MDMER explained: metal limits and sampling frequency
The Metal and Diamond Mining Effluent Regulations (MDMER) are the federal rules, under Canada’s Fisheries Act, that limit what a metal or diamond mine may discharge. In short: sample each final discharge point at least once a week, keep effluent pH between 6.0 and 9.5, test for acute lethality every month, report quarterly, and stay within the Schedule 4 limits for metals such as copper, lead, nickel and zinc.
What are the MDMER metal limits?
Schedule 4 of the MDMER sets three limits for each deleterious substance: a maximum monthly mean, a maximum in a composite sample, and a maximum in a grab sample. The limits are total concentrations in mg/L. These are the Schedule 4 figures for the four regulated metals most mines watch:
| Metal (total, mg/L) | Table 1 monthly mean | Table 1 grab | Table 2 monthly mean | Table 2 grab |
|---|---|---|---|---|
| Copper (Cu) | 0.10 | 0.20 | 0.30 | 0.60 |
| Lead (Pb) | 0.08 | 0.16 | 0.10 | 0.20 |
| Nickel (Ni) | 0.25 | 0.50 | 0.50 | 1.00 |
| Zinc (Zn) | 0.40 | 0.80 | 0.50 | 1.00 |
Source: MDMER (SOR/2002-222) Schedule 4, Tables 1 and 2; text current to 2026-09-30. Composite-sample limits sit between the monthly mean and the grab limit. Schedule 4 also sets limits for other substances, including cyanide, suspended solids, radium-226 and un-ionized ammonia.
Which table applies to your mine?
Table 1 applies to mines that the regulations first apply to on or after June 1, 2021, and to recognized closed mines that return to commercial operation after that date. Table 2 applies to every other mine. Table 1 limits are tighter: copper’s monthly mean, for example, is 0.10 mg/L under Table 1 and 0.30 mg/L under Table 2. Diamond mines have been covered since June 1, 2018.
How often must mines sample effluent under MDMER?
Weekly, at every final discharge point
Collect a grab or composite sample at least once a week, at least 24 hours apart, and record pH at collection (section 12).
Quarterly, once a substance stays low
A substance below 10% of its monthly-mean limit for 12 consecutive months may drop to once a quarter. At or above 10%, it returns to weekly (section 13).
Monthly acute lethality tests
A monthly grab sample from each final discharge point for acute lethality testing, which may move to quarterly after 12 consecutive non-lethal months (sections 14 and 16).
Environmental effects monitoring adds more: under Schedule 5, effluent characterization runs once per calendar quarter and receiving-water quality is monitored four times a year.
What must mines report, and when?
Effluent monitoring results go to the regulator in a quarterly report within 45 days of each quarter’s end (section 21), with an annual report by March 31 (section 22). Effluent pH must stay between 6.0 and 9.5 throughout (section 4).
What happens between weekly samples?
A weekly sample shows what the discharge was doing at the moment it was taken, and the result arrives days later. The question environmental teams ask is simpler: are we in spec right now? AquaValid answers it continuously. It measures dissolved metals in the discharge stream about a minute after each sample, every ~10 minutes, around the clock: about 1,000 readings a week, between the samples your accredited lab analyses.
From AquaValid’s published detection limits (tap-water matrix, mg/L): copper, nickel and zinc at 0.1, below the Schedule 4 Table 2 monthly-mean limits for all three, and below the Table 1 limits for nickel and zinc. Detection limits depend on the water, so we establish them on a sample of your discharge before deployment. Bringing lead detection down toward the 0.08 mg/L Table 1 level is one of our development priorities.
Your accredited lab results stay the MDMER compliance record. AquaValid adds the continuous trend between them, so a rising metal is something you see and act on before the next weekly sample.
“If you wait for the lab, you’re already out of compliance before you get their results.”
Read next: Lab turnaround vs real-time metals data · Real-time discharge compliance · Mining
MDMER FAQ
What does MDMER stand for?
The Metal and Diamond Mining Effluent Regulations (SOR/2002-222), made under Canada’s Fisheries Act.
How often do mines have to sample effluent under MDMER?
At least once a week at each final discharge point, with samples at least 24 hours apart. A substance that stays below 10% of its monthly-mean limit for 12 consecutive months may be sampled once a quarter instead. Acute lethality testing is monthly.
What is the difference between Schedule 4 Table 1 and Table 2?
Table 1 has the tighter limits and applies to mines that the regulations first apply to on or after June 1, 2021. Table 2 applies to all other mines. For example, the copper monthly-mean limit is 0.10 mg/L in Table 1 and 0.30 mg/L in Table 2.
How can continuous monitoring support MDMER compliance?
It fills the gap between weekly samples. AquaValid measures metals such as copper, nickel and zinc every ~10 minutes, so a rising trend shows up before the next lab result. Accredited lab analysis remains the compliance record.
This page summarizes the MDMER for orientation. The regulation text is authoritative, and your permit or regulator may set additional conditions.
Monitoring a discharge under MDMER?
Send us a sample and we’ll show you what AquaValid sees in your water.
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