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-64- WECC committed to two pre-subsidence field surveys of all monitoring points and annual resurvey of triangulation monuments with Second Order Class II horizontal accuracy. WF:CC committed to achieving vertical error no greater than + 0.2 feet. WECC will compare these field survey results with the results of an aerial photogrammetric survey of the monument grid. In order to avoid misunderstanding, the Division imposed a stipulation defining the accuracy standards to be achieved in completing both the field and aerial photogrammetric pre-subsidence surveys. Further, the Division believed the photogrammetric subsidence monitoring technique to represent an interesting potential technical innovation. However, the technique is unproven for the completion of subsidence monitoring surveys. Therefore, the Division believed it prudent to require the applicant to correlate its aerial photogrammetric monument surveys to traditional ground survey monitoring of selected triangulation monuments. In order to avoid misunderstanding, the Division imposed a stipulation defining the accuracy standards to be achieved in completing post-subsidence aerial photogrammetric surveys of the subsidence monumentation grid. In February of 1985, WECC submitted a permit revision application requesting the addition of 1,765 acres to its permit area. This revision application proposed the expansion of the mine plan, limited to areas north of the Minnesota Creek surface and ground water divide. In response to Division adequacy review comments, WECC clarified and amended the original revision application mine plan, as shown on Exhibit 3.4.4.B, to retain buffer zones to assure that no disturbance would cross south of that divide. A 200-foot wide buffer was delineated between development mined areas and the hydrologic divide, and a 760-foot wide buffer between panels to be retreat mined and the hydrologic divide. The Division found, therefore, that the proposed 1,765 acre permit area increase would not affect areas south of the Minnesota Creek surface water and ground water divide. Therefore, the subsidence findings did not require any substantive amendment as a result of the 1,765 permit area revision. No modifications to the subsidence monitoring or mitigation plan are required by the lower waste pile permit revision. The proposed lower waste pile is not in or adjacent to an area proposed to be mined. The Division finds that the following stipulations are necessary for a finding of compliance with subsidence related requirements of Rule 2.05.6(6) and 4.20. Stipulation No. 18 THE DIVISION DIRECTS WECC TO COMPLETE THE INSTALLATION OF THE SUBSIDENCE MONI~RING NETWORK PRIOR TO THE INITIATION OF EXTRACTION OF CDAL WITHIN THE PANEL DESIGNATED IN APPENDIX A `i0 THE NOVEMBER, 1984 PERMIT REVISION APPLICATION ENTITLED "APPLICATION Tt~ REVISE THE MINING AND RECLAMATION PLAN FOR THE NfP. GUNNISON NO. 1 UNDERGROUND MINE".