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June 25, 2010 11 of 15 <br />Installing equipment for dewatering is technically challenging to accomplish safely. <br />The mine has been shut down since 2000 and was sealed (bulkheaded) in 2007. Access to the <br />Schwartzwalder Mine is now limited to hiking down the Sunshine Decline. The Sunshine Decline is a <br />steeply sloping (>45°) adit and earthen/rock ramp that leads from the hillside well above the valley floor <br />down to the Steve Level. Descending this 150 - 200-ft ramp is dangerous, but can be achieved with ropes, <br />good lighting, and adequate care to overcome uneven surface, unstable footing, sudden drop offs, and other <br />potential hazards. At the bottom of the slope, all equipment and personnel must pass through a small <br />structural orifice (a metal framed hatch of perhaps 3 x 4 ft) designed to control mine ventilation flows. <br />Finally, several hundred feet of curving narrow shafts would have to be traversed to reach the mine pool <br />collar at former hoist station on the Steve Level. Cotter last entered the mine in December 2009 and found <br />the inner workings to be badly deteriorated. The mine is no longer safe for entry without significant repairs <br />and refurbishment, which could include installation of timber sets, roof bolting, debris/muck removal, and <br />other measures. <br />The bulkheads in the adits are capable of containing mine water, and were constructed under the approved <br />Technical Revision #9. <br />The Steve and Pierce adits were bulkheaded in December, 2007, followed by contact grouting in January <br />2008. The bulkheads were installed by Mining and Environmental Services (MES) in accordance with <br />Technical Revision #9 to the reclamation plan. The original reclamation plan called for hydrologic sealing <br />of the Steve Level adits (i.e, Steve Adit and Pierce Adit) using bulkheads constructed using sprayed gunite <br />concrete. Technical Revision #9 addressed upgrading the bulkhead seals from a sprayed gunite concrete <br />construction to a formed and pumped concrete with additional post-shrinkage grouting. The highly- <br />engineered bulkheads were designed and installed to withstand a hydrostatic head of 120 feet (MES, 2008). <br />Technical Revision #9 was approved by DRMS as part of the reclamation strategy which included the <br />flooding of the mine and construction of bulkheads capable of containing mine water. <br />Historical coreholes drilled from the valley floor into the deposit have been sealed to the extent possible. <br />Cotter's mine geologists and surveyors searched for all of the historical coreholes that were drilled from the <br />valley floor into the workings. These personnel had the technical expertise to locate and plug fifteen <br />boreholes, by searching from below ground and above ground. It is no longer possible to search from <br />below ground. Some additional boreholes could not be located during this targeted search, and it is <br />unlikely that they remain fully open and can be located decades after they were drilled. These collapsed <br />boreholes would, at most, provide a slight increase in permeability above that of the surrounding rock mass. <br />Due to the very low permeability of the rock mass, however, a very slight increase in permeability from a <br />collapsed borehole could be sufficient to affect the flow system. The low permeability of the bedrock was <br />demonstrated in underground packer tests, conducted for the mine closure hydrology study in 1999, which <br />gave a geometric mean hydraulic conductivity of 4.7 x 10'' cm/sec and a median hydraulic conductivity <br />was calculated to be 2.7 x 10 -7 cm/sec. The low permeability is also evident in the flow rates to the mine <br />during operations. At full dewatering to 2,200 feet below the Steve Level, inflow to the mine averaged <br />only 190 gpm. Compared to the very low permeability of the bedrock, a collapsed corehole or near surface <br />fracture would have a slightly higher hydraulic conductivity and could therefore affect the flow system near <br />the surface of the mine. However, the flow rates in Ralston Creek during mining, along with other <br />technical data, do not indicate that any significant conduits exist between the mine and Ralston Creek.