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Home My WebLink AboutBLD2007-01164 - BLD Engineering / Geo-tech Reports - 10/2/2007 RECEIVE OCT 04 2007 NMCCD - PLANNING Jerome W.Morrissette&Associates Inc.,P.S. Civil•Municipal•Ck-wechnical Engineering and Planning 1700 Cooper Point Road SW,#13-2,Olympia,WA 98502-1 1 1 0 (360)352-9456 / FAX(360)352-9990 02 October 2007 Mason County—Department of Community Development- Planning PO Box 279 Shelton,Washington 98584 ATTENTION: Mr. Robert Fink,Planning Manager SUBJECT: Consultant Review—Geological Assessment BLD 2007-01164—Minton-Tahja (JWMA N07123-014) Dear Mr. Fink: Pursuant to Mason County Geo Tech Work Order BLD 2007-01164, the associated Geotechnical Report Addendum has been reviewed for compliance with Mason County Resource Ordinance— 17.01.100 Landslide Hazard Areas. The report addendum provides supplemental information that addresses the items listed in my Comment Letter dated 17 August 2007 and I have no further exceptions or comments. Should you have any further questions or require clarification, kindly contact me at(360)352-9456. Yours very truly, J. W. MORRISSETTE&ASSOCIATES INC. P.S. �Pb'�jy APPROVED S cc MASON COUNTY DCD PLANNING r---- - BY — Date' 4—PM7 EXPIRES 09/11/2009 Edward A. Wiltsie,P.E. AA,- Ede Sr. Geotechnical Engineer/Associate a Wrc&-r'� . (1/1 TAHJA ENGINEERING, Inc. ` PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Mason County DCD Attention: Ryan Carter& Robert Fink PO Box 279 Shelton, WA 98584 Jerrison P. Minton 12951 Burchard Drive SW Port Orchard, WA 98367 (360) 876-6435 RE: Geotechnical Assessment Mason Co. Case No.s BLD2007-01164 RAP2007-00248 SPI2004-00293 SWG2007-00430 Mason Co. Prcl No. 12206-51-00024 Ryan & Robert, Enclosed please find two copies of an addendum I've prepared in answer to J.W. Morrissette &Associate's review and request for additional information pertaining to the Minton property located in the Belfair area. Also enclosed find a copy of your review cover letter requesting additional information, and a copy of the review comments from Mr. Wiltsie. As the attached addendum to my original geotechnical assessment states, published stability classifications were considered in my original site investigation and reporting, so I still consider the findings and recommendations made in my original assessment valid and applicable. Again I am compelled to complain that the County, in accepting Mr. Wiltsie's reviews, and is thereby supporting his non-compliance with Washington State's Board of Engineers and Surveyors requirements which require his review(s)to be stamped, signed and dated with his signature date and license expiration date. The next time I receive an improperly sealed review report, I will report it to the Engineer's and Surveyor's Board along with a complain that the County is supporting this unprofessional practice in retaining Mr. Wiltsie, in spite of being informed of his unprofessional work. Please feel free to contact me if there additional issues you feel need further consideration or action on. Sinc rely, an A. ahja, P. . File:C:TrojectsWintonlGeo-Addndm Cvr to Co 1 of 1 9/19/2007 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Mason County DCD Planning Division—Tammi Clark,Robert Fink PO Box 279 Shelton, WA 98584 Jerrison P. Minton 12951 Burchard Drive SW Port Orchard, WA 98367 (360) 876-6435 RE: Geotechnical Assessment Mason Co. Case No.s BLD2007-01164 RAP2007-00248 SPI2004-00293 SWG2007-00430 Mason Co. Prcl No. 12206-51-00024 As indicated in the attached letter from Mason County Department of Community Development, and the attached geotechnical report review letter prepared by Edward Wiltsie, P.E.,representing J.W. MORRISSETTE&ASSOCIATES, additional information is requested pertaining to Mason County case no. BLD2007-01164. Information requested by Mr. Wiltsie is followed by my responses; • 17.01.100.E.4(5&6 The report does not include a discussion slope stability characterizations published in the Washington State Coastal Zone Slope Stability Mapping or Map I-853-F, Relative Slope Stability of the Southern Hood Canal Area, Washington, which categorized the site as Unstable (see Figure 1). This categorization must be included in this report along with a discussion of observations and conditions that lead to the conclusions presented. Closer inspection of the Coastal Zone Atlas for this area finds an area northeast of the Minton property between Evergreen Drive and Highway 106 as"Unstable Recent Landslide". This area is generally located on my original site plan as a relatively level area 200 to 300 feet northeast of the Minton property. The areas surrounding this Unstable Recent Landslide area are characterized as Intermediate or Unstable. In the winter of 1997,properties located along Evergreen Road and Alderwood Road experienced stability problems associated with heavy rains,poor drainage, and saturated soils. None of the problem properties were located in the"Unstable Recent Landslide" area currently depicted on the Coastal Zone Atlas in the proximity of the Minton File:C.IProjectslMintonlGeo-AssmntAddndm I of 2 9/19/2007 •r • TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 property,but were located southwest of the Minton property at a distance approximated at an eighth of a mile away as stated in my original geotechnical assessment. These stability characterizations and knowledge of the problems experienced as recently as 1997 were all taken into consideration in my original geotechnical assessment. My original geotechnical assessment included recommendations for controlling drainage from the property, and no change to my original assessment or recommendations appears warranted. I hope this satisfies Mason County's and Mr. Wiltsie's concerns regarding this site's stability issues. Please feel free to call me if you have any questions regarding this information, or if you feel anything needs correction or changing. Sincerely, Alan A. Tahja, P.E. v� WAs 13 �784 ��' +P�+GISTY, �`SSIONAL VE, EXPIRES File:C:IProjectslMintonlGeo-Assmnt Addndm 2 of 2 9/19/2007 RECEIVED AUG 2 2 2007 Jerome W.Morrissette&Associates Inc.,P.S. MCCD - PLANNING Civil•Municipal•Ceotecimical Engineering and Planning 1700 Cooper Point Road SW,#13-2, Olympia,WA 98502-1110 (360)352-9456 / FAX (360)352-9990 17 August 2007 Mason County—Department of Community Development- Planning PO Box 279 Shelton, Washington 98584 ATTENTION: Mr. Robert Fink, Planning Manager SUBJECT: Consultant Review—Geological Assessment BLD 2007-01 1 64—Minton - Tahja QWMA N07123-014) Dear Mr. Fink: Pursuant to Mason County Geo Tech Work Order BLD 2007-0 1 1 64,the associated Geological Assessment was reviewed for compliance with Mason County Resource Ordinance— 17.01.100 Landslide Hazard Areas. My comments are as follows: • 17.01.100.E.4(5 &6)The report does not include a discussion slope stability characterizations published in the Washington State Coastal Zone Slope Stability Mapping or Map I-853-F,Relative Slope Stability of the Southern Hood Canal Area, Washington,which categorized the site as Unstable (see Figure 1). This categorization must be included in this report along with a discussion of observations and conditions that lead to the conclusions presented. � rJ r — r If tws j ad(fT4Y8 sy I Location M I'I�UIY I recommend that the subject report be returned to the proponent for revision to achieve compliance with the referenced ordinance. I have attached a copy of the Geo Tech Work Order provided by your office authorizing this review. Should you have any further questions or require clarification, kindly contact me at (360)352-9456. Yours very truly, J. W. MORRISSETTE & ASSOCIATES INC. P.S. Edward A. Wiltsie, P.E. Sr. Project Engineer/Associate TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Mason County DCD PO Box 279 Shelton, WA 98584 Jerrison P. Minton 12951 Burchard Drive SW Port Orchard, WA 98367 (360) 876-6435 RE: Geotechnical Assessment Mason Co. Case No.s BLD2007-01164 RAP2007-00248 SPI2004-00293 SWG2007-00430 Mason Co. Prcl No. , 42333-51-02922 INTRODUCTION Mr. Jerrison Minton wishes to improve his undeveloped property located in the plat of Alderwood Villa with a single family residence. He is in the process of pursuing permits for a driveway access, an onsite septic system, and building permit for a house roughly measuring 33 feet by 30 feet with a daylight basement. Slopes on and around the property were investigated, and the steepest slope potentially affecting the property was on the property itself with an average 30%downslope towards the northwest,with a vertical relief greater than 10 feet. Mason County's critical resource ordinance requires geotechnical investigation of any properties with slopes exceeding 15%and more than 10 feet of vertical relief. No greater slopes or instability indicators were found on or in the vicinity of the property which would require a more aggressive investigation than the County's geotechnical assessment requirements. The following nine elements are required to be addressed in geotechnical assessments prepared to meet the County's geotechnical assessment requirements. 1. Discussion of geologic conditions: The site is located on the hillside above the south shore of Hood Canal roughly 3 miles southwest of Belfair, Washington. The site is accessed off of East Evergreen Road, a plat road constructed during the development of Alderwood Villa, in the mid 1960s.The property measures 100 feet along E Evergreen Road, and extends 110 feet perpendicular to E Evergreen Road in a southeasterly direction. Measurement of the slope ascending towards the southeast found to average 30%, with small undulations near the bottom of the property,possibly caused by past grading activities. File:C:ProjectslMintonlGeo-Assmnt 1 of 4 8/6/2007 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 Three soil log holes were found on the property, as located on the attached site plan. The soil was found to be a gravelly sandy loam, with a fairly high silt and/or clay content. The gravelly sandy loam was found to average 25 to 32 inches in depth before a gray glacial till layer is encountered. Inspection of the Geologic Map of Washington indicates that the soil is classified as Qg, an unconsolidated deposit comprised of quaternary sediments, dominantly glacial drift, including alluvian. 2. Discussion of groundwater conditions at the site: The site was visited on July 29, 2007 when the site was in a dry condition. Small pockets of wetland vegetation in locations identified by the owner and Mason County Planning staff, generally developed in small pockets where stormwater perches between the surface vegetation and the underlying impervious glacial till material. Aside from the shallow stormwater perched in the shallow topsoil layer in isolated spots on the property, groundwater is expected to generally agree with the tidal elevation of Hood Canal, at a depth of roughly 120 feet below the property's elevation at the E Evergreen Road. The groundwater at this elevation should not affect the site's stability. Because of the shallow depth of the permeable soil above the impermeable glacial till layer, the shallow soils have a potential of becoming saturated if stormwater isn't relieved from the surface, and subsurface soil horizon(s). Mr. Minton has indicated his intention of installing a curtain drain across the "back"of the property to capture surface runoff and direct it in a tightline pipe to the E Evergreen Road drainage ditch. This curtain drain should be installed as far back on the property as possible, and certainly should be installed"above"a septic system drainfield if the back of the property is chosen for its location. The curtain drain should be excavated no less than 36"deep by 24 to 36"wide, with a 1-foot minimum excavation into the underlying glacial till layer. The excavated trench should have a layer of geosynthetic filter fabric (Mirafi 140 NSL or Mirafi 160N,Amoco 4552, Carthage Mills FX-60HS, or equivalent) wrapped around a drainage gravel fill material with a 6 inch perforated PVC drainline pipe installed in the bottom of the trench, connected to a 6 inch non- perforated PVC tightline pipe installed to convey collected surface and subsurface water down to the E Evergreen Road drainage ditch. 3. Approximate depth to hard or competent soil: Inspection of the soil log holes excavated on the site for design of an Onsite Septic System(OSS)found a hard glacial till layer generally within 3 feet of the ground's surface. The shallow topsoil horizon was found to be in a medium dense File:C.TrojectslMintoMGeo-Assmnt 2 of 4 8/6/2007 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 condition,capable of supporting standard building foundation loads in its natural unsaturated, undisturbed condition. 4. Discussion of geomorphic expression of past slope instability: Though the property surface undulates to a small extent,the surface appears to reflect the geometry and slope of the underlying glacial till layer.No clear evidence of slope instability was observed on or near the site. 5. Discussion of the history of landslide activity in the vicinity: Some properties in the Alderwood Villa plat have experienced landslide problems in the past, but the nearest problems were no nearer then an eighth of a mile away. Slumping of the slopes in the past is considered to be a by-product of poor stormwater runoff management and saturation of fairly deep pockets of the loamy soil outside the area of the subject property. 6. An opinion on whether the proposed development is within the landslide hazard area or its associated buffer or setback: Because of the site's underlying glacial till substrate,the proposed development site is not within a landslide hazard area, or within any buffers or setbacks from landslide hazards off-site. 7. A recommendation by the preparer whether a Geotechnical Report should be required to further evaluate site conditions and the proposed development of the subject property: A geotechnical report level investigation of the property does not appear warranted from the observations and findings already made. 8. If the presence of a hazard is determined within 300 feet of the proposed development, then the area of the proposed development, boundaries of the hazard, and associated buffers and setbacks shall be delineated(top, both sides, and toe) on a geologic map/site map. No hazard was found within 300 feet of the subject property. 9. 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: A site plan is attached which contains the required information. The house and Onsite Septic System(OSS) locations are conceptual, awaiting design and approval of the onsite septic system. File:C.•TrojectslMintoMGeo-Assmnt 3 of 4 8/6/2007 TAHJA ENGINEERING, Inc. PO Box 235, Hoodsport, WA 98548 (360) 877-9512 The proper disposal of surface water runoff is important to the continuing stability of the site. A curtain drain as intended by Mr. Minton should be made a condition for site development. A foundation drain should also be installed around the"back" side of the basement/foundation to ensure no build up of water or soil pore pressure. The shallow surface soils were found to be a fairly fine soil texture, susceptible to erosion and scour, and are considered to be an erosion hazard if not properly managed. As a first step to property development,a stabilized construction entrance constructed of a 6 inch or deeper quarry spall or clean pit run gravel driving surface should be installed along with a silt fence installed along the northerly boarder of the property(along E Evergreen Road's right of way), and maintained until project completion and permanent soil stabilization vegetation has established itself. Un-worked soils should be covered with a 3+ inch thick layer of straw or hay to protect bare soils from erosive precipitation. Grass or other ground cover vegetation should be planted and promoted to provide permanent scour and erosion protection for areas of the site where grading has been completed. Roof runoff should be collected and delivered to the E Evergreen Road drainage ditch in one or more tightline 4 or 6"diameter PVC pipes. This concludes my assessment of the Jed Minton property located in the Alderwood Villa plat in Belfair, Washington. With proper drainage control, development of the property should not produce any adverse impacts to either the subject property or neighboring properties. Please feel free to contact me if there are any additional concerns or issues required to be addressed by Mason County's Critical Resource Ordinance 17.01.100 E. 4.. Sincerely, A M Alan A. Tahja, P.E. �' !0}'0 1 Attached: 3 page plan set. lr -p1 w� BOA S TF, 4� �SSI0 L ma ms File:C:IProjectslMintonlGeo-Assmnt 4 of 4 8/6/2007 Rev# Description Date TAHJA ENGINEERING,INC. Vicinity Map-Alderwood Villa, Lot 24 ` .pa. Alan Tahja,P.E. Jerrison Minton Minton PO Box 235 12951 Burchard Dr. SW Hoodsport WA 98548 Port Orchard, WA 98367 Shm Mason County Pncl No.: 12206-51-00024 (360)877-9512 (360)876-6435 1 of 3 I � i � I o \�• I I O �p � M � C? 000C) Obi 1 ¢ 3 \ I i \ \ \ \ N o CL Q6, \ kn o \ O ♦ J O � � \ to \� 08 a \ \ N \\ OA 8 0e \ �\ O W \ o GO N E SCALE: I"=30' o to 20 30 S Qa�eR` oaa�v��'� tia e°� � / Lot 2 Instail Access e' ace t gto / e `.o RAP2 0002 Requirem s N`��av�� e t�a ` 10'Side ^w x G°O� B ing Setback, o 25' Front&Back 0 Building Setbacks W P a e "oo Conjectural Residence ` 00'0 4� vav� i/ °s with Daylight Basement 122 OIN Gravel Filled Curtain e Lot 23 Drain with 6"Dia. v� Perforated Drain Pipe A. T WAS f J1 \ QtoQ�1� 31)TS10 ww BLD2007-01164 N RAP2007-00248 w SP12004-00293 b Daum S W G2007-0043 s Vi C C- 'h o b. Q. Property Line 100' I SCALE: V'=30' O 0 10 20 30 I Conjectural Drainfield Area I ^wx � yQ+of A WA aU Conjectural Residence �.� 8j with Daylight Basement 0 3u7ea Deck v GISTE �S`�lONAL E I I Stabilized Construction a e b I Entrance,,o `4 p to o E I Conjectural Drainfield Area 3 to p Road Right of Way `^ � a a a Erosion Control Property Line 100' Silt Fence v E Evergreen Road Edge of Pavement Road Right of Way BLD2007-01164 w_00249 o, SP12004-00293 w-T e S WG2007-00430