2320 CALIFORNIA ST Geotech Report 2025-07-25

disturbed slopes to help reduce the risk of erosion during wet work periods and after the work is completed. We recommend that the erosion control blanket consist of Curlex I, manufactured by American Excelsior Company or SC150, manufactured by North American Green. We recommend that the erosion control blanket be installed in accordance with the manufacturer's recommendations and that the installation and stapling methods be observed during construction. Hyrdoseeding and installation of the erosion control blanket should occur as soon as possible and prior to the wet winter months. Hydroseeding should occur to allow proper germination before the winter. We also recommend that the hydroseed mix include a tackifier to increase adhesion between the hydroseed mixture and the granular native soils. Infiltration Considerations Sieve analyses were performed on soil samples collected from the glacial till. The design infiltration values ' described below are based on the results of the grain size analyses, the U.S. Department of Agriculture (U.S.D.A.) Textural Triangle, and the Washington State Department of Ecology Storm Water Management Manual (2005). The results of the sieve analyses indicated that the fines content (material passing the US No. 200 sieve) ranges from 39 to 45 percent. Due to the density and relative impermeability of the glacial till, infiltration should be assumed to be negligible when designing the stormwater pond system. An infiltration rate of no more than 0.06 inches/hour should be used in design. Recommended Additional Geotechnical Services Throughout this report, recommendations are provided where we consider additional geotechnical services to be appropriate. These additional services are summarized below: GeoEngineers should be retained to review the project plans and specifications when complete to confirm that our design recommendations have been implemented as intended. During construction, GeoEngineers should observe and evaluate the suitability of the foundation subgrades, observe the removal of unsuitable soils, evaluate the suitability of building slab subgrades, evaluate the suitability of pavement subgrades and other appurtenant structures, observe installation of subsurface drainage measures,observe and test structural backfill,evaluate stormwater pond subgrade, evaluate temporary and permanent slope conditions, and provide a summary letter of our construction observation services. The purposes of GeoEngineers construction phase services are to confirm that the ' subsurface conditions are consistent with those observed in the explorations and other reasons described in Appendix D, Report Limitations and Guidelines for Use. LIMITATIONS 1 We have prepared this report for the exclusive use of the Snohomish County PUD No. 1 and their authorized agents for the proposed Administration Building Office Expansion project in Everett,Washington. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions,express or implied,should be understood. I Page 12