St. Marys Lime Sludge Lagoons

About St. Marys Lime Sludge Lagoons

The primary purpose of St. Marys Lime Sludge Lagoons is tailings. Tailings dams contain waste material from mining operations — typically a slurry of finely ground rock left over after valuable minerals have been extracted. These structures require ongoing monitoring because tailings can contain heavy metals and other contaminants. The dam is owned by City Of St. Marys (local government). It impounds the Koop near St. Marys.

The dam stands 13 feet tall and stretches 2,640 feet across, creates a reservoir covering 12 acres, has a maximum storage capacity of 128 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1988, the structure is 38 years old.

This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 12/04/2024.

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