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1. An oxidation reaction in which dissolved zinc is exposed to oxygen as it flows down the <br />tunnel and becomes zinc hydroxide, which is basically not soluble. This is particularly likely <br />in Q4 2011 given the residence time provided by the ten partial cave -ins found along the <br />Revenue Tunnel between the Atlas Drift and the Yellow Rose Drift at the time the samples <br />were taken. They act as check dams and rock filters for the mine water flow. Organic <br />material in the Revenue tunnel, such as numerous old timbers, is known to help precipitate <br />zinc, especially at neutral pH levels. <br />2. Zinc is not a naturally soluble element in pH neutral or slightly alkaline water. The pH <br />levels in the underground water samples are consistently between 7.0 and 9.0, which would <br />lead to the zinc level decreasing slowly. <br />3. Some oxygenation and precipitation is likely occurring in the Revenue Pond.Clays and silts <br />are known to help precipitate zinc as hydroxides. <br />4. Rocks with magnesium in the form of silicates can replace zinc in solution. Andesite, which <br />is the host rock in the entire area and is the major portion of the waste rock at the site, has <br />feldspars which are magnesium silicates. Most of the Revenue Tunnel has been driven in <br />this rock and The mine water filters through this waste rock before it emerges in the <br />Revenue Seep. <br />The following citations are from the Agency for Toxic Substances and Disease Registry (ATSDR) <br />and EPA's toxicological profile for zinc, which was revised in 2004, which describe the methods by <br />which zinc can precipitate from solution. <br />Zinc occurs in the environment mainly in the +2 oxidation state (Lindsay 1979). Sorption is the dominant <br />reaction, resulting in the enrichment of zinc in suspended and bed sediments (EPA 1979d). Zinc in <br />aerobic waters is partitioned into sediments through sorption onto hydrous iron and manganese oxides, <br />clay minerals, and organic material. The efficiency of these materials in removing zinc from solution <br />varies according to their concentrations, pH, redox potential (Eh), salinity, nature and concentrations of <br />complexing ligands, cation exchange capacity, and the concentration of zinc. <br />In polluted waters in which the concentration of zinc is high, removal of zinc by precipitation of the <br />hydroxide is possible, particularly when the pH is >8 (EPA 1979d). In anaerobic environments and in the <br />presence of sulfide ions, precipitation of zinc sulfide limits the mobility of zinc. The relative mobility of zinc <br />in soil is determined by the same factors that affect its transport in aquatic systems (i.e., solubility of the <br />compound, pH, and salinity) (Clement 1985). Zinc is an essential nutrient that is present in all organisms. <br />Revenue Mine August 2012 T -4 <br />