HomeMy WebLinkAboutDRB140188_Geological_Hazard_1401226200.pdf
May 22, 2014
Project No. 500808001
Mr. Adam Bersin and Chateau d’Oex, LLC
45 Charlou Circle
Cherry Hills Village, Colorado 80111
Town of Vail Community Development Department
1 South Frontage Road West
Vail, Colorado 81657
Subject: Geologic Hazards Evaluation
Proposed Bersin Residence
3816 Lupine Drive
East Vail, Colorado
Dear Mr. Bersin:
In accordance with your request and authorization, Ninyo & Moore has prepared this geologic
hazards evaluation regarding the potential for geologic hazards related to the proposed Bersin
Residence located in Lot 8 of the Bighorn Subdivision at 3816 Lupine Drive in East Vail,
Colorado (see Figure 1). We understand that the site has been mapped by the Town of Vail within
a Geologically Sensitive Area. The purpose of this letter is to address the Town of Vail Hazard
Regulations Chapter 21 requirements for geological investigations. This report discusses our
findings, methodology, and conclusions in the following sections.
SITE AND PROJECT DESCRIPTION
Ninyo & Moore visited the project side on May 7, 2014 to conduct a visual geologic
reconnaissance of the site. Photographs taken during our site visit are presented in Appendix A.
The approximate location and direction of the photographs are depicted in Figure 2.
The subject lot is located in gently to relatively steeply sloping terrain ranging in elevation
between roughly 8,360 and 8,530 feet above mean sea level (MSL) at the north and south lot
lines, respectively. A moderately to relatively steep slope extends up from the proposed building
area toward the south (see Figure 2). The slope continues along the flanks of a ridge upward
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc 2
toward south from the south lot line to an elevation of approximately 11,000 feet above MSL.
This slope is the primary focus of this study. The lower portions of the slope in the proposed
building area are inclined at approximately 6:1 (horizontal:vertical), or 17 percent grade (see
Photograph Nos. 2, 3, 9, 10, and 24). The upper portions of the slope within the lot become
steeper, at inclinations of approximately 40 percent or greater (see Photograph Nos. 5 through 7,
11, 12, 16, and 21). The subject slope is moderately to thickly vegetated with grasses, immature
and mature aspen trees, and evergreen trees in the lower portions (see Photograph Nos. 2, 12, and
18) and with moderate vegetation consisting of brush, aspen trees, and evergreens along the
upper slopes (see Photograph Nos. 5 through 7, 11, 12, and 21).
The lower middle and portions of the site, as well as the neighboring properties to the east and
west, contain several large boulders (see Photograph Nos. 15, 16, 19, 20, 25, 26, and 31 through
40). Boulders are visible in the aerial photograph of the site taken in 1969, in the same locations
as those observed during our site visit.
Based on our review of the site plan by Jake’s Drafting Service (2014), we understand that the
project includes the construction of a new single-family residence with a building footprint of
approximately 2,000 square feet. The building pad will be at an elevation of approximately 8,369
feet above MSL. The front and rear of the building will be constructed approximately 50 feet and
100 feet south of Lupine Drive, respectively. The elevation of the main level of the residence, at
the rear, will be approximately 8,379 feet above MSL.
METHODOLOGY
The scope of our evaluation included a review of the referenced Town of Vail Avalanche, Debris
Flow, and Rockfall Hazards Maps; published geologic maps; the site topographic map; a
preliminary geotechnical report for site; and aerial photographs. An engineering geologist from
Ninyo & Moore performed a site visit on May 7, 2014 to observe and document the condition of
the slopes in the vicinity of the proposed improvements. Photographs taken during our site visit
are included in Appendix A. Our evaluation consisted of observing the condition of the slopes to
the south of, and topographically higher than, the area of the proposed residence structure. We
observed the slopes for indications of existing or previous debris flows, avalanche chutes,
unstable boulders, rock avalanches, or rockfall hazards. We also reviewed the site topographic
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc 3
maps and proposed plans to evaluate the distances to the proposed improvements from any
potential hazards.
GEOLOGIC CONDITIONS
The proposed building area is mapped by the Kennedy et al. (2003) as being underlain by Upper
Pleistocene-age Pinedale Till. Based on information for the preliminary soil and foundation
investigation by LKP Engineering (2014), the near-surface geologic materials in the proposed
building area consist of 4 to 6 feet of topsoil overlying clayey sand with organics and boulders.
We understand that a detailed geotechnical study that involves advancement of geotechnical
borings to sufficient depths will be performed by others. The slopes on the lot above an
elevation of approximately 8,400 feet above MSL are mapped as being underlain by Holocene
and Upper Pleistocene-age colluvium. The slopes above the subject property above an elevation
of approximately 8,600 feet above MSL are mapped as the Middle Pennsylvanian-age Minturn
Formation. The members of the Minturn Formation in order of ascending elevation are the
Robinson Limestone Member, the Middle Member, the White Quail Limestone Member, and the
Upper Member.
CONCLUSIONS AND OPINIONS
Based on our review of the referenced hazard maps, geologic and topographic data, proposed
development information, and our site observations, it is the opinion of Ninyo & Moore that the
proposed improvements are not subject to a significant risk of geologic hazards from debris
flows, rockfalls, or debris/snow avalanches. It is our opinion that the debris flow, rockfall, and/or
avalanche potential is limited and engineered mitigation measures are not required. Our opinion
is based on the following:
The proposed residence will be located at elevations ranging from approximately 8,364
feet above MSL (at the front) to 8,380 feet above MSL (at the rear). The topography in
the proposed building area is relatively level. The topographic map of the site by Peak
Land Consultants (2013) contains lines depicting “High Hazard” Snow or Debris
Avalanches, “Moderate Hazard” Snow or Debris Avalanches, and Maximum Extent of
Rockfall Hazard (see Figure 2). According to Peak Land Consultants, the hazard lines
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc 4
were derived from the Town of Vail Hazard Maps (Mears, 2001) and superimposed onto
the topographic map by the surveyor. The “High Hazard” Snow or Debris Avalanches
line extends to an elevation of approximately 8,400 feet MSL. The “Moderate Hazard”
Snow or Debris Avalanche line extends to an elevation of approximately 8,370 feet above
MSL.
The “High Hazard” zone for snow and debris avalanches is approximately 75 feet south
of the proposed building area. No structures are planned within the “High Hazard” zone.
The proposed building area will encroach approximately 50 feet into the “Moderate
Hazard” zone. However, the existing slope to the south of the proposed building area
within the “Moderate Hazard” zone is relatively level at an inclination of approximately
3:1 (horizontal:vertical). Therefore, the expected runout energy from a snow or debris
avalanche will be relatively low. There are no defined topographic chutes, which would
provide preferred pathways for avalanches to be directed toward the proposed
improvements. There is no evidence that would suggest the subject site has been
impacted by debris or snow avalanches in the historic past. It is our opinion that the risk
for debris or snow avalanche hazards at the site is low.
The sloping portions of the site are underlain by colluvial soils, which were deposited
over time by progressive downslope transfer of material, as opposed to short-duration
events such as a debris flow. We did not observe indications of active or previously
existing debris flow or rock avalanche deposits along the slopes in the vicinity of the
proposed improvements. We did not observe scarps, talus cones, loose boulders, or recent
rockslide debris at the base of the slopes to the south of the proposed building area. It is
our opinion that the risk for debris flow hazards at the site is low.
The subject lot contains a number of large boulders composed of similar geologic
material to that mapped further up the slope by Kennedy et al. (2003). These boulders
likely originated from the outcrops of sandstone and limestone exposed in the slopes
above the lot, and were transported to their present locations by past rockfall or debris
transport events. Evidence suggests that these boulders have been in-place in their present
locations for decades to hundreds (or potentially thousands) of years. Evidence for their
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc 5
age include their existence on the 1969 aerial photograph; lichens of significant size
growing in numerous locations on the boulders (see Photograph Nos. 26, 27, and 29); in-
place weathering and fracturing of the boulders (see Photograph Nos. 28, 31, and 32);
boulders embedded in the underlying and surrounding topsoil (see Photograph Nos. 34
through 40); and mature aspen trees having grown around in-place boulders (see
Photograph Nos. 38 and 39). No talus cones, rock chutes, or high-angle outcrops exist on
the property.
Based on this evidence, it is our opinion that rockfall events have not occurred at the site
in the historic past. The topography in the proposed building location is relatively level
and there is a large amount of vegetation on the slope. Thus, the energy of any rolling
rock would tend to dissipate prior to the rock entering the building area, should a rockfall
occur. It is our opinion that the risk for rockfall hazards at the site is low.
The subject lot is situated between three developed lots containing existing residences
(see photograph Nos. 2, 3, and 9). The majority of the subdivision has been built-out. The
proposed building area is located downslope from several of the neighboring properties
on slopes that are significantly less steep than the neighboring residences (especially
3828 Lupine Drive [Lot 10], see photograph Nos. 2, 8, 14, 15, and 17 through 19). The
proposed residence is located in an area that would be less hazardous than the
neighboring residences, and the proposed development would not pose an increased risk
of geologic hazards to neighboring properties.
Furthermore, the following is our opinion:
The site can be developed for the specific structure or use proposed without corrective
engineering or engineered construction or other mitigation or alterations.
The site is a geologically sensitive area but development will not increase the hazard to
other property or structures, or to public buildings, rights of way, roads, streets,
easements, utilities or facilities or other properties of any kind.
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc 6
DISCUSSION
The property Owner and the design team may want to consider implementing strategies during
site grading, landscaping, and development that would decrease the risk of hazards originating in
the slopes above the property. Such hazards could include shallow sloughing and slope failures,
shallow snow slides, drainage problems from snowmelt runoff water or precipitation events, etc.
Mitigation strategies could include re-planting the bare portions of the slopes above the site with
non-fire hazard vegetation to decrease erosion potential; creating a rock wall, berm, or catchment
area upslope from the building area to deflect material or runoff away from the proposed
structure. While we do not consider these measures to be mandatory, good development practice
suggests that these relatively inexpensive measures would improve the long-term performance of
the proposed improvements.
Based on our review of the proposed site plan, the landscape architect has planned a large rock
waste area located approximately 25 feet south of the rear of the residence, at an elevation of
approximately 8,388 feet above MSL. This large rock waste area would act as a buffer between
the slope and the development area and would meet the intent of the mitigation strategies
discussed above.
LIMITATIONS
The field observations and geologic evaluation presented in this report have been conducted in
general accordance with current practice and the standard of care exercised by geologic and
geotechnical consultants performing similar tasks in the project area. No warranty, expressed or
implied, is made regarding the conclusions, recommendations, and opinions presented in this
report. There is no evaluation detailed enough to reveal every geologic hazard condition.
Variations may exist and conditions not observed or described in this report may be encountered
during construction. Uncertainties relative to subsurface conditions can be reduced through
additional subsurface exploration. Please also note that our evaluation was limited to assessment
of the geologic aspects of the project, and did not include evaluation of geotechnical design
parameters, geotechnical global slope stability analysis, retaining wall design, environmental
concerns, or the presence of hazardous materials.
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
REFERENCES
Colorado Geological Survey, 2008, Geologic Map of the Larkspur Quadrangle, Douglas and El
Paso Counties, Colorado, CGS Open-File Report 08-17.
Fabre Engineering, 2011, Overall Grading and Drainage Plan, 15235 Furrow Road, Ponderosa
Retreat and Conference Center, USR Site Improvement Plan, US2010-021, dated February 18.
Jake’s Drafting Service, 2014, Site Plan for Chateau-D’Oex, 3816 Lupine Drive, Vail, CO
81657, Job# 14.01B, dated May 19.
LKP Engineering, 2014, Preliminary Soil and Foundation Investigation for a Proposed
Residence, Lot 8, Bighorn Subdivision, 3816 Lupine Drive, East Vail, Eagle County, Colorado,
Project No. 14-2930, dated May 5.
Peak Land Consultants, 2013, Partial Topographic Map, Lot 8, a Resubdivision of Lot 8 and 9,
Bighorn Subdivision Second Additions, Town of Vail, Eagle County, Colorado, PLC Job#
1010.2, dated December 27.
Town of Vail, 2014, Official Avalanche Hazard Map, Town of Vail, Colorado, dated March 5.
Town of Vail, 2000, Official Debris Flow Hazard Map, Town of Vail, Colorado, dated October
17.
Town of Vail, 2010, Official Rockfall Hazard Map, Town of Vail, Colorado, dated October 17.
Tweto, Ogden, 1979, Geologic Map of Colorado, Colorado Geological Survey Map.
Kellogg, K.S., Bryant, B., and Redsteer, M.H., 2003, Geologic Map of the East Vail Quadrangle,
Eagle County, Colorado Miscellaneous Field Studies Map MF-2375.
SITE LOCATION
FIGURE
1DATE:
5/14
file no: 0808vmap0514
PROJECT NO:
500808001
0
Approximate Scale:
1 inch = 3000 feet
3000
Note: Dimensions, directions, and locations are approximate.
3816 LUPINE DRIVE
EAST VAIL, COLORADO
N
Source: Macvan Map Company, Denver Metro Edition, Colorado, 2010.
APPROXIMATE
SITE LOCATION
N
Source: Macvan Map Company, Denver Metro Edition, Colorado, 2010.
APPROXIMATE
SITE LOCATION
APPROXIMATE
SITE LOCATION
N APPROXIMATESITE LOCATION
Source: US Geological Survey 7.5-minute topographic map, Vail East, Colorado, rev. 1987.
N
APPROXIMATE
SITE LOCATION
N
FIGURE
2
PHOTOGRAPH LOCATIONS
PROJECT NO:
500808001
DATE:
5/14
3816 LUPINE DRIVE
EAST VAIL, COLORADO
0
Approximate Scale:
1 inch = 75 feet
75
Source: Peak Land Consultants, Inc., 12/27/13.file no: 0808plm0514bLEGEND
Boring LocationB-2
RW-8RW-7RW-6RW-5RW-4RW-3RW-2RW-1B-4B-3B-2B-1
5
1011
9
4
8
141920
21
15
18
1
22
2423
2625
27
29
2830
35
32
31
44
43
363738
3940
4142
2,
3
12,
13
33,
34
16,
17
29
28
26
27
25
23
21
22
20
24
10
15
9
11
14
13
12
2
5
4
3
8 2
1
7
UNIT
150
UNIT
150 UNIT
150
UNIT
150 UNIT
150
UNIT
150
UNIT
150
UNIT
150
UNIT
150 UNIT
150
UNIT
150
STEEL POST (TYP)
29
28
26
27
25
23
21
22
20
24
10
15
9
11
14
13
12
2
5
4
3
86
1
7
UNIT
150
UNIT
140
UNIT
130
UNIT
145
UNIT
135
UNIT
125
UNIT
115
UNIT
120
UNIT
110
UNIT
100
UNIT
105
STEEL POST (TYP)
LEGEND
Photograph Location and Direction
Concrete Crack Location
29
15
16
17
18
19
20
21
22
23
24
43
5
6
2
13 14
12
1011
9
7
8
25
26
32
31 28
2927
30
33
41 38
34
39
40
1
35
37
36
3796 LUPINE DRIVE
SUBJECT
PROPERTY
3826 LUPINE DRIVE
3828 LUPINE DRIVE
3816 LUPINE DRIVE
15 16 17 18 19 2021 22 23 244356213141210119782526323128292730 33 41 383439 40 1 3537363796 LUPINE DRIVESUBJECTPROPERTY 3826 LUPINE DRIVE3828 LUPINE DRIVE3816 LUPINE DRIVEBOULDER
15
16
17
18
19
20
21
22
23
24
43
5
6
2
13 14
12
1011
9
7
8
25
26
32
31 28
2927
30
33
41 38
34
39
40
1
35
37
36
3796 LUPINE DRIVE
SUBJECT
PROPERTY
3826 LUPINE DRIVE
3828 LUPINE DRIVE
3816 LUPINE DRIVE
BOULDER
LEGEND
Photograph Location and Direction41
LEGEND
Photograph Location and Direction41
3816 Lupine Drive May 22, 2014
East Vail, Colorado Project No. 500808001
500808001 R.doc
APPENDIX A
PHOTOGRAPHIC DOCUMENTATION
Project No.: 500808001
Photo 1 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 2 Location: 3816 Lupine Drive Date: 05/07/2014
View of Proposed Buildig Area, Looking North
Project Name: 3816 Lupine Drive
View of Lot Address
500808001 Photo Template.xls Page 1 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 3 Location: 3816 Lupine Drive Date: 05/07/2014
.
Photo 4 Location: 3816 Lupine Drive Date: 05/07/2014
View of Upper Lot Slope Looking East
View of Proposed Buildig Area, Looking Northwest
500808001 Photo Template.xls Page 2 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 5 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 6 Location: 3816 Lupine Drive Date: 05/07/2014
View of Upper Lot Slope Looking Southeast at Topography Above
View of Upper Lot Slope Looking South at Topography Above
500808001 Photo Template.xls Page 3 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 7 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 8 Location: 3816 Lupine Drive Date: 05/07/2014
View of Slope Above 3828 Lupine Drive Looking North
View of Upper Lot Slope Looking Southeast at Drainage East of Property Line
500808001 Photo Template.xls Page 4 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 9 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 10 Location: 3816 Lupine Drive Date: 05/07/2014
View of Proposed Building Area, Looking North from South Property Line
View of Slope Above 3796 Lupine Drive Looking Northeast
500808001 Photo Template.xls Page 5 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 11 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 12 Location: 3816 Lupine Drive Date: 05/07/2014
View of Topography and Vegetation Up Slope From Lot, Looking Southwest
View of Topography and Vegetation Up Slope From Lot, Looking South From South Lot
Line
500808001 Photo Template.xls Page 6 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 13 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 14 Location: 3816 Lupine Drive Date: 05/07/2014
View of Neighboring Residences Looking East from Mid Slope
Survey Stakes Denoting Southwest Lot Corner
500808001 Photo Template.xls Page 7 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 15 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 16 Location: 3816 Lupine Drive Date: 05/07/2014
View of Slope Above Subject Lot Looking Southeast
View of Slope Above 3828 Lupine Drive Looking Northeast with Boulder in Foreground
500808001 Photo Template.xls Page 8 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 17 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 18 Location: 3816 Lupine Drive Date: 05/07/2014
View of 3828 Lupine Drive Looking East
Drainage Swale Above 3828 Lupine Drive Looking East
500808001 Photo Template.xls Page 9 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 19 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 20 Location: 3816 Lupine Drive Date: 05/07/2014
View of 3826 Lupine Drive Looking East with Boulders in Foreground
View of 3828 Lupine Drive Looking East with Boulders and Vegetation in Foreground
500808001 Photo Template.xls Page 10 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 21 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 22 Location: 3816 Lupine Drive Date: 05/07/2014
Survey Stake Denoting East Property Line
View Looking South from Mid Slope
500808001 Photo Template.xls Page 11 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 23 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 24 Location: 3816 Lupine Drive Date: 05/07/2014
View of Proposed Building Area, Looking North
View Looking West From Building Area Toward Lot 7
500808001 Photo Template.xls Page 12 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 25 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 26 Location: 3816 Lupine Drive Date: 05/07/2014
Boulder in Subject Lot Near West Property Line
View Looking Southwest From Building Area Toward Lot 7 with Boulders in Foreground
500808001 Photo Template.xls Page 13 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 27 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 28 Location: 3816 Lupine Drive Date: 05/07/2014
In-Place Weathering on Top of Boulder Shown in Photo 26
Closeup of Lichen Growth on Boulder Shown in Photo 26
500808001 Photo Template.xls Page 14 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 29 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 30 Location: 3816 Lupine Drive Date: 05/07/2014
Closeup of Lichen Growth on Boulder Shown in Photo 26
View Up Slope of Lot 7, Looking Southwest
500808001 Photo Template.xls Page 15 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 31 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 32 Location: 3816 Lupine Drive Date: 05/07/2014
In-Place Weathering and Fracturing of Boulder Along West Property Line
In-Place Weathering and Fracturing of Boulder Along West Property Line
500808001 Photo Template.xls Page 16 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 33 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 34 Location: 3816 Lupine Drive Date: 05/07/2014
View Up Slope of Subject Lot, Looking Southwest
Large Boulder in Proposed Building Area, Note that Boulder is Embedded in Underlying
Topsoil and Surrounded by Mature Trees
500808001 Photo Template.xls Page 17 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 35 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 36 Location: 3816 Lupine Drive Date: 05/07/2014
Large Boulders in Proposed Building Area, Looking South from Lupine Drive
View of Proposed Building Area, Looking South. Ground Disturbance From Geotechnical
Test Pit Locations
500808001 Photo Template.xls Page 18 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 37 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 38 Location: 3816 Lupine Drive Date: 05/07/2014
Large Boulders in Proposed Building Area, Looking South from Lupine Drive
Large Boulder in Proposed Building Area, Note that Boulder is Embedded in Underlying
Topsoil and Surrounded by Mature Trees
500808001 Photo Template.xls Page 19 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 39 Location: 3816 Lupine Drive Date: 05/07/2014
Photo 40 Location: 3816 Lupine Drive Date: 05/07/2014
Mature Aspen Tree Growing Around Boulder in Proposed Building Area
Large Boulder in Proposed Building Area, Note that Boulder is Embedded in Underlying
Topsoil and Surrounded by Mature Trees
500808001 Photo Template.xls Page 20 of 21
Project No.: 500808001Project Name: 3816 Lupine Drive
Photo 41 Location: 3816 Lupine Drive Date: 05/07/2014
View of Proposed Building Area Looking North
500808001 Photo Template.xls Page 21 of 21