Environmental contaminants and decontamination technologies glossary

From: Public Services and Procurement Canada

Consult the definitions of various terms used in the Guidance and Orientation for the Selection of Technologies (GOST).


This glossary is intended to assist in the understanding of the terms used in the Guidance and Orientation for the Selection of Technologies (GOST). Glossary definitions should not be considered as legal interpretations of these terms.

Contaminants starting with the letter A

Pertaining to or characterized by the absence of life or living organisms.
The process by which one material takes up and retains another through the penetration of the absorbed molecules into the mass of the absorbing material.
The process by which one material takes up and retains another through the bonding of the adsorbed molecules onto the surface of the adsorbing material.
The transport mechanism of a substance by a fluid due to the bulk motion of the fluid.
A process occurring only in the presence of molecular oxygen, as applied to certain chemical or biochemical processes such as aerobic decomposition.
Is the measure of the ability of a solution (like water), to neutralize acids. It involves measuring the presence of ions like carbon dioxide, bicarbonate, carbonate and hydroxides present in the water in its natural state. Synonym: basicity.
A biological process which occurs in the absence of oxygen.
A condition in which the concentration of dissolved oxygen is low enough that certain groups of micro-organisms prefer oxidized forms of nitrogen, sulfur, or carbon as an electron acceptor.
An underground water-bearing formation of permeable rock or unconsolidated material (gravel, sand, silt, or clay) from which large quantities of groundwater can be extracted.
Aquifer, confined
A saturated geological unit that is bounded above and below by impermeable layers.
Aquifer, semiconfined
A saturated geological unit overlain and/or underlain by a semi-pervious layer, through which flow into or out of the aquifer can take place.
Aquifer, unconfined
A partially saturated geological unit where the groundwater is subject to variations in atmospheric pressure.

Contaminants starting with the letter B

Baildown test
A baildown test is a widely used field method to evaluate the 'actual' thickness of LNAPL product in a monitoring well. Baildown testing involves the rapid removal of fluids from the well and subsequent monitoring of fluid levels, both water and free phase.
Is the measurement of marine depths and topography; to determine the topography of the sea floor; allows for the creation of bathymetric maps.
A general term for the rock, usually solid, that underlies soil or other unconsolidated, superficial material.
The biologically mediated breakdown of organic compounds into smaller molecules.
The use of microorganisms to breakdown or de-toxicity unwanted chemicals in the environment.
Describes an environment where the living world can develop; synonymous with biogenic and biota; about the living world.
Boiling point
The temperature at which the vapor pressure of a liquid equals the standard atmospheric pressure (101.325 kPa or 760 mm Hg).
Land which was previously used for industrial or commercial activities and is currently abandoned or underused.

Contaminants starting with the letter C

Capillary fringe
The subsurface layer which has its pores filled with groundwater due to capillary action.
CAS Number
A unique identifier assigned to a specific chemical compound by the Chemical Abstracts Service (CAS) of the American Chemical Society.
Chemical reduction
Chemical reduction happens when a chemical species captures one or more electrons. In a chemical reduction, the initial species is in an 'oxidized' state and after the reduction reaction, it is transformed to a 'reduced' chemical species.
The metabolic transformation of a substance while a second substance serves as primary energy or carbon source.
Cone of depression
A depression in the water table of a pumped well, which defines its area of influence.
Any chemical substance whose concentration exceeds background concentrations or that does not naturally occur in the environment.

Contaminants starting with the letter D

To determine the vertical and horizontal boundaries of a contaminant in soil, water and air.
Dense non-aqueous phase liquids (DNAPL)
DNAPLs are hydrocarbons that are heavier than water (have a density greater than 1). DNAPLs will move through and collect at the bottom of an aquifer, and are often difficult to detect using monitoring wells. Examples of DNAPLs: some chlorinated solvents, some pesticides, creosote.
Spreading of a constituent in a solid, liquid or gas, tending to make the composition of all parts uniform.
This is a chemical process which consists of the addition of a solvent or the reduction of the solute concentration in order to reduce a solution concentration.
A physical phenomenon which spreads the contaminants beyond the area where they would lie naturally if they were transported only by advection. This includes molecular diffusion and mechanical dispersion.
Lowering of the water table or piezometric surface due to the extraction of groundwater by pumping, by artesian flow from a bore hole, or by a spring emerging from an aquifer.

Contaminants starting with the letter E

Electron acceptor
A substance that accepts electrons during an oxidation-reduction reaction.
Electron donnor
A substance that donates electrons during an oxidation-reduction reaction.
Ex situ
A method for sol and groundwater decontamination where the contaminated matrix is removed from its natural environment and is treated either on the original site or off site at a specialized treatment center.

Contaminants starting with the letter F

Free phase (Free product)
Refers to immiscible liquid compounds or mixtures of compounds, existing in the soil subsurface which can be either denser or lighter than water.

Contaminants starting with the letter G

Ground water
Water which is being held in, and can usually be recovered from, an underground formation.

Contaminants starting with the letter H

Henry’s law constant
A constant that indicates the tendency of a substance to volatilize while being solubilized in water. This tendency is dependent on both the water solubility and vapor pressure of the substance.
An organism that obtains its energy through the oxidation of organic compounds.
Hydraulic conductivity
Hydraulic conductivity measures the inherent ability of a porous medium to conduct water. It is the proportionality factor between hydraulic gradient and flux in Darcy's Law.
Hydraulic gradient
Difference in the hydraulic head between two points of an aquifer per unit distance in the direction of flow.
Hydraulic head
Is a parameter defined by the Bernoulli equation. It is the height above a datum plane (such as mean sea level) of the column of water that can be supported by the hydraulic pressure at a given point in a groundwater system. Equal to the distance between the water level in a well and the datum plane. It determines the groundwater flow direction from areas of greater hydraulic head to areas of lower hydraulic head.
The cleavage of a chemical bond by the addition of water. Examples of substances that are readily hydrolyzed are esters and amides.
Describes a molecule which is attracted to water. Hydrophilic molecules tend to dissolve or absorb water, e.g. the polar molecule acetone is very soluble in water.
Describes a molecule which is attracted to water. Hydrophilic molecules tend to dissolve or absorb water, e.g. the polar molecule acetone is very soluble in water.

Contaminants starting with the letter I

Immiscible liquid
Two liquids are said to be immiscible if they're completely insoluble one within the other, e.g. oil and water.
In situ
A method for sol and groundwater decontamination where the contaminated matrix is treated without any displacement.
Living or occurring naturally in a specific area or environment.
Injection well
A well used for the injection of a solution (e.g. nutrient, detergent, oxidant, solvent, etc.), gas or other fluid.

Contaminants starting with the letter L

A solution produced by the percolation of water through solid waste, contaminated soils, or other solid substrate. As the water moves through the solids, it becomes loaded with chemical compounds or suspended solids.
A decontamination process by which soluble soil constituents are removed from soil by injection or infiltration of an aqueous solution which solubilizes the contaminants. The contaminants will then percolate into the groundwater where they can be pumped and treated.
Light non-aqueous phase liquid (LNAPL)
LNAPLs are hydrocarbons that are lighter than water (have a density less than 1). LNAPLs will float on the surface of water and groundwater. Examples of LNAPLs: BTEX which are slightly water soluble; ethers and alcohols which are highly soluble in water.
log Koc
The soil organic partition coefficient: this is the concentration ratio, of a contaminant, sorbed to the organic phase and in the water phase of a soil at equilibrium. It provides an indication of the tendency of a compound to adsorb to organic carbon, with a high log Koc values indicating strong adsorption to organic matter and low solubility.

Contaminants starting with the letter M

Melting point
The temperature at which a solid substance undergoes a phase change to a liquid.
Is an artificial experimental system (can be closed) designed to test hypotheses and operating models at an intermediate scale between microcosms and macrocosms. Mesocosm parameters such as temperature, humidity, light, concentration of pollutants, etc. can be controlled to measure the impact of these conditions on the biological, physical and chemical components of a system.
Is the product of microbial metabolism of complex organic compounds (including pollutants). Primary metabolites are involved in growth, development, and reproduction of the organism. Secondary metabolites are produced through the modification of primary metabolites and do not play a role in maintaining normal physiological processes. Example of primary metabolites: lactic acid, certain amino acids, ethanol. Example of secondary metabolites: atropine, erythromycin.
Group of bacteria which produce methane (± carbon dioxide) during anaerobic respiration.
A group of bacteria which use methane as a source of carbon and energy.
An artificial laboratory model in which selected environmental variables can be controlled to observe their effect on the biological, physical and chemical components of a system. The model test results are not always directly applicable to an actual ecosystem because the microcosm is, of necessity, a simplified collection of selected physical, chemical, and biological components.
Is the prokaryotic (bacteria) and eukaryotic (fungi and algae) component of an ecosystem. Soil microflora are involved in the geochemical cycles of elements (carbon, nitrogen, phosphorous), interactions with plants and the breakdown of complex organic molecules, including pollutants.
Microbial degradation of a complex organic compound into carbon dioxide and water.
Molecular weight
The weight of a chemical compound (in grams/mole) calculated using the molecular formula and the atomic weight of each element in the compound.
Monitoring well
Wells that are used to measure changes in water level or quality, so that appropriate preventative measures can be implemented.

Contaminants starting with the letter O

Observation well
Well used for monitoring and measuring the static head of groundwater, the frequency and magnitude of changes in the hydraulic head, or other physical and chemical parameters.
Chemical reaction in which a substance gives up electrons, often through a reaction with oxygen, and becomes oxidized.

Contaminants starting with the letter P

A measure of the ease with which a fluid can flow through a matrix.
Phase I (Environmental Site Assessment)
Site Information Assessment: as the first phase in an Environmental Site Assessment, Phase I consists of a review of all available information related to the site. This is conducted to evaluate existing environmental problems from past operations and potential environmental problems from current or proposed operations at a site.
Phase II (Environmental Site Assessment)
Preliminary site characterization: as the second phase of an Environmental Site Assessment, Phase II will characterize the types and concentrations of contaminants present in various media at the site.
Phase III (Environmental Site Assessment)
Detailed environmental site characterization: a testing and sampling campaign used to define the vertical and horizontal extent of the contamination based on environmental guidelines related to the usage of the site.
Phase IV (Environmental Site Assessment)
Environmental site rehabilitation: this phase of an environmental site assessment consists of restoring a contaminated area based on environmental criteria, which is related to the usage of the site.
Is the breakdown of a chemical compound by light. More precisely, an energetically charged photon breaks the chemical bonds of a compound. Photolysis is a part of the light-dependent reactions of photosynthesis.
Refers to a zone of dissolved contaminants. A plume will usually originate from the source of the contamination and extend down gradient for some distance depending on the hydrogeological and chemical site conditions.
Pneumatic test
This field test is used to assess soil gas permeability. This involves the injection or extraction of air at a constant rate from a single venting well while measuring the pressure/vacuum changes over time at several monitoring points in the soil away from the venting well. It helps in pumping volatile organic contaminants when using bioventing technology.
A substance present in the environment at higher than natural concentrations or above a maximum limit established through regulations, and determined to be harmful at this concentration.

Contaminants starting with the letter R

Recalcitrant substance
A substance whose chemical composition is not, or only slowly, changed by natural processes.
The entity (example: person, organism, population, community, or ecosystem) that might be adversely affected by contact with, or exposure to, a substance of concern.
Replenishment of groundwater naturally by precipitation or runoff, or artificially by injection.
Returning disturbed land to a stable, biologically-productive state.
Redox potential (Eh)
Value describing the oxidizing or reducing potential of an environment. It expresses quantitatively the potential of a substance to be oxidized or reduced, depending upon the tendency of that substance to undergo either of these reactions.
Redox reaction
A pair of reactions in which one compound becomes oxidized while another becomes reduced and takes up the electrons released in the oxidation reaction.
Returning a degraded ecosystem or population to an un-degraded condition, which may be different from its original condition.
Relative density
The unitless ratio of the density of a substance, at a given temperature, to the density of distilled water at 4°C (1,0000 g/ml).
Relative vapour density
A unitless ratio of the vapor density of a substance to that of air under the same pressure and temperature.
The removal of a contaminant from the environment to prevent, minimize, or mitigate damage to human health or the environment. This involves using various means, to remove, destroy or capture the contaminants, or reduce the availability to important receptors.
Residual contamination
Contamination which remains after steps have been taken to remove it.
The portion of the total precipitation of an area that flows into stream channels. Water from surface runoff does not enter the soil.

Contaminants starting with the letter S

Saturated Zone
The portion of the soil column in which all voids, large and small, are filled with water at a pressure superior to the atmospheric pressure.
Highly precise perforations in a well casing that allows water to flow through the well while preventing soil particles from entering.
Particulate matter that precipitates, or is transported or deposited by air, water, or ice and that forms a layer.
The maximum concentration of a substance that will dissolve in a solvent.
Solubility in water
The maximum concentration of a substance that will dissolve in water under given conditions (temperature, pressure, pH, etc). Higher solubility often indicates a low log Koc and low Henry's law constant, and therefore increased biodegradation rates.
A description study of the rock or soil strata, lithology, fossiliferous content, succession, and chronological classification.
The substance on which an enzyme acts, or the food on which a microorganism grows.
Surface Water
Water which flows over, or rests on, the surface of a land mass.

Contaminants starting with the letter T

Tessier sequential extraction
An analytical procedure involving the sequential extraction of particulate trace metals into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual.
The inherent potential or capacity of a material to cause adverse effects in a living organism.
Tracer test
This is a valuable tool for determining water flow within a system and characterizing the mobility of solutes in water. The tracer can be artificial (such as rhodamine or fluorescein) or natural (such as lycopodium spores). A groundwater tracer test involves the injection of a tracer at a point in the aquifer (wells or piezometers) and measuring the tracer concentration at a water sampling point (well, piezometer, resurgence) over time.

Contaminants starting with the letter U

Unsaturated Zone
The portion of the soil column that is not saturated where liquid, gas and solid phases coexist. This zone lies above the capillary fringe.

Contaminants starting with the letter V

Vadose zone
The portion of the soil column above the water table which includes the capillary fringe and the non-saturated zone.
Vapour pressure
The tendency of a substance to volatilize, defined as the pressure exerted by the vapors of that substance, in the presence of the liquid/solid state of the compound, at equilibrium in a closed container.

Contaminants starting with the letter W

Water table
The surface of the saturated zone.