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King Mountain Gravel LLC Memorandum <br />February 21, 2005 <br />Page 2 <br />5. The land use for the tributary 40 acres is estimated to be pasture in good <br />condition. The Curve Number is 61. For the pit, the Curve Number was estimated <br />to be 40 or less based on the high infiltration capacity. <br />6. The 100-year 24-hour precipitation depth for this location is 2.8 inches. Based on <br />the NRCS Method of calculating runoff volumes, the runoff depth from the 40 <br />acres tributary to the west pit walls would be 0.27 inches during the 100-year <br />recurrence interval precipitation event. There would be zero runoff from the pit <br />bottom. <br />7. Runoff from the tributary area would be distributed over several thousand feet of <br />pit rim as it entered the pit. The runoff would quickly infiltrate the pit sides and <br />bottom, and would not flow to the east side of the pit. <br />8. Conclusion: It is highly unlikely that any runoff would pond in the pit bottom <br />because of the high infiltration capacity of the pit soils. This conclusion is <br />supported by the operator's experience in the existing pit. If ponding should <br />occur as the result of an extreme precipitation event, it would be shallow and <br />would infiltrate quickly. The shallow depth and long distance between the <br />ponding area and the neazest drainage at the same elevation make breaching of the <br />pit wall virtually impossible. <br />Attachments: <br />Tributary Area Map <br />100-Year/24 Hour Precipitation Depth Map <br />Runoff Curve Number Table <br />Runoff Depth Table <br />