2008-09-29_REVISION - M1980244 - Laserfiche WebLink

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TA-1 41 so- a?,q t\ nn?I ON-bE&J-.t cZmm? P9,0M tlwt ,? %kvp . ?Aag 1oa VI. A.: On the contrary, it is misleading to state that the system will behave as a large homogenous batch reactor with uniform and unlimited acid-neutralizing capacity. Historical information indicating how rapidly the Carlton Tunnel drained the system after its completion suggests that the ground water flow in the system is fracture controlled (Eary et al., 2003). Thus it is possible that the flow along these fractures over the past 60+ years could have preferentially depleted the acid- neutralizing minerals. Therefore, the probability that infiltrating leachate from the waste rock will even come into contact with acid-neutralizing minerals that are not along fractures may be progressively decreasing. Available estimates of ground water travel times range from at least 25 years for travel from the level equivalent to the Roosevelt Tunnel down to the Carlton Tunnel (Eary et al., 2003, based on 3H concentrations) to 50-100 years for travel from ground surface to the Carlton Tunnel (MLE Project Application). If these estimates are correct, then there is a high probability that the leachate from the first waste rock placed at the mine back in the 1970's when open pit mining first started has not yet even reported to the Carlton Tunnel. Therefore, assertions that the diatreme carbonates are successfully neutralizing the acidic waste rock leachate are mere speculation, and it remains to be seen how the system will respond geochemically to the infiltration of the waste rock leachate and the ensuing water quality at the Carlton Tunnel. Based on the aforementioned, it is risky to assume that the Carlton Tunnel discharge will continue with the same water quality that existed prior to inception of surface mining. Prior to surface mining, there were not the volumes of waste rock accumulated on the ground surface as there are now. The Division accepts the Operator's rationale for not providing detailed spatial and temporal ABA data during waste rock placement. However, this does not preclude the Operator from detailed monitoring of waste rock ABA during and after placement. Considering the ground water travel times that are estimated in terms of decades for infiltration to report to the Carlton Tunnel, a long term monitoring program after closure and before reclamation release might be necessary. VI. M.: For the reasons stated in the Division's response to VI.A above, it remains to be seen whether the entire inventory of carbonate minerals in the diatreme will be available to infiltrating leachate. If the fracture-flow scenario plays out to the worst case, then elevated concentrations of sulfate, zinc and other constituents could be sustained. For that reason, long-term water quality monitoring will be needed to ensure that waste rock infiltration is indeed neutralized by the diatreme carbonates. VI. .: As mining faces are exposed, periodic spot-checking of ABA is recommended as a QA/QC on existing data. VI. R.: Whether this process is actually occurring or not is only speculation, and the answer should be apparent whenever the leachate from waste rock eventually reports to the Carlton Tunnel. VI. S.: We must consider the possibility that waste rock leachate may escape the capture system, as a result of unforeseen circumstances such as extreme precipitation events, dump geotechnical failures, short circuiting, etc., and therefore potential interactions of the leachate with geologic material outside the diatreme must be taken into account. Without such an assessment, the downgradient ground water monitoring must be extensive. The Operator cites the numerous