1415 BROADWAY CM HEATING 2023-09-25

• Geotechnical Engineering Evaluation NGA File No. 1213420 CM Heating Additions January 8,2021 Everett,Washington Page 4 Hazards associated with seismic activity include liquefaction potential and amplification of ground motion by soft deposits. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. The very dense native glacial soils interpreted to underlie the site at depth have a low potential for liquefaction or amplification of ground motion. Erosion Hazard The criteria used for determining the erosion hazard for the site soils includes soil type, slope gradient, vegetation cover, and groundwater conditions.The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units.The Soil Survey of Snohomish County Area, Washington, by the Natural Resources Soil Conservation Service (NSCS), was reviewed to determine the erosion hazard of the on-site soils.The site surface soils were classified using the NSCS classification system as Alderwood-Urban land complex, 2 to 8 percent slopes. The soil classification is listed as having a slight to moderate erosion hazard. It is our opinion that the site soils should have a slight hazard for erosion in areas that are not disturbed. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion from a geotechnical standpoint that the site proposed development is feasible. Our explorations generally encountered a surficial layer of topsoil and/or undocumented fill underlain by a medium dense or better deposit of gray to gray brown silty fine to medium sand with various amounts of gravel, in a medium dense or better condition, consistent with the description of glacial till at depth. The native glacial soils should provide adequate support for foundation,slab, and pavement loads. We recommend that the new structure be designed utilizing shallow foundations. Footings should extend through any loose soil, and be founded on the dense or better native bearing soil, or structural fill extending to these soils. The competent soil should typically be encountered approximately two to three feet below the existing surface throughout the site, based on our explorations. However, if loose soils or undocumented fill are encountered during construction, this condition would require deeper excavations in foundation,slab, and pavement areas to remove the unsuitable soils. Based on the dense, silty nature of the onsite soils, as well as the presence of iron-oxide weathering, it is our opinion that infiltration potential of the native soils underlying the site is low. Shallow low- impact infiltration systems may be feasible within the site; however,these systems should incorporate overflow components directed to an approved point of discharge. Alternatively, stormwater should be detained and directed to an existing stormwater system. NELSON GEOTECHNICAL ASSOCIATES, INC.