South Pasture Isa

About South Pasture Isa

The primary purpose of South Pasture Isa 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 The Mosaic Company (private). It impounds the Bowlegs near Ona.

The dam stands 48 feet tall and stretches 24,420 feet across, creates a reservoir covering 800 acres, has a maximum storage capacity of 36,000 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1990, the structure is 36 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. An emergency action plan is in place for this dam. The most recent inspection on record was 01/23/2006. That was over 20 years ago.

At 48 feet, this dam is taller than 92% of dams nationwide.

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