Minerals and metals sector

• The minerals and metals sector is not a large water user. In 2005, mining companies withdrew 459 MCM of freshwater, a moderate decrease from 1996.
• Key water management issues relate to mine dewatering (see sidebar), acid rock drainage, metal leaching, salt accumulation and wastewater treatment. Though mining impacts on water quality and aquatic ecosystems tend to be localized, they can extend over long periods. The release of contaminants from some orphaned and abandoned mine sites has been a significant problem across Canada.
• There are 700 million tonnes of waste rock that could generate acid and 1.8 billion tonnes of potentially acidic tailings in Canada.
• Overall, the sector discharged almost 2000 MCM of treated wastewater in 2005.
• The Mine Environment Neutral Drainage (MEND) Program has developed technologies and practices to prevent or mitigate acid drainage and metals contamination. MEND technologies have been in widespread use by the industry at active mines. They are also used by the industry and by provinces and territories to address the problem of orphaned and abandoned mine sites in Canada.
• Monitoring data collected as part of the Metal Mining Effluent Regulations, considered one of the world’s leading standards for mine effluent quality, indicate effluent quality from active mines is very good.
• Wastewater management and treatment methods have progressed considerably in recent decades, with improved effluent quality and reduced impacts on ecosystems as the result.
• Total water-related spending by the sector amounted to $480 million in 2005. In the mining industry, this amount was equivalent to $0.068 per cubic metre of gross water use. Compared with other natural resources industries, mining companies devoted a higher proportion of their water-related costs to recirculation, likely due to high dewatering volumes.
• Spending on discharge treatment accounted for approximately one quarter of the water costs for the minerals and metals sector. This amount is less than that spent by the forest products manufacturing industry because much of the water released by mining companies is directly from mine dewatering. Dewatering discharge does not usually require treatment because it is generally not used in processing.

Mine dewatering refers to the activity of pumping water out of a mine site. To prevent water in aquifiers, rivers or lakes from flooding a mine, many establishments must often run their pumps continually. Some of this water may be used in processing activities, but most is disposed of off-site. As a result of dewatering, mining establishments often have zero consumption; they may even in fact be net producers of water.