9404 18TH AVE W 2018-01-01 MF Import

III.Offsitc Anxlysis The upstream property to the south is undeveloped and highly vegetated with native plants and understory. No point of discharge w�s observed from the neighboring property to the south. It would appear that no significant drainaoe from the upstream property contributes to the site. No ditches were observed along the property frontape on the west side of l8"' Avc. W. Drainage from the slieet Flows tow�rd die north. A minimal amount of drainaoe from [he roadway may contribule to the site. However, this contribution would be negligible. Downstream Analysi:;: Rwioff from the site flows overl�nd toward the wetla�id to the wesL This wedand conVibutes to a steam that contributes to Swarnp Creek. IV. Analysis and llesign of Rcquired Grosion and Sedim�nt Control 13MFs According to the SCS Soi! Sur��ey for Snohomish Counry, the soils on site consist of rype 34 Mukilteo Muck �nd type 5 Alderwoad Urban Land Complex. Alderwood Urban Land Complex is on till plains. This unit is about 60 percent Alderwood geavelly sandy lo�m and about 25 percent Urban 11nd. The .4lderwood soil is moderately deep over a hardpan and is tnoderately well drained. It formed in glaciaql till. Permeability of the Alderwood sioil is moderately rapid above the hardpan and very slow tl�rough iL Available water capacity is low. Runoff is slow and [he hazard of water erosion is slight. This type of soil is classified as hydrological gro�p "C" �ccording to die SCS Soi! Survcl'.(iu• Snohomish Counry. Mukilteo Muck is very deep, very poorly drained sc,il in drewssional arens. It formed in organic material derived dominantly from sedges. Penne�biliry of this Mukilteo soil is moderate. Available water capacity is high. Runoff is ponded. In most nrens of this unit, the water table is artificinlly drained to 1 dep[h of 3 or 4 feet during the growing selson. Some nreas are ponded during the rainy season. This type of soil is classified as hydrological aroup "D" according to the SCS Soil S�u-ve� fnr Snohomish County. '1'he poten[ial for erosion for this type of soil is slight, however, special attention should be given to working the material iit wet weather (October I through March 31). Soil compaction will be difficult, if not impossible ro achieve during periods of sustained rainfall. De1d storage in the vatdt ��ill be the primary setding basin for the site. Other than rainfall, the source of erosion would come from dust and wheel traffic during construction. This risk would :ppear to be minimal. Additional risk would be tr�cking of mud onto the roadway. The rock construction entrance will help to minimize this risk. �ollowing final grading, all slopes will be stabilized with nuilch,jute mesh, hydroseed or other means. I(