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JD -7 Mine - Drainage Design Plan 24 <br />the pit floor (Figure 9). This pond is routed west around the existing waste rock pile via the Open Pit <br />Waste Rock Diversion Ditch (described in Section 4.4.3). Stormwater exiting the open pit (sub -basin D -1) <br />has contacted disturbed ground but has not contacted any designated EPP Facilities. To date, the pit has <br />not been excavated down to the ore horizon, and water quality samples from the pit pool met all applicable <br />standards (EPP [Whetstone, 2012]). During mining operations, any stormwater collecting in the open pit <br />will be pumped out and not routed directly to the diversion ditch. Post - mining stormwater routing for the <br />open pit is discussed in Section 6.1. <br />Sub -basin D -2 (0.84 acres) is located south of access road EE 17 and was modeled using a curve number of <br />86 (Attachment 2). This sub -basin is located west of a local divide and receives no runoff from adjacent <br />sub - basins. Stormwater runoff from D -2 flows north to an existing 12 -inch corrugated high - density <br />polyethylene (HDPE) culvert (CV2) below the access road into downstream receiving sub -basin D11. <br />Sub -basin D -3 encompasses 18.71 acres of disturbed and undisturbed ground south of the EE17 access road <br />and north of the existing open pit. Facilities within sub -basin D -3 include the shop, vent hole for the JD -7 <br />Underground Mine, and the planned ore transfer pad for the open pit mine (which is yet to be constructed). <br />Sub -basin D -3 receives no run -on from adjacent sub - basins. Stormwater in D -3 flows northwest to an <br />existing 30 -inch corrugated metal pipe (CMP) culvert (CV3) below the access road into downstream <br />receiving sub -basin D 11. <br />Sub -basin D -4 (3.51 acres) collects stormwater from north of the bermed open pit and south of the access <br />road (Figure 10, Table 11). The sub -basin contains a mixture of gravel road, disturbed ground, and <br />undisturbed ground with a weighted average curve number of 83. Sub -basin D -4 receives no run -on from <br />adjacent sub - basins. Stormwater in D -4 flows west and northwest to an existing 48 -inch CMP culvert <br />(CV1) below the access road, near the compressor shed, shop, and water tank into downstream receiving <br />sub -basin D12. <br />Sub -basin D -5 encompasses 0.87 acres south of the mine yard area (north of the open pit). The sub -basin <br />contains a mixture of disturbed and undisturbed ground with a weighted average curve number of 76. <br />Stormwater runoff from sub -basin D -5 flows onto the mine yard area (sub -basin D -6, 2.39 acres) which <br />includes the top of the underground - waste -rock pile, the shop, compressor shed, parking area, underground <br />portal, and water treatment plant. The mine yard area (sub -basin D -6) is graded nearly flat and perimeter <br />berms are maintained around the north, west, and south crest of the underground - waste -rock pile (Figure <br />11) which prevents stormwater from flowing down the face of the dumps and causing erosion. Snowmelt <br />and precipitation commonly pools at the surface and evaporates. <br />Sub -basin D -7 totals 21.82 acres and includes 13.56 acres of the existing OPWRP, 0.99 acres of <br />undisturbed pinon juniper, and 7.28 acres of disturbed ground north of the open pit and east of the <br />OPWRP. Sub -basin D -7 drains to the natural ephemeral channel to the north and has a weighted average <br />curve number of 69. <br />Sub - basins D -8 and D -9 encompass 6.42 and 13.94 acres of the southeast and southwest portion of the <br />existing open pit waste rock pile, respectively. Stormwater runoff from these sub - basins flows southward <br />toward the existing OPWRD diversion ditch. A runoff curve number of 63 was applied, corresponding to <br />sagebrush with grass understory in fair condition for the naturally revegetated areas of the waste rock pile. <br />Sub -basin D -10 encompasses 27.07 acres of the northern portion of the existing OPWRP. Stormwater <br />runoff from sub -basin D -10 flows northward and westward onto the valley floor to receiving sub -basin D- <br />13. A runoff curve number of 63 is applicable, corresponding to sagebrush with grass understory in fair <br />condition for the naturally revegetated areas of the waste rock pile. <br />Sub -basin D -16 includes the northern portion of the existing underground - waste -rock pile and water <br />treatment ponds (Figure 11). Stormwater runoff from this 1.55 acre area flows to the interceptor ditch and <br />the "00113-A North" retention pond. A weighted average curve number of 83 was applied (Attachment 2). <br />4149A.130926 Whetstone Associates • <br />