Geotechnical Report - Hermosa Tanks - 10-22-24.pdf

Dakota Testing & Engineering, LLC.

11920 Quaal Road, Ste. A, Black Hawk, SD 57718

605 484 8211

“The Foundation You Build On”

GEOTECHNICAL EXPLORATION AND ENGINEERING REVIEW

Hermosa Water Tank

Hermosa, South Dakota

DTE Project No. 24.0667

Prepared For:

Benesch 35 West Wacker Drive Suite 3300 Chicago, IL 60601

Hermosa, SD

DTE Project Number 24.0667

October 22, 2024

Benesch 35 West Wacker Drive Suite 3300 Chicago, IL 60601

Subject: Geotechnical Exploration and Engineering Review Hermosa Water Tank Hermosa, SD

DTE Project No. 24.0667

Attn: Anthony Theodorou, PE

In accordance with your request and subsequent authorization, Dakota Testing & Engineering, LLC.

(DTE) conducted a Geotechnical Exploration for the above referenced project. Our services included advancement exploratory borings and preparation of an engineering report with recommendations developed from our geotechnical services. Our work was performed in general accordance with our Proposal dated September 25, 2024.

Soil samples obtained at the site will be held for 30 days at which time they will be discarded. Please advise us in writing if you wish to have us retain them for a longer period. You will be assessed an additional fee if soil samples are retained beyond 30 days.

Dakota Testing & Engineering, LLC. appreciates the opportunity to have been of service on this project. If there are any questions regarding the soil explored or our review and recommendations, please contact us at your convenience at (605) 484-8211.

Adam Dando, EIT Operations Manager

Darrell Utter, PE Geotechnical Engineer October 22, 2024

Table of Contents

1.0 EXECUTIVE SUMMARY

2.0 INTRODUCTION

2.1 Site / Project Description

2.2 Scope of Services

3.0 Exploration Scope

3.1 Subsurface Conditions

3.2 Groundwater Conditions

3.3 Laboratory Test Program

4.0 ENGINEERING REVIEW AND RECOMMENDATIONS

4.1 Project Scope

4.2 Site Preparation

4.3 Shallow Foundation

4.4 Bearing Factor of Safety and Estimate of Settlement

4.5 Corrosion Considerations

4.6 Subsurface Drainage

4.7 Utilities

4.8 Slab-on-Grade Floors

4.9 Foundation Wall Backfill & Retaining Walls

4.10 Surface Drainage

4.11 Frost Considerations

5.0 CONSTRUCTION CONSIDERATIONS

5.1 Excavation Stability

5.2 Engineered Fill, Base Course & Winter Construction

6.0 CLOSURE

GEOTECHNICAL EXPLORATION AND ENGINEERING REVIEW

Hermosa Water Tank

DTE Project No. 24.0667

1.0 EXECUTIVE SUMMARY

The summary provided below is based on Dakota Testing & Engineering, LLC.’s geotechnical recommendations for the proposed project site. The summary is based on and must be used in conjunction with DTE geotechnical report. DTE should be contacted to provide construction verification as the project progresses.

DTE concludes you may support the proposed new tank, supported by a ring and mat foundation, on one (1) foot of scarified, moisture conditioned, and recompacted native soils.

DTE recommends that at excavation elevation or after removal of all topsoil and prior to the addition of fill, backfill, or structural elements that the upper 1 foot of the native subgrade beneath slabs, and pavements be scarified, moisture conditioned, and recompacted to report compaction criteria. Subgrades in structural areas should be protected from drying or rainfall during construction.

Footing and structural members for the new tank may be proportioned using the maximum net allowable soil bearing pressures of 4,000 pounds per square foot.

DTE recommends for foundations that drain tile be placed at the bottom of footing depth with excavation sloped towards drain tile and sloped towards sump pit or daylighted away from structure. See section 4.8 for details for drain tile.

DTE was requested to drill next to the existing tank and provide a bearing capacity for a proposed increase in capacity and elevation. Footing and Structural members for the tank addition may be proportioned using the maximum net allowable soil bearing pressures of 2,000 pounds per square foot.

Groundwater was not observed at the time of performing soil boring. The lack of observed groundwater in the borings is possibly due to the short duration for which the boreholes remained open combined with the relatively permeability of the on-site soils.

Overall, the on-site soils are slightly conducive to movement of groundwater both laterally and vertically over time. The on-site cohesive soils are not conducive to movement of groundwater both laterally and vertically over time.

DTE should be contacted at the time of excavation to confirm that the soil type and bearing are in accordance with our findings.

2.0 INTRODUCTION

2.1 Site / Project Description

The proposed water storage tank is located in Hermosa, SD and is to be constructed as defined within Table 1.

Table 1: Main Project & Site Description

Item Description Building Type Construction of a new 120,000 gallon, 30’ diameter, glass fused metal water tank on a ring and mat foundation and an addition of 40’ to an existing water tank of similar construction for increased capacity

At Grade Elevation (Estimated) 3409 ± 5 feet, for both sites Maximum Proposed Change in Site Elevation Assumed to be around 5 feet or less

Site Description Location of Project The new tank site is located 1.5 miles north of the town of Hermosa, on the west side of the Heartland Expressway, across from Paw Patch Acres

The existing tank is located on the eastern side of the Heartland Expressway, north of Highway 40, within a fenced compound for the water tank and support structures

Existing Land Use / Improvements to Parcel At the new tank location, the site is relatively undeveloped

The existing tank has a gravel approach, with a surrounding fence and support structures

Current Ground Cover Gravel roadway and native grasses Topography at Site The intended construction sites are at the top of small hills with moderate slopes to the north, south, east and west

2.2 Scope of Services

The purpose of this report is to present a summary of our geotechnical exploration only and provide generalized opinions and recommendations regarding the soil conditions and design parameters for this individual project site. DTE’s report is not intended to provide information on slope stability, environmental issues, or conditions of surrounding sites. DTE’s “scope of services” was limited to the following:

Explore the main project site subsurface by means of two (2) standard penetration borings. Site borings were to extend to a maximum depth of fifty (50) feet below ground surface to provide soil samples to conduct laboratory test(s) for characterizing the index and engineering properties of soils strata at site.

Prepare a report presenting our findings from our field exploration, laboratory testing, and engineering recommendations for foundation types, footing depths, allowable bearing capacity, estimated settlements, floor slab support, excavation, engineered fill, backfill, compaction and potential construction difficulties related to excavation, backfilling and drainage, utility installation, and pavements exploration program results.

3.0 Exploration Scope

Site geotechnical drilling occurred October 7, 2024, with individual borings advanced at approximate locations as presented on the diagram within the appendices.

DTE located and determined the elevation and location of the borings using a consumer hand held GPS unit. Boring elevations and locations should be considered approximate. Please refer to the Boring Location Diagram and the Boring Logs in Appendix C.

3.1 Subsurface Conditions

Please refer to the boring logs in Appendix C for a detailed description and depths of stratum at the borings. The boreholes were backfilled with auger cuttings. Minor settlement of the boreholes will occur. The Owner is responsible for final closure of the boreholes. Based on results of the current geotechnical exploration, Table 2, provides a general depiction of subsurface conditions at the project site. Additional comment on the evaluation of recovered soil samples is presented within the report attachments.

Refusal was met in soil borings 1 & 2 at depths of 42.0’ & 8.0’ relative to ground surface

Table 2: Typical Subsurface Stratigraphy at Project Site Note 1

Stratum

Depth to Base of Stratum below existing grade Material Description Notes

Topsoil 0.0 to 0.5 feet Topsoil (OH)

Classification by visual observation only and not intended to confer conformance with DOT or other municipal standards

Fine Alluvium 0.5 to 42.0 feet Lean Clay (CL), Fat Clay

(CH) & Weathered Shale

(CH)

Consistencies were Rather Stiff to Very Stiff

Note 1 Table summary is a generalization of subsurface conditions and may not reflect variation in subsurface strata occurring on site. The general geologic origin of retained soil samples is listed on the boring logs.

Typical depths are estimated to nearest one-half foot.

3.2 Groundwater Conditions

The drill crew observed the borings for groundwater depth during and at the completion of drilling activities. Groundwater was not observed at the time of performing soil boring. The lack of observed groundwater in the borings is possibly due to the short duration for which the boreholes remained open combined with the relative permeability of the on-site soils.

Overall, the on-site soils are somewhat conducive to movement of groundwater both laterally and vertically over time. The moisture content of such soils can vary annually and per recent precipitation.

Such soils and other regional dependent conditions may produce groundwater entry of project excavations.

DTE directs your attention to other report sections and the appendices concerning groundwater issues and subsurface drainage.

3.3 Laboratory Test Program

Our analysis and recommendations of this report are based upon our interpretation of the standard penetration resistance determined while sampling soils, laboratory test results and experience with similar soils from other sites near the project. The results of such tests are summarized on the boring logs.

4.0 ENGINEERING REVIEW AND RECOMMENDATIONS

The following recommendations are based on our present knowledge of the project. DTE requests that you or your design team notify us immediately if significant changes are made to project size, location, or design as we would need to review our current recommendations and provide modified or different recommendations with respect to such change(s).

DTE concludes you may support the proposed new tank, supported by a ring and mat foundation, on one (1) foot of scarified, moisture conditioned and recompacted native soils

DTE recommends that at excavation elevation or after removal of all topsoil and prior to the addition of fill, backfill, or structural elements that the upper 1 foot of the native subgrade beneath slabs, and pavements be scarified, moisture conditioned, and recompacted to report compaction criteria.

Subgrades in structural areas should be protected from drying or rainfall during construction.

Footing and structural members for the new tank may be proportioned using the maximum net allowable soil bearing pressures of 4,000 pounds per square foot.

DTE was requested to drill next to the existing tank and provide a bearing capacity for a proposed increase in capacity and elevation. Footing and Structural members for the tank addition may be proportioned using the maximum net allowable soil bearing pressures of 2,000 pounds per square foot.

4.1 Project Scope

DTE assumes the proposed structure will include concrete ring wall with a mat for the support of above grade construction. Our assessment of project soils, opinions, and report recommendations are based directly on application of estimated structural loads to site soils. DTE should be informed of any changes to the proposed scope of work to re-assess and provide updated recommendations as needed.

4.2 Site Preparation

DTE recommends removal of topsoil, organic soils, undocumented fill (if encountered), man-made structures (if encountered), soft clay soils in close proximity to the bottom of proposed foundation element, and/or any other unsuitable material(s) encountered during advancement of project excavations. Subgrades in structural areas should be protected from drying or rainfall during construction.

The Geotechnical Engineer of Record or their designated representative should review project excavations to verify removal of unsuitable material(s) and adequate bearing support of exposed soils.

All such observations should occur prior to the construction of footings and floor slabs.

DTE recommends you oversize all earthwork improvements and excavations where fill materials are placed below foundations. The minimum excavation oversize should extend per the requirements outlined in Appendix B. Excavation will be necessary to achieve frost protection of footing construction and may be necessary for the removal of unsuitable materials occurring below base of footing construction. No topsoil or undocumented fill should be constructed on unless approved by the Engineer.

DTE believes that site backfill that does support structural members, slabs or pads, may consist of on-site soils that are free of organic material. DTE requires that these soils be moisture conditioned and recompacted to specifications set forth in Appendix B.

DTE recommends structural backfill generally consist of granular engineered fill. Backfill should consist of material with a maximum particle size of 1 ½ inches and consist of sandy clay, lean clay, or clayey sand or imported material consisting of similar soils with a liquid limit less than 40 and a plasticity index of less than 20 for low volume change material beneath structures. In certain locations, sand or gravel may be imported and placed to help facilitate drainage, such as behind retaining walls and beneath pavements or slabs or to improve the strength of the subgrade beneath foundations. The aggregate, pit run sand or processed sand (sand cushion) should have 100 percent material passing the 1 inch, no more than 40 percent passing the No. 40 sieve and no more than 12 percent material passing the No.

200 sieve. If cohesive material is to be used for backfilling under structural members, material must be approved by the Geotechnical Engineer of Record.

All backfill for site corrective earthwork and for support of project footings should be tempered for moisture content, placed, and be compacted to the criteria presented within Appendix B.

4.3 Shallow Foundation

The following bearing recommendations are based on our understanding of the project. You should notify us of any changes made to the project size, location, design, or site grades so DTE can assess how such changes will impact recommendations. DTE assumes foundation elements will not exceed maximum vertical loads as previously noted within this report.

Foundations in unheated appurtenant areas, such as stoops and canopies, should be based at least 60 inches below the proposed finished grade for frost protection. Footings below structures anticipated to be heated (greater than 60 degrees F) in winter should be constructed at least 42 inches below proposed finished grade. Continuous strip footings under bearing walls should be at least 1 foot wider than the walls they support. Interior footings should be based at least 1.5 feet below design floor elevation.

Table 3: Recommended Maximum Net Allowable Soil Bearing Pressure1 - Conventional Shallow Foundation Construction – New Tank Location

Location Criteria

Perimeter Strip Footings, Perimeter Columns: Perimeter strip footings and perimeter column footings supported as recommended below depth of frost penetration.

Interior Strip Footings: Interior strip footings supported as recommended at a depth that provides no less than 6 inches of clearance between the top of footing and underside of floor slab (for cushion).

Interior Column Footings: Supported as recommended at a depth that provides no less than 6 inches of clearance between the top of footing and underside of floor slab (for cushion).

Maximum 4,000 psf

(All foundations)

1. Maximum net allowable soil bearing pressure recommendations predicated on footing design and construction complying with recommendations presented within this report. To minimize local failure of supporting soils, it is our opinion footing construction should comply with the International Building Code (IBC) requirements.

4.4 Bearing Factor of Safety and Estimate of Settlement

DTE estimates site prepared to report recommendations will provide a nominal 3 factor of safety against localized bearing failure when construction complies with report criteria and recommendations, and your design structure footings using the Table 4 maximum net allowable soil bearing recommendation(s).

DTE estimates that footings loaded per report recommendations may experience long term, total settlement of approximately 1/2 to 1 inch. Differential settlement will be on the order of 25 to 50 percent of total settlement. Generally, the greatest differential settlement occurs between lightly loaded and heavily loaded footings, particularly if heavily loaded footings are located adjacent to lightly loaded strip footings. Most of the settlement will occur on first loading, as the structure is erected.

Furthermore, total, and differential movement of footings and floor slabs could be significantly greater than the above estimates if you support construction on frozen soils. The moisture content of the bearing soils significantly changes from in-situ conditions when snow or ice lenses are incorporated into site earthwork.

4.5 Corrosion Considerations

DTE did no verification on corrosivity of the project soil. Contact DTE for information on testing and providing recommendations for corrosion.

4.6 Subsurface Drainage

DTE recommends the installation of a subsurface drain system at the bottom of excavation and bottom of over excavation, drained to a sump or daylighted away from the structure.

As a general guideline, subsurface drainage consists of a geotextile and coarse drainage encased slotted or perforated pipe extending to sump basin(s). We recommend exterior drainage be separated from interior drainage to reduce risk of cross flow and moisture infiltration below structure interior.

4.7 Utilities

Utility trenches should be backfilled in 8-inch maximum depth loose lifts. It is especially important that you compact trench backfill of underground utilities to minimize future settlement of green space and pavement areas. Please refer to Appendix B for compaction specifications.

The stability of embankments along utility excavations is dependent on soil strength, site geometry, moisture content, and any surcharge load for excavated soils and equipment. Cautionary comment on excavation stability is provided within this report section.

DTE recommends that, for at least the 5 feet closest to the building, trenches be backfilled with cohesive soils to reduce the potential for water intrusion. These soils should have at least 40 percent passing the No. 200 sieve and have a liquid limit less than 40.

If groundwater is encountered, temporary dewatering may be required during the utility trench excavations. Stabilization of the trench subgrade may be required to provide a stable platform for construction. Stabilization could consist of a one half to one-foot layer of crushed rock or sand with a maximum 12 percent material passing the No. 200 sieve and 50 percent passing the No. 40 sieve.

DTE herein notes that the Contractor is solely responsible for assessing the stability of and executing underground utility and project excavations using safe methods. Contractor is also responsible for naming the “competent individual” as per Subpart P of 29 CFR 1926.6 (Federal Register - OSHA).

4.8 Slab-on-Grade Floors

DTE recommends that placing of slabs should be on six (6) inches of ¾” max aggregate base course, pit run sand or processed sand (sand cushion) with 100 percent material passing the 1 inch, no more than 40 percent passing the No. 40 sieve and no more than 12 percent material passing the No. 200 Sieve.

Interior drain tile shall be placed to collect water to help prevent ponding. The moisture content of the cushion should be within plus or minus 2 percent of the optimum moisture content determined by the modified Proctor test.

For floor slabs constructed as described in the Site Preparation section, the design of the floor slab may be based on an estimated modulus of subgrade reaction (k) of 150 pci.

All interior at-grade floors with impervious or near impervious surfacing such as, but not limited to, paint, hardening agent, vinyl tile, ceramic tile, or wood flooring, should include provision for installation of a vapor retarder system.

Historically, vapor retarder systems can consist of many different types of synthetic membrane and can be placed either below cushion materials or at the underside of the concrete floor. All such issues are contentious and have both positive and negative aspects associated with long term performance of the floor. Overall, we recommend you install some form of vapor retarder below the project floor (for at-grade and basement construction, as appropriate). In addition, DTE recommends the design team consult with the selected flooring supplier to account for any product specific vapor suppression requirements.

DTE recommends you isolate floor slabs from other building components by placement of a nominal ½ inch thick expansion joint between the floor and walls, and/or columns. This construction must also apply a compatible sealant after curing of the floor slab to reduce moisture penetration though the expansion joint. As a minimum, you should install a bond breaker to isolate and reduce binding of building components.

4.9 Foundation Wall Backfill & Retaining Walls

Exterior backfill of at-grade foundations walls which do not retain soil should consist of approved native, non-organic, debris free soils or engineered fill. Placement of exterior backfill against at-grade non-earth retaining foundation walls should be performed concurrent with interior backfill to minimize differential loading, rotation and/or movement of the wall system.

A drain tile installed at the base of retaining walls is recommended to prevent hydrostatic loading on the walls. The drain tile should be sloped to provide positive gravity drainage or to a sump pit and pump or if possible daylighted away from the building. The drain tile should be surrounded by clean, free-draining granular material having less than 12 percent passing the No. 200 sieve. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within 2 feet of final grade, where it should be capped with compacted clay to reduce infiltration of surface water into the drain system.

The final one foot of exterior backfill for green areas may consist of clay or silt-based topsoil. The final exterior backfill for areas supporting sidewalks and/or pavements should consist of a free draining aggregate base as recommended for the respective construction.

Backfill should be tempered for correct moisture content, then placed and compacted in 8-inch individual lifts of exterior backfill per criteria presented within Appendix B of our report.

4.10 Surface Drainage

Effort should be made to maintain positive drainage during and after construction of project and eliminate ponding of water on site soils. We recommend you include provisions within construction documents for positive drainage of site. You should install sumps at critical areas around project excavations to assist in removal of seepage and runoff from site.

DTE recommends that sidewalks, curbing, pavements, and green space be designed to direct drainage away from the structure. DTE recommends that a 5 percent gradient should be maintained within 10 feet of building for drainage from lawn, and 2 percent minimum gradient from building for drainage of sidewalks and other pavements. All pavements should drain to on-site storm collection, municipal collection system, or roadside ditching.

Roof runoff should be directed away from building and drained or daylighted a minimum of 15 feet from the foundation by a system of interior roof and scupper drains, or rain gutters, down spouts, and splash pads. It is DTE’s opinion interior roof drains plumbed directly to the storm water piping system provide the most favorable method of conveying drainage from the roof as interior drains do not freeze or discharge runoff onto exterior sidewalks and pavements.

Planters located within 10 feet of the structure should be self-contained to prevent water accessing the building and pavement subgrade soils. Locate sprinkler mains and spray heads a minimum of 5 feet away from the building line. Low-volume, drip style landscaped irrigation should not be used near the building. Trees or other vegetation whose root systems have the ability to remove excessive moisture from the subgrade and foundation soils should not be planted next to the structure. Trees and shrubbery should be kept away from the exterior edges of the foundation element a distance at least equal to 1.5 times their expected mature height.

4.11 Frost Considerations

The soil on this site is minorly frost susceptible. Small amounts of groundwater, or infiltrated surface water, can be detrimental to the performance of slabs and pavements. Exterior slabs and pavements should be expected to heave. If frost action needs to be eliminated in critical areas, then we recommend the use of structurally supported exterior slabs (e.g., as structural stoops in front of building doors).

It is DTE’s opinion that placing non-frost susceptible material in large areas under exterior pavements and sidewalks would be exceedingly expensive and an unusual design and construction procedure in South Dakota.

A transition area between structurally supported slabs or non-frost susceptible materials should be constructed at a 3H:1V back slope to reduce the potential differential frost movements in the slabs or pavements. Drain-tile should be installed around the foundation perimeter and finger drains should be installed about catch basins and across low points in the pavement grades.

Non-frost susceptible fill should consist of sand or gravel with less than 12 percent material passing the number 200 sieve, and at least 50 percent retained on the number 40 sieve.

5.0 CONSTRUCTION CONSIDERATIONS

5.1 Excavation Stability

Excavation depth should not exceed those specified in local, state, or federal regulations. Excavations may need to be widened and sloped, or temporarily braced, to maintain or develop a safe work environment. Also, contractors should comply with local, state, and federal safety regulations including current OSHA excavation and trench safety standards. Temporary shoring must be designed in accordance with applicable regulatory requirements.

5.2 Engineered Fill, Base Course & Winter Construction

The Geotechnical Engineer of Record or their designated representative should observe and evaluate excavations to verify removal of undocumented fills, topsoil and/or unsuitable material(s), and adequacy of bearing support of exposed soils. Such observation should occur prior to construction of foundations.

Engineered fill and base course should be approved by the Geotechnical Engineer of Record prior to placement. In addition, the engineered fill and base course should be tempered for correct moisture content and then place and compact individual lifts of engineered fill and base course to criteria established within the appendices.

Frozen soil should never be used as engineered fill, base course or backfill, nor should you support foundations or pavement on frozen soils. Moisture freezing within the soil matrix of fine grained and/or cohesive soils produces ice lenses. Such soils gain moisture from capillary action and, with continued growth, heave with formation of ice lenses within the soil matrix. Foundations and pavement placed on frozen soils have the potential to settle once ice lenses thaw.

You should protect excavations, roadbeds, and foundations from freezing conditions or accumulation of snow, and remove frozen soils, snow, and ice from within excavations, fill section or from below proposed foundations. Replacement soils should consist of similar materials as those removed from the excavation with moisture content, placement and compaction conforming to report criteria.

6.0 CLOSURE

DTE’s conclusions and recommendations are predicated on observation and testing of the earthwork directed by the Geotechnical Engineer of Record. DTE’s opinions are based on test results and data assumed representative of the site. However, the area coverage of borings in relation to the entire project is very small. For this and other reasons, DTE does not warrant conditions below the depth of our borings, or that the strata logged from our borings are necessarily typical across the entire site.

Deviations from DTE’s recommendations by plans, written specifications, or field applications shall relieve DTE of responsibility unless DTE’s written concurrence with such deviations has been established.

The scope of services for this project does not include either specifically or by implication any environmental or biological assessment of the site or identification or presence of pollutants, hazardous materials, or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

The recommendations presented in this report are based on site soil conditions and DTE’s experience with similar sites, structures type, and construction methods. DTE’s recommendations are based on cost-effective construction as well as the understanding that by choosing to build on this site that the client is willing to accept that there may be a risk of post construction movements and damage to the foundation, floor slabs, utilities, exterior structures, sidewalks, and driveways. DTE’s recommendations do not eliminate all of the risk of post construction movement and cosmetic distress, but this risk could be further reduced by implementing significantly more expensive types of construction.

This report has been prepared for the exclusive use by Benesch for the specific application to the proposed water tank and tank addition in Hermosa, SD. Dakota Testing & Engineering, LLC. has endeavored to comply with generally accepted geotechnical engineering practice common to the local area. Dakota Testing & Engineering, LLC. makes no other warranty, expressed or implied.

Adam Dando, EIT Operations Manager

Darrell Utter, PE Geotechnical Engineer

October 22, 2024

APPENDIX A

GEOTECHNICAL EVALUATION OF RECOVERED SOIL SAMPLES

FIELD EXPLORATION PROCEDURES

GENERAL NOTES

WATER LEVEL SYMBOL

DESCRIPTIVE TERMINOLOGY

RELATIVE PROPORTIONS

PARTICLE SIZES

CLASSIFICATION of SOILS for ENGINEERING PURPOSES

EXCAVATION OVERSIZE

GEOTECHNICAL EVALUATION OF RECOVERED SOIL SAMPLES

DTE visually examined recovered soil samples to estimate distribution of grain sizes, plasticity, consistency, moisture condition, color, presence of lenses and seams, and apparent geologic origin.

We then classified the soils according using the Unified Soil Classification System (ASTM D2488). A chart describing this classification system and general notes explaining soil sampling procedures are presented within appendices attachments.

The stratification depth lines between soil types on the logs are estimated based on the available data. In-situ, the transition between type(s) may be distinct or gradual in either the horizontal or vertical directions. The soil conditions have been established at our specific boring locations only.

Variations in the soil stratigraphy may occur between and around the borings, with the nature and extent of such change not readily evident until exposed by excavation. These variations must be properly assessed when utilizing information presented in the boring logs.

DTE requests that you, your design team, or contractors contact DTE immediately if local conditions differ from those assumed by this report, as the Engineer of Record would need to review how such changes impact our recommendations. Such contact would also allow DTE to revise the recommendations as necessary to account for the changed site conditions.

FIELD EXPLORATION PROCEDURES

Soil Sampling – Standard Penetration Boring:

Soil sampling was performed according to the procedures described by ASTM D-1586. Using this procedure, a 2-inch O.D. split barrel sampler is driven into the soil by a 140-pound weight falling 30 inches. After an initial set of six inches, the number of blows required to drive the sampler an additional 12 inches is recorded (known as the penetration resistance (i.e., “N-value”) of the soil at the point of sampling. The N-value is an index of the relative density of cohesionless soils and an approximation of the consistency of cohesive soils.

Soil Sampling – Power Auger Boring:

The boring(s) was/were advanced with a 6-inch nominal diameter continuous flight auger. As a result, samples recovered from the boring are disturbed, and our determination of the depth, extent of various stratum and layers, and relative density or consistency of the soils is approximate.

Soil Classification:

Soil samples were visually and manually classified in general conformance with ASTM D-2488 as they were removed from the sampler(s). Representative fractions of soil samples were then sealed within respective containers and returned to the laboratory for further examination and verification of the field classification. In addition, select samples were submitted for laboratory tests. Individual sample information, identification of sampling methods, method of advancement of the samples and other pertinent information concerning the soil samples are presented on boring logs and related report attachments.

GENERAL NOTES

DRILLING and SAMPLING SYMBOLS LABORATORY TEST SYMBOLS

SYMBOL DEFINITION SYMBOL DEFINITION

C.S. Continuous Sampling W Moisture content-percent of dry weight P.D. 2-3/8” Pipe Drill D Dry Density-pounds per cubic foot C.O. Cleanout Tube LL, PL Liquid and plastic limits determined in accordance with ASTM D 423 and D 424 3 HSA 3 ¼” I.D. Hollow Stem Auger QU Unconfined compressive strength-pounds per square foot in accordance with ASTM D 2166-66 4 FA 4” Diameter Flight Auger 6 FA 6” Diameter Flight Auger 2 ½ C 2 ½” Casing 4 C 4” Casing D.M. Drilling Mud Pq Penetrometer reading-tons/square foot J.W. Jet Water S Torvane reading-tons/square foot H.A. Hand Auger G Specific Gravity – ASTM D 854-58 NXC Size NX Casing SL Shrinkage limit – ASTM 427-61 BXC Size BX Casing Ph Hydrogen ion content-meter method AXC Size AX casing O Organic content-combustion method SS 2” O.D. Split Spoon Sample M.A. Grain size analysis 2T 2” Thin Wall Tube Sample C* One dimensional consolidation 3T 3” Thin Wall Tube Sample QC Triaxial Compression

* See attached data Sheet and/or graph

WATER LEVEL SYMBOL

Water levels shown on the boring logs were determined at the time and under the conditions indicated. In sand, the indicated levels can be considered relatively reliable for most site conditions. In clay soils, it is not possible to determine the groundwater level within the normal scope of a test boring investigation, except where lenses or layers of more pervious water bearing soil are present; and then a long period of time may be necessary to reach equilibrium. Therefore, the position of the water level symbol for cohesive or mixed soils may not indicate the true level of the groundwater table. The available water level information is given at the bottom of the log sheet.

DESCRIPTIVE TERMINOLOGY

RELATIVE DENSITY CONSISTENCY

TERM N60 Value (corrected) TERM N60 Value (corrected) Very Loose 0 – 4 Soft 0 - 4 Loose 5 – 8 Medium 5 - 8 Medium Dense 9 – 16 Rather Stiff 9 – 15 Dense 16 – 30 Stiff 16 – 30 Very Dense Over 30 Very Stiff Over 30

RELATIVE PROPORTIONS PARTICLE SIZES

TERMS RANGE MATERIAL DESCRIPTION U.S. SIEVE SIZE

Trace 0 – 5% Boulders Over 3” A little 5 – 15% Gravel Coarse 3” to ¾” Some 15 – 30% Medium ¾” to #4 Sand Coarse #4 to #10 Medium #10 to #40 Fine #40 to #200 Silt and Clay Determined by Hydrometer Test

CLASSIFICATION of SOILS for ENGINEERING PURPOSES

ASTM Designation D-2487 and D2488 (Unified Soil Classification System)

Major Divisions Group

Symbol Typical Name Classification Criteria

Co ar se G ra in ed S oi ls

M or e th an

0% re ta in ed o n

N o.

s ie ve

G ra o r m or e of c oa rs e fr ac tio n re ta in ed o n

N o.

si ev e.

Cl ea n G ra

GW

Well –graded gravels and gravel-sand mixtures, little or no fines.

Cl as si fic at io n on b as is o f p er ce nt ag e of fi ne s.

Le ss th an p as si ng N o.

S ie ve

G

W , G

P, S

W , S

P M or e th an

2% p as sin g

N o.

S ie ve

G M

, G C, S M

, S C

Fr om to

2% p as sin g N o.

S ie ve

Bo rd er lin e

Cl as si fic at io n re qu iri ng u se of d ua l s ym bo

Cu = D60 / D10 greater than 4.

Cz = (D30)2 / (D10 x D60) between 1 & 3.

GP

Poorly graded gravels and gravel-sand mixtures, little or no fines.

Not meeting both criteria for GW materials.

G ra ve ls w ith

F in es

GM Silty gravels, gravel-sand-silt mixtures.

Atterberg limits below “A” line, or P.I. less than 4.

Atterberg limits plotting in hatched area are borderline classifications requiring use of dual symbols.

GC Clayey gravels, gravel-sand-clay mixtures.

Atterberg limits above “A” line with P.I. greater than 7.

Sa nd s M or e th an

0% o f c oa rs e fr ac tio n pa ss es

N o sie ve

Cl ea n Sa nd s SW

Well-graded sands and gravelly sands, little or no fines.

Cu = D60 / D10 greater than 6.

Cz = (D30)2 / (D10 x D60) between 1 & 3.

SP

Poorly graded sands and gravelly sands, little or no fines.

Not meeting both criteria for SW materials.

Sa nd s w ith

Fi ne s

SM Silty sands, sand-silt mixtures.

Atterberg limits below “A” line, or P.I. less than 4.

Atterberg limits plotting in hatched area are borderline classifications requiring use of dual symbols.

SC Clayey sands, sand-clay mixtures.

Atterberg limits above “A” line with P.I. > 7.

Fi ne

G ra in ed

S oi

M or e th an

0% p as se s N o.

s ie

Si lts a nd

C la ys

Li qu id L im it of

0% o r l es s ML Inorganic silts, very fine sands, rock flour, silty or clayey fine sands.

CL

Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays.

OL Organic silts and organic silty clays of low plasticity.

Si lts a nd

C la ys

Li qu id L im it gr ea te r t ha n

MH

Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts.

CH Inorganic clays of high plasticity, fat clays.

OH Organic clays of medium to high plasticity.

H ig hl y

O rg an ic

So ils

Pt Peat, muck, and other highly organic soils.

P la st ic it y

In d e x

C h ar t

0102030405060

L iq u id

L im it

Plasticity Limit

C ha rt f or c la ss if ic a ti o n o f fi ne g ra in ed so an d th e fi n fr ac ti on o f co ar se g ra in e d so il s.

A tt e rb e rg

L im it s p lo tt in g in h a tc h e d a re a ar e bo rd er li n e c la ss if ic a ti on s r e qu ir in g u se o f d ua l sy m bo ls

O H

M

H S o ils

C H

S o ils

C L

S o ils

O L

M

L S o ils

"A

Li ne

C L-

M L

S o

Index

EXCAVATION OVERSIZE

Excavation oversize facilitates distribution of load induced stress within supporting soils. Unless otherwise superseded by report specific requirements, all construction should conform to the minimum oversize and horizontal offset requirements as presented within the diagram and associated chart.

Definitions Oversize Ratio H: The ratio of the horizontal distance divided by the engineered fill depth (i.e., #

Horizontal / Depth D). Refer to Chart for specific requirements.

Horizontal Offset A: The horizontal distance between the outside edge of footing or critical position and the crest of the engineered fill section. Refer to Chart for specific requirements.

Note 1: Excavation depth and sidewall inclination should not exceed those specified in local, state, or federal regulations including those defined by Subpart P of Chapter 27, 29 CFR Part 1926 (of Federal Register).

Excavations may need to be widened and sloped, or temporarily braced, to maintain or develop a safe work environment. Contractor is solely responsible for assessing stability under “means and methods”.

Condition Unsuitable Soil Type Horizontal Offset A Oversize Ratio H Foundation Unit Load equal to or less than 3,000 psf.

SP, SM soils, CL & CH soils with cohesion greater than 1,000 psf

NA

Equal to or greater than one (1) times Depth D

Foundation Unit Load greater than 3,000 psf

SP, SM soils, CL & CH soils with cohesion less than 1,000 psf

NA

Equal to or greater than one (1) times Depth D

Foundation Unit Load equal to or less than 3,000 psf.

Topsoil or Peat 2 feet or width of footing, whichever is greater

Equal to or greater than two (2) times Depth D

Foundation Unit Load greater than 3,000 psf

Topsoil or Peat 5 feet or width of footing, whichever is greater

Equal to or greater than two (3) times Depth D

Figure 1: Excavation Oversize

APPENDIX B

GROUNDWATER ISSUES

PLACEMENT and COMPACTION OF ENGINEERED FILL

GROUNDWATER ISSUES

The following presents additional comment and soil specific issues related to measurement of groundwater conditions at your project site.

Note that DTE’s groundwater measurements, or lack thereof, will vary depending on the time allowed for equilibrium to occur in the borings. Extended observation time was not available during the scope of the field exploration program and, therefore, groundwater measurements as noted on the boring’s logs may or may not accurately reflect actual conditions at your site.

Seasonal and yearly fluctuations of the groundwater level, if any, occur. Perched groundwater may be present within sand and silt lenses bedded within cohesive soil formations. Groundwater typically exists at depth within cohesive and cohesionless soils.

Documentation of the local groundwater surface and any perched groundwater conditions at the project site would require installation of temporary piezometers and extended monitoring due to the relatively low permeability exhibited by the site soils. We have not performed such groundwater evaluation due to the scope of services authorized for this project.

DTE anticipates that a system of sump pits and pumps located outside of the foundation areas would be suitable for control if perched groundwater were to be encountered. DTE cautions that such seepage may be heavy and will vary based on seasonal and annual precipitation, and ground related impacts in the vicinity of the project.

PLACEMENT and COMPACTION OF ENGINEERED FILL

Unless otherwise superseded within the body of the Geotechnical Exploration Report, the following criteria shall be utilized for placement of engineered fill on project. This includes, but is not limited to, earthen fill placement to improve site grades, fill placed below structural footings, fill placed interior of structure, and fill placed as backfill of foundations.

Engineered fill should consist of natural, non-organic, competent material being a minus 2” material with less than 12 percent material passing the No. 200 sieve, and at least 50 percent retained on the No. 40 sieve. Such soils may include, but are not limited to gravel, sand, or clays with Unified Soil Classification System (ASTM D2488) classifications of GW, SP, CL, or SM. Use of silt or clayey silt as project fill will require additional review and approval of project Geotechnical Engineer of Record.

Such soils have USCS classifications of ML, MH, ML-Cl, MH-CH. Use of topsoil, marl, peat, other organic soils construction debris and/or other unsuitable materials as fill is not allowed. Such soils have USCS classifications of OL, OH, Pt.

Engineered fill, classified as clay, should be tempered such that the moisture content at the time of placement is equal to and no more than + 3/-3 percent optimum of modified proctors. Likewise, engineered fill classified as gravel or sand should be tempered such that the moisture content at the time of placement is +3/-1 percent of the optimum content.

All engineered fill for construction should be placed in individual eight (8) inch maximum depth lifts.

Each lift of fill should be compacted by large vibratory equipment until the in-place soil density is equal to or greater than the criteria established within the following tabulation.

Modified Proctor Test Requirements:

Type of Construction Compaction Criteria (% respective Proctor) 1

Clay Sand or Gravel General Embankment Fill Min. 92 Min. 92 Engineered Fill below Foundations Min. 95 Min. 95 Engineered Fill below Floor Slabs Min. 95 Min. 95 Engineered Fill greater than 8 feet below foundations Min. 96 Min 96 Engineered Fill placed as Pavement Aggregate Base NA Min. 95 Engineered Fill placed to within 3 feet of pavement aggregate base

Min. 95 Min. 95

Engineered Fill placed within 3 feet of pavement aggregate base

Min. 92 Min. 92

Note 1 Unless otherwise required, compaction shall be based on the Modified Proctor Test (ASTM D1557).

Density tests should be taken during engineered fill placement to document earthwork has achieved necessary compaction of the material(s). Recommendations for interior fill placement and backfill of foundation walls are presented within other sections of this report.

APPENDIX C

SOIL BORING DIAGRAM

SOIL BORING LOGS

RESISTIVITY TESTING

Existing Tank Location 24.0667

Legend

Soil Boring

900 ft

N

N Image © 2024 Airbus

Image © 2024 Airbus

New Tank Location 24.0667

Legend

Soil Boring

700 ft

N

N Image © 2024 Airbus

PROJECT TITLE: Hermosa Water Tanks

PROJECT NUMBER: 24.0667 GPS: 43.840495 -103.197881 1.1

DEPTH

IN GEOLOGIC N NO TYPE MC D Pocket PI

FEET Description of Materials ORIGIN (SPT) (%) (pcf) Pen

0.0' Brown Topsoil (OH) 1 Bag

5, 7, 8 2 SS 10.5

5.0' 4, 8, 6 3 SS

4, 6, 5 4 SS 18.2 58

10.0' 3, 5, 7 5 SS

4, 4, 5 6 SS 17.6

15.0' 2, 4, 6 7 SS

20.0' 4, 9, 9 8 SS 17.5

25.0' 5, 7, 8 9 SS

Elevation (ft) WATER TABLE MEASUREMENTS DATE: 10/7/24

3413 DNE METHOD OF DRILLING: TMG MC 23

Notes Existing Tank Site CREW CHIEF: RG

SAMPLE DATA LABORATORY TESTS

TEST BORING LOG

LL/PL

BORING NO:

Brown Silty Clay (CL)

Brown Silty Fat Clay (CH)

Dark Brown Weathered Shale (CH) with some Rust Staining, Yellow Staining and Gypsum Crystals

PROJECT NUMBER: 24.0667 GPS: 43.840495 -103.197881 1.2

DEPTH

IN GEOLOGIC N NO TYPE MC D Pocket PI

FEET Description of Materials ORIGIN (SPT) (%) (pcf) Pen

25.0'

30.0' 8, 15, 14 10 SS

35.0' 7, 18, 22 11 SS

40.0' 14, 22, 35 12 SS

Refusal at 42.0' due to stiff Weathered Shale

45.0'

50.0' Elevation (ft) WATER TABLE MEASUREMENTS DATE: 10/7/24

3413 DNE METHOD OF DRILLING: TMG MC 23

Notes Existing Tank Site CREW CHIEF: RG

TEST BORING LOG

BORING NO:

SAMPLE DATA LABORATORY TESTS

LL/PL

Dark Brown Weathered Shale (CH) with trace Yellow Staining and Gypsum Crystals

PROJECT NUMBER: 24.0667 GPS: 43.854750 -103.200005 2

DEPTH

IN GEOLOGIC N NO TYPE MC D Pocket PI

FEET Description of Materials ORIGIN (SPT) (%) (pcf) Pen

0.0' Dark Brown Topsoil (OH) 1 Bag

6, 8, 13 2 SS 8.6

5.0' 6, 14, 13 3 SS 5

5, 50/3" 4 SS 4.1

Refusal at 8.0' due to Gravel and Cobble

10.0'

15.0'

20.0'

25.0' Elevation (ft) WATER TABLE MEASUREMENTS DATE: 10/7/24

3411 DNE METHOD OF DRILLING: TMG MC 23

Notes New Tank Site CREW CHIEF: RG

TEST BORING LOG

BORING NO:

SAMPLE DATA LABORATORY TESTS

LL/PL

Brown Silty Lean Clay (CL) with trace Gravel

Brown Silty Lean Clay (CL) with Gravel and some Cobble