Holden Mine - Phase 2 Proposal SEPA Public Comment Period
Holden Mine Cleanup Site — Phase 2 Remedial Action
Site identifiers
Cleanup Site ID: 4414
Facility Site ID: 338
SEPA Mitigated Determination of Non-significance
Washington State Department of Ecology, Toxics Cleanup Program, Central Regional Office
Comment period: September 1–15, 2026
Why you are receiving this notice
Ecology is issuing a threshold determination under the State Environmental Policy Act (SEPA, Chapter 43.21C RCW) for the Phase 2 remedial action at the Holden Mine Cleanup Site in Chelan County. We are notifying agencies with jurisdiction or expertise so that you can determine whether the proposed action affects your programs, permits, or resources, and comment accordingly.
Site and regulatory context
Holden Mine is a former underground copper mine that operated from 1938 to 1957 in the Railroad Creek valley of the Okanogan-Wenatchee National Forest, adjacent to the Glacier Peak Wilderness. The site is accessible only by boat, barge, or floatplane up Lake Chelan to Lucerne, and then by a single gravel Forest Service road. Approximately 10 million tons of mill tailings and 250,000 tons of waste rock remain in three tailings piles along Railroad Creek.
The USDA Forest Service is the lead agency for cleanup under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), in cooperation with the U.S. Environmental Protection Agency, Ecology, Confederated Tribes and Bands of the Yakama Nation, and the Colville Tribe. Ecology is asserting concurrent cleanup authority under the Model Toxics Control Act (MTCA, Chapter 70A.305 RCW). A 2012 Record of Decision selected a two-phase remedy. Phase 1 was substantially complete in December 2018.
Mine-influenced groundwater from the unwalled sections of Tailings Piles 2 and 3 continues to discharge to Railroad Creek and to the wetlands east of Tailings Pile 3 at concentrations exceeding surface water criteria, although concentrations have declined since Phase 1 was completed.
Proposed Phase 2 action
The preferred alternative is groundwater containment without a barrier wall. Its principal components are:
• Installation of 15 groundwater containment wells along Tailings Pile 3, with 9 wells operating during the spring freshet and 6 redundant wells available during maintenance or well failure.
• Conveyance of an additional 290 to 690 gallons per minute of extracted mine-influenced groundwater to the existing Mine Water Treatment Plant, with NPDES-permitted discharge of treated water to Railroad Creek.
• Monitored natural attenuation of groundwater downgradient of containment, with an estimated restoration timeframe of approximately 40 years.
• Continuation of institutional controls and long-term performance monitoring under updated plans.
• Construction over two seasons, requiring barge deliveries at Lucerne and use of Forest Service Road 8301.
Ecology’s determination
Ecology has determined that the proposal will not have a probable significant adverse environmental impact, provided that the mitigation measures identified in the SEPA environmental checklist and the Mitigated Determination of Non-significance are implemented. This determination is issued under WAC 197-11-350.
The determination addresses construction-period effects including in-water and near-water work on Railroad Creek, effects on the wetlands east of Tailings Pile 3, air quality and noise, traffic and barge operations on Lake Chelan and Forest Service Road 8301, and effects on the Holden Village residential community.
Relationship to the federal process
The Forest Service accepted public comment on the Phase 2 Remedial Action Proposed Plan from June 15 through July 14, 2026. That comment period is closed. This SEPA comment period is a separate state process and does not reopen the federal Proposed Plan comment period.
Documents available for review
• Mitigated Determination of Non-significance (MDNS)
• SEPA Environmental Checklist
• Phase 2 Remedial Action Proposal
Contact Information
*Indicates Required Fields
Thank you for subscribing to the Holden Mine - Phase 2 Proposal SEPA Public Comment Period mailing list.
Holden Mine Cleanup Site — Phase 2 Remedial Action
Site identifiers
Cleanup Site ID: 4414
Facility Site ID: 338
SEPA Mitigated Determination of Non-significance
Washington State Department of Ecology, Toxics Cleanup Program, Central Regional Office
Comment period: September 1–15, 2026
Why you are receiving this notice
Ecology is issuing a threshold determination under the State Environmental Policy Act (SEPA, Chapter 43.21C RCW) for the Phase 2 remedial action at the Holden Mine Cleanup Site in Chelan County. We are notifying agencies with jurisdiction or expertise so that you can determine whether the proposed action affects your programs, permits, or resources, and comment accordingly.
Site and regulatory context
Holden Mine is a former underground copper mine that operated from 1938 to 1957 in the Railroad Creek valley of the Okanogan-Wenatchee National Forest, adjacent to the Glacier Peak Wilderness. The site is accessible only by boat, barge, or floatplane up Lake Chelan to Lucerne, and then by a single gravel Forest Service road. Approximately 10 million tons of mill tailings and 250,000 tons of waste rock remain in three tailings piles along Railroad Creek.
The USDA Forest Service is the lead agency for cleanup under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), in cooperation with the U.S. Environmental Protection Agency, Ecology, Confederated Tribes and Bands of the Yakama Nation, and the Colville Tribe. Ecology is asserting concurrent cleanup authority under the Model Toxics Control Act (MTCA, Chapter 70A.305 RCW). A 2012 Record of Decision selected a two-phase remedy. Phase 1 was substantially complete in December 2018.
Mine-influenced groundwater from the unwalled sections of Tailings Piles 2 and 3 continues to discharge to Railroad Creek and to the wetlands east of Tailings Pile 3 at concentrations exceeding surface water criteria, although concentrations have declined since Phase 1 was completed.
Proposed Phase 2 action
The preferred alternative is groundwater containment without a barrier wall. Its principal components are:
• Installation of 15 groundwater containment wells along Tailings Pile 3, with 9 wells operating during the spring freshet and 6 redundant wells available during maintenance or well failure.
• Conveyance of an additional 290 to 690 gallons per minute of extracted mine-influenced groundwater to the existing Mine Water Treatment Plant, with NPDES-permitted discharge of treated water to Railroad Creek.
• Monitored natural attenuation of groundwater downgradient of containment, with an estimated restoration timeframe of approximately 40 years.
• Continuation of institutional controls and long-term performance monitoring under updated plans.
• Construction over two seasons, requiring barge deliveries at Lucerne and use of Forest Service Road 8301.
Ecology’s determination
Ecology has determined that the proposal will not have a probable significant adverse environmental impact, provided that the mitigation measures identified in the SEPA environmental checklist and the Mitigated Determination of Non-significance are implemented. This determination is issued under WAC 197-11-350.
The determination addresses construction-period effects including in-water and near-water work on Railroad Creek, effects on the wetlands east of Tailings Pile 3, air quality and noise, traffic and barge operations on Lake Chelan and Forest Service Road 8301, and effects on the Holden Village residential community.
Relationship to the federal process
The Forest Service accepted public comment on the Phase 2 Remedial Action Proposed Plan from June 15 through July 14, 2026. That comment period is closed. This SEPA comment period is a separate state process and does not reopen the federal Proposed Plan comment period.
Documents available for review
• Mitigated Determination of Non-significance (MDNS)
• SEPA Environmental Checklist
• Phase 2 Remedial Action Proposal
Contact Information
*Indicates Required Fields