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March 21, 2014 Page 33 <br />rock type, making up 29% of the bounding strata in the HW -03 holes, 22% in the WP -05 -07 <br />hole, and 31% in the ST holes. The mudstone RQDs generally vary from 30 to 70. Siltstone and <br />interbedded siltstone, mudstone and sandstone make up the majority of the balance of the <br />bounding strata. Siltstone and interbeds containing siltstone are fairly intact, with RQDs <br />generally in the 60s. Although not abundant, the carbonaceous mudstone /shale can occur in the <br />immediate roof of the target seams. It has been the experience at Colowyo that weak mudstones <br />will fall if exposed in the roof, and top coal (about 4 inches) is typically left during highwall <br />miner operations. It is anticipated that this practice will be continued where the immediate roof <br />is not sandstone or siltstone. <br />The target seams are generally intact, with RQDs commonly above 60. The D2 Seam in <br />the East Pit holes was more heavily cleated than the other target seams, with an average RQD of <br />37 (NSA 2003). <br />2.3 Physical Property Test Results <br />Over the course of previous highwall mining studies, a physical property database has <br />been compiled for the F, E, D2, and C seams (Table 3). In addition, tests of the G78 Seam and <br />bounding strata from holes GT- 01 -02, -03, -05, -06, -08, and -09 were summarized by AAI for a <br />longwall feasibility study (AAI 2003), as shown in Table 4. Shannon and Wilson (2008) <br />presented test data for South Taylor holes from 2006 and 2007 drilling programs, as summarized <br />in Table 5. The abbreviations and strata location classifications given in the tables are defined as <br />follows: <br />Upper Roof 5 -10 ft above the top of the coal seam <br />Immediate Roof 0 -5 ft above the top of the coal seam <br />Immediate Floor 0 -10 ft below the base of the coal seam <br />6c Uniaxial compressive strength <br />E Young's modulus <br />6t Tensile strength <br />S Slake durability (second cycle %) <br />Based on a review of the three physical property data sources, it appears that: <br />1) The G78 bounding strata are of similar strength to the bounding strata of the F, E, D2, <br />and C seams. <br />2) The G78 coal has a lower compressive strength than the F, E, and C seams, and is <br />somewhat stronger than the D2 Seam. <br />3) The seams and bounding strata of the South Taylor area are of similar strength to those of <br />the East and West pits. <br />The slake durability test results shown in Tables 3 and 5 provide additional information <br />on the competence and resistance to weathering of the immediate roof and floor. Table 6 <br />provides the slake durability classification as proposed by Franklin and Chandra (1971). <br />Agapito Associates, Inc. <br />