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soil property. These properties and then used as input to a HEC-HMS(USACE,2023)hydrologic model of the <br /> Climax Mine site. <br /> G-5.4 Flood Development <br /> In hydrologic modeling, once evapotranspiration and infiltration have been accounted for and rainfall excess <br /> estimated,the direct runoff response from rainfall excess may be determined with a unit hydrograph.A unit <br /> hydrograph is defined as the time distribution of one inch of direct runoff from a storm of a specified duration <br /> for a given sub-basin. In conjunction with the CSU-SMA infiltration loss estimation method, the Clark Unit <br /> Hydrograph method is recommended by the DWR as the preferred technique for performing rainfall to runoff <br /> transformation in Colorado. <br /> G-5.5 Baseflow <br /> The Climax area experiences an annual snowmelt period that typically occurs in May and June. The runoff <br /> associated with this snowmelt must be considered when determining the appropriate baseflow condition for <br /> storms that could occur during this period. The seasonality of the various design storm types must be <br /> evaluated to determine the appropriate baseflow condition for each storm event. <br /> G-5.6 Flood Routing Results <br /> During mining, the storage capacities of the TSF water pools will be continuously changing as additional <br /> tailing is deposited in the facilities. Rather than attempt to model each expected change,a generalized model <br /> is established to determine the volume of flood storage that must be maintained on the TSFs to accommodate <br /> the design storm event with appropriate residual freeboard. The peak flow capacities needed by the decant <br /> and spillway structures on each water facility are also determined, in accordance with internal and external <br /> regulatory requirements. <br /> For the post-mining scenario,the flood modelling will be used to determine the appropriate capacities of the <br /> various flood management systems, including detention storage requirements and TSF spillway capacities, <br /> also in accordance with internal and external regulatory requirements. <br /> Exhibit G G-20 May 2024 <br />