Pend Oreille Mine Nw Tailings Dam Reservoir Report

Last Updated: December 15, 2025

The Pend Oreille Mine NW Tailings Dam in Pend Oreille, Washington, stands as a vital structure managed by a private entity, designed by Knight Piesold.


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Summary

Completed in 2002, this earth dam serves the primary purpose of storing tailings, with a hydraulic height of 67 feet and a length of 800 feet. Despite its modest surface area of 3 acres, the dam boasts significant storage capacity, with a NID storage of 2900 acre-feet.

Maintained by the Washington Dept of Ecology, the Pend Oreille Mine NW Tailings Dam has undergone regular inspections, with its condition assessed as satisfactory as of July 2019. This dam poses a significant hazard potential, yet the risk management measures remain unspecified. While the dam has not experienced modifications in recent years, its emergency action plan status and adherence to guidelines are unclear, pointing to potential areas for improvement in emergency preparedness.

Located offstream from the Pend Oreille River, this dam is a critical component of the region's water resource infrastructure. With its storage capacity and regulatory oversight, the Pend Oreille Mine NW Tailings Dam underscores the importance of proactive monitoring and maintenance in safeguarding against potential hazards and ensuring the safety of surrounding communities and ecosystems.

Year Completed

2002

Dam Length

800

River Or Stream

Offstream - Pend Oreille R.

Primary Dam Type

Earth

Surface Area

3

Hydraulic Height

67

Drainage Area

0.42

Nid Storage

2900

Structural Height

67

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

67
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.