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Run-on Water from the South (Basin A) <br /> Pre-development flows were calculated using the USDA winTR-55 method. Run-on water will <br /> be intercepted and diverted around the proposed project by Channel A: Offsite Stormwater <br /> Diversion Channel. <br /> Calculations using the USDA TR-55 method show flows of 43.85 cubic feet per second (cfs) <br /> for the 24-hour, 10-year storm event and a discharge of 121.6 cfs for the 24-hour, 100-year <br /> storm event. This water will flow into the natural drainage just below where Basin E starts at <br /> the south side of the project. <br /> Channel A has been divided into an upper (Al) and lower (A2) section to correspond to the 2 <br /> subbasins. Channel A is a trapezoidal channel with a 3-foot-wide bottom extending 1,100-feet <br /> west from the channel discharge into the natural drainage. The bottom width of the channel is <br /> eliminated further west. <br /> Grouted riprap structures will be installed from the discharge point to 1,100 feet upstream. The <br /> average channel slope with the grouted riprap is at 6-percent. Sixteen (16) — 3-foot-tall <br /> structures will be installed about 68-feet from each other. <br /> Operations Area (Basin B) <br /> Pre and post development runoff rates were calculated using the Rational Method and are <br /> indicated in Tables 2 and 3 above. Water in this basin will flow directly into the Contact Water <br /> Pond or into the pond after being intercepted by Channel B: Contact Water Pond Channel. <br /> Water from the pond will not be discharged until it is tested and meets water quality standards. <br /> Table 3 indicates 0 discharge for this basin post-development as a result. <br /> Channel B is a trapezoidal channel with a 3-foot-wide bottom extending from the Contact <br /> Water Pond south to the mine vent. A berm will be constructed on the downslope side of the <br /> channel to prevent water from the natural drainage entering the channel. <br /> Gabion drop structures will be installed for the length of the channel. The average channel <br /> slope with gabions is at 6-percent. Fourteen (14) — 3-foot-tall structures will be installed 38- <br /> feet from each other. <br /> Laydown, Stockpile Area (Basin Q and Detention Pond <br /> Pre and post development runoff rates were calculated using the Rational Method and are <br /> indicated in Tables 2 and 3 above. Water in this basin will run into a detention/sedimentation <br /> pond at the north side of the area after it is intercepted by Channel C: Onsite Stormwater <br /> Diversion Channel. N <br /> N <br /> O <br /> N <br /> Water from the detention pond will be discharged through a 24-inch culvert at a reduced rate o <br /> to account for increases in surface water flow in other areas of the site. <br />