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An update to the storm water management system is proposed for the development of <br />the East Cresson Overburden Storage Area (ECOSA) on the northeast flank of the MLE <br />area, overlooking Grassy Creek. While much of the area will infiltrate to the proposed <br />WHEX mine area and then into the diatreme, the addition of the ECOSA will require the <br />storm water plan to be designed to include the following features: <br />• Four proposed EMP ponds will be constructed near the toe of the ECOSA. Those <br />ponds are numbered EMP010 (at the same location as previously proposed for <br />Amendment No. 8 activities), and three new ponds numbered EMP0015 through <br />EMP017. <br />• EMP017 will be for storm water during operations and after closure. <br />• EMP010 will be used to co-lect runoff and sediment during operations. It will not be <br />needed post-closure, but is being proposed to remain as a wildlife watering pond. <br />• EMP015 and EMP016 will be associated with diversion ditches that will also <br />comprise post-closure drainage basins for the reclaimed ECOSA. Each pond will be <br />equipped with engineered spillways that lead into EMP017. <br />Laboratory testing of the superficial soils in the Grassy Valley pond sites were <br />performed. The test results confirmed that the pond design criteria, two times the 10- <br />year storm volume, should result in 96 to 98 percent removal efficiency (trap efficiency) <br />of the sediments within the storm water. Remaining sediment will be colloidal clays that <br />would not normally be removed by natural means such as sand or vegetative filters. The <br />pond sizing criteria will provide a substantial design margin and will ensure that <br />maximum sediment removal will occur. <br />Client:CC&V Gold Mining Co._ 4/12/08 <br />' Title: Storm Water Management, MLE Page 2 <br />