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:: ~ :., <br />DIVISION OF MINERALS AND GEOLOGY <br />Department o(Namral Resources <br />1313 Sherman 51., Room 215 <br />Denver, CO 80207 <br />Phone: (303) 866-3567 <br />FAX: (3031 832-8106 <br />DATE: November 23, 1993 <br />TO: Christine Johnston <br />FROM: Jim <br />III IIIIIIIIIIIII III <br />999 <br />STATE OF COLORADO <br />',..~~_ <br />RE: West Elk `Mime; adequacy Response, T.R. 66 <br />(Permit No: C-80-00'n <br />of ep~o <br />,.4',- A <br />~.; O <br />~~8'!6 ~• <br />koy Romer <br />Governor <br />Michael 8. Lang <br />Division Director <br />I have reviewed the responses to our T.R. 66 adequacy comments <br />submitted by Mountain Coal Company. I offer the following <br />suggestions for your consideration. <br />piezometer <br />Mountain Coal Company agrees to the installation of the stability <br />monuments but objects to the installation of the requested <br />piezometer. They express concern that the piezometer may allow the <br />communication of fluid pressure. A properly installed piezometer, <br />like a monitoring well, should be isolated to contact only the zone <br />of interest. In this case the piezometer should be installed <br />perhaps five feet outside the "not an underdrain" gravel french <br />drain. The purpose is to determine whether the refuse is saturated <br />above the elevation of the french drain, which the french drain is <br />intended to prevent. The piezometer should be .cased with plastic <br />pipe, perforated for the lowermost five feet, and then the annulus <br />gravel packed through the perforated interval. The remainder of <br />the annulus should be sealed with bentonite to prevent the <br />communication of fluids. <br />The quarterly surveyed stability monuments will allow the <br />documentation of settlement, after the fact. The piezometer, on <br />the other hand, should facilitate the early detection of a <br />potential problem. Hopefully, remedial steps could be taken to <br />increase drainage and prevent an actual structural failure. In <br />order to properly monitor the phreatic condition in the embankment, <br />the piezometer should initially be monitored frequently, perhaps <br />