Laserfiche WebLink
REVIEW OF THE 1993 FIRST SEMI-ANNUAL SUBSIDENCE REPORT <br />CYPRUS TWENTYMILE COAL COMPANY <br />FOIDEL CREEK MINE <br />The scope of work covered by this report involves reviewing subsidence data from the <br />first, 1993 semi-annual report, determining the validity of reported draw angles, and <br />commenting on any variance that exists between predicted and measured subsidence. <br />Review Results: The results of the review are contained in the attached tables and <br />corresponding figures. Please note that I have added the original predicted subsidence <br />(from tables 10 and 11 of the Permit Report) to both the tables and subsidence profiles <br />for Monitoring Lines 3000 and 4000 to illustrate the close relationship between predicted <br />and actual subsidence. <br />Data from monitoring line 3000 shows a maximum subsidence of 3.6 feet and a draw <br />angle on-the order of 14° (limit at point 3017). <br />Data from monitoring line 4000 shows a maximum subsidence of 3.6 feet and a draw <br />angle on the order of 16° (limit at point 4024). <br />Conclusions: As shown in the attached figures and tables, measured subsidence data <br />reported in the first semi-annual subsidence report is within a few percent of predicted <br />values. On inspection, the larger than predicted draw angle, reported in your September <br />13, 1993 report to the Colorado DMG, is in error when you consider the stated accuracy <br />of the survey work (0.1 ft). The revised draw angle is on the order of 16°, assuming point <br />4024 to be the subsidence limit. <br />