Aquifers, recharge and discharge

Aquifers

An aquifer is an underground layer of permeable rock, sediment, or soil that yields water. Aquifers can range in size from a few square kilometers to several thousand square kilometers.

In the Grand River watershed, aquifers provide water for both municipal and private water systems. Some aquifers are in bedrock. Others are in the overburden - a layer of materials such as sand, gravel and other unconsolidated sediment that is overtop bedrock.

For more information on the geology of the watershed, which is foundational to understanding the watershed's aquifers, read the report Geology of the Grand River Watershed (5.1MB PDF). (Please note this document may not be accessible to people with disabilities. If you have a disability and require a document in an alternate format, please contact us.)

Bedrock aquifers

There are numerous bedrock formations deep below the ground. They developed over hundreds of millions of years and under different conditions. As a result, each bedrock formation has its own unique characteristics. Some, called aquifers, are porous and can hold significant quantities of water. Others, called aquitards, are less porous and can slow water from moving through the ground.

The various layers of bedrock also have different chemical compositions that can affect the chemical composition of the groundwater in the bedrock. Some aquifers have high levels of naturally occurring chemicals such as fluoride, arsenic or iron.

Overburden aquifers

Some aquifers are located within the sediment that sits on top of the bedrock. The sediment can be made up of soil, sand, gravel and other materials. Many of the best aquifers are in the moraines, such as the Waterloo Moraine (in Waterloo Region) or the Paris Galt Moraines, which provide water to communities in Wellington and Brant counties.

Other, smaller aquifers are found in sand and gravel seams and supply water to domestic wells.

Recharge areas

Water from the surface - rain or melting snow - moves slowly down through the ground to the aquifers. This is called recharge. Water will move more easily and quickly through loose soils, sand and gravel so these areas have high recharge rates. Areas where there is a lot of fractured bedrock close to the surface also have high recharges rates.

Moraines, such as the Waterloo, Paris, and Galt moraines have high recharge rates, which is one reason why they are also rich sources of water.

Another area with a high recharge rate is the Norfolk Sand Plain in the Oxford-Brant area. Water moves easily through the sandy soil down to the aquifers.

Changes to the land in recharge areas can affect both the quality and the amount of water that moves from the surface into the ground. Paving over these areas, or installing tile drainage, can reduce the amount of water that soaks into the ground.

Discharge areas

When water moves out of the saturated ground to the surface through springs or seeps, it is referred to as groundwater discharge. Often groundwater discharges into wetlands, streams and rivers. In summer, groundwater is typically colder than surface water, at about 9 degrees C. The groundwater makes the surface water cooler and a better habitat for coldwater fish, such as brown trout, and other aquatic species. In winter, the groundwater can be warmer than the surface water.

The Grand River between Cambridge and Paris receives a lot of groundwater discharge. The flow of clean, cool groundwater into this area helps explain why water quality improves along this reach.

More information

For more information on aquifers, recharge, and discharge areas in the Grand River watershed, please visit Source Protection Water Budget Studies.