2010-03-16_REVISION - M1981185 (29)

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Mayday Mine and Mill Site, Wildcat Mining Corporation, 110(2) Permit Amendment Exhibit C • If acid or toxic producing materials are encountered during mining the material will be disposed above the groundwater in the old mine workings. It is important to note -acid mine drainage has not been identified with the historical Idaho, or Mayday mine areas or the waste rock. Benches Surface water runoff from the Mayday bench will be controlled by grading the bench towards the portal and collecting the water prior to use or release. Where water traverses the benches or access roads, an 18 inch culvert (Table C -Ola) will be installed to minimize sedimentation impacts to adjacent drainages. The culverts will be at least 12 feet long and installed at a down gradient slope of at least 5 %. The drainage structures are designed to convey the peak flow from the 100 year 24 hour storm. Water generated above Mayday Portal No. 2 (3.7 acres) will be conveyed beneath the road that crosses the bench. (Figure E -4A -1) Calculations (Table C -1) indicate an 18 inch CMP is capable of conveying the peak flow from the 24 hour -100 year storm which is estimated to be approximately 13 cubic feet per second. Water generated above the portals/benches will be diverted around the disturbed areas where practicable. Ponds /Impoundments As necessary, stored water (Figure 11 and 12- Attachment C -3) will be conveyed using water trucks from permitted water ponds to the Mayday for mine milling and mining activities. The ponds are to be constructed to manage water in accordance with the approved water right decree (see Water Rights Attachment C -3). • Point Discharge - Surface Water Mayday Mine No. 1 is a no- discharge facility. If unplanned or unforeseen discharges occur as a result of unusual events, discharges from the mine site will be in accordance with applicable Colorado Pollutant Discharge Elimination System (CPDES) permit requirements (Permit was submitted to Colorado Department of Public Health and the Environment on January 13, 2010; Rule 3.1.6 (a -c)). A potential point of discharge is located at the Mayday portal No. 1 (Figure E -3). The retention pond is designed (Table C -6) to contain the flow volume from the 10 year 24 hour storm (0.01 acre feet) and convey the peak flow of 1.8 cfs from the 24 hour -100 year storm event through a spillway that will have at least a 0.5 foot freeboard. Groundwater (Rule 3.1.7) Groundwater flow directions and rates have not been characterized for the Mayday mine site. Groundwater elevation is below the Brooklyn Level where the water level is estimated to be approximately 400 feet from the proposed Mayday mine workings Water quality from the mine is summarized in Table C -7. Water is characterized as being excellent with a total dissolved solid concentration of approximately 150 mg/L. A recommended secondary drinking water criterion by EPA/CDPHE for total dissolved solids is equal to or less than 500 mg/l. As described elsewhere in this permit, waste rock will be returned to historical stopes. Several chemicals used in ore processing are considered to be toxic to aquatic organisms (Attachment C -2, Material Safety Data Sheets [MSDS]): • March 12, 2010 Amendment M- 1981 -185 7