This is the story of a waste rock dump success/failure. The story is in a new paper from BiTech Publishers and their premier magazine Geotechnical News. The story is summarized in the conclusion section of the paper, Why Waste Rock Piles Will Seep for Many Years after Being Covered by D.J.Williams. I copy the text for your quick review:

“Over the nine years of monitoring, the maximum recorded infiltration through the trial store/release cover has been 1.1 % of incident rainfall, although most of these years have experienced below average annual rainfall. The instrumented store/release covers have undergone annual cycles of wetting up during each wet season, followed by drying during each succeeding dry season, with the dried-out states at each depth within the cover showing little net change with time. The water quality of the seepage emanating from the waste rock piles at Kidston has improved significantly and the seepage flow rate has reduced significantly since the store/release covers were completed. The seepage water quality is expected to improve further and the seepage flow rate is predicted to approach the slow rate of percolation through the store/release cover within 17 years. This extended period before the seepage flow rate is expected to decreased to the slow rate of percolation through the store/release cover is a consequence of the waste rock piles having been left open to rainfall infiltration and storage for the 15 years duration of mining and will delay the surrender of the mining lease. This delay could have been reduced by constructing the piles in cells to full height and covering with cells progressively to limit their exposure to rainfall.”

Here are links to some other papers by Williams on related topics: