Vulnerable Areas

There are four categories of areas defined by the Clean Water Act as in need of protection. These areas are called “vulnerable areas”.

Technical studies were carried out to define and map the four vulnerable areas:

  • Wellhead Protection Areas
  • Intake Protection Zones
  • Significant Groundwater Recharge Areas
  • Highly Vulnerable Aquifers

Wellhead Protection Area

A Wellhead Protection Area (WHPA) is the surface and underground area around a municipal water well or well field. Wells draw water from underground areas, called aquifers, where water fills cracks in bedrock or spaces between grains of sand, gravel or soil.

Aquifers are replenished when water from rain and melting snow soaks into the ground. Sometimes, the water can carry pollutants. It can take years, or even decades, for water to reach a well. The speed depends on the characteristics of the soil and bedrock in the area.

The surface and subsurface area surrounding a water well or well field showing travel time zones
Wellhead Protection Area Example

Intake Protection Zone

An Intake Protection Zone (IPZ) is the area of land and water immediately surrounding a surface water intake. It indicates the areas where dangerous materials may get to an intake so quickly that operators of the municipal water treatment plant may not have enough time to shut down the intake before the pollutant reaches it.

River and lake intakes can be contaminated when dangerous materials are spilled into the water or on nearby land.

 Area of land and water immediately surrounding a surface water intake
Intake Protection Zone Example

Significant Groundwater Recharge Area

A Significant Groundwater Recharge Area (SGRA) is the area where an aquifer is replenished when rain and snow fall and seep into the ground. The most obvious recharge areas are moraines such as the Oak Ridges Moraine or the Oro Moraine.

Groundwater recharge area graphic showing rain entering ground
Groundwater Recharge Area Example

Highly Vulnerable Aquifer

An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well. Underground aquifers are sources of our drinking water. Some are deep in the earth (hundreds of feet) and some are closer to the surface. An aquifer is considered highly vulnerable  if it can be easily exposed to contamination from human activities or natural processes.


Shows Highly Vulnerable Areas of land and underlying aquifers
Highly Vulnerable Aquifer Example