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STATE OF COLORADO <br />MINED LAND RECLAMATION DIVISION of DD~ <br />Department of Natural Resources ,~~: R~ <br />1313 Sherman St., Roam 215 ~! i <br />Denver, CO 80203 +'^- ~'J-~}+• <br />303 866-3567 're 76' <br />Fn x: 303 832-8706 <br />Ray Romer. <br />Governor <br />DATE: Apr i1 15, 1991 - _ Free R.seme. <br />DiviSian Director <br />T0: Dan Mathews //~~ ~ , <br />FROM: J im Pendl eton ~c^~ t~ <br />RE: Eastside Mine Subsi ce Monitoring Report - February, 1991 <br />(Permit No: C-84-063) <br />I have reviewed the March, 1991 Beni-annual subsidence monitoring report <br />submitted by the Eastside Coal Company, Inc. This report was prepared for the <br />operator by Epp 8 Associates, professional land surveyors. This report <br />appears to be factual and I recommend its acceptance. <br />Mining had not been conducted at the Eastside Mine for a period of 6 months <br />prior to the completion of the February, 1991 subsidence monument survey. <br />However, monument No. 1 has experienced some movement. As of August of 1990, <br />reported in the last subsidence monitoring report, monument No. 1 had <br />experienced 0.299' of vertical settlement. As of February, 1991 the monument <br />had settled a total of 0.260'. In other words, the monument has risen 0.039' <br />or approximately 1/2 inch. This is within tFre required accuracy of the survey <br />techniques employed. It may also be real, because cantilevering does occur in <br />similar situations. <br />Monument No. 2, which has only recently entered within the 25 degree <br />angle-of-draw boundary of the approaching undermining, has also exhibited some <br />erratic movement. This is consistent with earlier survey observations of this <br />monument and monument No. 8 at the Eastside Mine. Epp 8 Associates observed <br />in their August, 1990 subsidence report that these monuments are apparently <br />displaying the results of frost heave, rising in the winter and settling in <br />the spring. In December of 1990, in my memo to Bill Crick, I recommended that <br />Eastside Coal Company be required to replace these two monuments with more <br />stable installations. The monuments should be slip-collared and anchored <br />beneath the frost zone to control frost heave effects. I again recommend that <br />we require replacement of these two monuments in the attempt to obtain more <br />reliable future subsidence monitoring results. For purposes of control, both <br />the original and replacement monuments should be surveyed for the first two <br />surveys following the installation of the replacement monuments to correlate <br />their locations. <br />cc: Mike Savage <br />JP/jP <br />