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HomeMy WebLinkAbout821063024 Geotech Assessment,.-.--_~ NORTHWESTERN TERRITORIES, INC. 'r,';~ TtT SDtfiH PEABODY STREET, PORT ANf3EiES, WA 98362 '• ~`j_' __ Engineers ^ Lead Surveyors ^ ~eobgtsts ~l ~, Construction inspection ~ Materials Testing {360} 452-8491 f-90Q-654-5545 FAX 452-8498 E-Mall: irtfo(l~nti4u.C~t ~}`'^ ~ .f/.~,,,,,,,~ ~~, C„f jj~~C, i~ ~ Q ~' www.nti4n.coM ~` November 4, 2005 ~~~ ~ 7 ~~ Al Scalf, Director OEpr ~ ~phj RSpN ~aUNFy Jefferson County Department of Community Deveiapment ~~~f~'aF-'ECC 621 Sheridan Street Port Townsend, WA 98368 Subject: MLA#: MLA05-005; CASE#: BLD05-00649 Dear Al, DJ Today 1 met with. Kenna#h R Merritt and Janet Moore, applicants for the above action to discuss the storm drainage plan prepared by Mr. Merritt for application at their property. This property was the sutnect of an earlier Geo-technical analysis dated April 15, 2005, which made certain recommendations far addressing drainage. Your letter dated October 26, 2005 refers to this letter anci requests that NTI address the concurrence of the owner prepared drainage plan with the Geatechnical analysis. The Geo-technica! analysis was not specific in how the drainage was to be controlled but identified that minimal impact upon downstream properties should occur. The Owner has proposed the installation of a perforated pipeline system to collect the roof gutters and create a sheet flow distribution system. This technique is addressed in BMP T5-10 in the Department of Ecology Stormwater Manual for Western Washington which also addresses the minimum amount of pipeline per square foot of roof area. The use of a technique that accomplishes the same sheet flow characteristics as T5-10 in a sloped wooded or grassy area is consistent with the April 15, 2005 Geo-technical analysis. Sincerely, NTI Engineering acid Land Surveying Robert A. Leach, PE MBA Principal Engineer c: Kenneth Merril G:\Gen\Bob\E_TRS\Kenneth Merritt Drainage - No Name Rd.wpd a Prepared For Ken Merritt Apri115, 2005 rti ; °t~ OCT - 7 2005 For the Property Described as Tax # 821063024, No Name Road - --- - . „ .:i:'Piv1ENT ~ Section fi, Township 28 North, Range 1 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(d~nti4u.com GEOTECHNICAL REPORT { ~.. _. ;~ NORTHWESTERN TERRITORIES, INC. A JLS GROUP COMPAtdY ~~~ ~ ~ ~ 717 SOUTH PEABtmY STREET, PART ANGELES, WA 98362 ~ ^ Engineers ^ Land Surveyors ^ Geol°gtsts HT/ o Cvnstructron Inspection [] Materials Testing (380) 452-8491 FAX452-8498 twvw.Mi4u.COm E-Mail: iMol91nti4u.com JLS GROUP, 1NC, Geotechnica) Report Tax # 8210fi3024 April 15, 2005 ~~ ~ .~~ } OCT - 7 2005 - ` ~~ ... .. _..~.. _......,...._.. .; F I.~ E ti t Ken Merritt PQ Box 884 Port Hadlock, WA 98339 Subject: Geotechnica! report for Tax # 821063024 Located in Section 6, Township 28 North, Range 1 East, W.M., Jefferson County, WA Dear Mr. Merritt: background Atyouur request, Bill Payton,- Engineering Geologist with Northwestern Territories Inc. conducted a slope stability inspection. at the above-mentioned property on March .30, 2005. The. purpose of this inspection was to examine the slope west of the proposed home site by visual means in order to detem~ine the relative stability of the slope and make recommendations in regards to the proposed construction of a doublewide mobile home with detached garage, in accordance with the Jefferson County Critical Areas Qrdinance. Site Description The subject property is located near the end of No Name Road off of SR 19 south of Swansonville Road in Jefferson County. The hilly wooded property is bounded on the north and south by wooded residential property, on the east by No Name Rd. and on the west by SR 19 (Figures 1 and 2). The east side of the property, where the proposed home site is, slopes to the west at angles ranging from approximately 8 to 11 degrees (14%-20%). At about the 400' contour, as shown on Figure 2, the slope angle increases to approximately 20 degrees (37°!°}. At about the 350' contour, the slope angle again changes to approximately 35 degrees (70%) and continues at this angle to the west end of the property at SR 19. The property is predominantly vegetated with young to mature trees and brush (Photo 1). The property has been logged in the past and most of the trees are young, deciduous varieties. Some of the trees on the steeper slopes have curved trunks, suggesting that downslope creep of the surface soil is occurring in places. The slope i .,. , _ t 1~ ~~ ~~~ ......,__,.~. ~. ~. 0~7 " 7 5 , ` :~ i 3, was relatively dry except for a small amount of moisture above ~ silty Gayer part~+r~y x , ..,~,~r~r downsiope. Several old growth stumps were present on the sloes, ~ndicattl~t'~te~` slope has been stable for a long time. No landslides were noticed on the slope. There is a natural drainage running from near the proposed home site location in a northwest direction off the property. The property is undeveloped except for a driveway has been roughed in (Photo 2} and test pits for septic system design were present in the proposed drainfield location, which will be west of the proposed home. Site Geology The Department of Ecology's "Geology and Ground-Water Resources of Eastern Jefferson County, Washington" maps the western portion of the property as (Qu) Undifferentiated glacial, fluvial, glaciofluvial, lacustrine and glaciolacustrine deposits. These deposits are older than the Fraser glaciation and include sediments from. pre Fraser glaciations. This unit contains a variety of soil types and is generally mapped when more detailed data is not available. The eastern portion of the properly may contain Lodgement till from the Fraser glaciation. According to the Soif Survey of Jefferson County Area, Washington (United States Department of Agriculture, 1975), the subject site is in an area mapped as the Alderwood gravelly loam and. Sinclair gravelly sandy loam. These soils formed in glacial till. The Survey states that there is a seasonal perched water table at about 20" to 40" below the surface during the wet season. Runoff is medium to rapid and the hazard of water erosion is moderate to severe. Visual observations made at the site are generally consistent with the above soil descriptions. Conclusions and Recommendations The subject property. appears grossly stable and the project seems feasible. from a geotechnical perspective. We recommend that the proposed home, garage and septic system be Located on the east .half of the property, at least 30 feet east of the line where the slope increases from approximately 10 degrees to approximately 20 degrees, which is about the 400 foot contour line on Figure 2. The following recommendations should also be considered with regards to the proposal: 1. It will be necessary to maintain ground cover on the slopes and on the flat areas in order to reduce erosion from surface runoff. Existing bare areas and any future bare areas that develop should be revegetated. Native deep-rooted vegetation that requires little or no irrigation would be the most beneficial. Please consult the enclosed publications for further information. 2 2. Heavy irrigation or other activities that would contribute large quantities of water to the soil should be avoided. 3. Surface runoff from hard surfaces such as roofs, driveways, walkways and patios should be controlled and routed to a drainage control device such that surface water discharge to adjacent properties does not significantly exceed predevelopment conditions. It may be feasible to control release this water to the existing natural drainage swale with quarry spans or perforated pipe. 4. Surface water should not be allowed to flow freely down the face of the slopes and cause erosion of the slopes. If this occurs, the water should be directed away from the slopes and/or conveyed to a safe discharge area, possibly into the swale mentioned above. 5. Silt fences or other sediment control devices may be needed during construction so that sedimentation to adjacent properties does not significantly exceed pred®velopment conditions. 6. Drainage control devices should be maintained in good working order and inspected at least once a year. 7. All drainage control features should conform to the current regulations that apply to the development of this property and be constructed in acxordance with standard engineering practice in order to insure that surface water discharge or sedimentation to adjacent properties does not exceed predevelopment conditions. Based on the findings, recommendations and limitations of this report, with the control of post development runoff to predevelopment rates and the application of standard erosion and sediment control BMPs: 1: There should be minimal landslide hazard as suggested by a lack of evidence of recent landslide activity in the vicinity in the past. 2. Observations of slope stability indicate that the proposal should not be subject to risk of landslide. 3. The proposal should not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions. 4. The proposal should not decrease slope stability on adjacent properties. 5. The proposal should be stable under normal geologic conditions. For further information please review the three enclosed publications published by the Washington State Department of Ecology (DOE} entitled: "Slope Stabilization and 3 Erosion Control Using Vegetation", "Vegetation Management: A Guide for Puget Sound Bluff Property Owners" and "Surface Water and Groundwater on Coastal Bluffs". These publications are now out of print but can also be obtained from the DOE website at: http:l/www.ecYwa.govlbiblio/sea.html under the 1993 and 1994 year heading, The DOE website also contains additional useful information regarding slope. stability and site development; this reference is highly recommended. Limitations This report has been prepared for your exclusive use in conjunction with the above referenced project. The report has not been prepared for use by others or for other locations. Others may use it 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 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 si;~bject property at the time of our site visit; no laboratory tests were performed. Soii and geologic conditions can vary significantly between test holes andlor surface outcrops. If 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 TERRITORIES, INC. Robert A. Leach, P.E., MBA Principal Engineer ~"'~ ; ~ .: ~ , ~`~- ~:~ 1 '.. .. .. ~ ~ '. ~ ..,,~~ ! .~j~(,.C-mo't' ~~G~~~L^' Q~',~ ` 7 i "" i Bill Payton, L.E.G. i i Engineering Geologist _:__ _._: ____m.:~4'..A''T G:1Gen~Bi111ReportslMERR0501.sbpe stability.6{28-1 ~.No Name Ad.Chimacum Valley.dot 4/141a~ 4 iawu~s ~arsa2oos - Expires 11 J06105 _:.~ OCT - 7 ?~~5 J ~~ ~ ~ i . . ..__,~ . OCT - 7 ?_005 ~ t Trt.~: s.,.