REV05856

• Permit No: M1974015
• IBM Index Class Name: Revision
• Doc Date: 10/29/1999
• Doc Name: MEMO MINING SETBACKS WESTERN MOBILE BOULDER ROCKIN WP PN M-74-015
• From: DMG
• To: ERICA CROSBY
• Type & Sequence: AM6
• Media Type: D
• Archive: No

• iii iuiiiiiiiiu iii •
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Depanmenl of Natural Resources
1 313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: October 29, 1999
DIVISION OF
MINERALS
GEOLOGY
ft EC LA MA710N
MINING•SAF ETY
TO: Erica Crosby
S ail I Owens
Governor
FROM: Allen Sorenson
. Greg E. \Nalcher
Executive Dneclor
RE: Mining Setbacks, Western Mobile Boulder, Rockin' WP, Permit No. M-74-015 Michael e.IOng
Division Dueao~
The findings and recommendations presented in [his memorandum are based on observations and
discussions from our October 22, 1999 inspection at the Rockin' WP. If you haven't already sent i[, you
may want to incorporate portions of this memo into your inspection report.
Empirical evidence at the Miller Pit indicates that the Operator may mine to within 15 or 20 feet of the
Foothills Reservoir outlet ditch, AKA Highlands Seep, without any stability problems. The Operator will
propose a mining setback of 25 feet from the top of [he reservoir ditch bank. This setback is acceptable with
the condition [ha[ mining depth does no[ exceed 25 feet. Mining depth should no[ be an issue since coring
in the area of the reservoir outlet in the Rockin' WP South indicates a maximum depth [o bedrock of 17 fee[.
The Operator will propose a mining setback of 200 feet from the toe of the Foothills Reservoir dam. The
gravel resource pinches out as the dam is approached, so the pit depth parallel to the dam should only be 15
feet or less. A 200-foot setback is adequate [o protect the dam.
Gravel mining is proposed to the east and west of [he Southdown Cement Plant access road. There are
numerous valuable manmade structures in this corridor including the concrete access road, a rail spur, a
conveyor belt, utility poles and lines, a buried gas line and possibly other buried utilities, and [he Foothills
Reservoir inlet ditch. Of the visible, above ground structures, the cement plant access road will be the
closes[ structure [o mining on the west, and the reservoir inlet ditch will be closest to mining on the east. A
horizontal mining setback equal to two times the maximum pi[ depth in these areas will be adequate to
protect the road and the ditch. The buried gas pipeline, based on observations of markers in the field, is
located between the access road and [he reservoir inlet ditch. The surface markers indicate that the gas line
is approximately 80 feet east of the west edge of the access road. Assuming a 50-foot mining setback from
the road, the total setback to the gas line would be 130 fee[, which will be adequate to protect [he pipeline.
The following items should be addressed in the Applicant's adequacy response relative to the cement plant
access corridor.
• All above ground and subsurface utilities should be identified, illustrated on a map, and marked on the
ground. Mining setbacks must be specified to each of [he utilities.
• The Operator should obtain an agreement with the owner of the above ground utilities prior to working
within 100 feet during installation of the conveyor from the West Plant/Phase I pit. A copy of the
agreement must be filed with the Division.
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