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<br /> <br /> <br />1 <br /> <br />1 <br />1 <br /> <br />1 <br /> <br />1 <br /> <br /> <br /> <br /> <br />1 <br />1 <br />Solute Transport <br />As stated previously, leach ate water will percolate into the adjacent <br />overburden aquifer under the influence of potentiometric head. An analysis of <br />solute transport through the aquifer was performed, using flow equations to model <br />a plume of saline water as it would be distributed in a confined aquifer with <br />time. <br />The equations which describe the travel of contaminants through an aquifer <br />are the same as those used in tracer dye studies of porous media. The equations <br />contain complex mathematical functions which can be solved by algebraic <br />approximations. The basic components of the equations are: 1) aquifer <br />characteristics; 2) ground water flow velocity; 3) concentration of pollutant; <br />4) values of longitudinal and transverse dispersivity; and 5) retardation <br />factors to account for ion exchange, solute absorbtion and radioactive decay. <br />Aquifer characteristics are determined from pump tests and drill hole data <br />presented earlier. Ground water flow velocity is calculated using Darcy's <br />equation (Velocity = Permeability x Hydraulic Gradient). Concentration of <br />pollutant is measured through column leaching studies as shown in Figure 17, <br />Predicted Leach ate Concentration, Energy Mine No. 1. Dispersivity is a <br />parameter which is difficult to measure in the field and must be assumed. <br />Dispersivity is the ratio of solute dispersion to flow velocity. As the saline <br />water leached from the spoils enters the aquifer, a "plume" of solute spreads <br />through the aquifer in the direction of ground water flow. As the plume moves <br />through the aquifer, the pollutant is diluted, diffused and absorbed by physical <br />and chemical interaction with the natural ground water. The greatest effect on <br />dispersion in aquifers associated with coal strata is the heterogenous nature of <br />the formation. The lithology of the Williams Fork Formation is variable, <br />displaying many facies changes, pinch-outs and thin sandstone lenses. Ground <br />water movement in such an aquifer is non-laminar, thus absorption and diffusion <br />of highly saline water is enhanced. Longitudinal dispersivity is measured in <br />the direction of ground water flow; transverse dispersivity is measured in a <br />lateral direction. <br />5 <br />