Loading...
HomeMy WebLinkAboutGeological Assessment for BLD2005-01853 - BLD Engineering / Geo-tech Reports - 12/13/2005 _STAr lbo F0� NMIo MASON COUNTY ° ti = PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton, Washington 98584 1864 DATE: December 13, 2005 INTER-DEPARTMENTAL COMMUNICATIONS TO: Chuck M. --Planner PARCEL #12309-34-90090 FROM: Patricia C. — PW BUILDING PERMIT NUMBER: BLD2005-01853 SUBJECT: Geological Assessment Review NAME: Snazzy Homes/Randy Nelson Hi Chuck; The Geological Assessment Review prepared for the proposed deck and remodel of the existing home at 2853 Old Belfair Highway, Belfair, has been received and reviewed by Public Works. The assessment appears to satisfactorily address County requirements for Geological assessment. The assessment's author indicates that, in his opinion, the remodel of the two- story single family home will not cause stability problems for the subject property. From the contents of the assessment, I recommend accepting the assessment as satisfying the County's requirement(s) for stability investigation. Recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance The engineer suggested roof drains discharging onto splash blocks and discharging through vegetation along the south side of the driveway and / or the front yard to the existing ditch along Old Belfair Highway. Or if tight lines are desired, they may discharge in the existing ditch so long as an appropriate energy dissipater is installed. With the other recommendations of the engineer incorporated into the site's development, stability issues appear to have been adequately addressed. Adequate erosion and sediment control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. Please feel free to contact me at 461 or Bob Thuring ext. 452 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, Patricia Carroll y IL` WORK ORDER « PUBLIC WORKS DEPT, (1 Work Order • PP.RMIT� �����ems---o�,gs� . umbers Kequsarted bys . C;-C Lac - ► �_t � z�_ , Authorized bY; Dates Type of Wottc, CHARGE To: NAME AGENCY10OMPANY e1WN0 ADDRESS ' PHONE ubIn Tkno.tjno:. m•to catea ' TO Prq t t ' EdpnAWfk*h Oft. • hoV� EiTrwtTm TOTIII. , 115 win �Aut. !!fit G!t{d�l' !� fiGTILL$ EQUIPMENT usEDr.• --.. IAAtEiU11.VSEa . . " •• '�� � PRD.►Nt NrtN r1011rs sum" FJ1t1Q! TOTAL. EQUIPMENT U$ED., smi 8!t! IS2Tl t.t r.r.rrr.rrn r�r.n ■i i rr�r�..wrrrrr+r•■r�r ir��. i.rur..rrw �.�...�.� MATIRIAL VIED1 TOTAL ALL 3) GILLED DATE ---r• 0, PAID,DATE RED$�,,,,ri1101l „_ w ALKAICONSULTANTS, LLC. Environmental Engineering • Geotechnical Engineering • Wetland Consulting November 23,2005 ACL05-11-G108 Page No. 1 Snazzy Homes 17Z Ct/VFW Randy Nelson c/o Gordon Sargent P.O.Box 2486 NOV (7 Belfair, Washington 98528-2486 426 02 005 is Assessment Rep ort ort C ��� s� � P Single Family Residence 2853 Old Belfair Highway Mason County,Washington Dear Mr.Nelson: This geological report presents the results of a soil and slope assessment directed at evaluating existing slope conditions at the referenced site. The scope of this study was developed during our initial proposal visit on November 11, 2005 and outlined in our proposal to you dated November 14, 2005. The services performed under this authorization were in general compliance with the Mason County requirements for a Geologic Assessment as outlined in the Mason County Landslide Hazard Areas chapter of the Resource Ordinance (17.01.100 section EA) and the Mason County Code (17.01.100,E.7). The Geologic Assessment was based on readily available reference maps,field reconnaissance and our experience in the site vicinity. Site Description 'c"i The site is located near Belfair, Washington in Mason County west of Old Belfair Highway in Section 16, Township 23 N Range 1 W of the Willamette Baseline and Meridian,as shown in Figure 1. The site is currently occupied by a single family residence with a deck and dirt/gravel driveway. Vegetation consists mostly of grass and blackberries. The subject parcel is bounded to the north and south by single family residences,to the west by greenbelt,and to the east by Old-Belfair Highway with greenbelt beyond. A downward slope occupies the area between the subject site and the adjacent property to the north. The existing single family residence is approximately 24 feet from the top of slope. Project Description ALKAI understands that the project consists of the remodel of an existing two-story single family residence. A covered deck has been built around the front and north side of the residence. It does not 9465 Provost Road NW, Suite 202 • Silverdale,Washington 98383 • (360) 613-2407• Fax: (360) 613-2408 05-11-G10801A iUfai,Sbpe ACL05-11-G108 Page No.2 November 23,2005 appear that existing grades have been or will be changed for the current project. The only areas of bare soil observed at the time of our site visit were underneath the deck area. Methodology The subject property soil and slope conditions were visually examined by performing a reconnaissance of the slope and excavating a shallow hand auger boring. This information provided a basis for a general understanding of the local soil and geologic conditions as discussed below. In addition to the , reconnaissance of the area the following readily available resources were reviewed. Resources used: • "Geologic Map of Washington—Northwest Quadrant",Washington State Department of Natural Resources,Division of Geology and Earth Resources,GM—50,2002. • U.S.G.S. 7.5 minute series topographic map`Belfair,Washington Quadrangle". • "Soil Survey of Mason County Washington",United States Department of Agriculture, 1960. Geologic Setting The subject site lies within the central Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington,this lowland is glacially carved with a depositional and erosional history including at least four separate glacial advance/retreats. The Puget Lowland is bounded on the west by the Olympic Mountains and on the east by the Cascade Range. The lowland is filled with glacial and nonglacial sediments consisting of interbedded gravel, sand, silt,till,and peat lenses. The Geologic Map of Washington-Northwest Quadrant indicates that the site is located on glacial till (Qgt). Glacial till consists of unsorted,unstratified,highly compact mixture of clay, silt, sand,gravel and boulders deposited by glacial ice. The USDA Soil Conservation Service Soil Survey of Mason County,Washington, 1980, indicates that the site is located near a contact of Norma silt loam with 0 to 3 percent slopes originating in glacial drift and Indianola loamy sand with 5 to 15 percent slopes originating in glacial drift. Surface and Subsurface Conditions Vegetation in the site consists mostly of grass and blackberries. The slope on the north side of the site is approximately 35 degrees with a vertical height of approximately 10 feet. The existing single family — residence is approximately 24 feet from the top of slope. It is our understanding that the existing house was built in 1956 ard—hiligt a eared to have had a significant impact on the slope. Soils observed in the hand boring excavation to a depth of approximately 5 feet consisted of very silty sand to sandy silt Alkai Consultants ACL05-11-G108 Page No. 3 November 23,2005 and sandy clay. There was no visible evidence of natural ground water, springs, seeps,or visual erosion indicating past significant seepage observed on the slope face at the subject site at the time of the site visit. No visual evidence of surficial or deep-seated or rotational landsliding was observed on the property. Based on the soils exposed on and around the property it is our opinion that the site soil conditions are generally consistent with glacial till deposits. Generally differences between the geologic and soil maps and observed soil conditions occur as a result of mapping scale,availability of exposures,and intended map usage. These differences are generally minor and not unexpected. Conclusions and Recommendations Based on our site investigation involving field observations and review of available reference materials, it is our opinion that the slope on the north side of the property meets Mason County's criteria for a Landslide Hazard Area due to a slope greater than 40 percent(-22 degrees)with a vertical relief of approximately 10 feet. Indications of instability on the slope face or deep-seated landsliding were not observed under the current conditions. We rec��etation be maintained in its current condaion on the slope face. Also,roof drains and runoff from the driveway should not be allowed to discharge over the slope and vegetation consisting of a minimum of grass should be maintained within at least 5 feet from the top of the slope. Typically,vegetation would be required for 50 feet from the top of slope under Mason County Landslide Hazard Code. Our recommendation of 5 feet is based on the short height of the slope,apparent stability of the soils,current vegetation conditions, driveway that is gravel and not paved,and our recommendation that surface water be directed away from the slope. The parking area is at least 100 feet from Old Belfair Highway. It does not appear that soils on the site are sandy enough for onsite infiltration. The driveway and parking area for the residence are currently soil and gravel with some minor vegetation. We believe that the driveway runoff may be allowed to discharge through washed clean(washed)gravel in the driveway area and be directed to the south side of the driveway where it may discharge through vegetated areas to an existing ditch along Old Belfair Highway. Roof downspouts could discharge onto splash blocks and allowed to discharge through vegetation along the south side of the driveway and/or the front yard to the existing ditch along Old Belfair Highway. If tightlines are desired,they may discharge in the existing ditch so long as an appropriate energy dissipater is installed. We believe that the stormwater quality will be adequate under the recommendations of this assessment. It is our opinion that further evaluation under a geotechnical report is not necessary. Alkai Consultants ACL05-11-G108 Page No.4 November 23 2005 REPORT LIMITATIONS This report has been prepared for the exclusive use of Mr. Randy Nelson and his agents for use in planning of the referenced development. The conclusions and recommendations in this report are based on our interpretation of site conditions, as they presently exist, anticipated future construction activities, and the expectation that the exploratory efforts adequately define the subsurface conditions across the site. The soil conditions described in this report and the conclusions and recommendations contained in this report are provided for this specific site only and should not be expanded for use on adjacent properties without additional exploration and review of those sites by our firm. The data and report should be provided to prospective contractors for their bidding or estimating purposes, but the report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. There are possible variations in subsurface conditions. In the event that the scope or location of the project should change or subsurface conditions different from those encountered during this study be observed or suspected, we should be advised. At that time a review of the changed conditions will be made, and alternative or remedial recommendations given as required. NOTE: We have explored subsurface conditions to a limited extent as part of this study, but we have not evaluated the site for the potential presence of contaminated soil, nor have we evaluated or addressed ground water conditions or concerns except as noted in this report. The evaluation of possible environmental or geo-environmental considerations is beyond the scope of this report. The owner and the contractor should make themselves aware of and become familiar with applicable local, state, and federal safety regulations, including current OSHA/WISHA excavation and trench safety standards. Construction site safety generally is the sole responsibility of the contractor. The contractor shall also be solely responsible for the means, method, techniques, sequences, and operations of construction operations. The firm, Alkai Consultants, LLC is providing the preceding information and recommendations solely as a service to Mr. Randy Nelson. Under no circumstances should the provision of this information or recommendations be construed to mean that the firm Alkai Consultants, LLC (or subcontractors) are assuming responsibility for construction site safety or the contractor's activities; such responsibility is not implied and should not be inferred. Alkai Consultants ACL05-11-G108 Page No. 5 November 23, 2005 Within the limitations of scope, schedule, and budget for this work, it is warranted that the work has been done in accordance with generally accepted practices followed in this area at the time this is report was made. No other warranty, expressed or implied is made. Should you have any questions or concerns, which have not been addressed, or if we may be of additional assistance, please call our office at(360) 613-2407. Sincerely, t was David Hurum, L.G. Senior Staff Geologist y o 1 21 COsed Geo\o�. DAVID C. HURUM Alkai Consultants i N ; —V;1 pstri 1 W x 4, QIM~" �w f ! Old Belfair f 'i Highway �.�■. '`<_ t 1 i i a � } SIT E r, 5 LQ i IY 1 .. Figure adapted from TopoZone.com FIGURE 1 VICINITY MAP Project Name: Old Belfair Slope N ALKAI CONSULTANTS, LLC. Location: Bremerton,Washington Project No.: ACL05-11-G108 pavv Environmental Engineering• Geotechnical Engineering•Wetland Consulting Client: Snazzy Homes Date: 11/17/05