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-3- (4) The application observes, on page 24 of appendix 3.3-3a; "...sizing of the required blanket drain and drain collection system be performed after an appropriate borrow sources is located and size gradation of refuse are determined. The final plans and specifications should have sufficient flexibility to allow modifications during construction to account for the changes in the engineering characteristics of the coal refuse. It should be recognized that only through inspection and monitoring of the embankment, can proper design modifications or changes in construction methods be made." The applicant should detail the drain hydraulic and mechanical design parameters which will be attained in completing construction. Further, the application should detail the construction inspection and monitoring program which will be utilized during construction of the embankment. (5) The application contains monitoring recommendations for embankment seepage and movement. On pages 25-27 of appendix 3.3-3a, recommendations are made for monitoring of embankment seepage, phreatic surface levels within the embankment, pore water pressures, and movement of the structure. The Division concurs all of these recommendations. The application will need to be amended to detail specific type and location of monitoring installations, as well as the frequency of observations and reports to be completed. (6) On page 27 of appendix 3.3-3a, the final page of the design report text, the consultant recommends; ..the engineering characteristics of the coal refuse be evaluated once sufficient quantities of refuse are available." Approval of the embankment design will require the inclusion of a stipulation conditioned upon the submission of test results to properly verify the report's mechanical material assumptions. Failing verification of the engineering characteristics assumed in completing the original design, immediate redesign will be required. (7) The Division has requested that the US Bureau of Mines Denver Technical Center complete a review of the proposed embankment design. If their staff review determines any design inadequacies, appropriate supplement comments will be forwarded to the applicant. 2.05.6(6) Subsidence The application includes a narrative discussion of subsidence-related concerns within section 4.5.5, and a technical projection of the anticipated subsidence due to the proposed permit's mining activities within appendix 4.5-1. Review of these materials has determined several inadequacies. The technical projection of subsidence made within the application theorizes a mechanism which limits subsidence generation to gob formation on a panel by panel basis. No consideration is given to potential stoping of gob materials downdip into subsequently lower panel levels. If such stoping were to occur, projected subsidence magnitudes may be increased. Considerable elaboration upon the anticipated mechanism of subsidence will be necessary before the application can be considered adequate.