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• Pond 011 -Proposed Design <br />Pond 011 has been re-designed for the Mid Term Review of 2006 since there are some minor <br />changes to the drainage basin and to account for a base flow of 1.34 cfs from pit pumping. <br />Design Parameters <br />• Since the pre-mine drainage area is much larger than the post mine, the pre-mine condition <br />is the worst case and is the only case designed and presented. The pre-mine drainage area <br />is 126.8 acres while the post mine area is only 24.7 acres. For the larger area, the site is <br />basically undisturbed, which results in the curve number shown below. If a larger curve <br />number is used to reflect the mine disturbance, a lesser drainage area must also be used, <br />since the mine pit will not drain to the pond. <br />• There will be a continuous flow of 600 GPM from the active mine pit pump system into Pond <br />11. <br />• Pit pump water will need a retention time of approximate 2.5 days so the PH of the water <br />will stabilize and pass the WET toxicity test. <br />• Therefore, add: [(600gpm x 60mph x 24hpd x 2.5 days)/7.5 gal per cu-ft]/43560sq-ft per ac <br />= 6.6 ac-ft <br />• Primary spillway riser will have a partially opened 4 inch gate valve at the base so surface <br />water will be mixed with pond bottom water to better mix the pit pump water for water <br />quality purposes. <br />• There will be an 18 inch Riser/Barrel Primary Discharge with a 4" weep hole opening plus <br />an open channel, lined and riprapped Emergency Spillway in the embankment, for a <br />combined two separate discharge pond design. <br />• Curve Number (CN} to use: From SEDCAD 4 for Windows Help menu <br />I. Curve Numbers for Other Agricultural Land Category <br />II. Cover type: Pasture, grassland, or range -continuous forage for grazing <br />III. Hydrologic Condition: Good (Good: >75% ground cover) <br />IV. Hydrologic Soil Group = C <br />V. CN=74 <br />This curve number is supported by the table widely used for hydrologic design by the SCS in 1986, <br />as shown on the following page. <br />• <br />REVISED MARCH 2006 Attachment 2.05.3(3)-14-2 <br />