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DEVELOPMENT COMMITTEE <br /> ER-90-8 <br /> PAGE TWO <br /> 5. The extraction pits shall be left open for as brief a time as <br /> possible, particularly during periods of rainfall and shall <br /> be aligned perpendicularly to the streamflow. Details shall <br /> be shown in the Grading Plan. <br /> 6. The cross sectional area of the channel at the new bridge site <br /> shall be surveyed to determine the present channel capacity, <br /> and that information shall be included in the construction <br /> plans and permits for construction of the bridge. <br /> 7 . An Erosion Control Plan shall be included in the Grading Plan. <br /> 8 . Demolition of the old bridge site and construction at the new <br /> site shall be performed so as to prevent siltation of the <br /> river. Construction shall take place during dry weather and <br /> low streamflow. <br /> 9 . The retention/percolation basin shall designed to provide <br /> sufficient water storage capacity to allow percolation of <br /> surface water to the aquifer in the area of the proposed <br /> quarry excavation. Calculations for sizing the retention <br /> basin shall be approved by the Department of Public Works <br /> prior to inclusion in the Grading and Reclamation Plans. The <br /> Reclamation Plan should include detailed grading measures to <br /> provide drainage to the retention basin and to prevent ponding <br /> of water on the remainder of the site. Grading shall be <br /> performed to prevent direct runoff to the Mokelumne River. <br /> 10. The Grading Plan shall establish an adequate setback from <br /> their drainage pond to prevent inundation of the gravel <br /> extraction area in the event of rainfall grater than the 10 <br /> year storm. The setback shall be developed by a soils <br /> engineer or certified engineer geologist to ensure that it is <br /> adequate to prevent pond slope failure due to quarry <br /> excavation. <br /> 11. In the event that the water table is intersected during <br /> extraction, the excavation area shall be drained prior to <br /> further extraction. Details of drainage, extraction, and <br /> reporting to the Regional Water Quality Control Board and the <br /> Department of Public Works shall be included in the Grading <br /> Plan. <br />