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~~ <br />n <br />U <br />Snbsidenre <br />With respect to the potential for subsidence and subsequent impacts to the <br />surface should subsidence occur, this subject is dealt with in a very cursory <br />Fashion in the application. More specifically, [he application staCes that no <br />subsidence is evident over [he existi.nR Blue Ribbon Mine (although no <br />subsidence monitoring, other than visual observation has been in place) and <br />given Che extent and type of cover over the E-Seam (approximately 280 fee[ of <br />a competent, resistant shaly sandstone), less [h an 2 inches of subsidence (if <br />any) can he expected. Based on further questioning by OS M, Sunflower Energy <br />Corporation (SEC) has now estimated (apps rently not based on engineeri np, <br />calculations) that. subsidence if it occurred would he approximately half the <br />thickness of the coal to he mined (i.e., 3 Eeet of subsidence). The applicant <br />also notes that no folding or faulting, which may cause and/or excerba[e <br />subsidence, has been identified in air photos of the area. As further <br />confirmation, the applicant notes that no faults have been encountered in the <br />existing Rlue Rihhon Mine. However, OShf notes that faulting and iointing are <br />noted as being prevent in Che area in USGS Professional Paper 969 (C. Richard <br />Dunrud, "Some Engineerin.R Geological Factors Controlling Coal Mine Subsidence <br />in Utah and Colorado," 1976). <br />SEC has proposed subsidence monitoring and has specified monitoring locations; <br />however, a detailed subsidence monitoring plan has not been included in the <br />p l.nn. No subsidence monitoring presently is carried out over U.S. Steel <br />Cor pora[ion's Somerset Mine. <br />With respect co the presence of structures or renewable resources over the <br />areas to be underground mined in Section 35, the applicant has stated that no <br />structures pr e.sently exist and that [he only feature nv er the mine which might <br />qualify a~: a renewable resource is an, ephemeral drainage (see Hydrology <br />portion of this TA). The surface is generally overlain by undeveloped <br />rangeland and wildlife and recreation lands. A survey will he conducted by <br />OS`1 for the presence of cultural resources (see Cultural Resources section of <br />[his TA). However, as interpreted by OSM, renewable resources lands in terms <br />of water resources include si gni f.ic ant springs, perennial streams, and <br />aquifers tht supply springs and wells. Therefore, an ephemera] stre3rn like <br />that over the proposed mine area (see Hydrology portion of this TA for further <br />description of this drainage) is generally no[ considered a renewable resource <br />land and therefore does not have to he ev alua[ed concerning worst-case <br />subsidence and possible material damage to that resource. Howr_ver, Riven the <br />uxtent of. undergro and mining existing, and proposed in the No r.[h Fork Valley, <br />Uie potentials for subsidence (e..g., USCS Professional Paper 969), and since <br />the stream is in [he National Forest, OSM believes it is important to evaluate <br />the effects on water resources (including ephemeral screams). <br />1 <br />