10627 19TH AVE SE COOLEY SMILES DENTISTRY 2019-03-18

Geotechnical Engineering Evaluation NGA File No. 1008917 Cooley Smiles Commercial Development October 3,2017 Everett,Washington Page 2 7. Provide recommendations for pavement subgrade. 8. Provide recommendations for site drainage and erosion control. 9. Determine feasibility of on-site stormwater infiltration. 10. Provide long-term design infiltration rates based on three, on-site Small-Scale Pilot Infiltration Tests (PITs) per the 2014 DOE Stormwater Manual. Location and depth of tests were determined by the civil engineer. Water for the test was provided by client. 11. Provide recommendations for infiltration system installation. 12. Document the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site consists of three rectangular-shaped parcels covering a total area of approximately 1.03 acres. The ground surface within each of the properties is generally level to gently sloping. The northern parcel is occupied by an existing single-family residence. The central parcel is occupied by an existing commercial business structure. The southern parcel is occupied by an existing garage structure. Sparse to moderate landscaping plants and trees of varying maturity occupy the western margin of the property, and grass and weeds cover unpaved areas across the remaining portion of the properties. We did not observe surface water within the site during our visit on September 15, 2017. Subsurface Conditions Geology: The geologic units for this area are shown in the Geologic Map of the Everett 7.5-minute Quadrangle, Snohomish County. Washington,by James P. Minard (1985). The site is mapped as till of the Vashon Drift (Qvt). The glacial till is described as a compact diamict of mud, sand, pebbles, cobbles, and boulders. Our explorations generally encountered silty fine to medium sand with gravel soils consistent with the description of glacial till soils at depth. Explorations: The subsurface conditions within the site were explored on September 15, 2017 by excavating six test pits and three infiltration pits to depths ranging from 3.2 to 7.0 feet below the existing ground surface using a trackhoe. The approximate locations of our explorations are shown on the Schematic Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the test pits. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. The logs of our test pits are attached to this report and are presented as Figures 4 through 6. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions,the logs of the test pits should be reviewed. NELSON GEOTECHNICAL ASSOCIATES, INC.