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THE BIOPASS SYSTEM: <br />AN ALTERNATIVE TO HEAP LEACH PAD CLOSURE <br />Terry Mudder, Times Ltd. <br />Scott Miller, Golder Associates Inc. <br />Luke Russell, Coettr d'Alene Mines Corporation <br />Alan Cox, Homestake Mining Company <br />Dave McWhorter, Chemac Envuonmental Services <br />1.0 INTRODUCTION <br />This paper presents a cyanide heap leach pad <br />closure approach which utilizes physical <br />stabilization and lined containment of spent ore <br />solids along with long-term biological passive <br />treatmem for draindown of residual solutions. <br />This is a cost effective alternative to the <br />traditional approach to heap leach pad closure <br />which generally includes rinsing of spent ore <br />with fresh or treated water until compliance <br />standards for solids and solutions are achieved. <br />Heap leach pad closure typically consists of <br />both short-term and long-term goals. The short- <br />term goal is to eliminate process solutions, <br />stabilize heap solids, and control erosion. The <br />long-term goal is to restore the site to a <br />condition suitable for pre-mining uses of <br />mineral exploration, mining, livestock grazing <br />and wildlife habitat by restoring useable <br />vegetation similaz to that which existed on the <br />site prior to disturbance. In addition, objectives <br />include development and implementation of a <br />heap leach pad closure which eliminates <br />maintenance requirements and the potential for <br />furore environmental remedial action. <br />The traditional approach to heap leach pad <br />closure is to rinse the heaps with several pore <br />volumes of fresh of treated water. The effluent <br />from an initial rinse is often treated and <br />recirculated until the solutions passed through <br />~II ~I~II~II~~'~~~I~ <br />sas <br />~EC~IV~=r <br />SEP 0 8 x995 <br />Divisicn or ;,iine!21s & GeoiCOv <br />the heap meet the appropriate numeric and <br />narrative water quality standards. Column <br />rinsing tests are often completed during project <br />planning to determine the number of pore <br />volumes of fresh water required to rinse the <br />heap to meet the closure criteria. A traditional <br />closure plan generally includes provisions to <br />sample the rinse effluent and rinsed solids to <br />verify that the chemical requirements aze being <br />met. This closure approach, although a proven <br />technology for small heaps, presents a number <br />of technical difficulties for large leach pads <br />including: <br />• Rinsing the heaps with multiple pore <br />volumes requires years; <br />• Large quantities of solution requiring <br />treatment or land application are generated; <br />and, <br />• Due to preferential pathways in the heap, <br />complete rinsing and detoxification is <br />unlikely. <br />Recent evidence from actual heap leach <br />operations indicates that numerical cyanide and <br />pH standards can routinely be met by rinsing, <br />however, effluent standards cannot be achieved <br />due to leaching residual metals and other <br />inorganics. <br />1? The BioD~tss System <br />An alternate approach is needed to allow <br />stabilization of a heap leach pad that will meet <br />the existing closure objective in regard to <br />control of long-term effluent flows and <br />1- <br />