B08_Attach_02_MEVE_317500_Geotechnical_Investigation_Report_092123.pdf

Engineering from the ground down

GEOTECHNICAL INVESTIGATION REPORT

Mesa Verde National Park

Morefield and Wetherill Pipeline Replacement Project

Mancos, Colorado

September 21, 2023

2625 Redwing Road, Suite 160 Fort Collins, Colorado

970.373.3195 www.LithosEng.com

September 21 2023 Project No. 21152

HDR Engineering, Inc.

703 Main St #200 Rapid City, South Dakota 57701

Attention: Mr. Christopher Bailey, PE Project Manager

Regarding: Geotechnical Investigation Report

Mesa Verde National Park Morefield and Wetherill Waterline Replacement Project Mancos, Colorado

Mr. Bailey, This report presents the results of our geotechnical investigation and recommendations for the Morefield and Wetherill Waterline Replacement Project. This study was conducted in general accordance with the contract between Lithos Engineering and HDR Engineering, Inc. dated September 3, 2021 and updated per the contract addendum between Lithos Engineering and HDR Engineering, Inc. dated January 30, 2023. Contained herein are discussions of the general subsurface conditions, geotechnical engineering design, and construction considerations in support of the subject project.

If you have any questions regarding the contents of this report, please contact the undersigned.

Sincerely, Lithos Engineering

James Halverson, EI Lance Heyer, PE Staff Engineer Associate

Keely Stevenson, EI Nate Soule, PE, PG Staff Engineer Vice President

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page II

TABLE OF CONTENTS

EXECUTIVE SUMMARY .......................................................................................................................................... IV

INTRODUCTION

PROJECT BACKGROUND

2.1 Site Description

2.2 Local Geology

2.3 Proposed Construction

2.3.1 Morefield Alignment

2.3.2 Wetherill Alignment

GEOTECHNICAL INVESTIGATION

3.1 Subsurface Investigation

3.1.1 Morefield Alignment

3.1.2 Wetherill Alignment

3.2 Geotechnical Laboratory Testing

3.3 Field Resistivity Testing

3.4 Geophysical Testing

SUBSURFACE CONDITIONS

4.1 Morefield Subsurface Materials

4.1.1 Fine Alluvium

4.1.2 Coarse Alluvium

4.1.3 Rockfall Deposit

4.1.4 Landslide Deposit

4.1.5 Mancos Shale

4.2 Wetherill Subsurface Materials

4.2.1 Fine Colluvium

4.2.2 Quaternary Loess

4.2.3 Cliffhouse Sandstone

4.3 Corrosion Potential Data

4.4 Groundwater

GEOTECHNICAL DESIGN RECOMMENDATIONS

5.1 Lateral Earth Pressures

5.2 Thrust Restraint

5.3 Modulus of Soil Reaction (E’)

5.4 Soil Corrosivity

5.5 Pavement Recommendations

CONSTRUCTION CONSIDERATIONS

6.1 Temporary Excavations

6.1.1 Excavation and Subgrade Preparation

6.1.2 Trench Backfill Material

6.1.3 Fill Placement and Compaction

6.2 Bedrock and Oversized Material Excavation

6.3 Construction Dewatering

6.4 HDD Design Recommendations

6.5 Construction Observation and Quality Assurance

LIMITATIONS

REFERENCES

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page III

LIST OF FIGURES

Figure Number Title

1 Morefield Alignment North – Site Vicinity and Boring Location 2 Morefield Alignment South – Site Vicinity and Boring Location 3 Wetherill Alignment Northeast – Site Vicinity and Boring Location 4 Wetherill Alignment Northwest – Site Vicinity and Boring Location 5 Wetherill Alignment Central – North – Site Vicinity and Boring Location 6 Wetherill Alignment Central – South – Site Vicinity and Boring Location 7 Wetherill Alignment South – Site Vicinity and Boring Location SH-1 Morefield HDD Alignment 1 Geologic Profile SH-2 Morefield HDD Alignment 2 Geologic Profile SH-3 Morefield HDD Alignment 3 Geologic Profile

APPENDICES

Appendix Title

A Boring Log Key and Boring Logs B Laboratory Testing Results C Field Resistivity Measurements D Rock Core Photographs E Geophysical Letter Report

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page IV

EXECUTIVE SUMMARY

The Mesa Verde National Park Morefield and Wetherill Waterline Replacement project consists of replacing approximately 16 miles of existing 6-inch diameter pressurized waterline. The following summarizes our general conclusions and recommendations in support of the project:

The subsurface conditions encountered do not preclude the proposed waterline construction as we currently understand it.

Subsurface materials encountered during the subsurface investigation of the Morefield Alignment include the following:

o Fine Alluvium – encountered at surface and extends to depths of 1 foot to 33 feet, or to the end of exploration. Was encountered in 12 of the 15 geotechnical borings.

o Coarse Alluvium – encountered at surface and extends to a depth of 9 feet. Was encountered in 1 of 15 geotechnical borings.

o Rockfall Deposit – encountered at surface and extends to the end of exploration at approximately 80 feet below ground surface. Was encountered in 5 out of 15 geotechnical borings.

o Landslide Deposit – encountered at depths ranging from surface to 9 feet and extends to end of exploration at approximately 40 feet below ground surface. Was encountered in 2 of 15 geotechnical borings.

o Mancos Shale – encountered at depths ranging from 10 feet to 33 feet and extends to the end of exploration at approximately 80 feet below ground surface. Was encountered in 5 out of 15 geotechnical borings.

Subsurface materials encountered during the subsurface investigation of the Wetherill

Alignment include the following:

o Fine Colluvium – encountered at surface or just below the Pavement Section and extends to depths ranging from 9 feet to 15 feet or to the end of exploration. Was encountered in 5 of the 32 geotechnical borings.

o Loess – encountered at surface or just below the pavement section and extended to depths ranging from 0.5 feet to 15 feet or to the end of exploration. Was encountered in 3 of the 32 geotechnical borings.

o Bedrock of the Cliffhouse Sandstone – encountered at depths ranging from just below the Pavement Section to 14.8 feet below ground surface and extend to depths ranging from 15 feet to 30 feet or to the end of exploration. Was encountered in 30 out of 32 geotechnical borings.

Groundwater was encountered in 2 out of 47 geotechnical borings and ranged in depths from

15.0 to 41.0 feet below the existing ground surface. In general, we do not anticipate groundwater will not have a significant impact on design or construction.

Laboratory and field steel corrosion potential testing along the Wetherill Alignment indicated soil and bedrock are not corrosive to metallic piping. Laboratory and field steel corrosion potential testing along the Morefield Alignment indicated non-corrosive soil and bedrock

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page V conditions along the northern and southern ends of the alignment and corrosive conditions along the central portions of the alignment.

Open-cut excavations along the Morefield Alignment will encounter Fine Alluvium. The three

Morefield HDD alignments will encounter alluvium, rockfall, Mancos Shale, Point Lookout Sandstone, and Landslide deposits as presented on the Geologic Sections in the Construction Drawings.

Open-cut excavations along the Wetherill Alignment will be excavated almost exclusively in sandstone bedrock unless the existing waterline is removed and replaced. Replacing the existing waterline in-place will minimize bedrock excavation. Excavations extending into sandstone bedrock may require the use of specialty excavation equipment due to relatively high strength.

Asphalt replacement along the Morefield Alignment will occur in 1 section totaling roughly

1,400 linear feet. The Wetherill Alignment is nearly entirely underneath pavement, and approximately 55,000 linear feet of asphalt replacement is anticipated. Current Wetherill Mesa Road asphalt thickness ranges from 1- to 9-inches.

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 1

INTRODUCTION

In late 2021, Mesa Verde National Park retained HDR Engineering, Inc. (HDR) to serve as the lead design Engineer for the Morefield and Wetherill Waterline Replacement Project (Project). HDR retained Lithos Engineering (Lithos) to serve as the Project’s Geotechnical Engineer. The purpose of this report is to present subsurface data collected and provide geotechnical design recommendations and construction considerations for the Project.

PROJECT BACKGROUND

The following sections describe the Project site and the proposed construction. Figures 1 through 7 present the approximate location of the proposed waterline replacement alignment and geotechnical borings.

2.1 Site Description

The Project site is generally located in the Northeastern and Southwestern areas of Mesa Verde National Park, west of Mancos, CO. More specifically, the Morefield Alignment (Northeastern, see Figures 1-2) extends from South of the Visitor and Research Center (VRC) to the Morefield Water Tank adjacent to the Morefield Campground (approximately 3.3-miles). The alignment follows Road H.5 E from the VRC East to Road 35510H.5 where it turns South. The remainder of the alignment runs in or parallel to Road 35510H.5 to the Morefield Water Tank. Where the road begins noticeable elevation change and contains switch backs, the alignment crosses the road in a more direct, linear route up the hillside. The Wetherill Alignment (Southwestern, see Figures 3-7) extends from the Navajo Tank along the Wetherill Mesa Rd to the Badger House Community Wetherill Mesa Parking Area (approximately 13.0-miles). Most of the Wetherill Alignment is directly in Wetherill Mesa Rd with only two sections outside of the paved roadway.

Portions of the alignment not in the pavement roadway occur from the Navajo Tank down to the Wetherill Mesa Road, and the second occurs between the 300,000-gallon water tank and the Wetherill Mesa Road near the Wetherill Mesa Parking Area. Corrugated steel culverts occur frequently along the Northern section of the Wetherill Alignment. The existing waterline location is somewhat uncertain as the National Park Service was unable to accurately locate the entire length of both alignments.

2.2 Local Geology

The project site is located on the Mesa Verde Cuesta within the Colorado Plateaus province adjacent to the La Plata Mountains and lies completely within the Four Corners platform subdivision of the San Juan Basin. The Mesa Verde Cuesta slopes to the south at roughly 7 degrees. The cuesta was once 1,500 feet higher than it is presently and over millions of years of erosion has become the present day cuesta incised by rivers with mesas as the high points along the surface. The stratified layers of the Mesa Verde Group are (from youngest to oldest): the Cliffhouse Sandstone Formation; the Menefee Formation; and the Point Lookout Formation. The Mancos Shale underlies the Mesa Verde Group. The Laramide Orogeny along with several later orogenic sequences brought up the Mesa Verde Group and the Mancos Shale to its present prominence.

The surficial deposits range in depth of a few inches to tens of feet thick. The surficial deposits identified at the project site include alluvium, colluvium, and loess (windblown) deposits of Holocene and Pleistocene age. Rockfall deposits of the Holocene age and translational and rotational landslide deposits of Holocene and Pleistocene age were also identified in the project area and are prominent geologic

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 2 hazards. The landslide hazard observed at the site appears to be mostly relic and does not appear to be actively failing. A complete geologic hazard investigation was not included as part of this project.

2.3 Proposed Construction

The Project consists of replacing approximately 16.0-miles; 84,500 linear feet (LF) of an existing 6.0-inch diameter pressurized waterline. The replacement pipe will be 6.0-inch diameter stainless steel or FlexSteel with an invert of approximately 4.0-feet below existing grades except at locations where pipe is installed via horizontal directional drilling. We understand that the existing waterline’s age, variable materials, and frequent leaks are amongst the primary concerns for the National Park Service and are the motivation for this Project. For example, replacement of these waterlines will “significantly reduce the risk of a catastrophic failure of service that would prevent use of the Morefield and Wetherill areas of the park” (SOS Task Order NO. 140P2021F0221, PG. 3).

2.3.1 Morefield Alignment

The Morefield Alignment consists of 3.3-miles of existing waterline with three different types of pipe material and three different ages. The older two segments will be replaced as part of this project. The third segment was recently replaced with stainless steel pipe in 2010 and will not be replaced as part of this project. Open-cut construction will be utilized to replace the majority of the pipeline alignment. Three unique sections will utilize horizontal directional drilling (HDD) for waterline replacement as generally identified below:

A replacement length of approximately 1,400 feet under an isolated location where the Townsend Daisy (protected plant) grows naturally (See Figures 1-2).

A replacement length of approximately 4,400 feet where the waterline alignment extends from the valley floor up to Top Ruins Road due to steep topography.

A replacement length of approximately 1,300 feet from Top Ruins Road to the Morefield Water Tank due to steep topography and shallow, hard bedrock conditions.

The Morefield Alignment (18,000 LF) is mostly a double-track dirt road with two exceptions. The first occurs from the intersection of Rd H.5 and 35510H.5 South to the driveway for 35510 Road H.5, Mancos CO 81328, just North of LE-OC-02 (Figure 1, approximately 1,400 LF), which is a two-lane paved road. The second is where the alignment crosses Mesa Top Ruins Rd (Mesa Verde 1) Southwest of LE-HDD-11. This section of alignment includes approximately 200 LF of asphalt that will not be replaced due to the pipe installation of HDD. Outside of approximately 1,400 LF of asphalt replacement associated with this alignment, the remainder is situated in the double-track dirt road or open space.

2.3.2 Wetherill Alignment

The Wetherill Alignment consists of 13.0-miles of existing 6.0-inch diameter waterline that was routed underneath Wetherill Mesa Road in 1968. The Wetherill Alignment (59,000 LF) is mostly contained within the paved Wetherill Mesa Road section with two exceptions. The first occurs from the Navajo Tank to the Wetherill Mesa Road (1,800 LF), which is a double-track dirt road. The second occurs between the 300,000-gallon water tank and the Wetherill Mesa Road (370 LF) near the Wetherill Mesa Parking Area.

We understand the section of waterline replacement extending from the Wetherill Mesa Parking Area to the Badger House Community Area will be rehabilitated in-place and is therefore not further addressed

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 3 in this report. The Wetherill Alignment from the Navajo Tank to the Wetherill Mesa Parking Area includes 56,500 LF of asphalt replacement, the remaining 2,500 LF is in dirt roadways or open space.

A larger reinforced concrete box culvert is located near the southern end of the Wetherill Alignment. A crossing of the culvert will be required to complete the waterline replacement.

GEOTECHNICAL INVESTIGATION

The geotechnical investigation included a subsurface investigation, geotechnical laboratory testing, and corrosion potential testing. The subsurface conditions encountered during the investigation are discussed in Section 4. Based on the investigation and subsequent laboratory testing, Section 5 and 6 present recommendations for geotechnical design and considerations for construction.

3.1 Subsurface Investigation

Lithos conducted geotechnical drilling on October 11th, 2021, through June 22nd, 2023. A total of 47 geotechnical borings were completed to investigate the general subsurface conditions at the Project site (Figures 1-7). Borings were generally numbered sequentially from North to South. Boring depths ranged from 15 to 89.7 feet below the existing ground surface. Groundwater was encountered in 2 of the borings.

There are three different types of geotechnical borings called out on Figures 1 – 7 and Appendix A.

Geotechnical Boring denotations are structured as “LE-YY-XX”. Where:

“YY” = either OC, BC, or HDD o “OC” = Open-Cut Boring, typical exploration depth of 15 feet below ground surface (bgs) with sampling every 5 feet.

o “BC” = Shallow HDD, box culvert, or utility crossing Boring, typical exploration depth of between 20 – 30 feet bgs with sampling every 5 feet.

o “HDD” = Deep Geotechnical Boring associated with HDD design. Typical exploration depth of 80 feet bgs with sampling every 5 feet utilizing Hollow-Stem Auger drilling method into competent bedrock, and then switching to Rock Coring method for the remainder of exploration.

“XX” = numerical value, typically increasing in value the further South except for LE-OC-45 which is the furthest North; unique value for each boring location.

Geotechnical drilling was conducted by Drilling Engineers utilizing either a Central Mining Equipment (CME) 55 or 75 truck-mounted drilling rig (Appendix A). Drilling and sampling procedures were conducted in general accordance with ASTM’s identified in the following table:

Subsurface Investigation ASTM Standards Procedure ASTM Standard Standard Test Method for Penetration Test and Split-Barrel Sampling of Soils D 1586

Standard Practice for Thick Wall, Ring- Line, Split Barrel, Drive Sampling of Soils D 3550

Standard Practice for Rock Core Drilling and Sampling of Rock for Site Exploration D 2113

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 4

Continuous-flight hollow- or solid-stem augers were used to advance the borings below the existing ground surface. During drilling, Split Spoon (1.5-inch inner diameter) and Modified California (2.0-inch inner diameter) barrel samples were obtained in approximately 5-foot intervals. Collection of rock core samples with an HQ (2.5-inch inner diameter) rock core barrel was completed in select borings. The Split Spoon sampler was utilized to obtain disturbed samples of non-cohesive soils and the Modified California sampler was used to obtain relatively undisturbed samples of cohesive soils. Rock coring techniques were used to collect continuous runs of rock core suitable for logging and laboratory testing. The number of blows from a 140-pound hammer falling 30-inches required for 6-inch increments of sampler penetration, or drilling rate for rock core runs, are presented on the boring logs (Appendix A). Blow counts with less than 6-inches of penetration are presented showing the number of blows for the resulting depth of penetration (50/2” means 50 blows to drive the sampler 2-inches).

3.1.1 Morefield Alignment

A total of 15 geotechnical borings were completed for the replacement of the Morefield Alignment (Figures 1 – 2). Seven of the geotechnical borings were drilled to a depth of 15 feet to investigate subsurface conditions along the open-cut sections of the pipeline alignment. Drilling for these geotechnical borings utilized a solid-stem auger drilling method. Modified California samples were collected in even intervals for classification and geotechnical laboratory testing. Eight of the geotechnical borings were drilled to a depth of between 40 and 90 feet to investigate subsurface conditions along the potential HDD sections of the pipeline alignment. Drilling for these geotechnical borings utilized hollow-stem auger drilling in soils and HQ Rock Coring in bedrock. Modified California samples were collected in even intervals in soil and HQ Core for samples were collected in competent bedrock for classification and geotechnical laboratory testing.

3.1.2 Wetherill Alignment

A total of 32, relatively evenly spaced, geotechnical borings were completed for the replacement of the Wetherill Alignment (Figures 3 – 7). Borings were advanced to 15 feet along the open-cut sections of the alignment and between 20.0 and 30.0 feet for potential crossings of a reinforced concrete box culvert and a hillside. Drilling for these geotechnical borings utilized a solid-stem auger drilling method. Modified California samples were collected in even intervals for classification and geotechnical laboratory testing.

3.2 Geotechnical Laboratory Testing

A geotechnical laboratory testing program was selected by Lithos, and testing performed by Terracon, Advanced Terra Testing, Weld Laboratories, and University of Tennessee on representative samples collected during the subsurface investigation. A laboratory summary table and graphical testing results are provided in Appendix B. Laboratory tests conducted in general accordance with associated standards are presented in the table below.

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 5

Laboratory Testing Geotechnical Testing ASTM Corrosion

Testing

ASTM/

AWWA*

Rock Testing ASTM

#200 Sieve Wash D1140 Water Soluble Sulfates D4327 Point Load

Strength Index D5731

Unconfined Compressive Strength

D2166 Chlorides D512 CERCHAR

Abrasiveness D7625

In Place Moisture and Density D2937 Resistivity G57 Moh’s Scale of

Hardness C1895-20

Rock Moisture and Density

D2216 D7263 Redox 2580* Splitting Tensile

Strength D3967

Atterberg Limits D4318 pH of Soils 4500H* Slake Durability D4644 One-Dimensional Swell or Collapse of Soils

D4546 Sulfides 4500SD*

Standard Proctor D698 Soil Nutrient Testing WERA

California Bearing Ratio D1883 Horticulture Soil

Analysis 103

Horticulture Soluble Salts 103

The boring logs presented in Appendix A include field-logged soil descriptions, amended as necessary to reflect laboratory classification testing results. Laboratory testing results were utilized in developing geotechnical design criteria and construction recommendations presented in subsequent sections.

3.3 Field Resistivity Testing

In addition to the subsurface investigation and laboratory testing program, in-situ soil resistance measurements were gathered along the alignment to investigate soil resistivity, a key indicator of corrosion potential to metallic pipe. Soil resistivity measurements were conducted using the Wenner Method in general accordance with ASTM G57-06 Standard Test Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method. Measurements were taken parallel to the alignment at depths of 3- & 6-feet at locations shown in Figures 1 – 7.

The results of the field resistivity measurements were utilized to approximate the corrosion potential of the soils using the 10-Point System based on AWWA C105. The 10-Point System is based on the soil’s resistivity, pH, oxidation-reduction (redox), sulfide content, and moisture. The 10-Point System defines scores for each category of corrosion potential as described above based on ranges of the categories values; if the summation of the scores of each category is greater than or equal to 10 then the soil is corrosive.

Corrosion potential data and corrosion protection recommendations are provided in Sections 4 and 5, respectively.

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 6

3.4 Geophysical Testing

A subsurface geophysical investigation was completed by Collier Geophysics (Collier) using seismic refraction tomography and seismic reflection in June, 2023. Multichannel-Analysis of Surface Waves (MASW) seismic soundings were conducted at 4 locations. This testing produced survey of 1D shear-waves (Vs) velocity models up to 200 feet in depth. Results were interpreted to locate the subsurface contact between the rockfall deposit and Mancos shale in areas tested. Results are presented in Attachment E and were used in HDD profile development and design.

SUBSURFACE CONDITIONS

Subsurface conditions were characterized based on the findings of the geotechnical investigation described in the previous section. Soil and bedrock descriptions noted on the boring logs and below are in general accordance with ASTM D 2487 – Standard Practice for Classification of Soils for Engineering Purposes (USCS - Unified Soil Classification System) and D 2488 – Standard Practice for Description and Identification of Soils (Visual-Manual Procedure). Boring logs and a supplementary boring log key, explaining boring log details, are provided in Appendix A.

4.1 Morefield Subsurface Materials

Primary materials encountered during the Morefield Alignment subsurface investigation include fine alluvium, coarse alluvium, rockfall deposit, landslide deposit, and bedrock of the Mancos Shale.

Groundwater was encountered in 2 of the geotechnical borings, as further discussed in Section 4.4.

4.1.1 Fine Alluvium

Fine alluvium was encountered in 10 of the 15 geotechnical borings. Fine alluvium was encountered at ground surface to 0.5 feet below ground surface and extended to depths ranging from 1-foot to 33-feet below ground surface, or to the maximum depth of exploration (Appendix A). Fine alluvium was classified as the following in accordance with USCS:

Lean Clay (CL) Fat Clay (CH)

Lean Clay with sand (CL)

Where encountered and recovered, fine alluvium was described as medium stiff to hard; olive-brown, pale-olive, olive-gray, olive-yellow, dark-brown, and olive; and dry to moist. Fine alluvium recovered from drilling and sampling contained particles sizes ranging from clay to coarse gravel.

One representative sample of fine alluvium was tested for unconfined compressive strength. Unconfined compressive strength test results indicated a strength of 33 psi.

Four representative samples of fine alluvium were tested for swelling characteristics upon inundation.

Samples exhibited ranges of 0 to 4.3 percent swell.

4.1.2 Coarse Alluvium

Coarse alluvium was encountered in 1 of the 15 geotechnical borings near the Morefield Water Tank.

Coarse alluvium was encountered at ground surface and extended to a depth of 9-feet below ground surface (Appendix A). Fine alluvium was classified as the following in accordance with USCS:

Silty Sand (SM)

Where encountered and recovered, coarse alluvium was described as loose, reddish brown, and moist.

Coarse alluvium recovered from drilling and sampling contained particles sizes ranging from fines to fine gravel.

4.1.3 Rockfall Deposit

Rockfall Deposit was encountered in 4 of the 15 geotechnical borings on the steep slope from the valley floor to Top Ruins Road. Rockfall Deposit was encountered at ground surface and extended to depths between 37 feet and maximum depth of exploration. Rockfall deposit was noted as consisting of fine-grained matrix with intermittent boulders. Rockfall Deposit was classified as the following in accordance with USCS:

sandy Lean Clay (CL) sandy Lean Clay with gravel (CL) sandy Lean Clay with gravel & cobbles (CL) Lean Clay with sand, gravel, & cobbles (CL) Lean Clay with sand (CL) Lean Clay with sand & gravel (CL) clayey SAND (SC)

Boulders:

o Sandstone o Clayey Sandstone o Silty Sandstone o Siltstone o Claystone o Sandy Claystone o Interbedded Shale and Siltstone o Interbedded Claystone and Siltstone o Interbedded Claystone and Sandstone

Where encountered and recovered, Rockfall Deposit was described as soft to hard; olive, pale olive, olive-brown, olive-gray, olive yellow, dark-brown, yellowish brown, dark yellowish brown, reddish brown, dark bluish gray, and gray; and dry to moist. Boulders within the Rockfall Deposit were additionally described as slightly to highly weathered with noted frequent calcite deposits and iron oxide staining. Rockfall Deposit recovered from drilling and sampling as well as inferred based on drilling action contained particles sizes ranging from clay to boulders.

The Rockfall Deposit is best described as clay with varying amounts of fine and medium sand as the primary matrix. The clasts of the matrix range in size from coarse sand to larger boulders and are primarily composed of the Siltstone and Sandstone from the Point Lookout Sandstone Formation. Sizes and existence of cobbles and boulders or any clast larger than 2 inches was inferred based on drilling action.

Three representative samples of rockfall deposit were tested for unconfined compressive strength.

Unconfined compressive strength test results indicated a strength from 46 to 146 psi.

One representative sample was tested for CERCHAR abrasiveness. Corrected CAI test results indicate a CAI of 2.48.

4.1.4 Landslide Deposit

Landslide Deposit was encountered in 2 of the 15 geotechnical borings. Landslide Deposit was encountered at ground surface and 9-feet below ground surface and extended to depths of end of exploration (Appendix A). Landslide Deposit was classified as the following in accordance with USCS:

clayey Sand (SC) Lean Clay with sand (CL)

Boulders:

o Sandstone

Where encountered and recovered, landslide deposit was described as dense; pale olive, olive brown, yellowish brown; moist. Landslide deposit consists of a non-cohesive soil matrix containing boulders mostly of the Menefee Formation and some of the Point Lookout Formation.

Three representative samples of landslide deposit were tested for unconfined compressive strength.

Unconfined compressive strength test results indicated strength from 46 to 3,533 psi. An additional unconfined compressive strength was tested on a boulder of the Point Lookout formation resulting in a strength of 8 psi.

One representative sample was tested for splitting tensile strength. Splitting tensile strength test results indicate strength of 202 psi.

Two representative samples of sandstone boulders within the Rockfall Deposit were tested for CERCHAR abrasiveness. Corrected Cherchar-Abrasivity-Index (CAI) test results indicate values ranging from 2.09 to

3.83 generally indicating a moderately abrasive material.

One representative sandstone boulder sample within the Rockfall Deposit was tested on Moh’s scale of hardness. Test results indicated a hardness of 2.5 indicating a relatively soft material.

One representative sample was tested for slake durability. Two cycles were tested, and a durability type was assigned to the sample. Cycle durability for the 1st cycle test results show an 87.5% durability. Cycle durability for the 2nd cycle test results show a 80.3% durability. The sample was classified as type II. This indicates that the material tested “retained specimen consist of large and small fragments.”

4.1.5 Mancos Shale

Bedrock of the Mancos Shale was encountered in 5 of 15 geotechnical borings. Bedrock was encountered at depths ranging from 10 to 79 feet below the ground surface and extended to the maximum depth of exploration. Bedrock was classified as the following:

Shale Sandy Shale Sandstone

Siltstone Interbedded Shale and Siltstone

Where encountered and recovered, bedrock was described as fresh to highly weathered; very soft to hard;

very fine grained to fine grained; reddish orange, dark-blueish-gray, bluish gray, and gray; iron oxidation;

calcareous; and fossiliferous. Fossils were found throughout core samples at varying depths. This bedrock is relatively massive with rock-quality designations ranging from 0 to 100 percent. Blow counts in the Mancos shale ranged from 50/3” to 50/4”. Discontinuities are generally the same throughout the Rock Core, they are described as:

Discontinuity Type: Bedding Orientation: Horizontal Aperture: Tight

Roughness: Smooth Shape: Flat

Six representative samples of shale were tested for unconfined compressive strength. Unconfined compressive strength test results indicated strength from 9 to 31 psi.

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Twelve representative samples of shale were tested for point load strength. Corrected point load strength index test results indicate strengths ranging from 86.8 psi to 382.7 psi. Of these twelve samples, three samples were additionally subjected to diametrical shape point load strength index testing. Corrected point load strength index test results indicated a strength from 19.4 psi to 35.4 psi. Diametrical point load indicates testing was completed parallel to the bedding plane of the shale. As such, tested samples of shale showed a vertical strength (perpendicular to bedding planes) approximately 5 to 10 times greater than the horizontal strength (parallel to bedding planes).

Two representative samples of shale were tested for splitting tensile strength. Splitting tensile strength test results indicate a tensile strength of 532 psi and 708 psi.

Four representative samples of shale were tested for CERCHAR abrasiveness. Corrected CAI test results indicate a CAI from 2.00 to 3.01 generally indicating a non to low abrasive material.

Two representative samples of shale were tested on Moh’s scale of hardness. Test results indicated a hardness of 1.6 and 1.7 indicating a soft material.

Two representative samples of shale were tested for slake durability. Two cycles were tested and a durability type was assigned to each sample. Cycle durability for the 1st cycle test results show a 94.4% and 97.6% durability. Cycle durability for the 2nd cycle test results show a 89.3% and 95.8% durability.

Samples were classified as type I and II. This indicates that the shale tested “retained specimen remain virtually unchanged” and “retained specimen consist of large and small fragments.”

4.2 Wetherill Subsurface Materials

Primary materials encountered during the subsurface investigation include fine colluvium, quaternary loess, and bedrock of the Cliffhouse Sandstone. Groundwater was not encountered in any of the 32 geotechnical borings, as further discussed in Section 4.4.

4.2.1 Fine Colluvium

Fine colluvium was encountered in 5 of 33 geotechnical borings. Fine colluvium was encountered at depths ranging from ground surface to 1.3 feet below ground surface and extended to depths ranging from 9-feet to 15-feet bgs, or to the maximum depth of exploration. Fine colluvium was classified as the following in accordance with the Unified Soil Classification System (USCS):

sandy Lean Clay with gravel (ML) sandy Lean Clay (CL)

Lean Clay (CL) Lean Clay with sand (CL)

Where encountered and recovered, fine colluvium was described as stiff to hard, olive-brown, olive-yellow, yellowish-brown, and moist. Additional descriptions of the fine colluvium are frequent iron oxide staining and roots near the surface where encountered. Fine colluvium recovered from drilling and sampling contained particles sizes ranging from clay to coarse gravel.

One representative sample of fine colluvium was tested for swelling characteristics upon inundation. Test results showed a 3.4 percent swell.

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4.2.2 Quaternary Loess

Quaternary loess was encountered in 3 of 33 geotechnical borings at depths ranging from ground surface to 1.0 foot below ground surface and extended to depths ranging from 0.5 feet to 15 feet bgs or to the maximum depth of exploration. Quaternary loess was classified as the following in accordance with USCS:

sandy Lean Clay (CL) Lean Clay with sand (CL)

Lean Clay (CL)

Where encountered and recovered, quaternary loess was described as stiff to very stiff, dark-reddish-yellow to dark-brown, and moist. Coarse alluvium recovered from drilling and sampling contained particle sizes ranging from clay to fine gravel, with a maximum particle size of 0.5-inches.

4.2.3 Cliffhouse Sandstone

Bedrock of the Cliffhouse Sandstone was encountered in 30 of 32 geotechnical borings. Bedrock was encountered at depths ranging from 0.5 to 14.8 feet bgs and extended to the maximum depth of exploration. Bedrock was classified as the following:

Siltstone Interbedded Claystone and Siltstone Sandstone

Interbedded Claystone and Sandstone Claystone

Where encountered and recovered, bedrock was described as fresh to completely weathered; very soft to hard; clay size grains to fine sand size grains; olive-brown, yellowish-brown, reddish-brown, olive, olive-yellow, olive-gray, gray, and pale olive; and dry to moist. Additional descriptions of some of the Sandstone and Siltstone samples collected were calcite matrix and roots (top ten feet). Most bedrock samples collected contain iron oxide staining.

A boulder of the Cliffhouse sandstone was tested for unconfined compressive strength. Unconfined compressive strength test results indicated a strength of 38 psi.

4.3 Corrosion Potential Data

Field soil resistivity measurements were taken at pin spacings correlating to depths of 3- and 6-feet below ground surface at 8 separate locations along the 2 alignments. The table below presents the total number of soil resistivity measurements corresponding to each score of the AWWA 10-Point System.

Soil Corrosivity Based on Soil Resistivity – Field Measurements Soil Resistivity

(Ω-cm) 10-Point System Resistivity Score

Number of Tests Correlating to Score

<1,500 10 0 1,500-1,800 8 0 1,800-2,100 5 0 2,100-2,500 2 0 2,500-3,000 1 0

>3,000 0 16

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The table below presents the total 10-Point System score of tested samples submitted to the laboratory.

Soil Corrosivity Based on Soil Resistivity – Lab Measurements

Sample ID Sample Depth (ft.) Total 10-Point System Score Alignment

LE-OC-03 9 10 Morefield LE-HDD-07 9 10 Morefield LE-HDD-10 4 10 Morefield LE-OC-12 0 0 Morefield LE-OC-14 0 2 Wetherill LE-BC-18 9 0 Wetherill LE-OC-28 4 1 Wetherill

Any 10-Point System total scores greater than or equal to 10 correlates to a corrosive soil potential.

Laboratory corrosivity results and field resistivity measurements are presented in Appendices B and C.

4.4 Groundwater

Groundwater was encountered in 2 of 47 geotechnical borings immediately after drilling at depths ranging from 15.0 to 41.0 feet below the ground surface, as summarized in the table below.

Groundwater Depth [ft] Boring ID Depth1 Date

LE-HDD-09 41.0 10/21/21

LE-OC-12 15.0 10/18/21

1Groundwater depth as measured below the existing ground surface

Groundwater levels are expected to fluctuate based on precipitation, seasonal variations, site development, and nearby water sources.

GEOTECHNICAL DESIGN RECOMMENDATIONS

The following sections are intended primarily for engineering design of the Project. Design recommendations include: lateral earth pressures, thrust restraint, modulus of soil reaction (E’), soil corrosivity, and pavement replacement. If additional geotechnical design recommendations are necessary, Lithos can be contacted to provide required information.

5.1 Lateral Earth Pressures

Lateral earth pressures presented are recommended for use during structural design. Lateral earth pressure values are a function of the properties and the geometry of the backfill materials, such as density and internal friction angle, and anticipated magnitude of lateral retention deflection. Lateral earth pressures for recommended backfill materials above groundwater are provided in the table below.

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Lateral Earth Pressures – Above Ground Water Table

Backfill Material Type

Internal Friction Angle (deg)

Earth Pressure Coefficients Equivalent Fluid Pressure (pcf)

Active At-Rest Passive Active At-Rest Passive

CDOT Class 2 26 0.39 0.56 2.56 47 67 307 CDOT Class 5 or 6 32 0.31 0.47 3.25 38 59 407

Clean Coarse-Grained Import Backfill (like squeegee) 34 0.28 0.44 3.54 36 56 449

For the lateral earth pressures presented above to remain applicable, backfill material placement adjacent to below grade structural elements shall be in accordance with procedures outlined in this report. In addition, if onsite material is processed and used as backfill, material requirements outlined in this report should be followed. For the tabulated lateral earth pressures to apply, backfilled material must be placed within a 1 horizontal to 1 vertical (1H:1V) backfill geometry, up and away from the base of structures.

Consideration has not been given to vertical loads applied to the backfill surfaces during or after construction as a result of traffic and/or other surcharge loads, sloping backfill, or soil-wall interfacial friction. Standard design values for typical, non-construction related vehicular traffic result in an additional 250 pounds per square foot (psf) vertical pressure.

5.2 Thrust Restraint

Buried pressurized pipes experience thrust forces at various locations such as bends, reducers, offsets, tees, wyes, dead ends, and valves requiring restraint. To counteract thrust forces within pressurized pipes, thrust blocks or restrained joints are recommended. Thrust blocks bearing against native soils can be designed using a passive earth pressure. Passive earth pressure can be assumed to be fully mobilized when movement equals 0.01 times the height of the thrust block. Assuming a negligible amount of movement, a passive earth pressure of 300 pcf per foot of depth with an average pressure over the face of the thrust block not to exceed 1,500 psf may be used. A minimum of 2-feet of cover over thrust blocks is recommended and thrust blocks should be oriented such that the passive pressure influence zones do not overlap for adjacent blocks and do not impact other subsurface utilities.

If thrust blocks cannot be utilized for restraint, restrained joints may be considered. To assist with restrained joint design, coefficients of friction between anticipated compacted pipe bedding materials and potential pipe materials are presented in the table below. If a different type of pipe than the those listed below is utilized in the final design, Lithos should be contacted to update the below recommendations. The following coefficient of friction values are based on the approved backfill materials listed in Section 6.2.2.

Coefficient of Friction for Buried Pipe1,2 Pipe Type Coefficient of Friction FlexSteel 0.2

Steel 0.5 1Soil-Pipe Interface Friction Coefficients for Buried PE4710 Pipe (2018), 2Jacking Force Prediction: An Interface Friction Approach Based on Pipe Surface Roughness (2006)

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5.3 Modulus of Soil Reaction (E’)

The modulus of soil reaction (E’) is an empirically derived coefficient commonly used in flexible pipeline design. E’ is related to the nature and degree of compaction of the pipe bedding material and the stiffness of the compacted pipe bedding. E’ is not impacted as much by the pipe material as it is by the pipe bedding material (backfill) composition and compaction. For steel or FlexSteel pipe, Lithos recommends an E’ value of 1,600 psi be used for design. The E’ value presented above is applicable when there is 2-5 feet of cover;

the backfill material is a SW, SP, GW, or GP type soil with 12% or less of fines; and is compacted to a minimum 95% standard proctor as tested by ASTM D698.

5.4 Soil Corrosivity

Based on the field and laboratory corrosion testing results, we recommend that corrosion protection measures be included as part of the design. Previous pipe performance and leaks can be another key indicator as to where soils may be more corrosive in nature. A more thorough corrosion potential investigation may be needed during final design if a blanket approach of corrosion along large stretches or the entire alignment(s) are not considered, and specific lengths of alignment are identified for additional corrosion protection measures. The table below identifies locations along the alignment where soil corrosion was measured:

Corrosion Protection Intervals

Denotation Corrosion Potential

Type of data acquisition Alignment

FR-1 Non-corrosive (0) Field Morefield LE-OC-03 Corrosive (10) Lab Morefield

LE-HDD-07 Corrosive (10) Lab Morefield LE-HDD-10 Corrosive (10) Lab Morefield

FR-3 Non-corrosive (0) Field Morefield LE-OC-12 Non-corrosive (0) Lab Morefield

FR-4 Non-corrosive (0) Field Wetherill LE-OC-14 Non-corrosive (2) Lab Wetherill LE-BC-18 Non-corrosive (0) Lab Wetherill

FR-5 Non-corrosive (0) Field Wetherill LE-OC-28 Non-corrosive (1) Lab Wetherill

FR-6 Non-corrosive (0) Field Wetherill FR-7 Non-corrosive (0) Field Wetherill FR-8 Non-corrosive (0) Field Wetherill FR-9 Non-corrosive (0) Field Wetherill

The above corrosion potentials are based on the field and laboratory results produced from testing locations and samples relatively evenly spaced along both alignments.

5.5 Pavement Recommendations

Pavement reconstruction will be needed for the roadway crossings along the Morefield Alignment at the crossing of Mesa Verde 1 and potentially at the northern end of the alignment just South of the intersection of Rd 35510H.5 and Rd H.5. Pavement reconstruction will be needed for most of the Wetherill Alignment, approximately 56,500 linear feet, with a replacement width of the excavated trench or other

HDR Engineering Mesa Verde National Park Waterline Replacement Project Page 12 acceptable NPS minimum such as a single traffic lane. For pavement replacement following open-cut pipeline construction, we generally recommend matching the existing pavement sections, assuming satisfactory existing performance. Existing thickness of the pavement section ranges in thickness of 1- to 9-inches for the asphalt section and 0- to 10-inches for the base coarse section. Our experience with similar roadways utilized a pavement section consisting of 6 inches of base course and 5 inches of asphalt.

CONSTRUCTION CONSIDERATIONS

The following sections are intended for the Engineer producing specifications and the Contractor constructing the Project. Construction considerations include: temporary excavations, site grading and earthwork, bedrock and oversized material excavation, and construction dewatering.

6.1 Temporary Excavations

General site safety including temporary excavations are the sole responsibility of the Contractor performing construction. Lithos is providing temporary excavation information solely as an informational benefit to the Project team, specifically the general Contractor. An Occupational Safety and Health Administration (OSHA) defined competent person should be identified by the Contractor to be in charge of temporary excavations. In general, the Contractor’s competent person shall have experience or training in classifying soil types per OSHA standards, benching and shoring, and have the ability to detect potential temporary slope stability and protective system issues. OSHA regulation 1926 Subpart P should be followed in the construction and support of all excavations.

According to OSHA regulation 1926 Subpart P, OHSA defines an excavation as a man-made cut, trench, or depression formed by the removal of earth. A trench is a specific type of narrow excavation with a geometry of a greater depth than width and a width of 15-feet or less. Trenches 4-feet deep or greater shall be sloped, retained with shoring, or shielded appropriately. Shielding most commonly includes trench boxes. In general, shoring can include inclined, horizontal, or vertical systems depending on the excavation geometry and availability of retention alternatives. Sloping and benching shall be in accordance with OSHA recommendations. Benching shall include a maximum 4-foot vertical face for each bench and the overall excavation geometry less than or equal to the OSHA defined slope. All shielding or shoring in support of trench excavations greater than or equal to 20 feet, shall be designed by a Professional Engineer or be based on tabulated data prepared or approved by a registered professional engineer in accordance with OSHA 1926.652(b) and (c).

Temporary excavations and trenches are anticipated during the proposed construction. Lithos has evaluated and classified the soil and bedrock recovered from site explorations and anticipated to be exposed in excavations for the proposed construction. Based on the OSHA soil type classifications, the following table presents steepest recommended temporary excavation slopes to be utilized during construction.

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OSHA Temporary Excavation Slopes

Material Type3 OSHA Classification Maximum Recommended Slope (H:V) 1,2

Onsite Silt or Sand Fine to Coarse Alluvium – disturbed Type A

Type B 1:1 (45o)

Onsite Clay Fine Alluvium -undisturbed Type A ¾:1 (53o)

Solid Rock Stable Rock Vertical (90o) 1 H:V is an abbreviation for Horizontal:Vertical

2 Valid for trench excavations less than 20 feet in depth 3Reference OSHA Technical Manual – Section V: Chapter 2 for more detailed material descriptions

During construction, heavy equipment or excavated material stockpiles should be kept away from excavation edges to the furthest extent possible. Shoring design should consider the proximity of construction loads and stockpiled material to excavations. Underground utilities shall be fully understood and documented prior to initiating excavations. Finally, the Contractor’s competent person shall inspect trenches and excavations routinely for signs of instability including sliding, toppling, subsidence and bulging, heaving or squeezing, boiling, and/or other visual concerns. Site Grading and Earthwork

Site grading and earthwork considerations are presented in the following subsections.

6.1.1 Excavation and Subgrade Preparation

In general, excavation and subgrade preparation consist of removal of excavated material as required for the proposed construction and scarifying and conditioning subgrade materials. If existing materials are desirable as backfill, excavated materials shall be stockpiled conveniently and processed prior to use.

Material processing is discussed in the following section.

Subgrade materials encountered immediately below the proposed construction shall be observed and any unsuitable material shall be removed as determined by the Engineer. In addition, subgrades shall be scarified, moisture conditioned, and recompacted to a minimum depth of six inches below the base of the pipe bedding zone. Subgrade moisture and compaction specifications are provided in the following sections.

Material encountered near proposed pipe inverts ranged from very soft and very loose to medium stiff based on a blow count range of…