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C. Sedimentation Ponds <br />Sediment ponds are discussed under Section 4.8.1.4, Vol. IV of the permit <br />application. <br />The applicant uses sedimentation ponds in all disturbed drainages to control the <br />increased sediment loads within the ephemeral drainages on the mine site. All <br />sediment ponds are designed to contain or treat the 10-year, 24-hour event and <br />safely pass the 25-year, 24-hour event, at a minimum. One MSHA size pond <br />exists on the site in the Coyote drainage. <br />D. Surface and Ground Water Monitoring <br />1. The applicant will conduct monitoring of ground water in a manner approved <br />by the Division. The ground water monitoring plan can be found in Section <br />4.8.5.2a, Vol. IV of the permit application (4.05.13(1)). <br />2. The applicant will conduct monitoring of surface water in a manner approved <br />by the Division. The monitoring plan was submitted under 2.05.6(3)(b)(iv) <br />and can be found in Section 4.8.5.1 a of the permit application, Vol. IV <br />(4.05.13(2)). <br />The Division has reviewed the surface and ground water monitoring plans as part <br />of the revision process. These monitoring plans are adequate to monitor for the <br />development of impacts, if any should develop. The 2003 Annual Report <br />stipulated existing water monitoring well GP-09 as the groundwater point of <br />compliance. <br />E. Probable Hydrologic Consequences <br />The model for leachate formation and migration at the Trapper Mine is based on a <br />study conducted by the U.S. Geological Survey at the Seneca II Mine in Routt <br />County, approximately 14 miles east of the Trapper Mine (U.S. Geological Survey <br />Water Resources Investigations Report 92-4187). The model is described in the <br />probable hydrologic consequences of the permit application (section 4.8), and is <br />summarized below <br />Ground Water Impacts: <br />Leachate formation - Slightly acidic snowmelt and rainwater at the Trapper Mine <br />infiltrates into the spoil that fills the reclaimed pits. Groundwater may also seep into <br />the spoil from adjacent or underlying rocks. As the water percolates through the spoil, <br />a chemical reaction occurs with the spoil. The main reactions are dissolution, pyrite <br />oxidation, and cation exchange. These reactions enrich the infiltrating water with <br />minerals from the spoil, forming a leachate high in dissolved solids. The leachate is an <br />alkaline, magnesium-sulfate type water. The concentration of dissolved solids can be <br />Trapper Mine 22 July 25, 2008