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literature include 1) 1.25 by J.T. Boyd Company (1976) and 2) 1.1 to 1.2 by Hillman Associates, Inc. (1980) in a <br />study on effects of subsidence from thick coal seam mining. <br />Based on the lithology of the near -seam roof strata in the mining area, MSE experience on western Colorado longwall <br />panels, observations of the gob on full -extraction room -and -pillar panels, and the longwall panels at the EC Mine <br />complex, it is estimated that the swell factor in the permit area will be no less than 1.2. MSE believes that this is a <br />conservative, lower bound estimate of the swell factor for the permit area. In solving the Sovine equation utilizing an <br />estimated swell factor of 1.2, the Zone 1 cave -fracture height equals 5m. <br />Ropski and Lama (1973) and Kenny (1969) recognized two (2) subzones within the Zone 1 cave -fracture area. The <br />subzones are referred to on Figure 61, Distribution of Subsidence Effects and Overburden, as the primary caving zone <br />(Zone 1L) and the secondary caving (Zone IU). The primary caving zone is the zone of maximum overburden <br />disruption. This zone consists of highly fractured rock broken into re -orientated blocks, which have piled up to fill the <br />extracted area. Ropski and Lama (1973) indicate that the primary caving zone occupies from 50 to 60 percent of Zone <br />1. This is consistent with observations at the EC Mine complex. It is also consistent with the MSE observations at <br />other western Colorado longwall panels. MSE observations indicate that within two (2) to three (3) seam heights of <br />the mining horizon, the caved roof has bulked up to the point where the overlying strata are displaced but remain <br />relatively intact with little or no re -orientation of the rock mass blocks. Large horizontal movement and the <br />development of a network of horizontal and vertical cracks characterize the secondary caving zone. However, the <br />strata maintain some of its original spatial arrangement. <br />It is projected that the only water -bearing units in the overburden that could be significantly impacted by the planned <br />subsidence of the No. 5 and No. 6 Mines would have to lie within a zone from 2m to 3m above the mining horizon. <br />This is based on a Zone 1 height of 5m and a primary caving zone of 50 to 60 percent of the Zone 1 height. <br />Where multiple -seam mining is contemplated, the two (2) coal seams would have to lie within approximately 60 feet <br />of one another for the subsidence effects of mining to be additive to the point where they could have any significant <br />impact on overburden aquifers. Where the two (2) mining horizons are within 60 feet, it is estimated that the Zone I <br />thickness would possibly approach 5m' (where m'= extracted seam height of both coal seams). <br />Predicted Angle of Draw <br />The predicted angle of draw for the No. 5 and No. 6 Mines is based on the results of monitoring performed by EC and <br />is defined as follows: The angle of inclination from the vertical of the line that connects the edge of the workings <br />(ribside) with the edge of the subsidence area. 1) overburden depth, 2) geology, and 3) surface topography influence <br />the angle of draw resulting from mining -induced subsidence. <br />Overburden Depth. Hall and Orchard (1963) indicate that the draw angle generally decreases as the depth of <br />overburden cover increases. However, no quantitative relationships have been developed to relate the decrease in <br />angle of draw with the increase of overburden depth. Overburden depth is not expected to have a significant effect on <br />the angle of draw in the permit area. <br />Geology. Geologic conditions have the greatest influence on the angle of draw. It is generally accepted that thick <br />sandstone beds above a coal seam result in low values for the angle of draw (Knothe, 1959; Wardel, 1959; Kapp, <br />1974; and Gentry, Stewart, and King, 1981). <br />The existence of the large percentage of competent sandstone beds in the overburden at the EC Mine complex will <br />reduce the magnitude of the draw angle. This is consistent with the results of subsidence monitoring performed at the <br />EC Mines. <br />Surface Topography. Results from the York Canyon study (Gentry, Stewart, and King, 1981) indicate that <br />topography can influence the angle of draw. Slopes facing away from the mined -out area tend to decrease the angle <br />Permit Revision 04-34 2.05-62 Revised 7/2/04 <br />