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Whetstone <br />Associates <br />Technical Memorandum <br />• The bulkheads in the adits are capable of containing mine water, and were constructed <br />under the approved Technical Revision #9. <br />The Steve and Pierce adits were bulkheaded in December, 2007, followed by contact <br />grouting in January 2008. The bulkheads were installed by Mining and Environmental <br />Services (MES) in accordance with Technical Revision #9 to the reclamation plan. The <br />original reclamation plan called for hydrologic sealing of the Steve Level adits (i.e, Steve <br />Adit and Pierce Adit) using bulkheads constructed using sprayed gunite concrete. Technical <br />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 <br />highly-engineered bulkheads were designed and installed to withstand a hydrostatic head of <br />120 feet (MES, 2008). Technical Revision #9 was approved by DRMS as part of the <br />reclamation strategy which included the flooding of the mine and construction of bulkheads <br />capable of containing mine water. <br />• Historical coreholes drilled from the valley floor into the deposit have been sealed to the <br />extent possible. <br />A plugging and abandonment program was conducted in 2000. The Operator's mine <br />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 <br />fifteen boreholes, by searching from below ground and above ground. It is no longer <br />possible to search from below ground. Some additional boreholes could not be located <br />during this targeted search, and it is highly unlikely that they remain fully open and can be <br />located decades after they were drilled. These collapsed boreholes would, at most, provide a <br />slight increase in permeability above that of the surrounding rock mass. That said, the <br />Operator proposes to conduct a follow-up P&A study, and to plug any exploration holes that <br />may possibly be encountered while conducting targeted source removal in the alluvium and <br />fill at the site. <br />• The bedrock surrounding the mine has very low permeability, which prevents any <br />significant movement of groundwater. <br />Shaft Sinking. In the late 1950's, the shaft was being sunk from the Steve adit. No <br />dewatering was required until the shaft reached a depth of 250 feet below the Steve level. <br />The first dewatering pump was installed in September, 1958, when the total shaft depth was <br />285 feet and groundwater pumping was required for the first time. The mine was dewatered <br />by pumping for only two hours per day at 15 to 20 gallons per minute (gpm), which is the <br />equivalent of a sustained pumping rate of 1.25 to 1.67 gpm. If the mine had been in <br />hydraulic connection with the creek, pumping rates would have been significantly higher. <br />Underground Packer Tests. Packer permeability tests were conducted underground in <br />1999, before the mine shut down. The results of all 22 tests gave a geometric mean hydraulic <br />conductivity of 4.7 x 10"7 cm/sec. The lowest packer test result was 9.9x10"8 cm/sec and the <br />median value was 2.7x10-7 cm/sec. For comparison, the EPA requires that municipal <br />4109C.100731 15