415 RIVERSIDE RD 2019-02-14 - Laserfiche WebLink

ME Tl Al 6 /4A ND0UT 41/ 71/5" r,b, 0., z ,TB # 2120IL . obi 45.3.Stormwater System Capacity.Based on Port of Everett Riverside Business Park Stormwater Site Plan(Comprehensive Hydraulics Report),revised April 2000(the Report),the City and the.Port agree upon the following information from the Report: Pond#2(aka Pond D)in the Report is the large pond.Pumps 1,2,3,and 4 convey stormwater runoff from the Riverside Road storm drainage system into Pond#2.An additional future pump#5 needs to be designed and constructed to convey runoff from the eastern portion of the site into Pond#2(page 6). The existing pumps were designed to convey the following maximum flows,which included street drainage as well as some lot drainage(page 23): Pump# Design Flow ids) 1 2.39 3 2 _.....2.22 .�..._ .. •234 v. 4 2.87 Emergency overflow pipes are to be provided on the lots to prevent high flows in excess of the pump design flows from causing flooding of the street(page 21). These overflow pipes are to be discharged directly to the river:Pond#2 was designed to provide 128,972 cubic feet of treatment storage volume (page 21). The design calculations for Pond#2 assumed that roof runoff would be discharged directly to the river(page 6).Based upon the above information,the City agrees to accept flows up to the pump design flow into the existing pump stations. The Port agrees to provide high flow bypasses for flows exceeding the pump design flows.The City also agrees to accept into Pond#2 the runoff from a total drainage area with a required treatment volume of 128,972 cubic feet per the City's current standards I limited to runoff from general parking and pedestrian areas.Any runoff from industrial process area's would require treatment prior to discharging into the stormwater system. Current maximum required treatment volumes for"basic"stormwater treatment are as follows for the Riverside project site: Impervious area Pervious area 4,404 cubic feet per acre 1;694 cubic feet per acre This would equate to 29.3 acres of impervious area(128,972+4,404),or 76.1 acres of pervious area (128,972-1,694),or some equivalent combination of impervious and pervious area.