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Home My WebLink AboutGEO2016-00001 for BLD2016-00017 - GEO Geological Review - 7/14/2022 , owd I RECEIVED C (- JAN 0 8 2016 426 W. CEDAR ST. 80 Mason County Department of Community Development PLANNINGSubmittal Checklist For a Geotechnical Assessment Instructions: This checklist must be submitted with a Geotechnical Report and completed, signed, and stamped by the licensed professional(s)who prepared the Geotechnical Assessment for review by Mason County pursuant to the Mason County Resource Ordinance. If an item found to be not applicable, the report should explain the basis for the conclusion. Applicant/Owner Steve& Patricia Marksteiner Parcel# 32304-11-90953-- Site Address — 880 N Hamma Ridge Drive, Lilliwaup,Washington 98555 (1) A discussion of general geologic conditions in the general vicinity of the proposed development, with geologic unit designation based on reference maps. Located on page(s) P2s 1 thru 2 (2) (a) A discussion of the groundwater conditions at the site, Located on page(s) Page 2 (b) A discussion of the estimated depth to water Located on page(s) Page 2 (c) A discussion of the quantity of surface seepage Located on page(s) Page 2 (d) A discussion of the upslope geomorphology Located on page(s) Page 2 (e) A discussion of location of upland waterbodies and wetlands. Located on page(s) Page 2 (3) The approximate depth to hard or competent soil, e.g. glacial till or outwash sand. Located on Map(s) PaEe 2 & Plan Sht 2 (4) A discussion of any geomorphic expression of past slope instability(presence of hammocky ground or ground cracks, terraced topography indicative of landslide block movement, bowed or arched trees indicating downslope movement, etc.). Located on Map(s) Nee 3 (5) A discussion of the history of landslide activity, as available in the referenced maps and records. Located on Map(s) Paee 3 (6) An opinion on whether the proposed development is within the landslide hazard area or Its associated buffer or setback and the potential for landslide activity at the site in light of The proposed development. Located on Map(s) Nee 3 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Assessment. Page 1 of 2 Form Effective June 2008 (7) A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site conditions and the proposed development of the subject property. Located on page(s) Nee 3 (8) If the presence of a hazard is determined within 300 feet of the proposed development, then the following are delineated on a geologic map/site map: (a) the area of the proposed development Located on Maps None Found or Observed (b)the boundaries of the landslide hazard area (top, both sides, and toe), Located on Map(s) None Found or Observed (c) the associated buffers (top, both sides, and toe). Located on Map(s) None Found or Observed (d) building or other setbacks(top,both sides, and toe). Located on Map(s) None Found or Observed (9) 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 Maps Plan Sheets 1 & 2 I, Alan A.Tahia,P.E. 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 certrfy that the Geotechnical Assessment, dated 6/22/12 , and entitled Steve& Patricia Marksteiner Geotechnical Assessment meets all the requirements of the Mason County Resource Ordinance, Landslide Hazard Section, is complete and true, that the assessment demonstrates conclusively that the risks posed by the 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. (Signature and Stamp) .L ' NA �SSI0 hrAY,�G1 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Assessment. Page 2 of 2 Form Effective June 2008 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Mason County DCD PO Box 279 Shelton, WA 98584 Steve& Patty Marksteiner 5530 Sedalia Tr# 631 Benbrook, TX 761261811 (817) 914-0346 RE: Geotechnical Assessment Mason Co. Case No.s SWG2006-00954 Mason Co. Prcl No. 32304-11-90502 INTRODUCTION The Marksteiners are in the process of developing their property in the community of Hamma Ridge Drive with a single family residence. The property has been cleared and partially level at some past date, and has an existing septic system installed on the property in the location indicated on the attached site plan. Slopes on the property were investigated as well as slopes within 300 feet of the property. The property itself contains gentle slopes, typically measured between 10 and 20%. The slopes west of the Marksteiner property were investigated, and though found to exceed 40% in gradient,they were also found to be 400' plus away from the Marksteiner's property boundaries. Mason County's Critical Resource Ordinance requires geotechnical investigation of any properties with slopes exceeding 15% and more than 10 feet of vertical relief. No thresholds for a geotechnical report were found, but the property's slopes do warrant that a geotechnical assessment document be prepared to dispel the need for a geotechnical report. The slopes on and around the Marksteiner property place it in a category"b"classification under Mason County's Resource Ordinance requirements(MCRO Section E.1). Category b properties are required to be investigated under the requirements of Mason County's Geotechnical Assessment report requirements. The assessment is intended to investigate stability issues relating to the proposed development, and to determine whether a more aggressive Geotechnical Report is needed for the property's development. The following nine elements are required to be addressed in geotechnical assessments prepared to meet the County's geotechnical assessment requirements. 1. Discussion ofgeologic conditions: The site is located in the Hamma Ridge Community approximately 7 miles north of Hoodsport, Washington on the Olympic Mountain foothills situated above and to the west of US Highway 101. The general lay of the land has been described in the introduction as generally sloping at an average gradient of roughly 16% from the property's south corner to its north corner. Probing with a 4 foot rod found a moderately dense loamy sand covering most of the site to a depth between half a foot to three feet deep. Probe locations and depths to the underlying firm hard soil layer are shown on plan sheet 2. File:C:IProjec&Marksteiner Geo-Assn:nt I of 4 6/22/2012 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Inspection of the Washington State Interactive Geologic Map indicates that the site soils are Continental Glacial Deposit of the Fraser Glaciation,Vashon Stade described as soil category Qgt, which are described as follows: Till, late Wisconsinan(Pleistocene)-- Unsorted, unstratifted, highly compacted mixture of clay, silt, sand gravel, and boulders deposited by glacial ice of the Puget lobe; gray-, may contain interbedded strati- fied sand, silt,and gravel; sand-size fraction is very angular and con- tains abundant polycrystalline quartz which distinguishes this unit from alpine till; cobbles and boulders are commonly striated and(or) faceted; although unweathered almost everywhere, may contain cob- bles or small boulders of deeply weathered granitic rock. Inspection of the Soil Survey Map of Mason County found the soils listed as a Hoodsport soils which are described as a moderately shallow soil layer resting on top of a cemented glacial till layer, generally located on 10 to 15%slopes. The Hoodsport Gravelly Sandy Loam soils(Hg&Hf)are not listed under Mason County's Resource Ordinance as an erodable soil. Inspection of the Washington Coastal Atlas, landslide hazard section,found the site located in an area identified as"stable". The project area lies at the base of the Olympic Mountain Foothills which can be characterized as a mix of ravines, valleys, and a gentle sloping shelf which connects the foothill plateau with the steep Olympic Mountains to the west. The immediate upslope geomorphology of the Marksteiner property may be described as"hilly". The Marksteiner property is located on a north trending knoll which is surrounded to the west and north by steep slopes. The ground south of the Marksteiner property continues to ascend approximately 30 vertical feet over a distance of approximately 270-feet where it is fairly level over a distance of roughly 200-feet where it then begins a southerly descent. 2. Discussion of groundwater conditions at the site: The general slope of the property helps keep the property well drained and dry.No evidence of rutting or stormwater channeling on the Marksteiner or neighboring properties were evident during site visits to the property. The property is located fairly high(600-feet+)above the Hood Canal Sea Level elevation. No indications of groundwater surfacing or wetlands were found on or around the property. The groundwater elevation likely coincides with the Hood Canal sea level elevation. No surface seeps, flows or standing water were found anywhere near the site. 3. Approximate depth to hard or competent soil: Soil probe locations are shown on plan sheet 2 along with measured depths to the underlying hardpan layer. Most of the undisturbed areas have a moderately dense soil layer approximately 30-inches deep overlying the strongly cemented glacial till substrate. The Conjectural Building Area shown on plan sheet 2 was found generally to have a relatively thin moderately dense soil layer overlying the underlying/supporting glacial till layer. It appears soils graded off the building area were shoved towards the north and/or may have been used to provide additional soil cover depth over the septic drainfield already installed on the property, apparently in 2007. File:C.lProjectslMarksteinerlGeo-Assmnt 2 of 4 6/22/2012 TAHJA ENGINEERING,Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 A conjectural residence is shown on the attached site plans. The house location has good bearing soil typically at a depth of less than 30-inches. Footings for proposed structures should bear on the underlying hardpan layer,or on fill material placed as a structural fill in 6 to 8-inch lifts compacted to 95%or greater of the soil's maximum compacted density. The onsite soils may be used as.structural fill provided it is placed with the soil's proper moisture content to achieve the target compaction. 4. Discussion of geomorphic expression of past slope instability: The Marksteiner property and residential properties surrounding the site display no evidence of recent slope instability or earth movement. 5. Discussion of the history of landslide activity in the vicinity. Inspection of the Coastal Zone Atlas covering this area reveals that the upland area surrounding the Marksteiner property is stable. Areas of the access road(N Hamma Ridge Drive)have experienced varying degrees of slope movement and small scarping,but most of this activity is located in the outwash soils located along Highway 101 near the sea level elevation. A large landslide developed approximately a mile southwest of the Hamma Ridge Community on Highway 101. The highway was re-routed through this area and reconstructed and has remained stable since then. 6. An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or setback: The Marksteiner property is located approximately 400+feet away from the nearest potentially unstable slope(s)(slopes with a gradient greater than 40%), and the property itself reveals no evidence of stability problems, so I am lead to an opinion that the proposed property improvement(s)are located outside of a hazard area or any associated buffers or setbacks. 7. A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site conditions and the proposed development ofthe subject property: A geotechnical report level investigation of the property does not appear warranted from the observations and findings already made. 8. If the presence of a hazard is determined within 300 feet of the proposed development, then the area of the proposed development, boundaries of the hazard, and associated buffers and setbacks shall be delineated(top, both sides, and toe)on a geologic map I site map. No hazard areas or slopes exceeding 40%were found on or within 400+feet of the Marksteiner property. 9. 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: This report includes a site plan which contains the required information. The existing 3 Bedroom Onsite Septic System(OSS)and the approximate location of a proposed residence are shown on the attached site plan. File:C:IProjectslMarksteinerlGeo-Assmnt of 4 6/22/2012 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 This concludes my assessment of the Marksteiner property located in the Hamma Ridge community of Mason County, Washington. In brief, it is my opinion that the property and proposed improvements are not in jeopardy from instability or earth movements,and should be allowed to proceed without additional landslide stability investigation or reporting. Please feel free to contact me if there are any additional concerns or issues required to be addressed by Mason County's Resource Ordinance 17.01.100— 104. Sincerely, w �01 S ER SIGNAL ECG Alan A. Tahja, P.E. Attached: 2 page plan set. Geotechnical Assessment Checklist File:C:IProjectslMarksteineriGeo-Assmnt 4 of 4 6/22/2012 o � � 0 Existing / w p' Residential Features o {�9 0 Existing b \ Residential IO' / \ ��ij� Features 4 y Existing Onsite Septic ra j/ System Tank&Drainfield \ p, 00 kA N Proposed 10• \4k, t�'1 ae�, Residence \off ti S// •3z,. Location / \\a oo Conjectural � o \•F y \ Driveway o o 08. \ryarae Electric Meter 'be a" 06" - Water&Phone ZO` O lane \S A. v�of wasy�,F a �7 l � iQ• t;r✓ ,�, a�eJ �e0 � � � 3D784 y n tv `SS'IONAL S SCALF: 1"=50' <u rn 10 30 50 �J n Rev# Description Date TAHJA ENGINEERING,INC. SITE PLAN h*`b Alan Tabja,P.E. Steve&Patricia Marlcsteiner Markstainer PO Box 235 5530 Sedalia, TR 631 Hoodsport; WA 98548 Benbrook, TX 76126 1 of2 Jefferson Co.hW No.: 32304-11-90502 (360)877-9512 (817) 914-0346 `a ` FAO e o \ e� / Cp m / ON i `8 / o m 4170 Va