Although significant levels of copper and zinc were found downstream from the Tulsequah Chief mine, the mine’s drainage poses a low risk to fish in the Tulsequah River, according to a third-party water quality assessment released Dec. 20. The report also stated the discharge does not affect the Taku River.
Scientists from Palmer Environmental Consulting Group, Core6 Environmental Ltd. and Triton Environmental Consultants, firms based in British Columbia, performed a study of the water quality at four sites in the Tulsequah River, where the mine is located near the confluence of the Taku River in British Columbia about 40 miles north of Juneau.
The mine was originally operated in the 1950s, and according to a past Empire report Canadian inspectors have known since 1990 that the mine is leaking sulfuric acid into the Tulsequah River, down the Taku River and into Southeast Alaska.
The Taku River flows into U.S. waters about 10 miles southeast of Juneau, and is the largest salmon-producing river system in Southeast Alaska, according to the Alaska Department of Natural Resources website.
The British Columbia Ministry of Environment’s Ian Sharpe sent a letter in August 2013 to Toronto-based Chieftain Metals Inc., the owner of the mine, requiring the company to “hire a qualified professional, with experience in aquatic impact assessment and in particular, fisheries impact assessment, to provide the Ministry with a risk assessment of the current mine effluent discharge (into) the Tulsequah River from the Tulsequah Chief mine site,” the letter stated.
In April 2012, the ministry required the company to treat acid waters coming from the excavation and removal of historical waste rock at the mine through the Environmental Management Act, according to the letter.
When the mine was shut down in June 2012, the water treatment plant ceased to operate, putting the company out of compliance with the EMA. In a past Empire report, the company said cost overruns precipitated the shutdown and the water treatment plant would not run until the company secured adequate funds. The treatment plant had operated since December 2011.
In July 2012, the Ministry of Environment required the mine to determine an interim water treatment strategy and test water quality regularly, according to the letter.
“Since then, the Ministry has been receiving regular water quality submissions, and communicating with Chieftain to review the status of the project and obtain updates on the action plan to come into compliance with the EMA authorization,” the letter stated.
Chieftain Metals was required to submit its third-party-conducted risk assessment to the ministry by Oct. 31, 2013.
Risk to fish
To complete the risk assessment, four scientists studied water quality at four sites in the Tulsequah River: 4.5 kilometers upstream from mine site discharges; immediately downstream from interim water treatment plant discharge; about 325 meters downstream from a site exfiltration pond, used when the water treatment plant is not operating; and 2.7 kilometers from the site exfiltration pond.
They also studied the discharge’s impact on various types of fish: coho salmon, sockeye salmon, Dolly Varden and bull trout, and chinook salmon.
“Of the aquatic resources in the Tulsequah River, fish are likely the primary receptors with the highest risk of exposure to mine discharge,” the report stated.
Potential risks to fish were measured using the “hazard quotient” approach, “widely used in ecological risk assessments,” the report stated. When hazard quotients — or HQs — are less than or equal to 1, “no unacceptable risks will occur in the exposed aquatic population,” it stated. HQs greater than 1 can pose “unacceptable” risks to fish and other aquatic life.
The scientists identified cadmium, copper, lead and zinc as the contaminants of potential concern at the sites, based on tests from April 2012 to July 2013. “These dates represent the time period the (water treatment plant) was operational (February 2012 to June 2012) and when it was not operational (August 2012 to July 2013),” the assessment stated. The mine’s water treatment plant provided lower HQs while it was operating, the study found, but copper and zinc levels were at times greater than 1, regardless of water treatment. The sampling site 2.7 kilometers from the exfiltration pond had a maximum copper reading of 2.8, according to the assessment.
“It does not appear that the (water treatment plant) is capable of reducing mine discharge to levels where resulting HQs do not exceed the threshold of 1,” the report stated. “That said, regardless of whether the (plant) was operating or not, the HQs were less than 1 for the majority of the year including the critical time periods when chinook, sockeye and coho are migrating to spawn and the eggs are incubating and hatching.”
Fish tissue studies show trout were also unaffected by mine discharge, the assessment stated.
The study also found that Tulsequah waters are diluted six times when mixed with Taku waters. “This dilution would be more than required to reduce the maximum HQ to less than 1.”
“Overall, the potential risk to aquatic receptors as a result of mine discharge is considered low,” the report stated.
In a Dec. 20, 2013, letter to the British Columbia Ministry of Environment, Chieftain Metals CEO Victor Wyprysky outlined the steps the company took to fulfill the government’s directives.
“Based on the completed Aquatic Ecological Risk Assessment, Chieftain Metals is of the opinion that the extent of aquatic environmental risk is very low for the majority of the year and low to moderate during the winter and spring thaw events because some evidence is lacking as to whether fish use the Tulsequah River during the winter and spring thaw,” Wyprysky wrote in the letter.
According to the Ministry of Environment letter, the mine had funding for a 2013 exploration campaign and a “new timeline has been set for construction (2014 - Q1 2016), commissioning and production (Q1/Q2 of 2016).” Chieftain Metals purchased the property after former owner Redfern Corp. went bankrupt in 2009.
• Contact reporter Katie Moritz at 523-2294 or at firstname.lastname@example.org. Follow her on Twitter @katecmoritz.