10723 19TH AVE SE Geotech Report 2023-04-07

Geotechnical Engineering Evaluation NGA File No. 1014317 Zerzura Townhome Development November 9,2017 Everett,Washington Page 2 4. Provide a long-term design infiltration rate based on one on-site Pilot Infiltration Testing (PIT) per the 2014 Department of Ecology Surface Water Design Manual for Western Washington. 5. Provide recommendations for infiltration system installation. 6. Provide recommendations for earthwork and foundation support. 7. Provide recommendations for temporary and permanent slopes. 8. Provide recommendations for retaining walls. 9. Provide recommendations for slab subgrade preparation. 10. Provide recommendations for site drainage and erosion control. 11. Document the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site consists of a rectangular-shaped parcel covering approximately 0.40-acres. The ground surface within the property is generally level to gently sloping. The property is currently occupied by a single- family residence and detached garage structure within the western and eastern portions of the site, respectively. Sparse to moderate landscaping plants and trees of varying maturity and grass-covered yard areas surround the site structures. We did not observe surface water within the site during our visit on October 19,2017. 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 October 19, 2017 by excavating four test pits to depths ranging from 5.0 to 9.0 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 and 5. 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.