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The hydrologic conditions at the Siskin Pit consist mostly of surface water drainage along long- <br /> established pathways and areas. Site soils are identified in NRCS surveys as rock complexes that <br /> are predominantly hydrologic soil groups A, C, and D; see Appendix 3. <br /> The site contains Feltonia-Coutis sandy loams with 6-15% slopes (roughly 33%)that are <br /> Hydrologic Soil Group A. Also found on site are Woodhall-Rogert extremely cobbly sandy <br /> loams with 5-20% slopes (roughly 32%)that are Hydrologic Soil Groups C and D. These two <br /> soil units evenly cover most of the planned mining areas and are currently vegetated as native <br /> rangeland. Other soil profiles exist primarily in the drainage areas and are left out of the planned <br /> mining areas. <br /> During Mining Surface Hydrology <br /> During Phase I, the entire processing area will act as a 'sump' that allows stormwater to <br /> infiltrate into the porous processing area pad, see Map C-3. Fine sediment will be removed from <br /> the lowest settling area of the pad, as needed. Surface water within the disturbed area of the site <br /> will be controlled by perimeter berms which border the disturbed area. When paired with small <br /> perimeter berms, the designed pad elevation of the processing area will have the capacity to <br /> contain all stormwater that falls within the stormwater berms surrounding the site. Runoff <br /> calculations are shown in the next section. All stormwater is expected to infiltrate within the <br /> disturbed ground of the mining area within 72 hours. In the event that stormwater remains >72 <br /> hours following a storm event, sediment free stormwater will be pumped and discharged in <br /> accordance with the site discharge permit. <br /> Stormwater runoff associated with the drainage through the center of the site will be maintained <br /> with a culvert through the haul road crossing. The culvert design is shown on the mining map in <br /> Appendix 1, while the calculations are provided in Appendix 4. <br /> The typical 24-HR events for this area are listed below(NOAA Atlas 14 Point Precipitation <br /> Frequency Estimates: Westcliffe, Colorado <br /> (https://hdsc.nws.noaa.gov/pfds/pfds_map cont.html?bkmrk=co)) : <br /> Siskin Pit <br /> January 2024 G-2 i-ewicki& .Associates <br />