2005-01-31_REVISION - M1977208 (2)

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Attachment 2 -Point by Point Response to Adequacy Letters Page 3 of 4 December 17, 2004 Adequacy Letter from the Division of Minerals and Geology Adequacv Item No. 1: Dakota Formation Well Cemex has demonstrated through hydrogeologic modeling that there is no risk to groundwater quality in the Dakota formation. The proposal contained in this adequacy response takes astep- ~ by-step approach to confirm this through the proposed detection well and monitoring and control ~ plans put forth. Adequacv Item No. 2: C-Pit Water Ouality and Treatment Cemex has proposed, and the Division has accepted, that C-pit will be pumped down to within about 4 feet of the bottom of the pit in the vicinity of the pump. Cemex has calculated that this will occur on or before December 2005 (and the wildlife agencies have agreed that impacts to wildlife during this timeframe are not significant). Additional pumping to lower the water level even further will be difficult because Cemex has tried a sump pump and it constantly clogs with sediment if the pump intake is below about 4 feet from the bottom of the pond. Cemex believes that some water will remain in C-pit after December 2005, however, the volume and water quality of that water is not known. Based on studies done for the 1999 Technical Revision for C-pit, the pond was at a minimal level and the pH and selenium concentration meet applicable standards. If C-Pit water does not meet applicable standards after the target date, Cemex commits to a contingency mitigation plan to be determined at that time. We have previously submitted optional pH treatment techniques. Our research indicates that ti ti selenium treatment technology is not as reliable or proven and that the best available technology ,~~ results in a selenium rich sludge, which would also require proper disposal. Cemex has looked at \~~ ` ' other approaches such as water volume exchange that are more promising. Cemex proposes to ~p~ti ~' revisit this issue with the Division on or about December 2005 in the form of a Technical \ . Revision. If the water quality in C-pit meets applicable standards a contingency mitigation plan Ot ; should not be necessary. Sampling and analysis will continue in C-pit as long as there is ponded ~ `: ~ water present and any approved contingency mitigation plan will apply if water quality standards ~ ,~ are not met. ~ Adeouacv Item No. 3: Preference for COz Treatment for pH Cemex recognizes the Division's preference for pH treatment using carbon dioxide application. As mention previously, if treatment is warranted, Cemex with submit a technical revision in or about December 2005 and address the Division's concerns at that time. Adequacv Item No. 4: pH Standard Cemex proposes a pH standard of 8.9 units. v~ ~~. Adequacv Item No. 5: Use of Water Balance Analysis The water balance analysis was primarily used to predict the date when the C-Pit pond would be reduced to its smallest practical size.