The current National Pollution Discharge Elimination System (NPDES) permit prescribes specific timelines for closure of the mine. 90 days before the planned closure date, the mining company is required to submit a complete closure plan. Following the closure plan and 30 days before closure, an approvable reclamation and rehabilitation plan must be submitted. Crown/Kinross has expressed that the mine would close by the end of 2016.
The draft Closure Plan that Crown/Kinross submitted in September 2016 included very rosy predictions on how long it would take to complete the closure of the mine. Closure is the period of time, after reclamation of the mine surface, that it takes to bring the water in the underground mine area into permit compliance. During operations, the mine area is like a mixing zone in that it is allowed to exceed permit limits. The predominant reason why Crown/Kinross could make such optimistic predictions is that they used less restrictive water quality standards in their computer model than the criteria required by the NPDES permit.
The Department of Ecology (Ecology) has rejected Crown/Kinross’s use of state water quality standards, since the more rigorous, site-specific, background water quality values of the NPDES permit are the legal requirement.
Below are some highlights from Ecology’s comments regarding Crown’s Closure Plan.
Ecology’s comments include the following input:
- The submitted hydrologic closure plan does not clearly state the regulatory water
- quality limits as established in the renewed NPDES Permit. Replace water quality criteria with current NPDES permit limits.
- The liners should be removed from the site.
- Regarding installation of a bulkhead between the GB and SW zone workings, the Plan
- should include risk assessment for the possibility of blowout.
- Please state that the existing MWTP will remain operational until the mine water
- quality meets the permit limits.
- Please explain how the equilibrium will be restored if the pumping and recirculating
- is done continually.
- One of the major objectives of the Plan should be meeting the NPDES permit limits
- which is based on pre-Buckhorn mine conditions for the surface water, and seeps and springs and groundwater.
- The treatment system should be maintained until all the monitoring locations meet
- the limits
- Phase 3 should begin when all water quality monitoring locations meet permit limits
- and should end when that water quality has been maintained for a period of ten years
In addition, Ecology’s comments make it clear that the Plan lacks specificity in critical areas, citing:
- A lack of any adaptive management in order to achieve the objectives.
- A simplistic water budget model, lacking discussion of the model results such as flows
- and volumes with respect to time, etc.
- No discussion of how the capture zone is going to be maintained.
- Use of a single elevation value for the entire mine area for post-closure groundwater
- predictions, ignoring the topography and other variables such as seasonal variation in water table.
- No analysis of stormwater monito-ring data in the Plan.
- No information on which stormwater controls will be removed or criteria for decision-
- No explanation on how the construction fill would be characterized. The management
- of construction fill decisions should be based on the outcome of the characterization.
Ecology also raises concerns that the auxiliary water treatment system is a single-pass reverse osmosis system with half the capacity of the existing system; therefore, using the auxiliary system during closure would not be as effective and efficient.