10105 19TH AVE SE 2018-01-02 MF Import

r . � Smrmwafsr Sile Pfan,(or Northwest Animaf Care Moy 29, ?002 1 SECTION I PROJECT OVERVIEVV � ( The project is a new �eterinary clinic on a one-acre commercial lot. 'ihe development includes construction a single-story building (4,500 square-foot footprint), parking lot and sidewalk (12,000 square feet), and landscaping. The development will have two accesses onto 19`h i Avenue SE inside shared access easements. The sit� is located on the east side of 19'h Avenue SE,south of 100'h S�eet SE (see Figure 1)and i is inside the Silver Lake Drainage Basin (see Figure 2). Site area for drainage analysis is 0.99 acres and includes the subject property (0.97 actes) nnd the remainder of the proposed joint access easement to the north. IAdjacent property to the east is developed residential. The property adjoining the south boundary is paRially devel�ped commercial, and that to the noRh is undevetoped commercia! �- The existing site is cleared but undeveloped. Vegetative cover is pasture-type grass with some small trees. The qround slopes down from east to west at an average slope ef about three � percent. The existing site has no constructed drainag� sys!em. Existing site runoft' flows overland to the southwest to collect on the east curb of 19'h Avenue SE. Site soils are classified Lby the SCS as Alderwoo3-Urban land. Storm drainage improvements include collection, conveyance, watee quality treatment and detention facilities. The site drains to Silver Lake and therefore is subject tu special water- Iquality treatment requirements. The City Stormwater Manual requires a wetpond-biofiltration treatment system if infiltration of ( storm water is not feasible. The soils are silty sands consisting generally of about two feet of weathered till over dense till. Perched groundwater conditions exist over the till Iayer. The site Isoils aze therefore not suitable for infiltration. Runoff from the developed site will be collected by roof gutters and catch basins and conveyed in ( buried pipes to a combined detention/water quality vault. The vault will be located under the parking lot west of the proposed building. The dead storage in the vault will provide pretreatment for the vegetai..d wetpond and biofiltration swale. The volume of dead storege in i the vault exceeds 85 percent of the 6-month stortn runoff. Discharge from the pond will be to a lift station. The lift station will pump lower fluws to a ve�etated pond and biofiltration swale. H;gher flows will exceed the capacity of the pump, bypass the treatment facilities and flow idirectly to the public storm drain in 19'h Avenue. The flow pumped to the pond and swale exceeds the 6-month storm. The swale is designed to I Page 2 � �./