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GEOTECHNICAL INVESTIGATION
WOLF RANCH COMPRESSOR STATION
GARFIELD COUNTY, COLORADO
June 17, 2013
Prepared For:
Ms. Stephanie Meany
Hunter Ridge Energy Services, LLC
143 Diamond Avenue
Parachute, CO 81635
Prepared By:
Yeh and Associates, Inc.
1525 Blake Avenue
Glenwood Springs, CO 81601
Phone (970) 384-1500
Fax (970) 384-1501
Project No. 213-087
Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
TABLE OF CONTENTS
1.0 PROJECT INFORMATION 1
1.1 Purpose and Scope 1
1.2 Proposed Construction 1
1.3 Site Conditions 1
1.4 Site Geology 2
2.0 SITE INVESTIGATION 2
2.1 Subsurface Investigation 2
2.2 Subsurface Conditions 3
2.2.1 Groundwater 4
2.3 Site Grading 4
3.0 SETTLEMENT 4
4.0 FOUNDATION RECOMMENDATIONS 5
4.1 Footing Foundations 5
4.2 Mat Foundations 6
5.0 SEISMIC CONSIDERATIONS 6
6.0 CONCRETE AND CORROSIVITY 7
7.0 LIMITATIONS 7
UST OF TABLES
Table 1 — Structure/Test Hole Designations 2
Table 2 — Estimated Settlement 4
Table 2 — Seismic Design Parameters 6
Table 2 — Seismic Design Parameters for Site Class C 6
LIST OF FIGURES
Figure 1 -- Approximate Site Location
Figure 2 -- Approximate Test Hole Locations
Figure 3 — Drill Logs
Figure 4 -- Drill Log Legend
Summary of Laboratory Test Results
IA
Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
1.0 PROJECT INFORMATION
1.1 Purpose and Scope
This report presents the results of our geotechnical investigation for the proposed Wolf Ranch
Compressor Station in northern Garfield County, Colorado (Figure 1). The investigation was
performed to provide recommendations for foundation design and construction of a gas
processing facility at this site. The purpose of this study was to evaluate geotechnical
characteristics of the on-site soils and bedrock and provide geotechnical recommendations for
the proposed construction.
The site investigation consisted of geologic reconnaissance and exploratory test hole drilling to
investigate subsurface conditions. Test hole drilling was observed by a representative of Yeh
and Associates. Samples obtained during the field exploration were examined by the project
personnel and representative samples were subjected to laboratory testing to determine the
engineering characteristics of materials encountered. This report summarizes our field
investigation, the results of our analyses, and our conclusions and recommendations based on
the proposed construction, site reconnaissance, subsurface investigation, and results of the
laboratory testing.
1.2 Proposed Construction
We understand the proposed construction will consist of multiple structures related to natural
gas production. The proposed structures will Include but are not limited to a shop building, an
MCC building, slug catcher, glycol regeneration unit pad, compressors, pig launchers, discharge
meters, inlet filters, fuel gas skid, glycol contactors and dehydration filter pad and a future amine
plant. The structures will likely be supported on prefabricated steel bases supported by
concrete pad foundations or footings. From site plans dated May 14, 2013, provided by the
client, plans indicate cuts of up to 10 feet and fills of up to 22 feet will be necessary to achieve
an average finish pad elevation of approximately 8136 feet. Proposed cut and fill slopes will be
constructed at slopes of 3H:1 V.
1.3 Site Conditions
The proposed Wolf Ranch Compressor Station was approximately 22 road miles north and west
of Parachute, Colorado (Figure 1) and was located on the Roan Plateau in the northern
Piceance Basin of western Colorado, a major gas production area made up of high plateaus,
mesas, ridges and deep valleys. The proposed site was located on a north -south trending ridge
with the high point as a knob at an approximate elevation of 8149 feet. The site sloped down to
1 '�
Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
the north, west and south with moderate to strong slopes at grades of between 10 and 12
percent. The east face consisted of moderate to steep slopes at grades of between 27 and 39
percent. The site was accessed off Garfield County Road 403, approximately 1 mile north of
the "turkey track" intersection with County Road 401, north of the existing L24 496 compressor
and south of the existing Conoco/Phillips man camp. An existing two -track road was situated at
the south-southwest portion of the site. Existing vegetation included sage, scrub oak and other
natural brush and grasses.
1.4 Site Geology
The project site was located in the Piceance Basin of western Colorado, a structural basin that
is a major gas production area. The asymmetrical, arc -shaped basin is 100 miles long by 50
miles wide, is oriented northwest -southeast, and is deepest an the east edge. It is bounded
structurally on the northeast by the Axial Uplift, on the east by the White River Uplift/Grand
Hogback and the Elk Mountains, on the south by the Uncompahgre Uplift and on the west by
the Douglas Creek Arch.
Exposed in the project area was Tertiary age sedimentary rocks including the slopes and ledges
of light brown and gray siltstone and sandstone and slopes of siltstone and claystone of Unit D
of the Uinta Formation. The surficial deposits included alluvium and residuum of the erosional
surface of the Uinta Formation which included clay, silt, sand and gravel.
2.0 SITE INVESTIGATION
2.1 Subsurface Investigation
Eight test holes were drilled on May 23, 2013. Table 1 provides the structure investigated with
respect to the test hole location. Test hole locations were specified by Yeh and Associates and
were located using a hand held GPS. Location accuracy is only within the limits of the
methods/instrument used,
Table 1 -- Structure/Test Hole Designations
_ _ "Strudtuce _ _
Test Hole Designation
Shop Building
TH-1
MCC Building
TH-2
Inlet Slug catcher
TH-3
Glycol Regeneration Pad
TH-4
Compressors
TH-5, TH-6 and TH-7
Future Amine Plant
TH-8
2
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Wolf Ranch Compressor Station
Garfield County, Colorado Project No, 213-087
The locations of the test holes are presented in Figure 2. All test holes were advanced with a
CME 55 rubber track rig using 4 -inch continuous flight auger to pre -determined depths where a
modified California or split -spoon sampler was used to record blow counts and obtain samples.
Bulk samples were also obtained at depths indicated on test hole logs presented on Figure 3.
To perform the modified California penetration resistance tests, a 2.0 -inch inside diameter
sampler was seated at the bottom of the test hole, then driven up to 12 inches with blows of a
standard hammer weighing 140 pounds and falling a distance of 30 inches utilizing a "auto"
hammer (ASTM D1586). The number of blows (Blow Count) required to drive the sampler 12
inches or a fraction thereof, constitutes the N -value. The N -value, when properly evaluated, is
an index of the consistency or relative density of the material tested. Test hole logs and legend
are presented on Figures 3 and 4.
2.2 Subsurface Conditions
Subsurface conditions generally consisted of occasional topsoil aver silty and clayey sand
underlain by weathered to comparatively unweathered shale and/or sandstone bedrock.
Differentiation between the topsoil and natural silty and clayey sand was difficult and therefore,
where encountered topsoil depths were approximated. Hard to very hard shale and/or
sandstone bedrock was encountered in all test holes at depths of between 0.5 and 3.5 feet from
existing grades. The bedrock was occasionally cemented and silty. Practical drill rig refusal
was encountered in all test holes except TH-6 and TH-7.
Three shale bedrock samples tested had 65 to 76 percent fines (material passing the No. 200
sieve). Atterberg limit testing on these same samples indicated liquid limits of 37 to 41 percent
and plastic indices of 16 to 23 percent. Two sandstone samples tested had 11 and 42 percent
fines and both samples were non -liquid and non -plastic. One sandstone sample had an
unconfined compressive strength of 9950 psf.
Results of the laboratory testing are summarized in the Summary of Laboratory Test Results.
Chemical testing was also performed, and the results are presented under section 6.0.
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Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
2.2.1 Groundwater
Groundwater was not encountered during drilling. Delayed groundwater levels were not
possible. Variations in groundwater conditions may occur seasonally. The magnitude of the
variation will be largely dependent upon the amount of spring snowmelt, duration and intensity
of precipitation, site grading changes, and the surface and subsurface drainage characteristics
of the surrounding area.
2.3 Site Grading
Cuts of up to 10 feet and fills of up to 22 feet are planned for the proposed construction. Based
on drilling and aur observations, we believe that material can be excavated by conventional
construction equipment; however, hard to very hard shale and/or sandstone bedrock,
occasionally cemented, may need to be excavated by means of heavy ripping and/or blasting.
We believe that proposed fill and cut slopes of 2H:1 V or flatter, are appropriate for the soil
conditions at the site.
The on-site cut soils can be used in site grading fills provided the material is substantially free of
organic material, debris and particles are no larger than 6 inches. Areas to receive fill should be
stripped of vegetation, organic soils and debris. Topsoil is not recommended for fill material.
Fill should be placed in thin, loose lifts of 8 inches thick or less. We recommend fill materials be
moisture conditioned to within 2 percent of optimum moisture content and compacted to at least
95 percent of maximum standard Proctor dry density (ASTM D 698). Placement and
compaction of fill should be observed and tested by a representative of the geotechnical
engineer.
3.0 SETTLEMENT
We believe that improvements placed in areas where transitions from cut to fill or large
variations in fill depths occur could result in differential settlement of structures or flatwork.
Based on review of the grading plans, we believe improvements that could be affected would be
the west portion of the future Amine Plant. We believe movements in the compressor area
would be within tolerable limits. Provided the fill is placed according to the specifications above,
we would estimate differential and total movements as indicated the table below. Movement
tolerances should be determined by the structural engineer. Total and differential movements
cannot be eliminated. In order to decrease differential and total movements, if desired, several
alternatives could be utilized. Further discussion and recommendations for alternatives can be
4 IA
Wolf Ranch Compressor Station
Garfield County, Colorado
Project No. 213-087
provided, if needed. The table below provides anticipated differential and total movement for
selected areas, equipment and or structures constructed in cut/fill, fill and cut areas.
Table 2 -- Estimated Settlement
ArealE ui mentlS#ruc# lre
Q p
Estirnate'd Total
.Settlement ,
Estimated; Differential.
Settlement
Future Amine Plant
Approximately 1 -inch
Less than 1 -inch
All other areas, equipment
and structures
1 -inch or less
Less than 1 -inch
4.0 FOUNDATION RECOMMENDATIONS
We believe that the site is favorable for proposed construction. We believe all structures and
equipment can be supported by a footing, pad or mat foundations placed on natural soils,
bedrock, or controlled fill. We believe that consolidation of the controlled fill would be low and
therefore, a low risk of associated foundation movement as discussed in section 3.0 above.
Foundation recommendations for structures supported by natural soils, bedrock or controlled fill
are presented below.
4A Footing Foundations
Foundations should be constructed on undisturbed, natural soils, bedrock or controlled fill.
Loose, disturbed soils encountered at foundation level should be removed and the foundation
should be extended to natural soils, bedrock or undisturbed controlled fill. We recommend fill
be placed in accordance with the specifications presented in section 2.3. Placement and
compaction of fill should be observed and tested by a representative of a geotechnical engineer.
1. Foundations can be designed for a maximum allowable soil pressure of 3,000 psf.
2. Resistance to sliding at the bottom of the mat foundation can be calculated based on a
coefficient of friction of 0.35. Passive pressure against the side of the footing can also
be considered for the sliding resistance if it is properly compacted. Passive pressure
can be estimated based on an equivalent fluid density of 350 pcf for a level backfill.
3. The soils below foundations should be protected from freezing. We recommend the
bottom of foundations be constructed at least 3.5 feet below finished exterior grade or as
required by local municipal code.
4. All foundation excavations should be observed by a representative of the geotechnical
engineer prior to placement of concrete.
5
FA
Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
4.2 Mat Foundations
Foundations should be constructed on undisturbed, natural soils, bedrock or controlled fill.
Loose, disturbed soils encountered at foundation level should be removed and the foundation
should be extended to natural soils, bedrock or undisturbed controlled fill. We recommend fill
be placed in accordance with the specifications presented in section 2.3. Placement and
compaction of fill should be observed and tested by a representative of a geotechnical engineer.
1. Mat foundations placed on the undisturbed natural soils, bedrock and/or controlled fill
can be designed for a maximum allowable soil pressure of 3,000 psf or vertical subgrade
modulus of 250 psi times the correction factor, CF. The correction factor is based on the
mat width and is determined by the equation: cF1/ ((B+1)/2B)'2.
2. Mat foundations can be designed for dynamic loading using a shear modulus (G) of
10,000 psi and a Poisson's ratio (p) of 0.25.
3. The soils below foundations should be protected from freezing. We recommend the
bottom of foundations be constructed at least 3.5 feet below finished exterior grade or as
required by local municipal code.
4. All foundation excavations should be observed by a representative of the geotechnical
engineer prior to placement of concrete.
5.0 SEISMIC CONSIDERATIONS
The project is located at approximate latitude 39.692 and longitude -108.122. The site is
classified as Site Class C. The Peak Ground Acceleration (PGA), and the short- and long -
period spectral acceleration coefficients (SS and S1 respectively) for the site were obtained
using the USGS 2007 Seismic Parameters for an event with a 7% Probability of Exceedance
(PE) in 75 years and a Site Class B (reference site). An event with the above probability of
exceedance has a return period of about 1,000 years. The values were adjusted using Site
Factors for Site Class C in accordance with 2006 International Building Code, Table No.
1613.5.3 (1) and (2). The seismic parameters for this site are shown in the tables below.
Table 3 — Seismic Design Parameters
PGA (0.0 sec)
Ss (0 2 sec)
Si (1.0 sec)
0.084
0.171
0.041
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Wolf Ranch Compressor Station
Garfield County. Colorado
Project No. 213-087
Table 4 — Seismic Design Parameters far Site Class C
As (0.0 sec)
SDs (0.2 sec)
SDI (1'°!9c
Seismic
eis c
0.100 g
0.205 g
0.070 g
1
6.0 CONCRETE AND CORROSIVITY
The concentration of water-soluble sulfate measured in the laboratory on selected samples was
between 0.014 and 0.028 percent. This concentration of water-soluble sulfate represents a
negligible/low (Class 0 exposure) degree of sulfate attack on concrete exposed to this material.
The degree of attack is based on a range of 0.00 to less than 0.10 percent as presented in the
American Concrete Institute Guide to Durable Concrete. Due to the negligible/low degree
indicated by the test results, no special requirements for concrete are necessary for Class 0
exposure.
The pH and electrical resistivity was also determined for the same selected samples. Test
results measured pH values of between 8.0 and 8.2, considered slightly basic. The resistivity
measurement was between 1316 and 1379 ohm -centimeters and the water-soluble chloride
was between 0.0008 and 0.0009 percent. See the Summary of Laboratory Test Results. A
qualified corrosion engineer should review this data to determine the appropriate level of
corrosion protection.
7.0 LIMITATIONS
This study was conducted in accordance with generally accepted geotechnical engineering
practices in this area for use by the client for design purposes. The conclusions and
recommendations submitted in this report are based upon the data obtained from exploratory
test holes, field reconnaissance and anticipated construction. The nature and extent of
subsurface variations across the site may not become evident until excavation is performed. If
during construction, conditions appear to be different from those described herein; this office
should be advised at once so reevaluation of the recommendations may be made. We
recommend on-site observation of excavations by a representative of the geotechnical
engineer.
7
IA
Wolf Ranch Compressor Station
Garfield County, Colorado Project No. 213-087
The scope of services for this project did not include, specifically or by implication, any
environmental or biological (e.g., mold, fungi, and bacteria) assessment of the site or
identification or prevention of pollutants, hazardous materials or conditions or biological
conditions. If the owner is concerned about the potential for such contamination, conditions or
pollution, other studies should be undertaken.
The report was prepared in substantial accordance with the generally accepted standards of
practice for geotechnical engineering as exist in the site area at the time of our investigation.
No warranties, express or implied, are Intended or made,
Respectfully Submitted:
YEH AND ASSOCIATES, INC.
Keith E. Asay
Staff Engineer
8
Reviewed by:
Richard D. Johnson, P.E.
Project Manager
IA
Yeh and Associates, Inc.
Consulting Engineers & Scientists
DRAWN BYE SM
DATE. 6/10/2013
CHECKED BY: RDJ
DATE: 6/10/2013
DESIGNED FOR.
Hunter Ridge Energy Services, LLC
PRCIJECT:
Wolf Ranch Compressor Station
FIGURE
PROJECT
NUMBER: 213-007
SCALE
NORIZ. NOT TU SCALE VERT: NOT IU SCALE
Approximate
Site Location
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11111111II11
TH-1 Approximate test hole locations
-41
NOTE:
1- Test holes were located by Yeh &
Associates, Inc. based on field stake and
ptans provided by Hunter Ridge Energy
Services, LLC.
2. Drawing based on plan set dated May
14, 2013, provided by Hunter Ridge
Energy Services, LLC.
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Yeh and Associates, Inc.
Consulting Engineers 8c Scientists
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Wolf Ranch Compressor Station
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FENCES 13Y ELEVATION • A SITE 213-067 BORING LOGS.GPJ RDJ.GDT 6/17113
8.145
8,140
8,135
8,130
F
c 8,125
0
8,115
8,110
8.105
8,100
TH-3
TH-4
Elevation: 8147.5 ft
Eevabcn 8145.5 ft
TH-2
ElevaNan: 8138.0 ft
Elevation: 8148.5 ft
5015
Son
50/0
TH-5
Elevation: 8140.5 lt
50/4
50/1
TH-6
Elevation: 8142.0 ft
50/1
x
5011
al 50/4
TH-7
Elevation: 8141.0 ft
50!12
50/3
502.5
TH-B
Elevation: 8141.5 ft
8.145
8,140
8,135
8,130
8,125
8.120
8,115
8,110
8,105
8,100
NOTE: Dashed line indicates approximate proposed
pad elevation from plan set provided by client.
YEH AND ASSOCIATES, INC.
GEOTECHNICAL ENGINEERING CONSULTANTS
Wolf Ranch Compressor Station
Project Number. 213-087 Figure No. 3
IA
YEH AND ASSOCIATES, INC.
GEOTECHNICAL ENGINEERING CONSULTANTS
Project: Wolf Ranch Compressor Station
Project Number: 213-087
Legend for Symbols Used on Borehole Logs
Sample Types
Bulk sample was obtained from auger cuttings at the depths Indicated.
Modified California Sampler. The symbol 16/12 indicates that 16 blows from a 140 pound
hammer falling 30 inches was used to drive 2 -Inch 1.D. sampler 12 inches.
IISplit Spoon Sampler. The symbol 15112 indicates that 15 blows from a 140 pound hammer
falling 30 inches was used to drive 1.5 -inch I.D. sampler 12 inches.
Other Symbols
tIndicates practical drill rig refusal.
Indicates approximate elevation of proposed pad from plans provided by client.
Soil Lithology
Topsoil, brown, dark brown.
SAND, clayey, slightly moist, medium dense, brown (SC).
SAND, silty to gravelly, slightly moist, medium dense to very
dense, brown (SM).
Bedrock Lithology
Weathered Sandstone Bedrock, medium hard, slightly moist, white, light brown, rust.
SANDSTONE Bedrock, occasionally cemented, hard to very hard, slightly moist, white, light
brown, rust.
SHALE Bedrock, cemented, hard to very hard, slightly moist, white, light brown, rust.
NOTES:
1. Test holes were drilled on May 23, 2013 with 4 -inch continuous flight auger.
2. Groundwater was not encountered.
3. Test hole descriptions are subject to explanations contained in this report.
4. Elevations were estimated from topography by others.
Figure 4
YEH & ASS4_;IATES, INC
Project No:
Summary of Laboratory Test Results
213-087 Project Name: Wolf Ranch Compressor Station
Sample Location
Moisture
Content
(%)
Dry Density
(pcf)
Grain Size Analysis
Atte berg Limits
Water
Soluble
Sulfate
CA)
Water
Soluble
Chloride
(%)
Resistivity
(ohm -cm)
4
pH
Unconfined
Compressive
Strength
l1ps9
Soil Description
Test Hole
Depth (ft)Type
Sample
Gravel
> #4
(%)
Sand
(%)<
Fines
#200
(%)
LL
PL
PI
TH-1
10 to 14
4
Bulk
CA
13.7
13.6
107
73
42
40
NL
17 [23
NP NP
9946
SHALE Bedrock
SANDSTONE Bedrock, silty
TH-2
TH-3
9 to 13
Bulk
12.5
76
41
18 23
.
SHALE Bedrock
TH-4
4 to 9
Bulk
-f
0.028
0.0008
1379
8.2
SANDSTONE Bedrock
TH-5
-'
4 CA
0.014
0.0009
1316
8.0
SANDSTONE Bedrock
-
TH-7
4 CA
14.9
11
NL
NP NP
SANDSTONE Bedrock
TH-8
5 to 9 Bulk
12.5
65
37
21 16
SHALE Bedrock
1
--;
r—
CA - Indicates Modified California Sampler
NL - Indicates non -liquid
NP - Indicates non -plastic
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