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<br />• <br />River headwaters, and knowing that the pH of local water is circum-neutral to <br />slightly alkaline, it is extremely unlikely that elevated concentrations of these <br />metals could evolve from gravel mining in the proposed area. <br />Mercury. Mercury is found downstream of several turn-of-century gold <br />mines where mercury amalgamation was practiced. Mercury also occurs in higher <br />than normal concentrations in a few base-precious metal deposits in Colorado, and <br />apparently is enriched in rocks draining to an area the West Dolores River (see <br />Bureau of Reclamation report, ca. 1993). Moreover, McPhee Reservoir is one of <br />several reservoirs in southern Colorado cited by the Bureau of Reclamation as <br />containing elevated concentrations of Hg in sediments, and cited by the Colorado <br />Division of Wildlife as having elevated levels of Hg in older fish. Considering the <br />local mining history, local geology, and existing water quality measurements, it <br />seem extremely unlikely that elevate mercury concentrations are present in the <br />gravel or could develop due to gravel mining in this area. <br />Be , llium. Beryllium is rare in Colorado mineral deposits, occurring in some <br />Tertiary monzonitic rocks. Be is not typical of the kinds of rocks in the Dolores <br />River drainage. <br />Barium. Barium is common in trace concentrations in many igneous rocks <br />and shales, but is rare in Colorado streams above stream standards. <br />Dissolved salts. Soluble salts -metal salts for instance -are common in soils <br />and unsaturated zone rocks in most of Colorado and other grid lands. The <br />composition and concentration of salts is determined most directly by composition <br />of nearby bedrock and the tendency for such bedrock to produce high TDS waters: <br />salt composition is determined by the mineralogy of the bedrock; readily soluble <br />minerals in rocks leach quickly and thereby produce salts upon re-evaporation. <br />Rainfall amount determines whether salts will form; where rainfall is low, <br />evaporate minerals can form readily whereas salts form less or not at all in high <br />rainfall areas. <br />Soil salts are the typical products of evaporation of high TDS waters such as <br />occurs in the basins flanked by the Mancos Shale (Pierre Shale) and rock units <br />high in evaporate minerals. The relatively high TDS of local surface waters <br />increases the quantity of evaporate minerals that might form, and hence that might <br />be mobilized by gravel washing. The mobile salts would be confined to the zone <br />above the water table, which in the proposed mining area is shallow. The <br />composition of waters that will discharge from the proposed gravel operation will <br />be comparable to waters that flush through the unsaturated alluvium during each <br />spring snow melt or rain storm; metal salts are not likely; major evaporates of Na, <br />Ca, and SOa are more likely. Given the current degree of river salination and <br />periodic precipitation flushing, it is not likely that gravel mining will have a <br />substantial effect on salinity. Given the low concentrations of metals in the <br />io <br />