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<br />Question: Does any single operating factor represent a clear and present <br />risk relative to discharge of elevated levels of toxics from the facility? <br />The chemistry involved in all of the process modifications dloes not <br />indicate a major identifiable risk for future high level discharges ~%f metals <br />or cyanide from the facility BUT testing to confirm this has n'pt been <br />adequate to date. <br />Testing such as acid generating potential (AGP), acid neutralizing <br />potential (ANP), humidity cell leaching, and the EPA leach prat col are <br />useful approximation tests but do not provide data of the yua~ity and <br />certainty of conventional chemical composition analysis data. In short, <br />these are imperfect approximation tests which can give and iodic tiun of <br />relative behavior of tailings but they cannot accurately predict long term <br />behavior of tailings which are exposed to microbiological act vity, to <br />varied temperature and aerobic/anaerobic cycles, and to intr lion of <br />natural waters into the deposited tails. <br />Longer term, more comprehensive leach modeling tests would b useful <br />but I am not sure that they would go far enough to assure freed m from <br />future problems to warrant their conduct and cost. <br />Question: Are there mining and milling sites with a tailings history <br />similar enough to that at the BMG site to give us a better feeling for how <br />these wastes will behave in the future? <br />I am not aware of any other sites which have the "layer cake" of,tailings <br />represented by the BMG site with its progression from very high ~cyunide <br />pore waters through the CYTOX, hydrogen peroxide, and finall~ (NCO <br />sulfur dioxide impacted tailings. <br />While it is true that there may be other sites where some c f these <br />processes have operated .without major problems, the possible sy ergistic <br />effects of having this mixture of tailings and associated liyu'ds are <br />unknown. Even a relatively simple process such as the removal f sulfur <br />dioxide (one of the reactants in the (NCO process) with lime (c mmon <br />practice in utility power plants for sulfur dioxide emission cu trot) is <br />complicated by the formation of less stable calcium sulfite in addition to <br />stable calcium sulfate in the waste ponds. We do not know if (related <br />chemistry "surprises" may arise in the San Luis tailings deposits, <br />particularly in the long term. <br />DEH061693 <br /> <br />