2013-09-27_REVISION - M1979094HR (3)

Home Browse Search

JD -7 Mine — Drainage Design Plan 20 4. STORMWATER ROUTING (CURRENT CONDITION) Stormwater control at the JD -7 Mine currently includes diversion of stormwater runoff from upland areas around the open pit and the open pit waste rock pile, and the collection of stormwater runoff from the underground - waste -rock pile in two lined catchments. In addition, culverts, borrow ditches, and berms are used to route stormwater away from mine facilities into natural drainages. Stormwater modeling for the JD -7 Mine focuses on the project area within Sub -basin 133 (Figure 3). Upslope stormwater diversion is described in Section 4.1. Stormwater routing within the mine facilities area is described in Sections 4.2 and 4.5.1. 4.1 Sub - Basins Contributing Stormwater to Diversion Structures and Valley Floor Two main diversion structures currently exist to divert upslope, non - contact stormwater away from the JD- 7 open pit. The upper portion of the JD -7 open pit is surrounded by a double berm. Upslope of the berms, the existing "Pit Diversion East" intercepts runoff from sub -basin N -G on the Monogram Mesa escarpment and conveys it eastward into the natural channel in the adjacent major sub -basin 134 (Figure 3, Figure 10). Sub -basin N -G is 132.91 acres in size (Table 10) with steep slopes vegetated by pinon juniper with a grass understory. Similarly, the "Pit Diversion West" (Figure 6) intercepts runoff from sub -basin N -F on the Monogram Mesa escarpment and conveys it westward into a natural channel in sub -basin N -E. Sub - basins N -F and N- E are 109.11 and 140.91 acres in size, respectively (Table 10) with steep slopes vegetated by pinon juniper with a grass understory. The channel geometry for the Pit Diversion West is described in Section 4.4.1 and stormwater routing described in Section 4.6. A third major diversion structure routes water westward and northward around the existing open pit waste rock pile. This structure is labeled "Open Pit Waste Rock Pile Diversion" or OPWRD in Figure 3 and receives non - contact stormwater from sub - basins N -E, N -D, and N -F (via N -E) along with runoff from mine facilities from sub - basins D -1 (open pit), D -8 (southeast portion of the open pit waste rock pile), and D -9 (southwest portion of the open pit waste rock pile). The OPWRD Diversion routes stormwater runoff to north onto the valley floor where much of it infiltrates as described in Section 4.7. Table 10. Sub - Basins Contributing Non - Contact Stormwater to Diversion Structures and to the Valley Floor Sub -Basin Area Area (ft) (acres) Type Description N -A 3,358,500 77.10 Non - contact Escarpment to valley floor N -B 3,736,680 85.78 Non - contact Escarpment to valley floor N -C 109,100 2.50 Non - contact Small triangular area above valley floor N -D 1,491,300 34.24 Non - contact Triangle above existing OP WRP diversion ditch N -E 6,137,850 140.91 Non - contact Escarpment to OP WRP diversion ditch N -F 4,752,800 109.11 Non - contact Escarpment to pit diversion, routed west N -G 5,789,530 132.91 Non - contact Escarpment to pit diversion, routed east N -H 411,150 9.44 Non - contact Small triangular area above valley floor & planned WRP N -I 7,880,920 180.92 Non - contact Escarpment to valley floor, south of planned Waste Rock Pile N -J 5,056,460 116.08 Non - contact Escarpment to valley floor south of soil stockpile N -K 11,346,520 260.48 Non - contact Escarpment to valley floor west of soil stockpile 4149A.130926 Whetstone Associates