PERMFILE66994 - Laserfiche WebLink

Home Browse Search

• SEDIMENTATION STRUCTURE 004 PRINCIPAL SPILLWAY REDESIGN INTRODUCTION Sedimentation Pond 004 was originally constructed in ] 982 and re-evaluated in 1986 resulting in a modification to the principal spillway. It was determined that a 6 inch diameter pipe was the best practical size in order to increase detention time and still have enough storage above the peak stage for pit pumpage. Therefore a 36-inch corrugated metal pipe was installed with a 6-inch opening at the inlet Pond 004 was inspected during Apri12005 following snow and ice melt and it was determined that there was enough deterioration to the discharge barrel of the princpal spillway to warrant replacement of this pipe. It should be noted that the ptinapal spillway is still functioning as designed at this time. ABANDONMENT/REPLACEMENT PLAN The abandonment plan consists of digging up the existing pipe and replacing it with corrugated plastic pipe installed at the appropriate elevation. The new principal spillway will installed at the appropriate elevation in the trench dug across the width of the embattlement to remove the current metal pipe. The corrugated "plastic" pipe will be placed in the trench and the trench material compacted back azound it. The elevation and location aze shown on Exhibit 7-27, Pond 004 • Prinapal Spillway Redesign. Once the new spillway is in place a screened cage will be attached to the inlet to elitrtinate potential plugging by debris. Attached aze the SEDCAD demonstrations used to size the "neu~' prindpal spillway. The watershed map used to calculate runoff and to determine the hydrologic input criteria is attached as Exhibit 7- 22,Pond 004 & 008 Watershed Boundary. The design is graphically displayed on Exhibit 7-21, Pond 004 Ptindpal Spillway Redesign. $ should be noted that this redesign does not affect or include the existin¢ emereencv soillwav. This snillwav is adequate to safely Hass the 25 yr/24 hr orecioitation event L