HomeMy WebLinkAbout19 Geotechnical InfoSGM GEOTECHNICAL INFORMATION
O\OLSSON
ASSOCIATES
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O\OLSSON
ASSOCIATES
July 20, 2017
Mr. Glenn Hartman, Senior Planner
Garfield County Community Development
108 8th Street, Suite 401
Glenwood Springs, CO 81601
RE: Ursa Phase II Completeness Items
Dear Glenn,
6SGM
www.sgm-inc.com
Per our phone discussion late yesterday afternoon, I am providing this letter report to help clarify
questions and concerns that you had during your completeness review of the Ursa Phase 11 proposed oil
and gas development application in Battlement Mesa. The questions/concerns and/or requested
clarifications came in an email from you to Jennifer Lind and Cari Mascioli on June 29, 2017. From that
email, please note the following issues in your email that we are able to respond to on Ursa's behalf:
Relative to BMC A Pad:
o Documentation that the size of the detention pond will be consistent with the SGM drainage
study. The plans also need to address any downgradient impacts from the pond discharge.
As we discussed in our phone conversation, the design (and detailing) of the pond is to release
at the 25 -year historic rate of flow for the basin tributary to the pond. Note that the pond depth
(1.4') above the invert out of the 18" pipe is storing an instantaneous detention volume of 4,400
cubic feet with the required detention volume needing to be less at 2c855 cubic feet. There, the
pond design meets/exceeds the requirements of the county performance standards.
o Additional soils and geotechnical analysis on the soil nail wall and rock boulder walls, to
include as appropriate any height limitations and technical recommendations.
We understand that the geotechnical report that you reviewed initially for this application was
that of the 011son's geotechnical report that was generally prepared to address the entire
proposal as a whole. As we discussed, this report was not prepared specifically to address the
soil nail wall as we have collaborated with RJ Engineering in this regard. Therefore, we have a
letter report from Richard Johnson of RJ Engineering that should have also been in the
application and has been attached to this correspondence. The purpose for the inclusion of
consultation with RJ Engineering into this issue was concern with a prior slope grading
alternative that left the cut slope at 1:1 that nearly consumed the entire hillside up to Tamarisk
Village. Slope stability and constructability were the major concerns with this cut slope. During
our site investigation of the proposed pad area, no mitigating factors were observed (such as
GLENWOOD SPRINGS 1 18 West Sixth St, Suite 200 1 Glenwood Springs, CO 81601 1 970.945.1004
SSGM
www.sgm-inc.com
springs or elevated ground water conditions) that would exacerbate slope stability for either the
1:1 cut slope or the construction of an alternative soil nail wall. Give the site constraints for
access, it appears, however that the design/build of a soil nail would be "more constructible"
and more adaptable to the site conditions by reducing the massive amount of excavation and
surface impacts created by the 1:1 slope alternative. Also, the soil nail wall, as it is being
constructed, is highly adaptable toward horizontal underdrain construction if any ground water
is ever encountered. To that end, R.I Engineering prepared the report following their
recommendation of a design/build soil nail wall and provided details that will typically be
required. No height restrictions are placed with this alternative as the on-site testing of "soil
nail" strengths during construction are performed as part of the quality control/assurance
process.
o For the access roadway, the plans or related reports need to address proximity to existing
structures on the down slope side of the roadway.
Confusing this issue for you was the inaccurate description, on our part, of the roadway cross
section typical that did not represent the elements of the drainage plan to assure that the
roadway drainage does not impact existing structures on the down slope side of the roadway.
Note that we have revised the detail on Sheet A5 as the grading plan reflects and have attached
the revised sheet here to and represent the revisions in the following figure:
2'
t
11.0' 11.0'
2.0X
2.0X
EXISTING GRADE
1.5' DEEP
8" CLASS 6 ABC 1.5' DEEP
ROADSIDE DITCH ROADSIDE DITCH
ABC = Aggregate Bose Course
A'" = Minimum 4" Topsoil or Specified Alternative
1.0' HIGH BERM
AT TOE OF SLOPE
TO TRAP LOCAL TYPICAL ROAD SECTION
SLOPE DRAINAGE AND
SEDIMENT
With the intended design the downhill side of the roadway (as reflected in the grading plan), we
have immediately placed a borrow ditch at the edge of the road (prior to the revegetated slope)
to direct drainage from the roadway to the detention pond downstream of the BMC A facilities.
In that manner, any immediate access to spills or needed maintenance for the roadway and
borrow ditch can be quickly accessed from the road.
GLENWOOD SPRINGS 118 West Sixth St, Suite 200 1 Glenwood Springs, CO 81601 1 970.945.1004
SSGM
www.sgm-inc.com
o The drainage plan needs to confirm that all site drainage is conveyed away from the
adjacent Battlement Mesa Metro District facilities including any potential discharges or spills
from the site.
As we discussed on the phone, the drainage plan does function in a manner that all site drainage
is conveyed away from the adjacent Battlement Mesa Metro District facilities. The roadway
section previously submitted prompted your question and now clarified should be sufficient to
address your concern. As we discussed, the roadway borrow ditches drain to the detention
pond (where ample volume exists prior to any discharge) to capture any spills from either the
roadway or the pad. Drainage from the pad likewise drains to the detention pond.
Relative to the BMC F Pad:
The traffic assessment for the F pad restated the anticipated traffic needed to support the
typical well pad development. Note that the anticipated traffic for the F pad is much less than
what would be necessary for the typical drill pad as we are bringing in 100 "unloaded" frac tanks
and taking out 100 "unloaded" frac tanks (when done using F Pad). Therefore, the structural
implications are much less. It is Ursa's intent to fill the frac tanks remotely by pipeline thus just
needing to bring them in and out. There will be very limited times when water hauling will be
necessary (such as make up water needs or unforeseen emergencies). We felt we were being
conservative in stating the drill/production and reclamation traffic.
As we discussed on the phone, the other concern/issue you had was the timing in which the
tanks would be placed. We have discussed this with Ursa's and their indication is that the tanks
would be brought in over a 7 —10 day period and likewise, when removed, in the same length of
time period.
I hope this correspondence and it's attachments adequately address the issues/concerns raised with
your review. Upon your receipt and review, if you need further information or have further questions,
please don't hesitate to contact me.
GLENWOOD SPRINGS 118 West Sixth St, Suite 200 1 Glenwood Springs, CO 81601 1 970.945.1004
April 11, 2017
Mr. Jeff Simonson
SGM, Inc.
118 West Sixth Street, Suite 200
Glenwood Springs, Colorado 81601
Project No. 17 -007G -C1
Subject: Geotechnical Consultation, BMC A Pad in Garfield County, Colorado
Dear Mr. Simonson,
RJ Engineering & Consulting, Inc. was requested to observe conditions of the existing slope and
comment on the grading plan at the proposed BMC A Pad site in Garfield County, Colorado.
The BMC A Pad, which is associated with natural gas production, is planned at the base of a
very steep slope. Specifically, the south side of the pad is planned to be constructed into the
existing slope, and cut depths of more than 30 feet are planned. We were requested to provide
our opinions associated with the planned excavation and provide alternatives to maintain
stability of the existing slope.
OBSERVATIONS
We visited the site on March 3, 2017. The existing slope grades are very steep with grades
approaching 1H:1V. The slope is covered with native brush, trees and grasses. The soils
observed on the slope appeared to consist of clay and sands with abundant amounts of gravels,
cobbles and boulders. The cobbles and boulders consisted of basalt rock and were up to
several feet in diameter. We did not observe seeps or evidence of groundwater emerging from
the slope.
OPINIONS
Various construction techniques for the south side of the pad were discussed and included:
• A permanent cut slope at 1H:1V
• A concrete cast -in-place wall
• A soil nail wall with a shotcrete facing
Each construction technique has pros and cons associated with slope stability, aesthetics, water
quality and costs. The pros and cons of each technique are discussed below.
A 1H:1V permanent cut slope would be difficult to construct and problematic to maintain. The
top of the cut slope would likely be located about two-thirds to three-quarters the way up the
slope. Grading of the cut slope would likely require access to the slope from above, and the
excavation would be large and easily visible from a distance. In addition, stability of a 1H:1V cut
slope would be marginal for the materials observed at the site. Surface flows and/or
groundwater would greatly reduce stability of the slope. Care would have to be taken to divert
surface flows from above around the cut slope. Significant erosion control mitigation would
need to be installed to prevent erosion and maintain water quality leaving the site from
precipitation events. Long-term maintenance of these systems would be required. Also,
266 Red Cliff Circle, Glenwood Springs, CO 81601, (970) 230-9208
BMC A Pad, Garfield County
installation of erosion control measures on a 1 H:1 V slope is difficult. Our observations did not
suggest groundwater would be encountered, however, experience in the area suggests that
groundwater could be encountered in an excavation of this magnitude. Groundwater flows may
become evident in the spring and summer months.
A concrete cast -in-place wall was also considered. For wall heights of more than 30 feet,
temporary excavation stabilization of the slope would be required for installation. Based on
discussions with SGM, a concrete wall of this height would not be cost effective.
We believe a soil nail wall would be the most efficient system to stabilize the planned
excavation. A soil nail wall could be constructed by accessing the top of wall from the base of
the slope with minor to no disturbance to the slope above the wall. A soil nail wall is constructed
from the top down providing slope stability as the wall construction occurs. The construction
process reduces the area of disturbance beyond the proposed pad location.
SUMMARY
We believe a soil nail wall would be the most effective system for completing the proposed pad
at the base of the slope. Soil nail wall construction would reduce the overall surface disturbance
and be the most cost effective means for maintaining stability of the existing slope. Typically,
construction of a soil nail wall system is provided by a design -build contractor. If needed, we
can be contacted to provide design -build contractors with experience in installation of these
systems.
LIMITATIONS
This study has been conducted in accordance with generally accepted geological and
geotechnical engineering practices in this area for use by the client. The opinions submitted in
this report are based upon the data obtained from field reconnaissance. Geologic conditions
will also change over time periods, so that results of the analyses and recommendations will
also change over time as site conditions change. Changes in vegetation due to flooding or
grading will change the analyses and recommendations presented herein.
The report was prepared in substantial accordance with the generally accepted standards of
practice for geotechnical engineering as exist in the site area at the time of our investigation.
No warranties, express or implied, are intended or made.
If you have questions or need additional information, please call us at 970-230-9208.
Sincerely,
RJ Engineering & Consulting, Inc.
Richard D. Johnson, P.E.
Project Manager
Page 12
Revision
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5132.2 EG
5132.07 FG
5131.6 EG
5731.38 FG
5130.2 EG
5130.75 FG
5729.3 EG
5130.11 FG
5728.7 EG
5129.48 FG
5128.4 EG
5728.85 FG
5128.2 EG
5128.27 FG
5127.2 EG
512758 FG
5126.7 EG
5126.95 FG
5126.3 EG
5126.29 FG
5125.4 EG
5725.60 FG
5124.7 EG
5124.90 FG
5723.9 EG
5724.20 FG
5122.8 EG
5123.50 FG
5121.9 EG
5122.87 FG
5720.9 EG
512211 FG
5119.8 EG
5121.47 FG
5119.4 EG
512077 FG
5119.4 EG
5120.02 FG
5779.3EG
5119.27 FG
5717.9 EG
5718.20 FG
5176.0 EG
5716.80 FG
5115.0 EG
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5113.92 FG
5112.7 EG
5772.48 FG
5772.1 EG
5711.04 FG
5111.9 EG
5109.59 FG
5111.3 EG
5108.15 FG
5110.6 EG
5106.71 FG
5109.8 EG
5105.27 FG
5109.1 EG
5103.83 FG
0+00
0+50
1+00
11-50
2+00
2+50
3+00
3+50
4+00
41-50
5+00
PAD A ACCESS ROAD PLAN AND PROFILE
51-50
61-00
6+50
7-1-00
7+50
5145
5140
5135
5130
5125
5120
5115
5110
5105
5100
Preliminary
Not For
Construction
SSGM
118 West Sixth Street, Suite 200
Glenwood Springs, CO 81601
970.945.1004 www.sgm-inc.com
URSA Operating Company, LLC
Battlement Mesa PUD Phase 11
BMC A Pad
Graphic Scale
0 20 40 80
In Feet: 1 " = 40'
LINE TABLE
LINE
BEARING
LENGTH
L1
S11'3701 E
70.19'
L2
5132'0221"W
203.06'
L3
S15'46'45'W
47.78'
L4
534'46'17"W
122.44'
L5
559'36'38"W
700.00'
CURVE TABLE
CURVE
RADIUS
LENGTH
TANGENT
CHORD
BEARING
DELTA
01
150.00'
117.01'
61.66'
114.06'
59'41'32'W
44' 41' 36"
02
250 00 '
70.95'
35.71 '
7a 71'
523'54'33"W
16' 15' 35"
03
250.00'
82.86'
41.81'
82.48'
525-16'28"W
18' 59' 26"
PAD A ACCESS LINE AND CURVE TABLES
2'
FiLL
.0'
2.0.`B' 2� X�
1.5 DEEP
ROADSIDE DITCH
8" CLASS 6 ABC
ABC = Aggregate Bose Course
. ' = Minimum 4" Topsoil or Specified Alternative
1.0' HIGH BERM
AT TOE OF SLOPE
TO TRAP LOCAL TYPICAL ROAD SECTION
SLOPE DRAINAGE AND
SEDIMENT
EXISTING GRADE
1
1.5' DEEP
ROADSIDE DITCH
Access Road
Plan & Profile
Job No. 2006-479.062
Drawn by: AMC
Date: 3.13.17
QC: DJC
PE: JJS
File: BMC A Pad Base SGM
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