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-60- Stipulation No: 28 THE PERMITTEE SHALL PERFORM A SURVEY OF ADOBE CONSTRUCTED HOUSES ON A QUARTERLY REQUIREMENTS OF RULE 2.05.6(6)(c)(i)(D). THE FIVE POTENTIALLY AFFECTED BASIS, IN CONFORMANCE WITH THE The applicant also proposes to install a line of 15 high-resolution permanent subsidence monitoring monuments above the First North Mains of the Maxwell Mine. As depicted on Map 17 of the amended permit application, this monument line will be installed north of, and parallel to, Colorado Highway No. 12. Monuments will be installed on approximately 100-foot intervals. The "subsidence monitoring monuments will consist of two-inch diameter, 6-foot long iron pipes driven into nine-inch diameter, four-foot deep holes. A three-inch diameter, flat metal disc will be set on top of each two-inch iron pipe and the hole annulus will be backfilled with concrete." The applicant proposes to control subsidence within the renewable resource land areas of the Purgatoire River alluvial valley floor by restricting coal extraction to 50X of the in-place coal. The application, on page 2 of Exhibit 21, presents a clear statement of the development mining scheme to be utilized at the Maxwell Mine; ... 18-foot wide entries on 90-foot centers, leaving a pillar which has an average size of approximately 72 feet on each side." This extraction rate is equivalent to approximately 36X of the in-place coal. The following statement is made by the operator within Exhibit 21; "As mining continues in this renewable resource area, a maximum of 50X of the coal viii be extracted. Pillar sizes will not be less than 20 feet x 30 feet in size. Variance in pillar size will be dependent upon the configurations of the development entries, rooms, and geologic features associated with the Maxwell seam." The applicant has indicated, in response to the Division's proposed findings, that mining recovery rates will not approach the 501L level within the Maxwell Mine during the first five-year permit term. In order to determine whether the proposed limited extraction plan will prevent disruption of the renewable re~ouree lands through subsidence, the application should include an appropriate analytical pillar stability analysis. Therefore, in order to comply with Rule 2.05.6(6)(f)(ii), the following stipulation is necessary. Stipulation No. 29 THE PERMITTEE SHALL COMPLETE AN ANALYTICAL PILLAR STABILITY CALCULATION FOR THE PROJECTED LIMITED EXTRACTION CONFIGURATION CONTAINED WITHIN THE AMENDED APPLICATION FOR THE MAXWELL MINE. THESE ANALYTICAL CALCULATIONS, PREPARED IN ACCORDANCE WITH AN ANALYTICAL METHOD ACCEPTABLE TO THE DIVISION, SHALL BE SUBMITTED TO THE DIVISION FOR REVIEW WITHIN 60 DAYS FOLLOWING PERMIT ISSUANCE. The applicant presents predictive subsidence calculations within Exhibit 21 of the application. These calculations, which project subsidence occurrence at the Maxwell Mine prepared in accordance with techniques developed by Peng and Stefano, are acceptable with the addition of the pillar stability calculations stipulated above.