909 51ST PL SW Geotech Report 2022-10-25

Geotechncial Engineering Evaluation Garcia Property Additions Everett, Washington NGA Project No. 1040218 June 22, 2018 Page 7 The slopes should be protected from erosion. We recommend that all disturbed areas be replanted with vegetation to re-establish vegetation as soon as possible. The eastern steep slope should not be disturbed or graded for residence placement. No fills of any sort should be planned at the top of this slope. Stormwater runoff should not be allowed to concentrate and flow over the slope down to the wetland area. Specific recommendations for erosion control are presented in the Erosion Control and Slope Protection Measures subsection of this report. We recommend that NGA be retained to review final project plans and provide consultation regarding structure placement, site grading, and foundation support. We also recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. Erosion Control and Slope Protection Measures The erosion hazard for the on -site soils is designated as severe for exposed soils on the ravine slopes, but actual erosion potential will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing over the slopes. Stockpiles should be covered with plastic sheeting during wet weather. Disturbed areas should be planted as soon as practical, and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low. Protection of the setback and steep slope area should be performed as required by the City of Everett. Specifically, we recommend that the setback area and top of slope not be disturbed or modified through placement of any fill or removal of the existing vegetation as part of site preparations. No additional material of any kind should be placed on the slope or be allowed to reach the slope, such as excavation spoils, lawn clippings, and other yard waste, trash, or soil stockpiles. Trees should not be cut down or removed from the steep eastern slope unless a mitigation plan is developed, such as the replacement of vegetation for erosion protection. Vegetation should not be removed from the slopes. Replacement of vegetation should be performed in accordance with the City of Everett code. Any proposed development within the slope setback area should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes. NELSON GEOTECHNICAL ASSOCIATES, INC.