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Home My WebLink AboutA16_GeoResources Memo Technical Memo To: Bryan Telegin Telegin Law Project: TeleginLaw.DabobBayResidence From: William J. Cedzich II, PE, PG, PEng Senior Geotechnical Engineer Date: August 15, 2025 Re: TeleginLaw.DabobBayResidence STATEMENT OF PURPOSE The purpose of this memorandum is to present our professional review and findings regarding the geotechnical work performed to date for the proposed roadway improvements along Twana Way. This document identifies critical deficiencies—most notably the absence of required slope stability analyses—in relation to applicable Jefferson County Code, WSDOT Geotechnical Design Manual provisions, and AASHTO guidelines. It further outlines the heightened risk of slope instability posed by heavy construction traffic and grading activities in a mapped landslide hazard area, and establishes the technical basis for our opinion that additional geotechnical investigation and modeling are essential before any roadway improvements proceed. REVIEW As a licensed geotechnical engineering firm, we are prepared to testify that the geotechnical work performed to date for the proposed roadway improvements along Twana Way is fundamentally inadequate, particularly with respect to slope stability evaluation. Twana Way is located within a mapped landslide hazard area as designated by the WA Department of Ecology Coastal Atlas and WA DNR, which contains evidence of unstable slopes, historic landslide debris, and Holocene epoch mass wasting features. Despite this, no slope stability analysis—static, seismic, or construction-phase—has been performed, in direct contravention of Jefferson County Code (JCC) 18.22.530(4)(b) and 18.22.945(2)(d), the WSDOT Geotechnical Design Manual (GDM) Section 7.2 and 7.6.4, and AASHTO LRFD Bridge Design Specifications Section 11.6. These codes and guidelines require slope stability modeling with factors of safety (FOS) established for existing and proposed conditions before construction. The absence of such analysis is critical because heavy construction traffic, road grading, and widening activities can substantially alter loading conditions, drainage patterns, and pore water pressures, thereby increasing the likelihood of slope movement or failure. Without stability modeling, the potential for induced slope instability from haul trucks, construction equipment, and new embankment loads remains unquantified and unmitigated. TeleginLaw.DabobBayResidence  Page 2 In addition, no subsurface exploration (borings, test pits, or laboratory testing) has been undertaken, violating JCC 18.22.945(2)(b) and WSDOT GDM Section 4.3.2, leaving soil strength parameters, groundwater conditions, and stratigraphy undefined—data that are essential inputs for meaningful slope stability modeling. No erosion hazard assessment has been completed for cut and fill slopes or stormwater impacts, contrary to JCC 18.22.510(1)(b) and Ecology SWMMWW Volume II requirements. Further, no boundary or topographic survey has been conducted, and no plans developed, to confirm slope geometry, roadway centerline, right-of-way limits, or critical area buffer proximity, as required by JCC 18.22.905(3) and the WSDOT Survey Manual, undermining the reliability of any proposed setbacks or grading limits. The inconsistencies between earlier commentary — stating no improvements were planned — and later correspondence acknowledging potential roadway grading and widening, without updated geotechnical analysis or site mapping, highlighting procedural deficiencies in accordance with codes and regulations. No critical areas, steep slopes, or hazard overlays have been delineated in accordance with JCC 18.22.905(3) and WAC 365-190-120, despite the mapped hazard classifications. Furthermore, the unnamed stream intersecting the proposed work area has not been evaluated for buffer requirements or sediment delivery impacts to Dabob Bay, as required under JCC 18.22.905(3) and Ecology SWMMWW Volume II. In our professional opinion, before any roadway improvements are undertaken, the project must complete a full geotechnical program, including: (1) comprehensive slope stability modeling per JCC, WSDOT GDM, and AASHTO requirements; (2) subsurface exploration and laboratory testing; (3) erosion hazard and surface water impact assessments; and (4) updated site mapping with hazard overlays. Without these elements, the project lacks the technical foundation necessary to ensure that roadway improvements—particularly those involving heavy construction loads—can be carried out in compliance with governing codes, engineering best practices, and public safety obligations. METHODOLOGY Missing and/or Inaccurate Technical Foundations  No slope stability or landslide analysis for Twana Way (roadway in mapped landslide hazard zone). (JCC 18.22.530(4)(b), WSDOT GDM Section 7.2)  No subsurface exploration (borings, test pits, or geotechnical lab work). (JCC 18.22.945(2)(b), WSDOT GDM Section 4.3.2)  No erosion hazard evaluation for cut/fill slopes or stormwater flow. (JCC 18.22.510(1)(b), Ecology SWMMWW Volume II)  No boundary or topographic survey conducted:  No basis to verify slope angles, road centerline, ROW limits, or proximity to critical area buffers. (JCC 18.22.905(3), WSDOT Survey Manual)  Undermines the reliability of any proposed setbacks or safety assumptions. (JCC 18.22.945(2)(f))  Inconsistencies and Procedural Questions  Original report claimed no improvements were planned to Twana Way. (Contradicts updated design scope)  Later geotechnical letter (Doc No. 9) admits road grading/widening may be needed — without updated analysis. (JCC 18.22.945(2)(d)) TeleginLaw.DabobBayResidence  Page 3  No location map or site plan provided for road improvements. (JCC 18.22.905(3))  No delineation of critical areas, buffers, or steep slopes in the area of Twana Way per Jefferson County requirements. (JCC 18.22.905(3), WAC 365-190-120) Required Geotechnical and Supporting Work  Boundary & Topographic Survey  Establish accurate site boundaries, slope gradients, vertical relief, and limits of disturbance. (WSDOT Survey Manual, JCC 18.22.945(2)(a))  Confirm proximity to critical areas, streams, and buffer zones. (JCC 18.22.905(3))  Subsurface Investigation  Conduct test pits or borings along Twana Way and proposed home/driveway area. (JCC 18.22.945(2)(b))  Log soils, groundwater, and relevant engineering properties. (WSDOT GDM Section 5.4.2)  Slope Stability Modeling  Model both existing slope and proposed road widening sections. (JCC 18.22.945(2)(d), AASHTO LRFD 11.6)  Provide FOS values for static, seismic, and construction loading conditions. (JCC 18.22.945(2)(f), WSDOT GDM 7.6.4)  Erosion and Surface Water Risk Assessment/Evaluate potential sediment delivery to adjacent stream features and downstream impact to Dabob Bay. (Ecology SWMMWW Volume II, JCC 18.22.510)  Updated Site Plan with Hazard Mapping Overlay  Required per JCC 18.22.905(3) to show:  Limits of disturbance, Critical area buffers, All new or modified slopes, Slope hazard classification zones. (JCC 18.22.905(3), WAC 365-190-120) Fish and Wildlife Overlay Mapping – Additional Concerns  Mapped Landslide Hazards in Coastal Atlas and DNR Data  Portions of the roadway are mapped by the WA Department of Ecology Coastal Atlas as containing unstable, old, and recent landslide features. (JCC 18.22.510(1)(i)(B))  The slope classification falls within Coastal Atlas and WA DNR categories requiring hazard assessment. (JCC 18.22.510(1)(i)(C), WAC 365-190-120)  Historic Movement and Mass Wastage Indicators  The area meets the definition of Holocene epoch landslide activity due to mapped evidence of mass wasting debris. (JCC 18.22.510(1)(iii))  Unnamed Stream Crossing and Riparian Impact Risk  Unnamed stream shown crossing or bordering the proposed access/driveway raises need for buffer delineation and critical area review. (JCC 18.22.905(3), WAC 222-16- 030)  Potential sediment delivery to stream and Dabob Bay requires erosion and water quality controls. (Ecology SWMMWW Volume II, JCC 18.22.510(1)(b)) TeleginLaw.DabobBayResidence  Page 4 Process for Developing GIS Layouts LiDAR Processing (QGIS): 1. WA DNR LiDAR Portal: download most recent dataset that includes the area of interest 2. Clip Digital Terrain Model (DTM) to a smaller extent showing site area, using DGAL “Clip raster by extent tool” >> reduces file size and data processing 3. Reduce resolution of the clipped DTM to 6x6 (horizontal x vertical) pixels using “Save raster layer as…” tool >> generalizes data, removing unnecessary details shown at finer scales 4. Apply a Gaussian filter to the reduced resolution DTM using the SAGA version 7.8.2 “Gaussian Filter” tool. >> reduces irregularities associated with vegetation interference, which affects data quality a. Standard deviation: 10 b. Radius: 10 5. Use the file output from Step 4 for the following independent processes: 1) GDAL “Slope” tool, check box for ‘slope expressed as percent instead of degrees’ 2) “Contour” tool, creating individual contour files at desired intervals, often 2-, 10-, 20-, 50-, and/or 100-foot intervals 6. Use the file outputs from Step 5.2 as inputs in the QGIS SAGA version 7.8.2 “Line Smoothing” tool with method: ‘improved SIA model’ >> reduces influence of vegetation and man-made features (structures, roadways)