Upper Delta (north Offset Dam & West Offset Dam)

About Upper Delta (north Offset Dam & West Offset Dam)

The primary purpose of Upper Delta (north Offset Dam & West Offset Dam) 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 Sisecam (private). It impounds the Green River near Green River.

The dam stands 40 feet tall and stretches 8,900 feet across, creates a reservoir covering 652 acres, and has a maximum storage capacity of 9,992 acre-feet. Completed in 2013, the structure is relatively new.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 06/05/2025.

At 40 feet, this dam is taller than 87% of dams nationwide.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Wyoming dam safety program can provide more specific information about emergency planning for this structure.

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