1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

EXECUTIVE SUMMARY This report contains the results of our geotechnical engineering services for use in the design of the proposed Beverly Park. Substation Expansion project in Everett, Washington. The project includes expanding the existing 115kV yard, constructing a new 230kV yard, and installing a new control building. The 230kV yard will be located east of the 115kV yard and approximately 10 feet lower. The improvements will require retaining walls to accomplish site grading including a cast-in-place concrete wall between the 115kVyard and the 230kV yard and another along the south side of the 230kV yard adjacent to Scenic Drive. The project also includes a mechanically stabilized earth (MSE) wall in the northwest corner of the 115kV yard adjacent to the Interurban trail. The control building will be . constructed at-grade on the north side of the 115kV yard. Storm water infiltration is also being considered for the site. A summary of geotechnical considerations for the site development and design of proposed improvements is provided below. This summary is presented for introductory purposes only and should be used in conjunction with the complete recommendations presented in this report. Subsurface Conditions The subsurFace conditions at the site were evaluated by drilling nine borings, excavating seventeen test pits, completing two pilot infiltration tests (PIT), and by evaluating existing information. Based_ on our_ _ __ exploratioas,_.ih�.n�ar��urface soils.generally con�ist_of_up to.9�/� feet-of-#111 over.l.y.ing-eit-h�r-v�eather�d._ �lacial till or u�eathered glaci.�l_-�iW: Buried concrete debris, foundations, slabs, and walls were encountered in the fill and at the ground surface in some of the explorations. Weathered glacial till, where present, generally ranges from 3 to 9 feet thick. Medium dense to very dense native glacial till soiis were observed to the depths explored. Perched groundwater see�age was observed in several � m�_v_�uv� �._____ ._�,�.�� explorations within the fill,weathered till,and/or in sand lenses within the unweathered till. � .e� _...__..,d.=�____ �__. ,.._.�.��.._..w_�__a_..�.�._.,. . r .�_..__ _...._ _�_-_____��.. _.�a _,�..�.�._..._._� r �. ��, ��The native glacial deposits and fill soils encountered at the site are generally of low corrosivity based on �,iy\� our experience in the Puget Sound area. Y� , � G� ��,�\-' Seismic Design � ) In accordance with the 2012 International Building Code (IBC),the site is classified as Site Class C. Reu�e of On-site Materials The on-site soils are expected to be suitable for use as structural fill only during the dry summer months provided that the soil is properly moisture conditioned. We do not recommend using the on-site fill soils during wet weather (October through May). On-site soils containing rubble and debris should not be reused as structural fill. Imported Gravel Borrow should be planned for use as structural fill under structures. Suitable on-site fill soils may be used as utility trench backfill in areas only requiring 90 percent compaction. Gravel Borrow should be used as trench backfill where 95 percent compaction is required, below structures, and behind retaining walis (during wet weather). GEOENGINEER� October24,2014 Page ES-1 Fle No.0482-027-�2