2012-09-28_REVISION - M1977307 (27)

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6.0 Potential Pollution Sources Mining operations result in ore and waste rock stockpiles that are stored on the land surface adjacent to the mine entrance. The ore stockpile remains onsite only for short durations as the ore is hauled to the process mill shortly after removal from the mine. The waste rock will remain onsite permanently and be stabilized in- place. There will be a 500- gallon diesel fuel tank with secondary containment located near the mine portal. The tank is used to refuel equipment during mining operations but remains empty during extended cessations in mining activities. Other petroleum products used at the site will include hydraulic and lubricating oils. These oils are generally in 5- gallon containers and stored in one of the onsite buildings. 7.0 Drainage Design 7.1 Engineering Approach The drainage design is focused on preventing erosion and transport of the waste rock stockpile and ore storage areas during operation and long -term protection of the waste rock pile after reclamation. Currently, drainage at the site is controlled by berms and swales that route offsite runoff around existing stockpile areas. The effectiveness of these existing features has been analyzed for selected design storms and subsequent runoff to ensure compliance with BMPs to prevent erosion and offsite transport of potential pollution sources. Drainage improvements are proposed for the site. These include grading and installation of improved roadway ditches along portions of the mine access roads, installation of a containment berm along the eastern edge of the site, and excavation of a retention pond with installation of embankment to capture onsite runoff ( Onsite Basin 30). The attached drawings illustrate the locations and details of these proposed improvements. In addition, the attached drawings also illustrate: onsite basin topography, boundaries, and BMP components; offsite basin topography and boundaries; and mine permit boundaries. The National Resource Conservation Service (MRCS - formerly known as the Soil Conservation Service, or SCS) dimensionless unit hydrograph procedure is one of the most well -known methods for deriving synthetic unit hydrographs and determining runoff peaks and volumes. For drainage basins where no runoff has been measured, the Curve Number Method can be used to estimate the depth of direct runoff from the rainfall depth, given an index describing runoff response characteristics. This method was originally developed by the SCS for storm conditions prevalent in the United States and was the method used in this study. ESWMP-4