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Failure of the Capture Zone

A groundwater capture zone is the area in which any mine-related contaminants are captured by mine water management, rather than being released to the environment without treatment. Crown/Kinross has not been able to keep mine-related contaminants within the capture zone of the Buckhorn Mine.

Water quality monitoring data for South Fork Bolster Creek station SW-14 shows elevated concentrations of nitrite plus nitrate above background values in every sample collected since July 2008, which demonstrates that Crown has failed to maintain a capture zone on the west side of Buckhorn Mountain. The NPDES strictly forbids any discharges other than those that are permitted and there is no permit to discharge pollutants into Bolster Creek.
 
Nitrates (Nitrite plus Nitrate, mg/l as Nitrogen) at the SW-14 monitoring point in the South Fork of Bolster Creek are significantly above baseline, indicating escape of contaminants outside the capture zone.


By and large, the majority of the problems at the Buckhorn Mine are connected to the failure to maintain a capture zone. This was $376,000 of the $395,000 penalty assessed in July 2012. Crown attributes the problems to infiltration of storm water through contaminated rock, and so has not taken any actions to investigate or address the leaking of contaminants from the mine. (The actions they have initiated to date include doing assessments, identifying and evaluating with caveats of  “as appropriate” and “as needed,” so that business as usual prevails.)

  •     The company has not established reliable hydrologic control
  •     Contaminants continue to escape from underground mine
  •     Wells/seeps downgradient of mine exhibit increasing concentrations of mine related contaminants
  •     Cannot discern effects from effluent discharge vs. groundwater leaks from treated water stored in mine

In response to the capture zone failure, Crown says that they will evaluate the potential use of additional grouting and shotcrete, which has been part of the adaptive management plan to address the problems the mine has experienced. However, many of the places that were supposed to be grouted and shotcreted have already been filled with cemented backfill. Crown should consider removing cement in selected areas and putting grout/shotcrete where needed, as it was supposed to be from the beginning.

Crown says they will continue geophysical survey mapping. This was recommended in 2011 by their consultants as part of the Gold Bowl Action Plan to deal with water quality problems at that time. While Crown did some more geophysical mapping in 2012, no report was shared at that time; we are still waiting for results.

Crown’s proposal to install additional monitoring wells or piezometers, and use tracer studies where needed to better understand flow pathways, is spot on. These actions were required by the AMP early warning system and OHA has been urging the company to do this. We are anxious to see some action on this issue. Crown’s talk about increasing dewatering wells and/or pumping capacity has been heard for years, but no additional dewatering wells have been completed since 2010.

The problems with the Buckhorn Mine are not new. In 2010 a $40,000 penalty was issued for the same problem. The company’s solution, drilling additional dewatering wells, produced no measurable improvement, but instead of evaluating the results and adjusting the approach, the problem continues to this day. The penalty settlement forgives all past violations and provides a schedule for the mine to come into compliance, but does not include much in the way of on-the-ground actions to mitigate mine contaminants spreading into groundwater.

OHA continues to review the monitoring data, express concerns and provide recommendations to improve the mine’s water quality. In an effort to clarify understanding of the problems, Pacific Groundwater Group has developed a 3D visualization for OHA, which can help Ecology and Crown improve the data analysis and the understanding of how water moves through Buckhorn Mountain.