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Third national assessment

1.0 Introduction

The Metal Mining Effluent Regulations (MMER) came into force in 2002 under the Fisheries Act. The Regulations prescribe discharge limits for arsenic, copper, cyanide, lead, nickel, zinc, total suspended solids, radium 226 and pH, and require that the effluent not be acutely lethal to rainbow trout. These end-of-pipe limits provide a national standard that is intended to protect fish, fish habitat and the use of fisheries resources. The metal mining sector is achieving over 95% compliance with the prescribed discharge limits and meeting the requirement that effluent not be acutely lethal to rainbow trout (Environment Canada 2015).

In addition to complying with end-of-pipe limits, Canadian metal mines subject to the MMER (Appendix A, Figure A1) are required, as a condition governing their authority to discharge effluent, to conduct environmental effects monitoring (EEM) studies of the potential effects of metal mine effluents on fish, fish habitat and the use of fisheries resources. Information obtained through EEM supports the evaluation of the effectiveness of the Regulations in protecting the aquatic environment and of current and future pollution prevention and control technologies, practices and programs within the mining sector. The purpose of this report is to present the major findings of the EEM studies conducted by metal mines across Canada.

In the MMER, an “effect” is defined as a statistical difference between specific data collected from an exposure area and a reference area. An exposure area means all fish habitat and waters frequented by fish that are exposed to mine effluent and a reference area means water frequented by fish that is not exposed to mine effluent and that has fish habitat that, as far as practicable, is most similar to that of the exposure area. The presence or absence of an effect is considered confirmed when a similar type of effect or an absence of an effect has been observed in two consecutive studies.

Environmental effects monitoring studies required by the MMER consist of biological, effluent and water quality monitoring studies. Biological monitoring studies to assess potential effects of mine effluent are undertaken on the following components of the aquatic receiving environment:

  • fish population to assess effects on fish health;
  • benthic invertebrate community to assess effects on fish habitat; and
  • fish tissue to assess effects on the usability of fisheries resources when conditions specified in the MMER are met.

Biological monitoring studies to investigate observed effects are conducted in order to:

  • assess the magnitude and geographic extent of effects; and
  • determine the causes of effects.

EEM biological monitoring studies under the MMER constitute an iterative system of monitoring and interpretation steps which are conducted every three to six years according to conditions specified in the Regulations. The type and frequency of studies is determined by the results of previous studies. Initial biological monitoring studies are undertaken to assess and confirm the presence or absence of effects. When effects are confirmed, mines are required to determine the magnitude and geographic extent of those effects, and then to investigate their causes. If the absence of effects on the benthic invertebrate community, fish population and fish tissue (if required) is confirmed, biological monitoring frequency can be reduced. To assist mines in fulfilling the regulatory requirements for EEM, Environment and Climate Change Canada (ECCC) has developed technical guidance on all aspects of EEM studies, including study design, data analysis and interpretation (Environment Canada 2012a).

Specific indicators are measured to assess the presence or absence of effects on the fish population (Appendix B, Table B1) and the benthic invertebrate community (Appendix B, Table B2). The results of these assessments determine future monitoring study requirements and contribute to an understanding of the impact that metal mining effluent may have on aquatic receiving environments. The size of observed effects is used as a non-regulatory management tool to focus the effort of investigative studies towards the greatest risk to the environment. A critical effect size (CES) is a threshold above which an effect may be indicative of a higher risk to the environment. Critical effect sizes for the fish population and benthic invertebrate community indicators were initially developed for the pulp and paper sector after EEM studies showed that most mills observed an effect on at least one of the indicators. Once validated (Munkittrick et al. 2009), these CESs (Appendix B, Table B3) were adopted for use in the metal mining sector as well.

Effluent and water quality monitoring studies, consisting of the chemical characterization and sublethal toxicity testing (SLT) of final effluent and water quality monitoring in the environment, contribute to the assessment of effluent quality and aquatic environment conditions at individual mine sites.

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