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.