Crown/Kinross stated in its cover letter that it is “committed to proper and appropriate closure” and has “completed many of its mitigation and closure commitments.” OHA commented that the long history of permit violations and the ineffectiveness of mitigation measures installed to control mine contaminants does not instill confidence in these statements. In particular, any closure plan for the Buckhorn Mine must also include a plan to bring the mine into compliance with its current discharge permit.
Crown’s cover letter states that its objective is to expedite hydrologic closure with the goal of attaining state groundwater and surface water criteria. OHA criticized the poor quality of Crown’s approach and methodology and recommended that Ecology should reject this Plan. OHA is asking Ecology to require a plan premised on bringing water resources into compliance with the current National Pollution Discharge Elimination System (NPDES) permit limits, rather than the generally less stringent state water quality criteria.
The following provides a list of OHA’s primary issues, which should be included in a final closure plan. More detail can be found in our submitted comments, at the above link.
- Meeting Permit Limits: The closure plan should be based on meeting current NPDES permit limits rather than state water quality criteria.
- Hydraulic Barriers and Bulkheads: The potential for a blowout and other potential adverse consequences should be examined.
- Lowering Water Levels for Freshet: An alternative approach that does not require lowering the mine pool each year should be evaluated. Water-budget neutral recirculation and use of bleed values on bulkheads should be considered as alternatives.
- Stormwater: A plan for analysis of stormwater monitoring data should be included in the Plan so that the mass of contaminants captured and the effectiveness of the system are known. The Plan should require testing and reporting of stormwater quality and volumes.
- Plan for Bringing All Water into Compliance: Approaches for bringing all locations that exceed permit limits into compliance with the permit should be included in the Plan. All sites that currently do not meet permit limits should be listed in the plan.
- Closure Adaptive Management: A closure adaptive management plan should be included as an appendix to the hydrologic closure plan.
- Groundwater Elevations during Closure: The closure plan should estimate groundwater elevation changes during closure and interaction with ore and potentially acid generating development headings and Damaged Rock Zone areas using cross sections or the 3D visualization tool, and compare these levels with the predicted steady-state elevation.
- Transitions between Closure Phases: Phase 1 should end when the Gold Bowl Zone meets permit limits; Phase 2 should end when the Southwest Zone and all water quality monitoring locations meet NPDES permit limits. Phase 3 should end when that water quality has been maintained for a period of ten years. The final closure plan should describe in detail the steps involved in reaching the end of each phase.
- Additional Dewatering and Monitoring: Dewatering wells should be added to the workings during closure. Certain piezometers should be converted to monitoring wells to expand the network. Additional dewatering wells should be established to ensure protection of the environment until all groundwater meets applicable permit limits.
- Treatment Approaches: The existing Mine Water Treatment Plant (MWTP) should be maintained and used through Phase 2 of closure. An auxiliary or containerized reverse osmosis treatment approach could be used during post-closure (Phase 3), as long as it can treat water to meet applicable permit limits.
- Predicting Time to Closure: Water quality changes during closure should be examined from mines with similar geochemical conditions and closure approaches and applied to the prediction of times needed to meet permit limits. Testing, using techniques such as wall washing and acid-base accounting, should be done to estimate contaminant additions from workings and Damaaged Rock Zone areas that will be exposed during closure, and this information should be incorporated into predictions. Calculations should be provided that support estimation of cleanup times.
- Recirculation and Water Balance: Recirculation during closure is poorly defined and needs to include: a schematic showing the conceptual water balance and recirculation model; points of withdrawal and input and water sources; better estimates of how varying freshet inflow volumes (high, low, average) would affect infill rates; realistic MWTP production rates; pumping rates required to produce the proposed 200 gallons per minute recirculation and drawdown; and all methods and approaches used for recirculation.
- Monitoring Frequency: During Phase 1 of closure, monitoring should continue according to the NPDES permit. During Phase 2 of closure, monthly monitoring should continue at all sites that do not meet NPDES limits, for the parameters that do not meet the limits. Any monitoring site/parameter that maintains NPDES permit limits for five years may be reduced to quarterly monitoring and discontinued after ten years, upon approval from Ecology.
- Habitat condition and stream sediment quality monitoring should be conducted during closure for streams that have received mine water inputs. If needed, stream reclamation should be included as part of the closure process.
- The Plan should include information on the linear feet of shotcreted and unshotcreted potentially acid generating workings and headings above and below 4,950 ft elevation. The information should be used to estimate the potential addition of mine-related contaminants to the workings during closure and how these inputs would affect the time to meet closure goals.