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<br />Fred Banta and Brian Munson -2- June 19, 1981 <br />With the further resolution of some minor design configuration problems <br />and the materials durability issue, the entire fill .could probably be <br />approved. <br />Backfill and Grading <br />Significant inadequacies exist within the operation plan and reclamation plans <br />concerning backfilled configuration of the surface facility areas of the <br />proposed Northern No. 2 and No. 3 mines. While the application states that <br />the reclamation plan is to regrade the disturbed areas to approximate <br />original contour with slopes no steeper than 2:1 fhorizontal to vertical), <br />a close examination of the cross-sections included in the appendix to <br />chapter M determined that significant variations from approximate original <br />contour are actually proposed. A request for variance from approximate „~. <br />original contour should be included within the application, as required by ~~~~• . <br />Rule 2.06.5. The vague references to chapters A, C, and M included within <br />chapters T and U of the permit application are inadequate for this purpose. <br />Zn keeping with Rule 9.Z9, the applicant will have to prepare~a thorough <br />geotechnical and stability analysis of the final reclaimed configurations <br />for the Northern No. 2 and No. 3 surface facility areas, in order to demonstrate <br />conformance with the required minimum static Slope safety factor of 1.3 <br />(Rule 4.19.2(1)(b)). This analysis should select appropriate critical slope <br />sections (including station 105 + 00') for analysis. A thorough yeotechnical <br />site investigation should determine whether any inclement ground water <br />conditions exist, whether the site has been the locus of past landsliding, <br />and should collect appropriate specimens of soil and bedrock for mechanical . <br />strength testing. A mathematical analysis should then be completed for each <br />critical slope section, utilizing an appropriate "accurate" method of analysis. <br />The backfilZ and grading plan for the Northern No. 1 mine appears to be <br />relatively acceptable. An index map should be included which clearly locates <br />the cross-sections contained in exhibit M-1. The proposed final configuration <br />in station 5 + 00' appears to differ from the approximate original contour. <br />For this reason the Northern No. 1 mine should also be included in the <br />application for variance from approximate original contour. <br />The backfill and grading plan ofRiena~No. 2 mine should also~be included within <br />the application documents. The existing pre-permanent program approved plans <br />may require modification in order to be brought in to conformance with the <br />permanent regulatory program requirements. I suspect that the Rienau No. 2 <br />should also be included within the application for variance from approximate <br />original contour referred to above. <br />Subsidence <br />s <br />Northern Coal Company's subsidence evaluation for the Meeker Area mine complex <br />is fairly comprehensive. fJith the resolution of the following concerns it will <br />satisfy the requirements of Rule 2.05.6(6): <br />(I) The application contains "subsidence protection plan maps" for the G seam, <br />J seam and FF seam, delineated as exhibits 9-2, 9-3 and 9-9. A similar map <br />should be produced for P seam workings of the Northern No. 2 mine. The <br />