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Home My WebLink AboutPettygroves 2nd Block 96 - Geotechnical Report - 2005.09.27Subject Property _- s*.-4r :'*i- Fpfr+t Gl!tfr'sr GEOTECHNICAL REPORT Prepared For Christian Young September 27,2005 For the Property Described As Tax # 985209601 Section 2, Township 31 North, Range 1 West, W.M Jefferson County, Washington Prepared by NORTHWESTERN TERRITORIES, INC. 717 S. Peabody Street Port Angelos, Washington 98362 Phone 360452-8491 Fax 360-452-8498 Web Site www.nti4u.com E-mail info@nti4u.com NTI NORTHWESTERN TERRITORIES, INC. A JLS GROUP COMPANY 7I7 SOUTH PEABODY STREET, PORT ANGELES, WA 98362 Engineers Land Surueyors Geo/ogrsfs . Construction lnspection Materials Testiqg (360) 452-S491 FAX 452-8498 www.nti4u.com E-Mait: info@nti4u.com at an angle of approximately 18 (32o/o V"*ry"-{- J#d€,.sr. sse frtWec*{.*d' JLS GROUP,lNc. Geotechnical R.eport for Tax # 985209601 trSeptember 27,2005 Christian Young 330 P Street Port Townsend, WA 98368 Subject: Geotechnical Report for the Property Described as Tax # 985209601, Located in Section 2,T31N, R1W, W.M., Jefferson County, WA Dear Mr. Young: Background At your request, Bill.Pgytg!, Engineering Geologist, with Northwestern Territories; lnc. (NTl) conducted a geolechnical inspection of the aboVe-mentioned property on September 1, 2005.The purpose of this inspection was to examine the property by visual-means'and makerecommendations regarding the development of the property in accordance with Section 19.05.100 of the Port-Town-send Munici'pal Code (PTMi) ' It is our understanding that development plans for the property include the construction of a site built single-family residence on the property, similar to the existing house to the west. It is also understood that slopes on the subject property are listed as a landslide hazard areaaccording to the PT.MC. And as such requiies a geoteihnical evaluation. Reportedly, theproperty used to be the City's gravel pit. Site Description The subject property is located on the north slope of Morgan Hill in Port Townsend, south of unopened Q Street and west of Walnut Street (Figure 1). Curently the property is undeveloped.The property is bounded on the north by unopenei Q Street, and -on the edst, south jnO *eii by residential houses. The property slopgs down towards the south from Q Street, levels off,then slopes u.p towards the south property line (Figure 2). The property is vegetated with grass and weeds with some trees (Photo 1), No evidence of slope instability was n6ticed and ndsprings or seeps were noticed on the property. The north slope at the subject property is about 15 feet high and slopes down towards the south I is about 11 feet asa ed as the maximum slope or an n as specified by the 're pose"IS 1 gle at which loose , cohesion cal "of a remains stable^and typically rang"idpggEFfrtfproOaUty a result of Geologic Gonditions The SCS Soil Survey of Jefferson County maps the surface'soil:in the area of the subjecl - . piopurtv ui tn" cruri'u111 gravelly sandy lo'am (bmD). This soil formed in glacial till. Runoff of this ioit:li ti'sted as medium ind the hazaid of water erosion as moderate. .The Coast al Zone Aflas of WaShington describes the soil in the area of the subject property as the Vashon lodgement till (Qvtl), Jcompact mixture of boulders, cobbles, pebbles, sand, silt. ano ciiy, g"n"riily overlain ny i-s feet of ablalion till. The Atlas also describes this soil as belng exceilenifir foundation stability and good for seismic stability. The Atlas maps the slope stability - "r Stunt" 1S). The Atlas statesthat this soil stands in steep natural and cut slopes for long feriods. For comparison purposes, the vertical bluffs downtown along Water Street are mapped as this same soil tYPe. The Washington Department of Ecology's "Geolo_gi9.Mgq of Eastern Jefferson County" maps the soil at tf-re subject proper.ty as lodgement till (Qvt) of the Fraser Glaciation. The soil is described as a compact unsorted mixlure of boi.rlders, cobbles and pebbles in a matrix of sand, silt and clay. Generally overlain by a few feet of recessional drift or Holocene sediments. Visual observations made at.the site, including'soils from one hand dug test pit were consistent with the above mentioned soil descriptions. Conclusions and Recommendations The slopes on the subject property appear grossly stable and the development of the property ;;;;i;ibte from.g"oi".i'nic'at perspective. tne slope face is.well vegetated and no upprtunt slide activity ilas'noticed. The slope angle is well below the angle'of repose. No rpiingr or seeps were noticed on the slope face ind the toe of the slope is not being actively undeicut as is common with a marine bluff. After reviewing available literature and conducting a field visit including a ]e|t pit, it is out' b"inlon that s6oloqical ESA's and/or" their bufferfdo not exist on-site as defined.by Sections iI.OS.OZO iriO tg.'0S.t00(B) of the Port Townsend Municipal Code. The following recommendations should also be considered with regards to development of the subject propertY: 1. lt will be necessary to maintain ground cover to reduce erosion from surface. ru.nOff. Any nare jrear tfiit Cdvetop on the [roperty should be revegetated. Native vegetation that requires little or no iprigiation would be the most beneficial. 2. Heavy irrigation or other activities that would contribute large quantities of water to the:' soiisiioutd be ivoided. One cause of slope instability is the presence'of excessive groundwater. 3. Surface runoff from hard surfaces such as roofs, drivey?ys, walkways. and patios should G;;li"l[O anq routed to the city storm qewe1.'if available or to a drainage. control ,iyri"m rrcn nai surface water di|charge to adjacent properties does not significantly e-xceed pr,edevglopment conditions. es between 33 and 37 degrees on natural slopes. This site's its past use as a gravel Pit. 4. Silt fences or other sediment control devices may be needed during construction such that sedimentation to adjacent properties does not significantly exceed predevelopment conditions. 5. All drainage control devices should be maintained in good working order and inspected at least once a year. 6. An enginrlered drainage, erosion and sediment control plan consistent with the PTMC should-be developed fbr this property to address items 4, 5 and 6 above. NTI can perform this task if requested. Based on the findings, recommendations and limitations of this report, the proposal should pose no unreasonable threat to persons or property nor decrbase slope stability. Limitations This report has been prepared exclusively for your use in conjunction with the above referenced project. The report has not been prepared for use by others or for other locations. lt may be used by others only with the expressed written permission of the Engineer. Within the limits of scope, schedule and budget, this report was prepared in general accordance with acsepted professional engineering and geological principles and practices in this or similar localities at the lime the report was prepared. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. The observations, conclusions and recommendations presented in this report were based on our visual observations of the subject property at the time of our site visit; no laboratory tests were performed. Soil and geologic conditions can vary significantly across a project site. lf there is a substantial lapse of time, conditions at the site have changed or appear different than those described in this report, we should be contacted and retained to evaluate the changed conditions and make modifications to our report if necessary. Sincerely, NORTHWESTERN TERRITORI ES, INO. Robert A. Leach, P.E., MBA Principal Engineer EXPIRES 12t30t2006 Bill Payton, L.E.G. Engineering Geologist 5 G:\Gen\Bill\Reports\YNGC0501.slope stability.2(31-1).Morgan Hill.PT.doc 3 Expires 11/06/05 /otvRt William C. Fa n Jr. alezfo7 Figure 1 ScwkaffiJdkr*r Figure 2 ScwioccGtri a Photo .1. view of property looking west with north slope in view at right side of photo. 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