2024-03-12_REVISION - C1981022 (18)

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A. The Division has not approved surface mining at the Elk Creek Mine, therefore this section does not apply [4.19(1) and 4.22.4(1)]. XV. Subsidence Control The permit area includes three different mines which have been active through the term of the permit to date: the Somerset Mine, the Sanborn Creek Mine, and the Elk Creek Mine. These underlie different areas and, therefore, have had separate requirements for subsidence monitoring and control. A. The applicant used a subsidence control plan in accordance with Rule 2.05.6(6) and committed to adopt all measures in order to reduce the likelihood of subsidence and prevent material damage to Hubbard Creek, which was undermined by the Somerset Mine. The Division approved the plan [4.20.1(2) and 4.20.3(1)]. There were no structures within the area affected by the Sanborn Creek Tract subsidence. However, there are several landslide features above the proposed underground workings and OMLLC committed to monitor these features. To date, no impacts have been noted. B. The applicant conducted a subsidence monitoring program during the period the Sanborn Creek Mine was active, in accordance with Rule 2.05.6(6)(c), designed to determine the commencement and magnitude of subsidence movements. The monitoring program was designed to extend for a time, beyond cessation of mining in any area, consistent with the need for verification of the subsidence prediction. For the Elk Creek Mine, the applicant conducted an inventory of"all structures and renewable resource lands which exist within the proposed permit and adjacent area" as required by Rule 2.05.6(6)(a). The determination was that no such structures or features exist within the area to be undermined by the Elk Creek activity. Therefore, no further action was required. However, the operator submitted a subsidence evaluation for the area, which can be found in Exhibit 2.05- E8 (Vol. 12) of the PAP. Visual subsidence surveys are to be conducted in June and October, and the results submitted to the Division in a written report. XVI. Concurrent Surface and Underground Mining A. There is no approved concurrent surface and underground mining at the Elk Creek Mine, therefore this section does not apply (4.22.2). XVII. Operations on Alluvial Valley Floors A. The Division has determined that an alluvial valley floor exists in an adjacent area. Therefore, the following findings are in order for the alluvial valley floor that is located on the North Fork of the Gunnison River downstream from the mine site. 1. The Division finds that activities proposed by the applicant will not interrupt, 33