Laserfiche WebLink
Gob Vent Borehole Drill Pads <br />Alternate Sediment Control <br />Straw Log substitute for Silt Fences <br />The following table summarizes the peak water stage, trap efficiency and silt fence length <br />for various configurations of gob vent drill pads. <br />Page <br />Exhibit 8 <br />Description <br />GVB Drill Pad <br />Peak Water <br />Stage Feet <br />Trap <br />Efficiency % <br />Length <br />Feet <br />107 -115 <br />GVB Drill Pad on 3:1 Slopes <br />0.05 <br />59.99 <br />140 <br />116-124 <br />GVB Drill Pad on 5:1 Slopes <br />0.05 <br />59.81 <br />100 <br />125-133 <br />GVB Drill Pad on 10:1 Slopes <br />0.05 <br />59.99 <br />100 <br />134-142 <br />100'X 100' on 3:1 Slopes <br />0.08 <br />59.92 <br />200 <br />143-151 <br />100'X 100' on 5:1 Slopes <br />0.10 <br />59.92 <br />110 <br />152-160 <br />100'X 100' on 10:1 Slopes <br />0.09 <br />60.05 <br />100 <br />223-230 <br />150 X 200' on 10:1 Slopes <br />0.18 <br />59.49 <br />150 <br />The design flow rate for all of the silt fences is 10 gallons per minute per square foot. <br />The maximum peak water stage is 0.18 feet or 2.16". <br />The key factor in sediment control is the trap efficiency. According to data published by <br />American Excelsior Company, its 12" Curlex sediment log has a trap efficiency (% Soil <br />Retained) of 70.3% and a flow rate of 37.5 gallons per minute per square foot. Its 6 and 9 <br />inch sediment logs have a trap efficiency of 53.9% at 42.5 gallons per minute per square <br />foot. <br />The high flow rates of the sediment logs in relation to the silt fence design would indicate <br />run-off will not overtop the straw logs. The straw logs will filter the run-off faster that <br />the sediment fences. The favorable trap efficiency of the straws logs indicate they are as <br />good as or better than the designed silt fences. The 6 and 9 inch straw logs have a <br />slightly lower trap efficiency that is not considered significant. <br />Straw logs will be keyed into the natural soil below the gob vent hole drill pads. The <br />total length of the straw logs will be comparable to the length indicated in the approved <br />silt fence designs including tie back distances. The straw logs will be overlapped to <br />prevent flow bypass when pieces are joined to achieve the appropriate total linear <br />footage. <br />00 <br />°c,•,�,�41,� �y ' o, <br />°°Q e q <br />'d R. �e <br />MR -136 Exh-8 -106i - 06/13 <br />