PERMFILE100505

• Permit No: M2004078
• IBM Index Class Name: Permit File
• Doc Date: 3/28/2005
• Doc Name: Additional Comments from CDOT and Updated Stability Analysis
• From: DMG
• To: SW TKO Joint Venture LLC
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman St, Room 215 COI, <) RA D ~
Denver, Colorado 80203 DIVISION O F
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Phone: [phone] &
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FAX: [phone] G)r O 1. O G Y
RECLAMATION•MIN ING
SAFETY•SCIENCE
6111 OWenS
Governor
DATE: March 23, 2005 Russell George
Executive Director
TO: Erica Crosb
y Ronald W. Cottony
Division Director

FROM: Allen Sorenson Natural Resource Trustee
RE: Review of Modifted Proposal, Mining Setbacks from Permanent Valuable Structures,
SW TXD Joint Venture, LLC, Lupton Lakes Pit, File No. M-20D4-D78
The Division of Minerals and Geology (DMG) engineering staffhave completed a review ofmodified
stability analyses and proposed mining setbacks provided for the Lupton Lakes permit application. These
were provided as a letter and attachments dated March 22, 2005 from the Applicant's consultants, Civil
Resources, LLC. In accordance with DMG's discussions with Mazk Reiner of Civil Resources, the mining
setbacks aze established as horizontal distances measured from the toe of the mining slope to the various
structures located around the proposed pit. By establishing the setback as a distance from the toe of the
slope, DMG will not be in the position of having to regulate the pit wall slope angle. Also, in accordance
with the discussions between DMG and Civil Resources, lower effective friction angles for the weathered
claystone and sand and gravel strata were input to the analyses, as specified if the DMG memo dated March
12, 2005.
DMG has analyzed the new proposed setback distance from the edge of Highway 85 in the vicinity of
geotechnical borehole MW-03; this is the location of the Applicant's cross section C-C'. The results of the
DMG analyses are attached to this memo. DMG analysis no. 1 duplicates the Civil Resources' analysis,
and yields the same safety factor result. This analysis considers a 1:1 sloped pit wall; it is the DMG's
understanding that the Operator intends to mine at L 1 as the pit perimeter is approached in order to
facilitate clay liner installation. However, as mentioned above, DMG will not regulate the slope of the pit
wall during active mining. DMG analysis no. 2 considers the same potential slope failure surface as
analysis no. 1, but models a vertical pit wall with a 100-foot setback from Highway 85. Interestingly, the
safety factor increases appreciably under the analysis no. 2 scenario, as compared to DMG analysis no. 1.
This may seem counter-intuitive, given the steeper pit wall under analysis no. 2 and the conventional
wisdom that shallower pit slopes aze more stable. However, these analyses are designed to consider the
stability of the ground at the edge of Highway 85. In fact the slope in the vicinity of the assumed vertical
pit wall has a substantially lower safety factor than a 1:1 sloped pit wall, but this is an operational issue that
has no bearing on the stability of Highway 85. The physical reason that the vertical pit wall scenario is
more stable at the edge of the highway is that the weight of the sand and gravel on the assumed failure
surface increases the resisting force on that surface.
DMG analysis no. 3 shows that there is a more critical failure surface relative to Highway 85 than the
failure surface analyzed in the applicant's submittal. However, the safety factor result for this more critical
failure surface is 1.08, which is still sufficient to assure that the proposed gravel pit will not impact the
Office of Office of Colorado
Mined Land Reclamation Active and Inactive Mines Geological Survey