Contaminated and Hazardous
Waste Site Management
Data Quality Objectives (DQAs): Statements developed by data
users to define the quality of data needed to meet the objectives of a site assessment
Darcy's Law: An empirically derived equation for the flow of fluids
through porous media. It is based on the assumptions that flow is laminar and
inertia can be neglected, and it states that the specific discharge, q, is directly
proportional to the hydraulic conductivity, K, and the hydraulic gradient, I.
(DFTPP): Compound chosen to establish mass spectral instrument performance for
Decay: The gradual reduction in the magnitude of
Deconvolution: A type of inverse filtering; the process of recovering
information that has been removed by natural and/or instrumental processes (eg.
the Earth, recording equipment, etc.) from the true signal. Generally improves
resolution, sharpens images.
Degassing: Process of removing dissolved gases
from a liquid.
Degradation: The process by which a chemical is reduced to
a less complex form.
Degradation Potential: The degree to which a substance
is likely to be reduced to a simpler form by bacterial activity.
Water: Water from which all free ions have been removed.
De minimis: This
legal phrase pertains to settlements with parties who contributed small amounts
of hazardous waste to a site. This process allows the EPA to settle with small
or de minimis contributors, as a single group rather than as individuals, saving
time, money, and effort.
Denitrification: Bacterial reduction of nitrite
to gaseous nitrogen under anaerobic conditions.
Dense Non-Aqueous Phase
Liquid (DNAPL): A non-aqueous phase liquid (NAPL) with a specific gravity greater
than 1.0. Because the specific gravity of water is equal to 1.0, DNAPLs sink through
the water column until they encounter a confining layer. DNAPLs flow along the
surface of the confining layer and can migrate in directions contrary to the hydraulic
gradient. Because DNAPLs are found at the bottom of aquifers (rather than floating
on the water table) typical monitoring wells will not indicate whether DNAPLs
are present. DNAPL normally refers only to the immiscible phase liquid, however,
it sometimes is taken generally to refer to chemicals such as chlorinated solvents,
creosote and PCB oil and to include both the immiscible phase liquid and the mass
of dissolved-phase emitted from the immiscible phase. To avoid possibilities for
confusion, it is preferable to refer specifically to the immiscible phase of dissolved
phase when wishing to distinguish the phase.
Density: The amount of mass
per unit volume.
Desorption: Process of removing a sorbed substance by reversing
adsorption or absorption.
Detection Limit: The lowest concentration of a
chemical which can be reliably reported to be different from zero.
a) Removing water from a solid material by solid-liquid separation techniques
(e.g. titration, centrifugation) b) Removing or draining water from an enclosure
(e.g. a river bed) by pumping or evaporation.
Dielectric Constant: A measure
of the ability of a material to store charge when an electric field is applied.
Permittivity: Describes the charge separation or polarization in a medium.
The process by which molecules in a single phase equilibrate to a zero concentration
gradient by random molecular motion (Brownian motion). The flux of molecules is
from regions of high concentration to low concentration and is governed by Fick's
Diffusion Coefficient: A parameter that measures how rapidly
a constituent will diffuse in water.
Digestion Log: An official record of
the sample preparation (digestion).
Dimensionality: The number (1,2,3) and
orientation (vertical, areal, radial) of dimensions chosen when modelling aspects
of the subsurface.
Dipole: A pair of equal charges or poles of opposite
Discharge: The rate of flow at a given time, measured as volume per
Discharge Area/Zone: An area in which there is upward groundwater
flow in the subsurface. Groundwater flows toward the surface in a discharge area
and may escape as a spring, seep, or baseflow, or by evaporation and transpiration.
The process by which a substance or chemical spreads and dilutes in flowing groundwater
or soil gas.
Dispersion Coefficient: A measure of the spreading of a flowing
substance as a result of the nature of the porous medium.
The property of a porous medium which determines its dispersion characteristics
by relating the pore velocity components to the dispersion coefficient.
Currents: The movement of charge within a material by polarization, as opposed
to the flow of free ions or electrons. Related to the applied electric field by
the electric permittivity (dielectric constant).
Process of dissolving a solid or NAPL, to form ions or molecules uniformly distributed
in water or another solvent.
Domain: In modelling, the segment of the subsurface
being considered. It is defined by its boundaries and interior geometry (based
on its hydrostratigraphy), and its material properties (porosity, hydraulic conductivity,
Downgradient: A downward hydrologic slope that causes groundwater
to move toward lower elevations. Therefore, wells downgradient of a contaminated
groundwater source are prone to receiving pollutants.
The arrangement of natural stream courses in an area, in plan view. It depends
on local geologic/geomorphologic features and history.
Drawdown: A lowering
of the water table of an unconfined aquifer or the potentiometric surface
of a confined aquifer caused by pumping of groundwater from wells. The vertical
between the original water level and the new water level.
(glacial): Glacial drift includes all rock material in transport by glacier ice,
the deposits made by glacier ice and all materials mainly of glacial origin deposited
in the sea or in glacial melt water bodies including materials rafted in by ice
bergs or transported indirectly in the water itself. Glacial drift therefore includes
till, rock fragments and stratified drift.
Drill Bit: The device that actual
cuts through the subsurface materials. Usually advanced downward at the end of
a drill string.
Drill Cuttings: The rock fragments, sand grains, etc. produced
at the drill bit by the drilling action and circulated to the surface in the drilling
fluid where they can be sampled.
Drilling Fluid: A water- or air-based fluid
used during well drilling to remove cuttings, clean and cool the bit, hold the
borehole open and reduce friction between the drill string and the borehole sides.
Also called mud or drilling mud.
Drill Rod: Hollow jointed or coupled rods,
rotated in the borehole through their connection at the bottom, to the drill bit
and at the top, to the driving mechanism of the rig.
Drill String: The pipe
string which extends down from the driving mechanism and serves to rotate the
Drive Shoe: A forged steel collar on the bottom of a driven casing,
with a cutting edge to shear off irregularities in the hole as it advances.
Force: A force that produces movement of water, gas, NAPL, or of a chemical itself.
Irish term for a small hill. Consists of glacial drift shaped by ice action into
a "hog- back", which is oval in plan and has its long axis pointing
in the direction of ice movement. Drumlins often occur in groups.
The weight of a sample based on percent solids. The weight after drying in an
Dual-Phase Extraction: The active withdrawal of both liquid and gas
phases from a well usually involving the use of a vacuum pump.
Describes subsurface material in which groundwater flow occurs both through fractures
and through pore space. An example is a fractured till, where groundwater can
flow through the fractures and also through the pore space among the till particles.
A second aliquot of a sample that is treated the same as the original sample in
order to determine the precision of the method.
Dynamic Viscosity: A measure
of a fluid's resistance to tangential or shear stress.