HomeMy WebLinkAbout1.26 ImpactAnalysis-GeotechStudyHEPWORTH - PAWLAK GEOTECHNICAL
Hepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone: 970-945-7988
Fax: 970-945-8454
email: hpgeo@hpgeotech.com
GEOTECHNICAL ENGINEERING STUDY
PROPOSED RIVER EDGE COLORADO
PUD AND PRELIMINARY PLAN
HIGHWAY 82 AND CATTLE CREEK
GARFIELD COUNTY, COLORADO
JOB NO. 110 337A
NOVEMBER 15, 2010
PREPARED FOR:
CARBONDALE INVESTMENTS, LLC
ATTN: ROCKY SHEPARD
rshepard@westpacinv.com
CARBONDALE, COLORADO 81623
Parker 3013-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED DEVELOPMENT - 1 -
SITE CONDITIONS - 2 -
REGIONAL GEOLOGIC SETTING - 3 -
CARBONDALE EVAPORITE COLLAPSE CENTER - 3 -
GEOLOGICALLY YOUNG FAULTS - 4
PROJECT SITE GEOLOGY - 4 -
EAGLE VALLEY EVAPORITE (Pee) - 4
SURFICIAL SOIL DEPOSITS AND LANDFORMS - 5
GRADED AREAS (gr and ss) - g -
FIELD EXPLORATION - 8
SUBSURFACE CONDITIONS - 9 -
GEOLOGIC SITE ASSESSMENT - 10 -
SINKHOLE HAZARD - 10 -
STEEP TERRACE ESCARPMENTS - 13 -
ACTIVE STREAM BANK EROSION - 13 -
DEBRIS FLOWS AND FLOODS _ 13
EARTHQUAKE CONSIDERATIONS - 14 -
PRELIMINARY DESIGN RECOMMENDATIONS - 15 -
FOUNDATIONS - 15 -
FLOOR SLABS - 16 -
UNDERDRAIN SYSTEM - 16 -
SITE GRADING - 16 -
SURFACE DRAINAGE - 17 -
PAVEMENT SUBGRADE _ 18 -
WATER SOLUBLE SULFATES - 18 -
RADIATION POTENTIAL - 18 -
LIMITATIONS - 18 -
REFERENCES -20-
FIGURE 1 — PROJECT SITE LOCATION
FIGURE 2 — REGIONAL GEOLOGY MAP
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FIGURE 3 - WESTERN COLORADO EVAPORITE REGIONS
FIGURE 4 - GEOLOGICALLY YOUNG FAULTS AND LARGER HISTORIC
EARTHQUAKES
FIGURE 5 - PROJECT AREA GEOLOGY MAP - NORTH PART
FIGURE 6 - PROJECT AREA GEOLOGY MAP - SOUTH PART
FIGURE 7 - SINKHOLE HAZARDS ZONES - NORTH PART
FIGURE 8 - SINKHOLE HAZARDS ZONES - SOUTH PART
FIGURE 9 - TERRACE ESCARPMENTS AND ACTIVE BANK STREAM EROSION
- NORTH PART
FIGURE 10 - TERRACE ESCARPMENTS AND ACTIVE BANK STREAM
EROSION - SOUTH PART
FIGURES 11 AND 12 - LOGS OF EXPLORATORY BORINGS
FIGURE 13 - LEGEND AND NOTES
FIGURE 14 - SWELL -CONSOLIDATION TEST RESULTS
FIGURES 15 THROUGH 20 - GRADATION TEST RESULTS
FIGURE 21 - HVEEM STABILOMETER RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a geotechnical engineering study for the proposed River
Edge Colorado development (Project) to be located at Highway 82 and Cattle Creek,
Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the
study was to evaluate the geologic and subsurface conditions and their potential impacts
on the project and to support an application for PUD Plan review and Preliminary Plan
design. The study was conducted according to our proposal for geotechnical engineering
services to Carbondale Investments, LLC, dated September 20, 2010 and includes a
summary of previous engineering studies conducted on the property (Hepworth-Pawlak
Geotechnical, 2008).
A field exploration program consisting of exploratory borings and review of previous
geotechnical studies were conducted to obtain information on the site and subsurface
conditions. Samples ofthe subsoils obtained during the field exploration were tested in
the Iaboratory to determine their classification, swell -consolidation potential, strength and
other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for project planning and preliminary
design. This report summarizes the data obtained during this study and presents our
conclusions and recommendations based on the proposed development, subsurface
conditions encountered and the previous site studies.
PROPOSED DEVELOPMENT
The proposed development will cover about 160 acres and consist primarily of 0.13 to
0.25 acre single family lots with some garden homes and a neighborhood center.
Infrastructure will include a network of residential streets and utilities. Nearly 50% of the
development area will be parks and open space. The preliminary project layout at the
time of this study is shown of Figures 5 through 10. Grading plans were not available at
the time of this study. The development is mostly on nearly level river terraces that lie
about 50 to 80 feet above the Roaring Fork River. Since the proposed development area
is nearly level, major cuts and fills are not expected. Our review ofthe preliminary
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development and grading plans to assess compliance with the information presented in
this report will be presented under separate cover.
SITE CONDITIONS
The project site is located at the confluence of Cattle Creek with the Roaring Fork River,
about seven and one-half miles south of Glenwood Springs. The topography in the area is
shown by the contour lines on Figure 1. The proposed 160 acre development area is
located mostly on nearly level river terraces that stand between about 50 to 80 feet above
the Roaring Fork River. The terraces have an average down -valley slope of about fifteen
feet per mile. Steep escarpments separate the terrace levels and the escarpments typically
have slopes of around 60 percent. The natural landscape over much of the proposed
development area has been modified by grading for the proposed Bair Chase golf course
project that was abandoned. This grading took place in 2005 and the graded area is
shown on Figures 5 and 6 by map symbol gr.
Cattle Creek crosses through the property from east to west and roughly divides the
property in half Cattle Creek is a moderate sized perennial stream with a large drainage
basin to the east. Small alluvial fans (map symbol Qf on Figures 5 and 6) are present on
the terrace surfaces in the eastern part of project area. The upper parts of all of these fans
have been removed by grading for Highway 82 and development to the east of the
highway. The fans developed at the mouths of small drainage basins on the eastern
Roaring Fork River valley side. These basins support ephemeral steams that only flow
following heavy rainfall and snow melt.
Prior to the abandoned Bair Chase grading, the property was an operating ranch. The
higher level terrace surfaces in the vicinity of the proposed development were previously
irrigated hay fields and pasture. The large irrigation ditch that crosses through the
property was placed in a subsurface pipe as part of the abandoned Bair Chase grading.
The graded areas are essentially devoid of vegetation except for weeds. Vegetation
outside the previously irrigated areas is mostly sage, oak and other brush on the fans and
terrace escarpments. Cottonwood trees, grass and willows are present on the lower
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terraces adjacent to the Roaring Fork River and Cattle Creek. An abandoned railroad
grade that has been converted to a pedestrian and bicycle path follows the eastern side of
the development area. Residential and light commercial development is located to the
north of Highway 82. Residential development is located to the north and east. The area
to the south is ranches and rangeland.
REGIONAL GEOLOGIC SETTING
The regional geology in the project area is shown on Figure 2. The near surface
formation rock in the area is the Eagle Valley Evaporite (Pze on Figure 2). The evaporite
was deposited in the northwest -trending central Colorado trough during the ancestral
Rocky Mountain orogeny, about 300 million years ago. The evaporite between
Carbondale and about 3 miles south of Glenwood Springs is part ofthe Roaring Fork
diapir which forms the core of the north -trending Cattle Creek anticline (Kirkham and
Others, 2002). The west limb ofthe anticline in this part ofthe Roaring Fork River valley
coincides with the Grand Hogback monocline that marks the western limit of the
Carbondale evaporite collapse center.
CARBONDALE EVAPORITE COLLAPSE CENTER
The Carbondale evaporite collapse center is the western of two regional evaporite
collapse centers present in the western Colorado evaporite region, see Figure 3. The
Carbondale center covers about 460 square miles and as much as 4,000 feet of regional
ground subsidence is believed to have occurred during the past 10 million years in the
vicinity of Carbondale as a result of dissolution and flowage of evaporite from beneath
the region (Kirkham and Others, 2002). Much of this subsidence appears to have
occurred within the past 3 million years which also corresponds to high incision rates
along the Colorado River and its principle tributaries that include the Roaring Fork and
Crystal Rivers (Kunk and Others, 2002). In addition to the regional subsidence, evaporite
related deformations along the Roaring Fork diapir include back tilting a few degrees of
the older river terraces including the higher terraces at the project site (Kirkham and
Others, 2002). It is uncertain if the regional subsidence and evaporite deformation along
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the Roaring Fork diapir are still an active geomorphic process or if evaporite
deformations have stopped. If still active, present deformations are likely occurring at
rates similar to past long-term rates of between 0.5 and 1.6 inches per 100 years. These
slow deformation rates should not present a potential risk to buildings and other facilities
being considered at the project site.
GEOLOGICALLY YOUNG FAULTS
Geologically young faults related to evaporite tectonics are present in the Carbondale
evaporite collapse center in the vicinity of the project site but considering the nature of
evaporite tectonics these fault are not considered capable of generating large earthquakes.
The closest geologically young faults that are less than about 15,000 years old, not related
to evaporite tectonics, and considered capable of generating large earthquakes are located
in the Rio Grande rift to the east ofthe project site, see Figure 4. The northern section of
the Williams Fork Mountains fault zone Q50 is located about 62 miles to the northeast
and the southern section ofthe Sawatch fault zone Q56b is located about 67 miles to the
southeast. At these distances large earthquakes at the maximum probable level of around
M6.5 on the two closest geologically young fault zones should not produce strong ground
shaking at the project site that is greater than the ground shaking shown on the U. S.
Geological Survey 2002 National Seismic Hazards Maps (Frankel and Others, 2002).
PROJECT SITE GEOLOGY
The main geologic features in the project area are shown on Figures 5 and 6. The project
area geology map is based on our field observations, aerial photograph interpretations and
information for the subsurface exploration. The map is a modification of the regional
geology map by Kirkham and Others (1996). Geologic map units present in the proposed
development area are discussed below.
EAGLE VALLEY EVAPORITE (Pee)
The middle Pennsylvanian -age, Eagle Valley Evaporite is present below thin colluvium
(Qc/Pee) on (1) the lower terrace escarpments near the Roaring Fork River, (2) on the
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eastern Roaring Fork River valley side to the east of Highway 82, and (3) encountered in
a few of the deeper exploratory borings drilled in 2001 (Hepworth-Pawlak Geotechnical,
2008). Evaporite was encountered below the terrace alluvium at depths between 30 and
60 feet in Borings B104, B107 and B108 that are located on the higher terraces near the
river, see Figures 5 and 6. Evaporite was encountered below alluvial fan and terrace
alluvium at a depth of 113 feet in Boring B101 that is located near the terrace -valley side
transition in the eastern part ofthe project area. Penetration resistance values in the
borings that encountered evaporite were 127 ± 32 blows per foot. The thickness of the
evaporite in the project area is perhaps 9,000 feet where it is tectonically thickened in the
Roaring Fork diapir along the core of the Cattle Creek anticline (Kirkham and Others,
1996). The Eagle Valley Evaporite is a sequence of evaporite rocks consisting mainly of
massive to laminated gypsum, anhydrite and halite that is interbedded with light colored
mudstone and fine-grained sandstone, thin carbonate beds, and black shale (Kirkham and
Others, 1996). The Shannon Oil Company Ross No. 1 test well encountered a 935 -foot
thick halite sequence in the bottom of the well below a depth of 2,065 feet. This test well
is located on the west side ofthe Roaring Fork River near where Cattle Creek joins the
river. The evaporites in the Eagle Valley Evaporite are soluble in circulating groundwater
and shallow subsurface solution voids that can develop into sinkholes are locally present
in the formation. Several sinkholes are present in and close to the proposed development
area, see Figures 5 and 6.
SURFICIAL SOIL DEPOSITS AND LANDFORMS
The surficial soil deposits and landforms in the project area are largely associated with
cyclic deposition and erosion related to glacial and interglacial climatic fluctuations
during the latter part of the Quaternary, about the past 480 thousand years. During the
late Quaternary some minor modifications to the landforms related to evaporite tectonics
have occurred, such as river terrace tilting, but Iate Quaternary evaporite tectonics has not
substantially modified the climate related deposits and landforms. The main landforms at
the project site are (1) post -glacial alluvial terraces along the Roaring Fork River and
Cattle Creek, (2) Pinedale glacial outwash terraces along the Roaring Fork River and
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related alluvial terraces along Cattle Creek, and (3) coalescing alluvial fans along the east
margin of the valley floor.
Post -Glacial Terraces (Qt1-2 and Qa1-2)
The post -glacial alluvial terraces along the Roaring Fork River and Cattle Creek formed
during about the past 15,000 years since the end of the late Pleistocene -age, Pinedale
glaciations in the headwaters of the river. The lower Qtl terrace stands about 5 feet
above the river and the higher Qt2 terrace stands about 13 feet above the river. The Qal
and Qa2 Cattle Creek terraces respectively grade to the Qtl and Qt2 river terraces. A
small part of the proposed development area in the southern part of the project area is
located on the post -glacial Qt2 terrace. Elsewhere the proposed development will be
located on the higher Pinedale terraces. Exploratory borings have not been drilled in the
post -glacial terrace alluvium. The alluvium is described as a clast-supported deposit of
silty sand with occasional bouldery, pebble and cobble gravel interbedded and often
overlain by sandy silt and silty sand (Kirkham and Others, 1996). Pedogenetic soil
profiles on the post -glacial terraces are weakly developed A/C and A/Cg profiles
(National Resources Conservation Service, 2008). Shallow groundwater should be
expected below the Qt1 and Qal terraces.
Pinedale Terraces (Qt3-7 and Qa3-4)
The Pinedale outwash terraces (Qt3-7) along the Roaring Fork River and the associated
Cattle Creek terraces formed during the Pinedale glaciations in the headwaters of the
river. The Pinedale glaciations in the Rocky Mountains occurred between about 15 and
35 thousand years ago (marine oxygen -isotope Stage 2) and terrace Qt3 and Qt4 at the
project site probably formed at this time. The higher Qt5, Qt6 and Qt7 terraces may have
formed during the earlier 65 to 79 thousand year old marine oxygen -isotope Stage 4. The
lowest outwash terrace Qt3 lies about 40 feet above the river, the Qt4 terrace is about 50
feet above the river, the Qt5 terrace is about 65 feet above the river, the Qt6 terrace is
about 75 feet above the river and the Qt7 terrace is about 80 feet above the river. The
Qa3 and Qa4 Cattle Creek terraces respectively grade to the Qt3 and Qt4 river terraces.
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Terraces higher than level four are not present along Cattle Creek. Grading in 2005 for
the abandoned Bair Chase development has removed all of the Qt5 and Qt6 terraces.
Essentially all of the proposed development will be on the graded area and on the third,
fourth and seventh terrace levels.
Our exploratory borings show that the alluvium under the Pinedale terraces associated
with the Roaring Fork River and Cattle Creek are a clast-supported deposit of rounded
gravel, cobbles and boulders in a silty sand matrix. The silt fraction of the terrace deposits
is 14 ± 3 percent. The larger boulders in the terrace deposits have maximum dimensions
of 2.5 ± 0.4 feet. Practical 4 -inch diameter auger refusal on boulders occurred at depths
between 5 and 20 feet in most of our exploratory borings. Penetration resistance values in
the borings were 100 ± 51 blows per foot. An upper fine-grained soil layer is sometimes,
but not always, present at the terrace surfaces. When present, the fine-grained soils are
3.8 ± 2.0 feet thick. The fine-grained soils are sandy, low plasticity (P1 of 10 ± 3) clay
with 79 ± 8 percent passing the No. 200 sieve. Penetration resistance values in the
borings were 21 ± 9 blows per foot. Pedogenetic soil profiles are well developed in the
Pinedale terraces and include A/BtBk/C and A/Bt/Bk/Ck profiles (National Resources
and Conservation Service, 2008). This indicates that the terrace surfaces have been stable
with respect to erosion and deposition for over about 5,000 years.
Alluvial Fans (Qf)
Coalescing alluvial fans (Qf) have developed at the mouth of the numerous, small
drainage basins on the east Roaring Fork River valley side where the ephemeral streams
in these basins discharge on terrace surfaces. Before construction of Highway 82 and
development to the east of the highway, the alluvial fans formed a continuous apron at the
terrace -valley side transition. Most of the upper parts of the fans have been removed by
grading for these facilities. With the exception of the executive lot in the southern part of
the proposed development, development is not being considered on the alluvial fans. The
alluvial fans are largely the result of infrequent sediment deposition related to debris
flows and floods triggered by unusually intense thunderstorms over the relatively small
drainage basins on the east valley side. The alluvial fan deposits at our boring sites were
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12.1 ± 3.2 feet deep and overlie terrace alluvium. The fan deposits are sandy, low
plasticity clay (PI of 13 ± 4) with 78 ± 9 percent passing the No. 200 sieve. Penetration
resistance values in the borings were 15 ± 4 blows per foot. Swell -consolidation tests
show that the fan deposits do not have a high collapse potential (settlement after wetting
under a constant load) and are moderately compressible under increased loading after
wetting.
Pedogenetic soil profiles in the fan deposits are mostly weakly developed AIC and A/Ck
profiles (National Resources Conservation Service, 2008). This indicates that the fans are
geologically young landforms and are still potential sites of debris flow and flood
deposition.
GRADED AREAS (gr and ss)
The natural Iandscape over much of the proposed development area has been modified by
grading (gr) for the abandoned Bair Chase development in 2005. The previous Bair
Chase grading consists of both cut and fill areas and the fills are mostly composed of
coarse-grained terrace alluvium. The terrace topsoil and upper fine-grained deposits were
separated during grading and have been placed in several large stockpiles as shown by
map symbol ss on Figures 5 and 6. The character of the coarse- and fine-grained terrace
alluvium is described in the Pinedale Terraces (Qt3-7 and Qa3-4) section above.
Practical 4 -inch diameter auger refusal was encountered on boulders at depths between 3
and 5 feet in most of the borings drilled in the graded areas. Penetration resistance values
in the borings in the graded areas were 65 ± 31 blows per foot. It is uncertain if the fills
for the abandoned Bair Chase project were placed under the supervision of a geotechnical
engineer and if the fills are suitable to support building foundations.
FIELD EXPLORATION
The field exploration for the current project was conducted on October 17, 18 and 19,
2010. Exploration for the previous studies was conducted between August 16 and
September 13, 2001 (000 and 100 Series borings) and on May 23, 2005 (200 Series
borings). Twenty-one exploratory borings (300 Series borings) were drilled for the
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current study at the locations shown on Figures 5 and 6 to evaluate the subsurface
conditions throughout the proposed development area. The borings were advanced with
4 -inch diameter continuous flight augers powered by a truck -mounted CME -45B drill rig.
The borings were logged by representatives of Hepworth-Pawlak Geotechnical, Inc.
Samples ofthe subsoils were taken with 1 %-inch and 2 inch I.D. spoon samplers. The
samplers were driven into the subsoils at various depths with blows from a 140 pound
hammer falling 30 inches. This test is similar to the standard penetration test described
by ASTM Method D-1586. The penetration resistance values are an indication of the
relative density or consistency ofthe subsoils. Depths at which the samples were taken
and penetration resistance values are shown on the Logs of Exploratory Borings, Figures
11 and 12. The samples were returned to our laboratory for review by the project
engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface profiles encountered in the proposed development area are
shown on Figures 11 and 12. The subsoils encountered throughout the development area
typically consist of a shallow topsoil and fine-grained soil depth overlying relatively
dense, slightly silty sandy gravel alluvium containing cobbles and boulders. At Borings
B309 and B311, a medium dense silty sand layer about 2 feet thick was encountered
embedded in the gravel alluvium at depths of about 11 and 17 feet. The natural topsoil
and fine-grained soils were apparently stripped from the current graded areas by previous
construction activities and placed in stockpiles as shown on Figures 5 and 6. The graded
areas could also contain fill materials placed over the natural soils. Drilling in the dense
gravel alluvium with auger equipment was difficult due to the cobbles and boulders and
drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included moisture
content and density, gradation analyses, Atterberg limits and Hveem stabilometer value.
Results of swell -consolidation testing performed on relatively undisturbed drive samples
of the upper fine-grained soils, presented on Figure 14, indicate low compressibility under
existing moisture conditions and light Ioading and a minor to low expansion potential
when wetted. It has been our experience that some of the upper fine-grained soils can
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have a collapse potential (settlement under a constant load) when wetted and compress
under increased loading. Results of gradation analyses performed on small diameter
drive samples (minus 11/2 -inch fraction) and a bulk sample {minus 5 -inch fraction) of the
coarse granular soils are shown on Figures 15 through 20. Hveem stabilometer testing
performed on a bulk sample of the upper fine-grained soils resulted in an `R' value of 17
as shown on Figure 21. The laboratory testing is summarized in Table 1.
Free water was not encountered in the relatively shallow borings for the current study at
the time of drilling and the subsoils were slightly moist to moist. Groundwater levels
measured in the borings previously drilled in the sinkholes (100 Series borings) were
between depths of about 39 to 77 feet.
GEOLOGIC SITE ASSESSMENT
There are several conditions of a geologic nature that should be considered as project
planning and development proceeds. These conditions are (1) the potential sinkhole
hazard, (2) potential terrace escarpment instability, (3) active stream bank erosion, (4)
potential debris flows and floods and (5) earthquake considerations. These conditions, an
assessment of their potential risks and possible risk mitigations are discussed below.
SINKHOLE HAZARD
Nine general sinkhole areas SA (A) through SA (I) were observed in the field and on
aerial photographs in and close to the proposed development areas as shown on Figures 7
and 8. Sinkhole areas SA (A) through SA (D) were evaluated by deep exploratory
borings in 2001 before the abandoned Bair Chase grading in 2005 (Hepworth-Pawlak
Geotechnical, 2008). Grading for the abandoned Bair Chase development has destroyed
the sinkholes in areas SA (D), SA (E), part of SA (F), SA (H) and part of SA (I). The
sinkhole areas outside the graded areas were still observable during our site
reconnaissance in October 2010. Based on our October 2010 field observations and the
previous subsurface exploration, three sinkhole hazard zones have been identified at the
project site. The general character of the sinkholes, the previous subsurface exploration
and the hazard zones are discussed below.
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General Character of Evaporite Sinkholes
Evaporite sinkholes in western Colorado are typically 10- to 50 -foot diameter, circular
depression at the ground surface that result from upward caving of a soil rubble pipe to
the ground surface. The soil rubble pipe is formed by subsurface erosion (piping) of near
surface soils into subsurface solution voids in the underlying evaporite. New sinkholes
can develop at the ground surface with little or no advanced warnings and existing
sinkholes can be reactivated.' New sinkholes and reactivated sinkholes have the potential
for severe damage to buildings and other man-made facilities. Historic sinkholes have
developed in the western Colorado evaporite region shown on Figure 3 and this indicates
that sinkhole development is still an active geomorphic process.
Previous Sinkhole Exploration
Our 2001 subsurface exploration included rotary drilling and coring the evaporite in four
borings B101, B104, B 107 and B110 and 4 -inch diameter auger drilling in seven borings
B102, B103, B105, B106, B108, B109 and B110. Locations of these borings are
presented on Figures 7 and 8. Subsurface voids were not encountered in any of the
sinkhole exploratory borings but evidence of sinkhole rubble pipes was present in the
terrace deposits in Borings B101, B104 and B108. Boring B108 was an auger boring that
could be advanced through the 47 -foot deep sinkhole rubble pipe into the underlying
evaporite. In contrast, 4 -inch diameter auger borings not in rubble pipes encountered
refusal usually within 5 to 10 feet of the ground surface. The penetration resistance
values in sinkhole rubble pipes were 17 ± 14 blows per foot whereas penetration
resistance values in undisturbed terrace alluvium were 119 ± 51 blows per foot.
.Hazard Zone 1
Sinkhole Hazard Zone 1 areas are where sinkholes were observed in the field or on aerial
photographs. The limits of the hazard zone were based on an 80 -foot setback from center
of the small sinkholes and an 80 -foot setback from the rim of the large sinkholes. In our
opinion, the risk of new sinkholes or existing sinkhole reactivation in Zone 1 is high
during a reasonable exposure time for the proposed development. Buildings and
movement sensitive facilities should not be considered in Zone 1. We understand that all
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utilities in the preliminary plan have essentially avoided the Zone 1 sinkhole areas. With
mitigation, roads can be considered in Zone 1. A few roads are currently planned in Zone
1. Mitigation for roads could be ground improvement by compaction grouting or
structural bridging. Additional subsurface exploration at the specific road alignment will
be needed to evaluate if ground improvements or structural bridging are appropriate
mitigations for roads planned in Zone 1.
Hazard Zone 2
Sinkhole Hazard Zone 2 areas are where sinkholes have not been observed in the field or
on aerial photographs but align with well defined trends of known sinkholes. In our
opinion, the risk of new sinkholes in Zone 2 is uncertain based on the information
available at this time other than the risk is between the risks associated with Zone 1 and
Zone 3. Less than 6 residential lots are currently planned in Zone 2. Additional
subsurface exploration will be needed to assess the risk in Zone 2 if it is acceptable to
locate buildings in this zone.
Hazard Zone 3
Sinkhole Hazard Zone 3 covers all parts of the project area that are not in Zone 1 or Zone
2. In our opinion, the risk that a new sinkhole will develop at a specific building site in
Zone 1 is low during a reasonable exposure time for the proposed development. The risk
in Zone 1 does not appear greater than the risk at existing buildings and other facilities in
the Towns of GIenwood Springs and Carbondale and along the Roaring Fork River valley
between these two towns. The low.risk at a specific building site in this area is inferred
from the large extent of the sinkhole prone areas in the western Colorado evaporite region
(See Figure 3) in comparison to the small number of new sinkholes that have developed
during historic times. We are aware of only four new sinkholes in the Glenwood Springs -
Carbondale region since 2000 and these new sinkholes were in open areas and did not
damage occupied buildings.
The developer and prospective property owner should be aware of the low potential
sinkhole risk in Zone 1 and that the proposed development in Zone 1 cannot be
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considered totally risk free. Evidence of possible sinkhole related problems should be
looked for during building site specific subsurface studies for foundation design. Deep
foundation systems or shallow rigid foundation systems will present a lower risk of
potential building damage and harm to the building occupants than a conventional spread
footing foundation system should an undetected subsurface void develop into a sinkhole
after construction.
STEEP TERRACE ESCARPMENTS
Steep terrace escarpments that commonly have slopes of about 60 percent, 1.7:1
(horizontal to vertical) and vary from 40 to 80 feet high are present along the Roaring
Fork River and the Iower reaches of Cattle Creek, see Figures 9 and 10. These
escarpments are not suitable for building sites and buildings should be set back from the
top of the escarpments. The proposed development does not encroach into the steep
escarpments. The steep escarpments shown on Figures 9 and 10 include a setback at the
top of the escarpments. The setback is based on the projection of a 2:1 (horizontal to
vertical) slope from the base of the escarpment and a setback from the top of the projected
slope of one-third the escarpment height.
ACTIVE STREAM BANK EROSION
Active stream bank erosion during high flood flow is occurring along the Roaring Fork
River and Cattle Creek in several areas where these streams flow along the base of the
steep terrace escarpments, see Figure 9 and 10. Stream bank stabilization with rip rap or
other means should be considered in these actively eroding areas. If the erosion is left
uncontrolled it could lead to escarpment instability and could threaten buildings near the
top of the escarpments.
DEBRIS FLOWS AND FLOODS
The coalescing alluvial fans (Qf) at the project site are geologically young and still
potential sites of debris flow and flood deposition, see Figures 5 and 6. With the
exception ofthe executive lot in the southern part ofthe proposed development, the
proposed development does not extend onto the fans and should not be exposed to a
Job No. 110 337A
CPtech
App. J-17
-14 -
potential debris flow or flood deposition. Conventional surface drainage design should be
adequate to account for sheet flow on the terrace surface down slope ofthe fans. Grading
for Highway 82 and the development to the east of the highway has substantially
modified flow patterns on the fans. This grading should cause debris deposition at the
grade change between the road cuts and road platform and reduce the current extent of
deposition on the fan in comparison to the deposition pattern that occurred before road
and development grading.
EARTHQUAKE CONSIDERATIONS
Historic earthquakes within 150 miles of the project site have typically been moderately
strong with magnitudes of M 5.5 and less and maximum Modified Mercalli Intensities of
VI and less, see Figure 4. The largest historic earthquake in the project region occurred in
1882 (Kirkham and Rogers, 1985). It was apparently Iocated in the northern Front Range
about 117 miles to the northeast ofthe project site and had a estimated magnitude of M
6.2 ± 0.3 and a maximum intensity of VII. Historic ground shaking at the project site
associated with the 1882 and the other larger historic earthquakes in the region does not
appear to have exceeded Modified Mercalli Intensity VI (Kirkham and Rogers, 1985).
Modified Mercalli Intensity VI ground shaking should be expected during a reasonable
exposure time for the proposed development, but the probability of stronger ground
shaking is low. Intensity VI ground shaking is felt by most people and causes general
alarm, but results in negligible damage to structures of good design and construction.
The development facilities should be designed to withstand moderately strong ground
shaking with little or no damage and not to collapse under stronger ground shaking. For
firm rock sites with shear wave velocities of 2,500 fps in the upper 100 feet the U. S.
Geological Survey 2002 National Seismic Hazard Map indicates that a peak ground
acceleration of 0.06g has a 10% exceedence probability for a 50 year exposure time and a
peak ground acceleration of 0.22g has a 2% exceedence probability for a 50 year
exposure time at the project site (Frankel and Others, 2002). This corresponds to a
statistical recurrence time of about 500 years and 2,500 years, respectively. The soil
profiles in the proposed development area should be considered as Class D, stiff soil sites
Job No. 110 337A
G lortech
App. J-18
- 15 -
as described in the 2006 International Building Code unless site specific shear wave
velocity studies show otherwise.
PRELIMINARY DESIGN RECOMMENDATIONS
The conclusions and recommendations presented below are based on the preliminary
proposed development plan, geologic conditions identified at the project site, subsurface
conditions encountered in the exploratory borings and our experience in the area. The
recommendations are suitable for planning and preliminary design but site specific
studies should be conducted for individual buildings and for each lot development.
FOUNDATIONS
Bearing conditions will vary depending on the specific location of the building on the
property. In general, shallow foundations placed on the upper natural soils should
typically be suitable for structure support. The project site is underlain at depth with
Eagle Valley Evaporite with some risk of future ground subsidence. Relatively rigid
foundations such as heavily reinforced slabs and deepened foundation walls could be used
to reduce the risk of differential settlement and building distress. Spread footings bearing
on the natural subsoils could be used for building support provided the risk of future
settlement and distress from the underlying formation rock condition is accepted by the
owner. We expect allowable bearing pressures in the range of 1,500 psf to 2,500 psf for
footings bearing on the natural fine-grained soils with some potential for
settlement/heave. Expansive clays encountered in building areas may need to be removed
or the footings designed to impose a minimum dead load pressure to limit potential heave.
Footings bearing entirely on the natural gravel alluvium can be sized for allowable
bearing pressures in the range of 3,000 to 5,000 psf and should be used for heavily loaded
structures such as abutments for the bridge across Cattle Creek. Loose colluvial and
alluvial fan soils with collapse potential may need treatment such as enlarging footings or
placing compacted structural fill. Disturbed soils and existing fill will need to be
removed from beneath settlement sensitive structures or replaced compacted to the
project specifications. Foundation walls should be designed to span local anomalies and
to resist lateral earth loadings when acting as retaining structures. Below grade areas,
Job No. 110337A
Gtech
App. J-19
-16 -
such as basements, and retaining walls should be protected from wetting and hydrostatic
loading by use of an underdrain system. We expect that basement walls and foundations
that will be restrained from lateral movement can be designed for an earth pressure
loading of 50 pcf equivalent fluid unit weight for the on-site mainly granular soil as
backfill. The footings should have a minimum depth of 36 inches for frost protection.
FLOOR SLABS
Slab -on -grade construction should be feasible for bearing on the natural soils or
compacted structural fill. There could be some potential for post -construction slab
movement at sites with collapsible soils or expansive clays. Removal of the moisture
sensitive soils and replacement with compacted structural fill could be provided to reduce
the movement risk. To reduce the effects of some differential movement, non-structural
floor slabs should be separated from all bearing walls and columns with expansion joints.
Floor slab control joints should be used to reduce damage due to shrinkage cracking. A
minimum 4 -inch thick layer of free -draining gravel should underlie basement level floor
slabs to facilitate drainage.
UNDERDRAIN SYSTEM
Although free water was not encountered in the shallow exploratory borings, it has been
our experience in the area that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff An underdrain system should be provided to
protect below -grade construction, such as retaining walls, deep crawlspace and basement
areas from wetting and hydrostatic pressure buildup. The drains should consist of
drainpipe surrounded above the invert level with free -draining granular material. The
drain should be placed at each level of excavation and at least 1 foot below lowest
adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet.
SITE GRADING
The risk of construction -induced slope instability at the site appears low provided the
buildings and structures are located in the less steep parts of the property as planned and
cut and fill depths are limited. Cut depths for the buildings, structures and roadways
Job No. 110 337A
IZtech
App. J-20
-17 -
should not exceed about 15 feet. Fills should be limited to about 10 feet deep and not be
placed on steep downhill sloping areas. The cut and fill grading should be studied on an
individual basis. Structural fills should be compacted to at least 95% of the maximum
standard Proctor density near optimum moisture content. Prior to fill placement, the
subgrade should be carefully prepared by removing all vegetation, topsoil and existing
fill. The structural fill should be benched into slopes that exceed 20% grade. The on-site
soils excluding oversized rock and topsoil should be suitable for use in embankment fills.
Permanent unretained cut and fill slopes should generally be graded at 2 horizontal to 1
vertical or flatter and protected against erosion by revegetation, rock riprap or other
means. The dry field at the south end of the property (Boring B004 executive lot area) is
an alluvial fan terrace that has numerous sinkholes caused by subsurface erosion. Boring
B004 encountered 13 feet of low density sand and silt soils overlying the dense, river
gravel alluvium. It may be feasibility to mitigate the sinkholes in this area by completely
removing the upper sand and silt soils provided there are no deeper piping cavities into
the formation rock. Additional subsurface exploration should be conducted to evaluate the
feasibility of sinkhole mitigation.
SURFACE DRAINAGE
The grading plan for the subdivision should consider runoff from uphill basins that drain
through the project and at individual sites. Water should not be allowed to pond which
could impact slope stability and foundations. Wetting of moisture sensitive bearing soils
could result in building distress. To limit infiltration into the bearing soils next to
buildings, exterior backfill should be well compacted and have a positive slope away
from the building for a distance of at least 10 feet. Roof downspouts and drains should
discharge well beyond the limits of all backfill and Iandscape irrigation should be
restricted. Drywells that extend into the river gavel deposits should be suitable for
disposal of surface water runoff. If proposed, the infiltration properties of the gravel
deposits should be evaluated to size the drywells.
Job No. 110 337A
Gecptech
App. J-21
- 18 -
PAVEMENT SUBGRADE
The subgrade soils encountered throughout the current development area consist of sandy
silt and clay and river gravel alluvium. The fine-grained soils appear to be of limited
depth and extent partly due to prior grading. A Hveem `R' value of 17 was obtained on a
sample of the fine-grained soils. The fine-grained soils could be removed down to the
gravel alluvium to provide a suitable surface for pavement construction. A detailed
pavement design should be conducted when the traffic load information has been
determined.
WATER SOLUBLE SULFATES
The concentration of water soluble sulfates obtained on a sample of fine-grained soils
(Boring 019) was 0.013%. This concentration of water soluble sulfates represents a
negligible degree of sulfate attack on concrete exposed to these materials. The degree of
attack is based on the range presented in the U.S. Bureau of Reclamation Concrete
Manual. Based on the results, we recommend that concrete exposed to the on-site soils
contain Type I/II portland cement (less than 5% tri -calcium aluminate).
RADIATION POTENTIAL
The project site is not located on geologic deposits that would be expected to have high
concentration of radioactive minerals. However, there is a potential that radon gas could
be present in the area. It is difficult to assess future radon gas concentrations in buildings
before the buildings are constructed. Testing for radon gas levels could be done when the
residences and other occupied structures have been completed. New buildings are often
designed with provisions for ventilation of lower enclosed areas should post construction
testing show unacceptable radon gas concentration.
LIMITATIONS
This study has been conducted according to generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or
implied. The conclusions and recommendations submitted in this report are based upon
the data obtained from the field reconnaissance, review of previously published geologic
Job No. 110 337A
Ge&ech
App. J-22
- 19 -
maps and reports, the exploratory borings located as shown on Figures 5 and 6, the
proposed type of construction and our experience in the area. Our services to not include
determining the presence, prevention or possibility of mold or other chemical
contaminants (MOBC) developing in the future. If the client is concerned about MOBC,
then a professional in this special field of practice should be consulted. Our findings
include interpolation and extrapolation of the subsurface conditions identified at the
exploratory borings and variations in the subsurface conditions may not become evident
until excavation is performed. If conditions encountered during construction appear
different from those described in this report, we should be notified so that re-evaluation of
the recommendations may be made.
This report has been prepared for the exclusive use by our client for planning and
preliminary design purposes. We are not responsible for technical interpretations by
others of our information. As the project evolves, we should provide continued
consultation, conduct additional evaluations and review and monitor the implementation
of our recommendations. Significant design changes may require additional analysis or
modifications to the recommendations presented herein. We recommend on-site
observation of excavations and foundation bearing strata and testing of structural fill by a
representative of the geotechnical engineer.
Sincerely,
HEPWORTH - PAWLAK
Steven L. Pawlak, P.
And by:
le ,P,
Rale. G. Mock
Engineering Geologist
SLP/ksw
cc: 8140 Partners - Attn: Sam Otero, PE
Job No. 110 337A
Gtech
App. J-23
-20 -
REFERENCES
Frankel, A. D. and Others, 2002, Documentation for the 2002 Update of the National
Seismic Hazard Maps: U. S. Geological Survey Open File Report 02-420.
Hepworth-Pawlak Geotechnical, 2008, Preliminary Geotechnical Study, Proposed Cattle
Creek Crossing, Highway 82 and Cattle Creek, Garfield County, Colorado:
Prepared for Related Westpac, LLC, Aspen, Colorado (Job No. 107 0267, August
12, 2008).
Kirkham, R. M. and Others, 1996, Geology Map of the Cattle Creek Quadrangle,
Garfield County, Colorado: Colorado Geological Survey Open File 96-1.
Kirkham, R. M. and Scott, R. B., 2002, Introduction to Late Cenozoic Evaporite
Tectonism and Volcanism in West -Central, Colorado, in Kirkham R. M., Scott, R.
B. and Judkins, T. W. eds., Late Cenozoic Evaporite Tectonism and Volcanism in
West -Central Colorado: Geological Society of America Special Paper 366,
Boulder, Colorado.
Kirkham R. M. and Others, 2002, Evaporite Tectonism in the Lower Roaring Fork River
Valley, West -Central Colorado, in Kirkham R. M., Scott, R. B. and Judkins, T. W.
eds., Late Cenozoic Evaporite Tectonism and Volcanism in West -Central
Colorado: Geological Society of America Special Paper 366, Boulder, Colorado.
Kunk, M. J., and Others, 2002, 40Ar/39ArAges of Late Cenozoic Volcanic Rocks within
and Around the Carbondale and Eagle Collapse Centers, Colorado: Constraints
on the Timing of Evaporate -Related Collapse and Incision of the Colorado River,
in Kirkham R. M., Scott, R. B. and Judkins, T. W. eds., Late Cenozoic Evaporite
Tectonism and Volcanism in West -Central Colorado: Geological Society of
America Special Paper 366, Boulder, Colorado.
National Resources Conservation Service, 2008, Soil Survey of Aspen -Gypsum Area,
Colorado: Version 5, June 9, 2008.
Tweto, 0., 1979, Geology Map of Colorado: U. S. Geological Survey.
Tweto, O. and Others, 1978, Geology Map of the Leadville 1 °X 2 ° Quadrangle,
Northwestern Colorado: U.S. Geological Survey Map I-999.
Widmann B. L. and Others, 1998, Preliminary Quaternary Fault and Fold Map and Data
Base of Colorado: Colorado Geological Survey Open File Report 98-8.
Job No. 110 337A
G ligtech
App. J-24
Proposed Development Area
0 3000 ft.
L t I
Scale: 1 in. = 3000 ft.
Contour Interval = 40 ft.
November 2010
110 337A
Gtech
H FPWORTH-PAWL KGEOTECHN I CAI.
River Edge Colorado
Project Site Location
Figure 1
App. J-25
Pz
YXr
River
YXr
Pze iCarbondale
TKs
Basin
Snowmass
Pluton
Capitet
• F.
Snora
Mat
Explanation:
Post-Laramide Sediments
Post-Laramide Volcanics
Post-Laramide Intrusives
Laramide Basin Sediments
Laramide Intrusives
Ts
Tv
TKs 1
TKi
Pz
Pze
Pre-Laramide Mesozoic Sediments High -Angle Faults
Paleozoic Sediments • • Thrust Faults
Pennsylvanian Evaporites Synclines 0 7 mL
Precambrian Crystalline Rocks Anticlines l i
Scale 1 in. = 7 mi.
Contact_ — Highways November 2010
Modified from: Tweto (1979)
10 337A
Glartech
HEPWORTH-PAWLAK GEOTECHNICAL
River Edge Colorado
Regional Geology Map
Figure 2
App. J-26
ea. L E
a) co•
fa 0 0 S
WVU'
Sawatch Range Anticline
0
U
F-07.
U
Ul
110 337A
Gerftetcr,
HEPWORTH-PAWLAK GEOTECHNICAL
River Edge Colorado
Western Colorado Evaporite Regions
Figure 3
App. J-27
110 337A
Wyoming
Basin
Laramie Min.
1984
M 5.5
VI
150 mites
1977
M 5.0
Middle
CO.
ocky
Lily Park
1871
VI
A7dal Basin
1891
VI
Crai
Meeker
(0
0
Glenwood
Springs
Walden
0
Steamboat
Springs
Kreutm� ling ':
EEJJ\`
1
0
Eagle
Vail
N. Frontinge
1882
M 6.2
VII
Boulder
WY.
NB.
Fort
lies
Lovelan
0
Rocky Mtn. Ars
1962 to 1967
VI to VII
M 3.2 to M 5.3
CO.
Great
Greeley
al
❑ Fort 1
0
Golden
0
Frisco
Intermountain
Seismic Belt
Moab
0
Delta
Project Aspen
Site
Montrose ❑
D2u
O
Cimarron Ridge Gunnison.
1960 0
M 5.5
-33
Denver
❑ Parker
Castle
Rock
Plateau
056b
Salipa
0 \
067
t .
Ridgeway • Dfi9a
1913
VI
Lake City •-*.
1955
069b `.
VI UJ Wa#senburg
Kiowa
rado Sp.
Pueblo
0
0
UT. CO.
Explanation:
Post -Glacial Faults:
Fault younger than about 15,000 years.
U
Co▪ rtez
❑
Pagosa Springs
Durango !Juice
1966
M 5.1
VII
AZ. NM.
Larger Historic Earthquakes:
Earthquakes with maximum intensity greater than VI
or magnitude greater than M 5.0 from 1867 to
present.
-11K- Nuclear Explosion:
Large underground nuclear explosion for natural gas
reservoir enhancement.
0
JF4,„
Alamosa
i]F9FI
Chaeta
Historic Seismic Zones:
Areas with historically high seismic activity.
M Local, surface wave or body wave magnitude
VI Modified Mercalli intensity
References:
Widmann and Others (1998)
U. S. Geological Survey Earthquake Catalogs
Plains
❑Trinidad
❑ Raton
D 50 mi.
I I l
Scale: 1 in. = 5D mi.
G4,3
HEPWORTH-PAW LAI{ GEOTLCH N CAL
River Edge Colorado
Geologically Young Faults and Larger Historic Earthquakes
Figure 4
App. J-28
Explanation:
Graded Areas
Soil Stockpiles
Alluvial Fans
Post -glacial River Terraces
Pinedale Outwash Terraces
Bull Lake Outwash Terraces
Upland Deposits/Pre-Bull Lake
Outwash Terraces
gr
SS
Qf
Qt1-2
Qt3-7
Qt8
Qat-2
Qa3-4
Qu1-2
Qc/Tb
QcllPee
Post -Glacial Creek Terraces
8001 •
Pinedale Creek Terraces
Upland Bench Deposits
ColluviumlBasalt Flows O
Colluvium/Eagle Valley Evaporate
Contact:
Approximate boundary of map units.
Exploratory Borings
000 Series drilled in 2001
100 Series drilled in 2001
200 Series drilled in 2005
300 Series drilled in 2010
Small Sinkholes
Large Sinkholes
0 600 ft.
Scale: 1 in. = 600 ft.
Contour Interval: 4D ft.
November 2010
110 337A
Gtech
f- IEFWORTH-PAWLAK =TECHNICAL
River Edge Colorado
Project Area Geology Map - North Part
Figure 5
App. J-29
Explanation_
gr_l
SS
Qf
Qt1-2
Qt3-7
Qt8
Graded Areas
Soil Stockpiles
Alluvial Fans
Post -glacial River Terraces
Pinedale Outwash Terraces
Bull Lake Outwash Terraces
Upland Deposits/Pre-Bull Lake
Outwash Terraces
Qa1-2
Qa3-4
MIX
Qc/Tb
Qc/Pee
Post -Glacial Creek Terraces
Pinedale Creek Terraces
Upland Bench Deposits
Colluvium/Basalt Flows
Colluvium/Eagle Valley Evaporate
Contact:
Approximate boundary of map units.
8001•
0
0
Exploratory Borings
000 Series drilled in 2001
100 Series drilled in 2001
200 Series drilled in 2005
300 Series drilled in 2010
Small Sinkholes
Large Sinkholes
D 600 ft.
I I
Scale: 1 in. = 600 ft.
Contour Interval: 40 ft.
November 2010
110 337A
Glertech
FIEPWORTH FAW_AK GEOTECHNICAL
River Edge Colorado
Project Area Geology Map - South Part
Figure 6
App. J-30
Explanation:
Graded Areas
Areas where construction
grading has disturbed the
natural ground surface.
Z1
Hazard Zone 1
Areas where sinkholes were
observed in the field or on
aerial photographs. Some
sinkholes have been
removed by grading.
Z2
Z3
Hazard Zone 2
Areas where Sinkholes were
not observed in the field or
on aerial photographs but
align with well defined trend
of known sinkholes.
Hazard Zone 3
Areas where sinkholes were
not observed in the field or
on aerial photographs.
B101•
Contact:
Approximate boundary of
map units.
Exploratory Borings
100 Series drilled in 2001 to
evaluate some known sinkhole
areas.
SA {A) General Sinkhole Areas 0
0 Small Sinkholes
Large Sinkholes
600 ft.
Scale: 1 in. = 600 ft.
Contour Interval: 40 ft.
November 2010
110 337A 'tech
HEPWORTH-PAWLAK GEOTECHNICAL
River Edge Colorado
Sinkhole Hazards Zones - North Part
Figure 7
App. J-31
Z3
Development Are
Explanation:
Z1
Graded Areas
Areas where construction
grading has disturbed the
natural ground surface.
Hazard Zone 1
Areas where sinkholes were
observed in the field or on
aerial photographs. Some
sinkholes have been
removed by grading.
Z2
Z3
Hazard Zone 2
Areas where Sinkholes were
not observed in the field or
on aerial photographs but
align with well defined trend
of known sinkholes.
Hazard Zone 3
Areas where sinkholes were
not observed in the field or
on aerial photographs.
B101 •
Contact:
Approximate boundary of
map units.
Exploratory Borings
100 Series drilled in 2001 to
evaluate some known sinkhole
areas.
SA (A) General Sinkhole Areas
Q Small Sinkholes
42 Large Sinkholes
0 600 ft.
1 1
Scale: 1 in. = 600 ft.
Contour Interval: 40 ft.
November 2010
110 337A
G@CP ech
nEr=WORTH.FAWLAK. GEOTECI INICAL
River Edge Colorado
Sinkhole Hazards Zones - South Part
IFigure 8
App. J-32
arum- ti gar uri
‘11
ogoppo00)°
Development Area
Explanation:
Steep Terrace Escarpments:
Steep terrace escarpments and
building site setbacks. These areas
are not suitable for buildings.
Active Stream Erosion:
River and creek channel banks at
outside channel bends that are
actively eroding under high velocity
flood flows.
Contact:
Approximate boundary of map units.
0 600 ft.
Scale: 1 ir. = 600 ft.
Contour Interval: 40 ft.
November 2010
110 337A
G egtech
I River Edge Colorado I Fi ure 9
HEr�voxrH-aawvKGEOTECHNICAL Terrace Escarpments and Active Bank Stream Erosion - North Part 9
App. J-33
Explanation:
Steep Terrace Escarpments:
Steep terrace escarpments and
building site setbacks. These areas
are not suitable for buildings.
Active Stream Erosion:
River and creek channel banks at
outside channel bends that are
actively eroding under high velocity
flood flows.
Contact:
Approximate boundary of map units.
0 600 ft.
Scale: 1 in. = 600 ft.
Contour Interval: 40 ft.
November 2010
110 337A
Gootech River Edge Colorado
HEPWORTH.PAWLAKGEOTECHNLCAL Terrace Escarpments and Active Stream Bank Erosion - South Part
Figure 10
App. J-34
Depth - Feet Depth - Feet
Oto
CD 11
[0 ,- o,.0
O - + N o O
0Ilm m
Z Z 11
Fc
mW
OJa:. �o,
co LU
Q) c0
norooma II
N O N a
i
N
c)
co
CD II
Z
CC
mW
O
m
z 11
mu
N N_N _N
CO I� Cr) CCOO
4,6NMQ.ATI:VVNA:MMM
0 o CO
LO
Lo -4- -4. 0
N c7 y7 + [v
OLoo t4
r
I I I I I I 1 l'-111111
Depth - Feet
114 337A
H
H EPWORTH•PAWLAK G EOTECHN[CAL
o [a
:•174••• , 4.,
i
in
_c\I Tip
II T
O _
U` II h o i v❑o0
Z . V to +fi r ?y o vico in °-94:M•6 •••• • .Cf.-*;Mag.e6V.W4&.:6;SX,C3J<___
-
cc
o Lo s� co
Oco U o II E j {j O
NZiNJLL a- ❑
zlI
o XX/1. '
m LU
0
II II1II I11I
Depth - Feet
LOGS OF EXPLORATORY BORINGS
Note: Explanation of symbols is shown on Figure 13.
Figure 11
App. J-35
CO
i
011
Z
CC
o_1
CO W
L)
c) co
Depth - Feet
Depth - Feet
1 1 1 1 1 i 1 1 1 1 I 1 I 1 I 1 1 1 1
rn ,, CV 00
r- ,r II Q
U cr o N
CO0 II
Cr V;S:111,R;04:11j4ill(-
W
N
CO
!~
CO
M
O 11
Z
caw
� ro
TN Tr N
C? UcQCij
Z • 11.
O_1•
CO LLJ
Cr)
O 11
Z .
EL
CO
°ad (JL• .• • . °a,
a
N
N
N
o•••.• ) c')o
C0 N O co-
.-,
C 7 o
+ N 10
co
C•7
0 11
Z
E
CO Ll.[
c)
z fl
Fc"
cow
en
CO
UD
CO CD
CO �jU 4
r-
r -
II N T r
- NII II
CD
J d Q
O
CO -
CV 71. co
C)II II 1' O
vir)
co o
cr0
+
CD a
CV 0-i
o11 0 s
N 0 o v_
(o � + N CD
Q
o a
N CO
Ln r
'� LJ :d �7 1i• `� �'a •oB 084 �.• "
°.9°••�:0� 'o 9e.•'O�:l►o.°On. ,•: Cx�n: •:}o°C6; °f�: Q�'O �iQi
O � � O lf)
✓ r N
111111111111111111
Depth - Feet
110 337A
H
Hepworth—Powlak Geotechnical
LOGS OF EXPLORATORY BORINGS
Figure 12
App. J-36
LEGEND:
FILL; silty sandy gravel and cobbles, possible boulders, loose, slightly moist, dark brown.
TOPSOIL; root zone in graded areas, organic silty sandy clay in natural areas, dark brown.
SILT AND CLAY (ML -CL); sandy, stiff to very stiff, slightly moist, red -brown, low plasticity.
SAND (SM); very silty, medium dense, moist, brown.
GRAVEL, COBBLES AND BOULDERS (GM -GP); slightly silty, sandy, dense, slightly moist, brown, rounded
rock. Possible fill in previously graded areas.
Relatively undisturbed drive sample; 2 -inch I.D. California liner sample.
Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586.
20/5 Drive sample blow count; indicates that 20 blows of a 140 pound hammer falling 30 inches were
required to drive the California or SPT sampler 5 inches.
' Disturbed bulk sample.
— Caved depth when checked on November 3, 2010 (Borings 1 and 11).
Practical drilling refusal.
NOTES:
1. Exploratory borings were drilled on October 17, 18 and 19, 2010 with 4 -inch diameter continuous flight power auger.
2. The exploratory boring locations were staked by Tuttle Surveying Services.
3. Elevations of exploratory borings were obtained by interpolation between contours shown on the topographic plan
provided.
4. The exploratory boring locations and elevations should be considered accurate only to the degree implied by the
method used.
5. The lines between materials shown on the exploratory boring logs represent the approximate boundaries between
material types and transitions may be gradual.
6. No free water was encountered in the borings at the time of drilling or when checked on November 3, 2010.
Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD – Dry Density (pcf)
+4 = Percent retained on the No. 4 sieve
110 337A
HEPWORTH.PAWLAK GEOTECHNICAL
-200 = Percent passing No. 200 sieve
LL = Liquid Limit (%)
PI = Plasticity Index (%)
R' = NVEEM stabilometer "R" Value
LEGEND AND NOTES
Figure 13
App. J-37
Compression - Expansion
Compression - Expansion
2
1
0
1
2
1
0
1
2
3
Moisture Content = 6.7 percent
Dry Density = 116 pcf
Sample of: Sandy Clay
From: Boring 307 at 4.5 Feet
O Expansion
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
0.1
110 337A
1.0 10
APPLIED PRESSURE - ksf
H
Hepworth—Pawlak Geotechnical
SWELL -CONSOLIDATION TEST RESULTS
100
Figure 14
App. J-38
Moisture Content = 12.5 percent
Dry Density = 108 pcf
Sample of: Sandy Clay
From: Boring 308 at 5 Feet
O
Expansion
upon
wetting
0.1
110 337A
1.0 10
APPLIED PRESSURE - ksf
H
Hepworth—Pawlak Geotechnical
SWELL -CONSOLIDATION TEST RESULTS
100
Figure 14
App. J-38
'itgiIl:IW110101
HYDROMETER ANALYSIS I SIEVE ANALYSIS
TIME READINGS 1 U.S. STANDARD SERIES 1
24451W 175i4k1 IN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4
0
10
20
30
40
50
60
70
CLEAR SQUARE OPENINGS
3/8" 314" 1 1/2" 3" 5"6" 8"
80
90
11.08
100
.001 .002 .005 .005 .019 .037 .074 .150 .300 .660 1.18 2.36 4.75
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
SANG
FINE 1 MEDIUM 1 COARSE
GRAVEL 58 %
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
9.6 12.5 19.0
GRAVEL
37,5 78.2 152 203
127
FINE 1 COARSE
COBBLES
SAND 29 % SILT AND CLAY 13 %
PLASTICITY INDEX %
FROM: Boring 301 at 5 Feet
HYDROMETER ANALYSIS SIEVE ANALYSIS
24 R. 7 HR TIME READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 1
45 MIN.15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #B #4 318" 3/4" 1 112" 3" 5"6" 8"
100
10
20
30
40
50
60
70
80
90
100
100
90
80
70
60
50
40
30
20
10
a3
A
.w
1
1
1
.001 .002
.005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
FINE
SANG
MEDIUM 1 COARSE
90
80
70
60
50
40
30
20
10
0
4.75 9.512 519.0 37.5 76.2 12152 203
FINE
GRAVEL
COARSE
COBBLES
GRAVEL 58 %
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
110 337A
1-1
Hepworth—Pawlak Geotechnical
▪ ENT PASS1Nr
▪ R ENT PASSINe
SAND 29 % SILT AND CLAY 13 %
PLASTICITY INDEX %
FROM: Boring 302 at 4.5 and 10 Feet, Combined
GRADATION TEST RESULTS
Figure 15
App. J-39
' U'CENT BETA ► 1
' " ENT RET A ► i
HYDROMETER ANALYSIS I SIEVE ANALYSIS
TIME READINGS 1 U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 1
45 MIN. 15 MIN. 60MIN19MIN.4 MIN, 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 6"
100
10
20
30
40
50
60
70
80
90
100
f
.001 .002 .005 .009 .019 .037 .074 .150 .300 .000 1.18 2.36 4.75 9.5 19.0 37.5 762 152 203
125
CLAY TO SILT
DIAMETER OF PARTICLES IN MILLIMETERS
FINE
GRAVEL 61 %
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
SAND
MEDIUM I COARSE
FINE
GRAVEL
COARSE
127
COBBLES
90
80
CD
70 -
60 a_
H
50
U
40 W
0_
30
20
10
0
SAND 24 % SILT AND CLAY 15 %
PLASTICITY INDEX %
FROM: Boring 305 at 0 and 4 Feet, Combined
HYDROMETER ANALYSIS ! SIEVE ANALYSIS
TIME READINGS E U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
24 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8"
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36
DIAMETER OF PARTICLES IN MILLIMETERS
J
11111
1110
MMM
11111
CLAY TO SILT
SAND
100
90
80
C!3
70
U3
VJ
60 Q
50
U
40LLU
0
30
20
10
0
4.75 9.51a519.0 37.5 76.2 121152 203
GRAVEL
GRAVEL 63 %
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
110 337A
H
Hepworth—Pawlak Geotechnical
FINE
MEDIUM 1 COARSE
FINE 1 COARSE
COBBLES
SAND 25 % SILT AND CLAY 12 %
PLASTICITY INDEX %
FROM: Boring 309 at 5 and 8.5 Feet, Combined
GRADATION TEST RESULTS
AIM
Figure 16
App. J-40
i' • ENT RET' ► i
vaiwkiimmirAtmor
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIMI READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
456.1WHMIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8"3/4. 1 1/2' 3' 5"6" 8"
0 100
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 206 4.75 9.519.0 37.5 762 152 203
12.5 127
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
FINE
GRAVEL 59 %
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sandy Gravel
SAND
MEDIUM 1 COARSE
SAND 28 %
GRAVEL
FINE I COARSE r CCBEILES
SILT AND CLAY 13 %
90
80
70
60
50
40
30
20
10
PLASTICITY INDEX %
FROM: Boring 311 at 5 and 9 Feet, Combined
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME READINGS U.S.SSTANDARD SERIES 1 CLEAR SQUARE OPENINGS 1
451 N. 1MIN. 150MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 318" 3/4" 1 112' 3" 5"6" 8"
100
10
20
30
40
50
60
70
80
90
100
.001 .002
—,
90
80
70
60
50
40
30
20
10
0
.005 .009 .019 .037 .074 .150 -300 .600 1.18 2.36 4.75 9.512 519.0 37.5 76.2 12752 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
FINE
SAND
MEDIUM [COARSE
FINE
GRAVEL
COARSE
COBBLES
GRAVEL 41 %
LIQUID LIMIT %
SAMPLE OF: Silty Sandy Gravel
110 337A
H
Hepworth—Pawlak Geotechnical
SAND 36 % SILT AND CLAY 23 %
PLASTICITY INDEX %
FROM: Boring 312 at 2 Feet
GRADATION TEST RESULTS
TPAS!k.
Figure 17
App. J-41
' ENT RETAI . p
HYDROMETER ANALYSIS I SIEVE ANALYSIS
TIME READINGS 1 U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS 1
WAIN. 17 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6" 8"
0 100
E♦ -- 1
10
20
30
40
50
60
70
80
90
100
■ili�oui■
.001 .002 .005 .009 .019 .037 .074 .150 .300 .500 1.18 2.30 4.75 9.5 12.5 19.0 37.5 702 152 203
127
CLAYTO SILT
DIAMETER OF PARTICLES IN MILLIMETERS
SAND
FINE 1 MEDIUM I COARSE
FINE
GRAVEL
COARSE
COBBLES
90
80
70
50
50
40
30
20
10
0
▪ ENT PASSINr
GRAVEL 44 % SAND 44 % SILT AND CLAY 12 %
LIQUID LIMIT % PLASTICITY INDEX %
SAMPLE OF: Slightly Silty Sand and Gravel FROM: Boring 315 at 1.5 and 5 Feet, Combined
HYDROMETER ANALYSIS I SIEVE ANALYSIS I
24 R. 7 HR TIME READINGS U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS
45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4" 1 1/2" 3" 5"6' 8"
100
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.512 519.0 37.5 76.2 12-52 203
DIAMETER OF PARTICLES IN MILLIMETERS
90
80
70
60
50
40
30
20
10
0
CLAYTO SILT
GRAVEL 57 %
LIQUID LIMIT %
SAMPLE OF: Slightly Silty Sandy Gravel
110 337A
Hepworth—Fawlak Geotechnical
FINE
SAND
MEDIUM 1 COARSE
GRAVEL
FINE 1 COARSE
COBBLES
▪ ENT PA ► t
SAND 33 % SILT AND CLAY 10 %
PLASTICITY INDEX %
FROM: Boring 317 at 1 and 4 Feet, Combined
GRADATION TEST RESULTS
Figure 18
App. J-42
▪ ENT RETAIL It
• `CENT RETAI i
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
245 w11N.15HMIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 318" 314" 1 112" 3" 5"6" 8"
0 1 100
10
20
30
40
50
60
70
BO
90
100
1
J
.001
1
90
80
70
Cr)
(I)
60 eL
50 !uJ
U
4o LLLI
CL
33
20
50
0
.002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.35 4.75 9.5 72.5 19.0 37.5 76.2 152 203
127
CLAY TO SILT
DIAMETER OF PARTICLES IN MILLIMETERS
SAND
GRAVEL.
FINE 1 MEDIUM FCOARSE
FINE 1 COARSE
COBBLES
GRAVEL 64 %
LIQUID LIMIT
SAND 31 % SILT AND CLAY 5 %
PLASTICITY INDEX %
SAMPLE OF: Slightly Silty Sandy Gravel with Cobbles FROM: Boring 318 at 0 to 2 Feet, Combined
HYDROMETER ANALYSIS SIEVE ANALYSIS
24 R. 7 HR TIME READINGS I U.S. STANDARD SERIES I CLEAR SQUARE OPENINGS
45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 318" 314" 1 112" 3" 5"6" 8"
0
1 100
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36
DIAMETER OF PARTICLES IN MILLIMETERS
1
CLAY TO
CIAYTO SILT
GRAVEL 33 %
LIQUID LIMIT %
SANG
FINE 1 MEDIUM 1 COARSE
90
80
70
60
50
40
30
20
10
0
4.75 9.512.519.0 37.5 76.2 127 2 203
FINE
GRAVEL
1
COARSE
COBBLES
SAND 30 % SILT AND CLAY 37
PLASTICITY INDEX %
SAMPLE OF: Silty Sand and Gravel FROM: Boring 319 at 5 Feet
110 337A
Hepworth—Pawlak Geotechnical
i" IT PA ►
GRADATION TEST RESULTS Figure 19
App. J-43
'CENT RETAIN
HYDROMETER ANALYSIS I SIEVE ANALYSIS
24 HR. 7 HR TIME READINGS U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS 1
0 45 MIMIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 318' 3/4" 1 1/2" 3" 5" 6" 8" 100
ITLIMIIIMIMIIEIIIIIIIIIIr
L111
_
off___
30 _____________�
111111 Illig III
20
40
50 1111111111111191 IIIIIII1.k
ilimillibpj
80 Lij;IPM:=11101.111111111111
20
90 !oiii� =to
100 ITHWIELEMI 11iIfI• 111
0
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.5 19.0 37.5 76.2 152 203
12.5 127
10
90
80
70
60
50
60
40
70
DIAMETER OF PARTICLES IN MILLIMETERS
CLAYTOSILT
FINE
GRAVEL 68 %
SAND
MEDIUM I COARSE
GRAVEL
FINE 1
COARSE
COBBLES
SAND 23 % SILT AND CLAY 9 %
LIQUID LIMIT % PLASTICITY INDEX %
SAMPLE OF: Slightly Silty Sandy Gravel FROM: Boring 321 at 5 Feet
30
110 337A
1—I
Hepworth—Pawlak Geotechnical
GRADATION TEST RESULTS
Figure 20
App. J-44
TEST SPECIMEN
1
2
3
MOISTURE CONTENT (%)
15.9
13.9
12.5
DENSITY (pof)
106.7
109.1
109.4
"R" VALUE/EXUDATION PRESSURE (psi)
15/161
16/281
20/380
tR"
V
A
L
U
E
100
90
80
70
60
50
40
30
20
10
0
"R" VALUE AT 300 psi = 17
100 200
300
400
500 600
EXUDATION PRESSURE (psi)
SOIL TYPE: Sandy Silty Clay
SAMPLE LOCATION: Boring 320 at % and 2 Y2 Feet
GRAVEL %
LIQUID LIMIT 27%
110 337 A
H
700
SAND % SILT AND CLAY 77 %
Hepworth—Pawlak Geotechnical
800
PLASTICITY INDEX 11%
HVEEM STABILOMETER TEST RESULTS
Figure 21
App. J-45
n
Cr)
M
0
r -I
O
Z
ATTERBERG LIMITS
0
a
Ce 47
0 SG
O
to
w
z
O
F
2
iUJ
i CC
2
" x
w
❑
z
-
LIQUID LIMIT
cc
SAMPLE LOCATION
F-
a
0
ID
0
co
Slightly Silty Sandy Gravel
Slightly Silty Sandy Gravel
Sandy Silt and Clay
U
cts00
Slightly Silty Sandy Gravel
Very Silty Sand
Slightly Silty Sandy Gravel
f'-44
00
N
M
0o
10
N
N
Ch
CA
00
01
00
u
-
N
r
ti
00
a
CO
CA
a
M
a
N
Com)
71- O
N
m
N
•
a
Cr)
M
ao
U
N
N
00
Cr)
In
CA
a
App. J-46
Cr)
Cr)
0
c-1
O
z
.1]
O
2I: 1
— M
_i V)
V CC
Z N
2 w
u , 1--
1-w y,
o 0
w O
a
cc
a H o
LU m
m
. ~ O
I—
ec cc
O
a 2
w m
2 v)
ri
4-
0
N
v
GO
co
0
Silty Sandy Gravel
• N
Very Sandy Silt and Clay
Slightly Silty Sandy Gravel
Silty Sand and Gravel
Sandy Silty Clay
Slightly Silty Sandy Gravel
2 v
Lu
CC m
2
ATTERBERG LIMITS
1-
tE
n ae
z
N
tn
N
Cr)
N
GRADATION
❑
z -
N
J
W
cc
J F
1n
CC Z
LU
a❑ a
Z
N
H
M
m
N
00
SAMPLE LOCATION
W 4-
Z
r0~z
z O2 u
F-
0
0
n
N
CN
-'J
O
0
tn
,* .5
E
tn
N
m
N
Cr)
CO
m
App. J-47