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Geotech Evaluation.pdfJune 8, 2017 Updated March 23, 2018 ES-5264 Select Homes, Inc. 16531 —13th Avenue West, A107 Lynnwood, Washington 98037 Attention: Ms. Kayla Clark Subject: Geotechnical Evaluation Proposed Single -Family Residence 1122 Viewland Way Edmonds, Washington Reference: RAM Engineering, Inc. Preliminary Utility Plan March 14, 2018 Earth I Solutions N W «< Earth Solutions NW LLC • Geotechnical Engineering • Construction Monitoring • Environmental Sciences 7�_ GODUT��� Department of Ecology (DOE) 2012 Stormwater Management Manual for Western Washington (SMMWM) As Amended, December 2014 James P. Minard Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles Washington, 1983 Dear Ms. Clark: As requested, Earth Solutions NW, LLC (ESNW) has prepared geotechnical evaluation report for the proposed single-family residence. Our scope of services included subsurface investigation, engineering analysis, and preparation of this letter report with recommendations pertinent to the geotechnical aspects of the project. As part of the subsurface investigation, ESNW observed the excavation of two test pits on May 12, 2017. Proiect Description The subject site located at 1122 Viewland Way in Edmonds, Washington, as illustrated on the Vicinity Map (Plate 1). The site consists of one residential tax parcel, (Snohomish County parcel number 00548900001903) totaling approximately 0.46 acres of land area. The property is currently developed with a single-family residence and associated improvements. The majority of the site is relatively level; elevation changes two to four feet along the west and east property margins. The subject site is bordered to the north by Viewland Way, to west by Olympic Avenue, and to the east and south by residential structures. 1805 - 136th Place N.E., Suite 201 • Bellevue, WA 98005 0 (425) 449-4704 • FAX (425) 449-4711 Select Homes, Inc. June 8, 2017 Updated March 23, 2018 ES-5264 Page 2 Based on the site plan provided to us, a new single-family residential structure will be constructed at the subject site, improvements will also include underground utility installations. We anticipate grading activities will include cuts and fills to establish the planned building alignment. Based on the existing grades, we estimate cuts to establish building pad and foundation subgrade elevations will be on the order of up to five feet. However, grading plans were not available at the time this letter was prepared. At the time this letter was prepared, specific building load values were not available. However, we anticipate the proposed residential structure will consist of relatively lightly -loaded wood framing supported on conventional foundations. Based on our experience with similar developments, we estimate wall loads on the order of two kips per linear foot and slab -on -grade loading of 150 pounds per square foot (psf). If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this evaluation. ESNW should review the final design to verify the geotechnical recommendations provided in this letter have been incorporated into the plans. Subsurface Conditions As part of this geotechnical evaluation, An ESNW representative observed, logged, and sampled two test pits on May 12, 2017, excavated at accessible locations within the proposed development area, using a mini-trackhoe and operator provided by the client. The approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please refer to the test pit logs (attached) for a more detailed description of subsurface conditions. Representative soil samples collected at the test pit locations were analyzed in general accordance with the Unified Soil Classification System (USCS) and United States Department of Agriculture (USDA) methods and procedures. Topsoil and Fill Topsoil was observed extending to depths of approximately 4 to 6 inches below existing grades. The topsoil was characterized by dark brown color and fine organic material. Fill was encountered within both test locations extending to depths of two to five feet below the existing ground surface (bgs). The fill encountered attest pit location TP-1 was immediately underlain by the relic topsoil layer. Where fill is encountered during construction, ESNW should be consulted to verify the suitability for reuse as structural fill. Native Soil Underlying the topsoil and fill, soil conditions at the test pit locations were observed to consist of silty sand with gravel (Unified Soils Classification System: SM) deposits. The native soil deposits were generally observed to be in a medium dense condition beginning at depths of approximately three to five feet below existing grades. The native soils were observed to be in a dense condition beginning at depths of approximately five to six feet below existing grades, extending to the maximum exploration depth of about seven -and -one-half feet bgs. Earth Solutions NW, LLC Select Homes, Inc. June 8, 2017 Updated March 23, 2018 Geologic Setting ES-5264 Page 3 The referenced geologic map indicates the project location is underlain by Vashon advance outwash (Qva). The near -surface soil conditions observed at the test pit locations were generally not consistent with outwash soils. Groundwater Groundwater seepage was encountered at the time of our subsurface exploration at the test pit locations between depths of four -and -one-half to five feet below existing grades. The presence of groundwater seepage should be expected in excavations, especially in a perched condition at the contact between the fill and native soils. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater elevations and flow rates are higher during the winter, spring and early summer months. Critical Areas Based on our investigation and review of applicable codes, there are no critical areas (geologic) present on or adjacent to the site. Geotechnical Considerations Based on the results of our investigation, the proposed single-family structure can be supported on conventional spread and continuous footings bearing on undisturbed competent native soil or new structural fill placed on competent native soil. Based on our subsurface exploration, medium dense conditions suitable for foundation support are expected to be encountered beginning at depths of approximately three to five feet bgs. Existing fill and relic topsoil should be removed throughout footing subgrade areas. Removal of existing fill soils throughout slab subgrade areas should be evaluated by ESNW during construction. The soils encountered at the test pit locations generally have a high sensitivity to moisture based on the fines content of the soil. Compaction of the soil to the levels necessary for use as structural fill will be difficult during wet weather conditions. Structural fill should consist of suitable granular soils compacted to 95 percent of Modified Proctor (ASTM D1557), reuse of existing fill soils as structural fill should be evaluated by ESNW during construction. Provided the structure will be supported as described above, the following parameters can be used for design of the new foundations: • Allowable soil bearing capacity 2,500 psf • Passive earth pressure 300 pcf (equivalent fluid) • Coefficient of friction 0.40 A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind and seismic loading conditions. Earth Solutions NW, LLC Select Homes, Inc. June 8, 2017 Updated March 23, 2018 ES-5264 Page 4 With structural loading as expected, total settlement in the range of one inch is anticipated, with differential settlement of about one-half inch. The majority of the settlements should occur during construction, as dead loads are applied. Seismic Considerations The 2015 IBC recognizes ASCE for seismic site class definitions. In accordance with Table 20.3- 1 of ASCE, Minimum Design Loads for Buildings and Other Structures, Site Class D, should be used for design. In our opinion, the site is not susceptible to liquefaction. The native soil relative density and the absence of an established shallow groundwater table are the primary bases for this opinion. Drainage Surface grades must be designed to direct water away from the building. The grade adjacent to the building should be sloped away from the building at a gradient of at least 2 percent for a horizontal distance of at least four feet. In our opinion, perimeter footing drains should be installed at or below the invert of the building footings. On -site Stormwater Management Pursuant to City of Edmonds stormwater management requirements, implementation of on -site stormwater BMPs are required for proposed developments in accordance with specified thresholds, standards, and lists. The intent of BMP implementation is to infiltrate, disperse, and retain stormwater runoff on site to the extent feasible. The table below summarizes our evaluation of low impact development methods, as outlined in the referenced stormwater manual, from a geotechnical standpoint. It is instructed in the referenced stormwater manual that BMPs are to be considered in the order listed (from top to bottom) for each surface type, and the first BMP that is determined to be viable should be used. For completeness, however, we have evaluated each listed BMP for the proposed surface types. Earth Solutions NW, LLC Select Homes, Inc. June 8, 2017 Updated March 23, 2018 BMP Lawns and Landscaped Areas Limitations or Viable? ES-5264 Page 5 T5.13: Post -construction soil quality and depth Yes None. No slopes greater than 33 (Volume V, Chapter 5) percent are present. Roofs T5.30: Full dispersion (Volume V, Chapter 5) No The proposed project will not preserve at least 65 percent of the site. The existing fill and native soils T5.10A: Downspout full infiltration systems No observed at relatively shallow depths (Volume III, Chapter 3) generally exhibit very poor soil infiltration characteristics. The existing fill soils and native soil T7.30: Bioretention (Volume V, Chapter 7) No deposits observed at relatively shallow T5.14A: Rain Gardens (Volume V, Chapter 5) depths generally exhibit poor soil infiltration characteristics. No flooding or erosion impacts are T5.10B: Downspout dispersion systems Yes* anticipated. However, adequate (Volume III, Chapter 3) vegetative flow paths are likely not available. _ Perforated stub -out for Lot 2 should be T5.10C: Perforated stub -out connections Yes setback at least 25 feet from Lot 1 due (Volume III, Chapter 3) to the grade transition. Other Hard Surfaces No critical areas and/or buffers are present. No flooding or erosion T5.30: Full dispersion (Volume V, Chapter 5) No impacts are anticipated. However, adequate vegetative flow paths are likely not available. The upper existing fill soil and T5.15: Permeable pavement (Volume V, No underlying low to very low permeability native soils adjacent to sloped Chapter 5) topography indicate infeasibility of permeable pavement. _ _ The existing fill soils and native soil T7.30: Bioretention (Volume V, Chapter 7) NO deposits observed at relatively shallow T5.14A: Rain Gardens (Volume V, Chapter 5) depths generally exhibit poor soil infiltration characteristics. Sheet flow dispersion and T5.12: Sheet flow dispersion concentrated flow dispersion may be T5.11: Concentrated flow dispersion (Volume Yes* feasible, however, proper setbacks V, Chapter 5) and vegetated flow paths may not be available. *Viability is stated from a geotechnical standpoint, available flowpaths and setbacks will ultimately determine viability. Earth Solutions NW, LLC Select Homes, Inc. ES-5264 June 8, 2017 Page 6 Updated March 23, 2018 Small -Scale Stormwater Facility Feasibility We understand that a small-scale stormwater facility (tank or pipe) may be installed in lieu of detention vault construction. Provided competent native soil is used for stability and/or foundation purposes, it is our opinion installation of a smaller -scale tank or pipe will likely be feasible from a geotechnical standpoint. ESNW should be provided the opportunity to review stormwater tank and/or pipe design as project plans develop to ensure appropriate geotechnical considerations have been incorporated. Supplementary recormendations may be provided at the appropriate phase of design, where necessary. Utility Support and Trench Backfill In our opinion, the native soils anticipated to be exposed in utility excavations should generally be considered suitable for support of utilities. Organic or highly compressible soils encountered in the trench excavations should not be used for supporting utilities. The native soils should generally be suitable for use as structural trench backfill. Moisture conditioning of the soils will likely be necessary prior to use as structural backfill; reuse of existing fill soils should be evaluated by ESNW during construction. Utility trench backfill should be placed and compacted to 95 percent of the modified proctor, or to the presiding jurisdiction specifications. Limitations The recommendations and conclusions provided in this geotechnical evaluation 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 pit locations may exist, and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical evaluation letter if variations are encountered. Earth Solutions NW, LLC Select Homes, Inc. June 8, 2017 Updated March 23, 2018 ES-5264 Page 7 Should you require additional information, or have questions, please call. Sincerely, EARTH SOLUTIONS NW, LLC Adam Z. Shier, G.I.T. Staff Geologist Attachments: Plate 1 - Vicinity Map Plate 2 - Test Pit Location Plan Test Pit Logs Grain Size Distribution Henry T. Wright, P.E. Senior Project Engineer cc: RAM Engineering, Inc. Attention: Mr. Rob Long, P.E. (Email only) Earth Solutions NW, LLC 17 f .x•�2i� µ�7�G iB ww2 �s�d-. � ..! j� C f • � � Y fpl lira VA fill r. COL Mjt:TLtwill tot H1 Tiv 1 g� L'fu� � . I'�t firow ,btllir_li_ ry E� IrHR itUt. - ! r < � � � -•—'^� gun t, Igl!�1 s1. 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ESNW cannot be Drwn. MRS Date 05/26/2017 Proj. No. 5264 responsible for any subsequent misinterpretation of the information resulting from black & white reproductions of this plate. Checked AZS Date May 2017 Plate 1 LEGEND TP-1 I Approximate Location of — ■ — ESNW Test Pit, Proj. No. ES-5264, May 2017 Subject Site L—_J 0 25 50 100 1 "=50'- u u Scale in Feet 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. u� Q IN Earth 1 Solutions NWric: I- - - - - - - - - - VIEWLAND WAY �I1wil Test Pit Location Plan 1122 Viewland Way Edmonds, Washington Drwn. MRS Date 05/30/2017 Proj. No. 5264 Checked AZS Date May 2017 Plate 2 Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL DESCRIPTIONS GRAPH LETTER GRAVEL AND CLEAN GRAVELS qr q! • !ft.' 4011.400FINES GW WELL -GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO ° Q° ; Q° o ODo 0 Q (:3 °Q GP POORLY -GRADED GRAVELS, GRAVEL -SAND MIXTURES, LITTLE OR NO FINES GRAVELLY SOILS (LITTLE OR NO FINES) COARSE GRAINED SOILS MORE THAN OF COARSEE GRAVELS WITH FINES Q ° ° 0 GM SILTY GRAVELS, GRAVEL -SAND - SILT MIXTURES FRACTION ro 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 SC 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 - - - - - - - OL ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% OF MATERIAL IS SMALLER THAN NO.200 SIEVE MH INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS FINE SAND OR SLTY SOILS slzE SILTS LIQUID LIMIT AND CLAYS GREATER THAN50 CH INORGANIC CLAYS OF HIGH PLASTICITY OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS . �. �� 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 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425- 494711 CLIENT Select Homes, Inc. PROJECT NUMBER 5264 DATE STARTED 5/12/17 COMPLETED 5/12/17 EXCAVATION CONTRACTOR Select Homes EXCAVATION METHOD LOGGED BY AZS CHECKED BY HTW NOTES Depth of Topsoil & Sod 4": dress W 0. _ W rn 2 w _jg TESTS �O CL a z c� N TEST PIT NUMBER TP-1 PAGE 1 OF 1 PROJECT NAME 1122 Viewland Way PROJECT LOCATION Edmonds, Washington GROUND ELEVATION TEST PIT SIZE GROUND WATER LEVELS: AT TIME OF EXCAVATION AT END OF EXCAVATION AFTER EXCAVATION --- MATERIAL DESCRIPTION moist (Fill) TOPSOIL PS ,, ,, ,, 3.0 Brown silty SAND with gravel, medium dense, moist MC = 15.80% 5 -light groundwater seepage SM -iron oxide staining MC = 16.80% [USDA Classification: gravelly sandy LOAM] Fines = 35.00% -becomes wet, dense MC = 13.40% 7'0 Test pit terminated at 7.0 feet below existing grade. Groundwater seepage encountered at 4.5 feet during excavation. Caving observed from TOH to 2.0 feet. Bottom of test pit at 7.0 feet. J m J W Z w C7 Earth Solutions NW 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-149-4711 CLIENT Select Homes, Inc. PROJECT NUMBER 5264 DATE STARTED 5/12/17 COMPLETED 5/12/17 EXCAVATION CONTRACTOR Select Homes`_ EXCAVATION METHOD LOGGED BY AZS CHECKED BY HTW NOTES Depth of Topsoil $ Sod 6": grass w a. �Lu U 2 w TESTS Cd O � ¢ TEST PIT NUMBER TP-2 PAGE 1 OF 1 PROJECT NAME 1122 Viewland Way PROJECT LOCATION Edmonds, Washington GROUND ELEVATION TEST PIT SIZE GROUND WATER LEVELS: AT TIME OF EXCAVATION AT END OF EXCAVATION — AFTER EXCAVATION — MATERIAL DESCRIPTION pSL o 5 Dark brown TOPSOIL Brown silty SAND, medium dense, moist (Fill) MC = 23.10% Fines = 6.80% [USDA Classification: gravelly loamy SAND] SM 5 5.0 -light groundwater seepage at 5' Gray silty SAND, medium dense to dense, wet MC = 27.80% SM MC = 19.00% 5 [USDA Classification: slightly gravelly sandy LOAM] Fines = 35.00% Test pit terminated at 7.5 feet below existing grade. Groundwater seepage encountered at 5.0 feet during excavation. Caving observed from 5.0 to 6.5 feet. Bottom of test pit at 7.5 feet. Earth Solutions NW, ,LLC 1805 - 136th PL N.ESuite 201 GRAIN SIZE DISTRIBUTION Su Bellevue, WA 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME 1122 Viewland Way PROJECT NUMBER ES-5264 PROJECT LOCATION Edmonds U.S. SIEVE OPENING IN INCHES I U.S. SIEVE NUMBERS I HYDROMETER 6 4 3 2 1.5 1 U 1123/8 3 4 6 810 1416 20 30 40 50 60 100 140 200 100 I I IFi 1 1 1 95 90 85 80 75 — - 70 — — 65 — w 60 55 — — — — m o' 50 - z I- 45 — Z w 40 o- 35 — - — -- 30 25 20 — 15— 10 — 5 - L_[ 0 100 10 1 0.1 0.01 U 00 GRAIN SIZE IN MILLIMETERS COBBLES GRAVEL SAND SILT OR CLAY coarse fine coarse I medium fine _ —I Specimen Identification Classification Cc CU • TP-1 6.00ft. USDA: Tan Gravelly Sandy Loam. USCS: SM with Gravel. E TP-2 2.00ft. USDA: Brown Gravelly Loamy Sand. USCS: SM. A TP-2 7.50ft. USDA: Gray Slightly Gravelly Sandy Loam. USCS: SM. Specimen Identification D100 D60 D30 D10 LL PL PI %Silt %Clay TP-1 6.Oft. 19 0.365 0.105 24.4 m TP-2 2.011. 19 0." 0.165 16.8 TP-2 7.511. 19 0.253 35.0