Geotechnical Engineering Report Proposed Household Hazardous Waste Facility Astoria, Oregon

Transcription

1 Proposed Household Hazardous Waste Facility Prepared for: Mr. Michael Summers, Director Clatsop County Public Works 1100 Olney Avenue 97103

2 Geotechnical Engineering Report Proposed Household Hazardous Waste Facility Prepared for: Mr. Michael Summers Director Clatsop County Public Works 1100 Olney Avenue Prepared by: Timothy J. North, PE Project Engineer Reviewed by: Saiid Behboodi, PE, GE Principal Geotechnical Engineer This document was prepared for use only by the client, only for the purposes stated, and within a reasonable time from issuance, but in no event later than one year from the date of the report. Non-commercial, educational, and scientific use of this report by regulatory agencies is regarded as a fair use and not a violation of copyright. Regulatory agencies may make additional copies of this document for internal use. Copies may also be made available to the public as required by law. The reprint must acknowledge the copyright and indicate that permission to reprint has been received.

3 TABLE OF CONTENTS 1.0 INTRODUCTION General Purpose and Scope Geologic Map Review Subsurface Exploration Soils Testing Geotechnical Engineering Analysis Report Preparation Field Explorations Project Understanding SITE CONDITIONS Surface Description Geologic Setting Subsurface Soils Groundwater CONCLUSIONS AND RECOMMENDATIONS Geotechnical Design Considerations Foundation Alternatives Surcharge, Gravel Mat, and Spread Footings Deep Foundations Floor Slabs Ground Moisture General Vapor Flow Retarder Pavement Design Seismic Design Criteria CONSTRUCTION RECOMMENDATIONS Site Preparation Proofrolling/Subgrade Verification Subgrade Protection Wet-Weather/Wet-Soil Conditions Excavation Structural Fill On-Site Soil Borrow Material Select Granular Fill Crushed Aggregate Base Course Trench Backfill Stabilization Material ADDITIONAL SERVICES AND CONSTRUCTION OBSERVATIONS LIMITATIONS REFERENCES i

4 SUPPORTING DATA Figures Figure 1 Vicinity Map Figure 2 Site Plan Appendix A Field Explorations Table A-1 Terminology to Describe Soil Table A-2 Key to Test Pit and Boring Log Symbols Figures A1 A2 Logs for Borings B-1 and B-2 Figures A3 A6 Logs for Test Pits, TP-1 through TP-4 Appendix B Laboratory Testing Figure B1 Atterberg Limits Test Results ii

5 1.0 INTRODUCTION 1.1 General This report presents the results of the PBS Engineering and Environmental Inc. (PBS) geotechnical engineering services for the proposed new household hazardous waste facility in (site). The proposed new facility will include an approximate 2,500-square-foot- (sf), wood- or steel-frame, manufactured building, and a new three-lane driveway entrance to receive household waste. The location of our work and our explorations in relation to existing site features are shown on the Vicinity Map and Site Plan, Figures 1 and 2, respectively. 1.2 Purpose and Scope The purpose of our services was to develop geotechnical design and construction recommendations in support of the planned new facility. This was accomplished by performing the following scope of services Geologic Map Review Relevant geologic maps of the site area were reviewed for information regarding geologic conditions and hazards at or near the site. We also reviewed previously completed geotechnical reports for adjacent sites Subsurface Exploration Two borings were drilled to depths ranging from about 31.5 to 41.5 feet below the existing ground surface (bgs) in the vicinity of the proposed receiving building footprint. Additionally, four test pits were excavated within the vicinity of the proposed driveway area, each to a depth of about 8 feet bgs. The borings and test pits were logged and representative soil samples were collected by a member of the PBS geotechnical engineering staff Soils Testing All samples were returned to our laboratory and classified in general accordance with the Unified Soil Classification, Visual-Manual Procedure. Laboratory tests included natural moisture contents and Atterberg limits testing. Laboratory test results are included in the attached Appendix B Laboratory Testing Geotechnical Engineering Analysis Data collected during the subsurface exploration, literature research, and testing were used to develop site-specific geotechnical design parameters and construction recommendations Report Preparation This Geotechnical Engineering Report summarizes the results of our explorations and analyses, including information related to the following: Exploration logs Laboratory test results Earthwork and grading, cut, and fill recommendations structural fill and utility trench backfill materials and preparation wet weather/conditions considerations utility trench excavation and backfill requirements Groundwater considerations 1

6 Shallow foundation design recommendations: minimum embedment allowable bearing pressure estimated settlement and sliding coefficient Deep foundation design recommendations (if necessary): minimum pile length and embedment allowable axial (compression and uplift) and lateral capacities estimated settlement construction recommendations Suggested pavement sections for the new parking areas Slab and pavement subgrade preparation Seismic design criteria in accordance with the 2014 Oregon Structural Specialty Code (OSSC). 1.3 Field Explorations PBS completed two borings within the vicinity of the proposed receiving building. The borings, designated as B-1 and B-2, were advanced to depths of about 31.5 and 41.5 feet bgs, respectively. The drilling was performed by Hardcore Drilling, Inc. of Dundee, Oregon using a truck-mounted drill rig. PBS also completed four test pits within the vicinity of the proposed parking expansion area. The test pits, designated as TP-1 through TP-4, were each excavated to a depth of about 8 feet bgs. The test pits were excavated by Dan J. Fischer Excavating of Forest Grove, Oregon using a tracked mini-excavator. The borings and test pits were logged and representative soil samples were collected by a member of the PBS geotechnical engineering staff. The approximate exploration locations are shown on the Figure 2. Field exploration methods and interpreted boring and test pit logs are presented in Appendix A Field Explorations, attached at the back of this report. 1.4 Project Understanding Based on our conversation with Mr. Summers on April 16, 2014, we understand that the proposed new facility will be located west of the new Astoria Athletic Fields Complex (AAFC) on an approximate one acre site. The proposed development will include construction of a new 2,500-square-foot receiving building and a new three-lane driveway entrance to accommodate waiting vehicles. In the past, a portion of the site was used as a dump site for municipal waste. The site is underlain by waste, characterized for this report, as debris fill. Previous investigations at nearby sites within the dump area have found the debris fill to be mixed with varying amounts of soil. The thickness of the debris fill is expected to range from approximately 5 to 30 feet in thickness. In places, a thin layer of clay has been placed as a cap material for the landfill. The purpose of our services was to explore subsurface conditions at the site to develop geotechnical recommendations for the design and construction of the proposed new building and parking/driveway improvements. 2

7 2.0 SITE CONDITIONS 2.1 Surface Description The project site is located west of the unpaved Bonneville Powerline Road: an access road off Williamsport Road in. The site is bound to the north by an existing waste transfer facility operated by Recology Western Oregon, to the east by Bonneville Powerline Road, and to the south and west by undeveloped, heavily vegetated property. The area of the proposed new building and drive lanes is currently unused, but has previously functioned as a construction staging area for the adjacent new AAFC on the east side of Bonneville Powerline Road. As a staging area, the site has been leveled and surfaced with a thin layer of aggregate and stabilization rock. 2.2 Geologic Setting According to published geologic mapping of the site area (Niem & Niem, 1985), the site is underlain by Tertiay (lower Miocene to upper Eocene) mudstone of the Young s Bay Member (Tay) of the Astoria Formation. 2.3 Subsurface Soils PBS has summarized the subsurface units encountered as follows: FILL: LANDFILL DEBRIS: SILTY CLAY: WEATHERED SILTSTONE/ CLAYSTONE: In borings B-1, B-2, and all test pits undocumented, fill was encountered at the ground surface. This fill typically consisted of medium dense, silty gravel overlying medium stiff, silty clay. The silty gravel, encountered in B-1, TP-1, TP-2 and TP-3 to depths ranging from 3 to 8 feet, was likely placed during site grading activities in preparation for the site s current use as a staging area. The silty clay, encountered in B-2, TP-1 and TP-4 in thicknesses of about 2 to 3 feet, was likely placed atop landfill debris to function as a cap material. In borings B-1 and B-2, as well as all the test pits, highly variable debris fill was encountered below the gravel and clay fill at depths ranging from about 3 to 8 feet bgs. The site has a long history of use as a dump site. The landfill debris was found in the test pits to be intermixed with clayey sand and silt soil, with the debris content estimated to range from approximately 30 to 80 percent. Debris observed in the test pits and drill cuttings included cloth, plastic, glass and metal fragments. No samples were collected of the landfill debris. Silty clay was encountered in boring B-2 from approximately 20 to 35 feet bgs. The silty clay was soft to medium stiff, gray-yellow to gray-orange, with high plasticity. In borings B-1 and B-2, gray, stiff to hard, silty clay (weathered siltstone/claystone bedrock) was encountered at depths ranging from approximately 15.0 feet bgs in B-1 in the west to approximately 35.0 feet bgs in B-2 in the east within the proposed new building footprint. We believe that this unit is consistent with the mapped Young s Bay Member of the Astoria Formation. 3

8 2.3.2 Groundwater Static groundwater was not observed at the time of our explorations. We recommend that the contractor determine the actual groundwater levels at the time of construction to determine potential groundwater impact on the construction. 3.0 CONCLUSIONS AND RECOMMENDATIONS 3.1 Geotechnical Design Considerations The project site is underlain by undocumented fill, including a sandy gravel layer overlying clay fill and highly variable landfill debris to depths ranging from approximately 15 to 20 feet bgs. In addition, soft to medium stiff, high plasticity, silty clay alluvium was encountered below the proposed building footprint at depths ranging from 20 to 35 feet bgs. Consequently, conventional foundation support on shallow spread footings is not feasible without some form of mitigation and consideration of risk. For the purpose of our evaluation, we have considered three options for foundation support, each of which has different levels of risk associated with settlement due to both short- and long-term consolidation and decomposition. The following sections provide a detailed discussion of our analysis and recommendations. 3.2 Foundation Alternatives The soils at the site present several challenges for support of the proposed facility. The site is underlain by both compressible, fine-grained soils and decomposing debris fills (trash). Due to their relative thickness, resulting differential settlement could affect footings, mats, and slabs on grade. Despite the challenges of supporting foundations on the overlying soils, the underlying deeper, stiff, decomposed claystone soils would provide relatively competent support for deep foundations, which could extend to depths greater than 40 feet bgs. PBS developed two different foundation alternatives which are discussed in the paragraphs that follow. 1. Improve the compressible subsurface soils with soil improvement in the form of surcharging, and then found shallow foundations on a gravel mat 2. Deep foundations The use of isolated shallow spread footings without soil improvement is not considered feasible due to potential for total and differential settlement from consolidation and decomposition of the underlying landfill debris. Footings supported on improved, pre-consolidated soils, compacted granular mat, or piles can be used to support the proposed facilities, each with a different level of risk of damage. PBS also recommends raising the proposed finish grade about two to three feet above the existing subgrade elevation, using compacted crushed rock with the thickness depending upon whether shallow spread footings or deep foundations are selected to support the building Surcharge, Gravel Mat, and Spread Footings The risk of future differential settlement can be reduced by surcharging the soils within the building footprint prior to construction of the planned foundations. Our recommendations for the surcharge loading of the building footprint are as follows. The surcharge should be at least 8 feet high, extending 5 feet outside the limits of the building footprint. 4

9 The surcharge should have side slopes of 1H:1V (horizontal to vertical) or flatter. The surcharge material should consist of granular material, such as local pit run rock having a unit weight of no less than 115 pounds per cubic foot (pcf), in place on the fill. Four settlement monitoring points, in the form of settlement plates, should be set into the mass. PBS can provide details for settlement plate locations and installation upon your request. Settlement points should be surveyed every week for the first month and then monthly thereafter, the resulting data should be provided to us. The surcharge should be left in place at least 3 to 4 months and should not be removed until estimated remaining settlements (as determined by PBS) would be within acceptable limits. PBS performed a review of surcharge settlement for surcharging at the adjacent AAFC prior to construction. Based on the settlement observed AAFC under similar surcharge loading conditions, the thickness of the landfill debris layer encountered, and the composition of the landfill debris, PBS anticipates surcharge settlement at this site over the recommended minimum of 3 to 4 months surcharge period will be in the range of approximately ¼ to 4 inches. Using surcharging to pre-consolidate the subsurface profile prior to foundation construction, would allow for the use of shallow spread footings to support the proposed, relatively lightweight building. Because surcharging the building footprint does not remove the potential for settlement due to decomposition of the debris fill layer, PBS also recommends that a building pad consisting of three feet of crushed rock be placed, and that all footings be founded within the structural fill. The crushed rock building pad should be composed of material and prepared as specified in the Select Granular Fill section of this report. Additionally, we recommend all footings be connected with grade beams. Specific recommendations for design and construction of both footings and grade beams are included in the following sections. Footing Preparation Excavations for footings should be carefully prepared. A representative from PBS should confirm suitable bearing conditions and evaluate all footing subgrades. Observations should also confirm that loose or soft materials have been removed from new footing excavations and concrete slabs-on-grade areas. Localized deepening of footing excavations may be required to penetrate soft, wet, or deleterious materials. Footing subgrades should be compacted following excavation with multiple, overlapping passes of a vibratory-plate compactor. Footing Embedment Depths PBS recommends that all footings be founded a minimum of 18 inches below the lowest adjacent grade, and that there be at least 18 inches of compacted crushed rock beneath the footing. The footings should be founded below an imaginary line projecting upward at a 1H:1V slope from the base of any adjacent parallel utility trenches, or deeper excavations. 5

10 Footing Widths/Bearing Pressure Continuous wall and isolated spread footings should be at least 18 and 24 inches wide, respectively. Footings should bear on a minimum of 18 inches of crushed rock as discussed in the previous section, and should be sized using a maximum allowable bearing pressure of 1,500 pounds per square foot (psf). This is a net bearing pressure and the weight of the footing and overlying backfill can be disregarded in calculating footing sizes. The recommended allowable bearing pressure applies to the total of dead plus long-term live loads. Allowable bearing pressures may be increased by one-third for seismic and wind loads. Foundation Static Settlement Footings will settle in response to column and wall loads. Based on our evaluation of the subsurface conditions and our analysis, PBS expects long-term post-construction settlement will be less than two inches for the column and perimeter foundation loads. Lateral Resistance Lateral loads can be resisted by passive earth pressure on the sides of footings and grade beams, and by friction at the base of the footings. A passive earth pressure of 250 pounds per cubic foot (pcf) may be used for footings confined by new structural fills. The allowable passive pressure has been reduced by one half to account for the large amount of deformation required to mobilize full passive resistance. Adjacent floor slabs, pavements, or the upper 12-inch depth of adjacent unpaved areas should not be considered when calculating passive resistance. For footings supported on new structural fills, use a coefficient of friction equal to 0.4 when calculating resistance to sliding. These values do not include a factor of safety (FS). Grade Beams Grade beams are not intended to vertically support column footings, but to help hold the facility structure together during a design level earthquake and reduce the overall settlement impacts due to decaying of the landfill debris. Grade beams between footings should be designed in accordance with the requirements of the 2012 International Building Code (IBC) Section Deep Foundations The impacts from short- and long-term settlement of the foundations can be reduced by supporting the new facilities on deep foundations. Deep foundations would penetrate through the compressible and decomposing soils and landfill debris, deriving their support from the underlying stiff, decomposed claystone. Based on the estimated loading of the proposed new structure, PBS recommends that deep foundations for the proposed building, if used, consist of drilled helical piles, driven pin piles, or drilled and cased micropiles. Supporting facilities on deep foundations will reduce settlement of the building resulting from debris fill decomposition, but will not provide vertical support for on-grade slabs (unless specifically designed and supported in such a way). Advantages of pile foundations include: Ability to support the structures when penetrating soft soils Reduced static and differential building foundation settlement Disadvantages of pile foundations include: 6

11 Differential settlement between pile-supported facilities and utilities or non-pile supported structures, such as the floor slab-on-grade. Requires specialty construction equipment and an experienced contractor Specific recommendations for design and construction of deep foundations are included in the following sections. Axial Capacity Helical piles, pin piles, or micropiles can be used to obtain foundation support for the more competent, native soils present below the debris. These pile alternatives would have capacities on the order of 20 to 50 kips and be on the order 35 to 50 feet long. The helical pile, pin pile, and micropile foundation elements should be connected to the foundation structures by way of pile caps. The subgrade below the pile caps and grade beams should be prepared in accordance with recommendations presented in the Excavations" and Select Granular Fill sections of this report. PBS will work with you, your design team, and contractor to develop recommendations for construction if you select to incorporate deep foundation support. Additional consulting will be required to provide adequate information for design. 3.3 Floor Slabs Satisfactory subgrade support for building floor slabs can be obtained from the existing suitable fill, or native silt/clay subgrade prepared in accordance with our recommendations presented in the Site Preparation (Section 4.1), Wet Weather/Wet-Soil Considerations (Section 4.1.3) and Structural Fill (Section 4.3) sections of this report. A minimum 2-foot-thick layer of select granular fill should be placed and compacted over the prepared subgrade. Appropriate material descriptions are provided in Section Floor slabs supported on a subgrade and base course prepared in accordance with the preceding recommendations, may be designed using a modulus of subgrade reaction (k) of 125 pounds per cubic inch (pci). Unless the floor slab is designed as a structural member supported on shallow footings or deep foundations, PBS recommends that walls and partitions not be designed to be supported by the floor slab because some differential settlement and floor slab cracking should be anticipated. 3.4 Ground Moisture General The perimeter ground surface and hard-scaping should be sloped to drain away from all structures. Gutters should be tight lined to a suitable discharge and maintained as free flowing. Any crawl spaces should be adequately ventilated and sloped to drain to a suitable, exterior discharge Vapor Flow Retarder Some flooring manufacturers require specific slab moisture levels and/or vapor flow retarders to validate the warranties on their products. If a vapor flow retarder is used, care 7

12 should be taken not to trap moisture within any overlying granular fill and floor slab concrete. Barriers should be installed per the manufacturer s recommendations. The geotechnical scope of services did not include possible existence of potential methane gas generated from the debris beneath the proposed building. We suggest completing an evaluation to assess this risk prior to construction. 3.5 Pavement Design We anticipate that site pavements will consist of hot mix asphalt concrete (HMAC) over crushed rock base course. Recommendations for AC pavements were developed using the American Association of State Highway and Transportation Officials (AASHTO) design methods. The surficial soils across the site are medium dense, silty gravel and medium stiff, silt/clay. With proper preparation, these soils are suitable to provide limited pavement support. Loose areas should be compacted to an unyielding condition, or be excavated and replaced with structural fill. Soil may require moisture conditioning to be properly compacted. All pavement subgrades should be evaluated and prepared in accordance with the Site Preparation (Section 4.1) and Wet Weather/Wet-Soil Considerations (Section 4.1.3) sections of this report. The required layer of aggregate base rock should be placed and compacted over the prepared subgrade. Crushed aggregate base course recommendations are provided in Section of this report. Heavy construction traffic on pavements or partial pavement sections (such as base course over the prepared subgrade), may exceed the design loads and could potentially damage or shorten the life of the pavements. Therefore, we recommend the contractor take appropriate measures to protect the subgrades, base course, and pavement during construction. The HMAC pavement for access roads and drive aisles was evaluated using a pavement design life of 20 years and an assumed truck factor of 0.6 equivalent single-axle loads (ESAL) per truck. The subgrade under AC pavement areas, if disturbed during construction, should be prepared by scarifying, moisture conditioning, and re-compacting a minimum of 12 inches below the bottom of the base course. Our AC pavement design recommendations are based on the following design parameters: A resilient modulus of 4,500 pounds per square inch (psi) (equivalent to a California Bearing Ratio [CBR] value of 3) was used for the native medium stiff, silt/clay subgrade. A resilient modulus of 28,000 psi was assumed for the aggregate base rock Initial and terminal serviceability index of 4.2 and 2.5, respectively Reliability and standard deviation of 90 percent and 0.45, respectively Structural coefficient of 0.43 and 0.13 for the asphalt and crushed aggregate base course, respectively Site traffic was assumed to include ten trucks (0.8 truck factor) per day (60,000 ESALs) for access road pavement and two trucks per day (15,000 ESALs) for parking pavement 8

13 Table 1: Minimum AC Pavement Sections Traffic Loading (ESALs) AC (inches) Base Rock (inches) Parking (15,000) Access Road (60,000) These are the minimum acceptable pavement section thicknesses. Depending on weather conditions at the time of construction, a thicker aggregate base course section could be required to support construction traffic during preparation and placement of the pavement section. The asphalt cement binder should be PG Performance Grade Asphalt Cement according to the Oregon Department of Transportation (ODOT) ODOT SS Asphalt Cement and Additives. The AC should consist of Level 3, ½-inch, dense HMAC. The minimum lift thicknesses should be 2.0 inches. The AC should conform to ODOT SS and and be compacted to 91 percent of the Rice density of the mix, as determined in accordance with ASTM International (ASTM) D Due to the potential for long-term settlement associated with decomposition of the landfill debris, we suggest the asphalt concrete pavement be evaluated on an on-going annual basis to check for differential settlement against the building slab or foundation. Any gaps or depressions observed should be sealed, repaired, or otherwise water-proofed to prevent damage to the pavement or building foundations. Further, low spots may develop resulting in ponding and poor surface drainage. 3.6 Seismic Design Criteria The seismic design parameters, in accordance with the 2014 Oregon Structural Specialty Code (OSSC), are summarized in Table 2 as follows. Table 2: 2014 OSSC Seismic Design Parameters Maximum Credible Earthquake Spectral Acceleration Site Class Short Period S s = 1.31 g E 1 Second S 1 = 0.66 g Site Coefficient F a = 0.90 F v = 2.40 Adjusted Spectral Acceleration S MS = 1.17 g S M1 = 1.59 g Design Spectral Response Acceleration Parameters S DS = 0.78 g S D1 = 1.06 g Design Spectral Peak Ground Acceleration 0.31 g g acceleration due to gravity 4.0 CONSTRUCTION RECOMMENDATIONS 4.1 Site Preparation PBS current understanding of the site grading is limited; however, we estimate cuts and fills will be limited in depth/thickness to less than 3 feet within the proposed building addition, and less 9

14 than 2 feet within the proposed parking expansion. Stripped vegetation and topsoil should be transported off site for disposal, or with the owner s approval, stockpiled for reuse in landscaped areas. Due to the presence of plastic soils, subgrade soils should be maintained as moist and not allowed to dry by limiting exposure times and keeping exposed soil covered. In order to increase the thickness of the granular fill layer overlying the undocumented landfill debris material, PBS recommends raising the building site above the existing grade elevation by a minimum of 24 inches. In the case of shallow spread footings, PBS recommends placing 3 feet of crushed rock for the building pad, which will serve to eliminate cuts extending into the underlying undocumented fill layers, and in all cases will reduce the potential for differential settlement between the pavement, slab, and foundation elements Proofrolling/Subgrade Verification Following stripping/excavation and prior to placing fill, pavement or granular pads, the exposed subgrade should be evaluated by proofrolling or other subgrade verification methods. In dry conditions, the subgrade should be proofrolled with a fully loaded dump truck or similar heavy, rubber-tire, construction equipment to identify soft, loose, or unsuitable areas. We recommend that PBS be retained to observe the proofrolling. In wet conditions, the subgrade should be evaluated through the use of a probe or other standard of practice by a geotechnical engineer. We recommend that PBS be retained to perform these verifications. Soft or loose zones identified during the field evaluation should be excavated and replaced with structural fill Subgrade Protection If the fine-grained clay cap soils are exposed beneath footings, slabs, or pavements, they should not be allowed to dry. Once subgrades are approved, the clayey soils should be covered within four hours of exposure by a minimum of 4 inches of crushed rock or plastic sheeting Wet-Weather/Wet-Soil Conditions Due to the presence of silt/clay soils at the site, construction equipment may have difficulty operating on the near-surface soils when the moisture content of the surface soil is more than a few percentage points above optimum. Soils that have been disturbed during sitepreparation activities, or soft or loose zones identified during probing, should be removed and replaced with compacted structural fill. Protection of the subgrade is the responsibility of the contractor. Track-mounted excavating equipment may be required during wet weather. The thickness of the haul roads and staging areas will depend on the amount and type of construction traffic. The material used for haul roads should be stabilization material described as follows. A 12- to 18-inch-thick mat of stabilization material should be sufficient for light staging areas. The stabilization material for haul roads and areas with repeated heavy construction traffic typically needs to be increased to between 18 to 24 inches. The actual thickness of haul roads and staging areas should be based on the contractor s approach to site work and the amount and type of construction traffic, and is the contractor s responsibility. The stabilization material should be placed in one lift over the prepared, undisturbed subgrade and compacted using a smoothdrum, non-vibratory roller. Additionally, a geotextile fabric should be placed as a barrier between the subgrade and stabilization material. The geotextile should meet specifications ODOT SS Section and SS , Table for soil separation. The 10

15 geotextile should be installed in conformance with ODOT SS Geosynthetic Installation. 4.2 Excavation Near-surface soils at the site consist of medium dense, silty gravel and medium stiff, silt/clay that can be excavated with conventional earthwork equipment. Trench cuts should stand relatively vertical to a depth of approximately 4 feet bgs, provided no groundwater seepage is present in the trench walls. Open excavation techniques may be used in silt, sand, and clay provided the excavation is configured in accordance with the Occupational Safety and Health Administration (OSHA) requirements, groundwater seepage is not present, and with the understanding that some sloughing may occur. The trenches should be flattened if sloughing occurs or seepage is present. Groundwater was not observed during our test pit excavations, but may be present at excavation depths seasonally. Subsequently, the use of a trench shield, or other approved temporary shoring, is recommended for cuts that extend below groundwater seepage, or if vertical walls are desired for cuts deeper than 4 feet bgs. All excavations should be made in accordance with applicable OSHA and State regulations. The contractor is responsible for adherence to the OSHA requirements. 4.3 Structural Fill Structural fill, including crushed rock, should be placed over subgrades which have been prepared in conformance with the Site Preparation and Wet-Weather/Wet-Soil Considerations sections of this report. Structural fill material should consist of relatively well-graded soil, or an approved rock product that is free of organic material and debris, and contains particles not greater than 4 inches nominal dimension. The suitability of soil for use as compacted structural fill depends on the gradation and moisture content of the soil when it is placed. As the amount of fines (material finer than the US Standard No. 200 Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and compaction becomes more difficult to achieve. Soils containing more than about 5 percent fines cannot consistently be compacted to a dense, nonyielding condition when the water content is significantly greater (or significantly less) than optimum. With respect to the current plans, a brief characterization of some of the acceptable materials and PBS recommendations for their use as structural fill is provided as follows On-Site Soil Near-surface native soils at the site are highly variable and included silt/clay, cobbles and boulders. Due to the difficulty required to dry silt and clay to near optimum moisture content, and the difficulty in separating the various materials, reuse of native soils as structural fill is not likely feasible and not recommend Borrow Material Borrow material for general structural fill construction should meet the requirements set forth in ODOT SS Borrow Material. When used as structural fill, native soils should be placed in lifts with a maximum uncompacted thickness of approximately 8 inches and compacted to not less than 92 percent of the maximum dry density, as determined by ASTM D If suitable common borrow material is not available, use of selected general 11

16 backfill as specified in ODOT SS Selected General Backfill should be considered Select Granular Fill Selected granular backfill used during periods of wet weather for structural fill construction should meet the specifications provided in ODOT SS Selected Granular Backfill. Select granular fill should be composed of crushed rock or crushed gravel that is relatively well graded between coarse and fine, contains no deleterious materials, has a maximum particle size of 1 inch, and has less than 5 percent by dry weight passing the U.S. Standard No. 200 Sieve. Selected granular backfill should be placed in lifts with a maximum uncompacted thickness of 8 to 12 inches and be compacted to not less than 92 percent of the maximum dry density, as determined by ASTM D Selected Stone Backfill (ODOT SS ) and Stone Embankment Material (ODOT SS ) can also be used for the construction of general structural fill. However, we recommend that the larger size material (>6 inches) should be placed in the deeper portions of the fill and should not be used within 2 feet of the pavement subgrade. Considerations should also be given to the future excavation of utilities through this material, since it is relatively difficult to excavate through larger-size material Crushed Aggregate Base Course Crushed aggregate base course of hot mix asphalt concrete pavements should be composed of clean, crushed rock or crushed gravel that contains no deleterious materials and meets the specifications provided in ODOT SS Dense-Graded Aggregate, and have less than 5 percent by weight passing the U.S. Standard No. 200 Sieve. The crushed aggregate base course should be compacted to at least 95 percent of the maximum dry density, as determined by ASTM D Trench Backfill Pipe bedding placed to uniformly support the pipe should meet specifications provided in ODOT SS Pipe Zone Bedding. The pipe zone that extends from the top of the bedding to at least 8 inches above utility lines should consist of material prescribed by ODOT SS Pipe Zone Material. The pipe zone material should be compacted to at least 90 percent of the maximum dry density, as determined by ASTM D 1557, or as required by the pipe manufacturer. Under pavements, paths, slabs, or beneath building pads, the remainder of the trench backfill should consist of well-graded granular material with less than 10 percent by weight passing the U.S. Standard No. 200 Sieve, and should meet standards prescribed by ODOT SS Trench Backfill, Class B or D. This material should be compacted to at least 92 percent of the maximum dry density, as determined by ASTM D 1557, or as required by the pipe manufacturer. The upper 3 feet of the trench backfill should be compacted to at least 95 percent of the maximum dry density, as determined by ASTM D Controlled low-strength material (CLSM), ODOT SS Trench Backfill, Class E, can be used as an alternative. Outside of structural improvement areas (e.g., pavements, sidewalks, or building pads), trench material placed above the pipe zone may consist of general structural fill materials 12

17 that are free of organics and meet ODOT SS Trench Backfill, Class A. This general trench backfill should be compacted to at least 90 percent of the maximum dry density, as determined by ASTM D 1557 or as required by the pipe manufacturer or local jurisdictions Stabilization Material Stabilization rock should consist of pit or quarry run rock that is relatively well graded, angular, crushed rock consisting of 4- or 6-inch-minus material with less than 5 percent passing the U.S. Standard No. 4 Sieve. The material should be free of organic matter and other deleterious material. ODOT SS Stone Embankment Material can be used as a general specification for this material with the stipulation of limiting the maximum size to 6 inches. 5.0 ADDITIONAL SERVICES AND CONSTRUCTION OBSERVATIONS In most cases, other services beyond completion of a geotechnical engineering report are necessary or desirable to complete the project. Occasionally, conditions or circumstances arise that require the performance of additional work that was not anticipated when the geotechnical report was written. PBS offers a range of environmental, geological, geotechnical, and construction services to suit the varying needs of our clients. PBS should be retained to review the plans and specifications for this project before they are finalized. Such a review allows PBS to verify that our recommendations and concerns have been adequately addressed in the design. Satisfactory earthwork performance depends on the quality of construction. Sufficient observation of the contractor's activities is a key part of determining that the work is completed in accordance with the construction drawings and specifications. PBS recommends that we be retained to observe general excavation, stripping, fill placement, and footing subgrades. Subsurface conditions observed during construction should be compared with those encountered during the subsurface explorations. Recognition of changed conditions requires experience; therefore, qualified personnel should visit the site with sufficient frequency to detect whether subsurface conditions change significantly from those anticipated. 6.0 LIMITATIONS This report has been prepared for the exclusive use of the addressee, and their architects and engineers for aiding in the design and construction of the proposed development and is not to be relied upon by other parties. It is not to be photographed, photocopied, or similarly reproduced, in total or in part, without the expressed written consent of the Client and PBS. It is the addressee's responsibility to provide this report to the appropriate design professionals, building officials and contractors to ensure correct implementation of the recommendations. The opinions, comments, and conclusions presented in this report are based upon information derived from our literature review, field explorations, laboratory testing, and engineering analyses. Conditions between, or beyond, our exploratory borings may vary from those encountered. It is possible that fill, native soil, rock, or groundwater conditions could vary between or beyond the points explored. If fill, native soil, rock, or groundwater conditions are encountered during construction that differ from those described herein, the client is responsible for ensuring that PBS is notified immediately so that we may reevaluate the recommendations of this report. 13

18 Unanticipated soil and rock conditions and seasonal soil moisture and groundwater variations are commonly encountered and cannot be fully determined by merely taking soil samples or soil borings. Such variations may result in changes to PBS recommendations and may require that additional expenses to attain a properly constructed project. Therefore, PBS recommends a contingency fund to accommodate such potential extra costs. The scope of services for this subsurface exploration and geotechnical report did not include environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous substances in the fill, native soil, surface water, or groundwater at this site. If there is a substantial lapse of time between the submission of this report and the start of work at the site, if conditions have changed due to natural causes or construction operations at or adjacent to the site, or if the basic project scheme is significantly modified from that assumed, this report should be reviewed to determine the applicability of the conclusions and recommendations presented herein. Land use, site conditions (both on- and off-site), or other factors may change over time and could materially affect our findings. Therefore, this report should not be relied upon after three years from its issue, or in the event that the site conditions change. 14

19 7.0 REFERENCES AASHTO Guide for Design of Pavement Structures (1993). American Association of State Highway and Transportation Officials. Washington, D.C. International Building Code (2012). International Code Council. Niem, A.R. and Niem, W.A (1985), Oil and gas investigations of the Astoria Basin, Clatsop and northernmost Tillamook Counties, northwest Oregon, OGI-14. Oregon Department of Geology and Mineral Industries. ODOT SS. (2008). Oregon Standard Specifications for Construction, Volume 2. Salem, Oregon. Oregon Department of Transportation. OSSC. (2014). Oregon structural specialty code. Schlicker, H.G, Deacon, R.J., Beaulieu, J.D., and Olcott, G.W. (1972), Environmental geology of the coastal region of Tillmaook and Clatsop Counties, B-74. Oregon Department of Geology and Mineral Industries. 15

20 FIGURES

21 PROJECT LOCATION L:\Projects\73000\ \73129_HshldHazWsteFaclty\GeoDwg\ _figures 1-2.dwg Nov 19, :33am Jimb SITE PORTLAND SALEM EUGENE OREGON PROJECT # DATE NOV 2014 PREPARED FOR: CLATSOP COUNTY PUBLIC WORKS VICINITY MAP HOUSEHOLD HAZARDOUS WASTE FACILITY ASTORIA, OREGON SOURCE: USGS ASTORIA OR QUADRANGLE 1981, PHOTO REVISED ' 1,000' 2,000' 4,000' SCALE: 1" = 2,000' FIGURE 1

22 PROJECT SITE TP-2 TP-1 TP-3 B-1 B-2 TP-4 L:\Projects\73000\ \73129_HshldHazWsteFaclty\GeoDwg\ _figure 2b.dwg Nov 11, :25pm Jimb LEGEND B-1 BORING NUMBER AND APPROXIMATE LOCATION TP-1 TEST PIT NUMBER AND APPROXIMATE LOCATION PROJECT # DATE NOV 2014 SITE PLAN HOUSEHOLD HAZARDOUS WASTE FACILITY ASTORIA, OREGON SOURCE: 2011 GOOGLE EARTH PRO, 2012 GOOGLE 0' 20' 40' 80' SCALE: 1" = 40' PREPARED FOR: CLATSOP COUNTY PUBLIC WORKS FIGURE 2

23 APPENDIX A Field Explorations

24 APPENDIX A FIELD EXPLORATIONS A1.0 GENERAL PBS explored subsurface conditions at site by excavating four test pits on October 13, 2013 and advancing two borings on October 14, The approximate locations of the explorations are shown on Figure 2. The procedures and techniques used to advance borings, excavate test pits, collect samples, and other field techniques, are described in detail in the following paragraphs. Unless otherwise noted, all soil sampling and classification procedures are in general accordance with applicable ASTM standards. General accordance means that certain local and common drilling and descriptive practices and methodologies have been followed. A2.0 BORINGS A2.1 Drilling The borings, designated as B-1 and B-2, were advanced to depths of about 31.5 and 41.5 feet bgs, respectively, with a truck-mounted drill rig provided and operated by Hardcore Drilling, Inc. of Dundee, Oregon. Borings were advanced using hollow-stem auger drilling techniques. The borings were observed by a member of the PBS geotechnical engineering staff who maintained a detailed log of the subsurface conditions and materials encountered during the course of the work. A2.2 Sampling Disturbed soil samples were taken in the borings at selected depth intervals. The samples were obtained using a standard 2-inch outside diameter (OD), split-spoon sampler following procedures prescribed for the Standard Penetration Test (SPT). Using the SPT, the sampler is driven 18 inches into the soil using a 140-pound hammer dropped 30 inches. The number of blows required to drive the sampler the last 12 inches is defined as the standard penetration resistance, or N-value. The N-value provides a measure of the relative density of granular soils such as sands and gravels, and the consistency of cohesive soils such as clays and plastic silts. The disturbed soil samples were examined by the PBS geologist and then sealed in plastic bags for further examination and physical testing in the PBS laboratory. Due to disposal and handling concerns, no samples were obtained within or above the landfill debris material. A2.3 Boring Logs The logs show the various types of materials that were encountered in the borings and the depths where the materials and/or characteristics of these materials changed, although the changes may be gradual. Where material types and descriptions changed between samples, the contacts were interpreted. The types of samples taken during drilling, along with their sample identification number, are shown to the right of the classification of materials. Standard penetration resistances (N-values) and natural water (moisture) contents are shown further to the right. Measured groundwater levels and the dates of the readings are plotted in the column to the right. The groundwater levels are only for the dates shown and probably vary from time to time during the year. A3.0 TEST PITS A3.1 Excavation Test pits were excavated to depths of about 8.0 feet bgs by Dan J. Fischer Excavating, Inc. of Forest Grove, Oregon using a Hitachi EX30 excavator with a 24-inch bucket. The test pits were observed by a member of the PBS geotechnical engineering staff who located the general areas for exploration and maintained a detailed log of the subsurface conditions and materials A-1

25 encountered during the course of the work. Due to disposal and handling concerns, no samples were obtained within or above the landfill debris material. A3.2 Test Pit Logs Test pit logs describe the subsurface conditions and types of materials encountered in the test pits and the depths where the materials or conditions changed although the changes may be gradual. A4.0 MATERIAL DESCRIPTION Initially, soil samples were classified visually in the field. Consistency, color, relative moisture, degree of plasticity and other distinguishing characteristics of the soil samples were noted. Afterwards, the samples were re-examined in the PBS laboratory, various standard classification tests were conducted, and the field classifications were modified where necessary. The terminology used in the soil classifications and other modifiers are defined in Appendix A, Terminology Used to Describe Soil. A-2

26 Soil Descriptions Table A-1 Terminology Used to Describe Soil 1 of 2 Soils exist in mixtures with varying proportions of components. The predominant soil, i.e., greater than 50 percent based upon total dry weight, is the primary soil type and is capitalized in our log descriptions, e.g., SAND, GRAVEL, SILT or CLAY. Lesser percentages of other constituents in the soil mixture are indicated by use of modifier words in general accordance with the Visual-Manual Procedure (ASTM D ). General Accordance means that certain local and common descriptive practices have been followed. In accordance with ASTM D , group symbols (such as GP or CH) are applied on that portion of the soil passing the 3-inch (75mm) sieve based upon visual examination. The following describes the use of soil names and modifying terms used to describe fine- and coarse-grained soils. Fine - Grained Soils (More than 50% fines passing mm, #200 sieve) The primary soil type, i.e. SILT or CLAY is designated through visual manual procedures to evaluate soil toughness, dilatency, dry strength, and plasticity. The following describes the terminology used to describe fine - grained soils, and varies from ASTM 2488 terminology in the use of some common terms. Primary soil NAME, adjective and symbols Plasticity Description Plasticity Index (PI) ORGANIC SILT CLAY SILT & CLAY ML & MH CL & CH OL & OH SILT Organic SILT Non-plastic 0-3 SILT Organic SILT Low plasticity 4-10 SILT / Elastic SILT Lean CLAY Organic clayey SILT Medium Plasticity Elastic SILT Lean/Fat CLAY Organic silty CLAY High Plasticity Elastic SILT Fat CLAY Organic CLAY Very Plastic >40 Modifying terms describing secondary constituents, estimated to 5 percent increments, are applied as follows: Description With sand; with gravel (combined total greater than 15% but less than 30%, modifier is whichever is greater) Sandy; or gravelly (combined total greater than 30% but less than 50%, modifier is whichever is greater) % Composition 15% to 25% 30% to 50% Borderline Symbols, for example CH/MH, are used where soils are not distinctly in one category or where variable soil units contain more than one soil type. Dual Symbols, for example CL-ML, are used where two symbols are required in accordance with ASTM D2488. Soil Consistency. Consistency terms are applied to fine-grained, plastic soils (i.e., PI > 7). Descriptive terms are based on direct measure or correlation to the Standard Penetration Test N-value as determined by ASTM D , as follows. Note, SILT soils with low to non-plastic behavior (i.e. PI < 7) are classified using relative density. Consistency Unconfined Compressive Strength SPT N-value Term tsf kpa Very soft Less than 2 Less than 0.25 Less than 24 Soft Medium stiff Stiff Very stiff Hard Over 30 Over 4.0 Over 383

27 Table A-1 Terminology Used to Describe Soil 2 of 2 Soil Descriptions Coarse - Grained Soils (less than 50% fines) Coarse-grained soil descriptions, i.e., SAND or GRAVEL, are based on that portion of materials passing a 3-inch (75mm) sieve. Coarse-grained soil group symbols are applied in accordance with ASTM D based upon the degree of grading, or distribution of grain sizes of the soil. For example, well graded sand containing a wide range of grain sizes is designated SW; poorly graded gravel, GP, contains high percentages of only certain grain sizes. Terms applied to grain sizes follow. Material Particle Diameter Inches Millimeters Sand (S) Gravel (G) Additional Constituents Cobble Boulder The primary soil type is capitalized, and the amount of fines in the soil are described as indicated by the following examples. Other soil mixtures will provide similar descriptive names. Example: Coarse-Grained Soil Descriptions with Fines 5% to less than 15% fines (Dual Symbols) GRAVEL with silt, GW-GM SAND with clay, SP-SC 15% to less than 50% fines Silty GRAVEL: GM Silty SAND: SM Additional descriptive terminology applied to coarse-grained soils follow. Example: Coarse-Grained Soil Descriptions with Other Coarse-Grained Constituents Coarse-Grained Soil Containing Secondary Constituents With sand or with gravel With cobbles; with boulders > 15% sand or gravel Any amount of cobbles or boulders. Cobble and boulder deposits may include a description of the matrix soils, as defined above. Relative Density terms are applied to granular, non-plastic soils based on direct measure or correlation to the Standard Penetration Test N-value as determined by ASTM D Relative Density Term SPT N-value Very loose 0-4 Loose 5-10 Medium dense Dense Very dense > 50