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JUN 19 '96 02~25PM DIViP1INERRLS&GEOLOGY <br />P. 2/3 <br />STATE OF COLaRAD~ <br />DIVISION OF MINERALS AND GEOLOGY <br />Department d Natural Resour[es <br />1311 Sherman 51., ROOM 115 <br />Denver, Cnbrado 80103 <br />Phone: (3031888-3567 <br />EAX:.t303) 8]2-8706 <br />DATE: June 19, 1996 <br />TO: Larry Routten <br />-~~ \~~~- <br />FROM; Jim Pendleton <br />RS: Deseradq Mine <br />~POnd -4 <br />Remedial Plan <br />Rov Roma <br />Gor~mr <br />1+"4+ S. Lochhead <br />Ezecutse DirtROr <br />MichaN B. Long <br />Division DincWr <br />Y read the excerpt from the June, 1996, Deserado Mine inspection <br />report, forwarded to you by. ban Mathews. This excerpt reports <br />pervasive cracking of the RP-4 pond embankment at the Deserado Mine <br />refuse facility. I also reviewed the remedial plan submitted by <br />William C. Lepro, Colorado P.E. #30283. In this report Mr. Lepro <br />presents his opinion that the embankment cracking is due to <br />shrinkage of the clay soils used to construct the embankment- <br />Further, he proposes to fill and tamp the cracks as a remedy. <br />Many clay soils throughout semi-arid Colorado display significant <br />shrink/swell characteristics. In my experience, however, it is <br />unusual for shrinkage cracking to penetrate to a depth of four <br />feet, or to be 5o feet in length, Shrinkage of clays tends to <br />result in disaggregation of the affected surface, commonly referred <br />to as "popcorning'~. Desiccation cracking is normally very erratic <br />and randomly oriented, similar to mud cracks on a dried mud flat. <br />Further, it is my understanding that Pond RP-4 has been in <br />existence for several years. It seems odd that the northern <br />embankment of pond RP-4 would suddenly exhibit cracking, when it <br />has never done so before. It also seems odd that only the northern <br />embarilcment would exhibit cracking, while the others survive <br />unscathed. <br />I recommend that you impose two requirements upon Western Fuels. <br />First, the Division should require Western Fuels to notify the <br />Division within a day if any "unusual events or movements are <br />noted". Second, Western Fuels should perform a consolidation-swell <br />test of the clay soils comprising the northern embankment of Pond <br />RP-4. A sample of the effected clay materials may be obtained by <br />disturbed sampling or by Shelby tube. If a disturbed sample is <br />obtained, the test specimen should be prepared by lab compaction <br />designed to simulate the embankment construction effort. The <br />consolidating load applied should mimic the light loads applied by <br />the small embankment. The specimen should then be immersed to <br />simulate the effect of hydrating the soil. The observed swell <br /> <br />