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Sunnyside Mine-A&-"-e Water Addidoa <br /> always advantageous to both short-term and long-term water quality to accelerate the <br /> rate of re-saturation of underground workings. <br /> Adding Alkalinity to the Recharge Water <br /> The long-term effect of inundation of the mineralized zone is to reduce the generation <br /> of acidity, thereby also controlling the leaching of metals into mine-pool water. <br /> Compared to current conditions of acidic seeps within the mine workings, geochemical <br /> modeling of the bulkheaded condition predicts equilibrium pH values near neutral. <br /> The addition of alkalinity to the recharge water will permit the neutralization of the <br /> existing acidity of the natural recharge water and buffer the mine-pool water against <br /> future acid inputs. In effect, the addition of excess alkalinity by SGC during the <br /> artificial recharge of the mine workings will accelerate the rate at which the mine-pool <br /> chemistry moves from acidic toward neutral (or slightly alkaline) conditions. In <br /> addition, the incremental TDS in the recharge water will further limit the concentration <br /> of DO in the flooded workings, thus further limiting acid generation and leachability of <br /> metals. Under mildly alkaline conditions (e.g., pH < 8.5), leachability of base metal <br /> sulfides is strongly minimized an most m_ etals_ Nat- _'&i'in so1ution under t ie <br /> natural recfiar�e condiitions-w�Itie precipitated. too. So lon a --__ _._ <br /> p p �, s the bulk pH remains <br /> under about 8.5, there will be no enhanced solubility of Zn. In fact, the precipitation <br /> of iron and manganese oxyhydroxides within the slightly alkaline mine pool would be <br /> expected to significantly adsorb Zn and other metals and metalloids onto new solid �n <br /> phases in the muck of the flooded workings. <br /> CONCLUSIONS <br /> 1. Artificial recharge of the mine workings will shorten the time period over which the <br /> steady-state water table is re-established at Sunnyside, but it will not affect the <br /> elevation at steady state. <br /> 2. Rapid re-saturation of the system will minimize the amount and rate of acid <br /> generation and leaching of metals and other solutes. <br /> 3. Addition of alkalinity to the artificial recharge also will minimize the amount and <br /> rate of acid generation and leaching of metals and other solutes. <br /> 4. Therefore, the hydraulic and geochemical effects of artificial recharge using <br /> alkaline water will be beneficial to the long-term conditions of the bulkheaded <br /> Sunnyside Mine. <br /> Geochimica, Inc. 4 ALKALINI7716-Jun-95 <br />