The Appropriate Management of Tailings Dams (Slag Accumulation Sites)

Mineral Resources Business

Overview

a) Provide an overview of your tailings management system, and how you manage risk

  • SMM investiged the stability of its all tailing storage facilities (TSFs) after the Great East Japan Earthquake in 2011 based on significantly tightened technical regulations under the system of the Mine Safety Act in Japan.
  • SMM currently manages 42 TSFs which are subject to disclosure. The number of TSFs is scrutinized and adjusted from 56 to 42 due to mainly removal of the ancient TSFs which are difficult to be tracked down in spite of record in the old documents. These TSFs were intensively investigated and 11 TSFs were classified to be reinforced agaist the large scale earthquake.
  • These TSFs were intensively investigated and 11 TSFs were classified to be reinforced agaist the large scale earthquake.
  • The seismic reinforcement work for these 11 TSFs were completed before 2018.
  • Breakdown of the 11 TSF,
    • SMM found that 9 TSFs would not be able to keep their stability if "L1*1" or "L1 and L2*2" earthquake takes place and completed mandatory seismic reinforcement measures to comply with the Japanese new regulatory act before 2018.
    • 2 TSFs were recognized that possible failure may happen when "L2" earth quake takes place. Although this category did not mandate seismic reinforcement from regulatory perspective, we carried it out based upon SMM's own standard to minimize the risk.

We operate following maintenance method.

  • Daily inspection
  • Monitoring phreatic line of the tailing dam by the monitoring holes.
  • *1L1 category : Designed earthquake stipulated in the technical standards issued by the Ministry of Economy, Trade and Industry (METI), - standard -
  • *2L2 category : the maximum class strong earthquake motions that could occur at present or in the future. - guideline -

b) Confirm whether your approach to tailings management has changed or will change in light of the recent tailings disasters at Brumadinho, Mariana, Mt Polly and others. Have you, for example, reviewed all tailings storage facilities with upstream dam construction, and taken steps necessary to protect local communities and the environment e.g. buttressing, evacuation?

  • Highly intensive investigation regarding TSF stablization of all 42 TSFs was carried out after the outbreak of the Great East Japan Earthquake in 2011. The seismic reinforcement for the 11 TSF had been completed by 2018. Therefore, any additional works for our TSF are not currently planned even after the recent disaster. However, SMM will enhance monitoring activities to identify any risks related to stability of TFSs based upon our rigorous in-house risk management system.

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