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COLORADO LEGACY LAND
<br /> $CHWARTZWALDER MINE
<br /> through the same elevations in the mine.The green point at 6,432 feet above mean sea level(ft amsl)represents
<br /> the projected plant start-up day, when the mine pool is estimated to be a conservative 20 ft below the
<br /> regulatory limit. On the basis of empirical data collected,the physical stabilization of the mine pool has been
<br /> achieved for the last three consecutive years.On the basis of projections of the empirical data,the operational
<br /> periods of the WTP, observed gradients in monitoring wells, and active dewatering of the mine pool can be
<br /> timely and effective.
<br /> E.5.1. Chemical Stabilization of the Mine Pool Demonstration
<br /> The chemical stabilization of the mine pool water has been accomplished through in-situ treatments. The
<br /> in-situ treatment regimen is designed to create a sulfate-reducing environment for the reduction of soluble
<br /> uranium species to insoluble uranium species, e.g., from the hexavalent oxidation state (U[VI]) to the
<br /> tetravalent oxidation state (U[IV]). Numerous field-based studies have documented that a sulfate-reducing
<br /> environment is conducive to the reduction of U(VI) to U(IV) resulting in the decline in observed uranium
<br /> concentrations(e.g.,Anderson et al.,2003;Watson et al.,2013)1.The reducing environment is essential for the
<br /> reduction of U(VI) to U(IV) to immobilize uranium and the precipitation of iron sulfides. In addition to the
<br /> formation of insoluble uranium species,trace metals may coprecipitate with or adsorb on the surfaces of the
<br /> iron sulfides.
<br /> The in-situ treatment consists of injecting carbon sources,e.g.,molasses,alcohols such as ethanol and methanol,
<br /> to stimulate the activity of SRB.Oxidized sulfur compounds can be used as terminal electron acceptors for the
<br /> anaerobic respiration of organic matter by sulfate and SRB. Sulfate and SRB obtain energy by coupling the
<br /> oxidation of organic compounds to the reduction of sulfate or other sulfur compounds to sulfide. Soluble
<br /> sulfides are produced that react with chalcophile metals (e.g.,zinc,cadmium,lead,copper) to precipitate low
<br /> solubility metal sulfide phases.A phosphate source such as phosphoric acid is also added,as necessary,as a
<br /> nutrient for the microbes.
<br /> 'Anderson,R.T.,Vrionis,H.A.,Ortiz-Bernad,I.,Resch,C.T.,Long,P.E.,Dayvault,R.,Karp,K.,Marutzky,S.,Metzler,
<br /> D.R.,Peacock,A.,White,D.C.,Lowe,M.,Lovley,D.R.(2003)Stimulating the in situ activity of Geobacter
<br /> species to remove uranium from the groundwater of a uranium-contaminated aquifer,Appl.Environ.
<br /> Microbiol.,69,5884-5891.
<br /> Watson, D.B.,Wu, W., Mehlhorn, T., Tang, G., Earles,J., Lowe, K., Gihring,T.M., Zhang, G., Phillips,J., Boyanov,
<br /> M.I., Spalding, B.P., Schadt, C., Kemner, K.M., Criddle, C.S., Jardine, P.M., Brooks, S.C. (2013) In situ
<br /> bioremediation of uranium with emulsified vegetable oil as the electron donor,Environ.Sci.Technol.,
<br /> 47,6440-6448.
<br /> JUNE 2021 16 AMENDMENT 6
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