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of Sneffels Creek from upstream to downstream: the "missing zinc" is leaving the system at <br />a rate of 2.20 g/hr, over a distance of 1300 ft. <br />3. The significant amount of vegetation along the banks of Sneffels Creek could be absorbing <br />the zinc. Wetland plants are actually used to remove remaining metals from acid mine water <br />after it has been neutralized. <br />4. Clays and silts are known to help precipitate zinc as hydroxides. <br />5. Soils with organic material are known to precipitate zinc. <br />6. Rocks with magnesium in the form of silicates can replace zinc in solution. Andesite, which <br />is the host rock in the entire area, has feldspars which are magnesium silicates. <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 />Although biota appears to be a minor reservoir of zinc relative to soils and sediments, microbial <br />decomposition of biota in water can produce <br />ligands, such as humic acids, that can affect the mobility of zinc in the aquatic environment through zinc <br />precipitation and adsorption (EPA 1979d). <br />In water, zinc occurs in the environment primarily in the +2 oxidation state. It dissolves in acids <br />to form hydrated Zn +2 cations and in strong bases to form zincate anions, which are hydroxo complexes, <br />e.g., (Zn[OHJ3) -, (Zn[O1-114)2 -, and (Zn[OHJ4[H20J2)2- (O'Neil et al. 2001). In most waters, zinc exists <br />primarily as the hydrated form of the divalent cation. However, the metal often forms complexes with a <br />variety of organic and inorganic ligands (EPA 1979d, 1984b, 1987c). <br />Zinc can occur in both suspended and dissolved forms in surface water. Dissolved zinc may occur as the <br />free (hydrated) zinc ion or as dissolved complexes and compounds with varying degrees of stability. <br />Suspended (i.e., undissolved) zinc may be dissolved with changes in water conditions (e.g., pH, redox <br />Revenue Mine August 2012 T -4 <br />