2016-06-02_REPORT - M1977378 - Laserfiche WebLink

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developed into groundwater monitoring wells . Nine of these monitoring wells are within Sunnyside' s MLR permit area on Tailings Pond 4 (refer to map) . Preliminary findings are as follows; • The Animas River segment from Arrastra Creek to the 14th Street bridge in Silverton met water quality standards (metals) except for Cd and Cu for portion of the stream between Arrastra Creek and Boulder Creek during the high flow sampling event May 13th _14th. • The Animas River segment from Arrastra Creek to the 14th Street bridge in Silverton met water quality standards (metals) except for Cd throughout the segment and Cu (one stationin the portion of the stream between Arrastra Creek and Boulder Creek during the low flow sampling event . • Inflows were found that exceeded water quality standards for Al, Cd, Cu, Fe, Mn, Pb and Zn. • Using topography, mapped geology, borehole logs groundwater elevations and geophysical data, it appears that the alluvial aquifer extends under a large portion of the tailings ponds . • During low flow (September 21st - 24th, the groundwater is below the tailings with the exception of the western portion of Tailings Pond #4 . • The alluvial aquifer under Tailings Pond #4 appears to be hydraulically connected to the Animas River. • Increase in Mn and Zn concentrations in the Animas River appear to correlate with areas where Mn and Zn concentrations are highest in the groundwater wells during low flow. 2) American Tunnel area Cement Creek monitoring shows metals concentrations are similar between the points with some elevation for most metals between the upstream and downstream points . The metals with the largest increase are iron, manganese and zinc. The seep ATS2, originally from the toe of the American Tunnel waste dump, has either relocated or dried up. The seep ATS1 appears to have disappeared or relocated due to the reclamation of the waste dump. 8