2012-04-18_INSPECTION - M1980244

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OBSERVATIONS PERMIT #: M -1980 -244 INSPECTOR'S INITIALS: TC1 INSPECTION DATE: April 17, 2012 The Division conducted an inspection of the site on to observe and discuss two incidents that occurred the week of April 13, 2012 in the Arequa Gulch Phase V Valley Leach Facility (VLF) area. The first incident involved the sloughing of some of the drain cover fill (DCF) on the upper portion of the Phase V liner with a north to northeast facing slope. The second incident involved some process solution spilling onto an area off the VLF liner. Mr. Mark Vanoni (CC &V Sr. Environmental Coordinator) was present during the inspection. Inspection: DCF Sloughing: Mr. Vanoni provided a field overview from above the portion of the Phase V VLF where the sloughing occurred (see Photo 1). DCF has slid off the geosynthetic liner starting near the upper anchor trench down to the vicinity of the upper bench. This inspector estimates the sloughed distance to vary between 30 and 150 feet. The width of the sloughed area is approximately 200 feet. Mr. Vanoni indicated the sloughing has continued since it was first observed by CC &V personnel last week. Some tension cracking in the DCF was observed (see Photo 2). Some surface scratching of the geosynthetic liner was also observed. However, there was no evidence of liner movement, liner tearing or impacts to the anchor trench. Mr. Vanoni stated crews have been called to locate leaks in the liner and check for meteoric water in the underlying clay liner. The engineer of record has also made multiple site inspections. They are investigating the failure and formulating a mitigation plan. It should be noted that this area is not loaded with ore to be leached and is not scheduled to be loaded for quite some time. The DCF sloughing is cited as Problem 1 on page 1 of this inspection report. Process Solution Spill: The spill occurred in the vicinity of the perimeter safety berm overlying the anchor trench at the toe of the Phase V VLF directly south of the current fuel island. Mr. Vanoni indicated that no anomalies were observed during the VLF perimeter inspection late Wednesday, April 11, 2012. However, some seepage and pooling of water were observed on the outside of the safety berm on the morning of Thursday April 12, 2012. The spill occurred in an area where the edge of the VLF liner is relatively flat and where the edge of liner makes a 90 degree turn (see Photo 3). The water pooled near the edge of the liner and flowed downgradient back onto the liner. The water was determined to be process water, specifically pregnant solution and presumed to come from the adjacent slope of the VLF. The flow of process water to the adjacent slope was terminated and soils from the off -liner impacted area were excavated and moved onto an area underlain by liner on April 12, 2012 (see Photos 4 and 5). The concentration of WAD Cyanide in the spill area calculated using conservative values and parameters (i.e., values that would yield the highest probable concentration under the field conditions), and determined to be less than the EPA reportable limit of 10 lbs /ton. The apparent source of the pregnant solution is a 15 -inch diameter perforated ADS pipe designed to collect infiltrating water on the VLF and convey it to the PSSA. This pipe was observed to be surcharged with water discharging from the pipe perforations (see Photo 6). It should be noted that the water shown exiting the perforated pipe in Photo 6 is meteoric water (not process solution) originating from a snow storm that occurred April 12 — 13, 2012 amounting to the equivalent of 0.6 inches of water. The process solution spill is cited as Problem 2 on pages 1 and 2 of this inspection report. A water bar has been constructed on the perimeter road to limit snowmelt run - on. The Division did not inspect the high and low volume solution collection system transducers or record water level values during this inspection. Page 3 of 7