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ENVIRONMENTAL ASSESSMENT <br /> Direct and Indirect Effects <br /> The direct effects are measured by the risk and extent of subsidence to occur in the locations and <br /> allowable mining methods for the proposed LBA and conceptual mine plan. The risk and extent of <br /> subsidence would depend upon many factors, including mine plans, coal seam thickness, geologic strata, <br /> and overburden depth. The overburden range for the Project Area is similar to the King Mine II area, <br /> ranging from 100 ft to 300 ft(GCCE 2006; NKC 1999).Assuming a coal seam thickness of 5 to 10 ft, surface <br /> lowering after retreat mining could be measurable and result in detectable surface subsidence impacts. <br /> Based on subsidence monitoring at the King I Mine, with similar overburden thickness, mining the same <br /> seam, surface subsidence features were rarely encountered.Those observed averaged 1-foot-wide/deep <br /> and 100 ft in length(Photo 3-1).The features were self-healing and not discernable after 2 calendar years. <br /> Accordingly, direct impacts associated with subsidence are expected to be minor and short to long term. <br /> As described in the 2017 EA(BLM and OSMRE 2017),the thick Cliff House sandstone provides a great deal <br /> of ground stability and generally prevents subsidence from reaching the surface after pillars are extracted <br /> during mining. Nonetheless, it is possible that subsidence could occur post mining.To determine potential <br /> impacts from subsidence, the OSMRE requires an inventory of structures, renewable resource lands and <br /> the characterization of a "worst possible consequence of subsidence." Based on review of publicly <br /> available site-specific imagery(Google Earth 2018),the observable man-made features include structural <br /> remains, stock fences, stock ponds, and a two-track road system within the Project Area. <br /> The two-track road system is the main infrastructure above the existing and proposed LBA, which could <br /> be damaged because of subsidence. If a surface subsidence crack were to intersect a road, it is possible <br /> that some repair of the road would be required to allow its continued use.These roads are used primarily <br /> by the UMU Tribe for access to rangelands, hunting, and firewood cutting. The structural remains are on <br /> an edge of the Project Area boundary and at the toe of steep slopes associated with Alkali Gulch. There <br /> are no mining panels beneath this part of the lease and therefore no impacts from subsidence would <br /> occur to the homestead structure. <br /> Dunn Ranch Area Coal Lease by Application COC-78825 and Mine Plan Modification EA 3-30 <br />