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February 28, 2023 G-5835 <br /> 3821 -- Shore Ave Everett,WA Page 6 <br /> Geologic Hazard Area Mitigation <br /> We do not anticipate adverse impact to the slope hazard areas mapped by the City of Everett near <br /> the project site's western limits as a result of the project, however,our recommended measures <br /> to mitigate the potential for slope instability associated with the proposed retaining wall's <br /> constriction include the following: <br /> - Supporting the retaining wall on the site's competent native soils or a <br /> subgrade approved by the geotechnical engineer; <br /> Providing drainage behind the retaining wall to prevent development of <br /> hydrostatic lateral pressures; <br /> - Incorporating permanent drainage measures into the project design. The <br /> drainage system should be designed to prevent the concentrated flow of water <br /> from impervious areas and wall drains across the ground surface, and should <br /> disperse or direct the drainage toward an approved discharge location; <br /> Limiting permanent slopes in the project area to inclination no steeper than <br /> 2.5H:IV, with the additional condition that slopes steeper than 15 percent <br /> grade are stabilized against potential erosion with re-vegetation or placement <br /> of other protective surfacing(i.e. mulching,jute netting, etc.); <br /> And re-establish soil-stabilizing,non-invasive vegetation in disturbed areas <br /> for permanent erosion control. <br /> T arthwork <br /> Erosion Control <br /> During site clearing and demolition of the existing retaining wall, temporary erosion and <br /> sedimentation controls(TESCs) should be installed to prevent the flow of sediment-laden runoff <br /> from the site and to minimize the potential for on-site soil erosion. TESCs for the project include, <br /> silt fences, drainage swales and check darns, detention or settlement traps, straw mulch, hay <br /> bales, or other devices appropriate for the site conditions. TESCs should be maintained during <br /> the progress of the project until the ground disturbance activities are completed and disturbed <br /> soils have been stabilized. <br /> Concentrated surface water should not be allowed to flow over exposed slopes or into <br /> excavations. During wet weather, exposed slopes should be covered with plastic sheeting to <br /> minimize erosion, and accumulated surface water should be directed toward temporary <br /> 4 GEO Group Northwest, Inc. <br /> i <br /> i <br />