SD FLAP SDGFP AD Pavement Report.pdf

SUBMITTED TO:

HDR Engineering, Inc.

1670 Broadway, Suite 3400 Denver, CO 80202

BY:

Shannon & Wilson 5900 W. 38th Avenue Wheat Ridge, CO 80212

(303) 825-3800 www.shannonwilson.com

PAVEMENT DESIGN REPORT

SD FLAP SDGFP Parking (1) North Point Parking Lot

CHARLES MIX COUNTY, SOUTH DAKOTA

November 2025

Shannon & Wilson No: 114185-001

SD FLAP SDGFP Parking (1) North Point Parking Lot Pavement Design Report

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CONTENTS

1 Introduction

2 Project Site and Description

3 Field Explorations and laboratory testing

3.1 Subsurface Exploration

3.2 Geotechnical Laboratory Testing

3.3 Visual Pavement Assessment

3.4 Previous Subsurface Information

4 Subsurface Conditions

4.1 Regional Geology

4.2 Existing Pavements

4.3 Pavement Subgrade Soils

4.4 Groundwater

4.5 Subsurface Variability

5 Pavement Design Recommendations

5.1 Traffic Loading

5.2 Subgrade Soils

5.3 Recommended Pavement Sections

5.4 Full Depth Reclamation (FDR)

6 Additional Considerations

6.1 Expansive Subgrade Mitigation

6.2 Frost Damage

6.3 Corrosive Soil

7 Construction Considerations

7.1 Site Preparation

7.2 Earthwork

7.2.1 General

7.2.2 Subgrade Preparation and Compaction

7.2.3 Soft Subgrade

7.2.4 Low Permeable Fill

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7.3 Lime Treated Subgrade (LTS)

7.4 Paving Materials

8 Limitations

9 References

Exhibits Exhibit 3‐1: Visual Pavement Assessment Summary

Exhibit 3‐2: Boat Ramp Parking Lot Typical Pavement Distress

Exhibit 4‐1: Existing Pavement Section Thickness

Exhibit 5‐1: Pavement Thickness Design Recommendations

Exhibit 6‐1: Guidance on Subexcavation Depth of Expansive Soils

Exhibit 6‐2: Corrosion Testing Results

Exhibit 6‐3: Corrosivity Ratings Based on Soil Resistivity

Exhibit 6‐4: Corrosivity Ratings Based on Water Soluble Sulfate Exposure

Exhibit 7‐1: Recommended Materials for Pavements

Figures Figure 1: Vicinity Map

Figure 2: Site and Exploration Program

Appendices Appendix A: Subsurface Explorations

Appendix B: Laboratoy Test Results

Appendix C: Previous Subsurface Information

Appendix D: Drilling Photographs

Appendix E: Pavement Design Calculations

Important Information About Your Geotechnical Report

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1 INTRODUCTION

This pavement design report summarizes the results of our subsurface exploration and laboratory testing program, and provides pavement design recommendations for the proposed pavement reconstruction of the boat ramp parking lot at North Point Recreation

Area in Charles Mix County, South Dakota (the Project). Our services were conducted in general accordance with Task Order TO013/1000100116131 with HDR dated February 13, 2025.

Our scope of services included:

Coordinating a subsurface exploration program, which included observing and logging four geotechnical borings within the parking lot;

Performing geotechnical laboratory testing on selected soil samples retrieved from the borings;

Developing pavement design recommendations for reconstruction of the parking lot;

Providing construction consideration for the above Project elements; and

Prepared this pavement design report.

Our scope of services did not include environmental assessments or evaluations regarding the presence or absence of wetlands, or hazardous or toxic substances in the soil, surface water, groundwater, or air, on or below or around this site, or for the evaluation or disposal of contaminated soils or groundwater should any be encountered. If a service is not specifically indicated in this report, do not assume that it was performed.

2 PROJECT SITE AND DESCRIPTION

The Project is located at the approach to the boat ramp at the North Point Recreation Area near Pickstown, in Charles Mix County, South Dakota (Figure 1). The Project consists of an approximately 98,000 square foot (sf) parking lot for the boat ramp leading to Francis Case

Lake, upstream of the Fort Randall Dam on the Missouri River. The boat ramp appears to have been recently reconstructed with Portland cement concrete pavement (PCCP) and is not included in the Project. The project is completed under the direction of the Federal

Highway Administration, Central Federal Lands Highway Division (CFLHD), on behalf of

South Dakota Game, Fish & Parks (SDGFP).

At the time of our field exploration program, the parking lot was generally surfaced with asphalt concrete pavement (ACP) and chip seal that was observed to have signs of distress

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(refer to Section 3.3). Based on information provided by HDR, the Project consists of the reconstruction of the existing pavement to improve pedestrian and vehicular safety.

3 FIELD EXPLORATIONS AND LABORATORY TESTING

3.1 Subsurface Exploration

Shannon & Wilson conducted a subsurface exploration program on May 5, 2025, to explore subsurface conditions at the Project site. The subsurface exploration program consisted of drilling and sampling four borings (designated SW‐01 through SW‐04) to depths of approximately 5.5 feet below ground surface (bgs); see Figure 2 for approximate boring locations. Appendix A presents a discussion of the drilling, sampling, and testing procedures used to complete the borings. Appendix A also presents individual exploration logs, and an explanation of the symbols and terminology used.

3.2 Geotechnical Laboratory Testing

We completed geotechnical laboratory testing of selected samples retrieved from the borings to estimate index and engineering properties. The index tests included natural water content, grain size distribution, Atterberg limits, unit weight, and Proctor compaction.

The engineering property tests included Hveem Stabilometer (R‐value) and corrosion.

Laboratory test methods and results are provided in Appendix B.

3.3 Visual Pavement Assessment

A Shannon & Wilson field representative conducted a visual pavement assessment of the existing parking lot surfacing to characterize the general pavement conditions. This pavement assessment generally followed the terminology and descriptions provided in the

Federal Highway Administration (FHWA) Distress Identification Manual (FHWA, 2014) and included recording typical crack patterns and level of severity of cracking based on typical crack length and aperture. A summary of our observations is provided in Exhibit 3‐

1, and photographs of typical distress are provided in Exhibit 3‐2.

Exhibit 3-1: Visual Pavement Assessment Summary

Location Observed Pavement Condition Description

Boat Ramp

Parking Lot

Moderate to high severity fatigue, block, and longitudinal cracking. Majority of cracks were either unsealed or the bituminous crack sealant needs replacement.

Low to moderate severity rutting along travel lanes at the center and both sides of the parking lot.

Potholes were observed across the parking lot with aggregate base course material exposed. Some potholes had been previously patched, and the patches were generally in poor condition.

Exhibit 3-2: Boat Ramp Parking Lot Typical Pavement Distress

Typical Moderate to High Severity Fatigue Cracking (Left); Typical Pothole with Underlying Aggregate Base Course Material Exposed (Right).

3.4 Previous Subsurface Information

We reviewed previous subsurface information in the Project area to supplement our exploration program. GeoTek Engineering & Testing Services, Inc. (GeoTek) performed a subsurface exploration in 2018 which included drilling four borings in the boat ramp parking lot (GeoTek, 2018). We also reviewed the results of a 2024 pavement section exploration by GeoTek, which consisted of coring and measuring pavement and base thickness at eight locations in the boat ramp parking lot (GeoTek, 2024). Selected information from the previous subsurface explorations is included in Appendix C.

4 SUBSURFACE CONDITIONS

We based our understanding of the geology and subsurface conditions at the Project site on a review of regional geological maps, the results of our field explorations program, and laboratory testing on select samples retrieved from the borings. Photographs of the borings taken during drilling are included in Appendix D.

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4.1 Regional Geology

Mapping completed by South Dakota Geological Services (Hedges, L.S., 1975) shows the

Project area is underlain by glacial till, which is described as predominantly silty to clayey soils with sand to boulder sized glacial deposits.

4.2 Existing Pavements

Existing ACP pavement and chip seal thickness was measured from pavement cores collected at each boring location. Crushed aggregate base (CAB) thickness was measured from the bore hole annulus. Exhibit 4‐1 summarizes the observed pavement thicknesses.

Exhibit 4-1: Existing Pavement Section Thickness

Boring

ACP Thickness

(inches)

CAB

(inches)

SW-01 3 3

SW-02(1) 1½ 4

SW-03(1) <1 3

SW-04(1) 1 4

NOTE: (1) Indicates that the ACP encountered consists of chip seal.

As shown in Appendix C, the borings and pavement cores conducted by GeoTek encountered similar asphalt and chip seal at the ground surface overlying a layer of gravel

(interpreted to be CAB). In the explorations conducted by GeoTek, the asphalt and chip seal thickness ranged from 1 to 4.5 inches and the gravel thickness ranged from 3 to 8.25 inches.

Geotextile was not encountered in the explorations.

4.3 Pavement Subgrade Soils

The subgrade soils encountered in the borings generally consisted of a layer of artificial fill consisting of medium stiff to stiff, lean clay with varying percentages of sand (American

Association of State and Highway Transportation [AASHTO] soil classification A‐6 and A‐7‐

6), that extended to approximately 2 to 3 feet bgs. Below the fill layer, the borings encountered medium stiff to stiff, lean clay to fat clay with varying percentages of sand

(AASHTO soil classification A‐6 and A‐7‐6). The borings conducted by GeoTek encountered similar subgrade soils consisting of lean to fat clay with variable sand and gravel. Refer to the boring logs in Appendix C for more information.

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4.4 Groundwater

We did not observe groundwater during the subsurface exploration. It should be noted that groundwater level fluctuations are possible and depend on many factors, including seasonal variations and local precipitation.

4.5 Subsurface Variability

The explorations were completed to evaluate subsurface conditions at the project site. Our observations are specific to the locations and depths noted on the logs and may not be applicable to all areas of the site. Unanticipated subsurface conditions are commonly encountered, and no amount of exploration can precisely predict the characteristics, quality, or distribution of subsurface and site conditions. Potential variation includes, but is not limited to:

The conditions between and below explorations may be different.

The passage of time or intervening causes (natural and manmade) may result in changes to site and subsurface conditions.

Such unexpected conditions frequently require that additional expenditures be made to attain a properly constructed project. Therefore, some contingency fund is recommended to accommodate such potential extra costs. If conditions different from those described herein are encountered during construction, we should be retained to review our description of the subsurface conditions and reconsider our conclusions and recommendations.

5 PAVEMENT DESIGN RECOMMENDATIONS

Performance of a pavement system depends on the pavement material and thicknesses, subgrade strength, traffic loads and repetitions, design life, and subgrade drainage characteristics. The following sections discuss each of these aspects as they relate to the pavement reconstruction.

Our pavement design and results are based on the design procedures presented in the 1993

AASHTO Guide for the Design of Pavement Structures (AGDPS) (1993), with guidance from the U.S. Department of Transportation and Federal Highway Administration (FHWA)

Federal Lands Highway Project Development and Design Manual (PDDM) (2008).

5.1 Traffic Loading

Based on discussions with HDR, traffic data is not available for the Project. For pavement design, we assumed an 18‐kip equivalent single axle loading (ESAL) of 50,000 based on the

114185-001 November 2025 minimum recommended ESAL in the PDDM (2008), for low volume roadways with less than 500 vehicles per day.

5.2 Subgrade Soils

The subgrade soils encountered in the subsurface explorations primarily consisted of medium stiff, to stiff lean to fat clay with variable sand and trace gravel. We performed a single R‐value test on the subgrade material encountered in boring SW‐01, which indicates an R‐value of 12 for the sample tested (AASHTO A‐6 soil). For the pavement analysis, we used an AASHTO (1993) correlation between R‐value and resilient modulus to calculate a resilient modulus value of approximately 7,660 pounds per square inch (psi).

5.3 Recommended Pavement Sections

We considered paving alternatives consisting of full‐depth ACP on native subgrade, composite ACP over crushed aggregate base (CAB), full depth reclamation, and full‐depth

ACP over lime‐treated subgrade (LTS). We did not consider an overlay due to the relatively thin existing pavement. Due to the clayey subgrade soils, which may be susceptible to pumping and instability (see Section 7.2.3), particularly if exposed to water during construction, we consider paving full depth ACP on the native subgrade to have a higher risk of constructability challenges (i.e., subgrade pumping during paving) than the other alternatives.

Refer to Exhibit 5‐1 for the recommended pavement section alternatives. The pavement design calculations are provided in Appendix E. We recommend that all CAB be daylighted and subgrade sloped to avoid accumulation of water in the subgrade.

Exhibit 5-1: Pavement Thickness Design Recommendations

Pavement Alternative

ACP Thickness

(inches)

CAB

Thickness

(inches)

FDR

Thickness

(inches)

LTS

Thickness

(inches)

Full Depth ACP 5 - - -

ACP over CAB 4 4 - -

3.5 6 - -

ACP over FDR 4 - 4 -

ACP over FDR with Cement 3.5 - 4 -

ACP over LTS 3.5 - - 12 ACP = Asphalt Concrete Pavement, CAB = Crushed Aggregate Base, FDR = Full Depth Reclamation, LTS = Lime Treated Subgrade

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Based on discussions with HDR, we understand that the preferred pavement section alternative consists of 3.5 inches ACP over 6 inches CAB. A geotextile separator below the

CAB layer was requested by the stakeholders, to provide additional subgrade stabilization.

5.4 Full Depth Reclamation (FDR)

FDR generally consists of in‐place pulverization of the existing HMA pavement that becomes the base of a new HMA paving subgrade. The surface of the FDR can accommodate minor grading adjustments provided a minimum FDR thickness is maintained. A new HMA surface layer is then paved over the FDR prepared subgrade, typically resulting in an overall raise to the pavement grades, which may also require adjustments to the grade of adjacent pavements at transitions to the parking lot.

Rehabilitation with FDR effectively provides a new pavement and eliminates the potential for reflective cracking from the existing pavement. Portland Cement and water may be added to the FDR prior to final grading and compacting to create a stabilized base layer.

FDR with cement should meet the requirements provided in FP‐24 Section 305. If the FDR with cement option is selected, a mix design should be completed evaluate the proportioning of the Project materials and to demonstrate the required compressive strength of the stabilized layer may be achieved.

However, due to the relatively thin existing pavement thickness, at a minimum, we recommend placing 1 inch of CAB over the existing asphalt pavement in the parking lot and performing a 4‐inch‐thick FDR. Additional CAB may be required in areas of relatively thin existing pavement to provide the required FDR thickness. FDR also requires a specialty contractor and equipment. Due to the relatively small amount of pavement included in the

Project, and the relatively thin existing pavement thickness, full depth reconstruction may be more cost beneficial.

6 ADDITIONAL CONSIDERATIONS

6.1 Expansive Subgrade Mitigation

Clayey subgrade soils can be susceptible to volume change by swelling and/or shrinking.

This geologic phenomenon has the potential to cause substantial damage to lightly loaded structures, such as pavements, when exposed to water. To reduce long‐term swell potential, and to mitigate for potential constructability issues (pumping subgrade and difficulty achieving subgrade compaction), Section 11.3.2.1.3 of the FHWA PDDM (2008) provides guidelines on subgrade treatment depth based on the subgrade Atterberg limits (liquid limit and plasticity index), as shown in Exhibit 6‐1.

Exhibit 6-1: Guidance on Subexcavation Depth of Expansive Soils

Plasticity Index

(PI)

Liquid Limit

(LL)

Depth of Subexcavation (ft)

15 - 25 < 50 2

25 - 35 50 - 60 2 - 4

> 35 > 60 4 - 6

NOTES:

Based on Exhibit 11.3-C of the PDDM.

The existing pavement subgrade soils encountered in the borings generally consisted of medium stiff to stiff, lean to fat clay with variable sand content. As shown in Table B‐1 in

Appendix B, the samples of subgrade soils tested exhibited a maximum Liquid Limit of 54 and maximum Plasticity Index of 34. Based on the Atterberg limits test results, 2 to 4 feet of moisture treatment may be considered to help mitigate expansive soil conditions.

In general, soils that have been in place and covered with exiting pavement for several years have low swell susceptibility. This is due to the pavement inhibiting evapotranspiration of moisture in the subgrade and the subgrade moisture state being allowed to equilibrate. The subgrade soils appear to have elevated, in‐place moisture content, general at or above the plastic limit (PL) for the materials encountered, which is an indication of low swell potential.

Additionally, for soil to swell, the subsurface moisture regime must change such that the moisture content of the swell susceptible material can increase. In general, we do not anticipate that the proposed construction will significantly alter the moisture regime at the site. Considering the exiting parking lot has been paved for several years and does not appear to be exhibiting swell‐related damage, in our opinion, the risk of swell‐related damage to the Project pavement is low. Based on the relatively low swell risk for the site, we recommend moisture treating the upper 6 inches of the pavement subgrade in accordance with Section 7.2.2.

6.2 Frost Damage

Frost susceptible soils can lead to pavement performance issues due to heaving or deformation from ice lenses in the underlying soil and pavement fatigue damage due to thaw‐weakened subgrade of the springtime freeze‐thaw cycle (FHWA, 2008). Frost susceptible soils typically include fine‐grained soils such as silts and clays. In accordance with the PDDM, typical treatment for frost susceptible soils consists of assuring there is an adequate pavement layer structure to account for the loss of bearing capacity during the

114185-001 November 2025 spring thaw and removing or replacing highly frost susceptible soil for a portion of the expected frost depth.

Based on our experience on past CFLHD projects, we understand it is cost prohibitive to provide protection against frost heave on such projects. If this is not the case, we recommend partial removal and replacement (up to about 70% of the estimated frost depth of 42 inches (City of Yanktown, 2025)) and we should be contacted to provided alternative pavement sections based on the import material. If frost mitigation is included, there would be some savings resulting from a reduced pavement section.

6.3 Corrosive Soil

The soil encountered at the project site can be corrosive to steel and concrete in contact with the ground. To assist in estimating the corrosion potential in the project area, selected samples were tested for pH, resistivity, water soluble sulfates, and chlorides to assess corrosion potential at the project site. Test results are presented in Exhibit 6‐2 and

Appendix B.

Exhibit 6-2: Corrosion Testing Results

Boring Depth (feet) pH

Resistivity

(ohm-cm)

Sulfate Content

Chloride Content

SW-01 1.0 to 2.5 6.0 2,400 0.19 0.059

SW-04 4.0 to 5.5 - - 0.08 -

NOTES:

Water-soluble sulfate and chloride content values are shown as percent weight in dry soil.

ohm-cm = ohm-centimeter

The resistivity measured in the sample was 2,400 ohm‐centimeters. Based on correlations developed by Roberge (2012) as shown in Exhibit 6‐3, these values suggest a highly corrosive subsurface environment for metal in contact with subsurface materials.

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Exhibit 6-3: Corrosivity Ratings Based on Soil Resistivity

Soil Resistivity (ohm-cm) Corrosivity Rating

>20,000 Essentially Noncorrosive

10,000-20,000 Mildly Corrosive

5,000-10,000 Moderately Corrosive

3,000-5,000 Corrosive

1,000-3,000 Highly Corrosive

<1,000 Extremely Corrosive

The concentration of water‐soluble sulfates measured in the samples was 0.08 and 0.19 percent by weight (800 and 1,900 parts per million). Based on classifications as defined by

American Concrete Institute (ACI) ACI‐318‐21 (ACI, 2021) as shown in Exhibit 6‐4, these results suggest a negligible to moderate degree of sulfate attack on concrete exposed to site soils (exposure class S0 to S1).

Exhibit 6-4: Corrosivity Ratings Based on Water Soluble Sulfate Exposure

Water Soluble Sulfate in Soil (Percent by Weight)

Sulfate Severity (Class)

<0.10 Negligible (S0)

0.10-<0.20 Moderate (S1)

0.20-2.00 Severe (S2)

>2.00 Very Severe (S3)

The test results and the above discussion are provided to assist the designer in the selection of project materials, concrete type, or other features with respect to corrosion. As appropriate, the designer should consider protective measures, such as coatings or using alternative materials to reduce the corrosion potential.

7 CONSTRUCTION CONSIDERATIONS

The applicability of the pavement design recommendations provided herein is contingent on good construction practices. Poor construction techniques may alter conditions from those on which our recommendations are based, resulting in reduced pavement performance and service life. Our analyses assumed that this project is constructed according to FP‐24 U.S. Customary Units (U.S. Department of Transportation [USDOT] and

FHWA, 2024) construction standards. The following sections present additional construction and material considerations for this Project.

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7.1 Site Preparation

All surface and subsurface structures associated with current development of the site, including pavement materials, should be removed. Any existing surficial topsoil and soil containing visible organics should be stripped and removed from all areas to be paved.

7.2 Earthwork

7.2.1 General

Earthwork, including placement of fill and subgrade preparation, should conform to the requirements provided in the FP‐24 U.S. Customary Units, (FHWA, 2024) and the recommendations provided in the following sections.

7.2.2 Subgrade Preparation and Compaction

Proper subgrade preparation is required for adequate pavement performance. We recommend that at a minimum, the upper 6 inches of the pavement subgrade should be scarified in place, moisture treated, and recompacted to at least 95% maximum density, as determined by AASHTO T99 in accordance with FP‐24 Section 204.11.

The compacted surface should then be proof‐rolled with a fully‐loaded, tandem‐axle, 10‐ yard dump truck or equivalent. All soft, wet, or yielding subgrade areas should be overexcavated, removed, and replaced, as described in Section 7.2.3.

7.2.3 Soft Subgrade

Subgrade soils are anticipated to consist of medium stiff to stiff clayey soils with elevated moisture content with respect to the PL and optimum moisture content. These materials are prone to pumping and yielding from construction activities. Additionally, these soils will likely require drying to achieve adequate compaction.

The contractor will need to carefully control the movement of equipment around the site and minimize the passage of equipment to avoid disturbing exposed subgrades. Surface drainage will also need to be controlled to limit subgrade exposure to precipitation.

Limiting the amount of exposed subgrade at a given time should be considered to reduce the risk of subgrade instability related to these issues. Even with these precautions, compaction of the material will be difficult and extra working time may be needed.

Placement and compaction testing should be monitored on a full‐time basis to assist in this process.

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We recommend proof‐rolling or probing any exposed subgrade to evaluate the suitability of the subgrade. Areas that are identified as being loose, soft, or yielding should be recompacted in place, removed and reconditioned, or overexcavated to depth of 24 inches and replaced with granular fill such as Select Borrow (FP‐24 704.07), or Unclassified Borrow

(FP‐24 704.06) with the additional requirement of a maximum particle size of 3 inches. If granular fill is used, the base of the subexcavation must be daylighted. If daylighting the subexcavation is not feasible or is cost prohibitive, the overexcavation should be backfilled with Low Permeable Fill (see Section 7.2.4) If loose, soft, or yielding soils are encountered after over‐excavating 2 feet, a geogrid (FP‐24 Section 704.03) should be installed at the base of the excavation before backfilling with new fill material. Lime treatment may also be considered to stabilize soft subgrade soils and reduce the risk of subgrade instability during construction.

For estimating purposes, we recommend the design team assume overexcavation or other subgrade stabilization will be required for up to approximately 50% of the new pavement area. However, this estimate does not account for potential construction‐related issues that may exacerbate subgrade instability, such as precipitation during construction or exposure of prepared subgrades to construction traffic. The actual amount of subgrade stabilization will vary depending on these factors.

7.2.4 Low Permeable Fill

Low Permeable Fill should consist of soil that is free of organics, contaminants, debris, rock fragments larger than 3 inches, contain 20 to 40% fines, and has a plasticity index of 15 or less. Additionally, the material should have a swell potential of less than 1% in accordance with ASTM D4546 with an inundation pressure of 200 psf when compacted to at least 95% maximum dry density (ASTM D698), at optimum moisture content.

7.3 Lime Treated Subgrade (LTS)

Based on subgrade conditions encountered in the borings, lime treatment is a suitable option for treating subgrades at the Project site. Lime is typically placed during construction, after the site is graded. The subgrade is then disced, lime added, mixed, and compacted prior to the lime setting up. A chemical reaction occurs between the lime, subgrade soil, and water resulting in a low plasticity, stiff layer.

Soils containing high sulfate concentrations can result in a deleterious reaction between the sulfate ions, soil, and water resulting in long‐term heaving in the subgrade soils. Two samples from the subgrade soils were tested for water soluble sulfates and indicated a maximum sulfate content of 0.19%. The National Lime Association suggests a double‐ treatment method if the sulfates exceed 0.3% (2020) to mitigate a potential adverse sulfate

114185-001 November 2025 reaction. If LTS is used, the mix design should include additional sulfate testing to determine the mixing and application methodology (i.e., single or double treatment).

7.4 Paving Materials

The following exhibit summarizes our recommendations for pavement material selection using the FP‐24 specifications. We anticipate that a single ACP mix design will be used for the pavements.

Exhibit 7-1: Recommended Materials for Pavements

Material FP-24 Specification Additional Requirements/Comments

CAB Section 302 Use Gradation C, D, or E

ACP Section 403 ½-inch or ¾-inch Nominal Maximum Aggregate Size (NMAS) PG Binder: PG 64-34 Gyratory Number (N): 75

Subgrade Stabilization and Separator Geotextile Section 714.01

Conform to AASHTO M288 Table 1, Class 1 Maximum AOS 0.3 mm

NOTE:

ACP = Asphalt Concrete Pavement; CAB = Crushed Aggregate Base; PG = Performance Grade; AOS = Apparent Opening Size, mm = Millimeters

To determine an appropriate ACP binder for the site, we used software developed by the

FHWA Long Term Pavement Performance (LTPP) Bind (2005). The LTPP Bind software indicated a performance grade (PG) of PG 64‐34 for a 95% reliability for the site and anticipated traffic loading. Based on binder availability according to the South Dakota

Department of Transportation Standard Specifications for Roads and Bridges (2015), PG 64‐

34 is commonly used in South Dakota.

We recommend a gyratory number of 75 be used for the mix design. ACP lift thicknesses should be between 3 and 4 times the maximum aggregate thickness (i.e., a 3‐inch ACP section may consist of a single lift of ¾‐inch NMAS aggregate; a 4‐inch ACP section should consist of 2 lifts with a ½‐inch NMAS aggregate). A tack coat should be placed between subsequent lifts.

8 LIMITATIONS

This report was prepared for the exclusive use of HDR and Central Federal Lands Highway

Division for the purpose of providing geotechnical recommendations for the Project. This geotechnical report should not be used without our approval if any of the following occurs:

Assumptions stated in this report have changed.

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Project details change or new information becomes available such that our analysis and recommendations may be affected.

A substantial period of time has passed since the date of this report.

If any of these occur, we should be retained to review the applicability of our analyses and recommendations.

Within the limitations of scope, schedule, and budget, the analyses, conclusions, and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical and geological principles and practice in this area at the time this report was prepared. We make no other warranty, either express or implied.

Shannon & Wilson, Inc. has prepared and included “Important Information About Your

Geotechnical/Environmental Report,” to assist you and others in understanding the use and limitations of our reports.

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9 REFERENCES

American Association of State Highway and Transportation Officials (1993). AASHTO Guide for Design of Pavement Structures: Washington, D.C. (Vol. 2). AASHTO.

American Concrete Institute. (2021). Building code requirements for structural concrete and commentary (ACI 318‐21) Farmington Hills, Michigan. American Concrete Institute.

City of Yanktown, South Dakota. (2025). Ordinance #1087 Adoption of the 2021

International Residential Building Code (IRC).

https://www.cityofyankton.org/departments‐services/community‐economic‐ development/building‐services‐permits

Federal Highway Administration. (2005). LTPPBind Version 3.1 Beta.

https://infopave.fhwa.dot.gov/Page/Index/LTPP_BIND.

Federal Highway Administration. (2008). Federal Lands Highway project development and design manual (PDDM): U.S. Department of Transportation and Federal Highway

Administration. http://flh.fhwa.dot.gov/resources/manuals/pddm/.

Federal Highway Administration. (2014). Distress Identification Manual for the Long‐Term

Pavement Performance Program (5th rev. ed., Publication No. FHWA‐HRT‐13‐092), 142 p.

https://fhwa.dot.gov/publications/infrastructure/pavements/ltpp/13092/13092.pdf.

Federal Highway Administration. (2024). Federal standard specifications for construction of roads and bridges on Federal Highway projects (FP‐24 English Units). U.S. Department of Transportation and Federal Highway Administration.

http://flh.fhwa.dot.gov/resources/pse/specs/.

GeoTek Engineering & Testing Services, Inc. (2018). Geotechnical Exploration, Park Roads AST

Maintenance & Repair, 381st Ave., Boat Ramp Access, Main Boat Ramp Parking Lot, and

Picnic Shelter #1 Parking Lot, North Point Recreation Area, Charles Mix County, Pickstown, South Dakota (GeoTek #18‐054, GFP # NPnt20Pu). May 2.

GeoTek. (2024). Pavement Section Test Report, Pavement Section Observations, North Point

Recreation Area, Charles Mix County, South Dakota (Project: 23‐2199). January 2.

Hedges, L.S. (1975). Geology and Water Resources of Charles Mix and Douglas Counties, South

Dakota; Part I: Geology (Bulletin 22). South Dakota Geological Survey.

National Lime Association. (2020). Guidelines for stabilization of soils containing sulfates, August. (Technical Memorandum). https://www.lime.org/wp‐ content/uploads/technical‐memorandum‐1.pdf

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Roberge, P.R. (2012). Handbook of Corrosion Engineering (2nd ed.). McGraw‐Hill, New York, New York.

South Dakota Department of Transportation. (2015). Standard Specifications for Roads and

Bridges.

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Platte

M issou ri R iver

Yankton Reservation

Mitchell

Missouri River

Ponca (NE) Trust LandSources: Esri, TomTom, Garmin, FAO, NOAA, USGS, (c)

OpenStreetMap contributors, and the GIS User Community

0 10 20

Miles

SD FLAP SDGFP Parking (1) North Point Parking Lot

Charles Mix County, South Dakota

VICINITY MAP

FIG. 1

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Project Location

90 Sioux Falls

Pierre

South Dakota

Nebraska

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Geotechnical and Environmental Consultants

0 100 200

Approximate Scale In Feet

SITE AND EXPLORATION PLAN

FIG. 2

SW-02

SW-01

SW-03

SW-04

Maxar, Microsoft

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S&W Boring Designation and Approximate Location SD Highway 46

Pickstown

White Swan

South Dakota Game Fish and Parks, Esri, TomTom, Garmin, SafeGraph, METI/NASA, USGS, EPA, NPS, USDA, USFWS

Project Location

South Dakota

Nebraska

Missouri River

SD FLAP SDGFP Parking (1) North Point Parking Lot

Charles Mix County, South Dakota

November 2025 114185-001

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Appendix A: Subsurface Explorations

Appendix A

Subsurface Explorations

A.1 Introduction ........................................................................................................................... A‐1

A.2 Explorations ........................................................................................................................... A‐1

A.2.1 Soil Classification System ........................................................................................ A‐1

A.2.2 Standard Penetration Test (SPT) ............................................................................ A‐1

A.2.3 Bulk Sampling .......................................................................................................... A‐2

A.3 Pavement Cores ..................................................................................................................... A‐2

Figures Log Key

Boring Logs

Pavement Core Photographs

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A.1 INTRODUCTION

Shannon & Wilson’s field exploration program was conducted on May 5, 2025 and consisted of drilling and sampling 4 borings, designated SW‐01 through SW‐04, at the locations shown on Figure 2. The methods used to conduct the methods used to conduct the field exploration program are described below.

A.2 EXPLORATIONS

The borings were coordinated (including subcontractor coordination, utility locates, permitting, and traffic control) and observed by a representative of Shannon & Wilson. The exploration boring logs represent our interpretation of the contents of the field log and select results of laboratory testing.

The borings were drilled by Certified Testing Services of Sioux City, Iowa (under subcontract to Shannon & Wilson) using a Diedrich D50 truck mounted drill rig. The borings were advanced with 4‐inch outside diameter solid‐stem augers and sampled to depths of approximately 5.5 feet below existing grade. On completion of drilling, drill cuttings were spread on‐site, and the borings were backfilled with flow fill and patched with hot‐mix asphalt to match the existing pavement.

Borings locations were measured by Shannon & Wilson with a hand‐held recreational grade global positioning system (GPS) unit. The GPS coordinates are indicated on the individual boring logs and should be considered accurate to the degree implied by the method used.

A.2.1 Soil Classification System

During drilling, the Shannon & Wilson representative collected soil samples and prepared a field log of each boring. Soil classifications were based on ASTM International (ASTM)

Designation: D2487, Standard Practice for Classification of Soils for Engineering Purposes

(Unified Soil Classification System), and ASTM Designation: D2488, Standard Practice for

Description and Identification of Soils (Visual‐Manual Procedure). The system is referred to as the Unified Soil Classification System and is summarized in the Log Key.

A.2.2 Standard Penetration Test (SPT)

Disturbed samples were obtained in the borings in general accordance with the Standard

Penetration Test (SPT) (ASTM Designation: D1586). The SPT consists of driving a 2‐inch outside diameter, 1.375‐inch inside diameter split‐spoon sampler, a distance of 18 inches

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S with a 140‐pound hammer free‐falling a distance of 30 inches. An automatic hammer system was used to advance the samplers. During sampling, the Shannon & Wilson field representative recorded the number of blows for each 6‐inch increment of penetration and summed the blow counts for the last two 6‐inch increments. This sum is recorded as the penetration resistance number, or N‐value. If high penetration resistance prevented driving the entire 18 inches, the Shannon & Wilson field representative recorded the partial penetration depth and blow count. The N‐values provide a means for evaluating the relative density or compactness of cohesionless (granular) soils and consistency or stiffness of cohesive (fine‐grained) soils (see Log Key). The raw N‐values are shown on the individual boring logs. Representative portions of the split‐spoon sample obtained in conjunction with the SPT were placed in a screw‐top plastic jar and transported to our laboratory.

A.2.3 Bulk Sampling

A bulk soil sample was obtained by collecting the drill cuttings from boring SW‐01.

Approximately 20 to 30 pounds of cuttings SW‐01 were placed in a plastic bag and transported to our laboratory for further evaluation and testing. The bulk sample is composite samples sometimes spanning over several soil layers. The UCSC classification of the composite bulk samples has not been incorporated into the boring logs for this reason.

A.3 PAVEMENT CORES

A portable electric‐powered coring machine fitted with a 4‐inch‐diameter core barrel was used to take pavement cores of the existing pavement. The cores were brought to the

Shannon & Wilson laboratory where they were measured and then photographed.

SHANNON & WILSON | 5900 WEST 38TH AVENUE | WHEAT RIDGE, COLORADO 80212 | 303-825-3800 | www.shannonwilson.com

Poorly Graded Gravel; Poorly Graded Gravel with Sand

Well-graded Gravel; Well-Graded Gravel with Sand

Lean Clay; Lean Clay with Sand or Gravel; Sandy or Gravelly, Lean Clay

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Description

Term

LOG KEY

SOIL CLASSIFICATION

Organic

Inorganic

HIGHLY ORGANIC SOILS

Symbol / Graphic

Silty Sand; Silty Sand with Gravel

Silt; Silt with Sand or Gravel; Sandy or Gravelly Silt

Poorly Graded Sand; Poorly Graded Sand with Gravel

Silty Gravel; Silty Gravel with Sand

Clayey Gravel; Clayey Gravel with Sand

<5 5 to 10 15 to 25 30 to 45

>50

Term

Well-graded Sand; Well-graded Sand with Gravel

Organic

Major Divisions

Gravel (< 5% fines3)

Silty or Clayey Gravel (> 12% fines3)

Sand (< 5% fines3)

Silty or Clayey Sand (> 12% fines3)

SILTS AND CLAYS

(liquid limit > 50)

Primarily organic matter, dark in color, and organic odor

GW

GP

GM

GC

SW

SP

SM

SC

ML

CL

OL

MH

CH

OH

PT

Shannon & Wilson uses a soil identification system modified from the Unified Soil Classification System (USCS) as described on this Key.

Soil descriptions are based on visual-manual procedures (ASTM D2488) and available laboratory index test results (ASTM D2487).

SILTS AND CLAYS

(liquid limit < 50)

NOTE: For gravels and sands with 5 to 12% fines3, the following are added to the Group Name:

with Silt and/or Clay or Silty Clay.

Dual Symbols are used:

GW-GM, GP-GM, SW-SM, SP-SM

GW-GC, GP-GC, SW-SC, SP-SC

Organic Silt or Clay; Organic Silt or Clay with Sand or Gravel; Sandy or Gravelly, Organic Silt or Clay

Elastic Silt; Elastic Silt with Sand or Gravel; Sandy or Gravelly, Elastic Silt

Fat Clay; Fat Clay with Sand or Gravel; Sandy or Gravelly, Fat Clay

Organic Silt or Clay; Organic Silt or Clay with Sand or Gravel; Sandy or Gravelly, Organic Silt or Clay

COARSE-GRAINED

SOILS

(> 50% of soil is retained on the No. 200 sieve3)

FINE-GRAINED

SOILS

(> 50% of soil passes the No. 200 sieve3)

Typical Identifications (USCS Group Names)2,4

Sum of the count of hammer blows to penetrate the second and third 6-inch increments in blows per foot (bpf).

Refusal: 50 blows for 6 inches or less or 10 blows for 0 inch.

Percent1

Crumbles or breaks with handling or slight finger pressure.

Crumbles or breaks with considerable finger pressure.

Will not crumble or break with finger pressure.

Description

GRAVELS

(> 50% of coarse fraction retained on the No. 4 sieve3)

Inorganic

Peat or other Highly Organic Soils (see ASTM D4427)

Clayey Sand; Clayey Sand with Gravel

Dry

Moist

Wet

Term

Absence of moisture, dusty, dry to the touch.

Damp but no visible water.

Visible free water, from below water table.

Term140-pound weight with a 30-inch free fall. Hammer types vary (e.g., automatic, rope and cathead). If available, the hammer type and energy ratio (E-ratio) is noted on the boring log.

Description Term

Nonplastic

Low Plasticity

Medium Plasticity

Slickensided

Lensed

Laminated

Interbedded

Homogeneous

Fissured

Description

Barrel I.D. / O.D. = 1.5 inches / 2 inches (liner not used) Barrel Length = 30 inches; Shoe I.D. = 1.375 inches

Blocky Cannot roll a 1/8-inch thread at any water content.

A thread can barely be rolled and a lump cannot be formed when drier than the plastic limit.

A thread is easy to roll and not much time in rolling is required to reach the plastic limit. The thread cannot be rerolled after reaching the plastic limit. A lump crumbles when drier than the plastic limit.

It takes considerable time rolling and kneading to reach the plastic limit. A thread can be rerolled several times after reaching the plastic limit. A lump can be formed without crumbling when drier than the plastic limit.

Cohesive soil that can be broken down into small angular lumps that resist further breakdown.

Breaks along definite planes or fractures with little resistance.

Same color and appearance throughout.

Alternating layers at least 1/4 inch thick of varying material or color.

Singular: bed

Alternating layers less than 1/4 inch thick of varying material or color.

Singular: lamination

Inclusion of small pockets of different soils, such as small lenses of sand scattered through a mass of clay.

Fracture planes appear polished or glossy, sometimes striated.

High Plasticity

Term

Sampler

N-Value (N)1

Term

Hammer Very Soft Soft Medium Stiff Stiff Very Stiff Hard

Very Loose Loose Medium Dense Dense Very Dense

N2 (bpf)

0 - 4 4 - 10 10 - 30 30 - 50 > 50

TV3 (tsf)

0 - 0.12

0.12 - 0.25

0.25 - 0.5

0.5 - 1 1 - 2 > 2

N2 (bpf)

0 - 2 2 - 4 4 - 8 8 - 15 15 - 30 > 30

PP3 (tsf)

0 - 0.25

0.25 - 0.5

0.5 - 1 1 - 2 2 - 4 > 4

Description

Trace Few Little Some Mostly

Weak

Moderate

Strong

Term

SANDS

(> 50% of coarse fraction passes the No. 4 sieve3)

Exhibit A: Unified Soil Classification System (USCS)1

Exhibit G: Percentages

Exhibit E: Soil Moisture Content1

EXHIBIT A NOTES:

1. Adapted, with permission, from USACE Tech Memo 3-357, ASTM D2487, and ASTM D2488.

2. Borderline symbols (symbols separated by a slash) indicate that the soil characteristics are close to the defining boundary between two groups (e.g., CL/ML = Lean Clay to Silt; SP-SM/SM = Sand with Silt to Silty Sand).

3. No. 4 size = 4.75 millimeters (mm) = 0.187 inch; No. 200 sieve size = 0.075 mm = 0.003 inch. Particles smaller 0.075 mm are termed "fines".

4. Poorly graded indicates a narrow range or missing grain sizes. Well-graded indicates a full-range and even distribution of grain sizes.

5. If cobbles and/or boulders are observed, "with cobbles" or "with boulders" or "with cobbles and boulders" is added to the Group Name.

EXHIBIT E NOTE:

1. Adapted, with permission, from ASTM D2488 (Figure 2).

EXHIBIT G NOTE:

1. Percent estimated by weight for sand and gravel, and by volume for cobbles, organics, and other non-soil material (e.g., rubble, debris).

EXHIBIT D NOTE:

1. Adapted, with permission, from ASTM D2488.

Exhibit C: Soil Structure1 Exhibit D: Soil Plasticity1

EXHIBIT C NOTE:

1. Adapted, with permission, from ASTM D2488.

Exhibit B-3: Relative Density of Cohesionless Soils

Exhibit B-1: Standard Penetration Test (SPT)

EXHIBIT B NOTES:

1. N-values shown on boring logs are as recorded in the field and have not been corrected for hammer energy, overburden, or other factors. Where the hammer E-ratio is available, the N-value normalized to a ratio of 60% (N60) is listed.

2. Based on ASTM Standard D1586. Relative densities/consistencies noted on the boring logs are based on uncorrected N-values.

3. PP = pocket penetrometer; TV = torvane, tsf = tons per square foot. Correlations based on experience and multiple published references.

Exhibit B-2: Relative Consistency of Cohesive Soils

EXHIBIT F NOTE:

1. Adapted, with permission, from ASTM D2488.

Exhibit F: Soil Cementation1

SHANNON & WILSON | 5900 WEST 38TH AVENUE | WHEAT RIDGE, COLORADO 80212 | 303-825-3800 | www.shannonwilson.com

ATD

bpf dia, diam Elev.

ENV

ETR

FC

FeO ft or ' gal

GP

GWT

HSA

ID

in or " incl ksf lbs

LL

mm

N N60 NA, n/a

NE

NP

NR

NW

OC

OD

OW

pcf

PI

PID

PL

PMT

PP

ppm psi

PT

REC

REF

RQD

SC

SE

SPT

SW

TP

tsf

TV

UCS, qu

USCS

VST

VWP

WC

WOH

WOR

at time of drilling blows per foot diameter elevation environmental sample energy transfer ratio (hammer) fines content (< 0.075 mm) iron oxide foot or feet gallons geoprobe groundwater table hollow-stem auger inside diameter or identification inch inclinometer kips per square foot pounds liquid limit millimeter field (uncorrected) SPT N-value SPT N-value corrected for 60% ETR not applicable or not available northeast nonplastic no recovery northwest organic content outside diameter observation well pounds per cubic foot plasticity index photoionization detector plastic limit pressuremeter test pocket penetrometer reading parts per million pounds per square inch nonstandard penetration test N-value recovery refusal rock quality designation (ASTM D6032) sonic core southeast Standard Penetration Test (ASTM D1586) southwest test pit tons per square foot tor vane reading unconfined compressive strength Unified Soil Classification System vane shear test vibrating wire piezometer natural water content weight of hammer weight of rods

Bentonite-cement grout

Bentonite grout

Bentonite chips

Surface cement seal

Sand filter pack

Slough (hole caved)

Shannon & Wilson uses a rock classification system modified from the system recommended by the International Society for Rock Mechanics (ISRM).

Copyright limitations prevent us from reproducing summary tables from the ISRM system on this Key. General descriptions are provided in Exhibit M.

(continued)

Term

Strength

General Description

Weathering

Fabric

Ranges from extremely weak (qu = 36 to 135 psi) to extremely strong (qu > 36,250 psi), and is based on the ability to break the rock with a hammer or scrape the rock with a knife.

Ranges from fresh (no visible signs of weathering) to completely weathered, based on observed degree of discoloration, decomposition, and/or disintegration. When the rock material has completely converted to soil, it is termed a residual soil.

Describes the rock structure based on observed layering, tendency to break, and distribution of minerals (e.g., massive, bedded, foliated).

For discontinuities: Includes rough, smooth, and slickensided, and includes other descriptive terms (e.g., stepped, undular, irregular, planar).

For discontinuities: Ranges from extremely close (< 1 inch) to extremely wide (> 20 feet).

For discontinuities: Ranges from very low to very high.

Description of discontinuities (joints, fractures, bedding planes, etc.), observations of potential displacement, gouge, shear, etc.

Persistence

Roughness

Spacing

Term

REFERENCE: Brown, E. T., ed., 1981, Rock characterization, testing & monitoring: International Society of Rock Mechanics (ISRM) suggested methods:

Oxford, Pergamon Press, 211 p.

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LOG KEY

Sample Number Sample Type

Water Level Measured at Date in Well or VWP

Well/VWP ID No.

Water Level During Drilling

Measurement Date (M-D-YY)

Blank pipe or instrument casing

Perforated or slotted pipe

VWP and electric lead

Environmental Sample Taken

Split spoon (SS) (diameters vary)

Modified California (MC) sampler

Sonic core (SC) run (typically soil)

Other

REFERENCE: Loehr, J. E.; Lutenegger, A.; Rosenblad, B.; and Boeckmann, A., 2016, Geotechnical site characterization: U.S. Federal Highway Administration Report FHWA NHI-16-072, Geotechnical Engineering Circular no. 5, 1 v.

Rock Quality Designation (RQD) in %

Core Recovery (REC) in %

ROCK CLASSIFICATION

Graphic Description

Description

Irregular patches of different colors.

Soil disturbance or mixing by plants or animals.

Nonsorted sediment; sand and gravel in silt and/or clay matrix.

Material brought to surface by drilling action.

Material that caved from sides of borehole.

Disturbed texture, mix of strengths.

Sharp edges and unpolished planar surfaces.

Similar to angular, but with rounded edges.

Nearly planar sides with well-rounded edges.

Smoothly curved sides with no edges.

Width to thickness ratio > 3.

Width to thickness ratio < 3.

Term

Angular

Subangular

Subrounded

Rounded

Flat

Elongated

Term

Mottled

Bioturbated

Diamict

Cuttings

Slough

Sheared

Core run (typically rock)

Sheath (SH) (used for geoprobes)

Graphic Description

SYMBOLOGY AND GRAPHICS

Graphic Description Graphic Description

S-5

(SPT)

Description

Graphic Description Graphic Description

SOIL CLASSIFICATION

Gray bar indicates percent of sample length recovered.

Equation

SPT split spoon (2-inch OD)

Grab (GB) from cuttings or excavation

Tube (TB) (e.g., Shelby, piston)

ACRONYMS AND ABBREVIATIONS

Exhibit K: Hole Backfill and Instrument Graphics

Exhibit N: Rock Name Graphics

Exhibit O:…