Mine Seepage and Water Quality

The Contaminants:

The primary mine-related contaminants that have exceeded State water quality standards and permit limits in groundwater and surface water are nitrate, sulfate, total dissolved solids (TDS), and specific conductance. Chloride has also exceeded 2015 permit limits, but its primary value is as a tracer of the movement of mine-related contaminants in the environment. Exceedence of permit limits at compliance monitoring locations is considered a violation of the mine’s water discharge permit and is evidence of the lack of proper functioning of the capture zone. 

Each spring since 2010, water in the groundwater monitoring well “MW-14” has exceeded water quality standards for sulfate (250 mg/L), and total dissolved solids (TDS) values have exceeded the TDS standard (500 mg/L) each spring since 2009. The exceedences extended from April to November in 2013 for sulfate, and from April through December for TDS – the longest periods of exceedence yet recorded for this well. The MW-14 wellhead is located near Gold Bowl Creek in the Nicholson Creek drainage, downgradient from much of the underground mine and surface facilities. Sulfate concentrations in well MW-2R, which is located in the same area, also exceeded the water quality standard for the first time in 2013.

These and other contaminants have been elevated since mining began, and remain elevated in groundwater east of the mine. The worst time of year is in spring, when runoff seems to flush the contaminants. Nitrate in surface water west of the mine (upper S Bolster Creek) has also been elevated since mining began. By the time water is monitored in lower S Bolster Creek, the contamination has largely dissipated.

The Challenge:

Despite the implementation of a number of adaptive management measures, the capture zone continues to fail; certain groundwater, surface water, and spring/seep locations continue to exceed water quality standards and NPDES permit limits; and mine-related contaminants continue to migrate to downgradient locations. The challenge is to design a program that will bring water quality into compliance with the 2015 permit and return site waters to near baseline conditions.

Where are the Contaminants Coming From?

The primary sources of observed permit exceedences, according to information from Crown/Kinross reports, have been: treatment plant effluent when a primary ion-exchange system was used (2008-2009), construction fill, and the development rock stock pile(s). Because hydrologic capture is known to have failed in at least some areas of the site, the underground mine must also be examined as a potential source (using water quality data from mine sumps). 

The mining company and their consultants continue to attribute some the groundwater quality problems to discharge from the treatment facility. However, since the reverse osmosis treatment was introduced in 2010, effluent discharges have been of much higher quality than previously with the old ion exchange treatment method. The company consultant said that it takes time for the water and contaminants to move through the fractured bedrock groundwater system, and they predicted that concentrations would be back to normal in a couple of years. When time failed to materialize clean water, they introduced the theory that leachate from construction rock under the surface facilities was the culprit, and they began digging trenches in hopes of intercepting shallow contaminated groundwater and directing it to the treatment facility.

OHA believes that the groundwater quality problems are likely due, at least in part, to contaminated water being pushed out of the underground mine sumps. Millions of gallons of mine water are stored in these sumps, especially in spring, and hydraulic pressure generated by stored water could send contaminated water outside the mine along the faults. The mine is required to maintain a capture zone whereby no mine water escapes from the mine, and OHA believes that this leakage should be considered an unpermitted discharge.

Stemming from discussions initiated following OHA’s notification to Crown/Kinross of our intent to file a Clean Water Act lawsuit, the company has listened to our concerns. However, the company has so far made little progress in addressing the issues OHA has raised. OHA has made it clear that our patience is not limitless, and we have called on Crown/Kinross to initiate a comprehensive appraisal of the mine’s water quality problems and to take effective corrective actions. 

Why Do Sulfates Matter?

Many of the metals being mined in North America, including gold, tend to be found in rock that contains sulfide minerals. When ore and surrounding rock are excavated during mining, the sulfides become exposed to water and air, and may form sulfuric acid. This acid in turn leaches metals and other substances from the rocks that can harm ecosystems. Acid mine drainage is considered one of the most serious environmental threats posed by mining, and it can devastate aquatic resources for generations. 

The Buckhorn Mine permit limits for sulfate in surface water and groundwater are 72 and 69.5 mg/l, respectively. These values represent the highest pre-mining sulfate level found in healthy streams and groundwater on Buckhorn Mountain. The Washington State water quality standard for protection of groundwater is 250 mg/l, which is significantly higher than the natural levels on Buckhorn. Water flows easily between groundwater and surface water at many locations on and near the mountain.

Sulfates in the Water

The above image is from OHA’s March 2016 presentation at the Buckhorn annual mine coordination meeting. The graphs show that since the Buckhorn Mine began operating in 2008, sulfate concentrations have been increasing in groundwater and surface water downgradient from the mine to the north and east.

GW2, the Roosevelt mine adit, is located downgradient (east) from the Buckhorn mine and is pictured below. Levels of sulfates and nitrates in water from the adit have been steadily increasing since mining began.