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Volume V -Appendix M(viii) <br />Small Area Exemption No. 1 -SAE-1 <br />Calculation Rational and Results Summary <br />Check Dam and Silt Fence Design <br />Portal Area -Munger Canyon Mine <br />Purpose: <br />To control the runoff of water and sediment from the Munger Canyon Mine Site, a <br />sediment trap was installed when the mine was opened in 1977. The sediment trap was <br />a small pond. The small pond does not meet the recently revised DMG rules regarding <br />impoundments. Therefore, the pond embankment will be replaced by a rock check <br />dam. A silt fence will be installed immediately downstream of the rock check dam to <br />provide alternative sediment control. <br />Rational: <br />Calculated using SEDCADT"' 4 for Windows <br />Areas, slopes and flow paths obtained from the Sketch on following page M(viii)-1 i. <br />The soil type in the study area is very gravelly clay loam <br />The following Curve Numbers were utilized in the calculations: <br />• Mine Bench - 87 - C soil group, Herbaceous Mixture poor cover <br />Cut Slopes - 81 - C soil group, Herbaceous Mixture fair cover <br />Upland - 73 - C soil group, Juniper Woodland, fair cover, PAP page 4-120 <br />Table 2-2d Runoff curve numbers for arid and semiarid rangelands <br />10 year 24 hour storm event of 1.5" used in calculations to be conservative. <br />Results: <br />Structure Peak Flow (cfs) in/out Size/Length <br />Check Dam 1.3/1..3 3' high 50% porosity <br />Silt Fence 1.3/0.95 40-feet <br />The SEDCAD calculations ar~pRf~i~rr~~'fion~j <br />prepared by me during the~p~ofrOcsto <br />correct to the best of my I~ug~ge and be <br />a~°~ 19 <br />/ ~;es .Stover, <br />Regis~edPoofe~sfoi <br />• State b~'~4l4f3fl~, <br />~d on pages M(viii)-1 through M(viii)-1 ix were <br />and the information presented is true and <br />~. <br />a <br />19230 <br />M(viii)-1 <br />r z- <br />10/02 <br />