Every day in Ontario we lose 175 acres of what is often our best farmland to threats such as urban sprawl and aggregate mining. Most people are probably familiar with the impacts urban sprawl has on farmland, but the impacts from aggregate mining may not be as apparent. To help clarify this issue, we have put together this blog post to explain what aggregate mining is, and how it is threatening Ontario’s most valuable resource, farmland.

Aggregates are stones, sand, or gravel found underneath the soil in deposits across Ontario. These deposits were left here when the glaciers that sculpted our landscape were melting, around 10,000 years ago. In the thousands of years since then, agricultural soil formed on top of these deposits, effectively burying them.

However, aggregates are not just resources trapped beneath agricultural soil, they are actually an essential part of that soil. A vital component of productive agricultural soil is the soil horizons (pictured below). These layers of different types of soil are all important for farming, as each layer provides a service needed for growing crops. The top layers provide nutrients found from organic matter, the middle layers provide nutrients from minerals (rocks), and the bottom layer both helps with soil drainage, and contributes material to the formation of new soil (Parikh & James, 2012).

Today, aggregates are used in the construction of urban areas for building up roads or construction sites. However, this study by Ontario’s Ministry of Natural Resources (2010) determined that 93% of the aggregate deposits that are near high-demand areas also overlap with agricultural land and natural features.

When aggregate extraction occurs, the layers of soil on top of the aggregate deposits are scraped off and, in this process, mixed up, which destroys the soil horizons. This means that, even if the land is rehabilitated back to a condition where agriculture is possible, it can never be as productive as it was before. The horizons of the soil have been destroyed, and the soil is no longer ideal for growing crops. In fact, studies show that even if the land is rehabilitated back to what aggregate companies describe as an “agricultural condition”, it will never achieve the productivity it had before the extraction (Skelton Brumwell Associates Inc., 2009).

Once aggregate extraction occurs on agricultural land, it can never be as productive as it was before.

If extraction occurs below the water table resulting in a pond or small lake (which it often does), the land can never be rehabilitated back to an agricultural condition.

However, provincial legislation continues to insist that agricultural land, once mined for aggregates, can continue to be as productive as before, a fact which is simply not true. This belief in the success of rehabilitation means that even our prime agricultural and specialty crop areas are being mined for aggregates. When this happens, we are permanently losing production capabilities from our best agricultural lands.

This is why OFT fights to protect Ontario’s agricultural land, some of the best agricultural land in Canada, from being destroyed by aggregate extraction. In 2019, we provided recommendations to the government on the Aggregate Resources Act to help strengthen protections for agricultural land in Ontario. If you would like to read our submission and learn more about the consequences of aggregate mining on our agricultural land, click here.


Ontario Ministry of Natural Resources. (2010). State of the Aggregate Resource in Ontario Study. Retrieved from

Parikh, S. J. & James, B. R. (2012) Soil: The Foundation of Agriculture. Nature Education Knowledge 3(10):2.

Skelton Brumwell Associates Inc. (2009). SAROS Paper 6: Rehabilitation. State of the Aggregate Resource in Ontario Study.

Soil Science Society of America. (2019). Soil Horizons. Retrieved from