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HomeMy WebLinkAboutGEOtechnical Report Existing Bulkhead - GEO General - 7/25/2019 PLANNING GEmECHNICAL ENGINEERING REPORT FOR G EXISTIN BULKHEAD 61 Gull Place, Hoodsport, WA 98548 (Parcel #: 4220-5-552-000-51 f Prepared for: Scott and Kristin Merritt 410 214"' Ave S.E. Sammamish, WA 98074 Prepared by: MET Engineering, PLLC 1018 E. Wishkah St. Aberdeen, WA 98520 (360) 310-0270 cell (360) 289-0958 bus (360) 861-8493 fax e-mail: �i�lurtaurt���l.cE�r� Contact: Steven P. Morta, P.E. -o wns O�Pj, July 25, 2019 4:1 A� f• ,4 w f &,3075$�p C/STIE S/0N LEa July 25, 2019 Page I of 6 MET Elad;ineerinIf, PLLC To: Mason County Department of Community Development 615 W. Alder St. Shelton, WA 98584 (360)427-9670 To: Scott and Kristin Merritt 410 24'h Ave S.E. Sammamish. WA 98074 Subject: GEOTECHNICAL ENGINEERING REPORT for Property Located at 61 Gull Place, Hoodsport,Mason County,WA 98548 (Parcel#: 42205-52-00051) Introduction On Tuesday February 27, 2018 this geotechnical engineer licensed as a professional civil engineer in the State of Washington visited the above site to evaluate the overall stability of the site including the residence and Lake Cushman shoreline below. A detailed slope stability analysis was also completed which takes into account the steepness of slope. the type of soils that makes up the slope material, the cohesion of the soil as well as the cohesion of the soil itself. This geotechnical engineering report provides the rational for the need of a retaining wall. i.e.,a bulkhead. to at least significantly slow down the erosional process that is occurring on the shoreline primarily due the fact that Lake Cushman is a reservoir. So, when power is needed there is a drop in the lake level so that the turbines below can generate electricity. And when poser is not needed the lake will have a chance to fill back up. This geotechnical engineering report provides the rational for the need of a bulkhead to protect the residence above as well as protecting the shoreline directly below the residence to increase overall longterm slope stability. General Geologic and Site Description The general site is located on a relatively steep hill side with slopes of 30 to 50% near the top of the hillside where the residence is located and then the slope increases to at least one vertical to one horizontal. i.e., over a 100% slope and the placement of a bulkhead at the toe of the slope will reinforce the slope and slow down the erosional process at the shoreline and also protect the long tern stability of the residence near the top of the slope It is important that all remaining trees and vegetation remain undisturbed since their root systems help to reinforce the gravelly sandy loam soils and helps to dewater the slope through Wishkah tit.. Aherdeell. 6'nshingtom ,u (300)289-0958 Bits_(360)3111-02'0('01 S'Nlortatw pol.com July 25.2019 / 6 Page 2 of 6 MET En irreer�ing, I.q L (' the process of evapotranspiration where the extensive root systems help to absorb moisture from the slope and evaporate this moisture back into the atmosphere through their limbs. If one of the trees happen to adversely affect the view, it is recommended that the lower limbs of the tree can be removed rather than topping the tree. Delimbing the lower third of the tree is less detrimental to a tree versus topping which can affect the health of the tree. Geology Most of the Pacific Northwest area had been covered with extensive glaciers that advanced and receded at least four times in the last 10,000 to 40,000 years ago leaving sands. silts, and gravels during the last recession. Also, prior to this period there had existed an inland sea that existed several million years ago and left compacted silt and sand deposits. The last glaciation advance and recession resulted in the formation of Puget Sound due to the scouring action of the thick ice. Evidence of these glaciers can be seen in the smooth pebbles. cobbles. and boulders that were ground smooth by the sandpaper-like action of the glacier ice and the broken and fractured rock in the glacier's path. The last glacial advance and recession took place over 11,000 years ago with thicknesses of over half a mile high at present day Olympia area. The geologic unit is defined as a Qv. i.e.,quaternary volcanic rocks as indicated on Sheet 2.0. Upslope Geomorphology Upslope geomorphology indicates relatively steep heavily treed slopes with Douglas Firs and pines growing near vertical indicating mostly stable slopes over the life of these trees. Maple trees were also observed near the toe of the slope. Any downward slope movement due to potentially heavy rainfall and high winds would have caused the tree trunks to curve into a pistol butted handle shape. There was some relatively minor incidences of curved tree trunks upslope of the project site. Groundwater Conditions Little to no surface or subsurface groundwater or surface water drainage was observed on the site. Also, no upland waterbodies from the project site were present when this geotechnical engineer visited the site. Little to no significant signs of seeps or wetland areas along the face of the slope was observed. Upland Wetlands and Waterbodies This geotechnical engineer did not observe any upland waterbodies or wetlands that could cause problematic slides or unstable areas in the future. It is highly recommended that remaining trees and vegetation in the area be preserved and remain undisturbed to increase long term slope stability. llil8 1%. «ishkalt St.. \hert►ccn. %Aasliington 9852(1-2,37 (360)289-0958 13us.(360)310-0270 Cell tiltor•hk'rr aul.ruar q4 ,luly 25. 1019 Page 3 of 6 MET Enbineerinn, PLLC Geomorphology of the Lake Cushman Shoreline On an annual basis the level of Lake Cushman gets filled due to the Cushman dam that has artificially produced the man-made lake. Then typically, in the fall and winter. �\hcn electrical power is required for heating, then the elevated water conditions is used to run the electrical generators within the dam and,as a result, gradually lowers the lake level. This annual rising and lowering of the lake level has a tendency to saturate the otherwise dense granular material that comprises the local soils. The smooth, rounded cobbles and some boulders indicate that this material is glacial deposits as a result of the last major glacial advance and recession. Once this very dense till soils get saturated. there is then a tendency for the binding silt matrix that holds the cobbles and boulders together to loosen and slough away into the lake. This, in turn, can result in the potential erosion of the shoreline and the toe of the surrounding hillsides that can initiate slide conditions which has been observed in some case especially along the shoreline. Soil Exploratory Borings According to the USDA Web Soil Survey. the soils in this Lake Cushman shoreline area have been identified as a Hooclshori gravelly sauc/v loam (He) per the online Web Soil Survey prepared by the USDA Natural Resources Conservation Service as indicated on Sheet 4.0. The first soil exploratory site was near the face of the slope which indicated smooth gravels embedded in sandy loam soils for a depth of at least 15 feet or more. There was some evidence of slope movement near the toe due to the steepness of the slope and also the scouring wave action of Lake Cushman along the shoreline. The second soil exploration site was located approximately a third of the way up the slope where some slide activity exposed more sandy silty soils with gravels. Reference is made to Engineering Sheet 5.0 for the soil boring locations and a typical cross-section near the base of the slope is also shown. Slope Stability Analysis A detailed slope stability analysis was completed for the site as indicated on Engineering Sheet 3.0 which takes into account the height of the slope, the density of the insitu till soils, the cohesion of the native soils, and the internal friction angle of the slope material. For the static or non-seismic case. the resulting factor of safety was determined to be 1.061 and since this was less than the normally accepted value of 1.500. the lo\Ner third of the slope was considered unstable. The quasi-static case or seismic factor of safety was also computed that resulted in a factor of safety of 0.807 and since this was less than the normally accepted value of 1.200 this too was considered unsatisfactory. Reference is made to Sheet 6.0 that provides detailed calculations for the factor of safety for both the static as well as the seismic case. WI i._ ii ishkah ` I., 985211-21" , (360)289-0958 Bu%.(300)310-02'0 Cell Silort217i'itul.C011t July 25.2019 Page 4 of 6 MET Engin eerie , PL L C Land Slide Activity in the Area The Lake Cushman area was created by the construction of'the Cushman Dam that generates power from the Tacoma Power turbines below just off of Hwy 101. As a result,the annual rising and lowering of the lake level has a tendency to saturate the shoreline during summer months and then the water level starts declining during the winter months. This process can result in the removal of fines within the seemingly very hard and dense glacial till like soils. Over time. once these binders,that is fine silt has been removed, then there is little left to hold the smooth gravels and cobbles in place. This eventually can result in the gradual unraveling of the shoreline in some places especially where the slopes are steeper along the shoreline. Land Slide Mitigation The existing bulkhead retaining wall provides long term slope stability since in reinforces the toe of the slope and, thus, significantly slows down shoreline erosion due to the fluctuating lake level and also this bulkhead increases the long term stability of the residence near the top of the slope. Bio-retention Bulkhead Replacement This"soft" solution is not applicable for this slope since the base of the slope consists of gravel and cobblers and that any plantings in this area is not feasible. For this steep toe condition, the most effective solution is a mechanically stabilized wood bulkhead. It may be possible to hydroseed the bare slope areas near the bulkhead but would only be temporary in nature. Getting this kind of pumping equipment to spray the bare slope would be problematical at best. On-Site and Off-Site Impacts(if any) There will be little to no on-site or off-site impacts since all the work will be done within the same area as the original bulkhead located within the NE corner of the property as shown on Engineering Sheet 4.0. Final Development Conditions and Structural Mitigation Currently, the Lake Cushman water level is approximately 10 feet below the normal filled lake level height. The existing wood bulkhead increases long tern slope stability by reinforcing the toe of the slope which in-turn significantly increases the long term stability of the residence near the top of the steep slope. 1018 1:. W ishkth Si.. Aberdeen. W ishiu);ion 98+211-2937 (360)289-0958 Bus.(300)310-0270 Cell sNlorl-,01 Nul.cuo� July 25, 2019 Page 5 of 6 ME T Engin eering, PL L C Structural Mitigation Plan The existing bulkhead retaining wall is already in place and appears to be structurally sound with no signs of tipping or instability. Conclusions and Recommendations This geotechnical engineer concludes that the construction of the wood bulkhead was necessary to increase the long-term stability of the slope by reinforcing its toe. As a result, the shoreline erosion has been significantly slowed down and also, the overall longterm stability of the residence near top of the slope has increased. This geotechnical engineering report has been prepared per standard accepted engineering practice and that should there be any changes to the site conditions, this geotechnical engineer shall be contacted immediately to make the necessary updates to this geotechnical report, if necessary. It is to be noted that this report applies to this site only and not be used at any other location. Also, this geotechnical engineering report satisfies Mason County s requirements checklist for a geotechnical report which has been attached to this document as well. Any questions or comments regarding this geotechnical engineering report can be addressed by e-mail at . ._ or by calling this engineer directly at(360)310-0270. Respectfully Submitted, Steven P. Morta, P.E. JSN P.MO o 30753 CSS��NnL��G` tUiti 1•,. 1'1 is1)l.jth st.. :lbrrciccn, \!'aoitwiow 98520-2937' (300) 21N9-0959 1311".(300)311t-02.0 Celt `Morta'a auLcon) July 25.2019 7116 Page 6 of 6 MET Engineering, ILLLC References: I. Online Soil Web Survey prepared by the USDA Natural Resource Conservation Service that provides a detailed description of the soils and soil strata as well as its origin. 2. USGS Geological Map for Western Washington. 3. Stability Charts for Uniform Slopes by Radowslaw L. Michalowski, F.ASCE from the Journal of Geotechnical and Geoenvironmental engineering, April 2002. 1018 F. Wishkah tit.. Aberdeen. (360) 289-0958 Ba.,(360)310-02770 Cell tild��rt:):n aul.cum VICINITY MAP FOR BULKHEAD REPAIRS AND UPGRADE-1260 N.Potlatch Dr.,Hoodsport,WA 98548 -0 6 (Parcel#: 42318-51-00112) 61 GULL PLACE HOODSPORT M 98548 W N C C R I �i s 61 GULL PLACE IN HOODSPORT HOODSPORT WA 98548m Project Information: ----_ HOKUM PROPERTY ONAER. SCOTT and NRISTW MERRITT MAILINGADDRESS 410214Ih Ave S.E. ' Sammsmish.WA 98074 W E 1 a I t PROPERTYADDRESS: 61 GuN Hit- •�.� �� -+ Hoodwort.WA 98548 _#y E ACT' •_ -� •Ri -"�-��� L. PARCEL NUMBER, 42205-52 00051 .,r '• ` ��'' LEGAL DESCRIPTION: ENGINEER MET ENGWEER/NG,PLLC 1018 E.VA~St. Alaedeco,WA 98520-2937 N P. 36oj 38aaz7o e. ,��of W�dh�'P�, (360)861-84931 J `s Contact.Steven P Morta.PE. %.' �-,,. '� y, �•." j GENL CONTRACTOR. M(TEGRATEDNINCONSTRtUCTINJ,LLC P Wa �• > ;- z 60 N.Lake Cushman Road.Sule#10930758�p �, .• -x y s'- PO.Boa 1OD6 3• CUSTL0. G.? L . Hoodspon.W4 98W C S70NAL 1253)8885311 D. - f 206)771-3635 o. (206)3144239 0. -41 www Inle9faledNWConsWChOn Com f j� S7+' • '�4,p'�-�,--�-j"'. r GEOLOGIC UNIT FOR THE LAKE CUSHMAN REGION NORTH W E 91 GULL PLACE s HOODSPORT,WA 98548 ` - ' !�� 1• `�Tv TV Q1 �-- Qg� 1 I S Oa 106. Gls' ... (S %2Qad ��---- �' + ,Qa Tm .� Qgd I , Volcanic Rocks and Deposits Qv Quaternary volcanic rocks GEOLOGY OF THE LAKE CUSHMAN AREA Prepared by MET Engineering,PLLC, 1018 C.Wishkah St,Aberdeen.WA 98520-2937 (360)289-0958 bus,(360)310-0270 text. Prepared for SCOTT MERRITT July 25.2019 Site Visit on Tue.2-27-2018 SHEET 2.0 123'14' 123 13'45" 123 13'30- 123 13'15" 123 13' 123 12 45" 123 12'30" ,t Of 1 �:�_� - -_ v00 A, 1, w �r DOC l\-Slv • Beat Ram } -1 vile 20 :- z 'bS'odworf VA Sjbs:a- cr,,1 752 Cushman Darn to 4, ' 1� r' '•� :1 \` \ R` -l. ;� � �� N .% Sp�:Iway . — JA ~� o -51 Gagin'g Staten ' # 878 � .. i i � •t\ `\ ` - ' /� .- to f _ � N u � G 123'14' 123 13'45" 123 13'30" 123AVIS- 123 13' 123 12'45" 123 12 30' •. ..J t.m .. I.t•t•.•k.. 1.I.1. r.... 1•..�.t•1 In •• .i,l..... ...t••. .:1 .� .....t 7125/2019 Web Soil Survey v/1�0e Tr v n � z n; R et ' of �r•i •, � II � (rJ•� ;�� 1I� 4�� �l�..t,.,�—:.:�C:.--:_i-'.�Il^.�..""�"--- t :��?:ai�� :1 '1 I�►».��It+ill��t►-'lH�"7� Area of interest(AOi) Soil Data Explorer Download Soils Data Shopping Cart(Free) Printable Version) Add to Shopping Cart F .I I!l l I A—J 4 J SwN (nol w Me) T� rj lb t h'' Ak A, } a'l t, �Yr t� Warning:Soil Map may not be valid at this scale. _ xJ Printable Version https://websoilsurvey.sc.egov.usda.gov/AppIWebSoilSurvey.aspx 1/2 7125/2019 Web Soil Survey K— Report—Map Unit Description Mason County,Washington (WA645) Mason County, Washington (WA645) Mason County, Washington He—Hoodsport gravelly sandy loam,15 to 30 percent slopes Map Acres percent Map Unit Setting Unit Map Unit Name in of AOI National map unit symbol: 2hky Symbol AOI Elevation: 0 to 980 feet Gm Grove gravelly 0.5 15.4% Mean annual precipitation:60 inches sandy loam, 15 t0 Mean annual air temperature: 50 degrees F Frost-free period: 150 to 175 days 30 percent slopes Farmland classification: Not prime farmland Hd Hoodsport gravelly 1.0 30.0% Map Unit Composition sandy loam, 5 t0 Hoodsport and similar soils: 100 percent 15 percent slopes Estimates are based on observations, descriptions,and Iransects of the He Hoodsport gravelly 1.2 36.6% mapunit. sandy loam, 15 to Description of Hoodsport 30 percent slopes Setting Landforrn:T;II plains W Water 0.6 18.0% Parent material: Basal till Totals for Area of 3.4 100.0% Typical profile Interest HI -0 to 5 inches:gravelly medial sandy loam H2-5 to 24 inches: very gravelly medial sandy loam H3-24 to 60 inches:gravelly sandy loam FOlA i Accessibility Statement Pnva, properties and qualities Slope: 15 to 30 percent Depth to restrictive feature: 20 to 40 inches to densic material Natural drainage class: Moderately well drained Capacity of the most limiting layer to transmit water(Ksat):Very low to moderately low(0.00 to 0.06 in/hr) Depth to water table:About 18 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water storage in profile:Very low(about 1.6 inches) Interpretive groups Land capability classification(irrigated):None specified Land capability classification(nonirrigated):6s Hydrologic Soil Group: B/D Forage suitability group:Limited Depth Soils(0002XN302WA) Hydric soil rating: No Description—Map Unit Description httpsi//websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx 212 NORTH LOCATIONS OF SOIL EXPLORATORY BORINGS 13116 W E I S +Soil Exploratory#1 +Soil Exploratory#2 BULKHEAD REINFORCES TOE OF SLOPE'AND INCREASES LONG TERM SLOPE SjM141TY Soil Exploration ttt2 7W Soil Exploration PRESERVE ALL REMAINING 1 REES a n 760' AND VEGETATION ON SLOPE TO INCREASE LONG TERM SLOPE STABILTY TO PROTECT SHORELINE AND RESIDENCE b � 740' inn 9 oo • c � 726 FT (APPROX.) LAKF',,SHMAN 80' 60' 40' 20' 0' EN P. A1O WASfy7 �PJ. hC1; b BROWN SANDY LOAM WITH SOME 6"MINUS GRAVELS. ,} 8 TO 10%MOISTURE.1600 PSF ALLOWABLE BEARING VALUE. 75R.0 w� ST1aZl",G�� ® DENSE GLACIAL TILL SOILS WITH AN ALLOWABLE SOIL BEARING CAPACITY OF 2200 PSF AND A 9TO 12% MOISTURE CONTENT. EXPLORATORY SOIL BORINGS Prepared by MET Engineering,PLLC 1018 E.Wishkah St,Aberdeen,WA 98520-2937 (360)289-0958,(360)310-0270 text. Prepared for SCOTT MERR/rT July 25.2019 Site Visit on Fri.2-23-2018 SHEET 5.0 Slope Stability Analysis (Simplified Bishop's Method of Circles) 61 Gull PLace, Hoodsport, WA 98548 -- Potential Failure .� Plane 45 ft A�1' iI Not to scale(NTS) Afpha=43.5 deg (95%slope) 1. Compute factor of safety(FS)against sliding-Static Case(Ref: "Stability Charts for Uniform Slopes"by Radoslaw L. Michalowski, F.ASCE) - "Journal of Geotechnical and Geoenvironmental Engineering",April 2002. From Figure 3"Stability charts for uniform slopes'the following parameters are known for Hoodsport gravelly sandy loam soils(He) from the online USDA Soil Web Survey: c(cohesion)=200 psf, gamma(insitu unit density)= 136 pcf, H(height of slope)=35 ft, phi (internal friction angle)=23 deg, then c/[gamma x H x tan(phi)]=200/(136 x 35 ft x tan 23) =0.0990 Then for a 43.5 deg(95%)slope from Fig. 3: FS/tan(phi)= FS/tan(23) =2.5 or. FS=Factor of Safety Against Sliding= 1.061<1.500 NOT OKAY 2. Compute factor of safety(FS)against sliding-Quasi-Static(seismic)Case(Ref "Stability Charts for Uniform Slopes" by Radoslaw L. Michalowski, F.ASCE) - "Journal of Geotechnical and Geoenvironmental Engineering",April 2002. From Figure 4"Stability charts for uniform slopes"the following parameters are known for Hoodsport gravelly sandy loam soils(He): c cohesion 200 sf, gamma insitu unit density) 136 f, H(height of sloe =35 ft. (cohesion) P 9 ( Y)= Pc ( 9 slope) (internal friction angle) =23 deg, then `EN P. G amma x H x tan hi 200/ 136 x 35 ft x tan 23 0.0990 ,<,ti of w asy �Pj, Then for a 43.5 deg slope(95%slope)from Fig.4 for a quasi-static analysis coefficient of 0.1: 'A F/tan(23)=2 2 or FS=Factor of Safety=0.934 758 For a quasi-static analysis coefficient of 0.2: Ss/cr Te��G�t'ty nV,�LE F/tan(23)= 1.9 or FS= Factor of Safety=0.807 As a result,for a quasi static analysis coefficient of 0.15, the Factor of Safety FS=(0.934+0.807)/2=0.870<1.100 NOT OKAY v",j;d,`oTRu,_i iON OF A&_r'HEAD RETAINING WALL AT THE TOE OF THE SLOPE WILL INCREASE LONG TERM SLOPE STABILITY BY REINFORCING THE TOE OF THE SLOPE THIS HELPS TO CONTROL SHORELINE:EROSION AND PRESERVE THE S`ABID TY OF:THE RESIDENCE SLOPE STABILITY ANALYSIS Prepared by: MET Engineering,PLLC.1018 E.Wshkah St,Aberdeen,WA 98520-2937 (360)289.0958, (360)310-0270 text,(360)861-8493 fax. Prepared for SCOTT MERRITT July 25.2019 1 Site Visit on Fri.2-23-2018 SHEET 6.0 MASON COUNTY COMMUNITY SERVICES Geotechnical Report 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. Applicant/Owner S. Cn 7t MtOtr7f r Parcel# 2Z OS= J r?~�jon Site Address 9/ 6--(_ ll Plat-e 1490r/s.,)nrt 11V (1) (a) A discussion of general geologic conditions in the vicinity of the proposed development, Located on page(s) f&*/ 2. (b) A discussion of specific soil types, Located on page(s) (c) A discussion of ground water conditions, Located on page(s) a (d) A discussion of the upslope geomorphology, Located on page(s) Z (e) A discussion of the location of upland waterbodies and wetlands. Located on page(s) Z- (f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records. Located on page(s) 3 (2) A site plan which identifies the important development and geologic features. Located on Map(s) � Vgee f S C? (3) Locations and logs of exploratory holes or probes. Located on Map(s) t,LJP—f cS-, D (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) s�l�t 5 D (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) ghee t-,s o (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. r/ Located on page(s) as g e 3 add (,Fxe t' t (� (7) (a) Appropriate restrictions on placement of drainage features. Rev. February 2018 Located on page(s_ (b) Appropriate restrictions on placement of septic drain fields, Located on page(s) W- CC. (c) Appropriate restrictions on placement of compacted fills and footings, Located on page(s) /I.C( (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) '�% a (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes. Located on page(s) _n. 0 , (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) C , (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) (10) An analysis of both on-site and off-site impacts of the proposed development. Located on page(s) (11) Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths. Located on page(s) (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation. Located on page(s) 41e, (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) f;/A0t0 f � p Il-424.6Q4 P NO/' �-C( 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 �U Al �, 0l 9, and entitled NP. O vns j9 -' -- P/ meets all the requirements of the Mason County Resource Ordinance, / Geologically Hazardous Areas Section, is complete and true, that the o R 30758 p w4 assessment demonstrates conclusively that the risks posed by the FCfSTti�� landslide hazard can be mitigated through the included geotechnical SSIDNAL, design recommendations, and that all hazards are mitigated in such a (Signature and Stamp) manner as to prevent harm to property and public health and safety. Page 2 of Z Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report.