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Home My WebLink About969000021 Geotech AssessmentGEOTECHNICAL REPORT Prepared For Connie and Steven Rogel November 21, 2003 For the Property Described As 1011 and 1031 Ludlow Bay Road Section 16, Township 28 North, Range I East, W.M. Jefferson County, Washington Prepared by NORTHWESTERN TERRITORIES, INC. 717 S. Peabody Street Port Angeles, Washington 98362 Phone 360-452-8491 Fax 360-452-8498 Web Site www. nti4u.com E-mail info@nti4u.com JLS GROUP~ INC. NORTHWESTERN TERRITORIES, INC. A JLS GROUP COMPANY 7t7 SOUTH PEABODY STREET, PORT ANGELES, WA 98362 Engineers Land Surveyors Geologists Construction Inspection Materials. Testing (36.0) 452-8491 FAX452-8498 www. nti4u.com E-Mail: info@nti4u.com Geotechnical Report for 1011 and 103t Ludlow Bay Road November 11, 2003 Connie and Steven Rogel 12020 Nyanza Road SW Lakewood, WA 98499 Subject' Geotechnical Report for 1011 and 1031 Ludlow Bay Road, Located in Section 16, T28N, R1E, W.M., Jefferson County, WA. Dear Mr. And Mrs. Rogel' Background At your request, Bill Payton, Engineering Geologist, with Northwestern Territories, Inc. (NTI) conducted a geotechnical inspection of the above-mentioned property on November 6, 2003'. The purpose of this inspection was to .examine the marine bluff at the su'bject property by visual means and make recommendations regarding the development of the property in accOrdance with Jefferson County Unified Development' Code for Geotechnical Reports. It is our understanding that development plans for the property include the demolition of an existing cabin and construction of a site built single family residence with daylight basement and detached garage on .one lot, and the remodel of an existing house (Photo 1) on an adjacent tot, including the demolition of an existing attached garage and construCtion of a new deck. These plans-are shown on the enclosed site plan, except. that the revised 'location of the proposed new house will be 10 feet closer to the bluff than depicted on the drawing ' Site Description The subject waterfront property is located on Ludlow Bay Road south of Port LudlOw overlooking Port Ludlow Bay. The property consists of three lots that have been reconfigured into two lots. The property is bounded on the northeast and southwest by developed residential property, on the southeast by Ludlow Bay Road, and on the northwest by Port Ludlow Bay. The property slopes gently towards the northwest and is well vegetated with young to mature trees and brush (Photo 2). There is a drainage way down an old driveway along the northeast property line that drains into Port Ludlow Bay. The drainage was dry at the time of the site visit, hoWever, erosion of tliis drainage way has occurred (Photo 3). The bank at the subject property is about 20 feet high and slopes down towards the northwest at an average angle of approximately 28° (53%). This angle is well below the typical "an~le of repose" which is defined as the maximum slope or an~le at which loose, cohesionless material romains stable. It commonly ranges between 33 and 37 degrees on natural slopes. The bank is well vegetated with young i~o mature trees and brush (Ph'otos 4 and 5). No evidence, of slide activity was noticed and no springs or seeps were noticed. The beach appears to be a Iow energy beacbwith little waVe .... erosion. It also appears that Waves do.not normally contact the toe of the bank. There are at least two trees on the bank that are dead or damaged' (Photo 6). These trees. should be removed with the stumps left in place undistUrbed. Geologic Conditions The SCS Soil Survey of Jefferson County maps 'the surface soil in 'the area of the subject property as the Kitsap gravelly loam (KsD). The Survey. states that this soil formed in glacial lacustrine or marine sediments. Runoff is medium to rapid and the hazard of erosion and slippage .is moderate to severe. The Coastal Zone Atlas of Washington describes the soil in the area of the subject property as the Vashon advance outwash (Qva), a well sorted, well stratified sandy pebble to cobble sized gravel, with some silt and clay. The Atlas maps the bank as unstable and the upland as stable. The.Atlas labels the foundation stability of this soil. as good to excellent, except on slopes that approach the angle of repose. Slope stability of this soil is described as generally stable in slopes up to the angle of repose. Seismic stability of this soil is labeled as good'. The Washington Department of Ecology's "Geologic MaP of Eastern Jefferson County" maps the soil at the subject, property as Advance outwash (Qva) of the. Fraser Glaciation. The soil is described as gravel and sand with some silt and clay: Visual observations made at the site, including observations of drainfield Perc holes, were consistent with the above mentioned soil descriptions from the Coastal Zone Atlas and Geologic Map of Eastern Jefferson County. No fine grained soils as. mentioned by the Soil Survey were observed on site. Conclusions and Recommendati°ns The bank at the subject property appears grossly stable and the development of-the property seems feasible from a geotechnical persPective. The bank.face is'well vegetated and no apparent slide activity was noticed. The bank angle is well' below the angle of repose. No springs or seeps were'noticed on the bank face and it appears that the toe of the bank is not being.actively undercut by wave erosion, as is common with a marine bluff. Plans call for the new houSe to be about-40 feet back from the edge of the bank (10 feet closer than shown on the site plan). Based upon our investigation, we recommend.that the proposal be approved as shown on the enclosed site plan (and amended as mentioned above) with regards to setback distances. The following recommen.dations should also be considered with regards to development · of the subject property' · it will be necessary to maintain ground cover to reduce erosion from surface runoff. Any bare areas that develop on the property should be revegetated. Native vegetation that requires little or no irrigation would be the most beneficial. I ii 2. Vegetation on the bank face provides stabil.ization to the bank face soils. T. he vegetation on the bluff faCe should be .left in as natural a state'as possible. If an ................... enhanced view is desired' trees 'ShOuld be pruned such that the trees are not damaged. ExcePt that the damaged trees should be removed with the stumps left in place as mentioned above. It may be wOrthwhile to consult a tree expert in this matter. 3. Heavy irrigation or other activities that would contribute large quantities of Water to the soil should be avoided. One cause of 'slope instability is the presence of excessive groundwater. 4. Surface runoff from hard surfaces such.as roofs, driveways, walkways and patios should be control.led and routed to the beach via tightline such that surface water disCharge to adjacent properties does not significantly exceed predevelopment conditions. , Silt fences or other sediment control deVices may be needed during construction such that sedimentation to adjacent properties does.not signifiCantly exceed predevelopment conditions. 6. All drainage control devices should be maintained' in good working order and inspected at least once a year. · .7. If erosion of the drainage waY on the northeast property Ii'ne continues, it may · become necessary in the' future to Stabilize the slope to prevent sloughing of the slope. A proactive approach woUld be to channelize'the drainage in .pipe or an impervious ditch, or to place rock check dams i'n the existing ditch, to reduce ' erosion. This would require cooperation from the neighbor since it is .not on the subject property. .. 8. An engineered drainage and erosion.control plan. shoUld be developed for this -" pr°perty to address items 4, 5, _6.1and 7 ab°ve. NTI can-perform thiS task if · -r. eqUested. . -. 9 'FOoting drains' and a backdrainage system behind the baSement retaining wall are. recommended Th'ese drains should 'be kept separ.ate_ from roof'drains and be tightlined away from the ,house. 10. SePtic drain fields shoUld not be constructed between the house and bluff. Based On the findings, recommendations and limitations of this report' i There should be minimal-landslide hazard .as suggested by a lack of evidence of recent landslide' activity in the vicinity in the past. . 3~ Observations of slope stability indicate that. the proposal should not be subject to risk of landslide under the current conditions that exist at the site. The proposal should not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions. tl il ii m 0 jA?~. 2~ The .proposal should not decrease slope stability on adjacent properties',' · The proPosal should be stable under normal geologic conditions. For further information please. review, the three online publications published by the Washington State Depa.rtment of Ecology (DOE) entitled' '.Slope StabiliZation and Erosion Control Using Vegetation", "Vegetation Management: A.Guide for Puget So.und Bluff Property Owners" and "Surface Water and Groundwater on Coastal Bluffs". These publications are now out of print but can be obtained from the DOE website at' http'//www.ecy.wa..qov/biblio/sea.html under the 1993 and 1994 year heading. The DOE website also contains much more useful information regarding slope stability and site development;.this reference is highly recommended. Limitations This report has been prepared for the exclusive use Of our client in conjunction with the above referenced project. The report has not been prepared for use by others or for · other locations. It.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 accepted professional engineering and geological principles and practices in this or similar localities at the time the report was prepared.. No other. warranty, expressed o.r implied, is made as to.the conclusions.and Professional adVice incl'uded in this', repOrt. ' ..... · . The observations,., conclusions and rec°mmendations presented in this re'port.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. If there is a substantial lapse Of time, conditions, at the site have changed Or aPpear different than.those described in this. report,.we 'sho'uld-be contacted and retained to eValuate the-changed' conditions and make modifications to our 'repOrt if necessary. .,. · ~.. .. . . .. Sincerely',' .. .. NORTHWESTERN TERRITORi'Es, INC, .. Robert A. Leach, P.E., MBA Principal Engineer' Bill Payton, L E.G.. Engineering Geologist G:\Gen\Bill\Reports~ROGE0301 .bluff stability. 16(28-1E).Ludlow Beach.doc 4 iExpires 11/6/04 J , ... Photo 1. View of existing house. Photo 2. View of upland vegetation on property. Photo 3. View of drainage way. Photo 4. View of bluff at subject property. 4' Photo 5. Another view of beach at subject property. -,. . .. . . Photo 6.-View of dead/damaged trees on bluff. o, \ ) \ \~, / ,,/