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Key terms

Abandoned Well
A well that is deserted because it is dry, contains unpotable water, discontinued before completion, not being properly maintained, constructed poorly, or determined that natural gas may pose a hazard.

One or a series of related processes, natural or anthropogenic that occurs within a geographical area and may be related to a particular land use.

An underground saturated permeable geological formation that is capable of transmitting water in sufficient quantities under ordinary hydraulic gradients to serve as a source of groundwater supply.

Assessment Report

A technical document that is prepared by a Source Protection Committee under section 15 of the Clean Water Act, 2006 to record its knowledge of a Source Protection Area, and rank risks to drinking water within that Area. Each report is approved by the Ministry of the Environment, Conservation and Parks.

A substance used in conjunction with, or associated with, a land use activity or a particular entity, and with the potential to adversely affect water quality.

A drinking water condition refers to contamination that exists already and is associated with past activities.

Contaminant of Concern
A chemical or pathogen that is or may be discharged from a drinking water threat activity that could contaminate a drinking water source.

Designated System
A drinking water system that is included in a Terms of Reference for developing source protection plans, pursuant to resolution passed by a municipal council under subsection 8(3) of the Clean Water Act, 2006 or added by the Minister.

Drinking Water Issue
A substantiated (through scientific means) condition relating to the quality of water that interferes or is anticipated to soon interfere with the use of a drinking water source by a municipal residential system or designated system.

Drinking Water Threat
An existing activity, possible future activity or existing condition that results from a past activity, (a) that adversely affects or has the potential to adversely affect the quality or quantity of any water that is or may be used as a source of drinking water.

Ecological Integrity
The condition of ecosystems in which, a) the structure, composition and function of the ecosystem are unimpaired by stresses from human activity, b) natural ecological processes are intact and self-sustaining, and c) the ecosystems evolve naturally.

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 the 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.

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.

Hydrologic Integrity
The condition of ecosystems in which hydrological features and hydrological functions are unimpaired by stresses from human activity.

Hydrologic functions
The functions of the hydrological cycle that include the occurrence, circulation, distribution, and chemical and physical properties of water on the surface of the land, in the soil and underlying rocks, and in the atmosphere, and water’s interaction with the environment including its relation to living things

Imminent Threat to Health
A contaminant of concern that can affect human health in a short period of time.

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

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

Issues Contributing Area (ICA)
The area of land where drinking water threats may contribute to a known drinking water issue. For example, if Trichloroethylene (TCE) is determined to be an Issue, the area from which the source of TCE is determined is called the Issues Contributing Area.

Land Use
A particular use of space at or near the earth’s surface with associated activities, substances and events related to a particular land use designation.

Local Area
Specific area around a wellhead or surface water intake as determined through analysis. This area must encompass a drinking water system and surrounding potential quantity threats.

An assembly of concepts in the form of mathematical equations or statistical terms that portrays a behaviour of an object, process or natural phenomenon

Municipal Residential System
All municipal drinking-water systems that serve or are planned to serve a major residential development (i.e. six or more private residencies).

Parcel Level
A parcel is a conveyable property, in accordance with the provisions of the Land Titles Act. The parcel is the smallest geographic scale at which risk assessment and risk management are conducted.

A disease causing organism.

Raw Water
Water that is in a drinking-water system or in plumbing that has not been treated in accordance with, (a) the prescribed standards and requirements that apply to the system, or (b) such additional treatment requirements that are imposed by the license or approval for the system.

Recharge is the process by which water moves from the ground surface, through the unsaturated zone, to arrive at the water table.

Regulated Areas
Those areas for which Conservation Authorities delineate and restrict land uses by making regulations under subsection 28(1) of the Conservation Authority Act. This subsection applies to water courses, streams, lakes, valleys, flood plains, and wetlands in Ontario.

Reserve Amounts
Minimum flows in streams that are required for the maintenance of the ecology of the ecosystem.

Response Factor
Typical factors affecting the response include dilution, rate of discharge, absorption, and degradation of the contaminant or pathogen in question. Because of the nature of the water resource, certain contaminants and pathogens may not have an impact great enough to warrant concern or responsive action. The level of impact may not effectively degrade the water resource and therefore would not require a mitigative action.

The likelihood of a drinking water threat (a) rendering an existing or planned drinking water source impaired, unusable or unsustainable, or (b) compromising the effectiveness of a drinking water treatment process, resulting in the potential for adverse human health effects.

Sensitivity Area
That portion of a defined vulnerable area that has been assigned a vulnerability score.

The degree to which an impact is measured compared to an idealized value of some parameter of concern. In the case of water quality, the severity may relate to degree of measurable exceedance of some contaminant or pathogen. In the case of water quantity deviation from some measurable parameter (e.g. minimum annual flow, piezometric head or lake level) must also be established.

The most refined scale at which technical assessment of hydrological and hydrogeological conditions can be conducted. These assessments may contribute to water budgets, vulnerability assessments, and issues evaluation.

Source Protection Plan 

A document that is prepared by a Source Protection Committee under section 22 of the Clean Water Act, 2006 to direct source protection activities in a source protection area or region. Each plan is approved by the Ministry of the Environment, Conservation and Parks.

Source Water

Untreated water from lakes, rivers, streams or underground aquifers.

An area that is drained by an individual tributary into the main watercourse of a watershed.

Surface Water
Water that is present on the earth’s surface and may occur as rivers, lakes, wetlands, ponds, etc.

Tier 1, 2, and 3 Water Budgets
Numerical analysis at the watershed/subwatershed (Tier 1 and 2) or local area (Tier 3) level considering existing and anticipated amounts or water use within the watershed, as well as quantitative flow between the groundwater and surface water systems.

Time of Travel (TOT)
An estimate of the time required for a particle of water to move in the saturated zone from a specific point in an aquifer into the well intake.

Tolerance of a Water Supply System
A measure of the ability to sustain required pumping levels even during exposure events.

Transport Pathway
Transport pathways are features or activities occurring at the surface that disturb the surface above the aquifer, or which artificially enhances flow to an aquifer. The presence of a transport pathway can increase the vulnerability rate of an area.

Unconfined Aquifer
An aquifer whose upper boundary is the water table.

Valuation of the Supply
An evaluation of the importance of a particular municipal well or intake to the whole municipal drinking water supply. For example, where there are multiple supplies, value may be smaller, versus a single supply where value may be greater.

Vulnerable Area
An area referring to a groundwater recharge area, a highly vulnerable aquifer, and a surface water intake protection zone or wellhead protection area.

Water Intake Reliability
The probability that a wellhead or surface water intake can meet demand.

Water Reserve
A proportion of surface water flow that must be sustained to support anthropogenic or ecological requirements.

Water Source
An aquifer or surface water body being used to supply drinking water.

Water Source Supply
The total amount of water flowing through a surface water or groundwater system.

Water Supply System
The group of surface water intakes and/or groundwater wells that pump water to supply a municipal water distribution system.

A watershed is the area of land where all of the water that is under it or drains off of it goes into the same place. Its boundaries are defined by ridges of high land.

Wellhead Protection Area
The surface and subsurface area surrounding a water well or well field that supplies a municipal residential system or other designated system through which contaminants are reasonably likely to move so as to eventually reach the water well or well.