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iii iiiiuiiniiiiii 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Deparrmenl of Natural Resources 1313 Sherman 57., Room 215 Denver, Colorado 80203 Phone: U03) 866-3567 FA%: (3031 8 32-81 06 DATE: November 12, 1998 TO: Bill Carter FROM: Jim Pendleton RE: Sanborn.tireek~ - TR No. 32 - Geotechnical Completeness it No: C-81-022) ~I ~~~ 1 DEPARTMENT OF NATURAL RESOURCES Roy Romer Governor lames 5. Lochhead Eaecurive Dveclor Michael B. Long Division Direao~ I have completed a brief review of the TR No. 32 application for the construction of the Elk Creek Mine portals and support facilities. The principle geotechnical concerns appear to concern [he stability of the cut slope above the proposed portal fill bench, the structural stability of the proposed portal bench down-gradient face, and predictions of subsidence. Two of these topics, the stability of the cut slope above the portal facilities and subsidence prediction, are the subjects of report appendices prepared by .lohn F. Abel, jr, P.E., acting as a consultant for Oxbow Mining, Inc (OMI). I have briefly scanned both of these reports. Without reviewing the specifics of Dr. Abel's analyses, each appears to be an appropriately comprehensive treatment of their respective topics. The remaining topic, the down gradient facial structural stability of the D-seam portal bench fill is not addressed within the teclmical revision application. For two preliminary reasons I am concerned that [his topic will be of specific geotechnical concern.: First, the majority of the proposed fill will be borrowed from the existing landslide above the bench. This material has been demonstrated to be of low shear strength attd susceptible to displacement. Secondly, the bench will be constnlcted within the existing chamrel of Elk Creek, displacing the channel against the east valley wall. The creek's immediate superposed proximity to the till may result in relatively high saturation, unless unusual precautions are exercised. Because of the lack of any discussion of the portal bench's structural stability, it is my recommendation that OMI~s TR No. 32 application be found incomplete. Once a discussion of construction techniques and an appropriate structural analysis have been developed. the application can be rendered geoteclmically complete ce: Dan Hernandez due A1:\COAL\JAP\EIkCComp.WPD 1PhP