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<br />EXHIBIT D -MINING PLAN (continued) <br />• SWMP (Storm Water Management Plan) be developed and BMPs (best management practices] be <br />implemented. Through the use of high berms and excavation within the permit area, the entire <br />runoff from the 100 year - 24 hour event can be contained, therefore no storm~vater or SWMP <br />permits are needed for this site. This could only be accomplished by having the permit area avoid <br />Spring Creek and the unnamed central drainage as shown on Map Exhibit C-2. Both of these <br />drainages originate a few miles to the south of the property and flow to the north along the western <br />boundary of the permit area. A vast portion of the water rights in Spring Creek and the unnamed <br />drainage have been utilized upstream and both drainage basins have been drastically changed by <br />County airport construction and other development upstream. Spring Creek rarely flows, although <br />cottonwood trees tap some water below the surface. The unnamed drainage flows only during <br />irrigation periods, apparently due to water seeping through the porous gravel. <br />In order to demonstrate containment for the 100 year - 24 hour event, the following runoff <br />calculations are given: <br />• <br />100 year - 24 hour precipitation: 2.4 inches <br />Curve Number of Site: (assuming worst case acreage disturbed at any one time) <br />21 acres disturbed porous gravel: CN = 79 <br />8 acres undisturbed irrigated pasture: CN = 77 <br />Average CN = 78.4 for a total drainage area of 29.0 acres. <br />Runoff for 100 year storm @ CN 78.4 = 0.74 inches. <br />Total runoff volume = 0.74 inches x I fUl2 inches x 29 acres(within berms) = 1.78 acre-feet. <br />~J <br />Carol Ann Permit CDMG Application 1 B <br />