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The HELP model requires a lateral drainage layer and a barrier layer at the bottom of the fill to <br />calculate drainage that would be collected by an underdrain. To satisfy the model requirements, the <br />lower four feet of refuse was modeled as a lateral drainage layer, and the native colluvium was <br />modeled as a barrier layer. Discharge from the lateral drainage layer (refuse), as calculated by the <br />HELP model, is taken as the seepage rate that infiltration through the pile would discharge to the <br />underdrain. <br />The following eight conditions were modeled: <br />Reclaimed Refuse Conditions <br />1. Average refuse depth = 70 -feet refuse thickness and a 40 percent surface slope with 2 feet of <br />vegetated cover soil <br />2. Average refuse depth = 70 -feet refuse thickness and a 3 percent surface slope with 2 feet of <br />vegetated cover soil <br />3. Maximum refuse depth = 140 -feet refuse thickness and a 40 percent surface slope with 2 feet <br />of vegetated cover soil <br />4. Maximum refuse depth = 140 -feet refuse thickness and a 3 percent surface slope with 2 feet <br />of vegetated cover soil <br />Unreclaimed Refuse Conditions <br />5. Average refuse depth = 70 -feet refuse thickness and a 40 percent surface slope <br />6. Average refuse depth = 70 -feet refuse thickness and a 3 percent surface slope <br />7. Maximum refuse depth = 140 -feet refuse thickness and a 40 percent surface slope <br />8. Maximum refuse depth = 140 -feet refuse thickness and a 3 percent surface slope <br />3.1.3 Model Results <br />Percolation through the cover layer and refuse, and the resulting lateral drainage above the colluvium <br />layer that will be collected by the underdrain, were modeled for the design cases listed above. The <br />model results, shown in Table 6, indicate that there would be no drainage to the underdrain or head in <br />the refuse for all eight models. It is understood from these results that the low permeability of the <br />refuse controls the drainage rates predicted by the model. <br />16 <br />P:\Mpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />