2009-02-09_GENERAL DOCUMENTS - C1981022 (3)

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C-1981-022 RN-05 Findings February 2009 X. 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. 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 Oxbow Mining, LLC committed to monitor these features. To date, no impacts have been noted. The applicant conducted a subsidence monitoring program during the period the Sanborn Creek Mine has been active, in accordance with Rule 2.05.6(6)(c), designed to determine the commencement and magnitude of subsidence movements. The results of the monitoring program were submitted to the Division annually. 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. The operator, though, submitted a subsidence evaluation for the area, which can be found in Volume 12 of the permit, Exhibit 2.05-E8. In response to a stipulation on the federal coal lease, OMLLC conducted a reassessment of the hydrologic resources of the Elk Creek coal lease and an assessment of potential future monitoring needs for "high value" hydrologic resources. The report was produced in November 2003, and the BLM agreed to the findings of the hydrologic reassessment in January 2004. Also in January 2004, OMLLC further summarized the record of correspondence and field work for incorporation into the water replacement plan. These documents and pertinent maps were submitted to the Division under TR-45, which was subsequently approved in March 2004. XI. Operations on Alluvial Valley Floors 1. The Division has determined that an alluvial valley floor exists in an adjacent area. 29