Underground – Limestone – A dam at a mining operation overtopped due to a significant rainstorm. The escaping water entered a mine portal and partially blocked entries, including the primary escapeway. No miners were injured during this event. The close call accident occurred on August 22, 2017.
- Maintain the pool at or below the established maximum normal pool elevation calculated by an engineer.
- Ensure all decant pipes or open-channel spillways are structurally sound and free of obstructions.
- Ensure primary and backup pumps are regularly tested and there is adequate onsite fuel to operate the pumps. Regularly inspect all dams for signs of distress and promptly make repairs when necessary.
MSHA standards 30 CFR §§56/57.20010 address retaining dams. They state, “If failure of a water or silt retaining dam will create a hazard, it shall be of substantial construction and inspected at regular intervals. “Substantial construction” includes adequately maintaining the dam to safely retain the material behind it, even during large storms. Ensuring adequate freeboard, the vertical distance between the lowest point on the dam crest and the pool elevation, is a part of this maintenance.