Over time, sulphides react with oxygen to form suplhates, which dissolve in water and form suplhuric acid which then leaches heavy metals.

This can cause large amounts of water with low pH and high concentrations of heavy metals such as manganese, iron, nickel, copper and zinc.

Discharge of acid drainage into water bodies causes an instant threat to the biota and ecological balance. It can threaten drinking water supplies and irrigation systems downstream from a mining site.

Over 16 years, the Bowdens project will excavate 46.4 million tonnes of waste rock.

57% (26 million tonnes) of this is classified as Potentially Acid Forming (PAF) because it contains iron sulphide minerals with more than 0.3% total sulphur.

Bowdens plans to stack this acid forming rock above the Lawson Creek water table over a 77 hectare area called the Waste Rock Emplacement Area (WREA).

29.7 million tonnes of toxic tailings remaining in the tailings dam at the end of mining are also acid forming, and include toxic chemicals like Sodium Cyanide.

Bowdens propose to prevent acid drainage by a “capture and contain” strategy, which would involve sealing the base of the entire 77 hectare waste rock emplacement with a 1.5mm thick liner.

The tailings dam is proposed to be partially sealed from beneath by a 450mm thick clay liner.

There is no evidence of the success, effectiveness or safety of this method across this scale from any other mine sites.

Bowdens proposal uses predictive modelling and small scale field trials to claim its containment designs will prevent acid drainage today and for generations to come. Is this a risk we should be taking?

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