Laserfiche WebLink
As originally planned flow to the heap would be distributed over the breadth of the heap with <br />solution volumes applied within each drainage area complimenting the associated pump <br />capacity. However, as the VLF has matured unforeseen events have occurred complicating the <br />overall water balance. <br />Most notably, the catastrophic failure of the buried Phase 4 pregnant solution line and adjacent <br />barren solution line in October 2013 placed severe restrictions on the ability to manage flow over <br />to the VLF. Pregnant solution from Phase 4 could not be pumped directly to the recovery plant <br />and therefore the volume of solution applied within the drainage was restricted to that which <br />could be pumped to an existing injection well within the Phase 2 drainage using a diesel - <br />powered pump and temporary piping. <br />Planning for a replacement pipeline started soon after the failure, but the line could not be routed <br />through the pad and instead had to go over the full height and then back to the recovery plant. <br />This necessitated undertaking detailed engineering to resize the associated pumps, motors, <br />drives, and power supply as well as layout the pipe route thereby protracting re -commissioning <br />of the area. Flows planned to be apportioned to Phase 4 had to be absorbed into the leaching <br />plans for the other three drainages. <br />Stacking plans for 2015 were developed under the assumption that re -commissioning Phase 4 <br />would occur in April 2015. However, project setbacks and issues in fabrication of a critical <br />electrical assembly delayed installation. Because of this the leaching plan had to be altered and <br />flows scheduled to be placed on Phase 4 could not be moved as planned placing stress on the <br />water balance for Phase 1 and Phase 5. <br />Overall flows to Phase 1 and Phase 5 leading up to the incident were below the overall pumping <br />capacity at all times, but, following completion of the 10,300' lift on Phase 5 in May, the amount <br />of solution crossing over from the Phase 5 drainage into the Phase 1 drainage increased sharply. <br />Figures 2 and 3 show the pond flows and levels for the Phase 1 and 5 PSSAs, respectively. From <br />the figures it is clear that a significant fraction of the flow applied within the theoretical <br />boundary for Phase 5 actually reports to the Phase 1 PSSA. This is believed to be due to <br />hydraulic irregularities in the Phase 5 causing solution to migrate laterally toward the more <br />permeable - larger crush size - ore at the lower levels of Phase 1. In May 2015 the volume of <br />solution crossing over increased abruptly. It was this unplanned inrush for flow that <br />overwhelmed the Phase 1 PSSA leading to the high pond levels. <br />