1502 WALL ST IMAGINE CHILDRENS MUSEUM Geotech Report 2022-10-25

Imagine Children's Museum Building Addition Revised Geotechnical Engineering Report Everett, Washington Design Recommendations encountered below planned paving, we should be allowed to offer situation-specific recommendations. 6.2 Site Drainage and Surface Water Control Adequate temporary and permanent control of surface water runoff and possible subsurface seepage will be required in order to allow site access and grading for construction of the new building and remedial paving, installation of underground utilities, and other proposed improvements. Excavation, filling, subgrade, and grade preparation should be performed in a manner and sequence that will provide controlled drainage at all times and proper control of erosion. Surface water should be collected and pumped or drained to provide a suitable working platform. Successful drainage of wet zones due to perched groundwater flow and accumulations of surface water runoff could be accomplished by ditching and/or the installation of cut-off trenches or "french" drains. Exploration boring EB-7 encountered groundwater at an approximate depth of 12 feet (Elevation 131). We do not anticipate that excavations for the new building addition will be deep enough to encounter significant groundwater seepage. However, the contractor should be prepared to intercept and remove seepage from the excavation and may need to implement localized erosion control measures to limit erosion due to seepage. Such measures are best determined at the time of construction when field conditions are known; however, based on the available information, it appears likely that a system of ditches and pumped sumps inside the excavation will be adequate to intercept the amount of seepage that could be present. If localized erosion protection measures are required, it is likely that providing a thin layer of clean crushed rock above exposed seepage areas will be effective. The site should be graded to prevent water from ponding in construction areas and/or flowing into excavations. Exposed grades should be crowned, sloped, and smooth-drum rolled at the end of each day to facilitate drainage. Accumulated water must be removed from subgrades and work areas immediately prior to performing further work in the area. Equipment access may be limited, and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely sequence. If an effective drainage system is not utilized, project delays and increased costs could be incurred due to the greater quantities of wet and unsuitable fill, or poor access and unstable conditions. Final exterior grades should promote free and positive drainage away from the proposed building addition at all times. Water must not be allowed to pond or to collect adjacent to foundations or within the immediate building area. We recommend that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeter be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. March 28,2019;Revised April 16,2019 ASSOCIATED EARTH SCIENCES,INC. SGB/Id-190104E001-3-Projects\20190104\KE\WP Ci5age/T /0/ .0