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scouring cannot occur. When wire or polymeric back-up support <br />mesh is used, the wire or polymeric mesh shall extend into the <br />ground 3-inches min. <br />9. Drive or place the fence posts into the ground 18-inches min. A <br />12—inch min. depth is allowed if topsoil or other soft subgrade soil <br />is not present and 18-inches cannot be reached. Increase fence post <br />min. depths by 6 inches if the fence is located on slopes of 311:1 V <br />or steeper and the slope is perpendicular to the fence. If required <br />post depths cannot be obtained, the posts shall be adequately <br />secured by bracing or guying to prevent overturning of the fence <br />due to sediment loading. <br />10. Use wood, steel or equivalent posts. The spacing of the support <br />posts shall be a maximum of 6-feet. Posts shall consist of either: <br />• Wood with dimensions of 2-inches by 2-inches wide min. and <br />a 3-feet min. length. Wood posts shall be free of defects such <br />as knots, splits, or gouges. <br />• No. 6 steel rebar or larger. <br />• ASTM A 120 steel pipe with a minimum diameter of 1-inch. <br />• U, T, L, or C shape steel posts with a minimum weight of 1.35 <br />lbs./ft. <br />is• <br />Other steel posts having equivalent strength and bending <br />resistance to the post sizes listed above. <br />11. Locate silt fences on contour as much as possible, except at the <br />ends of the fence, where the fence shall be turned uphill such that <br />the silt fence captures the runoff water and prevents water from <br />flowing around the end of the fence. <br />12. If the fence must cross contours, with the exception of the ends of <br />the fence, place gravel check dams perpendicular to the back of the <br />fence to minimize concentrated flow and erosion. The slope of the <br />fence line where contours must be crossed shall not be steeper than <br />3H:1 V. <br />• Gravel check dams shall be approximately 1-foot deep at the <br />back of the fence. Gravel check dams shall be continued <br />perpendicular to the fence at the same elevation until the top of <br />the check dam intercepts the ground surface behind the fence. <br />Gravel check dams shall consist of crushed surfacing base <br />course, gravel backfill for walls, or shoulder ballast. Gravel <br />check dams shall be located every 10 feet along the fence <br />where the fence must cross contours. <br />• Refer to Figure 4.2.13 for slicing method details. Silt fence installation <br />using the slicing method specifications: <br />Volume II — Construction Stormwater Pollution Prevention - August 2012 <br />4-91 <br />