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Maximum Mining Area Runoff & Retention Volume <br />Runoff Curve Number and Runoff <br />Project: LaSalle Pit By: BL Date: <br />Location: Montrose, CO Checked: Date: <br />Present <br />1. Runoff curve number (Cn) <br />Cover description CN Soil Type Area <br />Crushed gravel 85 C 22.600 Acres <br />CN (weighted): 85 <br />2. Runoff <br />Frequency .............. 100 yr <br />Rainfall, P (24-hour) .. 2.40 in <br />Runoff, Q .............. 1.0993 in <br />Runoff Volume .......... 2.0704 Acre-Ft <br />Pit retention capacity behind 3' tall berm with 1' freeboard = 45.2 acre-ft <br />Maximum Undisturbed Area Runoff & Retention Volume <br />Runoff Curve Number and Runoff <br />Project: LaSalle Pit <br />Location: Montrose, CO <br />Present <br />1. Runoff curve number (Cn) <br />Cover description <br />Irrigated pasture <br />CN (weighted): 74 <br />3/13/2008 13:32 <br />3/13/2008 13:41 <br />By: BL Date: <br />Checked: Date: <br />CN Soil Type Area <br />74 C 22.600 Acres <br />2. Runoff <br />Frequency .............. 100 yr <br />Rainfall, P (24-hour) .. 2.40 in <br />Runoff, Q .............. 0.5529 in <br />Runoff Volume .......... 1.0412 Acre-Ft <br />Pit retention capacity behind l' tall berm with 6" freeboard = 11.3 acre-ft <br />The runoff from both areas will be allowed to seep back into the ground. Therefore, there will <br />not be an NPDES permit for the site. <br /> <br />• <br />• <br />LaSalle Pit, April 09 D-2