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<br />protection of waters of the State. The <br />alternative approach is to encapsula[e the leach <br />pad employing a vegetated soil cover, and leave <br />intact the liners to minimize the infiltration of <br />future seepage and to collect and treat any <br />storm related seepage in a biological passive <br />treatment cell. This concept for dealing with <br />residual drainage, if it occurs, from the spent <br />leach pads is to convert one of the existing <br />solution ponds at the base of each pad into an <br />in-situ anaerobic biochemical system, capable <br />of passively receiving and treating this drainage <br />on an as needed and long term basis. The basic <br />system consists of an emptied and lined solution <br />pond in which a layer of organic matter is <br />placed upon a set of evenly spaced perforated <br />pipes which have been laid upon the liner to <br />receive and distribute any pad drainage. The <br />organic matter, consisting of composted manure <br />and the distribution system aze then covered <br />with fill and a reclaimed soil and vegetative <br />cover to enclose the entire system to m;n;m;~e <br />infiltration, while promoting evapotranspiration <br />and the necessary anoxic conditions. <br />For purposes of this discussion, the passive in- <br />situ anaerobic biochemical treatment system is <br />referred to as the "Biopass System." The <br />Biopass System fmds its origins in the <br />evaluation of natural and manmade wetlands for <br />treatment of low pH and metals containing <br />drainage from abandoned mine adits, waste <br />rock disposal areas, and historical tailings. The <br />drainage was initially referred to as acid mine <br />drainage (AMD), and more recently acid rock <br />drainage (AltD). <br />During project planning, column rinse [ests aze <br />routinely completed to evaluate closure <br />requirements for cyanide heap leach pads. The <br />fresh water rinse requires three to five pore <br />volumes or more to achieve the water quality <br />standards. For Large heap leach pads, rinsing <br />could require hundreds of millions of gallons of <br />fresh or treated water. Additionally, during <br />rinsing constituents such as mercury, arsenic, <br />and selenium are mobilized above compliance <br />standards. The large quantities of fresh water <br />required for rinsing and removal of other <br />constituents unrelated to the cyanide complexes <br /> <br />make this approach problematic. Problems with <br />this approach include: <br />• Difficulty in detoxification, evaporation, or <br />discharge of large quantities of residual <br />rinse solution; <br />• Generation and disposal of sludge; <br />• Numerical standards for certain metals or <br />inorganics may not be attainable on either a <br />short- or long-term basis; and, <br />• The time needed [o rinse the ore and <br />evaporate the solutions from large heap <br />leach pads tray take years. <br />Each heap leach pad closure should be designed <br />to account for site-specific climatic and <br />envvonmental factors. The closure plan should <br />be consistent with the long-term goal of <br />restoring the site to a condition suitable for the <br />pre-mining land uses of mineral exploration, <br />mining, livestock grazing and wildlife habitat <br />by restoring useable vegetation similaz to that <br />which existed on the site prior to disturbance. <br />In areas like Nevada there is little potential for <br />infiltration of precipitation through the rinsed <br />ore to discharge in significant quantities due to <br />the following factors: <br />• Evaporation exceeds precipitation for all <br />months of the year; <br />• Uptake of precipitation moisture by the ore <br />is srsotrificanr and, <br />• The relatively low permeability of the soil <br />cover material, in combination with <br />evapotranspiration will minimize <br />infiltration. <br />The proposed procedure for stabilization of the <br />heap will be to recircula[e leach solution <br />without cyanide addition until the process is no <br />longer economic. Once extraction is complete <br />the leach pad will be allowed to draindown, and <br />will subsequen[ly be physically stabilized by <br />recontouring, compacting, topsoiling and <br />revegetation. One of the process ponds at each <br />leach pad will be converted to a bioreactor/ <br />evaporator to treat potential seepage from the <br />heaps. A pos[-closure monitoring plan will be <br />developed and implemented to confirm that <br />closure objectives are met. The closure plan <br />-2- <br />