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

INTRODUCTION The purpose of this study is to provide geotechnical engineering conclusions and recommendations for the design and cor�struction of the planned Beverly Park Substation Expansion project. The substation site is located at 1707 Scenic Drive in Everett, Washington, as shown on the Vicinity Map, Figure 1. The layout of the proposed improvements is shown on the Site Plan, Figure 2. We previously prepared a geotechnical report for the proposed expansion project titled "Geotechnical Engineering Services, Beverly Park Switching Station Expansion, Everett, Washington" A dated June 29, 2009. The design of the project has changed since we issued our 2009 geotechnical �, report. This geotechnical report replaces the previously prepared report in its entirety. GeoEngineers recently completed a wetland and stream delineation study at the site and summarized the findings in a report titled, "Wetland and Stream Delineation Report, Beverly Park Substation Expansion, Everett, Washington," dated January 16, 2014. Project Description The site is partially developed with an existing 115kV switching station located on the southwest portion of the property. The planned expansion will be roughly 800 feet by 300 feet and �vill consist of two levels separated by a retaining wall up to 10 feet high. The planned improvements will include expanding the existing 115kV yard on the upper level and constructing a new 230kV yard on a lower level to the east. The upper yard will be at about the same elevation as the existing yard and the eastern 230kV yard will be about 10 feet lower. The existing control building�vill be demolished and a new control building will be constructed north of the existing 115kV yard on the upper level. The proposed control building will be approximately 73 feet by 27 feet and constructed at-grade with no basement or below-grade levels. A 230kV/115kV transformer will be constructed on the east side of the upper level and west of the planned retaining wall. A second transformer pad will be prepared to the south to support a future transformer. Separate access roads are planned for the 115kV and 230kV yards entering off of Scenic Drive. We understand that structures for the substation will include dead end structures, bus support structures, transformers, circuit breakers, and switches. We aiso understand that the dead end structures may be supported on drilled piers and the bus support structures, transformers and other equipment may be supported on mat foundations. The transformers weigh approximately 340,000 to 495,000 pounds each and are planned to be supported on a 25-foot by 30-foot mat foundation. We understand the new control building is planned to be supported on shallow foundations near existing site grades. Cast-in-place concrete cantilever walls are planned between the two substation levels and along the south side of the 230kV yard adjacent to Scenic Drive. A mechanically stabilized earth (MSE) wall/slope may be constructed in the northwest corner of the site. The entire substation site within the security fence will be surfaced with crushed rock. Purpose and Scope The purpose of our services is to explore the subsurFace conditions at the site as a basis for providing geotechnical recommendations for design and construction of the proposed project. Our geotechnical GEOENGINEER� October24,2014 Page 1 Fie No.oasz-oz7-oz