HomeMy WebLinkAbout1.13 Application Part14Battlement MesaRulisonCarbonateN/CDE BEQUE FPDRIFLE FPDLOWER VALLEY N/CN/CGRAND VALLEY FPDBURNING MOUNTAINS FPDN/CN/CGYPSUM FPDGLENWOOD SPRINGS FDCARBONDALE AND RURAL FPDN/CN/CN/CN/CRifleSiltGlenwood SpringsNew CastleCarbondaleParachute§¨¦70§¨¦70§¨¦70UV13UV139UV82UV6UV325UV133£¤6£¤6£¤6T2NT5ST1NT2ST1ST5ST4ST6ST7SR93WR91WR99WR96WR89WR97WR90WR92WR88WR98WR101WR102WR95WR103WR104WR94WR100WR105W107°5'W107°5'W107°10'W107°10'W107°15'W107°15'W107°20'W107°20'W107°25'W107°25'W107°30'W107°30'W107°35'W107°35'W107°40'W107°40'W107°45'W107°45'W107°50'W107°50'W107°55'W107°55'W108°0'W108°0'W108°5'W108°5'W108°10'W108°10'W108°15'W108°15'W108°20'W108°20'W108°25'W108°25'W108°30'W108°30'W108°35'W108°35'W108°40'W108°40'W108°45'W108°45'W108°50'W108°50'W108°55'W108°55'W109°0'W109°0'W40°10'N40°10'N40°5'N40°5'N40°0'N40°0'N39°55'N39°55'N39°50'N39°50'N39°45'N39°45'N39°40'N39°40'N39°35'N39°35'N39°30'N39°30'N39°25'N39°25'N39°20'N39°20'N39°15'N39°15'N$WeldMoffatMesaBacaParkRouttYumaLas AnimasGarfieldLincolnLarimerPuebloGunnisonBentElbertSaguacheGrandRio BlancoLoganEagleKiowaEl PasoMontroseOteroDeltaWashingtonLa PlataKit CarsonProwersJacksonFremontPitkinMontezumaCheyenneHuerfanoMorganAdamsCostillaConejosArchuletaDoloresChaffeeHinsdaleMineralSan MiguelCusterTellerDouglasCrowleyPhillipsBoulderOurayAlamosaArapahoeSummitRio GrandeLakeSedgwickJeffersonSan JuanClear CreekGilpinDenverBroomfieldUtahUtahKansasKansasWyomingWyomingNew MexicoNew MexicoNebraskaNebraskaOklahomaOklahomaGarfield County Community Wildfire Protection PlanMap 7: Wildland Fire Susceptibility IndexGarfield County, CONAD83 UTM Zone 13NU:\Projects\901162_0001_010_GarfieldCWPP\map_mxd\GarfieldCWPP_WildfireSusceptibility_ANSID.mxd 9/25/2012010MilesUtility LinesRailroadsCounty Roads - GarfieldLocal Roads - GarfieldInterstate-ExpresswayHighwayStreamsTownshipsCity LimitsFire Districts (N/C = Not Covered)Wildland Urban InterfaceLakes-ReservoirsWildland Fire Susceptibility IndexNR240,661 AcresLow1,194,700 AcresModerate246,396 AcresHigh145,838 AcresVery High65,790 AcresSource: CSFS
AES Peace Bear Ranch Solar – Land Use Change – Major Impact permit application (11/5/2021)
AES Peace Bear Ranch Solar – Garfield County 57
Please see the following pages for the Geotechnical Engineering Report performed for AES Peace Bear
Ranch Solar, LLC in February 2021.
GEOTECHNICAL ENGINEERING REPORT
Appendix C11
REPORT COVER PAGE
DRAFT - Geotechnical Engineering
Report
__________________________________________________________________________
Holy Cross Solar Project – Peace Bear Ranch Site
2714 County Road 331
Silt, Colorado
February 7, 2021 (Revised February 9, 2021)
Terracon Project No. 25205263A
Prepared for:
HDR Engineering, Inc.
Denver, Colorado
Prepared by:
Terracon Consultants, Inc.
Denver, Colorado
Terracon Consultants, Inc. 10625 W I -70 Frontage Rd N, Ste 3 Denver , Colorado 8 0033
P (303) 423 -3300 F (303) 423 -3353 terracon.com
REPORT COVER LETTER TO SIGN
February 7, 2021 (Revised February 9, 2021)
HDR Engineering, Inc.
1670 Broadway, Suite 3400
Denver, Colorado 80202
Attn: Mr. Dave Phillips
P: (303) 323-9805
E: dave.phillips@hdrinc.com
Re: DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site
2714 County Road 3311
Silt, Colorado
Terracon Project No. 25205263A
Dear Mr. Phillips:
We have completed the DRAFT - Geotechnical Engineering services for the above referenced
project. This study was performed in general accordance with Terracon Proposal No. P25205263
dated August 12, 2020. This report presents the findings of the subsurface exploration and provides
geotechnical recommendations concerning earthwork and the design and construction of
foundations and unpaved access roads for the proposed project.
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report or if we may be of further service, please contact us.
Sincerely,
Terracon Consultants, Inc.
DRAFT DRAFT
Nick M. Novotny, P.G., C.E.G. Scott B. Myers, P.E.
Senior Staff Geologist Regional Senior Consultant
Subject Matter Expert Reviewed By: Scott D. Neely, P.E. G.E. (CA)
Responsive ■ Resourceful ■ Reliable 1
REPORT TOPICS
INTRODUCTION ............................................................................................................. 1
SITE CONDITIONS ......................................................................................................... 1
PROJECT DESCRIPTION .............................................................................................. 2
GEOTECHNICAL CHARACT ERIZATION ...................................................................... 3
Site Geology ............................................................................................................................... 3
Typical Profile ............................................................................................................................. 4
Laboratory Test Results .............................................................................................................. 4
Consolidation/Expansive Soil and Bedrock Test Results ................................................. 4
Corrosion Potential Test Results ..................................................................................... 5
Laboratory Thermal Resistivity Test Results ................................................................... 6
Groundwater Conditions .............................................................................................................. 6
SEISMIC CONSIDERATIONS ........................................................................................ 7
GEOTECHNICAL OVERVIEW ....................................................................................... 7
Foundations ................................................................................................................................ 7
Expansive Soils and Bedrock ...................................................................................................... 8
Shallow Bedrock ......................................................................................................................... 8
SOLAR PANEL RACKING SYSTEM FOUNDATIONS .................................................. 9
Axial Capacity Design Recommendations ................................................................................... 9
Lateral Capacity Design Recommendations .............................................................................. 10
Frost Heave Considerations ...................................................................................................... 11
Construction Considerations ..................................................................................................... 11
SHALLOW FOUNDATIONS ......................................................................................... 12
Shallow Mat Foundation Design Parameters – Compressive Loads........................................... 12
Shallow Mat Foundation Construction Considerations ............................................................... 13
EARTHWORK............................................................................................................... 14
Site Preparation ........................................................................................................................ 14
Fill Material Types ..................................................................................................................... 15
Fill Compaction Requirements................................................................................................... 16
Excavation ................................................................................................................................ 17
Grading and Drainage ............................................................................................................... 17
Slopes ...................................................................................................................................... 17
Earthwork Construction Considerations ..................................................................................... 18
UNPAVED ACCESS ROADS ....................................................................................... 18
Access Road Recommendations ............................................................................................... 19
Access Road Construction Recommendations .......................................................................... 20
GENERAL COMMENTS ............................................................................................... 21
Note: This report was originally delivered in a web-based format. For more interactive features, please view your project
online at client.terracon.com.
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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FIGURES
GEOMODEL
ATTACHMENTS
EXPLORATION AND TESTING PROCEDURES
SITE LOCATION AND EXPLORATION PLANS
EXPLORATION RESULTS
Note: Refer to each individual Attachment for a listing of contents.
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INTRODUC TION
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site
2714 County Road 331
Silt, Colorado
Terracon Project No. 25205263A
February 7, 2021 (Revised February 9, 2021)
INTRODUCTION
This report presents the results of our subsurface exploration and geotechnical engineering
services performed for the proposed future Peace Bear Ranch photovoltaic solar power facility to
be located at 2714 County Road 331 in Silt, Colorado. The purpose of these services is to provide
information and geotechnical engineering recommendations relative to:
■ Subsurface soil and bedrock
conditions
■ Foundation design and construction
■ Groundwater conditions ■ Seismic site classification per IBC
■ Site preparation and earthwork ■ Lateral earth pressures
■ Frost considerations ■ Aggregate-surfaced pavement design
and construction ■ Excavation considerations
The geotechnical engineering Scope of Services for this project included the advancement of ten
test borings to depths of about 15 to 20 feet below existing site grades.
Maps showing the site and boring locations are shown in the Site Location and Exploration
Plan sections, respectively. The results of the laboratory testing performed on soil and bedrock
samples obtained from the site during the field explora tion are included on the boring logs and as
separate graphs in the Exploration Results section.
SITE CONDITIONS
The following description of site conditions is derived from our site visit in association with the
field exploration and our review of publicly available geologic and topographic maps.
Item Description
Parcel Information
The project is approximately 100 acres in size and located at 2714 County
Road 331 in Silt, Colorado. Garfield County Parcel No. 217523400130.
Approximate Coordinates: 39.5091° N, 107.8511° W
See Site Location
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Item Description
Existing
Improvements The subject site generally consists of vacant land with dirt access drives.
Current Ground
Cover
The subject site is currently covered by native vegetation consisting of sparse
weeds and grasses.
Existing Topography The site topography generally consists of rolling hills, plains, and mesas with
elevation differences on the order of about 100 feet.
PROJECT DESCRIPTION
Our initial understanding of the project was provided in our proposal and was discussed during
project planning. A period of collaboration has transpired since the project was initiated, and our
final understanding of the project conditions is as follows:
Item Description
Project Description
We understand that the approximate 100-acre site will be developed as a
15 MWac photovoltaic (PV) solar power facility. We assume the power facility
will also include pads for electrical equipment such as switchgear,
transformers, and inverters; and buried and/or overhead power lines.
We assume the solar array field grade will follow the existing site grade with
minimum grading required to bring the site to finished grade.
The PV array field is assumed to be comprised of PV modules attached to a
racking system that is supported on driven steel piles (W6x9 or similar).
A substation is also likely planned as part of the solar power facility. However,
the location of the substation was not provided and therefore
recommendations are not included as part of this report.
Anticipated
Foundation Systems
■ Solar Array: Driven piles
■ Equipment Pads: Mat foundation
Maximum Loads
(assumed)
Structural loads were not provided, but have been estimated based on our
experience on similar solar projects:
Arrays (axis tracking rack systems):
■ Downward: 1 to 7 kips
■ Lateral 1 to 2 kips
■ Uplift: 0.5 to 3 kips
■ Moments: 0.1 to 30 kip-ft
Equipment Pads:
■ Mat foundation: 1,200 pounds per square foot (psf)
Grading/Slopes Less than 3 feet (+/-) max
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Item Description
Access Roadways
We understand that access road cross sections used for construction of the
project will be the responsibility of the EPC, and that only post construction
traffic with an allowable rut depth of 2 inches is what we are to design for in
this report. We anticipate low-volume, aggregate-surfaced and native soil
access roads will have a maximum vehicle load of 30,000 lbs. and will travel
over the access roads only once per week.
Underground Utilities
We anticipate installation of underground utilities within about 5 to 8 feet of
finished grade.
GEOTECHNICAL CHARACTERIZATION
Site Geology
The majority of the site surficial geology is mapped as loess and sheetwash alluvium (Qsw/Qlo)
with outcrops of the Shire Member of the Wasatch Formation (TWS) throughout the site (Shoba,
2001 1). A geologic map of the area is presented in the Exploration Plan section of this report.
Based on the geologic data we reviewed for the area, the bedrock units of the Shire Member dip
about 4 to 6° to the northwest , forming the southern arm of a synclinal fold. This folding event is
believed to have formed the Piceance basin, in which the subject site sits, and is thought to be
one of the final tectonic eve nts associated with the Laramide Orogeny (Donnell, 1969 2). The
Shire Member of the Wasatch Formation is stratigraphically above the Arkosic ledge -forming
sandstone of the Molina Member of the Wasatch Formation and stratigraphically below the
massive sandstone of the Douglas Creek Member of the Green River Formation. Therefore, the
Shire Member represents a time of relative geologic calm Piceance Basin allowing for the slow
deposition of fine clay and silt sediments.
A detailed description of the geologic units mapped in the area of the project site are provided
below:
■ Qsw/Qlo: Loess and sheetwash deposits (Holocene to Pleistocene): Loess consisting of
wind-blown silt and clay from glacial erosion and sheetwash depistis consisting of fine-
grained sand, silt, and clay from seasonal flooding events.
1 Shoba, R.R., and Scott, R.B., 2001, Geology Map of the Silt Quadrangle, Garfield County, Co lorado, USGS
Miscellaneous Field Studies Map MF-2331, Scale 1:24,000
2 Donnel, J.R., 1969, Paleocene and Lower Eocene Units in the Southern Part of the Piceance Creek Basin Colorado,
Geological Survey Bulletin 1274-M
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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■ TWS: Wasatch Formation – Shire Member (Eocene): The Wasatch formation is generally
consists of fine-grained mudstones and siltstones with sparse sandstone and rare
conglomerate (Shoba, 2001). The Shite member is the uppermost member of the Wasatch
Formation, and its principle rock type is claystone with lesser amounts of thick lenticular beds of
arkosic sandstone (Donnell, 1969). Claystone beds of the Shire member are thought to be
volcanically derived sediments rich in iron and magnesium, and have potential to exhibit very high
swell potential when wetted.
Typical Profile
We have developed a general characterization of the subsurface conditions based upon our
review of the subsurface exploration, laboratory data, geologic setting and our understanding of
the project. This characterization, termed GeoModel, forms the basis of our geotechnical
calculations and evaluation of site preparation and foundation options. Conditions encountered at
each exploration point are indicated on the individual logs. The individual logs can be found in the
Exploration Results section and the GeoModel can be found in the Figures section of this report.
As part of our analyses, we identified the following model layers within the subsurface profile. For
a more detailed view of the model layer depths at each boring location, refer to the GeoModel.
Model Layer Layer Name General Description
1 Native Clay Lean clay; with various amounts of silt and sand; very stiff to
hard
2 Wasatch Formation Interbedded claystone, shale, and sandstone bedrock; soft to
very hard
Laboratory Test Results
The following sections present the results of the laboratory testing performed on selected soil and
bedrock samples collected during our subsurface exploration. A summary of laboratory test
results is included in the Exploration Results.
Consolidation/Expansive Soil and Bedrock Test Results
Consolidation/expansion testing was performed on samples obtained at various depths and from
various borings across the site. Laboratory test results indicate that the clay and claystone
samples tested exhibit low compression at in-situ water contents. When exposed to increases in
moisture content, the clay and claystone samples tested exhibited low to very high swell potential.
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Corrosion Potential Test Results
The table below lists the results of the pH; water-soluble sulfate, chloride, and sulfide; redox
potential; electrical conductivity (total salts); and electrical resistivity tests. These values may be
used to estimate potential corrosive characteristics of the on -site soils with respect to contact with
the various underground materials that will be used for project construction, including concrete,
pile foundations, and underground utilities, and should be considered during design and
construction of underground materials.
Corrosivity Test Results Summary
Boring
No.
Sample
Depth
(feet)
Soil
Description
Soluble
Sulfate
(%) 1
Soluble
Chloride
(%) 1
Electrical
Resistivity
(Ω-cm)
pH
Redox
Potential
(mv)
2 0 to 5 Lean clay with
sand (CL) 0.008 0.0040 1,598 8.0 428.6
8 0 to 5 Sandy lean
clay (CL) 0.003 0.0008 2,450 7.8 388.7
1. Percent by weight
Results of soluble sulfate testing indicate samples of the on -site soils tested possess negligible
sulfate concentrations when classified in accordance with Table 19.3.1.1 of the ACI Design
Manual. No minimum Portland Cement type is recommended for soils with negligible sulfate
concentrations. Concrete should be designed in accordance with the exposure class S0
provisions of the ACI Design Manual, Section 318, Chapter 19 .
The resistivity measured on soil samples tested ranged between 1,598 and 2,450 ohm-centimeter.
Resistivity results indicate the soil samples tested have moderate to high corrosive potential to buried
ferrous metal pipes, following the guidelines of J.F. Palmer, “Soil Resistivity Measurements and
Analysis”, Materials Performance, Volume 13, January 1974. The table below outlines the guidelines
for soil resistivity versus corrosion potential.
Corrosion Potential of Soil on Steel
Soil Resistivity (Ω-cm) Corrosion Potential
0 to 1,000 Very High
1,000 to 2,000 High
2,000 to 5,000 Moderate
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
Responsive ■ Resourceful ■ Reliable 6
Soil Resistivity (Ω-cm) Corrosion Potential
> 5,000 Mild
Terracon recommends that an experienced corrosion engineer be retained to design a suitable
corrosion protection system for underground structures and components for EPCs to consider at this
site.
Laboratory Thermal Resistivity Test Results
A bulk sample of near-surface subsurface material obtained from Boring No. 9 was sent to
Geotherm USA for thermal resistivity testing. The testing was performed on specimens remolded
to about 80 and 90 percent of the maximum dry unit weight as determined by ASTM D1557
(Modified Proctor). Thermal dry-out curves were generated for each sample from optimum
moisture down to zero moistu re content. Testing was conducted in general accordance with the
IEEE standard 442-2017 and ASTM D5334.14. The results are summarized in the table below
and the Geotherm USA report is presented in the Exploration Results.
Boring No.
(Depth, feet)
Compaction
Effort
(%, ASTM
D1557)
Dry Density
(pcf)
Optimum
Moisture
Content (%)
Thermal Resistivity
(oC cm/W)
Wet 1 Dry
9 (0 – 5) 80 97 12 75 158
9 (0 – 5) 90 109 12 67 132
1. Sample prepared at optimum moisture content.
Groundwater Conditions
The borings were observed while drilling for the presence and level of groundwater. Groundwater
was not observed during drilling or immediately after drilling in the ten boreholes completed at
this site. The water levels observed in the boreholes can be found on the boring logs in Exploration
Results.
These observations represent groundwater conditions at the time of the field exploration and may
not be indicative of other times or at other locations. Groundwater levels can be expected to
fluctuate with varying seasonal and weather conditions.
Zones of perched and/or trapped groundwater may also occur at times in the subsurface soils
overlying less permeable soils and/or bedrock, on top of the bedrock surface or within permeable
fractures in the bedrock materials. The location and amount of perched water is dependent upon
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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several factors, including hydrologic conditions, type of site development, irrigation demands o n
or adjacent to the site, fluctuations in water features, seasonal and weather conditions.
Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff,
and other factors not evident at the time the borings were performed. Groundwater levels during
construction or at other times in the life of the structures may be higher or lower than the levels
indicated on the boring logs. The possibility of groundwater level fluctuations should be
considered when developing the de sign and construction plans for the project.
SEISMIC CONSIDERATIONS
Based on our subsurface exploration and laboratory testing, it is our opinion that the soils have a
low risk of liquefaction. The following table presents the seismic site classification based on the
2015 International Building Code (IBC), and the subsurface conditions encountered within the
borings:
Code Used Site Classification
2015 International Building Code (IBC) 1,2 C
1. In general accordance with the 2015 International Building Code, Section 1613.3.2.
2. The 2015 International Building Code (IBC) requires a site subsurface profile determination extending a
depth of 100 feet for seismic site classification. The current scope requested does not include the required
100-foot subsurface profile determination. The deepest borings of this exploration extended to a
maximum depth of about 20 feet and this seismic site class definition considers that similar subsurface
conditions exist below the maximum depth of the subsurface exploration.
GEOTECHNICAL OVERVIEW
Based on the results of our field investigation, laboratory testing program and geotechnical
analyses, development of the site is considered feasible from a geotechnical viewpoint provided
that the conclusions and considerations provided herein are incorpo rated into the project.
Foundations
A final site development plan was not provided at the time of this report. We have provided
recommendations for shallow mat foundations for support of the proposed equipment pads and
ancillary structures at the site and recommendations for driven piles to support the proposed solar
arrays.
Final driven pile design parameters for support of the panel arrays should be based on full -scale
pile load test results. A full-scale pile load testing program was not completed as part of our
geotechnical investigation at this site. We have provided recommendations for driven pile
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
Responsive ■ Resourceful ■ Reliable 8
foundations for support of the proposed solar panels in the Solar Panel Racking System
Foundations section of this report.
The on-site clay soils are susceptible to becoming unstable when exposed to increased moisture
conditions. These soils are highly susceptible to pumping, even during fill placement, when
subjected to dynamic loading, such as construction equipment and vehicle traffic. A contractor
experienced with these soils should be retained for construction.
W e recommend new shallow mat foundations be supported on a 3 foot zone of new engineered
fill. On-site soils meeting the material properties in Earthwork are considered suitable for reuse
as engineered fill beneath foundations.
It is our opinion that supporting the shallow mat foundations on recompacted on-site low plasticity
clay soils may result in movement of the structures greater than 1 -inch, depending on the
remolded swell potential. Movement of structures supported on the encountered clay soils may
be further quantified if remolded swell potential testing is performed. We estimate that movements
could be up to 2 to 3 inches when supporting structures on recompacted on -site low plasticity clay
soils, depending on the overall quality of the processing for fill placement and maintainin g effective
drainage for the life of the structure.
Expansive Soils and Bedrock
Based on the laboratory testing, the native clay soils and claystone bedrock exhibit l ow to very
high expansive potential. This report provides recommendations to help mitiga te the effects of
soil shrinkage and expansion. However, even if these procedures are followed, some movement
in the structures is possible. The severity of movement of the proposed structures will probably
increase if modification of the site results in excessive wetting or drying of the expansive clays or
bedrock. Eliminating the risk of movement is generally not feasible, but it may be possible to
further reduce the risk of movement if significantly more expensive measures are used during
construction, such as additional removal and replacement of soils and bedrock, or supporting the
proposed pads on a deep foundation system. It is imperative the recommendations described in
section Grading and Drainage of this report be followed to reduce potential movement.
Additional foundation information pertaining to the proposed structures can be found in the Solar
Panel Racking System Foundations and Shallow Foundations sections of this report. The
Unpaved Access Roads section addresses the design of aggregate surfaced access roadways.
The General Comments section provides an understanding of the report limitations.
Shallow Bedrock
Bedrock consisting of claystone, sandstone, and shale was encountered as shallow as 1 foot
during our exploration at this site. Pre-drilling will most likely be required for the installation of
drilled piles for the majority of the subject site.
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
Responsive ■ Resourceful ■ Reliable 9
It is anticipated that excavations for the proposed improvements can be accomplished with
conventional earthmoving equipment; however, specialized heavy -duty equipment capable of
ripping or jack hammering may be required for bedrock excavation to facilitate rock br eakup and
removal. Consideration should be given to obtaining a unit price for difficult excavation in the
contract documents for the project.
SOLAR PANEL RACKING SYSTEM FOUNDATIONS
We understand that driven pile foundations are the preferred foundation t ype for support of the
panel racking system. In our opinion, traditional driven pile foundations could be used for the
panel racking system but may be difficult to construct due to the shallow bedrock at the site.
Predrilling will most likely be required f or the installation of driven piles for the majority of the
subject site. Alternative foundation systems could be considered to support the proposed PV
array, such as ballast or micropile foundations. Additional recommendations for these foundation
options can be provided upon request.
We have provided geotechnical design parameters for foundation evaluation based on the results
of our subsurface characterization and have used these parameters to perform pile capacity
analyses.
The actual foundation design should be performed in consideration of the preconstruction full-
scale pile load testing (PLT) program. The results of a PLT program performed in conjunction with
subsurface site characterization are usually successful in reducing the design embedme nt depth
when compared to design based on site characterization and analytical methods alone.
The recommended PLT program should be performed when more details regarding foundation
type and loads become available. The PLT program should also be performed using the intended
production and installation methods, equipment, and procedures. The final structural design for
pile foundations should consider anticipated steel loss due to corrosion and the design loads
provided by the racking manufacturer.
Axial Capacity Design Recommendations
The axial tensile (pull-out) capacity can be developed from skin friction while axial compressive
capacity can be developed from skin friction and end bearing of individual piles.
The below table provides ultimate unit skin friction and end bearing pressure for design of piles for
varied soil depth.
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Soil Layer
Depth interval
below existing
ground surface
(ft)
Ultimate skin friction
(psf) 3
Ultimate end bearing
pressure (psf) 1, 2
Native Clay Soils 0 to 2 4 300 --
Claystone, Shale,
and Sandstone 2 to 20 1,500 20,000
1. Bedrock was encountered as shallow as 1-foot from existing site grade and will likely be encountered
during some pile installations. Driving piles into bedrock may require special installation techniques.
2. Minimum 5-foot embedment below adjacent grade for end bearing.
3. The skin friction should be ignored in the upper 12 inches due to ground disturbance
4. In Boring Nos. 8 and 10 native soils extended to depths of about 5 feet. Native soil depth is anticipated
to vary across the site.
The above values are to be used in the following equation to obtain the ultimate uplift or compression
load capacity of a pile:
Qult = H x P x fs
Qult = Ultimate uplift or compression capacity of post (lbs.)
H = Depth of embedment of pile (ft)
P = Box perimeter area/ft. of pile. (i.e. W6x9 = 1.64 ft.)
fs = Skin friction per table above (psf)
The skin friction is appropriate for uplift and compressive loading and represents ultimate values.
A factor of safety of 2 should be applied to the skin friction values. The end bearing pressure is
also an ultimate value and should have a factor of safety of 3 applied for desig n.
Piles should have a minimum center-to-center spacing of at least 5 times their largest cross-
sectional dimension to prevent reduction in the axial capacities due to group effects. If the piles
are designed using the above parameters, settlements are not anticipated to exceed 1 inch.
Lateral Capacity Design Recommendations
We understand that the structural engineer may perform p -y based analyses to model the soil
structure interaction for driven pile foundations subjected to lateral load. We developed L-pile
parameters for this use based on the results of our subsurface investigation. These values are
presented in the tables below:
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
Responsive ■ Resourceful ■ Reliable 11
Soil Layer
Depth
(feet
bgs)
p-y model
Total Unit
Weight γ,
(pcf)
Cohesion (psf) Strain, 50 (%)
Native Clay
Soils 0 to 2 1 Stiff Clay w/o
Free Water 110 5002 Default
Claystone,
Shale, and
Sandstone
2 to 20 Stiff Clay w/o
Free Water 125 2,000 Default
Production piles should have a minimum center-to-center spacing of at least 5 times their largest
cross-sectional dimension in the direction of lateral loads, or the lateral capacities should be
reduced due to group effects.
Frost Heave Considerations
The soils on this site are susceptible to frost heave. However, due to groundwater not being
encountered in the borings, the potential for development of an ice lens and subsequent frost heave
is considered negligible. We therefore recommend frost heave loads not be considered in design
for this project.
Construction Considerations
Based on the field exploration pile refusal in the bedrock materials is considered very likely, and
therefore, pre-drilling of undersized holes will likely be required to drive pi les to their embedment
depths. A pile load test program that incorporates different pre -drilled hole diameters is
recommended for development of ultimate skin friction and lateral design parameters. A
geophysical exploration could be performed to further explore the bedrock depth and identify
areas of shallow bedrock.
Soil expansion could result in additional loading on the piles. The grading and drainage and other
recommendations in Earthwork should be followed to reduce the risk of soil expansion. Due to
the expansive potential of the claystone bedrock, in the event that water is allowed to pond in
areas adjacent to pile foundations, movements on the order 1 to 2 inches are possible. To reduce
the risk of movement, site drainage should be performed in accordance with the
recommendations in this report.
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SHALLOW FOUNDATIONS
We understand equipment pads and ancillary structures will be constructed as part of site
development. The proposed equipment pads and ancillary structures can be supported on mat
foundations bearing on a zone of compacted engineered fill.
We recommend subgrade be prepared as described in Earthwork and additional subgrade
evaluation at the time of construction. The following sections present our recommendations for
shallow mat foundation design and construction.
Design recommendations for mat foundation systems are presented in the following table.
Shallow Mat Foundation Design Parameters – Compressive Loads
Item Description
Maximum Net Allowable Bearing
Pressure 1, 2
2,500 psf (foundations bearing on a 3 foot zone of new
engineered fill)
Estimated Modulus of Subgrade
Reaction 8
k1 = 90 pounds per square inch per inch (psi/in)
𝐾(𝐵𝑋𝐵)= 𝐾1 (𝐵+1
2𝐵)
2
𝐾(𝐵𝑋𝐿)=
𝐾(𝐵𝑋𝐵)(1 +0.5 ∗ (𝐵
𝐾))
1.5
Where:
k1 = modulus of subgrade reaction of a foundation
measuring 1 ft x 1 ft
K(BXB) = modulus of subgrade reaction for a foundation
having a square dimension B
K(BXL) = modulus of subgrade reaction for a foundation
having dimensions of B by L
Required Bearing Stratum 3 Minimum of 3 foot zone of new engineered fill
Foundation Dimensions Maximum width 12 feet
Ultimate Passive Resistance 4
(equivalent fluid pressures)
210 pcf
Ultimate Coefficient of Sliding Friction 5 0.3
Minimum Embedment below
Finished Grade 6 36 inches
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Item Description
Estimated Total movement from
Structural Loads 2 About 1 to 2 inches
Estimated Differential movement 2, 7 About ½ to 1 of total movement
1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding
overburden pressure at the base foundation elevation. An appropriate factor of safety has been applied.
The allowable bearing pressure may be increased by one-third when considering the alternative load
combinations of Section 1605.3.2 of the 2015 International Building Code, however, it should not be
increased when loads are determined by the basic allowable stress design load combinations of Section
1605.3.1. Values assume that exterior grades are no steeper than 20% within 10 f eet of structure.
2. Values provided are for maximum loads noted in Project Description and the use of on-site low plasticity
soils for engineered fill. The foundation movement will depend upon the variations within the subsurface
soil profile, the structural loading conditions, the embedment depth of the foundations, the thickness of
compacted fill, the quality of the earthwork operations, and maintaining uniform soil water content
throughout the life of the structure. The estimated movements are based on maintaining uniform soil water
content during the life of the structure. Additional foundation movements could occur if water from any
source infiltrates the foundation soils; therefore, proper drainage and irrigation practices should be
incorporated into the design and operation of the facility. Failure to maintain soil water content and positive
drainage will nullify the movement estimates provided above.
3. Unsuitable or soft soils should be over-excavated and replaced per the recommendations presented in the
Earthwork.
4. Use of passive earth pressures require the sides of the excavation for the foundation to be nearly vertical
and the concrete placed neat against these vertical faces or that the foundation forms be removed and
compacted engineered fill be placed against the vertical foundation face.
5. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should
be neglected for foundations subject to net uplift conditions.
6. Embedment necessary to minimize the effects of frost and/or seasonal water content variations.
Requirement not necessary for structures that can tolerate seasonal water content variations. For sloping
ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.
7. Differential settlements are as measured over a span of 40 feet.
8. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade
condition, the requirements noted in Earthwork, and the bearing stratum as noted in this table.
Foundations should be proportioned based on equal total dead load pressure to reduce
differential movement between adjacent fo undations. Additional foundation movements could
occur if water from any source infiltrates the foundation soils; therefore, proper drainage should
be provided in the final design and during construction and throughout the life of the structures.
Failure to maintain the proper drainage will nullify the movement estimates provided abo ve.
Shallow Mat Foundation Construction Considerations
As noted in Earthwork, the foundation excavations should be evaluated under the direction of
the Geotechnical Engineer. The base of all foundation excavations should be fre e of water and
loose soil, prior to placing concrete. Concrete should be placed soon after the placement of new
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Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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engineered fill. Care should be taken to prevent wetting or drying of the bearing materials during
construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the
foundation excavations should be removed/reconditioned before foundation concrete is placed.
If unsuitable bearing soils are encountered at the base of the planned over-excavation, additional
measures will need to be taken to stabilize the bearing soils. This could include additional over -
excavation and replacement, stabilization with geotextile, or replacement of the unsuitable soils
with lean concrete. Unstable subgrade conditions should be observed by Terracon to assess the
subgrade and provide suitable alternatives for stabilization. Stabilized areas should be proof -
rolled prior to continuing construction to assess the stability of the subgrade.
Over-excavation for engineered fill placement below f oundations should be conducted as shown
below. The over-excavation should be backfilled up to the foundation base elevation with
engineered fill placed as recommended in the Earthwork section.
EARTHWORK
The following presents recommendations for site preparation, excavation, subgrade preparation,
and placement of engineered fills on the project. All earthwork on the project should be observed
and evaluated by Terracon.
Site Preparation
Strip and remove existing vegetation, organics, and other deleterious materials from proposed
mat and shallow foundation areas and aggregate-surfaced roadway areas. Stripping of
vegetation and topsoil may not be necessary at solar array areas where final grades will match
existing grades. Keeping existing topsoil and vegetation within the array could minimize
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Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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stormwater erosion during construction and maintain overall ground surface stability for the life
span of the facility.
Foundation and roadway subgrade should be proof -rolled with an adequately loaded vehicle such
as a fully loaded tandem axle dump truck. The proof-rolling should be performed under the
direction of the Geotechnical Engineer. Areas excessively deflecting under the proof -roll should
be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should
either be removed or modified by stabilizing with geotextile . Excessively wet or dry material should
either be removed or moisture conditioned and recompacted.
The stability of subgrade soils may be affected by precipitation, repetitive construction traffic or
other factors. Based on the results of our field exploration, we anticipate unstable soils will likely
be encountered within portions of the site once construction commences. If unstable conditions
are encountered or develop during construction, workability may be improved by over -excavation
of wet zones and mixing these soils with crushed gravel. Use of geotextiles could also be
considered as a stabilization technique. Lightweight excavation equipment may be required to
reduce subgrade pumping. Terracon should be retained to provide observations and
supplemental recommendations during construction.
Fill Material Types
Fill required to achieve design grade should be classified as engineered fill and general fill.
Engineered fill is material used below or within 5 feet of structures. General fill is material used to
achieve grade outside of these areas. Earthen materials used for engineered and general fill
should meet the following material property requirements:
Soil Type 1 USCS Classification Acceptable Locations for Placement
On-site lean clay soils CL, CL-ML On-site lean clay soils are considered suitable for re-use
as compacted fill beneath foundations.
On-site sandstone
and claystone bedrock N/A
Properly processed sandstone, claystone, and siltstone
bedrock may be reused as either engineered and/or
general fill after processing to a soil like consistency with
a maximum particle size of 3 inches in diameter.
Imported soils Varies
Imported soils meeting the gradation outlined herein
can be considered suitable for use as structural and/or
general fill.
1. Structural and general fill should consist of approved materials free of organic matter and debris. Frozen
material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material
type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.
Imported soils for use as structural and/or general fill should conform to the following:
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Gradation Percent finer by weight (ASTM C136)
3” 100
No. 4 Sieve 50-100
No. 200 Sieve >50
Soil Properties Value
Liquid Limit 30 (max)
Plastic Index 10 (max)
Expansive Potential 1 1.5 percent (max)
1. Measured on a sample compacted to approximately 95 percent of the ASTM D698 maximum dry density
at optimum water content. The sample is confined under a 200 psf surcharge and submerged.
Fill Compaction Requirements
Structural and general fill should meet the following compaction requirements.
Item Structural and General Fill
Maximum lift thickness
8 inches or less in loose thickness when heavy, self-
propelled compaction equipment is used.
4 to 6 inches in loose thickness when hand-guided
equipment (i.e. jumping jack, plate compactor) is used.
Minimum compaction requirements 1, 2, 3 95% of the material’s maximum dry density
Water content cohesive soils
(clay soils) 2, 4
0 to +3% of the optimum moisture content in pavement
areas
Water content granular soils
(sand soils) 2, 4
-2 to +2% of the optimum moisture content in pavement
areas
1. We recommend that engineered fill be tested for water content and compaction during placement. Should
the results of the in-place density tests indicate the specified water or compaction limits have not been met,
the area represented by the test should be reworked and retested as required until the specified water and
compaction requirements are achieved.
2. Maximum dry density and optimum water content as determined by the Standard Proctor t est (D698).
3. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content,
compaction comparison to relative density may be more appropriate. In this case, granular materials should
be compacted to at least 70% relative density (ASTM D4253 and D4254).
4. Moisture conditioned clay soils should not be allowed to dry out. A loss of moisture within these materials
could result in an increase in the materials expansive potential. Subsequent wetting of these materials
could result in undesirable movement.
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Excavation
Excavations into the subsurface soils and bedrock will encounter a variety of conditions. The
individual contractor(s) is responsible for designing and constructing stable, temporary
excavations as required to maintain stability of both the excavation sides and bottom. All
excavations should be sloped or shored in the interest of safety following local and federal
regulations, including current Occupational Safety and Health Administration (OSHA) excavation
and trench safety standards.
Soils and bedrock penetrated by the proposed excavations may vary significantly across the site.
The soil and bedrock classifications are based solely on the materials encountered in the
exploratory borings. The contractor sh ould verify that similar conditions exist throughout the
proposed area of excavation. If different subsurface conditions are encountered at the time of
construction, the actual conditions should be evaluated to determine any excavation modifications
necessary to maintain safe conditions.
Grading and Drainage
All grades must provide effective drainage away structures during and after construction and
should be maintained throughout the life of the project. Water retained next to structures can
result in soil movements greater than those discussed in this report. As a result, any estimations
of potential movement described in this report cannot be relied upon if positive drainage is not
obtained and maintained, and water is allowed to infi ltrate to fill and subgrade soils and bedrock.
Exposed ground should be sloped and maintained at a minimum 5 pe rcent away for at least 10
feet beyond the perimeter of the structures. After construction final grades should be verified to
document effective drainage away from structures has been achieved. Grades around the
structures should also be periodically inspected and adjusted as necessary as part of the
structure’s maintenance program.
Slopes
For permanent slopes in unreinforced compacted fill areas, recommen ded maximum
configurations are as follows:
Material Maximum Slope (Horizontal: Vertical)
Cohesive soils 3:1
Recommendations are for maximum 10 -foot high slopes. If steeper or higher slopes are required
for site development, stability analyses should be completed to design the grading plan. The face
of all slopes should be compacted to the minimum specification for fill embankments. Fill slopes
should be overbuilt and trimmed to compacted material.
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February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Earthwork Construction Considerations
Bedrock consisting of claystone, sandstone, and shale was encountered as shallow as 1 foot
during our exploration at this site. Excavations that encounter bedrock may become more difficult
and necessitate the use of specialized equipment or techniques. Upon completion of filling and
grading, care should be taken to maintain the subgrade water content prior to construction of
foundations and aggregate-surfaced roads. Construction traffic over the completed subgrades
should be avoided. The site should also be graded to prevent ponding of surface water on the
prepared subgrades or in excavations. Water collecting over or adjacent to construction areas
should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected
material should be removed, or th e materials should be scarified, moisture conditioned, and
recompacted, prior to foundation, slab, or aggregate -surfaced roadway construction.
Unstable subgrade conditions could develop during general construction operations, particularly if
the soils are wetted and/or subjected to repetitive construction traffic. Should unstable subgrade
conditions develop, stabilization measures will need to be employed. Options for subgrade
stabilization can include removal of unsuitable material and replacement with approved fill material
or by crowding rock into the unstable subgrade soils. An alternative can also include the use of
Tensar TX -160 geogrid (or approved equivalent) overlain by a granular engineered fill. The depth of
engineered fill will depend on the severity of unstable soils.
As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926,
Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, and/or
state regulations.
Construction site safety is the sole responsibility of the contractor who controls the means,
methods, and sequencing of construction operations. Under no circumstances shall the
information provided herein be interpreted to mean Terracon is assuming responsibility for
construction site safety, or the contractor's activities; such responsibility shall neither be implied
nor inferred.
UNPAVED ACCESS ROADS
Access roadways for this project are expected to consist of aggregate surfaced roads over
prepared subgrades.
Close evaluation of the roadways should be provided, prior to moving critical equipment,
particularly after a rainfall event. Critical access roads can be constructed with geogrid
reinforcement or chemical stabilization to reduce the risk of instability associat ed with elevated
water contents.
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Access Road Recommendations
Design traffic loads and volumes were not available for our analysis. A sample of near surface
soil was collected from Boring No. 5 which yielded an R -Value of 41. Due to the variability of the
subsurface materials across the site, we used a design R-Value of 15 and an Mr value of 3,500
psi for the design of aggregate surfaced access roads . Roadway subgrades should be prepared
as recommended in the Earthwork section of this report. On-site soils can be re-used as
compacted engineered fill within roadway areas.
Section thickness design of the aggregate surfaced roadways for the project has been based on
the procedures outlined in the 1993 Guideline for Design of Pavement Structures by the American
Association of State Highway and Transportation Officials (AASHTO) for low volume design . We
have provided two alternatives for construction of aggregate surfaced roadways depending on
the amount of risk the owner is willing to accept with respect to subgrade support, particularly
during extended wet periods.
The following design section does not take into account heavy traffic that may occur during
construction. The following thickness recommendations a ssume approximately 5,500 Equivalent
Single Axial Loads (ESALs) and rut depth of 2 to 3 inches is acceptable. These design
assumptions are based on pick-up truck traffic for operations and maintenance after construction
operations have been completed.
Based on the subsurface conditions encountered at the borings, the assumed traffic, subgrade
support, and our experience on similar projects, we recommend that the roadway section consist
of a minimum 5 to 6-inch thick layer of compacted crushed aggregate base course placed on a
minimum of 12-inches of scarified, moisture conditioned, and recompacted subgrade soils. Prior to
placement of aggregate base, we recommend the use of a geotextile, such as a Mirafi RS380i (or
equivalent), or a Geogrid, such as a Tensar TX160 (or equivalent) in conjunction with a separation
fabric.
We understand it is preferable to construct the roadway section supported on on-site soils, however
there is a higher risk of failure and maintenance based on the results of our field exploration . As
a higher-risk alternative, the roadway section could consist of a minimum 5 -inch thick layer of
compacted crushed aggregate base course placed on scarified, moisture conditioned, and
recompacted on-site soils, with a separation fabric consisting of a Mirafi 140N filter fabric, or
equivalent, placed at roadway subgrade elevation .
Aggregate base course should consist of a blend of sand and gravel which meets Colorado
Department of Transportation (CDOT) Class 5 or 6 specifications. Aggregate base course should
be placed and compacted as recommended in the Earthwork section of this report.
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Access Road Construction Recommendations
Site grading is generally accomplished early in the construction phase. However, as construction
proceeds, the subgrade may be disturbed due to construction traffic, desiccation, or rainfall. As
a result, the subgrade construction and corrective action will be required. If subgrade soils
become unstable, we recommend removing the soft or yielding soils and replacing the material
with approved imported fill. As an alternative, consideration can be given to placing geogrid and
additional base course on top of the unstable area.
Positive surface drainage of the roadway and subgrade should be provided a nd maintained. The
roadway should be sloped to provide surface water drainage at all times. Water should not be
allowed to remain within the roadway section and subgrade soils. In addition, the subgrade soils
should be prepared in accordance with the Earthwork section of this report.
The following recommendations should be considered at minimum:
■ Site grading at a minimum 2% grade away from the roadways
■ The subgrade surfaces have a minimum ¼ inch per foot slope to promote proper surface
drainage
■ Consider appropriate edge drainage and ditches/culverts
■ The roadway subgrade should be slightly above surrounding grades to promote positive
drainage. Aggregate base course should not be placed in a “trough” condition within the
roadway section that is prone to holding water.
We emphasize that gravel surfaced roadways, regardless of the section thickness or subgrade
preparation measures, will require on -going maintenance and repairs to keep them in a
serviceable condition. It is not practical to design a gravel section of suff icient thickness that on-
going maintenance will not be required. This is due to the porous nature of the gravel that will
allow precipitation and surface water to infiltrate and soften the subgrade soils, and the limited
near surface strength of unconfined gravel that makes it susceptible to rutting. When potholes,
ruts, depressions or yielding subgrades develop they must be addressed as soon as possible in
order to avoid major repairs. Failure to make timely repairs will result in more rapid deterioratio n
of the roadways, making more extensive repairs necessary.
The roadways should be carefully reevaluated at the time of the use by heavy equipment or critical
component delivery for signs of disturbance or excessive rutting. Roadway reevaluation should
include proof rolling immediately prior to use by heavy or critical equipment, particularly after a
rainfall event. If disturbance and/or excessive wetting have occurred, roadway areas should be
reworked, moisture conditioned (if necessary), and properly co mpacted as indicated in this report.
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GENERAL COMMENTS
Our analysis and opinions are based upon our understanding of the project, the geotechnical
conditions in the area, and the data obtained from our site exploration. Natural variations will occur
between exploration point locations or due to the modifying effec ts of construction or weather.
The nature and extent of such variations may not become evident unti l during or after construction.
Terracon should be retained as the Geotechnical Engineer, where not ed in this report, to provide
observation and testing services during pertinent construction phases. If variations appear, we
can provide further evaluation and supplemental recommendations. If variations are noted in the
absence of our observation and testing services on-site, we should be immediately notified so
that we can provide evaluation and supplemental recommendations.
Our Scope of Services does not include either specifically or by implication any environmental or
biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of
pollutants, hazardous materials or conditions. If the owner is concerned about the potential for
such contamination or pollution, other studies should be undertaken.
Our services and any correspondence or collaboration through this system are intended for the
sole benefit and exclusive use of our client for specific application to the project discussed and
are accomplished in accordance with generally accepted geotechnical engineering practices with
no third-party beneficiaries intended. Any third-party access to services or correspondence is
solely for information purposes to support the services provided by Terracon to our client.
Reliance upon the services and any work product is lim ited to our client, and is not intended for
third parties. Any use or reliance of the provided information by third parties is done solely at their
own risk. No warranties, either express or implied, are intended or made.
Site characteristics as provided are for design purposes and not to estimate excavation cost. Any
use of our report in that regard is done at the sole risk of the excavating cost estimator as there
may be variations on the site that are not apparent in the data that could significantly im pact
excavation cost. Any parties charged with estimating excavation costs should seek their own site
characterization for specific purposes to obtain the specific level of detail necessary for costing.
Site safety, and cost estimating including, excavation support, and dewatering
requirements/design are the responsibility of others. If changes in the nature, design, or location
of the project are planned, our conclusions and recommendations shall not be considered valid
unless we review the changes and either verify or modify our conclusions in writing.
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FIGURES
Contents:
GeoModel
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
ELEVATION (MSL) (feet)Holy Cross Solar Project - Peace Bear Ranch Site ■Silt, Colorado
February 9, 2021 ■ Terracon Project No. 25205263A
Layering shown on this figure has been developed by the
geotechnical engineer for purposes of modeling the subsurface
conditions as required for the subsequent geotechnical engineering
for this project.
Numbers adjacent to soil column indicate depth below ground
surface.
NOTES:
01 02 03 04 05 06 07 08 09 10
GEOMODEL
This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.
Model Layer General DescriptionLayer Name
Lean to silty clay; with varying amounts of sand; very stiff to
hard1
Interbedded claystone, shale, and sandstone bedrock; soft to
very hard2
LEGEND
Lean Clay with Sand
Claystone
Shale
Sandy Lean Clay
Sandstone
Lean Clay
Silty Clay with Sand
Native Clay
Wasatch Formation
1
2
1
20
1
2
2
20
1
2
1
20
1
2
2
15
1
2
2
8.5
1
2
2
20
1
2
2
20
1
2
5
15
1
2
1
15
1
2
5
20
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ATTACHMENTS
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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EXPLORATION AND TESTING PROCEDURES
Field Exploration
Number of Borings Boring Depth (feet) Planned Location
10 15 to 20 Planned solar array areas
Boring Layout and Elevations: Boring locations were developed by Terracon at the beginning
of the project. Coordinates were obtained with a handheld GPS unit (estimated horizontal
accuracy of about ±10 feet). Ground surface elevations were not determined in the field.
Subsurface Exploration Procedures: We advanced the borings with a truck-mounted CME-45
drill rig using continuous flight solid-stem augers. Three samples were obtained in the upper 10
feet of each boring and at intervals of 5 feet thereafter. Relatively undisturbed samples were
obtained at selected intervals utilizing a 2½-inch outside diameter modified California barrel
sampler. Bulk samples were obtained from auger cuttings. In the split-barrel sampling procedure,
a standard 2½-inch outer diameter split-barrel sampling spoon is driven into the ground by a
140-pound automatic hammer falling a distance of 30 inches. The number of blows required to
advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the
Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as
N-values, are indicated on the boring logs at the test depths. Ring-lined, split-barrel sampling
procedures are similar to standard split spoon sampling procedure; however, blow counts are
typically recorded for 6-inch intervals for a total of 12 inches of penetration. We did not encounter
groundwater in our borings during drilling and sampling. For safety purposes, all borings were
backfilled with auger cuttings after their completion.
The sampling depths, penetration distances, and other sampling information was recorded on the
field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory
for testing and classification by a Geotechnical Engineer. Our exploration team prepared field
boring logs as part of the drilling operations. These f ield logs included visual classifications of the
materials encountered during drilling and our interpretation of the subsurface conditions betw een
samples. Final boring logs we re prepared from the field logs. The f inal boring logs represent the
Geotechnical Engineer's interpretation of the field logs and include modifications based on
observations and tests of the samples in our laboratory.
Field Electrical Resistivity Testing: Terracon proposed to perform one electrical resistivity test
at the site. The field electrical resistivity test was conducted following the Wenner Four-Electrode
method (ASTM G57). The test was completed along two mutually perpendicular lines. The
Wenner arrangement (equal electrode spac ing) test was performed with the a -spacings of 1, 2,
5, 10, 20, 50 and 80 feet. Results can be found in the Exploration Results section.
DRAFT - Geotechnical Engineering Report
Holy Cross Solar Project – Peace Bear Ranch Site ■ Silt, Colorado
February 7, 2021 (Revised February 9, 2021) ■ Terracon Project No. 25205263A
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Laboratory Testing
The project engineer reviewed the field data and assigned la boratory tests to understand the
engineering properties of the various soil and rock strata, as necessary, for this project. Testing
included the following:
■ Visual classification
■ Moisture content
■ Dry unit weight
■ Atterberg limits
■ Grain size analysis
■ Swell/consolidation
■ Corrosion suite – water-soluble sulfate, water-soluble chloride, pH, “soil box” resistivity,
and oxidation-reduction potential
■ Modified Proctor test and thermal resistivity (rho) testing
■ Hveem Stabilometer (R-Value) testing
The laboratory testing program often included examination of soil samples by an engineer. B ased
on the material’s texture and plasticity, we described and classified the soil samples in accordance
with the Unified Soil Classification System.
Rock classification was conducted using locally accepted practices for engineering purposes .
Thermal Resistivity (RHO) Testing: We obtained a sample of the site soils and performed
laboratory thermal resistivity testing on one bulk soil sample (auger cuttings) from a depth
between 0 and 5 feet below existing site grades. Thermal resistivity testing was completed by
GeoTherm in general accordance with ASTM D5334 and IEEE standard 442 on the specimen
remolded to approximately 8 0 and 90 percent of the maximum dry unit weight as determined by
ASTM D1557 (Modified Proctor). Dry-out curves were generated for each sample from optimum
moisture down to zero moisture content with a minimum of three data points.
Responsive ■ Resourceful ■ Reliable
SITE LOCATION AND EXPLORATION PLANS
Contents:
Site Location Plan
Exploration Plan
Electrical Resistivity Location Plan
Exploration Plan with Aerial Image
Exploration Plan with Geologic Map Overlay
Note: All attachments are one page unless noted above.
SITE LOCATION PLAN
Holy Cross Solar Project - Peace Bear Ranch Site ■ Silt, Colorado
February 9, 2021 ■ Terracon Project No. 25205263A
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT
INTENDED FOR CONSTRUCTION PURPOSES TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY
QUADRANGLES INCLUDE: SILT, CO (1/1/1987) and HUNTER MESA, CO (1/1/1987).
SITE
EXPLORATION PLAN WITH AERIAL IMAGE
Holy Cross Solar Project - Peace Bear Ranch Site ■ Silt, Colorado
February 9, 2021 ■ Terracon Project No. 25205263A
AERIAL PHOTOGRAPHY PROVIDED BY
MICROSOFT BING MAPS DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT
INTENDED FOR CONSTRUCTION PURPOSES
ELECTRICAL RESISTIVITY LOCATION PLAN
Holy Cross Solar Project - Peace Bear Ranch Site ■ Silt, Colorado
February 9, 2021 ■ Terracon Project No. 25205263A
AERIAL PHOTOGRAPHY PROVIDED BY
MICROSOFT BING MAPS DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT
INTENDED FOR CONSTRUCTION PURPOSES
EXPLORATION PLAN WITH GEOLOGIC MAP OVERLAY
Holy Cross Solar Project - Peace Bear Ranch Site ■ Silt, Colorado
February 9, 2021 ■ Terracon Project No. 25205263A
AERIAL PHOTOGRAPHY PROVIDED BY
MICROSOFT BING MAPS DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT
INTENDED FOR CONSTRUCTION PURPOSES
Responsive ■ Resourceful ■ Reliable
EXPLORATION RESULTS
Contents:
General Notes
Unified Soil Classification System
Boring Logs (1 through 10)
Consolidation/Swell (4 pages)
Grain Size Distribution (3 pages)
Moisture Density Relationship (2 pages)
Thermal Resistivity (4 pages)
R-Value
Corrosivity
Summary of Lab Results
Field Electrical Resistivity
Note: All attachments are one page unless noted above.
Soft
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A
Soil Classification
Group
Symbol Group Name B
Coarse Grained Soils:
More than 50% retained
on No. 200 sieve
Gravels:
More than 50% of
coarse fraction retained
on No. 4 sieve
Clean Gravels:
Less than 5% fines C
Cu 4 and 1 Cc 3 E GW Well-graded gravel F
Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F
Gravels with Fines:
More than 12% fines C
Fines classify as ML or MH GM Silty gravel F,G,H
Fines classify as CL or CH GC Clayey gravel F,G,H
Sands:
50% or more of coarse
fraction passes No. 4
sieve
Clean Sands:
Less than 5% fines D
Cu 6 and 1 Cc 3 E SW Well-graded sand I
Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I
Sands with Fines:
More than 12% fines D
Fines classify as ML or MH SM Silty sand G,H,I
Fines classify as CL or CH SC Clayey sand G,H,I
Fine-Grained Soils:
50% or more passes the
No. 200 sieve
Silts and Clays:
Liquid limit less than 50
Inorganic: PI 7 and plots on or above “A” line J CL Lean clay K,L,M
PI 4 or plots below “A” line J ML Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OL Organic clay K,L,M,N
Liquid limit - not dried Organic silt K,L,M,O
Silts and Clays:
Liquid limit 50 or more
Inorganic: PI plots on or above “A” line CH Fat clay K,L,M
PI plots below “A” line MH Elastic Silt K,L,M
Organic: Liquid limit - oven dried 0.75 OH Organic clay K,L,M,P
Liquid limit - not dried Organic silt K,L,M,Q
Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-inch (75-mm) sieve
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded
gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded
sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay
E Cu = D60/D10 Cc =
6010
2
30
DxD
)(D
F If soil contains 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
H If fines are organic, add “with organic fines” to group name.
I If soil contains 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,”
whichever is predominant.
L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to
group name.
M If soil contains 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
N PI 4 and plots on or above “A” line.
O PI 4 or plots below “A” line.
P PI plots on or above “A” line.
Q PI plots below “A” line.
50/9"
19-20
50/3"
50/1"
50/2"
+3.4
@
500
psf
859.0
12.8
6.7
109
113
136
32-17-15
LEAN CLAY (CL), with sand, calcareous, light brown
CLAYSTONE, sandy, pink to orange, very hard
SHALE, gray to tan, very hard, thin bedding
CLAYSTONE, gray to yellow, very hard
Boring Terminated at 20 Feet
1.0
7.0
17.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5116° Longitude: -107.6710°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 1
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
17-25
15-17
50/1"
50/2"
50/2"
729.3
7.1
4.0
104
111
114
39-22-17
LEAN CLAY (CL), with sand, calcareous, light brown
CLAYSTONE, sandy, pink to orange, firm to medium hard
SHALE, light brown to gray, very hard, thin bedding
Boring Terminated at 20 Feet
2.0
8.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5107° Longitude: -107.6691°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 2
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
50/2"
50/4"
50/3"
50/2"
50/2"
538.7
3.6
5.2
104
110
25-17-8
SANDY LEAN CLAY (CL), calcareous, light brown
SANDSTONE, fine grained, light brown to white, very hard
SHALE, gray to light brown, very hard, thin bedding
CLAYSTONE, light brown to orange, very hard
Boring Terminated at 20 Feet
1.0
6.0
12.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5113° Longitude: -107.6661°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 3
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
14-18
12-13
50/2"
50/1"
897.0
4.8
4.4
114
117
118
33-17-16
LEAN CLAY (CL), calcareous, light brown
CLAYSTONE, orange to brown, firm
SANDSTONE, fine grained, light brown to orange, firm
SHALE, light brown to gray, very hard, thin bedding
Boring Terminated at 15 Feet
2.0
4.0
8.0
15.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5089° Longitude: -107.6713°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 4
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-03-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-03-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
16-22
19-29
50/0"
+9.7
@
500
psf
744.2
7.8
121
125
27-20-7
SILTY CLAY (CL-ML), with sand, calcareous, light brown
CLAYSTONE, gray to orange, medium hard
SANDSTONE, light brown to orange, very hard
Auger Refusal at 8.5 Feet
2.0
8.0
8.5
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5087° Longitude: -107.6667°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 5
CLIENT: HDR Engineering Inc
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
50/12"
17-24
50/7"
50/2"
50/2"
+12.8
@
500
psf
868.5
7.6
4.5
105
125
133
35-16-19
LEAN CLAY (CL), calcareous, light brown
CLAYSTONE, brown to orange, medium hard to hard
SHALE, light brown, very hard, thin bedding
Boring Terminated at 20 Feet
2.0
13.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5093° Longitude: -107.6631°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 6
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
20-22
6-11
50/7"
50/1"
50/1"
796.8
6.3
3.6
114
102
123
27-15-12
LEAN CLAY (CL), with sand, calcareous, brown to reddish brown
CLAYSTONE, sandy, gray to light brown, soft to hard
SHALE, varies to mudstone, light gray, very hard, thin bedding
Boring Terminated at 20 Feet
2.0
13.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5097° Longitude: -107.6609°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 7
CLIENT: HDR Engineering Inc
Driller: Unlimited
Boring Completed: 12-02-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
See Supporting Information for explanation of
symbols and abbreviations.
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-02-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
11-18
17-23
50/9"
50/7"
61
6.0
6.9
9.7
121
125
126
27-17-10
SANDY LEAN CLAY (CL), calcareous, light brown, very stiff to hard
CLAYSTONE, light brown to yellowish brown and gray, hard
Boring Terminated at 15 Feet
5.0
15.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5072° Longitude: -107.6642°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 8
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-03-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-03-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
50/10"
50/8"
50/3"
50/9"
5310.0
6.8
9.6
107
115
129
35-17-18
SANDY LEAN CLAY (CL), calcareous, pale brown
CLAYSTONE, sandy, light brown to tan, medium hard
SANDSTONE, fine grained, pale grayish brown, hard
CLAYSTONE, gray to purple, hard to very hard
Boring Terminated at 15 Feet
1.0
4.0
7.0
15.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5070° Longitude: -107.6660°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 9
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-03-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-03-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
17-22
10-16
21-25
50/6"
50/1"
+0.2
@
500
psf
877.0
8.0
6.7
114
108
123
31-20-11
LEAN CLAY (CL), calcareous, brown, very stiff to hard
CLAYSTONE, brown to orange and reddish brown to purple,
medium hard to very hard
SHALE, reddish brown, very hard, thin bedding
Boring Terminated at 20 Feet
5.0
17.0
20.0
Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 25205263A - DAVIS SITE.GPJ TERRACON_DATATEMPLATE.GDT 1/29/21WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSSWELL (%)PERCENT FINESWATERCONTENT (%)DRY UNITWEIGHT (pcf)ATTERBERG
LIMITS
LL-PL-PI
LOCATION See Exploration Plan
Latitude: 39.5054° Longitude: -107.6618°GRAPHIC LOGMODEL LAYERDEPTH
Page 1 of 1
Advancement Method:
4-inch solid stem continuous flight power auger
Abandonment Method:
Boring backfilled with soil cuttings upon completion.
Notes:
Project No.: 25205263A
Drill Rig: CME-45
BORING LOG NO. 10
CLIENT: HDR Engineering, Inc.
Driller: Unlimited
Boring Completed: 12-03-2020
PROJECT: Holy Cross Solar Project - Peace Bear Site
See Exploration and Testing Procedures for a
description of field and laboratory procedures used
and additional data (If any).
2714 County Road 331
Silt, Colorado
SITE:
Boring Started: 12-03-2020
10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
None encountered while drilling
WATER LEVEL OBSERVATIONS
1
2 SAMPLE TYPE
-15
-10
-5
0
5
10
15
100 1,000 10,000AXIAL STRAIN, %PRESSURE, psf
NOTES: Water was added at 500 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 25205263A
SITE: 2714 CR 331
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. TC_CONSOL_STRAIN-USCS-NO ASTM 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21 1 4 - 5 ft CLAYSTONE 113 12.8
Specimen Identification Classification , pcf WC, %
-15
-10
-5
0
5
10
15
100 1,000 10,000AXIAL STRAIN, %PRESSURE, psf
NOTES: Water was added at 500 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. TC_CONSOL_STRAIN-USCS-NO ASTM 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21 5 4 - 5 ft CLAYSTONE 125 7.8
Specimen Identification Classification , pcf WC, %
-15
-10
-5
0
5
10
15
100 1,000 10,000AXIAL STRAIN, %PRESSURE, psf
NOTES: Water was added at 500 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. TC_CONSOL_STRAIN-USCS-NO ASTM 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21 6 9 - 10 ft CLAYSTONE 133 4.5
Specimen Identification Classification , pcf WC, %
-15
-10
-5
0
5
10
15
100 1,000 10,000AXIAL STRAIN, %PRESSURE, psf
NOTES: Water was added at 500 psf.
SWELL CONSOLIDATION TEST
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. TC_CONSOL_STRAIN-USCS-NO ASTM 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/2110 LEAN CLAY (CL)4 - 5 ft 108 8.0
Specimen Identification Classification , pcf WC, %
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
2006810142
GRAIN SIZE IN MILLIMETERSPERCENT FINER BY WEIGHTASTM D422 / ASTM C136
46 16 20 30 40
GRAIN SIZE DISTRIBUTION
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
4 1 3/4 1/2 60
HYDROMETER
3/8 3 100 1403501.5
A-6 (12)
A-6 (11)
A-4 (1)
A-6 (13)
LEAN CLAY with SAND (CL)
LEAN CLAY with SAND (CL)
SANDY LEAN CLAY (CL)
LEAN CLAY (CL)
1
2
3
4
1
2
3
4
Boring ID Depth D100 D60 D30 D10
Boring ID Depth USCS Classification AASHTO Classification LL PL PI
%Gravel %Sand %Silt
mediumcoarsecoarsefine fineCOBBLESGRAVELSAND SILT OR CLAY
%Fines %Clay
WC (%)
2
4.75
9.5
2
84.6
71.6
53.2
88.7
0.12
0.0
0.0
1.2
0.0
15.4
28.4
45.6
11.3
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
15
17
8
16
17
22
17
17
32
39
25
33
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GRAIN SIZE: USCS & AASHTO DESC COMBINED 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21Cc Cu
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
2006810142
GRAIN SIZE IN MILLIMETERSPERCENT FINER BY WEIGHTASTM D422 / ASTM C136
46 16 20 30 40
GRAIN SIZE DISTRIBUTION
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
4 1 3/4 1/2 60
HYDROMETER
3/8 3 100 1403501.5
A-4 (3)
A-6 (15)
A-6 (7)
A-4 (4)
SILTY CLAY with SAND (CL-ML)
LEAN CLAY (CL)
LEAN CLAY with SAND (CL)
SANDY LEAN CLAY (CL)
5
6
7
8
5
6
7
8
Boring ID Depth D100 D60 D30 D10
Boring ID Depth USCS Classification AASHTO Classification LL PL PI
%Gravel %Sand %Silt
mediumcoarsecoarsefine fineCOBBLESGRAVELSAND SILT OR CLAY
%Fines %Clay
WC (%)
4.75
9.5
4.75
9.5
73.9
86.1
78.9
60.8
0.0
0.2
0.0
0.2
26.1
13.7
21.1
39.0
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
0 - 5
7
19
12
10
20
16
15
17
27
35
27
27
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GRAIN SIZE: USCS & AASHTO DESC COMBINED 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21Cc Cu
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
2006810142
GRAIN SIZE IN MILLIMETERSPERCENT FINER BY WEIGHTASTM D422 / ASTM C136
46 16 20 30 40
GRAIN SIZE DISTRIBUTION
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
4 1 3/4 1/2 60
HYDROMETER
3/8 3 100 1403501.5
A-6 (6)
A-6 (9)
SANDY LEAN CLAY (CL)
LEAN CLAY (CL)
9
10
9
10
Boring ID Depth D100 D60 D30 D10
Boring ID Depth USCS Classification AASHTO Classification LL PL PI
%Gravel %Sand %Silt
mediumcoarsecoarsefine fineCOBBLESGRAVELSAND SILT OR CLAY
%Fines %Clay
WC (%)
12.5
4.75
53.0
87.0
0.111 8.0
0.0
39.0
13.0
0 - 5
0 - 5
0 - 5
0 - 5
18
11
17
20
35
31
PROJECT NUMBER: 25205263A
SITE:
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GRAIN SIZE: USCS & AASHTO DESC COMBINED 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21Cc Cu
75
80
85
90
95
100
105
110
115
120
125
130
135
0 5 10 15 20 25 30 35 40 45DRY DENSITY, pcfWATER CONTENT, %
Z
A
V
f
o
r
G
s =
2
.
8
Z
A
V
f
o
r
G
s =
2
.
7
Z
A
V
f
o
r
G
s =
2
.
6
MOISTURE-DENSITY RELATIONSHIP
ASTM D698/D1557
PROJECT: Holy Cross Solar Project - Peace Bear PROJECT NUMBER: 25205263A
Site
SITE: 2714 CR 331
Silt, Colorado CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. COMPACTION - V2 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21ASTM D698 Method A
Source of Material 6 @ 0 - 5 feet
Description of Material
Remarks:
Test Method
PCF
%
TEST RESULTS
LEAN CLAY(CL)
Maximum Dry Density
%
35
LL
107.4
86.1
Optimum Water Content
PIPL
16 19
ATTERBERG LIMITS
17.2
Percent Fines
75
80
85
90
95
100
105
110
115
120
125
130
135
0 5 10 15 20 25 30 35 40 45DRY DENSITY, pcfWATER CONTENT, %
Z
A
V
f
o
r
G
s =
2
.
8
Z
A
V
f
o
r
G
s =
2
.
7
Z
A
V
f
o
r
G
s =
2
.
6
MOISTURE-DENSITY RELATIONSHIP
ASTM D698/D1557
SITE: 2714 CR 331
Silt, Colorado
PROJECT: Holy Cross Solar Project - Peace Bear PROJECT NUMBER: 25205263A
Site
CLIENT: HDR Engineering Inc10625 W I70 Frontage Rd N Ste 3
Wheat Ridge, CO
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. COMPACTION - V2 25205263A - DAVIS SITE.GPJ 02195238 US 50 AND CHIPMAN.GPJ 1/26/21ASTM D1557 Method B
Source of Material 9 @ 0 - 5 feet
Description of Material
Remarks:
Test Method
PCF
%
TEST RESULTS
SANDY LEAN CLAY(CL)
Maximum Dry Density
%
35
LL
121.3
53.0
Optimum Water Content
PIPL
17 18
ATTERBERG LIMITS
12.2
Percent Fines
COOL SOLUTIONS FOR UNDERGROUND POWER CABLES
THERMAL SURVEYS, CORRECTIVE BACKFILLS & INSTRUMENTATION
Serving the electric power industry since 1978
21239 FM529 Rd., Bldg. F
Cypre ss, T X 77433
Tel: 281-985-9344
Fax: 832 -427-1752
i nfo@geothermusa.com
http://www.geothermusa.com
January 25, 2021
Terracon Consultants , Inc
10625 W. I -70 Frontage Rd N, Ste 3
Wheat Ridge, CO 80033
Attn: John T. Taylor
Re: Thermal Analysis of Native Soil Sample
Holy Cross Solar - Peace Bear Ranch Site – Parachute, CO (Project No. 25205263A)
The followin g is the repo rt of thermal dryou t char a cterization tests conducted on one (1)
bulk sample of native soil from the referenced project sent to our laboratory .
Thermal Resistivity Tests: The sample w as test ed at the ‘optimum ’ moisture content
and at 80% of the maximum d ry den sit y p rovided by Terraco n. The tests were
conducted in accordance with the IEEE standard 442 -2017 . The results are tabulated
below and the thermal dryout curve is presented in Figure 1.
Sample ID, Description, Thermal Resistivity, Mo isture Conte nt a nd Densi ty
Sample
I D
Effort
(%) 1
Depth
(ft)
Description
(Terracon )
Thermal Resistivity
(°C-cm/W) Moisture
Content
(%)
Dry
Density
(lb/ft 3 ) Wet Dry
B -9 80 0 ’-5 ' Sandy Lean
Clay (CL) 75 158 12 97
Plea se contact us if you have an y questi ons or if we can be o f furt h e r a ss is ta n ce.
Geotherm USA
Deepak Parmar
1. Based on ASTM 1557
2
Silt, CO
COOL SOLUTIONS FOR UNDERGROUND POWER CABLES
THERMAL SURVEYS, CORRECTIVE BACKFILLS & INSTRUMENTATION
Serving the electric power industry since 1978
21239 FM529 Rd., Bldg. F
Cypre ss, T X 77433
Tel: 281-985-9344
Fax: 832 -427-1752
i nfo@geothermusa.com
http://www.geothermusa.com
January 20, 2021
Terracon Consultants , Inc
10625 W. I -70 Frontage Rd N, Ste 3
Wheat Ridge, CO 80033
Attn: John T. Taylor
Re: Thermal Analysis of Native Soil Sample
Holy Cross Solar - Peace Bear Ranch Site – Parachute, CO (Project No. 25205263A)
The followin g is the repo rt of thermal dryou t char a cterization tests conducted on one (1)
bulk sample of native soil from the referenced project sent to our laboratory .
Thermal Resistivity Tests: The sample w as test ed at the ‘optimum ’ moisture content
and at 90% of the maximum d ry den sit y p rovided by Terraco n. The tests were
conducted in accordance with the IEEE standard 442 -2017 . The results are tabulated
below and the thermal dryout curve is presented in Figure 1.
Sample ID, Description, Thermal Resistivity, Mo isture Conte nt a nd Densi ty
Sample
I D
Effort
(%) 1
Depth
(ft)
Description
(Terracon )
Thermal Resistivity
(°C-cm/W) Moisture
Content
(%)
Dry
Density
(lb/ft 3 ) Wet Dry
B -9 90 0 ’-5 ' Sandy Lean
Clay (CL) 67 1 3 2 12 109
Plea se contact us if you have an y questi ons or if we can be o f furt h e r a ss is ta n ce.
Geotherm USA
Deepak Parmar
1. Based on ASTM 1557
2
Silt, CO