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• These monuments consist of a 4"PVC pipe buried 3 - 4' in [he 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 rebar <br />inside the pipe design was used to minimize the potential for frost heave on the rebar. <br />Minimizing 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 underneath the Palisade Water Line, Ute Water Line, and Cottonwood, <br />Rapid, Jerry and Coal Creeks. In azeas where more stability is needed by structures, a block of coal <br />is lefr 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 1996 year. Due to the 70 - 75% extraction in much of the <br />RSS mining area, subsidence has occurred and is expected to occur in the future. Portions of the <br />second loop over the 10 & 11 West panels had been mined with a 70 -75% extraction ratio, part had <br />• been mined with a 50 - 55 % extraction rate and the remainder of the loop had been mined with an <br />extraction ratio of 35 - 45%. Subsidence was not evident on any of the route. No evidence of <br />subsidence was expected or found on the third RSS loop which had an extraction ratio of around <br />42%. The 34 - 49% extraction for the majority of the RSN has not shown and is not expected to <br />show subsidence affects over the currently developed area. The 70 - 80% extraction projected for <br />mined azeas this next year may show subsidence affects in the future but due to the steep terrain it <br />will be difficult to see. Observations made of subsided azeas have not indicated any destructive or <br />dangerous affects. The cracks found are no more dangerous than the normal hazazds of steep terrain <br />and cliffs already common to the azea. Also due to the high relief of the surface, areas lowered by <br />subsidence will not create depressions or other obvious surface affects. There has been no evidence <br />that the 50% maximum extraction under the creeks is not adequate. Limited extraction practices <br />under the creeks and pipelines will continue. <br />• Page 5 <br />