PERMFILE115827

• Permit No: C1981014
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 23 Part 2
• Media Type: D
• Archive: No

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SOUTHFIELD MINE
SEMI-ANNUAL SUBSIDENCE REPORT
FOR PERIOD MAY - OCTOBER, 1986
(STIPULATION NO. 11 OF PERMIT C-81-014)
Introduction
This report has been prepared to summarize subsidence monitoring
results and to state subsidence predictions based upon the present
subsidence monitoring program. Survey monitoring for the purpose
of this report was performed on the South Grid, City of Florence
Water Line, Thompson Ranch Structures, and the Newlin Creek
Streambed as required.
Survey data has been presented on four summary tables, each of
which compares results of the most recent survey to the pro-
ceeding survey and to the original survey to indicate the magni-
tude and direction of movement for each monument and structure.
The survey data for both monument lines of the South Grid 1s
portrayed in cross sectional form to depict the total subsidence
as of the most recent survey.
• The report is presented in sections, for each of the items moni-
tored, with observations and predictions.
South Subsidence Grid
Survey data for the South Grid monuments indicates similar trends
as compared to the previous six month survey period. The maximum
subsidence detected to date is 1.88 feet at Monument 15, a change
of 0.16 from the preceeding survey. The subsidence ie much less
than the predicted 5.0 feet based on the retreat mining of the 2
South "B" and °C" Panels. Maximum subsidence as a result of
retreat mining "A" Panel is a total of 1.14 feet at Monument 4.
The maynitude of movement is comparable to the maximum predicted
subsidence of 1.46 feet by Rocky Mountain Geotechnical (RMG) in
the Mining Permit.
The rate of subsidence continues to be greatest along the north
arm of the grid from Monument 11 to Monument 15. Survey date
indicate changes ranging from 0.14 to 0.16 feet for the current
period. Data from the previous six month report indicate movement
of the same monuments ranging from 0.19 to 1.43 feet. The measur-
ed decrease in the rate of subsidence is probably due to the
consolidation of the underground caved area. It is anticipated
that the rate of movement will continue to decrease resulting 1n
minimal additional subsidence.
. Survey data from the south arm of the grid as portrayed on the
cross section indicates an apparent angle of draw of between 19
and 29 degrees. This is generally consistent with the range of 20
to 25 degrees predicted by RMG in the Mining Permit. Continued
survey monitoring should improve the reliability of predicting the