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TABLE 7 -6 -7 -3 <br />• "K" FACTOR <br />Hydrologic Erodibility (K) <br />Soil Type Soil Group Factor <br />10 D D 0.25 <br />Topsoil Removed D 0.24 <br />Gravel Road N/A 0.10 <br />u <br />• <br />Sedimentology The SEDCAD+ computer program was also utilized to <br />calculate the sediment flowing to the facility outlet using the <br />DEPOSITS portion of the program. The Revised Universal Soil Loss <br />Equation (RUSLE) was used to determine sediment loading. <br />After the initial sedimentology runs were made, the results <br />indicated that sediment would be flowing from the site. There <br />were several options discussed that would clean up discharge <br />waters. Most of the options were not viable. Constructing <br />sediment ponds would be costly and not very feasible. The runoff <br />from these areas was such that there was not a good location for <br />pond construction. The same problem came up with the sediment <br />trap option. Silt fencing was a viable option but little <br />information is available pertaining to silt fence efficiency. <br />SEDCAD+ does not have a silt fence option for sedimentation. <br />In a telephone conversation with Dr. Richard Warner, co- author of <br />SEDCAD +, it was determined that the rock check dam would best <br />simulate the potential for sediment retention with the aide of a <br />silt fence. Different sources have estimated various efficiencies <br />for silt fences. The state of Virginia estimated that a silt <br />fence would remove 99.6% of the sediment (Dallaire, 1976). Mirafi <br />Corporation estimates a 75% retention efficiency. In a paper <br />presented at the OSM Sediment Forum (September 1992), Tom Munson <br />stated silt fence efficiencies in the range of 80 to 93 %. <br />1 0 4 N " �" �w <br />� <br />The attached SEDCAD+ results indicate that the trap efficiencies <br />range from 69 to 93 %. This appears to be in line with the above <br />7 -6 -7 -5 t4OR 006607 <br />