2015-09-21_INSPECTION - M1980244

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Response: In May 2015 the water balance of the VLF was upset by an increased and unexpected volume of flow crossing over from the Phase 5 drainage to the Phase 1 drainage. Discussion of the factors and effects are detailed in the response communicated to DBMS on July 7, 2015. After weighing various options CC&V elected to install misters on the solution piping network in order to 1) bring all pond levels in to compliance as soon as possible and 2) reduce the overall volume of circulating solution. The efforts were successful on both accounts and flows have stabilized. Due to the unusually wet weather in the late spring and early summer, shedding the excess solution from the circuit required prolonged use of the misters/evaporators. This resulted in above normal accumulation of precipitated salts on the surface near the misters. The salts formed a surficial scale/crust that prevented the unevaporated solution from infiltrating into the pad efficiently. This caused an increase in the incidence and persistence of ponding on the VLF. CC&V took measures to mitigate the ponds as they formed by re -ripping areas, installing sumps/drains, and relocating/rotating flows to areas. Starting in mid-August CC&V began removing/plugging the installed misters. A staged step- wise approach was adopted to avoid making any abrupt flow changes that could otherwise progress through the circuit and cause future upsets. In preparation of the upcoming change in seasons, targets were set to have all non -drip flows shut off by the end of September. The schedule has been followed and it has been possible to advance the completion date. All misters/evaporators should be out of service the week of 21 September 2015. INSPECTION TOPIC: Support Facilities Not On-site PROBLEM/POSSIBLE VIOLATION: Problem: The observed ponded water on the AGVLF surface appears to have saturated the surface and may pose geotechnical slope instability problems. CORRECTIVE ACTIONS: Provide a geotechnical slope stability analysis assuming saturated material exits to the appropriate depth to assess the impact on the factors of safety presented in the MLE2/Amendment 10 slope stability exhibit. CORRECTIVE ACTION DUE DATE: 9/23/15 Response: No evidence that saturation of the ore near surface, or deeper, occurred has been observed by CC&V. The principle reason for occurrence ofponding has been accumulation of scale/precipitates (primarily calcium carbonate) from process solutions occluding the surface and reducing the infiltrateablity. In all instances ponding has been able to be mitigated expeditiously by breaking up the surficial crusts. There has been no indication of saturation any appreciable distance below the surface beyond conditions already considered in MLE2/Amendment 10 slope stability exhibit.