Laserfiche WebLink
• MINOR REVISION N0.2 <br />TO PERMIT NO. C-005-80 <br />Sediment Pond 8004 Redesign <br />Introduction <br />Originally Sediment Pond No. 004 was designed to have a capacity of 19.04 acre-feet. <br />The embankment was nearly complete when excavating of the pond had to be halted. It <br />appeared that further excavation would result in hitting the ground water table. It was <br />obvious at this point that the pond design would have to be changed. A number of alter- <br />native plans were suggested to solve the problem but the most feasible plan is described <br />below. <br />The original design called for a pond to treat runoff from drainage basins totalling 547 <br />acres. It was determined that one of the basins could be diverted and this proposed <br />drainage' plan revision would still meet the regulations regarding sediment control. The <br />basin (154 acres) is immediately west of the sediment pond and except for a haulage road <br />• is otherwise undisturbed. <br />Pond Design Changes <br />Comparison of revised Exhibit "7-12", Proposed Pond No. 004 (attached) with that pre- <br />viously submitted shows that the originally proposed area to be excavated has been <br />substantially reduced. This reduction in ores was due to marshy conditions as exca- <br />vations neared the ground water table. The dewatering pipe was installed in the em- <br />bankment. However, because of the aforementioned unforeseen groundwater conditions, <br />it was not possible to excavate below the pipe. Removing and raising the pipe was not <br />feasible due to virtually homing to reconstruct the entire dam. Therefore, a riser pipe <br />was designed in order for the pond to have sufficient capacity for sediment storage plus <br />contain The ten-year storm without discharge through The principal spillway. The gate <br />valve was installed on the riser pipe rather than on the downstream end of the pipe as <br />originally planned. This was done to reduce pressure on the valve and the culvert joints. <br />The velocity of the flow through the emergency spillway (approximately 6.9 fps) warrants <br />• the use of riprap. Refer to calculation sheets for further details. <br />7-6-2a-2 <br />Revised 8-27-82 <br />