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CANOD and geotech reports BLD20120738.pdfCity of Edmonds Critical Area Notice of Decision Applicant: Property Owner:, -Critical Area FilePermit Number: Site Location:Parcel Number: Project Description: tv F, -le E] Conditional Waiver. No critical area report is required for the project described above. 1. There will be no alteration of a Critical Area or its required buffer. 2. The proposal is an allowed activity pursuant to ECDC 23.40.220, 23.50.220, and/or 23.80.040. 3. The proposal is exempt pursuant to ECDC 23.40.230. F-1 Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and sediment control plan in compliance with ECDC 18.30. @,Critical Area Report Required. The proposed project is within a critical area and/or a critical area buffer and a critical area report is required. A critical area report has been submitted and evaluated for compliance with the following criteria pursuant to ECDC 23.40,160: 1. The proposal minimizes the impact on critical areas in accordance with ECDC 23.40-.120, Mitigation sequencing; 2. The proposal does not pose an unreasonable threat to the public health, safety, or welfare on or off the development proposal site; 3. The proposal is consistent with the general purposes of this title and the public interest; 4. Any alterations permitted to the critical area are mitigated in accordance with ECDC 23,40.110, Mitigation requirements, 5. The proposal protects the critical area functions and values consistent with the best available science and results in no net loss of critical functions and values; and 6. The proposal is consistent with other applicable regulations and standards. ❑ Unfavorable Critical Area Decision. The proposed project is not exempt or does not adequately mitigate its impacts on critical areas and/or does not comply with the criteria in ECDC 23.40.160 and the provisions of the City of Edmonds critical area regulations. See attached findings of noncompliance. Favorable Critical Area Decision. The proposed project as described above and as shown on the attached site plan meets or is exempt from the criteria in ECDC 23,40.160, Review Criteria, and complies with the applicable provisions of the City of Edmonds critical area regulations. Any subsequent changes to the proposal shall void this decision pending re -review of the proposal. Conditions. Critical Area specific condition(s) have been applied to the permit number referenced above. See referenced permit number for specific condition(s). Ake Reviewer Signature i1 (("I ( "P - Date Appeals: Any decision to approve, condition, or deny a development proposal or other activity based on the requirements of critical area regulations may be appealed according to, and as part of, the appeal procedure, if any, for the permit or approval involved. Revised 12/16/2010 August 2, 2012 Denny and Holly Onslow 621 Wellington Avenue Seattle, Washington 98122 Subject: Geotechnical Engineering Services Revised Critical Areas Report 17528 Talbot Road Edmonds, Washington File No. 20718-001-00 This letter presents the results of our geotechnical engineering services for the proposed residence located at 17528 Talbot Road in Edmonds, Washington. The site is shown relative to surrounding improvements on the Site Plan, Figure 1. We completed our services in general accordance with our proposal dated July 23, 2012. This letter has been revised from the version issued July 27, 2012 to include recommendations regarding on-site infiltration of stormwater. According to preliminary plans, the proposed residence will be located in the same general vicinity as the existing residence, although slightly further to the northwest. The proposed residence will be supported on columns and shallow foundations, independent of the foundation system supporting the existing residence. Portions of the basement of the existing residence will be retained for use as a crawlspace and storage. A deck will also be constructed on the northwest (downslope) side of the residence. We understand that the City of Edmonds has identified the need for a geotechnical assessment due to the Plaza 600 Building 600 Stewart Street, Suite 1700 Seattle, Washington 98101 206.7208-2674 2. GObkiNdP,,Hf Photograph 1. Looking down from top of steep slope toward BNSF railroad tracks and Puget Sound 17528 Talbot Road Proposed Residence August 2, 2012 Page 2 erosion and landslide hazards at the site, based on the Critical Areas Determination from the city dated May 24, 2012. The city of Edmonds Municipal Code (EMC) Chapter 23.80 specifies a landslide hazard area buffer of 50 feet. In addition EMC Chapter 23.40.280 specifies a 15 -foot building setback. This letter is intended to serve as a Critical Areas Report for the project to address the geologically hazardous areas requirements specified in EMC Chapter 23. SITE CONDITIONS The site is a narrow rectangular parcel 0.62 acre in size, oriented in a southeast -northwest direction, as shown on the Site Plan, Figure 1. The site is bounded by Talbot Road on the southeast, the BNSF railroad on the northwest and residential properties on the other two sides. The site generally slopes down from southeast (Elevation 87 feet) to northwest (Elevation 45 feet) with grades of up to 25 percent across most of the site, with a sharp drop-off at the northwest edge of the property. There is a grade difference of approximately 30 feet from the top to the bottom of this steep slope area, which extends beyond the property line. Photograph 1 on the previous page shows this steep slope area from above, and Photograph 2 to the right shows this steep slope area from below, at the level of the BNSF tracks. The existing residence is located in a gently -sloping area of the site. Vegetation on the upper portion of the site includes trees and landscaping extending to the top of the steep slope. Vegetation on the steep slope generally Photograph 2. Looking up from base of steep slope toward site consists of vines, brush, and several deciduous trees with pistol -butted trunks (one tree with a pistol -butted trunk is visible in Photograph 2). There is also a large pile of accumulated yard waste that was dumped on the slope in previous years, as shown in Photograph 3 below. Photograph 3. Accumulated yard waste on slope File No. 20718-001-00 Stormwater drains for the site have been collected into a tightline that extends to the base of the slope (as shown in Photograph 2), where the tightline discharges into a ditch along the BNSF railroad tracks, eventually draining through a culvert into Puget Sound. Regional Geology We reviewed the "Geologic Map of the Edmonds East and part of the Edmonds West quadrangles, Washington" by J.P. Minard, dated 1983. The geology in the vicinity of the site is mapped as glacial till. GEOENGINEERS 17528 Talbot Road Proposed Residence August 2, 2012 Page 3 We also reviewed the online Washington State Department of Natural Resources surface geology database. Based on this mapping, the site is located in an area of transition between glacial till and advance outwash, with the advance outwash located at a lower elevation and west of the glacial till. Glacial till is generally a medium dense to very dense, unsorted mixture of clay, silt, sand and gravel deposited below glaciers. In the greater Seattle area, glacial till is often underlain by advance outwash and glaciolacustrine deposits. Advance outwash is generally a dense to very dense well sorted sand and gravel with occasional silt lenses, deposited from streams emanating from advancing glaciers. The glaciolacustrine deposits generally consist of very stiff to hard silts and clays deposited in pro -glacial lakes. Environmentally Critical Areas The City of Edmonds Municipal Code (EMC) defines slopes of 15 to 40 percent as erosion hazards and slopes greater than 40 percent as landslide hazards. Based on this definition, most of the site is classified as an erosion hazard area, with only the far northwest edge of the site classified as a steep slope hazard area, as shown on the Site Plan, Figure 1. Based on our review of a draft inventory map prepared for the City of Edmonds, this is also how the site has been mapped by the city. The Washington State Department of Ecology Coastal Atlas shows the upper portions of the site mapped as stable, with the steep slopes mapped as unstable. GEOLOGIC RECONNAISSANCE We visited the site on July 24, 2012 to complete a geologic reconnaissance of the site and adjacent steep slope area. Subsurface Conditions We observed several open excavations on the property and completed hand holes around the site to evaluate the subsurface conditions. Based on our observations, the undisturbed native soils on the gently -sloping portions of the site are glacial till, consistent with the geologic mapping. Most of the steep slope area is overgrown with vegetation and inaccessible. However, we were able to use a ladder to climb down the slope at the south edge of the site, as shown in Photograph 2. We observed that the soils on the face of the slope generally consisted of sand with variable silt and gravel content. The face of the slope is highly disturbed, with numerous voids due to burrowing by large animals (possibly otters). Although we could not see areas of undisturbed native soils, the soils appeared to be advance outwash, consistent with the geologic mapping. Slope Stability We observed that there are several small rockeries on site that are in generally poor condition. The rocks are rounded and it appears that the poor conditions of the rockeries are due to poor construction, rather than instability. We did not observe signs of instability in the gently -sloping portions of the site. We observed that there are several deciduous trees on the steep slope with pistol -butted trunks. We did not observe signs of seepage on the steep slope. Although we observed numerous areas of exposed, loose soil on the steep slope, it is difficult to determine what is due to slope instability and sloughing, and what is due GiEOENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence August 2, 2012 Page 4 to animal burrowing. However, it appears that the slope has experienced numerous small, surficial slope failures in the past, which is consistent with steep slopes in the Greater Seattle Area. As previously noted, we observed a large amount of yard waste piled on a portion of the slope, as shown in Photograph 3. In our experience, this tends to increase the weight on the slope and can result in an increased risk of slope failure. We generally recommend this practice cease and that the yard waste be removed from the site. However, given the limited access available to this area, it is not likely feasible to haul the yard waste off site. CONCLUSIONS General The following sections describe our conclusions and recommendations, including a landslide hazard area buffer reduction. The adoption of these recommendations is consistent with EMC Chapters 23.80.060 and 23.80.070 and will not increase the risk to the site or adjacent properties, nor impact other critical areas. The predevelopment condition of the slope will be maintained or improved by adoption of these recommendations. Environmentally Critical Areas Erosion Hazard Area The upper landscaped portion of the site is a low risk of erosion hazard. We recommend, however, that appropriate erosion control best management practices (BMPs) be used during construction and appropriate landscaping installed for permanent stabilization of the site. In accordance with EMC Chapter 23.80.070, A.2, it is our opinion that the proposed residence and site redevelopment will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions, decrease slope stability on the site or adjacent properties; and will not adversely impact other critical areas. Landslide Hazard Area - Minimum Buffer and Building Setback Based on our observations of the steep slope area, it is our opinion that this area has a significant risk of ongoing instability, likely characterized by continuing shallow surficial slope failures that result in debris moving downslope toward the BNSF tracks and encroachment of the top of slope into the yard area above. We recommend that the owner not place additional yard waste on the slope and periodically inspect the tightlines to confirm that they are connected properly and are not discharging concentrated water onto the slope. Additionally, we recommend that the owner continue to keep the gate in the chain link fence locked to prevent access to the landslide hazard area. In accordance with Edmonds City Code 23.80.70 A.1, it is our opinion that a minimum buffer of 35 feet should be used for the landslide hazard area, along with a building setback of 15 feet, per EMC Chapter 23.40.280. The recommended buffer and building setback are shown on the Site Plan, Figure 1. Per EMC Chapter 23.40.280, uncovered decks are allowed in the building setback area. This buffer of 35 feet is slightly greater than the height of the slope, and it is our opinion that this reduced buffer and building setback are consistent with protection against property damage or injury from landsliding. GEOENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence August 2, 2012 Stormwater Management Page 5 Subsurface conditions at the site consist of glacial till and it is our opinion and experience that a design infiltration rate of less than 0.25 inches per hour is typically appropriate for glacial till. However, it is also our opinion that on-site infiltration would likely increase the risk of slope instability in the landslide hazard area. We therefore recommend against on-site infiltration of stormwater. Stormwater should be collected and directed to the storm sewer system or else tightlined to the base of the steep slope area. LIMITATIONS We have prepared this report for the exclusive use of Denny and Holly Onslow and their authorized agents for the proposed residence at 17528 Talbot Road in Edmonds, Washington. Our report and interpretations should not be construed as a warranty of the subsurface conditions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood. Our services were provided for a proposed residence that will extend into an environmentally critical area setback. However, all construction on or near slopes involves risk, only part of which can be mitigated through qualified engineering and construction practices. Favorable performance of structures in the near term does not imply a certainty of long-term performance, especially under conditions of adverse weather or seismic activity. Any electronic form, facsimile or hard copy of the original document (email, text, table and/or figure), if provided and any attachments are only a copy of the original document. The original document is stored by GeoEngineers and will serve as the official document of record. Please refer to Attachment A titled "Report Limitations and Guidelines for Use" for additional information pertaining to use of this report. GE®ENGINEERS File No. 20718-001-00 si ?_B iaiu t 3?aa fir,<. csec R sider:c Au!,:1_*t 2, 2G i.% Para F We trust that this report provides the information you require. Please contact us if you have any questions regarding the information and recommendations presented in this report. Sincerely, GeoEngineers, Inc. P } 6P 44203 � 4 �e Timothy D. Bailey, PE Project Engineer TDB:11M:sml Attachments: Figure 1. Site Plan Attachment A. Report Limitations and Guidelines for Use A f; 4?,1� °,7 z' f` Bo McFadden, PE, LEG Principal Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Copyright© 2012 by GeoEngineers, Inc. All rights reserved. GEoE NGIHEE �r X0718 001-n0 --77-- — r7 LLI LLJ O 1 00 a O _ der 9j r LU oZ / �\ A AtCDo� Y U W } O � O Z cWn -g O� aW ODc �a W Q C 1 5 o _Q \ / o om 7 5 W LLJ Z IL LU, m I- O O uiLL fr OZ:91 - ZIOZ '9Z lnr No antlwolwl 43 a3131aow 3dV3S0NVl:8Vil9Ma'NVld 3115 00-I008110Z10V311009ICOZ10ZV f 1_ a rn ii _ CD � c ca ® D -0 t8D 'S ~ Lu in o c Lu LO E z Of W z L3J ui OZ:91 - ZIOZ '9Z lnr No antlwolwl 43 a3131aow 3dV3S0NVl:8Vil9Ma'NVld 3115 00-I008110Z10V311009ICOZ10ZV f ATTACHMENT A Report Limitations and Guidelines for Use 17528 Talbot Road Proposed Residence August 2, 2012 Page A-1 ATTACHMENT A REPORT LIMITATIONS AND GUIDELINES FOR USE-' This attachment provides information to help you manage your risks with respect to the use of this report. Geotechnical Services Are Performed For Specific Purposes, Persons and Projects This report has been prepared for the exclusive use by Denny and Holly Onslow and their authorized agents. This report may be made available to agencies for review. This report is not intended for use by others, and the information contained herein is not applicable to other sites. GeoEngineers structures our services to meet the specific needs of our clients. For example, a geotechnical or geologic study conducted for a civil engineer or architect may not fulfill the needs of a construction contractor or even another civil engineer or architect that are involved in the same project. Because each geotechnical or geologic study is unique, each geotechnical engineering or geologic report is unique, prepared solely for the specific client and project site. No other party except Denny and Holly Onslow and their authorized agents may rely on the product of our services unless we agree in advance to such reliance and the additional party of reliance agrees, in writing, to be bound by the terms and conditions under which these services have been performed. This is to provide our firm with reasonable protection against open-ended liability claims by third parties with whom there would otherwise be no contractual limits to their actions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with our Agreement with the Client and generally accepted geotechnical practices in this area at the time this report was prepared. This report should not be applied for any purpose or project except the one originally contemplated. A Geotechnical Engineering Or Geologic Report Is Based On A Unique Set Of Project -Specific Factors This report has been prepared for evaluation of the proposed residence at 17528 Talbot Road in Edmonds, Washington. GeoEngineers considered a number of unique, project specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, do not rely on this report if it was: ■ not prepared for you; ■ not prepared for your project; ■ not prepared for the specific site explored; or ■ completed before important project changes were made. 1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org. 17528 Talbot Road Proposed Residence August 2, 2012 Page A-2 For example, changes that can affect the applicability of this report include those that affect: ■ the function of the proposed structures; ■ elevation, configuration, location, orientation or loads of the proposed structures; ■ composition of the design team; or ■ project ownership. If important changes are made after the date of this report, GeoEngineers should be given the opportunity to review our interpretations and recommendations and provide written modifications or confirmation, as appropriate. Subsurface Conditions Can Change This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by manmade events such as construction on or adjacent to the site, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. Always contact GeoEngineers before applying a report to determine if it remains applicable. Most Geotechnical And Geologic Findings Are Professional Opinions Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field data and then applied our professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ, sometimes significantly, from those indicated in this report. Our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. Geotechnical Engineering Report Recommendations Are Not Final Do not over -rely on the preliminary construction recommendations included in this report. These recommendations are not final, because they were developed principally from GeoEngineers' professional judgment and opinion. GeoEngineers' recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for this report's recommendations if we do not perform construction observation. Sufficient monitoring, testing and consultation by GeoEngineers should be provided during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective method of managing the risks associated with unanticipated conditions. GWENGINEERS Pile No. 20718-001-00 17528 Talbot Road Proposed Residence August 2, 2012 Page A-3 A Geotechnical Engineering Or Geologic Report Could Be Subject To Misinterpretation Misinterpretation of this report by other design team members can result in costly problems. You could lower that risk by having GeoEngineers confer with appropriate members of the design team after submitting the report. Also retain GeoEngineers to review pertinent elements of the design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering or geologic report. Reduce that risk by having GeoEngineers participate in pre-bid and preconstruction conferences, and by providing construction observation. Do Not Redraw The Exploration Logs Geotechnical engineers and geologists prepare final boring and test pit logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk. Give Contractors A Complete Report And Guidance Some owners and design professionals believe they can make contractors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give contractors the complete geotechnical engineering or geologic report, but preface it with a clearly written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes of bid development and that the report's accuracy is limited; encourage them to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. A pre-bid conference can also be valuable. Be sure contractors have sufficient time to perform additional study. Only then might an owner be in a position to give contractors the best information available, while requiring them to at least share the financial responsibilities stemming from unanticipated conditions. Further, a contingency for unanticipated conditions should be included in your project budget and schedule. Contractors Are Responsible For Site Safety On Their Own Construction Projects Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and to adjacent properties. Read These Provisions Closely Some clients, design professionals and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. GeoEngineers includes these explanatory "limitations" provisions in our reports to help reduce such risks. Please confer with GeoEngineers if you are unclear how these "Report Limitations and Guidelines for Use" apply to your project or site. Geotechnical, Geologic And Environmental Reports Should Not Be Interchanged The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a GWENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence August 2, 2012 Page A-4 geotechnical engineering or geologic report does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. Biological Pollutants GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention, or assessment of the presence of Biological Pollutants in or around any structure. Accordingly, this report includes no interpretations, recommendations, findings, or conclusions for the purpose of detecting, preventing, assessing, or abating Biological Pollutants. The term "Biological Pollutants" includes, but is not limited to, molds, fungi, spores, bacteria, and viruses, and/or any of their byproducts. GMENGINEERS File No. 20718-001-00 October 15, 2012 Denny and Holly Onslow 621 Wellington Avenue Seattle, Washington 98122 Subject: Geotechnical Design Recommendations 17528 Talbot Road Proposed Residence Edmonds, Washington File No. 20718-001-00 •�� pis o�, I— i Plaza 600 Building 600 Stewart Street, Suite 1700 Seattle, Washington 98101 206.7208-2674 This report presents the results of our geotechnical design recommendations for the proposed residence located at 17528 Talbot Road in Edmonds, Washington. We understand the City of Edmonds provided plan review comments for the project in a letter dated October 2, 2012. GeoEngineers, Inc. (GeoEngineers) previously provided geotechnical recommendations with regard to environmentally critical areas at the site in a letter dated August 2, 2012. As discussed in our previous letter, subsurface conditions at the site generally consist glacial till, consistent with geologic mapping. According to the plans, the proposed residence will be located in the same general vicinity as the existing residence, although slightly further to the northwest. The proposed residence will be supported on columns and shallow foundations, independent of the foundation system supporting the existing residence. Portions of the basement of the existing residence will be retained for use as a crawlspace and storage. A deck will also be constructed on the northwest (downslope) side of the residence. A ►1:x'ATM TAT We understand that the City of Edmonds has identified the need for a geotechnical confirmation of the structural design assumptions noted on project plan sheet 51.0. We have reviewed the project structural and civil plans. Our geotechnical recommendations presented in the following sections are consistent with these plans. 17528 Talbot Road Proposed Residence October 15, 2012 Page 2 CONCLUSIONS AND RECOMMENDATIONS Earthquake Engineering 2009 IBC Seismic Design Information We recommend the use of the following 2009 International Building Code (IBC) parameters for soil profile type, short period spectral response acceleration (Ss), 1 -second period spectral response acceleration (Si) and seismic coefficients (FA and Fv) for the project site. 2009 SBC Parameter Recommended Value Soil Profile Type D Short Period Spectral Response Acceleration, Ss (percent g) 121.1 1 -Second Period Spectral Response Acceleration, S, (percent g) 42.5 Seismic Coefficient, FA 1.02 Seismic Coefficient, Fv 1.58 Shallow Foundations The following sections provide recommendations for design of shallow foundations, which in our opinion are appropriate for support of the proposed improvements. Perimeter foundation drains should be included, as discussed in the "Drainage and Waterproofing" section below. Allowable Bearing Pressure For foundations bearing on undisturbed dense native soils or structural fill extending down to these soils, the foundations may be designed using an allowable soil bearing pressure of 2,000 pounds per square foot (psf) for isolated spread footings and continuous footings. The allowable soil bearing value is a net value that applies to the total of dead and long-term live loads and may be increased by up to one-third for wind or seismic loads. Settlement Provided all loose soil is removed and the subgrade is prepared as recommended under Construction Considerations below, we estimate the total settlement of shallow foundations will be on the order of 1/2 to 1 inch. The settlements will occur rapidly, essentially as loads are applied. Size and Embedment We recommend that the exterior footings be founded a minimum of 18 inches below the lowest adjacent grade for frost protection. Interior footings should be founded a minimum of 12 inches below top of slab. Continuous wall footings and individual column footings should have minimum widths of 24 inches. Lateral Resistance Lateral foundation loads may be resisted by passive resistance on the sides of footings and by friction on the base of the shallow foundations. The allowable passive resistance on the sides of the footings may be computed using an equivalent fluid density of 300 pounds per cubic foot (pcf) (triangular distribution). These values are appropriate for foundation elements that are poured directly against undisturbed dense soils or GEOENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence October 15, 2012 Page 3 surrounded by structural fill. For shallow foundations supported on native soils or structural fill, the allowable frictional resistance may be computed using a coefficient of friction of 0.4 applied to vertical dead -load forces. The above coefficient of friction and passive equivalent fluid density values incorporate a factor of safety of about 1.5. Construction Considerations If soft or loose soil is present at the foundation subgrade elevation (as discussed above), the soft areas should be removed and replaced with structural fill at the direction of GeoEngineers. In such instances, the zone of structural fill should extend laterally beyond the footing edges with a horizontal distance at least equal to the thickness of the fill. The condition of all subgrade areas should be observed by GeoEngineers to evaluate if the work is completed in accordance with our recommendations and that the subsurface conditions are as anticipated. Slab -On -Grade Floors We recommend that the basement floor slabs be constructed as slab -on -grade. Subgrade Preparation The exposed subgrade should be evaluated after site grading is complete by probing. The exposed soil should be firm and unyielding, and without significant groundwater. Disturbed areas should be re -compacted if possible or removed and replaced with compacted structural fill. Design Parameters Conventional slabs may be supported on -grade provided the subgrade soils are prepared as recommended under the "Subgrade Preparation" above. We recommend that the slab be founded on either undisturbed native soils or on structural fill placed over the native soils. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 200 pounds per cubic inch (pci) may be used for subgrade soils prepared as recommended. The capillary break layer below the slab should consist of 4 inches of clean crushed gravel, with a maximum particle size of 11/2 inches and negligible sand or silt. We recommend that a vapor retarder be placed over the capillary break layer in the basement and in the garage to retard migration of moisture through the floor slabs. The vapor retarder should consist of a heavy plastic sheet, such as 10 -mil plastic sheeting intended for this purpose, and include sealed seams. The contractor should be made responsible for maintaining the integrity of the vapor retarder during construction. Retaining Walls General The project will include basement retaining walls for the proposed residence, and may also include miscellaneous retaining walls to support grade transitions on the site. GMENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence October 15, 2012 Design Parameters Page 4 The retaining wall foundations should be designed using the recommendations previously presented for shallow foundations. Retaining walls should be backfilled with a 12 -inch wide zone of drainage aggregate, with a perimeter foundation drain at the base of the drainage zone, as discussed in the "Drainage and Waterproofing" section below. For miscellaneous retaining walls on site, weep holes can be used instead of a foundation drain, provided the weep holes do not conflict with the aesthetic requirements for the walls. The lateral soil pressures acting on the retaining walls depend on the nature, density and configuration of the soil behind the wall and the amount of lateral wall movement which can occur as backfill is placed. For walls that are free to yield at the top at least 0.1 percent of the height of the wall, soil pressures will be less than if movement is limited. Assuming that the walls are backfilled and drainage is provided as discussed above, we recommend that yielding walls supporting horizontal backfill be designed using active earth pressures. Non -yielding walls supporting horizontal backfill be designed using at -rest earth pressures. Retaining Wall Design Parameters Unit Weight (pcf) 125 Friction Angle (degrees) 35 Active Earth Pressure (pcf) - triangular distribution 35H At Rest Earth Pressure (pcf) - triangular distribution 55H Seismic Pressure (psf) - uniform distribution 7H Drainage and Waterproofing We recommend that perimeter foundation drains be installed around the basement of the new residence and garage, as well as around the accessory building. As discussed above in the "Retaining Walls" section, either foundation drains or weep holes should be provided for the miscellaneous retaining walls on site. For the in -ground trampoline, an area drain should also be provided. The drains should be provided with cleanouts and should consist of a 4 -inch -diameter perforated pipe placed on a 4 -inch -thick bed of, and surrounded by 6 inches of, drainage aggregate enclosed in a non -woven geotextile fabric such as Mirafi 140N (or approved equivalent) to prevent fine soil from migrating into the drain material. Gradation recommendations for the drainage aggregate are presented below in the "Earthwork" section of this report. We recommend that the perforated drain pipe consist of either heavy -wall solid pipe (SDR -35 polyvinyl chloride [PVC], or equivalent) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, or equivalent). We also recommend against using flexible tubing for drainpipes. The drains should be sloped to drain by gravity, if practicable, to a suitable discharge point. We recommend that the cleanouts be covered and be placed in flush -mounted utility boxes. Water collected in roof downspout lines must not be routed to the foundation drain lines. GMENGINEERS File No. 20718001-00 17528 Talbot Road Proposed Residence October 15, 2012 Page 5 LIMITATIONS We have prepared this report for the exclusive use of Denny and Holly Onslow and their authorized agents for the proposed residence at 17528 Talbot Road in Edmonds, Washington. Our report and interpretations should not be construed as a warranty of the subsurface conditions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, express or implied, should be understood. Our services were provided for a proposed residence that will extend into an environmentally critical area setback. However, all construction on or near slopes involves risk, only part of which can be mitigated through qualified engineering and construction practices. Favorable performance of structures in the near term does not imply a certainty of long-term performance, especially under conditions of adverse weather or seismic activity. Any electronic form, facsimile or hard copy of the original document (email, text, table and/or figure), if provided and any attachments are only a copy of the original document. The original document is stored by GeoEngineers and will serve as the official document of record. Please refer to Attachment A titled "Report Limitations and Guidelines for Use" for additional information pertaining to use of this report. GE®ENGINEERS File No. 20718-001-00 I 3ai1.ot Road €=i"oposed {e-,Nence 0 t ,—r'.3, li:'d_2 We trust that this report provides the information you require. Please contact us if you have any questions regarding the information and recommendations presented in this report. Sincerely, GeoEngineers, Inc. NP i rv. 6r 4 Attachment: Attachment A .Report Limitations and Guidelines for Use Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Copyright@O 2012 by GeoEngineers, Inc. All rights reserved. Gt EC GEIN]EE-R!� w File Na. 20 7, 1i? -001 0'0 i , t Timothy D. Bailey, PE �' Ido McFadden, PE, LEG Project Engineer .=`Principal TDB:JJM:csv Attachment: Attachment A .Report Limitations and Guidelines for Use Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record. Copyright@O 2012 by GeoEngineers, Inc. All rights reserved. Gt EC GEIN]EE-R!� w File Na. 20 7, 1i? -001 0'0 ATTACHMENT A Report Limitations and Guidelines for Use 17528 Talbot Road Proposed Residence October 15, 2012 Page A-1 ATTACHMENT A REPORT LIMITATIONS AND GUIDELINES FOR USE1 This attachment provides information to help you manage your risks with respect to the use of this report. Geotechnical Services Are Performed For Specific Purposes, Persons and Projects This report has been prepared for the exclusive use by Denny and Holly Onslow and their authorized agents. This report may be made available to agencies for review. This report is not intended for use by others, and the information contained herein is not applicable to other sites. GeoEngineers structures our services to meet the specific needs of our clients. For example, a geotechnical or geologic study conducted for a civil engineer or architect may not fulfill the needs of a construction contractor or even another civil engineer or architect that are involved in the same project. Because each geotechnical or geologic study is unique, each geotechnical engineering or geologic report is unique, prepared solely for the specific client and project site. No other party except Denny and Holly Onslow and their authorized agents may rely on the product of our services unless we agree in advance to such reliance and the additional party of reliance agrees, in writing, to be bound by the terms and conditions under which these services have been performed. This is to provide our firm with reasonable protection against open-ended liability claims by third parties with whom there would otherwise be no contractual limits to their actions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with our Agreement with the Client and generally accepted geotechnical practices in this area at the time this report was prepared. This report should not be applied for any purpose or project except the one originally contemplated. A Geotechnical Engineering Or Geologic Report Is Based On A Unique Set Of Project -Specific Factors This report has been prepared for evaluation of the proposed residence at 17528 Talbot Road in Edmonds, Washington. GeoEngineers considered a number of unique, project specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, do not rely on this report if it was: ■ not prepared for you; ■ not prepared for your project; ■ not prepared for the specific site explored; or • completed before important project changes were made. 1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org. 17528 Talbot Road Proposed Residence October 15, 2012 Page A-2 For example, changes that can affect the applicability of this report include those that affect: ■ the function of the proposed structures; elevation, configuration, location, orientation or loads of the proposed structures; ■ composition of the design team; or ■ project ownership. If important changes are made after the date of this report, GeoEngineers should be given the opportunity to review our interpretations and recommendations and provide written modifications or confirmation, as appropriate. Subsurface Conditions Can Change This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by manmade events such as construction on or adjacent to the site, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. Always contact GeoEngineers before applying a report to determine if it remains applicable. Most Geotechnical And Geologic Findings Are Professional Opinions Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field data and then applied our professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ, sometimes significantly, from those indicated in this report. Our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. Geotechnical Engineering Report Recommendations Are Not Final Do not over -rely on the preliminary construction recommendations included in this report. These recommendations are not final, because they were developed principally from GeoEngineers' professional judgment and opinion. GeoEngineers' recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for this report's recommendations if we do not perform construction observation. Sufficient monitoring, testing and consultation by GeoEngineers should be provided during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective method of managing the risks associated with unanticipated conditions. GWENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence October 15, 2012 Page A-3 A Geotechnical Engineering Or Geologic Report Could Be Subject To Misinterpretation Misinterpretation of this report by other design team members can result in costly problems. You could lower that risk by having GeoEngineers confer with appropriate members of the design team after submitting the report. Also retain GeoEngineers to review pertinent elements of the design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering or geologic report. Reduce that risk by having GeoEngineers participate in pre-bid and preconstruction conferences, and by providing construction observation. Do Not Redraw The Exploration Logs Geotechnical engineers and geologists prepare final boring and test pit logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk. Give Contractors A Complete Report And Guidance Some owners and design professionals believe they can make contractors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give contractors the complete geotechnical engineering or geologic report, but preface it with a clearly written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes of bid development and that the report's accuracy is limited; encourage them to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. A pre-bid conference can also be valuable. Be sure contractors have sufficient time to perform additional study. Only then might an owner be in a position to give contractors the best information available, while requiring them to at least share the financial responsibilities stemming from unanticipated conditions. Further, a contingency for unanticipated conditions should be included in your project budget and schedule. Contractors Are Responsible For Site Safety On Their Own Construction Projects Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and to adjacent properties. Read These Provisions Closely Some clients, design professionals and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. GeoEngineers includes these explanatory "limitations" provisions in our reports to help reduce such risks. Please confer with GeoEngineers if you are unclear how these "Report Limitations and Guidelines for Use" apply to your project or site. Geotechnical, Geologic And Environmental Reports Should Not Be Interchanged The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a GWENGINEERS File No. 20718-001-00 17528 Talbot Road Proposed Residence October 15, 2012 Page A-4 geotechnical engineering or geologic report does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. Biological Pollutants GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention, or assessment of the presence of Biological Pollutants in or around any structure. Accordingly, this report includes no interpretations, recommendations, findings, or conclusions for the purpose of detecting, preventing, assessing, or abating Biological Pollutants. The term "Biological Pollutants" includes, but is not limited to, molds, fungi, spores, bacteria, and viruses, and/or any of their byproducts. GMENGINEERS File No. 20718-001-00