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-54- Exhibit Sa of the application also includes a stability analysis for a main entryway configuration proposed by the applicant to prevent subsidence of the surface above those entryways. This analysis, using material strength parameters derived from testing of cored samples of the coal, floor and overburden materials, and accepted analytical methodology developed by Wilson and Ashwin, projects a factor of stability in excess of 2.4 for the proposed pillar and entry configuration. This relatively limited extraction configuration recovers less than 40% of the resource in-place. Exhibit 5a, utilizing the predictive methods developed by the British National Coal Board, includes a prediction of maximum subsidence above the proposed Foidel underground mine workings. This worst case prediction projects 5.0 feet of surface subsidence. The applicant also includes a description of overburden response to subsidence, which is in keeping with the prudent state-of-the-art of subsidence prediction. The applicant predicts no effects to the identified renewable resource lands. Foidel Creek and its associated alluvial aquifer will be protected through limited extraction of the portal entryway mains, as described and analyzed in Exhibit 5a. The applicant projects a plausible scenario of overburden response, which includes a worst case caving of the roof to 11U feet above the seam, and the occurrence of bed separation and associated fracturing to 330 feet (30 extracted seam thicknesses) above the roof of the mined seam. Above the zone of bed separation, the overburden response is anticipated to be limited to gentle deflection of existing beds. Asa result, the Twentymile sandstone, which lies approximately 600 feet stratigraphically above the mined seam, is not predicted to suffer any impacts from subsidence. The applicant proposes a monitoring program to verify the projections of structural and hydrological effects included within the permit application. The applicant proposes to install subsidence monuments, depicted in figure No. 7, to verify those mechanical projections included within Exhibit 5a. As indicated on Map 4b, a high-resolution grid of subsidence monuments will be installed above one of the southeasternmost panels within the Foidel Creek mine workings. This panel is scheduled for extraction in 1985/1986. Observations above this panel should serve to verify the angle of draw, as effected by cross slopes, and the observed magnitude of vertical subsidence. Monuments are also proposed for installation above the portal entryway mains beneath Foidel Creek, in order to verify the stability of the limited extraction method proposed for use beneath the creek and its adjoining alluvial aquifer. All monuments will be surveyed quarterly, weather permitting. Subsidence monitoring reports, prepared in accordance with the format contained in Exhibit 11, will be submitted to the Division once every six months. The unoccupied structure located in the SE i/4 of the SW 1/4 of Section 29, outside but closely adjoining the projected area of potential subsidence, will also be monitored quarterly. County Road No. 27 and the Denver and Rio Grande Western Railroad spur will be visually inspected on a weekly basis.