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JD -8 Mine — Drainage Design Plan 1 <br />1. INTRODUCTION <br />1.1 Purpose <br />This report presents the design analysis for the storm water drainage facilities at the JD -8 Mine, located in <br />Montrose County, Colorado. The report addresses aspects of storm water collection, conveyance, and <br />retention design necessary to comply with the Colorado Division of Reclamation Mining and Safety <br />(DRMS) drainage criteria. <br />The JD -8 Mine is currently not actively mined. However, the JD -8 Mine is expected to be operational in <br />the future, and the existing waste rock pile will be expanded as the underground workings are further <br />developed. This drainage design plan is intended to address both the current and expected final drainage <br />conditions. The design criteria and methodology are described in Section 2. <br />1.2 Background - Lower Runoff Areas and Routing <br />Stormwater runoff at theJD -8 Mine occurs from both disturbed and undisturbed areas. Runoff from <br />undisturbed areas is considered "non- contact" stormwater because it has not had potential exposure to <br />industrial pollutants (roof runoff, access roads, employee parking areas, waste rock piles, etc.). The fuel <br />storage area is bermed and lined, and does not contribute stormwater to any catchment onsite. As shown in <br />Figure 2 and Table 1, drainage areas have been divided into four runoff zones and two receiving zones. <br />Table 1. Drainage Basin Areas at the JD -8 Mine under Current Conditions <br />Area Area <br />Zone (ft2) (acres) Type <br />1 50,280 1.15 Non - contact area (undisturbed) <br />2 49760 1.14 Disturbed area <br />3 24,660 0.57 Receiving area (near soil stockpile) <br />4 73,550 1.69 Non - contact area (undisturbed) <br />5 137,600 3.16 Disturbed area <br />6 8,050 0.18 Receiving area (Constructed Catchment) <br />Drainage at the site is controlled by ditches, berms, culverts, and topography. Areas above the Lower Mine <br />Permit Area that would contribute run -on to the site during extreme storm events under current site <br />conditions are shown in Figure 1 and Table 1. <br />Surface flow from undisturbed runoff Zone 1 and disturbed runoff Zone 2 is routed to retention Pond 1 in <br />Zone 3, near the topsoil stockpile. In addition, a portion of the western waste rock pile area (on which the <br />mine facilities have been constructed) slopes westward toward receiving area 3 (Figure 2). <br />Similarly, runoff from undisturbed areas above the mine (Zone 4) and disturbed areas associated with the <br />access road, ore storage area, and a portion of the eastern waste rock pile (Zone 5) are routed to the <br />constructed retention Pond 2 in Zone 6. The eastern portion of the waste rock pile is sloped gradually <br />westward while the berm along the crest of the waste rock pile diverts flow westward and prevents runoff <br />from eroding the face of the pile (Photo 2). Runoff from the waste rock is intercepted by a constructed <br />notch in the berm, where water is routed down the face of the waste rock pile to the constructed catchment <br />(Pond 2). Photo 3 shows a former rivulet that developed into a small gully on the face of the pile, and was <br />then mitigated by repairing the berm along the crest of the waste rock pile. <br />4122A. 120325 Whetstone Associates 4 <br />