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Home My WebLink About18b_PSE Talbot Substation CLR Geotechnical Addendum Letter 2101 4th Avenue, Suite 950 Seattle, Washington 98121 206.728.2674 January 29, 2019 Puget Sound Energy 35131 SE Center Street, SQE-OTC Snoqualmie, Washington 98065 Attention: Christopher Russell, PE Subject: Addendum Letter Geotechnical Engineering Services Talbot Hill Substation CLR Improvements Renton, Washington File No. 0186-953-06 INTRODUCTION AND PROJECT UNDERSTANDING This letter presents the results of GeoEngineers, Inc. (GeoEngineers) additional geotechnical engineering services for the proposed current limiting reactor (CLR) improvements at the Puget Sound Energy (PSE) Talbot Hill Substation located at 2400 Puget Drive SE in Renton, Washington. We previously provided geotechnical recommendations for this project in our revised report dated February 1, 2017 and have provided geotechnical construction observation services during Phases 1 and 2 of the substation improvements. This letter incorporates and supersedes a previous draft dated January 25, 2019. The Talbot Hill substation is located adjacent to the Bonneville Power Administration (BPA) Maple Valley substation, and the two substations are interconnected. We understand BPA has identified potential risks to their substation equipment in the event of an interconnection electrical fault. The site is shown in relation to existing improvements in the Vicinity Map, Figure 1 and the Site Plan, Figure 2. This project involves constructing six CLRs, one for each phase of the two transmission line interties, which will act as surge protectors. The CLRs will be installed on elevated pedestals in a new yard area at the southeast corner of the existing PSE Talbot Hill Substation (approximately 190 feet long and 85 feet wide). The CLR yard area will be accessed by a new gravel access road. We understand the new yard area will involve some grading but will not require retaining walls. The existing topography in the area of the proposed CLR yard is slightly uneven, ranging from Elevation 441 to 445 feet. Our geotechnical engineering services were completed in accordance with our proposal dated December 10, 2019. Our scope of work included developing geotechnical conclusions and recommendations and preparing this addendum letter. Puget Sound Energy | January 29, 2019 Page 2 File No. 0186-953-06 SITE CONDITIONS Based on explorations completed for our previous geotechnical report, the proposed CLR yard area is underlain by fill and glacial till. Boring GEI-5 was completed in the area of the proposed CLR yard area. Subsurface conditions observed in this boring (attached for reference) consist of fill overlying glacial till overlying advance outwash. The fill generally consists of medium dense silty sand placed during previous regrading at the site, extending to a depth of 7 feet. The underlying glacial till consists of medium dense to very dense silty sand with variable gravel content extending to a depth of 23 feet, where it is underlain by advance outwash consisting of very dense sand with silt. CONCLUSIONS AND RECOMMENDATIONS Critical Areas We reviewed the City of Renton online maps showing geologic critical areas including coal mine, erosion, flood, landslide and steep slope hazard areas. The site is not mapped in erosion, seismic or flood hazard areas. The site is mapped in a moderate coal mine hazard area. However, based on the depth of historical coal mining activity and the relatively shallow depth of the proposed improvements, it is our opinion there is a low coal mine hazard at the site. The site is mapped in a 25 to 40 percent steep slope area and in a moderate landslide hazard area. It is our opinion that the proposed improvements and grading will not adversely affect the stability of the slopes in or around the site. Based on our evaluation it is our opinion the soils underlying the CLR yard area have a low risk of liquefying under the design earthquake event. It is also our opinion that soils underlying the site have a low risk of lateral spread and earthquake-induced slope movement. The site is approximately 5 miles south of the Seattle Fault Zone. Based on the distance from the mapped fault, it is our opinion there is a low risk of fault rupture at the site. Geotechnical Design Recommendations We recommend the earthquake engineering, foundation design, and earthwork recommendations previously presented in our geotechnical report be used for design of the proposed CLR improvements. Stormwater Recommendations We understand the proposed stormwater improvements will be designed in accordance with the 2017 City of Renton Surface Water Design Manual. In accordance with the requirements of Chapter 5.2 of the Manual, we evaluated the site for infiltration potential. Due to the presence of shallow, medium dense to very dense glacial till, it is our opinion infiltration is not feasible on site. 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The locations of all features shown are approximate.2. This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. cannot guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication.3. It is unlawful to copy or reproduce all or any part thereof, whether for personal use or resale, without permission. Transverse Mercator, Zone 10 N North, North American Datum 1983North arrow oriented to grid northOffice: RedmondPath: \\red\projects\0\0186953\GIS\018695300_F1_VicinityMap.mxdMap Revised: 10/3/2014 ELSite CED A R R I V E R P I P E L I N E - L O C A T I O N NO T V E R I F I E D 431 427 430 4 3 5 43 8436438 438 435 436 43042 5 432 4 3 1 43 0 43 5 440 443 444 445 443445433434435 445 451 4434424414 3 9 425 430 435 435440437435430 435 438 440 438438 435 43 0 430 435 43 7 428 44443042 5 432 432 43 0425 446 4 44 445 445 43 4 436437435433 432 433434 432431 437436435 434 435 436 437 438 4 38 433 440439441442443444443442441440 446447448449450439438437436435 450449448447446444443 447 444 446 447 4 4 8ZZNNYYXXWWVVUUEE 445441442443444 DIRT RO A D 441440443 444 445 445 446 446 447448449450 446 447 436435 434433432431430 430429 430 437 435434439440438439 438 440438 436437437436438439441440439438 438437436435434433432431430429428427426425 Proposed CLR Yard Area Existing Substation Access Gate Access Road to Puget Drive SE B e a c o n W a y S o u t h Approximate Location of City of Seattle Water Main BPA Maple Valley Substation Stormwater Pond Unverified Approximate Location of Underground Cable to BPA Maple Valley Substation GEI-4 GEI-6 GEI-3 GEI-7 GEI-5 GEI-2 GEI-1 WWWWWWWWW W WWW W W WWWWWFigure 2 PSE Talbot Substation CLR Improvements Renton, Washington Site Plan W E N S Legend P:\0\0186953\CAD\06\GeoTech\018695306_F02_Site Plan.dwg TAB:F02 Date Exported: 01/14/19 - 15:42 by hmaraNotes: 1.The locations of all features shown are approximate. 2.This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. cannot guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication. Data Source: Base received from PSE on 1/9/2019. Projection: WA State Plane, North Zone, NAD83, US Foot Boring by GeoEngineers (September 25, 2014) Feet 020 20 GEI-1 1A 1B 2 3SA 4 5MC 6 18 18 18 18 18 18 17 15 30 28 42 63 6 inches topsoil/root zone Brown silty fine to medium sand withoccasional gravel and trace organics (loose,moist) Brown with oxidation staining silty fine to medium sand (medium dense, moist) (fill) Gray silty fine to medium sand with occasionalgravel (medium dense, moist) (fill) Gray brown silty fine to medium sand withoccasional gravel (medium dense, moist)(glacial till) Gray brown silty fine to medium sand (mediumdense, moist) Light gray brown silty fine to medium sand withoccasional gravel (dense, moist) TS SM SM SM SM SM SM 158 14 TotalDepth (ft) HammerData SystemDatum Start End Checked By Logged By CEWDrilled Notes: DML Surface Elevation (ft) Vertical Datum Driller Groundwater Depth toWater (ft)Date Measured Elevation (ft) Easting (X)Northing (Y) Mini Track Rig Geologic Drill DrillingMethod Hollow-stem Auger31.5 Rope & Cathead140 (lbs) / 30 (in) Drop DrillingEquipment 9/26/20149/26/2014 None Observed 443 Note: See Figure A-1 for explanation of symbols. FIELD DATA Depth (feet)0 5 10 15 20 IntervalElevation (feet)440435430425Sample NameTestingRecovered (in)Graphic LogCollected SampleBlows/footMATERIAL DESCRIPTION GroupClassificationWater LevelLog of Boring GEI-5 PSE Talbot Substation Improvements Renton, Washington 0186-953-00 Project: Project Location: Project Number:Figure A-6 Sheet 1 of 2Seattle: Date:11/2/14 Path:C:\USERS\KJANCI\DESKTOP\018695300.GPJ DBTemplate/LibTemplate:GEOENGINEERS8.GDT/GEI8_GEOTECH_STANDARDREMARKS FinesContent (%)MoistureContent (%)Page A-1 7%F 8 18 18 67 51 Gray brown fine to medium sand with silt andoccasional gravel (very dense, moist)(advance outwash) SP-SM 117 Note: See Figure A-1 for explanation of symbols. FIELD DATA Depth (feet)25 30 IntervalElevation (feet)420415Sample NameTestingRecovered (in)Graphic LogCollected SampleBlows/footMATERIAL DESCRIPTION GroupClassificationWater LevelLog of Boring GEI-5 (continued) PSE Talbot Substation Improvements Renton, Washington 0186-953-00 Project: Project Location: Project Number:Figure A-6 Sheet 2 of 2Seattle: Date:11/2/14 Path:C:\USERS\KJANCI\DESKTOP\018695300.GPJ DBTemplate/LibTemplate:GEOENGINEERS8.GDT/GEI8_GEOTECH_STANDARDREMARKS FinesContent (%)MoistureContent (%)Page A-2