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C-1981-019 TR-81 PAR - mlt 16 Feb 2009 Page 2 of 7 • Map 20B, Section B-B' - The extent and steepness of the permanent valley (West) fill (Station 0+00 to 20+), are dramatically different that what was previously proposed and approved. • Map 20B, Section C-C' - The extent and steepness of the permanent valley (East) fill have changed only slightly with TR-81, as has the PMT. However, the PMT (proposed and previously approved) is more than 200' lower in elevation than the pre-mining topo was. • Map 20B, Section D-D' - The PMT from Station 40+00 to 82+00 is substantially higher than what existed pre-mining (no change proposed with TR-81). This configuration (increasing the backfill elevation above the mined-out area) seems preferable to increasing the size of valley fills. • Map 20B, Section E-E' - The PMT across the pit is up to 200' lower than the pre-mining topo. No changes are proposed with TR-81. A detailed summary of all the issues associated with South Taylor may be premature, until the AOC issue is resolved. What follows is a list of my adequacy comments, to be passed along to Colowyo. Exhibit 21 Item 1 - Shannon & Wilson Geotechnical Stud - South Taylor Excess Spoil Fills Background The original Geotechnical Study (Study) by Shannon & Wilson (S&W) was dated July 7, 2006 and addressed two permanent valley fills (West and East) and two temporary fills (one on top of the East fill and a stand-alone fill to the east). In addition to the text and a list of works referenced, the July 2006 study included Figures numbered I through 9 and Appendices A, B and C. Two borings were drilled. The Study noted the existence of possible landslide features and possible subsidence from burning coal seams. It was concluded that the proposed fills would act to buttress these features (which were not located near the toes of fill) and that the landslide features would not affect the stability of the proposed fills. The Study made the following recommendations: • Outslopes of 3.8H:1 V for East and West permanent valley fills • Maximum slope for the West fill - 3H:1 V • Maximum slope for the East fill - 4H:1 V • Benches not required for stability, but may be desirable to control runoff • A system of Main and Lateral drains for natural drainages and springs/seeps was designed • Benching of the ground surface; keyways; and rock toe buttresses not required • Lift thicknesses of 50' to 100' should be used in constructing the fills • Installation of groundwater monitoring well(s) to monitor water in fill over time