REV05658

• Permit No: C1981038
• IBM Index Class Name: Revision
• Doc Date: 2/6/1992
• Doc Name: MEMO CYPRUS ORCHARD VALLEY MINE TR-16 SUBSIDENCE MONITORING REDUCTION PN C-81-038
• From: MLRD
• To: STEVE SHUEY
• Type & Sequence: TR16
• Media Type: D
• Archive: No

~~~ ~~~~~~ 99 STATE OF COLORADO
MINED LAND RECLAMATION DIVISION of ~o~
Department of Natural Resources ~~,q9
NQ ~,. „ o
1313 Sherman St., Room 215 cy~~~
Denver, CO 80203 ' .~ ~~;
303 866-3567 '•ie~b•
Fnx~303 832-8106
Roy Ramer,
Governor
Fretl R. Banta.
Division Director
DATE: February 6, 1992
T0: Steve Shuey ~' j
FROM: Jim Pendleton `~`~
F~f,^•
RE: Cyprus 0`chard V~1-ley Mine - TR-16 - Subsidence Monitoring Reduction
(Permit #: C-81-038)
I have reviewed Cyprus Orchard Valley Coal Company's (COVCC) technical
revision application TR-16, which you forwarded to my attention. This
technical revision application requests permission to reduce its subsidence
monitoring program at the Cyprus Orchard Valley (COV) Mine.
As the operator observes within the application, COVCC originally completed a
full blown subsidence survey, including detailed predictions of anticipated
maximum vertical subsidence and the angle of draw. They predicted maximum
vertical subsidence magnitude in the 7 foot range and a maximum angle of draw
of approximately 20 degrees from vertical. The approved and amended permit
also includes a detailed subsidence monitoring program. This program includes
survey monitoring of two types of subsidence monument grids. High resolution,
closely-spaced monument grids were installed above specific panels of interest
in the pre-fire area of the mine. Wide-spaced monuments were installed near
section corners throughout the actively mined area and in adjacent areas to
active mining. All of these monuments have been monitored semi-annually. In
addition, a visual "walk-over" inspection has been conducted semi-annually.
Data reports are submitted semi-annually, with a detailed text evaluation and
summary of the past year's data included in the annual Subsidence Report. The
annual reports discuss the relationship between predicted and observed
subsidence character.
COVCC concludes that sufficient information has been collected to date to
demonstrate: (1) that their initial projections of maximum vertical subsidence
magnitude and angle of draw were conservative; and, (2) that many of the
previously monitored mined areas have reached cessation of active subsidence.
I concur that COV's data consistently demonstrates a maximum vertical
subsidence magnitude in the range of 3 1/2 to 4 feet, and a maximum angle of .
draw of approximately 16 degrees from vertical. I also agree that the
high-resolution monitoring grid panels, all above the old pre-fire mined
portions of the COV mine, have apparently reached cessation of active
subsidence. I further agree that many of the wide-spaced monuments affected
by subsidence to-date have also reached apparent cessation of active
subsidence.