2016-07-21_REVISION - M1980244 (4)

Home Browse Search

Mill Fluids which cannot be recycled back into the mill process as make-up water,will be pumped via a 4-inch HDPE pipe to one of two infiltration wells that are drilled into the 9970 bench of the AGVLF (Figure 1 and Drawing 30-647-501). The fluids will drain through slotted piping running the length of the boreholes (one is 175 feet deep and the other is 190 feet deep). See Figure 2 & 3 and note that the borehole lining is not slotted within 20 feet of the surface nor is it within 100 feet of the liner at the bottom. The boreholes are not capped at the top or bottom so fluid drains into the boreholes at a maximum of 180 gpm and an average of 100 gpm. When this change was originally described, DRMS raised several questions regarding the angle on the wells, precipitates, and rehabilitation of the wells. Please see Newmont's response below. Angle holes—The infiltration wells are vertical. A survey of several companies determined that angle holes were not feasible. At the chosen location there was insufficient room on the bench to accommodate the drill rig in the necessary orientation. On the lower existing basin,a rig could not be located that was capable of drilling/casing at the necessary angle and depth required to allow sufficient head and maintain appropriate distance to the liner. It should be noted that the installed wells are dimensionally similar with existing wells installed in the VLF. Precipitates—The solution will contain some turbidity(ultrafine solids) from the milling process and has the potential to precipitate out following exposure to the atmosphere. Accumulation of the solids will impact permeability—hence the poor surface drainage in current areas. Injection in the wells limits exposure to the atmosphere so greatly reduces risks from precipitation, but will not eliminate the fine process solids. Over time these will accumulate in the well/bore . It may be necessary at some point to address the build up by jetting or other means to clear the fine solids and restore drainage. This would be done via our conventional injection method and while one infiltration well is being"cleaned",the other infiltration well would be used in it's place. Mill Discharge Characterization-The injection fluid is from the high pH circuit at the mill, meaning it's on the cyanide leach side and cannot be mixed back in with the floatation circuit. The chemistry of the solution is essentially the same as that which is already circulating within the VLF (both are the same pH level and cyanide level). Monitoring& Closure—The existing infiltration pond area will be closed in the summer of 2016. This includes removing bird balls and recontouring the facility. Mill Operators will monitor the infiltration well and the flow will be manually directed between the two wells. If conductivity wanes over time to an extent where the volume cannot be accommodated we plan to use our pad injection pump set up to inject solution at high pressure/volume to flush the area around the wells. This would be exactly the same as what we have been doing since 2010. If the mill were to shut down or the infiltration wells could not operate for some reason, it would be necessary to have a temporary holding area for mill solution. A small bermed earthen sump will be constructed just below the the mill area, see Drawing 30-647-501, within the lined VLF