Attach_9_-_Klamath_Falls_NFH-Geotech_Report_0001.pdf

Report of Geotechnical Engineering Services

Klamath Falls National Fish Hatchery Lower Klamath Lake Road Klamath Falls, Oregon

Prepared for

KPFF Consulting Engineers U.S. Fish and Wildlife Service

January 5, 2021 154‐124‐002

300 West 15th Street

Vancouver, Washington 98660-2927

360.448.4189

Report of Geotechnical Engineering Services

Klamath Falls National Fish Hatchery Lower Klamath Lake Road Lake Road Klamath Falls, Oregon

Prepared for

KPFF Consulting Engineers U.S. Fish and Wildlife Service

Prepared by

Hart Crowser, a division of Haley & Aldrich.

Reza Behzadpour, PE Daniel J. Trisler, PE, GE Staff, Geotechnical Engineer Principal, Geotechnical Engineer

Contents

1.0 INTRODUCTION 1

2.0 SCOPE OF SERVICES 1

3.0 SITE CONDITIONS 2

3.1 Surface Conditions 2

3.2 Geology and Soils 3

3.2.1 Geology 3

3.2.2 Soils 4

3.3 Subsurface Conditions 4

3.3.1 General 4

3.3.2 Groundwater 7

3.3.3 Laboratory Testing 7

4.0 GEOLOGIC AND SEISMIC HAZARDS ASSESSMENT 7

4.1 Seismicity 7

4.2 Seismic Shaking 8

4.3 Ground Motion Amplification (Site Class) 9

4.4 Liquefaction 9

4.5 Surface Fault Rupture 9

4.6 Landslide 10

5.0 Ground Settlement and Global Stability 11

5.1 General 11

5.2 Settlement Analysis 11

5.3 Global Stability 11

6.0 CONCLUSIONS 12

7.0 STRUCTURAL DESIGN RECOMMENDATIONS 14

7.1 Foundation Design 14

7.1.1 Discussion 14

7.1.2 Building Foundations Option 1: Interlocking Spread Footings with Removal of Expansive Soils 15

7.1.3 Building Foundations Option 2: Structural Slab/Mat/Raft 16

7.1.4 Kettle Structure Foundations 18

7.1.5 Footing Construction Considerations 19

7.2 Retaining Structure Design Recommendations 20

7.3 Seismic Design 20

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January 5, 2021

8.0 PAVEMENT DESIGN AND CONSIDERATIONS 21

8.1 General 21

8.2 Pavement Sections 21

8.2.1 Assumptions 21

8.2.2 Pavement Sections 22

8.3 Pavement Materials 22

8.3.1 Flexible AC 22

8.3.2 Aggregate Base/Gravel Surfacing 22

8.3.3 Separation Geotextile 23

8.3.4 Soil Subgrade 23

9.0 SOIL CORROSIVITY 23

10.0 EARTHWORK RECOMMENDATIONS 23

10.1 Discussion Regarding On‐Site Soils 23

10.2 Site Preparation 24

10.2.1 Demolition 24

10.2.2 Subgrade Preparation and Evaluation 25

10.2.3 Fill on Slope Subgrade Preparation 25

10.2.4 Haul Roads 25

10.3 Excavation 26

10.3.1 Mass Excavations 26

10.3.2 Temporary Open Cuts 26

10.4 Permanent Slopes 27

10.4.1 General 27

10.4.2 Tall Embankment Construction 27

10.5 Structural Fill and Backfill 28

10.5.1 On‐Site Soils 28

10.5.2 Imported Select Structural Fill 29

10.5.3 Aggregate Base 29

10.5.4 Drain Rock 29

10.5.5 Stabilization Material 29

10.6 Fill Placement and Compaction 30

11.0 CONSTRUCTION OBSERVATIONS 31

12.0 LIMITATIONS 31

13.0 REFERENCES 32

Contents | iii

January 5, 2021

TABLES

1 Lateral Earth Pressure Parameters 20

2 Seismic Design Parameters 20

3 Guidelines for Uncompacted Lift Thickness 30

4 Fill Compaction Criteria 31

FIGURES

1 Vicinity Map

2 Existing Site Plan

3 Site Plan

APPENDIX A

Field Explorations

APPENDIX B

Laboratory Testing

APPENDIX C

Stability Analyses

Report of Geotechnical Engineering Services

Klamath Falls National Fish Hatchery

1.0 INTRODUCTION

Hart Crowser, a division of Haley & Aldrich, is pleased to submit our report of geotechnical engineering services for the proposed Klamath Falls National Fish Hatchery (NFH) improvements in Klamath Falls, Oregon. Our work was completed in general accordance with our agreement with KPFF dated July 20, 2020.

We understand that the U.S. Fish and Wildlife Service (USFWS) proposes to construct a sucker fish hatchery at the site. The proposed hatchery will include a series of 36 neoprene‐lined ponds for fish with harvest kettle structures built into their berms, water supply, and effluent storage. The ponds will typically be 3 to 4 feet deep with berms that are 5 to 6 feet tall. In a few locations cut and fill slopes up to 25 feet tall may be present. Several one‐story structures, including hatchery office building as well as maintenance and storage sheds, will be constructed.

The location of the site is shown on Figure 1, the existing site layout is shown on Figure 2, and the proposed site layout is shown on Figure 3. Appendix A contains the logs for subsurface explorations and a description of exploration methods and equipment. Appendix B contains the results of the laboratory testing. Appendix C presents the results of stability analyses for various cut and fill slopes.

2.0 SCOPE OF SERVICES

The purpose of our work was to evaluate subsurface conditions at the site and to provide geotechnical engineering design evaluation of and recommendations for specific project elements. Our scope of work was described in our July 16, 2020 scope and fee estimate and is summarized below.

Reviewed relevant, readily available geologic maps that cover the site vicinity to evaluate geologic hazards and regional soil mapping and local soil and groundwater conditions.

Notified the "One‐Call" service for public utility locates to identify the locations of existing underground utilities in the vicinity of the proposed explorations.

Conducted a field investigation, including:

Advancing 14 mechanically drilled boring to depths between approximately 16.5 and 31.5 feet below ground surface (bgs) within the proposed construction staging area

Excavating 18 test pits between approximately 4.5 and 10 feet bgs

Installing 1 groundwater monitoring well

Observed explorations, logged the subsurface conditions, collected representative soil samples, and transported samples to our laboratory for further visual examination and testing.

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Conducted a program of laboratory testing on select soil samples. The laboratory tests conducted included general index determination testing, strength testing, as well as corrosivity testing.

Evaluated code‐based seismic hazards, including ground shaking, ground shaking amplification, and liquefaction.

Conducted engineering analyses and developed geotechnical design recommendations for berm construction, settlement, building foundations, lateral earth pressures, building seismic design criteria, earthwork considerations, and pavement.

Prepared this report outlining our findings and recommendations, including the following:

Subsurface soil and groundwater conditions

Seismic hazards

Structure foundation design parameters

Ground settlement and stability analyses

Soil corrosion potential

Pavement design (gravel and asphalt)

Site preparation and grading

Construction considerations

Provided project management and support services, including coordinating staff and subcontractors and conducting telephone consultations and email communications with you and the design team.

3.0 SITE CONDITIONS

3.1 Surface Conditions

The 25‐acre site is located immediately east of Lower Klamath Lake Road and approximately 12 miles south of Klamath Falls in southern Klamath County, Oregon. The site lies at the southwest flank of the

Klamath Hills adjacent to farmland reclaimed from the former Lower Klamath Lake. The site can be divided into two areas, including an irregularly shaped 21‐acre area (identified as the northern portion from here

on) as well as an approximately 4.7‐acre rectangular area adjacent to the Lower Klamath Lake Road

(identified as the southern portion here on). The site is currently occupied by a private fish hatchery. The majority of the site is lightly developed with facilities operated by the current fish hatchery, which includes several dozens of lined hatchery ponds and three tarp‐covered workshops. The hatchery site is surrounded by undeveloped juniper and sagebrush grassland. Roadways at the site are mostly surfaced with gravel;

however, many of the pathways are undeveloped and consist of native soils. A geothermal well is located south of the southern portion of the site with metal piping that routes the hot geothermal water to cooling ponds far northeast of the northern portion of the site.

Based on topographic information provided by KPFF, elevations at the site range from approximately

4,135 to 4,139 feet above mean sea level (MSL) near Lower Klamath Lake Road and gently rise in a series of flat to gently sloping, graded benches to the north and northeast at approximate elevations 4,130, 4,135, and 4,150 feet above MSL. Natural slopes continue to the north up to approximate elevation

4,185 feet above MSL.

Klamath Falls National Fish Hatchery | 3

The southern ponds and a covered workshop are adjacent to Lower Klamath Lake Road and drain into an unlined ditch to the west of the ponds. The northern ponds drain through an underground piping system to the wetlands adjacent to Lower Klamath Lake Road. The highest bench contains the upper

“quarter‐acre” ponds that are routed through an underground drainpipe to large, unlined ditches at the far northwest end of the site. A concrete utility channel exists at the center of the upper ponds to allow for fish collection during hatchery operations.

In addition to the grading at the lined ponds, unlined drainage ditches have been excavated in the northwest portion of the site with cut and fill slopes approximately 12 feet in height. Surface water and hatchery wastewater eventually drain to a tree‐lined pond at the west edge of the site adjacent to Lower

Klamath Lake Road. The undeveloped portion of the site beyond the hatchery facilities to the north and east rises in elevation to the north with smooth slopes that are up to approximately 20 degrees. The highest point at the site is approximately 4,185 feet above MSL in the north of the property. Natural grades continue above the site to the east to elevation 4,195 feet or higher.

3.2 Geology and Soils

3.2.1 Geology

The geology of the site and vicinity is mapped in the Preliminary geologic map of the Hamaker Mountain, Worden, and Lost River 7.5' quadrangles, Klamath County, Oregon at 1:24,000 scale (Hladky and Jenks, 2007), which incorporates data from previous mapping by Sherrod and Pickthorn (1992). Geologic conditions at the site are controlled by the geologic deposits, structure, and tectonic setting of the Klamath

Basin. Located at the northwestern margin of the Basin and Range Province, the Klamath Basin is dominated by north‐to‐northwest trending sediment‐filled valleys (grabens) and mountain blocks (horsts).

This “horst and graben” topography is formed by faulting associated with the ongoing extensional tectonics of the Basin and Range, with the valleys dropping relative to the mountains along high‐angle normal faults. Offset along faults in the Klamath Basin ranges from hundreds to thousands of feet and is estimated to be as much as 3,000 feet on the west side of the Klamath Hills (Hladky and Jenks 2007) adjacent to the project site.

The site is mapped by Hladky and Jenks (2007) as being underlain by Pliocene and Miocene sedimentary rocks (Tms) that are composed of light colored tuffaceous mudstone with minor claystone and sandstone formed in shallow lacustrine settings. This unit is described as extensive in the Klamath Basin and has been found to contain diatoms; Sherrod and Pickthorn (1992) similarly describe this unit as “thinly bedded to very thick bedded ashy diatomite.” The mudstone is described as soft but consolidated and generally massive but can be thin‐bedded where sandstone and siltstone layers are found. Thickness of these deposits can be as much as 1,600 to 3,000 feet in the region. Localized areas of silicified rocks, including silica‐cemented sandstone are mapped at the site and are likely the results of hydrothermal activity. Our explorations encountered materials generally consistent with the sedimentary rocks as described by

Hladky and Jenks (2007).

The site also lies within the Klamath Hills Geothermal Area, which is an area of extensively silicified rocks and water wells with water temperatures exceeding 180 degrees Fahrenheit (Sammel and Peterson 1976).

Groundwater heated at depth is channeled up along major fault zones and can be extracted via

4 | Klamath Falls National Fish Hatchery geothermal wells. Hundreds of shallow geothermal wells currently heat schools (including the Oregon

Institute of Technology), industrial buildings, apartments, and houses in Klamath Falls, a separate geothermal area north of the site (Sammel and Peterson 1976). Currently, a geothermal well at the south end of the site pumps hot geothermal water for use in the current hatchery operation.

Several water wells greater than 100 feet in depth have been drilled near the project site (OWRD 2020). A review of these well logs indicated subsurface conditions similar to those described in the geologic mapping discussed above, with lithological descriptions such as “yellow and gray claystone,” “yellow chalk or clay,” and “brown clay and sandstone” beneath 2 to 5 feet of topsoil. According to Hladky and Jenks

(2007) “local drillers typically describe [Tertiary Sedimentary Rocks] as ‘chalk rock’, clay, or ‘shale’.”

3.2.2 Soils

The near surface soils at the site have been mapped in the U.S. Department of Agriculture (USDA) online web soil survey (USDA 2020). According to the USDA resource, the near‐surface soils at the site are mapped as Capona loam, 5 to 15 percent slopes. Capona soils are described as moderately deep, well drained, loam to gravelly sandy clay loam to weathered bedrock derived from weathered tuff, diatomite, and basalt. Tuffaceous bedrock is commonly found at a depth of 20 to 40 inches, which is also the extent of root penetration. The soils have hydraulic conductivities estimated to range from 0.57 to

1.98 inches/hour and low water storage (4.6 inches) in the soil profile. The upper range of linear extensibility tested for this soil is listed as up to 2.9 percent, indicating a moderate shrink‐swell (frost action) potential.

3.3 Subsurface Conditions

3.3.1 General

We explored subsurface soil and groundwater conditions at the site by drilling 14 borings to between approximately 17 and 31 feet bgs and excavating 18 test pits between approximately 4.5 and 10 feet bgs.

The exploration locations are shown on Figures 2 and 3. Appendix A summarizes our exploration methods and presents our exploration logs.

The subsurface information used for this study represents conditions at discrete locations across the project site and actual conditions in other areas could vary. Furthermore, the nature and extent of variations may not become evident until additional explorations are performed or until construction begins. If significant variations are observed at that time, we may need to modify our conclusions and recommendations accordingly to reflect actual site conditions.

Deposits encountered during our explorations at the site include gravel road base, reworked site soil fill, and residual soil overlying Tertiary sedimentary rocks that extended to the depths explored. Topsoil was observed in few of the explorations. although generally poorly developed due to the arid weather at the site (less than 14 inches of precipitation per year). We interpret fine‐ to coarse‐grained soils overlying bedrock as residual soil derived from the weathering of the mudstone and sandstone bedrock. Residual soil extends between 2 and 8 feet bgs across the site. However, they were not observed in all explorations.

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3.3.1.1 Gravel Road Base

Gravel road base was encountered in explorations completed in developed roadways adjacent to the hatchery ponds at the site. These roadways are located adjacent to Lower Klamath Lake Road and around the hatchery ponds. Thickness of the gravel road base varied between 2 and 7 inches in our explorations and consisted of imported angular crushed rock. Gravel road base was not observed outside of the roadways on site.

3.3.1.2 Fill Soil

Fill soil consisting of a variable mix of silt, sand, and gravel was encountered in a total of 14 test pits and borings, representing over half of the explorations completed at the project site. Fill soils were encountered generally near the hatchery ponds, a large area north and west of the upper “quarter acre” ponds, and at the divide between two drainage ditches at the north end of the site. Based on communication with the property owner, fill was placed around the site during initial grading of the existing hatchery using cut and fill methods. Additional fill was placed during pond excavation and utility installation after grading was completed. This correlates well with the similarity in appearance between the fill and natural soils observed at the site. Organic debris was observed in the fill with minor rootlets extending up to 4 feet bgs.

Thickness of the fill was between 2.0 and 3.5 feet at the north and west portion of the site near the

“quarter acre” ponds. Approximately 2.5 to 5.0 feet of fill was observed at the northwest edge of the middle ponds and northern end of the lower ponds near Lower Klamath Lake Road. Near the existing geothermal well at the south end of the site, 3.5 feet of fill was observed in a test pit adjacent to newly constructed ponds. Approximately 7 feet of fill was observed overlying native soils in boring B‐6 between the two large drainage ditches at the northwest corner of the property. The thickest section of fill observed at the site was adjacent to the underground drainage pipe for the “quarter acre” ponds at TP‐6, where fill extended to approximately 12.5 feet bgs. This corresponded with the depth of the drainage pipe in this area.

Standard penetration test (SPT) samples were collected in the drilled borings. SPT blow count (N‐values) obtained during drilling in the fill were between 3 and 8 blows per foot (bpf) across the site, indicating a very loose to loose or soft to medium stiff consistency. Laboratory test results indicated moisture content between 15 and 76 percent with an average of approximately 38 percent and a plasticity index between

10 and 16 based on two Atterberg limit tests. This soil unit is generally characterized as weak and subject to settlement.

3.3.1.3 Residual Soil

Medium to high plasticity fine‐grained soils with minor sand and gravel were observed in 15 of our explorations across the site. This soil unit was generally observed at the ground surface or immediately below gravel road base or fill. We interpret this unit to be derived from natural weathering of the mudstone bedrock at the site. Where gravel and sand was observed in this soil, it consisted of intact to highly weathered mudstone and rarely basalt particles, similar to the fill soil but with a lower proportion of sand‐ and gravel‐sized particles. Organic content was generally higher in this unit compared to the fill owing to its relatively undisturbed condition, with more extensive rootlets and organic debris.

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The thickness of this unit varied between approximately 2 and 5 feet and was most prevalent outside of developed areas at the site, especially in the north and west portions of the site. N‐values generally increased with depth in this layer and ranged between 4 and 22 bpf indicating a soft to very stiff relative density. Laboratory test results indicated moisture content between 18 and 37 percent with an average of

27 percent based on four tests. A plasticity index of 17 was determined for one sample in this soil unit.

3.3.1.4 Tertiary Sedimentary Rocks

All of our explorations encountered and terminated in Tertiary sedimentary rocks at the site, which consist of tuffaceous mudstone with minor occurrences of sandstone. While considered bedrock, relative hardness of these materials was generally R0 to R1 (extremely soft to very soft) with minor zones of R2 and R3 (soft to medium hard) and was easily excavated/drilled through during our explorations. The bedrock was observed below a thin layer of topsoil or crushed rock or directly at the surface in many explorations, especially in areas where cuts were made during initial grading at the site. Where not exposed at the surface, depth to bedrock varied between 2 and 7 feet bgs across the site, although it is deeper in areas of extensive fill, such as at exploration location B‐6 where bedrock was observed at approximately beneath 12.5 feet bgs.

The tuffaceous mudstone observed at the site is composed of silt‐ and clay‐sized particles with minor sand and trace gravel. An undisturbed sample collected at 28 feet bgs also contained intact mineral crystals that we interpret as gypsum, a relatively weak hydrous sulfate mineral that is prone to dissolution (Selley, Cocks, and Plimer 2004). This interpretation is also supported by the elevated sulfate content in samples collected from the site. Microscope imaging of samples taken in this deposit appears to indicate the presence of gypsum in other samples, plus the presence of diatoms, a silica‐based fossil formed by single‐ cell microalgae in freshwater lake environments typically 5 to 200 micrometers in size and hollow (Selley, Cocks, and Plimer 2004). The presence of these minerals and fossils can affect physical soil properties such as density, porosity, as well as engineering properties such as compressibility and shear strength.

Representative microscope photographs of the select samples, some showing the presence of diatoms and gypsum, are presented in Appendix B after the laboratory test results.

During our explorations, samples taken in the mudstone easily broke down to soil under finger pressure.

N‐values in the tuffaceous mudstone deposits ranged between 2 and 34 bpf with an average value of

14 bpf, indicating predominantly soft to stiff with minor zones of very stiff to hard relative consistency.

Several explorations indicated soft relative density (N‐values less than 4 bpf) to at least 30 feet bgs;

however, this material was relatively hard and brittle where it was exposed at ground surface and desiccated. Zones of silicification associated with fractured bedrock were also observed at several exploration locations, generally corresponding to an increase in relative density.

Moisture content ranged from 27 to 198 percent with an average moisture content of 120 percent based on 38 samples. We note that over 70 percent of the samples tested had moisture contents over

100 percent with several results approaching 200 percent. Laboratory test results for plasticity index ranged from 12 to 112 with an average of 75 based on nine samples, indicating the tuffaceous mudstone is highly plastic; eight of the samples had a plasticity index equal or higher than 65. Based on the results of index testing, this unit can be generally be classified as elastic silt with some material classified as a fat clay.

Klamath Falls National Fish Hatchery | 7

Sandstone was observed in four of our explorations and is composed of weakly‐cemented clayey sand and gravel with cobbles noted in one test pit location. Relative density of the sandstone unit was medium dense to very dense based on excavation effort during test pit excavation and one SPT sample with an

N‐value of 98 bpf (90/11”). Relative hardness in test pits was noted as R1 to R3 where thinly bedded sandstone was interbedded with the tuffaceous mudstone. Laboratory test results indicate moisture content in the sandstone ranges from 30 to 66 percent.

3.3.2 Groundwater

Groundwater was observed in one boring at the site, B‐9 near Lower Klamath Lake Road, at approximately

8 feet bgs. A groundwater monitoring well (MW‐1) with a pressure transducer to take automated water level readings was installed in the borehole. Water levels measured between July 31 and August 26, 2020 ranged from approximately 8.2 to 9.3 feet bgs.

Based on the location of the monitoring well and topography relative to an unlined pond drainage ditch, we interpret groundwater observed at this location to be related to the infiltration of pond wastewater.

During our explorations, we noted that surface water currently drains through unlined ditches and swales to the wetlands at the west edge of the site adjacent to Lower Klamath Lake Road. Additionally, a drainage ditch adjacent to Lower Klamath Lake Road may influence the flow and depth of perched groundwater at the site. Groundwater levels will likely fluctuate seasonally based on rainfall amounts and water level within the adjacent drainage ditch and wetlands.

3.3.3 Laboratory Testing

A program of laboratory testing was completed on select soil and rock samples to evaluate moisture content, grain size distribution, Atterberg limits, undisturbed and remolded strength, remolded moisture density relationships (Proctor), consolidation, corrosion and other tests. The results of some tests are briefly described in the prior sections and a summary of the results is provided on Figure B‐2 in

Appendix B. All of the laboratory tests are described and their results provided in Appendix B.

Of key import, the testing revealed that the site soils are moderately compressible, are weak, have high sulphate content, are corrosive to the steel and concrete, and have very high moisture content. The impact of these factors is discussed in later sections.

4.0 GEOLOGIC AND SEISMIC HAZARDS ASSESSMENT

The site is in a seismically active area. In this section, we describe the seismic setting, identify the seismic basis of design, provide a code‐based design response spectra, and discuss the seismic hazards at the site.

4.1 Seismicity

The seismicity of the site is controlled by the South Klamath Lake West Fault Zone and the Cascadia

Subduction Zone. Contributions from each of these sources to the total site seismic hazard were evaluated using the U.S. Geological Survey (USGS) Unified Hazard Tool (USGS 2020a).

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Intraslab and Interface Sources Subduction zones are characterized by the interaction of the oceanic Juan de Fuca Plate and continental

North American Plate. As the oceanic plate subducts beneath the continental plate, the two plates lock together. As the plates move together, stresses that can be thought of as similar to a spring build in the overlying continental plate. When the magnitude of the stresses become large enough to overcome the stresses locking the plates together, the plates will suddenly rupture causing an interface earthquake.

Interface earthquakes (such as the 2011 magnitude M9.0 Tohoku earthquake in northern Japan) are some of the largest magnitude earthquakes on record.

Intraslab earthquakes originate from a deeper zone of seismicity that is associated with bending and breaking of the subducting Juan de Fuca Plate. Intraslab earthquakes (such as the 2001 magnitude M7.0

Nisqually earthquake in west central Washington) occur at depths of 40 to 70 kilometers (km) and can produce earthquakes with magnitudes up to and greater than magnitude M7.0.

Crustal Sources Shallow crustal faults are caused by cracking of the continental crust resulting from the stress that builds as the subduction zone plates remain locked together. Many small crustal faults are mapped near the site that are a part of the West and Klamath Graben Fault system (USGS 2020a). The South Klamath Lake section of Klamath Graben Fault system is mapped to cross through the site at the western portion of the site. Refer to Section 4.5 Surface Fault Rupture for further discussion.

4.2 Seismic Shaking

We evaluated potential seismic shaking at the site using data obtained from the USGS Seismic Design

Maps (USGS 2020b). The expected peak bedrock acceleration having a 2 percent probability of exceedance in 50 years (2,475‐year return period) is 0.422 g. This value represents the peak acceleration on bedrock beneath the site and does not account for ground motion amplification due to site‐specific effects. The peak ground acceleration (PGA) is determined by applying a site class factor to the peak bedrock acceleration. Refer to Section 4.3 Ground Motion Amplification (Site Class) for a discussion of ground motion amplification.

We obtained a deaggregation of the seismic sources contributing to the expected peak bedrock acceleration shown above from the National Seismic Hazard Mapping Project website (USGS 2020c).

Seismic sources contributing to this potential ground shaking included intraplate (e.g., Cascadia Subduction

Zone), interplate, and crustal faults. The data indicated that the “modal source” for shaking at the site is a magnitude 6.2 earthquake with an epicenter approximately 3.5 km from the site. The modal source generally signifies the earthquake with one of the highest contributions to the site earthquake hazard. In this instance, a full rupture of the South Klamath Lake West section of Klamath Graben Fault system will control a significant portion of the site seismic hazard. Other specific sources of significant seismicity affecting the site include the Cascadia Megathrust system (Interface faults).

Klamath Falls National Fish Hatchery | 9

4.3 Ground Motion Amplification (Site Class)

Thick sequences of unconsolidated, soft sediments typically amplify the shaking of long‐period ground motions, such as those associated with subduction zone earthquakes; whereas, areas underlain by shallow soil profiles are not likely to amplify seismic waves.

The “Site Class” is a designation used by the International Building Code (IBC) (ICC 2018) and Oregon

Structural Specialty Code (OSSC) (ICC 2019) to quantify ground motion amplification. The classification is based on the stiffness in the upper 100 feet of soil and bedrock materials at a site, as evaluated with SPT or shear wave velocity data. Based on our analysis of SPT data from our borings, the site soils are estimated to have shear wave velocity profile consistent with Site Class E. To complete this analysis, SPT values below the maximum depths explored (31.5 feet bgs) were extrapolated to a depth of 100 feet.

4.4 Liquefaction

Liquefaction is a phenomenon caused by a rapid increase in pore water pressure that reduces the effective stress between soil particles, resulting in the sudden loss of shear strength in the soil. Granular soils, which rely on interparticle friction for strength, are susceptible to liquefaction until the excess pore pressures can dissipate. Sand boils and flows observed at the ground surface after an earthquake are the result of excess pore pressures dissipating upwards, carrying soil particles with the draining water. In general, loose, saturated sand soils with low silt and clay contents are the most susceptible to liquefaction. Silty soils with low plasticity are moderately susceptible to liquefaction under relatively higher levels of ground shaking.

For any soil type, the soil must be saturated for liquefaction to occur.

We did not encounter coarse‐grained soils in our explorations. In addition, no ground water was observed within the depth of the majority of explorations. We evaluated susceptibility of the fine‐grained soils using

Bray and Sancio (2006). In addition, we evaluated susceptibility of the soils to cyclic softening using Idriss and Boulanger (2008). Based on our analysis, the site are not be susceptible to liquefaction or cyclic softening. However, these soils have low shear strength and slopes built with these soils are susceptible to failure during seismic events. Refer to Section 5.0 Ground Settlement and Global Stability for further discussion.

4.5 Surface Fault Rupture

Geologic hazards at the project site are predominantly related to seismicity from earthquakes based on the many relatively young faults mapped throughout the Klamath Basin. The relatively young and undissected sections of the major fault scarps as well as absence of established streams within much of the mapped area indicate that the most recent movements on the major northwest‐trending faults are relatively young. The vertical displacement along these faults have formed the highlands versus the valleys in the area (Hladky and Jenks 2007). Historical records and geologic evidence suggest that one or more earthquakes with moment magnitude (Mw) of 4 to 6 occur in south‐central Oregon every few decades

(Wiley et al. 1993). A seismic‐reflection survey of Upper Klamath Lake discovered evidence of at least three faulting events that postdate 7,000‐year‐old Mazama (Crater Lake) tephra with vertical offset up to 10 feet

(Colman et al. 2000), indicating ongoing seismicity in the project area.

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In addition to the geologic mapping, we reviewed readily available geologic hazard data from the Oregon

Department of Geology and Mineral Industries (DOGAMI) and the USGS. According to these sources, a well constrained strand of the Klamath graben fault system is mapped crossing the site from northwest to southeast near Lower Klamath Lake Road (Hladky and Jenks 2007; Personius 2002). The presence of silicified rocks and geothermal wells also indicate the potential presence of a fault at the site but the exact trace of the fault is poorly defined and may be represented by a wide zone of deformation in the subsurface. The most recent movement on the fault is listed as “Latest Quaternary (less than

15,000 years)” with an estimated slip rate between 0.2 and 1.0 millimeters per year (0.008 and 0.04 inches per year) (Personius 2002). Sense of motion on the fault is classified as “normal” with a dip of 51 to

58 degrees to the west (Personius 2002), implying land west of the fault is being displaced downward relative to land on the east side of the fault. The recurrence interval on this fault is estimated to be one earthquake in 3,000 to 7,000 years based on studies of related fault zones nearby (Coleman et al. 2000;

Personius 2002). Additionally, a study of a fault zone approximately 50 miles north of the site found evidence of 3.3 to 6.6 feet of vertical offset that could be attributed to a single seismic event (Bacon, Lanphere, and Champion 1999).

There are no historical earthquakes recorded on the fault that passes through the site. However, the site is in a historically active seismic area. A series of strong earthquakes occurred on September 20, 1993, which was centered approximately 25 miles northwest of the site and near the city of Klamath Falls, Oregon. The earthquake sequences included M3.9, M5.9, and M6.0 earthquakes followed by several months of aftershocks (Wiley et al. 1993). These earthquakes were fatal and caused damage to more than

1,000 buildings. In addition, they initiated landslides throughout an area of approximately 162 square miles surrounding the epicenter. While no surface rupture or evidence of liquefaction were found, ground cracking due to the earthquakes were observed typically confined to artificial fill, especially in roadways elevated above the surrounding terrain (Wiley et al. 1993).

Based on our review of available fault mapping and the activity of the faults in the area, we anticipate the hazard from ground fault rupture to the site to be higher than normal and special provisions should be taken in structural and foundation design. Refer to Section 7.1 Foundation Design for more discussion.

4.6 Landslide

Landslide susceptibility at the site is mapped as “moderate – landsliding possible” within the generally low gradient areas that encompass the majority of the site while steeper topography in the vicinity of the site are mapped as “high – landsliding likely.” We noted that no historical landslides are mapped near the project area (Hadly and Jenks 2007; DOGAMI 2020b). Mapped mass wasting deposits, including fan deposits along the southwest flank of the adjacent Klamath Hills and talus‐colluvium deposits near the crest of the hills, are associated with areas where basalt is mapped at the surface. Hadly and Jenks note that large blocks of basalt at the base of the hills along Klamath Lake Road north of the project site indicate

“rockfall from normal erosion or from seismic events has happened in the past.” Unmapped landslides may exist in the vicinity of the site.

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5.0 Ground Settlement and Global Stability

5.1 General

The residual soil and Tertiary sedimentary bedrock encountered at the site is relatively weak and compressible. The placement of thick sections of fill will induce settlement in these native soils. Also, the construction of tall cut or fill slopes may result in slope instability (e.g., landsliding). Therefore, we conducted settlement and global stability analyses to evaluate the potential effects on these conditions on the proposed site improvements.

We conducted a settlement analysis to estimate the settlement that can be induced due to embankment construction. The soil properties used for the settlement analysis in this study were developed based on the results of consolidation testing performed on a relatively undisturbed sample of extremely soft (R1 rock hardness) mudstone. For conservatism and to account for potential variability in soil behavior across the site, we did not consider in our settlement analyses the presence of interbedded stiff layers of material that were often present in our explorations.

We conducted global stability analyses to evaluate the taller proposed cut and fill slopes at the site. The soil properties used for the stability analyses were developed based on the result of Proctor and unconfined compressive strength tests on remolded samples (representative of native soils used as fill) and a triaxial consolidated‐undrained (CU) strength test on a relatively undisturbed sample (representative of in situ materials).

5.2 Settlement Analysis

We evaluated the potential for ground settlement induced by proposed maximum embankment thickness

(20 feet) in the northwest portion of the site. We used a unit weight of 83 pounds per cubic foot (pcf) for the fill materials assuming the on‐site soils will be used for fill to model the ponds loads. The estimated settlement due to this thickest fill section is approximately 8 inches over an approximately 4‐ to 6‐week period. An additional 2 inches of settlement will occur with time due to secondary compressions.

5.3 Global Stability

We evaluated the stability of proposed cut and fill slopes at four representative sections, as shown on

Figure 3. We completed analyses for both static and seismic (pseudo‐static) conditions. Limit equilibrium methods were used in accordance with Chapter 7 of the Oregon Department of Transportation (ODOT)

Geotechnical Design Manual (GDM). A detailed description of the analysis methods and results are included as Appendix C.

A PGAM value of 0.572 g was used in our analyses. For the pseudo‐static stability analyses, the coefficient of horizontal acceleration (kh) was taken to be 0.29 g (1/2 As) and the coefficient of vertical acceleration

(kV) was assumed to be zero. Strength parameters of soils for different conditions were obtained from strength testing on the remolded and relatively undisturbed samples obtained during our explorations.

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We performed these analyses for three proposed 3 horizontal to 1 vertical (3H:1V) cut slope sections at north, east, and south of the site (Sections A, B, and D) with heights between approximately 10 feet at the north and 17 feet at the east and 20 feet at the south of the site. In addition, we performed stability analyses for an approximately 16‐foot 3H:1V tall fill section at Ponds D‐7 and D‐8 at the northwest corner of the site (Section C). The locations of these sections are shown on Figure 3 and results of the analyses are included in Appendix C as Figures C‐1 through C‐14.

Based on our evaluation, the proposed cut slopes are stable in static conditions and during seismic events.

For the tall fill slope represented by Section C‐C, we evaluated both short‐term, construction stability

(undrained soil parameters) and long‐term stability (drained soils parameters). Our short‐term, construction stability analyses indicated that due to the low undrained strength of the soils on site, embankments taller than 10 feet built with native soils as fill are not stable in the short‐term, unless provided time to allow excess pore water pressures to dissipate. Therefore, embankments over 10 feet tall that are constructed with native soils as fill should be constructed in a staged manner to heights up to

20 feet. Under staged construction conditions, both short‐term and long‐term static stability are acceptable. However, tall embankment slopes constructed with native soils as fill are potentially unstable in seismic conditions. Alternatively, if the first 10 feet of the embankment is built using imported structural fill materials, the full embankment can be constructed without staging the construction. The embankment constructed using the latter method will also be stable during a seismic event given the existing alluvium and fill are removed and replaced with imported fill. Refer to Section 10.4 Permanent Slopes for construction staging recommendations.

It should be noted that the slopes such as those proposed for the site that do not support structures are often not designed for seismic stability. Detailed seismic evaluation and stability mitigation methods are not part of the current study and further analyses is needed if increasing seismic stability of the sections is required.

6.0 CONCLUSIONS

Based on our research, explorations, laboratory testing, and engineering analyses, it is our opinion that the site is suitable for the proposed improvements, provided the recommendations in this report are included in design and construction. We offer the following general summary of our conclusions.

The site soils generally consist of thin layers of fill, alluvium, and residual soil underlain by mudstone.

These units have variable relative consistencies varying between soft to very stiff across the site. The site soils and mudstone contain variable amounts of diatoms and gypsum. The presence of these constituents causes these materials to have unique engineering properties, such as low dry unit weight, high moisture content, low strength, and moderate to high compressibility.

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The site soils, particularly the in situ mudstone materials, have very high moisture contents (typically ranging from approximately 50 to nearly 200 percent). As a result, site soils will be sensitive and prone to pumping and rutting during earthwork. Furthermore, they will generally need to be dried out to be used as on‐site structural fill. Typically, the soils would be aerated to physically dry them or amended with lime or cement to reduce moisture content. However, conventional “farming” to dry the soils will prove difficult unless significant time and effort is expended during dry, hot weather to aerate the soils. Additionally, due to the high sulfate content of the site soil, the use of lime or cement cannot be used without specialized measures being taken to reduce post‐amendment weakening and swelling of the soils.

Groundwater was not encountered through most of the site, except in the lower portion along Lower

Klamath Lake Road at MW‐1. The water observed in MW‐1 is expected to be shallow perched surface water; however, long‐term water level readings will be collected from the well to better identify the fluctuations of the water table at that location.

Due to the high plasticity of the site soils, they are expansive. This will require the foundation system be designed per OSSC Section 1808.6. Removal and replacement of expansive soil from beneath proposed building or the use of a mat‐slab, raft foundation, or post‐tensioned slab will be required.

Due to the high moisture content of the site soils, footing subgrades should be capped with a layer of imported crushed rock to reduce the potential for disturbance to the subgrades during construction and to increase sliding resistance.

The site is located in a seismically active area with mapped fault traces potentially crossing through the site. As such, surface rupture/distortion due to movement of fault going through the site has a higher than normal risk at the site. Therefore, the building foundation design will also need to account for the deformations due to long‐term fault movements and potential seismic events. However, design for resistance to a full fault rupture has not been considered.

Due to the relatively weak nature of the site soil, all proposed cut and fill slopes should have a maximum inclination of 3H:1V.

At this inclination, proposed cut slopes are stable under static conditions and during seismic events.

At this inclination, proposed fill slopes taller than 10 feet should be built in stages to allow sufficient time for excess pore pressures to dissipate and for the soils to achieve drained condition strengths. Alternatively, embankments taller than 10 feet can be constructed with imported granular soils as fill. Additionally, fill slopes constructed with native soils as fill taller than approximately 10 feet are expected to be unstable during seismic conditions. If increased seismic stability is desired, then additional evaluation and measures will need to be taken to stabilize the slopes.

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The following sections present our specific recommendations for earthworks and structural components of the project. We have developed our recommendations based on our current understanding of the project and the subsurface conditions encountered by our explorations. If the nature or location of the development is different than we have assumed, we should be notified so we can change or confirm our recommendations.

7.0 STRUCTURAL DESIGN RECOMMENDATIONS

7.1 Foundation Design

7.1.1 Discussion

We understand the planned structures for the project include harvest kettle structures between the ponds, a Hatchery building and a Maintenance Shed at the west side of the site, and maintenance and chemical storage sheds at the south of the site. The buildings at the west of the site are between 5,000 and

6,500 square feet in size and have finish floor elevation of 4,136 feet MSL. The southern maintenance shed is approximately 2,800 square feet in size and has a finish floor elevation of 4,140 feet MSL.

Based on the finish floor elevations, all footings for the proposed buildings will bear directly on mudstone except the maintenance shed at the west of the site, which will bear on up to approximately 6 feet of fill.

Kettle structures are expected to be embedded in proposed pond berms and to be founded in native soils, although some may be founded in mass fill.

Due to plastic nature of the site soils, they are considered to be expansive, and therefore, foundations should be designed in accordance with OSSC Section 1808.6. This will require removal and replacement of expansive soils from beneath the buildings or the use of a mat‐slab, raft foundation, or post‐tensioned slab. Additionally, due to the greater than normal potential for fault rupture at or near the site, we recommend the foundation system also be designed to resist potential fault zone deformations per criteria outlined in ASCE‐7‐16 (ASCE/SEI 2016) Section 12.13.9. (We note that section references design for soil liquefaction, and while liquefaction is not present at the site, the recommended criteria are appropriate for potential seismic ground deformation.)

The foundation design and construction guidelines provided in this section of the report will help improve resistance to expansive soil movements and the seismic performance of the proposed buildings. The design philosophy behind the OSSC/IBC is that a building will not become structurally distressed due to seasonal soil movement nor collapse during a design‐level earthquake. However, cosmetic distress may result from seasonal movements and during an earthquake functional and structural distress is likely to result, potentially rendering the structure unusable until repaired or replaced. If these performance criteria are not acceptable, we should be notified so we can modify our recommendations.

With this basic understanding of the building design and performance, we are providing recommendations for using a semi‐rigid foundation system, such as post‐tensioned slab or interlocking grade beams overlying select imported fill. The intent of the foundation system is to increase the rigidity of the building and help the foundations to deflect more uniformly (i.e., “tilt” vs. “bend”), resulting in less building

Klamath Falls National Fish Hatchery | 15 distress, as opposed to direct offsets that can occur with a conventional, lightly reinforced spread footing system. The intent is not to resist, but accommodate, the anticipated ground movements.

These foundation design and construction guidelines will help improve the service level performance of the proposed improvements.

7.1.2 Building Foundations Option 1: Interlocking Spread Footings with Removal of Expansive Soils

7.1.2.1 Dimensions and Bearing Capacity

The proposed buildings can be supported by grid‐style foundation system, where interior and perimeter footings are interlocked and no isolated footings are used. The footings should then be underlain by a minimum of 3 feet of non‐expansive, granular imported fill.

The footings should be tied together per Section 12.13.9 of ASCE‐7‐16 (ASCE/SEI 2016). For the design matrices, the structural engineer should assume that there is 6 inches of lateral spreading displacement and 0.75 foot of vertical movement over an approximately 50‐foot span (or equivalent ratio for different distances).

Footings should be at least 12 inches wide. The bottom of perimeter footings should extend at least 2 feet below the adjacent exterior grade, while interior footings should extend at least 12 inches below the base of the floor slab. Footings bearing on imported granular fill as noted below may be designed for a maximum allowable bearing pressure of 2,500 pounds per square foot (psf) for static (e.g., dead plus long‐ term live loads). This value may be increased by one‐third for short‐term loads (e.g., wind and seismic loads). These bearing pressure values represent net bearing pressures; the weight of the footings and overlying backfill can be ignored in calculating footing sizes.

The entire structure should be underlain by a minimum of 3 feet of non‐expansive, granular fill as described in…