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Page 6 Carol Russell April 8, 1981 potential only begins to be significantly above zero when the W/H (width/height) ratio is less than the value of the pressure arch resulting in massive failure stress exerted on the remnant pillars." The applicant should clarify what is meant by the expression "Value of the pressure arch" within this context. The applicant should also provide appropriate references and data to support the opinion expressed in the third and fourth paragraphs of page SV-113 and within the first and second paragraphs of page IV-1I4. This section of the application refers to appendix N-9, which contains photographs of examples which the applicant hypothesizes represent the Eagle Mine Complex's worst case overburden fracturing. The narrative of appendix IV-9 should be expanded to demonstrate that the example cases shown are from analogous rock type, overburden and stress situations. The projected worst case damage to the private residence ~f "minor cracks" and "minimal to negligible stresses" is inadequately supported and the structure will have to be monitored in accordance with Rule 2.05.6(6)(c). Further, the applicant must conform with the performance .standards of Rule 4.20 with regard to public notice and surface owner protection, including repair, replacement or purchase of the private residence .if any material damage wEre to occur, in accordance with Rule 4.20.3(2). The applicant's projection of possible consequences for the high-pressure oil pipeline drastically understate the potential consequences of subsidence involving this structure. During a "potential temporary disruption of flow" (N-116) the spillage of crude oil could have serious environmental, health and safety consequences. As discussed above, a thorough contingency plan and monitoring program will be necessary. State Highway Z3 will also require monitoring in order to avoid hazards to the public utilizing that state right-of-way. The applicant's observation that; "This road has settled greater amounts as a result of its construction" (Page IV-Z17), should be explained and supported by appropriate data presentation. The applicant projects settlement of the Denver and Rio Grande Railroad Spur by from 3~~to 16", ~ohich the applicant considers insufficient to require repair. The applicant should describe the criteria by which a I6" change in vertical alignment of the railroad spur is judged insignificant, particularly in the case of a railroad spur utilized by coal hauling unit trains in close proximity to the Yampa and Williams Fork Rivers. As mentioned above, the applicant should describe how it .intends to mitigate the effects of a potential 2.6~vertical change in grade o_f the irrigation ditches throughout the alluvial valley floor for which subsidence is projected to occur. (cont'd)