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COMMENTS ON PROPOSED PILOT TESTING OF MICROBIOLOGICAL WATER TREATMENT Comment 1. P. 1, ¶ 3. The text indicates that Fe-bearing rocks (presumably pyritic rocks) will react with dissolved sulfide to precipitate metal-bearing solids. Is this correct or; it seems that the already dissolved metals are what will combine with dissolved sulfide to form stable sulfide-bearing solids. If not, then what will happen to the dissolved metals? Comment 2. Same. How can dissolved Mn concentrations decrease under reducing conditions generated by the addition of organic carbon without addition of carbonate? Comment 3. P. 2, top ¶ and elsewhere. How will water in the Pink Gneiss (PG) pit be managed? Particularly, how will incoming flows be controlled or will they need to be controlled? Will there be a discharge from the PG pit and if so, will specific controls be placed on that discharge? If there is a discharge, where will the discharge go? Comment 4. P 3. 4 2. Text indicates that "sulfur' was precipitated. Does this mean native sulfur, sulfide or sulfate minerals? If native sulfur, will there be a need to protect from further dissolution once the organic carbon-rich environment is removed? Comment 5. Same. How will the excess Mn be controlled? Comment 6. P. 3, 11 4. Text indicates that early-formed manganese and iron oxides will serve as "catalysts for the formation of additional metal oxides, and effectively scavenge [additional] dissolved metals." This doesn't seem to make sense as catalysts do not scavenge. The process is not clear. Please re-address Comment 7. P. 3 & 4. The column tests provide information for two systems: a sulfate reducing, anaerobic system and an aerobic system for Mn-oxidation. The aerobic system is not to be employed in the proposed in-situ treatment, according to the text, so it is curious why this information was provided in context with the proposed in-situ treatment. Please clarify. Same. The text indicates, without supporting data, that Mn concentrations decreased after 18 weeks of reaction, but it is not clear from the text whether dissolved Mn actually precipitated as Mn-solids or was simply washed out of the system. Please clarify. Same. The text (top of p. 4) indicates that a microbial biomass formed in the process. Does this mass have the potential to plug pore spaces, reduce efficiencies or curtail contact between reactants? If so, is there any way to show that essential reactions will be maintained or is this to be part of the test? What monitoring will be employed to assure adequate flow through the system.