6101 23RD DR W NORPRO 2025-07-29

I Section II: Site Assessments U Topography The topography of the site in the project area of the subject property is moderately sloped with I slopes ranging from 4% — 10%. Outside of the project area the site slopes steeply down to Narbeck Creek. I There is a gentle ridge within the project area that splits the runoff between two separate basins. The western portion of the site is tributary to the East Fork Powdermill Gulch Creek and the eastern portion of the site is tributary to Narbeck Creek. I See Exhibit A - Existing Conditions Drainage I The natural drainage pattern for the Powdermill Gulch Creek drainage basin consists of sheet flow and concentrated overland flow across the forest floor to either the property to the north or 23`d Drive W along the western property line. I The natural drainage pattern for the Narbeck Creek drainage basin consists of sheet flow and concentrated overland flow across the forest floor to either the property to the north or down the steep slope to Narbeck Creek. I Soils Per the Geotechnical Report by Terra Associates, Inc, dated February 19, 2007, the site is I immediately underlain by 12 inches of forest debris (duff) and topsoil. Beneath the topsoil, the glacial sediments were encountered. The site is split between glacial outwash on the western half and glacial till on the eastern half. The near-surface weathered glacial soils consist of loose to ' medium dense, fine-grained reddish-brown to grayish-brown silty sand with gravel (glacial till). The glacial till was noted to be in a moist and dense condition when first encountered, becoming very dense with depth. The western portion of the site consists of grayish-brown gravel with sand and silt (recessional outwash) beneath the weathered surface soils. The gravel was wet to moist I and was in a medium dense to dense condition. The USDA defines the site soils as Alderwood Gravelly Sandy Loam (hydrologic soil group C). I Ground Cover The existing land coverage is entirely pervious and made up of second growth conifer and I deciduous trees with moderate ground cover. Critical Areas Narbeck Creek runs through the eastern portion of the site. There is a Native Growth Protection I Area (NGPA) associated with Narbeck Creek. The steep slopes above Narbeck Creek are also contained within the NGPA. No development is proposed within the NGPA or on the steep slopes above Narbeck Creek. I Adjacent Areas There are existing industrial developments on the properties to the north and south of the project I site. A multi-family residential development is to the east of the site, opposite the deep Narbeck Creek gully, and 23`d Drive W is along the western property line. There is an existing water main and associated easement parallel to the 23`d Drive W I approximately 300 feet east of 23`d Drive W. This water main and easement will be relocated onsite as part of the development of Lot 3B-1. 6/16/2011 Stormwater Site Plan Page 6 I