Contaminated and Hazardous
Waste Site Management Glossary
O
Obligate
Aerobes: organisms that require the presence of molecular oxygen (O2) for their
metabolism. Obligate
Anaerobes: Organisms for which the presence of molecular oxygen is toxic. These
organisms derive the oxygen needed for cell synthesis from chemical compounds. Observation
Well: A well constructed for the objective of undertaking observations such as
water levels, pressure readings and groundwater quality. Occlude:
To cause to become obstructed or closed and thus prevent passage either into or
out of. Octanol/Water
Partition Coefficient (Kow): A coefficient representing the ratio of the solubility
of a compound in octanol (a non-polar solvent) to its solubility in water (a polar
solvent). The higher the Kow, the more non-polar the compound. Log Kow is generally
used as a relative indicator of the tendency of an organic compound to adsorb
to soil. Log Kow values are generally inversely related to aqueous solubility
and directly proportional to molecular weight. Off-Gas
Treatment System: Refers to the unit operations used to treat (i.e. condense,
collect, or destroy) contaminants in the purge gas from the thermal desorber. Olefins:
See Alkenes. Orifice
Plate: A flow measurement device for liquids or gases that uses a restrictive
orifice plate consisting of a machined hole that produces a jet effect. Typically
the orifice meter consists of a thin plate with a square-edged, concentric and
circular orifice. The pressure drop of the jet effect across the orifice is proportional
to the flow rate. The pressure drop can be measured with a manometer or differential
pressure gauge. Optimum
Offset: Seismic reflection technique employing optimum window. Optimum
Window: The best shot-geophone separation for obtaining reflections from a given
interface. Chosen to lie between the earlier refractions and the later surface
waves. Organic
Contaminant or Compound: Substances containing carbon, with the exception of carbon
dioxide (CO2) and carbonates (e.g. calcium carbonate, CaCO3). Orphan
Site: A contaminated site whose owner cannot be found or who cannot be held responsible
for its clean-up. Outcrop:
Exposed bedrock or strata which projects through overlying unconsolidated sediments
or soils. Outwash
Deposits: Stratified drift deposited by meltwater streams flowing away from melting
ice. Overburden:
The layer of fragmented and unconsolidated material including loose soil, silt,
sand and gravel overlying bedrock, which has been either transported from elsewhere
or formed in place. Overland
Runoff: That part of precipitation flowing overland to surface streams. Oxidation-Reduction
(redox): A chemical reaction consisting of two half-reactions; an oxidation reaction
in which a substance loses or donates electrons, and a reduction reaction in which
a substance gains or accepts electrons. Redox reactions are always coupled because
free electrons cannot exist in solution and electrons must be conserved.
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