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REVIEWED BLD2023-1125+CA Report+9.6.2023_1.34.22_PM+3766945FJQ0F05ZP P) O�ZGT V50f Optic View PriVa GIrl OF ZPX01VP5 ALDERWOOD July 281h , 2022 This letter describes the proposed landscape improvements (Project) at 9309 Olympic View Drive, Edmonds, WA 98020 (APN 27031300102200) (Site) by documenting the site conditions, anticipated conditions, rational for what is proposed and how it will be accomplished. SITE CONDITIONS As described in the Critical Areas Determination, there was a steep slope discovered on site. The report identified slopes of 40% or more with at least 20 feet or rise. The report mentions any land disturbing activity within 50 feet of the slope to require a geotechnical report. The geotechnical report recommends a 15 foot buffer from the top of the slope. Adjacent to this Site, 9305 Olympic View Drive (Neighboring Property) completed a permitted backyard patio and landscaping project similar in nature to the proposed project. It was determined by the City that the patio and water feature would not adversely affect the stability of the slope by being within the building setback from the buffer. It was also determined that storm water runoff and water feature overflow could be routed into existing drainage systems which are piped down to the bottom of the slope. Currently the proposed project is of near identical nature to this Neighboring Property's approved project. See included geotechnical engineer report for further site conditions of the parcel and reccomendations. PROPOSED PROJECT The proposed project includes removal of existing concrete pad, concrete stepping stones, concrete steps, and lawn areas. Proposed improvements include expansion of a paver walkway, paver patio, boulder retaining walls, water feature, flagstone stepping stones, and an on -grade hot tub. A portion of this work extends within the building setback line similar to what was approved on the Neighboring Property. The top of slope has been located on site using high precision RTK GPS receivers and drone aerial photogrammetry. The location of this is consistent with determinations from similar designations on neighboring properties and past reports from this Site. The existing drainage systems in place routes stormwater discharge to pipes that extend down the slope. As approved on the Neighboring property, any surface water or water feature overflow is proposed to drain into the existing system drain lines. 866,467.8298 1 alderwoodlandscaping.com CITY OF EDMONDS 121 511 Avenue North, Edmonds WA 98020 Phone: 425.771.0220 • Fax: 425.771.0221 • Web: www.edmondswa.gov PLANNING & DEVELOPMENT DEPARTMENT • PLANNING DIVISION 'hC. t 8913 5/4/2023 JEANNE DUBOIS KIEWICZ-BROOKS 9309 OLYMPIC VIEW DR EDMONDS, WA 98020-2397 Subject: Critical Areas Determination (CRA2023-0083) Site Address: 9309 OLYMPIC VIEW DR Dear Applicant/Owner, Please find the enclosed critical area determination for the Critical Areas Checklist you submitted to the City of Edmonds Planning Division. The critical area determination for your property is "CRITICAL AREA PRESENT." Note that this determination is a site -specific determination and not a project -specific determination. If the critical area determination is "CRITICAL AREA PRESENT," additional critical areas information or critical areas specific studies may be required for development or alteration of your property depending on the location of the activity. "WAIVER" means no further critical area review is required for development or alteration of your property. If you have any questions regarding this critical area determination, please contact the planner on duty at 425.771.0220. Regards, TRISTAN SEWELL Planning Division Planning & Development Department Enc: Critical Area Determination CITY OF EDMONDS 121 511 Avenue North, Edmonds WA 98020 Phone: 425.771.0220 • Fax: 425.771.0221 • Web: www.edmondswa.gov PLANNING & DEVELOPMENT DEPARTMENT • PLANNING DIVISION 'nc. 18`)V Critical Area Determination (CRA2023-0083) Based on a review and inspection of the subject site, staff determined that one or more critical areas are located on or near the site. Critical areas are ecologically sensitive or hazardous areas that are protected to maintain their functions and values. Site Location 9309 OLYMPIC VIEW DR Tax Account Number 27031300102200 Property Owner JEANNE DUBOIS KIEWICZ-BROOKS Applicant BRYAN NAVARRO Critical Area(s) Present ❑ Wetlands (ECDC 23.50): NA ❑ Frequently Flooded Areas (ECDC 23.70): Yes ❑ Geologically Hazardous Areas (ECDC 23.80) ❑ Erosion Hazard Areas: Yes ❑ Landslide Hazard Areas: Yes ❑ Seismic Hazard Areas: NA ❑ Fish & Wildlife Habitat Conservation Areas (ECDC 23.90) ❑ Mapped Fish & Wildlife Habitat: Yes ❑ Streams: NA Site Description The subject property is located west of Olympic View Drive and is currently developed with a single- family home. The site is relatively level along the eastern property boundary and then slopes precipitously to the shoreline on the west face. According to the Soil Survey of Snohomish County, soils on the subject site consist of Alderwood Everett Gravelly sandy loams, 25-70% slopes on the northwest portion and Alderwood gravelly sandy loam, 15-15% on the southeast portion. According to the City LiDAR data, portions of the site contain slopes greater than 40% and thus are classified as a potential landslide hazard. Any land disturbing activity within 50 feet of the steep slopes will require a geotechnical report per requirements of ECDC 23.80, with specific reference to ECDC 23.80.060 and ECDC 23.80.070. Additionally, an Erosion and Sediment control plan compliant with chapter 18.30 ECDC may be required for development on a site containing an erosion hazard area which would be reviewed as part of a building permit. The site is adjacent to critical areas, including Puget Sound and its associated floodplain and fish and wildlife habitat. A qualified professional will need to assess the area to determine appropriate buffers for these areas. Given the BNSF right-of-way lies between Puget Sound and the subject property, the buffer may be determined to be interrupted. What does this mean? The critical area regulations are only triggered when an alteration is proposed to a critical area or its buffer. However, once an alteration in or near critical area is proposed, critical area studies and City review and approval may be required. What is an 'Alteration'? According to Section 23.40.005 of the Edmonds Community Development Code (ECDC): "Alteration" means any human -induced action which changes the existing conditions of a critical area or its buffer. Alterations include, but are not limited to: grading, filling; dredging; draining; channelizing; cutting, pruning, limbing or topping, clearing, relocating or removing vegetation; applying herbicides or pesticides or any hazardous or toxic substance; discharging pollutants; paving, construction, application of gravel; modifying for surface water management purposes; or any other human activity that changes the existing landforms, vegetation, hydrology, wildlife or wildlife habitat value of critical areas. Unpermitted alteration of a critical area or buffer (including tree trimming or topping, dumping yard waste, or application of pesticides or fertilizers) can lead to enforcement action and fines. Before undertaking any work, please contact the City to verify whether critical area studies and City review is necessary. TRISTAN SEWELL Planner Cited sections of the Edmonds Community Development Code (ECDC) can be found at http://www.codepublishing.com/WA/Edmonds Environmentally Critical Areas General Provisions (ECDC 23.40) Wetlands (ECDC 23.50) Frequently Flooded Areas (ECDC 23.70) Geologically Hazardous Areas (ECDC 23.80) Fish and Wildlife Habitat Conservation Areas (ECDC 23.90) Building permits — Earth Subsidence and Landslide Hazard Areas (ECDC 19.10) May 4, 2023 City of Edmonds GIS map tool with approximate location of critical areas: http://maps.edmondswo.gov Page 12 City of Edmonds CRA2023-0083 goo Ov ! N Legend W = Creeks Seismic Hazard Areas Earth Subsidence and Landslide / ! Minimum Buffer Adjacent to Ha: O ^ O ` s Wetlands Wetlands Boundary Wetland Boundaries Not Completel = Wetland Known Extents / de, o�d-�ve� . Grave.'sari loams --7 Floodplains ® A AE VE Aldt-.,wood Gravelly X 9 sally`, loam, 1 5-25 % -lopes 13 ReZones —, a PRD �♦,� 7 ROW USGS Soils Alderwood Gravelly sandy loam, 15 Alderwood Gravelly sandy loam, 2-� ■ Alderwood Gravelly sandy loam, 8- . Aldenwood Urban land complex, 2-£ 9 ry V _ . Alderwood Urban land complex, 8-' Alderwood-Everett Gravelly sandy I Custer fine sandy loam, 0-2 % slope Everett gravelly sand loam, 0-8 % s Everett oraveliv sand loam. 15-25 9 0\-" 1.758 =0 Notes 0 63.15 126.3 Feet 28 WGS_1984_Web-Mercator _Auxiliary -Sphere © City of Edmonds 94.0 This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION 9309 Olympic View Dr Grading/Landscaping NELSON GEOTECHNICAL ASSOCIATES. INC. July 7, 2023 Bryan Navarro VIA Email: bryannavarro@alderwoodlandscaping.com Geotechnical Engineering Evaluation Olympic View Drive Landscaping 9309 Olympic View Drive Edmonds, Washington NGA File No. 1443123 17311-135' Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com Dear Bryan, This letter summarizes our opinions and recommendations regarding the critical steep areas within the vicinity of the planned landscaping development located at 9309 Olympic View Drive in Edmonds, Washington. The parcel number for the property is 27031300102200, as shown on the Vicinity Map in Figure 1. INTRODUCTION The property is rectangular in shape and covers approximately 0.62 acres in area. It is currently occupied by a single-family residence. The property is bordered by a steep and tall bluff slope down to the BNSF railroad and Puget Sound to the northwest, by a vacant property to the southeast, and by adjacent residential properties to the northeast and southwest. Topographically, the site slopes gently to the northwest, which gives way to a steeply sloping bluff. We understand you are planning a landscaping project on the site, and due to the proximity to the bluff, the City of Edmonds is requiring a geotechnical letter to comment on the stability of site slopes and evaluate impacts of the proposed work on the nearby critical slope. SCOPE The purpose of this study is to review the conditions on the slope, characterize the soil conditions within the vicinity of the proposed landscaping development with hand tool explorations and provide geotechnical recommendations for site improvements. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 2 Specifically, our scope of services included the following: 1. Reviewing available soil and geologic maps of the area. 2. Exploring the subsurface soil and groundwater conditions within the proposed landscaping area with hand tool explorations, where possible. 3. Mapping the conditions on the site slopes using shallow, hand -tool explorations where possible to construct geological cross sections and qualitatively evaluate slope stability. 4. Performing laboratory grain -size sieve analysis on soil samples, as necessary. 5. Determining the presence of Geologically Hazardous Areas in accordance with the City of Edmonds Municipal Code. 6. Providing recommendations for grading as needed. 7. Providing recommendations for vegetation management, as needed. 8. Providing general recommendations for site drainage and erosion control. 9. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The property is rectangular in shape and covers approximately 0.62 acres in area. It is currently occupied by a single-family residence. The property is bordered by a bluff slope down to the BNSF railroad and Puget Sound to the northwest, by a vacant property to the southeast, and by adjacent residential properties to the northeast and southwest. Topographically, the site slopes gently to the northwest, which gives way to a steeply sloping bluff. The slope to the northwest of the existing residence descends downwards at inclinations in the range of 32 to 65 degrees (71.1 to 144.4 percent of slope, respectively), resulting in a vertical relief of approximately 165 feet as shown on Cross -Section B'B' in Figure 5. We did not observe standing water within the site or seepage emitting from the upper portion of the slope during our site visit on May 12, 2023. We also did not observe any indication of major recent slope instability within the site; however, indications of past shallow failures on the slope extending into neighboring properties were noted. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Olympic View Drive Landscaping Edmonds, Washington Subsurface Conditions NGA File No. 1443123 July 7, 2023 Page 3 Geology: The geologic units for this site are shown on Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington by Minard, J.P. (US6S, 1983). The site is mapped as glacial till (Qvt) and transitional beds (Qtb) with Olympia gravel (Qog) nearby. Till is described as an unsorted mixture of clay, silt, sand, pebbles, cobbles, and boulders, all in variable amounts. Transitional beds are described as clay, silt, and fine to very fine sand. Olympia gravel is described as stratified, fluvial sand and gravel. Based on our explorations within the site and review of the geologic mapping in this area, we interpret that the site is underlain by glacial till soils. In the paragraph below we give a brief description of the soils encountered within our explorations. For a more detailed log of our explorations Figure 6 should be reviewed. Explorations: We explored the site with four hand tool explorations to depths in the range of 2.0 to 4.0 feet below the existing ground surface. At the surface of all of our explorations we encountered a surficial layer of undocumented fill and/or topsoil. Underlying the surficial fill/topsoil. We encountered brown to gray -brown, silty fine to medium sand with varying amounts of gravel and cobbles which we interpreted as undocumented fill soils likely associated with previous grading. Hand Augers 1 and 3 were terminated within the undocumented fill soils at a depth of 2.0 and 2.75, respectively. Underlying the fill soils in Hand Auger 2 we encountered a weathered horizon of silty sand which we interpreted as undocumented fill. Hand Auger 2 was terminated within the fill at a depth of 3.75 feet below the existing ground surface. In Hand Auger 4, we encountered orange -brown to gray -brown silty sand with gravel and cobbles which we interpreted as native weathered glacial till soils. Hand Auger 4 was terminated within the glacial till soils at a depth of 4.0 feet below the existing ground surface. Hydrogeologic Conditions Groundwater seepage was not encountered within the upper portion of the slope during our site visit on May 12, 2023. If groundwater is encountered during construction, we would interpret this water to be perched groundwater. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Olympic View Drive Landscaping Edmonds, Washington SENSITIVE AREA EVALUATION Seismic Hazard NGA File No. 1443123 July 7, 2023 Page 4 We reviewed the ASCE 7-16 and the 2018 International Building Code (IBC) for seismic site classification for this project. Since dense soils are interpreted to underlie the site at depth, the site best fits 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 two percent 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 Design Spectral Spectral Acceleration Spectral Acceleration Site Coefficients Response Site Class at 0.2 sec. (g) at 1.0 sec. (g) Parameters SS S1 Fa F SDs SD1 D 1.302 0.46 1.000 Null 0.868 Null 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. 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 Natural Resources Conservation Service (NRCS) for this area of Snohomish County lists the soil type as Alderwood gravelly sandy loam, 15 to 30 percent slopes and Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes. The erosion hazard for these soils is rated as severe. The City of Edmonds has mapped this area as an erosion hazard area. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Olympic View Drive Landscaping Edmonds, Washington Landslide Hazard/Slope Stability NGA File No. 1443123 July 7, 2023 Page 5 The criteria used for evaluation of landslide and steep slope hazards include soil type, slope gradient, groundwater conditions, as well as vegetative and geomorphological indicators. The ground surface within the subject parcel generally slopes gently to steeply from the existing residence towards the northwest. The slope descends at gradients in the range of 32 to 65 degrees (71.1 to 144.4 percent, respectively), resulting in a vertical relief of approximately 165 feet. We did not observe evidence of recent significant erosional activity or slope instability within the site slopes or within the immediate vicinity of the planned development during our investigation. We also did not observe seepage emitting from site slopes during our visit on May 12, 2023. In our opinion, the site and core of the steep slope appear to be relatively stable with respect to deep seated landslide activity. The City of Edmonds has mapped this site as a landslide hazard area. According to The City of Edmonds Municipal Code (EMC) 23.80.020, the subject site meets the definition of a landslide hazard area. The core of the slope is inferred to consist primarily of medium dense or better native glacial till soils. Relatively shallow sloughing and soil creep as well as surficial erosion are natural processes and should be expected on the steeper site slopes during extreme weather conditions as has occurred in the past along this bluff line. It is our opinion that there is significant potential for ongoing erosion, soil creep, and shallow failures within the loose surficial and exposed soils on the steep slopes. However, it is also our opinion that there is not a significant potential for deep-seated slope failures within the short term under current site conditions. Backwasting (movement of near -surface soil) through erosion processes or local surface slides are common to these steep slopes, particularly where exposed to weathering processes such as rain, wind, and freeze -thaw cycles. Based on our observations, it is our opinion that there is potential for shallow slides to occur on the steep slopes within this area especially during extreme weather or a seismic event. This condition can be exacerbated by surface water flowing over the top of slope, and the over -steepening caused by erosion and surface sliding. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 6 CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned landscaping development within this site is feasible from a geotechnical standpoint as long as our recommendations stated within this report are strictly followed. It is also our opinion that the soils that underlie the site and form the core of the site slopes should be stable with respect to deep-seated landslides, even though the potential for shallow sloughing and erosional episodes is high. Proper erosion and drainage control measures as recommended in this letter should reduce this potential. Our reconnaissance indicated that the site is underlain by medium dense or better native glacial till soils at depth. These soils should provide adequate support for the proposed retaining walls, slabs, and landscaping features. Retaining walls and/or slabs should be supported on material that extends through any loose surficial soil and be keyed into the underlying competent native soils, or structural fill resting on competent soils. These soils should be encountered roughly 3.00 or more feet below the existing ground surface. 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 site slopes, not reduces it. We recommend a buffer zone of approximately 15 feet from the top of slope not be disturbed in any way as to mitigate any future failures that could occur due to construction activities. General construction traffic, along with equipment and material storage, should be avoided in this buffer area. Excavation spoils should not be stockpiled within this buffer zone 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. This is further discussed in the remainder of this report. We recommend a curtain drain be implemented to catch any runoff generated from existing structures and from the proposed water feature if a leak or failure develops over time. This would consist of a 4- foot-deep trench that is approximately 12-inches wide. A 4-inch perforated pvc pipe would be placed at the base of the trench with perforations pointed downward and free -draining crushed rock placed around the pipe. We recommend the crushed rock be wrapped in non -woven, geotextile fabric to prevent silt build up within the pipe. After the trench is backfilled with free draining rock the top 6 inches can be backfilled with sandy topsoil for landscaping purposes. The pipe should be connected to an existing approved stormwater system. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 7 We understand the current stormwater system consists of a corrugated pipe that is tightlined down the face of the slope towards the bottom of the slope. We recommend a full inspection of the downhill pipe to confirm any damage or repairs needed to safely disperse the stormwater at the base of the steep slope. This could consist of visually inspecting the pipe all the way down the slope to the outfall and/or running a camera through the pipe to verify its competence. If any damaged, missing, or penched sections of the pipe exist, they should be replaced or repaired. The contractor should also confirm the existence of a diffuser at the bottom of the slope. This could consist of a 'T' diffuser placed on a pad of rock spalls. We highly recommend NGA is retained to provide observations and recommendations during construction regarding grading and implementation of the curtain drain. We also recommend the slope be monitored by NGA twice per year for two years following construction through visual inspections and monitoring instrumentation installed between the top of slope and development area. Future vegetation management on the slopes should be the subject of a specific evaluation and a plan approved by the City of Edmonds. Lawn clippings and any other household trash or debris should never be allowed to reach the slopes. 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. Under no circumstances should water be allowed to flow over or concentrate on the site slopes, both during construction, and after construction has been completed. We recommend that stormwater runoff from the roof and yard drains be collected and tightlined to a suitable discharge point, well away from the slopes. The slopes should be protected from erosion. We recommend that all disturbed areas be replanted with vegetation to re-establish vegetation cover as soon as possible. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 8 Erosion Control and Slope Protection Measures The erosion hazard for the on -site soils is interpreted as severe, but the actual hazard will be dependent on how the site is graded and how water is allowed to concentrate. A 15-foot buffer should be maintained between construction activities and top of slope. 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. 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. Protection of the slope areas should be performed as required by the City of Edmonds. Specifically, we recommend that the slope not be disturbed or modified through placement of any fill or removal of the existing vegetation. Trees should not be cut down or removed from the slopes. Replacement of vegetation should be performed in accordance with the City of Edmonds code. The clearing of vegetation within the area of the proposed landscaping development should not affect slope stability, provided any disturbed areas outside the footprint are revegetated as soon as practical and protected from erosion. 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. Site Preparation and Grading After erosion control measures are implemented, and the 15-foot buffer from the top of the steep slope is established, site preparation should consist of stripping any grass or loose soils to expose medium dense or better native soil within the area of the proposed retaining walls and hard surfaces. The stripped materials should be removed from the site. If the ground surface, after site stripping, should appear to be loose, it should be compacted to a non - yielding condition. Areas that are observed to pump or weave during compaction should be over - excavated and replaced with properly compacted structural fill or rock spalls. 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 9 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. Temporary and Permanent Slopes Temporary 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 water 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 soil and groundwater conditions encountered, and able to monitor the nature and condition of the cut slopes. 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 site soils be no steeper than 2 Horizontal to 1 Vertical (2H:1V). If significant groundwater seepage is encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. The slope protection measures 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. Permanent cut and fill slopes should be no steeper than 2H:1V, unless specifically approved by NGA. Also, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated, and the vegetative cover maintained until established. We should specifically review all plans for grading on steep slopes for this project. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Olympic View Drive Landscaping Edmonds, Washington Retaining Walls NGA File No. 1443123 July 7, 2023 Page 10 The retaining walls planned as a part of this project are relatively short and may not need an engineered design. This, however, should be decided by the landscape architect. In general, 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 40 pcf for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls. A seismic design loading of 8H in psf 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 granular backfill and are based on the assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height of the wall, and do not account for 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, slopes, or other surface loads. We could consult with the structural engineer regarding additional loads on retaining walls during final design, if needed. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this letter. 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. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this letter. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Olympic View Drive Landscaping Edmonds, Washington Structural Fill NGA File No. 1443123 July 7, 2023 Page 11 General: Fill placed beneath retaining walls, slabs, 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. Sloping areas to receive fill should be benched using a minimum 6-foot-wide horizontal benches into competent soils. 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 structural 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). Due to the relatively silty nature of the site soils, it is our opinion that the on -site soils are not suitable for use as structural fill. We should be retained to evaluate 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 should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this letter, 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. Slope Monitoring We recommend NGA be retained to monitor the slope through visual observations and instrumentation. Instrumentation would consist of drilling down approximately 40-feet with a limited access drill rig and installing an inclinometer casing within the drilled hole. The casing is a small diameter PVC pipe. The purpose of the inclinometer well is to track slope movement over time and develop trends relating to direction, rate, and depth of earth movement activity. Potential movement is tracked by a probe that is inserted in the casing and casing alignment is measured at specific intervals. We recommend that this NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 12 be implemented as soon as possible and that NGA perform these observations twice a year for two years following the completion of the project. Site Drainage Surface Drainage: The finished ground surface should be graded such that all stormwater generated on this site is directed to an approved stormwater collection system that terminates at the bottom of the slope. Water should not be allowed to stand in any areas where retaining walls or slabs are to be constructed. Final site grades should allow for drainage away from the development area and site slopes. We suggest that the finished ground be sloped at a minimum gradient of three percent, for a distance of at least 10 feet away from the slope. Surface water should be collected by permanent catch basins and drain lines and be discharged into an appropriate 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 a curtain drain setback roughly 20 feet from the top of the slope, as shown on the Improvements Site Plan in Figure 3. The drain should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric placed at the bottom of a minimum 4-foot-deep by 12-inch-wide trench. We recommend that the free - draining material consist of pea gravel or drain rock. The free -draining material should extend up to six inches below the finished surface. The top six inches of backfill should consist of sandy topsoil. The drain should be routed into the existing drain that extends down the slope, after the existing system is inspected and repaired, as warranted. USE OF THIS LETTER This letter has been prepared for Bryan Navarro and associated agents, for use in the planning and design of the planned landscaping 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 letter, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the project budget and schedule. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1443123 Olympic View Drive Landscaping July 7, 2023 Edmonds, Washington Page 13 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 differ from those anticipated, and to evaluate whether or not the subgrade complies with our recommendations. We should be contacted a minimum of one week prior to construction activities. All people who own or occupy homes on or near hillsides should realize that erosion and 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. Therefore, the homeowner should take responsibility for performing such maintenance. 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 letter 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 Olympic View Drive Landscaping Edmonds, Washington NGA File No. 1443123 July 7, 2023 Page 14 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. Daniel J. O'Dell Staff Geologist II � M.Sr r 4e o' x 35215 �w ISTtig��G�� Khaled M. Shawish, PE Principal DJO:FKS:KMS:dy Seven Figures Attached 7.07.2023 NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale ®Safeway _8thSts. i E ` Picnic i Point -North T Lynnwood Q " 1• Meadowdale 1 Beach Park A x v Meadowdale Playfields fir,; 7641hStSW 4,ialmartQ "4 a' Fred Meyers '68thstsw ?I A . is I Y -o Project L S y Site .1 F L t76thstsr; p�\ , ^ U I I N County Park QCostco-Wholesale H Mart Lynnwood ® \�:/ � � 'B-hSt$yy QAlderwo6, d' 'a E y N Lynnwood Q Recreation center Hobby Lobby o 3 , Best>B y 4 a Edmonds ®� z °i College Lynnwood4._- Whole Foods,Market ® N i z a / W E / o s+ U ui ze w ALDERWOOD 4 � U Aid N SEATTLE HEIGHTS 208thStSW ��•:h s� a v U O v L U 2' 2t h St S W 2'2thStSW a o 0 Edmonds, WA Project Number �ELSOn GEOTECHnICAL No. Date Revision By CK CD Olympic View Drive '' 1443123 Landscaping p� g pSSOCIpTES,111C 6/6/23 Original FKS ono r Figure 1 Vicinity Map W135th ° NE,0A We^a'°hee°St. 17311-1351h Ave. NE, A-500 105 Palouse SL Wood-ille, WA 98072 Wenatchee, WA 98801 y www.nelsongeolech.com (425) 486-1669 / Fax. 481-2510 (509) 665-7696 / Fax 665-7692 U Site Plan t 6 LEGEND Property line HA-1 Number and approximate location of hand auger A A' Approximate location tJof cross-section 0 60 120 Scale: 1 inch = 60 feet ■o Reference: Site Plan based on field measurements, observations, and aerial parcel map review. Project Number nELSOn GEOTECHnICRL No. Date Revision By CK Olympic View Drive ASSOCIATES, lI1C 1443123 Landscaping 6/6/23 Original FKs ono p� g u Plan Woodinville Office Wenatchee Office Figure 2 Site 173„-, 351h Ave. NE, A-500 105 Palouse St. Wcotllnville,WA98072 Wenatchee, WA 98801 www.nelsangeotech.cam (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692 C i����\,,• / /� // �, � ,'i p n' �� v A A' Y U o T � IY1 LL C Southwest ° Northeast A 80 80 o M 0 Zo O Z 60 60 CE 0"3 Lw cn LU O O a W o0 > 40 40 o C cry o = a LU p Q LL tn o M o cu IC Q Area of ° 20 Development 20 HA-2 3 \' 3 Fill 0 0 > Q I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I .Q o 0 20 40 60 80 100 120 140 a) M > (n � Distance (feet) C.) Exploration _E J o L O U Hand Auger Designation ---> HA-1 Groundwater Level ----> 1 NOTES: a) During Exploration 1) Stratigraphic conditions are interpolated between E N "T the explorations. Actual conditions may vary. z Geologic Contact ? _ —? ch � 2) Elevations are arbitrary. � � � (approximate) IL �O L Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure. C:\Users\Alexander(Alex)Baucc\OneDrive - Nelson Geotechnical Associates, Inc\2023 NGA Project\14431-23 Olympic Drive Landscape\Drafting\CS.dwq Northwest 160 120 N c O CU 80 W a ,, X BY , E---- I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 40 80 120 160 200 240 280 Distance (feet) Exploration Hand Auger Designation ---> HA-1 Groundwater Level ----> 1 During Exploration Geologic Contact --> (approximate) Reference: Cross Section is based on Snohomish County Topography review . -,\Users\Alexander(Alex)Baucc\OneDrive - Nelson Geotechnical Associates, Inc\2023 NGA Project\14431-23 Olympic D Southeast 160 120 M 40 U NOTES: 1) Stratigraphic conditions are interpolated between the explorations. Actual conditions may vary. 2) Elevations are arbitrary. Y � U o U) m LL O y m N rn o d N O Z CE w o?3� W Cn 3� I— W ® I— WCC o C7 c C cCA o� O ><dLL CnLU oM C E ME 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 GEOTEnninl_ No. Date Revision By cK Olympic View Drive � 1443123 Landscaping ASSOCIATES, inc , 6/6/23 Original FKS DJO Figure 6 Soil Classification Chart "� ""135thA°e°""e Wa"a`°hee.S"e 17311-1351h Ave. NE, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 www.nelsongeoiech.com (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) USCS SOIL DESCRIPTION HAND AUGER ONE 0.0 - 0.75 GRASS UNDERLAIN BY DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH ROOTS (LOOSE, MOIST) (FILL) 0.75-2.0 BROWN TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND TRACE COBBLES (MEDIUM DENSE, MOIST) (FILL) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TERMINATED ON ROCK AT 2.0 FEET ON 5/12/2023 HAND AUGER TWO 0.0 - 0.75 GRASS UNDERLAIN BY DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH ROOTS (LOOSE, MOIST) (FILL) 0.75-2.75 BROWN TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND TRACE COBBLES (MEDIUM DENSE, MOIST) (FILL) 2.75-3.75 BROWN TO ORANGE -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL, TRACE COBBLES, AND WOOD DEBRIS (MEDIUM DENSE, MOIST) (FILL) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TERMINATED ON ROCK AT 3.75 FEET ON 5/12/2023 T-PROBE YIELDED 1.25 FEET AT BASE OF HAND AUGER HAND AUGER THREE 0.0 - 0.75 GRASS UNDERLAIN BY DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH ROOTS (LOOSE, MOIST) (FILL) 0.75-2.75 BROWN TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND TRACE COBBLES (MEDIUM DENSE, MOIST) (FILL) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TERMINATED ON ROCKS AT 2.75 FEET ON 5/12/2023 T-PROBE YIELDED 2.75 FEET AT BASE OF HAND AUGER HAND AUGER FOUR 0.0-3.0 DARK BROWN TO BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL, ORGANICS, AND ROOTS (LOOSE, MOIST) (FILL) 3.0-4.0 SM ORANGE -BROWN TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND COBBLES (MEDIUM DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TERMINATED ON ROCKS AT 4.0 FEET ON 5/12/2023 FKS:DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1443123 FIGURE 7