foot prints, burrows, feeding marks, etc.).
Transgressive sedimentary sequence:
sediment with vertically increasing finer grains,
commonly indicates increasing water depths and decreasing energy.
Transmissivity:
a measure of the amount of water horizontally transmissible through a
unit width by the full saturated thickness of an aquifer under a unit of hydraulic
gradient per unit of time.
Transition zone:
a diffuse boundary in the saturated subsurface where freshwater and
saline water mix. Also referred to as zone of dispersion.
Trihalomethanes:
a group of volatile organic compounds where three of the four atoms of
methane are replaced by halogen atoms.
Trophic level:
the position an organism occupies in a food chain.
Turbulent diffusion:
random and chaotic mixing of a liquid.
Type section:
a location where a particular stratigraphic column is considered complete or
representative of a given geologic formation or unit.
Unconfined aquifer:
a saturated geologic material where the surface of the saturated layer
is equal to atmospheric pressure.
Unconformity:
a buried erosional surface separating two rock masses or sedimentary
strata of different ages; indicates sediment deposition was not continuous.
Unsaturated zone:
that portion of Earth between the surface and the water table or zone
of saturation. Also referred to as the vadose zone.
Urban geologic map:
geologic map of an urban area.
Urban heat island:
higher urban temperatures resulting from the excess energy input
into the atmosphere from anthropogenic activities. The primary source of the
additional energy comes from the replacement of vegetation with structures and
pavement.
Urbanization:
the processes contributing to urban growth; specifically, an increased
number of people coming to the cities to live, and the subsequent city expansion
through the annexation of surrounding land and adjacent communities.
Vadose zone:
that portion of Earth between the surface and the water table or zone of
saturation. Also referred to as the unsaturated zone.
Vapor pressure:
the pressure of a vapor in thermodynamic equilibrium with its condensed
phases in a closed container.
Varve:
stratification formed from the seasonal fluctuation in clastic, biological, or chemical
laying of sediment.
Virus:
a subcellular agent capable of replicating itself inside the cells of another organism.
Vitrification:
a form of solidification using electrical power to transform contaminated
subsurface soil into a glass-like substance.
Volatile organic compounds:
organic compounds tending to volatilize or evaporate read-
ily under normal atmospheric pressure and temperature.
Volatilization:
conversion into a vapor or gas without chemical change.
Vug:
small- to medium-sized cavity inside a rock.
Watershed:
the extent of land drained by a given water feature, such as a river system,
lake, swamp, estuary, reservoir, wetland, bay, sea, or ocean.
Watershed management:
the minimization of the human impacts within and between
different land use systems, with the objective of achieving a sustainable landscape.
Water table:
the top of the zone of saturation. Also referred to as phreatic surface.
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