1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC Geotech Report 2022-10-25

Stripping,Clearing and Grubbing We recommend that all new pavement and foundation areas be stripped of organic-rich soils (sod, grass, topsoil) and vegetation. Based on our experience, we anticipate that stripping depths will generally be approximately 6 inches or less. The stripped organic soil may be stockpiled for later use as topsoil for landscaping purposes. Subgrade Preparation The exposed subgrade should be evaluated after site clearing and grubbing is complete. Proof-rolling with heavy, rubber-tired construction equipment should be used for this purpose during dry weather and if access for this equipment is practical. Probing should be used to evaluate the subgrade during periods of wet weather or if access is not feasible for construction equipment.Soft areas noted during proof-rolling or probing should be excavated and replaced with compacted structural fill. Erosion and Sedimentation Control Potential sources or causes of erosion and sedimentation depend upon construction methods,slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. Implementing an erosion and sedimentation control plan will reduce the project's impact on erosion-prone areas. The plan should be designed in accordance with applicable city, county and/or state standards. The plan should incorporate basic planning principles including: • scheduling grading and construction to reduce soil exposure; ■ revegetating or mulching denuded areas; a directing runoff away from denuded areas and slopes; a decreasing runoff velocities; ■ preparing drainage ways and outlets to handle concentrated or increased runoff; ■ confining sediment to the project site; and a inspecting and maintaining control measures frequently. 111 In addition, we recommend that sloped surfaces in exposed or disturbed soil be restored so that surface runoff does not become channeled. Some sloughing and raveling of slopes with exposed or disturbed soil should be expected. Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. Permanent erosion protection should be provided by paving or landscape planting. Until the permanent erosion protection is established and the site is stabilized, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures and to repair and/or modify them as appropriate. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. GEOENGINEERS� April 22,2016 + Page 9 He r;o.10'SSS-610.01