Laserfiche WebLink
<br />salts certainly should occur in this setting, and would be more evident in the dryer parts of <br />the year. <br />Mineralogy -Mineral Chemistry. <br />Major element compositions of ground and surface water are controlled by dissolution of <br />the most readily soluble minerals (see next sections). These mostly also control the total <br />dissolved solids contents. <br />Acidification associated with oxidation of pyrite, such as occurs in mineral deposits at <br />Rico, is responsible locally for elevated sulfate, aluminum, iron, and manganese. Release <br />of metallic elements from key minerals associated with these deposits controls the amounts <br />of other metals in receiving waters. Zinc, lead and copper derive predominantly from <br />dissolution of sulfide minerals in such deposits; trace concentrations are present in most <br />rocks and also contribute to the overall metal content of waters. <br />Trace concentrations of radionuclides such as uranium and radon are common in some <br />igneous rocks and in shales. Weathering of such rocks controls concentrations of <br />radionuclides in waters. Outside the Dolores basin, to the west, higher radionuclide <br />concentrations occur in uranium-vanadium deposits of the Uravan district. None of these <br />deposits appear to drain to the portion of the Dolores near the proposed deposit. <br />Background uranium concentrations are higher in certain igneous and metamorphic rocks, <br />shale, and glacial drift than in most other earthen materials. Uranium deposits such the <br />sandstone hosted uranium deposits of the Colorado Plateau are also, of course, high in <br />uranium. Thus, radionuclides in the uranium decay series are mostly abundant where <br />uranium concentrations are highest. <br />Radon, which is derived through radioactive decay of uranium, is high in Colorado <br />counties where one of more of the high-uranium earthen materials are commonly present <br />at the surface. Maps published by EPA and available on the intemet - ntco:~~w.vw.eQa.g°.,~ - <br />depict average radon concentrations by county for the entire nation. These maps express <br />radon concentrations as follows (see map attached): <br />• Zone 1: counties where predicted average indoor radon screening level exceeds <br />4 pCi/L (picocuries per liter) <br />• Zone 2: counties where predicted average indoor radon screening level is <br />between 2 and 4 pCi/L, and <br />• Zone 3: counties where predicted average indoor radon screening level is <br />< 2 pCi/L. <br />2 <br />