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Memo to Steve Shuey ~ 3 • March 3, 1999 <br />over the collar of the no. 1 winze. It assumes second, that AMD is generated in the deeper pans of <br />the mine and is now being somehow driven up-section. The first assumption would seem <br />hydrologically plausible if fracture-confined water had been encountered during mining below the <br />9360 level, and if such water had a piezometric surface above the no. 1 winze collar elevation. The <br />latter assumption is less plausible. In the latter case, AMD would have higher TDS and salinity than <br />local, non-AMD water, so would be denser. Because of the higher density, AMD water could not <br />move upgradient unless in a confined aquifer and under pressure, or unless heated. AMD in this <br />case could not be continuously generated from sub-9360 level veins because they are currently <br />foundered, are cut off from oxygen, and thus cannot generate acid. This option cannot be ruled out, <br />but is the least plausible. <br />If the water level does not rise to the no. 1 winze level, then it might be concluded that natural ARD is <br />the source of metals and acid in the adit discharge. The fact that the adit dischazge water composition <br />differs, notab]y in lead and manganese concentrations, from the Creede Formation well water does not <br />necessarily argue for two separate water sources but rather for two separate water courses, possibly from <br />two types of mineralization both in the same formation. Given the variations in mineralization <br />throughout the district, such variations in water quality, while unusual for waters flowing through the <br />same formation inclose proximity, should not be uncommon. <br />Overall, given the above interpretations, there seems to be no reason to delay closing the plug valve, <br />provided the pressure is monitored. L` the pressure indicates more than 25 feet of head behind the plug, <br />then the plug would have to be re-opened in acordance with the contingency plan approved in the <br />permit. The operator should evaluate what safety factors should be applied, beforehand, and be prepared <br />to re-open the valve if pressure approaches design strength of the plug. If the pressure approaches 25 <br />feet, then it could be assumed that water is either overtopping the lip of the no. 1 winze, or that water <br />previously confined to the Creede formation/rhyolite bedrock contact has backed up into the adit rather <br />than flowing downward along the contact. <br />cc: Allen Sorenson <br />M:~minthhptBul Idog groundwater edited <br />