The URL can be used to link to this page

Home My WebLink AboutBLD2007-01857 - BLD Engineering / Geo-tech Reports - 12/28/2007 +c t_o r F N 6 ! N E F t I N 6 1 N C 309 WASHINGTON STREET NE • OLYMPIA WA 98501• TEL:360 352-2477• FAX: 360 352-0179 www.vectorengineeringinc.com Review of Geotechnical Report January 9,2008 Permit#s:BLD 2007-01857 Parcel No.32236-75-00070,Lot 4 Applicant:Damon Ernst Planner: Grace Miller VEI#: 7054-033 The geotechnical report dated around April 20, 2006 and letter dated December 28, 2007 prepared by Geotechnical Testing Laboratory; 10011 Blomberg Street SW, Olympia, WA 98512 for a proposed single-family residence at 9991 East State Route 106, Union, WA 98592 along Hood Canal overlooking the Narrows was received and reviewed by Vector Engineering, Inc. The Department of Community Development requested the review for the purpose assisting the Department in determining the amount of potential for landslide activity and the proposed development would not cause significant adverse impacts or there is adequate geological information available on the area to determine the impacts of the proposed development and appropriate mitigating measures. The Department of Community Development reviews all development applications to determine if they are likely to be in or near a landslide hazard area per Mason County Resource Ordinance (MCRO), Geologically Hazardous Areas, Landslide Hazard Areas 17.01.100, Seismic Hazard Areas 17.01.102, and Erosion Hazard Areas 17.01.104 approved December 27,2006. The geotechnical report states the proposed residence with septic drainfield will be in an area of moderate residential development. A site plan with locations of the proposed residence and proposed garage was provided with the report. A revised site plan was also received from the owner and another was included with the letter. The revised site plan shows the proposed residence further away from the top of the hazard area. Page 1 of 6 K\7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Ernst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc Findings 1. Areas identified on the Mason County Soil Survey Map as having slopes greater than 15%is one guide used by the County to indicate areas that have a higher likelihood of meeting the classification criteria for landslide hazard areas. MCRO 17.01.100 A.2.a. • Slopes in the north and west portions of the site are in excess of 55 percent. 2. A 50-foot buffer of undisturbed natural vegetation is required around the Landslide Hazard Area or as recommended by the geotechnical engineer. MCRO 17.01.100 D.6.a. • No landslide hazard area or buffer was shown on the site plan. • A landslide hazard area with a 30-foot vegetative buffer was shown on the revised site plan. The response is adequate. 3. Based upon the results of the Geotechnical Report or Geological Assessment, the Director may increase the buffer.MCRO 17.01.100 D.6.b. 4. Development 300 feet of areas with slopes greater than 40 percent will require a geotechnical report.MCRO 17.01.100 E.l.a. • Slopes in the north and west portions of the site are in excess of 55 percent and 44 feet in height. 5. The geotechnical report shall be prepared by a licensed civil engineer or a licensed engineering geologist. MCRO 17.01.100 E.3 • Harold Parks, a licensed engineering geologist, prepared the report. Mr. Parks died in November 2007 after the report was submitted to the County. Curtis Cushman,a licensed engineering geologist prepared the letter. 6. The report includes a discussion of geologic conditions in the general vicinity, including soil types, groundwater conditions, upslope geomorphology, location of upland waterbodies and wetlands, and a history of the landslide activity. MCRO 17.01.100 E.S. (1). • The report state the site is within the Puget Sound glacial upland with Alderwood gravelly sandy loam underlain with advance outwash deposits. Depth to groundwater is presumed deep. There was no mention of upslope geomorphology, upland water bodies,wetlands,or a history of landslide activity. • The letter mentions upslope geomorphology,upland water bodies,wetlands, and a discussion of landslide activity in the area. 7. The report is to include a site plan identifying important development or geologic features.MCRO 17.01.100 E.S. (2). • A site plan identifying the access driveway, proposed building location, proposed garage location,an easement,and presumed property boundaries was provided. Page 2 of 6 XA7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Ernst)GR\AdminUransmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc • The proposed building location does not match the parcel description on the Mason County website. The parcel number in the report seems to be for the access driveway from State Route 106. • The drainfield is proposed to be located offsite to the southeast. • The letter states the building is located in parcel 322367500070 and the access driveway is in parcel 322365100032. The response is adequate. The building is reported to be on Lot 4 in parcel 322367500070. The reviewer did not have access to a site plan of the entire parcel 322367500070. 8. The report is to include the locations and logs of exploratory holes or probes. MCRO 17.01.100 E.S. (3). • No exploratory holes were dug. • The letter no exploratory holes were drilled at the site. Soil testing was done from a sample taken from the exposed western slope. 9. The report is to include a geologic map of the site showing the area of the proposed development with the boundaries of the hazard, and associated buffers and setbacks delineated on the map.MCRO 17.01.100 E.S. (4). • No geologic map of the site showing the area of the proposed development was provided. No boundaries of the hazard, and associated buffers and setbacks were shown on the site plan. • The letter includes a revised site plan showing the boundaries of the hazard, and associated buffers and setbacks. The response is adequate. 10. The report is to include a cross-section at a scale adequately depicting the subsurface profile.MCRO 17.01.100 E.S. (5). • The cross-section in the report is at a scale adequately depicting the subsurface profile. • The letter includes a cross-section showing the subsurface profile. The response is adequate. 11. The report is to include a description and results of the slope stability analysis. The analysis should include the Simplified Bishop's Method of Circles. The minimum static factor of safety is 1.5. The minimum seismic safety factor is 1.1. The quasi- static analysis coefficient should be 0.15.MCRO 17.01.100 E.S. (6). • The report states slope stability was modeled using GeoStudio 2004 program, which uses the Simplified Bishop's Method of Circles. The minimum static factor of safety was not provided. The minimum seismic or dynamic safety factor was also not provided. Documentation is needed for the source of the unit weight, cohesion, and shear angle values. The unit weight value needs to be specified whether it is wet or dry. Page 3 of 6 XA7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Ernst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc • The letter includes a revised stability analysis. The minimum static and dynamic factors of safety were 2.27 and 1.35. The source for the unit weight,cohesion,and shear angle values was from the sample obtained nearby. The unit weight value was stated to be a wet value. The response is adequate. 12. The report is to include appropriate restrictions on placement of drainage features, septic drainfields and compacted fill and footings,including recommended buffers and setbacks from the landslide hazard areas.MCRO 17.01.100 E.S. (7). • The report did not include restrictions on placement of drainage features and any recommendations on buffers and setbacks from the landslide hazard areas. • The letter included restrictions. The response is adequate. 13. The report is to include recommendations for the preparation of a detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation and replanting, and the method of vegetation removal. MCRO 17.01.100 E.S. (8). • The report includes recommendations for clearing and grading. 14. The report is to include recommendations for the preparation of a detailed temporary erosion control plan, which identifies the specific mitigating measures to be implemented. MCRO 17.01.100 E.S. (9). • The report includes recommendations for the preparation of a detailed temporary erosion control plan. 15. The report is to include an analysis of both on-site and off-site impacts. MCRO 17.01.100 E.S. (10). • No adverse on-site or off-site impacts were described in the report. 16. The report is to include specifications of final development conditions, such as, vegetative management, drainage control, and buffer widths. MCRO 17.01.100 E.S. (10). • The report includes recommendations for vegetation management and drainage control. No specifications are shown for buffer widths. • The letter includes specifications for buffer widths. 17. The report is to include recommendations for the preparation of structural mitigation or details of other proposed mitigation.MCRO 17.01.100 E.S. (11). • The report includes recommendations for retaining walls, cut and fill slopes, foundation support, structural fill, floor slab support, roof drains, and footing drains. 18. The report is to include a site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of the proposed development on the site.MCRO 17.01.100 E.S. (12). Page 4 of 6 XA7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Ernst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc • A reduced site plan showing the almost of the property boundaries, scale, north arrow, and the location and nature of the proposed development on the site is a part of the report. • The site plan with a scale of 1:50 or larger, showing the entire property boundaries should be submitted. • The letter includes a revised site plan showing the property boundaries. The response is adequate. 19. If the site is in a Seismic Hazard Area, then the Geological Report shall include a description of the geology of the site, conclusions and recommendations regarding the effect of geological conditions on the proposed development, and opinions and recommendations for compensating for the seismic hazards present. MCRO 17.01.102 D.3.a. • The report includes an analysis of the seismic hazard and the site was detemlined to have a low liquefaction potential. 20. If the site is in an Erosion Hazard Area,then the Geological Report may include a Soil Erosion and Control Report as an attachment.MCRO 17.01.104 D.3. • The report mentions that the site meets the requirements of an erosion hazard area. The report should be revised to mention that uses and activities in erosion hazard areas are subject to erosion hazard area development standards including the submittal of a Soil Erosion and Sediment Control Plan prepared by a professional engineer. • The letter includes general erosion control notes. The revised site plan includes a note stating uses and activities in erosion hazard areas are subject to erosion hazard area development standards including the submittal of a Soil Erosion and Sediment Control Plan prepared by a professional engineer. The response is adequate. Conclusions and Recommendations In the reviewer's opinion, the report and letter were prepared by two qualified engineering geologists and does provide sufficient information to determine the proposed residence will not decrease slope stability at the site or on adjacent properties and the risk for such occurrence would be minimal. It is recommended that the Geotechnical report be accepted. No further review by Vector Engineering is necessary. 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 Page 5 of 6 XA7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Ernst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc applicant's property will be considered a violation of County and State water quality protection regulations. The conclusions presented in this report are based on Vector Engineering, Inc.' understanding of the project requirements.Vector Engineering,Inc. warrants that its services were performed with the level of care and skill ordinarily exercised by members of the same profession currently practicing in the same locality under similar conditions. No other warranty or representation,expressed or implied,is included or intended hereunder. Sincerely, (Signature) (Date) Russell W. La Force, P.E. Seal: Design Engineer Vector Engineering, Inc. 309 Washington Street NE ZONE r Olympia, WA 98501 (360) 352-2477 � �c0�1" a z 9 42651 o��aa�ON E. EXPIRES 05-25- of� Page 6 of 6 XA7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Emst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review.doc c t o r E E t 1 N 6 1 N r 309 WASHINGTON STREET NE • OLYMPIA WA 98501• TEL:360 352-2477• FAX: 360 352-0179 www.vectorengineeringinc.com January 9,2008 a Mr.Robert D.Fink,AICP Y Mason County—Department of Community Development Mason County Bldg 1 P.O.BOX 279 Shelton,WA 98584 Subject: Geotechnical Report Acceptance Permit#s:BLD 2007-01857 Parcel No.32236-75-00070,Lot 4 Applicant:Damon Ernst Planner: Grace Miller VEI#: 7054-033 Dear Mr.Fink, The geotechnical report dated around April 20, 2006 and letter dated December 28, 2007 prepared by Geotechnical Testing Laboratory; 10011 Blomberg Street SW, Olympia, WA 98512 for a proposed single-family residence at 9991 East State Route 106, Union, WA 98592 along Hood Canal overlooking the Narrows was received and reviewed by Vector Engineering, Inc. It is recommended that the geotechnical report be accepted. No further review by Vector Engineering is necessary. The 30-foot buffer may need to go through the variance process. We have enjoyed working with you on this geotechnical review to support the goals of the Department of Community Development of Mason County, Washington. We look forward to cooperating with you on any future project or review. The invoice, the geo tech work order, the geotechnical report, letter with the revised site plan and our review are enclosed. Please feel free to contact me if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, _p , c 4 �1w - Russell W. La Force, P.E. Design Engineer Enc. Page 1 of 1 X:\7000 Files\7054 Mason County Geotech Reviews\7054-033 Mason_Co(Emst)GR\Admin\Transmittal Letters\Geotechnical Report BLD 2007-01857 Review Acceptance.doc