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REVIEWED PLN_BLD2020-0750_GEOTECH LETTER_1151019__Foster_Deck_Rebuild_Meadowdale (3)NELSON GEOTECHNICAL ASSOCIATES. INC. February 27, 2020 Mr. Chris Foster 16211— 70th Place West Edmonds, Washington VIA Email: cfoster45@gmail.com Geotechnical Engineering Evaluation Foster Residence Deck Replacement 16211— 70th Place West Edmonds, Washington NGA File No. 1151019 17311-135th Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com Dear Mr. Foster: This letter summarizes our opinions, evaluation, and recommendations regarding the proposed deck redevelopment within the steep slopes of the site located at 16211 — 70th Place West in the Meadowdale area of Edmonds, Washington, as shown on the Vicinity Map in Figure 1. INTRODUCTION The property covers approximately 0.28 acres and is currently occupied by an existing single-family residence with an associated double -deck in the backyard. The upper southwestern portion of the site slopes gently to moderately northeast, gradually steepening to the northeast. The northeast portion of the residence and double deck are situated within a steep, northeast facing slope, mapped as a moderate to severe landslide and erosion hazard area by the City of Edmonds. Based on our observations and conversations with you, the proposed deck development will be a replacement for the old deck, which is still currently standing, but has settled over time. That is, the double deck is to be rebuilt within the same approximate size as the current deck, but may extend downslope past the existing footings by a few feet. The downhill deck footings are located on the steep northeast facing slope, and that you have requested this report for a geotechnical engineering evaluation of the soil conditions and slope stability conditions in support of the deck redevelopment as required by the City of Edmonds. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 2 SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions within the vicinity of the proposed deck addition, and provide geotechnical recommendations for site development. Specifically, our scope of services includes the following: 1. Review available soil and geologic maps of the area. 2. Explore the subsurface soil and groundwater conditions within the proposed location of the deck with hand tools. 3. Map the conditions on the slope, constructing geological cross sections. 4. Qualitatively evaluate current slope stability conditions. 5. Perform shallow hand holes on the slope, as necessary. 6. Perform laboratory testing on soil samples, as needed. 7. Provide our opinions of the stability of the site steep slopes. 8. Provide recommendations for structure setback from the steep slope, if necessary. 9. Provide general recommendations for new deck foundation support. 10. Provide general recommendations for site drainage and erosion control. 11. Document the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The property covers approximately 0.28 acres and is currently occupied by an existing single-family residence with an associated double -deck in the backyard. The northeast portion of the residence and double deck are situated within a steep, northeast facing slope, mapped as a moderate to severe landslide and erosion hazard area by the City of Edmonds. The upper southwestern portion of the site slopes gently to moderately northeast surrounding the existing residence, but drops off to a moderate to steep slope area starting beneath the deck down toward the northeast past the northeast property line. The steep slopes step down beneath the deck at gradients up to up to 35 degrees (percent slope) and is lightly terraced by retaining walls, paths, and steps all the way down to the property line, as shown on Cross -Section A -A' and B-B' in Figures 3 and 4. The overall vertical relief within this steep slope area on the property is approximately 40 feet, but continues down to the northeast past the property line to a flat plain with residences below. The steep slopes below the deck are vegetated with a moderate density of mature evergreen trees, shrubs, and groundcover plants. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 3 We did not observe seepage or indications of significant recent movement on the site slopes during our site visit on February 13, 2020. However, we did notice surficial soil erosion features throughout the slopes including the undermining of the shallow -spread deck footings, undermining of a concrete slab lower on the slope, undermining and tilting out of old 1 to 2-foot tall timber steps and retaining walls terracing the slope, as well as some patches of bare soils, exposed roots, and surficial slope colluvium. 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 Minard, J. P. (USGS, 1983). The site is mapped as Vashon advance outwash (Qva), with recessional outwash (Qvr) mapped in the immediate vicinity. Advance outwash is described as well -sorted sand and gravel; deposited by streams issuing from advancing ice sheet. Recessional outwash is described as stratified sand and gravel with minor silt and clay layers. Our explorations generally encountered undocumented fill soils underlain by brown gray to gray, fine to coarse sand with varying amounts of gravel and silt, consistent with the description of advance outwash at depth. Explorations: We visited the site on February 13, 2020 to explore the subsurface conditions within the proposed deck and steep slope areas with five hand auger explorations. The approximate locations of our 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 5. The logs of our explorations are presented as Figures 6 and 7. 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. At the surface of each exploration we generally encountered approximately 3.0 to 4.3 feet of dark brown to brown silty fine to coarse sand with gravel, organics, and roots, which we interpreted as topsoil, undocumented fill soils, or slope colluvium. Underlying the topsoil and fill we encountered gray gravelly medium to coarse sand and gray fine to coarse sand with varying amounts of gravel and silt in a medium dense or better condition, which we interpreted as native advance outwash deposits. Hand Auger explorations 1 through 5 terminated at respective depths of 6.0, 5.0, 4.5, 4.2, and 4.0 feet below the existing ground surface. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington Hydrogeologic Conditions NGA File No. 1151019 February 27, 2020 Page 4 Groundwater seepage was not encountered in our explorations. If groundwater were to be encountered during construction, we would interpret it to be perched water. 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. SENSITIVE AREA EVALUATION Seismic Hazard 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 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 Sps Sol D 1.317 0.518 1.000 1.500 0.878 LIL 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 dense glacial deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. NELSON GEOTECHINICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 5 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 have the potential for shallow sloughing failures during seismic events. Such events should not affect the planned deck, provided the foundations are designed as described in this letter. 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 development portions of the site is listed as Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes, and lists the erosion hazard as moderate to severe, likely due to the steepness of the site slopes. Based on our experience in the area and the material encountered, we would interpret this site as having a moderate to severe erosion hazard where the surficial soils are exposed. It is our opinion that the erosion hazard for site soils should be low to moderate in areas where the site is not disturbed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. The northeast portion of the residence and double deck are situated within a steep, northeast facing slope, mapped as a moderate to severe landslide and erosion hazard area by the City of Edmonds. The steep slopes step down beneath the deck at gradients up to 35 degrees (percent slope) and is lightly terraced by retaining walls, paths, and steps all the way down to the property line, as shown on Cross - Section A -A' and B-B' in Figures 3 and 4. The overall vertical relief within this steep slope area on the property is approximately 40 feet, but continues down to the northeast past the property line to a flat plain with residences below. The steep slopes below the deck are vegetated with a moderate density of mature evergreen trees, shrubs, and groundcover plants. We did not observe groundwater seepage or indications of significant recent movement on the site slopes during our site visit on February 13, 2020. However, we did notice surficial soil erosion features throughout the slopes including the undermining of the shallow -spread deck footings, undermining of a concrete slab lower on the slope, undermining and tilting out of old 1 to 2-foot tall timber steps and NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 6 retaining walls terracing the slope, as well as some patches of bare soils, exposed roots, and surficial slope colluvium. The core of the 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 site slopes during extreme weather conditions or seismic events. 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 site slopes within the eastern portion of the site, there is not a significant potential for deep-seated slope failures under current site conditions. The property is located immediately south of the designated 'Meadowdale Landslide Complex,' which has experienced prevalent documented failures, and was augmented by extensive monitoring and drainage improvements by the City of Edmonds over the past four decades. Weathered and disturbed surface soils on the steep slope have the potential for shallow sloughing failures triggered by severe weather or seismic events. Relatively shallow failures as well as surficial erosion are natural processes and could occur in the loose surficial and/or undocumented fill soils on the site slopes. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils and undocumented fill on the site slopes, the potential for deep-seated slope failure under current site conditions is low. Based on geologic mapping and observations of surface features at this and adjoining sites, the risk of failure does not appear to be greater than what would be expected on similar sites between the beach and top terrace within this area of the City of Edmonds. Further explorations, such as deep soil borings, would be required to refine the risk of deep-seated slope failures. Proper site grading and drainage as well as slope maintenance, as recommended in this letter, should help maintain current stability conditions. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion from a geotechnical standpoint, that the planned deck should not adversely impact the existing slope stability conditions, and is feasible, provided the recommendations outlined within this report are followed. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 7 Our explorations within the existing deck and sloping area generally encountered up to 4.3 feet of unsuitable undocumented fill soils underlain by medium dense or better native advance outwash glacial soils at depths. In our opinion, the native glacial soils should provide adequate support for the planned deck loads. The site 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. 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 designed as recommended in this letter. Due to the significant loose undocumented fill soils encountered directly underlying the existing deck footings, for the proposed new deck replacement we recommend installing deep 12" diameter sonotube foundations drilled at least 1 foot into competent native advance outwash soils to support and transfer deck loads down to underlying native soils. The project structural engineer should be consulted for overall design, layout, and need for lateral support of deck foundation improvements. The recommended deeper foundation support systems should provide adequate support for the deck and allow for normal slope recession during a reasonable life span of the structures provided that the site slopes are not disturbed during or after construction. This is further discussed in the Deck Foundations subsection of this letter. Earthwork associated with the proposed deck foundation repairs 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, any excavation spoils should be hauled off site and not allowed to reach the slope. 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 recently constructed 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. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 8 The on -site soils are interpreted as having 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 the excavations and the steep site slopes. If any vegetation is removed from the area above the slope, silt fences or straw bales should be erected to prevent muddy water from flowing over the site slopes. Disturbed areas should be replanted with vegetation at the end of construction and the vegetation should be maintained until it is established. 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. Protection of the slope areas should be performed as required by the City of Edmonds. Specifically, we recommend that the site slopes, and rockery areas 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. Any sloping areas 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 slopes. Deck Foundations Due to the presence of approximately 4.0 to 4.5 feet of undocumented fill underlying the current deck foundations, we recommend that the proposed new deck foundations be supported on 12" diameter concrete sonotubes extending down and embedded into competent native soils. We recommend that the sonotubes be drilled down and embedded a minimum of 1.0 foot into native soils. We anticipate the overall depth of the sonotubes would be about 6.0 to 7.0 feet below the existing ground surface, based on our explorations. A bearing capacity of a maximum 1500 psf should be considered at this depth. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 9 We recommend that NGA be retained to review final project plans and provide consultation regarding structure placement, site grading, and foundation support. We also recommend that NGA be retained to provide monitoring and consultation services during construction and particularly during drilling to confirm adequate sonotube embedment and that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. Site Drainage We do not anticipate that the recently constructed 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 be tightly 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. We should be retained to evaluate the drainage plans. All runoff generated on this site, including roof downspouts, yard and footing drains, and hard surfaces, should be collected and routed into a permanent discharge system at the bottom of the slope or an existing, approved system. Under no circumstances should water be allowed to flow uncontrolled over the slopes. All existing drainage systems should be inspected and maintained such that no water is allowed to reach the slope. Water should not be allowed to collect in any area where foundations are to be constructed. USE OF THIS LETTER This letter has been prepared for Mr. Chris Foster and his agents, for use in the planning and design of the proposed deck repairs 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 GEOTECHINICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 Page 10 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 deck 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 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 Foster Residence Deck Replacement Edmonds, Washington NGA File No. 1151019 February 27, 2020 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. Katelyn S. Brower, GIT Staff Geologist Maher A. Shebl, PhD, PE, M.ASCE Senior Engineer KSB:MAS:dy Seven Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale N 152.,d St SW Fairbank Animal Farm - SV/ 5,1� 9 N Lunds Gulch a D _ 154th St SW Tiffany Hansen Sales r � a QMeadowdale 1561h St SW Q Crozier Photography Beach Park io s Project � `�� Site `° 1601h st sw MEADOWDALL , a °4 a Keeler's / o Northwest Cane Supply 1 , (uodSGuIchC1� Meadowdale % Community Clubhouse L Meadowdale Playfields Q P nwood atment Q = Dairy Queen Deb the Dog Walker Q ® _ Meadowdale © Meadowdale BEVERLY A C R E S Residential Locks Middle School Meadowdale High School ® Neighborhood Dunn L a Edmonds WA io Park ' a 169th PI SW D Lynn < 170th P/SW g ' c Walmart n 0 t x Neighborhood Market Jae+` 4Q t"17nd St SW ® p n < 41P O a '7z7d St SN' r F 172nd P1 SW G 3 Q D 'fS 1D a4le ac4, od P� stv �Ra ,n D 173rd PI S%V m 'Oo u10i Korean restaurar- - {� rst5W 174th st SW ' Northwest Motorsport Saint Thomas More Parish ® Village Market ; ° Q C 176th St SW Colorific Porcelain A -._. Edmonds, WA Project Number NELSON GEOTECHNICAL No. Date Revision By I CK 1151019 Foster Deck Rebuild NGA ASSOCIATES, INC. 1 2/18/20 Original DPN KSB Vicinity Map GEOTECHNICAL ENGINEERS & GEOLOGISTS 1E Woodinville Office East Wenatchee Office C Figure 1 17311-135th Ave. NE, A-500 5526Industry Lane, #2 Woodinville, WA 98072 East Wenatchee, WA 98802 (425) 486-1669 / Fax: 481-2510—elsongeotech.com (509) 665-7696 / Fax: 665-7692 ? Schematic Site Plan 1;10/h p/ LEGEND Property line HA-1 Number and approximate I location of hand auger 0 30 60 A A' Approximate location Approximate Scale: 1 inch = 30 feet of cross-section Reference: Site Plan based on field measurements, observations, and aerial parcel map review. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 1151019 Foster Deck Rebuild NGA ASSOCIATES, INC. 1 2/18/20 Original DPN KSB Schematic Site Plan GEOTECHNICAL ENGINEERS & GEOLOGISTS Woodinville ice East Wenatchee Office Figure 2 17311-135th Ave. NE, A-500 5526 Industry Lane, #2 Woodinville, WA 98072 East Wenatchee, WA 98802 (425) 486-1669 / Fax: 481-2510 viww.nelsongeolech.com (509) 665-7696 / Fax: 665-7692 N o A A' T 11 � 0 lVmm O G'CD U South North (D I I 80 80 Existing House C) 0 0 m Fill Cn to (HA-2 60 HA-4 Retaining Wall 60 0CDR D aoi D� - Q C 33° O co 40 23° 40 c� w � o a.�°o i --- m ^ "'= n Y J Z "- 3s° =p > a � r r z 20 20 Z yr Z (n O m 0 z M n 3 A m �, -► 0 v dm cmnm 0 0 2,'aF o Tm Z Z 0 20 40 60 80 100 120 140 -t A � r Distance (feet) Exploration o N 0 m fD Hand Auger Designation --> HA-1 o � y' Groundwater Level ---> 1 NOTES: During Exploration 1) Stratigraphic conditions are interpolated between Geologic Contact --> ? _ _ —? 2) the explorations. Actual conditions may vary. Elevations are arbitrary. oo z (approximate) 1 Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure. 7 W X \\HILL\company\2019 NGA Project Folders\11510-19 Foster Deck Rebuild Meadowdale\Drafting\CS.dwg o B B, T 11 � �mm j 0 (D O � D m Southwest Northeast 80 80 Existing House C) 0 0 m Fill to HA-2 cD 0 60 60 O 25' O CD O \ \ 00 a 25' ' Q C O R co 40 29� Fill 40 c� w HA-4 o Z ,_. M 6 x DDZ /d L 290 a r r z 20 20 Z yr Z (n O m 0 z m n � 3 A m �, -► 0 v dm cmnm 0 0 mF o Z Z l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l 0 20 40 60 80 100 120 140 -t A � r Distance (feet) Exploration o N 0 m fD Hand Auger Designation --> HA-1 o � y' Groundwater Level ---> 1 NOTES: During Exploration 1) Stratigraphic conditions are interpolated between Geologic Contact --> ? _ _ —? 2) the explorations. Actual conditions may vary. Elevations are arbitrary. oo z (approximate) 1 Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure. 7 W X \\HILL\company\2019 NGA Project Folders\11510-19 Foster Deck Rebuild Meadowdale\Drafting\CS.dwg UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 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 NELSON GEOTECHNICAL No. Date Revision By CK 1151019 Foster Deck Rebuild Soil Classification Chart ASSOCIATES, INC. N A GEOTECHNICAL ENGINEERS & GEOLOGISTS Woodinville Office East Wenatchee Office 1 2/18/20 Original DPN KSB Figure 5 17311-135th Ave. NE, A-500 5526Industry Lane, #2 Woodinville, WA 98072 East Wenatchee, WA 98802 (425) 486-16691 Fax: 481-2510 w.nelsongeotech.com (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION HAND AUGER ONE 0.0 - 2.0 DARK BROWN ORGANIC RICH SILTY FINE TO MEDIUM SAND AND WOOD DEBRIS (LOOSE, MOIST) (FILL) 2.0 - 4.3 BROWN SILTY FINE TO COARSE SAND WITH GRAVEL, ORGANICS AND ROOTS (LOOSE, MOIST) 4.3 - 6.0 SW-SM GRAY GRAVELLY MEDIUM TO COARSE SAND WITH SILT (MEDIUM DENSE TO DENSE, MOIST) SAMPLES COLLECTED AT 4.0, 5.0 AND 6.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER ONE MET REFUSAL AT 6.0 FEET ON 2/13/2020 HAND AUGER TWO 0.0 - 3.0 DARK BROWN TO BROWN SILTY FINE TO COARSE SAND WITH GRAVEL AND ORGANICS, ROOTS, (LOOSE, MOIST) (FILL) 3.0 - 5.0 SW GRAY GRAVELLY MEDIUM TO COARSE SAND AND MEDIUM TO COARSE SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) SAMPLES COLLECTED AT 3.3 AND 5.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TWO MET REFUSAL AT 5.0 FEET ON 2/13/2020 HAND AUGER THREE 0.0 - 4.0 BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND ORGANICS, ROOTS (LOOSE, MOIST) (FILL) 4.0 - 4.5 SW-SM GRAY FINE TO COARSE SAND WITH SILT AND TRACE GRAVEL AND IRON OXIDE STAINING (MEDIUM DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 4.5 FEET ON 2/13/2020 HAND AUGER FOUR 0.0 - 3.9 BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND ORGANICS, ROOTS, (LOOSE, MOIST) (FILL) 3.9 - 4.2 SW GRAY MEDIUM TO COARSE SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TWO MET REFUSAL AT 4.2 FEET ON 2/13/2020 KSB:KMS NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO. 1151019 FIGURE 6 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION HAND AUGER FIVE 0.0 - 3.5 DARK BROWN TO BROWN SILTY FINE TO COARSE SAND WITH GRAVEL AND ORGANICS, ROOTS, (LOOSE, MOIST) (FILL) 3.5 - 4.0 SW-SM GRAY FINE TO COARSE SAND WITH SILT AND GRAVEL (MEDIUM DENSE TO DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER TWO MET REFUSAL AT 4.0 FEET ON 2/13/2020 KSB:KMS NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO. 1151019 FIGURE 7