REP12181

• Permit No: C1981038
• IBM Index Class Name: Report
• Doc Date: 7/6/1987
• Doc Name: MEMO COLO WESTMORELAND IND 1986 ANNUAL HYDROLOGY & SUBSIDENCE REPORT
• From: MLRD
• To: TOM SCHREINER
• Permit Index Doc Type: SUBSIDENCE REPORT
• Media Type: D
• Archive: No

• • III IIIIIIIIIIIIIIII
999
STATE OF COLORADO
Roy Romer, Govei
DEPARTMENT OF NATURAL RESOURCES
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
MEMORANDUM
July 1987
T0: Tom Schreiner
FROM: Jim Pendleton
RE: Colorado We relan Inc., 1986 Annual Hydrology 8 Subsidence Report
Pursuant to your request, I have completed a review of the subsidence portions
of CWI's 1986 Annual Hydrology & Subsidence Report for the Orchard Valley
Mine. The visual and survey subsidence data appears properly gathered and
tabulated. The data shows subsidence response over the 11 North Panel to have
been very similar to that of the 12 North Panel, which was retreat mined the
previous year. A maximum elevation change of 1.57' was recorded at station
38. The majority of the subsidence was observed to occur within the first 3
1/2 months.
I have one concern regarding the operator's determination of the
representative angle of draw, Three observations have been made of the angle
of draw adjoining Panels 11 North and 12 North. Based on the observations to
date the operator has determine three angles of draw:
East side of Panel 11 North = 16.1 degrees from vertical
West side of Panel 12 North = 15.8 degrees from vertical
East side of Panel 12 North = 20.0 degrees from vertical
Based on these three determinations and the rationale that "it is difficult to
determine the exact location at which possible subsidence could actually be
surveying instrument or human incapacity", the operator proposes that the
angle of draw be assumed to equal 16.0 degrees. With a sample of only three
observations I do not believe that this assumption is warranted. I believe
that it woulkd be more appropriate to conservatively assume that the angle of
draw is 20.0 degrees, until more definitive information becomes available.
Therefore, I recommend that we accept the visual and survey subsidence
monitoring data as reported. However, for purposes of determining buffer zone
boundaries in the future, I believe the data only warrants the assumption of
20.0 degrees from vertical as the projected angle of draw.
The operator projects insignificant subsidence for the year 1987, due to the
development nature of mining within the West Mine. No retreat mining will be
performed during 1987. I concur with the operator's projection.
cc: Rob Liddle
423 Centennial Building, 7313 Sherman Street Denver, Colorado 80203-2273 Tel. [phone]