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MEMORANDUM At <br /> Adrian Brown <br /> infiltrating precipitation, downward flow to the water table, and flow through drainage tunnels as <br /> described above.As the ARD is generated above the water table,the removal of carbon by this <br /> mechanism also takes place largely above the water table. <br /> 2. Dissolution by groundwater infiltrating vertically from ground surface. Calcite and dolomite are sparingly <br /> soluble, but over geological time can be removed by dissolution in passing infiltrating precipitation. In <br /> general this process rapidly saturates the infiltrating water with calcite, so tends to take place in the <br /> shallow rockmass, frequently above the water table (but is not restricted to that zone). <br /> Accordingly, carbon removal in geologic time occurs predominantly above the water table, and so it is <br /> reasonable to expect that above the water table the carbon content of the rock will decrease from its <br /> geologically emplaced level;this reduction can be used as a marker for the presence of the water table during <br /> geologic time. <br /> The carbon concentration in the diatremal rocks has been computed as a function of elevation, and the results <br /> are presented in the center panel in Plate 10.As can be seen,the average carbon concentration remains <br /> between 0.1%to 0.2%down to elevation 9,650 ft amsl,which is interpreted to be at or somewhat below the <br /> upper location of the geologic water table.The concentration then increases rapidly to 0.5%at 9,400 ft amsl, <br /> which is interpreted to be the lower location of the geologic water table.The concentration then increases <br /> slowly with depth, ultimately reaching the likely geologic emplacement concentration of 1%-2%. <br /> Based on the carbon data,the pre-mining water table was located between 9,400 ft amsl and above 9,650 ft <br /> amsl in the locations where carbon data was available.This is consistent with the results of the groundwater <br /> analysis above. <br /> Oxidation <br /> Natural oxidation (also known as weathering)occurs in the rockmass as a result of the entry of atmospheric <br /> oxygen via airflow in the unsaturated zone, and to a lesser extent by transport of dissolved oxygen (or other <br /> oxidants like dissolved ferric iron) into the saturated zone. Accordingly, the location of the geologic water table <br /> (the top of the zone of saturation)can be approximately identified by locating the bottom of the zone where <br /> oxidation occurs. <br /> The average degree of oxidation in the diatremal rocks has been computed as a function of elevation, and the <br /> results are presented in the right-hand panel in Plate 10.As can be seen,the average degree of oxidation drops <br /> rapidly to approximately 20% by elevation 10,600 ft amsl, and then stays in the 13%-15%range down to <br /> elevation 9,650 ft amsl,which is interpreted as representing the upper location of the geologic water table.The <br /> average degree of oxidation then decreases rapidly to 2%at 9,400 ft amsl,which is interpreted to be the lower <br /> location of the geologic water table. Below this depth, there is very limited oxidation, likely restricted to the <br /> more permeable pipe areas in the diatreme. <br /> Page 5 <br /> Adrian Brawn Consultants, Inc. <br /> 130 W.4rh Ave.,Denver CO 80223 <br /> 303-698-9080 www.abch2o.com <br />