4909 NARBECK RD 2023-06-22 - Laserfiche WebLink

The soils on the site are Alderwood series (5)per the SCS Soil Map and a soil investigation by Cobalt GeoSciences found the soils to be infeasible for the use of total infiltration for the disposal of storm runoff. Infiltration and Dispersion cannot be implemented based on the Geotechnical Report submitted by Cobalt Geosciences, LLC. There is a storm drain in the area so a direct connection is practical. Erosion Control can be provided by a construction entrance and silt fence around the north and west sides of the property. Section 3 Site Development The site was visited on March 1,2017. The downstream drainage system was field. verified and the drainage patterns and ground cover were observed. The site consists of a vacant lot with grass,brush, ivy and few trees. The site slopes down to the southwest at • 20%to 40%. To the north is Darlington Beach. To the Southeast is Narbeck Ave., which has drainage, curbs and gutters and slopes down to the northeast. There is a SFR to the west which does not appear to drain any significant amount of water onto the property. To the west is Narbeck Rd that does not appear to drain onto the site. The site slopes down to the southeast. The site will be developed with a new 1,910sf Single Family Residence and a1,697sf driveway, sidewalk and porch for a total impervious area of 3,607sf or 25.10%. See site plan. A quarter mile downstream inspection was performed. The inspection concluded no visual impacts or potential problems will occur from the development of the subject site. The downstream course consists of sloping roadways (+/-20% )wooded hillsides and Narbeck creek approximately 250 ft from the site. The driveway and roof downspouts will be routed to the existing drainage ditch which will drain into the existing catch basin along W Mukilteo Blvd in between Narbeck rd and Narbeck Ave. The driveway will be sloped 15%to flow toward Narbeck Rd. This is the only practical method of storm water control as the site is not suitable for either dispersion or infiltration per the Geotechnical Report see attached at end of report. Section 4 Stormwater Pollution Prevention Plan The site does not require any special stormwater pollution prevention. See SPPP. Section 5 Source Control of Pollution Due to the small size of this project and residential nature of this project no significant amount of Pollution will be generated. The roof downspouts will be connected to the existing roadside ditch with a 6" PVC pipe. The ditch drains to the existing catch basin along W Mukilteo Blvd in between Narbeck Road and Narbeck Ave. Section 6 Special Reports and Studies No special reports or studies are available on this site. A Geotechnical report has been submitted by Cobalt Geosciences, LLC. See attached. r)2/ AE2018-97