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,- ,. Memo RECEIVED To: J;m Stover MAR 0 5 200 From: Corm Stewart arx! Greg Hunt Darr. 3r5.~04 avisxxt of M:rtertis 8 Gsdpgy Ro: Rock Fall Design Parameter Seloctiort In this memo2ndum I wAl attempt to address two issues of concern relative to the ongany review o1 our application before t1w Division of Minarets and Gedogy for the construction of rock fall berms al the Bowie Resources. LLC. Mine No 2. These issues are. 1 Small area of influence potontiapy impacted by mining subsidence 2. Oesign parameter of a SR rode cube br the proposed rock tail bens. Issue t. Small Area of Influence D< Mining Subsldena3 There is a small area of the channel sandstone outcrop that Is ~~`~ / ~,, potentlalty impaled by mining subsidence hem the WD1 bngwaA I panel. The majority of the channel sandstone outcrop lies outside 'f a.. the zone of pdenbal impacts of mining subsidence based on the 25 '~' - o.°.~n.p ~ degree angle of draw. It should be rated that in the specific C geometry at the comer of a bngwaH panel, espeaally for iha first ~, -~ panel in a new mining drSUil, it is common lathe angle of draw to ,+ ~ be less than that observed at other nfs ~ pa akxtg the edges of the p ~ ~ r-•no••° longwall panel. 1 Vr Issue 2. Rook Size Design Parameter for Rock Fall Berm Bowlo Resources. LLC has condoled numerous excavations with in the slump area during the past two years These excavatons have vaned in size and have inducted: • Access roads to dnp pads • Grill pads • The &seam portal area box cut The detorminebon of the Sft cube size for the rode felt dosgn basis was based on observations during these oxcavatlons as wep as observations both along the outaop and areas down slope 6om Ute dtannel sand outcrop. Construction of access roads and doll pads indx~ted a maximum block size dlmensbn of less than 3 legit