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Ouray Silver Mines Inc. <br /> Technical Revision 09 February 1,2017 <br /> 4.3 Water Quality Monitoring Update <br /> Under this proposal,water discharging from the mine and the treated Mill discharge would <br /> comingle before entering the Mine Water Pond. OSMI proposes that a new monitoring station <br /> MWP Inlet take the place of current monitoring at UG-5 (Map 1). Monitoring at the MWP Inlet <br /> will capture the water quality and flow conditions of water before it enters passive portions of the <br /> water management system and after all sources of water have comingled. <br /> All locations (Tables 3 through 5)will be sampled for Permit groundwater standards and <br /> compared to Permit standards (Table 6). OSMI proposes changes to the Permit groundwater <br /> standards. Proposed changes to the Permit groundwater standards are described below with a <br /> brief rationale that is expounded upon in section 5. <br /> • Cease total metals analysis (aluminum, cadmium, copper, iron, lead,mercury, and zinc) <br /> because there is no groundwater standard and total metals are not likely to represent <br /> actual groundwater chemistry. Total metals concentrations are highly sensitive to redox <br /> conditions that may cause solid phase precipitates (metal oxyhydroxides)to form, <br /> resulting in a buildup of sediments in the bottom of the well,as groundwater passes <br /> through the well. Incidental inclusion of particulate matter in sample fluids can <br /> significantly alter the result concentration for total metals. <br /> • Change the chloride standard from 2 mg/L to 250 mg/L. The previous standard had been <br /> based on a combination of the maximum observed in the wells and the CDPHE standard <br /> for chlorine(0.011 mg/L),rather than chloride. Additionally,the 2 mg/L standard is so <br /> low that it is within the margin of error for common chloride analytical methods,which <br /> have a PQL of 2 mg/L. In-stream segment standards and agricultural groundwater <br /> standards do not exist for chloride. Therefore,the stricter 250 mg/L drinking water <br /> standard is proposed as a groundwater Permit standard. <br /> • Stop analyzing for WAD cyanide, and set the total cyanide limit to 0.005 mg/L. The total <br /> cyanide analysis is protective of the WAD cyanide standard(0.005 mg/L). <br /> • Stop analyzing for dissolved hexavalent chromium and dissolved trivalent chromium, as <br /> there is no standard,and the dissolved chromium standard of 0.1 mg/L is protective. <br /> • Change the sulfate standard from 160 mg/L, which had been based on a maximum of <br /> wells and consideration of an incorrectly instream segment sulfide standard of 0.006 <br /> mg/L. In-stream segment standards and agricultural groundwater standards do not exist <br /> for sulfate. Therefore,the stricter 250 mg/L drinking water standard is proposed as a <br /> groundwater Permit standard. <br /> 4.4 Buildings <br /> The properties, including new square footage, location and description are presented for each <br /> building project below. Table 7 presents the square footage changes. Structures that are <br /> covering already used areas and do not have foundations are not included in the square footage <br /> summary. The change in area associated with the proposed building expansions and upgrades is <br /> 10,904 square feet. The new buildings will be constructed in a style becoming to their location, <br /> similar to other recent construction. <br /> Mill Building <br /> Page 8 of 14 <br />