Crushing myths about gravel pits
Pits and quarries are where the stone, sand and gravel used to build the roads, houses, hospitals, schools and infrastructure we all use every day comes from. These sites have been safely supplying the essential raw materials used for hundreds of years to build communities — yet they are often the subject of controversy.
Two of the largest myths about gravel pits and quarries are about water: that they somehow harm the local water supply or, that they use a significant amount of water and remove water from the watershed. Let’s set the record straight.
The mechanical process of removing aggregate from the ground is clean and safe. No chemicals are involved in the extraction or processing of aggregate materials. In fact, sand and gravel are the very materials used in our water filtration systems. It will likely surprise you that several municipalities across Ontario use water stored in former quarries as their primary water reserve — with testing showing it to be some of the cleanest water in the province.
Before a licence for a new quarry or gravel pit can be issued under the Aggregate Resources Act, extensive studies are required to determine the potential effects from the proposed operations on nearby wells, streams, wetlands or other sensitive environmental features.
These studies take into consideration the geology and hydrogeology of the area, including groundwater levels and flows, to ensure that the final depth of extraction does not negatively impact natural infiltration or groundwater recharge.
Groundwater and surface water monitoring programs are implemented to monitor for potential effects of operations on local quantity and quality. On the rare occasion that a domestic water supply may be impacted by an aggregate operation, there are legal requirements to ensure water supplies are restored.
Now let’s talk about how much water is actually used on a site.
Prior to beginning operations, the producer applies to the Ministry of Environment, Parks and Conservation for a permit to take water. But where are they “taking” it? The answer is nowhere.
Unlike water bottling or beverage companies that are taking water away, aggregate producers pump water from one area of the quarry and either recirculate it or discharge it off site (into the same watershed). For example, after a heavy rainfall or when the snow melts, they may need to relocate large volumes of water to keep the quarry floor dry so that workers can extract the rock. That big number listed on the permit is what critics of the industry often use to demonstrate that the industry uses a lot of water. But that number is the maximum and is very rarely needed.
The actual amount of water used by pits and quarries in Ontario is only 0.13 per cent of the total water taken by all industries. That is worth repeating — less than a quarter of one per cent!
Aggregate producers also sometimes use water to wash the product. To meet specifications for road building and construction projects, sand, gravel and crushed stone often need to be washed to remove fine particles. The water is typically taken from an on-site source pond and fed to the wash plant, which rinses the product with water. Again, no chemicals are used in this process.
Washing facilities use a closed loop system design, where the rinse water is collected in a series of ponds to allow the particles to settle to the bottom, then is recirculated back to the wash plant source pond to be reused, over and over again. The only water lost is through evaporation and the small amount of residual water that remains on the product as it leaves the site.
One final use of water at a pit or quarry is for dust control. Suppressing dust at a pit or quarry is the law. To minimize dust — a byproduct of extracting and crushing rock — water is sprayed on internal haul roads, processing equipment, stockpiles and trucks exiting the site. Quarries have developed best management practices for water conservation that are designed to use only the amount of water that is needed to control dust.
Aggregate sites are safe and clean and do not harm our drinking water. Aggregate producers are water managers accountable to the public and the government to ensure water quality and quantity are protected in private wells and the surrounding environment.