2019-01-18_REVISION - M1974086 (16)

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Graphical Peak Discharge Thu Sep 06 13:30:56 2018 Project: Ralston Quarry Project:South Pond Emergency Spillway By:B Langenfeld Date:09/06/18 Location:Ralston Quarry Checked: Date: Present 1. Data: Drainage area:....................A=4.8990Acres Runoff Curve Number:.............CN=87 Time of Concentration:...........Tc=0.11 Storm Type:....................... =II Pond and swamp areas spread throughout watershed...............=0.00 percent of A 0.0000 Acres 2. Frequency........................yr=10 3. Rainfall,P(24-hour)..............in =2.96 4. Initial abstraction,la............=0.2989 5.Compute la/P.......................=0.1010 6. Unit peak discharge,qu......csm/in=972.23 7. Runoff,Q.........................in=1.7042 8. Pond&swap adjustment factor....Fp=1.00 9. Peak Discharge,gp...............cfs=12.7 The emergency spillway (constructed earthwork), on the South Pond, has been sized to handle the 10-YR discharge. The storm water discharged from this pond will flow to a discharge point shown on Map C-2. Maps C-2 and C-4 show the location of the South Pond and its associated collection ditches. 2.3.3 North Area Drainaze The North Area consists of all of the old tailings deposition area that has been determined to require reworking for slope stability. While not all of this area may be disturbed during slope stabilization work, it is assumed that all of it will be regraded for stormwater control purposes. All water handling improvement designs can be found on Maps C-4 and C-6 for this area. 2.3.3.1. Rock Stormwater Filter Berm A berm will be constructed at the downhill side of the disturbed North Area. This berm will consist of rock piled 6 feet high with 3H:1 V sideslopes. This will provide a 36-foot-wide filter for stormwater runoff in the North Area to pass through. Stormwater will flow through this berm, and then into a collection ditch which will then take it to the NPDES discharge point located at Ralston Quarry GM I.cwicki and Asa wtm PIRA' January 2019 G-4