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REVIEWED RESUB 1-Geotech Letter BLD2022-0284NELSON GEOTECHNICAL ASSOCIATES. INC. July 6, 2022 Megan Walla VIA Email: miwalla@windermere.com Geotechnical Engineering Evaluation 226th Place SW Deck Reconstruction 10406 — 226th Place SW Edmonds, Washington NGA File No. 1364422 Dear Megan: 17311-135th Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com RESUB Jul 07 2022 Reviewed by ' DEVELOPMENT SERVICES DEPARTMENT City of Edmonds BLD2022-0284 Planning Division I- - - - - - - - - - - - - -' NELSON GEOTECHNICAL ASSOCIATES, INC. (NGA) is pleased to submit this letter for a subsurface geotechnical evaluation for the deck reconstruction project located at 10406 — 226th Place SW in Edmonds, Washington. The parcel number for the property is 00610400001900. INTRODUCTION The property is irregular in shape and covers 0.35 acres in area. It is currently occupied by a single- family residence. The property is bordered by 226' Place SW to the north, and on all other sides by existing residential development. Topographically, the site is flat to slightly sloping adjacent to the residence and climbs moderately to steeply toward the south in the south portion of the site. A deck extends southeast of the residence in the flat portion of the yard. We understand that the existing deck is to be replaced with a new deck that will have the same footprint. The City of Edmonds requires a geotechnical report to address steep slope, erosion, and seismic hazards that are partially mapped on the site. We have been requested to provide this letter for determination of geological hazards affecting the site, as well as development considerations for the proposed deck. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions within the vicinity of the proposed deck replacement and provide geotechnical recommendations for site development. Geotechnical Engineering Evaluation 2261h Place SW Deck Reconstruction Edmonds, Washington Specifically, our scope of services included the following: 1. Reviewing available soil and geologic maps of the area. NGA File No. 1364422 July 6, 2022 Page 2 2. Exploring the subsurface soil and groundwater conditions within the proposed deck replacement area 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. Determining the presence of Geologically Hazardous Areas in accordance with the City of Edmonds Municipal Code, as warranted. 6. Providing recommendations for structure setbacks from geologic hazards, as necessary. 7. Providing recommendations for deck foundation support. 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 irregular in shape and covers 0.35 acres in area. It is currently occupied by a single- family residence. The property is bordered by 226' Place SW to the north, and on all other sides by existing residential development. The vegetation within the site generally consists of grass and landscaping shrubs in the yard areas and young to mature trees with native underbrush on the moderate to steep slopes. Topographically, the site is flat to gently sloping adjacent to the residence. A deck extends southeast of the residence in the flat portion of the yard. The southern portion of the site climbs moderately to steeply toward the south with gradients as steep as 23 degrees (42 percent). Several landscaped terraces have been constructed in the sloping southern yard, with stacked timber and block retaining walls up to a few feet at the downslope side of each terrace. The southern slope steepens south of the southern property line and has an inclination of approximately 37 degrees (74 percent). The upper portion of the slope is heavily vegetated with shrubs and young to mature trees. We measured a cross- section across the southern slope using a hand-held clinometer and a tape measure. Cross -Section A -A' is presented in Figure 3. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation 2261h Place SW Deck Reconstruction Edmonds, Washington NGA File No. 1364422 July 6, 2022 Page 3 Subsurface Conditions 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 James P. Minard. (1983). The site is mapped as advance outwash (Qva) with glacial till (Qvt) mapped nearby. Advance outwash is typically a thick section of mostly clean, gray, pebbly sand with increasing amounts of gravel higher in the section. Glacial till is an unsorted mixture of clay, silt, sand, pebbles, cobbles, and boulders. Explorations: We visited the site on May 20, 2022 to explore the subsurface conditions within the vicinity of the deck and on the southern slope with three hand auger explorations. The approximate locations of our hand auger explorations are shown on the Schematic Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc. (NGA) completed the explorations, examined the soils and geologic conditions encountered, and maintained logs of the explorations. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 4. The logs of our explorations are presented as Figure 5. The following paragraph contains a brief description of the subsurface conditions encountered in the explorations. For a detailed description of the subsurface conditions, the hand auger logs should be reviewed. Hand Augers 1 and 2 were located close to the existing deck and Hand Auger 3 was located on the southern slope. The hand augers encountered one foot of topsoil, followed by loose to medium dense silty sand with gravel and some roots. At depths of 1.5 to 3 feet we observed sand with silt and gravel that was medium dense to dense. Hydrogeologic Conditions No active seepage was encountered in our explorations or on the site slopes during our site visit. If seepage were to be encountered in the future, we would interpret it as perched groundwater. Perched water conditions may occur on the site during periods of wet weather. 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 rainfall. 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 NGA File No. 1364422 2261h Place SW Deck Reconstruction July 6, 2022 Edmonds, Washington Page 4 SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2018 International Building Code (IBC) and ASCE 7-16 for seismic site classification for this project. 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 and ASCE7-16, which specify 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 Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec. (g) at 1.0 sec. (g) Response S, S1 Parameters Fa Fv Sos Sol D 1.281 0.45 1.000 Null7854 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. The site is located within the South Whidbey Island Fault Zone (SWIFZ): an active, shallow region of seismicity within central Puget Sound stretching from the Strait of Juan de Fuca to North Bend. Information published in 2013 by the Washington State Department of Natural Resources suggests the SWIFZ last ruptured less than 2,700 years ago, and that the fault zone can produce a M7.5 earthquake. The nearest mapped fault strand is less than one-half mile northeast of the site. It is our opinion based on available information that the site has a low potential for surface rupture associated with the SWIFZ. 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 to dense soils interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. The competent glacial soils interpreted to form the core of the site slope are considered stable with respect to deep-seated slope failures. However, the loose surficial soils and undocumented fill on and near the sloping portions of the site may have the potential for shallow sloughing failures particularly during inclement, extreme weather and during seismic events. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1364422 2261h Place SW Deck Reconstruction July 6, 2022 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 Natural Resources Conservation Service (NRCS) of the Snohomish County area was reviewed. The soil in the developed portion of the site is listed as Everett very gravelly sandy loam, 0 to 8 percent slopes, and in the moderate to steep slopes as Alderwood gravelly sandy loam, 25 to 70 percent slopes. The erosion hazard is mapped as moderate and severe, respectively. Based on our experience in the area and the material encountered, we would interpret this site as having a low erosion hazard in the developed portion of the site and moderate to high on the site slopes, 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, and vegetation remains in place. Per the Edmonds Community Development Code (ECDC) the steeply sloping portion of the site meet the definition of erosion hazard areas as defined by ECDC 23.808.020.A due to their classification as Alderwood gravelly sandy loam, 25 to 70 percent slopes by the NRCS. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. Topographically, the northern portion of the site consists of a relatively level terrace containing landscaping and the single-family home. A moderate to steep north -facing slope with a vertical relief of approximately 45 feet is partially within the southern part of the site. That slope descends toward the residence structure at gradients in the range of 23 to 37 degrees (42 to 75 percent) as shown in Cross -Section A -A' in Figure 3. The lower portion of the slope is terraced with timber and block retaining walls up to 3 feet tall. The upper steeper portion of the slope is heavily vegetated with shrubs, ground cover plants, and young to mature trees and the lower terrace portion of the slopes are vegetated with grass yard areas and landscaping plants. We did not observe indications of recent slope instability, and no surface water or springs were observed within the site on our visit on May 20, 2022. The southern steep slope is considered to be a landslide hazard area as defined by ECDC 23.80.020.E due to the presence of gradients exceeding 40 percent on a slope with a vertical relief of more than 10 feet over a 25-foot vertical run. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1364422 2261h Place SW Deck Reconstruction July 6, 2022 Edmonds, Washington Page 6 The core of the site slope is inferred to consist primarily of competent native glacial soils. Upon reviewing available MAR data, we found no evidence of previous landsliding within the site. Based on our explorations and slope mapping, it is our opinion that the risk of deep-seated landslides is low under current site conditions. There may be a potential for erosion, soil creep, and shallow failures within the loose surficial and undocumented fill soils on the steeper site slopes during extreme environmental conditions. Proper site grading and drainage as well as slope maintenance, as recommended in this letter, should help maintain current stability conditions. CONCLUSIONS AND RECOMDATIONS General It is our opinion from a geotechnical standpoint that the proposed deck reconstruction is feasible. Our explorations close to the existing deck encountered medium dense to dense native glacial soils at depths of 2 to 3 feet. These soils should provide adequate support to the replacement deck. Footings for the new deck should be supported on conventional shallow foundations extending down to the competent native soils or structural fill extending down to those soils. We should note that areas of deeper loose or unsuitable soils may be present below the deck. If these conditions are encountered in footing areas, deeper excavation may be necessary. We interpret that the core of the site slopes primarily consists of native sandy soils which should be stable with respect to deep-seated earth movements. Like any steep slope in the Puget Sound region, there is a potential for shallow slope failures to occur; however, it is our opinion that the proposed deck replacement will not adversely impact the currently stability conditions, provided that the recommendations stated within this letter are followed. It is our opinion that the existing deck location, at least 10 feet from the base of the southern slope, should adequately mitigate the risk of shallow slope failures during the design life of the replacement deck. The steep southern slope should not be disturbed during the deck replacement. Further discussion of the deck setback can be found in the Steep Slope and Deck Setback subsection of this letter. 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 site 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 site. Any disturbed areas should be promptly repaired. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1364422 2261h Place SW Deck Reconstruction July 6, 2022 Edmonds, Washington Page 7 Erosion Control The on -site soils are listed as having a moderate to severe potential for erosion, depending 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 any excavations and away from site slopes. If any vegetation is removed from the site, silt fences or straw wattles should be erected to prevent muddy water from leaving the area. Disturbed areas should be replanted with vegetation at the end of construction and the vegetation should be maintained until it is established. Site Preparation and Grading After erosion control measures are implemented, site preparation for the new deck foundations should consist of stripping the topsoil and loose soils from footing areas to expose medium dense native 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 footing excavations on the order of 2 to 3 feet will be needed to expose competent native soils. However, additional stripping may be necessary if areas of thicker loose soil are encountered. After stripping, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding condition. Areas that remain loose after compaction should be reworked to structural fill specifications or 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. Deck Foundations We recommend the new deck foundations consist of shallow conventional pad foundations or 8- to 12- inch diameter sonotube foundations. Foundations should be founded on competent native bearing glacial soils or structural fill extending to these soils. Medium dense or better soils in the vicinity of the proposed deck should be encountered between approximately 2 to 3 feet below the existing ground surface based on our explorations. We should be retained to verify subgrade conditions once foundations excavations are made. Where undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be over -excavated to expose suitable bearing soil. 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1364422 2261h Place SW Deck Reconstruction July 6, 2022 Edmonds, Washington Page 8 For foundations constructed as outlined above, we recommend an allowable design bearing pressure of 1,500 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing soils or rock spalls extending to the competent native bearing 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 150 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. Steep Slope and Deck Setback Uncertainties related to building along the toe of steep slopes are typically addressed by the use of setbacks. The purpose of the setback is to establish a "buffer zone" between the structure and the toe of the slope so that ample room is allowed for debris fall due to natural erosional activity 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 gradient, soil type, and groundwater conditions. 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 there is a potential for shallow failures to take place on the steeper site slopes, especially during wet weather. It is our opinion that maintaining the existing structure setback of 10 feet from the base of the slope should be adequate to mitigate any impacts of the proposed development on slope stability and mitigate the new deck from slope failures. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation 2261h Place SW Deck Reconstruction Edmonds, Washington NGA File No. 1364422 July 6, 2022 Page 9 Site Drainage We do not anticipate the new deck will have significant impact on site drainage patterns. The finished ground surface underlying the deck should be graded such that runoff is directed away from the residence. City of Edmonds Code Because the existing deck is to be replaced by a new deck with the identical footprint and the landslide hazard and erosion hazard areas will not be disturbed, it is our opinion that the deck replacement will not increase hazards to adjacent properties beyond predevelopment conditions, will not adversely impact other critical areas, and the hazard to the proposed deck will be mitigated to a level equal to the predevelopment condition. Provided our recommendations are followed, it is our opinion that the deck replacement will not increase the threat of landsliding within the site beyond predevelopment conditions. USE OF THIS LETTER This letter has been prepared for Megan Walla and associated agents, for use in the planning and design of the proposed deck construction 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 sunroom 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 homes 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 NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation 2261h Place SW Deck Reconstruction Edmonds, Washington NGA File No. 1364422 July 6, 2022 Page 10 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 2261h Place SW Deck Reconstruction Edmonds, Washington NGA File No. 1364422 July 6, 2022 Page 11 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. Sarah L. Dunn Staff Geologist II ?022 Khaled M. Shawish, PE Principal SLD:JDK:KMS:dy Five Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. Condominiums Point Pine St o Makah Rd o v_ m Bella Coola Rd L\ N DO PAPo °a<II VICINITY MAP Not to Scale N F m F Pine St Pine St < 2161h St SW m D Forsyth Ln T n D Kirsten Johnson Q 217 w y \\; y Fr St 3 2181h St y \ PINE PARK NEIGHBORHOOD 5 a QAFH (Provi#11AAAA Elm St Westgate Pt Elementary School T? s a � 0 > F f ofo�9� `�; F N \rL Project '`ew Woodway — � 224th St SW 2241h St SW Site FIVE a SW St 6th r N s Terry Vehrs 22 Q "' J s N ., ©Edmonds Memorial °d Cemetery W e, n 3 Y m i n F F c WESTGATE Edmonds Goodwill c ®PCC Community Q Westgate C Markets - Edmonds s 1 N beet Sherwood Ono Authentic rn Elementary School Hawaiian Poke'/ Deer Creek Park a soee` f North American Martyrs Catholic Church a Roq, D PRC Edmore_ C yo v F 3 °o- ` o c I A Wachusett Rd 14 Q Edmonds Heights K-12 > 7 SHERWOOD 2341n s< SW i ? FOREST F a Diversified Q Electric Services 3 � 5 a T 3 T v 3 F F 3 John Bush Play Area © ©'woodway Reserve 1 m a 3 ; Hickman Park o s $ y'� 238th St SW 238t 1 2371n� Madrona K-8 School0 c 240th Sl SW ,AMh DI CW DI c 1 i Edmonds, WA Project Number nELSOn GEOTECHninL No. Date Revision By I cK 1364422 Walla Deck & Slope 1111mb I ASSOCIATES, Inc 1 6/9/22 Original DPN ABR Vicinit Map p • � Woodinville Office Wenatchee Office Figure 1 11311-135th Ave. NE, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 ww.nelsongeotech.com (425)486-1669/Fax . 481-2510 (509) 665-7696 / Fax: 665-7692 Schematic Site Plan 226th PI SW - -.�,•� ` _ N Existing Residence Q� HA-1 4L .iiW r z�l HA-3Y='.�` i- a fir' �r . + "►' '� •�; � `r;►, . ",fit}• • w.w' LEGEND — Property line HA-1 Number and approximate location of hand auger A A' Approximate location L± of cross-section 0 40 80 Approximate Scale: 1 inch = 40 feet Reference: Site Plan based on field measurements, observations, and aerial parcel map review. Project Number ' II son GEOTECHIIICAL No. Date Revision By cK 1364422 Walla Deck & Slope ASSOCIATES, In 6/9/22 Original DPN ABR j Schematic Site Plan W1111 Woodinville Office Wenatchee Office Figure 2 17311-135th Ave. NE, A-500 05 Palouse St. W. nville, WA 98072 Wenatchee, WA 98801 w.nelsongeotechcom (425)486-1669I1`ax.481-2510 (509)665-76961 Fax: 665-7692 C T 1 W 00 0 (D N W N 3 U cu o U in 60 m CD o' go U) Do D-0 -m F \\ �\a e 3 cas o TD o N = a m 0 m —1 c=-) z 0 v N a� c 0 cu W LLI a) cu C X O Q Q Q n Interpreted from South Snohomish County Parcel Map 340 \ R 320 \ 300 M A' Residence North — 340 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 0 20 40 60 80 100 120 140 Distance (feet) Exploration 320 300 280 260 N fD Hand Auger Designation --> HA-1 o A m y' Groundwater Level ---> 1 NOTES: During Exploration 1) Stratigraphic conditions are interpolated between the explorations. Actual conditions may vary. Geologic Contact � ? — —? 2) Elevations are approximate. z 1,07 (approximate) Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure. inyNelson\Nelson Geotechnical Associates, Inc\Nelson Geotechnical Associates, Inc - Company\2022 NGA Project\13644-22 Walla Deck Rebuild Edmonds\Drafting\CS.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 GM OF COARSE FRACTION OF SILTY GRAVEL 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 CH 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 IIELSOn GEOTECHnICAL No. Date Revision By cK 1364422 Walla Deck & Slope Soil Classification Chart ASSOCIATES, inc 1 6i9i22 Original DPN ABR Figure 4 Woodinville Office Wenatchee Office 17311-135th Ave. NE, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 ww.nelsongeotech.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 - 1.0 GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS AND ORGANICS (LOOSE, MOIST) (TOPSOIL) 1.0 - 3.0 SM ORANGE -BROWN TO LIGHT BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS AND IRON - OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) 3.0 -4.0 SW-SM GRAY, FINE TO COARSE SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 4.0 FEET ON 05/20/2022 HAND AUGER TWO 0.0 - 1.0 GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS AND TRACE GRAVEL (LOOSE, MOIST) (TOPSOIL) 1.0-2.0 SM ORANGE -BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS, AND IRON -OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) 2.0 - 4.0 SP-SM GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 4.0 FEET ON 05/20/2022 HAND AUGER THREE 0.0 - 1.0 DARK BROWN, ORGANIC -RICH, SILTY FINE TO MEDIUM SAND WITH ROOTS AND GRAVEL (LOOSE, MOIST) (TOPSOIL) 1.0 - 1.5 SM ORANGE -BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, TRACE ROOTS, AND IRON - OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) 1.5 - 4.5 SP-SM GRAY, FINE TO MEDIUM SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 4.5 FEET ON 05/20/2022 DPN:ABR NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1364422 FIGURE 5