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~. ~ ~ i <br />BMRI -San Luis we#t Pit Backfill <br />GEOCIiEMICAL EVALUATIONS OF BACKFILLING <br />PURPOSE (See Geochimica. 18 Oct 95: Posev 12 Aug 96): <br />DETERMINE IF THE BACKFILL WOULD BECOME ACID <br />GENERATING UNDER FULLY SATURATED CONDTIONS <br />IDENTIFY METALS THAT MAY BE RELEASED <br />CONCLUSIONS: <br />• AS DISPOSED, BACKFILL WILL NOT GENERATE ACID~iC <br />SOLUTIONS <br />• PINK GNEISS HAS POTENTIAL TO RELEASE MN, BUTT HIGH <br />MN IS CHARACTERISTIC OF THE LOCAL WATERS <br />• "Interaction of the gneiss with ground water produces leach es with <br />alkalinities in excess of 100 mg/L CaC03 eq. Indicating that the <br />ground water /rock system of a saturated backfill has suffici nt <br />bicarbonate alkalinity to maintain pH of solutions in the allra~line <br />range. <br />"The observation of (a) 0.23% to 2.86% "unidentified sulfu " in the <br />static ABA tests and (b) leachability of K and S04 in the bat h tests <br />indicatyes that the gneiss samples contain discernible concen rations <br />of a jarosite-like phase that has slight solubility when the rock is <br />leached with low-K local ground water... This "wash-off" of <br />ephemeral sulfate phases from rock surfaces is commonly observed in <br />many hydrogeologic settings and does not indicate a signif cunt ARD <br />threat, provided the samples will remain fully saturated (as rill be the <br />case at San Luis). " <br />Geochimica, Inc. 22-Jan-99 <br />