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CANOD.pdfTECHNICAL MEMORANDUM TO: Ms. Darah Cooney Northwest Care Senior Living FROM: Carlo Evangelisti, P.E. Lwm ASSOCIATES DATE: December 28, 2015 Jt 4 201 DEPART RE: LIMITED GEOTECHNICAL ENGINEERIN . ,,., = 10P EOMONtM WEPrr ADDITION TO ROSEWOOD COURTE AT 728 EDMONDS WAY EDMONDS, WASHINGTON INTRODUCTION This technical memorandum summarizes the results of our limited geotechnical engineering services related to the Rosewood Courte building addition located in Edmonds, Washington. Our services included developing limited geotechnical engineering recommendations for the proposed building addition based on explorations and previously provided recommendations that are presented in our geotechnical report titled Geotechnical Engineering Services, Proposed Alzheimer Courte Community Facility, Edmonds Washington (Landau Associates 1998). The general project location is shown on the Vicinity Map (Figure 1). The general configuration of the proposed building addition and some of the existing site features are shown on the Site and Exploration Plan (Figure 2). The approximate locations of Landau Associates' test pits from .our 1998 study are also illustrated on Figure 2. Project Description We understand that an addition to the existing Rosewood Courte facility is planned. The addition is approximately 680 square feet and will be located on the northwest corner of the existing structure. Based on our review of plans provided by Wright Architecture, and our site visit on December 17, 2015, it appears that the proposed addition encroaches into the 50 foot buffer and 15 foot building setback required at the toe of the steep slope located to the south and west of the proposed building addition. The existing structure was the subject of our Geotechnical Engineering Report dated April 15, 1998. In that report, Landau Associates concluded that the steep slope was relatively stable and opined that the buffer could be reduced to 10 feet and have no adverse impact to the slope, the public, or other private parties. Scope of Services The purpose of our services was to provide limited geotechnical engineering recommendations for the proposed building addition. Our scope of services for this project is outlined in our proposal dated 130 2nd Avenue South • Edmonds, WA 98020 9 (425) 778-0907 • fax (425) 778-6409 • www.landauinc,com December 7, 2015. Notice to proceed was provided by Darah Cooney of Northwest Care Senior Living via email on December 8, 2015. Our scope of services included reviewing previously explored subsurface conditions and evaluations to assess the applicability of this information to the current project, providing updated geotechnical recommendations for the proposed building addition, and preparing this technical memorandum. This technical memorandum includes: • A site plan showing the approximate locations of the previous explorations in relation to the planned building addition • Summary of present surface conditions and visual evaluation of the nearby steep slope • Summary of subsurface conditions previously observed within the project area • Applicability of the recommendations provided in our Geotechnical Engineering Report dated April 15, 1998, to the current project including: — Evaluation of the steep slope buffer zone reduction — Site preparation and earthwork — Foundation support — Lateral earth pressures — Floor slab support — Paved areas — Construction monitoring. • Updated site factors for use in seismic design of the building addition in accordance with the 2012 International Building Code. SITE CONDITIONS We met with Patrick Shepard, Facility Manager, and Joe Brown, Director of Environmental Services on the morning of December 17, 2015 to access the property and discuss the extent and purpose of our site visit. Site photographs were taken of the existing site surface conditions and development. The surface of the proposed building addition site is relatively level and currently has grass lawn, landscaping planting areas, and sidewalks. A wood fence with a three foot high rockery extending approximately 3 feet below the existing grade is located along and near the western property line. The top face of the rockery extends approximately 4 feet beyond the fence. The closest corner of the proposed addition is approximately 45 feet northeast from the closest toe of slope. The surface conditions appear generally free draining with limited ponding water in landscaping area. No obvious areas of settlement or surface soil tension cracking was observed in the area of the planned building addition or along and adjacent to the existing rockery. 12129/15 PM 574\001\R\TM Rosewood Courte Addition,docx tANDAu ASSOCIATES 2 Subsurface Soil Conditions This section discusses the general subsurface conditions observed at the project site at the time of our previous investigation. Interpretations of the site conditions are based on the results of our review of previous subsurface explorations from 1998, and associated laboratory testing. Subsurface conditions were explored in March of 1998, by excavating seven test pits at the approximate locations shown on Figure 2. The test pits were excavated to depths ranging from 8 to 10 feet below ground surface (BGS). Subsurface conditions observed in the test pits indicated that the site is generally underlain by undisturbed native soil of glacial origin. The native soil encountered in the test pits consisted of stratified glacial advance outwash sand and gravel deposits. The glacial deposits were typically overlain by less than 1 foot of topsoil consisting of dark brown silty sand contain varying amounts of roots, gravel, and cobbles. The advance outwash deposits underlying the topsoil horizon generally consist of fine to medium sand containing varying amounts of silt, organic material, gravel, and cobbles or fine to coarse gravel with sand, cobbles and isolated boulders. The outwash deposits generally ranged from rust -brown, moist, and loose to medium dense near the contact with the topsoil to gray, moist and dense with increasing depth. Based on our visual observations during the site reconnaissance conducted on December 17, 2015, we anticipate that the soil conditions observed in our 1998 report are still current. However, it should be noted that varying thicknesses of fill, topsoil, rockery drainage rock, concrete flatwork, and utilities associated with the construction of the existing building may be present beneath the planned addition. We anticipate that any fill encountered may extend to the approximate depth of the existing footing, about 2 to 3 feet BGS. The soil gradation and compaction condition of this anticipated fill was not evaluated during our recent site visit and will need to be evaluated during the time of the addition construction. Groundwater Conditions Groundwater was not encountered in any of the previous explorations conducted for the existing building in 1998. Based on our understanding of the geology of the site, we expect groundwater levels to be well below the base of the previous test pits excavations. The native outwash sand and gravel are expected to be relatively permeable, and surface water impacting the site would likely infiltrate rapidly. If site subsurface water is encountered during construction of the proposed building addition, this will need to be evaluated during construction. CONCLUSIONS AND RECOMMENDATIONS The building addition is expected to be located in an area that is underlain by medium dense to dense advance outwash based on the subsurface conditions observed in TP -4 located near the proposed 12/29/15 P:N574\001\R\TM Rosewood Courte Addition docx tANDAu ASSOCIATES 3 building addition location. This soil type is capable of providing good foundation support with moderate to high bearing pressures with tolerable amounts of settlement, provided that adequate subgrade preparation is performed. Subsurface conditions at the site are considered to be generally conducive to the planned building addition. Conventional shallow isolated and continuous footings, slab -on -grade floors, and below grade walls are all considered feasible for the proposed building addition. It is our opinion that the recommendations provided in our Geotechnical Engineering Report dated April 15, 1998 for the following project elements remain valid and can be used for design and construction of the proposed building addition: — Site preparation and earthwork — Foundation support — Lateral earth pressures — Floor slab support — Paved areas — Construction monitoring. Seismic Design Considerations The Pacific Northwest is seismically active and the site could be subject to ground shaking from a moderate to major earthquake. Consequently, earthquake shaking should be anticipated during the design life of the proposed addition and the proposed addition should be designed to resist earthquake loading using appropriate design methodology. The site soils are not subject to seismic hazards such as soil liquefaction or seismically -induced settlement. We understand that the proposed building addition will be designed using the seismic design provisions presented in the 2012 International Building Code (IBC), which references ASCE 7 (ASCE 2010). The U.S. Seismic Design Maps Tool, developed by the U.S. Geological Survey (USGS) and available on the USGS website (USGS 2015), was used to identify the spectral accelerations for a seismic event with a 2 percent probability of exceedance in 50 years (1 -in -2,475 -year return period). The project site is underlain by relatively dense to very dense advance outwash soil; therefore, the site is classified as Site Class C according to Chapter 20 of ASCE 7. Based on the project location (approximately Latitude 47.793 and Longitude -122.371), the following spectral accelerations should be used to estimate the design response spectrum: Spectral Acceleration for short periods (Ss): 126.3% of gravity (1.263g) 12/29/15 PM 574\o®1\RVTM Rosewood Courte Addition docx LANDAU ASSOCIATES 4 Spectral Acceleration for 1 -second period (Si): 49.5% of gravity (0.495g) The above values can be modified for Site Class C using 1.0 for site coefficient Fa, and 1.305 for site coefficient F,,. The design spectral response acceleration parameters can be taken as two-thirds of the maximum considered earthquake spectral response acceleration presented above. Using the above site class and design adjustments, the following design spectral acceleration parameters can be used: SDs = 0.842 SDI= 0.430, Critical Areas According to the Snohomish County Landslide, Erosion, and Volcanic Hazards Map (Snohomish County 2007) the Rosewood Courte addition is located in an area with many slopes classified as "slope 33% or greater." The Snohomish County Tomorrow, Critical Areas Planning Project, Geologic Hazard Areas (GeoEngineers 1991) classifies the slopes in the vicinity of the subject property as a "Moderate Landslide Hazard Area" containing areas sloping between 15 and 40 percent and underlain by soils that consist largely of sand, gravel, bedrock, or glacial till. Erosion potential is moderate to high. The inclination of the slope located to the southwest of the building addition generally ranges from about 50 to 70 percent and therefore, appears to meet the criteria for a "Landslide Hazard Area" as defined in Chapter 23.80 of the Edmonds City Code and Community Development Code. The slope also appears to meet the criteria for an "Erosion Hazard Area" as defined in Chapter 23.80 of the Edmonds City Code and Community Development Code because of the presence of slopes with inclinations between 25 and 70 percent that are comprised of soils mapped by the U.S. Department of Agriculture's Natural Resources Conservation Service as Alderwood/Everett series soils. Landslide hazards and erosion hazards as defined in Chapter 23.80 of the Edmonds City Code and Community Development Code require a 50 -ft minimum buffer in addition to a 15 -ft building setback unless technical justification is provided to support a reduced buffer width. The proposed addition, as noted above, is to be located about 45 ft from the toe of the existing landslide and erosion hazard area. In our 1998 geotechnical report, we concluded that reducing the buffer zone to 10 ft from the toe of the slope would not have an adverse impact on the site, the public, or other private parties. Based on our review of available aerial photographs (Google Earth 2015) dating back to 1998, it does not appear that any new development has occurred on the project site, or above the landslide and erosion hazard area. During our site visit on December 17, 2015, we did not observe any evidence of recent 12/29/15 P,\1574\001\R\TM Rosewood Courte Addition,docx LANDAU ASSOCIATES or prior slope failures or instability that would alter our original analyses and recommendations presented in our 1998 geotechnical report. It is our opinion that the proposed building addition, assuming that is has been appropriately designed, can be constructed within the critical area buffer with no adverse impact on the site, to the public, or other parties. Our opinion is based on the observed condition of the slope, our understanding of site geologic conditions, the absence of observance of surface or groundwater (seeps, springs, etc.); and a review of slope stability analyses and recommendations in our previous report. This opinion is predicated on the assumption that development of the building addition will be performed in accordance with the recommendations provided in our 1998 geotechnical report, and subsequent geotechnical recommendations developed for that purpose. Although the undisturbed material underlying the slope is expected to be dense to very dense, the surficial soil on the slope is generally loose. We anticipate the surficial soil to be prone to erosion if impacted by surface water, particularly where vegetation is thin or non-existent. In addition, many of the trees observed on the slope during our December 17, 2015 site visit appear to be alders and a variety of evergreen trees. Alders typically have poor root structure and are highly susceptible to toppling during adverse weather conditions. We recommend that slope vegetation be routinely inspected and maintained and may include regularly scheduled evaluations and inspections by an arborist to evaluate the condition and behavior of the trees on the slope. USE OF THIS TECHNICAL MEMORANDUM Landau Associates prepared this technical memorandum for the exclusive use of Northwest Care Senior Living and their design consultants for specific application to the design of the Addition to Rosewood Courte at 728 Edmonds Way project in Edmonds, Washington. Use of this technical memorandum by others or for another project is at the user's sole risk. Within the limitations of scope, schedule, and budget, our services have been conducted in accordance with generally accepted practices of the geotechnical engineering profession; no other warranty, express or implied, is made as to the professional advice included in this technical memorandum. The conclusions and recommendations contained in this technical memorandum are based in part upon the subsurface data obtained from the explorations completed for our 1998 report for Geotechnical Engineering Services for the Proposed Alzheimer Courte Community Facility. There may be some variation in subsurface soil and groundwater conditions at the project site, and the nature and extent of the variations may not become evident until construction. Accordingly, a contingency for unanticipated conditions should be included in the construction budget and schedule. 12/29/15 P:\1574\001\RUM Rosewood Courte Addition.docx tANDAu ASSOCIATES 6 If variations in subsurface conditions are encountered during construction, we should be notified for review of the recommendations of this technical memorandum, and revision of such, if necessary. If there is a substantial lapse of time between submission of this technical memorandum and the start of construction, or if conditions change due to construction operations at or adjacent to the project site, we recommend that we review this technical memorandum to determine the applicability of the conclusions and recommendations contained herein. We appreciate the opportunity to provide engineering services on this project and look forward to assisting you during the construction phase of the project. If you have any questions regarding the information contained in this technical memorandum, or if we may be of further service, please call. CE/BEC/SZW/rgm Attachments: Figure 1 - Vicinity Map Figure 2 - Site and Exploration Plan REFERENCES ASCE. 2010. Minimum Design Loads for Building and Other Structures (ASCE 7-10). American Society of Civil Engineers. GeoEngineers. 1991. Snohomish County Tomorrow, Critical Areas Planning Project, Geologic Hazard Areas, July. Google Earth. 2015. Edmonds. Accessed on December 21.International Code Council. 2012. 2012 International Building Code. International Code Council. Landau Associates. 1998. Report, Geotechnical Engineering Services, Proposed Alzheimer Courte Community Facility, Edmonds, Washington. April 15. Snohomish County. 2007. Snohomish County Landslide, Erosion, and Volcanic Hazards Map. October 1 µ USGS. 2015. U.S. Seismic Design Maps Tool. U.S. Geological Survey. Available at Itk�a://earlclu� c.a �scw/rlem�pl'�t�licaticarx. ill,1_Accessed on December 21. 12/29/15 P:\1574\001\R\TM Rosewood Courte Addition docx LANDAU ASSOCIATES 7 4 I Ct �;t r PNwo; /V z" mm" z R Pitt tg Fill I Q) LL