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. , <br />Seneca Coa] Company <br />MSHA I.D. OS-00304 <br />Highwal] Mining Addendum <br />March 15, 2004 <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 maybe ]eft <br />depending on roof conditions. Multiple passes in each opening may be 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 pillaz thickness will be <br />determined for each highwa]] mining pane] (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 20 <br />openings, depending on conditions and mining experience. In areas of the pit where an <br />upper or lower seam has been previously mined, this practice maybe adjusted in order <br />to columnized barrier pillars of adjacent seams. Minimum barrier pillaz width for the <br />active panel will be recorded in a book approved by the Secretary. Eaeh panel is <br />designed for the greatest mining height anticipated based on interpolation of the <br />geologic mode]. The design depth will be based on a weighted average as 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 pillaz charts <br />(Figures 34b-35b) and interpolating the seam height and cover depth, the total panel width <br />(bamer pillar center to center) is based on the following formula: <br />P„, = No(N'o) + (A'o - i)(K'w) +Wb <br />Where P„. =panel width, ft <br />No =the number of openings <br />Wo =opening width, ft <br />Ww =web pillar width, ft <br />Wb =barrier pillar width, ft <br />Ground Control Procedure <br />A. Planning <br />No known active or abandoned undergound workings are located in areas <br />identified for highwall mining. <br />2. In the unlikely event of contact with undergound workings, the mining plan will <br />be modified to prevent further intersection with old workings and the potential for <br />the release of impounded water and damage to existing surface structures. MSHA <br />. will be contacted in the event of contact with underground workings. <br />