OHA recommends that Ecology require Crown to take the following actions that would help clarify monitoring and closure requirements and lead to the eventual restoration of mine site water quality:
Add monitoring wells to the underground mine: There is currently only one monitoring point in each of the two zones to analyze water quality changes in the Buckhorn underground mine during closure. More monitoring is needed to understand how recirculation is affecting mine water quality, especially in a fractured bedrock setting. Water quality monitoring wells should be added to the more distant portions of the underground mine (not along the preferential pathway) to evaluate the effectiveness of recirculation during closure.
Modify the Hydrologic Closure Plan: A modified Closure Plan should include the issues discussed in Ecology’s approval letter, especially a requirement to have all monitoring locations on the site meet applicable permit limits for five freshets after recirculation, dewatering, and treatment have stopped. During this time, the treatment plant, dewatering, and recirculation should be available to resume if permit limits are not met. The Closure Plan should clarify that all monitoring locations on the site should meet permit limits by the end of closure, including those inside the capture zone.
Require a Closure Adaptive Management Plan: A separate Closure Adaptive Management Plan should be required to address changes in water quality, stream flows, and groundwater elevations during closure and post-closure. This plan should include monitoring locations and criteria, trigger levels, mitigation measures to be taken, responsibilities, and evaluation of mitigation effectiveness. The Closure Adaptive Management Plan should also include contingencies that expand the time period and potentially restart water treatment if water quality degrades during the five-year period of the closure phase after treatment has ceased, and during the ten-year period of post closure. The trigger for adaptive management actions should be a comparison to permit limits rather than historical concentrations or trends. Finally, Ecology should require that all water on the site, including areas inside the former capture zone, meets discharge permit limits at the end of closure.
Require a Closure Hydrologic Monitoring Plan: A Monitoring Plan is needed for closure. A closure-specific monitoring plan should include descriptions of hydrologic and water quality monitoring, including parameters, frequency, and locations, during closure and post-closure periods. A decrease in monitoring frequency between Phases 1 and 2 of closure is not warranted.
Require a map showing underground workings, wells, flow directions, and high and low water during closure: Ecology should require Crown/Kinross to create a 3D representation showing the location of the recirculation inflow pipe and outflow well, piezometers, monitoring and dewatering wells, the sampling locations for the Gold Bowl and Southwest Zone sumps, and the Gold Bowl workings. Expected flow directions in the underground mine with and without pumping should also be included, as well as the separation between the two zones. High and low water levels from dewatering should be represented in 3D, including the mine workings that are inundated during high water but exposed at low water.