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Bulldog Mine Tailings Pondr Evaluation <br />movement can be calculated from the so-called "retardation factor" (Freeze and Cherry, 1979). <br />The retazdation factor for a constituent represents the relative reduction in the velocity of <br />movement of a constituent in relation to the velocity of ground water. The retardation factor is <br />calculated from the distribution coefficient (Kd), which is a representation of the partitioning of <br />the solute between liquid and solids, as follows: <br />Kd = (mg metal sorbed/g soil)/(mg metal in solution/mL of solution). <br />The calculated Kd values for manganese, lead, antimony, and sulfate from the attenuation test <br />data are shown in Table 5.5. Higher Kd values indicate a higher proportion of the solute sorbed <br />to or attenuated by the solid. The lowest Kd values for the metals in these tests were: 81.6 mL/g <br />for manganese, 6.2 mL/g for lead, and 1.8 mL/g for antimony. As previously stated, these Kd <br />values indicate that significant attenuation of these metals would occur in unsaturated zone <br />sediments before reaching saturated conditions in the event of seepage of tailings pore water <br />from the impoundments. <br />The average Kd for the metals in the five test vessels containing sediment/soil samples were: <br />• > 1,200 mL/g for manganese, > 350 mL/g for lead, and 34 mL/g for antimony. All of the Kd <br />values for manganese and lead in the investigation fall within the reported ranges of Kd values <br />for various soils and clays by Dragun (1988) (0.2 mL/g to 10,000 mL/g for manganese, and 4.5 <br />mL/g to 7,640 mL/g for lead). Dragun (1988) does not report Kd values for antimony or sulfate. <br />The retazdation factor can be calculated from the Kd of the solute, the bulk density (pb) of the <br />sediment/soil material, and the porosity (n) of the sediment/soil material using the equation: <br />retardation factor = 1 + (pbin) Kd (Freeze and Cherry, 1979). <br />Assuming a bulk density of 1.8 tonnes per cubic meter and a porosity of 30 percent for aquifer <br />materials in the vicinity of the tailings impoundments, and using the lowest K~ values for <br />manganese, lead, and antimony observed in the tests summarized above, the resultant retazdation <br />factors for each element aze: 490 for manganese, 38 for lead, and 12 for antimony. The <br />reciprocal of the retardation factor gives the relative velocity of the constituent of concern to the <br />regional ground water. These retardation factors imply that the constituents of concern will <br />• move with velocities that are on the order of 0.2%, 2.6%, and 8% of the velocity of the local <br />Hometmke Almmg Comporry• $hepGerd •L1i(ler. /nc. <br />p i/r.~~nb.~n,~,p.pu 35 .dpril 1-!. 199: <br />