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<br />leachate flux previously calculated for the closed CKD disposal site (0.74 inches <br />per year), suggests that the interim capping scenario will reduce the leachate flux <br />through the open disposal site by about 40 percent. <br />An additional HELP model run was made to simulate a closed CKD disposal site <br />that used the interim capping approach. This additional model run was simulated <br />as a 20-acre CKD disposal site with approximately 20 feet of CKD capped by a <br />compacted shalelclay cover overlain by an additional 15 feet of CKD capped by a <br />compacted shale/clay cover. The upper compacted shale/clay cap was covered <br />with two feet of topsoil and vegetated with a poor stand of grass. The topsoil, <br />disposed CKD, and compacted shale/clay layers were simulated using material <br />textures S, 10, and 25, respectively. Default evapotranspiration and precipitation <br />data for Denver, Colorado were used in the simulation. <br />The model results of the closed CKD disposal site indicates that the flux of <br />leachate that will be generated at the base of the disposed CKD is about 0.04 <br />inches per year, or an annual leachate volume of 3,232 cubic feet. A comparison <br />of the leachate flux under this modified closure scenario (0.04 inches per year) <br />versus the leachate flux for the previously simulated closed CKD disposal site <br />(0.74 inches per year), suggests that the modified closure scenario will reduce <br />the leachate flux through the closed disposal site by about 95 percent. <br />The HELP model output for each of the model runs is attached. <br />Item No. 3: Clarification of HELP Model Data Sets. <br />The HELP model runs presented in previously submitted Appendix D were made <br />using the HELP model default soil types that most closely approximated the <br />estimated saturated hydraulic conductivities of the topsoil cover, disposed CKD, <br />and the underlying shaley bedrock formations (i.e., Niobrara Formation, Carlile <br />Shale, Greenhorn Limestone, Graneros Shale, and Mowry Shale). The soil type <br />and material textures used to simulate each of these components and the <br />effective saturated hydraulic conductivities simulated are listed in the table below. <br />Material (Thickness) Default Soil Type Effective Saturated <br /> (material texture number) Hydraulic Conductivity <br /> cm/sec <br />To soil Cover 2 feet Silt (8) 3.70E-04 <br />Dis osed CKD 35 feet Cla a Silt 10 1.20E-04 <br />Shaley Bedrock Formations (700 Compacted Clay (16) 1.00E-07 <br />feet <br />