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Seneca Coal Company <br />MSHA I.D. OS-00304 <br />Highwall Mining Addendum <br />March 15, 2004 <br />mining will only be attempted after design parameters have been verified by practical <br />mining experience. <br />C. The height of the openings will vary with the seam height. At this time, it is <br />anticipated that the entire seam height will be taken, although roof coal may be left <br />depending on roof conditions. Multiple passes in each opening maybe taken in order <br />to extract the entire seam height. <br />D. Web pillar thickness will vary in each seam as cover depth and mining height vary <br />from location to location (see Figures 34a and 35a). Web pillar thickness will be <br />determined for each highwall mining panel (5-20 openings) as mining proceeds, with <br />the minimum web pillar width for the active panel recorded in a book approved by the <br />Secretary. In addition, a mine map will be maintained at the site showing depth of cut, <br />hole spacing, and projection of cuts. <br />E. Likewise, barrier pillar thickness will vary in each seam as cover depth and mining <br />height vary (see Figures 34b through 35b). Barrier pillars will be left after a maximum <br />of 20 openings, depending on conditions and mmmg experience. In areas of the pit <br />w erg e an upper or lower seam has been previously mined, this practice maybe <br />adjusted in order to columnized barrier pillars of adjacent seams. Minimum barrier <br />pillar width for the active panel will be recorded in a book approved by the Secretary. <br />Each panel is designed for the greatest mining height anticipated based on interpolation <br />• of the geologic model. The design depth will be based on a weighted average as <br />follows: <br />Design depth = 0.75 (maximum depth) + 0.25 (minimum depth) <br />Referring to the web pillar design charts (Figures 34a-35a) and the barrier pillar charts <br />(Figures 34b-35b) and interpolating the seam height and cover depth, the total panel width <br />(barrier pillar center to center) is based on the following formula: <br /> <br />Where P„, =pane[ width, ft <br />No =the number of openings <br />Wo =opening width, ft <br />W„, =web pillar widtk, ft <br />Wb =barrier pillar width, ft <br />Ground Control Procedure <br />A. Planning <br />1. No known active or abandoned underground workings are located in areas <br />identified for highwall mining. <br />2. In the unlikely event of contact with underground workings, the mining plan will <br />be modified to prevent further intersection with old workings and the potential for <br />