10111 9TH AVE W EMERALD COURT APARTMENTS Geotech Report 2022-10-20

5 � Geotechnical Engineering Evaluation NGA File No.910814 Emerald Court Apartment Building November 21,2014 Everett,Washington Page 5 shallow foundations. Footings should extend through any undocumented fill or loose soil, and be founded on the underlying medium dense or better native soil, or structural fill extending to these soils. The medium dense or better soil should typically be encountered approximately six inches to two feet below the existing surface,based on our explorations. Three underground detention pipes are planned within the southeastern corner of the site along the southern property line. In this location, we encountered moderate groundwater seepage in the tests pits explorations. Due to the potential "bath tub" effect when the pipes are excavated in the impermeable till and surrounded by gravel, we recommend that the pipes be designed to resist uplift and buoyancy forces with the assumption that the pipes would be fully submerged. We also recommend that underslab drains be installed below the building slab to help prevent damp conditions in the building. This is further discussed in the Site Drainage subsection The soils encountered on this site are considered moisture-sensitive, and will disturb when wet. We recommend that construction take place during the drier summer months, if possible. If construction is to take place during wet weather,the soils may disturb and additional expenses and delays may be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls to protect exposed subgrades and construction traffic areas. The non-organic on-site soils could be used as structural fill provided they could be compacted to specifications. This will highly depend on the moisture content of the soils at the time of construction. The use of the on-site soils for fill during wet weather will be extremely difficult if not impossible. NGA should be retained to determine if the on-site soils can be used as structural fill material during construction. Erosion Control Measures The erosion hazard for the on-site soils is interpreted to be slight, but the actual hazard 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. 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. NELSON GEOTECHNICAL ASSOCIATES,INC.