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geotechnical report (4)South Sound Geotechnical Consulting P.O. Box 39500, Lakewood, WA 98496 (253) 973-0515 June 16, 2022 Mr. Matt Weber c/o AHBL 2215 North 30th Street, Suite 200 Tacoma, Washington 98403-3350 Subject: Geotechnical Engineering Report The Summit at Thompson Creek 14444 Berry Valley Road Yelm, Washington SSGC Project No. 22029 Mr. Weber, South Sound Geotechnical Consulting (SSGC) has completed a geotechnical assessment for the planned development at the above addressed property in Yelm, Washington. Our services have been completed in general conformance with our proposal P21150 (dated March 31, 2022) and authorized per signature of our agreement for services. Our scope of services included completion of twenty test pits and one infiltration test on the site, laboratory testing, engineering analyses, and preparation of this report. PROJECT INFORMATION The site is composed of several individual parcels totaling about 30 acres, west of the current terminus of Berry Valley Road. Development plans include dividing the properties into 93 individual single-family lots. SITE CONDITIONS The eastern portion of the site is lower in elevation and generally level. This area is grass field. The western portion is characterized by a southwest-northeast trending knoll. An existing residence and several outbuildings are in the eastern side of the western portion. The remainder of the western portion is undeveloped and partially forested. Overall elevation change across the site is on the order of 70 (+/-) feet from the highest point on the knoll in the western portion to the lower eastern portion of the site. Elevation change in the western portion is on the order of 50 feet (+/-). SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing twenty test pits and one infiltration test on April 14, 2022. Explorations were advanced to final depths between 2.5 and 11 feet below existing ground surface. Approximate locations of the explorations are shown on Figure 1, Exploration Plan. A summary description of observed subgrade conditions is provided below. Logs of the test holes are provided in Appendix A. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 2 Soil Conditions Topsoil and isolated fill was at the surface of the test pits and extended to depths between 6 inches and 2.5 feet. Native soils below the topsoil/fill varied across the site. In general, the lower eastern portion contains loose sandy gravel with cobbles, occasional boulders and minor fines. These soils are considered to be outwash deposits and extended to the termination depth of the test holes in this area. Native soils in the western portion consisted of upper layers of soft to stiff clayey silt (interpreted as glacial lake deposits) or outwash over glacial till/drift consisting of silty sand with gravel and variable cobbles. Upper soils extended to depths from less than 1 foot to about 5 feet. Till/drift was in a medium dense grading to very dense condition and extended to the termination depth of the test pits, where encountered. Groundwater Conditions Groundwater was observed in test pit TP-17 (adjacent infiltration test PIT-1 in the lower eastern portion) near Thompson Creek at an elevation of about 7 feet at the time of excavation. Seepage was observed in several of the test pits in the western portion above the glacial till/drift. Groundwater levels and seepage will vary throughout the year due to seasonal precipitation and on- and off-site drainage patterns. Geologic Setting Soil types mapped on the site per the USDA Soil Conservation Service map of Thurston County consist of both glacial outwash and glacial drift. Outwash soils are generally mapped in the lower eastern portion of the site, with drift in the higher western portion. Native soils appear to generally conform to the mapped soil types. GEOTECHNICAL DESIGN CONSIDERATIONS The planned development is considered feasible based on observed soil conditions in the test pits. Properly prepared native soils are considered suitable for support of conventional spread footing foundations, slab- on-grade floors, and conventional pavements. Native (outwash) soils are suitable for infiltration, where encountered. Soils with higher fines content and drift/till are predominant in the higher elevated western portion. These soils will limit infiltration facilities to shallow dispersion or detention systems. Infiltration is not feasible in the silty (lake deposits) or dense drift/till soils. Depth to seasonally high groundwater levels should be considered in the design of infiltration facilities in the lower eastern portion. We anticipate grading (cuts and fills) will be used to modify existing topography for final design grades of the development, particularly in the western portion. Final grades should be considered relative to the feasibility of infiltration systems. Recommendations presented in the following sections should be considered general and may require modifications when earthwork and grading occur. They are based upon the subsurface conditions observed Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 3 in the test pits and the assumption that finish site grades will be similar to existing grades. It should be noted that subsurface conditions across the site may vary from those depicted on the exploration logs and can change with time. Therefore, proper site preparation will depend upon the weather and soil conditions encountered at the time of construction. We recommend SSGC review final plans and assess subgrade conditions at the time of construction. General Site Preparation Site grading and earthwork should include procedures to control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soils, resulting in increased export of impacted soil and import of fill materials, thereby potentially increasing the cost of the earthwork and subgrade preparation phases of the project. Site grading should include removal of all fill and any organic materials in future building and pavement areas. Subgrades should consist of firm native soils following stripping. Final stripping depths can only be determined at the time of earthwork. General Subgrade Preparation Subgrades in building and pavement areas should consist of firm native soil or compacted structural fill. We recommend exposed subgrades in building and conventional pavement areas are proofrolled using a large roller, loaded dump truck, or other mechanical equipment to assess subgrade conditions following stripping. Proofrolling efforts should result in the upper 1 foot of subgrade soils achievin g a firm and unyielding condition and a compaction level of at least 92 percent of the maximum dry density (MDD) per the ASTM D1557 test method. Wet, loose, or soft subgrades that cannot achieve this compaction level should be removed (over-excavated) and replaced with structural fill. The depth of over-excavation should be based on soil conditions at the time of construction. A representative of SSGC should be present to assess subgrade conditions during proofrolling. Grading and Drainage Positive drainage should be provided during construction and maintained throughout the life of the development. Surface water should not be allowed into cut/fill areas, utility trenches, building footprints, or pavement areas. Structural Fill Materials The suitability of soil for use as structural fill will depend on the gradation and moisture content of the soil when it is placed. Soils with higher fines content (soil fraction passing the U.S. No. 200 sieve) will become sensitive with higher moisture content. It is often difficult to achieve adequate compaction if soil moisture is outside of optimum ranges for soils that contain more than about 5 percent fines. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 4 Site Soils: Topsoil is not considered suitable for structural fill and should be wasted from the site or used in landscape areas. The clayey silt and glacial till/drift will be difficult to use due to higher fines content of these soils. Native outwash soil is generally considered suitable for use as structural. Soils with higher fines content could be used provided they can be moisture conditioned to within optimal ranges. Silt content will vary in the native soils and can make them moisture sensitive, requiring conditioning (drying or wetting) to obtain optimum moisture content. Optimum moisture is considered within about +/- 2 percent of the moisture content required to achieve the maximum density per the ASTM D-1557 test method. Import Fill Materials: We recommend imported structural fill placed during dry weather consist of material which meets the specifications for Gravel Borrow as described in Section 9-03.14(1) of the Washington State Department of Transportation (WSDOT) Specifications for Road, Bridge, and Municipal Construction manual (Publication M41-10). Gravel Borrow should be protected from disturbance if exposed to wet conditions after placement. During wet weather, or for backfill on wet subgrades, import soil suitable for compaction in wetter conditions should be provided. Imported fill for use in wet conditions should conform to specifications for Select Borrow as described in Section 9-03.14(2), or Crushed Surfacing per Section 9-03.9(3) of the WSDOT M41-10 manual, with the modification that a maximum of 5 percent by weight shall pass the U.S. No. 200 sieve for these soil types. Structural fill placement and compaction is weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend site grading and earthwork be scheduled for the drier months of the year. Structural fill should not consist of frozen material. Structural Fill Placement We recommend structural fill is placed in lifts not exceeding about 10 inches in loose measure. It may be necessary to adjust lift thickness based on site and fill conditions, and type of compaction equipment used during placement and compaction. Finer grained soil used as structural fill and/or lighter weight compaction equipment may require significantly thinner lifts to attain required compaction levels. Coarser granular soil with lower fines contents could potentially be placed in thicker lifts (1 foot maximum) if they can be adequately compacted. Structural fill should be compacted to attain the recommended levels presented in Table 1, Compaction Criteria. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 5 Table 1. Compaction Criteria Fill Application Compaction Criteria* Footing areas (below structures and retaining walls) 95 % Upper 2 feet in pavement areas, slabs and sidewalks, and utility trenches 95 % Below 2 feet in pavement areas, slabs and sidewalks, and utility trenches 92 % Utility trenches or general fill in non-paved or -building areas 90 % *Per the ASTM D 1557 test method. Trench backfill within about 2 feet of utility lines should not be over-compacted to reduce the risk of damage to the line. In some instances the top of the utility line may be within 2 feet of the surface. Backfill in these circumstances should be compacted to a firm and unyielding condition. We recommend fill procedures include maintaining grades that promote drainage and do not allow ponding of water within the fill area. The contractor should protect compacted fill subgrades from disturbance during wet weather. In the event of rain during structural fill placement, the exposed fill surface should be allowed to dry prior to placement of additional fill. Alternatively, the we t soil can be removed. We recommend consideration be given to protecting haul routes and other high traffic areas with free-draining granular fill material (i.e. sand and gravel containing less than 5 percent fines) or quarry spalls to reduce the potential for disturbance to the subgrade during inclement weather. Structural fill placed on sloping ground should be constructed using a benched (stairstep) methodology. Benches should be cut level or with a slight downward incline into the slope in firm native soil. Benches should be at least 3 feet wide and wide enough to accommodate compaction equipment, and be a maximum of two feet high. Earthwork Procedures Conventional earthmoving equipment should be suitable for earthwork at this site. Earthwork may be difficult during periods of wet weather or if elevated soil moisture is present. Excavated site soils may not be suitable as structural fill depending on the soil moisture content and weather condit ions at the time of earthwork. If soils are stockpiled and wet weather is anticipated, the stockpile should be protected with securely anchored plastic sheeting. If stockpiled soils become unusable, it may become necessary to import clean, granular soils to complete wet weather site work. Wet or disturbed subgrade soils should be over-excavated to expose firm, non-yielding, non-organic soils and backfilled with compacted structural fill. We recommend the earthwork portion of this project be completed during extended periods of dry weather. If earthwork is completed during the wet season (typically late October through May) it may be necessary to take extra measures to protect subgrade soils. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 6 If earthwork takes place during freezing conditions, we recommend the exposed subgrade be allowed to thaw and be re-compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen soil can be removed to unfrozen soil and replaced with structural fill. The contractor is responsible for designing and constructing stable, temporary excavations (such as utility trenches) to maintain stability of excavation sides and bottoms. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. Temporary excavation cuts should be sloped at inclinations of 1.5H:1V (Horizontal:Vertical) or flatter, unless the contractor can demonstrate the safety of steeper inclinations. Deeper excavations may require shoring. Permanent cut and fill slopes should be graded at inclinations of 2H:1V, or flatter. A geotechnical engineer and accredited testing material laboratory should be retained during the construction phase of the project to observe earthwork operations and to perform necessary tests and observations during subgrade preparation, placement and compaction of structural fill, and backfilling of excavations. Foundations Foundations can be placed on native soils or on structural fill above prepared native subgrades as described in this report. The following recommendations are for conventional spread footing foundations: Bearing Capacity (net allowable): 2,000 pounds per square foot (psf) for footings supported firm native soils or structural fill over native subgrades prepared as described in this report. Footing Width (Minimum): 18 inches (Strip) 24 inches (Column) Embedment Depth (Minimum): 18 inches (Exterior) 12 inches (Interior) Settlement: Total: < 1 inch Differential: < 1/2 inch (over 30 feet) Allowable Lateral Passive Resistance: 300 psf/ft* (below 18 inches) Allowable Coefficient of Friction: 0.35* *These values include a factor of safety of approximately 1.5. The net allowable bearing pressures presented above may be increased by one-third to resist transient, dynamic loads such as wind or seismic forces. Lateral resistance to footings should be ignored in the upper 12-inches from exterior finish grade. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 7 Foundation Construction Considerations All foundation subgrades should be free of water and loose soil prior to placing concrete, and should be prepared as recommended in this report. Concrete should be placed soon after excavating and compaction to reduce disturbance to bearing soils. Should soils at foundation level become excessively dry, disturbed, saturated, or frozen, the affected soil should be removed prior to placing concrete. We recommend SSGC observe all foundation subgrades prior to placement of concrete. Foundation Drainage Ground surface adjacent foundations should be sloped away from buildings. We recommend footing drains are installed around perimeter footings. Footing drains should include a minimum 4-inch diameter perforated rigid plastic or metal drain line installed at the base of the footing. The perforated drain lines should be connected to a tight line pipe that discharges to an approved storm drain receptor. The drain line should be surrounded by a zone of clean, free-draining granular material having less than 5 percent passing the No. 200 sieve or meeting the requirements of section 9-03.12(2) “Gravel Backfill for Walls” in the WSDOT M41-10 manual. The free-draining aggregate zone should be at least 12 inches wide and wrapped in filter fabric. The granular fill should extend to within 6 inches of final grade where it should be capped with compacted fill containing sufficient fines to reduce infiltration of surface water into the footing drains. Alternately, the ground surface can be paved with asphalt or concrete. Cleanouts are recommended for maintenance of the drain system. On-Grade Floor Slabs On-grade floor slabs should be placed on native soils or structural fill prepared as described in this report. We recommend a modulus subgrade reaction of 150 pounds per square inch per inch (psi/in) for native soil or compacted granular structural fill over native soil. We recommend a capillary break is provided between the prepared subgrade and bottom of slab. Capillary break material should be a minimum of 4 inches thick and consist of compacted clean, free-draining, well graded course sand and gravel. The capillary break material should contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve. Alternatively, a clean angular gravel such as No. 7 aggregate per Section 9-03.1(4) C of the WSDOT (M41-10) manual could be used for this purpose. We recommend positive separations and/or isolation joints are provided between slabs and foundations, and columns or utility lines to allow independent movement where needed. Backfill in interior trenches beneath slabs should be compacted in accordance with recommendations presented in this report. A vapor retarder should be considered beneath concrete slabs that will be covered with moisture sensitive or impervious coverings (such as tile, wood, etc.), or when the slab will support equipment or stored materials sensitive to moisture. We recommend the slab designer refer to ACI 302 and/or ACI 360 for procedures and limitations regarding the use and placement of vapor retarders. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 8 Seismic Considerations Seismic parameters and values in Table 2 are recommended based on the 2015 International Building Code (IBC). Table 2. Seismic Parameters PARAMETER VALUE 2018 International Building Code (IBC) Site Classification1 D Ss Spectral Acceleration for a Short Period 1.39 S1 Spectral Acceleration for a 1-Second Period 0.521g 1 Note: In general accordance with the 2018 International Building Code for risk categories I,II,III. IBC Site Class is based on the estimated characteristics of the upper 100 feet of the subsurface profile. Ss, and S1 values based on the OSHPD Seismic Design Maps website. Liquefaction Soil liquefaction is a condition where loose, typically granular soils located below the groundwater surface lose strength during ground shaking, and is often associated with earthquakes. The risk of liquefaction at this site is low for the design level earthquake based on the Thurston County Liquefaction Hazard Map, dated April 2011. A site-specific liquefaction analyses was not part of our scope and would be required to fully assess liquefaction potential and impacts. Infiltration Characteristics Infiltration facilities will be used to assist in control of stormwater, where feasible. An assessment of infiltration potential of the outwash in the lower eastern portion of the site was completed by performing one Pilot Infiltration Test per procedures in the Thurston County Drainage Design and Erosion Control Manual. Results of the test is presented in Table 3. Table 3. Infiltration Rates Sample ID and Depth (ft) Soil Type Measured Infiltration Rate (in/hr) Corrected Infiltration Rate (in/hr) Correction Factors* (Fg/Ft/Fp) PIT-1, 3 ft Outwash 62 28 (1.0/0.5/0.9) *Correction Factors from the Thurston County Drainage Design and Erosion Control Manual. The measured infiltration rate is considered appropriate for the soil tested and are similar to infiltration tests completed at other sites with similar soil throughout Thurston County. We recommend a design infiltration rate of 28 inches per hour (in/hr) for native outwash soils. However, groundwater was encountered at about Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 9 7 feet below the surface in this area and should be considered in the design of infiltration facilities. Infiltration in the clayey silt and till soils is not considered feasible. Additional infiltration assessment may be necessary in other portions of the site to assess infiltration potential once final grades have been established. Cation Exchange Capacity (CEC) and organic content tests were completed on samples of the outwash soil. Test results are summarized in the table below. Table 4. CEC and Organic Content Results Test Site, Sample Number, Depth CEC Results (milliequivalents) CEC Required* (milliequivalents) Organic Content Results (%) Organic Content Required* (%) TP-1, S-1, 3 ft 13.3 ≥ 5 5.30 ≥1.0 PIT-1, S-1, 3 ft 13.5 5.45 * Values from the Thurston County Drainage Design and Erosion Control Manual. Organic content and CEC results of the tested samples satisfy County requirements. Conventional Pavement Sections Subgrades for conventional pavements should be prepared as described in the “Subgrade Preparation” and “Structural Fill” sections of this report. Subgrades below pavement sections should be graded or crowned to promote drainage and not allow for ponding of water beneath the section. If drainage is not provided and ponding occurs, subgrade soils could become saturated, lose strength, and result in premature distress or failure of the section. In addition, the pavement surfacing should also be graded to promote drainage and reduce the potential for ponding of water on the pavement surface. We recommend a separation fabric (such as Mirafi N180, or other) is placed on roads underlain by clayey silt subgrades prior to placement of pavement section materials. The purpose of the fabric is to maintain segregation of the coarser fill and the lower finer grained native soil. Coarser fill will have the tendency to migrate into the looser native soil over time which can compromise the structural integrity of the pavement section fill and result in premature distress in the pavement without the separation fabric. Separation fabric is not considered necessary in roadways underlain by till or outwash. Minimum recommended pavement sections for conventional asphalt or concrete pavements are presented in Table 5. Pavement sections in public right-of-ways should be designed per City of Yelm (or Thurston County) standards. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 10 Table 5. Preliminary Pavement Sections Traffic Area Minimum Recommended Pavement Section Thickness (inches) Asphalt Concrete Surface1 Portland Cement Concrete2 Aggregate Base Course3,4 Subbase Aggregate5 Driveways 2 4 4 12 Access Roads 3 6 6 12 1 1/2 –inch nominal aggregate hot-mix asphalt (HMA) per WSDOT 9-03.8(1) 2 A 28 day minimum compressive strength of 4,000 psi and an allowable flexural strength of at least 250 psi 3 Crushed Surfacing Base Course per WSDOT 9-03.9(3) 4Although not required for structural support under concrete pavements, a minimum four-inch thick base course layer is recommended to help reduce potentials for slab curl, shrinkage cracking, and subgrade “pumping” through joints 5 Gravel Borrow per WSDOT 9-03.14(1) or Permeable Ballast WSDOT 9-03.9(1) or native soil compacted to 95% of ASTM D-1557 Conventional Pavement Maintenance The performance and lifespan of pavements can be significantly impacted by future maintenance. The above pavement sections represent minimum recommended thicknesses and, as such, periodic maintenance should be completed. Proper maintenance will slow the rate of pavement deterioration, and will improve pavement performance and life. Preventive maintenance consists of both localized maintenance (crack and joint sealing and patching) and global maintenance (surface sealing). Added maintenance measures and reduced pavement life should be anticipated over the lifetime of pavements if any existing fill or topsoil is left in-place beneath pavement sections. REPORT CONDITIONS This report has been prepared for the exclusive use of Mr. Matt Weber for specific application to the project discussed, and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or implied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the site, or due to the modifying effects of construction, or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. This report was prepared for the planned type of development of the site as discussed herein. It is not valid for third party entities or alternate types of development on the site without the express written consent of Geotechnical Engineering Report The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 SSGC SSGC. If development plans change we should be notified to review those changes and modify our recommendations as necessary. The scope of services for this project does not include any environmental or biological assessment of the site including identification or prevention of pollutants, hazardous materials, or conditions. Other studies should be completed if the owner is concerned about the potential for contamination or pollution. We appreciate the opportunity to work with you on this project. Please contact us if additional information is required or we can be of further assistance. Respectfully, South Sound GeoteMchnical Consulting RO Timothy H. Roberts, P.E. Member/Geotechnical Engineer Attachments: Figure 1 — Exploration Plan Appendix A — Field Exploration Procedures and Test Pit Logs Appendix B — Laboratory Testing and Results Unified Soil Classification System TP-1 South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1 – Exploration Plan The Summit at Thompson Creek Yelm, WA SSGC Project #22029 Base map from sheet drawing titled “Preliminary Site Plan - The Summit at Thompson Creek ”, by Informed AHBL, dated 3-16-22. N Legend Approximate Test Pit Location No Scale PIT - 1 PIT - 1 Approximate Infiltration Test Location TP-10 TP-4 TP-1 TP-5 TP-6 TP-3 TP-2 TP-9 TP-8 TP-11 TP-12 TP-13 TP-14 TP-15 TP-16 TP-17 TP-18 TP-19 TP-20 TP-7 Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 Appendix A Field Exploration Procedures and Test Pit Logs Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 A-1 Field Exploration Procedures Our field exploration for this project included twenty test pits and one Pilot Infiltration Test completed on April 14, 2022. The approximate locations of the explorations are shown on Figure 1, Exploration Plan. Test pit locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from topographic data from Google Earth satellite imagery and the Thurston County GIS. Test pit locations and elevations should be considered accurate only to the degree implied by the means and methods used. A private excavation company dug the test pits. Soil samples were collected and stored in moisture tight containers for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note that backfill in the explorations may settle with time. Backfill material located in roads or building areas should be re-excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the explorations at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 1 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-1 Depth (feet) Material Description 0 – 1 1 – 4.5 4.5 – 5 Topsoil Fine to coarse sandy GRAVEL with some cobbles: Loose, moist, brown. (GP)(Glacial Outwash)(Sample S-1 @ 3 feet) Silty SAND with some gravel and a few cobbles: Medium dense, moist, gray. (SM) (Glacial Till). Test pit completed at approximately 5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 380 feet Test Pit TP-2 Depth (feet) Material Description 0 – 1 1 – 4.5 4.5 – 5.5 Topsoil Clayey SILT/Silty CLAY with some fine gravel: Soft to stiff, moist, mottled reddish brown to gray. (ML/CL) (Glacial Lake Deposits). Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 5.5 feet on 4/14/22. Slight seepage at 4 feet at time of excavation. Approximate surface elevation: 360 feet. Test Pit TP-3 Depth (feet) Material Description 0 – 1.0 1.0 – 4.5 4.5 – 5.5 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, moist, brown grading gray. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, gray. (SM) (Glacial Till). Test pit completed at approximately 5.5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 360 feet Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 2 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-4 Depth (feet) Material Description 0 – 1 1 – 3 3 – 4 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, moist, brown grading gray. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, gray. (SM) (Glacial Till). Test pit completed at approximately 4 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 365 feet Test Pit TP-5 Depth (feet) Material Description 0 – 1 1 – 4 4 – 5.5 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, moist, reddish brown. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, gray. (SM) (Glacial Till). Test pit completed at approximately 5.5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 380 feet Test Pit TP-6 Depth (feet) Material Description 0 – 0.5 0.5 – 1.5 1.5 – 2.5 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, moist, reddish brown. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 2.5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 395 feet Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 3 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-7 Depth (feet) Material Description 0 – 2.5 2.5 – 4 4 – 4.5 Topsoil/fill Organic silt, sand, gravel: Loose, moist dark brown. Silty SAND with gravel and some cobbles: Medium dense to dense, moist, mottled brown to gray. (SM) (Weathered Glacial Till). Silty SAND with gravel and cobbles: Dense to very dense, moist, gray, massive. (SM) (Glacial Till) Test pit completed at approximately 4.5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 380 feet Test Pit TP-8 Depth (feet) Material Description 0 – 0.5 0.5 – 4 Topsoil Silty SAND with gravel and a few cobbles: Medium dense to dense, moist, brown grading gray. (SM) (Glacial Till). Test pit completed at approximately 4 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 360 feet. Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 4 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-9 Depth (feet) Material Description 0 – 0.5 0.5 – 4 4 – 5 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, dry to moist, light brown grading gray. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 360 feet Test Pit TP-10 Depth (feet) Material Description 0 – 0.5 0.5 – 5 5 – 5.5 Topsoil Sandy GRAVEL with trace to some silt and occasional cobble: Loose, dry to moist, light brown grading gray. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 5.5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 360 feet Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 5 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-11 Depth (feet) Material Description 0 – 0.5 0.5 – 3 3 – 5 5 – 6 Topsoil Fine to coarse sandy GRAVEL and a few cobbles grades medium to coarse gravelly fine to medium sand at 2.0-3.0 feet: Loose, moist, brown. (SP/GP). (Outwash) Fine to medium SAND with a trace of gravel: Loose, moist, gray. (SP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 6 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 358 feet Test Pit TP-12 Depth (feet) Material Description 0 – 0.5 0.5 – 3.5 3.5 – 4 Topsoil Clayey SILT/Silty CLAY with some fine gravel: Soft to stiff, moist, reddish brown grading to gray at 4.0 feet (ML/CL) (Glacial Lake Deposits). Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 4 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 350 feet Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 6 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-13 Depth (feet) Material Description 0 – 0.5 0.5 – 2 2 – 5.5 Topsoil SILT with variable clay and fine gravel: Soft to stiff, moist, reddish brown grading to gray at 4.0 feet (ML) (Glacial Lake Deposits). Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 5.5 feet on 4/14/22. Moderate seepage at 2 feet observed at time of excavation. Approximate surface elevation: 350 feet Test Pit TP-14 Depth (feet) Material Description 0 – 0.5 0.5 – 5 5 – 6 Topsoil SILT with variable clay and fine gravel: Soft to stiff, moist, reddish brown grading to gray at 4.0 feet (ML) (Glacial Lake Deposits). Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 6 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 355 feet. Test Pit TP-15 Depth (feet) Material Description 0 – 0.5 0.5 – 4 4 – 5 Topsoil Sandy GRAVEL with some cobbles and a few boulders: Loose, dry to moist, light brown grading to gray at 3.0 feet. (GP) (Outwash) Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 5 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 355 feet Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 7 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-16 Depth (feet) Material Description 0 – 0.5 0.5 – 6 6 – 7 Topsoil SILT with variable clay and fine gravel: Soft to stiff, moist, reddish brown grading to gray at 4.0 feet (ML) (Glacial Lake Deposits). Silty SAND with gravel and a few cobbles: Dense, moist, brownish gray. (SM) (Glacial Till). Test pit completed at approximately 7 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 380 feet. Test Pit TP-17 Depth (feet) Material Description 0 – 0.5 0.5 – 11 Topsoil Cobbly fine to coarse GRAVEL with sand: Loose to medium dense, moist to wet, black grading to light brown below 3.0 feet. (GP) (Outwash) Test pit completed at approximately 11 feet on 4/14/22. Groundwater and sloughing observed at 7 feet at time of excavation. Approximate surface elevation: 335 feet. Test Pit TP-18 Depth (feet) Material Description 0 – 0.5 0.5 – 10 Topsoil Medium to coarse sandy GRAVEL with cobbles and boulders: Loose to medium dense, moist to wet at 9 feet, black grading to light brown below 3.0 feet. (GP) (Outwash). Test pit completed at approximately 10 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 335 feet. Project: Summit at Thompson Creek SSGC Job # 22029 EXPLORATION LOGS PAGE 8 OF 8 Location: 14444 Berry Valley Rd, Yelm, WA EXPLORATION LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 to TP-20, PIT-1 Logged by: THR Test Pit TP-19 Depth (feet) Material Description 0 – 0.5 0.5 – 8 Topsoil Medium to coarse sandy GRAVEL with cobbles and boulders: Loose, moist, black grading to light brown below 3.0 feet. (GP) (Outwash). Test pit completed at approximately 8 feet on 4/14/22. Groundwater not observed at time of excavation. Approximate surface elevation: 340 feet. Test Pit TP-20 Depth (feet) Material Description 0 – 0.5 0.5 – 5.0 Topsoil Medium to coarse sandy GRAVEL with cobbles and boulders: Loose, moist, black grading to light brown below 3.0 feet. (GP) (Outwash). Test pit completed at approximately 5 feet on 4/14/22 due to caving. Groundwater not observed at time of the excavation. Approximate surface elevation: 340 feet. Infiltration Test PIT-1 Depth (feet) Material Description 0 – 0.5 0.5 – 5 Topsoil Cobbly fine to coarse GRAVEL with boulders with some sand: Loose, moist, black grading to light brown below 3.0 feet. (GP) (Glacial Outwash) (Sample S-1 @ 3 feet). Test hole completed at approximately 5 feet on 4/14/22. Groundwater not observed at time of excavation. Infiltration test completed at 3 feet. Approximate surface elevation: 335 feet. Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 Appendix B Laboratory Testing and Results Geotechnical Engineering Report SSGC The Summit at Thompson Creek Yelm, Washington SSGC Project No. 22029 June 16, 2022 B-1 Laboratory Testing Select soil samples were tested for organic content and cation exchange capacity (CEC) by Northwest Agricultural Consultants of Kennewick, Washington. Results of the laboratory testing are included in this appendix. 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity Pit-1, S-1 5.45% 13.5 meq/100g TP-1, S-1 5.30% 13.3 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 59040-1-1 Date: April 25, 2022 Project No: 22029 Project Name: Berry Valley UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu  4 and 1  Cc  3E GW Well-graded gravelF Cu  4 and/or 1  Cc  3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu  6 and 1  Cc  3E SW Well-graded sandI Cu  6 and/or 1  Cc  3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI  7 and plots on or above “A” lineJ CL Lean clayK,L,M PI  4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried  0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried  0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 2 30 DxD )(D F If soil contains  15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains  15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains  30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains  30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI  4 and plots on or above “A” line. O PI  4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line.