Identify areas where drinking water sources could be at risk

Overview

Drinking water protection zones are areas of land where drinking water sources could be at risk of contamination from certain activities. This is the area where your management efforts should be focused to protect your source. You can create a protection zone by using:

• land use information
• information about the vulnerability of your area
• a scientific method to create protection zones around your drinking water well or intake

If you are thinking about establishing a new municipal residential drinking water system within a source protection area or adding new wells or intakes to an existing municipal residential drinking water system within a source protection area, there are rules under the Clean Water Act for creating protection zones. Use the Source Protection Information Atlas to find out if you are located in an established source protection area.

It’s important to know the specific areas of land where certain activities may pose a risk to your drinking water source. You can also learn more about the different approaches to manage these activities.

Use land use information

Drinking water sources can be contaminated by nearby activities that are associated with various land uses. You can look at current and future land use to determine which areas you need to protect and base the protection zone on property lines (lots and concessions or parcels of land). You can use this approach when you have information about land use activities that may pose a risk to your drinking water source. It is a cost effective and easy way to identify a protection zone with minimal effort. However, its limited scientific basis could lead to overprotecting some areas or not protecting others.

For municipalities and planning authorities

Where there is little or no development around your well or intake, you may want to designate that area for protection and direct some or all development to other areas.

Where there is an activity near your well or intake that is causing or could cause a problem with your drinking water, you may want to focus protective action in those areas where the activities are occurring.

You can also protect shared drinking water sources.

Use vulnerable area information

Vulnerability is a way to describe how easily a drinking water source could be contaminated by nearby activities. The vulnerability of a drinking water source is based on the natural characteristics of the environment that determine how easily contaminants move. For groundwater sources, these characteristics include the type of soil and rock in the area and how quickly water can travel through it. For surface water sources, these characteristics include the type of source (lake or river), water flow and wind conditions, rainfall, the slope of the land, presence of vegetated or paved surfaces, and the soil type.

A vulnerable area under the Clean Water Act is a protection zone where activities that may pose a risk to drinking water are managed or restricted. Vulnerability assessments were conducted as part of the technical work in support of the development of source protection plans under the Clean Water Act. Vulnerable areas are assigned a number score (2 to 10) that indicates how vulnerable (i.e., sensitive) the drinking water source is to contamination. Generally, the higher the assigned vulnerability score within a vulnerable area, the more vulnerable the drinking water source. The Source Protection Information Atlas displays vulnerability scoring and has links to local source protection plans to help you learn more about the policies that affect activities and land use planning decisions in vulnerable areas.

Highly Vulnerable Aquifers

If you are located in an established source protection area under the Clean Water Act, you can view Highly Vulnerable Aquifer mapping for your area in the Source Protection Information Atlas. You may also be able to see aquifer mapping for areas outside source protection areas as a result of municipal groundwater studies.

Highly Vulnerable Aquifers are aquifers that can easily be contaminated because overlying soil layers are thin or permeable. They may or may not represent drinking water sources. Local source protection assessment reports will provide more information about how local Highly Vulnerable Aquifers were delineated and which aquifers are presented in the Highly Vulnerable Aquifer mapping. Highly Vulnerable Aquifer mapping and scoring helps delineate other vulnerable areas where source protection plan policies may apply.

Highly Vulnerable Aquifer mapping can help you create a protection zone where you can take action to protect your drinking water source.

Use a scientific method

Protection zones can be created around a drinking water well or intake. These protection zones can be determined using scientific methods and information about the ground and water around the well or intake. There are two approaches to creating protection zones:

• Use a set distance from the well or intake to determine the boundary of the protection zone, also known as a fixed radius.
• Base the distance to the boundary of the protection zone on the time it would take for contaminants to get to the well or intake, also known as the time of travel.

There are several methods available to calculate the distance to the boundary of the protection zone from the well for a groundwater source and from the intake for a surface water source. A map is helpful to display the protection zone you create around the well or intake.

Time of travel calculations may constitute geoscience work. Geoscience is a regulated profession in Ontario under the Professional Geoscientists Act. Hydrogeology, or the study of water underground, is an area of geoscience. Professional Geoscientists, and Professional Engineers who are both competent and qualified, conduct hydrogeological work.

Groundwater protection zones

Groundwater protection zones represent the area of land at the ground surface where water is captured by the well. Within this area, certain activities may pose a risk of contamination to the water used for drinking. Outside of these areas, groundwater does not move toward the well and does not need to be considered when determining protection zones.

Your well’s water supply comes from the capture zone of the well, which includes upland recharge areas and the zone of influence.

Recharge areas are where rain and melting snow infiltrate directly into the ground rather than flowing over the land.

The water table is the location below the ground where the spaces in soil or cracks in rock are filled with water. Groundwater does not move in underground rivers, but rather flows under the influence of gravity along a gradient from areas of higher water table elevation (upgradient) to areas of lower water table elevation (downgradient).

The zone of influence is the area that contributes water to the pumping well. When groundwater is pumped from a well, it is pulled towards the well from every direction. This action is strongest at the well and decreases as you move away from the well.

You can use one or more scientific methods to create one or more protection zones around your drinking water well to protect the source.

Method	Cost and complexity	Accuracy	Resources needed
Arbitrary fixed radius  – groundwater	Low cost, quick and easy	Not the most accurate	Very few
Calculated fixed radius	Low cost, easy to apply	Somewhat accurate	Few
Uniform flow method	Moderate cost, moderately complex	Accurate	Some
Two-dimensional analytical model	Moderate cost, moderately complex	Accurate	Some
Computer based three-dimensional model	High cost, very complex	Can be very accurate	Many

Arbitrary fixed radius – groundwater

This method is as simple as drawing a circle around your well. You can use it when data and information resources are limited or when you want to quickly create a protection zone with little technical expertise. It is a cost effective and easy way to identify a protection zone with minimal effort. However, its limited scientific basis could lead to overprotecting some areas or not protecting others.

You will need to know the location of the well and the distance you want to protect. You can base the distance on very generalized considerations of soil and groundwater and/or professional judgement.

Or you may also want to consider:

• The Director’s Technical Rules under the Clean Water Act, which uses a fixed radius of 100 metres to protect the most vulnerable area next to a well.
• Ontario Regulation 267/03 under the Nutrient Management Act also protects municipal wells with a 100-metre buffer.
• In British Columbia, an arbitrary fixed radius of 300 metres is often used.

Choosing a large fixed radius can increase protection but may also mean that more people living and working in the protection zone would be affected than is necessary. It also might make it more difficult to defend the protection zone boundaries if they are challenged later. Public support for using this method is an important consideration.

You may want to establish multiple protection zones. With this strategy, you can use more stringent tools to manage activities that could pose a risk to drinking water in the protection zones closer to the well and softer tools to manage activities in the protection zones farther from the well.

Suggested arbitrary fixed radiuses

These are based on averages in provincially approved source protection plans.

• 100 metres to protect the most vulnerable area next to the well.
• 500 to 900 metres to protect against pathogens like bacteria and viruses that usually die off within about 2 years of travel time before getting to the well.
• 1,000 to 1,600 metres to protect against chemical contaminants and pathogens that usually break down within about 10 years of travel time before getting to the well.
• 1,700 to 3,000 metres to protect against persistent and hazardous chemicals that usually persist in the environment for about 25 years of travel time before getting to the well.

If you know which contaminants you want to protect against, you can choose to delineate protection zones that correlate with the times of travel above.

Calculated fixed radius

This method, also known as the “cylinder method,” creates a circular protection zone. The radius of the circle is calculated using either:

• the volume of water pumped by the well over a specified period of time
• calculating the speed of the groundwater and multiplying by a chosen time of travel.

It is based on simple hydrogeologic principles and requires limited technical expertise.

You will need data on the pumping rate and/or water use, the thickness of the aquifer or well screen length, and the porosity of the aquifer. Porosity represents the amount of spaces between grains of soil, estimated as a percentage of the total volume of pore space held by water, for different soil types.

You can delineate multiple zones using this method and take a similar management approach to that presented in the arbitrary fixed radius method.

Modified calculated fixed radius method

The calculated fixed radius method does not account for the direction that groundwater is flowing. Therefore, this method may over-protect the zone downgradient of the well (where the groundwater has already moved past your well) and under-protect the zone upgradient of the well (where the groundwater is coming from). You can apply a modified calculated fixed radius method if you know the groundwater flow direction. This shifts the circle upgradient and may provide better protection of upgradient activities that can pose a risk to your drinking water source.

To use this modified method, first calculate the fixed radius. The upgradient portion of the protection zone is estimated as one and a half times the calculated radius. The downgradient extent of the protection zone is one half of the calculated radius. The resulting shape is a circle with a radius of R, shifted upgradient by a distance of 0.5R.

To determine the groundwater flow direction, you will need advice from a Professional Geoscientist or Professional Engineer who is both competent and qualified to undertake such activities. Professionals can be found through local listings in your area. You can also view public registers of Professional Geoscientists on the Professional Geoscientists Ontario website and Professional Engineers on the Professional Engineers Ontario website.

Half circle calculated fixed radius method

The half circle calculated fixed radius method incorporates flow direction by replacing the circular shape of the protection zone with a half circle that has the same area. This method results in a protection zone that more closely resembles shapes derived from the uniform flow method. The half circle is oriented in the upgradient direction of groundwater flow.

To provide protection for the downgradient zone of influence, a small circle is delineated around the well. Lines are drawn out from the smaller circle to the boundary of the half circle. The radius of the small circle is dependent on the pumping rate of the well. Generally, if the pumping rate is 9.5 cubic metres per day or less, the radius of the small circle is 15 metres.

Uniform flow method

This method calculates the distance to the protection zone boundary by solving analytical equations using a known time of travel. It assumes groundwater moves at a steady state and that the natural conditions are fairly uniform. The uniform flow method can be done with hand calculations or with the help of relatively simple computer programs. Hire a Professional Geoscientist or Professional Engineer who is qualified to conduct hydrogeological assessments to do this work for you. Professionals can be found through local listings in your area. You can also view public registers of Professional Geoscientists on the Professional Geoscientists Ontario website and Professional Engineers on the Professional Engineers Ontario website.

You will need to have data on the geology of the area and the hydrogeology of the aquifer. The uniform flow method is more flexible than standard analytical equations since it can adjust to changes in flow direction. The disadvantage is that this method generally does not take into account hydrogeological boundaries like streams, lakes, recharge areas, etc. or variability in hydrogeology.

Two-dimensional analytical model

This method calculates the distance to the protection zone boundary by solving analytical equations (such as the uniform flow method) using a known time of travel. The model equations map protection zones in plan view (two dimensions). It’s reasonably easy to apply with some technical expertise. Hire a Professional Geoscientist or Professional Engineer who is qualified to conduct hydrogeological assessments to do this work for you. Professionals can be found through local listings in your area. You can also view public registers of Professional Geoscientists on the Professional Geoscientists Ontario website and Professional Engineers on the Professional Engineers Ontario website.

You will need to have data on the geology of the area and the hydrogeology of the aquifer. Computerized two-dimensional analytical models, such as the Wellhead Protection Area (WHPA) Model and the Wellhead Analytic Element Model (WhAEM), are available free of charge from the United States Environmental Protection Agency, or other computer programs can be used.

An analytical model can often provide a good approximation of the time of travel boundaries. However, locations with variable natural features may require more sophisticated methods, such as detailed hydrogeological mapping or numerical modeling.

Computer based three-dimensional model

This method uses a computer to solve mathematical equations to simulate or ‘model’ how water and contaminants move in groundwater. Essentially, the computer program creates a three-dimensional grid that simulates the aquifer. At each grid node, hydrogeological information is input into the program, allowing the model to predict groundwater flow and the movement of contaminants. When properly set-up and calibrated, these models produce more realistic time of travel estimates than the analytical or semi-analytical approaches.

You will need a lot of good quality data on:

• the geology of the area
• hydrogeology of the aquifer
• water quality

Computer based three-dimensional models account for local information and complex natural features for better accuracy but poor data quality can impact model predictions.

Running computer based three-dimensional models requires specialized technical expertise. Hire a Professional Geoscientist or Professional Engineer who is qualified to conduct hydrogeological assessments to do this work for you. Professionals can be found through local listings in your area. You can also view public registers of Professional Geoscientists on the Professional Geoscientists Ontario website and Professional Engineers on the Professional Engineers Ontario website.

Surface water protection zones

Drinking water from a surface water source is transported through a pipe directly from the lake, river or stream. The entry point of your raw water supply is called the intake. Surface water protection zones are made up of the land and water near the location of the intake. The land portion of the protection zone is called the setback. In these areas, certain activities and land uses can pose a risk to drinking water sources.

Setbacks are areas of land that drain into the surface water source. This part of the land next to a surface water source helps to control the runoff flow (slow down the water speed) and to allow enough time to let water infiltrate into the ground. When it rains a lot or snow melts, some streams and rivers overflow into a flat low-lying area called a floodplain. When the stream or river is just about to spill onto its floodplain, the water level in the channel is called the high water mark. Setbacks can be measured from the high water mark or you can use the area of land within floodplain mapping for a 100-year flood event, similar to the conservation authority regulation limit. The high water mark can be measured using a physical marker or observed as a natural line on the landscape.

Floods and floodplains are rated statistically for the expected time between flood events.

Generally, 120 metres measured from the high water mark is an adequate setback. This distance (or the conservation authority regulation limits, whichever is greater) is used in the Director’s Technical Rules under the Clean Water Act to develop protection zones. You can also use this distance in the absence of data or technical resources.

Setbacks can also be extended to consider local information such as the type of surface soil, local topography of the land, size of the water course, preferential pathways and land use. Smaller setbacks can be used if the area within 120 metres does not drain into the protection zone associated with the water course.

The provincial land use planning framework generally suggests that if there is a proposed land use within 120 metres of a surface water feature (such as a lake, river or stream), a hydrological evaluation is required to establish a vegetative protection zone around the feature. This is consistent with Policy 4.2.4 in the Growth Plan and the Oak Ridges Moraine Conservation Plan, which use the terminology “key hydrologic features” instead of the more general “surface water” and can help protect the feature and its function, provided a minimum 30-metre setback be maintained.

Conservation authorities have flood maps that show their regulation limits. Where floodplain mapping isn’t available within the conservation authority watershed, other mapping such as fill regulation mapping or regulated areas mapping may be available. Floodplain and other mapping resources can be found on Conservation Ontario's website. In areas where there are no conservation authorities, the Ministry of Natural Resources and Forestry has published technical guides on natural hazards to support municipal implementation of the natural hazard policies in the Provincial Policy Statement. These can be ordered directly from the Ministry of Natural Resources and Forestry to assist with flood mapping when needed.

You can use one or more scientific methods to create one or more protection zones around your drinking water intake to protect the source.

Method	Cost and complexity	Accuracy	Resources needed
Arbitrary fixed radius – surface water	Low cost, quick and easy	Not the most accurate	Very few
Analytical approach	Moderate cost, varying complexity	Accurate	Some
Numerical model	High cost, very complex	Can be very accurate	Many

Arbitrary fixed radius – surface water

This method involves drawing a circle or semi-circle around the intake. You can use it when data and information resources are limited or when you want to quickly create a protection zone with little technical expertise. It is a cost effective and easy way to identify a protection zone with minimal effort. However, its limited scientific basis could lead to overprotecting some areas or not protecting others.

You will need to know the type of water body (river, lake or both), the location of the intake and the distance you want to protect. The Director’s Technical Rules under the Clean Water Act use the following fixed radiuses to protect the most vulnerable areas next to the intake:

Drinking water source	Common fixed radius distances
Lake	Full circle of 1000 metres
Large river or river connecting the Great Lakes	Semi-circle of 1000 metres upstream of the intake and a 100 metre rectangle extending downstream
Small or inland river	Semi-circle of 200 metres upstream of the intake and a 10 metre rectangle extending downstream

When the circle or semi-circle is fully in water, the protection zone does not need to include land. Where the circle or semi-circle intersects the land, a setback should be included in the protection zone. In the absence of data or technical resources, you can use 120 metres from the high water mark as the setback.

You can also establish multiple protection zones using the fixed radius method. With this strategy, you can use more stringent tools to manage activities that could pose a risk to drinking water in the protection zones closer to the intake and softer tools to manage activities in the protection zones farther from the intake. Below are some suggested arbitrary fixed radiuses you can use to establish multiple protection zones. These are rough estimates based on averages in provincially approved source protection plans.

For inland rivers and lakes:

• 200 metres to protect against contaminants that would have little to no chance for dilution before they reach the intake (where you wouldn’t have time to respond to a spill)
• 500 to 1000 metres to provide about 2 hours to respond to spills
• 1500 metres or the watercourse of the entire watershed

For large water bodies like the Great Lakes and their connecting channels:

• 1000 metres to protect against contaminants that would have little to no chance for dilution before they reach the intake (where you wouldn’t have time to respond to a spill)
• 2000 metres to provide about 2 hours to respond to spills
• 3000 metres

Analytical approach

This method calculates the distance along the surface water body to the protection zone boundary by solving analytical equations using a known time of travel, such as 2 hours. Distances are determined from the simple concept of speed, time and distance (Distance = Speed × Time). It is reasonably easy to apply with some technical expertise.

Three features that contribute to the source water can be included in the calculations:

• the type of water body (river, lake or both)
• storm or sewer pipeline systems (if there are any)
• a setback on the land (if needed)

You will need to have data on the size and shape of the channel, the speed of the water, and the characteristics of sewer systems if present. The Manning equation is the most common way to estimate the speed of the water (Speed = 1/_n × R^2/3 × S^1/2), where n is the Manning coefficient (friction coefficient), which varies from 0.001 to 0.03 based on the type of material along the river bottom and the flow, R is the hydraulic radius (in metres), which in most cases is equivalent to the depth of the water in the river, and S is the slope of the river.

You can use a 2 hour time of travel or increase the time of travel if you know your drinking water system’s spill response time, also known as the time needed to shut down or provide treatment in the case of a spill.

Numerical model

This method uses a computer to solve mathematical equations to simulate or ‘model’ how water and contaminants move in rivers, streams and lakes. You will need a lot of good quality data on the size and shape of the channel, water depth and speed, wind speed, water currents and water quality parameters such as temperature and turbidity (a measure of how cloudy the water is due to sediments suspended in the water). Numerical models account for local information and complex natural features for better accuracy but poor data quality can impact model predictions.

Numerical model equations are solved for multiple locations and times under different conditions to reflect changes in the natural environment. Single (constant) values can be used for various parameters such as water depth, speed and temperature if the numerical model is being used to simulate a short period of time. If there is enough data available, models can simulate longer periods of time to reflect changes to the system from things like weather and climate. In this case, the water depth, speed and temperature cannot be assumed constant and multiple values would be needed.

Several numerical modelling codes are available and can represent the natural environment in one, two or three dimensions. The option you pick depends on the complexity of the natural environment and the data available. One- and two-dimensional numerical codes are commonly used. Three-dimensional numerical codes can be used for situations where the circulation of water is too complicated to be represented by a one- or two-dimensional model such as for the Great Lakes.

Running numerical models requires specialized technical expertise from a hydrologist or Professional Engineer. You can hire a specialist to do this work for you.

New or changing municipal residential drinking water systems

A new or changing municipal residential drinking water system within an established source protection area may not yet be included in a source protection plan.

Ontario Regulation 205/18 under the Safe Drinking Water Act requires municipalities within source protection areas to ensure sources of drinking water for new or changing municipal residential drinking water systems are protected before providing water to the public. In these cases, technical work to identify protection zones must follow the Director’s Technical Rules under the Clean Water Act.

Provincially approved source protection plans generally use computer based three-dimensional modelling to delineate protection zones; however, this is not the only way to delineate these areas, and the Director’s Technical Rules allow for less complicated methods. You can use the scientific methods provided above, where appropriate, to help you identify the best method to incorporate your drinking water system into your local source protection plan that meets the requirements of the Director’s Technical Rules and is appropriate to local conditions and available data and resources.

For groundwater sources, where the protection zone boundaries need to be determined using a time of travel method, these include:

• a computer based three-dimensional groundwater flow model
• two-dimensional analytical method
• uniform flow method
• calculated fixed radius method

For surface water sources, you can use the analytical approach or numerical model in accordance with Part VI of the Director’s Technical Rules.

For municipalities

Communal drinking water systems can end up under your care and control. Whether this is a planned transition or becomes necessary due to inadequate operation of the system by the owner, this transition can result in responsibilities that you may not have planned for, including:

• Responsibilities to incorporate the drinking water system into the local source protection plan at your expense.
• Legally binding source protection plan policies that can affect existing property owners, businesses and your municipality.

Consider the long-term ownership of any proposed communal drinking water systems. You can require that development proposals that rely on such systems be subject to conditions as part of the development approval. Conditions could include requiring the developer to complete any potentially required source protection plan technical work or financial assurance to complete such work should the system become your responsibility in the future.

Learn about how Ontario Regulation 205/18 applies to you.