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• SMO1 ~ <br />SM02 1,022,251.71N <br />1,021,954.58N 107,868.15E <br />105,246.28E 4868.81 <br />4898.44 <br />SM03 1,023,150.24N 101,689.75E 4970.17 <br />SM04 1,020,533.47N 103,268.01E 4985.44 <br />SMOS 1,018,495.90N 100,993.03E 5120.97 <br />These monuments consist of a 4"PVC pipe buried 3 - 4' in the ground with an 8' rebaz roof bolt <br />driven into the bottom of the hole until the top of the bolt is even with the top of the pipe. The rebaz <br />inside the pipe design was used to minirize the potential for frost heave on the rebaz. Monitoring <br />of subsidence monuments was done twice during this yeaz with the following results: <br />Monument 4/17/97 12/18/97 <br />SMO1 4868.75 4868.90 <br />SM02 4898.29 4898.47 <br />SM03 4960. ] 3 <br />SM04 4985.50 <br />SMOS 5121.00 <br />The minor variations in elevation are typical of surveying error using trig calculations. For the <br />second survey only monuments near past mining were monitored. <br />• ~VIinimizin~Subsidence <br />In order to minimize the possibility of subsidence in azeas where creeks, pipelines, or other <br />permanent structures overlay the mine the extraction ratio is lowered to less than 50 %. This has <br />specifically been the case undemeath the Palisade Water Line, Ute Water Line, and Cottonwood, <br />Rapid, Jerry and Coal Creeks. In areas where more stability is needed by structures, a block of coal <br />is left underneath the structure to further minimize the possibility of subsidence. <br />Conclusion <br />To comply with Stipulation 12 of the Mining and Reclamation Permit C - 81 - 041, spring and fall <br />inspections were conducted during the 1997 yeaz. Due to the 70 - 75% extraction in much of the <br />RSS mining azea mined prior to 1995, subsidence has occurred and is expected to occur in the future. <br />The 4 South Mains and 6th and 7th East panels were mined with an extraction ratio of 42 to 50% <br />and no subsidence is expected. The 34 - 49% extraction for the majority of the RSN mined in 1995 <br />and 1996, 1st West panel and 3 North Mains, has not shown and is not expected to show subsidence <br />affects. The 60 - 70% extraction for portions of 1997 and projected for mined areas this next yeaz <br />may show subsidence affects in the future but due to the steep terrain it will be difficult to see. <br />Observations made of subsided azeas have not indicated any destructive or dangerous affects. The <br />cracks found aze no more dangerous than the normal hazards of steep terrain and cliffs already <br />• common to the azea. Also due to the high relief of the surface, areas lowered by subsidence will not <br />Page 4 <br />