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Post Mine Drainage <br />• 166.1 acre drainage area <br />• During mining, the maximum pit pumping rate will be 600 gpm from the active mine pit <br />pump system into Pond 11. <br />• Pit pump water will need a retention time of approximate 1 day so the PH of the water <br />will stabilize and pass the WET toxicity test. <br />• Therefore, add: [(600gpm x 60mph x 24hpd x 1 days) /7.5 gal per cu- ft] /43560sq -ft per <br />ac =2.6 ac -ft <br />Runoff Curve Number and Runoff (SurvCAD) <br />Project: Pond 011 By: B Langenfeld Date: 09/01/09 <br />Location: New Horizon #2 Checked: Date: <br />Developed <br />1. Runoff Curve Number (CN) <br />Cover description CN <br />Mined Land, Disturbed (Poor) 87 <br />Herbaceous mixture (Good) 74 <br />Pasture Grassland Range (Good) 80 <br />Soil Type Area(Acre) <br />C 14.700 <br />C 48.430 <br />D 102.944 <br />CN (weighted): 78.9 <br />Total Area: 166.074 Acre <br />2. Runoff <br />Return Period: 10 -Year <br />Rainfall, P: 2.00 in <br />Runoff, Q: 0.5174 in <br />Runoff Volume: 7.1608 Acre -Ft <br />The pond volume below the emergency spillway will be comprised of three design needs: <br />1) 10 year storm inflow of 7.2 acre -ft, as described above <br />2) 3 year sediment delivery of 0.1 acre -ft, as based on the calculations shown below. <br />3) 2.6 acre -ft of pit pump water. <br />REVISED AUGUST 2009 Attachment 2.05.3(3) -14 -9 <br />