6-4-CS27018-26381900-Hazmat Survey.pdf

GEOTECHNICAL ENGINEERING

INVESTIGATION

Brigham City UDOT Maintenance Facility Tow Plow Shed Geotechnical Investigation

Prepared For:

State of Utah – Division of Facilities Construction and Management

Attn: Carl Francis P.O. Box 141163

Salt Lake City, UT 84114

Prepared By:

Civil Solutions Group, Inc.

Prepared by: David Robison, P.G.

Reviewed by: John Powell, P.E.

498 West 100 South

Providence, Utah 84332

Original Submittal: June 30, 2026 REV1 July 1, 2026 REV2 July 15, 2026 Job Number: 26-154

RE: Brigham City UDOT Maintenance Facility

Tow Plow Shed Geotechnical Investigation

Dear Mr. Francis, Per your request this geotechnical engineering investigation is submitted for the subject property located approximately at 1423 Power Plant Road in Brigham City, UT. This report contains the findings of the field investigation and the analysis conducted by Civil Solutions Group (CSG). This report also contains recommendations pertaining to construction and design of earth related portions of this project.

CSG completed the field investigation on May 21, 2026 at which time two bore holes were drilled, examined, and recorded in detail. The bore locations were selected based upon the proposed location of the building footprint and other site features. CSG recommends the site is suitable for proposed construction within the parameters defined within this report. Thank you for the opportunity to provide these services to you.

Sincerely, John Powell, P.E.

Civil Solutions Group, Inc.

Table of Contents

Executive Summary

Introduction

General

Objectives and Scope

Authorization

Professional Statements

Proposed Construction

Existing Site Conditions

General

Site Topography & Drainage Features

Site Soils

Subsurface Exploration and Testing Programs

General

Field Program

Laboratory Program

Sieve Analysis

Chemical

Discussions & Recommendations

Summary of Findings

Earthwork

Site Preparation

Temporary Excavations

Structural Fill

Fill Placement and Compaction

Utility Trenches

Drainage

Structural Considerations

Spread and Continuous Wall Foundations

Lateral Resistance

Floor slabs

Pavements

Pavement Maintenance

Soil Corrosiveness

Cement Use

Construction Considerations

Geoseismic Setting

Faulting

Soil Class

Liquefaction

Groundwater

Closure

Glossary/Explanation of Terms or Procedures

Appendix

Table of Figures Figure 1 - Vicinity Map Figure 2 - Site Map Figure 3 - Looking North Figure 4 – Looking South Figure 5 – Looking West Figure 6 – Looking East Figure 7 – Key to Soil Logs

Table of Tables Table 1 - Gradation & Soil Classifications Table 2 - Chemical Properties of Soil Table 3 – Structural Fill Gradation Requirements Table 4 - Fill Compaction Requirements Table 5 - Structural Design Parameters Table 6 – Lateral Earth Pressure Table 10 - Pavement Recommendations Table 7 - Groundwater Depth

Utah Division of Facilities Construction and Management Brigham City UDOT Shed Geotechnical Investigation 1 July 15, 2026

Executive Summary A geotechnical study was performed for the subject property at 1423 Power Plant Road in Brigham City, UT. Our scope of services included drilling two bore holes designated B-1 to B-2. The boreholes were drilled with hollow stem augers and advanced to a maximum depth of 26.5-feet below existing site grade. All field work was contained in the proposed development area and was completed on May 21, 2026.

The findings and recommendations generated from this exploration are summarized below:

• Onsite Soil – The site is composed mostly of gravelly sand with silt. Groundwater was not encountered.

• Foundations - The planned structure should be supported entirely on continuous spread footings or spot footings. The recommended bearing capacity of in-situ soil is 3,000 pounds per square foot.

• Seismic Considerations - The 2024 International Building Code (IBC) Seismic Design Category for this site is Category D (Risk Category II), with a soil site class of D. The site is located in an area with very low liquefaction potential according to the Utah Geological Survey, and the in-situ soils encountered on site.

• Pavement - Minimum pavement sections are as follows:

Section Recommended Pavement Sections (Inches)

Asphalt Portland Cement Concrete

Untreated Base Course

Granular Borrow

Total

Heavy Duty Asphalt Parking

4.0 - 8.0 - 12.0

Heavy Duty Concrete

Pad

- 6.0 6.5 - 12.5

This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The entire report should be read for an understanding of the report limitations.

Brigham City UDOT Shed Geotechnical Investigation 2 July 15, 2026

Introduction

General

Civil Solutions Group, Inc. (CSG) was contacted by Mr. Francis and was asked to conduct a geotechnical engineering investigation on the subject property located at 1423 Power Plant Road in Brigham City, UT. The general location of the site may be seen in Figure 1, Vicinity Map. A more detailed location of the site showing the proposed development and surrounding improvements is shown in Figure 2, Site Map. It was described that the proposed construction for the Brigham City UDOT Maintenance Facility Tow Plow Shed is anticipated to be a two-bay, slab-on-grade metal shed to store a tow plow.

Objectives and Scope

The objectives and scope of our study were defined between Mr. Francis and Mr. David Robison of CSG. In general, the objectives of this study were to:

• Define and evaluate subsurface soil and groundwater conditions across the site

• Provide foundation, earthwork, drainage, and geo-seismic recommendations

To accomplish these objectives, our scope has included the following:

• A field program consisting of the drilling, logging, and sampling of the two borings

• A laboratory testing program

• An office program consisting of correlating available data, engineering analyses, and report preparation

Authorization

CSG was authorized to proceed with this scope of work through an executed contract returned to our office by Mr. Francis of State of Utah – Division of Facilities Construction and Management.

The executed contract was dated April 29, 2026.

Professional Statements

CSG certifies that our professional services have been performed, our findings developed, and our recommendations prepared in accordance with generally accepted engineering principles and practices in this area at this time. Supporting data upon which our recommendations are based is presented in the subsequent sections of this report. Recommendations made herein are governed by the physical properties of the soils encountered in the exploration borings, observed and projected groundwater conditions, and the layout and design data as summarized in the Proposed Construction section of this report. If subsurface conditions other than those described in this report are encountered and/or if design and layout changes are implemented, CSG must be informed so that our recommendations can be reviewed and amended, if necessary.

Proposed Construction The proposed construction for the structure in this development will be a 40’x90’, two-bay, slab-on-grade metal shed to store a tow plow. If structural engineering plans are different than assumed, they should be provided to our office for review.

Brigham City UDOT Shed Geotechnical Investigation 3 July 15, 2026

The site development will likely require minimal earthwork. It is estimated that in certain areas 2 to 3-foot cuts and/or fills will be required to achieve site grades and tie in-to the adjacent properties.

Traffic is assumed to consist of medium to heavy weight trucks and occasionally automobiles.

Column and wall loadings are anticipated to be on the order of 30-70 kips and 2-4 kips per lineal foot respectively.

Existing Site Conditions

General

The site lies approximately at 1423 Power Plant Road in Brigham City, UT. The existing property contains maintenance buildings and sheds. The surrounding properties are associated with sand and gravel borrow pits and mining. The surface and subsurface soils that were explored appeared to be free of hazardous debris and other foreign objects.

Site Topography & Drainage Features

The majority of the site is relatively flat. On-site there were no springs, streams, canals or standing water observed at the time of the site visit.

Site Soils

The soil conditions encountered in each of the two borings, to the depths explored, were relatively similar. In bore hole number 1 (B-1), there was approximately 1-foot of asphalt and road base. From approximately 1-foot beneath existing grade to the full depth explored, 26.5-feet, gravelly sand with silt was encountered. The remaining bore hole at the site had similar characteristics as B-1.

Groundwater was not encountered in the boreholes. Soil encountered during the investigation can be referenced in the Soil Logs in the Appendix of this report. Materials encountered in the bore holes are anticipated to exhibit strength and compressibility characteristics under the anticipated loading range.

Subsurface Exploration and Testing Programs

General

To define and evaluate the subsurface soil and groundwater conditions across the site, two borings were drilled to depths of up to 26.5-feet below existing grade. The borings were drilled using a truck mounted drilling rig equipped with 3.25-inch inside diameter hollow stem augers. Soil sampling equipment was advanced through the hollow stem to retrieve both disturbed and relatively undisturbed samples of the in-situ soil. Locations of the borings are presented in Figure 2.

Field Program

The field portion of our study was conducted on May 21, 2026. Continuous logs of the subsurface findings were created and maintained as part of the field program. The field portion of our study was under the direct control and continual supervision of an experienced member of our geotechnical staff. Field classifications were logged, and any adjustments made once the laboratory data and analyses were received.

Brigham City UDOT Shed Geotechnical Investigation 4 July 15, 2026

The CSG geotechnical team collected both disturbed and relatively undisturbed samples of typical soils that were found in the bore holes. The disturbed samples were taken using bagged grab samples and a SPT split spoon sampler. The SPT split spoon sampler had an outside diameter of 2-inches and an inside diameter of 1.38-inches. The sampler was driven into the undisturbed soil a total of 18-inches utilizing a 140-pound auto hammer falling a vertical distance of 30-inches. The blow counts recorded on the Soil Logs represent the total number of blows from the safety hammer that were required to drive the sampler the final 12-inches.

Graphical depictions of the subsurface findings are shown in the Soil Logs contained within the Appendix of this report.

Laboratory Program

CSG partnered with RB&G Engineering to conduct a laboratory testing program on the samples retrieved from the sites. This laboratory testing program was conducted to provide data necessary for our engineering analyses. The program included moisture and density, partial gradation (sieve) analysis, and chemical tests. The following describes the tests and summarizes the test data. Samples from the field will be maintained in our office for a period of 90 days at which time they will be disposed of unless a written request is received from State of Utah – Division of Facilities Construction and Management that they should be retained.

Sieve Analysis

Gradation tests (sieve analysis) were conducted on disturbed samples which were collected from the site. The gradation test aids in classifying the soils and can provide general index parameters.

Gradation tests aid the design team in determining the overall composition of the soil and behaviors that the soil may exhibit under certain situations. The results of the tests are shown in Table 1 below:

Table 1 - Gradation & Soil Classifications

Boring Sample No.

Depth (feet) Percent Passing #200 Sieve

Soil Classification

B-1.2 5.0-6.5 10 SP-SM

B-1.5 15.0-16.5 8 SP-SM

B-1.7 25.0-26.5 5 SP-SM

B-2.3 7.5-9.0 5 SP-SM

Chemical

To determine if the site soils will react detrimentally with concrete, a chemical sulfate test was performed on a representative sample of the natural soils at approximately the depth of the soil that will come into direct contact with concrete improvements for the proposed development. The results of the chemical tests are shown in Table 2 below:

Table 2 - Chemical Properties of Soil

Boring Sample No. Depth (feet) Sulfate (mg/kg) B-2.1 2.5-4.0 <10

Brigham City UDOT Shed Geotechnical Investigation 5 July 15, 2026

Discussions & Recommendations

Summary of Findings

It is recommended that the owner have a CSG field engineer or a qualified assistant oversee the site work, especially the footing excavation and preparation. Also, the building code requires inspection and reports on all structural site work.

Detailed discussions pertaining to earthwork, structural considerations, geoseismic setting, and groundwater are included in the following sections:

Earthwork

Site Preparation

Initial site preparation will consist of the removal of surface asphalt, vegetation, topsoil, root balls, sod or any other deleterious materials extending at least three feet beyond the perimeter of all areas to be developed. Non-engineered fills will be completely removed three feet beyond the extents of all spread and continuous footings, rigid pavement areas, floor slabs and other areas that require a stabilized foundation. Stripped materials consisting of vegetation and organic materials should be wasted from the site or used to revegetate landscape areas.

Non-engineered fills may remain in areas where flexible pavements are to be placed if they are properly prepared. Proper preparation will consist of scarifying and moisture conditioning the upper nine inches and recompacting to the requirements of structural fill. It should be noted that compaction of fine-grained soils (silts and clays) as site grading fill will be very difficult, if not impossible, during wet and cold periods of the year.

The exposed natural subgrade should be proof-rolled prior to the placement of structural site grading fill, footings, floor slabs, or any other structural improvement made to the site. The proof-roll should be completed by driving a loaded piece of construction equipment, mounted with rubber tires, over the exposed natural subgrade surface at least twice. A CSG field engineer should oversee the proof roll and provide recommendations as needed. Soft spots should be completely excavated and removed if they are discovered. The soft spots should be replaced with stabilization fill. It is not anticipated that removal depth would be more than 2 vertical feet. If an excavation of more than 2 vertical feet is required, CSG should be notified to provide further recommendation.

In flexible pavement areas, unsuitable materials encountered during compaction and proof-rolling operations must be removed to a maximum depth of two feet and replaced with compacted granular structural fill.

Although evidence of underground facilities such as utilities, septic tanks, cesspools, basements, etc.

was not observed during the field investigation, such features could be encountered during construction. If unexpected fills, debris or underground facilities are encountered, such features should be removed, and the excavation thoroughly cleaned prior to backfill placement and/or construction.

Brigham City UDOT Shed Geotechnical Investigation 6 July 15, 2026

Temporary Excavations

All temporary excavations should follow OSHA Sloping and Benching – 1926 Subpart P App B requirements, which take precedence over any recommendations presented in this report.

Temporary excavations in cohesive soil, above or below the water table, not exceeding four feet in depth, may be excavated with nearly vertical sideslopes. Excavations within loose and/or cohesionless soils will be very difficult as they tend to flow into the excavation. They will require very flat sideslopes and/or shoring, bracing and dewatering.

All excavations must be inspected periodically by qualified personnel. If any signs of instability, excessive sloughing or other signs of potential failure are noted, immediate remedial action shall be initiated.

Structural Fill

The on-site native soils were finer by nature and cannot be used as structural fill. However, the on-site soils can be used as fill in landscape areas that are not expected to carry a load. The use of fine-grained soils (silts and clays) as landscape fill will be very difficult, if not impossible, during wet and cold periods of the year. Proper moisture control and conditioning will be required.

Fine-grained soils (silts and clays) are not recommended as structural fill in confined areas, such as around foundations and within utility trenches. This fill material should be composed of granular material.

All imported granular structural fill should consist of a fairly well-graded mixture of sand and gravel containing less than 15 percent fines (percent by weight of material passing the No. 200 sieve).

To stabilize soft subgrade conditions (if required), a mixture of coarse gravels and cobbles (stabilizing fill) should be utilized. A layer of 12 to 18 inches thick of stabilizing fill is typically sufficient to stabilize most soft/disturbed areas.

Table 3 shown below is indicative of the material that should be used as structural fill and road base throughout the site:

Table 3 – Structural Fill Gradation Requirements

Fill Type * Application Requirements

Gradation Plasticity

Size % Finer by Weight

Structural Fill (A-1a)

/Granular Borrow

Required for all fill under foundations, floor slabs, and pavements

3-inch No. 10 Sieve No. 40 Sieve No. 200 Sieve

50-max 30-max 15-max

Plasticity Index 6-max

Site Grading Fill

Fill in pavement and non-structural areas

4-inch No. 200 Sieve

35-max

Liquid Limit 36-max Plasticity Index 10-max

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Stabilization Fill

Fill used to stabilize soft, potentially pumping subgrade

5-inch No. 200 Sieve

5-max

NA

Free Draining Granular Backfill

Retaining Walls 1½-inch 1-inch ½-inch No. 4

95 – 100 25 – 60 5-max

NA

Untreated Base Course

(APWA Spec)

Fill used under the pavement sections

3/4” 3/8” No. 4 No. 16 No. 200

78-92 55-67 28-38 7-11

Non-Plastic

*All fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the geotechnical engineer for evaluation.

**All fill to follow these requirements, or the requirements of the reviewing agency if different than those provided here.

Fill Placement and Compaction

All fill should be placed in lifts not exceeding 8 inches in loose thickness. Moisture should be adjusted to within ± 2% of optimum moisture content. Lifts will need to be compacted in thinner lifts if smaller compaction equipment is used. Structural fills should be compacted in accordance with the percent of maximum dry density as determined by the AASHTO T-180 (ASTM D-1557) compaction criteria and according to Table 4 below:

Table 4 - Fill Compaction Requirements

Location Total Fill Thickness (feet)

Minimum Percentage of Maximum Dry Density

Beneath an area extending at least 3 feet beyond the footprint of a structure

0 to 8 95

Beneath pavements and travelled ways

0 to 8 95

Landscaped areas or areas not expected to carry a load

0 to 5 85

Landscaped areas or areas not expected to carry a load

5 to 8 92

Road Base - 96

Prior to placement of fills, the subgrade must be prepared as discussed in the Site Preparation section of this report. In confined areas, subgrade preparation should consist of the removal of all loose and disturbed soils. Fill should be tested frequently for moisture content and compaction during placement. Should the results of the in-situ density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and

Brigham City UDOT Shed Geotechnical Investigation 8 July 15, 2026 retested as required until the specified compaction is achieved. This may require adjustment of the moisture content.

Utility Trenches

We recommend that all utility trenches on-site or as a part of this site, should utilize a Type A-1a or A-1b (AASHTO Designation) soil as backfill material. The on-site materials can be used for trench backfill if they meet these classifications and are properly moisture conditioned. This should be verified by the materials testing agency. All utility trenches which will ultimately bear structural loads should be compacted at the structural density requirements established in Table 4.

Drainage

Positive drainage should be provided during construction and maintained throughout the life of the development. Infiltration of water into utility trenches or foundation excavations should be prevented. Planters and other surface features which might retain water in areas adjacent to the buildings or pavements should be sealed, mechanically drained, or eliminated. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with a minimum grade of approximately five percent for at least 10 feet from perimeter walls. Backfill against footings, exterior walls, and in utility and sprinkler line trenches should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration. Roof runoff should be collected in rain gutters and downspouts. Downspouts, roof drains or scuppers should discharge into extensions when the ground surface beneath such features is not protected by exterior slabs or paving to divert collected water a minimum of 10 feet away from structures.

Sprinkler systems should not be installed within five feet of foundation walls. Landscaped irrigation adjacent to the foundation systems should be minimized.

Structural Considerations

Spread and Continuous Wall Foundations

It is understood that the proposed structure will be supported on conventional spread and continuous wall foundations. These foundations should be established on suitable natural soils.

Under no circumstances shall footings be placed overlying non-engineered fills, loose soils, frozen soils, soil containing foreign debris, and any other deleterious material. Unsuitable material must be removed and replaced with an adequate structural fill as discussed in this report. For structural fill replacement beneath footings, the width of the structural fill shall be equal to width of the footing plus one foot on each side for each foot of fill thickness. For example, if the depth of structural fill is three feet, then three feet of structural fill needs to extend past the edge of the footing on each side.

For design, the following parameters are provided:

Table 5 - Structural Design Parameters

Design Element Standard Recommended minimum depth of embedment for frost conditions 30-inches

Recommended minimum depth of embedment for non-frost conditions 15-inches

Recommended maximum bearing capacity of in-situ soil 3,000 pounds per square foot

Brigham City UDOT Shed Geotechnical Investigation 9 July 15, 2026

Recommended width for continuous wall footings 18 to 36-inches

Recommended width for isolated spread footings 36 to 84-inches

Recommended bearing capacity increase for seismic loading 33%

Coefficient of friction between footing and native soils 0.45

Settlement of foundation elements are expected to be on the order of 1” or less with approximately 50% occurring during construction. This settlement is expected if the project is constructed in accordance with recommendations found within this report.

Lateral Resistance

Lateral earth pressure are the lateral forces of the backfill material on walls. These forces can be represented as equivalent fluid density for foundation calculations. Lateral earth pressure can be assumed to be much higher if material behind structural walls is not free draining. The lateral pressures will vary if groundwater is encountered. At this site, groundwater was not encountered and is well below the anticipated depth of foundations and therefore should not affect lateral pressure.

The lateral earth pressures are shown in the table below:

Table 6 – Lateral Earth Pressure

Condition Lateral Pressure Coefficient

Equivalent Fluid Density (pcf)

Passive 4.40 532

Active 0.23 28

At-Rest 0.35 42

Floor slabs

Due to the intended use and anticipated loading, floor slabs should be constructed with a minimum of 4” of concrete (4,000 psi, air-entrained – 6% ± 1%) over 4" of clean gravel material. The subgrade material shall be properly prepared as discussed previously in this report. Under no circumstances should floor slabs be established over non-engineered fill, loose or disturbed soils, sod, rubbish, construction debris, other deleterious materials, frozen soils, or soils with ponded water. If constructed in accordance with this section, settlements of at-grade floor slabs supporting loads of 200 pounds per square foot should be on the order of ¼” or less.

Where appropriate, saw-cut control joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations refer to the ACI Design Manual. Joints or any cracks that develop should be sealed with a water-proof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

The use of a vapor barrier should be considered beneath concrete slabs on grade that will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor barrier, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor barrier.

Brigham City UDOT Shed Geotechnical Investigation 10 July 15, 2026

Pavements

Pavement sections were designed using AASHTO 93 design methodologies and assumed traffic volumes. Based on laboratory test results and N-values obtained from the SPT tests during the field exploration a CBR value of 25% was used for the underlying subgrade soils. This resulted in a subgrade resilient modulus (MRSG) of 20,048 pounds per square inch. The anticipated traffic loading consists of mostly automobiles with the occasional medium to heavy weight truck. The following design traffic (18-k Equivalent Single Axle Loads) were assumed.

Section Design ESALs*

Heavy Duty Asphalt /Concrete Parking 147,000

*If the traffic anticipated on site is different from that assumed, Civil Solutions Group should be notified.

Considering the underlying subgrade material and anticipated traffic and loading, the following pavement sections are recommended as shown in Table 7:

Table 7 - Pavement Recommendations

Section Recommended Pavement Sections (Inches)

Asphalt Portland Cement Concrete

Untreated Base Course

Granular Borrow

Total

Heavy Duty Asphalt Parking

4.0 - 8.0 - 12.0

Heavy Duty Concrete

Pad

- 6.0 6.5 - 12.5

The rigid pavement section is for non-reinforced Portland cement concrete. Concrete should be designed in accordance with the American Concrete Institute (ACI). The concrete should have a minimum 28-day unconfined compressive strength of 4,000 pounds per square inch and contain 6 percent ± 1 percent air entrainment.

Public pavement areas are to follow minimum design standards set by the reviewing authority, or the recommendations found in this report if they are greater than the minimum design standards. In areas where heavy truck loads are expected frequently, there should be 4” of asphalt, 6” of road base, and 10” of sub-base.

Pavement Maintenance

All paved areas should have adequate crown and slope to provide positive drainage and prevent ponding of surface water and infiltration below the pavement section. Water collection devices such as gutters and ditches should be incorporated into the parking lot design to prevent percolation of surface water below the pavement section.

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Pavement sections have not been designed to support construction equipment. As such, the contractor should protect pavement areas from damage that may result from construction traffic.

The pavement sections provided in this report are minimums for the given design criteria. Periodic maintenance is critical to the long-term performance of the pavement sections. A maintenance program that includes surface sealing, joint cleaning and sealing, joint grinding, repair and replacement of cracked slabs and timely repair of cracks and deteriorated areas will be critical to the pavement meeting its design life.

Soil Corrosiveness

The soil was sampled for sulfate levels at soil depths that will come into direct contact with the footings and foundations. These chemical levels are shown in Table 2 for reference.

Cement Use

Type I or IA mixes may be used in the design of these improvements. The soil tested contained a negligible number of water-soluble sulfates. Based on our test results, concrete in contact with the in-situ soils will have a low potential for sulfate reaction and therefore the mix types of I or IA are acceptable. Other types of mixtures may be used by the design team if other strength/functionality parameters are desired.

Construction Considerations

On most project sites, the site grading is generally accomplished early in the construction phase.

However, as construction proceeds the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab or footing subgrade may not be suitable for placement of crushed gravel and concrete and corrective action will be required. We recommend areas underlying floor slabs and footings be rough graded and then thoroughly proof-rolled with a loaded tandem axle water or dump truck prior to final grading and placement of crushed gravel or concrete. Attention should be given to high traffic areas that were rutted and previously disturbed and to areas containing backfilled trenches. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with properly compacted structural fill. All structural subgrade areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to placement of the gravel and concrete.

Geoseismic Setting

Faulting

Based on a review of Utah Geological Survey fault maps, the site is approximately 0.17 miles (885 feet) west southwest of the Wasatch Fault Zone – Brigham City Section.

Soil Class

A site-specific seismic analysis was not a part of this scope of work, nor was it performed for the site at this time. The seismic values provided are determined using the ASCE 7 Hazard tool using the following inputs.

The soil site class is D (S1 =0.52 g & SS = 1.46 g), with a Seismic Design Category D (Risk Category II) in accordance with ASCE 7-22 and IBC 2024.

Brigham City UDOT Shed Geotechnical Investigation 12 July 15, 2026

Liquefaction

The site is in an area that has been classified as very low liquefaction potential by the Utah Geological Survey. Liquefaction requires water, seismic activity, and loose sandy soils. Groundwater was not encountered to the depths explored. Sandy soils were encountered in the field investigation and therefore present some risk during a seismic event. A full liquefaction analysis is beyond the scope of this investigation.

Groundwater

Immediately following drilling operations, the groundwater was measured in each boring. Seasonal and longer-term groundwater fluctuations on the order of one and one-half to three feet are projected, with the highest seasonal levels generally occurring during the late spring and early summer months. The groundwater measurements (as measured down from existing grade) are tabulated in Table 8 below:

Table 8 - Groundwater Depth

Bore Hole Number Time of Drilling* (feet) Stabilized (feet) B-1 Not Encountered Not Encountered

B-2 Not Encountered --

*While drilling, not a stabilized condition.

Closure CSG should be retained to provide observations during grading, excavation, foundation construction, and other earth-related construction activities related to this project. The conclusions and recommendations presented in this report are based on the results of the field and laboratory tests which, in our opinion, define the characteristics of the soils at this site in a satisfactory manner.

However, this report does not reflect variations that may occur between borings, across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If during or after construction, conditions are encountered which appear to be different than those presented in this report, it is requested that our office be advised, in order that appropriate action be taken.

Our professional services have been performed, our findings obtained, and our recommendations prepared in accordance with generally accepted geotechnical engineering principles and practices.

Any persons using this report for bidding or construction purposes should perform independent investigations as they deem necessary to determine subsurface conditions. The scope of services for this project does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. If changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and

Brigham City UDOT Shed Geotechnical Investigation 13 July 15, 2026 recommendations contained in this report shall not be considered valid unless CSG reviews the changes and either verifies or modifies the conclusions of this report in writing.

Brigham City UDOT Shed Geotechnical Investigation 14 July 15, 2026

Glossary/Explanation of Terms or Procedures

Throughout this report, we have used a number of words or phrases which may be unfamiliar in nature. Also, several procedural concepts have been mentioned repeatedly. For this reason, we have decided to define or discuss these items to better communicate with the reader(s).

Compaction and Lift Size - Contractors should be aware that there is direct relationship between lift size and size of the compacting equipment. The smaller the compactor, the smaller the maximum lift height. With “wacker” compactors, the maximum lift should be held at about 3-4-inches. With walk-behind trench compactors (2-tons or so), the lifts should be no more than 6-inches thick.

Eight-inch lifts can be used with large ride-on devices (7-10-tons or greater) that roll and vibrate/pound. Hoe pack devices on track hoes or backhoes can compact 6-8-inch lifts depending on size. However, the maximum lift size should not exceed 8-inches for most compactors. Note: a lift is defined as the loose or un-compacted thickness of the soil layer being compacted

Groundwater level - The groundwater level is a “rough guess” of where the uppermost water level is in a soil. We look for the first sign of free water coming in from the trench walls or appearing on the soil. In the soil logs, the groundwater level is identified by a solid or darkened triangle with a wavy line below it.

Liquefaction - Loss of bearing strength of saturated and very fine-grained silts and sands during severe earthquakes. This strength-loss is due to the slow dissipation of pore pressure (due to low permeability) and the subsequent reduction of particle-to-particle contact induced by the shaking motion of the earthquake.

Piezowater or Piezometer - To measure the groundwater level after a soil test pit is excavated, a pipe (a piezometer) is placed in the pit and left for at least 48-hours. The bottom 12-inches of the piezometer is slotted and capped to keep soil from entering and plugging up the pipe. The piezometer is then backfilled. After 48-hours, the water level in the piezometer is recorded. This level is the piezowater level. It is often higher than the point where water is first seen in a test pit during excavation. The importance is that the piezometer level is the potential depth of the groundwater for a site location should a ‘dig’ be done at the site. However, this level may change over time depending on weather conditions (wet or dry years and periods); rust or mottling of the soils may indicate an historical level of the water. In the soil logs, the piezowater level is a line with an “open” triangle above it and a wavy line below the triangle. The “open” triangle signifies the fact that the overlying soil “cap” has been removed.

Topsoil - It is generally defined as surface soils (silts or clays) with greater than 2-percent organics;

this soil is often dark brown to black in color. It generally has visible roots or organic matter and is highly compressible. Topsoil should never be used under a footing or load bearing structure; it is generally, too compressible and with loading, settles over time. It should be stockpiled for use in landscaped areas, used for wetland mitigation/re-seeding, as a pond liner, or exported from the site.

Undisturbed soil - This is soil in its natural state, undisturbed by past excavation, farming, construction, or perturbation of any type. It is a most important feature. Areas that have been filled are always considered disturbed. On the other hand, “cut” areas can be considered undisturbed if the soil was cut with a straight bladed bucket edge, and not tines. If soils are disturbed, and footings or walls will be bear on these soils, they must be re-compacted.

Brigham City UDOT Shed Geotechnical Investigation 15 July 15, 2026

Non-Engineered Fill – Non-engineered fill material is non-native (imported) material that has not been tested in the lab for engineering properties nor has a record of proper placement and compaction. Therefore, it should not be used for structural fill. This material can be used if properly prepared, but Civil Solutions Group recommends any non-engineered material in which loads will bear on be tested prior to placement. Once placed, this material should be tested to ensure structural properties are met. Recommendations in this report are based upon the materials encountered during the field investigation.

Brigham City UDOT Shed Geotechnical Investigation 16 July 15, 2026

Appendix

Figure 1 - Vicinity Map

Brigham City UDOT Shed Geotechnical Investigation 17 July 15, 2026

Figure 2 - Site Map

Brigham City UDOT Shed Geotechnical Investigation 18 July 15, 2026

Figure 3 - Looking North

Figure 4 – Looking South

Brigham City UDOT Shed Geotechnical Investigation 19 July 15, 2026

Figure 5 – Looking West

Figure 6 – Looking East

Brigham City UDOT Shed Geotechnical Investigation 20 July 15, 2026

Figure 7 – Key to Soil Logs

D ep th

Ground Surface

Lithologic Description

Asphalt

0.33 ft

Roadbase Dark Brown

1.00 ft

_Gravelly _Sand _with _Silt, SP-SM Yellowish Brown, Moist, Very Dense, Fine to Coarse Grained

Dense

Very Dense

Sy m bo l

Sa m pl es

SS

SS

SS

SS

SS

Gradation (%)

G ra ve l

Sa nd

35.0 55.0 10.0

27.0 65.0 8.0

Atterberg Limits

LL

PL

M oi st ur e

2.5

2.1

Bl ow

Co un t

51.00

53.00

50.00

73.00

68.00

Bl ow

Co un t

Standard Penetration Test

(SPT)

BORE LOG: B-1

DATE: 2026-05-21

Tow Plow Shed 26-154

Division of Facilities Construction and Management

SHEET:

PROJECT TITLE:

CLIENT:

PROJECT NO.:

1423 Power Plant Road, Bringham City UT

LONGITUDE:

41.50223LATITUDE:

-111.99461

ADDRESS:LOGGED BY: REVIEWER:Carlos Vasquez John Powell

Fines th

Lithologic Description

(continued)

Yellowish Brown, Moist, Dense, Fine to Coarse

Grained

Very Dense

26.50 ft Test Hole Terminated at 26.5 ft

Sy m bo l

Sa m pl es

SS

SS

Gradation (%)

G ra ve l

Sa nd

46.0 49.0 5.0

Atterberg Limits

LL

PL

M oi st ur e

1.3

Bl ow

Co un t

45.00

77.00

Bl ow

Co un t

Standard Penetration Test

(SPT)

BORE LOG: B-1

DATE: 2026-05-21

Tow Plow Shed 26-154

Division of Facilities Construction and Management

SHEET:

PROJECT TITLE:

CLIENT:

PROJECT NO.:

1423 Power Plant Road, Bringham City UT

LONGITUDE:

41.50223LATITUDE:

-111.99461

ADDRESS:LOGGED BY: REVIEWER:Carlos Vasquez John Powell

_Gravelly _Sand _with _Silt, SP-SM th

Ground Surface

Lithologic Description

Asphalt

0.33 ft

Roadbase Dark Brown

1.00 ft

_Gravelly _Sand _with _Silt, SP-SM Yellowish Brown, Moist, Dense, Fine to Coarse Grained

Very Dense

Dense

16.50 ft Test Hole Terminated at 16.5 ft

Sy m bo l

Sa m pl es

Gradation (%)

G ra ve l

Sa nd

Atterberg Limits

LL

PL

M oi st ur e

Bl ow

Co un t

Bl ow

Co un t

Standard Penetration Test

(SPT)

BORE LOG: B-2

1423 Power Plant Road, Bringham City UT

LONGITUDE:

41.50223LATITUDE:

-111.99461

ADDRESS:LOGGED BY: REVIEWER:Carlos Vasquez John Powell

DATE: 2026-05-21

Tow Plow Shed 26-154

Division of Facilities Construction and Management

SHEET:

PROJECT TITLE:

CLIENT:

PROJECT NO.:

SS

SS

SS

SS

SS

37.0 58.0 5.0 1.8

34.00

55.00

40.00

36.00

36.00