Canada’s Metal and Diamond Mining Effluent Regulations

Last updated: 8 November 2022

Canada’s Metal and Diamond Mining Effluent Regulations (“MDMER”) establishes effluent concentration limits for the following "deleterious substances": arsenic, copper, cyanide, lead, nickel, zinc, suspended solids, radium 226, and un-ionized ammonia. The regulation requires the owner or operator of the mine to monitor the environmental effects of effluent deposits at each final discharge point and submit the results of these studies to the Minister of the Environment. Effluent sample tests must be taken once a month to determine whether the effluent is acutely lethal to a number of aquatic species in particular: rainbow trout, threespine stickleback, daphnia magna, and acartia tonsa.
In 2021, the Regulation was amended to include stricter discharge limits for concentrations of arsenic, cyanide, and lead, as well as for un-ionized ammonia.

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