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mining during reclamation. Each mining map in Exhibit C shows the stormwater berm and sump <br /> configuration for each given phase of mining. <br /> The hydrologic conditions at the Young Ranch Resource consist mostly of surface water <br /> drainage along long-established pathways and areas. Site soils are identified in NRCS surveys as <br /> rock complexes that are predominantly hydrologic soil group D. There are portions of the <br /> Tahana-Legault-Complex (roughly 40%) that are hydrologic soil group B. This soil unit <br /> corresponds strongly with greater tree density. Therefore, in drainage areas where the Tahana- <br /> Legault-Complex is the majority soil,the hydrologic soil group will be assumed to be B. Based <br /> on the NRCS method of calculating the surface water runoff volume and peak discharge for the <br /> existing areas, the curve numbers of the baseline drainages are either 79 (hydro soil group D) or <br /> 70 (hydro soil group B). Appendix 4 lists the curve numbers for each area in the pre-mine <br /> conditions. Appendix 4 lists all storm event data for each area. The basin/area numbering on that <br /> table correspond to the numbering found on Map G-1 —Surface Hydrology: Baseline Conditions. <br /> During Mining Surface Hydrology <br /> During Phase 1, 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 paired with sumps. When <br /> paired with small perimeter berms, the designed pad elevation (-3 foot lower in elevation than <br /> the current CCP) of the processing area will have the capacity to contain 100 year 24-hour rain <br /> events. All runoff from a 100 year 24-hour rain event will be trapped on site and waters will <br /> infiltrate the processing area floor within 72 hours. The calculated available storage volume, >30 <br /> acre-feet, of the processing area is able to hold>2 back-to-back 100-year storm events (4.44 <br /> inches/24 hours; Appendix 4). <br /> The typical 24-HR events for this area are listed below: <br /> Young Ranch Resource <br /> December 2021 G-2 a Lewicki&Associates <br />