2011-12-28_HYDROLOGY - M1977300 - Laserfiche WebLink

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In -situ Treatment of the Mine Pool Alexco Resource US Corp (Alexco) has provided Cotter with a technical basis and conceptual plan to implement in -situ treatment of mine pool water to reduce concentrations of uranium and other metals through in -situ formation of sulfide minerals similar to those that likely existed in the Schwartzwalder ore body prior to mining. The proposed treatment, involving controlled introduction of molasses and alcohols, will also form non - pyritic iron sulfide (FeS) within and throughout the mine pool workings to encapsulate the precipitated minerals and form a film on wall rocks and other solid materials. This will inhibit the potential for further leaching of uranium and other metals. This process is expected to greatly accelerate a consistent trend over the past 5 years of steadily declining uranium concentrations in the mine pool. The Alexco in -situ treatment process is not expected to reduce Ra -226 concentrations. However, the immobility of radium in oxidizing environments is well documented (Ames, et al. 1983; Banks, et al. 1995; Langmuir & Riese, 1985; Szabo and Zapecza, 1991) and is also evident in water quality data from the site. Even if radium were transported from the reducing environment of the mine pool into oxidizing environments such as zones of mixing with oxygenated groundwater from the shallow alluvium, it would readily precipitate or adsorb onto natural solid materials. This theoretical expectation is supported by site data indicating very low Ra -226 leaching or migration potential due to oxygenated groundwater in contact with mine waste rock in the alluvial fill. It is also supported by the fact that groundwater sampled from a historic exploratory core hole discovered in 2010 (permanently sealed January 2011) had uranium concentrations approaching those of the mine pool, yet Ra -226 concentrations were essentially absent. Both theoretical considerations and site - specific data indicate that any potential seepage of mine pool water that could reach oxidizing conditions in ground water regimes closer to the near - surface environment would become subject to geochemical processes that readily attenuate radium and prevent further migration of this constituent. There is no scientific justification for an additional in -situ treatment process to reduce Ra -226 concentrations in the mine pool. In -situ treatment of the mine pool would involve similar limitations to that of mine dewatering /active treatment of mine water with respect to Criterion 1. This includes slow groundwater travel times that could significantly delay any potential uranium reductions that might be achieved in Ralston Creek once uranium levels in the mine pool have been significantly reduced. However, the amount of time required to implement this measure would be considerably less than that of mine dewatering /active treatment (estimated to be on the order of 4 months to arrange permitting and install treatment delivery and maintenance infrastructure). This would minimize the amount of time necessary to realize any beneficial effects in terms of improvements in Ralston Creek water quality. Other aspects of in -situ treatment have advantages with respect to each of the other remedial selection criteria. First, the sustainability (Criterion 2) of in -situ treatment would be significantly more favorable than that of mine dewatering /active treatment. Start up and operational costs would be much lower, yet method effectiveness (Criterion 1) would likely be similar. Alexco estimates that a 90% reduction in uranium concentrations in the mine pool could be achieved within a matter of months following initiation of in -situ treatment. Once maximum reductions in uranium concentrations in the mine pool are achieved, periodic administration of additional treatment media may be required, but Alexco believes that due to very slow groundwater 7