2102 ROSS AVE 2018-01-02 MF Import

02/26/2008 TUE 11:10 FAX ®001 ##+ FAX TX REPORT «+i TRANSMISSION OK JOB N0. 1212/, CamV-, 5L� DESTINATION ADDRESS 94252593230 WV 6 PSWD/SU©ADDRESS DESTINATION ID ST. TIME 08/26 11:09 USAGE T 01' 24 PGS. 3 RESULT OK U � oa U SITE INFORMATION 0 FA EXISTING DRAINAGE The site is mounded with about 10 feet of ricer dredge spoils. The Snohomish River bank bisects the site in a 14 northwest to southeast direction, such that the river bank slope is approximately 17 percent and the slope from top of bank toward Ross Avenue is approximately 3 percent. Drainage can be characterized as sheet Flow on each side of the bank. If surface water accumulates on the northeast side of the bank it will flow northward to the ditch along Ross Avenue. Stormwater within the ditch will flow in a northwest direction and eventually discharge into the Snohomish River. Due to the sandy nature of the soil on site, a large part of the surface water will infiltrate into the soil before entering the collection system on Ross Avenue. DEVELOPED DRAINAGE The proposed project involves the construction of a metal fabrication building and office encompassing a gross building area of 33,750 R' with associated asphalt paving and landscaping. Due to sites location adjacent to the Snohomish River no detention is proposed. This report will address all Minimum Requirements for New Development or Redevelopment as listed in the Department of Ecology (DOE) 2005 Storurwater Management Manual for western Washington with the exception of Minimum Requirement #7 Flow Control. (o. Ito • tkc nuNlhefS no kr+aor acicl �p The 9.44 acre site consists of 33,750 square feet (0.77 acre) roo�Q area and 109,235 square feet (2.51 acres) of pavement used for parking and storage. The rema' ' g .34 acres onsists of pervious landscaping, buffer enhancement and untouched riverside. The impervious ar rc rvided into pollution generating surfaces and non -pollution generating surfaces. Pollution generating surfacing will be routed to one of scveml DOE approved Contech Stormwater StormFilters sized to treat a small tributary basin. Additionally, the City of Everett requires pretreatment in the form of a wet vault or any DOE approved pretreatment carrying the GULD rating. Because of elevation constraints, a wet vault was chosen to store 30 percent of the runoff volume from the 6-month, 24-hour storm event, see Appendix for calculations. The project will discharge at the ordinary high water elevation of the existing drainage ditch on Ross Avenue in order to mimic prcdevclopment hydrology and drainage patterns. The rooftop area is a non -pollution generating surface and will be discharged directly into the bioswale/ditch system along Ross Avenue. See Appendix for wQ Analysis and Design CONVEYANCE SYSTEM ANALYSIS The conveyance system is analyzed using Bentley Culvertblaster program, by Bentley Systems, Inc. The 25-year peak runoff rate for Basins A and F were calculated using StormShed hydrology modeling software by Engenious Systems Inc. and was found to be 0.30cfs.