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Memo to Susan Burgmaier <br />Moffat Area Stability <br />page 2 <br />The 1990 stability analysis was performed assuming a critical <br />cross-section projected through the out of box cut spoil pile. <br />This section included a low wall unmined barrier whose presence may <br />have improved the bedrock sections resistance to shear failure. As <br />an offsetting factor, however, this section included the surcharge <br />of the additional spoil pile placed on top of the reclaimed <br />surface. The analysis determined the slope safety factors to <br />exceed 1.5, rather than the required 1.3 for reclaimed surfaces. <br />Recommendation <br />In my opinion it is not warranted to require Edna to amend the <br />existing stability analysis. As long as the existing bedrock and <br />spoil phreatic surface relationships are maintained the reclaimed <br />slope should remain stable. In order to ensure that the phreatic <br />relationships are maintained, Edna should take several steps to <br />enhance drainage of the reclaimed pit. <br />(1) When grading down the high wall coarse spoil should be <br />concentrated along the base of the highwall and laterally <br />along the base of the low wall. This should enhance the <br />dissipation of any waters which enter the spoil from the <br />bedrock or from precipitation. <br />(2) If not already penetrated, the parting between the Wadge and <br />the Lower Wadge seams should be ripped and excavated to create <br />drainage windows along the low wall. This will enhance <br />drainage of water from the Lower Wadge seam and preclude the <br />development of any artesian head beneath the parting. <br />If Edna is not willing to accommodate these preventative measures <br />in its final amended reclamation plan, then I believe the Division <br />would be warranted to require them to reanalyze the stability of <br />the proposed reclaimed pit configuration. This analysis should <br />project a critical cross-section without low wall bedrock barrier. <br />It should also assume a phreatic highstand in the Lower Wadge <br />equivalent to the lowest elevation of the low wall pit lip plus 25 <br />feet and no ground water within the Wadge seam. <br />cc: Kent Gorham <br />Larry Routten <br />Doc: M:\COAL\JAP\MOFSTAB.MEM <br />JP/JP <br />