Attachment J08.1 Geotechnical Report.pdf

PRELIMINARY GEOTECHNICAL REPORT

PUEBLO PINTADO HEALTH CENTER

TBD INDIAN SERVICE ROUTE 9

MCKINLEY COUNTY

PUEBLO PINTADO, NEW MEXICO

March 11, 2022

Prepared for:

Matthew Conard HFG Architecture 142 N. Mosley Wichita, KS 67202

(Pueblo Pintado Health Center architectural concept courtesy HFG Architecture)

Pueblo Pintado Health Center prelim geotech report 3-11-22 Project #2021-170-GEO Page i

TABLE OF CONTENTS

Introduction

Construction Plans

Site Conditions

Geology

Geologic Hazards

5.1 Runoff & Erosion

5.2 Flooding

5.3 Expansive and Compressible Soil and Rock

5.4 Seismicity

5.5 Radon Gas

Soil Characteristics

6.1 Field Investigation Procedures

6.1 Field Findings

6.2 Laboratory Testing

Engineering Analysis

7.1 Pavement Design

7.1.1 Traffic & Pavement Design Considerations

7.1.2 Design Parameters

7.1.3 Flexible Pavement Recommendations

7.2 Foundation Engineering Assessment

7.2.1 Seismic Design Accelerations

7.2.2 Liquefaction

7.2.3 Engineering Assessment for Foundations

Sewage Lagoon Site

Preliminary Recommendations

9.1 General Design Criteria

9.2 Seismic Design Criteria

9.3 Foundation for the Medical Center Building

9.4 Foundation for the Water Tower

9.4.1 Drilled Shafts

9.4.2 Micropiles

9.4.3 Mat Foundation

9.5 Floor Systems

9.6 Retaining Structures

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9.7 Foundation Drainage and Ventilation

9.8 Site Preparation and Grading

9.9 Concrete

9.10 Exterior Concrete Flatwork

9.11 Excavation and Shoring

Closing Considerations

10.1 Standard of Care and Interpretation of Subsurface Data

10.2 Use of This Report

10.3 Retention of Samples

Additional Services

References

APPENDIX A - Project Maps ................................................................................................ A

APPENDIX B - Borehole Logs ............................................................................................... B

APPENDIX C - Laboratory Results ........................................................................................ C

APPENDIX D – Engineering Analysis .................................................................................... D

TABLES

Table 1: Borehole Summary Information Table 2: ASTM Exploration Standards Table 3: Summary of Laboratory Results Table 4: Traffic Loading Table 5: Pavement Design Parameters Table 6: Recommended Flexible Pavement Section Table 7: Recommended Rigid Pavement Section Table 8: Seismic Design Parameters Table 9: Percolation Test Results Table 10: Foundation Design Parameters Table 11: Substation Drilled Pier Recommendations Parameters Table 12: LPILE Input Parameters Table 13: Preliminary Micropile Bond Strength Table 14: P-Multipliers for Pile Groups Table 15: Water Tower Foundation Design Parameters Table 16: Lateral Earth Pressures Table 17: Gradation Requirements for Fill Material Table 18: Compaction Requirements for Fill Material

INTRODUCTION

Buckhorn Engineering, Inc. (BEI) conducted an evaluation of subsurface and site conditions on October 25-28, 2021, at the proposed Pueblo Pintado Medical Center site in Pueblo Pintado, New Mexico. Our services were performed at the request of project architect, Matt Conard with HFG Architecture, on behalf of the Navajo Area Indian Health Service (NAIHS) to evaluate the site for a large medical center, water tower, and sewage lagoon. Residential staff quarters for the medical personnel will a part of the overall project, but a geotechnical evaluation of those structures was not part of our scope of work. The evaluation consisted of a site reconnaissance, drilling of 14 boreholes, logging and testing of representative materials found, percolation testing at the sewage lagoon site, and analysis of available data. This report presents the findings of our evaluation and our preliminary geotechnical engineering recommendations for site preparation, foundation design, and management of drainage.

CONSTRUCTION PLANS

Building plans were not yet available for the proposed Health Center and associated improvements for this site. However, we understand the Health Center will be a 118,000 square foot outpatient facility in one to two stories, as depicted on the architectural concept image on the cover of this report. In addition, there will be a helipad with a small (20 x 50 foot) EMS post building on the north side of the center, roughly 300 paved parking spaces (in an upper and lower parking lot), a sewage lagoon on the northeast side of Route 9, and a water tower upslope to the southwest of the Health Center. Approximately 82 acres will be required for this project, which is currently on undeveloped land. The Health Center will be a steel structure, with concrete slab floors (no crawl spaces). The north wing of the building will not have a basement and the finished floor elevation of that portion of the building will be 6,616-6,619 feet, while the remainder of the building will have a basement and the finished floor elevation will be 6,600-6,603 feet. That will result in the north wing being constructed 9-14 feet above existing grade and the ground floor/basement being constructed 2-12 feet below existing grade.

Exterior materials will consist of a combination of masonry, metals, and terra cotta. For purposes of our preliminary evaluation, we have assumed that the structure will have loads on the order of 2,000 to 6,000 pounds per linear foot to the foundation level with maximum point loads of 160,000 pounds from a column within the 2-story area. The water tower will be a spheroid steel tower that will hold approximately 200,000 gallons. Based on information from the architect, the tower height will be roughly 125 feet with a dead load plus snow of 1,885 kips and a wind load 35 kips. Maximum excavation depths of 10-12 feet are anticipated for the ground floor/basement of the Health Center and at least 10 feet of excavation is expected at the sewage lagoon site.

Since site grading, design and structural plans are not available now, the recommendations contained herein should be considered preliminary and subject to review and amendment when more formalized plans are available. BEI should be provided an opportunity to review such plans and revise or supplement our recommendations as appropriate.

SITE CONDITIONS

Pueblo Pintado is located roughly 65 miles southeast of Farmington and mid-way between Crownpoint and Cuba, New Mexico, in McKinley County (see Vicinity Map, Map 1, Appendix A).

The proposed Health Center site is located about 2 miles southeast of the Pueblo Pintado Chapter House in Pueblo Pintado, along U.S. 197/Indian Service (BIA) Route 9. The attached Site Layout (Map 2, Appendix A) shows the topography of the proposed Health Center site and the approximate locations of our boreholes with respect to the Health Center, water tower, and the sewage lagoon, while Map 3 shows more details of the Health Center Site Plan. According to the site survey, the average elevation of the water tower is 6,642 feet, the health center is at 6,610 feet, and the lagoon site is at 6,565 feet. Slopes at these sites are generally around 2-4% down to the northeast. The Gaia GPS app was used during our field testing to locate the pre-determined borehole locations shown on the Site Layout (Map 2). The following photographs were taken of the Health Center and water tower sites at the time of our field evaluation.

Photo 1 (left) view northwest from within the Health Center site as BH#8 was being drilled. Photo 2 (right) view south towards Burning Bridge Wash as BH#2 was being drilled at the water tower site. These photos show the vegetative cover, local topography, and conditions at the time of our site visit.

The Health Center site is located on a northeast sloping, dry upland with the Burning Bridge Wash on the east and an unnamed wash on the west. Both drainages are intermittent streams that outfall into Chaco Wash, which flows to the northwest, and there are no drainages that cross the building sites. The site is undeveloped and vegetated with mostly sagebrush and a sparse understory of dryland grasses and forbs.

GEOLOGY

According to the 1:24,000 scale USGS geologic maps of the area (Weide et al, 1980), the bedrock underlying the site is the Cretaceous Lewis Shale (Kl), as seen in Figure 1 below. The Lewis Shale formation contains calcareous sandy shale with light brown sandstone beds typically 1-5 feet thick in the upper part as it transitions into the Pictured Cliffs Sandstone (Kpc), with light gray to dark olive-gray claystone and siltstone with thin sandstone lenses and scattered beds of sandy concretionary limestone in the middle part, and sandstone in the lower part as it transitions to the Cliff House Sandstone (Kch). Since the Cliff House Sandstone is located immediately south of the site and regional dip is to the northeast, the Health Center site is likely in the lower part of the Lewis Shale as it intertongues with the Cliff House Sandstone.

The Lewis Shale formed near the western edge of the shallow Cretaceous Seaway and some marine invertebrates are found in this formation. It is typically 100-115 feet thick when found in the Pueblo Pintado and Pueblo Alto Trading Post Quadrangles (Weide et al, 1980). Figure 1 is a composite of these two quadrangles since the site spans both maps. The matchline where the maps join can be seen in Figure 1 to the left of center as a faint vertical line.

Figure 1. Geologic Map of the Pueblo Pintado Health Center Site

(Weide et al, 1980)

Figure 1 shows the approximate locations of the three components of the Health Center project in blue: the Health Center building and parking areas, the sewage lagoon, and the water tower.

Note that only the water tower and the southeast portion of the Health Center are shown as being on Lewis Shale (Kl). The remainder of the Health Center and the sewage lagoon are on Quaternary sheetwash alluvium (Qc) over the Lewis Shale. This surficial deposit is described on the geologic maps as “Poorly consolidated clay, silt and coarse- to medium-grained sand containing sandstone fragments.” These slopewash deposits are derived from surrounding shale and sandstone outcrops that collect in low-lying areas and they have a weak yellowish-brown B horizon up to 2-feet thick and an underlying whitish, floury calcium carbonate (Cca horizon) accumulation zone. This valley fill can be up to 16 feet thick in the region. Other valley fill deposits in the area include wind-blown (eolian) sand (Qes) and Naha alluvium (Qn), which is

Health Center water tower sewage lagoon

Pueblo Pintado Quad (USGS MF-1219) Pueblo Alto Trading Post Quad (USGS MF-1220) cross-stratified sand and gypsiferous silt filling washes of ephemeral streams such as the Burning Bridge Wash, the unnamed wash, and Chaco Wash. These cut and fill channels often form terraces about 20 feet above the current arroyo floors. The following photographs show the typical exposures the sandstone and shale layers of the Lewis Shale in the roadcut of BIA Route 9 adjacent to the project site to the northeast.

Photo 3 (left) and Photo 4 (right) view southwest at various locations of the BIA Route 9 roadcut northeast of the Health Center site. This is an exposure of the Lewis Shale formation with massive and thinly bedded sandstone forming ledges and benches interbedded and the weaker shale forming sideslopes covered in soil and colluvium above and below the sandstone.

Also, worth noting on the geologic map (Figure 1), is the presence of an east-northeast striking normal fault (with down-drop to the south-southeast) between the Health Center and the water tank. There are numerous east-northeast striking faults in the region, so this is typical of what is found in the area. There is no topographic expression of this fault observed in the field near the proposed development and, like most of the faults in the region, they are ancient faults that offset bedrock units, but not Quaternary deposits. As discussed in the Geologic Hazards section under Seismic risk, the closest Quaternary fault is over 40 miles to the east and is in a different physiographic province with a different set of tectonic stresses.

According to the Natural Resource Conservation Service (NRCS) Web Soil Survey (www.websoilsurvey.nrcs.usda.gov) the primary soil unit for all of the components of the Health Center site is the Doakum-Betonnie Complex (1-8% slopes), which is a sandy clay loam to sandy loam. This complex forms on ridges, hills, cuestas, mesas, and valley sides in eolian deposits over alluvium derived from sandstone and shale. The Hydrologic Soil Group is B, the depth to water table and a restrictive layer are greater than 80 inches, the drainage class is somewhat excessively drained, the runoff class is low, and the calcium carbonate content is a maximum of 5%. The secondary soil unit on the property, which is mapped in the northeast corner of the sewage lagoon area, is the Councelor-Calladito Complex (1-8% slopes), which is a sandy loam, silt, silty clay loam, loamy sand, and loam. This complex forms on stream terraces on valley floors and alluvial fans on valley sides in eolian deposits over fan and stream alluvium derived from sandstone and shale. The Hydrologic Soil Group is C, the depth to water table and a restrictive layer are greater than 80 inches, the drainage class is well drained, the runoff class is medium, and the calcium carbonate content is a maximum of 5%.

http://www.websoilsurvey.nrcs.usda.gov/

The soils and formational material found in our boreholes are consistent with the mapped slopewash and eolian deposits overlying the lower parts of the Lewis Shale Formation. The soil and bedrock materials found in our boreholes at this site will be discussed in more detail in the Soil Characteristics Section of this report.

GEOLOGIC HAZARDS

This section of the report is included so that the client is aware that construction in the area comes with certain risks. Some buildings and roadways throughout the region have experienced negative impacts due to slope movement and sensitive soils. Typical accepted structural engineering practice for design and construction can be used to reduce the potential for undesirable soil performance. However, because of the overall dynamic characteristics of the area, almost every structure is subject to at least some degree of potential risk. The primary geologic hazards relevant to the subject property are discussed below.

5.1 Runoff & Erosion

Surface runoff from rainfall and snowmelt drains as sheetflow across the building, water tower, and sewage lagoon sites down to the northeast to northwest. Evidence of gullying and erosion were observed across the property, likely caused by intense, but infrequent, summer thunderstorms. The sandy and fine-grained soils at this site are susceptible to erosion, so care to manage runoff from developed portions of the property will be important to reduce soil loss and minimize potential damage to infrastructure from erosion and undercutting. Also, managing outfall from drains so that discharge is dispersed, not concentrated, will be important.

5.2 Flooding

According to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM), the Health Center and water tower are in “Zone X, unshaded.” This zone is designated for areas with minimal flood hazard. A preliminary flood analysis of the project area, as presented in the Phase II Site Selection & Evaluation Report (SSER) for Pueblo Pintado Health Center & Staff Quarters (NAIHS, 2020), found that the health facility and staff quarters lots are located outside any areas of significant flooding in the 100- and 500-year events. The Phase II SSER report also indicates that the sewage lagoon site is roughly 250 feet east of the Burning Bridge Wash Zone A area (where there is a 1% annual chance of flooding, meaning it is in the 100-year floodplain). Although the preliminary flood analysis of this site does not indicate a significant risk of flooding in this area, the Phase II SSER report recommends that the sewage lagoon is placed as far from the Zone A portion of the wash as possible. In addition, during final design of the sewage lagoon site, the Phase II SSER report recommends that a more detailed analysis of slope stability and 500-year elevations of the Burning Bridge Wash are completed.

5.3 Expansive and Compressible Soil and Rock

Soil materials containing some types of clay, especially bentonite (montmorillonite), can expand in volume with water absorption and then shrink upon drying. In some areas of New Mexico these expansive soils cause serious damage to foundations, roadways, pavements, and embankments. In the Pueblo Pintado area, expansive clays can be derived from the Lewis Shale, the dominant formational material on and around the Health Center Site. Compressible soils are generally soils that have been laid down rapidly, have a weak matrix containing voids, and/or are not naturally in a dense or compacted state. Compressible soils typically have a large proportion of fine-grained materials, especially silt, but they can also contain a mixture of material if deposited in a chaotic manner. For example, wind-blown and slopewash deposits can be compressible because they are in a loose, non-densified state. In dry, high desert sites like this, wind-blown and slopewash deposits are found throughout the site, as discussed in the Geology section of this report.

The potential hazard from expansive and compressible soil is the differential movement of foundation soils when they react with water while loaded. This hazard can be partly reduced by managing on-site drainage so that water accumulation, ponding or penetration into the soil near foundations and slab/pavement areas is reduced to as great a degree as practical. Further reduction of these hazards can be attained through design of foundation and floor systems that extend to firmer material or which have sufficient strength to resist differential movements. The removal of problematic soil and replacement with structural fill is another option. These methods are discussed in further detail below in the Recommendations Section.

5.4 Seismicity

Pueblo Pintado is in the San Juan Basin of the Colorado Plateau Physiographic/Tectonic Province in northwest New Mexico (Ryder, 1983). According to the online U.S. Geological Survey (USGS) 2014 Seismic Hazard Map of New Mexico (www.usgs.gov), the Four Corners area of the Colorado Plateau, which include Pueblo Pintado, is in a relatively low seismic hazard zone where the 2% in 50 years Peak Ground Acceleration (PGA) Hazard (%g) is less than 10%. It is a relatively seismically quiet region of New Mexico. Review of the USGS interactive map viewer for U.S. Quaternary Faults (www.usgs.maps.arcgic.com), indicates that the nearest Quaternary (geologically recent) fault is the Nacimiento Fault, located over 40 miles to the east. Refer to the Seismic Design Criteria Section of the Recommendations section for site-specific seismic design recommendations based on the Applied Technology Council (ATC) website (www.hazards.atccouncil.org) that relies on the ASCE7-16 guidelines and U.S. Geological Survey Seismic values determined from the latitude and longitude coordinates for the site.

5.5 Radon Gas

Radon gas is produced by decay of radioactive minerals contained in subsurface rock and soil.

The U.S. Environmental Protection Agency (EPA) has determined that radon is the second leading cause of lung cancer, and it is believed to be the number one cause of lung cancer among non-smokers. Radon can enter buildings from under slabs, crawlspaces or basement and it can accumulate if the gas is not adequately ventilated. The EPA map of Radon Zones indicates that most of New Mexico, including McKinley County, is in Zone 2 (www.epa.gov/radon/zonemap.html). Although there is no known safe level of radon, Zone 2 is the zone of moderate risk for exposure to radon gas [i.e., between 2 and 4 picoCuries per Liter (pCi/L)]. More specific testing performed by the New Mexico Radiation Control Bureau (RCB) indicates that McKinley County has average indoor radon levels of 4.5 pCi/L, while the national average is 1.3 pCi/L. The EPA recommends that radon should be mitigated if annual indoor radon averages 4 pCi/L or more.

The EPA and the New Mexico Environment Department (NMED) do not specifically address testing and management of radon in commercial structures. However, the NAIHS should be aware of the potential health implications of constructing upon radon emitting soils, assess risks, and take appropriate action. Although there are no tests which can be performed on undeveloped sites, radon should be assumed to be present at the Pueblo Pintado site and at least passive mitigation measures installed. Once the building is constructed, indoor radon tests http://www.hazards.atccouncil.org/ can be performed, and the system can be made to be active (with the installation of one-way electric fans) if elevated radon levels are recorded. Additional information about radon gas can be found on the EPA radon website www.epa.gov/radon/ or the NMED radon website www.env.nm.gov/rcb/indoor-radon-outreach-program.

SOIL CHARACTERISTICS

6.1 Field Investigation Procedures

Fourteen (14) borings (BH#1 - BH#14) were drilled by Colorado Drilling and Sampling under the direction of a BEI geologist on October 25-28, 2021, using a Simco 2800 truck-mounted drill rig at the locations shown on the Site Layout (Map 2) and the Site Plan (Map 3, Appendix A).

The locations of the borings were selected by us prior to the field work and approved by the architectural design team to correspond to the locations of the water tower, Health Center, parking lots, and the sewage lagoon. Buckhorn used the coordinates of each borehole, loaded into the Gaia smart phone application, to locate each borehole in the field. Table 1 summarizes the boring locations, approximate surface elevations (based on a topographic survey by Buckhorn Engineering), and the total depth of each boring.

Table 1: Borehole Summary Information

Borehole

Location/ Purpose

Latitude Longitude Surface

Elevation (ft)

Total Depth of Boring

BH#1 Water tower 35.9455 -107.6254 6,636.4 30.5

BH#2 Water tower 35.9452 -107.6257 6,639.2 25.5

BH#3 Sewage lagoon 35.9533 -107.6163 6,572.6 21.2

BH#4 Sewage lagoon 35.9536 -107.6154 6,563.6 21.1

BH#5 Sewage lagoon 35.9544 -107.6157 6,560.2 21.5

BH#6 Sewage lagoon 35.9552 -107.6148 6,562.7 21.5

BH#7 Health Center building 35.9493 -107.6229 6,605.1 30.5

BH#8 Health Center building 35.9488 -107.6228 6,607.4 25.5

BH#9 Health Center building 35.9480 -107.6225 6,611.9 26.0

BH#10 Health Center building 35.9484 -107.6229 6,608.4 15.0

BH#11 Health Center building 35.9486 -107.6233 6,605.3 16.0

BH#12 Health Center building 35.9489 -107.6239 6,600.5 18.0

BH#13 Health Center parking 35.9479 -107.6236 6,611.5 5.7

BH#14 Health Center parking 35.9488 -107.6222 6,614.1 6.5

Drilling methods were determined based on previous preliminary geotechnical work at this site by Ninyo & Moore (2019) for evaluation of the potential of this site for the Health Center. For their exploratory study, they used hollow stem augers on a CME 75 truck-mounted drill rig to auger three boreholes. No coring of bedrock was performed by Ninyo & Moore, and no swell/consolidation or other tests were performed on the formational materials.

The boreholes were drilled with a 4.5-inch solid stem continuous flight auger. Soil samples were obtained at generally 5-foot intervals by withdrawing the auger and inserting either a standard 1.375-inch inside diameter (I.D.) split-spoon sampler without liners or a 2-inch I.D. split-spoon California sampler to perform in-situ Standard Penetration Tests (SPTs). The number of blows required to drive the sampler 12 inches in 6-inch increments were recorded as field “blow counts” (SPT “N” penetration resistance values) and indicate the relative density or consistency http://www.epa.gov/radon/ http://www.env.nm.gov/rcb/indoor-radon-outreach-program of the soils. Upon reaching formational material, the center drill string was removed, and an HQ wireline coring assembly was used to obtain continuous core samples as it advanced, generally in 5-foot runs, into the bedrock. We conducted our field exploration referencing the following ASTM standards in Table 2 below.

Table 2: ASTM Exploration Standards

Test Method Purpose

ASTM D6151

Standard Practice for Soil Exploration and Sampling by Hollow Stem Augers

ASTM D1586 Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils

ASTM D3550 Standard Practice for Thick Wall Ring-Lined, Split barrel, Drive Sampling of Soils

ASTM D2487 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)

ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedure)

6.1 Field Findings

The soil, bedrock, and groundwater conditions were logged and the borehole logs for the 14 boreholes are presented in Appendix B. For the six boreholes at the Health Center building (BH#7-BH#12) and the two boreholes in the parking lots of the Health Center (BH#13-BH#14), we plotted these boreholes logs relative to elevation, producing a composite soil profile for the building site shown in Soil Profile (Exhibit P-1) in Appendix B. Representative samples of soil and rock materials were tested in our laboratory with the results presented in Appendix C.

Laboratory results are also summarized on the borehole logs in Appendix B.

Our boreholes reached depths of 25.5-30.5 feet at the water tower site (BH#1-BH#2), 21.1-

21.5 feet at the sewage lagoon site (BH#3-BH#6), 15.0-30.5 feet at the Health Center building site (BH#7-BH#12), and 5.7-6.5 feet at the Health Center parking lots (BH#13-BH#14). Our findings and recommendations are based on materials found within these depths. Soil conditions may change between boreholes and below these depths. If deeper excavations are contemplated or if soil/rock materials different than those found in the exploratory boreholes are encountered during construction, BEI should be called to verify soil continuity and validity of our recommendations. This may require drilling boreholes or excavation of additional test pits into the subgrade material below foundation grade, or other typical excavation verification.

Water Tower – At this site (BH#1-BH#2) we found 7-8 feet of dry, stiff to very stiff, sandy lean clay underlain by weathered (Lewis) shale and clay that was augered to 11 to 14.5 feet and then cored to a total depth of 25.5-30.5 feet, as seen in Photo 6 below.

Photo 5 (left) view north at BH#1. Photo 6 (right) core of the Lewis Shale from 15 ft (upper left) to 22.4 ft (lower right) in BH#1. Note the highly weathered nature of the claystone and the salts in thin seams.

Although some weathered sandstone and siltstone was found in BH#1 between 7 and 14.5 feet, no hard sandstone layers were found below this depth to 30.5 feet in BH#1 and to a total depth of 25.5 feet in BH#2. Interestingly, a buried waterline that is located to the north and northwest of the water tower, appears to have trenched through some hard sandstone layers near the surface that was not encountered at the water tower site. This suggests that the Lewis Shale in the vicinity of the water tower is dominated by moderately to highly weathered shale/claystone and that sandstone layers are not continuous. Although core recovery was generally excellent, rock quality was poor, with RQD’s of 0 to 54% in BH#1 and 36 to 52% in BH#2. Field intact rock strength classifies as R0 (extremely weak rock, 35-150 psi). No groundwater was found in either borehole at the water tower site.

Health Center (building) – In the boreholes at the Health Center building site (BH#7- BH#12), we found 2-4 feet of light brown, dry, stiff sandy lean clay underlain by moderately to highly weathered shale/claystone with sandstone lenses (Lewis Shale). See Soil Profile P-1 (Appendix B) for the stratigraphy across the Health Center building site. Boreholes BH#7-BH#9 were cored from roughly 5 to 25-30 feet. A portion of a core run from BH#7 is shown in Photo 8 below. This is typical of the weak claystone of the Lewis Shale with low RQD (18-34% in the upper 22 feet) and field intact rock strength of R0 (extremely weak rock). The sandstone typically has a higher RQD (63-76%), rock strength of R2 (weak rock, 725-3,625 psi), and is slightly to moderately weathered (W2/W3). The more massive, denser, and less weathered sandstone strata were found in the core samples at 22-28 feet in BH#7, 18.2-22.6 feet in BH#8, and at 16-18.3 feet and 23.7-26 feet in BH#9.

Photo 7 (left) view north at BH#9. Photo 8 (right) core of the Lewis Shale from 13.7 ft (upper left) to 23.3 ft (lower right) in BH#7. Note the highly weathered and weak claystone until 22 feet where massive sandstone was encountered. The sandstone extended to 28 ft followed by claystone to 30.5 ft.

Boreholes BH#10-BH#12 in the building footprint were augered to determine N-values of the rock/soil and where auger refusal was. Harder sandstone was found at 13-15 feet in BH#10, at 13 feet and again at 15 feet in BH#11, and in lenses at various depths in BH#12. N-values were typically greater than 40 and 50 bpf throughout the soil and rock in these three boreholes until refusal was reached at 15-18 feet in dense sandstone. As seen in Photos 3 and 4 of the rock exposed in the nearby Indian Service Road 9 roadcut, the sandstone within the Lewis Shale ranges from weak, highly weathered and thinly bedded to massive, thickly bedded, and slightly weathered. No groundwater was found in any of the building site boreholes and there is no evidence of a seasonal water table. The soils are consistently moist to dry, but not wet.

Health Center (parking areas) –Photo 9 below shows the eastern parking lot and Photo 10 shows the transition from the surficial sandy clay soil to highly weathered shale and siltstone/sandstone found at both parking lot areas.

Photo 9 (left) view southwest at BH#14 at the eastern parking lot. Photo 10 (right) is sample of sandy clay soil that transitions to highly weathered shale and thinly bedded siltstone/ sandstone obtained from BH#14 from 2 to 3.5 feet.

In the boreholes at the Health Center parking lots (BH#13-BH#14), we found dry, stiff, sandy lean clay to 1.5 to 2.5 feet underlain by highly weathered sandstone and shale with sandy clay interstitial soil. BH#13 was terminated at 5.7 feet in SPT refusal, while BH#14 was terminated at 6.5 feet. These soils were dry and there was no evidence of groundwater.

Sewage Lagoon – In the boreholes at this site (BH#3-BH#6), we found light brown, dry, stiff to very stiff fine sandy lean clay to silty/clayey fine sand to 5.5-8 feet in the upper borings (BH#3-BH#4) and 12 to 15 feet in the lower borings (BH#5-BH#6) underlain by highly weathered formational Lewis Shale was encountered. Despite the presence of formational material, it could be augered to just over 20 feet and N-values ranged from 24 blows per foot (bpf) to over 50 bpf. This soil appears to be eolian and slopewash deposits over highly weathered siltstone, sandstone, and claystone (Lewis Shale). Photo 12 shows the nature of the weathered bedrock with weak bedding structure and salts.

Photo 11 (left) view north at BH#5 in the sewage lagoon site. Photo 12 (right) of the highly weathered sandstone from BH#4 at 20 feet.

6.2 Laboratory Testing

Laboratory tests were performed on the predominant native soil types to evaluate the range of physical characteristics and the results are presented in Appendix C and most of the tests are summarized in Table 3 below.

Table 3: Summary of Laboratory Results

As seen from these results, the predominant soil type in the upper 2 to 10 feet is a lean clay to sandy lean clay with a Plasticity Index (PI) of 12 to 23. A soil with a PI of less than 15 is considered to have a low potential for swelling when wetted and shrinking when dried, while a soil with a PI of between 15 and 30 is considered to have moderate potential for swelling or shrinking. These soils are composed of 32 to 44% clay, 23 to 34% silt, 11 to 44% sand (mostly fine sand), and less than 5% gravel. Based on these laboratory test results these soils classify as lean clay (CL) to sandy lean clay (CL) according to the Unified Soil Classification System (USCS). Natural moisture contents of the samples typically ranged from 4 to 10%.

Six swell/consolidation tests were performed on samples taken from our borings. When exposed to similar loading patterns, the samples showed potential for consolidation and swelling. Two of the samples collapsed 12.3% and 12.5% under a total load of 2,000 psf, while four samples swelled 2.0 to 6.5% under loads of 100 psf and had constant volume swelling pressures of 650 to 1,130 psf. The Nino & Moore (2019) geotechnical report included one swell/consolidation test from a clayey sand (SC) soil sample from 1-2.5 feet in their boring B-1 at the sewage lagoon and it collapsed 12.0% under a load of 1,100 psf when water was added. Total consolidation of chloride s pH

(ft) (%) LL PL PI gravel sand silt clay pcf psi % % µS/cm

BH#1 DS1 CL 5-6.6 9.1% 90.7 0.050 0.042 394 8.1

BH#1 DS2 CL 10-11.5 10.4% 111.4

BH#1 DS3 CL 15-16 10.3% 0.160 0.045 1108 8.0

BH#1 C1 clay shale 21.5 6.9% 119.7 107

BH#2 DS4 CL 5-6.5 7.2% 31 14 17 0.0 30.5 34.0 35.5

BH#2 DS5 CL 10-11.5 8.8%

BH#2 C2 clay shale 18.0 7.3% 146.1 160

BH#4 DS11 CL 10-11.5 8.0% 36 13 23 0.2 11.1

BH#5 DS14 CL 5-6.5 6.5% 31 14 17 0.0 28.7

BH#6 DS19 SM 10-11.5 2.8% NP NP NP 1.9 82.8

BH#7 DS22 CL 5-6 10.1% 33 14 19 4.9 30.1 27.2 37.8 113.1

BH#7 C3 clay shale 13.7 6.6% 117.9 74

BH#7 C4 sandstone 22.6 2.6% 124.2 1,900

BH#8 DS23 CL 5-6 6.1% 29 14 15 0.0 39.4 23.7 36.9 95.6 0.150 0.063 1902 7.9

BH#8 C5 clay shale 11.6 6.2% 123.7 198

BH#8 C6 sandstone 19.0 0.8% 157.9 5,500

BH#9 DS24 CL 5-6 8.0% 36 15 21 0.0 30.9 25.6 43.5 115.9

BH#9 DS25 CL 11-11.4 4.5%

BH#9 C7 sandstone 24.7 3.0% 123.3 2,490

BH#10 DS26 CL 2.5-4 7.3% 31 16 15 0.2 34.8 27.0 38.0

BH#10 DS27 CL 5-6.5 8.0%

BH#10 DS28 CL 10-11 8.5% 0.020 0.042 837 7.8

BH#11 DS31 CL 10-11.5 10.0%

BH#11 DS32 CL 15-16.5 4.4%

BH#12 DS33 CL 5-6.5 10.8% 26 14 12 0.8 44.5 22.9 31.8

BH#12 DS34 CL 10-11.5 10.3%

BH#12 DS35 CL 15-15.5 7.1%

BH#13 DS36 CL 2-3.5 5.8%

BH#13 DS37 CL 5-5.7 4.1%

BH#14 DS38 CL 2-3.5 5.6% 26 14 12 0.8 39.3 26.1 33.8

BH#14 DS39 CL 5-6.5 7.1%

*LL = Liquid Limit, PL = Plastic Limit, PI = P lasticity Index, NP = Non-Plastic

Moisture content

Sieve Analysis

Atterberg

Limits* %

Soil Chemistry

UCSBorehole

Sample

USCS

Classifi-cation

Sample

Depth % Fines

88.7

71.3 electro-conduc-tivity

Water Tower

Sewage Lagoon

Health Center and Parking water soluble sulfates

Dry

Density

15.3 that sample was 20.5% under a final load of 1,500 psf. These results show the potential for swelling, consolidation, and collapse.

Unconfined Compressive Strength (UCS) tests were performed on sandstone and claystone core samples. There were few core samples of the shale/claystone that were long enough to test using this method. The three sandstone cores had UCS’s of 1,900-5,500 psi and the four shale/ claystone core samples had UCS’s of 74-198 psi. All other claystone core samples were either too short or too fractured to test for UCS.

Soil strength and moisture-density (Standard Proctor) tests were performed on a bulk sample obtained from a depth of 0 to 4 feet in BH#14 (parking area borehole). The Standard Proctor was 117.0 pcf at 12.3% moisture content. The California Bearing Capacity (CBR) test result was

7.3 at a 95% Molded Dry Density (MDD) of 111.2 pcf.

A series of geochemical tests were conducted on four soil samples (see Table 3). The samples had water-soluble sulfate concentrations of 0.02-0.16%, chlorides content of 0.042-0.063%, electro-conductivity of 394-1,902 µS/cm, and pH of 7.8-8.1. The water-soluble sulfates content and electro-conductivity are indicative of corrosive soil. Recommendations for addressing the corrosive nature of the soil are presented in the Recommendations Section of this report.

ENGINEERING ANALYSIS

7.1 Pavement Design

The primary purpose of a pavement section is to distribute concentrated wheel loads to the subgrade in a manner such that the subgrade is not over-stressed. Performance of the pavement section is a function of subgrade strength and traffic loading. For purposes of designing a pavement section, subgrade soil is represented by a soil support value (resilient modulus) for flexible pavements (asphaltic concrete). Subgrade strength decreases when the moisture content of the subgrade increases. Therefore, proper drainage, both surface and subsurface, is essential for long-term pavement performance. Pavement design procedures are based upon strength properties of the subgrade soil and pavement materials, along with the design traffic conditions.

7.1.1 Traffic & Pavement Design Considerations

This Health Center site will serve passenger vehicles and pickup trucks, occasional busses, and various delivery and service trucks. According to the Phase II NAIHS (2020) report, there will be roughly 303 parking spaces and they recommend that pavement is on minimum 12 inches of engineered fill with additional consideration for frost depths. They recommend parking areas and driveways have a 20-year design life with cumulative ESALs up to 60,000.

Site specific traffic information was not available for this site, so we made some assumptions based on the amount of parking and intended use of the facility. If our assumptions about vehicle types, loads, and potential daily traffic volumes are incorrect, these loads should be re-evaluated by BEI for the pavement design. To determine the equivalent single axle loads (ESAL’s) we assumed the mixture of vehicle types presented in Table 4 (Traffic Loading) and applied equivalency factors (per AASHTO, 1993) to convert the anticipated traffic mixture to an equivalent number of 18-kip axle loads. We also assumed an annual growth rate of 2%.

Table 4: Traffic Loading

Vehicle Type Trips per Day

Passenger cars 200

Pickup trucks/passenger vans 75 Buses 2

Garbage truck 1

Delivery trucks 5

Combination trucks 2

7.1.2 Design Parameters

We used the pavement design parameters shown in Table 5 below.

Table 5: Pavement Design Parameters

Pavement Design Parameter Design Value

Source

ADT estimate

Design life 20 years NMDOT 2015 PDM Exhibit 620-3

Traffic growth rate 2% Assumed

Flexible Pavement ESAL’s (calculated) 109,000 Calculated based on Table 4

Initial serviceability 4.2 NMDOT 2015 PDM Section 620-7.3

Terminal serviceability 2.0 NMDOT 2015 PDM Section 620-7.3

Reliability 75% NMDOT 2015 PDM Exhibit 620-4

Drainage coefficient 1.15-1.2 NMDOT 2015 PDM Exhibit 620-22

California Bearing Ratio (CBR) 7.3 Laboratory Testing (see Appendix C)

Structural Number required 2.45 Calculations (see Appendix D)

Flexible Pavement

Asphalt layer coefficient 0.44 NMDOT 2015 PDM Exhibit 620-14

Standard deviation 0.44 NMDOT 2015 PDM Section 620-8.5

Base layer coefficient 0.15 NMDOT 2015 PDM Exhibit 620-14

Subbase layer coefficient 0.11 NMDOT 2015 PDM Exhibit 620-14

Subgrade resilient modulus 6,000 psi Calculations using CBR value

7.1.3 Flexible Pavement Recommendations

Based on our design calculations, anticipated traffic, and the field conditions, the pavement design results are included in Appendix D (Engineering Analysis) and our recommended flexible pavement section is presented in Table 6 and the rigid pavement section is shown in Table 7.

Table 6: Recommended Flexible Pavement Section

Pavement Section

Asphalt Thickness

(in)

Aggregate Base Course Thickness

(ABC) (in)

Subbase Course

Thickness (in)

Structural Number

(Sn) Option 1

(recommended) 3 6 6 2.88

Option 2 3.5 8 0 2.74

Table 7: Recommended Rigid Pavement Section

Pavement Section

Concrete Thickness

(in)

Aggregate Base Course Thickness

(ABC) (in)

Subbase Course

Thickness (in)

Option 1 (recommended)

6 6 --

Option 2 5.5 6 6

Construction Considerations

a. Moisture condition and recompact at least 12 inches of the exposed subgrade soil.

b. Moisture condition and compact the base course and subbase course material (item ‘f’ below) as required to accommodate any proposed modifications to the road profile.

c. Proof-roll the compacted base using a loaded dump truck or water truck. Proof-rolling should be observed by a BEI representative and soft areas should be repaired at our discretion.

d. Sub-excavate any unstable areas and replace with moisture conditioned and compacted aggregate base. Place and compact structural fill in level lifts, not more than 6-inches in loose thickness, up to planned grade.

e. Grade pavement such that surface water drains into the roadside swales at a minimum two percent slope. This may require elevating the hangar structures to achieve this grade since the site is essentially flat.

f. New Base Course and Subbase Course shall meet the requirements for Type I Base Course in Section 303, Base Course, in NMDOT (2019).

g. Asphalt shall meet the requirements in Section 423, Hot Mix Asphalt (HMA), and the Contractor shall test the HMA in accordance with AASHTO T283, as specified in

NMDOT (2019).

h. Portland cement concrete shall meet the requirements in Section 450, Portland Cement Concrete Pavement (PCCP), and the Contractor shall sample and test the aggregate production and PCC mixture in accordance with Section 902 (Quality Control), Section 903 (Quality Assurance), and Section 906 (Minimum Testing Requirements), as specified in NMDOT (2019).

Site Preparation and Grading

a. Design and construction of the pavement should promote drainage away from the paved areas. Where needed, ditches and culverts should either be constructed or modified to accept road drainage to reduce the potential for erosion.

b. Compaction requirements of fill material: aggregate base course should be compacted to 95% of modified Proctor (AASHTO T180) maximum dry density at +2% of optimum moisture content.

c. A representative of BEI should be called out to the site to observe placement of roadbase and base course and verify the compacted density. The Client should contact BEI in advance of any required excavations to discuss the specific testing requirements, budget, and scheduling needed for these services.

d. All paving construction activities should be monitored and tested by a competent civil/geotechnical engineering firm for compliance with the recommendations contained in this report and with the specifications in NMDOT (2019).

e. Corrosivity testing indicated that subgrade soil is corrosive to steel and concrete.

Separating any pavement surface from the native soils by placing pavement on granular material (aggregate base course) and elevating the roadbed will help in keeping salts from migrating up into the pavement. Even though these salts are not corrosive to asphalt, the forces of salt growth can cause physical pavement damage over time.

Pavement Maintenance

a. The pavement's life will be dependent on achieving adequate drainage throughout the section and especially at the subgrade.

b. Surface of subgrade, crushed surfacing, and asphalt surfaces shall slope at no less than 2% to an appropriate stormwater disposal system or other appropriate location that does not impact adjacent buildings of properties.

c. Maintain grades outside of paved areas to prevent the collection of water adjacent to the pavement.

d. Seal cracks and perform surface maintenance on all pavement surfaces every 3 to 5 years to reduce the potential for surface water infiltration into the underlying pavement subgrade.

e. Water that ponds at the pavement subgrade surface can induce heaving during freeze-thaw process, which can readily damage pavement.

f. Never allow inverted crowns at the subgrade or pavement surfaces without center concrete gutters designed to have asphalt overlap.

7.2 Foundation Engineering Assessment

7.2.1 Seismic Design Accelerations

BEI used site stratigraphy from our drilling, available geologic mapping and our knowledge of the local geology, the project location, the 2010 American Society of Civil Engineers 7 (ASCE7-

16) and the National Earthquake Hazards Reduction Program to evaluate seismic characteristics of the site. Based on the ASCE7-16 guidelines, we recommend that this site be designated as Site Class D (soft soil with N<15 or PI>20). This classification is based on limited shallow exploratory data, is based on the predominant soil condition near the surface and assumes similar conditions for a depth of 100 feet. For Seismic Risk Category IV (for medical facilities) and soil Site Class D, the maximum spectral response acceleration at short periods (0.2 second, SMS) is 0.296g and at one second (SM1) is 0.157g. These values are taken from the Applied Technology Council (ATC) website (www.hazards.atccouncil.org) that relies on the U.S.

Geological Survey Seismic Design Web Services and is based on the latitude and longitude coordinates for the site. See ATC seismic parameter output in Appendix D. We recommend seismic design reference the seismic design parameters provided in Table 8 below. These values also comply with the method described in AWWA D100-11.

Table 8: Seismic Design Parameters

Period (seconds)

Modified Acceleration

Coefficient for Site Class D (g)

0.0 (peak) PGAM = 0.14

0.2 (short) SDS = 0.198

1.0 (long) SD1 = 0.105

Notes: g = gravity

7.2.2 Liquefaction

Liquefaction is the partial or total loss of strength of soils that can occur during strong earthquake shaking of significant duration. Earthquake-induced liquefaction generally occurs only under particular conditions, including high groundwater table, strong earthquake ground shaking of long duration, and loose uniform sands. Typically, liquefaction occurs where the groundwater table is shallow (5 to 10 feet deep) and generally only at depths less than about 50 feet. Due to the presence of cohesive soil, and lack of groundwater, it is our opinion the potential for liquefaction is low.

7.2.3 Engineering Assessment for Foundations

Our exploration and lab testing indicated roughly 3-5 feet of sandy lean clay soil overlying moderately to highly weathered shale/claystone with discontinuous lenses of harder sandstone and siltstone. The variability of the sandstone layers within the Lewis Shale formation can be seen in the nearby Route 9 roadcut (Photos 3 and 4). Based on laboratory testing the sandy clay overlying the shale has the potential to collapse, resulting in settlement when the moisture content increases. We recommend that foundation and/or over-excavations below the foundations extend through this soil stratum. Additionally, there is the potential for the clayey layers in the shale to swell when the moisture content increases.

Based on our analysis the movement below foundation loaded to 1,000 psf will be less than ½-inch; however, there is the potential for over an inch of movement below lightly loaded floor slabs. Movement associated with expansive clay is typically differential movement because the moisture content of the soil does not increase uniformly across the site. It is our opinion that the buildings can be constructed on conventional spread footings; however, the risk of slab movement is high. To reduce the risk of slab movement the best alternative is to construct a structural slab over a void. If the project owner can tolerate the potential for some slab movement, the building can be over-excavated and non-expansive soil placed below the slab.

The depth of the over-excavation depends upon the tolerable slab movement. We provide more recommendations in the following sections.

In addition to the measures discussed above provide good drainage away from the building can help reduce the probability that the swell and collapse potential will be realized. We provide drainage recommendations in Section 9.7.

SEWAGE LAGOON SITE

The drainfield site tested was located downhill to the northeast of the building site and Indian Service Route 9 (see the Site Layout, Map 2). This site was selected by others and is desirable due to the gentle slopes, distance from the Health Center, and sufficient area. We understand there will be at least 10 feet of excavation of the site for sculpting of the lagoon. As presented in the Phase II SSER report (NAIHS 2020), a USDA hydrological soil map for the project area shows the majority of the soil in the area as Type B, with a small amount of Type C near the NE corner of the sewage lagoon site. Based on our four boreholes (BH#3-BH#6), the sewage lagoon site contains a mixture of wind-blown and slopewash fine-grained soils (fine sandy clay to silty fine sand) to roughly 5.5 to 8 feet in the upper (southern) portion of the site and to roughly 12 to 15 feet in the lower (northern) portion of the site. The underlying formational material is highly weathered shale/claystone and thinly bedded siltstone/sandstone. Using augers, all four boreholes could be drilled to at least 20 feet. This indicates these soils and weathered bedrock can be excavated and ripped using conventional excavation equipment. It appears that there is a denser sandstone layer at around 21 feet. It is our understanding that excavations will be on the order of 10+ feet in the sewage lagoon, so if excavations will exceed 20 feet, additional exploration is recommended.

As part of the review process for this project, a percolation test was requested of the surface soils within the lagoon site. Therefore, we hand-dug three percolation holes in the vicinity of BH#5. The depth of the holes were 12- to 13-inches deep and they were 9-inches wide. Once dug, the holes were pre-soaked at the end of a day and the percolation tests were performed the following morning. The tests were run from roughly 3 inches from the top of the hole to 4 inches above the bottom of the hole so that there were 5 to 6 successive 1-inch readings per test run. There was a total of three runs per hole. The results of three percolation tests are shown in Table 9 below.

Table 9: Percolation Test Results

Borehole Test Hole

Depth

(inches) Percolation Rate (mpi)

Soil Description

BH#5

1 13 7.6 Fine sandy lean clay

2 12 7.7 Fine sandy lean clay

3 13 2.9 Lean clayey fine sand

The variability of these rates is likely due to slight differences in soil texture, structure, and…