10025 19TH AVE SE BASE FILE 2018-01-02 MF Import

INTRODUCTION The Silver I.alce Mortgage property is located just south of 100'h on the east side of 19'h. An cye clinic exists immediately south ofthe proposed project. The site is approximately I.12 acres and consists of olci buildings and houses which will be demo!ished for this project. It also has existing drives which will be removed. The drainage t'rom the site flows westerly and discharges into thc storm drainage system on 19`h. The drainage system pipes slope southerly and eventually discharge into Silver Lake. RunoFfcoefficients will be based upon a hybrid and conservative number of CN=83 (a cross between lhe treed areas and the grassPouilding arcas). A time of concer.iration will be based upon the cross of trees and gravel driveway or as shorl prairie grass/lawns and will be more conservative than maximum. PROPOSED COIYDITIONS Thc proposal is to constnict one building to house retail or other approved uses. Drainage reqairemen[s will conform to thc City Drainagc Manual which requires RetentionlDetention for floN�control, a water quality pond, ar d, in the Silver Lake basin, a biofiltration sw;jle. Calculations �•�ill be providcd using the SI3UIi modcling and usir.g Watenvorks software. Special considerations include a pump to dischargc the 2-year storm cvent into the biofiltration swale and water quality feature. In addition, the RID system will be designed so that if thc pump 1'ails the 2-ycar stom� will discharge by gravity in to the storm system on 19`�'. This will be accomplished with the restrictor (located inside the vault) will dischazge into a largc catch basin outside the vault which also acts as a pump chambcr. lf the pump can't kcep up, the water will discharge into the sireet system. The pump is designed at IG.S gpm and so that affects the swale sizing. If the flow is grcater than 16.5 gpm the additional �ow from the 10 and 100 year storms will flow by gravity to the street after being controllcd. CALCULATIONS VAULT Wc �vill use a 20 x GO foot vault with three fcet beneath the invert out for dead storage. Thc vault calculations are based upon a 40 foot l�ng vault, but with a 50%safety factor the actual constructed vault is 60 feet long. /!