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REVIEWED BLD BLD2021-0259+Geotechnical_Report+2.16.2021_5.15.29_PM+2050233RECEIVED Apr 12 2021 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT May 29, 2019 ES-6693 Real Property Funding Group, LLC 7500 Roosevelt Way Northeast Seattle, Washington 98115 Attention: Mr. Ryker Young Subject: Geotechnical Evaluation Proposed Residential Short Plat 20114 — 83rd Avenue West Edmonds, Washington Tax Parcel No. 00431200000402 Reference: Donna Breske & Associates, LLC Civil Plans, dated July 13, 2018 Dear Mr. Young: %iEarth l Solutions NW«C Earth Solutions NW I_I_c Geotechnical Engineering, Construction Observationjesting and Environmental Services In accordance with your request and based on review comments provided by City of Edmonds design review, Earth Solutions NW, LLC (ESNW) has prepared this letter summarizing our geotechnical consulting services performed for the subject property. A representative of ESNW visited the site on April 30, 2019 to conduct explorations at accessible locations of the parcel. Project Description Based on the conceptual plans provided to us, the existing residence and associated improvements will be demolished and the property will be subdivided into a two -lot residential short plat. Grading plans were not available at the time this letter was prepared; however, we anticipate cuts and fills of about five feet or less will be required to establish the subgrade for the new buildings. We anticipate the proposed residential structures will be two to three stories in height and will consist of relatively lightly -loaded wood framing supported on conventional foundations. We also anticipated no basement levels will be included in the plans. Based on our experience with similar developments, we estimate wall loads of roughly one to two kips per linear foot and slab - on -grade loading of about 150 pounds per square foot (psf) will be incorporated into the construction. ESNW should review the structural plans to confirm the estimates are consistent with the design and to provide additional recommendations. 1805 - 136th Place N.E., Suite 201 0 Bellevue, WA 98005 0 (425) 449-4704 • FAX (425) 449-4711 Real Property Funding Group, LLC ES-6693 May 29, 2019 Page 2 We understand that infiltration is being investigated as part of the site designs. We understand individual lot infiltration devices, such as drywells may be used for reach lot to infiltrate roof runoff and bioretention facilities will be used. Surface The subject site is located at 20114 — 83rd Avenue West in Edmonds, Washington, just north of Pine Ridge Park. The site consists of a single residential tax parcel (APN 00431200000402) bordered to the north, south and west by existing residential parcels and to the east by 3rd Avenue West. The property is currently occupied by a single-family residential structure and associated improvements. In general, the site topography descends to the east with about 30 feet of total elevation change with average inclinations of about 20 to 23 percent. Vegetation is comprised primarily of lawn grass and general landscape features. Subsurface Conditions A representative of ESNW observed, logged, and sampled three test pits excavated using a mini-trackhoe and operator retained by our firm, at accessible locations of the site for the purpose of assessing soil and groundwater conditions. The approximate locations of the test pits are illustrated on the Test Pit Location Plan (Plate 1). Due to existing developed areas, we were very limited to accessible locations for our test pits. Please refer to the provided test pit logs for a more detailed description of subsurface conditions. Representative samples collected at the test pit locations were analyzed in accordance with Unified Soil Classification System (USCS) and United States Department of Agriculture (USDA) methods and procedures. Topsoil and Fill In general, topsoil was encountered to depths ranging up to approximately 18 inches at the test pit locations. Topsoil was identified by the dark brown color and organic content. Fill was encountered at test pit location TP-2 that consisted of about two feet of medium dense silty sand with grave (Unified Soil Classification: SM) during our fieldwork. Native Soils Underlying topsoil and fill, native soils were encountered consisting primarily of medium dense to dense silty sand with gravel (USCS: SM) and silty gravel with sand (GM). Soil relative density generally increased with depth. In general, native soils were observed primarily in a damp to moist condition. Geologic Setting Review of a readily available geologic map resource indicates the site is underlain primarily by glacial till (Qvt) deposits. As described in WSS NRCS USDA soil mapping resource, Alderwood soils (AgC) are present on the subject site. Alderwood material formed in plain -deposited tills. Earth Solutions Nw, LLC Real Property Funding Group, LLC ES-6693 May 29, 2019 Page 3 We interpret the native soil conditions encountered at the test pit locations to represent a glacial till deposits. Groundwater No groundwater seepage was encountered in the test pit locations during the date of exploration (April 30, 2019), which were advanced to a maximum depth of 10 feet. However, groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. Groundwater seepage flow rates are typically higher during the winter, spring and early summer months. Therefore, perched groundwater seepage should be expected in deeper site excavations, particularly if excavations are made in winter, spring and early summer months. Geologic Hazard Areas Based on our review of the Critical Areas Checklist (P-20) and Chapter 23.40 — Environmentally Critical Areas of the Edmonds Community Development Code ECDC, the subject property is located within a mapped erosion hazard area. The erosion hazard designation largely relates to grading activities and reducing the potential for off site migration of sediment and potential impacts to neighboring properties. Based on review of the Critical Areas Checklist, the majority of the site is mapped as a general Erosion Hazard (15 to 40 percent slopes). On this site, grading will be fairly limited in scope and standard erosion and sediment control (ESC) measures will provide an adequate level of protection for adjacent properties and off site migration of sediment. ESC measures must be actively maintained during grading to ensure proper function. Provided the ESC measures perform as intended, in our opinion, no adverse impacts to neighboring properties will occur during grading. Permanent ESC measures on this project will be related to vegetation and landscape elements. Foundations Based on the conditions encountered at the test pit locations, construction of a single-family residences and associated improvements at the subject site is feasible from a geotechnical standpoint. We anticipate competent native soil suitable for foundation support will be encountered at depths of about two to three feet below existing grades. Where loose or unsuitable conditions are encountered at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with structural fill may be necessary and should be observed by ESNW prior to placing concrete formwork. For design the following parameters may be used for the foundation design: ■ Allowable soil bearing capacity 2,500 psf ■ Passive earth pressure • Coefficient of friction 300 pcf MR Earth Solutions NW, LLC Real Property Funding Group, LLC ES-6693 May 29, 2019 Page 4 The passive earth pressure value provided above assumes the foundations will be backfilled with structural fill. A factor -of -safety of 1.5 has been applied to the passive earth pressure and friction values provided in this section. For short-term wind and seismic loading, a one-third increase in the allowable soil bearing capacity may be assumed. With structural loading as expected, total settlement in the range of one inch, as well as differential settlement of approximately one-half inch, is anticipated. The majority of the settlements should occur during construction, as dead loads are applied. Subgrade Preparation Following site stripping and removal of the existing structural improvements, minor cuts and fills will likely be completed to establish the proposed subgrade levels throughout the site. ESNW should observe the subgrade during the initial site preparation activities to confirm soil conditions and to provide supplemental recommendations for subgrade preparation. The process of removing the existing building structure may produce voids where the old foundations are removed, and where basement or crawl space areas may have been present. Thorough restoration of voids from old foundation and/or basement areas must be completed as part of the overall subgrade and building pad preparation activities. The following guidelines for preparing the building subgrade areas should be incorporated into the final design: • Where voids and related demolition disturbance extend below the planned subgrade level, restoration of these areas should be completed. Structural fill should be used to restore voids or unstable areas resulting from the removal of existing structures. • Re -compact or overexcavate and replace areas of existing fill (if present) exposed at building subgrade elevations. ESNW should confirm subgrade conditions and the required level of re -compaction, or overexcavation and replacement during the site preparation activities. Overexcavations should extend to competent (medium dense) native soils and be replaced with structural fill. ■ ESNW should confirm overall suitability of the prepared subgrade areas following the site work activities. In -Situ and Imported Soil From a geotechnical standpoint, native soils may not suitable in structural fill applications unless the soil is placed at or slightly above optimum moisture content as determined from a Modified Proctor (ASTM D-1557) test. If the native soils cannot achieve structural fill specifications, imported soil will be required. Imported soil intended for use as structural fill should consist of a well -graded, granular soil with a moisture content that is at (or slightly above) the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well -graded, granular soil with a fines content of 5 percent or less (where the fines content is defined as the percent passing the Number 200 sieve, based on the minus three -quarter -inch fraction). Earth Solutions NW, LLC Real Property Funding Group, LLC May 29, 2019 Structural Fill ES-6693 Page 5 Structural fill is defined as compacted soil in foundation, slab -on -grade, and driveway areas. Fills placed within utility trench backfill areas are also considered structural fill. Soils placed in structural areas should be placed in maximum 12-inch loose lifts and be compacted to a relative compaction of 95 percent, based on the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM D1557). Fill should be placed on a firm level surface. ESNW should be consulted during early grading activities to provide additional recommendations. Temporary Excavations and Permanent Slopes The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. The fill and weathered native soils and where groundwater is exposed are classified as Type C by OSHA and WISHA. Temporary slopes over four feet in height in Type C soils should be sloped no steeper than 1.5H:1V (Horizontal:Vertical). Steeper temporary excavation slopes may be possible based on the exposed conditions, but must be observed by ESNW at the time of excavation. ESNW should observe temporary and permanent slopes to confirm the inclinations are appropriate for the exposed soils and to provide additional grading recommendations as necessary. If temporary slopes cannot be constructed in accordance with OSHA and WISHA guidelines, temporary shoring may be necessary. Permanent slopes should maintain a gradient of 2HAV, or flatter, and should be planted with an appropriate species of vegetation to enhance stability and to minimize erosion. Slab -on -Grade Floors Slab -on -grade floors should be supported on a suitable capillary break material underlain by undisturbed, competent native soil or a compacted structural fill subgrade. Structural fill in slab - on -grade areas should be compacted to a minimum relative compaction of 95 percent throughout the upper one foot of subgrade. Unstable or yielding areas of the subgrade should be recompacted, or overexcavated and replaced with suitable structural fill, prior to construction of the slab. Slab -on -grade areas should be provided with a minimum four -inch capillary break. Capillary break soils should consist of a granular, free -draining sand and gravel soil that contains less than 5 percent fines (percent passing the Number 200 sieve, based on the minus three -quarter - inch fraction). In general, to help facilitate grading of the slab subgrade, the maximum aggregate size of the capillary break material should generally be one -and -one -quarter inch. In areas where slab moisture is undesirable, installation of a vapor barrier placed below the slab should be considered. If a vapor barrier will be utilized, it should consist of a material specifically designed for that use and should be installed in accordance with the specifications of the manufacturer. Earth Solutions NK LLC Real Property Funding Group, LLC May 29, 2019 Retaining Walls ES-6693 Page 6 If retaining walls will be used on this project, they should be designed to resist earth pressures and applicable surcharge loads. For design, the following parameters may be used: Active earth pressure (yielding condition) • At -rest earth pressure (restrained condition) Traffic surcharge (passenger vehicles) ■ Passive earth pressure • Coefficient of friction • Seismic surcharge 35 pcf (equivalent fluid) 55 pcf 70 psf (rectangular distribution) 300 pcf (equivalent fluid) 0.40 6H (where H = retained height) Additional surcharge loading from foundations, sloped backfill, or other loading should be included in the retaining wall design. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design. ESNW should review the retaining wall designs to verify that recommended earth pressure values have been incorporated and to provide additional recommendations as necessary. Retaining walls should be backfilled with free -draining material that extends along the height of the walls and a distance of at least 18 inches behind the wall. The upper one foot of wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of retaining walls and tightlined to an approved discharge location. Seismic Design The 2015 International Building Code specifies several soil profiles that are used as a basis for seismic design of structures. Based on the soil conditions observed at the test sites, Site Class D should be used for design. In our opinion, the site is not susceptible to liquefaction based on the absence of a uniformly established groundwater table and the relative density and gradation of the site soils observed at the test pit locations. Drainage Groundwater seepage was not observed at the time of our fieldwork. However, localized perched zones of groundwater seepage could be encountered in the excavations, particularly during the winter, spring and early summer months. Temporary measures to control surface water runoff during construction would likely involve interceptor trenches and sumps. Based on the soil and groundwater conditions observed at the test sites, active dewatering (such as well points) will likely not be necessary; however, ESNW should observe conditions relating to drainage during construction to provide recommendations. Earth Solutions NW, LLC Real Property Funding Group, LLC ES-6693 May 29, 2019 Page 7 In our opinion, footing drains should be installed around the perimeter of the new building below the invert of the building footings. Exterior grades should be sloped away from buildings at a gradient of at least 2 percent for at least ten feet or to the maximum extent afforded by property line setbacks. Utility Support and Trench Backfill In our opinion, the soils observed at the test sites are generally suitable for support of utilities. Excessively loose, organic, or otherwise unsuitable soils encountered in the trench excavations should not be used for supporting utilities. In general, the on -site soils observed at the test sites may not be suitable for use as structural backfill in the utility trench excavations, unless the soil is at or near the optimum moisture content at the time of placement and compaction. Moisture conditioning of the soils may be necessary at some locations prior to use as structural fill. Utility trench backfill should be placed and compacted to the specifications of structural fill provided in this report, or to the applicable specifications of the City of Edmonds, or applicable jurisdiction or agency. Limitations The recommendations and conclusions provided in this report are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test sites may exist and may not become evident until construction. ESNW should reevaluate the conclusions in this report if variations are encountered. Additional Services ESNW should have an opportunity to review the final design with respect to the geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during the earthwork phase of construction. Earth Solutions NW, LLC Real Property Funding Group, LLC May 29, 2019 We trust this letter meets your current needs information is required, please call. Sincerely, EARTH SOLUTIONS NW, LLC Si , L.�. E.G. S for' ct Mana� Attachments: Plate 1 — Vicinity Map Plate 2 — Test Pit Location Plan Test Pit Logs Laboratory Data ES-6693 Page 8 Should you have questions, or if additional o Kyle R. Campbell, P.E. Principal Engineer Earth Solutions NW, LLC Reference: NORTH Snohomish County, Washington NW LLC Geotechnical Engineering, Construction [Wap454 Observation/Testing and Environmental Services ByThe Thomas Guide Rand McNally Vicinity Map 32ndEdition Edmonds SP Edmonds, Washington NOTE: This plate may contain areas ofcolor. ESNYVcannot bo responsible for any subsequent misinterpretation ofthe information resulting from black & white reproductions ofthis plate. i I I � I -410 400 390 Proposed 1;I-2II / p rod sed Drivew y / I ,---,��/ TP-1 Lot 1 / 380 /rP_3 c 410 400 390 3'0 I LEGEND TP-1 Approximate Location of — ■ — ESNW Test Pit, Proj. No. ES-6693, April 2019 Subject Site Proposed Building NOTE: The graphics shown on this plate are not intended for design purposes or precise scale measurements, but only to illustrate the approximate test locations relative to the approximate locations of existing and / or proposed site features. The information illustrated is largely based on data provided by the client at the time of our study. ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black & white reproductions of this plate. E 0 20 40 80 1 "=40' Scale in Feet Drwn. CAM Date 05/15/2019 Proj. No. 6693 Checked SES Date May 2019 Plate 2 Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL DESCRIPTIONS GRAPH LETTER GRAVEL AND CLEAN GRAVELS ' �' ' `� • * .0 ■� GW WELL -GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO FINES ■C o d o paQ Q Q np GP POORLY-GRADED GRAVELS, GRAVEL- SAND MIXTURES, LITTLE OR NO FINES GRAVELLY SOILS (LITTLE OR NO FINES) COARSE GRAINED SOILS MORE THAN 50% OF COARSE GRAVELS WITH FINES ' Q ° �° ° D a GM SILTY GRAVELS, GRAVEL -SAND - SILT MIXTURES FRACTION GC CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES RETAINED ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) SAND AND CLEAN SANDS SW WELL -GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES MORE THAN 50% OF MATERIAL IS SP POORLY -GRADED SANDS, GRAVELLY SAND, LITTLE OR NO FINES LARGER THAN NO. 200 SIEVE SIZE SANDY SOILS (LITTLE OR NO FINES) SANDS WITH FINES SM SILTY SANDS, SAND - SILT MIXTURES MORE THAN 50% OF COARSE FRACTION S`+ CLAYEY SANDS, SAND - CLAY MIXTURES PASSING ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) INORGANIC SILTS AND VERY FINE ML SANDS, ROCK FLOUR, SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY FINE GRAINED SOILS SILTS LIQUID LIMIT AND LESS THAN 50 CLAYS CL INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS, LEAN CLAYS -u OL ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% OF MATERIAL IS MH INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS FINE SAND OR SMALLER THAN NO.200 SIEVE SILTY SOILS SIZE SILTS LIQUID LIMIT AND CLAYS GREATER THAN 50 CH INORGANIC CLAYS OF HIGH PLASTICITY OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY. ORGANIC SILTS HIGHLY ORGANIC SOILS T' ' ' ' ' ' PT PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS DUAL SYMBOLS are used to indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. Earth Solutions NW 1805 - 136th Place N.E., Suite 201 NNWBellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6693 DATE STARTED 4/30/19 COMPLETED 4/30/19 EXCAVATION CONTRACTOR NW Excavating, EXCAVATION METHOD LOGGED BY SES CHECKED BY SSR NOTES Depth of Topsoil & Sod 18": grass w }of U _ wg I— w TESTS = O z c� SM MC = 6.20% MC = 6.50% TEST PIT NUMBER TP-1 PAGE 1 OF 1 _ . PROJECT NAME Edmonds SP GROUND ELEVATION 408 ft TEST PIT SIZE GROUND WATER LEVELS: AT TIME OF EXCAVATION AT END END OF EXCAVATION --- AFTER EXCAVATION -- MATERIAL DESCRIPTION Brown silty SAND with gravel, medium dense, damp -becomes dense -becomes very dense MC = 8.30% 1116.0 [USDA Classification: gravelly sandy LOAM] Fines = 24.30% Test pit terminated at 6.0 feet below existing grade. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 6.0 feet. Earth Solutions NW TEST PIT NUMBER TP-2 1805 - 136th Place N.E., Suite 201 PAGE 1 OF 1 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6693 PROJECT NAME Edmonds SP DATE STARTED 4/30/19 COMPLETED 4/30/19 GROUND ELEVATION 400 ft TEST PIT SIZE EXCAVATION CONTRACTOR NW Excavating GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION -- LOGGED BY SES CHECKED BY SSR AT END OF EXCAVATION NOTES Surface Conditions: soil fill AFTER EXCAVATION --- w �Q�(6U ag TESTS O MATERIAL DESCRIPTION p d=) Z (� Q c o Brown silty SAND with gravel, medium dense, damp (Fill) MC = 9.40% SM (USDA Classification: very gravelly loamy SAND] Fines = 17.20% z o -topsoil/root horizon at 2' 398.0 Brown silty SAND with gravel, dense, damp 5 MC = 9.50% SM -becomes gray, very dense, moist, weakly cemented MC = 12.20% 9.0 391.0 Test pit terminated at 9.0 feet below existing grade. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 9.0 feet. Earth Solutions NW TEST PIT NUMBER TP-3 1805 - 136th Place N.E., Suite 201 ' ' I Bellevue, Washington 98005 PAGE 1 OF 1 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6693 PROJECT NAME Edmonds SP DATE STARTED 4/30/19 COMPLETED 4/30/19 GROUND ELEVATION 378 ft TEST PIT SIZE EXCAVATION CONTRACTOR NW Excavating GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION --- LOGGED BY SES CHECKED BY SSR AT END OF EXCAVATION NOTES Depth of Topsoil & Sod 3": grass AFTER EXCAVATION --- w U Lu ww TESTS 2 O MATERIAL DESCRIPTION o_ z Q Z C9 Cn 0 ° Brown silty GRAVEL with sand, medium dense, damp -root intrusions to 4' MC = 6.70% ° a Fines = 19.00% b [USDA Classification: very gravelly sandy LOAM] -becomes gray, dense, weakly cemented GM ° 5 - b MC = 10.70% ° ° -becomes moist MC = 14.70% a.o s7o.o Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 8.0 feet. Earth Solutions NW 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER E5-6693 W } m w z z w U tY Lu a U.S. SIETE OPENING IN INCHES I - �U.SSIEVE NUMBERS I HYDROMETER J1111 lllomillillismillilliom INS 11 il11111 11 INS NEIIIIIIINNIINIIINE 111i IN 111111 MENOMONEE INN 111111 111111111 liiiiiinmiiiiii INS iiiiiiinmi 0 lmiiiiiiimmiiii IN ME Millillism 1 111 liiiiiism 111111 0 INN 11111 INS I INN 1111111111 iiiiiiism I ismillillin GRAIN SIZE IN MILLIMETERS OB13LES GRAVEL �:E SAND SILT OR CLAY S pecimen Identification Classification TP-01 6.Oft. USDA: Gray Gravelly Sandy Loam. USCS: SM with Gravel. 1.5ft. USDA: Brown "e Gravelly Loamy Sand. USCS: SM with Gravel. Em 2.Oft. USDA: Brown Very Gravelly Sandy Loam. USCS: GM with Sand. GRAIN SIZE DISTRIBUTION W o Specimen Identification D100 I D90 D60 D30 D10 LL PL PI %Silt TP-01 6.Oft. 19 12.419 0.742 0.152 24.3 o m n TP-02 1.5ft. 19 14.007 1.948 0.218 17.2 L ♦ V TP-03 2.Oft. 37.5 29.154 5.926 0.234 19.0