12011 19TH AVE SE PARKING LOT 2021-12-23

STORM WATER SITE PLAN OCTOBER 23,2019 EMORYS ON SILVER LAKE PAGE 3 EXISTING CONDITIONS SUMMARY DESCRIPTION The Emorys on Silver Lake valet parking project is located at 12011 120th Place SE in Everett, Washington. The site is at the northeast corner of the intersection of 19th Avenue SE and 120th Place SE. The 0.44 acre site currently contains a building, adjacent to 19th Ave SE, with a gravel parking area to the east, see Figure 2: Existing Site Map. Runoff from the site currently flows towards the southwest into the drainage along 120th Place SE. SOILS DESCRIPTION The underlying soils on the site, according to SCS, is Alderwood-Urban land complex. The Alderwood soil is moderately deep over a hard pan and is moderately well drained. Typically the surface layer is very dark grayish brown gravelly sandy loam about 7 inches thick.The upper part of the subsoil is dark yellowish brown and dark brown very gravelly sandy loam about 23 inches thick. The lower part is olive brown very gravelly sandy loam about 5 inches thick. A weakly cemented hardpan is at a depth of about 35 inches. Depth to hardpan ranges from 20 to 40 inches. Permeability of the soil is moderately rapid above the hardpan and very slow through it. According to the DOE Manual, this soil is in hydrologic group C. EXISTING BASIN In the undeveloped condition the basin contains both the portion of the site being developed and an offsite portion of 120th Place SE that will flow to the detention facility. The basin has the following areas: Forest 0.40 ac Pavement 0.06 ac The existing site flow frequency runoff rates are: 2 year 0.055 cfs 10 year 0.09 cfs 50 year 0.12 cfs UPSTREAM ANALYSIS The uphill area to the east and north of the site is developed as a condominium complex with an access drive adjacent to the sites the property line. The storm drain system in the access drive collects upstream runoff and routes it around the project site. DOWNSTREAM ANALYSIS Runoff from the site exits the property near the northwest corner where it sheetflows into a wetland on the adjacent condominium complex. Once in the wetland area runoff flows northerly about 300 feet until entering the storm drainage in 19th Avenue SE and flows to the west in a 24" pipe under the road and discharging to a detention pond. This pond then discharges to Silver Lake. There are no known drainage issues in the local area. With implementation of the proposed runoff treatment and flow control facilities there will be no significant impact to the downstream system. P:\Work\Projects\2018\18-141 Emory's\CE\DOCS\Final SSP 18-141.doc