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a~~N ~ ~ III IIIIIIIIIIIIIIII <br />~~~,~ <br />INC. <br />A Sutssidmn' <br />yl...,,. <br />Wevem FueLr <br />AtWnalKm. Int. 7 l ~ ~ d <br />July 5, 1989 JUL 101989 <br />Mr. Tom D. Gillis MINED LAID <br />Colorado Mined Land Reclamation Division RECLAMATIpN J1y;5tOnl <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203-2273 <br />Re: Survey Accuracy for Subsidence Monitoring <br />Dear Mr. Gillis: <br />The approved subsidence monitoring plan for the Western Fuels-Utah, <br />Inc. Deserado Mine states that WFU will complete a Second Order <br />Class II Survey of the 22 Ground Control Points. It is my <br />professional opinion that this language was inserted without <br />benefit of input by the Mines Land Surveyor at the time. My <br />reasoning for this conclusion is as follows: <br />The original horizontal control net for the Mine was <br />established from two 3rd order triangulation stations, <br />therefore, on a national level, 3rd order accuracy is the <br />highest that could be attained on this site. The original <br />vertical control was established from a V.A.B.M. (Vertical <br />Angle Bench Mark) with 3rd order accuracy. Therefore, 3rd <br />order accuracy on a National level for elevation is the <br />highest that could be attained on site. <br />The subsidence monitoring that has been completed to date has <br />been performed using procedures which can be expected to yield <br />accuracies of +/-0.10 foot both horizontally and vertically <br />vn '3' bite: Scidtl?%~ bafi1:£.' _Tr .S .Rty Op 1P_1Cn tlldt these <br />accuracies are sufficient for the purposes of the monitoring <br />plan. <br />I hope that this letter answers any questions you may have had <br />regarding this matter. If you require any further information, <br />please contact me at your convenience. <br />~S,incerely, <br />~~~ <br />David G. Anderson, P.L.S. <br />Colo. Reg. #20668 <br />Chief Surveyor/western Fuels-Utah, Inc. <br />Deserado Mine <br />P.0. Box 1067 <br />Rangely Colorado 81648 <br />Telephone 303/675-&131 <br />Telempier 303/675-5229 <br />