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~~ Heap Leach Pads 130 to 300 gpad 300 to 3,000 gpad 3,000 gpad ~~ Report to MLRD. Locate areas of leakage and operate ponds to minimize leakage if possible or repair. Repair Leaks Pond shutdown, replace primary liner. The sump wells will be monitored by mine site personnel. The data collected will be submitted to the Division monthly. Diivision staff will field verify the data during regular site inspections. The leak detection system will be ovelain by 60 mil high density polyethelene (HDPE). This material is considered to be impermeable. Quality control and quality assurance reports will be submitted to the Division to verify proper installation of the HDPE liner. The barren and pregnant ponds are both underlain by the same type of dual liner and leak detection system as the pad. The pond system has been designed so that they can contain without discharger all sodium cyanide solutions contained in the heap leach system, as well as the runoff from a 100-year, 24-hour storm event falling directly on the heap and ponds, and still maintain 2 feet of dry storage space. A Geotechnical evaluation of the pond embankments was submitted by the applicant. This evaluation demonstrates that the pond embankments would be stable under normal operating conditions, and under earthquake loading conditions. The entire heap and pond area is surrounded by a compact soil berm. This berm serves to divert any upgradient overland flow away from the heap and ponds. By diverting these flows, the heap and pond system is effectively isolated from the surrounding environment. The Division undertook to determine the potential impacts from a sodium cyanide discharge to either ground-or surface-waters. Should a discharge to the surface occur, solution from the heap or ponds would flow southwest (away from Rito Seco) into an ephemeral arroyo. Due to road grading and topography, the flow would continue to travel south, southwest either along a dirt road or into a second ephemeral arroyo. However, topographic gradients are low, thus flows would be slow and subject to infiltration and evaporation. The remaining flow could possibly be impounded within an abandoned gravel pit east of San Luis, or continue to travel south within the second arroyo to the Vega area just east of San Luis. If the discharge occurred during a precipitaton or snowmelt runoff event, cyanide would be attenuated due to mixing with suspended sediment materials, aeration, ultraviolet degradation and dilution throughout the flow event. However, given the volume of solution and the area topography, it does not appear likely that flows would enter San Luis. -5-