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REVIEWED PLN BLD BLD2024-0678+Geotech Report+5.17.2024_3.38.38_PM+4265839NELSON GEOTECHNICAL ASSOCIATES. INC. May 8, 2024 Ms. Carol Rippey c/o Mr. Eric Miller E. Miller, Inc. VIA Email: ericmillerl4@gmail.com Geotechnical Engineering Evaluation Rippey Residence Deck Addition 19031 Ocean Avenue Edmonds, Washington NGA File No. 1508924 Dear Ms. Rippey, BLD2024-0678 RECEIVED May 21 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT 17311-135t" Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com ,.,.,.,.,.,.REVIEWED BY CITY OF EDMONDS BUILDING DEPARTMENT: APPROVED BY PLANNING Jun 06 2024 ;� This letter summarizes our opinions and recommendations regarding the deck addition located at 19031 Ocean Avenue in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. INTRODUCTION The subject property is currently occupied with a single-family residence within the central portion of the property. The ground surface within the site is generally gently sloping down from the southeast to the northwest. A steep northwest -facing slope is located off of the property across Ocean Avenue that descends to the railroad tracks below. We understand that the proposed development will include replacing the existing deck along the western side of the residence. Two new pier foundations are also proposed to support the deck. Based on review of the City of Edmonds GIS map, the steep slope areas off the property are mapped as a landslide hazard area. We understand that the City of Edmonds has requested a geotechnical evaluation of the proposed development due to the development area being located within 50 feet of the mapped landslide hazard area. SCOPE The purpose of this study is to map the conditions on the slope, characterize the soil conditions within the vicinity of the residence structure and slope with limited hand tool explorations and provide geotechnical recommendations for site improvements. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 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 in the vicinity of the proposed deck additions with hand tool explorations, where possible. 3. Mapping the conditions on the site slopes using shallow, hand -tool explorations where necessary to construct geological cross sections and qualitatively evaluate slope stability. 4. Performing laboratory grain -size sieve analysis on soil samples, as necessary. 5. Providing recommendations for structure setbacks from geologic hazards, as necessary. 6. Providing recommendations for earthwork and deck foundation support. 7. Providing general recommendations for site drainage and erosion control. 8. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The site consists of a triangular -shaped parcel covering approximately 0.28 acres. It is currently occupied with a single-family residence within the central portion of the property. The ground surface within the site is generally gently sloping down from the southeast to the northwest. A steep northwest -facing slope is located off of the property across Ocean Avenue to the northwest and descends from the northern roadway shoulder of Ocean Avenue to the BNSF railroad tracks below at an approximate gradient of 47 degrees (107 percent) as show in Cross -Section A -A' in Figure 3. The overall height of the steep northwest -facing slope is approximately 10 feet. The slope is vegetated with grass and underbrush. Vegetation across the site generally consisted of grass yard areas and landscaping. We did not observe evidence of significant slope instability within or in the immediate vicinity of the subject property during our investigation, such as deep-seated landsliding. We also did not observe surficial groundwater seepage or signs of erosion or sloughing within or within the vicinity of the property during our site visit. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Rippey Residence Deck Addition Edmonds, Washington Subsurface Conditions NGA File No. 1508924 May 8, 2024 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 Whidbey formation (Qw). The Whidbey formation is described as compact, commonly oxidized, medium to coarse grained sand. Our explorations generally encountered a surficial layer of undocumented fill underlain by silty, fine to medium sand with gravel, consistent with the description of Whidbey formation deposits. Explorations: We visited the site on April 12, 2024, to explore the subsurface conditions around the proposed area of development. We performed two hand tool explorations within the vicinity of the proposed deck pier foundations. The approximate location of our exploration is shown on the Schematic Site Plan in Figure 2. A geologist from 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. The soils were visually classified in general accordance with the Unified Soil Classification System, presented as Figure 4. The logs of the explorations are presented as Figure 5. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, the exploration logs should be reviewed. Our hand auger explorations generally encountered 1.8 to 2.0 feet of dark brown, silty, fine to medium sand with gravel, roots, and organics, in a loose condition, which we interpreted as undocumented fill soils. Underlying the fill soils within each exploration, we encountered gray to gray -brown, silty, fine to medium sand with gravel, in a medium dense or better condition, which we interpreted as competent native Whidbey formation deposits. Our hand auger explorations met refusal within the native Whidbey formation deposits at depths in the range of 2.5 to 2.75 feet below the existing ground surface. Hydrogeologic Conditions We did not encounter any groundwater seepage in our explorations. If groundwater seepage is encountered during construction, we would interpret this to be a perched groundwater condition. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of underlying, less permeable soils. 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 precipitation. We would expect the amount of perched water to decrease during drier times of the year and increase during wetter periods. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Rippey Residence Deck Addition Edmonds, Washington SENSITIVE AREA EVALUATION Seismic Hazard NGA File No. 1508924 May 8, 2024 Page 4 We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project. Since very 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 Fv SDs SD1 D 1.295 0.457 1.000 Nu7 0.863 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. It is our opinion that the medium dense or better glacial deposits interpreted to underlie the site and nearby vicinity have a low potential for liquefaction or amplification of ground motion. 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 maps the site as consisting of Everett very gravelly sandy loam, 8 to 15 percent slopes. The erosion hazard for this soil is listed as moderate. Based on our observations and the material encountered, we would interpret this site as having a low to moderate erosion hazard where the surficial soils are exposed. It is our opinion that the erosion hazard for site soils should be low in areas where the site is not disturbed. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Rippey Residence Deck Addition Edmonds, Washington Landslide Hazard/Slope Stability NGA File No. 1508924 May 8, 2024 Page 5 The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The ground surface within the site is generally gently sloping down from the southeast to the northwest. A steep northwest -facing slope is located off of the property across Ocean Avenue to the northwest that descends from the northern roadway shoulder of Ocean Avenue to the BNSF railroad tracks below at an approximate gradient of 47 degrees (107 percent) as show in Cross -Section A -A' in Figure 3. The overall height of the steep northwest -facing slope is approximately 10 feet. The City of Edmonds has mapped the steep northwest -facing slope below and to the northwest of the subject development as a landslide hazard area. We did not observe evidence of significant slope instability within or in the immediate vicinity of the subject property during our investigation, such as deep-seated landsliding. We also did not observe surficial groundwater seepage or signs of erosion or sloughing within or within the vicinity of the property during our site visit. ECDC 23.80.020 (B) defines landslide hazard areas as: 1. Areas of ancient or historic failures in Edmonds which include all areas within the earth subsidence and landslide hazard area as identified in the 1979 report of Robert Lowe Associates and amended by the 1985 report of GeoEngineers, Inc., and further discussed in the 2007 report by Landau Associates; 2. Coastal areas mapped as class u (unstable), uos (unstable old slides), and urs (unstable recent slides) in the Department of Ecology Washington coastal atlas; 3. Areas designated as quaternary slumps, earthflows, mudflows, or landslides on maps published by the United States Geological Survey or Washington State Department of Natural Resources; 4. Any slope of 40 percent or steeper that exceeds a vertical height of 10 feet over a 25 foot horizontal run. Except for rockeries that have been engineered and approved by the engineer as having been built according to the engineered design, all other modified slopes (including slopes where there are breaks in slopes) meeting overall average steepness and height criteria should be considered potential landslide hazard areas); 5. Any slope with all three of the following characteristics: a. Slopes steeper than 15 percent; b. Hillsides intersecting geologic contacts with a relatively permeable sediment overlying a relatively impermeable sediment; and c. Springs or ground water seepage; 6. Any area potentially unstable as a result of rapid stream incision or stream bank erosion; 7. Any area located on an alluvial fan, presently subject to, or potentially subject to, inundation by debris flow or deposition of stream -transported sediments; and 8. Any slopes that have been modified by past development activity that still meet the slope criteria. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 6 Due to the steep northwest -facing slope located below and well to the northwest of the proposed development having an inclination of greater than 40 percent and overall height of 10 feet or greater, it appears that this slope meets the classification of a landslide hazard area per ECDC 23.80.020(B). The core of the neighboring site slope is 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 slopes during extreme weather conditions. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial and undocumented fill soils on the steeper neighboring slopes located to the northwest of the subject site, there is not a significant potential for deep-seated slope failures under current site conditions. The new deck foundations will be located as close as approximately 65 feet from the top of the steep northwest -facing slope located across and to the northwest of Ocean Avenue. In our opinion, the proposed setback from the steep slope should allow for normal slope recession during a reasonable life span of the structure and should not adversely impact the existing slope stability conditions. We do not anticipate significant grading as a result of the proposed deck construction. Proper site grading and drainage as well as adequate foundation placement as recommended in this report should help maintain current stability conditions. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned residence deck addition development is feasible from a geotechnical standpoint. Our explorations indicated that the site is generally underlain by undocumented fill with competent native glacial soils at depth. The native glacial soils encountered at depth should provide adequate support for the proposed deck foundation loads. The nearby steep slopes are considered currently stable with respect to deep-seated failures, but shallow failures could occur on the site slopes in the loose surficial soil and undocumented fill likely mantling these slopes. We do not anticipate any adverse impacts to the existing slope stability conditions as a result of the proposed deck development provided that the deck foundations are setback and designed as recommended in this letter. We recommend that the replacement deck foundations consist of concrete pier foundations embedded a minimum of one foot into medium dense or better native glacial soils. The medium dense or better native bearing glacial soils should typically be encountered approximately 2.0 feet below the existing surface, based on our explorations within the proposed deck footprint. As a result, we recommend that the deck foundations extend to a minimum of 3.0 feet below the existing ground surface to satisfy the minimum embedment. This is further discussed in the Deck Foundations subsection of this letter. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 7 We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require deeper excavations in the proposed foundation location to remove the unsuitable soils. The new deck foundations will be located as close as approximately 65 feet from the top of the steep northwest -facing slope located across and to the northwest of Ocean Avenue. In our opinion, the proposed setback from the steep slope should allow for normal slope recession during a reasonable life span of the structure and should not adversely impact the existing slope stability conditions. The planned earthwork associated with the deck addition should be minor. However, the soils encountered on this site are considered moisture -sensitive and may disturb easily when wet. To lessen the potential impacts of construction on the slopes and to reduce cost overruns and delays, we recommend that foundation preparation take place during dry weather if possible. If earthwork takes place during wet weather, additional expenses and delays should be expected. These extra expenses could include additional erosion control and temporary drainage measures to protect the slope. In any case, the excavation spoils should be hauled off site and not allowed to reach the slope areas. Also, the vegetation on the slope should not be disturbed. Any disturbed areas should be promptly repaired. Erosion Control and Slope Protection Surface water appears to be adequately controlled on the site under current conditions. We do not anticipate that the planned deck addition will significantly alter drainage patterns at the site. Adequate spaced decking on joist framing should not concentrate runoff from the deck. If the decking will not be spaced and will concentrate runoff from the deck, the water should be collected in gutters and downspouts and be directed to the roof drain system. Water runoff should not be allowed to reach the slope. The erosion hazard for the on -site soils is interpreted to be low to moderate for exposed soils, but actual erosion potential 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. Disturbed areas should be planted as soon as practical, and the vegetation should be maintained until it is established. The erosion potential of areas not stripped of vegetation should be low. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 8 Runoff generated within the site, including roof downspouts, yard areas, and hard surfaces should be collected into catch basins and yard drains and tightlined into an approved stormwater management system. Under no circumstances should runoff be allowed to concentrate on the slope either during construction or after construction has been completed. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of stripping the topsoil and loose soils from the foundation and other structural areas, to expose medium dense or better native bearing glacial outwash soils. The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. Based on our observations, we anticipate stripping depths of approximately 2.0 to 3.0 feet within the proposed deck pier 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 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. 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. 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 areas of prepared subgrade. 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 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 at all times as indicated in OSHA guidelines for 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 9 For planning purposes, we recommend that temporary cuts in the upper undocumented fill/surficial soils be no steeper than 2 Horizontal to 1 Vertical (2H:1V). Temporary cuts in the competent native glacial soils at depth should be no steeper than 1H:1V. If significant groundwater seepage or surface water flow were 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. If tall cuts are not able to be sloped back as recommended above, alternative shoring wall systems should be utilized to support temporary cuts. We are available to provide specific recommendations for alternative temporary shoring systems once grading plans have been finalized. Permanent cut and fill slopes should be no steeper than 2H:1V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated, and the vegetative cover maintained until established. Deck Setback Uncertainties related to building along the top of steep slopes are typically addressed by the use of building setbacks. The purpose of the setback is to establish a "buffer zone" between the structure and the top of the slope so that ample room is allowed for normal slope recession during a reasonable life span of the structure. In a general sense, the greater the setback, the lower the risk of slope failures to impact the structure. From a geological standpoint, the setback dimension is based on the slope's physical characteristics, such as slope height, slope angle, material composition, and hydrology. Other factors such as historical slope activity, rate of regression, and the type and desired life span of the development are important considerations as well. Based upon the conditions described above, it is our opinion that the potential for shallow sloughing - type failures during severe weather exists on the neighboring steep slopes. We understand that the proposed deck foundations will be setback approximately 65 feet from the top of the steep northwest - facing slope located across and to the northwest of Ocean Avenue. In our opinion, this setback is adequate provided our recommendations for foundation embedment and slope protection presented in this letter are followed. In addition to the recommended setback, we also recommend that the deck footings extend through any loose surficial or undocumented fill soils and be embedded a minimum of 12 inches into the competent native soils at depth. We should be retained to evaluate the deck footing subgrade soil and setback distances prior to placing the footings. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 10 Protection of the slope areas should be performed as required by the City of Edmonds. Specifically, we recommend that the setback area and steep slope area not be disturbed or modified through placement of any fill or removal of the existing vegetation. No material of any kind, such as excavation spoils, lawn clippings, debris, and soil stockpiles, should be placed on or near the slope. As the proposed development area is located within the subject property and the nearby steep slope areas are located well off of the property, we do not anticipate that any grading or construction activities will occur within the neighboring steep slope areas. However, any sloping areas that may be disturbed during construction should be planted as soon as practical to reduce the potential for erosion. The new vegetation should be maintained until it is established. Replacement of vegetation should be performed in accordance with the City of Edmonds code. Under no circumstances should water be allowed to concentrate on the slope. Deck Foundations We recommend the new deck be supported on concrete pier foundations extending below the surface. Our soil explorations indicated competent native glacial soils should be encountered at an approximate depth of 2.0 feet below existing grade; however, this could be deeper in unexplored areas of the site. Deck foundations should extend through any loose undocumented fill encountered and be embedded a minimum of 12-inches into the competent native glacial soils. 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 2,000 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing soils. 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 11 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 12-inches of soil be neglected when calculating the passive resistance. 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). The on -site soils are not suitable for use as structural fill. 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 NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 12 compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. Site Drainage We do not anticipate that the new deck will significantly alter drainage patterns at the site. Adequately spaced decking on joist framing should not concentrate runoff from the deck. If the decking is tightly spaced and will concentrate runoff from the decks, the water should be collected in gutters and downspouts and be directed to an approved system. We should be retained to evaluate the drainage plans. The soil below the deck should be covered with erosion control matting. All runoff generated on this site, including roof downspouts, yard and footing drains, and hard surfaces, should be collected and routed into a permanent approved system. Under no circumstances should water be allowed to flow uncontrolled over the nearby slopes. All existing drainage systems should be inspected and maintained to maintain functionality. Water should not be allowed to collect in any area where foundations are to be constructed. CONSTRUCTION MONITORING We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, setbacks, and fill compaction. USE OF THIS LETTER This letter has been prepared for Ms. Carol Rippey and associated agents, for use in the planning and design of the new deck supports planned 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. 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 foundation support installation complies with our recommendations. We should be contacted a minimum of one week prior to construction activities. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1508924 Rippey Residence Deck Addition May 8, 2024 Edmonds, Washington Page 13 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 Rippey Residence Deck Addition Edmonds, Washington NGA File No. 1508924 May 8, 2024 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. I A- 3? g �'- Faith K. Stelter Staff Geologist II o� 1Nashi �a o C .u, Lee S. Bellah Senior Geologist .08.2024 Khaled M. Shawish, PE Principal FKS:LSB:KMS:dy Five Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP N Not to Scale North MEADOWDALE Lynnwood a�Ptayfields 0 3 BEVERLY ACRES ; o � r � Project =" par` Southwest V > = Site 9Courtly Pare H Mart Lynnwooc PERRINVILLE u Lynnwood Q Q . R reatlon Center m > Q c 3 Pu 4et v °o00 Lyn L ood g i n Garder ` attle'Lynn-r o THE BOWL Edrnonca Colleye © WyndhamLa uinta Inn by Lynnwood0 0 OFEDMONDS w CEDAR VALLEY 2Mimi Stsw A.`o Edmonds „air st SEATTL EIGHTS Emb Suites by Hilton flea S e North Lynnwood 9 212thStSW d a C P19 N ,vinCo Foods 0 2201h St S r, 3 1. a, " p p d Woodway D n t; Q Esperance ° ; " " Z w i m N 22BthStSW o <' Mountlake SHERWOOD WnlrlyBall Terrace o FOREST r , 236tnstSw a e a Brier L U N O N (D Edmonds, WA N Project Number mson GEOTEnnim No. Date Revision By CK Rippey Residence '' 1508924 Deck Addition pSSOCIpTES,1nC 424z4 Original FKS DJO Q Figure 1 Vicinity Map '� Woodinvliie Office Wenatchee Office 173„-135th Ave. NE, A-500 105 PaInuse St. Woodinville,WA98072 Wenatchee, WA 98801 N y www.nelsongeotech.com (425) 486-1669 / Fax. 481-2510 (509) 665-7696 / Fax: 665-7692 1 1 1 1 U U Site Plan ,AN LEGEND Property line HA-1 Number and approximate location of hand auger A AApproximate location t± of cross-section 0 40 80 Scale: 1 inch = 40 feet Reference: Site Plan based on field measurements, observations, and aerial parcel map review. Project Number Rippey Residence , nELSOn GEOTECHnICAL No. Date Revision By CK 1508924 Deck Addition ASSOCIATES, inc 1 4124124 Original FKs DJO Site Plan Woodinville Office Wenatchee Office Figure 2 173, 1-135th Ave. NE, A-500 105 Palouse St. Wcodlnville,WA 98072 Wenatchee, WA 98801 www.nelsangeotech.cam (425) 486-1669 / Fax. 481-2510 (509) 665-7696 / Fax: 665-7692 A A' Y U o T Ib � LL Northwest Southeast C N @ I 80 I 80 o N v 0 V N V O Z 60 60 CE w 0"3 Existing Residence and Proposed Deck W cry C O LU O a R yJ o > 40 Driveway 40 Co c W < o=a- w Ocean o C= Q a d " HA-1 Avenue 3mN CU BNSF W Railroad c Q o 20 47° 20 \� 3 3 0 L 0 N Q U � 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 (D O C 0 20 40 60 80 100 120 140 `n CO � Q � Distance (feet) Exploration Q_ 0 0 � U Hand Auger Designation ---> HA-1 Groundwater Level ---> 1 NOTES: a) During Exploration 1) Stratigraphic conditions are interpolated between E N co the explorations. Actual conditions may vary. z M Geologic Contact _ —� 00 � 2) Elevations are arbitrary. � o � (approximate) LO O ILL L Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure. C:\Users\LeeBeIIah\OneDrive - NGA\2024 NGA Project\15089-24 Rippey Res Deck Addition Edmonds\Draftinq\Cross Section.dwq 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 Rippey Residence � 1508924 Deck Addition Soil Classification Chart ASSOCIATES, inc ui " 135th"°e CA Wenatchee Office 17311-1351h Ave. NE, A-500 105 e , q�24�Z4 Original FKS ono Figure 4 h Woodinville, WA 98072 Wenatchee, WA 98801 , W 98 www.nelsongeolech.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 - 1.8 DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND ORGANICS (LOOSE, MOIST) (FILL) 1.8-2.75 SM GRAY TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND IRON -OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLE WAS COLLECTED AT 2.75 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER MET REFUSAL ON A ROCK AT 2.75 FEET ON 4/12/2024 HAND AUGER TWO 0.0-2.0 DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND ORGANICS (LOOSE, MOIST) (FILL) 2.0-2.5 SM GRAY TO GRAY -BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND IRON -OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER MET REFUSAL ON A ROCK AT 2.5 FEET ON 4/12/2024 FKS:DJO NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1508924 FIGURE 5