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HomeMy WebLinkAboutBLD2008-00035 Geotechnical Report • • STRATUM GROUP 1451 Grant Street,Bellingham,WA 98225 Phone(360)714-9409 January 24, 2007 J A N 3 0 2008 Lori and John Bugaj 210 21 St Avenue East Seattle, WA 98112 Re: Geology Hazard Assessment Tax Parcel 701201012 Piper Road Quilcene, WA Dear Mr. and Ms. Bugaj: Stratum Group is pleased to present the results of our geology hazard evaluation of the above referenced property on a shoreline bluff. The purpose of this geology evaluation was to assess the risk of slope failures impacting the proposed development on the subject property and provide general site development and maintenance recommendations. This evaluation included a visual inspection of the property and vicinity, a visual inspection of the slopes on the property and vicinity,review of available geologic mapping in the area, and inspection of the shoreline at the base of the bluff. The property location is indicated on Figure 1. The property is located on the east side of the Bolton Peninsula in the northeast quarter of Section 20, Township 27, Range 1 West W.M. The property extends from the shoreline of Dabob Bay on the east up the slope to an elevation of approximately 150 feet on the west side of the property. SCOPE OF SERVICES The scope of our services included the following: 1) Conducted a site visit to visually inspect the subject property including the slope conditions, shoreline conditions, and relevant conditions in the vicinity of the property. 2) Observed surface soil conditions on the slope and on the uplands above the slope. 3) Prepared this report summarizing our findings, including a qualitative evaluation of the slope stability in regards to the proposed building site on the property, recommendations for site development, and recommendations for further investigation, if necessary. • • January 24,2007 Tax Parcel 701201012,Piper Road,Quilcene,WA JAN 3 0 2008 Geology Assessment GENERAL GEOLOGY Northwestern Washington has been occupied by continental glaciers at least four times during the Pleistocene Epoch(1.6 million to 10,000 years ago). During these glacial and accompanying interglacial periods,the underlying bedrock was eroded and a relatively thick layer of glacial related and interglacial fluvial sediments were deposited over the underlying bedrock in the vicinity of the subject property. The Geologic Map of Surficial Deposits in the Seattle 30' by 60' Quadrangle, Washington (Yount, Minard, and Dembroff, 1993) indicates the bluff is underlain by undifferentiated Pleistocene deposits. These deposits are described as consisting of poorly exposed gravel, sand, silt, and clay of uncertain provenance. The Geologic Map of East-Central Jefferson County, Washington(Birdseye, 1976) indicates the shoreline and bluff exposed on the subject property and vicinity is underlain by Pre-Vashon glaciation stratified deposits. Birdseye indicated that there are three glacial till deposits on the bluff in the vicinity of the property: the Possession Till, the Double Bluff Till, and the Vashon Till. The Vashon Till is the youngest of the tills and the Double Bluff Till is the oldest. The till deposits were deposited directly by glacial ice and consist of a mix of rock fragments embedded in a matrix of fine grained material consisting of clay and silt sized rock particles. The Pre-Vashon stratified deposits are described as consisting of sand, gravel, silt and clay deposited prior to the last ice age. These deposits were deposited by glacial melt water and by interglacial streams and rivers. Observations on the subject property, slopes in the vicinity of the property, and upland areas above the subject property are consistent with the mapping described above. However, based on mapping I have conducted along the east side of the Bolton Peninsula a relatively thin discontinuous layer ice margin deposit is present on the terrace-like topography on the east side of the peninsula including on the subject property. The ice margin deposit consists of very poorly sorted sand and gravel and silt deposited along the margin of wasting glacial ice that would likely have occupied Dabob Bay near the end of last glacial period. Most of the property is underlain by compact sand and gravel. Compact sand and gravel deposits underlay most of the steep shoreline slope. A very compact sandy silt with gravel glacial till unit is located along the mid section of the steep shoreline bluff. Glacial till is present at two locations on the steep slopes of the property and till deposits underlie the lower bluff slopes to the north of the subject property. The till at the base of the bluff is likely the Double Bluff Till and the till observed on the mid portion of the slope is likely the Possession Till. Stratum Group File. I.12.07 2 • • JAH302C January 24,2007 Tax Parcel 701201012,Piper Road,Quilcene,WA Geology Assessment The Relative Slope Stability in East-Central Jefferson County, Washington(Birdseye, 1976) map indicates slopes in the vicinity of the subject property are unstable and identifies areas of recent landsliding in the immediate vicinity of the subject property. Observations confirm that there are potential unstable slopes on the subject property and the vicinity. The shoreline at the base of the bluff is erosional and thus the slopes above the shore are potentially unstable and in some places are unstable. Unstable slopes are located on the steep slopes west(inland) of the subject property,particularly in areas of convergent topography near the upper slopes of the Bolton Peninsula and along the steep sided ravines on the slopes of the peninsula. SPECIFIC SITE OBSERVATIONS A sketch map of the property with pertinent features indicated is provided in Figure 2. A spur driveway off of Piper Road crosses the west side of the property and provides access to the upland portion of the site. The slopes on the upland portion of the lot slope to the east between 5 and 20 degrees. The upland area is tree-covered with mostly mature Douglas fir with an understory of salal and ferns. Soils in the upland area consist of sand and gravel to cobbles. The top of the steep shoreline slope breaks very sharply. The shoreline slope slopes down to the beach below at an average angle of approximately 70 degrees. This slope is underlain by mostly compact sand and gravel that I interpret to be glacial outwash. A layer of sandy silt with gravel is present on the upper portion of the bluff is glacial till. Despite the steepness of the slope and compact soils, trees are scattered on the slope. The steep shoreline slope down to the beach has had shallow surface soil failures in the past. The slope along the bluff is primarily tree-covered but areas of bare soil are present on portions of the very steep slope where slides have taken place in the more recent past or where slopes are extremely steep. An approximately 4-foot thick layer of soil and logs from past slides is located on the upper beach along most of the property. These slide deposits have trees and brush growing on them. No springs or seeps of water were present anywhere on the steep shoreline bluff slope of the property and there are no indications of seasonal wet areas on the bluff slope on the subject property. There was no evidence of surface water flow in either of the two dry drainage swales located on the upland portion of the property. Other similar swales in the area are also dry. The very porous soil underlying these low areas appears to preclude surface water flow. These dry drainages may be the result of initial drainage of the area shortly after the last glacial period. During extreme weather events subsurface water may appear in these swales. Surface water flow appears to Stratum Group File: 1.12.07 3 • i jAN 3 0 2TCc3 January 24,2007 Tax Parcel 701201012,Piper Road,Quilcene,WA Geology Assessment occur on a periodic basis at the end of the swale on the south side of the property. The flow of water at this steep slope location has caused erosion back into the bluff face creating an amphitheatre-like alcove in the bluff face just south of the subject property. A very small seep of water was present within the alcove area below the swale at the time of my site visit in January 2007. I observed the same location during an extreme rain fall event in winter of 2006 and noted a similar flow of water. As noted above there are a number of dry drainage swales that appear to never or only very rarely have surface water flow in the vicinity of the property. Based on my observations it appears that a small volume of water reaches the bluff face in the swale along the south boundary of the property during periods of very wet weather. The swale on the north side of the property and another swale on the property north of the subject property show no evidence of surface water flow impacting the bluff face. A large deeper swale on the property south of the subject property shows evidence of periodic surface water flow only at the lower end of the swale. The primary difference between the swales is the surface area of the catchment areas above the swales. The swale on the south property line has a larger catchment area than the dry swales to the north. The swale on the property south of the subject property has a much larger catchment area and has subsequently had more frequent surface water flow at the end of the swale with corresponding deep erosion. The shoreline conditions along this section of shoreline are very good. The beach consists of a sand and gravel beach. Landslide debris is present along the toe of the slope at numerous locations along this reach of shoreline. The landslide debris generally contains woody material and is acting as an effective armor against future shoreline erosion. For the most part the shoreline in this area is in a natural condition with little if any shoreline armoring. Sediment derived from slope erosion as well as stream erosion to the south and north is maintaining beach conditions such that toe erosion at the base of the bluff is very slow. The shoreline bluff failures are the result of toe erosion at the base of the bluff. Based on the presence of mature trees on the steep slope,the recurrence interval of bluff failures that impact the entire slope appears to be on the order 50 years or more. CONCLUSIONS AND RECOMMENDATIONS Based on my inspection of the subject property and vicinity, I conclude that a residence can be located on the upland portion of the property as indicated on the site plan sketch. Any residence should be located at least 40 feet back from the top of the steep shoreline bluff slope. A residence located at this site should not be at risk from bluff erosion or landsliding that would threaten the structure within the expected life of the structure(100 years) as long as our recommendations are Stratum Group File:1.12.07 4 • • January 24,2007 JAN 3 0 2Ina Tax Parcel 701201012,Piper Road,Quilcene,WA Geology Assessment followed. No debris should be placed on the top of the bluff or on the steep bluff slope. Thinning and trimming of trees on the bluff slope or within the 40-foot bluff setback should be limited to topping of alders and maples and limbing for view corridors of Douglas fir. Douglas fir can be thinned such that at least one tree per 30-foot center is left. Any debris from thinning on the bluff slope itself should be removed from the slope. At least 65%of the upland area should be left as tree-covered. Storm water run off from the roof gutters should be routed into dispersion trenches to the south and north of the building area. Water should be able to readily infiltrate into the ground at these sites. The septic drain field will not cause any stability problems on the steep slopes as long as the drain field is located at least 40 feet back from the steep shoreline bluff slope. A very rough trail descends to the shoreline between the east facing bluff slope and the alcove area associated with the swale on the south side of the property. Use of the this trail will not cause any slope stability problems on the site as long as the trail is no more than one foot wide. Please note, however,that the trail appears to leave the property on its lower reaches. CLOSURE Please note that there are inherent risks associated with lots near or adjacent to steep slopes. These are risks that the building owner should recognize and be willing to accept. If conditions appear different than those described in this report, or other concerns arise, we request that we be notified so we can review those areas and modify our recommendations as required. We appreciate the opportunity to be of service to you. Should you have any questions regarding please contact our office at(360) 714-9409. Sincerely yours, "iolt /4; am Stratum Group Dan McShane, M.Sc., L.E.G. Licensed Engineering GeologistsitiOs 13 ,6 � Darnel McShane 1 Stratum Group File: 1.12.07 5 7.! map printed on 01/25/07 from "Untitleao" W 122°49.000' W 122°51.000' W 122°50.000' WGS84 122°48.000' Vti' l I ! } � ' ` 5 / e t" r ! ,N t \ 1 `:-- !SrI I - j fr J ,t �'} , t!• 'F 11 ,;0' I: ,ems O � r 7 p I t' O O :yrr �' Ga' ;V5 1', N 27 r `, • )f • \32J,,,.. :-.-':- ._,-.„ '"-; . ,:I ,_', ,-;' .' . 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S , '''C'O'''f%.,*,r,,.,„-,"N-,,,6,9''-!1---.6,.',''r':'''-'."--i 11-'.'-4N7" : , .t \ , .,,,...,(0 ,A Ice; r.... 'i, 1,:-... i ts -cy (1. r fi � j \ l ti • • • STRATUM GROUP 1451 Grant Street, Bellingham,WA 98225 Phone(360)714-9409 May 5, 2008 REcEit _ Lori and John Bugaj �,, 4,��--�" 210 21st Avenue East Seattle, WA 98112 HAY - 8 2008 Re: Geology Hazard Assessment � � ' �� COUNTY ��D Site Plan and Storm Water Plan t,U Tax Parcel 701201012 Piper Road Quilcene, WA Dear Mr. and Ms. Bugaj: I have reviewed the attached site plan for consistency with the recommendations I made in my geology hazard assessment of the site. The building setbacks and storm water infiltration location are consistent with my recommendations and will not increase the risk of landslides impacting the property, other properties or public resources. The site is underlain by very permeable soils and storm water infiltration using a French drain type system located as indicated on the site plan map will be sufficient for handling storm water run off from the roof area. The existing sheet run off from the driveway is readily infiltrated. Should you have any questions please contact our office at(360) 714-9409. Sincerely yours, Stratum Group ®\ ZilL Dan McShane, M.Sc., L.E.G. \\<„ E Licensed Engineering Geologist � 13iP --• ''`� Daniel McShane • • B fY. _..t / 1 I. _ 40. A‘C pep— I I `/ I .7 ' , \ \ it . I I / I 1.R — / joti I I \,� �� rt I I / 1 l N.� -� 1 \\ ilf '..'. .k.„. ----i ,,4i .,. . iLl N r CI, i , ' l / d I 3 00 -00 4\ I \ II .`� -If- r 0 C 1I. 0 \ , ' b . { 91t i2 _ I kt MAY — 8 2008 f0f ga .• .....„ - `\ i,ii , ao JEFFERs € COt11 tie 1► 'o per \ 4r /7 i I' 4 E ib 23 C � c 0e . 0 D3 H j •Dm .3�mjg a -,,c F; mho CG cn _ S^ BUGAJ RESIDENCE $*�e ° w o XXXX PIPER ROAC TAX PARCEL 701201012 n Ie L~1 m OUILCENE.WASHINGTON 98368 3 \ --------. \.____ / ,-- _,-- .., AI • _ 1_ __ — ii,_ 2„ ---_______:736 Aill ' ' . s cA-NA< ________-:----_- I \ % � 1 1 :`l ! Nmaluillimaullimmillatifte�immiiiNiestiftwimirai''�,==ice 1 I7" --le..--"A---,"' ' -_____/ 1, 7 0 \ ,ci --) I /9Z *.> ry —o -1 77 i f9,er- J \ .--_- 40' SB 128 N s Iii \ gyp,\ .+ ; -ri yt. S /12�o / 20 N �' N , \ \ ,A i,,,, ,30 7 / 7 7 6,Ni(:_____ IQ 0 / ------------,&,,,D.,\ kP TpA9 \ \ 4, ir , '4 a MAY — 8 2�� ; z taw . s , ; Us OCD co .v. ' , cl ) ig. \ y� 9? ,ice s/" • • [B] HEIGHT, BUILDING. The vertical distance from grade plane to the average height of the highest roof surface. [B] GRADE PLANE. A reference plane representing the average of the finished ground level adjoining the building at all exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 ft (1829 mm) from the building between the structure and a point 6 ft(1829 mm) from the building • STRATUM GROUP 1451 Grant Street,Bellingham, WA 98225 Phone(360) 714-9409 August 6, 2012 Lori and John Bugaj 210 21 St Avenue East Seattle, WA 98112 Re: Geology Hazard Assessment Consistency Inspection Tax Parcel 701201012 Piper Road Quilcene, WA Dear Mr. and Ms. Bugaj: I visited the site in July 2012 to inspect the development of the site for consistency with the recommendations made in Stratum Group's Geologic Hazard Assessment (January 24, 2007) for the site. Development of the site has met or exceeded the recommendations of the geology hazard assessment. The building setbacks and storm water infiltration locations are consistent with my recommendations and will not increase the risk of landslides impacting the property, other properties or public resources. The site is underlain by very permeable soils and storm water infiltration using a French drain type system is designed and located to be sufficient for handling storm water run off from the roof area. The existing sheet run off from the driveway is readily infiltrated along margins of the driveway. Should you have any questions please contact our office at (360) 714-9409. Sincerely yours, ew * Str um Group 14.7�� " '. •.��� /;1 ✓ Dan McShane, M.Sc., L.E.G. t": r4p c,, 333 Licensed Engineering Geologist 4, ' • • STRATUM GROUP 1451 Grant Street,Bellingham,WA 98225 Phone(360)714-9409 May 5, 2008 RECEIVED Lori and John Bugaj 210 21 St Avenue East Seattle, WA 98112 MAY - 8 2008 Re: Geology Hazard Assessment JEFFER�O�I COUNIY OCR Site Plan and Storm Water Plan Tax Parcel 701201012 Piper Road Quilcene, WA Dear Mr. and Ms. Bugaj: I have reviewed the attached site plan for consistency with the recommendations I made in my geology hazard assessment of the site. The building setbacks and storm water infiltration location are consistent with my recommendations and will not increase the risk of landslides impacting the property, other properties or public resources. The site is underlain by very permeable soils and storm water infiltration using a French drain type system located as indicated on the site plan map will be sufficient for handling storm water run off from the roof area. The existing sheet run off from the driveway is readily infiltrated. Should you have any questions please contact our office at(360) 714-9409. Sincerely yours, 01 133h f • Stratum Group w� O ; Dan McShane, M.Sc., L.E.G. \ <rr- !! +�,�:' Licensed Engineering Geologist 'P Dante! McShane • • — — T9;� Z ' r. .f' _ :, l - — Cam:-. -l'e \ \ N. /4. '' ,:I.:17--\' . . 1- 7./ _ _\___I eiiiii., I ___ _,,,,,,_..-_,..„. /77\ , .,., / - --. 1--- --- -4-- 7/ . n —_ • 1 II�� �� y , �t 1 D \ `� �� ---..._._..1111 --- ❑ mot; N \a\ '' I I / I 1 A� \ I I _� - /-I I A '4 _ I Q ,\ '\ I \ .' — I4 S M \ �'l - \ \\ih, *- — -. ;%, I — d S I � -t '' ' =. I i v - - R -No,- IVED � MAY — 8 2008 RX''K- �� A o$i JEFFEEIN COUN1Y OCEJ bo .�: #gym , °� D NR.rn — , = , ...'it \� . g:= APPI °C�K D — ! 'c D :Ot �4, F g9 j -(> � ,� • STORMWATER PLAN 0 . CJ 1 Res cs W . 4 °_ . • MAY - 9 200 t 4 , 8 1EFFERS.� ,O Y c DEPT.OF Ct FF g a SIGNATURE /�/�r4 '�PM „5�g� c u Vim. a� ' • bra m •• =r BUGAJ RESIDENCE NxPry� X%%X PIPENAOAO TA%VARCEL70'""12 Stormwa -r . '' 23 CUILCENE.NNS/MIGTON 93733 SS Required ill 1.I. _4' • .„------Th \\.,..__ \II\ ..._.. \i/ ,, f ,,,, -- ___ • . • • , .. . . : 736-1,L--- -91( ------- --_______ 50' I ,Rn7T-L-- \'‘ ' ..' ' . aft.* ° alft""Illftmr......._ ' '' ''Mk.s's ‘: \%ift 1 'Ili �`�.�. V. / / gZ 1,� 2(1L-7 - \ I -- 7,.,, „D m 4, -,;-: , /07' 73 I i \ --__ _____ _IIE 6 N /— \ N r. 40. S B- 728 / / -720 co \ 7 0.\ 3"-Ly .\'',... .....,frt {� _:__ / i ,7 `-DO \ 76 Ti , \ iv / -------g'\ k* \------- r g --� . .,:.,1 APPROVED � . MAY - 8 21 i), �- �- 2 f, "= . ° '. STORM WATER PLAN �t1%r JEFFER DM ' = MAY - 9 2008 ;�.• ,, 1 . � / r,4 :LI: wat 'S ____ /" JEFFERS• equir . 9) SIGNATUR i i��.�i ���.I' L