Glossary of Terms, E – J

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One or a series of related objects, natural or anthropogenic that may be related to a specific process. Examples: Storage Tank, Bird Colony, Abandoned Well, Mine Tailing, Natural Radiation Source.


Occurrence of an incident (isolated or frequent) with the potential to promote the introduction of a threat into the environment. An event can be intentional as in he case of licensed discharge or accidental as in the case of a spill.

Existing Drinking Water Source

The aquifer or surface water body from which municipal residential systems or other designated systems currently obtain their drinking water. This includes the aquifer or surface water body from which back-up wells or intakes for municipal residential systems or other designated systems obtain their drinking water when their current source is unavailable or in the event of an emergency.


The extent to which a contaminant or pathogen reaches a water resource. Exposure, like a drinking water threat, can be quantified based on the intensity, frequency, duration and scale. The degree of exposure will differ from that of a drinking water threat dependent on the nature of the pathway or barrier between the source (threat) and the target (receptor) and is largely dependent on the vulnerability of the resource.


Fens are peatlands characterized by surface layers of poorly to moderately decomposed peat, often with well-decomposed peat near the base. The waters and peat in fens are less acid than in bogs, and often are relatively nutrient rich and minerotrophic since they receive water through groundwater discharge from adjacent uplands. Fens usually develop in situations of restricted drainage where oxygen saturation is relatively low and mineral supply is restricted. Usually very low internal drainage occurs through seepage down very low gradient slopes, although sheet surface flow may occur during spring melt or periods of heavy precipitation or if a major local or regional aquifer discharges into the wetland. Some fen wetlands develop directly on limestone rock where minerotrophic waters are emerging through constant groundwater discharge.

Future Municipal Water Supply Areas

An area corresponding to a wellhead protection area or a surface water intake protection zone, or an aquifer or surface water area identified for potential future municipal water supply.


High level achievements to aim for with respect to source protection (e.g. to protect drinking water sources). Provides an opportunity to add value statements. Not measurable through numeric means.

Great Lakes

The five (large) lakes located in Canada and United States: Lake Ontario, Lake Superior, Lake Huron, Lake Erie, and Lake Michigan.

Great Lakes Connecting Channels

The large rivers that connect the Great Lakes (e.g. St. Clair River, St. Lawrence River, Ottawa River).


Subsurface water that occurs beneath the water table in soils and geological formations that are fully saturated.

Groundwater Recharge Area

The area where an aquifer is replenished from (a) natural processes, such as the infiltration of rainfall and snowmelt and the seepage of surface water from lakes, streams and wetlands, (b) from human interventions, such as the use of storm water management systems, and (c) whose recharge rate exceeds a threshold
specified in the regulations. The Director’s rules will specify the acceptable methodologies to determine groundwater recharge rates i.e. what qualifies as significant.


In the context of this guidance, a hazard is equivalent to a contaminant and pathogen threat.

Hazard Rating

The numeric value which represents the relative potential for a contaminant of concern to impact drinking water sources at concentrations significant enough to cause human illness. This numeric value is determined for each contaminant of concern in the Threats Inventory and Issues Evaluation of the Assessment Report.

Highly Vulnerable Aquifer (HVA)

An aquifer that can be easily changed or affected by contamination from both human activities and natural processes as a result of (a) its intrinsic susceptibility, as a function of the thickness and permeability of overlaying layers, or (b) by preferential pathways to the aquifer. The Director’s rules will permit the use of various methods, such as the Intrinsic Susceptibility Index (ISI), to determine those aquifers that are highly vulnerable. Ontario’s ISI defines a highly vulnerable aquifer as having a value of less than 30. An ISI is a numerical indicator that helps to indicate where contamination of groundwater is more or less likely to occur as a result of surface contamination due to natural hydrogeological features. The ISI is the most commonly used method of index mapping and was the prescribed method set out in the provincial 2001/2002 Groundwater Studies.


Hydrogeology is the study of the movement and interactions of groundwater in geological materials.

Imminent Threat to Health

A contaminant of concern that can affect human health in a short period of time.


Often considered the consequence or effect, the impact should be measurable and based on an agreed set of parameters. In the case of source water protection, the parameters may be and acceptable list of standards which identify a maximum raw water levels of contaminants and pathogens of concern. In the case of water quantity, the levels may relate to a minimum annual flow, piezometric head or lake level.

Inland Lake

An inland body of standing water, usually fresh water, larger than a pool or pond or a body of water filling a depression in the earth’s surface.

Inland Rivers

A creek, stream, brook and any similar watercourse inland from the Great Lakes that is not a connecting channel between two Great Lakes.

Intake Protection Zone (IPZ)

The contiguous area of land and water immediately surrounding a surface water intake, which includes:
•the distance from the intake.
•a minimum travel time of the water associated with the intake of a municipal residential system or other designated system, based on the minimum response time for the water treatment plant operator to respond to adverse conditions or an emergency.
•the remaining watershed area upstream of the minimum travel time area (also referred to as the Total Water Contributing Area) – applicable to inland water courses and inland lakes only. (See also “Surface Water Intake Protection Zone”)

Intrinsic Vulnerability

The potential for the movement of a contaminant(s) through the subsurface based on the properties of natural geological materials.

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