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Home My WebLink AboutGEO2017-00068 - BLD Engineering / Geo-tech Reports - 12/14/2017 GE0200 - WOC(1� Mason County Review Checklist for a Geotechnical Report Instructions: This checklist is intended to assist Staff in the review of a Geotechnical Report. The Geotechnical Report is reviewed for completeness with respect to the Resource Ordinance. If an item is found to be not applicable, the Report should explain the basis for the conclusion. The Report is also reviewed for clarity and consistency. If the drawings, discussion, or recommendations are not understandable, they should be clarified. If they do not appear internally consistent or consistent with the application or observations on site, this needs to be corrected or explained. If resolution is not achieved with the author, staff should refer the case to the Planning Manager or Director. Applicant's Name: t-W C, Permit#: 8 LD 20 V1— olIpLt Parcel#: 3 23 3'-t— 2,4 —ooaoo Date(s) of the Document(s) reviewed: 1V lS 1201-7 1. (a) A discussion of general geologic conditions in the vicinity of the proposed development, OK? Comment: 2— (b) A discussion of specific soil types OK? Comment: I— (c) A discussion of ground water conditions OK? Comment: 'Z- (d) A discussion of the upslope gWmorphology OK? Comment: (e) A discussion of the location of upland waterbodies and wetlands OK? Comment: 2- (f) A discussion of history of landslide activity in the vicinity, as available in the referenced maps and records OK? Comment: 2 2. A site plan that identifies the important development and geologic features. OK? Comment: Vit 2,°S 3. Locations and logs of exploratory holes or probes. OK? Comment: NL 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. OK? Comment: F i!i 2 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. OK? Comment: . 1;'j 3 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 an coeffients should be a value of 0.15. OK? Comment: A- 7. (a) Appropriate restrictions on placement of drainage features OK? Comment: 3 (b) Appropriate restrictions on pl cement of septic drain fields OK? Comment: (c) Appropriate restrictions on placement of compacted fills and footings. OK? Comment: WW Page 1 of 2 Form Effective June 2008 v (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes. OK? Comment: ?.;, (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes. OK? Comment: 3 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. OK? Comment: L 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. OK? Comment: 9 10. An analysis of both on-site and off-site impacts of the proposed development. OK? Comment: 4 11. Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths. OK? Comment 12. Recommendations for the preparation of structural mitigation or details of other proposed mitigation. OK? Comment: N/y9- 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. OK? Comment: F:n Z Are the Documents signed and stamped?Y—C-5- By whom? Wr W-04� 0e�be*+ License#: 5(LQ License type: F—&I FIRST REVIEW ft/Approved ❑ Need more info. If not approved, what is the next action/recommendation for further action? Reviewed by on ��'< ls� l� Time spent in review: :WS SECOND REVIEW/ UPDATE ❑ Approved ❑ Need more info. Reviewed by on . Time spent in second review: THIRD REVIEW/ UPDATE ❑ Approved ❑ Need more info. Reviewed by on . Time spent in third review: Disclaimer. Mason County does not certify the quality of the work done in this Geotechnica/Report. Page 2 of 2 Form Effective June 2008 Mason County Department of Community Development Submittal Checklist For a 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 found to be not applicable,the report should explain the basis for the conclusion. Applicant/Owner 3eon;{'er Cka%vis- Parcel# 3733yzg000-)0 Site Address 3/0 NG kSsin Fr-cc- `n /nG>on Co,n14 1yiq (1) (a)A discussion of general geologic conditions in the vicinity of the proposed development, Located on page(s) Pcv,z. 2- (b) A discussion of specific soil types Located on page(s) Paqe, Z (c) A discussion of ground water conditions Located on page(s) hc,,,e L (d) A discussion of the upslope geomorphology Located on page(s) ro <, Z (e) A discussion of the location of upland waterbodies and wetlands Located on page(s) Pa-�e 2- (f) A discussion of history of landslide activity in the activity in the vicinity, as available in the referenced maps and records Located on page(s)Vie. Z- (2) A site plan which identifies the important development and geologic features. Located on Map(s) 7- (3) Locations and logs of exploratory holes or probes. Located on Map(s) N/q (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) Fi!�Vrc Z (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) Fii-1 cure 3 (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;Ttte rrjini[num static safety factor is 1.5,the minimum seismic safety factor is 1.1.and fhe guasi=stati -,analysis coeffients should be a value of 0.15. Located on page(s) N/4' �isc.vss5o. OiSG_3) (7) (a)Appropriate restrictions"on orkement of`drainage features Located on page(s) If, k3 (b) Appropriate restrictions on placement of septic drain fields Located on page(s) / 0r ? ' 3 (c) Appropriate restriction's on placement of compacted fills and footings Located on page(s) NIA Page 1 of 2 Form Effective June 2008 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report. (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes on the property. Located on page(s) fpc,c�c 3 (e) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes on the property. Located on page(s) (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) (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) R".(J C_ L-1 (10) An analysis of both on-site and off-site impacts of the proposed development. Located on page(s) P,a)' `I (11) Specifications of final development conditions such as, vegetative management, drainage, erosion control, and buffer widths. Located on page(s) Pr�C 3 , -I (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation. Located on page(s) IV (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) ♦'tc, %�Z. Z ____ I, U11#i(',vn 9"-,lbe4 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 /Z �` 1~ and entitled reu1o<<;�. Nc%?b,r-d PO r 1 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.J&i2nature and Stamp) s°tWashj 0' used Gea William E. Halbert Page 2 of 2 orm Effective June 2008 Disclaimer: Mason County does not certify the quality of the work done in this Geotechnical Report. INSIGHT GEOLOGIC, INC. December 14, 2017 Jennifer Chavis 310 NE Kissin Tree Lane Tahuya, Washington Geotechnical Report 310 NE Kissin Tree Lane Tahuya, Washington Project No. 1007-001-01 INTRODUCTION Insight Geologic, Inc. is pleased to provide our geotechnical report of your property located at 310 NE Kissin Tree Lane in the unincorporated community of Tahuya in Mason County, Washington. The location of the site is shown relative to surrounding physical features in the Vicinity Map, Figure 1. We understand that you are interested in constructing a single-family residence on the parcel. According to Mason County staff, the property contains areas that may meet the definition of a steep slope (25 percent slopes greater than 10 feet in height) under Mason County's Critical Areas Ordinance for Geologically Hazardous Areas. SCOPE OF SERVICES The purpose of our services was to evaluate geologic conditions as they relate to slope stability on the subject property. We performed our evaluation in general accordance with the procedures outlined in Mason County's Critical Areas Ordinance. The specific tasks performed for this project are outlined below. 1. Evaluate critical slopes on the property relative to the definition of steep slopes and the potential for landslide hazard in conformance with Mason County Resource Ordinance, Title 8, Chapter 8.52. 2. Evaluate local geology in the area of the parcel by reviewing readily available geologic reports and local water well logs, as well as conducting a site reconnaissance to view exposed geologic units in the critical slope areas. 3. Prepare a report for review by Mason County summarizing our activities and presenting our opinion on slope stability at the subject site. LANDSLIDE HAZARD AREAS The regulations established in the Mason County Resource Ordinance, Title 8, Chapter 8.52 Landslide Hazard Areas are intended to "identify areas that present potential dangers to public health and safety, to prevent the acceleration of natural geological hazards, to address off-site impacts, and to minimize the risk to the property owner or adjacent property owners from 1015 EAST 4TH AVENUE, OLYMPIA, WASHINGTON 98506 PHONE: 360.754.2128 FAX: 360.754.9299 Chavis Property Geotechnical Report December 14, 2017 development activities." Pertinent landslide and erosion hazard issues related to the site are addressed in the remainder of this report. The purpose of this study and report is to evaluate the slope stability of the site in accordance with Mason County Resource Ordinance, Title 8, and Chapter 8.52. "Landslide hazard areas" means those areas with any indications of earth movement such as debris slides, earth flows, slumps and rock falls; areas with artificial over-steepened or unengineered slopes; areas containing soft or liquefiable soils; areas over-steepened or otherwise unstable as a result of stream incision, stream bank erosion and undercutting by wave action; slopes greater than 15 percent (8.5 degrees) or having the following: a.) hillsides intersecting geologic contacts with relatively permeable sediment overlying relatively impermeable sediment or bedrock and having springs or groundwater seepage; b.) any area with a slope of 40 percent (21.8 degrees), or steeper and a vertical relief of ten or more feet, except areas composed of consolidated rock. Surface Conditions The project site is bounded by residential properties to the west and undeveloped wooded properties to the east, south and north. Topographically, the site slopes to the northeast from an elevation of approximately 430 feet above mean sea level (MSL) in the southwest corner of the site to approximately 390 feet MSL along the upper portion of a steep-sided ravine trending south to north along the eastern third of the site. The bottom of the ravine is at an approximate elevation of 290 feet and contains a small creek that flows to the north. The proposed home location, in the northwest quarter of the site, has recently been logged. The remainder of the site is vegetated with second growth cedar and fir trees with a thick understory of woody shrubs, such as salal and huckleberry. The site is accessed from the eastern end of NE Kissin Tree Lane, which terminates at the northwest corner of the property. The general site layout is shown in the Site Plan, Figure 2. Geology Based on our review of available published geologic maps, Vashon age glacial till deposits underlie the project site and surrounding area and form a relatively level upland area. Glacially compacted advanced outwash, consisting of sands and gravels, is exposed within the majority of the ravine on the site. No upland wetlands or waterbodies appear to be present on the property. We were unable to identify any mapped landslides within 1,000 feet of the site using the Washington State Department of Natural Resources landslide database. General site geology is shown in the geologic cross section, Figure 3. The surficial soils encountered are generally consistent with Alderwood gravely sandy loam, which is mapped for the area. These soils are formed from glacial drift or outwash and tend to have hydraulically restrictive layers occurring at depths between 2 and 3 feet below grade. Groundwater A review of the Washington State Department of Ecology Well Log Records for the surrounding area indicates groundwater levels at a depth of approximately 120 feet below ground surface. No well FILE No. 1007-001-01 2 (! R' Chavis Property Geotechnical Report December 14, 2017 logs were found for the subject parcel, however a well log was located for a property to the north of the site. The referenced well log is shown in Attachment A. It is likely that a seasonal, perched groundwater layer will form during the winter season within the Alderwood soils, above the hydraulically restrictive layer. FINDINGS Insight Geologic visited the site on December 13, 2017 to evaluate the site slopes and surface conditions. The proposed building site is located approximately 200 feet west of the ravine identified on the site. The soils exposed at the building site and the top of the ravine edge generally consisted of silty fine to medium sands with minor gravels (Alderwood soils). Soils exposed along the ravine slopes consisted of compacted fine to coarse sands and fine to coarse gravels with occasional cobbles and silt. These soils are consistent with Vashon-age glacial till and advance outwash deposits that have been glacially compacted and are generally equivalent with soils identified in the well log for the nearby property. No evidence of bedding planes were noted during our site reconnaissance. The contact between the glacial till and overlying Alderwood soils was observed near the ravine edge. We did not observe the presence of groundwater seeps or the presence of hydric vegetation on the slopes indicating the presence of groundwater discharge. No seeps were seen along the base of the slope. Additionally, we did not observe the presence of historical soil failures or landslide features, such as hummocky or back-tilted topography, ponded drainage, or butt-bowed trees on the slope. Based on multiple measurements we made using a hand-held clinometer, the slopes at the site ranged from approximately 10 percent (6 degrees) in the proposed building site and upland areas, to 80 to 92 percent (39 to 43 degrees) on the slopes of the ravine. CONCLUSIONS AND OPINION Based on the site visit observations and published information of soils in the area of subject parcel, it is our opinion that the ravine portion of the subject site meets the definition of a "Landslide Hazard Area" due to the angle of the measured slopes. The slopes within the ravine exceed the 40 percent inclination criteria as outlined in the Mason County Resource Ordinance. The remainder of the slopes on the property are all less than about 15 percent and do not exhibit geologic contacts, springs or seeps as outlined in the ordinance. No evidence of past landslides was observed. A completed Geotechnical Report Checklist is included in Attachment B. The site geology consists of a thin layer of Alderwood soils, over glacially consolidated till and advanced outwash units. We interpret the upper till unit and underlying sands and gravels as Vashon age glacial deposits. It is our opinion that the glacial deposits on the site have inherent internal strength and a high angle of internal friction, which are not prone to deep-seated failures. Minor sloughing may occur on steeper slopes due to weathering of the outer few inches of soil, but these sloughs do not represent a risk to the proposed residential structure. We do not believe that the ravine slopes present a risk to the proposed dwelling. FILE No. 1007-001-01 3y., Chavis Property Geotechnical Report December 14, 2017 Based on our observations and evaluation of the site, we would normally recommend a setback of 50 feet from the top of the ravine slope. The proposed distance of about 200 feet between the top of slope and the proposed house will exceed that requirement. No additional setback is required. No additional subsurface geotechnical explorations or slope stability analyses are required for this project. In general, care should be taken during and after construction to maintain good, positive drainage from all impervious surfaces. Drainage should be collected into catch basins and contained in non- perforated piping for discharge at the base of the slope. Drainage from roof downspouts should also be collected into non-perforated piping and directed away from the slope for discharge. All stormwater infiltration and septic drainfields should be sited outside of the setback area. Native vegetation should be maintained whenever possible and exposed soil protected from rainfall. Detailed clearing and grading plans and temporary erosion control plans should be prepared and submitted by an appropriate contractor. The wet weather season in this area generally begins in October and continues through May. However, periods of wet weather may occur during any month of the year. If wet weather earthwork is unavoidable, we recommend that: • The ground surface is sloped so that surface water is collected and directed away from the work area to an approved collection/dispersion point. • Earthwork activities not take place during periods of heavy precipitation. • Slopes with exposed soil be covered with plastic sheeting or otherwise protected from erosion. • Measures are taken to prevent on-site soil and soil stockpiles from becoming wet or unstable. Sealing the surficial soil by rolling with a smooth-drum roller prior to periods of precipitation should reduce the extent that the soil becomes wet or unstable. • Construction traffic is restricted to specific areas of the site, preferably areas that are surfaced with materials not susceptible to wet weather disturbance. • A minimum 1-foot thick layer of 4-to 6-inch quarry spalls is used in high traffic areas of the site to protect the subgrade soil from disturbance. LIMITATIONS We have prepared this geotechnical report for use by Jennifer Chavis and her authorized agents for the property located at 310 NE Kissin Tree Lane in Mason County, Washington. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geological engineering in this area at the time this report was prepared. No warranty or other conditions express or implied, should be understood. Please refer to Attachment C, Report Limitations and Guidelines for Use, for additional information pertaining to use of this report. FILE No. 1007-001-01 4 !! i., Chavis Property Geotechnical Report December 14, 2017 We appreciate the opportunity to be of service to you on this project. Please contact us if you have questions or require additional information. Respectfully Submitted, INSIGHT GEOLOGIC, INC. ti0 p Wei 0 William E. Halbert, L.E.G., L.HG. 0 815 �g Principal & ed Geo William E. Halbert Attachments FILE No. 1007-001-01 5 . FIGURES \i t77 Bo e j rf � f { SITE i .r r J) . l J LILLIWAUP, WASHINGTON 7.5 MINUTE QUADRANGLE Year1985 SCALE:1:24000 CHAVIS PROPERTY MASON COUNTY,WASHINGTON ~ � Figure 1 INSIGHT GEOLOGIC, INC. �;" �.• Vicinity Map + _y X'c- Nw- t a r►" � �✓ ,rig � ~� • '4 r: I e� SCALE: 1'=200' CHAVIS PROPERTY MASON COUNTY,WASHINGTON Figure 2 INSIGHT GEOLOGIC, INC. Site Plan C 420 r RESIDENCE 400 Qgt Qgt 380 --------- 360 2 O j 340 w Qga Qga w 320 300 P80 CREEK 260 FEET -��- � -T- -- 0 100 200 300 400 500 600 WEST EAST .A. VIEW NORTH SCALE VIRnCAU I'=SO' CHAVIS PROPERTY SCALE HORIZONTAL I'=IW MASON COUNTY,WASHINGTON --I w,-C,INc. Figure 3 I Geologic Cross Section ATTACHMENT A WELL LOG o WATER WELL REPORT CURRENT Original&1'teopy—Ecology,2"d copy—owner,Yd copy—driller Notice of intent No.WE27168 ECOLOGY Construction/Decommission("x"it2 circle) Unique Ecology Well ID Tag No.ALH 687 {�("a wain nRton ❑■ Construction Water Right Permit No. ❑ Decommission ORIGINAL INSTALLATION Notice of Intent Number Property Owner Name Emily Davis �) PROPOSED USE: (] Domestic ❑ Industrial ❑ Municipal Well Street Address 297 NE Kissing Tree Lane ❑ De Water ❑ Irrigation ❑ Test Well ❑ Other City Tahuya County Mason t.n TYPE OF WORK: Owner's number of well(if more than one) ❑a New well ❑ Reconditioned Method_❑ Dug ❑ Bored ❑ Driven Location 9_\N/4-I14MAI/4 Sec 34 Twn 23N R 3 EWM ❑ 4-J ❑ Deepened 2 Cable ❑ Rotary ❑ Jetted (s,t,r S611 REQUIRED) Or p DIMENSIONS: Diametero(we116 inches,drilled 152 ft. Lat/Long wtivM Q Depth of com leted well JU ft. L.at Deg Lat Min/Sec e— CONSTRUCTION DETAILS Long Deg Long Min/Sec Q Casing [E Welded 6 Diam.from +1 ft.to 147 R. Installed: ❑ Liner installed Diam,from ft.to ft. Tax parcel No.(Required)32334759OO4Z ❑ Threaded Diam.From tt to ft. Perforations: ❑ Yes N No16— CONSTRUCTION OR DECOMMISSION PROCEDURE Type of perforator used Formation:Describe by color,character,size of material and structure, and the kind and nature of the material in each stratum penetrated,with at SIZE of perfs_in.by_m and no.of perfs_from_ft.to_ft. least one entry for each change of information. (USE ADDITIONAL ' Screens: ❑ Yes ❑ No M K-Pac Location 145 SHEETS IF NECESSARY.) Manufacturer's Name Alloy Machine Works MATERIAL FROM TO Type stainless Model No. Topsoil 0 2 Diam.5 slot size 20 from 147 lit,to 152 ft. Cemented sand&gravel 2 10 Diam. Slot size from ft.to fi Light brown cemented sand&gravel w/b 10 70 Gravel/Filterpacked: ❑ Yes 0 No Sizeofgravel'sand Grey sand&gravel w/b 70 77 Materials placed from ft.to ft. Brown sand&gravel w/b 77 100 Surface Seal: IN Yes ❑ No To what depth? 18 ft. Brown cemented sand&gravel w/b 100 130 Material used in seal BentonitP_ Brown sand&gravel w/b 130 152 Did any strata contain unusable water? ❑ Yes Q No rti Type of water? Depth of strata L•� Method of sealing strata off - PUMP: Manufacturer's Name Gfundfos ♦..r Type:sub HP. 1 1/2 WATER LEVELS: Land-surface elevation above mean sea level ft. Static kvei 122 R.below top of well Date Artesian pressure lbs.per square inch Date Artesian water is controlled b (cap,valve,etc.) WELL TESTS: Drawdown is amount water level is lowered below static level Was a pump test made? N Yes ❑ No If yes,by whom? Yield:20 QA/min.with 3 ft.drawdown after 1 hrs. Yield:20 gal./min.with 3 ft.drawdown after 2 hrs. Yield:__gal/min.with_ft.drawdown after hrs. Recovery data(time taken as zem when pump turned of g(water level measured from ( well top to water level) Time Water Level Time Water Level Time Water Level 0 125 1 min 123 2 min 122 Q Date of test WA Statenepartment j� Bailer test 20 gal./min.with 3 ft.drawdown after 1 hrs. _ I,.) Airtesf gal./min.with stem set at ft.for hrs. LLJ a+. Artesian flow g.p.m. Date Temperature of water Was a chemical analysis made.? ❑ Yes N No Start Dak7/17/1 7 Completed Date 8/10117 WELL CONSTRUCTION CERTIFICATION: I constructed and/or accept responsibility for construction of this well,and its compliance with all Washington well construction standards. Materials used and the information reported above are true to my best knowledge and belief. Q Driller❑Engineer❑Trainee Name Emily Davis Drilling Company Davis Drilling ice. Driller/Engineer/Trainee Signature Address 340 NE Davis Farm RD Driller or trainee License No.3142 City,State,Zip B lair,WA 98528 IF TRAINEE:Driller's License No: Contractor's !,1 I r' Driller's Signature: �A Registration No. DAVISDI1100A Date August 2017 ECY 050-1-20(Rev 02-2010) To request A JOATaccommodation including materials in a format for the visually impaired,call Ecology Water Resources Program at 360-407-6872. Persons with impaired hearing may call Washington Relay Service at 711. Persons with speech disahithy may call TTY at 8 7 7-833-6341. ATTACHMENT B MASON COUNTY DEPARTMENT OF COMMUNITY DEVELOPMENT SUBMITTAL CHECKLIST FOR A GEOTECHNICAL REPORT