What are Vulnerable Areas?

Most communities in the Lake Erie Source Protection Region get their drinking water from groundwater wells. They draw water from underground areas called aquifers where water fills cracks in bedrock or spaces between grains of sand, gravel or dirt.

Water moves vertically from the surface, down through the ground, to the aquifer. It also moves horizontally through the aquifer. How quickly water moves depends on the type of material it is moving through. Water moves quickly through sandy soil or fractured bedrock and slowly through clay or silt.

Scientists study every municipal well to learn how easily water can travel from the surface to the aquifer and then through the aquifer to the well. 

They use this information to draw areas on maps called Wellhead Protection Areas (WHPA). A WHPA is a vulnerable area that surrounds a groundwater well. These areas shows how quickly water moves horizontally through the aquifer. The horizontal flow of water is measured in years: 

• WHPA-A is a 100-metre circle around the well
• WHPA-B is the 2-year time-of-travel zone 
• WHPA-C is the 5-year time-of-travel zone 
• WHPA-D is the 25-year time-of-travel zone  

Scientists also study the vertical flow of water. They combine their understanding of vertical flow with the horizontal flow to calculate a vulnerability score for different areas within each WHPA. The score is between 2 and 10.  

Whether or not a human activity is or would become a significant drinking water threat depends on:  

• where it is located in the WHPA (WHPA-A,B,C or D and the vulnerability score of that area; and 
• the type of materials and hazard rating of the activity. 

Significant drinking water threats are likely to be in areas closest to the well (100-metre, 2-year and 5-year time-of-travel zones). 

River and stream intakes 

Some communities get some or all of their water from intakes found in rivers and streams. Pollutants on land can spill into a river or stream and reach an intake within hours.

The operators of municipal water intakes can close the intake until the spill passes by but they need enough warning time to make sure it can be closed. There may not be enough time to close the gate if the spill happens close to the intake. Therefore, it is important to reduce the number of threats to water in areas close to the intake.

Scientists measure how quickly water moves in the rivers and streams. They use that information to draw areas called Intake Protection Zones (IPZ) for river and stream intakes. The zones are given vulnerability scores on a scale from 0.8 to 10:

• IPZ-1 is the area immediately surrounding the intake, including an area 200 to 1000 metres upstream, with a vulnerability score of 8 to 10.
• IPZ-2 is the area where water (and pollutants) can reach the intake in a specified time, usually two hours minimum. It has a vulnerability score of 5.6 to 9.
• IPZ-3 is all other areas upstream of the intake. Vulnerability scores are from 0.8 to 9. 

Lake Erie intakes 

Some communities have intakes in Lake Erie. Usually they are deep and far away from shore. This makes them less vulnerable to pollutants. However, operators of these municipal intakes still need time to close the gate if a spill happens nearby. 

Scientists study how water moves in the lake by looking at currents, wind patterns, the proximity of rivers and stream outlets and other factors. 

They use this information to draw IPZs for Lake Erie intakes. The zones are given vulnerability scores from 3.5 to 7:

• IPZ-1 is usually a one-kilometre circle around the intake with a vulnerability score of 5 to 7.
• IPZ-2 is the area where water (and pollutants) can reach the intake in a specified time, usually two hours. The vulnerability score can be from 3.5 to 6.3.