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Mineral Joe Mine — Drainage Design Plan 14 <br />4.3 Sub - Basins Supplying Stormwater Run -on to the Site <br />Stormwater from upslope that is not diverted around the site may run on to the site and report to the borrow <br />ditches, channels, and stormwater retention pond in the mine facilities area. Sub - basins have been <br />delineated to identify how run -off flows to individual conveyance structures (culverts or ditches) or to <br />segments of individual drainage structures that receive increasing runoff along their length. The sub -basins <br />contributing runoff to the site are shown in Figure 2 and listed in Table 9. <br />The largest sub -basin contributing non - contact stormwater to the site is sub -basin N -F (1.86 acres), which <br />contributes runoff to the north- flowing branch of the LDS, which then reports to the stormwater and <br />sediment retention pond. The remaining sub -basins that contribute non- contact stormwater to the mine <br />facilities area range in size from 0.35 acres (sub -basin N -H) to 0.81 acres (sub -basin N -J). Stormwater <br />routing from these sub - basins to the retention pond is discussed in Section 4.6. <br />Table 9. Sub - Basins Contributing Run -On to Mine Facilities Area <br />Sub -Basin Area Area (ft) (acres) Type Description / Type <br />N -F <br />81,040 <br />1.86 <br />Non- contact <br />Reports to Lower Diversion Structure, flowing north <br />N -H <br />15,040 <br />0.35 <br />Non - contact <br />EE 19 Road CL to culvert on switchback <br />N -I <br />29,420 <br />0.68 <br />Non - contact <br />EE 19 Road CL to NJ via culvert <br />N -J <br />35,210 <br />0.81 <br />Non - contact <br />Road & slope above stormwater retention pond <br />MFA <br />130,990 <br />3.01 <br />Contact <br />Mine Facilities Area reporting to SWRP <br />The central facilities area is relatively flat (Figure 3). A perimeter berm around the crest of the waste rock <br />piles prevents stormwater from flowing down the face of the dumps and causing erosion. Snowmelt and <br />precipitation commonly pools at the surface and evaporates. During higher magnitude storms, runoff from <br />the 3.01 -acre mine facilities area (Figure 4, Table 9) flows into the stormwater and sediment retention pond <br />(SWRP). <br />414813.131029 Whetstone Associates <br />