While Imperial Metals claims the tailings pond waste water is almost drinkable, The Ministry of Environment has released details about what the slurry actually contains.
The Mount Polley tailings impoundment includes selenium concentration 2.8 times greater than normal drinking water guidelines.
Also mixed in is nitrate, cadmium, copper, iron which have “exceeded aquatic life guidelines” sporadically in the last few years.
The Ministry has conducted 14 inspections since 2012.
The company was cited in May for exceeding the height of the effluent, and in April for bypassing necessary treatment work after experiencing high flows.
Imperial Metals also wants to double to amount of ditch water it can release into Polley Lake.
That application is being considered.
Mount Polley has had an effluent permit (#11678) with the Ministry of Environment since 1997.
Mount Polley mine operates with an annual water surplus, and had 6.5 million cubic metres of water stored in the tailings storage facility.
In 2009, Mount Polley applied for an permit amendment to discharge up to 1,400,000 m3/year of dam seepage effluent from the tailings storage facility to nearby Hazeltine Creek. The amended permit limits discharge to 35% of that creek’s daily flow rate, with contaminant limits, and requires an annual discharge plan.
Prior to this permit being granted, concerns were raised about the proposal, prompting an independent report by a third party.
This report was commissioned to provide a review of the application submitted, requesting authority to discharge water from the mine to Hazeltine Creek.
The scope of the third-party review included consideration of the environmental impacts on the receiving environment, monitoring of the discharge and management conditions pertaining to the discharge. These recommendations were considered carefully in the amendment process and provided a basis for some of the conditions in the amended permit, which was approved in 2012.
Mount Polley has since submitted a further permit amendment request to discharge up to 3,000,000 m3/year of treated effluent (ditch water) to Polley Lake, which overflows to Hazeltine Creek.
This application was received by the ministry this summer and is being considered.
B.C. Water Quality Guidelines are levels at which the potential exists for impacts on various water uses. Environmental Protection Division staff reviewed the tailings supernatant (i.e., the liquid in the tailings pond) data sent by Mount Polley Mining Corporation on Aug. 4, 2014 and found that for the impounded tailings supernatant:
The selenium concentration exceeded the drinking water guideline of 10 ug/L by a factor 2.8 times.
Sulphate did not exceed the drinking water guideline of 500 mg/L in May 2014. However, there have been frequent small exceedances of this guideline over the last few years.
Molybdenum concentrations were well below drinking water guidelines over the last two years. However, recent molybdenum concentrations in the supernatant exceeded livestock watering and irrigation guidelines of 0.05 mg/L.
Organic carbon concentrations exceed the 4 mg/L guidelines for chlorination (water treated with chlorine that contains >4 mg/L of organic carbon can result in toxic chlorination by-products).
In addition, the concentration of several parameters in the supernatant exceed aquatic life guidelines, such as nitrate, cadmium, copper, iron and selenium; some of these only sporadically in the last few years.
Effluent Discharge Compliance:
The Ministry of Environment is not responsible for inspecting the geotechnical integrity of the tailings pond structure; this is the responsibility of the Ministry of Energy and Mines. The Ministry of Environment is responsible to ensure no unauthorized effluent discharge from the tailings pond structure. With that respect, the ministry conducted 14 inspections (office review and on-site) on the Mt. Polley Mine since 2012. The following non-compliances were observed:
May 24, 2014: The ministry issued an advisory to Mount Polley Mining Corporation for exceedance of the height of effluent within the tailings impoundment. The effluent level returned to authorized levels commencing June 30, 2014.
April 18, 2014: The ministry issued an advisory to Mount Polley Mining Corporation for bypass of authorized treatment works. The site experienced high flows due to spring freshet which caused the pump system to become blocked and resulted in an overflow of effluent to the long ditch. Flow did not reach the creek and was directed into Till Borrow Pit.
January and April 2012: The ministry issued an advisory to Mount Polley Mining Corporation for not submitting monitoring data for one of the groundwater monitoring wells (GW05-1).
Aug. 30, 2012: The ministry issued a warning to Mount Polley Mining Corporation for failure to report exceedance of the height of effluent for the perimeter pond (E7). This perimeter pond overflowed, releasing approximately 150 cubic metres of effluent over 13 hours to ground.