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_~ Ms. Christine Johnston Mr. James Pendleton Mr. David Berry December 7, 1994 Page 2 The conceptual model uses aprocess-oriented format to determine the amount of subsidence and its affects on the surface and the overburden. Studies throughout the world, including several in western Colorado, have resulted in a reliable method for evaluating subsidence due to longwall mining. The conceptual model can efficiently evaluate the way in which mining, geologic and topographic factors control subsidence amount, rate and duration. The conceptual model will also be used to determine the extent of caving due to roof collapse; the extent and magnitude of the fractures up from the mine, and the extent and magnitude of the fractures down from the surface. Rich Dunrud noted that WWE will utilize two empirical computer models: (a) Surface Deformation Prediction System (SDPS), which is the primary model that will be utilized, and (b) Comprehensive and Integrated Subsidence Prediction Model (CISPM), a model which will be used for "reasonableness checking." After some discussion, it was agreed that this would be a reasonable modelling approach for Box Canyon and mini-SOD. 5. There was considerable discussion regarding "probable hydrologic consequences. " Jim Pendleton noted that MCC has collected an extensive PHC database which is now reaching the same quality as the Somerset database. WWE noted that, in general, based upon our review of the available data to date, we agreed with the important conclusions reached by CDMG in the October 24, 1994 Decision Document for the West Elk Mine, Jumbo Mountain'I'ract. As two examples: (a) the Rollins sandstone will not be affected by longwall mining in the B or E seams, and (b) there are no aquifers that will be disrupted, based upon the available data. WWE stated that to "avoid reinventing the wheel," our desired approach would be to build upon the text and findings in the Jumbo Mountain tract decision document. CDMG stated that this is an appropriate approach, as long as WWE provides the information necessary to demonstrate that the findings that apply to Jumbo can be translated into findings that apply in the Box Canyon and mini-SOD areas.