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Report (13) rns--c-auct- OOl RECEIVED I`-‘` �� , FEB 7 2019 CITY OF TIGARD GeoP BUILDING DIVISION Engineering,Inc. Real-World Geotechnical Solutions Investigation•Design•Construction Support March 9, 2018 Project No. 17-4800 OFFICE COPY Nicholas Peets Lennar Northwest, Inc. 11807 NE 99th Street, Suite 1170 Vancouver, Washington 98682 Via email: Nicholas.PeetsLennar.com SUBJECT: GEOTECHNICAL INVESTIGATION TOUCHSTONE TOWNHOMES SW OAK STREET —TIS R1W SECTION 35AA TAX LOT 3800 TIGARD,WASHINGTON COUNTY, OREGON This report presents the results of a geotechnical engineering study conducted by GeoPacific Engineering, Inc. (GeoPacific)for the above-referenced project. The purpose of our investigation was to evaluate subsurface conditions at the site and to provide geotechnical recommendations for site development. This geotechnical study was performed in accordance with GeoPacific Proposal No. P-6318, dated December 7, 2017, and your subsequent authorization of our proposal and General Conditions for Geotechnical Services. SITE DESCRIPTION AND PROPOSED DEVELOPMENT The subject site is located off the north side of SW Oak Street in Tigard, Washington County, Oregon (Figure 1). The site is approximately 0.7 acres in size and topography is gently sloping to the southeast. The property is currently occupied by SW Akilean Terrace and SW Elena Lane, which were likely constructed during development of the property to the south. Vegetation consists primarily of short grasses (Figure 2). We understand that the proposed development will consist of 28 townhome units which will likely be constructed as 3 to 4 structures and associated underground utilities. The structures will likely be two to three stories in height. REGIONAL AND LOCAL GEOLOGIC SETTING Regionally, the subject site lies within the Willamette Valley/Puget Sound lowland, a broad structural depression situated between the Coast Range on the west and the Cascade Range on the east. A series of discontinuous faults subdivide the Willamette Valley into a mosaic of fault- bounded, structural blocks (Yeats et al., 1996). Uplifted structural blocks form bedrock highlands, while down-warped structural blocks form sedimentary basins. 14835 SW 72nd Avenue Tel(503)598-8445 Portland,Oregon 97224 Fax(503) 941-9281 Touchstone Townhomes Project No. 17-4800 The site is underlain by the Quaternary age(last 1.6 million years) Willamette Formation, a catastrophic flood deposit associated with repeated glacial outburst flooding of the Willamette Valley(Yeats et al., 1996). The last of these outburst floods occurred about 10,000 years ago. These deposits typically consist of horizontally layered, micaceous,silt to coarse sand forming poorly-defined to distinct beds less than 3 feet thick. Regional studies indicate that the thickness of the Willamette Formation in the vicinity of the subject site is less than 30 feet(Madin, 1990). Regional geologic mapping indicates the Willamette Formation is underlain by the Columbia River Basalt Formation (Gannett and Caldwell, 1998; Madin, 1990). The Miocene aged (about 14.5 to 16.5 million years ago) Columbia River Basalts are a thick sequence of lava flows which form the crystalline basement of the Tualatin Valley. The basalts are composed of dense,finely crystalline rock that is commonly fractured along blocky and columnar vertical joints. Individual basalt flow units typically range from 25 to 125 feet thick and inter-Flow zones are typically vesicular, scoriaceous, brecciated, and sometimes include sedimentary rocks. REGIONAL SEISMIC SETTING At least three major fault zones capable of generating damaging earthquakes are thought to exist in the vicinity of the subject site. These include the Portland Hills Fault Zone, the Gales Creek- Newberg-Mt. Angel Structural Zone, and the Cascadia Subduction Zone. Portland Hills Fault Zone The Portland Hills Fault Zone is a series of NW-trending faults that include the central Portland Hills Fault, the western Oatfield Fault, and the eastern East Bank Fault. These faults occur in a northwest-trending zone that varies in width between 3.5 and 5.0 miles. The combined three faults vertically displace the Columbia River Basalt by 1,130 feet and appear to control thickness changes in late Pleistocene (approx. 780,000 years)sediment(Madin, 1990). The Portland Hills Fault occurs along the Willamette River at the base of the Portland Hills, and is about 6.1 miles northeast of the site. The Oatfield Fault occurs along the western side of the Portland Hills, and is about 4 miles northeast of the site. The Oatfield Fault is considered to be potentially seismogenic(Wong, et al., 2000). Madin and Mabey(1996) indicate the Portland Hills Fault Zone has experienced Late Quaternary(last 780,000 years)fault movement; however, movement has not been detected in the last 20,000 years. The accuracy of the fault mapping is stated to be within 500 meters (Wong, et al., 2000). No historical seismicity is correlated with the mapped portion of the Portland Hills Fault Zone, but in 1991 a M3.5 earthquake occurred on a NW-trending shear plane located 1.3 miles east of the fault(Yelin, 1992). Although there is no definitive evidence of recent activity, the Portland Hills Fault Zone is assumed to be potentially active (Geomatrix Consultants, 1995). Gales Creek-Newberg-Mt. Angel Structural Zone The Gales Creek-Newberg-Mt. Angel Structural Zone is a 50-mile-long zone of discontinuous, NW- trending faults that lies about 14.2 miles southwest of the subject site. These faults are recognized in the subsurface by vertical separation of the Columbia River Basalt and offset seismic reflectors in the overlying basin sediment (Yeats et al., 1996; Werner et al., 1992). A geologic reconnaissance and photogeologic analysis study conducted for the Scoggins Dam site in the Tualatin Basin revealed no evidence of deformed geomorphic surfaces along the structural zone (Unruh et al., 1994). No seismicity has been recorded on the Gales Creek Fault or Newberg Fault(the fault closest to the subject site); however, these faults are considered to be potentially active because they may connect with the seismically active Mount Angel Fault and the rupture plane of the 1993 M5.6 Scotts Mills earthquake (Werner et al. 1992; Geomatrix Consultants, 1995). 4800-Touchstone Townhomes GR 2 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 Cascadia Subduction Zone The Cascadia Subduction Zone is a 680-mile-long zone of active tectonic convergence where oceanic crust of the Juan de Fuca Plate is subducting beneath the North American continent at a rate of 4 cm per year(Goldfinger et al., 1996). A growing body of geologic evidence suggests that prehistoric subduction zone earthquakes have occurred (Atwater, 1992; Carver, 1992; Peterson et al., 1993; Geomatrix Consultants, 1995). This evidence includes: (1)buried tidal marshes recording episodic, sudden subsidence along the coast of northern California, Oregon, and Washington, (2) burial of subsided tidal marshes by tsunami wave deposits, (3) paleoliquefaction features, and (4) geodetic uplift patterns on the Oregon coast. Radiocarbon dates on buried tidal marshes indicate a recurrence interval for major subduction zone earthquakes of 250 to 650 years with the last event occurring 300 years ago(Atwater, 1992; Carver, 1992; Peterson et al., 1993; Geomatrix Consultants, 1995). The inferred seismogenic portion of the plate interface lies roughly along the Oregon coast at depths of between 20 and 40 miles. FIELD EXPLORATION Our site-specific exploration for this report was conducted on December 28, 2017. A total of 3 exploratory test pits were excavated with a small sized trackhoe to depths of 8.5 to 10 feet. The approximate locations of the explorations are shown on Figure 2. It should be noted that exploration locations were located in the field by pacing or taping distances from apparent property corners and other site features shown on the plans provided. As such, the locations of the explorations should be considered approximate. A GeoPacific geologist continuously monitored the field exploration program and logged the explorations. Soils observed in the explorations were classified in general accordance with the Unified Soil Classification System (USCS). During exploration, our geologist also noted geotechnical conditions such as soil consistency, moisture and groundwater conditions. Logs of the test pits are attached to this report. The following report sections are based on the exploration program and summarize subsurface conditions encountered at the site. SUBSURFACE CONDITIONS Results of the field exploration program indicate the site is underlain by undocumented fill and soils belonging to the Willamette Formation. The observed soil and groundwater conditions are summarized below. Undocumented Fill—Undocumented fill was encountered in test pits TP-1 through TP-3. In test pits, the fill generally consisted of medium stiff to stiff, clayey silt(ML)with trace gravel. The fill extended to a depth of approximately 1.5 to 2.5 feet below the existing ground surface, as indicated on Figure 2. A thin, topsoil horizon with a low organic had developed at the ground surface. It is possible that other areas and thicker areas of fill may exist outside of our explorations - especially in the vicinity of the existing roadways. Willamette Formation—The fill in test pits TP-1 through TP-3 was directly underlain by soils belonging to the Willamette Formation. These soils typically consisted of stiff to very stiff clayey silt (ML) that exhibited subtle to strong orange and gray mottling. In test pits, soils belonging to the Willamette Formation extended beyond the maximum depth of exploration (10 feet). 4800-Touchstone Townhomes GR 3 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 Groundwater On December 28, 2017, soils encountered in test pits were moist. Neither static groundwater nor groundwater seepage was encountered in explorations to a maximum depth of 10 feet. Regional geologic mapping indicates that static groundwater is present at a depth of less than 20 feet below the existing ground surface (Snyder, 2008). Experience has shown that temporary perched storm- related groundwater conditions often occur within the surface soils over fine-grained native deposits such as those beneath the site, particularly during the wet season. It is anticipated that groundwater conditions will vary depending on the season, local subsurface conditions, changes in site utilization, and other factors. CONCLUSIONS AND RECOMMENDATIONS Results of this study indicate that the proposed development is geotechnically feasible, provided that the recommendations of this report are incorporated into the design and construction phases of the project. Our explorations indicate the soils on site are suitable for development utilizing conventional spread footing foundations. The primary geotechnical constraint to project development is the presence of undocumented fill. Fill was encountered in test pits TP-1 through TP-3 to depths of 1.5 to 2.5 feet below the ground surface. Site.Preparation Areas of proposed buildings, streets, and areas to receive fill should be cleared of vegetation and any organic and inorganic debris. Existing fill should be completely removed. Fill was encountered in all of our explorations conducted for this study and ranged in thickness from 1.5 to 2.5 feet. Other areas and thicker areas of fill may be encountered on site, especially in the vicinity of the existing roadways. Existing buried structures such as septic tanks, should be demolished and any cavities structurally backfilled. Inorganic debris should be removed from the site. Organic-rich topsoil should then be stripped from native soil areas of the site. The estimated depth range necessary for removal of topsoil in cut and fill areas is approximately 6 to 9 inches, respectively. The final depth of soil removal will be determined on the basis of a site inspection after the stripping/excavation has been performed. Stripped topsoil should preferably be removed from the site due to the high density of the proposed development. Any remaining topsoil should be stockpiled only in designated areas and stripping operations should be observed and documented by the geotechnical engineer or his representative. Once topsoil stripping and removal of organic and inorganic debris is approved in a particular area, the area must be ripped or tilled to a depth of 12 inches, moisture conditioned, root-picked, and compacted in-place prior to the placement of engineered fill or crushed aggregate base for pavement. Exposed subgrade soils should be evaluated by the geotechnical engineer. For large areas, this evaluation is normally performed by proof-rolling the exposed subgrade with a fully loaded scraper or dump truck. For smaller areas where access is restricted, the subgrade should be evaluated by probing the soil with a steel probe. Soft/loose soils identified during subgrade preparation should be compacted to a firm and unyielding condition, over-excavated and replaced with engineered fill (as described below), or stabilized with rock prior to placement of engineered fill. The depth of overexcavation, if required, should be evaluated by the geotechnical engineer at the time of construction. 4800-Touchstone Townhomes GR 4 GEOPACIFIC ENGINEERING, INC. Touchstone Townhomes Project No. 17-4800 Engineered Fill All grading for the proposed construction should be performed as engineered grading in accordance with the applicable building code at time of construction with the exceptions and additions noted herein. Proper test frequency and earthwork documentation usually requires daily observation and testing during stripping, rough grading, and placement of engineered fill. Imported fill material must be approved by the geotechnical engineer prior to being imported to the site. Oversize material greater than 6 inches in size should not be used within 3 feet of foundation footings, and material greater than 12 inches in diameter should not be used in engineered fill. Engineered fill should be compacted in horizontal lifts not exceeding 8 inches using standard compaction equipment. We recommend that engineered fill be compacted to at least 90% of the maximum dry density determined by ASTM D1557(Modified Proctor)or equivalent. Field density testing should conform to ASTM D2922 and D3017, or D1556. All engineered fill should be observed and tested by the project geotechnical engineer or his representative. Typically, one density test is performed for at least every 2 vertical feet of fill placed or every 500 yd3, whichever requires more testing. Because testing is performed on an on-call basis, we recommend that the earthwork contractor be held contractually responsible for test scheduling and frequency. Site earthwork will be impacted by soil moisture and shallow groundwater conditions. Earthwork in wet weather would likely require extensive use of cement or lime treatment, or other special measures, at considerable additional cost compared to earthwork performed under dry-weather conditions. Excavating Conditions and Utility Trenches We anticipate that on-site soils can be excavated using conventional heavy equipment such as trackhoes to a depth of at least 10 feet. All temporary cuts in excess of 4 feet in height should be sloped in accordance with U.S. Occupational Safety and Health Administration (OSHA) regulations (29 CFR Part 1926), or be shored. The existing native soil is classified as Type B Soil and temporary excavation side slope inclinations as steep as 1 H:1 V may be assumed for planning purposes. This cut slope inclination is applicable to excavations above the water table only. Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the contractor. Actual slope inclinations at the time of construction should be determined based on safety requirements and actual soil and groundwater conditions. Saturated soils and groundwater may be encountered in utility trenches, particularly during the wet season. We anticipate that dewatering systems consisting of ditches, sumps and pumps would be adequate for control of perched groundwater. Regardless of the dewatering system used, it should be installed and operated such that in-place soils are prevented from being removed along with the groundwater. Vibrations created by traffic and construction equipment may cause some caving and raveling of excavation walls. In such an event, lateral support for the excavation walls should be provided by the contractor to prevent loss of ground support and possible distress to existing or previously constructed structural improvements. PVC pipe should be installed in accordance with the procedures specified in ASTM D2321. We recommend that trench backfill be compacted to at least 95% of the maximum dry density obtained by Standard Proctor ASTM D698 or equivalent. Initial backfill lift thickness for a 3/"-0 crushed aggregate base may need to be as great as 4 feet to reduce the risk of flattening underlying flexible pipe. Subsequent lift thickness should not exceed 1 foot. If imported granular fill material is used, then the lifts for large vibrating plate-compaction equipment(e.g. hoe compactor attachments) may 4800-Touchstone Townhomes GR 5 GEOPACIFIC ENGINEERING, INC. Touchstone Townhomes Project No. 17-4800 be up to 2 feet, provided that proper compaction is being achieved and each lift is tested. Use of large vibrating compaction equipment should be carefully monitored near existing structures and improvements due to the potential for vibration-induced damage. Adequate density testing should be performed during construction to verify that the recommended relative compaction is achieved. Typically, one density test is taken for every 4 vertical feet of backfill on each 200-lineal-foot section of trench. Erosion Control Considerations During our field exploration program, we did not observe soil types that would be considered highly susceptible to erosion. In our opinion, the primary concern regarding erosion potential will occur during construction, in areas that have been stripped of vegetation. Erosion at the site during construction can be minimized by implementing the project erosion control plan, which should include judicious use of straw wattles and silt fences. If used, these erosion control devices should be in place and remain in place throughout site preparation and construction. Erosion and sedimentation of exposed soils can also be minimized by quickly re-vegetating exposed areas of soil, and by staging construction such that large areas of the project site are not denuded and exposed at the same time. Areas of exposed soil requiring immediate and/or temporary protection against exposure should be covered with either mulch or erosion control netting/blankets. Areas of exposed soil requiring permanent stabilization should be seeded with an approved grass seed mixture, or hydroseeded with an approved seed-mulch-fertilizer mixture. Wet Weather Earthwork Soils underlying the site are likely to be moisture sensitive and may be difficult to handle or traverse with construction equipment during periods of wet weather. Earthwork is typically most economical when performed under dry weather conditions. Earthwork performed during the wet- weather season will probably require expensive measures such as cement treatment or imported granular material to compact fill to the recommended engineering specifications. If earthwork is to be performed or fill is to be placed in wet weather or under wet conditions when soil moisture content is difficult to control, the following recommendations should be incorporated into the contract specifications. ➢ Earthwork should be performed in small areas to minimize exposure to wet weather. Excavation or the removal of unsuitable soils should be followed promptly by the placement and compaction of clean engineered fill. The size and type of construction equipment used may have to be limited to prevent soil disturbance. Under some circumstances, it may be necessary to excavate soils with a backhoe to minimize subgrade disturbance caused by equipment traffic; ➢ The ground surface within the construction area should be graded to promote run-off of surface water and to prevent the ponding of water; > Material used as engineered fill should consist of clean, granular soil containing less than 5 percent fines. The fines should be non-plastic. Alternatively, cement treatment of on-site soils may be performed to facilitate wet weather placement; ➢ The ground surface within the construction area should be sealed by a smooth drum vibratory roller, or equivalent, and under no circumstances should be left uncompacted and exposed to moisture. Soils which become too wet for compaction should be removed and replaced with clean granular materials; 4800-Touchstone Townhomes GR 6 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 ➢ Excavation and placement of fill should be observed by the geotechnical engineer to verify that all unsuitable materials are removed and suitable compaction and site drainage is achieved; and ➢ Geotextile silt fences, straw wattles, and fiber rolls should be strategically located to control erosion. If cement or lime treatment is used to facilitate wet weather construction, GeoPacific should be contacted to provide additional recommendations and field monitoring. Spread Foundations Based on our understanding of the proposed project and the results of our exploration program, and assuming our recommendations for site preparation are followed, native deposits and/or engineered fill soils should be encountered at or near the foundation level of the proposed structures. These soils are generally stiff to very stiff, and should provide adequate support of the structural loads. Shallow, conventional isolated or continuous spread footings may be used to support the proposed structures, provided they are founded on competent native soils, or compacted engineered fill placed directly upon the competent native soils. For footing subgrade soils at depths of 4 feet or less, we recommend maximum allowable bearing pressures of 1,500 pounds per square foot (psf). The recommended maximum allowable bearing pressures may be increased by 1/3 for short term transient conditions such as wind and seismic loading. All footings should be founded at least 18 inches below the lowest adjacent finished grade. Minimum footing widths should be determined by the project engineer/architect in accordance with applicable design codes. Assuming construction is accomplished as recommended herein, and for the foundation loads anticipated, we estimate total settlement of spread foundations of less than about 1 inch and differential settlement between two adjacent load-bearing components supported on competent soil of less than about%2 inch. We anticipate that the majority of the estimated settlement will occur during construction, as loads are applied. Wind, earthquakes, and unbalanced earth loads will subject the proposed structure to lateral forces. Lateral forces on a structure will be resisted by a combination of sliding resistance of its base or footing on the underlying soil and passive earth pressure against the buried portions of the structure. For use in design, a coefficient of friction of 0.42 may be assumed along the interface between the base of the footing and subgrade soils. Passive earth pressure for buried portions of structures may be calculated using an equivalent fluid weight of 320 pounds per cubic foot(pcf), assuming footings are cast against dense, natural soils or engineered fill. The recommended coefficient of friction and passive earth pressure values do not include a safety factor. The upper 12 inches of soil should be neglected in passive pressure computations unless it is protected by pavement or slabs on grade. Footing excavations should be trimmed neat and the bottom of the excavation should be carefully prepared. Loose, wet or otherwise softened soil should be removed from the footing excavation prior to placing reinforcing steel bars. The above foundation recommendations are for dry weather conditions. Due to the high moisture sensitivity of on-site soils, construction during wet weather may require overexcavation of footings and backfill with compacted, crushed aggregate. GeoPacific should observe foundation 4800-Touchstone Townhomes GR 7 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 excavations prior to placing formwork and reinforcing steel, to verify that adequate bearing soils have been reached. Concrete Slabs-on-Grade Preparation of areas beneath concrete slab-on-grade floors should be performed as recommended in the Site Preparation and Undocumented Fill Removal section. Care should be taken during excavation for foundations and floor slabs, to avoid disturbing subgrade soils. If subgrade soils have been adversely impacted by wet weather or otherwise disturbed,the surficial soils should be scarified to a minimum depth of 8 inches, moisture conditioned to within about 3 percent of optimum moisture content, and compacted to engineered fill specifications. Alternatively, disturbed soils may be removed and the removal zone backfilled with additional crushed rock. For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method, a modulus of subgrade reaction of 150 kcf(87 pci)should be assumed for the medium stiff native silt soils anticipated at subgrade depth. This value assumes the concrete slab system is designed and constructed as recommended herein, with a minimum thickness of crushed rock of 8 inches beneath the slab. Interior slab-on-grade floors should be provided with an adequate moisture break. The capillary break material should consist of ODOT open graded aggregate per ODOT Standard Specifications 02630-2. The minimum recommended thickness of capillary break materials on re-compacted soil subgrade is 8 inches. The total thickness of crushed aggregate will be dependent on the subgrade conditions at the time of construction, and should be verified visually by proof-rolling. Under-slab aggregate should be compacted to at least 90% of its maximum dry density as determined by ASTM D1557 or equivalent. In areas where moisture will be detrimental to floor coverings or equipment inside the proposed structure, appropriate vapor barrier and damp-proofing measures should be implemented. A commonly applied vapor barrier system consists of a 10-mil polyethylene vapor barrier placed directly over the capillary break material. Other damp/vapor barrier systems may also be feasible. Appropriate design professionals should be consulted regarding vapor barrier and damp proofing systems, ventilation, building material selection and mold prevention issues, which are outside GeoPacific's area of expertise. Drains The outside edge of perimeter walls should be provided with a drainage system consisting of 3-inch diameter, slotted, flexible plastic pipe embedded in a minimum of 1 ft3 per lineal foot of clean, free-draining gravel or 1 1/2"- 3/4"drain rock. The drain pipe and surrounding drain rock should be wrapped in non-woven geotextile(Mirafi 140N, or approved equivalent)to minimize the potential for clogging and/or ground loss due to piping. Water collected from the footing drains should be directed into the local storm drain system or other suitable outlet. A minimum 0.5 percent fall should be maintained throughout the drain and non-perforated pipe outlet. Down spouts and roof drains should not be connected to the foundation drains in order to reduce the potential for clogging. The footing drains should include clean-outs to allow periodic maintenance and inspection. Grades around the proposed structure should be sloped such that surface water drains away from the building. Footing drains are recommended to prevent detrimental effects of surface water runoff on foundations—not to dewater groundwater. Footing drains should not be expected to eliminate all potential sources of water entering a basement or beneath a slab-on-grade. An adequate grade to 4800-Touchstone Townhomes GR 8 GEOPACIFIC ENGINEERING, INC. Touchstone Townhomes Project No. 17-4800 a low point outlet drain in the crawlspace is required by code. Underslab drains are sometimes added beneath the slab when placed over soils of low permeability and shallow, perched groundwater. Seismic Design The Oregon Department of Geology and Mineral Industries(Dogami), Oregon HazVu: 2017 Statewide GeoHazards Viewer indicates that the site is in an area where severe ground shaking is anticipated during an earthquake (Dogami HazVu, 2017). Structures should be designed to resist earthquake loading in accordance with the methodology described in the 2015 International Building Code(IBC)with applicable Oregon Structural Specialty Code (OSSC) revisions (current 2014). We recommend Site Class D be used for design per the OSSC, Table 1613.5.2 and as defined in ASCE 7, Chapter 20, Table 20.3-1. Design values determined for the site using the USGS (United States Geological Survey)2017 Seismic Design Maps Summary Report are summarized in Table 1, and are based upon existing soil conditions. Table 1. Recommended Earthquake Ground Motion Parameters (2010 ASCE-7) Parameter Value Location (Lat, Long), degrees 45.445, -122.768 Mapped Spectral Acceleration Values(MCE): Peak Ground Acceleration PGAM 0.459 g Short Period, SS 0.984 g 1.0 Sec Period, S1 0.425 g Soil Factors for Site Class D: Fa 1.107 F, 1.575 SD,= 2/3XFaxSs 0.7268 SDI = 2/3xF„xS1 0.446g Seismic Design Category D Soil liquefaction is a phenomenon wherein saturated soil deposits temporarily lose strength and behave as a liquid in response to earthquake shaking. Soil liquefaction is generally limited to loose, granular soils located below the water table. According to the Oregon HazVu: Statewide Geohazards Viewer, the majority of the subject site is regionally characterized as having a high risk of soil liquefaction (DOGAMI:HazVu, 2018). Our explorations indicate liquefaction hazard in the upper 10 feet of soils is low; however, statewide hazard mapping indicates a high liquefaction hazard for the site. GeoPacific can further evaluate the effects of seismic induced liquefaction hazards such as vertical settlement and lateral deformation, if desired. We anticipate that our additional explorations on the site for the purpose of evaluating seismic hazards would include at least one cone penetrometer test and analysis. 4800-Touchstone Townhomes GR 9 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 UNCERTAINTIES AND LIMITATIONS We have prepared this report for the owner and their consultants for use in design of this project only. This report should be provided in its entirety to prospective contractors for bidding and estimating purposes; however, the conclusions and interpretations presented in this report should not be construed as a warranty of the subsurface conditions. Experience has shown that soil and groundwater conditions can vary significantly over small distances. Inconsistent conditions can occur between explorations that may not be detected by a geotechnical study. If, during future site operations, subsurface conditions are encountered which vary appreciably from those described herein, GeoPacific should be notified for review of the recommendations of this report, and revision of such if necessary. Sufficient geotechnical monitoring, testing and consultation should be provided during construction to confirm that the conditions encountered are consistent with those indicated by explorations. The checklist attached to this report outlines recommended geotechnical observations and testing for the project. Recommendations for design changes will be provided should conditions revealed during construction differ from those anticipated, and to verify that the geotechnical aspects of construction comply with the contract plans and specifications. Within the limitations of scope, schedule and budget, GeoPacific attempted to execute these services in accordance with generally accepted professional principles and practices in the fields of geotechnical engineering and engineering geology at the time the report was prepared. No warranty, expressed or implied, is made. The scope of our work did not include environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous or toxic substances in the soil, surface water, or groundwater at this site. We appreciate this opportunity to be of service. Sincerely, GEOPACIFIC ENGINEERING, INC. PIk1FS ki O: 1474 PE rai ORr*[V .1 li a it ii iiri'/ ! raft- �j►11T! OREGD a, ` '1. 0 S D.IMS °°RiN GO t-Re 1111 EXPIRES:06/30/200 Beth K. Rapp, C.E.G. James D. Imbrie, G.E., C.E.G. Senior Engineering Geologist Principal Geotechnical Engineer Attachments: References Figure 1 —Vicinity Map Figure 2—Site and Exploration Plan Test Pit Logs (TP-1 through TP-3) 4800-Touchstone Townhomes GR 10 GEOPACIFIC ENGINEERING,INC. Touchstone Townhomes Project No. 17-4800 REFERENCES Atwater, B.F., 1992, Geologic evidence for earthquakes during the past 2,000 years along the Copalis River, southern coastal Washington:Journal of Geophysical Research,v. 97, p. 1901-1919. Carver, G.A., 1992, Late Cenozoic tectonics of coastal northern California: American Association of Petroleum Geologists-SEPM Field Trip Guidebook, May, 1992. Gannett, M.W. and Caldwell, R.R., 1998, Geologic framework of the Willamette Lowland aquifer system, Oregon and Washington: U.S. Geological Survey Professional Paper 1424-A, 32 pages text, 8 plates. Geomatrix Consultants, 1995, Seismic Design Mapping, State of Oregon: unpublished report prepared for Oregon Department of Transportation, Personal Services Contract 11688. Goldfinger, C., KuIm, L.D., Yeats, R.S., Appelgate, B, MacKay, M.E., and Cochrane, G.R., 1996, Active strike-slip faulting and folding of the Cascadia Subduction-Zone plate boundary and forearc in central and northern Oregon: in Assessing earthquake hazards and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P.223-256. Madin, I.P., 1990, Earthquake hazard geology maps of the Portland metropolitan area, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report 0-90-2, scale 1:24,000, 22 p. Madin, I.P. and Mabey, M.A., 1996, Earthquake Hazard Maps for Oregon, Oregon: Oregon Department of Geology and Mineral Industries GMS-100. Oregon Department of Geology and Mineral Industries, 2018, Oregon HazVu: Statewide Geohazards Viewer (HazVu): https:t/gis.dogami.oregon.qov/hazvut Peterson, C.D., Darioenzo, M.E., Burns, S.F., and Burris, W.K., 1993, Field trip guide to Cascadia paleoseismic evidence along the northern California coast: evidence of subduction zone seismicity in the central Cascadia margin:Oregon Geology, v. 55, p. 99-144. Snyder, D.T., 2008, Estimated Depth to Ground Water and Configuration of the Water Table in the Portland, Oregon Area: U.S. Geological Survey Scientific Investigations Report 2008-5059, 41 p., 3 plates. United States Geologic Survey, 2018, U.S. Seismic Design Maps Online Tool, http://earthquake.usgs.govldesignmaps/uslapplication.php Unruh,J.R.,Wong, I.G., Bott,J.D., Silva,W.J., and Lettis,W.R., 1994, Seismotectonic evaluation:Scoggins Dam,Tualatin Project, Northwest Oregon: unpublished report by William Lettis and Associates and Woodward Clyde Federal Services, Oakland, CA,for U. S. Bureau of Reclamation,Denver CO (in Geomatrix Consultants, 1995). Werner, K.S., Nabelek, J., Yeats, R.S., Malone, S., 1992, The Mount Angel fault: implications of seismic- reflection data and the Woodburn, Oregon, earthquake sequence of August, 1990: Oregon Geology, v. 54, p. 112-117. Wong, I. Silva, W., Bott, J., Wright, D., Thomas, P., Gregor, N., Li., S., Mabey, M., Sojourner,A., and Wang, Y., 2000, Earthquake Scenario and Probabilistic Ground Shaking Maps for the Portland, Oregon; Metropolitan Area; State of Oregon Department of Geology and Mineral Industries; Interpretative Map Series IMS-16. Yeats, R.S., Graven, E.P., Werner, K.S., Goldfinger, C., and Popowski, T., 1996,Tectonics of the Willamette Valley, Oregon: in Assessing earthquake hazards and reducing risk in the Pacific Northwest, v. 1: U.S. Geological Survey Professional Paper 1560, P. 183-222, 5 plates, scale 1:100,000. Yelin, T.S., 1992, An earthquake swarm in the north Portland Hills (Oregon): More speculations on the seismotectonics of the Portland Basin: Geological Society of America, Programs with Abstracts, v. 24, no. 5, p. 92. 4800 Touchstone Townhomes GR 11 GEOPACIFIC ENGINEERING,INC. - p 14835 SW 7 ��r Portland,Oregon2ndAvenue 97224 VICINITY MAP Engineering.inc. Tel:(503)598-8445 Fax: (503)941-9281 . , „„,7 i il. "14 ...ignoi.p.,ef.,,„,, ,,,,,,,J,:z. 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Mi t 4006* . TP-3 atE ® '" I , North Legend Date:3/7/2018 Drawn b Test Pit Designation and 1 5, Depth of Undocumented 0 60' y:EKR T_1 6i Approximate Location Fill Encountered APPROXIMATE SCALE 1"=60' Project: Touchstone Townhomes Project No.17-4800 FIGURE 2 Tigard,Oregon -4134110"` 14835 SW 72nd Avenue GeoirePortland,Oregon 97224 TEST PIT LOG fllginee„„,,,, Tel: (503)598-8445 Fax:(503)941-9281 Project: Touchstone Townhomes Project No. 17-4800 Test Pit No. TP-1 Tigard, Oregon A C. F- c 3 N E o ° c n co m W e o a. a E o Material Description a. UJ U CO Stiff,clayey SILT(ML),trace gravel, light brown, subtle orange and gray mottling, trace roots, trace inorganic debris, 3 inch thick topsoil developed at 1 — 1.5 surface, moist(Undocumented Fill) 2— 2.5 3— 2.5 Stiff to very stiff, clayey SILT(ML), light brown to gray, micaceous, subtle to strong orange and gray mottling,trace fine roots throughout upper 3.5 feet,trace black staining, moist(Willamette Formation) 4 3.0 5 6— 7 8- 9— 10 rest Pit Terminated at 10 Feet. 11— Note: No seepage or groundwater encountered. 12—, LEGEND T1 Date Excavated: 12/28/2017 swift! % °�° Logged By: B. Rapp 1,000 g Bag Sample Bucket Sample Shelby Tube Sample Seepage Water Bearing Zane Water Level at Abandonment Surface Elevation: 14835 SW 72nd Avenue 6 a4i1[ Portland,Oregon 97224 TEST PIT t: ......... Tel: (503)598-8445 Fax:(503)941-9281 LOG Project: Touchstone Townhomes o1 Prject No. 17-4800 Tigard, Oregon Test Pit No. TP-2 , 0 - .. C Yw. T .. - �� E� H ��, � �N 0 owc a C II (7) mc' o 0- R a� 2 0 m Material Description (la CO ❑ U 1 1 1.5 Medium stiff to stiff, clayey SILT(ML), trace gravel up to 6 inches in diameter, light brown, subtle orange and gray mottling,trace roots, 5 inch thick topsoil developed at surface, moist(Undocumented Fill) 2 0.5 3 2.0 Stiff to very stiff, clayey SILT(ML), light brown to gray, micaceous,strong orange 4 2.5 and gray mottling, trace fine roots throughout upper 3 feet, trace black staining, moist(Willamette Formation) 5� 6—/ 7— --I 81 9— Test Pit Terminated at 8.5 Feet. 10-1Note: No seepage or groundwater encountered. 111 12 LEGEND A 7" Date Excavated: 12/28/2017 ioo. ,5 Gal — AA 7 7 'Logged By: B. Rapp 1,600 g Surface Elevation: Bag Sample Bucket Sample Shelby Tube Sample Seepage Water Bearing Zone Water Level at Abandonment 14835 SW 72nd Avenue GP rme Portland,Oregon 97224 TEST PIT LOG Eng nearing.int. Tel:(503)598-8445 Fax:(503)941-9281 Project: Touchstone Townhomes Project No. 17-4800 Test Pit No. TP-3 Tigard, Oregon it 4-En a N� m° o 0 022 a 9On CI)We 0 a. E, E z - il o ' Material Description a. en U m Medium stiff to stiff, clayey SILT(ML),trace gravel up to 4 inches in diameter, light brown,subtle orange and gray mottling,trace roots, 3 inch thick topsoil 1 11.0 developed at surface, moist(Undocumented Fill) 2.5 2 1.5 3 2.5 Stiff to very stiff, clayey SILT(ML), light brown to gray, micaceous, subtle orange 4-1 2.5 and gray mottling, trace fine roots throughout upper 3 feet, trace black staining, moist(Willamette Formation) 5— 6-1 7 8 9 Test Pit Terminated at 8.5 Feet. 10 Note: No seepage or groundwater encountered. 1 111 12— , LEGEND a Date Excavated: 12/28/2017 "`" 5 Gel, T a� got Logged By: B. Rapp 000 II A. 7 Surface Elevation: Bag Sample Bucket Sample Shelby Tube Sample Seepage Water Bearing Zone Water Level at Abandonment