Mine Waste Rock Hydrogeology — The Effect of SurfaceConfiguration on Internal Water Flow

摘要

A better understanding of the hydrogeology within mine waste rock andrncover systems is essential for the quantification, prediction andrnprevention of metals loading to the environment surrounding waste rockrnpiles. The effect of surface condition on the internal flow mechanismsrnwithin an intermediate-scale constructed waste rock pile is beingrninvestigated at the Cluff Lake Mine, Saskatchewan. Changes in the waterrnbalance, the outflow distribution and water residence time have beenrnobserved in the waste rock pile following successive modifications of thernsurface condition. The three year old, run of mine, free-dumped surfacernwas ripped to a depth of 30 cm to 40 cm, and levelled in October of 2001.rnIn August 2002, a 10 cm to 15 cm cover of compacted waste rock wasrnplaced on the pile. Outflow, precipitation and run-off data collectedrnduring natural and artificial rainfall events have been used to quantify thernmaximum infiltration rate, and the spatial pattern of discharge andrncumulative volume of water that infiltrated into the waste rock underrneach surface condition. Infiltration data together with the outflow datarnprovide a basis to address the residence time of water within waste rockrnand the dominant flow mechanisms for different surface conditions. Withrna free dump surface spatially distinct wetting fronts are observed at thernbase of the pile that vary in flow rate by an order of magnitude (measuredrnat a 2 m by 2 m scale) and in time by up to a week. Following rippingrnand levelling, similar cumulative outflows were observed, but thernmagnitude and arrival time of wetting fronts changed across the pile. Arndecrease in outflow volume, a decrease in infiltration volume, a two-foldrnincrease in the response time of wetting fronts and a more spatiallyrnuniform distribution was observed following placement of the compactedrnsurface layer. Based on preliminary data, the internal structure appears tornbe the dominant factor controlling outflow variability.