Holden Mine Remediation, CERCLA/MTCA/NRDA Support

US Forest Service

Okanogan-Wenatchee National Forest, Washington

Holden Mine Slope Grading

For over 10 years, Hart Crowser has supported the USFS on the CERCA/MTCA investigation and $400-million cleanup of this large, remote, abandoned underground copper mine site Chelan County. We are also supporting the Trustees in developing and negotiating a NRDA claim.

Remedial Investigation: We provided expert review of several phases of Remedial Investigations, Feasibility Studies (RI/FS), and Terrestrial Ecological Evaluations and conducted independent ecological risk assessments of terrestrial and aquatic (fresh water) environments. Our reviews included work plans, health and safety plans, sampling plans to characterize nature and extent of contamination and identify sources, quality assurance/quality control (QAQC) plans, quality assurance project plans, and community relations plans. Investigations included soil, mine wastes, groundwater, surface water (including the hyporheic zone), freshwater sediment, and terrestrial and aquatic biota (plants, soil invertebrates, aquatic invertebrates, and fish). We also reviewed and conducted groundwater modeling to characterize groundwater-to-surface water pathways and to identify contaminant source areas.

Feasibility Study: We conducted two supplemental Feasibility Studies (including a 741-page Supplemental Feasibility Study and a 420-page addendum) that compared the effectiveness of remedial alternatives, identified and screened a wide range of remedial technologies, including innovative and alternative technologies such as low-energy water treatment, deep groundwater barrier wall, and in situ soil remediation. We then developed a more limited number of remedial action alternatives and evaluated them for consistency with Model Toxics Control Act (MTCA) and other Applicable or Relevant and Appropriate Requirements (ARARs); and technical, environmental, public health, and institutional factors; and conducted disproportionate cost analyses. Our work included engineering analysis and detailed cost estimates and constructability reviews of alternatives.

Cleanup Action Plan: We prepared the Proposed Plan (fulfilling the MTCA Cleanup Action Plan requirements) and Record of Decision on behalf of USFS, Ecology, and EPA. The plan identified selected cleanup alternative and specified cleanup standards and other requirements at the site. We also coordinated public hearings; incorporated public input into revised documents; and prepared a responsiveness summary.

Remedial Design: We provided technical review of all Remedial Design documents including cost estimates, plans and specifications, pre-design investigation plans and reports, treatability study plans and results, operations and maintenance plans, permit documents, and habitat mitigation plans. Design elements included a mile-long, 30-60 ft deep groundwater barrier wall, a 1.5 MGD mine water treatment plant, stream relocation, interception of adit and seep discharges, grading, slope reinforcement, and capping tailings and waste-rock piles, demolition of dilapidated mill building, sediment remediation, institutional controls, and in situ soil treatment. We also assessed long-term Operation & Maintenance costs to determine the degree of financial surety required.

Remedial Action: We provided observations of key aspects of remedial action, including jet-grout columns for reinforcement of seismically vulnerable tailings slopes, and reviewed construction QC documents and design-change requests.  We also reviewed materials testing result, including grout, soil-cement slurry, aggregate, and rip rap. We provided engineering recommendations and field oversight for stabilization of failing tailings piles over a 3-year period.

Compliance Monitoring: We developed the technical framework for post-construction compliance monitoring and are reviewing compliance monitoring plans. Compliance endpoints include groundwater, surface water, the hyporheic zone (i.e., groundwater-to-surface water pathway), freshwater sediment, and aquatic biota (fish and macroinvertebrates).

Public Involvement and Stakeholder Engagement: We are responsible for maintaining the administrative record for the project, coordinating public meetings (e.g., during the Record of Decision (ROD) phase), creating fact sheets, mailing lists, press releases, and web text, developing responsiveness summaries, working with the Yakama Nation, and Holden Village, and other public involvement activities as needed.

Sediment: We evaluated impacts to freshwater sediments in Railroad Creek and Lake Chelan by applying Sediment Management Standards (WAC 173-204) criteria to chemical and bioassay data. We also evaluated contaminant inputs to sediment through groundwater recharge, erosion of mine wastes, and surface water and modeled the rate of natural recovery that would be expected from recruitment and re-deposition of clean material following completion of site cleanup activities.