607 RIVERSIDE RD 2020-09-18 - Laserfiche WebLink

Basin 28A is connected to a gravity storm system designed to handle the additional flows. See Appendix D for the pump information, head loss, and storage volume calculations. The existing Eighth Street is served by two outfalls, one 8-inch and one 12-inch. In order to provide an outfall for Lot 5 in the Riverside Business Park a pressurized storm drain system is proposed to connect to these two outfalls. The new portions of the system will be constructed of C-900 PVC pipe and manholes designed to withstand the increased pressure. The existing pipes and outfall will be lined with a cast-in-place liner to withstand the higher pressures. This system will be able to discharge between 2 to 5 cubic feet per second (CFS) depending on the allowable headwater elevation and Snohomish River tailwater elevation of 12.75-feet NAVD 88. The final development of Lot 5 will determine the allowable headwater elevation and maximum flow through the outfall. The current project will not discharge any stormwater through these outfalls. See Appendix C for Amendment 2, March 8, 2017, by KPFF describing the proposed system and supporting backwater calculations. See Appendix C for Amendment 1, October 19, 2016,by Reid Middleton describing the Snohomish River tailwater elevation of 12.75-feet NAVD 88. The gravity conveyance system on Eighth Street is designed to convey the 100-year return event to Storm Drain Lift Station 5. See Appendix D for calculations. See Appendix C for Amendment 2, March 8, 2017, by KPFF showing the anticipated 100-year return event peak flow from Eighth Street. See Appendix A for the site development plans showing the proposed improvements. G. MAINTENANCE AND OPERATIONS PLAN As the storm drainage system proposed is intended to be transferred over to the City of Everett, we anticipate the pumps, storm drain pipes, catch basins, and manholes will be maintained according to the existing citywide maintenance program. An additional Maintenance and Operations plan potentially duplicating the existing citywide plan is not included. Riverside Business Park—Public Access Trails and Roadway Improvements 9