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XXIII. Subsidence (2.05.6(6), 4.20) <br />The original permit application submitted by WECC for the Mt. Gunnison <br />No. 1 coal mine contained a one page narrative treatment (page 3-93) of <br />subsidence and a map exhibit 3.4.8.A indicating a proposed subsidence <br />monitoring program. The Division expressed major concern with this <br />inadequate response and requested that WECC prepare and submit a <br />subsidence evaluation which properly addressed the requirements of Rule <br />2.05.6(6). WECC prepared, submitted and subsequently revised a report <br />entitled "Subsidence Evaluation for Mt. Gunnison No. 1 Mine", prepared <br />by WECC's Mine Engineering Staff and included as exhibit 3.4.8.A within <br />the amended permit application. <br />As a portion of its November, 1984, "Application to Revise the Mining <br />and Reclamation Plan for the Mt. Gunnison No. 1 Mine", WECC submitted a <br />revised subsidence monitoring plan. WECC states in the application <br />that the requested 320 acre permit area expansion "...is, in part, to <br />accommodate a revision to the underground mining sequence necessitated <br />by geologic conditions encountered during mining which required that <br />the mains be relocated". Further, the requested area expansion will <br />allow the relocation of the required subsidence test panel. WECC <br />observes, and the Division concurs, "Relocating the 5-year permit <br />boundary westward will permit a 400 foot barrier pillar width <br />(adjoining the mains) and a subsidence test panel in excess of 500 <br />feet. The wider barrier pillar will reduce the possibility of <br />overriding loading on the life-of-mine mains being developed in the <br />area." <br />WECC originally proposed a basic subsidence control scenario <br />emphasizing data collection during the first five-year permit period. <br />The results of the first five year's collection will then be utilized <br />to finalize design of subsidence control specifics in later permit <br />periods. WECC acknowledges that subsidence will occur but proposes to <br />prevent damage to significant permit area features such as the Dry Fork <br />of Minnesota Creek, and Beaver and Minnesota Reservoirs, by utilizing a <br />limited extraction plan beneath these critical features. In addition, <br />extraction will be limited to development beneath the landslide body <br />delineated above the Somerset townsite. Exhibit 3.4.8.A, in its <br />amended form states "a detailed analysis of the slope stability, <br />incorporating the influence of subsidence on the stability of the <br />landslide, will be performed prior to pillar robbing beneath the <br />landslide. This analysis shall be submitted to MLRB for approval <br />before pillar recovery begins". (page 30, exhibit 3.4.8.A) <br />The subsidence evaluation prepared by WECC reflects the current <br />state-of-the-subsidence-prediction-art. It includes an analysis of <br />pillar strength in areas proposed for protection by limited extraction <br />without pillar recovery upon retreat. The originally approved WECC <br />plan also included the installation and monitoring of the subsidence <br />monitoring network over the first panel to be fully mined, during the <br />