By the mid-20th century we knew, though, and began implementing controls on existing methods. Those controls didn’t help us deal with new technology. Heap leach mines used a cyanide or sulfuric acid solution to extract gold, copper and nickel from crushed ore.
The pregnant solution then drifted down to an impermeable layer where it was collected so the metals could be removed. The scientists, planners and mine owners KNEW the layer was impermeable — until it wasn’t. They KNEW there was no risk — until there was. Unfortunately, leaks weren’t typically discovered until the nearby groundwater was poisoned.
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