REP04400

• Permit No: C1981014
• IBM Index Class Name: Report
• Doc Date: 6/7/1993
• Doc Name: SEMI ANNUAL SUBSIDENCE MONITORING REPORT
• Permit Index Doc Type: SUBSIDENCE REPORT
• Media Type: D
• Archive: No

Energy Fuels Coal, Inc.
Southfield Mine
Semi-Annual Subsidence Monitorine Repoli
(November 1, 1992- April 30, 1993)
Introduction
This report presents a summary of field monitoring data and discussion of subsidence predictions for
Energy Fuels Coal, Inc. (EFCI) Southfield Mine for the six month monitoring period referenced above. The
discussion of subsidence survey data includes comparisons of measured subsidence to predicted values. In
addition, survey field data is presented on three summary tables accompanied by two cross section diagrams
of the high resolution monument grid.
Discussion
A. Structure Subsidence Monitoring
EFCI monitored the Thompson Ranch structures (3 buildings), Florence Water Line (8 Monuments),
and Newlin Creek (1 Monument) on a quarterly basis for the period of this report. Summarized survey
monitoring data for the above structures are presented on Table 2, Florence Water Line and Table 3,
Thompson Ranch Structures and Newlin Creek Point.
The survey data obtained during this reporting period indicates that no measurable subsidence has
occured at the Thomson Ranch Structures or Newli^ Creek Point. These findings are to be expected
because no additional mining has occured in the vacinity of the structures.
Field survey data obtained at the eight monuments along the Florence Water Line indicate no
current subsidence effects with exception of the western most Monument 'E'. A review of the survey data
for this monument (refer to Table 2) indicates movement of 0.07 feet and 1.57 feet since the previous and
original surveys respectively. The relatively large displacement since the previous survey is either a result
of survey error or indications of additional ground collapse due to retreat mining this area during 1986. The
total 1.57 feet of subsidence is however well within the maximum predicted value of 2.79 feet as presented
in the permit application.
B. High Resolution Grid Monitoring
EFCI monitored the 23 monuments of the high resolution (south) grid on asemi-annual basis during
the reporting period. Summarized survey monitoring data for the grid monuments are presented on Table 1,
South subsidence Grid. These data are also presented in cross section diagrams attached as Figure 1 and
Figure 2.
The results of the field survey indicate that only minor additional subsidence is occuring at the South
Grid monuments. These data suggest that the underground cave area is almost completely consolidated and
that only minor additional subsidence is expected to occuro. Through the date of this survey, the maximum
measured subsidence of 2.31 feet (Monument 15) is well below the maximum predicted value of 5.40 feet as
presented in the permit application. In addition, the estimated 25 degree draw angle depicted on figure l is
conservative and in agreement with the 20-25 degree draw angle predicted in the permit application.