Geotechnical_Report.pdf

FINAL GEOTECHNICAL REPORT

NEW SUNSHINE SUBSTATION

Publish Date: 10/19/2023

Submitted to:

City of Gallup

110 West Aztec Avenue Gallup, NM 87301

Submitted By:

YeDoma Consultants, LLC

523 Louisiana Blvd SE Albuquerque, NM 87108

YeDoma Consultants, LLC | 523 Louisiana Blvd SE Albuquerque, NM 87108 | Office: (505) 933-5030

Advancing Sustainable Infrastructure

10/19/2023

Attn: Mr. David Martinez City of Gallup PO Box 1270 Gallup, New Mexico 87305-1270

Subject: Geotechnical Investigations- New Sunshine Substation Gallup NM

Dear Mr. Martinez

YeDoma Consultants, LLC (YeDoma) is appreciative of the opportunity to support the subject project. We have enclosed our final Geotechnical Investigation Report for the subject project located in the City of Gallup, McKinley County, New Mexico. The attached report is the final deliverable for the authorized Scope of services.

We appreciate the opportunity to support the project. Should you have any questions or require additional information, please do not hesitate to contact us.

Respectively Submitted, YeDoma Consultants, LLC.

Copies: Addressee (1)

Jesse Reinikainen, PE Principal Geotechnical Engineer

TABLE OF CONTENTS

Page

1.0 INTRODUCTION

2.0 PROJECT DESCRIPTION

3.0 EXISTING SITE CONDITIONS

CLIMATE

GROUNDWATER

SOILS

GEOLOGIC SETTING

4.0 GEOLOGIC HAZARDS

STRONG GROUND MOTION

GROUND RUPTURE

LIQUEFACTION

EXPANSIVE SOILS

HYDROCONSOLIDATION

SOIL DISTURBANCE

ABANDONED COAL MINING REMNANTS

MINE TAILINGS- CORROSIVITY HAZARD

5.0 SUBSURFACE INVESTIGATION AND LABORATORY TESTING

DYNAMIC PROBING INVESTIGATION

GEOPHYSICS

FIELD RESISTIVITY STUDY

LABORATORY TESTING

R-VALUE TESTING

PROCTOR TESTING

RESISTIVITY TESTING

THERMAL RESISTANCE OF SOIL BACKFILL MATERIAL

DIRECT SHEAR STRENGTH

DENSITY AND UNCONFINED COMPRESSIVE STRENGTH OF COHESIVE SOILS

6.0 FOUNDATION DESIGN ANALYSES

FROST DEPTH

BURIED CABLE TRENCHES

SITEWIDE SUBSURFACE PROFILE

DESIGN PARAMETERS

LATERAL LOAD GEOTECHNICAL EVALUATION

SEISMIC HAZARD ANALYSIS

7.0 FOUNDATION TYPE SELECTION

DRILLED PIERS

8.0 CONSTRUCTION RECOMMENDATIONS

BURIED CABLE TRENCHES

CORROSION PROTECTION

CONSTRUCTION CONSIDERATIONS

CONCLUSIONS

LIMITATIONS

9.0 REFERENCES

LIST OF TABLES

Table 1 Geotechnical Project Summary Table 2: Climate Summary Table 3: OSE Well Summary Table 4: Summary of Soil Report Table 5: Summary of Geologic Units Table 6: Subsurface Investigation Summary Table 7: Seismic Refraction P-Wave Arrays Table 8: Major Index Properties Summary Table 9: R-Value Summary Table 10: Proctor Summary Table 11: Effect of Resistivity on Corrosion Table 12: Electrochemical Summary Table 13: Thermal Conductivity Summary Table 14: Direct Shear Test Summary Table 15: In-situ Specimen Unit Weight and Unconfined Compressive Strength Table 16: Sitewide Subsurface Profile Table 17: Axial Load Design Parameters Table 18: Lateral Load (L-Pile) Design Parameters Table 19: Seismic Design Parameters

FINAL GEOTECHNICAL REPORT: NEW SUNSHINE SUBSTATION

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1.0 INTRODUCTION

YeDoma Consultants, LLC. (YeDoma) was authorized by the City of Gallup to provide geotechnical services (Probing, Subgrade Testing, and Geotechnical Parameters) for the New Sunshine Substation (project). The project is a consultant design led by T&D Services. YeDoma has provided site investigations and our findings, conclusions, and construction recommendations for the project are included herein. The site is in the City of Gallup, north of Interstate I-40 in McKinley County. A location map is illustrated in Figure 1. It is our understanding that the project will add electric capacity infrastructure to further improve the City of Gallup’s electric grid network. The new site work will be north of a housing development in Sunshine Canyon. Historically, this area had prior land use, coal mining. The Gallup coal field historically provided an important resource as early as 1870, by 1882 the rail lines led to a boom in annual production which exceeded 4,000,000 tons per year. This report includes a discussion about tailings which were spread across the site and present challenges with regard to corrosion issues. In our site evaluation, our finding is that the tailings were spread across the site more than one hundred years ago and have undergone consolidation sufficient to build upon assuming that construction materials are protected against a severe corrosive environment (steel and concrete provisions) based on our electrochemical testing. The project is feasible from a geotechnical viewpoint.

2.0 PROJECT DESCRIPTION

The New Sunshine Substation general layout was provided in the T&D Services work statement and supplemental Google Format “Kmz” file. A figure of the concept layout of the substation is illustrated in Figure 2. YeDoma used a publicly available lidar data set from 2018 to generate a digital terrain model for our study. Our understanding is that the City of Gallup substation will improve capacity and reliability of the power grid. The site design work being undertaken with T&D Services is still in the concept phase and we reached out to request probable structural loads for our study. We understand that the foundations will require resisting vertical pile head reactions on piers of up to 100 kips based on the concept plans. The work will also be anticipated to include civil site improvement work (earthwork, grading, shaping, and blading, road access and drainage improvements). A geotechnical summary of the project is presented in Table 1 and includes our project specific recommendations.

Table 1 Geotechnical Project Summary

Client: City of Gallup | New Sunshine Substation Project Coordinate: Lat:35.54227 Long: -108.72996 Scope of Investigation: Total of eight (8) probing locations, two seismic refraction (P-wave) and ground resistivity arrays (4-point Wenner Method), eight (8) Dynamic Probes (DCP-SH) utilizing a track rig, subsurface sampling, and testing. Dynamic probing has same theoretical energy (140# Hammer with 30” Fall) as Standard Penetration Test, continuously probed to total depths up to 25 feet, all probing and laboratory testing conducted under oversight of YeDoma’s Licensed Professional Engineer.

Project Improvements (Major Features):

1. New Construction: High Voltage Electric System Facility (Substation) Summary of Site-Specific Features and Geologic Hazards

1. Undulating terrain, variability in subsurface conditions within short lateral offsets.

2. Corrosive soil environment, include provisions for corrosion protection for all exposed metal and use of a Type V cement.

3. Past coal mines adjacent to site, history of coal mine fires

Geotechnical Site Classifications Soil Description: Material varies from mine tailings to valley alluvium to carbonaceous shale and sandstone rock (Upper Cretaceous Mesaverde Group). firm to hard, dense to very dense sand, silty sand, silty clayey sand. Localized areas of soft ground present exhibiting weak low bond strength.

AASHTO (Soil) A-2-4, A-6, A-7-6, A-4

ASTM (Soil) CL, SC, SM, SC-SM

Seismic Site Classification Site Class “C”

Foundation Selection Type (Preferred): Deep foundations- Drilled Shaft (Piers)

Summary Information included in Geotechnical Report

1. Soil Profile: Mine Tailing Fill, silty sand, shale and sandstone bedrock conditions

2. Laboratory Testing: At locations tested, Natural Gravimetric Moisture Content varied from 2.8 – 10.0% from grab samples and

7.1 -12.3 % in-situ. pH varies from 7.06 to 8.21, soil resistivity determined in lab ranging from 409 - 1409 ohm-cm, Groundwater Conditions: Free water not present to the depths explored

Construction Recommendations:

1. Protect against a severe attack potential to concrete and metal. Exposed metal should have polymeric precoated galvanized steel or aramid fiber bonded galvanized steel protection. Concrete must be specified as Type V.

2. Classify and test compacted fill material (Proctor, Index testing)

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3. Compliance construction material testing to verify densities, lift thickness during placement and compaction of compacted fill.

4. Inspect reinforcement and formwork for shape, location and dimensions of the concrete member being formed.

5. Inspect drilled shafts and bottom of hole conditions for adequacy of bearing.

6. Verify use of required design mix, prepare concrete cylinders for strength testing, determine slump, volumetric air content, temperature of concrete brought to the site.

Project Schedule: Geotechnical Work completed in September 2023, Facility Construction: TBD

3.0 EXISTING SITE CONDITIONS

The project is in the Gallup area, which is a prominent urban center for the adjoining Navajo Nation communities.

The New Sunshine Substation is on the north side of I-40 within the Sunshine Canyon area. Access is available from local roads with controlled access through a locked gate. YeDoma conducted a desktop study and presents a summary of our understanding including climatic, groundwater, soils, and geologic setting in the subsections below.

Climate A climatic summary is presented in Table 2. Seasonal variability and climatic factors (environmental effects) are characterized as typical for the Colorado Plateaus region. For this project, the climate data from the Gallup Municipal Airport (Western Regional Climate Center, Station Number 293422) is referenced. The period of record is from 1973 to 2016. Average daily temperatures below freezing (freezing degree-days) are common during the months of January and December. The air-freezing index (Base 32° Fahrenheit) for the site is 685 Degree-Days based on a 100-year return period probability. YeDoma used a US Army Corp of Engineers Method to determine depth of frost is about 2.9 feet (with a factor of safety of 1.5). We recommend that footings be seated a minimum of 34 inches below the ground level to protect against frost heaving and thaw weakening conditions.

Table 2: Climate Summary

Month Average Total Precipitation (inches)

Average Total Snowfall, (inches)

Average Max.

Temperature (°F)

Average Min.

Temperature (°F)

Average Daily Temperature (°F)

January 0.80 6.4 44.3 13.6 29.0 February 0.70 6.1 48.8 18.1 33.5

March 0.75 3.8 56.3 22.7 39.5 April 0.52 2.3 64.8 28.2 46.5 May 0.55 0.6 74.2 36.6 55.4 June 0.42 0.0 85.1 45.0 65.1 July 1.72 0.0 87.7 53.9 70.8

August 1.92 0.0 85.1 52.8 69.0 September 1.13 0.0 78.9 43.9 61.4

October 1.00 0.7 67.8 30.9 49.4 November 0.84 4.1 54.3 20.2 37.3 December 0.72 6.6 45.1 13.4 29.3

Annual 11.08 30.6 66.0 31.6 48.8 Note: Data from the Western Regional Climate Center, based on unofficial values for station 293422.

The precipitation increases from July to October relative to the rest of the year (monsoon season). Freezing temperatures may be expected during the months of October to April; however, daily temperatures typically are above freezing.

Groundwater State Engineer Office (OSE) public well records were reviewed, and three wells (refer to Appendix B figures) tagged by the project team to provide context for the hydrogeologic conditions. Table 3 is a summary of the well data reviewed in this study. Of the wells studied, G-03261 may have the most reliable data due to it being a relatively young well, drilled in 2020, with depth of water logged at 400 feet, however there were data gaps in the public information made available. G-00215 well log was used to determine a depth of ground water of about 160 feet reported in 1993. The upper 80 fete is alluvium, consolidated deposits at depth include shale, coal and sandstone.

It should be noted that the actual locations of these wells were not field verified, and therefore the locations may

3 | P a g e vary from the plotted locations derived from the OSE database. We anticipate that the subsurface hydrogeologic conditions will be similar to the G-00215 well upon a cursory review, with the exception that however this would need to be validated with a deep exploratory drill program into the sandstone layer. The shallow well G-02893 is an environmental well developed for water quality testing purposes in an urban area.

Table 3: OSE Well Summary

Well/Water Right File No. G-00215 G-02893 G-03261

Borehole Proximity 1 mile Southeast of Site 1 mile Southwest of Site 0.75 miles East of Site

Date of Completion 06/1993 12/2011 05-2020

Depth of Well, ft bgs 160 30 560

Depth to Static Water Level, ft bgs 80 10 400

Water-Bearing Formation

Fractures in sandstone (140-160 ft bgs)

High plasticity Clay (0-30 ft bgs)

Sandstone (360-560 ft bgs)

Other Types of Material

Encountered

Alluvial Fill (0-80 ft bgs) Shale (80-100 ft bgs, 102-120 ft bgs)

Coal (100-102 ft bgs) & Sandstone (120-160 ft bgs)

N/A N/A

Estimated Yield, GPM 20+ 1 20

Note: ft=Feet, bgs=Below Ground Surface, GPM=Gallons per Minute, N/A=Not Available

Soils Available soil mapping was reviewed. The United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) mapped the entire McKinley County. A copy of the site-specific soil report is included in Appendix B. The mapping occurred at a scale of 1:24,000 and accessed through an online portal (Web Soil Survey) for the Gallup Sunshine Substation Project. In our review, the entire project area is classified as a single soil type.

Table 4 illustrates a summary of the soil mapping information. The soil is characterized as clay and sandy clay (CL, SC) with a low to medium plasticity which is consistent with our site-specific material test results.

Table 4: Summary of Soil Report

Map Unit Name Mentmore loam 1-8% slopes Borehole Locations All

Symbol 241 Parent Material Fan and slope alluvium derived from sandstone and shale

Landforms Dip slopes on cuestas, fan remnants on valley sides, and drainageways Drainage/Runoff Well drained, medium runoff

Transmissivity Moderately high (0.20 to 0.57 in/hr) Salinity Nonsaline to very slightly saline

Depth to Restrictive Feature > 80 inches Depth to Water Table > 80 inches

Plasticity Low to Medium plasticity, PI Range (7-25) AASHTO Classification A-7-6

Unified Classification System CL Note: PI=Plasticity Index, NP=Sample Nonplastic

Geologic Setting The project is within the Colorado Plateau physiographic province of New Mexico. The area is underlain by sedimentary rocks that range in age from Cambrian to Tertiary, bedrock outcrops in the area are Permian and younger Mesaverde strata in the Gallup-Zuni coal basin. Hillslope alluvial fan and eolian deposits typically overlie the lowlands which have been incised by young stream channel deposits in undifferentiated alluvium (Pleistocene to modern channels). Regionally, sedimentation and erosion has been ongoing throughout the Cenozoic time.

Topography is relatively flat with the sandstone caprock sedimentary rock sequences and volcanic episodes which have been eroded to form ridgelines and flat-topped plateaus, buttes, and mesa features. The anticline in the Gallup area exposes upper sandstone layers of the Crevasse Canyon Formation. The sedimentary rocks in the project area range from very weak to medium strength.

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The topographic features were studied using a digital terrain map within the Sunshine Canyon study area. The Sunshine Mine (Nickelson, 1988) was situated in this area, which was one of the early mines (1889-1892) within Section 10, T15N, R18W, and later included the Black Diamond Mine (Diamond Canyon to the West) and the Biava No.2 and No.3 mines which employed hundreds of employees at the turn of the 20th century. The mine sites included shafts and mine entrances which excavated laterally into the hillslopes, typically at the base of sandstone bluffs. The coal seams were about five to six feet in thickness and were mined laterally up to several thousand feet with narrow gauge rail. Many of the abandoned mine entrance works have been sealed and there is also noted to be occasional fires that occurred within coal seams (rust colored mounded soil). Rail spurs were constructed to access the coal and shelters were dug out of the rimrock. The refuse from the mines was stockpiled and spread across (fill) the Sunshine Canyon valley floor, which is the site of the New Sunshine Substation. Most coal mining occurred prior to regulatory oversight and control measures. The site may require consideration of grading, runoff, and sediment control measures to limit offsite flow. The site’s soil is corrosive due to leaching of coal byproducts, exposure to metal and concrete material should include corrosion protection measures.

Table 5: Summary of Geologic Units

Geologic Unit Identifier Unit Description Alluvium Surficial Deposits (Holocene and Pleistocene)

Qa Alluvial deposits undifferentiated. Silt, sand, and gravel in small stream valleys and on flood plains. Valley fill deposits of gravel, sand, silt and clay, grades upslope to colluvium, contains some eolian deposits locally.

Qae Alluvial and (or) Eolian, Windblown silt and sand on mesas, benches, and in broad valleys; reworked in part by running water.

Qao Alluvium and (or) eolian deposits of older surfaces such as terraces and pediments- Brown clay and silty sand and gravel; commonly cemented by caliche and veneered with eolian deposits.

Crevasse Canyon Formation (Upper Cretaceous)

Kcb, Kcd Bartlet Barren Member, light-gray and light-olive gray, very fine grained lenticular interbedded, sandstone, gray siltstone, gray and brown carbonaceous shale and beds of coal. Contains more sandstone, less carbonaceous shale, coal beds typically less than 14 inches thick, forms ledge slopes. Mining operations: Dilco Coal Member (Kcd), light-colored sandstone and shale with valuable widespread coal beds

4.0 GEOLOGIC HAZARDS

Strong Ground Motion The intensity of the ground motion at a site is a function of the distance to the fault rupture, local soil/bedrock condition, earthquake magnitude, direction of rupture among other factors. The risk of ground motion is mitigated by designing structures to resist seismic loads in accordance with building codes and other applicable design guidance documents.

Ground Rupture Ground rupture caused by movement along a fault could result in catastrophic structural damage to infrastructure constructed along a fault trace, however, the potential for fault rupture at this site is low and no special mitigation is needed.

Liquefaction Soil liquefaction results from the earthquake-induced temporary buildup of excess pore water pressure, which can result in a condition of near-zero effective stress and the temporary loss of strength. This condition typically occurs in loose to medium dense strata beneath the groundwater table, typically within the upper 50 feet of a site.

Groundwater was not present to the maximum depth investigated. The material present is mine tailings, dense clayey sand which are not considered susceptible to liquefaction.

Expansive Soils Expansive soils consist of moderate to high plasticity (CL, CH) known to damage near-surface improvements due to shrinking and swelling upon wetting and drying cycles. The near surface soils present across the site have a high fines content and classify as clay and clayey sand, which will be prone to some expansion when compacted on the low side of optimum. Expansive soil conditions are typically mitigated by removal and replacement with select fill to suitable cover height to offset the expansion pressure, maintaining positive drainage away from structures and pavements, increasing the amount of steel reinforcement in foundations and slabs, deepening footings and or placing mats of non-expansive soil below structures. There is not anticipated to be excessive expansion based on

5 | P a g e the plasticity of the material, structural features should rest on about two feet of non-expansive soil to minimize the effects of underlying expansive material.

Hydroconsolidation Hydroconsolidation collapse is a geologic hazard where soils undergo a decrease in volume (settlement) upon wetting. The saturation occurs through environmental changes, irrigation, pipe breaks or leaks, or other factors.

The site is underlain by stiff fine-grained materials that are not considered susceptible to collapse unless the soil is disturbed. There is minimal risk of hydroconsolidation at the site.

Soil Disturbance Soils disturbed by earthwork operations have been known to undergo further loss of strength over time, due to a change in the soil structure. Control of surface water is typically part of the site development and grading plan.

Abandoned Coal Mining Remnants Remnants of past mining activity are evident in the Sunshine Canyon and immediately beneath the project area, refer to inset map with mines from Section 10, T15N R18W. Prominent mines include the Sunshine mine #GE-11 and Biava #GE 10,32 33,34 to the northeast of the substation. In our desktop review, mining ranged small workings with sparse information to large mining operations that employed several hundred people at a time with rail spurs set up to transport the coal for processing and distribution. The by-product of coal mining is tailing spoils.

Finely ground rocks, coal chips, and mining era rubbish and debris have been buried in the tailing mounds. The tailings fill the Sunshine Canyon valley in the project location, typically comprised of red and purple hues of silt, clay, and sand with small gravel chips of coal are the primary constituents. Site development should anticipate variability within short lateral offsets from the locations probed and risk of buried debris including larger cobbles and boulders. Our geotechnical investigation provided a continuous data set through the tailings and established bedrock contact at depth. A potential hazard is unmarked coal mine shaft in the vicinity dug prior to existing records.

Mine Tailings- Corrosivity Hazard AT the site, coal mine tailing piles are present. The material is corrosive to steel and concrete. The resistivity of the soils and sulfate content (geochemistry) along with other harmful chemical compounds within the soil mass present a geohazard.

Refer to Figure 1 which illustrates corrosion and pitting attack of steel, photo from site geotechnical investigation for the Gallup Sunshine Substation. Corrosivity is a geohazard and should be properly mitigated due to the extremely aggressive soil conditions in the subsurface. Chemical constituents that were evaluated for this project include pH, sulfate and chloride ions, the sulfate exceeded 2000 ppm in three of the four samples, and minimum resistivity of soil was about 400 ohm-cm, indicators of highly corrosive soil conditions.

5.0 SUBSURFACE INVESTIGATION AND LABORATORY TESTING

Our geotechnical investigation program consisted of site reconnaissance, conducting probing, augering and sampling of subsurface strata. We conducted seismic refraction and resistivity arrays for site characterization purposes. There was a total of eight locations investigated, notably one added above the minimum specified in our pre-work exploration plan. This added location was used to gain confidence in the lateral and vertical continuity of soil subunits.

Dynamic Probing Investigation YeDoma conducted a drilling investigation on September 18th -20th 2023. Probing locations are illustrated Figure 3.

Soil probing logs are collated in Appendix C. The workplan was developed considering drilling conditions, access constraints, local, state, and regional standards, and guidance documents. The probing work was carried out with our two-person field crew under the oversight of a licensed geotechnical engineer. The work included continuous probing and shallow auger sampling techniques. Refer to geotechnical site map for probing locations. The probing equipment is referred to as a “Grizzly”, it is a small track rig that is equipped with tooling that includes a standard

6 | P a g e penetration (140-pound hammer with 30” drop height) equivalent to 4200-lbs-inch of theoretical energy (DCPSH) deployed with each consecutive blow, with about 80% hammer energy efficiency. The Anvil is made of high strength steel and the fixed 3 square-inch cone has an apex angle of 90° The technique is referred to as "dynamic probing" and is standardized under British Standard BS 22476-2. The number of blows required to drive the penetrometer over 8" (N20) is used by YeDoma to evaluate in-situ strength conditions. Refusal is logged as 20 blows per 4” increment and/or bouncing of the rods on rock. Table 6 presents a summary of the investigation. YeDoma evaluates the number of blows per foot based on the data collected and has determined that this number closely matches with the Standard Penetration Test results based on past comparisons with twin test results. For identification and classification purposes, YeDoma collects samples using the continuous sampler and auger tooling at various depths of the investigation. The elevations were derived from 2018 DTM data converted to imperial units.

Table 6: Subsurface Investigation Summary

ID Date Easting (Feet)

Northing (Feet)

Latitude (Decimal Degrees

Longitude (Decimal Degrees)

Elevation (1-Meter

DTM)

Total Depth (feet)

B-1 9/19/2023 2456441.0 1653776.8 35.541942 -108.729661 6587.4 13.78

B-2 9/19/2023 2456359.2 1653777.6 35.541942 -108.729936 6588.3 23.62

B-3 9/18/2023 2456499.8 1653792.5 35.541986 -108.729464 6586.3 15.75

B-4 9/18/2023 2456417.4 1653817.5 35.542053 -108.729742 6587.9 8.53

B-5 9/20/2023 2456499.3 1653827.9 35.542083 -108.729467 6587.2 16.73

B-6 9/18/2023 2456416.9 1653852.9 35.54215 -108.729744 6589.2 15.42

B-7 9/18/2023 2456318.6 1653860.8 35.542169 -108.730075 6592.4 24.93

B-8 9/19/2023 2456480.7 1653795.7 35.541994 -108.729528 6587.6 15.75

Note: Easting and Northing are Grid Coordinates/ NAD 83 State Plane Coordinate Datum (3003) New Mexico West/Feet.

Geophysics Yedoma conducted two seismic refraction arrays on September 20th 2023. Seismic-refraction methods are typically used in geological engineering applications such as transportation studies to determine a feet per second (fps) first arrival compression wave velocity (P-wave), depth to bedrock, and characterize the subsurface strata with lateral continuity. YeDoma conducts the work with a three-person crew, the equipment includes a geode (Geometrics), twenty-four, 4.5 hertz, geophones, and a laptop with Seisimager software to collect the data files. Surface elevations were derived from the project survey files provided by . First arrivals are picked manually and post-processed using the time-term interpolation method to generate an initial model. The model is used to prepare a 2-D seismic velocity tomographic section view. The section-view is generated from surface elevations at each geophone and typically extends about 1/3 of the array length. P-wave seismic velocities are a measure of the time it takes for a compressional sound wave (first arrival) to travel downward through substrata to the contact with a denser layer and registered as a time of arrival at each of the 24 geophone detectors. It is analogous with 24 drill holes tightly spaced apart. Ambient noise can be a limitation, however at the site, relatively minimal disturbances from pedestrian traffic and wind were noted. The method has a limitation with respect to hidden layers, described as dense strata underlain by loose strata. P-waves will not detect the “hidden” loose strata. Probing and deep borings at the site were used to confirm that the effect of hidden layers was negligible. There can be some ambiguity in resolving the subsurface layers, as the increase in seismic velocity is a function of both increases in porosity as well as increases in density of the medium. This can be problematic in areas with a shallow groundwater table or where the moisture content of unsaturated soil fluctuates, loose/soft cohesive soil in some cases can have a higher velocity than dry, densely packed sol. This limitation can also be overcome by probing and sampling the subsurface strata and identifying shallow groundwater. Sitewide, the seismic data confirmed the geologic profile of the subsurface, two major units were delineated in each of the seismic lines, with a transitional layer that is described as residual soil.

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Refer to Table 7 for a summary of each seismic line which are illustrated in Appendix D. It is noted that there is variability in the seismic section and station is specified in the table to provide corresponding subunit velocities and thickness noted at that specific station. The velocities below 1400 fps are an indication of loose/soft strata with anticipated low bond strength conditions.

Table 7: Seismic Refraction P-Wave Arrays

Seismic Array ID (station)

Surface Elevation

(feet)

Subunit A

Seismic Velocity

(fps)

Subunit A

Layer Bottom

Elevation (feet)

Subunit A1

Seismic Velocity

(fps)

Subunit A1

Layer Bottom

Elevation (feet)

Subunit B

Seismic Velocity

(fps)

Subunit B

Layer Bottom elevation (feet)

Subunit C

Seismic Velocity

(fps)

Subunit C

Layer Top

Elevation (feet)

Comment

SL-1

@ +30 feet

6587 1540 (Tailings)

8 feet thick layer

2900 6562 16 feet thick layer

13 feet thick layer

5080 - B-3 refusal at

’ 15.7’.

SL2

@ +125 feet

6590 1750 6578 12 feet thick layer

2350 6560 12 feet thick layer

13 feet thick layer

4850 - B-7 refusal at

’ 15.7’.

Field Resistivity Study Field resistivity arrays were conducted at two locations, coinciding with the seismic refraction array lines. The field resistivity testing was conducted using the 4-point Wenner Method per ASTM G57-20. Results are provided in Appendix C plotted with each probe spacing. in addition to the laboratory resistivity measurements conducted per AASHTO T288 which were tested at full saturation levels. The spacing of the rods varied from 3 to 150 feet and based on widely fluctuating results within the 3 to 20-foot spaced probe range, there is an indication of locally severe conditions.

Laboratory Testing YeDoma's senior engineer provided final approval of our laboratory testing regime. The final testing regime was based on major soil type (granular), site improvements, and the local site conditions present at the time of the investigation. The samples were logged in the field and transported to our AASHTO Resources (formerly AMRL) nationally accredited laboratory in Albuquerque, New Mexico. The testing regime included both ASTM and AASHTO test methods and standard procedures. The natural moisture content was preserved in the field using sealed tins and were tested per ASTM D2166. The index tests included determination of the particle size distribution per ASTM D6913, Atterberg limits including the Liquid and Plastic Limits per ASTM D4318. Evaluating the soil-moisture characteristics (soil subgrade strength and expansion pressure) was conducted under the R-value test per ASTM D2844. The moisture density relationship of the compaction characteristics of native soil per ASTM D698.

Electrochemical testing included minimum resistivity and pH determination per AASHTO T288/289. Determined the parts per million (ppm) of Sulfate, per AASHTO T290, and Chloride, per AASHTO T291, present in the soil. The drained shear strength was determined per ASTM D3080. A summary table which includes major index properties is presented in Table 8 with individual tests included on the lab reports in Appendix E.

Table 8: Major Index Properties Summary

Sample Location / ID

Depth (feet)

Soil Description

LL

(%) PI MC

Soil Type

(USCS)

Gravel

Coarse Sand

Med-Fine Sand

Silt and Clay

B-01 216-01

0’-10’ Clayey sand 26 10 - SC 0.2 1.2 48.8 49.8

B-01

ILZ

6.5’-7.5’ - - - 7.1 - - - - -

B-02 216-06

0-10’ Sandy lean clay 27 11 - CL 0.2 2.2 42.8 54.9

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Sample Location / ID

Depth (feet)

Soil Description

LL

(%) PI MC

Soil Type

(USCS)

Gravel

Coarse Sand

Med-Fine Sand

Silt and Clay

B-02

DI1

4.5’ - - - 10.0 - - - - -

B-02

UUL

10’-11’ - - - 8.8 - - - - -

B-03 216-11

0’-6’ Silty sand 23 3 - SM 0.3 0.7 62.5 36.4

B-03

AGU

5’-6’ - - - 5.1 - - - - -

B-03 B1

6’-6.5’ - - - 5.1 - - - - -

B-03 B2

7.5’-8’ - - - 7.5 - - - - -

B-03

HUF

9’-10.4’ - - - 8.8 - - - - -

B-04 216-16

0’-12’ Silty, clayey sand 23 5 - SC-SM 0.7 1.3 58.6 39.4

B-04

PTU

11’-12’ - - - 4.7 - - - - -

B-04 216-21

12’-14’ Silty sand NV SNP 6.1 SM 0.6 1.2 65.7 32.6

B-05 216-24

0’-6’ Silty sand NV SNP - SM 1.5 4.1 54.3 40.0

B-05

OKN

5.5’-6’ - - - 6.6 - - - - -

B-05 216-28

6’-9’ Silty sand NV SNP 5.7 SM 4.1 1.9 46.5 47.5

B-05 216-30

9’-13’ Silty sand NV SNP - SM 1.7 2.8 60.3 35.1

B-05 X7S

12’ - - - 5.3 - - - - -

B-05 216-32

13’-15’ Silty sand NV SNP 5.1 SM 2.7 2.8 57.1 37.4

B-06 216-34

0’-15’ Clayey sand 25 9 4.8 SC 0.9 0.8 53.2 45.1

B-06 216-39

15’-15.5’ Clayey sand 29 14 8.2 SC 1.7 0.5 54.2 43.7

B-07 216-41

3’-6’ Clayey sand 24 8 - SC 1.5 4.2 50.1 44.2

B-07 216-44

6’-9’ Sandy lean clay 24 8 - CL 0.1 1.6 48.1 50.2

B-07

3QV

7.5’-9’ - - - 5.2 - - - - -

B-07 9’-12’ - - - 4.2 - - - - -

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Sample Location / ID

Depth (feet)

Soil Description

LL

(%) PI MC

Soil Type

(USCS)

Gravel

Coarse Sand

Med-Fine Sand

Silt and Clay

C2 B-07 C3

12’-15’ - - - 2.8 - - - - -

B-07 216-49

15’-18’ Clayey sand 22 8 3.1 SC 0.1 0.8 55.7 43.4

B-07

VG2

20’ - - - 3.4 - - - - -

B-07 C5

21’-24’ - - - 3.7 - - - - -

B-07 216-53

24’-27’ Sandy lean clay 30 17 - CL 0.1 0.1 43.7 56.1

B-07 D1

25’-27’ - - - 7.0 - - - - -

B-07

OB2

27’ - - - 9.0 - - - - -

B-07 D2

27’-28’ - - - 7.2 - - - - -

B-08 216-55

0’-9’ Sandy lean clay 26 11 4.8 CL 0.6 0.8 45.8 52.7

B-08

RFZ

8’-9’ - - - 6.2 - - - - -

B-08 D4

9’-13’ - - - 7.3 - - - - -

Note: MC=Moisture Content, PI=Plasticity Index, LL= Liquid Limit, NV=No Value, SNP=Sample Nonplastic, “-“ =Not Determined

R-Value Testing YeDoma's R-value equipment includes a James Cox and Sons kneading compactor and 50-kip press. YeDoma conducted R-value tests per ASTM 2844, to evaluate the compressive and lateral resistance of native subgrade material. The R-value test is typically used in evaluating the strength of subgrade soil for pavement design at 300 psi exudation (saturation) conditions. The test is very useful in determining settlement potential, bond strength, and expansion pressure which makes it useful in geotechnical engineering applications. The test has multiple stages over three days, which includes prepping the sample, curing 12 hours, compacting, and testing the exudation test, placing the molds in frames for an additional 12-hour period to determine the expansion pressure of the compacted specimen, and finally on the third day, extracting the sample into the stabilometer and loading compressive force while logging the horizontal pressures and lateral strength at saturated conditions. The tests are semi-automated with LabVIEW software developed by Caltrans. The compacted soil was tested to determine soil behavior under various loading conditions. Bond strength values were determined for each test, with an average of all values reported as 25 psi. Refer to the test reports in Appendix D for additional information about the samples. The R- Value test summary is presented in Table 9 below.

Table 9: R-Value Summary

Sample ID Borehole ID Depth (feet) R-Value

Geotechnical Properties of Compacted Soils

MC (%) Dry Density (pcf)

Expansion Pressure (psf)

Bond Strength (psi)

216-03 B-01 0’ – 10’ 21 13.3 114.2 236 22 216-08 B-02 0’ – 10’ 15 14.2 113.9 213 15

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Sample ID Borehole ID Depth (feet) R-Value

Geotechnical Properties of Compacted Soils

MC (%) Dry Density (pcf)

Expansion Pressure (psf)

Bond Strength (psi)

216-18 B-04 0’ – 12’ 24 12.1 123.0 278 25 216-26 B-05 0’ – 6’ 58 12.5 110.1 266 24 216-36 B-06 0’ – 15’ 20 11.7 119.8 266 19 216-43 B-07 3’ – 6’ 39 12.1 119.7 235 26 216-47 B-07 9’ – 12’ 27 11.3 121.9 362 34 216-59 B-08 9’- 13’ 16 12.5 115.4 319 37

Note: R-Value at 300 psi exudation, MC=moisture content, Expansion Pressure= swell, Bond Strength=compacted soil peak bond strength, “-“ not determined

Proctor Testing

We conducted three tests to determine the moisture-compaction characteristics of native soil according to ASTM D698. YeDoma summarized results in Table 10 and included in the Appendix.

Table 10: Proctor Summary

Sample ID Location Depth (feet) Max Dry Density (pcf) Optimum Moisture (%)

216-13 B-03 0’ - 6’ 114.8 13.3 216-27 B-05 0’ - 6’ 105.4 16.0 216-60 B-08 9’ - 13’ 111.7 12.9

PCF=pounds per cubic foot

Resistivity Testing The relative level of corrosiveness, commonly accepted by the engineering community (FHWA NHI-09-087) as indicated by resistivity levels, is included in Table 11. The resistivity ranges in the moderately corrosive to mildly corrosive ranges are generally chosen as lower bound values (assuming the material is tested per AASHTO T288).

Researchers have roughly established a correlated increase in corrosion rate of 25 percent in each successive aggressiveness range.

Table 11: Effect of Resistivity on Corrosion

Aggressiveness Resistivity (Ω-cm) Very Corrosive <700 Corrosive 700 – 2,000 Moderately Corrosive 2,000 – 5,000 Mildly Corrosive 5,000 – 10,000 Non-Corrosive > 10,000

As part of YeDoma’s evaluation of site conditions, the soil resistivity and pH were tested on representative subsurface samples, refer to Table 12 and individual test reports in the Appendix E. The AASHTO T288 test method for resistivity includes saturating the soil sample with increasing moisture until the lowest resistivity value is reported. The pH was determined based on the AASHTO T289 test method. The water-soluble sulfate and chloride ion content in the soil was determined based on AASHTO T290 and AASHTO T291, respectively. Three of the four samples classify as very corrosive to metal and concrete.

Table 12: Electrochemical Summary

Probing Location

Sample

ID

Depth (feet) Soil

Description Chloride

(ppm)

Minimum Resistivity (ohm-cm) pH (SU) Sulfate (ppm)

B-03 216-15 0’ – 6’ Silty sand < 3 1409 7.1 165 B-04 216-23 12’ – 14’ Silty sand 40 416 7.6 2948

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Probing Location

Sample

ID

Depth (feet) Soil

Description Chloride

(ppm)

Minimum Resistivity (ohm-cm) pH (SU) Sulfate (ppm)

B-07 216-48 12’ – 15’ Clayey sand < 3 416 8.2 2712 B-07 216-52 21’ – 24’ Clayey Sand 13 409 8.1 2252

Thermal Resistance of Soil Backfill Material The technical scope of work included provisions for thermal conductivity testing. YeDoma developed recommended Rho values for the design of buried cables as part of the design phase work. YeDoma saturated five samples and periodically testing them as they dried out, and oven dried to a zero percent moisture test to conclude the lab work.

The results are presented in Table 13. The processing and testing occurred over a four-day period and the results were used to develop thermal dryout curves.

A total of five samples were tested. Thermal resistivity (rho) measurements were conducted on re-constituted samples which were moisture conditioned and left overnight to cure. The test equipment included our C-Therm TLS sensor, and each test was conducted in accordance with ASTM D5334 and the IEEE Guide for Thermal Resistivity Measurements of Soils and Backfill Materials. The test sample dimensions were 100 mm (4 inch) diameter x 200 mm (8 inch) membrane compacted to 90 – 95% compaction at optimal moisture content to simulate field conditions.

The TLS system was set at 0.25 W power and used a 4-minute read time which matched the calibrations conducted by YeDoma on glycerin prior to testing each batch of samples at the lab. All measurements were performed at room temperature. Thermal dryout curves were interpolated between the saturated wet, intermittent intervals, and final dry conditions. The complete set of test results were plotted in a combined thermal resistance chart presented below, whilst the individual tests are in the Appendix.

Table 13: Thermal Conductivity Summary

Sample Soil Description In-Situ Moisture Content

Rho Value Thermal

Resistivity (°C-cm/W)

Re- Constituted

Moisture content (%)

LL PI Dry Density

(pcf)

Wet Dry

B-1 Clayey Sand (SC) 7.1 62 755 12.6 26 10 106.2

B-2 Clay (CL) 8.8 65 323 17.3 27 11 106.4

B-4 Silty, clayey Sand (SC-SM) 6.6 73 470 15.5 23 5 110.0

B-6 Clayey Sand (SC) 4.8 46 370 14.9 25 9 112.2

B-7 Clayey Sand (SC) 5.2 96 263 15.3 24 8 105.8

Discussion:

The soils all have similar index properties such as Atterberg limits, moisture contents and particle size distributions (about 50% fine grained material) with subtle changes in particle sizes that led to different classifications.

A chart of the dryout curves is proved on the next page of this report. The moisture content of 9% is considered to be an appropriate threshold for in-situ moisture content based on our intact sampling. The sample B-6 is considered to be representative of the tailings material which has a rho value of about 110 at 9% moisture content. We recommend a single material for the design of buried cables.

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Direct Shear Strength The drained shear strength was determined in the laboratory per ASTM D3080. The sand material was reconstituted and tested by YeDoma's senior engineer. The conditions specified for the test considered the in-situ moisture conditions, the probable mode of failure and the incremental stress conditions anticipated at the site. The laboratory soil test conditions and results are summarized in Table 14. The detailed test reports are included in Appendix E.

Table 14: Direct Shear Test Summary

Sample ID Borehole Depth (feet) Angle of Shear Resistance (°)

Cohesion (psi)

216-04 B-01 0’-10’ 31.6 0.0 216-09 B-02 0’-10’ 30.3 2.6 216-14 B-03 0’-6’ 25.2 0.7 216-19 B-04 0’-12’ 29.0 4.2 216-37 B-05 0’-15’ 28.9 1.6 216-51 B-07 18’-21’ 24.4 5.5 216-57 B-08 0’-9’ 28.1 3.3 216-61 B-08 9’-13’ 25.7 0.2

Density and Unconfined Compressive Strength of Cohesive Soils The moist density, dry density, and unit weight of soils specimens were determined in the laboratory per ASTM D7263. All samples analyzed were in-situ material sampled from a split spoon in the field and tested under the supervision of YeDoma's senior engineer. The unconfined compressive strength (UCS) of intact samples was determined per ASTM D2166. All samples analyzed were in-situ material sampled from an SPT split spoon in the field and tested under the supervision of YeDoma's senior engineer. Multiple samples were collected at the same interval and the degree of disturbance was variable, low-density measurements may reflect minor post-sampling disturbance and were not considered in our assessment of the strength of soils. We considered the shear strength to be about one-half the magnitude of the UCS value. The average UCS value of 28.9 matches closely with our remolded samples determined by the R-value bond strengths. The laboratory soil test results are summarized in the following table. The detailed test reports are included in Appendix D.

Table 15: In-situ Specimen Unit Weight and Unconfined Compressive Strength

Borehole Depth (feet) Moisture Content

Dry Density (pcf) Unit Density (pcf)

Unconfined Compressive Strength (psi)

Shear Strength, Su (psi)

B-2 10 - 11 6.1 104.5 110.9 72.5 36.3 B-2 10 - 11 8.4 109.1 118.3 177.4 88.7 B-2 10 - 11 8.2 101.5 109.8 76.4 38.2 B-3 8 - 9 7.5 93.5 100.5 36.7 18.4 B-3 8 - 9 7.5 95.4 102.6 41.4 20.7 B-3 9.8-10.3 9.2 107.4 117.3 25.6 12.8 B-3 9.8-10.3 9.9 105.1 115.5 21.0 10.5 B-3 12.6 - 13.1 12.3 101.6 114.1 41.7 20.9 B-4 13.7 - 15 8.6 99.2 107.8 34.4 17.2 B-4 13.7 - 15 9.7 104.7 114.8 45.9 23.0 B-4 13.7 - 15 9.2 108.2 118.2 62.3 31.2

6.0 FOUNDATION DESIGN ANALYSES

The foundation design conducted by YeDoma considered site specific conditions, information from the in-situ probing, laboratory testing, findings from our desktop study and experience with similar soils.

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Frost Depth The minimum design frost depth is 34 inches below the ground surface.

Buried Cable Trenches Excavation of utility trenches is anticipated for buried cables and duct work. YeDoma has conducted soil thermal conductivity testing and provided design rho values in this report. The excavation material is anticipated to be suitable for re-use as thermally stable backfill. The excavation work is anticipated to be accomplished with a backhoe or excavator. Trenches should be braced or sloped in accordance with the requirements of OSHA. Utility trench backfill should be governed by the provisions of this report relating to minimum compaction recommendations. In general, backfill for buried cables should include moisture conditioning and compaction control, documenting a minimum testing of one nuclear densometer test per 100 feet of trench per lift. The compactive effort should meet a minimum of 90% of the ASTM D698 maximum dry density (MDD) and +/- 2% of optimum moisture content (OMC) as tested by a geotechnical laboratory (AASHTO accredited) and documented in the project construction files.

Where utility trench backfill is placed in the vicinity of structural features, the backfill should be compacted to at least 95% of the ASTM D698 MDD and OMC properties of the backfill. Foundation construction and site preparation may involve the construction of temporary slopes and shoring systems. The design of temporary slopes and shoring should consider support of adjacent foundations, utilities, and pipelines. Particular attention should be made to pressurized lines that may rely on the lateral support of the ground to constrain the pipeline against movement.

These considerations regarding utilities and foundations are general in nature. Poorly compacted backfill in pipeline trenches can result in settlement or impacts to adjacent structures that would normally not occur. Gravel bedding and granular backfill materials can serve as conduits that allow groundwater to infiltrate areas where it would not normally flow. The locations of existing and new utilities relative to foundations and grading should be considered in the foundations, structural, and grading plans for the project.

Sitewide Subsurface Profile There are three subunits delineated by YeDoma based on the seismic refraction P-wave study and ground truthed by continuous probing of the subsurface strata. The typical subunit section with elevations and thickness of units is based on Geoph-07/ B-13. The soil profile is expected to have lateral variability in other areas of the site; however, we anticipate that in general terms, similar subunit profiles can be interpreted with variable thickness of subunits.

It is noted that Subunit A was subdivided into an upper and lower section in the logs, however, upon further review of the seismic data, these soils have differences that relate more to the calcic development of the soils and likely to be gradational. The subsurface profile is presented in Table 16. The upper unit, Subunit A is clayey sand, Subunit B is an aged weakly cemented clayey sand to silty sand, and Subunit C is characterized as the Ceja Formation, the upper surface of the Santa Fe Group.

Table 16: Sitewide Subsurface Profile

Soil Profile Unit

Estimated Top Elevation (feet)

Estimated Thickness

(feet)

Estimated Seismic Velocity

Range (ft/s)

Average Blow Count (blows/foot)

Typical Lithology

Subunit A 6587 8 1640 21 Clayey Sand (SC)

Subunit A1 6578 16 2625 32 Clayey Sand (SC)

Subunit B 6500.3 13 4160 >50 Crevasse Canyon Formation, carbonaceous shale and coal beds

Subunit C 6489.1 - 4960 >50 Crevasse Canyon Formation, interbedded sandstone and siltstone

Design Parameters The following parameters were developed for the project based on field testing, understanding of the site subsurface conditions based on geophysics conducted at the site, laboratory testing under specified loading regimes. In determining parameters, reliability was considered using geostatistics and past experience with similar materials.

The design assumptions should be confirmed during the construction phase, sampling the formation will provide further confidence that the discrete strata layers and properties of material are re consistent with design assumptions.

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Table 17: Axial Load Design Parameters

Subunit Estimated Thickness (feet) Moist Unit Weight (pcf) Undrained Bond

Shear Strength (ksf)

Subunit A 8 110 0.9

Subunit A1 16 120 2.8

Subunit B 13 125 125

Subunit C - 128 288

Lateral Load Geotechnical Evaluation The geotechnical engineering work included analyzing soils in the laboratory and developing office recommendations for lateral loading using LPile (V2022.12.02). LPile is an Ensoft, Inc. software program with a closed solution for evaluating soil-structure interaction. Lateral load testing was conducted for the project to evaluate direct measurements of surface deflection at different loads.

Table 18: Lateral Load (L-Pile) Design Parameters

Subunit Moist Unit

Weight (pcf) qur

(psi) Cohesion

(psf) Strain Factor

(e50) ks, (pci) kc, (pci) L-Pile Soil

Interaction Material Type

Subunit A 110

- 0.01 500 200 Stiff Clay without Free Water

Subunit A1 120

28 0.005 1000 400 without Free

Subunit B 125

9360 0.004 640 640 without Free

Subunit C 128 300 Weak rock

Seismic Hazard Analysis YeDoma considered the seismic hazard conditions for the project and presented the results in Table 19. We estimated ground motion parameters for the design of structures. From a review of our subsurface conditions, the seismic soil classification is “C” very dense soil and soft rock, noted as Sc. We used a NAD83 Lat/Long Decimal Degree coordinate for the site to determine the parameters for use in building code-based seismic design. Our evaluation is based on AASHTO 2009 Seismic Design Reference for 7% Probability of Exceedance in 75 years (1,000-year Return Period).

Table 19: Seismic Design Parameters

Parameter Description Value Site Coordinates Latitude, degrees 35.54227°

Longitude, degrees -108.72996°

PGA Mapped Horizontal Peak Ground Acceleration, in units of g 0.067

FPGA Site coefficient from PGA 1.2 As Design Peak Ground Acceleration, in units of g 0.081 Ss mapped short-period (0.2 second) spectral acceleration, in units of g 0.135

Fa Site coefficient for Ss 1.2 S1 Mapped 1-second spectral acceleration, in units of g 0.036 Fv Site coefficient for S1 1.7

SD1 Design 1-second spectral acceleration, in units of g 0.061

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Parameter Description Value SDC Seismic Design Category A

7.0 FOUNDATION TYPE SELECTION

As part of the project geotechnical services, YeDoma conducted site characterization of subsurface units and used this information to review the foundation types that may be appropriate for the site. The main issue with the site is related to corrosive ground conditions with anticipated attack to metal and concrete. Another limitation with the site is excessive variability upon short lateral offsets from our investigation points.