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4 1 <br /> Geotechnical Plan Review and Comment Memorandum NGA File No.974316 <br /> Scriven Residence Improvements December 7,2016 <br /> Everett,Washington Page 2 <br /> improvements between the residence and the top of slope include removal of the existing deck and <br /> hardscapes and lowering the overall ground surface within this area by approximately 42-inches to be <br /> relatively level with the existing residence basement elevation. A new concrete patio and vegetation will <br /> be placed within the yard area between the residence and the top of slope. We also understand that all <br /> existing residence roof and foundation drains within the property will be directed into a new catch basin <br /> within the yard area and then into a new HDPE pipe that will descend down the steep slope face and <br /> discharge within the lower gently sloping area below the residence. We understand that the City of <br /> Everett has requested our opinion on the proposed grading and development plan. <br /> In our opinion, the proposed grading and improvements along the top of the steep slope should not <br /> adversely impact the overall slope stability conditions provided all of our other recommendations from <br /> our previous report are strictly followed. However, as discussed in our previous report, due to the <br /> presence of loose,undocumented fill soils within the yard area and within the vicinity of the top of the <br /> steep slope, it is also our opinion that these soils may experience continued settlement and failures <br /> potentially impacting the back yard area,especially during a seismic event or periods of extended rainfall, <br /> even after the proposed grading activities along the top of the steep slope are performed. If this potential <br /> can be understood and managed by you and future property owners, we do not anticipate the need for <br /> elaborate stabilization measures at this time along the upper portion of the slope,such as a retaining wall, <br /> provided our grading and drainage recommendations as discussed in our previous report are strictly <br /> followed. If any indications of settlement or movement are observed after the proposed improvements are <br /> constructed, we recommend that NGA be promptly notified to evaluate and provide stabilization <br /> recommendations. If the risk of future failures along the top of the slope cannot be tolerated, it is our <br /> opinion that construction of a soldier pile retaining wall along the top of slope is the only feasible method <br /> to permanently stabilize the top of slope area along the yard area and limit potential impacts associated <br /> with potential slope movements on the yard area and residence. We can work with you and your designer <br /> if this is desired. We also recommend that the yard area be adequately vegetated and no bare ground <br /> remains after grading activities. <br /> A note regarding the site drainage On Sheet A1.1 specifies"Replace the existing drainage system per the <br /> geotechnical report prepared by Nelson Geotechnical Associates,Inc.dated 11/29/16." It does not appear <br /> that specific plans regarding the site drainage improvements were included in the provided plans. We <br /> should be retained to review specific drainage plans once they have been developed. We recommend that <br /> the proposed drainage improvement recommendations provided in our previous report along with the <br /> input of a civil engineer be utilized to develop the most suitable drainage system for this property. <br /> 23 <br /> NELSON GEOTECHNICAL ASSOCIATES, INC. <br />