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REVIEWED APRVD ENG BLD PLN WC3-BLD2022-0527 Westgate Station II - Geotechnical ReportNELSON GEOTECHNICAL ASSOCIATES. INC. April 14, 2020 Mr. Marc Wislen 4412 Russell Road, Unit A Mukilteo, Washington 98275 Via email: marc@platers. net Geotechnical Engineering Evaluation Westgate Station Commercial Development 9601 Edmonds Way Edmonds, Washington NGA File No. 1156720 Dear Mr. Wislen: 17311-13511 Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com We are pleased to submit this report titled "Geotechnical Engineering Evaluation — Westgate Station Commercial Development — 9601 Edmonds Way — Edmonds, Washington." This report documents our surface and subsurface explorations within the site, and provides general recommendations for future site development. Our services were completed in general accordance with the agreement which was authorized by you on February 5, 2020. The site is currently vacant and generally consists of a relatively level gravel parking area within the southern and central portion of the site. A moderate to steep south -facing slope is located above the lower parking area within the northern portion of the property. We understand that the proposed development will include construction of a new multi -level commercial structure within the lower relatively level area and extending into the lower portion of the moderate to steep slope within the northern portion of the property. We performed three geotechnical borings using a track -mounted drill rig along within seven backhoe-excavated test pits in the areas of potential development and within the steeply sloping areas. Our explorations generally encountered surficial undocumented fill soils underlain by competent native glacial till and advance outwash soils at relatively shallow depths within the proposed development areas. It is our opinion that the proposed site development is feasible from a geotechnical engineering standpoint, provided that our recommendations for site development are incorporated into project plans. In general, the native glacial soils underlying the site should adequately support the planned structure. Foundations should be advanced through any loose soils down to the competent glacial bearing soils interpreted to underlie the site, for bearing capacity and settlement considerations. These soils should generally be encountered approximately two to three feet below the existing ground surface, based on our explorations. If loose soils or undocumented fill are encountered in unexplored areas of the site, they should be removed and replaced with structural fill for foundation and pavement support. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Summary - Page 2 It is also our opinion that the soils that underlie the site and form the core of the site slopes within the vicinity of the site should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, there is a potential for shallow sloughing and erosion events to occur on the steeper site slopes within the property especially within the loose surficial and fill soils mantling some of the slope areas. We understand that the majority of the proposed structure will be located along the toe of the steep slope areas. In our opinion, this should be feasible, provided the upslope side of the proposed structure is designed to retain the slope and extends a minimum of three feet above finished ground surface, to protect the structure against debris impact generated from potential failures on this slope. This is intended to provide a catchment measure should any sloughing debris travel towards the proposed structures during extreme weather or as a result of an earthquake. Specific grading plans were not available at the time this report was prepared. However, we anticipate that tall cuts and retaining walls will likely be needed for the planned structure especially along the northern side of the proposed structure along the toe of the steep slope. Due to the proposed depth of the anticipated cuts, tight site constraints and to limit significant temporary excavations extending into the steep slope areas, we recommend that temporary/permanent soldier pile shoring walls be utilized to support cut excavations for the structure construction. We recommend that any temporary cuts that are greater than four feet and not able to be sloped back to a safe inclination should be supported with soldier pile shoring wall. These walls can ultimately be incorporated into the building as permanent retaining walls, if feasible. The City of Edmonds utilizes the 2014 WSDOE Stormwater Management Manual for Western Washington to determine long- term design infiltration rates for the site. In accordance with the manual, long-term design infiltration rates for this site were determined by performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT). We performed two small- scale PIT tests within the site in accordance with the manual to determine the infiltration capabilities of the site soils. It is our opinion that the more granular native advance outwash soils encountered at depth within our explorations are suitable for stormwater infiltration. In the attached report, we have also provided general recommendations for site grading, slabs -on -grade, structural fill placement, foundations, retaining walls, soldier pile wall installation, erosion control, and drainage. We should be retained to review and comment on final development plans and observe the earthwork phase of construction. We also recommend that NGA be retained to provide monitoring and consultation services 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 differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. It has been a pleasure to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. rZOMM, Khaled M. Shawish, PE Principal NELSON GEOTECHNICAL ASSOCIATES, INC. TABLE OF CONTENTS INTRODUCTION............................................................................................................................................1 SCOPE..........................................................................................................................................................1 SITECONDITIONS.........................................................................................................................................2 SurfaceConditions......................................................................................................................................... 2 SubsurfaceConditions................................................................................................................................... 3 Explorations................................................................................................................................................... 3 HydrogeologicConditions.............................................................................................................................. 4 SENSITIVE AREA EVALUATION......................................................................................................................4 SeismicHazard............................................................................................................................................... 4 ErosionHazard............................................................................................................................................... 5 Landslide Hazard/Slope Stability................................................................................................................... 5 CONCLUSIONS AND RECOMMENDATIONS...................................................................................................6 General.......................................................................................................................................................... 6 Erosion Control and Slope Protection Measures........................................................................................... 8 SitePreparation and Grading........................................................................................................................ 9 Temporaryand Permanent Slopes.............................................................................................................. 10 Foundations................................................................................................................................................. 10 ShoringWall................................................................................................................................................. 11 Tie-Backs...................................................................................................................................................... 13 OtherRetaining Walls.................................................................................................................................. 14 StructuralFill................................................................................................................................................ 15 Slabson Grade............................................................................................................................................. 16 Pavements................................................................................................................................................... 16 Utilities......................................................................................................................................................... 16 SiteDrainage................................................................................................................................................ 16 CONSTRUCTION MONITORING...................................................................................................................18 SLOPEMONITORING..................................................................................................................................18 USEOF THIS REPORT..................................................................................................................................19 LIST OF FIGURES Figure 1— Vicinity Map Figure 2 —Site Plan Figure 3 — Cross Section A -A' Figure 4 —Cross Section B-B' Figure 5 — Cross Section C-C' Figure 6—Soil Classification Chart Figures 7 through 9 — Boring Logs Figure 10 —Test Pit Logs Figure 11— Schematic Soldier Pile Wall Detail NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Westgate Station Commercial Development 9601 Edmonds Way Edmonds, Washington INTRODUCTION This report presents the results of our geotechnical engineering evaluation of the proposed Westgate Station Commercial Development project located at 9601 Edmonds Way in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. The purpose of this study is to explore and characterize the surface and subsurface conditions within the site and to provide general opinions and recommendations for the future site development. The site is currently vacant and generally consists of a relatively level gravel parking area within the southern and central portion of the site. A moderate to steep south -facing slope is located above the lower parking area within the northern portion of the property. We understand that the proposed development will include construction of a new multi -level commercial structure within the lower relatively level area and extending into the lower portion of the moderate to steep slope within the northern portion of the property. Specific grading and stormwater handling plans were not available at the time this report was prepared. However, we do understand that stormwater generated within the property may be directed to onsite infiltrations systems, if feasible. The existing site layout and proposed building location are shown on the Site Plan in Figure 2. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions, to provide an assessment of the site's geologic hazards, and to provide our geotechnical opinions and preliminary recommendations regarding potential site development. Specifically, our scope of services includes the following: 1. Review available soil and geologic maps of the area, available plans, and any available geotechnical reports for the property. 2. Explore the subsurface soil and groundwater conditions within the site with three geotechnical borings using a track -mounted drill rig. Drilling was subcontracted by NGA. 3. Provide long-term design infiltration rates based on on -site Small Scale Pilot Infiltration Test (PIT) per the 2014 DOE Stormwater Manual. Provide our opinion on the feasibility of infiltration for the onsite soils. 4. Perform laboratory classification and analyses on soil samples obtained from the explorations, as necessary. 5. Qualitatively map conditions on site slopes by constructing a geological cross section using hand-augered explorations where necessary, and evaluate current slope stability conditions. 6. Provide recommendations for site grading and earthwork, including structural fill materials and construction standards. 7. Provide recommendations for steep slope setbacks. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 2 8. Provide recommendations for temporary and permanent slopes. 9. Provide recommendations for temporary and permanent shoring, as needed. 10. Provide recommendations for permanent retaining walls, as well as shoring walls. 11. Provide recommendations for pavement subgrade. 12. Provide recommendations for drainage and erosion control. 13. Document the results of our conclusions and recommendations in a written geotechnical engineering report. SITE CONDITIONS Surface Conditions The site consists of an irregular -shaped parcel covering approximately 1.1 acres. The property is currently undeveloped. The property is bordered to the north and east by existing residential properties, to the south by Edmonds Way and to the east by a gas station. The ground surface within the southern and central portion of the site is relatively level to gently sloping down from the northeast to the southwest. Steep to very steep southeast -facing slopes are located within the northern portion of the property. The steep to very steep southeast -facing slopes descend from the northern property line to the lower relatively level parking area within the central portion of the site at gradients in the range of approximately 24 to 45 degrees (45 to 100 percent). Near vertical exposures of glacial till were also observed within portions of the upper slope areas along the very northern portion of the site. The overall height of the steep slopes within the site range from approximately 30 to 40 feet. The existing site topography and interpreted subsurface conditions are presented as Cross Sections A -A', B-B', and C-C' in Figures 3 through 5, respectively. The slopes are generally vegetated with sparse trees and underbrush. We did not observe significant signs of recent slope movement within the site such as deep-seated landsliding. However, we did observe some indications of past surficial sloughing and erosion that appears to have occurred on the upper steeper site slopes in the past. We did not observe any ponding water or groundwater seepage emitting from the site slopes during our site visits. Subsurface Conditions Geology: The Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington (MF-1541), by James P. Minard, (USGS, 1983) was reviewed for this site. This geologic map indicates the location of the subject property is underlain by Vashon till (Qvt) and advance outwash deposits (Qva). Vashon till typically consists of a concrete -like mixture of relatively equal parts of silt, sand, and gravel, while advance outwash is generally comprised of mostly clean, gray, pebbly sand. Our explorations generally encountered silty fine to medium sand with gravel and fine to medium sand with silt and gravel that we interpreted as native glacial till and advance outwash soils, respectively. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 3 Explorations We visited the site on February 28 and March 3, 2020 to explore the subsurface soil and groundwater conditions by drilling three exploratory borings and seven test pit explorations using a track -mounted drill rig and excavator, respectively. The approximate locations of our explorations are indicated on the Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. A Standard Penetration Test (SPT) was performed on each of the samples during drilling to document soil density at depth. The SPT consists of driving a 2- inch outer -diameter, split -spoon sampler 18 inches using a 140-pound hammer falling 30 inches. The number of blows required to drive the sampler the final 12 inches is referred to as the "N" value and is presented on the boring logs. The N value is used to evaluate the strength and density of the deposit. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 6. The logs of our borings are presented as Figures 7 through 9, and the log of the test pits are presented as Figure 10. The following paragraphs contain a general description of the subsurface conditions encountered in the explorations. For a detailed description of the subsurface conditions, the boring and test pit logs should be reviewed. Borings B-1 through B-3 were performed within the lower relatively level to gently sloping portion of the property. Borings B-2 and B-3 encountered surficial gravel surfacing underlain by approximately 7.0 feet of dense to very dense, gray silty fine to medium sand soils that we interpreted as native glacial till soils. Underlying the ground surface in Boring B-1 and the glacial till soils in Borings B-2 and B-3, we encountered medium dense to very dense, fine to coarse sand with varying amounts of silt and gravel that we interpreted as native advance outwash soils. Borings B-1 through B-3 were terminated within the native advance outwash soils at depths in the range of approximately 30.0 and 30.5 feet below the existing ground surface. All of our test pit explorations encountered approximately 0.5 to 6.0 feet of surficial gravel surfacing or undocumented fill soils. Underlying the undocumented fill in Test Pits 2 through 5 and Infiltration Pit 2, we encountered approximately 1.0 to 8.0 feet of medium dense to very dense, gray silty fine to medium sand and gravel that we interpreted as native glacial till soils. Below the undocumented fill in Test Pits Test Pits 1, 6 and Infiltration Pit 1, and the glacial till soils in Test Pits 2 through 5 and Infiltration Pit 2, we encountered medium dense to very dense fine to coarse sand with gravel that we interpreted as native advance outwash soils. Test Pit 3 was terminated within the native glacial till soils at a depth of approximately 6.0 feet below the existing ground surface while Test Pits 1, 2, 4, 5, 6 and Infiltration Pits 1 and 2 were terminated within the native advance outwash deposits at depths in the range of approximately 5.0 to 10.0 feet. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 4 Hydrogeologic Conditions We did not encounter groundwater within our explorations to the depths explored. If groundwater is encountered during construction we would interpret this as perched water. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of a relatively low permeability material. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard The 2018 International Building Code (IBC) seismic design section provides a basis for seismic design of structures. Since medium dense or better native glacial soils were generally encountered underlying the site at relatively shallow depths throughout the site, the site conditions best fit the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the 2018 IBC, which specifies a design earthquake having a 2% probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1— 2018 IBC Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec. (g) at 1.0 sec. (g) Response Ss S1 Parameters Fa Fv SDs SD1 D 1.263 0.494 1.061 1.506 0.842 0.496 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the competent native glacial soils interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. The competent native glacial soils interpreted to form the core of the site slopes are considered stable with respect to deep-seated slope failures. However, the overlying loose surficial and fill soils mantling the portions of the steep slopes have the potential for shallow sloughing failures during seismic events. Such events should not affect the planned structure provided the foundations, retaining walls along with the slope stabilization measures are designed as described in this report NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 5 Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS) was reviewed to determine the erosion hazard of the on -site soils. The surface soils for this site were mapped as Alderwood-Urban land complex, 8 to 15 percent slopes and Everett very gravelly sandy loam, 0 to 8 percent slopes. The erosion hazard for these materials is listed as slight. It is our opinion that the erosion hazard for site soils should be low in areas where the site is not disturbed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The ground surface within the central and southern portions of the property is generally relatively level to gently sloping down from the northeast to the southwest. Steep to very steep southeast -facing slope areas are located within the northern portion of the property. The steep to very steep southeast -facing slopes descend from the northern property line to the lower relatively level parking area within the central portion of the site at gradients in the range of approximately 24 to 45 degrees (45 to 100 percent). Near vertical exposures of glacial till were also observed within portions of the upper slope areas along the very northern portion of the site. The overall height of the steep slopes within the site range from approximately 30 to 40 feet. We did not observe evidence of significant slope instability within or in the immediate vicinity of the property during our investigation, such as deep-seated landsliding. However, we did observe some indications of past surficial sloughing and erosion that appears to have occurred on the upper steeper site slopes in the past. We did not observe any groundwater seepage emitting from the site slopes during our site visits. We reviewed the City of Edmonds GIS Website and portions of the site are mapped as a landslide hazard area. It is our opinion that the steep to very steep southeast -facing slopes within the northern portion of the property meet the classification as a landslide hazard area in accordance with Edmonds Community Development Code 23.80.020.B.4. This is due to the overall height of the sloping areas being greater than 10 feet and slope inclinations within the steep slope areas being greater than 40 percent. The core of the site slopes within the site and within the near vicinity of the site are inferred to consist primarily of dense or better native glacial soils. Relatively shallow sloughing failures as well as surficial erosion are natural processes and should be expected on the steeper site slopes during extreme weather conditions. This is especially true within the loose surficial and undocumented fill soils on the slopes. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the steep slope, there is not a significant potential for deep-seated slope failures under current site conditions. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 6 We understand that the proposed structure will be located along the toe of the steep slope area. We anticipate that temporary cut excavations along the lower portion of the slope will be reduced by installing a soldier pile shoring wall where temporary cut excavations cannot be sloped back safely or are greater than four feet in overall height. As a result, we anticipate that the proposed development will have minimal impact on the existing steep slope stability conditions. The stability conditions of the steep slope area will ultimately be improved as the proposed structure will be designed to support the steep slope areas above. It is our opinion that the proposed commercial development should not adversely impact or decrease the existing stability of the steep slope areas, neighboring properties, or critical areas; and is in compliance with the City of Edmonds Codes 23.80.060 and 23.80.070, provided our recommendations are incorporated into the proposed plans and followed during construction. We should be retained to review the proposed development and grading plan to analyze the slope stability of the proposed conditions once finalized. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the proposed commercial development within the site is feasible from a geotechnical standpoint. Our explorations indicated that the site is generally underlain by competent native glacial soils at relatively shallow depths throughout the site. The native glacial deposits encountered at depth should provide adequate support for foundation, slab, and pavement loads. We recommend that the planned structures be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native glacial bearing soils, or structural fill extending to these soils. The competent native glacial bearing soils should typically be encountered approximately two to three feet below the existing surface, based on our explorations. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. It is also our opinion that the soils that underlie the site and form the core of the steep slopes within the northern portion of the subject site should be stable with respect to deep-seated earth movements, due to their inherent strength and slope geometry. However, shallow failures could occur on the slopes in the loose surficial and undocumented fill soils, especially during adverse weather or a significant seismic event. We understand that the proposed structure will be located along the toe of the steep slope area within the northern portion of the property. In our opinion, this should be feasible, provided the upslope side of the proposed structure is designed to retain the slope and extends a minimum of three feet above finished ground surface, to protect the structure against debris impact generated from potential failures on this slope. This is intended to provide a catchment measure should any sloughing debris travel towards the proposed structures during extreme weather or as a result of an earthquake. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 7 We anticipate that tall cuts and retaining walls will likely be needed for the planned structure especially along the northern side of the proposed structure along the toe of the steep slope area. Due to the proposed depth of the anticipated cuts, tight site constraints and to limit significant temporary excavations extending into the steep slope areas, we recommend that temporary/permanent soldier pile shoring walls be utilized to support temporary cut excavations for the structure construction. We recommend that any temporary cuts that are greater than four feet in height that are not able to be sloped back to a safe inclination should be supported with soldier pile shoring wall. The soldier pile shoring wall can ultimately be incorporated into the building as permanent retaining walls, if feasible. We provided recommendations for temporary and permanent cut slopes in the Temporary and Permanent Slopes section of this report. We also provide recommendations for the soldier pile shoring walls in the Soldier Pile Shoring Wall subsections of this report. We should be retained to review grading and retaining wall plans once development plans are finalized. Under no circumstances should fill be placed on any slopes without engineering analysis and specific recommendations by NGA. The City of Edmonds utilizes the 2014 WSDOE Stormwater Management Manual for Western Washington to determine long-term design infiltration rates for the site. In accordance with the manual, long-term design infiltration rates for this site were determined by performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT). We performed two small-scale PIT tests within the site in accordance with the manual to determine the infiltration capabilities of the site soils. It is our opinion that the more granular native glacial advance outwash soils encountered at depth within our explorations are suitable for stormwater infiltration. We have included details of our on -site infiltration testing in the Infiltration Testing subsection of this report. All grading operations and drainage improvements planned as part of this development should be planned and completed in a matter that enhances the stability of the steep slopes, not reduces it. Excavation spoils associated with the structure excavations should not be stockpiled near the site slopes or be allowed to encroach on the slopes. Also, all runoff generated within the site should be collected and routed into a permanent discharge system and not be allowed to flow over the slopes. Future vegetation management on the slopes should be the subject of a specific evaluation and a plan approved by the City of Edmonds. The site slopes should be monitored on an ongoing basis, especially during the wet season, for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clipping and any other trash or debris should never be allowed to reach the slopes. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 8 The soils encountered on this site are considered moisture -sensitive and will disturb easily when wet. To lessen the potential impacts of construction on the slopes and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months. If construction takes place during the rainy months, additional expenses and delays should be expected. Additional expenses could include the need for placing erosion control and temporary drainage measures to protect the slopes, the need for placing a blanket of rock spalls on exposed subgrades, and construction traffic areas prior to placing structural fill, and the need for importing all-weather material for structural fill. We recommend that NGA be retained to review final project plans and provide consultation regarding structure placement, site grading, drainage plans, and foundation support. We also recommend that NGA be retained to provide monitoring and consultation services 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 comply with contract plans and specifications. Erosion Control and Slope Protection Measures The erosion hazard for the on -site soils is interpreted as low to moderate but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site or flowing over the slopes. Stockpiles should be covered with plastic sheeting during wet weather and stockpiled material should be kept away from the steep slope on the southern property line. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential for areas not stripped of vegetation should be low to moderate. Protection of the steep slope areas should be performed as required by the City of Edmonds. Specifically, we recommend that the site slopes not be disturbed or modified through placement of any fill or removal of the existing vegetation. No additional material of any kind should be placed on either slope or be allowed to reach the slopes, such as excavation spoils, lawn clippings, and other yard waste, trash, and soil stockpiles. Vegetation should not be removed from the slopes. Replacement of vegetation should be performed in accordance with City of Edmonds code. Under no circumstances should water be allowed to concentrate on the slopes. The clearing of vegetation within the area of the proposed development area should not affect slope stability, provided the temporary cut slopes are supported as recommended in this report and disturbed areas outside the building are revegetated as soon as practical and protected from erosion. In areas that are disturbed during or after construction, planting, hydro seeding, and/or straw mulching are effective ways to minimize erosion and allow vegetation to be re- established rapidly. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 9 Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of stripping any loose soils and undocumented fill to expose medium dense or better native soil in foundation, slab -on -grade, and pavement areas. The stripped materials should be removed from the site or stockpiled for later use as landscaping fill. Based on our observations, we anticipate stripping depths of two to three feet, depending on the specific locations. However, additional stripping may be required if areas of deeper undocumented fill and/or loose soil are encountered in unexplored areas of the site. If the ground surface, after site stripping, should appear to be loose, it should be compacted to a non -yielding condition. Areas observed to pump or weave during compaction should be over -excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in any slab areas, the loose soils should be removed and replaced with rock spalls or granular structural fill. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition. This site is underlain by moisture -sensitive soils. Due to these conditions, special site stripping and grading techniques might be necessary, especially if grading is attempted in wet weather. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and promptly covering exposed subgrades with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted as this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around prepared subgrade. Shallow groundwater, if encountered, should be intercepted with cut-off drains and routed around the planned grading area, or the groundwater should be controlled with sump -pumps or dewatering systems. Failure to follow these recommendations could cause erosion and failures on the slopes, as well as result in inadequate subgrades. The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend that construction take place during the drier summer months if possible. However, if construction takes place during the wet season, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also require additional erosion control and site drainage measures. Some of the on -site soils may be suitable for use as structural fill, depending on the moisture content of the soil at the time of construction. NGA should be retained to evaluate the suitability of all on -site and imported structural fill material during construction. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 10 Temporary and Permanent Slopes In general, cut -slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations since they are continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the surficial fill soils and native glacial soils near the steep slope area of the site be no steeper than 2.0 Horizontal to 1.0 Vertical (2H:1V). Temporary cuts in the competent native glacial soils within the relatively level southern portion of the property away from the steep slopes should be no steeper than 1H:1V. If temporary cut excavations are not able to achieve the recommended inclinations or are greater than four feet in overall height along the toe of the steep slope area, we recommend that the cuts be shored with a soldier pile shoring wall as discussed in the Soldier Pile Shoring Wall subsection of this report. If perched groundwater or loose soils are encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. Measures taken may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. We recommend that the final slope inclinations for structural fill and the native soils be no steeper than 2HAV. However, flatter inclinations may be necessary in areas where loose soils are encountered. Final slopes should be vegetated and covered with jute netting. The vegetation should be maintained until it is established. Foundations Conventional shallow spread foundations should be placed on medium dense or better native glacial bearing soils, or be supported on structural fill or rock spalls extending to those soils. Medium dense soils should be encountered approximately two to three feet below ground surface within the proposed development area based on our explorations. Where undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be over - excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or the footing may be extended down to the competent native bearing soils. If footings are supported on structural fill, the fill zone should extend outside the edges of the footing a distance equal to one half of the depth of the over -excavation below the bottom of the footing. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 11 Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the 2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure. Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable design bearing pressure of not more than 3,000 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing glacial soils or structural fill extending to the competent native material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and %-inch differential between adjacent footings or across a distance of about 20 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured "neat" against the native medium dense soils or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the passive resistance. Shoring Wall General: We understand that tall cuts will be necessary along the northern side of the building along the toe of the steep slopes. These temporary cuts will require shoring systems to complete the earthwork and foundation installation. We would recommend that the proposed shoring system consist of a soldier pile shoring wall. A solider pile wall typically consists of a series of steel H-beams placed vertically at a certain spacing from one another (typically six to ten feet). The beams are usually placed in drilled shafts that are filled with structural concrete or a lean mix. The concrete shafts are typically embedded below the bottom of the planned excavation a distance equals one to two times the exposed height of the wall. The steel beams are extended above finished ground surface to provide shoring capabilities for the area to be NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 12 retained. The beams are typically spanned by pressure treated timber lagging or concrete panels. The H-beam size, shaft diameter, shaft embedment, and pile spacing are dependent on the nature of the soils anticipated to be retained by the wall and the soils at depth, wall height, drainage conditions, and the final geometry. A schematic detail of the wall is shown on the Conceptual Soldier Pile Wall Detail in Figure 11. Wall Design: The shoring wall should be designed by an experienced structural engineer licensed in the State of Washington. The lateral earth pressure acting on the shoring wall will be dependent on the nature and density of the soil behind the wall, structure and traffic loads on the wall, and the amount of lateral wall movement that may occur as material is excavated from the front of the wall. If the shoring wall is free to yield at least one -thousandth of the retained height, an "active" loading condition develops. If the wall is restrained from movement by stiffness or bracing, the wall is considered in an "at -rest" loading condition. Active and at -rest earth pressure can be calculated based on equivalent fluid densities. The shoring wall should be designed to resist a lateral load resulting from a fluid with a unit weight of 45 and 65 pounds per cubic foot (pcf) for the active and at -rest loading conditions, respectively. A uniform surcharge 8H (in psf) should be applied to the wall design to account for seismic loading, respectively if the shoring walls are intended to provide permanent support. H in this case is the exposed height of the wall. These loads should be applied across the pile spacing above the excavation line. These loads can be resisted by a passive pressure of 200 pcf on the below grade medium dense or better soils. The passive pressure should be applied on two -pile diameters under the excavation line. These values of the passive pressure incorporate a factor of safety of 2.0. The upper two feet of pile embedment should be neglected when calculating the passive resistance for the permanent condition. Also, for the permanent condition, the below -grade portion of the wall should be no less than 1.5 times the wall stick-up height. The above loads should be applied on the full center -to -center pile spacing above the base of the exposed portion of the wall. A 50 percent reduction of the active pressure could be applied for the purpose of designing the wall lagging. The above pressures assume that the on -site soils retained by the shoring wall are not significantly disturbed and that hydrostatic forces are not allowed to build up behind the wall. These values do not include the effects of surcharges other than what is described above. The retained soils should be readily drained and collected water should be routed into a permanent storm system. Adequate gaps should be maintained between the lagging elements to allow for any potential water seepage buildup to flow through the wall. If a concrete wall is proposed to be cast on the face of the shoring wall, we recommend that a drainage composite such as a Miradrain mat be placed between the face of the shoring wall and the concrete wall. The drainage composite should be directed to flow into a drainage collector at the base of the shoring wall and ultimately to an approved discharge point. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 13 The wall designer should calculate the predicted wall deflection, including deflection resulting from the below -grade movement of the piles. The predicted deflection values should be confirmed in the field through a survey monitoring program. Also, surrounding structures should be monitored for any adverse effects resulting from shoring wall installation. Shoring Wall Installation: The shoring wall should be installed by a shoring contractor experienced with this type of system. We anticipate that an open -hole drilling method may prove difficult to achieve for installing the soldier piles in the on -site soils, and therefore we recommend that the shoring contractor should have the capability of casing the holes as sloughing and/or water seepage if encountered. It might be prudent to perform one or more "test" holes to confirm installation conditions prior to finalizing budget and work plans. Any sloughing or water that may collect in the drilled holes should be removed prior to pumping grout. Grout should be readily available on site at the time the holes are drilled. If groundwater seepage is encountered, we recommend that water be pumped out of the holes and the concrete be tremied from the bottom of the excavations to displace the groundwater to the surface. Extra Portland Cement, or other additives, may also be placed in the excavations to reduce the effects of seepage. The spoils from the soldier pile excavations are expected to be moisture -sensitive materials and should be removed from the site. We should be retained to monitor on site activities during the shoring wall installation on a full-time basis. Tiebacks General: If tiebacks are needed to support lateral loads, we recommend that these systems consist of drilled, grouted tieback anchors. All nearby existing utilities and structures should also be fully understood prior to finalizing the tieback design. We recommend that at least two of the anchors be performance tested to a minimum of 200 percent of the design loads to confirm design values. We recommend that measurements be made by the contractor in the field at the time of tieback installation to verify that tiebacks do not encounter any existing structures or underground utilities. No -Load Zone: The anchor portion of all tiebacks must be located a sufficient distance behind the wall face to develop resistance within a stable soil mass. We recommend the anchorage be obtained behind an assumed no-load zone. The no- load zone is defined by a line extending horizontally from the base of the shoring wall back towards the cut a distance of six feet. This line should then extend up from the base elevation at an angle from the horizontal of 60 degrees. We recommend that we monitor soil conditions during anchor installation in order to evaluate adequate penetration into competent soils. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 14 Soil Design Values: The tiebacks must terminate in native, competent soil interpreted to exist below the fill. For use in design of the anchors, we estimate an allowable grout to soil adhesion of 1,500 pounds per square foot (psf) be utilized for anchors terminated within the competent native glacial soils. This value should be verified through two performance tests prior to ordering the production anchors. Tieback Installation and Testing: The contractor should be responsible for using equipment suited for the site conditions. We do not recommend the use of an open -hole method for the purpose of installing the tiebacks due to the potential for soil caving. Secondary grouting to increase soil adhesion may be used; however, if secondary grouting is used, the anchors should be tested using the methods outlined for the performance testing. All anchors should be installed at an approximate inclination of 15 to 20 degrees below horizontal. Two anchors should be performance -tested to 200 percent of the anchor design capacity. The performance test should consist of cyclic loading in increments of 25 percent of the design load, as outlined in the Federal Highways Administration (FHA) report No. FHWA/RD-82/047. The test locations should be determined in the field by NGA, based on soil conditions observed during anchor installation. All other tiebacks should be proof -tested to at least 130 percent of design capacity. Other Retaining Walls The lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 45 pounds per cubic foot (pcf) for yielding (active condition) walls, and 65 pcf for non -yielding (at -rest condition) walls. To account for seismic loading, a uniform surcharge of 8H should also be included in the wall design where "H" is the total height of the wall. These recommended lateral earth pressures are for a drained backfill and are based on the assumption of a maximum 2H:1V slope above the wall for a distance of at least the subsurface height of the wall, and do not account for additional surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab loads, or other surface loads. We could consult with you and your structural engineer regarding additional loads on retaining walls during final design, if needed. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 15 All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand -operated compactors within a distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand -operated equipment. The recommended level of compaction should still be maintained and should be tested. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. Structural Fill General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in -place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4-inch sieve). Some of the more granular on - site soils may be suitable for use as structural fill, but this will be highly dependent on the moisture content of these soils at the time of construction. We should be retained to evaluate all proposed structural fill material prior to placement. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over -excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 16 Slab -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches of free -draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. A suitable vapor barrier, such as heavy plastic sheeting (6-mil, minimum), should be placed over the capillary break material. An additional 2-inch- thick moist sand layer may be used to cover the vapor barrier. This sand layer may be used to protect the vapor barrier membrane and to aid in curing the concrete. Pavements Pavement subgrade preparation and structural filling where required, should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft or yielding areas that require repair. The pavement section should be underlain by a minimum of six inches of clean granular pit run or crushed rock. We should be retained to observe the proof -rolling and recommend subgrade repairs prior to placement of the asphalt or hard surfaces. Utilities We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas should be compacted to 95% of the modified proctor as described in the Structural Fill subsection of this report. Trench backfill should be compacted to a minimum of 95% of the modified proctor maximum dry density. Trenches located in non-structural areas and five feet below roadway subgrade should be compacted to a minimum 90% of the maximum dry density. The trench backfill compaction should be tested. Site Drainage Infiltration: The subsurface soils within our explorations generally consisted of granular glacial advance outwash soils to the depths explored. In accordance with the 2016 King County Surface Water Design Manual, we conducted a Small PITS within Infiltration Pit 1 and 2, as shown on the attached Schematic Site Plan in Figure 2. Infiltration Pit 1 measured 4.0- feet long by 3.0-feet wide by 5.0-feet deep. Infiltration Pit 2 measured 4.0-feet long by 3.0-feet wide by 8.5-feet deep. The pits were filled with 12-inches of water at the beginning of the day and we began the soaking period of the PIT for approximately 6 hours. At this time, the water flow rate into the holes was monitored with a Great Plains Industries (GPI) TM 075 water flow meter for the pre-soak period. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 17 Infiltration Pit 1 (Western): After the 6-hour soaking period was completed, the water level was maintained at approximately 12-inches for one hour for the steady-state period. The flow rate for Infiltration Pit 1 stabilized at 0.285 gallons per minute (17.10 gallons per hour), which equates to an approximate infiltration rate of 2.3 inches per hour. The water was shut off after the steady-state period and monitored every 15 minutes for one hour. After one hour, the water level within the pit had dropped 1.75 inches, resulting in an infiltration rate of 1.75 inches per hour. Infiltration Pit 2 (Eastern): After the 6-hour soaking period was completed, the water level was maintained at approximately 12-inches for one hour for the steady-state period. The flow rate for Infiltration Pit 2 stabilized at 1.90 gallons per minute (114 gallons per hour), which equates to an approximate infiltration rate of 15.2 inches per hour. The water was shut off after the steady-state period and monitored every 15 minutes for one hour. After one hour, the water level within the pit had dropped 8.0 inches, resulting in an infiltration rate of 8.0 inches per hour. It is our opinion that the more granular advance outwash soils within the site are suitable for traditional stormwater infiltration. The subsurface soils within the proposed development area generally consisted of surficial fill underlain by silty fine to medium sand that we interpreted as native glacial till soils with fine to medium sand and gravel soils that we interpreted as native advance outwash soils at depth. These granular advance outwash sand and gravel soils were generally encountered at approximately 3.0 and up to 9.0 feet below the existing ground surface within the southwestern and southeastern portions of the property, respectively. We have selected the overall measured field rates of 1.75 in/hr obtained from the falling head portion of the test within Infiltration Pits 1 be utilized in determining the long-term design infiltration rate for the infiltration systems within the southern portion of the property. This rate is conservative compared to the rate obtained from the more eastern infiltration test and should be utilized in the initial design of the infiltrations systems within the site. In accordance with the Table 3.5 of the Department of Ecology 2014 Stormwater Management Manual for Western Washington, correction factors of 0.8, 0.5, and 0.9 for site variability and number of locations tested (CF ), testing method (CFt), and degree of influent control to prevent siltation and bio-buildup (CFm), respectively were applied to the field measured infiltration rate of 1.75 inches per hour, selected from the falling -head portion of the testing. A total correction factor of 0.36 was applied to the measured field infiltration rate obtained from the falling head portion of the test to determine the long-term design infiltration rate. Using this correction factor, we calculated a long-term design infiltration rate of 0.63 inches per hour to be utilized in designing the proposed infiltration systems founded within the native granular advance outwash soils. We recommend that the base of the on -site infiltration systems be terminated in the native advance outwash deposits. We did not encounter groundwater or indications of groundwater within the site to the depths explored. It is our opinion that proposed infiltration systems should be able to maintain the minimum separation from the base of the infiltration systems to any impermeable surfaces and/or groundwater table. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 18 We recommend that any additional infiltration systems be placed as to not negatively impact any proposed or existing nearby structures and also meet all required setbacks from existing property lines, structures, and sensitive areas as discussed in the drainage manual. In general, infiltration systems should not be located within proposed fill areas within the site associated with site grading or retaining wall backfill as such condition could lead to failures of the placed fills and/or retaining structures. We should be retained to evaluate the infiltration system design and installation during construction, if necessary. Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an approved stormwater collection system. Water should not be allowed to stand in any areas where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from the structures. We suggest that the finished ground be sloped at a minimum downward gradient of three percent, for a distance of at least 10 feet away from the structures. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an approved discharge system. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into a permanent storm drain. We recommend the use of footing drains around the structures. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric. We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free -draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. 'AfI► I111:11111I411111910VA191►1111t9]C11►1:0 We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. SLOPE MONITORING We also recommend that we be retained to periodically observe the steep slopes and evaluate the existing stability conditions, especially after a significant storm event. If any distress is observed, we can then provide recommendations for mitigation measures at that time. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1156720 Westgate Station Commercial Development April 14, 2020 Edmonds, Washington Page 19 USE OF THIS RERORT This preliminary report has been prepared for Mr. Marc Wislen, and his agents, for use in the planning and design of the proposed development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our letter. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. We recommend that NGA be retained to provide monitoring and consultation services 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 retaining wall and foundation support installation complies with our recommendations. We should be contacted a minimum of one week prior to construction activities. All people who own or occupy strucrtures on or near hillsides should realize that landslide movements are always a possibility. The landowner should periodically inspect the slope, especially after a winter storm. If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative measures. The probability that landsliding will occur is substantially reduced by the proper maintenance of drainage control measures at the site (the runoff from the roofs and all other hard surfaces should be led to an approved discharge point). Therefore, the homeowner should take responsibility for performing such maintenance. Consequently, we recommend that a copy of our report be provided to any future homeowners of the property if the home is sold. Within the limitations of scope, schedule and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Westgate Station Commercial Development Edmonds, Washington NGA File No. 1156720 April 14, 2020 Page 20 We appreciate the opportunity to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Project Geologist Khaled Shawish, PE Principal LSB:KMS:sw Eleven Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale U Birch St A� 9 N 9� Q P IAA Way SW 104 14th St SW 224th St SW 0 s < > FIVE 15tt151 S{y 226th St SW P ro a ct © Edmonds Memorial s s Cemetery Site = D D WEST - 22Bth s1 SW Goodwill Edmonds Q 228th St SW ` PCC CornnwnitY' �amonds Wdy Q Westgate Chapel QFC Markets - Edmond Sherwood 0 itary School 1O0 - o a o � - � S D D 231sP 231ary} f _ h f z 2J2nc S( SW RoW Hood © Scriber Lake High School Former Woodway ® g High School ➢ > 234th St SW Nottingharn Rd M f w 235th Pt SVt S n 9 D D Robb —Rohs: Re � f Z 2361h St SW 236th St SW 236th Pt SW 3 Hickman Park o Madrona K-8 School 0 s r - y s o a 23M St SW a. 3 Woodway Elementary 0 Edmonds, WA N 222nd St SW 224th St SW 224th St SW 5 F E s p e r a n, 228th St SW �y c QLocal Roots Marijuana 236th �N Project Number NELSON GEOTECHNICAL No. Date Revision By CK o Westgate Station � ASSOCIATES INC. N 1156720 Commercial Development �+A 1 3/16/20 Original DPN DJO etL GEOTECHNICAL ENGINEERS & GEOLOGISTS E Figure 1 Vicinity Map W°35th Av.. NE, East Wenatchee Office 17311-135[h Ave. NE, A-500 552fi Industry Lane, it2 a J Woodinville, WA 98072 East Wenatchee, WA 98802 (425) 486-16691 Fax:481-2510 ww—lsongeotech.com (509) 665-76961 Fax: 665-7692 = D I D I D o -oa �§ CD (n 3 m v A cu m 0 o a0 oC o� r 3 v 3 0, C m o 07 m o v In� o v � D � � Z: �- -0 o x 5.o 3 3 cn CD CD �r �1 v o Z 0 C .4 y 3 '• ,'.. —0 3 CD \ •� \ .;. � E \ - E -. E E \ E e Fes, I � Fs y F s Map ^ ¢ I Qz v_ i *1i II111111� \ G Z a Project Number 1156720 Westgate Station NELSON GEOTECHNICAL NGA ASSOCIATES, INC. No. Date Revision By CK 0 s 1 3/16/20 Original DPN DJO Commercial Development GEOTECHNICAL ENGINEERS & GEOLOGISTS Site Plan Figure 2 Woodinville Office East Wenatchee Office U 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 ? Woodinville, WA98072 East Wenatchee, WA 98802 (425) 486-1669 / Fax: 481-2510-nelsongeotech.com (509) 665-7696 / Fax: 665-7692 A A' T ,o ,C CrI CD -4C N CD m Northwest Southeast 420 420 0 0 o 3 C,mm Ta a Cn v 0 p m 390 390 0 0 D a v D-0 0 0 -CD o 0 360 w 360 � na m Dn m 4 45' o x TP-4 x'm Z y 0 INF-1 B-3 n � Z Q 330 54 50-6 330 m m Z r 50-4 _ N (n o O 50-6 m O Z 50-5 m 0 � 50-4 3 N M Q 0-5 m W m 300 300 n z I I I I I I I I I I I I I I I TS Z - ^^- 0 30 60 90 120 150 180 210 i "N r Distance (feet) Exploration z ° d Boring Designation B-1 23 Test Pit Designation TP-1 T. 23 Groundwater Level ---> 1 <-- SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration 23 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact --> ? _ —? Geologic Contact --> the explorations. Actual conditions 2) Elevations are approximate. may vary. W z � (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg o B B, T , ,C CrI CD -4C N cD m Northwest Southeast 420 420 0 0 o 3 C,mm Ta a Cn v 0 p m 390 390 0 0 00 o v p0 -0 = c -CD o 0 360 w 360 a�� m ° ° o Z c6 24° Dpi� X TP-3 B-2 Z > Q 62 n r19 Z Q 330 72 50-6 330 m zy r 50-4 N in Z N o 50-6 m 0 z 50-6 m 00 3 N 06 m -1 0 m in m 300 300 n z Z I I I I I I I I I I I I I I I TS - ^^- 0 30 60 90 120 150 180 210 i "N r Distance (feet) Exploration z ° d m Boring Designation ---> B-1 23 Test Pit Designation ---> TP-1 y z3 Groundwater Level 1 SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration z3 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact ? _ —? Geologic Contact --> 2) the explorations. Actual conditions may vary. Elevations are approximate. W z � (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg C C' C CD __4C N CD m Northwest Southeast 420 420 0 0 0 3 in 0 CD v v &CD p m 390 390 0 0 < cn C� o v n-0 0 c -� 0 0 360 w 360 m 0 o Z 35° D � M� x X - 5 B-1 x'm Z y 0 INF-2 54 �nm o n � Z 0- Q 330 �TP ao 50-4 330 m Z> r 50-6 o Z N o 50-5 M 0 Z 50-4 m n C) 3 00 N m 0 m m 300 300 n z Z I I I I I I I I I I I I I I I TS - ^^- 0 30 60 90 120 150 180 210 i "N r Distance (feet) Exploration z ° d Boring Designation B-1 23 Test Pit Designation TP-1 T. 23 Groundwater Level ---> 1 <-- SPT N-value Groundwater Level � 1 NOTES: 3 23 During Exploration 23 During Exploration 1) Stratigraphic conditions are interpolated between 23 Geologic Contact ---> ? _ —? Geologic Contact --> 2) the explorations. Actual conditions may vary. Elevations are approximate. W z � (approximate) Reference: Cross Section is based (approximate) on field measurements using a hand-held clinometer and 100-ft tape measure. o `o 0 X \\HILL\company\2020 NGA Project Folders\11567-20 Westgate Station Edmonds Way Commercial Development\Drafting\CS.dwg UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 % GRAVEL GM SILTY GRAVEL OF COARSE FRACTION RETAINED ON SOILS NO.4 SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES SC CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 % PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist - Damp, but no visible water. 3) Descriptions of soil density or Wet - Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 1156720 Westgate Station NGA ASSOCIATES, INC. Commercial Development GEOTECHNICAL ENGINEERS & GEOLOGISTS 1 3/16/20 Original DPN DJO Figure 6 Soil Classification Chart W°35thAv..NE,°e Ea=1We"at°yLanehee 2 311-1%[h Ave.NE,A-500 Industry Lane,88 Woodinville, WA 98072 East Wenatchee, WA 98802 East W (425) 486-1669 / F_ 481-2510 www. nelsongeotech.com (509) 665-7696 1 Fax: 665-7692 BORING LOG B-1 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance 0) (Blows/foot -) 10 20 30 40 50 50+ I I I I N Piezometer Installation - `—' ` Ground Water Description a Q o 0 Q ° � Moisture Content o Data o f o CO v E la L 0 (Percent - �) O (Depth in Feet) (D fn cn 10 20 30 40 50 50+ p J Gray, fine to medium sand with silt and gravel (medium dense, moist) 30 -becomes medium dense :... •.. 23 5 ................................................... 5 SP-SM -becomes dense 32 -becomes very dense 94-11 '10 .......................................... ........ 10 -----------------:• Gray, fine to coarse sand with gravel and trace silt (very dense, moist) .. 15 .................................................... 15 50-4 Sp 50-6 20 .................................................... 41 20 50-5 25 .................................................... 41 25 No recovery LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits 0 Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 7 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-1 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-0 Boring terminated below existing grade at 30.0 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 7 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-2 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance (Blows/foot -) 10 20 30 40 50 50+ 0) N Piezometer Installation - �, ` Ground Water Description a rn Q o = - a) a ° � Moisture Content o Data o f o m v E m L 0 (Percent - 0) o (Depth in Feet) C7 fn cn 10 20 30 40 50 50+ m p J Gray, silty fine to medium sand with gravel (very dense, moist) SM 62 'Ilk 72 5 ................................................... 5 Gray, fine to coarse sand with gravel and trace silt (medium dense, moist) 19 ' becomes very dense 50-6 ' .. 50-4 ' 15 .................................................... 15 SP ' ~ 50-6 20 1 ............... ..... .... ..... 20 50-6 ' 25 .................................................... 25 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits ❑ Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap `" Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 8 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-2 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-6 Boring terminated below existing grade at 30.5 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 8 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-3 Approximate Ground Surface Elevation: ?? Soil Profile Sample Data Penetration Resistance 0) (Blows/foot -) 10 20 30 40 50 50+ N Piezometer Installation - �, ` Ground Water Description a rn Q o = - a) a ° � Moisture Content o Data o f o m v E m L 0 (Percent - 0) o (Depth in Feet) C7 fn cn 10 20 30 40 50 50+ m p J Gray, silty fine to medium sand with gravel (very dense, moist) SM 54 ' -becomes dense, less silt _ 40 5 ...................................... ............ 5 Gray, fine to medium sand with silt and trace gravel (very dense, moist) 50-6 ' SP-SM 10 .................................................... 10 50-4 ' ---------------:• Gray, fine to coarse sand with gravel and trace silt (very dense, moist) .. 50-6 ' 15 .................................................... 15 SP 20 .................................................... 20 50-5 ' 50-4 ' 25 .................................................... 25 No recovery LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content Limits 0 Slotted PVC Pipe Bentonite A AtterbergGrain-size Depth Driven and Amount Recovered P G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P �k Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 9 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 1 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 BORING LOG B-3 (cont.) Soil Profile Sample Data Penetration Resistance (Blows/foot - 10 20 30 40 50 50+ Piezometer Installation - �, Ground Water Description a 0- �° 3 Q Moisture Content m Data J o o m v m L (Percent - �) o (Depth in Feet) c� fn cn 0 CL 10 20 30 40 50 50+ -p J 50-5 Boring terminated below existing grade at 30.5 feet on 3/3/20. Groundwater seepage was not encountered during drilling. 35 .................................................... 35 40 .................................................... 40 45 .................................................... 45 50 .................................................... 50 55 .................................................... 55 LEGEND ❑ Solid PVC Pipe Concrete M Moisture Content 0 Slotted PVC Pipe Bentonite A Atterberg Limits Depth Driven and Amount Recovered G Grain -size Analysis with 2-inch O.D. Split -Spoon Sampler Monument/ Cap Native Soil DS Direct Shear to Piezometer PP Pocket Penetrometer Readings, tons/ft Depth Driven and Amount Recovered ❑ Silica Sand P * Liquid Limit P Sample Pushed with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log. Project Number NGEOTECHNICAL No. Date Revision By CK Westgate Station ASSOCIATES,NELSON NGA ATINC. 1156720 Commercial Development Boring Log GEOTECHNICAL ENGINEERS & GEOLOGISTS � 3�,s�zo Original DPN DJO Figure 9 Woodinville Office East Wenatchee office 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Page 2 2 of (425)486-1669/Fax: 4812510-nelsongeutech.corn (509)6 5-7696/ Fax: 6657692 LOG OF EXPLORATION DEPTH (FEET) TEST PIT ONE 0.0 - 0.5 0.5 - 1.0 1.0 - 10.0 TEST PIT TWO 0.0 - 0.5 0.5 - 3.0 3.0 - 8.5 8.5 - 10.0 TEST PIT THREE USC SOIL DESCRIPTION GRAVEL SURFACING (UNDOCUMENTED FILL) GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ORGANICS (MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE TO VERY DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE COLLECTED AT 2.0, 4.0, 8.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 10.0 FEET ON 2/27/2020 GRAVEL SURFACING (UNDOCUMENTED FILL) SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (WEATHERED GLACIAL TILL) SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) SP BROWN, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE COLLECTED AT 2.0, 5.0, AND 9.0 GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 10.0 FEET ON 2/27/2020 0.0 - 6.0 DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 6.0 - 8.0 SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) SAMPLES WERE COLLECTED AT 3.0 AND 6.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 8.0 FEET ON 2/27/2020 TEST PIT FOUR 0.0-2.0 DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 2.0 - 3.0 SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (GLACIAL TILL) 3.0 - 7.5 SP GRAY, FINE TO MEDIUM SAND WITH TRACE GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLE WAS COLLECTED AT 6.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 7.5 FEET ON 2/27/2020 DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1156720 FIGURE 10 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION TEST PIT FIVE 0.0 - 2.0 DARK BROWN TO BLACK, SILTY FINE TO MEDIUM SAND WITH ROOTS, ORGANICS, AND GRAVEL (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 2.0-4.0 SM BROWN -GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) (GLACIAL TILL) 4.0 - 7.5 SP GRAY, FINE TO MEDIUM SAND WITH TRACE GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLE WAS COLLECTED AT 4.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 7.5 FEET ON 2/27/2020 INFILTRATION PIT ONE 0.0 - 0.5 GRAVEL SURFACING (UNDOCUMENTED FILL) 0.5 - 1.0 GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ORGANICS (MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 1.0 - 5.0 SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND SILT (DENSE TO VERY DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 5.0 FEET ON 2/27/20 INFILTRATION PIT TWO 0.0 - 0.5 GRAVEL SURFACING (UNDOCUMENTED FILL) 0.5 - 7.5 SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (DENSE TO VERY DENSE, MOIST) (GLACIAL TILL) 7.5 - 8.5 SP GRAY, FINE TO COARSE SAND WITH GRAVEL AND TRACE SILT (DENSE, MOIST) (ADVANCE OUTWASH) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 8.5 FEET ON 2/27/20 DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1156720 FIGURE 10 Conceptual Soldier Pile Wall Detail NOT FOR CONSTRUCTION USE -, Lean concrete above UO excavation line 0 Iz x w Concrete wall Miradrain drainage matting full height & width centered between piles, installed with fabric to lagging Waterproofing membrane along length of wall Pressure treated timber lagging with 1/4-inch gap between boards Multiflow drainage collector 4-inch diameter weep holes Project Number NELSON GEOTECHNICAL 1156720 Westgate Station Commercial NGA ASSOCIATES, INC. Development Conceptual Soldier Pile Wall Detail GEOTECHNICAL ENGINEERS & GEOLOGISTS Figure 11 "Wo dine pe WA 8 7200 Weoetohee Che en (509 6377666 (425)486-16691 Fax 481-2510-nelsongeolech.com 4-inch diameter PVC pipe tightlined to storm drainage system NOT TO SCALE No. I Date I Revision I By I CK 1 1 3/29/20 1 Original I LSB I KMS