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• Dispersion is represented by Fick's Law and remains constant for a given simulation; <br />• Sorption is treated as linear equilibrium partitioning between aqueous and solid phases; <br />and <br />• MYGRT simulates the transport of a single constituent, which is assumed adequate, as <br />interactions between constituent species are not simulated. <br />3 Input Data and Assumptions <br />Constituent transport simulations were developed fox TDS, selenium, chloride, sulfate, thallium, <br />and pH in C-Pit water released to the Dakota sandstone. The bedrock formations between the C- <br />Pit and the Dakota sandstone were assumed to be saturated and to exhibit uniform porous <br />medium characteristics. Assumptions and model parameters used to develop the flow and <br />transport model are discussed below. Model input data are summarized in Attachment B. <br />An average hydraulic conductivity value for the unweathered shales of the Carlile, Graneros, and <br />Mowry formations was estimated based on packer tests in similar shales of the Niobrara <br />Formation conducted by Fox Consultants (1985), Rocky Mountain Consultants (1988), and <br />Morrison Knudsen Corporation (1993). These packer tests were conducted in bedrock shales of <br />the present-day Dowe Flats quarry to determine the suitability of the area as a reservoir. The <br />results of the packer tests conducted by Fox Consultants at pressures of 30 to 40 pounds per <br />square inch (psi) resulted in no flow to the surrounding unweathered shales. These pressures <br />correspond to about 70 to 90 ft of hydraulic head. Test results indicate that the bedrock is <br />generally tight and of very low permeability (< 10~ centimeters per second [cm/s] or < 1 foot per <br />year [fUyr]). <br />Subsequent hydraulic testing in unweathered shales conducted by Morrison Knudsen (1993) at <br />packer pressures between 60 and l00 psi (about 140 to 230 ft of head) indicated that the shale <br />permeability ranged between about 41 and 2 ft/yr (4.0 x 10-5 and 2.1 x 10~ cm/s). Packer tests <br />conducted at these high pressures would force water along the bedding planes, joints, and <br />fractures of the shales and likely result in an overestimate of the permeability. Considering that <br />these packer tests were conducted at such high hydrostatic head pressures compared to the <br />pressure head exerted by the approximately 15 ft of water ponded in the C-Pit (about 7 psi), the <br />bulk permeability of the claystones, siltstones, and shales lying between the C-Pit and Dakota <br />sandstone was conservatively estimated at 1 fr/yr (about 1 cm/s) <br />Since the hydmulic conductivity of the Dakota sandstone aquifer is not known, it was assumed to <br />be about 2,000 ft/yr (2 x 10"' cm/s) based on the range of values reported for afine- to medium- <br />grained sandstone (Kasenow, 2001). A range of reasonable hydraulic gradients, 0.01 foot per <br />October 29, 2004 3 Revision 0 <br />