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Memo to Tony Waldron Bowie No. 2 Geotechnical Adequacy page 3 extracted in order to encounter the low quality coal. The application should expand on this proposal to clarify the approach to be implemented. If)Iv)IB) Monitoring The application proposes to visually inspect the permit area to determine whether new mass movement features have developed. If new landslides are detected "they will be brought to the attention of the Division". The Division will require a more detailed proposal for action in the event of rejuvenation of old landslides or the development of new landslides. At a minimum the applicant will need to evaluate each rejuvenated or new landslide to determine what the apparent cause of the modern movement might be. If appropriate, mitigative methods should be proposed to minimize hazard to the mine facilities, public health & safety, and the environment. Exhibit 15 -Subsidence Prediction The analysis presented within the application employs empirical methods of prediction. The empirical methodology is based largely upon the proven methods developed by Britain's National Coal Board (NBC), published in 1975 as "The Subsidence Engineer's Handbook". The NBC's empirically derived predictive relationships were developed predominantly for subsidence above longwall underground extraction. During the past two decades a myriad of authors in the USA have developed correlation factoring to correct for mechanical differences between overburden response of the USA and England, as well as the mechanical differences between subsidence above longwall and room & pillar extraction. These techniques, which have been employed by previous permitted operators within Colorado, are acceptable to the Division. The author of Exhibit 15 references a report prepared by T. Brooks in 1983, as a source for geologic and hydrologic properties and a previous subsidence impact evaluation ["Hydrology and Subsidence Potential of Proposed Coal-Lease Tracts in Delta County, Colorado". USGS, Water Resources Investigation Report 83-4069). It would be helpful if the operator could provide a copy of this report to the Division. The remainder of my comments will correspond to the report format.