5034 OCEAN AVE Geotech Report 2022-10-25

current stability of the site provided that it is developed in accordance with the recommendations contained in this report. Erosion Hazard The onsite soils in the development area have a moderate erosion potential due to the slope of the property. The proper use of"best management practices"BMPs should be used during development of the project to minimize the potential for erosion and sediment transport. The following is a partial list of BMPs that should be implemented as part of an erosion control plan for the project. • Keeping all exposed soils covered when not actively worked • Establish a silt fence across the northern extent of the clearing limits • • Scheduling earth work activities during dry conditions • Establish temporary/permanent vegetation as soon as possible after foundation installation and utility hook-up. With proper implementation of best management practices,the property may bedeveloped without significant erosion or sediment transport. Seismic Hazard Generally,there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture;2)seismically induced landslides;3)liquefaction; and 4) ground.motion. The potential for each of these to impact the site is discussed below. The lot is not within the vicinity of a known fault zone. Fault zones in the Puget Sound region are currently being studied by the United States Geological Service(USGS)and have been determined to be active and capable of producing large earthquakes. Much is still to be learned about these fault systems but it is generally hypothesized that their recurrence interval is several thousand years. Due to the suspected long recurrence interval and the uncertainty of where the next surface rupture may occur,the potential for surficial ground rupture is.considered to be unpredictable and no mitigation is possible or necessary. Based on the dense, consolidated nature of the glacial advance outwash sediments underlying the property,the risk of a seismically triggered landslide is considered to be low. Based on the dense characteristic of the advance outwash sand and lack of saturated ground conditions, it is our opinion that the risk of liquefaction on this site is low. Seismic hazards that will affect the house will be due to the intensity and duration of the gronnd shaking. Based on the encountered stratigraphy,structural design of the project should be consistent with 2009 International Building Code (IBC) guidelines. In accordance with Table 16115.2 of the 2009 MC, the subject site would be classified as Site Class C. Geotechnical.Engineering Recommendations • From a geotechnical engineering standpoint,the property is considered to be suitable for the planned development of a single family residence. The dense advance outwash sand sediments will provide suitable foundation bearing support for the planned residence. Since the residence foundation is being developed on a moderate slope it will be necessary to key the foundation into the dense sand BGC, pllc 14267 2096' Avenue NE Woodinville, WA 98077 (425) 273-5062