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Table 6. Area Storm Events. <br /> Event Probability Event Rainfall (inches) <br /> 100-YR 24-HR 4.44 <br /> 25-YR 24-HR 3.26 <br /> 10-YR 24-HR 2.60 <br /> Surface water within the disturbed mining area will be trapped within the quarry following storm <br /> events and will coalesce in the lowest area of the processing area pad, aka the sump. This <br /> designated sump may move as mining phases are opened over time; Maps C-2 through C-7 show <br /> designed locations for sumps at final mined elevation for each phase. Most stormwater within the <br /> quarry will evaporate or infiltrate the processing area pad across phases and through the life of <br /> the mine. Water captured onsite that does not evaporate or infiltrate after 24 hours will be <br /> discharged from the site via the pathways identified on the mining maps. During Phases 1 <br /> through 4, stormwater will be pumped via a pipe through the CCP underpass to flow down the <br /> CCP fill slope to enter the working surface of the WRL. Stormwater will flow across the WRL <br /> and infiltrate its porous structure enroute to the CDPHE discharge points located at the WRL toe. <br /> In this way all stormwater runoff is returned to the natural water system within 72 hours, thus <br /> protecting local water rights. During Phase 5 and in final reclamation, the quarry floors will <br /> discharge via the mine ramp/haul road to drainages to the south, as the underpass will now be <br /> significantly higher in elevation. <br /> All stormwater discharges during mining are via CDPHE discharge outfalls. Exhibit C maps <br /> show the stormwater handling for each stage. Map G-1 shows the location of the discharge <br /> points. <br /> WRL Surface Water Handling <br /> The creation of the WRL just northeast of the quarry will modify the pre-mine drainage area <br /> where the WRL will be constructed. The areas created by these activities within the mining area <br /> can be seen on Map G-1 —Surface Hydrology: Mining Conditions. A curve number of 89 is <br /> applied to disturbed areas during mining. A curve number of 79 is applied to areas that have seen <br /> Young Ranch Resource <br /> December 2021 G-3 Lewicki&Associates <br />