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Mr. Brad Gosche - 2 - January 23, 1991 <br /> Further, the Terzaghi and Rankine methods analyze the bulk stability of the <br /> refuse structure. They were intended to determine whether the overall mass <br /> would remain in a selected location. They do not address the important <br /> consideration of the facial slope stability of the structure. The more <br /> sophisticated and contemporaneous techniques do accommodate analysis of the <br /> surficial stability of the structure. An analysis will have to be completed <br /> using one of the more comprehensive methods capable of evaluating the <br /> surficial zone stability of the proposed refuse structure. In order to <br /> complete such an analysis it will be necessary for Mr. Johnson to determine <br /> appropriate values for the angle of internal friction and cohesion of the <br /> refuse material . This will entail the collection of appropriate samples and <br /> the completion of laboratory mechanical tests of the refuse shear strength. <br /> Rule 4.10.4(4) limits the facial gradient of a coal refuse structure to no <br /> steeper than 2 (horizontal ) : 1 (vertical ). The cross sections contained <br /> within Mr. Johnson 's analysis indicate the following proposed slope gradients <br /> for the proposed structure: <br /> Station Cross-Section Slope Gradient <br /> 0 + 27 ' 1 .53 (h) : 1 (v) <br /> 0 + 40' 1 .39 (h) : 1 (v) <br /> 0 + 60' 1 .57 (h ) : 1 (v) <br /> 0 + 80' 1 .76 (h) : 1 (v) <br /> 1 + 00' 1 .81 (h ) : 1 (v) <br /> 1 + 40' 1 .85 (h) : 1 (v) <br /> Rule 4.10.4(4) allows no variance from this facial gradient limitation. The <br /> design will have to be amended to conform with the regulatory limitation. <br /> Due to the nature of the complex issues involved in correcting these adequacy <br /> issues, National King Coal may require additional time past the 60 day <br /> decision due date of February 18, 1991 , in which to respond. If this is <br /> indeed the case, then please submit a request to waive the right for a <br /> decision within the 60 day time frame and include a date by which you estimate <br /> your response will be completed. <br /> If you have any questions regarding this matter, please give me a call . <br /> Sincerely, <br /> ct,vvu2� G S` c, L� <br /> James C. Stevens <br /> Senior Reclamation Specialist <br /> JCS/kw <br /> 2967F <br />