2022-09-29_PERMIT FILE - C1980007 (2)

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West Elk Mine . 2. Mine inflows in any given area aze dependent on the proximity of water-bearing sandstone units within the overburden to the mine zone and the extent of hydrologic connection with these units due to pre-existing or mining-induced fractures and faults. Both factors are difficult to predict or quantify. 3. Zones of weakness in the overburden (i.e., where more fracturing presumably exists) have been generally identified by photogrammetric methods. Flows into existing mines, such as the Bear Mine, appear to increase when these azeas are mined. This increased flow has been observed at West Elk Mine in areas of low cover neaz the Sylvester Gulch and Lone Pine Gulch fans. Although evidence indicates that zones of weakness do lead to increased flows, it is not feasible to quantify the magnitude of these flows. 4. Groundwater movement within fractures and faults is inconsistent because of the irregularity of the flow azea. Available analytical approaches require information about fracture and fault geometry which is not readily obtainable. In order to account for this, analytical solutions must be generalized and, therefore, may not apply. Given these limitations, several attempts have been made to estimate mine inflows using flow equations developed by Jacob and Lohman (1952) and McWhorter (1981). Use of these theoretical approaches in previous permit documents has resulted in estimates of greater than 40 gpm for average inflow, considerably higher than the observed average of between 5 and 25 gpm prior to encountering groundwater contained within the fault systems in the eastern portion of the mine in 1996 and 1997 (see Figure 23). Much of the error results from the use of predictive equations developed for conditions in which the assumptions of an isotropic, homogeneous and infinite aquifer are met. The various members of the Mesaverde Formation fail to meet the definition of an aquifer, let alone the conditions assumed for most of the predictive analytical models. Review of Figure 23 demonstrates that prior to 1996 the maximum average mine inflow observed over aone-year period was approximately 28 AF (17 gpm) in 1985. Because of fault water inflows, the one-year maximum average increased to approximately 200 gpm in 1996. This is based on measured inflows from the BEM Fault averaging 235 gpm over 291 days (181 gpm over 365 days) and an assumed average inflow of 12 gpm from the rest of the mine during the entire yeaz. The period of record represented by Figure 23 (1983 - 2003) includes only F Seam mining (1980s), the beginning of B Seam longwall mining in (July 1992) and mining after encountering the fault inflows (after 1996). Initial inflows during the B Seam longwall mining indicate no increase in inflows as a result of this mining method. However, an estimated peak inflow rate (short duration) of 50 gpm is reported in the 1994 AHR from a location at the north end of 4NW longwall panel (beneath Lone Pine Gulch) where overburden thickness had decreased to approximately 400 feet. The reported peak inflow was observed to diminish to less than 1 gpm within a few weeks after its first encounter, Since encountering the water-bearing fault zones in 1996, the average inflow to the mine has increased. As anticipated, the inflows emanating from the fault zones have diminished since its peak in 1997 (709 AF or 440 gpm) as reflected in Figure 23. The average inflow rate observed during 2003 was 161 AF (99.8 gpm). 2.05-256 Revtsed June 2005 PRIO; Rev. March 2006; Rev. May 2006 PRI G