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iii iiiiiiiiiiiu iii <br />NORTHWEST PIPELINE CORPORATION <br />.~ <br />GgLi LAKE f~'~ nw B<I lq 15}6 <br />PCB '~PI e9f%I <br />June 21, 1983 <br />J <br />ll EiY9~•~~ L If~P~ <br />' ul ~ ~ ,> ~,qa3 <br />Mr.~Dave Shelton <br />Colorado Mined Land Reclamation Division <br />1313 Sherman St., Room 423 <br />Denver, CO 80203 <br />Attn: Dan Mathews <br />Dear Mr. Mathews: <br />fv11NED LAN() F;~ULAf~1A`I ION <br />Colo. Dept. of Natural Resources <br />Enclosed please- find a complete history of data of Western Slope Carbon's <br />(WSC) subsidence monitoring program to date. Per permit stipulation <br />No. 20, we shall perform these surveys until cessation is approved in <br />writing from your office. This letter is to request the cessation of por- <br />tions of this survey where we feel adequate data has been obtained <br />and to reschedule the frequency of the survey on the remaining portions, <br />in order to collect meaningful long-term data during the period our <br />mine is under temporary cessation status. I ~ <br />t <br />As can be seen on the majority of monitoring point.., observed subsidence <br />is essentially nothing to date. This conclusion is` based on discussions <br />with the survey company and their opinion that ;he variances observed <br />are within the expected instrument and atmosphe is variances for this <br />type of survey. This is substantiated in that the differences don't <br />trend either plus of minus, but randomly vary to Loth sides. <br />WSC proposes to continue monitoring on a yearly basis points A, G, <br />1, and N from the East Base location, point A from LJMp2 gun station, <br />and discontinue, for now, monitoring on the remainder of the points. <br />These points were selected because they have shown the greatest varia- <br />tions to date and exemplify a diversity of type points grading from <br />being located over a very mined out area to an unmined area. <br />We hope you find this proposal acceptable. All our points are secured <br />from incidental damage so in the future if it appears desirable to do <br />another check of all points, we would be in the position to do this. <br />If you should have any questions, please call. <br />Sincerely, <br />NORTHWEST P EELIN= CORPORATION <br />lack Cushing <br />Environmental Affairs <br />enc: Subsidence Survey ending with Nov. 5, 1982 check <br />A,SUBSIDIARY OF NORTEIWEST ENERGY COMPANY <br />I ]nS feiPr lq WAY SgilinxF fi rv, UleN 9a~Ofl <br />