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iii iiiiiiiiniiiiii <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman SI.. Room 215 <br />Denver, CO 80203 <br />Phone: 13031 865-356 7 <br />FAX:1303)832-8106 <br />DATE: October 18, 1993 <br />TO: Christine Johnston <br />FROM: Jim Pendleton <br />RE: West Elk <br />OF ~O/0 <br />F~ <br />.,~ g . <br />a-/ <br />lB t6 ~ <br />Roy Romer <br />Governor <br />Michael B. LOng <br />Division Dneclor <br />~1 f~~ <br />Investigation, T.R. No. 65 <br />No: C-80-00'n <br />As you requested, I reviewed Mountain Coal Company's (MCC) <br />supplemental response to our adequacy concerns regarding their <br />"Subsurface Investigation". I apologize for the time required to <br />provide a response. <br />MCC indicated that the originally analyzed Pond MM-2R's HPDE liner, <br />which may have had stability problems when dry, particularly during <br />periods of elevated water table, is to be replaced with a <br />"geotextile clay liner". I assume MCC is referring to a geotextile <br />fabric installed over a compacted clay liner. This liner system <br />can also experience stability concerns in steep pond slope <br />installations. The original stability analysis should be amended <br />to properly reflect the current proposal. <br />MCC also indicated, in response to our concern regarding monitoring <br />the phreatic surface in the vicinity of Pond MB-2R, that the <br />concern voiced by their own consultant was merely a "standard <br />disclaimer utilized by many engineering firms". While I concur <br />that this concern is fairly commonplace in facility designs of this <br />sort, I would allow as it is commonly appropriate. MCC proposes to <br />use the monitoring wells installed at their Phase III coal storage <br />location. If these wells are to be accepted, we will need <br />sufficient seasonal phreatic surface information to determine what <br />elevation of the water table at the monitoring wells represents a <br />water level stand at the liner elevation in the immediate vicinity <br />of Pond MB-2R. I believe it will entail considerably less effort <br />and expense for MCC to install appropriate monitoring wells <br />immediately adjacent to the pond. <br />cc: David Berry <br />