HomeMy WebLinkAboutSubsoils ReportTEST HOLE P-1
GROUND
PAGE 1
OF 1
ENGINEERING
PROJECT: Rifle Airport - Fuel Farm
JOB NO: 25-6000
CLIENT: Vantage Aviation LLC
SITE LOCATION: Rifle CO
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ROAD BASE:Approximately 4 inches of aggregate
base course.
FILL: Clays and silts with varying fractions of sand.
They were moist, slightly plastic, stiff to hard, and
brown in color.
CLAYS and SANDS: Silty to sandy clays with local
clayey to silty sands. The granular fractions consisted
of fine sands with scattered medium to coarse sands
and gravels. Claystone and siltstone fragments and
5 clasts were also noted locally within these soils. They
were moist to wet, slighlly to moderately plastic, stiff to
hard, and brown to gray -brown in color. Iron staining
was doted commonly. Secondary carbonates and iron
staining were encountered locally.
Bottom of test hole at approx. 7 feet
14/12
" 15/12 1 14 1 117.8 1 0 1 29 1 71 1 27 1 9 1 -0.4 (600) 1 (CL)s
TEST HOLE 2
PAGE 1 OF 1
GROUND
ENGINEERING
PROJECT: Rifle Airport -Fuel Farm JOB NO: 25-6000
CLIENT: Vantage Aviation LLC SITE LOCATION: Rifle, CO
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ROAD BASE:Approximately 3 inches of aggregate
base course.
FILL: Clays and silts with varying fractions of sand.
They were moist, slightly plastic, stiff to hard, and
brown in color.
CLAYS and SANDS: Silty to sandy clays with local
clayey to silty sands. The granular fractions consisted
of fine sands with scattered medium to coarse sands
and gravels. Claystone and siltstone fragments and
14/12
13.9
112.2
0
17
83
25
8
-0.6 (500)
(CL)s
95
5
clasts were also noted locally within these soils. They
were moist to wet, slightly to moderately plastic, stiff to
hard, and brown to gray -brown in color. Iron staining
was noted commonly. Secondary carbonates and iron
staining were encountered locally.
Fuel like odor noted at 9 feet.
9/12
15.3
112.1
0
22
F78
23
9
(CL)s
90
10
85
15
11/12
80
20
18/12
75
25
17/12
Bottom of test hole at approx. 25 feet.
TEST HOLE 1
PAGE 1 OF 1
ENGINEERING
PROJECT: Rifle Airport -Fuel Farm
CLIENT: Vantaae Aviation. LLC
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10
20
ASPHALT: Approximately 5 inches of asphalt.
ROAD BASE:Approximately 7 inches of aggregate
base course.
FILL: Clays and silts with varying fractions of sand.
They were moist, slightly plastic, stiff to hard, and
brown in color.
CLAYS and SANDS: Silty to sandy clays with local
clayey to silty sands. The granular fractions consisted
of fine sands with scattered medium to coarse sands
and gravels. Claystone and siltstone fragments and
clasts were also noted locally within these soils. They
were moist to wet, slightly to moderately plastic, stiff to
hard, and brown to gray -brown in color. Iron staining
was noted commonly. Secondary carbonates and iron
staining were encountered locally.
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JOB NO: 25-6000
SITE LOCATION: Rifle CO
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39/12 1 16.1 1 107.41 0 1 12 1 88 1 26 1 6 1 -0.1 (250) 1 CL-ML
16/12 111.7 1 121.1 1 0 1 20 1 80 1 24 1 9 1 j (CL)s
19/12 114.9 1 118.7 1 0 1 18 1 82 , 25 1 10 I I (CL)s
17/12 110.9 1 123.2 1 8 1 30 1 62 1 22 1 8 1 1 s(CL)
15/12
Bottom of test hole at approx. 28 feet.
Appendix A
Detailed Logs of the Test Holes
angufra
ENGINEERING
Rifle Airport - Fuel Farm
TABLE 2: SUMMARY OF SOIL CORROSION TEST RESULTS
Sample Location
j Water-
Soluble
pH
Potential
of nti
Sulfide
Readlvity
Resistivity
USCS
Equivalent
AASHTO
Equivalent
Sample Description
Test
Depth
Hole
Sulfates
Classification
Classification
No.
(feet.)
!%)
(mvJ
(ohm -cm)
(Group Index
( P )
1
7
0.01
9.3
115
Positive
12.353
CL)s
A� (5)
CLAY with Sand
Job No 25-6000
ENGINEERING
Rifle Airport - Fuel Farm
TABLE 1: SUMMARY OF LABORATORY TEST RESULTS
Sample
Loca I Eon
Natural
Moisture
Content
(9�
Natural
Dry
DensityGravel
(pc�
Gradation
Atterbe Limits
SwolliCorsaildallon
USCS
Equivalent
Classification
AASHTO
Equivalent
Classiation
(GroufiIndex
(Group Index)
Sample Description
Test
Hale
No.
Depth
(feefJ
(%)
Sand
(%)
Fines
(%)
Liquid
Limit
Plasticity
Index
Volume
Change
g
(%J
Surcharge
Pressure
(psll
1
2
16,1
107.4
0
12
87.7
26
6
-0.1
250
CL-ML
A-4 (4)
FILL: Silty CLAY
1
7
11.7
121.1
0
21
79.5
24
9
-
(CL)s
A-4 (5)
CLAY with Sand
1
12
14.9
118.7
0
18
82.2
25
10
(CL)s
A-4 (6)
CLAY with Sand
1
22
10.9
123.2
8
30
61.8
22
8
s CL
A-4 2
Sandy CLAY
2
4
13.9
112.2
0
17
83.4
25
8
-0.6
500
(CL)s
A-4 (5)
CLAY with Sand
2
9
15.3
112.1
0
22
78.4
23
9
-(CL)s
A-4 4
CLAY with Sand
P1
6
1 14.0
117.E
0
29
71.4
27
9
-OA
600
[CL)s
A-d 4
CLAY with Sand
Job No. 25-6000
BROUND
ENGINEERING
100
90
80
70
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Rifle Airport - Fuel Farm
Gradation and Hydrometer (ASTM D422-63[2007])
US Standard Sieves Hydrometer
,�v_^ 9" ,14^ 1. 1Z^ v" W. a 6 10 16 20 30 40 5060 100 140 200
Job No: 25-6000
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D�hirlc Civc /mm1
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0.001
Coarse
Fine
Coarse Medium
Fine
Silt and Clay
u
GRAVELS
SANDS
FINES
Coarse Gradation
Fine Gradation
Hydrometer
Particle Size Passing by
(mm) Mass (%)
Grading
US Standard
Sieve
Particle Size
(mm)
Passing by
Mass (%)
US Standard
Sieve
Particle Size
(mm)
Passing by
Mass (%)
Coefficient
Value
6 in
150
-
No. 4
4.75
0.031
54
D90
0.134
5 in
125
-
No. 8
2.36
0.020
46
D85
0.104
4 in
100
-
No. 10
2.00
-
0.012
41
D80
0.081
3 in
75
i
No. 16
1.18
100
0.009
38
D60
0.039
2.5 in
63
No. 20
0.85
-
0.006
35
D50
0.025
2 in
50
No. 30
0.60
-
0.003
30
D40
0.011
1.5 in
37.5
No. 40
0.425
99
0.001
26
D30
0.003
1 in
25.0
No. 50
0.300
98
-
D15
-
3/4 in
19.0
No. 60
0.250
-
D10
1/2 in
12.5
No. 100
0.150
92
-
D05
3/8 in
9.5
No. 140
0.106
-
-
C
No.4
4.75
-
No.200
0.075
78•4
-
C�
"
Location: Test Hole 2 at 9 feet Classification: (CL)s / A-4 (4) Gravel (%): 0
Description: CLAY with Sand Liquid Limit: 23 Sand (%): 22
Plasticity Index: 9 Silt/Clay (%): 78.4
Activity: 0.3 < .002 mm (%): 28
Results apply only to the specific items and locations referenced and at the time of testing. For the hydrometer portion of the lest, a composite temperature correction and meniscus correction were applied
to each reading This report should not be reproduced, except in full, without the written permission of GROUND Engineering Consultants, Inc.
FIUGRE: 4
www.groundeng.com
Englewood, Commerce City, Loveland, Granby, Gypsum, Colorado Springs
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ENGINEERING
PROJECT: Rifle Airport - Fuel Farm_
CLIENT: Vantage Aviation, LLC_
MATERIAL SYMBOLS
■ ASPHALT
ROAD BASE
® FILL
CLAYS and SANDS
NOTE: See Detailed Logs for Material descriptions.
LEGEND AND NOTES
JOB NO: 25-6000
SITE LOCATION: Rifle, CO
SAMPLER SYMBOLS
eModified California Liner Sampler
23 / 12 Drive sample blow count indicates 23 blows of a
140 pound hammer falling 30 inches were required to drive
the sampler 12 inches.
NOTES
1. Test holes were drilled on 1/30/2025 with 4" solid stem auger.
2. Locations of the test holes were determined in the field using a hand
held GPS device by GROUND.
3. Elevations of the test holes were not measured and the logs of the test
holes are drawn to depth. Nominal elevation of 100 feet" indicates existing
ground level at the test hole at the time of drilling.
4. The test hole locations and elevations should be considered accurate
only to the degree implied by the method used.
5. The lines between materials shown on the test hole logs represent the
approximate boundaries between material types and the transitions may be
gradual.
1 6. Groundwater level readings shown on the logs were made at the time
and under the conditions indicated. Fluctuations in the water level may
occur with time.
7. The material descriptions on these logs are for general classification
purposes only. See full text of this report for descriptions of the site
materials & related information.
8. All test holes were immediately backfilled upon completion of drilling,
unless otherwise specified in this report.
ABBREVIATIONS
2 Water Level at Time of Drilling, or as Shown
NV No Value
1 Water Level at End of Drilling, or as Shown NP Non -Plastic
3 Water Level After 24 Hours, or as Shown
FIUGRE: 3
ENGINEERING
PROJECT: Rifle Airport - Fuel Farm
CLIENT: VBrtlageAviation LLC
1
ELEV. 100
841
LOGS OF THE TEST HOLES
JOB NO: 25-6000
SITE LOCATION: Rifle. CO
.. ........... 10
2 P-1
ELEV.100 ELEV.100
10
ianz
FIGURE: F
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,r FUEL FARM LEASE AREA EXHIBIT
Alf, a
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(71
2
Indicates test hole numbers and approximate
locations.
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GOOGLE EARTH AERIAL IMAGE (07/16/2023) I
SITE PLAN PROVIDED BY CLIENT
NOT TO SCALE
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
constitutes understanding and acceptance of the conclusions with regard to risk and other
information provided herein, associated improvement performance, as well as the
limitations inherent within such estimates.
Ensuring correct interpretation of the contents of this report by others is not the
responsibility of GROUND. If any information referred to herein is not well understood,
then Vantage Aviation, LLC, or other members of the design team, should contact the
author or a GROUND principal immediately. We will be available to meet to discuss the
risks and remedial approaches presented in this report, as well as other potential
approaches, upon request.
GROUND makes no warranties, either expressed or implied, as to the professional data,
opinions or conclusions contained herein. This document, together with the concepts and
conclusions presented herein, as an instrument of service, is intended only for the specific
purpose and client for which it was prepared. Reuse of, or improper reliance on this
document without written authorization and adaption by GROUND Engineering
Consultants, Inc., shall be without liability to GROUND Engineering Consultants, Inc.
GROUND appreciates the opportunity to complete this portion of the project and
welcomes the opportunity to provide Vantage Aviation, LLC with a proposal for
construction observation and materials testing.
Sincerely,
GROUND Engineering Consultants, Inc. R
I 'Q t. V- Ad
L'V
Ben Fellbaum, P.G., P.E. Reviewed by Brian H. Reck, P.G., C.E.G., P.E.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 48
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
in project plans or schedule should be brought to the attention of a geotechnical engineer,
in order that the geotechnical conclusions in this report may be reevaluated and, as
necessary, modified. If our described understanding/interpretation of the proposed
project is incorrect or project elements differ in any way from that expressed herein,
including changes to improvement locations, dimensions, orientations, loading
conditions, elevations/grades, etc., and/or additional buildings/structures/site
improvements are incorporated into this project, either after the original information
was provided to us or after the date of this report, GROUND or another geotechnical
engineer must be retained to reevaluate the conclusions and parameters presented
herein.
The geotechnical conclusions in this report relied upon subsurface exploration at a limited
number of exploration points, as shown in Figure 1, as well as the means and methods
described herein. Subsurface conditions were interpolated between and extrapolated
beyond these locations. It is not possible to guarantee the subsurface conditions are as
indicated in this report. Actual conditions exposed during construction may differ from
those encountered during site exploration. Design modifications may be necessary by the
project team; this may result in an increase in project costs and schedule delays.
If during construction, surface, soil, bedrock, or groundwater conditions appear to be at
variance with those described herein, a geotechnical engineer should be retained at once,
so that reevaluation of the conclusions for this site may be made in a timely manner. In
addition, a contractor who obtains information from this report for development of his
scope of work or cost estimates may find the geotechnical information in this report to be
inadequate for his purposes or find the geotechnical conditions described herein to be at
variance with his experience in the greater project area. The contractor is responsible for
obtaining the additional geotechnical information that is necessary to develop his
workscope and cost estimates with sufficient precision. This includes current depths to
groundwater, etc.
ALL DEVELOPMENT CONTAINS INHERENT RISKS. It is important that ALL aspects of
this report, as well as the estimated performance (and limitations with any such
estimations) of proposed improvements are understood by Vantage Aviation, LLC.
Utilizing these criteria and measures herein for planning, design, and/or construction
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 47
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
accumulate in the subsurface relatively easily, which can lead to increased settlement or
heave from factors unrelated to ice formation. Therefore, where a section of open graded
granular soils is placed, a local underdrain system should be provided to discharge
collected water. GROUND will be available to discuss these concerns upon request.
CLOSURE
Geotechnical Review The author of this report or a GROUND principal should be
retained to review project plans and specifications to evaluate whether they comply with
the intent of the measures discussed in this report. The review should be requested in
writing.
The geotechnical conclusions and parameters presented in this report are contingent upon
observation and testing of project earthworks by representatives of GROUND. If another
geotechnical consultant is selected to provide materials testing, then that consultant must
assume all responsibility for the geotechnical aspects of the project by concurring in writing
with the parameters in this report, or by providing alternative parameters.
Materials Testing Vantage Aviation, LLC or the owner should consider retaining a
geotechnical engineer to perform materials testing during construction. The performance
of such testing or lack thereof, however, in no way alleviates the burden of the contractor
or subcontractor from constructing in a manner that conforms to applicable project
documents and industry standards. The contractor or pertinent subcontractor is ultimately
responsible for managing the quality of his work; furthermore, testing by the geotechnical
engineer does not preclude the contractor from obtaining or providing whatever services
that he deems necessary to complete the project in accordance with applicable
documents.
Limitations This report has been prepared for Vantage Aviation, LLC as it pertains to
the design and construction of the proposed fuel farm as well as other related
improvements as described herein. It may not contain sufficient information for other
parties or other purposes.
In addition, GROUND has assumed that project construction will commence by spring
2026 and be completed within 1 year of the project commencement date. Any changes
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 46
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
3) Specify a minimum, 28-day, compressive strength of 4,500 psi for all exterior
concrete.
4) Including "fibermesh" in the concrete mix also may be beneficial for reducing
surficial scaling.
5) Cure the concrete effectively at uniform temperature and humidity. This
commonly will require fogging, blanketing and/or tenting, depending on the
weather conditions. As long as 3 to 4 weeks of curing may be required, and
possibly more.
6) Avoid placement of concrete during cold weather so that it is not exposed to
freeze -thaw cycling before it is fully cured.
7) Avoid the use of de-icing salts on given reaches of flatwork through the first winter
after construction.
We understand that sometimes it is not practical to implement some of these measures
for reducing scaling due to safety considerations, project scheduling, etc. In such cases,
where these measures are not implemented, additional costs for flatwork maintenance or
reconstruction should be incorporated into project budgets.
Frost and Ice Considerations Nearly all soils other than relatively coarse, clean,
granular materials are susceptible to loss of density if allowed to become saturated and
exposed to freezing temperatures and repeated freeze —thaw cycling. The formation of ice
in the underlying soils can result in heaving of pavements, flatwork, and other hardscaping
("ice jacking") in sustained cold weather up to 3 inches or more. This heaving can develop
relatively rapidly. A portion of this movement typically is recovered when the soils thaw,
but due to loss of soil density, some degree of displacement will remain. This can result
even where the subgrade soils were prepared properly.
Where hardscape movements are a design concern, e.g., at doorways, replacement of
the subgrade soils with 36 or more inches of clean, coarse sand or gravel should be
considered or supporting the element on foundations similar to the fuel tanks and spanning
over a void. Detailed guidance in this regard can be provided upon request. It should be
noted that where such open graded granular soils are placed, water can infiltrate and
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 45
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
ranges. Therefore, the contractor should take particular care with regard to proper
subgrade preparation in the immediate building exteriors.
Concrete Scaling Climatic conditions in the project area including relatively low humidity,
large temperature changes and repeated freeze —thaw cycles, make it likely that project
sidewalks and other exterior concrete will experience surficial scaling or spalling. The
likelihood of concrete scaling can be increased by poor workmanship during construction,
such as "over -finishing" the surfaces. In addition, the use of de-icing salts on exterior
concrete flatwork, particularly during the first winter after construction, will increase the
likelihood of scaling. Even use of de-icing salts on nearby roadways, from where vehicle
traffic can transfer them to newly placed concrete, can be sufficient to induce scaling.
Typical quality control/quality assurance tests that are performed during construction for
concrete strength, air content, etc., do not provide information with regard to the properties
and conditions that give rise to scaling.
We understand that some municipalities require removal and replacement of concrete that
exhibits scaling, even if the material was within specification and placed correctly. The
contractor should be aware of.the local requirements and be prepared to take measures
to reduce the potential for scaling and/or replace concrete that scales.
In GROUND's experience, the measures below can be beneficial for reducing the
likelihood of concrete scaling. Which measures, if any, used should be based on cost and
the owner's tolerance for risk and maintenance. It must be understood, however, that
because of the other factors involved, including weather conditions and workmanship,
surface damage to concrete can develop, even where all of these measures were
followed. Also, the mix design criteria should be coordinated with other project
requirements including criteria for sulfate resistance presented in the Water -Soluble
Sulfates section of this report.
1) Maintaining a maximum water/cement ratio of 0.45 by weight for exterior concrete
mixes.
2) Include Type F fly ash in exterior concrete mixes as 20 percent of the cementitious
material.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 44
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
1) Remedial earthwork to prepare flatwork subgrades is subject to the same factors
discussed in the Pavement Sections section of this report, and should be
undertaken to the same depth.
Regardless of the depth of subgrade preparation, due to the potentials for hydro -
consolidation at this site, greater than typical maintenance, including the removal
and replacement of portions of flatwork, should be anticipated for project exterior
flatwork. Greater depths of subgrade preparation will tend to reduce the extent
and frequency of extra maintenance, however.
2) Prior to placement of flatwork, a proof roll should be performed to identify areas
that exhibit instability and deflection. The deleterious soils in these areas should
be removed and replaced with properly compacted fill. The contractor should take
care to achieve and maintain compaction behind curbs to reduce differential
sidewalk settlements. Passing a proof roll is an additional requirement to placing
and compacting the subgrade fill soils within the specified ranges of moisture
content and relative compaction in the Project Earthwork section of this report.
Subgrade stabilization may be cost-effective in this regard.
3) Flatwork should be provided with control joints extending to an effective depth and
spaced no more than 10 feet apart, both ways. Narrow flatwork, such as
sidewalks, likely will require more closely spaced joints.
Construction and Drainage Between Structures and Pavements Proper design,
drainage, construction and maintenance of the areas between individual structures and
parking/driveway areas are critical to the satisfactory performance of the project.
Sidewalks, slabs and roofs, fountains, raised planters and other highly visible
improvements commonly are installed within these zones, and distress in or near these
improvements is common. Commonly, proper soil preparation in these areas receives
little attention during overlot construction because they fall between the structure and
pavement areas which typically are built with heavy equipment. Subsequent landscaping
and hardscape installation often is performed by multiple subcontractors with light or hand
equipment, and necessary over -excavation and soil processing is not performed.
Consequently, subgrade soil conditions commonly deviate significantly from specified
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 43
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Temporary Fire Access Routes Commonly, construction sites are required by local fire
departments to provide temporary access for emergency response. It has been
GROUND's experience these access drives are to provide support for trucks weighing up
to 90,000 pounds and are typically desired to be gravel/aggregate-surfaced.
Based on our experience, a temporary section consisting of at least 12 inches of material
meeting the requirements of CDOT Class 5 or Class 6 Aggregate Base Course or at least
8 inches of CDOT Class 5 or Class 6 Aggregate Base Course over a layer of
stabilization geotextilelgeofabric, such as Mirafi® RS380i or the equivalent, could be
utilized provided the owner understands that this section is for temporary access during
construction only and is not a replacement or an equal alternate to the pavement
section(s) that was indicated previously. The aggregate base course placed for this
purpose should be compacted to at least 95 percent of the maximum modified Proctor dry
density. It should be noted that the aggregate base course sections indicated above are
not intended to support fire truck outriggers without cribbing or similar measures.
The aggregate comprising such a wearing course will be displaced and rutted under the
loads imposed by heavy vehicles. Therefore, regular maintenance including re -grading
and application of additional aggregate should be implemented to ensure proper drainage,
repair distressed/damaged areas, and reestablish grades. Additionally, the ability of a
temporary aggregate -surfaced route to accommodate loads as indicated above is directly
related to the quality of the subgrade materials on which the aggregate is placed, not only
on the aggregate section. If water infiltrates these areas, additional rutting and other
distress, including a reduction in capacity, will result, requiring additional maintenance.
EXTERIOR FLATWORK
We anticipate that the exterior of the proposed fuel farm may be provided with concrete
flatwork. Like other site improvements, flatwork will experience post -construction
movements as soil moisture contents increase after construction and distress likely will
result. The following measures will help to reduce damages to these improvements, but
will not prevent all movements.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 42
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
This is particularly the case in the later stages of project construction after landscaping
has been emplaced but heavy construction traffic has not ended. Heavy vehicle traffic
over wetted subgrade commonly results in rutting and pushing of flexible pavements, and
cracking of rigid pavements. In relatively flat areas where design drainage gradients
necessarily are small, subgrade settlement can obstruct proper drainage and yield
increased infiltration, exaggerated distress, etc. (These considerations apply to project
flatwork, as well.)
Also, GROUND's experience indicates that longitudinal cracking is common in asphalt -
pavements generally parallel to the interface between the asphalt and concrete structures
such as curbs, gutters, or drain pans. Distress of this type is likely to occur even where
the subgrade has been prepared properly and the asphalt has been compacted properly.
The anticipated traffic loading does not include excess loading conditions imposed by
heavy construction vehicles. Consequently, heavily loaded concrete, lumber, and building
material trucks can have a detrimental effect on the pavement.
Most pavements will not remain in satisfactory condition and achieve their "design lives"
without regular maintenance and rehabilitation procedures performed throughout the life
of the pavement. Maintenance and rehabilitation measures preserve, rather than improve,
the structural capacity of the pavement structure. Therefore, an effective program of
regular maintenance should be developed and implemented to seal cracks, repair
distressed areas, and perform thin overlays throughout the lives of the pavements. The
greatest benefit of pavement overlaying will be achieved by overlaying sound pavements
that exhibit little or no distress.
Crack sealing should be performed at least annually and a fog seal/chip seal program
should be performed on the pavements every 3 to 4 years. After approximately 8 to 10
years after construction, patching, additional crack sealing, and asphalt overlay may be
required. Prior to overlays, it is important that all cracks be sealed with a flexible,
rubberized crack sealant in order to reduce the potential for propagation of the crack
through the overlay. If actual traffic loadings exceed the values used for development of
the pavement sections, however, pavement maintenance measures will be needed on an
accelerated schedule.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 41
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Geotechnical criteria for fill placement and compaction are provided in the Project
Earthwork section of this report. The contractor should be prepared to either dry the
subgrade materials or moisten them, as needed, prior to compaction.
Proof Rolling Immediately prior to paving, the subgrade should be proof rolled with a
heavily loaded, pneumatic tired vehicle. Areas that show excessive deflection during proof
rolling should be excavated and replaced and/or stabilized. Areas allowed to pond prior
to paving will require significant reworking prior to proof -rolling. Establishment of a firm
paving latform as indicated by proof rolling) is an additional requirement beyond proper
fill placement and compaction. It is possible for soils to be compacted within the limits
indicated in the Project Earthwork section of this report and fail proof rolling, particularly in
the upper range of moisture content.
Additional Observations The collection and diversion of surface drainage away from
paved areas is extremely important to the satisfactory performance of the pavements. The
subsurface and surface drainage systems should be carefully designed to ensure removal
of the water from paved areas and subgrade soils. Allowing surface waters to pond on
pavements will cause premature pavement deterioration. Where topography, site
constraints, or other factors limit or preclude adequate surface drainage, pavements
should be provided with edge drains to reduce loss of subgrade support. The long-term
performance of the pavement also can be improved greatly by proper backfilling and
compaction behind curbs, gutters, and sidewalks so that ponding is not permitted and
water infiltration is reduced.
Landscape irrigation in planters adjacent to pavements and in "island" planters within
paved areas should be carefully controlled or differential heave and/or rutting of the nearby
pavements will result. Drip irrigation systems are suggested for such planters to reduce
over -spray and water infiltration beyond the planters. Enclosing the soil in the planters
with plastic liners and providing them with positive drainage also will reduce differential
moisture increases in the surrounding subgrade soils.
In our experience, infiltration from planters adjacent to pavements is a principal source of
moisture increase beneath those pavements. This wetting of the subgrade soils from
infiltrating irrigation commonly leads to loss of subgrade support for the pavement with
resultant accelerating distress, loss of pavement life and increased maintenance costs.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 40
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Subgrade Preparation Although subgrade preparation to a depth of 12 inches is
common in the general project area, the local soils are sufficiently collapsible that we do
not consider 12 inches to be a sufficient depth of subgrade preparation. Remedial
earthwork to any depth will not prevent pavement distress on these soils, but will tend to
reduce it and improve perceived rideability. At this site, it is likely that greater than typical
maintenance measures, including the removal and replacement of pavements will be
required.
Remedial Earthwork Based on the plasticity of the soils and MOT guidelines, the
pavements should be constructed, in general, on a section of properly moisture -
conditioned and compacted to a depth of at least 24 inches or a depth that removes
and replaces all undocumented fill soils and all soft, wet, otherwise unsuitable soils,
whichever is greater. This section assumes that a) traffic speeds in the parking areas
and driveways will be relatively slow, and b) the facility owner will be tolerant of significant
total and differential pavement post -construction movements (on the order of several
inches) and the associated maintenance costs that that are necessary to reestablish
effective drainage, replace distressed pavement, etc.
We understand, however, that it may not be practical remove and replace all the
undocumented fill soils or soft, yielding, or otherwise deleterious soils as properly
compacted fill due the presence of utility lines and the proximity of existing improvements.
Therefore, if the owner opts to reduce the fill section beneath the pavements, additional
post -construction movements, accelerated pavement distress, and additional
maintenance should be anticipated. We suggest remedial earthwork should be performed
to no less than 24 inches in such a case. Similarly, where existing utility lines or other site
constraints limit the depth to which remedial earthwork can be accomplished, remedial
earthwork should be completed to the extent practical, but additional maintenance should
be anticipated.
In general, increasing the depth of fill beneath the pavements will decrease the risk of
post -construction movements.
Subgrade preparation of the selected depth should extend the full width of the pavement
from back -of -curb to back -of -curb. The subgrade for any sidewalks and other project
hardscaping also should be prepared in the same manner.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 39
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
standards in the Project Earthwork section of this report. Aggregate composed of recycled
asphalt should not be expected to provide the same support for the wearing course as
native, Class 6 material and should not be considered as an equivalent for it. Our
experience suggests that recycled asphalt is difficult to compact properly when placed and
can hold water after the wearing course is placed on it.
Pavement concrete should consist of a plant mix composed of a mixture of aggregate,
portland cement and appropriate admixtures meeting the requirements of a job -mix
formula established by a qualified engineer as well as applicable municipal design
requirements design requirements. Concrete should have a minimum modulus of rupture
of third point loading of 650 psi. Normally, concrete with a 28-day compressive strength
of 4,500 psi should develop this modulus of rupture value. The concrete should be air -
entrained with approximately 6 percent air and should have a minimum cement content of
6 sacks per cubic yard. Maximum allowable slump should be 4 inches.
These concrete mix design criteria should be coordinated with other project requirements
including any criteria for sulfate resistance presented in the Water -Soluble Sulfates section
of this report. To reduce surficial spalling resulting from freeze -thaw cycling, we suggest
that pavement concrete meet the requirements of CDOT Class P concrete. In addition,
the use of de-icing salts on concrete pavements during the first winter after construction
will increase the likelihood of the development of scaling. Placement of flatwork concrete
during cold weather so that it is exposed to freeze -thaw cycling before it is fully cured also
increases its vulnerability to scaling. Concrete placing during cold weather conditions
should be blanketed or tented to allow full curing. Depending on the weather conditions,
this may result in 3 to 4 weeks of curing, and possibly more.
Concrete pavements should contain sawed or formed joints. CDOT and various industry
groups provide guidelines for proper design and concrete construction and associated
jointing. In areas of repeated turning stresses, such as truck loading and unloading areas,
the concrete pavement joints should be fully tied and doweled. PCA, ACI, and ACPA
publications also provide useful guidance in these regards. Joint spacings less than the
15-foot maximum indicated in in CDOT's M standards, e.g., 10 feet or 12 feet, may be
beneficial to reduce concrete cracking.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 38
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
An ESAL value of 219,000 (corresponding to an EDLA value of 30 for a 20-year design
life) was estimated for the "moderate wight" (truck) pavements immediately surrounding
the proposed fuel farm. If design traffic loadings differ significantly from these assumed
values, GROUND should be notified to reevaluate the pavement sections below.
Pavement Sections The soil resilient modulus and the ESAL values were used to
determine the required structural number for the project pavements which then was then
used to develop the pavement sections based on the DARWinTM computer program that
solves the 1993 AASHTO pavement equations. A reliability level of 85 percent and a
terminal serviceability of 2.0 were utilized for design of the pavement sections. A structural
coefficient of 0.44 was used for hot bituminous asphalt and 0.12 was used for aggregate
base course. The minimum pavement sections for a 20-year design are tabulated below.
MINIMUM PAVEMENT SECTIONS
Full Depth Asphalt
Composite Section
Rigid Section
(inches Asphalt /
(inches Concrete /
(inches Asphalt)
inches Aggregate
inches Aggregate
Base)
Basel
8
5/10
7/6
In our experience, asphalt pavements (including composite sections) will not perform as
well as rigid pavement in areas of high turning stresses or prolonged static loading, and
additional maintenance costs (repairing of tearing and pushing distress) should be
anticipated if either of these sections were selected. Furthermore, the use of full -depth
asphalt sections is anticipated to result in accelerated distress such as rutting and
cracking; the use of composite asphalt/aggregate base course pavement sections
commonly provides better, long-term performance in our experience.
Pavement Materials Asphalt pavement should consist of a bituminous plant mix
composed of a mixture of aggregate and bituminous material. Asphalt mixture(s) should
meet the requirements of a job -mix formula established by a qualified engineer as well as
applicable municipal design requirements.
Aggregate base material should meet the criteria of CDOT Class 6 Aggregate Base
Course. Base course should be placed in and compacted in accordance with the
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 37
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
PAVEMENT SECTIONS
A pavement section is a layered system designed to distribute concentrated traffic loads
to the subgrade. Performance of the pavement structure is directly related to the physical
properties of the subgrade soils and traffic loadings.
Standard practice in pavement design describes a typical flexible pavement section as a
"20-year" design pavement. However, a pavement should not be anticipated to remain in
satisfactory condition without routine maintenance and rehabilitation procedures
performed throughout the life of the pavement.
Pavement sections for the private pavements at the subject facility were developed in
general accordance with the guidelines and procedures of the American Association of
State Highway and Transportation Officials (AASHTO) and local pavement construction
practice.
Note that the pavement sections provided in this report consider only automobile traffic
and light aircraft traffic, and may not be appropriate for areas subject to larger, heavier
aircraft.
Subgrade Materials Our data indicate that the shallow soils at the site classify primarily
as A-4 soils with group index values up to 6 in accordance with the AASHTO classification
system. Such soils generally provide relatively poor subgrade support.
Based on our experience with similar projects, and data obtained during previous
geotechnical evaluations at the airport, a resilient modulus value of 4,000 was estimated
for the on -site materials. It is important to note that significant decreases in soil support
have been observed as the moisture content increases above optimum. Pavements that
are not properly drained may experience a loss of the soil support and subsequent
reduction in pavement life.
Anticipated Traffic Project -specific traffic loads had not been provided to GROUND at
the time of preparation of this report. Therefore, assumed traffic loadings were used to
develop the pavement section alternatives based on our experience with similar facilities.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 36
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
already have entered the subgrade, leading to subsequent distress and failures.
The contractor should maintain effective site drainage throughout construction so
that water is directed into appropriate drainage structures.
5) In no case should water be permitted to pond adjacent to or on sidewalks,
hardscaping, or other improvements as well as utility trench alignments, which are
likely to be adversely affected by moisture -volume changes in the underlying soils
or flow of infiltrating water.
SUBSURFACE DRAINAGE
As a component of project civil design, properly functioning, subsurface drain systems
("underdrains") can be beneficial for collecting and discharging saturated subsurface
waters. Although the subsurface drainage system anticipated for this project may consist
of perimeter underdrains along the fuel tank perimeters and underdrains constructed
beneath flatwork, they are addressed as underdrains herein.
Underdrains will not collect water infiltrating under unsaturated (vadose) conditions, or
moving via capillarity, however. In addition, if not properly constructed and maintained,
underdrains can transfer water into foundation soils, rather than remove it. This will tend
to induce heave or settlement of the subsurface soils, and may result in distress.
Underdrains can, however, provide an added level of protection against relatively severe
post -construction movements by draining saturated conditions near the fuel tanks should
they arise, and limiting the volume of wetted soil.
If the project team would like to consider underdrains for the shade structure, GROUND
is available to discuss the above options as well as other underdrain alternatives upon
request. Geotechnical parameters and details can also be provided upon request.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 35
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
1) Wetting or drying of the underslab areas should be avoided during and after
construction. Permitting increases/variations in moisture to the adjacent or
supporting soils may result in increased total and/or differential movements.
2) Measures for positive surface drainage away from the fuel tanks should be
provided and maintained to reduce water infiltration into foundation soils.
Underdrains should not be relied upon in surface drainage design to collect and
discharge surface waters.
A minimum slope of 12 inches in the first 10 feet in the areas not covered with
pavement or concrete slabs should be established. For areas covered with asphalt
pavement or concrete slabs, slopes should comply with ADA requirements
where required. Increasing slopes to a minimum of 3 percent in the first 10 feet
in the areas covered with pavement or concrete slabs will reduce, but not eliminate,
the potential for moisture infiltration and subsequent volume change of the
underling soils.
In no case should water be allowed to pond near or adjacent to foundation
elements, hardscaping, etc.
3) Drainage also should be established and maintained to direct water away from
sidewalks and other hardscaping as well as utility trench alignments which are not
tolerant of increased post -construction movements.
The ground surface near foundation elements should be able to convey water
away readily. Cobbles or other materials that tend to act as baffles and restrict
surface flow should not be used to cover the ground surface near the foundations.
Where the ground surface does not convey water away readily, additional post -
construction movements and distress should be anticipated.
4) In GROUND's experience, it is common during construction that in areas of
partially completed paving or hardscaping, bare soil behind curbs and gutters, and
utility trenches, water is allowed to pond after rain or snow -melt events. Wetting
of the subgrade can result in loss of subgrade support and increased settlements.
By the time final grading has been completed, significant volumes of water can
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 34
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
restrained joints to reduce the potential for failure at joints. Connections to the fuel tanks
or other structures should be flexible and easily replaced or adjusted. Non -pressurized
lines should be evaluated periodically for deformations such as pipe "bellies" that would
impair their efficiency, and appropriate repairs made. Maintenance plans should
anticipate greater than typical utility line maintenance and replacement because of the
undocumented fill soils that will remain beneath utility lines.
SURFACE DRAINAGE
The site soils are relatively stable with regard to moisture content —volume relationships at
their existing moisture contents. Other than the anticipated, post -placement settlement of
fills, post -construction soil movements will result primarily from the introduction of water
into the soils underlying the proposed fuel tanks, hardscaping, and pavements. Based on
the site surface and subsurface conditions encountered in this study, we do not anticipate
a rise in the local water table sufficient to approach foundation elevations. Therefore, local
saturation of project foundation soils likely will result from infiltrating surface waters
(precipitation, irrigation, etc.), and water flowing along constructed pathways such as
bedding in utility pipe trenches.
The following drainage measures should be followed both for during construction and as
part of project design. However, we understand that given the nature of the proposed
structures and their locations, some of these measures may not be practical to implement.
Where they are not implemented, there exists a risk of the post -construction movement
estimates listed in this report being exceeded.
The following drainage measures should be followed both for during construction and as
part of project design. The facility should be observed periodically to evaluate the surface
drainage and identify areas where drainage is ineffective. Routine maintenance of site
drainage should be undertaken throughout the design life of the proposed facility.
Maintenance should be antici ated to include removal and re lacement of sidewalk
stones, curb and gutter, sections of pavement, etc., to restore effective drainage. If these
measures are not implemented and maintained effectively, the movement estimates
provided in this report could be exceeded.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 33
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
should be free of vegetation, organic debris, and other deleterious materials. Fragments
of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) coarser than 3
inches in maximum dimension should not be incorporated into trench backfills.
Soils placed for compaction as trench backfill should be conditioned to a relatively uniform
moisture content, placed, and compacted in accordance with the parameters in the Project
Earthwork section of this report.
Pipe Bedding Pipe bedding materials, placement and compaction should meet the
specifications of the pipe manufacturer and applicable municipal standards. Bedding
should be brought up uniformly on both sides of the pipe to reduce differential loadings.
As discussed above, the use of CLSM or similar material in lieu of granular bedding and
compacted soil backfill should be considered where the tolerance for surface settlement
is low. (Placement of CLSM as bedding to at least 12 inches above the pipe can protect
the pipe and assist construction of a well -compacted conventional backfill, although
possibly at an increased cost relative to the use of conventional bedding.)
If a granular bedding material is specified, with regard to potential migration of fines into
the pipe bedding, design and installation should follow ASTM D2321, Appendix X1.8. If
the granular bedding does not meet filter criteria for the enclosing soils, and we do not
anticipate that it will, then non -woven filter fabric (e.g., Mirafio 140N, or the equivalent)
should be placed around the bedding to reduce migration of fines into the bedding which
can result in severe, local surface settlements. Where this protection is not provided,
settlements can develop/continue several months or years after completion of the project.
In addition, clay or concrete cut-off walls should be installed to interrupt the granular
bedding section to reduce the rates and volumes of water transmitted along the sewer
alignment which can contribute to migration of fines.
If granular bedding is specified, the contractor should not anticipate that the shallow on -
site soils may be suitable for that use with significant processing. Materials proposed for
use as pipe bedding should be tested for suitability prior to use.
Other Considerations Because of the potential for local consolidation of site soils to
result in significant, extensional strains to utility pipes, pipes should be provided with
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 32
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Areas allowed to pond water will require excavation and replacement with properly
compacted fill. The contractor should take particular care to ensure adequate support
near pipe joints which are less tolerant of extensional strains.
Where thrust blocks are needed, the parameters provided in the Lateral Loads section of
this report may be used for design.
Trench Backfilling Some settlement of compacted soil trench backfill materials should
be anticipated, even where all the backfill is placed and compacted correctly. Typical
settlements are on the order of 1 to 2 percent of fill thickness. However, the need to
compact to the lowest portion of the backfill must be balanced against the need to protect
the pipe from damage from the compaction process. Some thickness of backfill may need
to be placed at compaction levels lower than specified (or smaller compaction equipment
used together with thinner lifts) to avoid damaging the pipe. Protecting the pipe in this
manner can result in somewhat greater surface settlements. Therefore, although other
alternatives may be available, the following options are presented for consideration:
Controlled Low Strength Material Because of these limitations, the entire depth of the
trench (both bedding and common backfill zones) should be backfilled with "controlled low
strength material' (CLSM), i.e., a lean, sand -cement slurry, "flowable fill," or similar
material along all trench ali nment reaches with low tolerances for surface settlements.
CLSM used as pipe bedding and trench backfill should exhibit a 28-day unconfined
compressive strength between 50 to 150 psi so that reexcavation is not unusually difficult.
Placement of the CLSM in several lifts or other measures likely will be necessary to avoid
"floating" the pipe. Measures also should be taken to maintain pipe alignment during
CLSM placement.
Compacted Soil Backfilling In areas that are tolerant of surface settlements, conventional
soil backfilling may be used. Where compacted soil backfilling is employed, using the site
soils or similar materials as backfill, the risk of backfill settlements entailed in the selection
of this higher risk alternative must be anticipated and accepted by Vantage Aviation, LLC.
We anticipate that the on -site soils excavated from trenches will be suitable, in general,
for use as common trench backfill within the above -described limitations. Backfill soils
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 31
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
well points to draw down the water level may be appropriate methods. Other methods
may also be necessary. The dewatering approach should ultimately be determined by the
contractor based on their means and methods experience. Dewatering operations may
be necessary as both temporary and long-term/permanent installations. Dewatering
design should consider the potential effect on existing structures in vicinity.
If seepage or groundwater is encountered during excavation or at any time during
construction, the project geotechnical engineer and project team should be contacted to
evaluate the conditions. The presence of groundwater in these types of situations and
associated potential design changes can have an impact to both the financial and
schedule components of a project.
Surface Water The contractor should take proactive measures to control surface waters
during construction and maintain good surface drainage conditions to direct waters away
from excavations and into appropriate drainage structures. A properly designed drainage
swale should be provided at the tops of the excavation slopes. In no case should water
be allowed to pond near project excavations.
Temporary slopes should also be protected against erosion. Erosion along the slopes will
result in sloughing and could lead to a slope failure.
PIPING INSTALLATION
The measures and criteria below are based on GROUND's evaluation of the local,
geotechnical conditions. Where the parameters herein differ from applicable municipal
re uirements the latter should be considered to govern.
Pipe Support The bearing capacity of the site soils appeared adequate, in general, for
support of typical piping. The pipes and their contents are less dense than the soils which
will be displaced for installation. Therefore, in general GROUND anticipates no significant
pipe settlements in these materials where properly bedded from loading alone.
Trench bottoms may expose existing fill soils, or soft, loose, or otherwise deleterious
materials. Firm materials may be disturbed by the excavation process. All such unsuitable
materials should be excavated and replaced with properly compacted fill.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 30
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
within the test holes, materials that may be awkward or otherwise difficult to handle (e.g.,
relatively large pieces of construction or bedrock debris) may be encountered. (See the
Site Conditions section of this report.)
Aside from these potential issues, in general, we anticipate no unusual excavation
difficulties in these materials, for the proposed construction with conventional, heavy duty,
excavating equipment, though some greater than typical efforts may be needed locally,
as discussed above.
Temporary Excavations and Personnel Safety Excavations in which personnel will be
working must comply with all applicable OSHA Standards and Regulations, particularly
CFR 29 Part 1926, OSHA Standards -Excavations, adopted March 5, 1990. The
contractor's "responsible person" should evaluate the soil exposed in the excavations as
part of the contractor's safety procedures. GROUND has provided the information in this
report solely as a service to Vantage Aviation, LLC, and is not assuming responsibility for
construction site safety or the contractor's activities.
The contractor should take care when making excavations not to compromise the bearing
or lateral support for any adjacent, existing improvements.
Should site constraints prohibit the use sloped excavations, temporary shoring should be
used. GROUND is available to provide shoring design upon request. Stockpiling of
materials should not be permitted closer than 5 feet to the tops of temporary slopes, or a
distance equal to the depth of the excavation, whichever is greater.
Groundwater Groundwater was not encountered in the test holes at the depths explored.
Therefore, based on conditions at the time of this subsurface exploration, relatively
shallow excavations at the site appear unlikely to encounter groundwater, except limited
volumes of perched groundwater. Significant volumes of perched or transient
groundwater may be encountered at shallow depths during periods of seasonal runoff,
significant snowmelt events, and/or after relatively large precipitation events.
It is possible that groundwater may be encountered in project excavations at depths both
shallower and deeper than those indicated above. The contractor should be prepared to
dewater the excavation during construction. Pumps adequate to discharge water and/or
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 29
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
use can be considered on a case -by -case basis. Where squeegee meets the project
requirements for pipe bedding material, however, it is acceptable for that use.
Settlements Settlements will occur in newly filled ground, typically on the order of 1 to 2
percent of the fill depth. This is separate from settlement of the existing soils left in place.
For a 6-foot fill, for example, that corresponds to a total settlement of about 1 inch. If fill
placement is performed properly and is tightly controlled, in GROUND's experience the
majority (on the order of 60 to 80 percent) of that settlement typically will take place during
earthwork construction, provided the contractor achieves the compaction levels indicated
herein. The remaining potential settlements likely will take several months or longer to be
realized, and may be exacerbated if these fills are subjected to changes in moisture
content.
Cut and Filled Slopes Permanent, unretained, graded slopes supported by local soils
up to 5 feet in height should be constructed no steeper than 3:1 (horizontal : vertical).
Minor raveling or surficial sloughing should be anticipated on slopes cut at this angle until
vegetation is well reestablished. Surface drainage should be designed to direct water
away from slope faces into designed drainage pathways or structures.
Steeper slope angles and heights may be possible but will require detailed slope stability
analysis based on final proposed grading plans. A geotechnical engineer should be
retained to evaluate this on a case -by -case basis.
EXCAVATION CONSIDERATIONS
Excavation Difficulty Test holes for the subsurface exploration were advanced to the
depths indicated on the test hole logs by means of conventional, buggy -mounted,
geotechnical drilling equipment. Practical auger refusal conditions were not encountered
during this exploration; however, such conditions have been encountered elsewhere at
the Rifle —Garfield County Airport. Additionally, relatively high penetration resistance
values were measured at variable depths within several of the test holes, included
penetration resistance values as high as 50 blows for 11 inches of penetration at a depth
of about 17 feet below existing grade. Such variations in penetration resistance values
indicate layers of denser soils and possible cobbles/boulders. Additionally, given the
inherent nature of undocumented fill soils and the recorded penetration resistance values
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 28
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Compaction areas should be kept separate, and no lift should be covered by another until
relative compaction and moisture content within the specified ranges are obtained.
Compaction Criteria Soils that classify as GP, GW, GM, GC, SP, SW, SM, or SC in
accordance with the USCS classification system (granular materials) should be
compacted to 95 or more percent of the maximum dry density at moisture contents within
3 percent of the optimum moisture content as determined by ASTM D1557, the modified
Proctor.
Soils that classify as ML, MH, CL, or CH should be compacted to at least 95 percent of
the maximum dry density at moisture contents between within 3 percent of the optimum
moisture content as determined by ASTM D698, the standard Proctor.
Use of Squeegee Relatively uniformly graded fine gravel or coarse sand, i.e., "squeegee,"
or similar materials commonly are proposed for backfilling foundation excavations, utility
trenches (excluding approved pipe bedding), and other areas where employing
compaction equipment is difficult. In general, this procedure should not be followed for
the following reasons.
Although commonly considered "self -compacting," uniformly graded granular materials
require densification after placement, typically by vibration. The equipment to densify
these materials is not available on many job -sites.
Even when properly densified, uniformly graded granular materials are permeable and
allow water to reach and collect in the lower portions of the excavations backfilled with
those materials. This leads to wetting of the underlying soils and resultant potential loss
of bearing support as well as increased local heave or settlement.
Wherever possible, excavations should be backfilled with approved, on -site soils placed
as properly compacted fill. Where achieving adequate compaction is difficult, then
Controlled Low Strength Material' (CLSM), i.e., a lean, sand -cement slurry ("flowable fill')
or a similar material should be used for backfilling.
Where "squeegee" or similar materials are proposed for use by the Contractor, the design
team should be notified by means of a Request for Information (RFI), so that the proposed
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 27
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
General Considerations for Fill Placement Fill soils should be thoroughly mixed to
achieve a uniform moisture content, placed in uniform lifts not exceeding 8 inches in loose
thickness, and properly compacted.
Excavated bedrock materials, such as those present in the native colluvium, will require a
well -coordinated effort to moisture treat, process, place, and compact properly. In -place
bedrock fragments were hard to very hard, and should be broken down in to a soil -like
mass. Greater than typical watering, and compaction equipment that aids in breaking
down such material (e.g., a Caterpillar 825 compactor -roller), likely will be needed.
Crushing or other methods should be anticipated to sufficiently reduce sandstone bedrock
fragments where encountered. Applied water will be taken up into the structures of the
claystone. The contractor should anticipate that handling and processing the excavated
bedrock more than once may be necessary to achieve the requirements herein.
Excavated bedrock, such as those present in the native colluvium, to be used as trench
backfill, will require additional moisture conditioning and processing in an open area
outside of trenches prior to placement as backfill.
No fill materials should be placed, worked, rolled while they are frozen, thawing, or during
poor/inclement weather conditions.
Where soils on which foundation elements will be placed are exposed to freezing
temperatures or repeated freeze —thaw cycling during construction, commonly due to water
ponding in foundation excavations, bearing capacity typically is reduced and/or
settlements increased due to the loss of density in the supporting soils. After periods of
freezing conditions, the contractor should rework areas affected by the formation of ice to
reestablish adequate bearing support.
Care should be taken with regard to achieving and maintaining proper moisture contents
during placement and compaction. Materials that are not properly moisture conditioned
may exhibit significant pumping, rutting, and deflection at moisture contents near optimum
and above. The contractor should be prepared to handle soils of this type, including the
use of chemical stabilization, if necessary.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 26
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Use of Existing Native Soils Based on the samples retrieved from the test holes, we
anticipate that the existing site soils that are free of organic materials, coarse cobbles,
boulders, or other deleterious materials will be suitable, in general, for reuse as compacted
fill.
Fragments of rock and cobbles, (as well as inert construction debris, e.g., concrete or
asphalt) up to 3 inches in maximum dimension may be included in project fills, in general.
Such materials should be evaluated on a case -by -case basis, where identified during
earthwork.
Silty Soils Significant portions of the site soils are silty. Such materials commonly require
greater than typical efforts to place as compacted fill because they can become unstable
and difficult to compact at moisture contents near or above the optimum. Stable and
compacted soils can become unstable if allowed to become wetted. The contractor should
be prepared to work in these materials, or to export and replace them.
Clayey Soils If local volumes of moderately to highly plastic soils are encountered during
grading, they should not be included in project structural fills, but placed in non-structural
areas or exported.
Imported Fill Materials Materials imported to the site as (common) fill should be free of
organic material, and other deleterious materials. Imported material should exhibit 70
percent or less passing the No. 200 Sieve and a plasticity index of 10 or less. Materials
proposed for import should be approved prior to transport to the site.
Fill Platform Preparation Prior to filling, the top 12 inches of in -place materials on which
fill soils will be placed (except for utility trench bottoms where bedding will be placed)
should be scarified, moisture conditioned and properly compacted in accordance with the
criteria below to provide a uniform base for fill placement.
If surfaces to receive fill expose loose, wet, soft, or otherwise deleterious material,
additional material should be excavated, or other measures taken to establish a firm
platform for filling. A surface to receive fill must be effectively stable prior to placement of
fill, including trench bottoms prior to placement of bedding.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 25
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
PROJECT EARTHWORK
The earthwork criteria below are based on our interpretation of the geotechnical conditions
encountered in the test holes. Where these criteria differ from applicable municipal
specifications, e.g., for trench backfill compaction along a public utility line the latter
should be considered to take recedence.
General Considerations Project grading should be performed as early as possible in the
construction sequence to allow settlement of fills and surcharged ground to be realized to
the greatest extent prior to subsequent construction.
Prior to earthwork construction, existing construction debris, vegetation, and other
deleterious materials should be removed and disposed of off -site. Relic underground
utilities should be abandoned in accordance with applicable regulations, removed as
necessary, and properly capped.
Topsoil and other organic materials present on -site should not be incorporated into
ordinary fills. Instead, topsoil should be stockpiled during initial grading operations for
placement in areas to be landscaped or for other approved uses. These materials should
be removed and replaced where fill will be placed above them or where they will be
beneath a proposed improvement.
Use of Existing Fill Soils Fill materials were recognized at the test holes during our
subsurface exploration, and likely are present elsewhere on the site, given the apparent
grading. (See the Site Conditions section of this report.) Because not all the fill soils were
sampled or tested, it is possible that some of the fill soils may not be suitable for reuse as
compacted fill, due to the presence of deleterious materials such as trash, organic
material, coarse cobbles and boulders, or construction debris. Therefore, excavated fill
materials should be evaluated and tested, as appropriate, with regard to reuse. We
anticipate, however, that the majority of the existing site fill soils will be suitable for reuse
as fill.
Additionally, it should be noted that environmental assessment of the suitability of the
existing fill was not part of our scope of services. If this is a concern for the project team,
an environmental consultant should be retained.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 24
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Table A.1 Soil -Test Evaluation
Soil Characteristic / Value Points
Redox Potential
< 0 (negative values)....................................................................................... 5
0 to +50 mV.................................................................................................... 4
+50 to +100 mV...................................................... ............................. 3'/z
> +100 mV.........................:........................... ............................ 0
Sulfide Reactivity
Positive........................................................................................................... 3'/2
Trace............................................................................................................... 2
Negative........................................................................................................... 0
Soil Resistivity
<1,500 ohm-cm............................................................................................. 10
1,500 to 1,800 ohm-cm................................................................................ 8
1,800 to 2,100 ohm-cm................................................................................. 5
2,100 to 2,500 ohm-cm................................................................................. 2
2,500 to 3,000 ohm-cm................................................................................. 1
>3,000 ohm-cm.................................................................................. 0
pH
0 to 2.0...................................................................................... .................. 5
2.0 to 4.0........................................................................ ............................... 3
4.0 to 6.5......................•.................................................................................. 0
6.5 to 7.5........................................................................................................ 0.
7.5 to 8.5......................................................................................................... 0
>8.5..................................................... ....... .............................................. 3
Moisture
Poor drainage, continuously wet...................................................................... 2
Fair drainage, generally moist....................................................................... 1
Good drainage, generally dry ........................................................................ 0
* If sulfides are present and low or negative redox-potential results (< 50 mV) are
obtained, add three (3) points for this range.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 23
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Soil Resistivity In order to assess the "worst case" for mitigation planning, samples of
materials retrieved from the test holes were tested for resistivity in the laboratory, after
being saturated with water, rather than in the field. Resistivity also varies inversely with
temperature. Therefore, the laboratory measurements were made at a controlled
temperature. Measurement of electrical resistivity indicated a value of approximately
12,353 ohm -centimeters in a sample of site soils.
pH Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5 to
7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range above
8.5, soils are generally high in dissolved salts, yielding a low soil resistivity.6 Our testing
indicated a pH value of 9.3.
Corrosivity Assessment The American Water Works Association (AWWA) has
developed a point system scale used to predict corrosivity. The scale is intended for
protection of ductile iron pipe but is valuable for project steel selection. When the scale
equals 10 points or higher, protective measures for ductile iron pipe are indicated. The
AWWA scale is presented on the next page.
The soil characteristics refer to the conditions at and above pipe installation depth. We
anticipate that drainage at the site after construction will be effective. Nevertheless, based
on the values obtained for the soil parameters, the fill and native soils appear to comprise
a severely corrosive environment for ferrous metals (11'/2 points).
If additional information or evaluation is needed regarding soil corrosivity, then the
American Water Works Association or a corrosion engineer should be contacted. It should
be noted, however, that changes to the site conditions during construction, such as the
import of other soils, or the intended or unintended introduction of off -site water, might
alter corrosion potentials significantly.
6 American Water Works Association ANSI/AWWA C105/A21.5-05 Standard.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 22
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Class l(Moderate)
1) ASTM C150 Type II or V.
2) ASTM C595 Type IP(MS) or IP(HS)
3) ASTM C150 Type III. Type III shall have no more than 8 percent C3A.
4) ASTM C595 Type IL(MS), IL(HS), IT(MS), or (HS).
Class C fly ash shall not be substituted for cement.
In addition, all concrete used shall have a minimum compressive strength of 4,000 psi.
Additional water-soluble sulfate testing may be useful to confirm appropriate class of
cement to use.
The contractor should be aware that certain concrete mix components affecting sulfate
resistance including, but not limited to, the cement, entrained air, and fly ash, can affect
workability, set time, and other characteristics during placement, finishing and curing. The
contractor should develop mix(es) for use in project concrete which are suitable with
regard to these construction factors, as well as sulfate resistance. A reduced, but still
significant, sulfate resistance may be acceptable to the owner, in exchange for desired
construction characteristics.
SOIL CORROSIVITY
Data were obtained to support an initial assessment of the potential for corrosion of ferrous
metals in contact with earth materials at the site, based on the conditions at the time of
GROUND's evaluation. The test results are summarized in Table 2.
Reduction -Oxidation testing indicated a red-ox potential of approximately -116 millivolts.
Such low potentials typically create a more corrosive environment.
Sulfide Reactivity testing indicated a "positive" result in the local soils. The presence of
sulfides in the soils suggests a more corrosive environment.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 21
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
WATER-SOLUBLE SULFATES
The concentration of water-soluble sulfates measured in a selected sample of site soils
was approximately 0.01 percent. (See Table 2.) Such a concentration of soluble sulfates
represents a negligible environment for sulfate attack on concrete exposed to these
materials. Degrees of attack are based on the scale of "negligible," "moderate," "severe,"
and "very severe" as described in the "Design and Control of Concrete Mixtures,"
published by the Portland Cement Association (PCA). The Colorado Department of
Transportation (CDOT) utilizes a corresponding scale with four classes of severity of
sulfate exposure (Class 0 to Class 3) as described in the table below.
REQUIREMENTS TO PROTECT AGAINST DAMAGE TO
CONCRETE BY SULFATE ATTACK FROM EXTERNAL SOURCES OF SULFATE
Severity of
Water -Soluble
Sulfate (SO4)
Water
Cementitious
Sulfate
Sulfate (SO4)
In Water
Cementitious Ratio
Material
Exposure
In Dry Soil
(ppm)
(maximum)
Requirements
Class 0
0.00 to 0.10
0 to 150
0.45
Class 0
Class 1
0.11 to 0.20
151 to 1500
0.45
Class 1
Class 2
0.21 to 2.00
1501 to 10,000
OA5
Class 2
Class 3
I 2.01 or greater
10,001 or greater
0.40
Class 3
Based on our test results and PCA and CDOT guidelines, sulfate -resistant cement should
be used in all concrete exposed to site soils, conforming to one of the following Class 0
requirements:
Class 0 [Negligible)
1) ASTM C150 Type I, II, III, or V.
2) ASTM C595 Type IL, IP, IP(MS), IP(HS), or IT.
However, based on our experience in the greater project area, elevated sulfates may be
present in the site soils. Therefore, the project team should consider using cement that
meets Class 1 or higher requirements. Class 1 requirements are presented below:
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 20
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
10) All piping should be carefully tested before operation. Where piping penetrates a
slab, a positive bond break should be provided.
11) The contractor should take adequate care to keep excavated surfaces free of
standing water.
LATERAL LOADS
Values for equivalent fluid pressures and the coefficient for frictional resistance to sliding
are provided below. These values were based on moist unit weight ('y) of 127 pcf and an
angle of internal friction (0) of 21 degrees for site soils reworked as properly compacted
fill and are unfactored. Appropriate factors of safety should be included in design
calculations.
Shallow Elements Resisting Lateral Loads A friction coefficient of 0.26 between a
foundation element and the site soils may be used for design of shallow foundations and
thrust blocks resisting lateral loads.
Passive soil pressure at this site may be estimated using an equivalent fluid pressure of
230 pcf for drained conditions, to a maximum of 2,300 psf. The upper 1 foot of
embedment should be neglected for passive resistance, however. Where passive soil
pressure is used to resist lateral loads, it should be understood that significant lateral
strains will be required to mobilize the full value indicated above, likely 1 inch or more. A
reduced passive pressure can be used for reduced anticipated strains, however.
At -Rest and Active Lateral Earth Pressures Site soils placed as backfill against a
structure in an at -rest condition may be considered to exert an equivalent fluid unit weight
of 82 pcf.
Site soils placed as backfill where the full, active earth pressure condition applies may be
considered to exert an equivalent fluid unit weight of 61 pcf.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 19
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Slip joints should be observed periodically, particularly during the first several
years after construction. Slab movement can cause previously free -slipping joints
to bind. Measures should be taken to assure that slab isolation is maintained in
order to reduce the likelihood of damage.
5) Concrete slabs -on -grade should be provided with properly designed control joints.
ACI, AASHTO, and other industry groups provide guidelines for proper design and
construction concrete slabs -on -grade and associated jointing. The design and
construction of such joints should account for cracking as a result of shrinkage,
curling, tension, loading, and curing, as well as proposed slab use. Joint layout
based on the slab design may require more frequent, additional, or deeper joints,
and should reflect the configuration and proposed use of the slab.
Particular attention in slab joint layout should be paid to areas where slabs consist
of interior corners or curves (e.g., at column blockouts or reentrant corners) or
where slabs have high length to width ratios, significant slopes, thickness
transitions, high traffic loads, or other unique features. Improper placement or
construction will increase the potential for slab cracking.
6) Post -construction settlement may not displace slabs -on -grade and utility lines in
the soils beneath them to the same extent. Design of slab penetrations,
connections, and fixtures should accommodate up to 2 inches of differential
movement.
Construction Considerations for Slab -on -Grade Floors
7) Loose, soft, or otherwise unsuitable materials exposed on the prepared surface on
which the slab will be cast should be excavated and replaced with properly
compacted fill.
8) The fill section beneath a slab should be of uniform thickness.
9) Concrete slabs should be constructed and cured in accordance with applicable
industry standards and slab design specifications.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 18
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
FLOOR SYSTEMS
The floor system parameters and considerations provided below were developed based
on the performance expectations, geotechnical risks, and site conditions discussed in the
prior sections of this report. The use of these parameters assumes that the above
discussed risks and post -construction movement estimates are acceptable for the project.
The geotechnical parameters below may be used for design of slab -on -grade floors for
the proposed fuel farm. ACI Sections 301/302/360 provide guidance regarding concrete
slab -on -grade design and construction.
Geotechnical Parameters for Design of Slab -on -Grade -Floors
1) A slab -on -grade floor system should bear on the native clays and silts or a section
of properly compacted fill soils as discussed in the Geotechnical Considerations
for Design section of this report.
2) Floor slabs should be adequately reinforced. Floor slab design, including slab
thickness, concrete strength, jointing, and slab reinforcement should be developed
by a structural engineer.
3) An allowable vertical modulus of subgrade reaction (Kv) of 60 pci may be used for
design of a concrete, slab -on -grade floor bearing on a remedial fill section
constructed of site -derived soils.
If the floor slab bears on 24 or more inches of CDOT Class 5 or 6 Aggregate Base
Course compacted to 95 or more percent of the maximum dry density at moisture
contents near the optimum moisture content as determined by ASTM D1557, then
an allowable Kv of 250 pci may be used for design of a concrete, slab -on -grade
floor
This value is for a 1-foot by 1-foot plate; they should be adjusted for slab
dimension.
4) Floor slabs should be separated from all bearing walls and columns with slip joints,
which allow unrestrained vertical movement.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 17
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Shallow Foundation Construction
11) The contractor should take adequate care when making excavations not to
compromise the bearing or lateral support for nearby improvements.
12) Care should be taken when excavating the foundations to avoid disturbing the
supporting materials particularly in excavating the last few inches.
13) Foundation excavation bottoms may expose loose, organic, or otherwise
deleterious materials, including debris. Firm materials may become disturbed by
the excavation process. All such unsuitable materials should be excavated and
replaced with properly compacted fill or the foundation deepened.
14) Foundation -supporting soils may be disturbed or deform excessively under the
wheel loads of heavy construction vehicles as the excavations approach footing
bearing levels. Construction equipment should be as light as possible to limit
development of this condition. The movement of vehicles over proposed
foundation areas should be restricted.
15) All foundation subgrade should be compacted prior to placement of concrete.
16) Fill placed against the sides of the foundations should be properly compacted in
accordance with the Project Earthwork section of this report.
17) Concrete mat slabs should be constructed and cured in accordance with applicable
industry standards and slab design specifications.
Mat movements are directly related to the increases in moisture contents to the underlying
soils after construction is completed. The precautions and parameters itemized above will
not prevent the movement of mat slabs if the underlying materials are subjected to
moisture fluctuations. However, these steps will reduce the damage if such movement
occurs.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 16
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
compacted fill, placed in accordance with the Project Earthwork section of this
report. The mat subgrade should be properly moisture -density treated prior to
placement of concrete.
8) Concrete mats should be placed on properly prepared subgrade. They should also
be constructed and cured according to applicable standards and be provided with
properly designed and constructed control joints. The design and construction of
such joints should account for cracking as a result of shrinkage, tension, and
loading; curling; as well as proposed slab use. Joint layout based on the slab
design may require more frequent additional, or deeper joints, and should also be
based on the ultimate use and configuration of the slabs. Areas where slabs
consist of interior corners or curves (at column blockouts or around corners) or
where slabs have high length to width ratios, high degree of slopes, thickness
transitions, high traffic loads, or other unique features should be carefully
considered. The improper placement or construction of control joints will increase
the potential for slab cracking. ACI, AASHTO, and other industry groups provide
many guidelines for proper design and construction of concrete slabs -on -grade
and the associated jointing.
9) Connections of all types must be flexible and/or adjustable to accommodate the
anticipated, post -construction movements of the structure.
10) To the extent possible, piping should not be routed under shallow foundations,
particularly isolated pad foundations, nor in the soils supporting the foundations.
Where doing so cannot be avoided, there is increased risk to both the pipe and the
foundation. Measures should be included in design to protect the mats and
structures from increased settlement, and to protect the pipe from deformation.
Where piping penetrate footings or stem walls, etc., measures should be included
to accommodate the likely total and differential, post -construction movements
discussed in this report. Some footings also may experience lateral displacements
as structural loads are applied.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 15
Rifle -Garfield County Airport
Fuel Farm
Rifle, Colorado
This estimate of foundation movement from immediate compression of the
foundation soils is a component of the total, likely, post -construction movement
estimated for the fuel tanks at this site. (See the Geotechnica/ Considerations for
Design section of this report.) It is in addition to movements from post -construction
volume change in the native soils underlying the site.
To reduce differential settlements, foundation loads should be distributed as
uniform as possible. Differentially loaded foundations will settle differentially.
3) Spread footings should have a minimum lateral dimension of 16 or more inches
for linear strip footings and 24 or more inches for isolated pad footings. Actual
footing dimensions should be determined by the structural engineer.
4) An allowable vertical modulus of subgrade reaction (Kv) of 60 pci may be used for
design of a concrete, mat foundation bearing on the native site soils or a section
of properly placed and compacted fill.
If the floor slab bears on 24 or more inches of CDOT Class 5 or 6 Aggregate Base
Course compacted to 95 or more percent of the maximum dry density at moisture
contents near the optimum moisture content as determined by ASTM D1557, then
an allowable Kv of 250 pci may be used for design of a concrete, slab -on -grade
floor
These values are for a 1-foot x 1-foot plate; they should be adjusted for slab
dimension.
5) Foundations for all improvements should bear at an elevation 36 or more inches
below the lowest adjacent exterior finish grades to have adequate soil cover for
frost protection.
6) Geotechnical parameters for lateral resistance to foundation loads are provided in
the Lateral Loads section of this report.
7) The prepared surface on which the mat will be cast should be observed by a
geotechnical engineer prior to placement of reinforcement. Exposed loose, soft, or
otherwise unsuitable materials should be excavated and replaced with properly
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 14
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
FOUNDATION SYSTEMS
The foundation parameters and considerations provided below were developed based on
the performance expectations, geotechnical risks, and site conditions discussed in the
prior sections of this report. The foundation systems used should be based on the owner's
tolerance of post -construction movements and the associated cost -risk trade-offs. The
use of these parameters assumes that the above discussed, system -associated risks and
post -construction movement estimates are acceptable for the project.
Shallow Foundations The geotechnical parameters below may be used for design of
foundations for the proposed fuel tanks.
Geotechnical Parameters for Shallow Foundation Desi n
1) Spread footings or a mat plus road base system should bear on the native site
clays and silts or a section of properly compacted fill as discussed in the
Geotechnical Considerations for Design section of this report.
2) Footings bearing on the native site clays and silts or a section of properly placed
and compacted fill may be designed for an allowable soil bearing pressure of 2,000
psf for footings up to 6 feet in width.
A mat bearing on a properly placed and compacted fill section or on the native
clays and silts may be designed for an allowable soil bearing pressure of 750 psf
for a mat up to 20 feet in width.
These values may be increased by for transient loads such as wind or seismic
loading. For larger footings, a lower allowable bearing pressure may be
appropriate.
Compression of the bearing soils under the provided allowable bearing pressure
is estimated to be '/2 inch, based on an assumption of drained foundation
conditions. If foundation soils are subjected to an increase/fluctuation in moisture
content, the effective bearing capacity will be reduced and greater post -
construction movements than those estimated above may result.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 13
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
inches. Where improvement bear on the existing native site soils, which we anticipate will
be exposed at footing or mat bearing elevations, we estimate that post -construction
movements likely will be on the order of 1 inch. Lateral movements will result, as well.
Foundation and slab/flatwork movements of these magnitudes can result in significant
damage. Nearly all the proposed improvements are vulnerable in this regard.
Fuel Tank Foundation Types In GROUND's opinion, supporting the proposed fuel tanks
on drilled piers or driven piles foundation systems will provide the lowest estimates of likely
post -construction foundation movement (about'/2 inch, with similar differential movements
over spans of about 40 feet) and will provide the least risk of excessive foundation
movements. However, deep foundation systems may not be practical because they may
not be required to carry the structural loads and because the depth to bedrock at the site
is relatively great. (Bedrock was not encountered at the depths explored in our test holes,
which extended up to depths of 28 feet below existing grade.)
As a higher risk but commonly used alternative, shallow foundations (spread footings or a
mat) and slab -on -grade floor systems appear to be geotechnically feasible at this site.
Spread footing foundations for the proposed fuel tanks may bear on the native site soils
(encountered at approximately 3 feet below existing grades) or a section properly
compacted fill. Mat foundations or other slab -on -grade may bear on at least 6 inches of
CDOT Class 5 or 6 Road Base properly placed and compacted on the native clays and
silts or remedial fill section. Should undocumented fill soils be encountered at shallow
foundation or slab -on -grade bearing elevations, the undocumented fill soils should be
removed and replaced as properly compacted fill to a uniform depth across the entire fuel
tank footprint. As discussed elsewhere in this report, there may be significantly greater
depths of fill present at or near the proposed fuel farm footprint.
In general, we anticipate that the majority of the existing site soils will be suitable
geotechnically to be reused as fill. However, because not all the fill material was sampled
and tested, materials that are not suitable for reuse in project fills could be encountered in
the undocumented fill soils.
Additional geotechnical parameters for design of shallow foundations and slabs -on -grade
are provided in subsequent sections of this report.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 12
Rifle -Garfield County Airport
Fuel Farm
Rifle, Colorado
improvements supported directly on these soils have experienced damaging post -
construction movements where their effects have not been mitigated.
Another source of geotechnical risk at the site is the presence of undocumented fill soils,
which were recognized to depths of about 3 feet below existing grade. Testing records
for the fill were not available for review. GROUND, therefore, cannot guarantee that these
fill soils were placed in a controlled manner or that the compaction criteria used, if any,
was suitable to support the proposed construction. Thus, GROUND considers these fill
soils to be undocumented fill soils that are unsuitable to support to the proposed
construction in their current condition.
Given that the proposed fuel tank mat foundations are anticipated bear at depths greater
than the undocumented fill soils at the site, we do not anticipate that they pose a significant
risk to the foundation elements. Other shallow improvements, such as slabs -on -grade,
flatwork, and pavements, that are supported on directly on the undocumented fill soils
could experience significant and potentially damaging post -construction movements.
Additionally, due to the antecedent drainage in the area, much greater depths of
undocumented fill soils could be present beneath the proposed fuel farm footprint. Should
greater depths of undocumented fill soils be encountered, those fill soils should be
removed to their full depth and replaced as properly compacted fill.
There are several existing improvements within and near the proposed fuel tank footprints.
Where project excavations extend underneath shallow foundation elements of existing
improvements, there will be a loss in soil bearing support. In the case of lost soil bearing
support, additional settlements are likely to occur. Care should be taken when performing
project excavations to not compromise the bearing support of nearby improvements.
In general, we anticipate that the native clays and silts at the site will provide sufficient
support for relatively lightly loaded structures without excessive settlements.
Improvements imposing relatively heavy loads, may experience significant settlements if
supported directly on the underlying native soils.
Likely Post -construction Movements Based on our data, the selected depth of wetting,
and our experience with similar sites, we estimate improvements supported directly on the
existing fill soils are subject to likely, post -construction, vertical movements of 1'/2 to 2'/2
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 11
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
We encourage Vantage Aviation, LLC, upon receipt of this report, to discuss the risks and
the geotechnical information presented in this report with us.
Depth of Wetting at the Site The "depth of wetting" (the depth to which foundation soils
will gain moisture and experience volume change over the design -life of a structure)
estimated for a given site strongly affects the anticipated performance of structures at that
site. Based on the data obtained at this site and our experience with similar geotechnical
settings, a depth of wetting of 20 feet was used to develop geotechnical parameters for
foundation system design. A depth of wetting of 20 feet is equal to or greater than the
depth of wetting found at about 72 percent of the sites evaluated in a study by Walsh and
others (2009).4
"Depths of wetting" of 30, 40, or 70 feet or more have been considered (e.g., Chao and
others, 2006)5 and have been encountered locally in the field. Depths of wetting of such
magnitudes, however, generally are in unusual geologic conditions, such as the Dipping
Bedrock Overlay District near Denver, Colorado, or identified forensically in unusual
circumstances such as a pipe leak that has remained unrepaired for an extended period.
In our experience, such deep depths of wetting are considered only rarely in engineering
consulting practice in more typical geologic settings in the Western Slope area.
GROUND considers wetting to a depth of 20 feet to be appropriately conservative for the
proposed project. However, if Vantage Aviation, LLC prefers that a more conservative (or
less conservative) depth be used to develop geotechnical parameters for design,
GROUND should be contacted to revise the criteria provided herein.
General Geotechnical Risk In GROUND's opinion, the primary geotechnical risk at this
site is the presence of consolidating materials within the native soils. During this
exploration, consolidations up to about 0.6 percent were measured against surcharge
loads approximating in -place overburden pressures. Consolidations of similar and greater
magnitudes have been measured is similar soils in the greater project area, and
^ Walsh, K.D., C.A. Colby, W.N. Houston and S.A. Houston, 2009, Method for Evaluation of Depth of Wetting in Residential
Areas, Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers, Vol. 135,
No. 2, pp. 169 — 176.
e Chao, K-C, D.D. Overton, and J.D. Miller, 2006, The Effects of Site Conditions on the Predicted Time Rate of Heave,
Unsaturated Soils 2006, American Society of Civil Engineers, Special Publication No. 147, pp. 2086 — 2097.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 10
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
It has been our experience that surface and groundwater levels fluctuate greatly in
Colorado's mountainous areas, primarily due to seasonal conditions such as spring runoff.
These conditions are often highly variable and difficult to predict. Although these
conditions generally exist for 1 to 3 months annually, their impact on design can be
significant. In Garfield County, Colorado, it is common during construction to encounter
dry conditions in the fall and wet conditions in the spring with relative groundwater
fluctuations of 10 feet or more. This is particularly critical for foundation and deep utility
excavations, cut slopes, culvert sizing, and for development adjacent to intermittently dry
streams or rivers. Furthermore, if development has not established positive surface
drainage, particularly prior to temporary winter shutdown procedures, other components
of partial and complete development are compromised. The contractor and the project
team should consider these complex conditions prior to commencing, as well as during,
construction.
Swell -Consolidation Testing of selected samples of on -site soils recovered from the test
holes indicated consolidations of up to 0.6 percent when measured under surcharge loads
approximating in -place overburden pressures. Swells were not measured in the tested
samples. (See Table 1.)
GEOTECHNICAL CONSIDERATIONS FOR DESIGN
The conclusions and parameters provided in this report were based on the data presented
herein, our experience in the general project area with similar structures, and our
engineering judgment with regard to the applicability of the data and methods of
forecasting future performance. A variety of engineering parameters were considered as
indicators of potential future soil movements.
Our parameters and conclusions were based on our judgment of "likely movement
potentials," (i.e., the amount of movement likely to be realized if site drainage is generally
effective, estimated to a reasonable degree of engineering certainty) as well as our
assumptions about the owner's willingness to accept geotechnical risk. "Maximum
possible" movement estimates necessarily will be larger than those presented herein,
They also have a significantly lower likelihood of being realized in our opinion, and
generally require more expensive measures to address.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 9
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
The existing fill soils may contain coarse gravels and cobbles, as well as similarly sized
pieces of construction debris, even where these materials were not recognized in the test
holes. Delineation of the complete lateral and vertical extents of the fills at the site and
their compositions was beyond our present scope of services. If more detailed information
regarding fill extents and compositions at the site are of significance, they should be
evaluated using test pits.
Similarly, coarse gravel and larger clasts are not well represented in small diameter liner
samples collected from the test holes. Therefore, such materials may be present even
where not called out in the material descriptions herein.
Fill consisted of clays and silts with varying fractions of sand. They were moist, slightly
plastic, stiff to hard, and brown in color.
Clays and Silts consisted of silty to sandy clays with local clayey to silty sands. The
granular fractions consisted of fine sands with scattered medium to coarse sands and
gravels. Claystone and siltstone clasts were also noted locally within these soils. The
clays and silts were moist to wet, slightly to moderately plastic, stiff to hard, and brown to
gray -brown in color. Iron staining was noted commonly. Secondary carbonates were
noted locally.
Groundwater was not encountered in the test holes at the time of drilling to the depths
explored. The test holes were backfilled upon drilling completion per Code of Colorado
Regulations (2 CCR 402-2). Additionally, review of estimates of saturation of the samples
suggested that the shallow site soils had not been saturated recently.
Groundwater levels can be expected to fluctuate, however, in response to annual and
longer -term cycles of precipitation, irrigation, surface drainage, nearby rivers and creeks,
land use, and the development of transient, perched water conditions. The groundwater
observations performed during our exploration must be interpreted carefully as they are
short-term and do not constitute a groundwater study. In the event the Vantage Aviation,
LLC desires additional/repeated groundwater level observations, GROUND should be
contacted; additional exploration and fees will be necessary in this regard.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 8
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
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Local Conditions In general, the test holes penetrated approximately 3 to 4 inches of
road base or 5 inches or asphalt3 underlain by approximately 7 inches of road base. Below
the surficial materials, undocumented fill soils were encountered in all the test holes to
depths of 2 to 3 feet below existing grades. Beneath the fill soils, clays and silts extended
to the depths explored.
We interpret the fill soils to be materials placed during the construction of the airport and
related improvements, the clays and silts are interpreted to be interbedded colluvial and
alluvial deposits.
Fill materials were recognized in the test holes and are likely are present across the site.
(See the Site Conditions section of this report.) Note that due to the antecedent drains e
in the area and the inherent limitations of test hales. significantly -greater thickness
de the of fill may be encountered beneath the fuel farm footprint.
' Asphalt and concrete pavement thicknesses, as well as the underlying road base, if present, are difficult to determine
with precision in small diameter test holes. If existing pavement thicknesses are of significance to the project, then
additional, larger diameter test holes or pavement cores should be drilled.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 7
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
laboratory testing program are summarized in Tables 1 and 2. A hydrometer plot is
provided in Figure 4.
SUBSURFACE CONDITIONS
Geologic Setting Published geologic maps, e.g., Shorba and Scott (2001),2 depict the
site as underlain by colluvial sheetwash deposits over loess (Qsw/Qlo). Holocene and
Pleistocene Alluvium and Colluvium (Qac) and other alluvial and colluvial deposits were
mapped in the greater project area. These surficial deposits are mapped as being
underlain by the Eocene Shire Member of the Wasatch Formation (Tws). A portion of that
map is reproduced on the next page.
In the project area, alluvial (stream, terrace, and outwash) and colluvial (landslide, slope
wash, etc.) deposits typically consist of fine to coarse sands, gravels, and cobbles with
silts and clays. Boulders also can be present locally. The larger clasts present in alluvial
deposits may be awkward or difficult to handle and may not be appropriate for reuse in all
project fills.
Loess, an eolian (windblown) deposit, typically consists of fine sands and silts with varying
fractions of clays. Weathering typically increases the clay contents of these deposits.
Eolian deposits, such as loess, can be subject to hydro -consolidation ("collapse").
The Shire Member of the Wasatch Formation, in the project area, consists largely of
claystones, siltstones, sandstones, and conglomerates. The formation includes well
cemented beds which can be very hard and difficult to excavate, handle, and/or process.
Additionally, the siltstones and claystones can be moderately to highly expansive.
2 Shroba, R.R. and Scott, R.B. (2001) Geology map of the Silt quadrangle, Garfield County, Colorado. U.S. Geological
Survey. Miscellaneous Field Studies Map MF-2331. 1:24,000.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 6
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
SUBSURFACE EXPLORATION
Subsurface exploration for the project was
conducted in January 2025. A total of 3
test holes were drilled with a conventional,
buggy -mounted drilling rig advancing 4-
inch diameter, solid stem, continuous flight
auger to evaluate the subsurface
conditions and retrieve samples for
laboratory testing. Of these, 2 test holes
were advanced within/near the proposed
approximate fuel farm footprint to depths
of about 25 and 28 feet below existing grade. The remaining test hole was advanced to
a depth of about 7 feet, within the area proposed for paving. GROUND directed the
subsurface exploration, logged the test holes in the field, and prepared the samples for
transport to our laboratory.
Samples of the subsurface materials were retrieved with a 2-inch inner diameter California
liner sampler. The sampler was driven into the substrata with blows from a 140-pound
hammer falling 30 inches. Penetration resistance values, when properly evaluated,
indicate the relative density or consistency of soils. Depths at which the samples were
obtained and associated penetration resistance values are shown on the test hole logs.
The approximate locations of the test holes are shown in Figure 1. Summary logs of the
test holes are presented in Figure 2. A legend and notes are provided in Figure 3.
Detailed logs are provided in Appendix A.
LABORATORY TESTING
Samples retrieved from our test holes were examined and visually classified in the
laboratory by the project engineer. Laboratory testing of soil samples included standard
property tests, such as natural moisture contents, dry unit weights, grain size analyses,
and Atterberg limits. Swell —consolidation, water-soluble sulfate content, and a suite of
corrosivity tests were completed on selected samples as well. Laboratory tests were
performed in general accordance with applicable ASTM protocols. Results of the
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 5
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Marks for buried utilities were observed at the site, as well as overhead utilities. A
significant amount of the buried utilities in the area appeared to be adjacent to the
perimeter fence, just outside the site footprint.
Review of historical aerial imagery available on Google Earth indicated that development
of the site began sometime between 1993 (earliest available image) and 2002. Between
2006 and 2010, the fuel infrastructure to the west was constructed. The fuel tanks were
relocated to their existing configuration in between 2014 and 2016. Between 2016 and
2022, the garage structures were constructed; the fuel farm has remained in that general
configuration since. Additionally, further historic images depict several drainages at the
site that were filled during construction of other portions of the airport. Therefore, grater
depths of fill, up to 40 feet or more, may be encountered locally at other portions of the
airport. Select images of the development of the site are provided below.
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Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 4
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
SITE CONDITIONS
At the time of our subsurface exploration
program, the site was developed as a
vehicle storage lot. Two pole barns
provided protection for maintenance
equipment within the approximate fuel
farm footprint. Four fuel tanks supported
on a concrete pad surrounded by bollards
were present to the northwest of the site.
A maintenance building with associated
garages and perimeter concrete flatwork
were present on the northwest side. Other ancillary structures to the south included a
smaller garage, a cell tower with
associated equipment room, and smaller
utility structures
The site was bordered to the west by oil
and gas infrastructure, additional fuel farm
infrastructure to the north, airport
infrastructure to the east, and undeveloped
land to the south. The project site was
generally flat to gently sloping toward the
east.
The majority of the ground was aggregate -
surfaced. Asphalt pavements surrounded
the fuel tanks and surfaced the access
drive from the airport. The asphalt
pavements were moderately distressed;
evidence of local rutting was observed, as
was cracking, both longitudinal and
transverse. Some of the larger cracks had
been sealed.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 3
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
PROPOSED CONSTRUCTION
Based on the provided information and plans,' we understand an approximately 5,075
square -foot fuel farm is planned south of the existing fuel farm at the Rifle —Garfield County
Airport. The fuel farm is anticipated to consist of three 20,000-gallon, one 12,000-gallon,
and one 2,000-gallon fuel tanks supported on shallow foundations. New moderate -weight
(truck) pavement areas are also planned around the fuel farm.
We understand that no new FAA aircraft pavement sections are planned as part of
construction or will be addressed by others.
Grading information was not provided to GROUND at the time of the preparation of this
report, but we anticipate that grade changes will be relatively limited, on the order of 3 feet
or less.
If our described understanding/interpretation of the proposed project is incorrect
or project elements differ in any way from that expressed above, including changes
to improvement locations, dimensions, orientations, loading conditions,
elevations/grades, etc., and/or additional buildings/structures/site improvements
are incorporated into this project, either after the original information was provided
to us or after the date of this report, GROUND or another geotechnical engineer
must be retained to reevaluate the conclusions and parameters presented herein.
Performance Expectations Based on our experience with similar projects, we
understand that post -construction, structure foundation movements on the order of 1 inch
are acceptable to, and anticipated by Vantage Aviation, LLC, as are the resultant distress
and maintenance measures. Similarly, we anticipate that movements of somewhat
greater magnitude (2 to 3 inches) are acceptable and anticipated for pavements.
GROUND will be available to discuss the risks and remedial approaches outlined in this
report, as well as other potential approaches, upon request if post -construction
movements of these magnitudes are not acceptable and anticipated.
'Hauser Architects (March 12, 2024) Vantage Rifle—RIL A-5 AND A-6, RIL, Site Plan. Sheet A1.1.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 2
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
PURPOSE AND SCOPE OF STUDY
This report presents the results of a geotechnical evaluation performed by GROUND
Engineering Consultants, Inc. (GROUND) in support of design and construction of the
proposed fuel farm to be constructed on the west side of the Rifle —Garfield County Airport
in Rifle, Colorado. Our study was conducted in general accordance with GROUND's
Proposal Number 2501-0084 dated January 22, 2025 between Vantage Aviation, LLC and
GROUND.
A field exploration program was conducted to obtain information on the subsurface
conditions. Material samples obtained during the subsurface exploration were tested in
the laboratory to provide data on the classification and engineering characteristics of the
on -site soils. The results of the field exploration and laboratory testing are presented
herein.
This report has been prepared to summarize the data obtained and to present our findings
and conclusions based on the proposed development/improvements and the subsurface
conditions encountered. Design parameters and a discussion of engineering
considerations related to the proposed improvements are included herein. This report
should be understood and utilized in its entirety; specific sections of the text, drawings,
graphs, tables, and other information contained within this report are intended to be
understood in the context of the entire report. This includes the Closure section of the
report which outlines important limitations on the information contained herein.
This report was prepared for design purposes of Vantage Aviation, LLC, based on our
understanding of the project at the time of preparation of this report. The data,
conclusions, opinions, and geotechnical parameters provided herein should not be
construed to be sufficient for other purposes, including the use by contractors, or any other
parties for any reason not specifically related to the design of the project. Furthermore,
the information provided in this report was based on the exploration and testing methods
described below. Deviations between what was reported herein and the actual surface
and/or subsurface conditions may exist, and in some cases those deviations may be
significant.
Job No. 25-6000 GROUND Engineering Consultants, Inc. Page 1
TABLE OF CONTENTS
Page
Purposeand Scope of Study......................................................................................
1
ProposedConstruction................................................................................................
2
SiteConditions............................................................................................................
3
SubsurfaceExploration...............................................................................................
5
LaboratoryTesting ................. •...................................................................................
5
SubsurfaceConditions .............................................................................................
6
Geotechnical Considerations for Design
..................................................................... 9
FoundationSystems..................................................................................................
13
FloorSystems............................................................................................................
17
LateralLoads.............................................................................................................
19
WaterSoluble Sulfates...............................................................................................
19
SoilCorrosivity...........................................................................................................
21
ProjectEarthwork.......................................................................................................
24
Excavation Considerations.........................................................................................
28
PipingInstallation.......................................................................................................
30
SurfaceDrainage.......................................................................................................
33
SubsurfaceDrainage.................................................................................................
35
PavementSections....................................................................................................
36
ExteriorFlatwork........................................................................................................
42
Closure.......................................................................................................................
46
Locationsof Test Holes....................................................................................
Figure 1
Logsof the Test Holes.....................................................................................
Figure 2
Legendand Notes............................................................................................
Figure 3
Hydrometer Test Results.................................................................................
Figure 4
Summary of Laboratory Test Results........................................................
Tables 1 & 2
Detailed Logs of the Test Holes..................................................................
Appendix A
GRIEMU"'OE10
ENGINEERING
Geotechnical Evaluation
Rifle —Garfield County Airport
Fuel Farm
Rifle, Colorado
Prepared For:
Vantage Aviation, LLC
3543 East Penedes Drive
Gilbert, Arizona
Attention: Mr. Ryan Maxfield
Job Number: 25-6000
March 4, 2025
41 Inverness Drive East I Englewood, CO 80112 (303) 289-1989 1 www.groundeng.com
ENGLEWOOD I COMMERCE CITY I LOVELAND GRANBY I GYPSUM I COLORADO SPRINGS