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20121128081951523.pdf..,, .., . .m, � ,IIS . � " _ v . J. S -1L"1` A T'4T ,,,, INC. Richard Svangren 9209 Olympic View Drive Edmonds, Washington 98020 Subject: Geotechnical Engineering Study Proposed Residence Remodel and Deck Addition 9209 Olympic View Drive Edmonds, Washington Dear Mr. Svangren: 13250 Nur hei isl 2ft Street, SuiUc, 16 Bellevue,, Washington 99005 (d25) '/47-5618 FAX (42.5) 747-8561 July 10, 2009 JN 09154 { ppp @r, r 01 n We are pleased to present this geotechnical engineering report for the proposed residence and deck addition project in Edmonds, Washington. The scope of our services consisted of exploring site surface and subsurface conditions, and then developing this report to provide conclusions and recommendations regarding the geotechnical engineering aspects of the project. We observed two test holes in order to determine the subsurface conditions. Based on our conversations with you, we understand that the roofline of your residence will be changed, but no addition to the residence will be done. Also, a deck will be constructed on the northern (project north) side of the residence. We understand that the northern side of the residence is approximately 60 feet from the top of an existing steep slope, while the deck will be located approximately 50 feet from the slope. Conventional footings are proposed for support of the deck. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS The Svangren property is located on a private driveway that extends north of Olympic View Drive. The property is located on the western (project west) side of the driveway. The existing residence is located on the eastern side of the property near the driveway. The main floor of the residence is near the driveway grade, while a basement level daylights to the west. An existing main floor deck extends off the northwestern portion of the residence. Most of the property slopes down to the west at a moderate inclination (estimated to be in the range of 25 percent). However, near the western edge of the site is a very steep slope that is over 50 feet tall. The residence is located approximately 60 feet from the steep slope. The area between the residence and steep slope is landscaped and contains a wood shed. The steep slope is heavily vegetated. Some large evergreen trees are located at the top of the steep slope. This slope is defined as a landslide hazard area per Section 23.80.020 of the Edmonds Municipal Code due to its steepness. We did not observe indications of soil instability near the top of the slope. We were not able to traverse and observe the middle and base of the tracks. However, we are " P" "10, Y' Richard Svangren JN 09154 July 10, 2009 Page 2 aware that at the base of this slope are twin railroad tracks belonging to the Burlington Northern Railway. Beyond these tracks is Puget Sound. Two hand -excavated test holes were excavated on the site on July 3, 2008. One hole was located near the northwestern corner of the proposed deck, while the other was near the southwestern corner. The southwestern test hole revealed approximately 18 inches of loose, native sand that then became medium -dense. At a depth of approximately 4.5 feet, the sand became gravelly and dense. In the northwestern test boring, approximately 3 feet of loose fill was revealed overlying the loose native sand. This sand became medium -dense at approximately 4 feet and dense around 6 feet. Our firm observed the drilling of some deep test borings near a similarly sloped area about one-half mile south of the site; similar dense soils were found as the core soils on that site. THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY RELYING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The development of the proposed residence remodel and the deck addition is very suitable from a geotechnical engineering standpoint in our opinion. Medium -dense or denser, native sand soil was revealed in test holes at depths ranging from about 1.5 to 4 feet. The deck addition can be founded on conventional footings as planned, provided they bear on the competent sand soil. A bearing capacity of 2000 pounds per square foot can be used for the footings. We found that the area near the deck and at the top of the slope appeared to be stable, and founding the deck footings on the competent soil will have no negative affect on stability of the adjacent area or the slope. Section 23.80.020B of the Edmonds Municipal Code (the Code) defines a landslide hazard area to include any area "... with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet except areas composed of consolidated rock". As noted earlier, the steep slope on the western of the property is considered to be a landslide hazard area per the Code. A minimum building setback of 15 feet is required from the edges of all critical area buffers, per Section 23.40.280 of the Code. A minimum buffer of 50 feet is generally recommended per Section 23.80.070A of the Code. However, this section of the Code also states that the buffer width can be reduced to a minimum of 10 feet "... when a qualified professional demonstrates ... that the reduction will adequately protect the proposed development, adjacent developments and uses and the subject critical area". Based on our site explorations and our nearby explorations, it is apparent that the core of the steep slope west of the subject property is comprised of very competent, native glacially -compacted sand soils. In addition, we did not observe indications of soil instability near the top of the slope during our site visit. Because of these reasons, it is our opinion that the buffer can be reduced to 30 feet, resulting in a total minimum building setback of 45 feet from the top of the western slope. The residence is located well outside this buffer and total setback distance, and the proposed deck is well outside this recommended buffer. Therefore, it is Richard Svangren JN 09154 July 10, 2009 Page 3 our opinion that the project can be constructed as planned provided the recommendations contained in this report are followed. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. LIMITATIONS The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the test pits are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated soil conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking soil samples in test pits. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. This report has been prepared for the exclusive use of the Svangren family and their representatives for specific application to this project and site. Our recommendations and conclusions are based on observed site materials and engineering analyses. Our conclusions and recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Our services also do not include assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development. We appreciate the opportunity to be of may be of further service, please do not M DRW: jyb ice on this project. If you have any questions, or if we itate to contact us. Respectfully submitted, GEOTECH CONSULTANTS, INC. D. Robert Ward, P.E. Principal