REP40682

• Permit No: C1980007
• IBM Index Class Name: Report
• Doc Date: 3/13/1985
• Doc Name: WEST ELK COAL CO PROPOSED AERIAL PHOTOGRAMMETRIC SUBSIDENCE MONITORING PROGRAM
• From: MLRD
• To: SUSAN MOWRY
• Permit Index Doc Type: SUBSIDENCE REPORT
• Media Type: D
• Archive: No

Richard D. Lamm
Governor
III IIIIIIIIIIIII III
999
DEPARTMENT OF NATURAL RESOURCES
David H. Getches, Executive Director
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
DATE: March 13, 1985 --~'"~
T0: Susan Mowry
FROM: Jim Pendleton ~=- ~-~~U
RE: West Elk Coa VComp s Proposed Aerial Photogrammetric Subsidence
Monitoring P m
WECC commits to pre-subsidence field surveys of each subsidence monitoring
monument and annual resurveys of triangulation points with Second Order Class
II horizontal accuracy. Due to topographic considerations vertical control
will be slightly less accurate. WECC commits to holding vertical error to
less then plus or minus 0.2 feet. WECC will compare these field surveys
results with the results of an aerial survey of the highest obtainable
accuracy. This aerial photogrammetric evaluation will be completed with first
order equipment and will be controlled by the field survey triangulation
stations.
However, WECC proposes the following criteria for photogrammetric survey
acceptability: "The results of the air and field surveys will be compared for
all profile points. In the event that the two surveys correlate within an
error of less than 0.4 feet 95% of the time, the aerial survey will be
accepted as accurate and will be used for subsequent monitoring. If the
aerials surveys proves to be unacceptable, field surveys will be used, but the
terrain considerations will dictate that the surveying be a lower level of
accuracy, specifically, third order."
WECC's proposal is inconsistent with my understanding from our meeting with
the company of February 14, 1985. I recommend the Division apply criteria for
success to approval of the requested permit revision application which reflect
WECC's commitments for survey accuracy. It is important to avoid cofusion in
the future. The findings document should contain clear and unambiguous
criteria for judgin the acceptability of the initial and subsequent aerial
photogrammetric surveys. For this reason I suggest we amend the findings
document to include the following discussion.
The results of the pre-subsidence aerial photogrammetric and field
surveys shall be compared for each survey point. The aerial survey
will be accepted as accurate and will be used for subsequent
monitoring, in the event that the aerial photogrammetric and field
surveys correlate with a average survey point location deviation of
less than 0.2 feet vertically and horizontally, with survey point
location deviations of less than 0.4 feet vertically and horizontally
for at least 95% of the survey points, and with no survey point
location deviation in excess 0.8 feet vertically or horizontally.
(These limit criteria reflect allowed variances of 1, 2 and 4 standard
survey deviations, respectively.)
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