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BOWIE NO. 2 MINE — SUMMARY OF RECENT GEOTECHNICAL ANALYSES <br />FOR PERMITTING OF COAL MINE WASTE DISPOSAL AREAS <br />STABILITY ANALYSES <br />Page 5of10 <br />Buckhorn Geotech has prepared a series of geotechnical reports addressing the various disposal <br />areas for coal mine waste at the Bowie No. 2 Mine. The initial reports prepared in 2006 and <br />2007 for TR -42, TR -44 and TR -45, were the most comprehensive in nature. For TR -56 (2008) <br />and TR -64 (2009), the complexity of the analyses was reduced somewhat based on the <br />dissipation of pore pressures that had been observed with the initial series of Vibrating Wire <br />Piezometers (VWPs). The newest series of stability analyses, beginning with TR -75 in 2012, are <br />noticeably simpler in nature, evaluating fewer variables and assuming that no phreatic surface <br />is present. <br />A brief summary of the pertinent revisions and related Buckhorn Geotech stability analyses for <br />the mine's Coal Mine Waste Disposal Area Nos. 2, 4, and 3 is provided here. <br />Gob Pile #2 <br />• TR -42 (WD) - Steepen Upper Slopes from 5h:1v to 4h:1v <br />Buckhorn Feb -2006 (this report is referenced by many later Buckhorn studies) <br />Total Stress (Undrained) and Effective Stress (Drained) analyses were conducted <br />• TR -56 — Steepen Upper Slopes from 5h:1v to 3h:1v <br />Buckhorn Sep -2008 <br />Pore pressures observed to be dissipating, therefore Undrained analysis not appropriate <br />(pp. 6 & 10) <br />Evaluated 2 phreatic surfaces: one as indicated by pore pressure readings from <br />piezometers, and the second at a conservative, higher level <br />• TR -76 — Connect Gob Piles #2 & #4, increase pile heights <br />Buckhorn Nov -2012 <br />No phreatic surface modeled, since "ultimate pile stability assumes dewatering which is <br />reasonable given the decreasing pore pressures... over the past 3 years" <br />• TR -81 — Revise bench spacing, steepen one section (between #2 and #4) from 3h:1v to <br />2.5h:1v <br />Buckhorn Jul -2013 <br />See comment from TR -76, above, re: phreatic surface (none modeled) <br />Recommendations regarding keying -in the piles as they are joined <br />• TR -85 (Currently in Review) — Temporary Drying Area on top of valley fill portion <br />Buckhorn Sep -2013 & Dec -2013 <br />Gob Pile #4 <br />• TR -44 — 2h:1V excavation slopes; outer slope 2.5h:1v first 50'; 15' bench; 3h:1v; pile height <br />118' <br />Buckhorn Feb -2007 <br />Total Stress (Undrained) and Effective Stress (Drained) analyses <br />• TR -64— Increase pile height from 118' to 150'; assumed excavation slope 1.3h:1v <br />Buckhorn May -2009 <br />