3610 W MUKILTEO BLVD Geotech Report 2022-10-25

Geotechnical Engineering Evaluation NGA File No. 1129119 Zahler Residence Development Octqber 14,2019 Everett,Washington Page 5 CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site planned development is feasible from a geotechnical standpoint. Our explorations indicated that the site is generally underlain by competent native glacial soils at depth. The native glacial soils encountered at depth should provide adequate support for foundation, slab, and pavement loads. We recommend that the planned structures be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native bearing soil, or structural fill extending to these soils. The medium dense or better native glacial soils should typically be encountered approximately two to three feet below the existing surface,based on our explorations. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation,slab, and pavement areas to remove the unsuitable soils. Based on the results from the infiltration testing and the relatively dense and silty nature of the onsite native soils, it is our opinion that traditional stormwater infiltration systems within this site are not feasible. We recommend that stormwater generated from impervious surfaces within the site be directed to an approved point of discharge likely found in the neighboring roadway. Low impact shallow systems such as pervious pavement, rain gardens, and shallow infiltration bioswales may be feasible, but such systems should be further evaluated during final design. The surficial soils encountered on this site are considered moisture-sensitive and will disturb easily 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. Some of the native on- site soils may be suitable for use as structural fill depending on the moisture content of the soil during construction. This will depend on the moisture content of the soils at the time of construction. NGA should be retained to determine if the on-site soils can be used as structural fill material during construction. NELSON GEOTECHNICAL ASSOCIATES, INC.