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tivity, residual moismre content, grain-size distributiotu, and moisture characteristic curves. Reclamation plans generally call for recontouring the spent ore sideslopes to an overall angle of 2.SH:IV or 3.OH:1V. Ofren this will require pushing a portion of the spent ore outside of the lined azea. The consequences of placement of ore outside the lined area will depend upon the fatal geochemical chazacter of the ore and the potential for precipitation to infiltrate and discharge from the leached ore. Five alternatives for protecting groundwater resources from effluent leaching from spent ore were evaluated. They include: • Placement of slow-permeability compacted soil liner under regraded ore; • Extension of the geomembrane liner that presently underlies the leach pad; • Creating an infiltration barrier over this portion of rinsed ore; • Evalua[ion of the soil capacity to attenuate heavy metals through land application; or, • No action. 2 4 Reclamation/Revegetation of the Heao Leach Pads Following recontouring and compaction of the heap surface and spreading of topsoil, revegetation of the spent ore will commence. Vegetation establishment on the leach pads will minimize infiltration and deep percolation of precipitation into the leached ore and decrease erosion. Infiltration and deep percolation will be minimized due to uptake within the heap and evapo[ranspiration of rainfall by vegetation. The vegetation will also prevent the spent ore from being eroded by either wind or water, by reduction of runoff flow velocities. 3.0 THE PASSIVE TREATMENT SYSTEM -4- r~ L The primary goal with respect to decommissioning and closure of a spent heap leach pad involves the prevention of long term deterioration of local surface and groundwater. According to environmental regulations, the operation and site must be closed in a manner that will not degrade the wa[ers of the State. There are various methods for demonstrating that degradation of surface and groundwater will not occur following closure. The traditional approach has involved drilling and sampling the solids within the spent leach pad, and subjec[ing those solids to leach tests either Meteoric Water Mobility Procedure (MWMP) or Synthetic Precipitation Leaclting Procedure (EPA Method 1312). The purpose of the extraction tes[ is to simulate the pad effluent that could originate from contact of infiltration with the spent ore. A successful passage of the leach tests occurs if the resultant extraction solution does not contain constituent levels greater than ten-fold their respective Maximum Contaminant Level (MCL). Unfortunately, compliance with the MWMP does not ensure that environmental impacts wilt not occur. More recently, the assessment and prediction of potential water quality impacts following closure of spent heap leach pads has included a Fate Transport Analysis (FTA), which involves predictive mathematical modeling of the hydrological and chemical aspects of solutions and seepage. In the current study, the hydrological modeling of the three spent heap leach pads has indicated that once their surfaces are reclaimed, the quantity of precipitation and infilvation entering the pads will be insufficient to generate drainage. Closure of spent leach pads includes conversion of one of the exis[ing solution ponds at [he base of each pad in[o an in-situ anaerobic biochemical system, capable of passively receiving and treating this drainage on an as- needed and long-tent[ basis. The basic Biopass System (Figure 1) consists of an emptied solution pond in which first a layer of organic maser is placed upon a set of evenly spaced perforated drain pipes, which have been laid in such a manner to receive and distribute any pad