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© MONTGOMERY WATSON Minitq 6rou~ ~1 • 1\lac, ?000 1\Ir. Tom rnderson Oxbow Dlining, Inc. P.O. Box 535 Somerset, CO 81434 Re: Slope Stability rlrtalysis for Elk Creek Mine Brnch Fills and Sot] Stockpile Dear bit. Anderson: Montgomery Watson is pleued to present this lettu report containing our slope stability analysis completed for the proposed portal bench fills and soil stockpile foc the Elk Creek Mine. This ' report has bern prepazed in response to questions rased by the Colondo Division of btinuals & ~ Geology in their lettu dated Much 17, 2000. Using appropriate material sttengrh properties and a range of phratic surfaces, stability analyses wen completed Eor the proposed brnth fills. A sensitit~ty analysis using a Hoge of usumed phreatic surface devotions was puformed in ordu to deteanine whether and how variations in the phrntic surface would affect snbility. Appropriate ~ remedial design measures are suggested based on this sensitivity analysis. Using appropriate ~ material strength properties a stability analysis wu pufomted for the pond D embankmrnt. A consen•ative phreatic surface was projected for the pond D ernbankmrnt using accepted analysis • ~ techniques. A stability analysis Eor the topsoil stockpile ~u performed using appropriate material strength properties Eor the topsoil and the subgnde soils. General As pan of the planned mine devdopment Eor the Elk Creek Mine, fill will be placed to allow construction of the usodated mine faalities as shown in Figure I. A detailed plan view of the proposed faalities is also shown on the Grnenl Faalitin Map (Map 205-M1), of the Oxbow Mining, Inc., Mining and Reclamation Plan document The maximum slope angle for the proposed fills dill be 2H:1V. Approtdmately 150,000 cubic yuds of fill material required for construction of the portal brnrh and road will be obtained from an upslope borrow source on the west side of the Elk Creek valley. The upslope borrow source u a shallow surfiaal slide that toes out on the casting unimproved road Homing up the Elk Creek valley. Borrow phns for the portal bench focus on removal of material from the uppu and crntnl portions of the slide and placement of this material at the toe of the slide as compacted fills. The fills will consist of a mixture of soi4 unconsolidated alluvial/colluvial materials Ezom the Mesa Verde Formation. In addition, soil materials recovered from new disturbwce azeas will be hatiled to the designated soil stockpile u shown in Figure 1. The soil stockpile wiD be located away from active operations to the extrnt possible and is located and configured to minerni>e the potrnfial for loss, erosion, or i contamination of the soil resotuce Detailed descriptions of materials and methods of placement aze presrnted in Sections 2.04.6, 204.9, and 2.05.3 of the Ozbow Mining, Inc. (OMn, Mining and i Acclamation Plan documrnt ifis souN union fiwd. rei: 3a3 2s3 suo Surta al0 Fsa: 3037fi38003 Serv:np the World'a En vrronmenra~ Needs Lakewood. Colorado 80228 O.~~ba. Scb'd'~ 4rrn llw/Yl.dr