What is groundwater?
Groundwater is the water below the Earth’s surface. It fills the cracks and spaces in sand, gravel, clay, earth and bedrock.
Groundwater is part of the water cycle. Water moves constantly through the air as water vapour and as rain and snow; on the ground as oceans, lakes, rivers, wetlands and glaciers; and underground as groundwater. Water is also absorbed and released by plants, trees and other living things.
Water moves through the soil, sand, gravel and bedrock until it reaches a depth where the spaces between the particles and cracks are completely filled, or saturated, with water. This level is called the water table. The water table may be near the surface of the ground or many metres below it. As it moves, groundwater is constantly replaced by water flowing from the Earth’s surface.
Why is some aggregate extracted below the water table?
Some layers of sand, gravel, or bedrock can act like groundwater reservoirs. These reservoirs are known as aquifers. The sand, gravel and bedrock that hold water in aquifers can also be valued as building material for the infrastructure essential to our society, such as roads, bridges, sewers and buildings. Extracting this aggregate involves removing material in aquifers below the water table.
How does aggregate extraction affect groundwater?
Aggregate extraction in pits and quarries can take place both above and below the water table. Aggregate extraction above the water table usually has no significant impact on the local groundwater system or local wells.
Pits that extract sand or gravel from below the water table use equipment that digs or dredges the wet aggregate from a pond that forms and expands as the sand or gravel is removed. This allows most of the water to stay in the ground and usually maintains the water table. Possible effects on groundwater include local changes to groundwater flow and temperature near the ponds.
Rock quarries that remove bedrock below the water table can only operate if the water table is lowered artificially – called “dewatering.” This allows the quarry floor to stay dry. The drop in the water table can affect the groundwater flow in a limited area beyond the quarry, called the “zone of influence.” Quarries may also affect the temperature of the local groundwater. Water wells and natural features such as wetlands within the affected area must be carefully studied to predict how they may be affected and what steps should be taken to protect them.
In addition, activities such as fuel handling and storage, which may occur as part of the operation of pits and quarries, are managed to ensure groundwater quality is protected.
How does Ontario protect our groundwater resources during aggregate extraction?
A detailed groundwater and surface water assessment report prepared by a qualified person is required for any new pit or quarry operation that proposes to operate near or below the water table. Existing aggregate operations that extract above the water table also require assessment if they propose to extract near or below the water table.
The assessment report may recommend measures to manage groundwater and surface water, including monitoring and advance planning in case unexpected changes to the site are detected. The reports are reviewed by the Ministry of Natural Resources, the Ministry of the Environment, municipalities and the local conservation
authority to ensure the groundwater is protected.
All the recommendations in the report must be included in the site plan required by the Ministry of Natural Resources for all aggregate operations that receive a licence or permit. Once a licence or permit is issued, the operator is legally bound to operate and rehabilitate the site as described in the site plan.
Operations where dewatering occurs may also require a Permit to Take Water or Environmental Compliance Approval from the Ministry of the Environment to protect surface water and groundwater in the area of the pit or quarry.
