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-55- Two separate conservative strengths were assumed for the floor clay beneath the F-Seam (angle of internal friction = 9°, cohesion = 1,350 lbs per square foot: angle of internal friction = 0°, cohesion = 4,320 lbs per square foot), resulting in safety factors greater than 1.62. Further, the waste disposal pile will be constructed with granular underdrains, designed to prevent saturation or invasion of water into the waste pile. These five underdrains have been appropriately sized to ensure that tfie pile will not become saturated. West Elk Coal Company proposes to monitor both the ground water saturation beneath and within the pile, in order to ensure that the pile remains dry. The operator also agreed to install several survey monuments to monitor slope stability of the completed structure and adjoining areas. The original permit includes a statement of intended possible secondary mining of coal beneath the coal pile. In order to assure the assumptions made in completing the stability analysis are correct, the Division believes it appropriate to impose the following stipulation upon approval of this permit revision. Stipulation No. 13 THE DIVISION DIRECTS WEST ELK COAL COMPANY, PRIOR TO ANY DISTURBANCE AT THE WASTE PILE SITE, 70 SUBMIT AN APPROPRIATE AMENDMENT TO THE OPERATION PLAN WITHIN THE EXISTING PERMIT TO LIMIT EXTRACTION BENEATH THE WASTE PILE TO PRIMARY DEVELOPMENT ONLY. NO SECOtJDARY EXTRACTION SHALL BE ALLOWED BENEATH THE PILE OR THE IMMEDIATELY ADJOINING AREA. During the past several years slope instability has occurred in the surficial deposits above the portals of the Mt. Gunnison No. 1 Mine. The area effected lies downslope from the toe of the proposed pile. Because of this evidence of surficial instability adjoining the proposed pile area, the Division desires additional surface monumentation and stability monitoring. For this reason, the Division believes it appropriate to impose the following stipulation upon approval of the permit revision application. Stipulation No. 14 THE DIVISION DIRECTS WEST ELK COAL COMPANY, PRIOR TO ANY DISTURBANCE AT THE UPPER WASTE SITE, TO INSTALL SEVERAL ELECTRONIC TILT METER TUBES DOWNSLOPE FROM THE TOE OF THE PROPOSED WASTE STRUCTURE. WITHIN 30 DAYS FOLLOWING APPROVAL OF PERh1IT REVISION APPLICATION, WEST ELK COAL COh1PANY SHALL SUBMIT TO THE DIVISION A PLAN FOR THE INSTALLATION OF THE TILT METER FACILITIES. THESE TILT METER INSTALLATIONS SHALL OCCUR IN THE VICINITY OF MONUMENTS 51 AND