Laserfiche WebLink
.' <br />~~ <br />Berhan Keffelew/Posey & York-Fenn re: Cresson leach tests <br />February 23, 1995 <br />Page 3 <br /> <br />at depth, the available oxygen (for deeper infdtration) will be reduced. I believe this was <br />agreed to during the introductory meeting held to discuss the submission." <br />Whether there was "agreement," and between whom is not known to us. Neither of us has ever <br />agreed that a simple soil cap would be sufficient; seeing the results of the leaching data, we defmitely <br />would not recommend approval of a simple soil cap. <br />If capping is chosen to be the protective measure that will be employed, we recommend, generally, <br />that the cap be a composite cap, that it be adequately protective both of the waste and of the topsoil, <br />that it be sized in consideration of the local environment (temperature, precipitation, and topography). <br />Upland diversions, bactericides, and alkaline amendments are measures that should be considem,.d for <br />the overall system. <br />Knowing that CC&V is presently mining and compiling ore and waste rock, we recommend that <br />whatever protective measures design work needs to be done be completed as soon as possible. We <br />remind you that the Cresson ores and wastes with which we are familiar have a poor ability to produce <br />low permeabilities. We caution that the old pits should be filled quickly and not partially; leaving the <br />pits part-filled with mine waste could generate enough acid to release sufficient quantities of ferric iron <br />to in essence become acid self-generating. Whether this should be figured into the bond is something <br />that we should discuss. <br />A fmal note. Our original assessment of this ore body, based mostly on our past exploration and <br />mining experience in base and precious metal systems, was that it had a very low potential for <br />producing environmental problems. Although we still believe that it certainly has a lower problem <br />potential than most metal mines, we both were rather surprised with the results of the leaching tests <br />and the higher than expected acid and metals generating capacity of the samples. We are presently <br />receptive to review of control mechanisms other than composite caps, but are skeptical of the controls <br />that we have heard so far. <br />cc: Bruce Humphries <br />Carl Mount <br />Jim Pendleton <br />M: MIN\HHP\CRESSON2. REC <br />