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Home My WebLink AboutGEO2025-00019 Slope Landslide Hazard - BLD Engineering / Geo-tech Reports - 3/20/2025 MASON COUNTY COI 4 UNITY SERVICES Geotechnical Report Swldng,Awn ftEm�HmWcCm*=4"'pFhQM Instructions: This checklist must be submitted with a Geotechnical Report and completed, signed, and stamped by the licensed professional(s) who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County Resource Ordinance. If an item is found not applicable, the report should explain the basis for the conclusion_ Note: Unless specifically documented this report does not provide compliance to the International Residential Code Sections R403.1.7 for foundations on or adjacent to slopes Section R403.1.8 for expansive soils or section 1808.7.1 of the International Building Code Section for Foundations on or adjacent to slopes. ApplicanVOwner Dale& Sharon Tahia Parcel# 32331-22-00800 Site Address N Arnolds Way, Hoodsport, WA 98548 (1) (a)A discussion of general geologic conditions in the vicinity of the proposed development, Located on page(s) Pgs 1 -3 (b) A discussion of specific soil types, Located on page(s) Pgs 4 & 5 (c) A discussion of ground water conditions, Located on page(s) Pg 3 (d) A discussion of the upslope geomorphology, Located on page(s) Pg 3 (e) A discussion of the location of upland waterbodies and wetlands, Located on page(s) Pg 3 (f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records. Located on page(s) Pg 4 (2) A site plan which identifies the important development and geologic features_ Located on Map(s) 1 thru 5 (3) Locations and logs of exploratory holes or probes_ Located on Map(s) Sheet 2 (4) The area of the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall be delineated (top, both sides, and toe) on a geologic map of the site. Located on Map(s) Sheets 1 -5 (5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which incorporates the details of proposed grade changes. Located on Map(s) Sheet 5 (6) A description and results of slope stability analyses performed for both static and seismic loading conditions. Analysis should examine worst case failures_The analysis should include the Simplified Bishop's Method of Circles. The minimum static safety factor is 1.5,the minimum seismic safety factor is 1.1, and the quasi-static analysis coefficients should be a value of 0.15. Located on page(s) Pqs 4—5 and attached GALENA printouts (7) (a) Appropriate restrictions on placement of drainage features, Located on page(s Pq 5 (b) Appropriate restrictions on placement of septic drain fields, Located on page(s) Pg 4 (c) Appropriate restrictions on placement of compacted fills and footings, Located on page(s) Pg 6 (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) Pq 5 (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) Pq 5 (8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the method of vegetation removal. Located on page(s) Pg 5 (9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific mitigating measures to be implemented during construction to protect the slope from erosion, landslides and harmful construction methods_ Located on page(s) Pq 5 (10) An analysis of both on-site and off-site impacts of the proposed development. Located on page(s) Pg 5 (11) Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths. Located on page(s) Pq 5 (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation. Located on page(s) Pq 6 (13) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site_ Located on Map(s) Sheets Sheets 1 - 5 1, Alan A. Tahja hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical Report, dated March 24t", 2025 and entitled �F tugs Dale&Sharon Tahja Geotechnical Report rIIV �`� meets all the requirements of the Mason County Resource Ordinance, Geologically Hazardous Areas Section, is complete and true, that the assessment demonstrates conclusively that the risks posed by the 'P �7 S 4J try landslide hazard can be mitigated through the included geotechnical �SSI0 L E�G� design recommendations, and that all hazards are mitigated in such a manner as to prevent harm to property and public health and safety Page 2 of 2 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report. TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 Mason County DCD Planning Division WA 615 W Alder Street Shelton, WA 98584 Dale& Sharron Tahja 2450 W Deegan Road 78Q9 4>� Shelton, WA 98584 1S'?V., (360) 426-5940 SIGNAL E� Re; Geotechnical Report Arnolds Way Hoodsport, WA 98548 Parcel No.: 932331-22-00800 County Case No-s: INTRODUCTION I was contacted by Mr. Dale Tahja who requested my assistance in investigating and documenting slope stability and landslide hazard issues relating to the residential use of Mason County Parcel Number 932331-22-00800. The property located on N Arnolds Way in the Starr White Community area of Hood Canal,approximately 3 miles north of Hoodsport on US Highway 101. The property is located in the southerly foothill region of the Olympic Mountain Range on the Olympic Peninsula. Mr. Tahja is in the process of making property improvements to improve the marketability of the property as a single family residential property. A site plan is attached to help visualize the layout of the property. I've visited the property on several occasions over the years to collect topographic information and verify measurements and feature locations. Measurements were made using a Trimble T5415 total station, a 4-foot range pole, a Sokkia model No. 8047-55 inclinometer, a 300 foot long fiberglass surveyor's tapes and other field equipment common to surveying. Software employed in creating a site plan and writing this report included AutoCAD 2024, GALENA Slope Stability Analysis software and Microsoft Office Word 2003. Contouring outside of the Tahja property was derived from Mason County's GIS website mapping. The parcel encompasses roughly 2.1 acres. The property can be visualized as a trapezoid with Arnolds Way(a private driveway)bisecting the property with approximately 1.1 acre north of the driveway and approximately 1.0 acres located south of Arnolds Way. The site was logged approximately 20 years ago and has second growth timber scattered over the property- The areas surrounding the property contain slopes measured between 26 and 38%with two slopes within 300' measuring 40%or greater. With a slope within 300 feet of the property measuring 40%or more slope with a height of 10 feet or more,Mason County requires a geotechnical report be developed to safely develop the property. The following thirteen elements are required by Mason County to be Projects1Tahja1Geo-RptPrc1 932331-22-00800 1 of 10 3/24/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 addressed in geotechnical reports prepared to comply with Mason County's Critical Resource Ordinance Sections 17.01.100 through 17.01.104. 1. SURFACE AND GEOLOGIC CONDITIONS: The property has been logged and partially cleared roughly 25 years ago. A conjectural residence location can be sited either north of Arnolds Way or south of the Arnolds Way easement. Inspection of the Geologic Map of Shelton 1:100,000 Quadrangle, Washington) on the following page finds the property located in an area between the Olympic Mountain foothills to the west and Hoods Canal to the east. The map reveals that the upland soils are classified as Qgo& Qga, Continental Glacial Deposits of the Fraser Glaciation,Vashon Stade described as follows: QgD Prnglacial and rr ressional outheash. late %Visconsinan (Pleisto cone)--Typically poorly to moderately sorted, rounded gravel and ..and with localized coarser--and finer-grained constituents; lithologi- cally varied mixture of mostly northern-provenance clasLc,especially containing granitic and metamorphic rocks that identify the unit as being deposited by the Puget lobe of the Cordilleran glacier;also con- tains varying amounts of locally derived Crescent Formation basalt, and in the Mox Chehalis Creek valley,central Cascade Range- derived andesitic clasts, typically shades of gray where fresh or brown where stained especially in proglacial and morainal areas,- buff staining near the ground surface; fine sand,silt,and clay constitute local overbank sediments having relatively poor permeability or del- taic forecet bedding along north sides of valleys with higher permea- bility; porous and permeable enough to yield small to moderate quan- tities of groundwater, very poorly consolidated to loose; moderately to well-rounded clasts; mostly unweathered with rare weathered reworked clasts;thickness varies and is not well known; most com- monly occupies outwash channels scoured into or through till. C2ga Ad%ance out%%ash.late %Viscousinan (Pleistocene-�Aaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained-with interlayered coarser sand,gravel, and cobbles and silt rip-up lag deposits at their bake; may contain nonglacial sedi- ments; generally overlain by till. As the following portion of the Geologic Map of Shelton 1:100,000 Quadrangle reveals,the Tahja property is located in the vicinity of several fault lines identified on the following map as(1) the terminus of two faults emanating from the north and terminating approximately 2 miles to the northwest of the Tahja property on the north side of Dow Mountain(2)a fault line runs southwest to northeast through Lake Cushman approximately 5%4 miles northwest of the Tahja site, and(3)a fault line which follows Hood Canal is located approximately a mile east of the Tahja property. The presence of these features does not represent an unusual hazard,and standard seismic analysis of the site is intended to 'DNR OFR2003-15 Geologic Map of Shelton 1:100,000 Quadrangle,Washington Projects7ahj&Geo-Rpt Prc1 932331-22-00800 2 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 anticipate potential tectonic impacts. Further inspection and soil analysis finds the soil to be classified under the Unified Soil Classification System(USCS) as a GW-GC (well graded or gap graded sandy gravel) soil division. Inspection of the cut slopes in the neighborhood reveals loamy gravelly sands to a depth in excess of 5-feet. Inspection of the hillside to the southwest of the Tahja property reveals a substrate composed of solid basalt rock which underlies the entire region. A"Fish Bearing"stream is located roughly 1020-feet south of the property. Hood Canal is located roughly 1,200-feet east of the parcel. The upslope geomorphology of the property may be described as hilly or mountainous.No wetlands or waterbodies are in the property's vicinity. Ems+' i aw � �°��s �,�,-•,,� - d' awn .. a . ' t tip` -` aft v de CQU UqW ; t 3 s 2. SITE PLAN WITH IMPORTANT DEVELOPMENT AND GEOLOGIC FEATURES: A site plan showing the general topography of the area surrounding the Tahja property is attached in the appendix which shows the locations of a conceptual residence and the septic system. Inspection of the Coastal Zone Atlas finds the Tahja property located in an area designated as"Unstable". The shallow soils overlying the sedimentary rock and consolidated Hoodsport soils have tended to slip off of the underlying stable rock subgrade, giving rise to the unstable designation. Modeling of the site and my investigation of stability issues regarding the Tahja property lead me to claim that the site is stable and suitable for development with a single family residence. For scale, I've inserted two 1,728 square foot houses in the northern& southern areas of the property. The septic system drain field is planned to be sited in the southerly portion of the property,which can accommodate either a residence in the northern or southern portions of the property. 3. LOCATIONS OF LOGS OF EXPLORATORY HOLES OR PROBES: Soil log locations for the septic system drain-field are shown on plan sheet 2. Grading on the lot reveals that the surface soils are 5 to 6 feet deep. Groundwater in a well in the neighborhood is commonly 20 to 40 feet below the surrounding ground- Projects l Tahja lGeo-Rpt Prcl 932331-22-00800 3 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 4. AREA OF PROPOSED DEVELOPMENT&BOUNDARIES OF HAZARDS, BUFFERS, AND SETBACKS: The attached site plan shows the general locations of a conjectural residence locations. Stability analysis of the 45%f slope to the west& south of the Tahja property found Factors of Safety above the County's minimum requirements . The slopes exceeding 40%in the Tahja property vicinity are identified on the attached site plans as"HAZARD AREAS"as required by Mason County's critical resource ordinance. None of the Tahja property lies inside a hazard area or its 50-foot buffer. A three or a four bedroom Onsite Septic System(OSS)has been designed for the Tahja property in the general location depicted on the attached site plans. The OSS location is acceptable. The attached site plan has the standard 20' side &back yard building setbacks shown along with a standard 25' front yard building setback. Hazard areas(areas containing slopes greater than 40%)are delineated with a 50' Hazard Area Dashed line. 5. CROSS SECTION WITH PROPOSED GRADE CHANGES: A cross section view of the property is provided in the attached plan sheets as well as part of the GALENA Stability Analysis Print-Out.No major grade changes are anticipated for the slopes on or near the Tahja property at this time.No structural fills will be required for the conjectural residence's foundation(s). 6. SLOPE STABILITY ANALYSIS: The steepest slopes on the property in its present condition contain no obvious recent mass landslides or stability problem indicators. The building area conceptually shown on the attached plans show no discernable irregularities, settlements,fissures,or evidence of consolidation problems. Historically the soils have exhibited a potential to slide off of the underlying glacial till and basalt substrate. Instability tends to be along the Highway 101 backslopes. This area has been stable for over a century though the DOE Coastal Zone Atlas labels the area as"Unstable Slope" (blue area). 9�asL,nxi�+w im irr ❑�,e+cm.....��..s„rwH�;.- �sue.. �•,a...a1 ,�,�. Unified Soil Classification System typing places the soil in a GW-GM category. The surface soils(<5' deep)have a soil unit weight of 123 lbs/ft3,a phi angle of 38°, and a cohesion character of 1501bs/ft2. The deeper consolidated till soils are modeled with a soil unit weight of 125 lbs/ft, a phi angle of 39°, cohesion value of 3001bs/fl. ProjectslTahjalGeo-Rpt Ped 932331-22-00800 4 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 The slope geometry and soil characteristics provide a Factor of Safety (FoS)for the site in a static and a dynamic analysis that exceed the County's minimum safety requirements. Analysis of the site by the Bishop Method indicates Factors of Safety of 3.18 in a static condition and 2.33 in a dynamic condition.. Mason County requires FoSs of 1.5 for a static analysis and 1.1 for a dynamic analysis. 7. RECOMMENDED SETBACKS &DRAINAGE: The slope stability analysis indicates that the slopes present on or near the Tahja property are stable in their present geometry and condition and do not represent a landslide or geological hazard to the proposed Tahja property development. The slopes surrounding the Tahja property are stable,but a minimum building setback of 5-feet from the crest or toe of any slope greater than 30%is recommended. The gravelly character of the soil at the Tahja site effectively infiltrates all rainfall except in areas compacted by vehicle traffic. Splash blocks located on the downhill side of proposed structures should disperse roof runoff into vegetated areas maintained between the splash blocks and the top of the easterly descending steep slope(s). 8. CLEARING,GRADING,AND VEGETATION MANAGEMENT: The property is already in a semi-cleared condition. The areas indicated as the residence,driveway, and drainfield have already been cleared and leveled in preparation of the residential development of the property.No activities have been planned for the sloping areas of the properties,though vegetation will be encouraged to continue growing,covering, and protecting the steep slopes.No compacted fills or excavated cuts are necessitated by the conjectural residential development of the property.No formal planting plan appears needed for the completed development which will likely be maintained in a semi- natural vegetated condition. 9. EROSION AND SEDIMENT CONTROL: Inspection of the Soil Survey of Mason County found the site to be located in an area with Hoodsport soil type(s) (Hd&Hf),which are not identified in the County's Critical Resource Ordinance as susceptible to severe erosion when disturbed so a formal Erosion and Sediment(E&S) Control Plan is not required to be prepared for this site. The site already has an access route installed on the property from Arnolds Way (a private driveway)which is stable in its present condition.Upon completion of site grading and structure foundation backfilling,bare soils should be seeded to grass and the temporary erosion and sediment control features kept in place until the site becomes permanently stabilized with vegetation or compacted driving and parking surfaces. 10. ON-SITE AND OFF-SITE IMPACTS: Construction and completion of the conjectural improvements are not expected to result in any adverse on-site or off-site impacts. 11. SPECIFICATIONS OF FINAL DEVELOPMENT: Upon completion of the residential features on the property,the grounds can be expected to be maintained as a permanent residence,possibly with a lawn and other landscaping shrubbery. Other ProjectslTahjalGeo-Rpt Prd 932331-22-00800 5 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 undeveloped areas of the property are expected to be maintained in a natural vegetated state.No formal planting schedule appears to be needed. 12. RECOMMENDATIONS FOR THE PREPARATION OF STRUCTURAL MITIGATION OR DETAILS OF OTHER PROPOSED MITIGATION: Modeling of the slopes in the proximities of the conjectural residence indicates that the locations of the conjectural structures are safe,and no structural measures appear necessary other than ensuring foundations bear on hard firm compacted soil. A minimum 5-foot building setback should be observed between the existing top&toe of slopes and structure foundations.No structural fills are necessary to develop the property with a single family residence and appurtenant features. 13. SITE PLAN WITH THE LOCATION OF EXISTING AND PROPOSED DEVELOPMENT ON THE SITE: A site plan is attached as an appendix to this report including three plan views, a cross- section view of the property, and a stability analysis printout. Summary& Conclusions: The Tahja property,though in the vicinity of slopes identified as unstable in the Washington Coastal Zone Atlas, can be developed according to the owner's plans with a minimal concern about the site's stability. Please feel free to contact me if 4ere are any questions or concerns regarding this report or my findings. Sincerely, T*h Alan A. Tahja,P.E. Attached: Geotechnical Report Checklist Plan Views& Cross Section Sheets GALENATM Stability Analysis Printout(Bishop) Projects1Tahj&Geo-RptPrc1 932331-22-00800 6 of 10 3/24/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 80 3tatic.gmf Processed: 24 Mar 2025 12:23:44 DATA: Analysis 1 Material Properties (2 materials)------------------- Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles)----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points)------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points)---------------- 50.00 340.00 140.00 305.00 Failure Surface--------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Variable Restraints------------------- Parameterdescriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface --------------------------- Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 3.612 Analysis Summary ________________ There were: 122 successful analyses from a total of 125 trial failure surfaces 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Projects1Tahja1Geo-RptPrc1 932331-22-00800 7 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Critical (minimum) Factor of Safety: 3.18 Results Summary - Lowest 99 Factor of Safety circles ---------------------------------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FoS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 3.184 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 3.214 3 99.50 359.14 167.75 330.09 144.61 370.43 46.50 3.238 4 99.50 359.14 166.50 330.42 143.57 369.43 45.25 3.248 5 97.00 360.00 166.50 330.42 142.37 370.17 46.50 3.250 6 98.25 359.65 167.75 330.09 143.62 369.84 46.50 3.270 7 98.25 359.65 166.50 330.42 142.56 368.82 45.25 3.286 8 99.50 359.14 169.00 329.86 144.81 369.57 46.50 3.291 9 95.75 360.00 166.50 330.42 141.27 369.48 46.50 3.298 10 99.50 359.14 167.75 330.09 143.78 368.47 45.25 3.308 11 97.00 360.00 167.75 330.09 142.58 369.19 46.50 3.312 12 99.50 359.14 166.50 330.42 142.71 367.44 44.00 3.326 13 98.25 359.65 169.00 329.86 143.81 368.95 46.50 3.328 14 97.00 360.00 166.50 330.42 141.51 368.15 45.25 3.332 15 99.50 359.14 170.25 329.66 145.00 368.71 46.50 3.348 16 98.25 359.65 167.75 330.09 142.76 367.81 45.25 3.351 17 94.50 360.00 166.50 330.42 140.17 368.75 46.50 3.356 18 95.75 360.00 167.75 330.09 141.47 368.46 46.50 3.365 19 99.50 359.14 169.00 329.86 143.96 367.55 45.25 3.370 20 98.25 359.65 166.50 330.42 141.67 366.75 44.00 3.375 21 98.25 359.65 170.25 329.66 143.99 368.04 46.50 3.390 22 95.75 360.00 166.50 330.42 140.39 367.38 45.25 3.392 23 99.50 359.14 167.75 330.09 142.90 366.40 44.00 3.397 24 97.00 360.00 167.75 330.09 141.69 367.09 45.25 3.405 25 99.50 359.14 171.50 329.47 145.19 367.81 46.50 3.411 26 98.25 359.65 169.00 329.86 142.93 366.84 45.25 3.419 27 99.50 359.14 166.50 330.42 141.80 365.31 42.75 Projects7ahjalGeo-Rpt Prcl 932331-22-00800 8 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 80 Dynamic.gmf Processed: 24 Mar 2025 14:04:22 DATA: Analysis 1 Material Properties (2 materials)------------------- - Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles)----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points)------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points)---------------- 50.00 340.00 140.00 305.00 Failure Surface--------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Earthquake Force--------- -- Pseudo-static earthquake (seismic) coefficient: 0.150 Variable Restraints------------------- Parameterdescriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - -- -- -- -- -- -- - RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface---------------------------- Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 2.645 Analysis Summary There were: 122 successful analyses from a total of 125 trial failure surfaces ProjectsMahjalGeo-RptPrcl 932331-22-00800 9 of 10 3/24/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Critical (minimum) Factor of Safety: 2.33 Results Summary - Lowest 99 Factor of Safety circles --------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FoS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 2.329 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 2.352 3 99.50 359.14 167.75 330.09 144.61 370.43 46.50 2.365 4 99.50 359.14 166.50 330.42 143.57 369.43 45.25 2.378 5 97.00 360.00 166.50 330.42 142.37 370.17 46.50 2.380 6 98.25 359.65 167.75 330.09 143.62 369.84 46.50 2.390 7 99.50 359.14 169.00 329.86 144.81 369.57 46.50 2.401 8 98.25 359.65 166.50 330.42 142.56 368.82 45.25 2.407 9 95.75 360.00 166.50 330.42 141.27 369.48 46.50 2.415 10 99.50 359.14 167.75 330.09 143.78 368.47 45.25 2.419 11 97.00 360.00 167.75 330.09 142.58 369.19 46.50 2.422 12 98.25 359.65 169.00 329.86 143.81 368.95 46.50 2.430 13 99.50 359.14 166.50 330.42 142.71 367.44 44.00 2.437 14 99.50 359.14 170.25 329.66 145.00 368.71 46.50 2.439 15 97.00 360.00 166.50 330.42 141.51 368.15 45.25 2.442 16 98.25 359.65 167.75 330.09 142.76 367.81 45.25 2.452 17 94.50 360.00 166.50 330.42 140.17 368.75 46.50 2.458 18 99.50 359.14 169.00 329.86 143.96 367.55 45.25 2.461 19 95.75 360.00 167.75 330.09 141.47 368.46 46.50 2.462 20 98.25 359.65 170.25 329.66 143.99 368.04 46.50 2.472 21 98.25 359.65 166.50 330.42 141.67 366.75 44.00 2.475 22 99.50 359.14 171.50 329.47 145.19 367.81 46.50 2.482 23 99.50 359.14 167.75 330.09 142.90 366.40 44.00 2.486 24 95.75 360.00 166.50 330.42 140.39 367.38 45.25 2.487 25 97.00 360.00 167.75 330.09 141.69 367.09 45.25 2.492 26 98.25 359.65 169.00 329.86 142.93 366.84 45.25 2.499 ProjectslTahjalGeo-Rpt Prcl 932331-22-00800 10 of 10 3/24/2025 Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN P Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodsport, WA 98548 Shelton, WA 98584 1 of5 Mason Co.Pre]Nas: 32331-22-00800 (360)877-9512 (360)463-8023 i ^Al j z Ito %AC., ct tr .� a ' ,tom �a w C m E. 1 0 ?b, 44O < o 0 Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN Pq.Pik Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodspor4 WA 98548 Shelton, WA 98584 2 of 5 Mason Co.hd No.s: 32331-22-00800 (360)877-9512 (360)426-5940 8 N N Q M �'"--.,� z C$ -- *U kV 4'� O r0 r0`O COO 1 ' C �. o cn co�w a 4. -. Y NE GOVT LOT I �1;pa C4aE i�71li G+d' f o 9En,a 6,6;-%b tow 32331-22-00800 . I I � T o N I I r.. I I N SCALE: V=80' g r. 444 0 20 40 60 80 b F_A3ToGt "I�a OF REMNV A SAT o °° y�of WA sx f L3B1�C� &°p to 30784 �V4 r ^lIINrC1Ki4lJM I OA�,SS GISTEg�Gti'�� ZONAL E � AUDMAS CMFICATI `° Oa is ft- Ar POM a VIM NV%KW 60 444FAM TUPOWWL LAM+Tv Plrx� fturry � $FJR'Vft cam IdAl Vw in ISM JQ rztan" )Y a5Ft�3 b�G�f:'rS r �,z, Rev# Description Date TAHJA ENGINEERING,RVC. SITE PLAN '"ma y b Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd s„ Hoodspor4 WA 98548 Shelton, WA 98584 4 of Mason Co.Prcl No.s: 32331-22-00800 (360)877-9512 (360)426-5940 p 8 0 O �c� T co Gil � cL W N � � �n 0 U O - ^� o 00 0 g _ r 0 q L v °O C. e� 250 N 260 o � — o - U °0 270 H %06 o 280—� +CD U 0 L N � N O Y h it 1cC ± o\1 1 R J�O �O O) v p i O b 4t 400 SCALE: V=20' 0 0 5 10 20 390 ° o w b: ti N 370 Tr. 80 y�o A 43 S10 360 Pez tz w� I Glacial Till Below 4' \ �OA �s ERF,9 �' oo p y a 350 ,\ GP-SM shallow < 4' �s �11� -4 `�Cj SIGNAL E� w P� 340 ' 330 320 \ �� .. • c ��bh�7 310 fD 300 60 80 100 120 140 160 180 200 Project Analysis 1 GALENA version 7.2 File:CAGALENA\Dales TR 80.gmf C GALENA Model Cross Section "A" . ,L__%-,.*"I V `L-1 as � 9 MAR 2 0 2025 MASON COUNTY/V. Alder Street COMMUNITY SERVICES Geotechnical Report Building,Planning,Environmental Health,Community Health Instructions: This checklist must be submitted with a Geotechnical Report and completed, signed, and stamped by the licensed professional(s) who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County Resource Ordinance. If an item is found not applicable, the report should explain the basis for the conclusion. Note: Unless specifically documented, this report does not provide compliance to the International Residential Code Sections R403.1.7 for foundations on or adjacent to slopes. Section R403.1.8 for expansive soils or section 1808.7.1 of the International Building Code Section for Foundations on or adjacent to slopes. ApplicanVOwner Dale & Sharon Tahia Parcel# 32331-22-00740 Site Address 110 N Arnolds Way, Hoodsport, WA 98548 (1) (a)A discussion of general geologic conditions in the vicinity of the proposed development, Located on page(s) Pgs 1 -3 (b) A discussion of specific soil types, Located on page(s) Pg 4 (c) A discussion of ground water conditions, Located on page(s) Pg 4 (d) A discussion of the upslope geomorphology, Located on page(s) Pg 3 (e) A discussion of the location of upland waterbodies and wetlands, Located on page(s) Pg 3 (f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records. Located on page(s) Pg 4 (2) A site plan which identifies the important development and geologic features. Located on Map(s) 1 thru 6 (3) Locations and logs of exploratory holes or probes. Located on Map(s) Sheets 3 &4 (4) The area of the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall be delineated (top, both sides, and toe) on a geologic map of the site. Located on Map(s) Sheets 3 &4 (5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which incorporates the details of proposed grade changes Located on Map(s) Sheets 5 &6 (6) A description and results of slope stability analyses performed for both static and seismic loading conditions. Analysis should examine worst case failures. The analysis should include the Simplified Bishop's Method of Circles. The minimum static safety factor is 1.5, the minimum seismic safety factor is 1.1, and the quasi-static analysis coefficients should be a value of 0.15. Located on page(s) Pq 5 (7) (a) Appropriate restrictions on placement of drainage features, Rev. February 2018 t � Located on page(s Pg 5 (b) Appropriate restrictions on placement of septic drain fields, Located on page(s) Pg 4 (c) Appropriate restrictions on placement of compacted fills and footings, Located on page(s) Pg 6 (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) Pg 6 (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) Pq 6 (8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the method of vegetation removal. Located on page(s) Pg 6 (9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific mitigating measures to be implemented during construction to protect the slope from erosion, landslides and harmful construction methods. Located on page(s) Pq 5 (10) An analysis of both on-site and off-site impacts of the proposed development. Located on page(s) Pg 6 (11) Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths. Located on page(s) Pg 6 (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation. Located on page(s) Pq 6 (13) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site. Located on Map(s) Sheets Sheets 1 -6 1, Alan A_ "i'ahja hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical Report, dated March 101h, 2025 and entitled WAA Dale&Sharon Tahja Geotechnical Report c o meets all the requirements of the Mason County Resource Ordinance, Geologically Hazardous Areas Section, is complete and true, that the p� assessment demonstrates conclusively that the risks posed by the 3D78h w� GIS�ER�'9 �w landslide hazard can be mitigated through the included geotechnical �43' ONAL S %j' design recommendations, and that all hazards are mitigated in such a manner as to prevent harm to property and public health and safety. Page 2 of 2 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report. TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 Mason County DCD Planning Division WA A T 615 W Alder Street Shelton, WA 98584 Dale& Sharron Tahja 2450 W Deegan Road Shelton, WA 98584 GIs ER�G��`s' (360) 426-5940 I�NAL E Re; Geotechnical Report 110 Arnolds Way Hoodsport, WA 98548 Parcel No.: 932331-22-00740 County Case No.s: INTRODUCTION I was contacted by Mr. Dale Tahja who requested my assistance in investigating and documenting slope stability and landslide hazard issues relating to the residential use of the property located at N 110 Arnolds Way in the Starr White Community area of Hood Canal,approximately 3 miles north of Hoodsport on US Highway 101. The property is located in the southerly foothill region of the Olympic Mountain Range on the Olympic Peninsula. Mr. Tahja is in the process of making property improvements to improve the marketability of the property as a single family residential property.A site plan is attached to help visualize the layout of the property. I've visited the property on several occasions over the years to collect topographic information and verify measurements and feature locations. Measurements were made using a Trimble T5415 total station, a 4-foot range pole, a Sokkia model No. 8047-55 inclinometer,a 300 foot long fiberglass surveyor's tapes and other field equipment common to surveying. Software employed in creating a site plan and writing this report included AutoCAD 2006, GALENA Slope Stability Analysis software and Microsoft Office Word 2003. Contouring outside of the Tahja property was derived from Mason County's GIS website mapping. The property can be visualized as a trapezoid with Arnolds Way(a private driveway)bisecting the property with approximately 1 acre north of the driveway and approximately a half acre located south of Arnolds Way. The site has been cleared of trees and underbrush for many years and has a cleared level area generally in the middle of the northerly portion of the property.The areas surrounding the property contain slopes measured between 26 and 38%with a slope within 300' measuring 46%. With a slope within 300 feet of the property measuring 40%or more slope with a height of 10 feet or more,Mason County requires a geotechnical report be developed to safely develop the property. The following File:C:ProjectslTahjalGeawR t 1 of 6 3/10/2025 TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 thirteen elements are required by Mason County to be addressed in geotechnical reports prepared to comply with Mason County's Critical Resource Ordinance Sections 17.01.100 through 17.01.104. 1. SURFACE AND GEOLOGIC CONDITIONS: The property has been logged and partially cleared roughly 25 years ago and the conjectural residence location will likely be in an area already cleared and graded. The areas outside of the central cleared area are covered with light vegetation and young to medium age second growth conifer trees. Inspection of the Geologic Map of Shelton 1:100,000 Quadrangle, Washington) on the following page finds the property located in an area between the Olympic Mountain foothills to the west and Hoods Canal to the east. The map reveals that the upland soils are classified as Qgo& Qga,Continental Glacial Deposits of the Fraser Glaciation,Vashon Stade described as follows: Proglacial and recessional oub%-ash, late Wisconsinan (Pleisto- cene)—Typically poorly to moderately sorted, rounded gravel and sand with localized coarser-and finer-grained constituents; lithologi- cally varied mixture of mostly northern-provenance clasts,especially containing granitic and metamorphic rocks that identify the unit as being deposited by the Puget lobe of the Cordilleran glacier; also con- tains varying amounts of locally derived Crescent Formation basalt, and in the Mox Chehalis Creek valley,central Cascade Range— derived andesitic clasts; typically shades of gray where fresh or brown where stained especially in proglacial and morainal areas;buff staining near the ground surface; fine sand,silt,and clay constitute local overbank sediments having relatively poor permeability or del- taic foresee bedding along north sides of valleys with higher permea- bility;porous and permeable enough to yield small to moderate quan- tities of groundwater; very poorly consolidated to loose; moderately to well-rounded clasts; mostly unweathered with rare weathered reworked clads; thickness varies and is not well known; most com- monly occupies outwash channels scoured into or through till. Advance outwash, late Wisconsinan (Pleistocene)- Aaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained,with interlayered coarser sand,gravel, and cobbles and silt rip-up lag deposits at their base; may contain nonglacial sedi- ments; generally overlain by till. As the following portion of the Geologic Map of Shelton 1:100,000 Quadrangle reveals,the Tahja property is located in the vicinity of several fault lines identified on the following map as (1) the terminus of two faults emanating from the north and terminating approximately 2 miles to the northwest of the Tahja property on the north side of Dow Mountain(2)a fault line runs southwest to northeast through Lake Cushman approximately 5'/4 miles northwest of the Tahja site,and(3)a fault line which follows Hood Canal is located approximately a mile east of the Tahja property. The presence of these 'DNR OFR2003-15 Geologic Map of Shelton 1:100,000 Quadrangle,Washington File:C:IProjeets1Tahja1Geo-Rpt 2 of 6 3/10/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 features does not represent an unusual hazard, and standard seismic analysis of the site is intended to anticipate potential tectonic impacts. Further inspection and soil analysis finds the soil to be classified under the Unified Soil Classification System(USCS)as a GW-GC (well graded or gap graded sandy gravel)soil division. Inspection of the cut slopes in the neighborhood reveals loamy gravelly sands to a depth in excess of 5-feet. Inspection of the hillside to the southwest of the Tahja property reveals a substrate composed of solid basalt rock which underlies the entire region. A"Fish Bearing"stream is located roughly 1020-feet south of the property. Hood Canal is located roughly 1,200-feet east of the parcel. The upslope geomorphology of the property may be described as hilly or mountainous. Lk Evd co--/A 1 so �p ��SaP e ;. •..�'._ s pa anpa r �1 55 i�yp� )_09d me V� by TT C�Evd pga apo i pap °a Eva _-` CWO u a' Evd Knkanec \- papo SIP Q J/- Qa 2. SITE PLAN WITH IMPORTANT DEVELOPMENT AND GEOLOGIC FEATURES: A site plan showing the general topography of the area surrounding the Tahja property is attached in the appendix which shows the locations of a conceptual residence and the septic system. Inspection of the Coastal Zone Atlas finds the Tahja property located in an area designated as"Unstable". The shallow soils overlying the sedimentary rock and consolidated Hoodsport soils have tended to slip off of the underlying stable rock subgrade, giving rise to the unstable designation. Modeling of the site and my investigation of stability issues regarding the Tahja property lead me to claim that the site is stable and suitable for development with a single family residence. For scale, I've inserted a 1,200 square foot house in the northern area of the property. The septic system drain field is planned to be sited in the southerly portion of the property. 3. LOCATIONS OF LOGS OF EXPLORATORY HOLES OR PROBES: Soil log locations for the septic system drain-field are shown on plan sheet 4. Grading on the lot reveals that the surface soils are 5 to 6 feet deep. File:C.lProjectslTakalGeo-Rpt 3 of 6 3/10/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 4. AREA OF PROPOSED DEVELOPMENT&BOUNDARIES OF HAZARDS,BUFFERS,AND SETBACKS: The attached site plan shows the general locations of a conjectural residence location. Stability analysis of the 42%f slope to the west of the Tahja property found Factors of Safety above the County's minimum requirements. The slopes exceeding 40%in the Tahja property vicinity are identified on the attached site plans as"HAZARD AREAS"as required.by Mason County's critical resource ordinance. None of the Tahja property lies inside a hazard area or its 50-foot buffer. A four bedroom Onsite Septic System(OSS)has been designed for the Tahja property in the general location depicted on the attached site plans. The OSS location is acceptable. The attached site plan has the standard 20' side&back yard building setbacks shown along with a standard 25' front yard building setback. Hazard areas(areas containing slopes greater than 40%)are delineated with a solid line,and the 50-foot hazard area buffer lines are delineated with a dashed line. 5. CROSS SECTION WITH PROPOSED GRADE CHANGES: A cross section view of the property is provided in the attached plan sheets as well as part of the GALENA Stability Analysis Print-Out.No major grade changes are anticipated for the slopes on or near the Tahja property at this time.No structural fills will be required for the conjectural residence's foundation(s). 6. SLOPE STABILITY ANALYSIS: The steepest slopes on the property in its present condition contain no obvious recent mass landslides or stability problem indicators. The building area conceptually shown on the attached plans show no discernable irregularities, settlements,fissures,or evidence of consolidation problems. Historically the soils have exhibited a potential to slide off of the underlying glacial till and basalt substrate. Instability tends to be along the Highway 101 backslopes. This area has been stable for over a century though the DOE Coastal Zone Atlas labels the area as"Unstable Slope"(blue area). v**AM❑MIPM +s,m O s.r.s. a..... ■„re�.s.-awao ,r o om u G fw..Pro.aa�'r'�-'^� sr ■ .r.w P om nos uw- Unified Soil Classification System typing places the soil in a GW-GM category. The surface soils (<5' deep)have a soil unit weight of 123 lbs/f13, a phi angle of 38°, and a cohesion character of 1501bs/ft2. File:C.WrojectslTahjalGeo-Rpt 4 of 6 3/10/2025 TAfUA ENGINEERING,Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 The deeper consolidated till soils are modeled with a soil unit weight of 125 lbs/f 3,a phi angle of 39°, cohesion value of 300 lbs/f The slope geometry and soil characteristics provide a Factor of Safety(FoS) for the site in a static and a dynamic analysis that exceed the County's minimum safety requirements. Analysis of the site by the Bishop Method indicates Factors of Safety of 3.18 in a static condition and 2.33 in a dynamic condition. Analysis of the site by the Spencer-Wright Method indicates Factors of Safety of 3.60 in a static condition and 2.42 in a dynamic condition. Mason County requires FoSs of 1.5 for a static analysis and 1.1 for a dynamic analysis. 7. RECOMMENDED SETBACKS &DRAINAGE: The slope stability analysis indicates that the slopes present on or near the Tahja property are stable in their present geometry and condition and do not represent a landslide or geological hazard to the proposed Tahja property development. The slopes surrounding the Tahja property are stable,but a minimum building setback of 5-feet from the crest or toe of any slope greater than 40%is recommended. The gravelly character of the soil at the Tahja site effectively infiltrates all rainfall except in areas compacted by vehicle traffic. Splash blocks located on the downhill side of proposed structures should disperse roof runoff into vegetated areas maintained between the splash blocks and the top of the easterly descending steep slope(s). 8. CLEARING,GRADING,AND VEGETATION MANAGEMENT: The property is already in a semi-cleared condition. The areas indicated as the residence, driveway, and drainfield have already been cleared and leveled in preparation of the residential development of the property.No activities have been planned for the sloping areas of the properties,though vegetation will be encouraged to continue growing, covering,and protecting the steep slopes.No compacted fills or excavated cuts are necessitated by the conjectural residential development of the property.No formal planting plan appears needed for the completed development which will likely be maintained in a semi- natural vegetated condition. 9. EROSION AND SEDIMENT CONTROL: Inspection of the Soil Survey of Mason County found the site to be located in an area with Hoodsport soil type(s) (Hd&Hf), which are not identified in the County's Critical Resource Ordinance as susceptible to severe erosion when disturbed so a formal Erosion and Sediment(E&S)Control Plan is not required to be prepared for this site. The site already has an access route installed on the property from Arnolds Way(a private driveway)which is stable in its present condition.Upon completion of site grading and structure foundation backfilling,bare soils should be seeded to grass and the temporary erosion and sediment control features kept in place until the site becomes permanently stabilized with vegetation or compacted driving and parking surfaces. 10. ON-SITE AND OFF-SITE IMPACTS: Construction and completion of the conjectural improvements are not expected to result in any adverse on-site or off-site impacts. File:C.AProjects1Tahja1Geo-Rpt 5 of 6 3/10/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 11. SPECIFICATIONS OF FINAL DEVELOPMENT: Upon completion of the residential features on the property,the grounds can be expected to be maintained as a permanent residence,possibly with a lawn and other landscaping shrubbery. Other undeveloped areas of the property are expected to be maintained in a natural vegetated state.No formal planting schedule appears to be needed. 12. RECOMMENDATIONS FOR THE PREPARATION OF STRUCTURAL MITIGATION OR DETAILS OF OTHER PROPOSED MITIGATION: Modeling of the slopes in the proximities of the conjectural residence indicates that the locations of the conjectural structures are safe, and no structural measures appear necessary other than ensuring foundations bear on hard firm compacted soil. A minimum 5-foot building setback should be observed between the existing top&toe of slopes and structure foundations.No structural fills are necessary to develop the property with a single family residence and appurtenant features. 13. SITE PLAN WITH THE LOCATION OF EXISTING AND PROPOSED DEVELOPMENT ON THE SITE: A site plan is attached as an appendix to this report including two plan views,a cross- section view of the property,and a stability analysis printout. Summary & Conclusions: The Tahja property,though in the vicinity of slopes identified as unstable in the Washington Coastal Zone Atlas,can be developed according to the owner's plans with a minimal concern about the site's stability. Please feel free to contact me if there are any questions or concerns regarding this report or my findings. Sincerely, ��. A Alan A. Tahja,P.E. Attached: Geotechnical Report Checklist Plan Views&Cross Section Sheets GALENATM Stability Analysis Printout(Bishop) File:C kProjects1Tahj&Geo-Rpt 6 of 6 3/10/2025 Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN .Fib Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodsport, WA 98548 Shelton, WA 98584 1 of 6 Mason Co.Prcl No.s: 32331-22-00740 (360)877-9512 (360)463-8023 _ r CNIO I A r i `y6 I n kn W + § o W N Jff�F} H r� � F N f ! O 0 Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN N41% Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodsport, WA 98548 Shelton, WA 98584 2 of 6 Mason Co.Prcl No.s: 32331-22-00740 (360)877-9512 (360)426-5940 N N II cd �- - r \\ W) r• o C?� N Z Cf} N r N N ?f o,o l� n ti. C/1 w t3 o cu •. I� O JGJJ 1'GG'VV/`FV PL 239' PL- 195' PL-260.04' b � O 00 �1`� A T Tr. 77 11�O v ry F WA Site I Bldg t W E w a I � Bldg Site �yAID W �7Bh 7 �c g �' I O+d' N Bldg Site �`sS10NAL E��l� M $ a Tr. 80 t b .a a > Septic Tank Conjectural Waterline b 1 Route 430' g o Arnold's Way �� z �l Survey Pin / 00 Q1' ti v, p Tr. 60 �y .End of existing 2" PVC 1 j � ury o ao z Schdl 40 Line & Conjectural r Conjectural Connection between Canal \ 59 Connection Lo i Mutual System & Existin Tr. \ with Back- ow Tahja System. \ Prevent' D is , \ Power Vault Met & oster 1 Tr. 53 & 56 Cd SCALE: 1"=80' 0 20 40 60 80 Rev# Description Date TAMA ENGINEERING,INC. SITE PLAN Alan Tahja,P.E. Dale&Sharon Tahja Tabja PO Box 235 2450 W Deegan Rd sbw Hoodsport WA 98548 Shelton, WA 98584 4 of 6 Mason Co.Prd Nox 32331-22-00740 (360)877-9512 (360)426-5940 O - z � - _ N t u \ ^W it � � ��,• H - N M a ` 9z- r- 1 1 AID Rev## Description Date TAHJA ENGINEERING,INC. SITE PLAN Pftj�Fib Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodsport, WA 98548 Shelton, WA 98584 5 of 6 Mason Co.NO No.s: 32331-22-00740 (360)877-9512 (360)426-5940 8 0 u Y Jay � 'fir d R mw � rn o 0 o 0 + a N y O � O O � O + L O 2 O o CD250 N o � 260 ,o U °O 270 / L: + CA rn 280 \ N + U 00 0 / + / o 3VO + m N / o p 320 N o� a 0 S o aaa000pp0oppa0000 pQo �vi<MN.--BOO W!� O v <MN.--•8P W N N N N N N N N N N^^ C - C � 400 SCALE: V=20' n 0 0 5 10 20 O 390 0.150 n. b w o' w b 380 •—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—-—--- N A 370 Tr. 74 �v WA ofj b 4S°/a 360 H •—-—-—-—-—-—-—-—-—-—-—-—- -- ao O \ 30784 �� Q Glacial Till Below 4' �O�' �� TEg-S 350 .\ GP-SM Shallow < 4 �`S`SIONAL b 340 �\ '� 00� 'Phr 330 `ic surf \ ace w �tib� 320 ` .. o vi', y c Coco h7 310aoZ � — odo 300 — — 60 80 100 120 140 160 180 200 Prow Analysis 1 GALENA Vfton7.2 File:CAGALENA1Dales TR 74 with Restraints 3.gmf C, c. GALENA Model Cross Section "A" 400 390 380 .—.—.—.—.—.—.—.—.—_—.—.—.—_—.—.—.—.—.—_—.—__._.—.—.—.—.—.—.—.—.—. —.—.—.—• 370 360 350 Glacial Till Below 4' GP-SM shallow <4' 340 330 °S@pac e 320 310 300 60 80 100 120 140 160 180 200 Project Analysis 1 GALENA Vw 7.2 Fla:Ci0ALE1MO Ms TR 74 wile R.&.m 4 pl GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 74 with Restraints 4.gmf Processed: 12 Mar 2025 14:05:19 DATA: Analysis 1 Material Properties (2 materials) ------------------- Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties ---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles) ----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points) ------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points) --- ----- 50.00 340.00 140.00 305.00 Failure Surface --------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Earthquake Force ---------------- Pseudo-static earthquake (seismic) coefficient: 0.150 Variable Restraints ------------------- Parameter descriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface ---------------- Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 2.645 Analysis Summary =__-________ There were: 122 successful analyses from a total of 125 trial failure surfaces 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Critical (minimum) Factor of Safety: 2.33 Results Summary - Lowest 99 Factor of Safety circles --------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FOS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 2.329 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 2.352 3 99.50 359.14 167.75 330.09 144.61 370.43 46.50 2.365 4 99.50 359.14 166.50 330.42 143.57 369.43 45.25 2.378 5 97.00 360.00 166.50 330.42 142.37 370.17 46.50 2.380 6 98.25 359.65 167.75 330.09 143.62 369.84 46.50 2.390 7 99.50 359.14 169.00 329.86 144.81 369.57 46.50 2.401 8 98.25 359.65 166.50 330.42 142.56 368.82 45.25 2.407 9 95.75 360.00 166.50 330.42 141.27 369.48 46.50 2.415 10 99.50 359.14 167.75 330.09 143.78 368.47 45.25 2.419 11 97.00 360.00 167.75 330.09 142.58 369.19 46.50 2.422 GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 74 with Restraints 4.gmf Processed: 12 Mar 2025 14:30:04 DATA: Analysis 1 Material Properties (2 materials) ------------------- Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties ---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles) ----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points) ------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points) --------- 50.00 340.00 140.00 305.00 Failure Surface --------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Earthquake Force ---------------- Pseudo-static earthquake (seismic) coefficient: 0.150 Variable Restraints ------------------- Parameter descriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface -------------------- Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 2.645 Analysis Summary There were: 122 successful analyses from a total of 125 trial failure surfaces 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Critical (minimum) Factor of Safety: 2.33 Results Summary - Lowest 99 Factor of Safety circles ---------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FoS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 2.329 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 2.352 3 99.50 359.14 167.75 330.09 144.61 370.43 46.50 2.365 4 99.50 359.14 166.50 330.42 143.57 369.43 45.25 2.378 5 97.00 360.00 166.50 330.42 142.37 370.17 46.50 2.380 6 98.25 359.65 167.75 330.09 143.62 369.84 46.50 2.390 7 99.50 359.14 169.00 329.86 144.81 369.57 46.50 2.401 8 98.25 359.65 166.50 330.42 142.56 368.82 45.25 2.407 9 95.75 360.00 166.50 330.42 141.27 369.48 46.50 2.415 10 99.50 359.14 167.75 330.09 143.78 368.47 45.25 2.419 11 97.00 360.00 167.75 330.09 142.58 369.19 46.50 2.422 12 98.25 359.65 169.00 329.86 143.81 368.95 46.50 2.430 13 99.50 359.14 166.50 330.42 142.71 367.44 44.00 2.437 14 99.50 359.14 170.25 329.66 145.00 368.71 46.50 2.439 15 97.00 360.00 166.50 330.42 141.51 368.15 45.25 2.442 16 98.25 359.65 167.75 330.09 142.76 367.81 45.25 2.452 17 94.50 360.00 166.50 330.42 140.17 368.75 46.50 2.458 18 99.50 359.14 169.00 329.86 143.96 367.55 45.25 2.461 19 95.75 360.00 167.75 330.09 141.47 368.46 46.50 2.462 20 98.25 359.65 170.25 329.66 143.99 368.04 46.50 2.472 21 98.25 359.65 166.50 330.42 141.67 366.75 44.00 2.475 22 99.50 359.14 171.50 329.47 145.19 367.81 46.50 2.482 23 99.50 359.14 167.75 330.09 142.90 366.40 44.00 2.486 24 95.75 360.00 166.50 330.42 140.39 367.38 45.25 2.487 25 97.00 360.00 167.75 330.09 141.69 367.09 45.25 2.492 26 98.25 359.65 169.00 329.86 142.93 366.84 45.25 2.499 MASON COUNTY COMMUNITY SERVICES Geotechnical Report F.xul.ln,2$!srr,rm,T,Fms rm,�tt.+nail N.xM^,'�Frc+ruxntp Fitud'th Instructions: This checklist must be submitted with a Geotechnical Report and completed, signed, and stamped by the licensed professional(s) who prepared the Geotechnical Report for review by Mason County pursuant to the Mason County Resource Ordinance. If an item is found not applicable, the report should explain the basis for the conclusion. Note:Unless specifically documented,this report does not provide compliance to the International Residential Code Sections R403 17 for foundations on or adjacent to slopes. Section R403.1.8 for expansive soils or section 1808.7.1 of the International Building Code Section for Foundations on or adjacent to slopes. Applicant/Owner Dale&Sharon Tahja Parcel# 32331-21-00740 Site Address 110 N Arnolds Way, Hoodsport, WA 98548 (1) (a)A discussion of general geologic conditions in the vicinity of the proposed development, Located on page(s) Pgs 1 - 3 (b) A discussion of specific soil types, Located on page(s) Pg 4 (c) A discussion of ground water conditions, Located on page(s) Pg 4 (d) A discussion of the upslope geomorphology, Located on page(s) Pq 4 (e) A discussion of the location of upland waterbodies and wetlands, Located on page(s) Pg 4 (f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records. Located on page(s) Pg 4 (2) A site plan which identifies the important development and geologic features. Located on Map(s) 1 thru 6 (3) Locations and logs of exploratory holes or probes. Located on Map(s) Sheets 3 &4 (4) The area of the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall be delineated (top, both sides, and toe) on a geologic map of the site. Located on Map(s) Sheets 3 &4 (5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which incorporates the details of proposed grade changes. Located on Map(s) Sheets 5 &6 (6) A description and results of slope stability analyses performed for both static and seismic loading conditions. Analysis should examine worst case failures.The analysis should include the Simplified Bishop's Method of Circles. The minimum static safety factor is 1.5,the minimum seismic safety factor is 1.1, and the quasi-static analysis coefficients should be a value of 0.15. Located on page(s) Pq 5 (7) (a) Appropriate restrictions on placement of drainage features, Located on page(s Pq 5 Rev. February (b) Appropriate restrictions on placement of septic drain fields, Located on page(s) Pq 4 (c) Appropriate restrictions on placement of compacted fills and footings, Located on page(s) Pq 6 (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) Pg 6 (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes Located on page(s) Pq 6 (8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the method of vegetation removal. Located on page(s) Pq 6 (9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific mitigating measures to be implemented during construction to protect the slope from erosion, landslides and harmful construction methods. Located on page(s) Pq 5 (10) An analysis of both on-site and off-site impacts of the proposed development. Located on page(s) Pq 6 (11) Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths Located on page(s) Pq 6 (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation. Located on page(s) Pg 6 (13) A site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site Located on Map(s) Sheets 1 -6 ,1 Zu '� hereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local conditions. I also certify that the Geotechnical Report, dated 4/14/2025 and entitled WAsk Dale & Sharron Tahja Geotechnical Report \a' meets all the requirements of the Mason County Resource Ordinance, �'Q. Geologically Hazardous Areas Section, is complete and true, that the SERA assessment demonstrates conclusively that the risks posed by the sfONAL�� landslide hazard can be mitigated through the included geotechnical design recommendations, and that all hazards are mitigated in such a manner as to prevent harm to property and public health and safety Page 2 of 2 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report. TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 Mason County DCD Planning Division A T WA 615 W Alder Street Shelton, WA 98584 Dale& Sharon Tahja 2450 W Deegan Road 30� � Shelton, WA 98584 �ss"t- i, (360)463-8023 Re; Starr White Addition Geotechnical Report 110 N Arnolds Way Hoodsport, WA 98548 Parcel No.: 32331-21-00740 County Case No.s: INTRODUCTION I was contacted in early Spring of this year by my brother,Dale Tahja who is in the process of developing the property as a residential property. The property is located in the easterly foothills region of the Olympic Mountain Range. A plan set is appended to this report which shows the locations and layout of the Tahja property with existing and proposed improvements. I've visited the property on several occasions in the past to collect topographic information and verify measurements and feature locations. Measurements were made using a Sokkia model No. 8047-55 inclinometer, 100 foot and 200 foot long fiberglass surveyor's tapes and other field equipment common to surveying. Software employed in creating a site plan and writing this report included AutoCAD 2024, a GALENA Slope Stability Analysis software and Microsoft Office Word 2003. Contouring outside of the Tahja property was derived from Mason County's GIS website mapping. The property is located on a hillside with an overall average slope of approximately 28%.A slope measuring 42%exists roughly 100' southeast of the property's southeast property line. With slopes on or within 300 feet of the property exceeding 40%with a height of 10 feet or more,Mason County requires a geotechnical report to be developed to address stability issues relating to the property's development. The following thirteen elements are required by Mason County to be addressed in geotechnical reports prepared to comply with Mason County's Critical Resource Ordinance Sections 17.01.100 through 17.01.104. 1. SURFACE AND GEOLOGIC CONDITIONS: The central area of the site has been cleared of trees and underbrush where a residence will likely be constructed. An Onsite Septic System(OSS) is likely to be designed and installed on the lower portion of the property below the access road,Arnolds Way. The areas outside of the central cleared area are covered with light vegetation and young to medium age second growth conifer trees and underbrush. File:C.Wrojects1Tahja1Geo-RpAPrc1 74 1 of 6 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 Inspection of the Washington Interactive Geologic Map below finds the property located in an area between the Olympic Mountain foothills to the west and Hoods Canal to the east. The map reveals that the upland soils are classified as Qgo& Qga fully surrounding the Tahja property. cam \ as ago CumGFM r G _ q E. � I E+r IN Oap 09t r \ C�a >rf ru.10rlala>.i Nw1.X1WUi�"=z4Mi4a .U%awceumj%k Lose Mli.c.a+aa�f1°Iti+iworar.l--l;l�c�intharial avtr•1-7ipically rAwh in mdcrnch c.etod-mmfdcd ilairl and ti3nd JDd rlat'rl and Lw lrint:CIaL silt,and sand dtgositrd during sandu-nh14"undem T-:udfirer-rranodcxrrn-tnaznxcInhnharr 1,11 xancd minnrr.w-rn-,711v nxrthctrrrrcncnanur rla b:.t,-gv,:WJ, the a&-awr of fl ao rs_-�'nits mmmnnh•thick well sort.:&mW 4%mumnir Frank:and tnma nphic rocker thu ul'w tr ale ann a fine minrd,aah inii-A"ewd exw-rr sand-Varrl_and cobbles and >,rmw drrrnncd K Ill_P46 kdr,*the r'4ddlcran r-Lu3ff:also err sift r p-T lar de losiis at ihcir base:ffm comin nmrlacial scdi- lains can inr amcmtns'4l.ralh dmvMt'ra»cm Kummxm basalt and in the Ahw t Lchal»CMA I Alk-:eennal Casc:adc R.KWV- nwi ls-acwx-dl h-ovcYlam ire tiff. dem ed andmnw ch ac n-rscalh*tacks,d gray 4 hrrr fresh 4r hruam whirr a4 i r r+ 7=1h in rr<rlarnddn �an ruainal arca huff siaiamr nrarthr rr.uud uft"-fire san&ah and clay.tee amur kwal tnr ounk srdiausn,h:nnrnr rrlwj dh Van ru rarahilm to det tar JML'd 11"Unr akinr nnih+dry r6Aallnc xith hTlrr TkTr a- hilm-_Twins and rrnrralilr rncrnrh io»rld anal]w rno&rxr qu:rr attics.�_rnonrtdaata:.rn rrwrll uarsadidaWd k Lwt:c_m..irratrh.- w,arlt mmndod rla.2,mrtsah nnuratherrd%vh rye wr-vherrd rruvvL-d chyle 1hwlnrvs a arks and is.ntl uxll kna n:mna cm n- nmrnit mimfwv omu-ash chanruls s. =M vnn or thnwrh WE File:C:Wrojects7ahjalGeo-RptWrc174 2 Of 6 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 As the portion of the Mason County GIS o the following page reveals,the Webb property is located in the vicinity of "unstable slopes"in the southeasterly corner of the property. The majority of the parcel is identified as having"stable" slopes. My mapping of the property found several areas of the property that contained slopes exceeding 40%which requires that a geotechnical report if the slopes are within 300 feet of the property's boundary. All 4 parcels are within 300 feet of what the County terms hazardous slopes. Three fault lines are within approximately I l miles of the Webb property. The furthest is approximately 11 miles southwest of the Webb property and courses through Lake Cushman.A second fault line courses through Dow Mountain and is approximately six miles southwest of the Webb parcel. The nearest fault line nuts roughly north to south near the middle of Hood Canal and is roughly one and a half miles east of the Webb property. The presence of these features does not represent an unusual hazard,and standard seismic analysis of the site is intended to anticipate potential tectonic impacts. Washington State Ecology Coastal Atlas records were inspected,but no stability issues were apparent near the Webb property. Geologic_Hazard Layers Slope Stability-DOE Coastal Zone Atlas . Unstable-recent slide Unstable-old slide . Unstable slope 0 Stable slope . Modified Intermediate slope t r I I i I I I 1 ti r - I File:C:Wrojects1Tahja1Geo-RptWrc174 3 of 6 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Further inspection and soil analysis finds the soil to be classified under the Unified Soil Classification System(USCS)as a GP-SM soil division. Inspection of the exposed hillside along Arnolds Way found the surface soil layer to be fairly homogenous most of the height of the driveway banks along Arnolds Way with a high percentage of clay, silt and sand intermixed with large cobbles ranging from 2 to 8"in diameter with a small number measuring up to a foot on their long axis. No wetlands or upland waterbodies were found on or near the property. The groundwater is assumed to be approximately 20' below the ground's surface which I modeled the phreatic surface in my stability analysis. The upslope geomorphology of the property may be described as hilly or mountainous. 2. SITE PLAN WITH IMPORTANT DEVELOPMENT AND GEOLOGIC FEATURES: A site plan showing the general topography of the area surrounding the Tahja property is attached in the appendix which shows the locations of existing features and the location of the proposed work. 3. LOCATIONS OF LOGS OF EXPLORATORY HOLES OR PROBES: Soil probe locations are shown on plan sheet 2 which also shows the approximate depth to the compacted consolidated soils underlying the site. 4. AREA OF PROPOSED DEVELOPMENT& BOUNDARIES OF HAZARDS, BUFFERS, AND SETBACKS: The attached site plan shows the proposed location of the conceptual residence, onsite septic system and the property layout. Stability analysis of the 46%f slope near the east areas of the property found Factors of Safety above the County's minimum requirements. The slopes exceeding 40%near the Tahja property vicinity are identified on the attached site plan as "HAZARD AREAS"as required by Mason County's critical resource ordinance. The location of the conjectural residence is in a small area sloping at less then 40%which I consider acceptable. The attached site plan has the hazard areas(areas containing slopes greater than 40%) and the 50-foot hazard area buffer areas delineated. 5. CROSS SECTION WITH PROPOSED GRADE CHANGES: Cross section views of the property are provided in the attached plan sheets as well as part of the GALENA Stability Analysis Print-Out.No grade changes are proposed for any of the slopes exceeding 40%on or near the Tahja property at this time. 6. SLOPE STABILITY ANALYSIS: The steep slopes on the property in their present condition appear stable. The conceptual building shown on the attached plans shows no discernable irregularities, settlements, fissures,or evidence of consolidation problems. The level areas of the Tahja property typically contain an approximately 3 to 4' deep soil composed of the weathered glacial till underlying the site. The soil layers beneath the surface soil were found to be overconsolidated clays& sands with a minor percent of cobbles and File:C.1Projects1Tahj&Geo-RpAPrcl74 4 of 6 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 boulders in the soil matrix.Unified Soil Classification System typing places the soil in a GP- SM category. The site's soils were modeled with the shallow soil having a soil unit weight of 123 lbs/ft3, and the deeper soils with a 125 lbs/ft3. A phi angle of 38'was used for shallow soils and a phi angle of 39'was used for the glacial till layer. A cohesion character of 150 lbs/ft was used for the weathered surface soils and 300 lbs/fl for the consolidated glacial clay/till layer(s). A phreatic surface is modeled 20' below the ground's surface. The slope geometry and soil characteristics provide a factor of safety for the site in a static and a dynamic analysis that exceed the County's minimum safety requirements. Analysis of the site indicates Factors of Safety of(Bishop 3.18, Spencer-Wright 3.60) in a static condition and(Bishop 2.33, Spencer-Wright 2.42)under dynamic conditions. 7. RECOMMENDED SETBACKS &DRAINAGE: The slope stability analysis indicates that the slopes present on or near the Webb property are currently stable in their present geometry and condition and do not represent a landslide or geological hazard to the existing Tahja property features,or the proposed development of the property for residential use. I feel a 5' building recommendation is acceptable and will enable the owner to locate the structure in the location shown on the plans. Stormwater shed by a residential building will add a very modest volume of runoff and I feel there is ample room and vegetation between the conceptual residence and the property boundaries to adequately treat and infiltrate the structure's roof runoff. The existing drainage for the site is and has been adequate,so no alteration of the existing stormwater control features appears needed. 8. CLEARING, GRADING,AND VEGETATION MANAGEMENT: The property is already in a semi-cleared condition and drain-field has been cleared in preparation of a septic system design.No compacted fills or excavated cuts are necessitated by the proposed improvements.No formal planting plan appears needed for the completed development which is being maintained in a semi-natural vegetated condition. 9. EROSION AND SEDIMENT CONTROL: Inspection of the Soil Survey of Mason County found the site to be located in an area with Hoodsport soil type(s),which are not identified in the County's Critical Resource Ordinance as susceptible to severe erosion when disturbed so a formal Erosion and Sediment(E&S) Control Plan is not required to be prepared for this site. The site already has an access route installed to the property from Arnolds Way which is stable in its present condition.Upon completion of a residence,bare soils should be seeded to grass and any temporary erosion and sediment control features installed to protect the adjacent neighboring properties. 10. ON-SITE AND OFF-SITE IMPACTS: Construction and completion of the anticipated residential improvement of the property are not expected to result in any adverse on-site or off-site impacts. File:C.-WrojectslTahj&Geo-RplWrcl 74 5 of 6 4/14/2025 TAHJA ENGINEERING,Inc. PO Box 235,Hoodsport, WA 98548 (360) 877-9512 11. SPECIFICATIONS OF FINAL DEVELOPMENT Upon completion of the residential development of the property,the grounds can be expected to be maintained as a permanent/seasonal residence,with a fairly natural yard. Other undeveloped areas of the property are expected to be maintained in a natural vegetated state. 12. RECOMMENDATIONS FOR THE PREPARATION OF STRUCTURAL MITIGATION OR DETAILS OF OTHER PROPOSED MITIGATION: Modeling of the slopes in the proximities of the conceptual residence locations indicates that the structures are or will be safe. The lot can be developed without the need for structural fills. 13. SITE PLAN WITH THE LOCATION OF EXISTING AND PROPOSED DEVELOPMENT ON THE SITE: site plan is attached as an appendix to this report and made a part of this report along with the cross-section views of the property and the stability analysis printout. Summary& Conclusions: The Tahja property,though in the vicinity of slopes identified as unstable can be developed according to the owner's plans with minimal concern about the site's stability. Please feel free to contact me if there are any questions or concerns regarding this report or my findings. Sincerely, Alan A. Tahja, Attached: Geotechnical Report Checklist Plan Views& Cross Section Sheets GALENATM Stability Analysis Printout File:C.VProjects1Tahja1Geo-RpAPrcl74 6 of 6 4/14/2025 e �j b Tr. 77 ITr. 7 Tr. 80 "� y >, G.L.6 t 5 N �. OF Tr. 76 Tr. 75 \✓ b � N �j Tr. 59 I I b �- 5 r. Q G.L.6 1 O+{'S EOISTEg � 57�� ' OOVT LOT EX PTN W OF E 430 Qi Q U& S'IONAL E� S 35/28,S 53/226227 aC w b ti J 000 '"3a v1 + I V k &�t7l ell 00 r r 4 f_ r 7 N ob� HOOD b CANAL ' N � ti y I Restawfiile '' - scALE: V=4ao' • '.Park 1 0 105 210 315 420 n ` �+y ~ y W E y V! S Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN "" Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd Hoodsport, WA 98548 Shelton, WA 98584 2 of 6 Mason Co.Prcl No.s: 32331-22-00740 (360)877-9512 (360)426-5940 � 8 CIS N II W � H U � oo -TIN 0 T� 00, w `s cV N t-„ A:X- \ vo ti 1 " JGJJI-GL-VV/`FV PL-239' PL- 193' PL-230' e 0 Tr. 77 I I Q'of N z Bldg Site o y I I W E N �. Conceptual Bldg I I Sites I - 0 ,Q� 76 4 - I N I ISTS Bldg Site I �`SsjO AL PLO I Tr. 80 a b I Pump Cham er a- „ & Septic Tan c Conjectural Waterline w b y 1— Route —430' o W w� yvn — _ _ _. Arnold's Way �� N \ Survey Pin 00, 4ti ti I � ^w ytib Tr. 60 a End of existing 2" PVC A_ 2 Schdl 40 Line & Conjectural l Conjectural a Connection between Canal 4 3 \ 59 Connection Lo i Mutual System & Existin Tr. \ Tahja System. with Back- w \ Prevent' D is , \ Power Vault Met & oster 1 Tr. 53 & 56 1 �fi SCALE: 1"=80' 0 20 40 60 80 Rev# Description DaW TAHJA ENGINEERING,INC. SITE PLAN Alas Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd HoodvoA WA 98548 Shelton, WA 98584 4 of 6 Mason Co.Pncl No.s: 32331-22-00740 (360)877-9512 (360)426-5940 w - o.._ zN s W . ` •1 -` `k9z- 1•+1 f� - k, �• �� a f ti- �, � ° 4• GJ Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN Pi m' Alan Tahja,P.E. Dale&Sharon Tahja Tahja PO Box 235 2450 W Deegan Rd HoodspoA WA 98548 Shelton, WA 98584 5 of6 Mason Co.Pncl No.s: 32331-22-00740 (360)877-9512 (360)426-5940 8 u .a m w a 63 o 0 + 00 0 0 + 0 4 0 a o H 250 260 ,o °O 270 ri1 H � � 280 6151 00 0 _ o 300 o 31� M N p 320 " r` fH,�Q ± o� 1 �b , . _; . _ . _ _. ._ .._. _ : .. s � f� _. ,. _ - -- . . _ _ _. : ,. _ -.. •t ,- � .. __.. .�._:a-.. i- '- y K'. .._ .. _ _ ._ .. _ r �_ . -V�Y�.:c _ .. .� .� �, �. A _,. •� _ � •A jam,� +y' �'i ' _ .. .. J r F i F 7 � \ 'x. v � .. ._ , i i `. 1 C b � 400 SCALE: P=20' c 0 5 10 20 o 390 0.160► w b W b 380 •---•—•---•-------•----------- -----------------•-----•-------------•--------------- 5'Building Setback from banks over 5'Wl 370 TT'. 74 �F WA 1 b 46i 360 L S�One `� w :-g •-----------•-----------. ... Glacial Till Below 4' \ �EGIISTE0 GP-SM Shallow < 4, LZ's 350 `S"ONAL 340 G� 330 ar face n 320 310 $ aoa C,m� 300 60 80 100 120 140 160 180 200 Project Analysis 1 GALENA v.,jon7.2 File:C:IGALENA1Dales TR 74 with Restraints 3.gmf C GALENA Model Cross Section "A" TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 74 with Restraints 3.gmf Processed: 27 Feb 2025 12:06:30 DATA: Analysis 1 STATIC Material Properties (2 materials) ------------------- Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties ---------------- Unit weight of water: 62.40 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles) ----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points) ------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points) ---------------- 50.00 340.00 140.00 305.00 Failure Surface --------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Variable Restraints ------------------- Parameter descriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface ------------------ Critical Failure Surface Search using Multiple Circle Generation Techniques GALENA 7.2 Analysis Results Version: 7.2.3.05 Licensee: Tahja Engineering, Inc. File: C:\GALENA\Dales TR 74 with Restraints 3.gmf Processed: 27 Feb 2025 12:23:03 DATA: Analysis 1 Material Properties (2 materials) ------------------- File:C:IProjectslTahj&Geo-Rpt 1 of 4 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties ---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles)----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points) ------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points)---------------- 50.00 340.00 140.00 305.00 Failure Surface --------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Variable Restraints ------------------- Parameter descriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface ----------------- Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 3.612 Analysis Summary There were: 122 successful analyses from a total of 125 trial failure surfaces 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Critical (minimum) Factor of Safety: 3.18 Results Summary - Lowest 99 Factor of Safety circles ------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FoS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 3.184 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 3.214 File:C:IProjectslTahjalGeo-Rpt 2 of 4 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 FDsRynpms --IW >1AD7 r1M >12D -1A0 >IAD HalendKeys Bata ataa me 3fa[a 3711 ia.13.11=PLI r 4' »9 gwLum <4' :{4[9 331a 32p aria Amk= I WkMWSLUEy 3W ►ooW Bdaup s-pdod saacr_QwLdw so eo aao asp 1� afU 18p 2W kes�As car.eiIA ....,> f]tc2I F2ckz d S3W.. Z33 „cGMDWJAeam7,.ft AaioEilg Wigi,YIG ATA: Analysis 1 Material Properties (2 materials) ------------------- Material: 1 (Mohr-Coulomb Isotropic) - GP-SM Shallow < 4' Cohesion Phi UnitWeight Ru 150.00 38.0 123.00 Auto Material: 2 (Mohr-Coulomb Cu increases with depth) - GP-SM Glacial Till Cohesion Phi PI UnitWeight Ru 300.00 39.0 0 125.00 Auto Water Properties ---------------- Unit weight of water: 62.400 Unit weight of water/medium above ground: 62.400 Material Profiles (2 profiles) ----------------- Profile: 1 (2 points) Material beneath: 1 - GP-SM Shallow < 4' 50.00 380.00 200.00 380.00 Profile: 2 (7 points) Material beneath: 2 - GP-SM Glacial Till 50.00 356.00 97.40 356.00 119.10 346.00 137.50 336.00 149.10 331.00 168.10 326.00 200.00 321.00 Slope Surface (9 points) ------------- 50.00 360.00 97.40 360.00 109.64 355.00 119.00 350.00 130.60 345.00 137.50 340.00 149.10 335.00 168.10 330.00 200.00 325.00 Phreatic Surface (2 points) ---------------- 50.00 340.00 140.00 305.00 File:C:IProjeets1Tahj&Geo-Rpt 3 of 4 4/14/2025 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Failure Surface --------------- Initial circular surface for critical search defined by: XL,XR,R Intersects: XL: 97.00 YL: 360.00 XR: 169.00 YR: 329.86 Centre: XC: 140.85 YC: 363.67 Radius: R: 44.00 Earthquake Force ---------------- Pseudo-static earthquake (seismic) coefficient: 0.150 Variable Restraints ------------------- Parameter descriptor: XL XR R Range of variation: 5.00 5.00 5.00 Trial positions within range: 5 5 5 - -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- RESULTS: Analysis 1 Bishop Simplified Method of Analysis - Circular Failure Surface ------------------ Critical Failure Surface Search using Multiple Circle Generation Techniques Initial failure surface approximation - Factor of Safety: 2.645 Analysis Summary ---------------- ---------------- There were: 122 successful analyses from a total of 125 trial failure surfaces 2 analyses terminated due to unacceptable geometry 1 analyses that failed to produce a valid result Critical (minimum) Factor of Safety: 2.33 Results Summary - Lowest 99 Factor of Safety circles ----------------------------- Circle X-Left Y-Left X-Right Y-Right X-Centre Y-Centre Radius FoS 1 99.50 359.14 166.50 330.42 144.38 371.32 46.50 2.329 <-- Critical Surface 2 98.25 359.65 166.50 330.42 143.40 370.78 46.50 2.352 3 99.50 359.14 167.75 330.09 144.61 370.43 46.50 2.365 4 99.50 359.14 166.50 330.42 143.57 369.43 45.25 2.378 5 97.00 360.00 166.50 330.42 142.37 370.17 46.50 2.380 6 98.25 359.65 167.75 330.09 143.62 369.84 46.50 2.390 7 99.50 359.14 169.00 329.86 144.81 369.57 46.50 2.401 8 98.25 359.65 166.50 330.42 142.56 368.82 45.25 2.407 9 95.75 360.00 166.50 330.42 141.27 369.48 46.50 2.415 10 99.50 359.14 167.75 330.09 143.78 368.47 45.25 2.419 11 97.00 360.00 167.75 330.09 142.58 369.19 46.50 2.422 12 98.25 359.65 169.00 329.86 143.81 368.95 46.50 2.430 13 99.50 359.14 166.50 330.42 142.71 367.44 44.00 2.437 File:C:IProjects7ahjalGeo-Rpt 4 of 4 4/14/2025 -- _ := �. • �-y �. :7 ._ �H+ �''� �' i#:: L- - '� f� - ,.� ._ - .. - ,��, r .. � �� _ �;" �. 1 !-.