Laserfiche WebLink
OCT-16-98 09:O6AM FROMFMcCULLEY~KiGILMAN 3034471636 . T-233 P.02/04 F-492 <br />CASH MINE !GOLD HILL MILL <br />GOLD H1LL, COLORwDO <br />TAILINGS IMPOl1NAMENT ExPwNSION <br />AM£NDMfNT TO TECHNICAL REVISION <br />DwTEA 10/09/98 <br />The Technical Revision (TR) submitted w the Colorado Dtvtston of Minerals and Geology (DMG) <br />on October 9, 1998 presented, in part, a proposal to install a layzr of ballast material on the remaining <br />exposed tailing, in the original tailmgs impoundment at the Gold Aill Mill site. The effects of t}ns ballast <br />material will be to preconsohdate those [silmgs, prior to placement of the liner system for the expanded <br />tmpotmdmrnt factltry, and to enhance the stability of the embankment raise constructed partly on the <br />a~jaccnt portion of the originally tmpotmded tailmgs. The proposal presented m that TR was based on die <br />outcome of field dtscussrons and follow-up telephone conversations between representatives of the DMG <br />and the operator's consultant, as well as the DMG inspection repon of October 7, 1998. <br />Subsequent to preparaAon and submittal of that TR, additional data has barn obtained rcgazdmg the <br />depths of tailings at various locanons along she approximate ccnterltne of the remaining exposed pomon of <br />the original tailings tmpoundmrnt The tailings depths range from less than one foot to a tnaxtmum of <br />appzoximately 4 51'eet. A plot of the approximate locanons of the soundings and the corresponding Depths <br />oftatlmgs is attached. There is a significant area m the cenval portion of the exposed tailings cmpoundment <br />where she depth of tailings is approrumately one foot or less. "f his area of shallow depths is consistent with <br />the alignment of an tutderlyutg bedrock ridge that was encountered dtuing excavation of the western pomon <br />of the expanded impoundment and the mtermedtate berm. Another area at the nonh rnd of tlu impoundment <br />reflects a shallowtng of the tailings towards the la[eral boundary of the origmal basm_ The data regarding <br />depths of the exposed tailmgs is consts[ent with the dcp[h nrnd identified dtutng earlier limited sotmdmgs <br />along the upstream toe of the new cmbartlartent raise- The data from these soundings are also shown on the <br />attached plot. <br />In light of the newly obtained data, tt is suggested that it would be neither necessary nor appropnzte <br />to universally apply the consoltdatton and stahtltry enhancing measures proposed in the TR over the hill area <br />of thz exposed tailings. The block failure analysis conducted in support ol'the TR, and desenbed therein, <br />conservatively evaluated conditions for the maxtmtuncross-section through the impoundment. Similarly, <br />the esttmare of possible consolidation and surface senlemcnt in the retnamtng area of exposed tailmgs was <br />based on [he mazimiun cross-section with tailings deptlts under the embankmrnt raise taken to be as much <br />as ten feet. The new data indicatts that these analysts were overly conservative. <br />Accordingly, it is propuscd that the tailings consoltdatton and stability enhancing ac[ions described <br />to the '1'R be refined as follows: <br />Remove stuficial organic materials from the tntlittgs (now completed). <br />t wet~7x-~v.+ErtD.wpp 1 O~~tober 1 G. 1918 <br />