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• Arsen <br />Expected range of concentrations: 0.02 to 1.2 mg/L <br />Expected discharge standard: Unknown, Segment 3a of the Lower Dolores River has a <br />water quality standard of 0.10 mg/L <br />Dissolved arsenic can be precipitated from water by raising the pH to 10.00 or higher, by <br />the addition of lime or caustic. This is considered unrealistic for this project due to the <br />resulting high volume of sludge produced. Elevated levels of arsenic can be also be <br />removed from water to achieve levels of less than 10 parts per billion (<0.01 mg/L) by <br />elevating the pH to a range of 8.7 to 8.8, if sufficient levels of iron are present. <br />The current available data shows that the average pH of the mine drainage is 8.5 to 8.8; <br />this pH range should be sufficiently high to precipitate the metals species of concern <br />without addition of lime to raise the pH. <br />A co-precipitation occurs with the arsenic and the available iron. Dissolved iron is <br />relatively low in the mine water (<0.1 mglL) but can be increased by adding ferric sulfate <br />(FeSOa) during treatment with an approximate ratio of 3:1, Iron (as Fe+3) to arsenic. Imn <br />should only be added in sufficient quantity to precipitate the arsenic to meet the site- <br />specific discharge standard, while remaining incompliance with the Colorado discharge <br />. limit for dissolved iron (i.e., 0.3 mg2). <br />Selenium <br />Expected range of concentmtions: 0.02 to 0.35 mg/L <br />Expected discharge standard: Unknown. The Lower Dolores River Standard is 0.02 <br />mg/L; however, natural backgrouttd levels of selenium are elevated and a discharge <br />standard for selenium was not included in the discharge permit for previous operations in <br />the azea. <br />Selenium is difficult to remove from water with conventional treatment. In fact, Lyntek is <br />not aware of any current treatment system that has been proven to be effective in <br />removing Selenium. It has been shown that Selenium can co-precipitate with iron. The <br />water treatment system proposed will provide excess iron that could potentially co- <br />precipitate some of the Selenium. However, it is unproven that any reduction in selenium <br />levels will occur with this treatment process on this water. <br />• <br />