5034 OCEAN AVE 2019-06-11 - Laserfiche WebLink

51xx Ocean Avenue (Parcel#00571700100100) November 1, 2017 Everett, Washington Project#17110 Landslide Hazards/Steep Slopes There are steep slopes on the subject property, however,significant portions of these slopes were created due to previous grading. The proposed location of the new home will provide some grade separation in the previously graded slope area. It is our opinion that the combination of the location of the proposed new home, the embedment into the slope and resulting retaining wall, and the required mitigation of the existing fill soils for foundation support will provide an overall improvement to the slope conditions onsite and buffers and setbacks from existing slopes are not necessary. Erosion Hazards/Temporary Erosion and Sediment Control (TESC) Based on our site reconnaissance it is our opinion that accelerated erosion during construction can be mitigated by implementing a relatively simple TESC plan during construction. The proper use of"best management practices" (BMPs) should be utilized during earthwork activities to reduce the potential for erosion and sediment transport off the property. The following is a partial list of BMPs that should be implemented: • Phasing and scheduling earthwork activities during dry conditions • Rock construction entrances • Plastic sheeting/soil stockpile cover • Perimeter controls, as required • Keeping exposed soils and stockpiles covered when not actively worked • Establish temporary/permanent vegetation as soon after grading is completed Implementation of a TESC plan will likely be a requirement of the clearing and grading permit or the building permit. South Fork Geosciences is available to assist in the design of the TESC plan and to provide any required inspections during construction. Seismic Hazards Upon review of the King County Sensitive Area maps and considering the geologic context of the area,the subject property is not located in a seismic hazard area. However,this report will address general seismic hazards and risks associated with a seismic event with respect to project design. In general,there are four elements of hazard associated with large seismic events:ground rupture; seismically induced landslides; liquefaction;and ground motion. The potential for each of these to impact the subject property is discussed below. Ground Rupture Most large earthquakes in the Puget Sound area are sub-crustal events with epicenters ranging from 50 to 70 kilometers in depth.The subject property is approximately 1.5 miles east of the Southern Whidbey Island Fault Zone (SWIFZ) (Johnson et al, 2016).Though the subject property is near the SWIFZ,to our knowledge, there are no signs of past ground rupture in the immediate vicinity of the subject property. Based on the location of the subject property to the east of the known fault zone and the soil units overlying the bedrock geology, it is our opinion SOUTH FORK GEOSCIENCES, PLLC 7 Page,a_,. PO Box 1275 / NORTH BEND,WA 98045 -7 ! 425-831-2023 I ANDREW@SFGEO.COM