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-36- perched system will develop due to the relative differences in the permeabilities between the waste of the pile and the lower permeability colluvial base. This aquifer may be as thick as 27 feet, as calculated in a conservative model. In reality the top of the water table surface will most probably be lower than 27 feet above the base of the pile. From the high point the water table surface will dip to the underdrains to which the majority of the leachate will flow. Some leachate will infiltrate into the underlying colluvium. Several monitoring wells located in the colluvium have not identified and aquifer and the waste pile is not expected to increase infiltration into the underlying colluvium. The majority of the leachate will be intercepted by the underdrains. Since no aquifer has been identified in the colluvium and the majority of the leachate will be intercepted by the underdrains negligible impact to the ground water system in the vicinity of the waste pile is expected. In the permit revision for the lower waste pile WECC proposes to monitor the effluent from the underdrains. However, the application indicates that one of the drains will collect water from a natural spring on site. Since spring discharge will also pe collected by the underdrains the effluent will not be representative of the waste pile leachate. For this reason the following stipulation is added. Stipulation No. 7 WEST ELK COAL COMPANY SHALL SUBMIT WITHIN NINETY (90) DAYS OF THE APPROVAL OF THE WASTE PILE PERMIT REVISION A PLAN TO MONITOR THE FORMATION OF A PERCHED AQUIFER LVITHIN THE WASTE PILE. MONITI~RING SHALL INCLUDE STANDARD WELL WATER QUALITY PARAMETERS AND WATER LEVEL MEASUREMENTS. THE PLAN SHALL BE IMPr.FMH~rrFn UppN APPROVAL BY THE DIVISION. Surface Water Effects from Proposed Permanent Lpwer Waste Pile The proposed lower refuse pile is expected to have no significant effects to the surface water system even under worst case low flow conditions. The amount of leachate expected to be generated from the pile is pected to be small in relation to the adjacent drainage areas. The quality of the leachate is predicted to be comparable to similar waste piles in the North Fork Valley with moderately high TDS, elevated sodium and sulfates, and low concentrations of metals. WECC provided an analysis of the worst case effects to the North Fork of the Gunnison from leachate generated by the pile. For the analysis they assumed a 10 year 7 day low flow in the river, maximum leachate production, and all of the leachate would reach the river undispersed and undiluted. The results of the analysis showed that the discharge would not violate any receiving stream standards. The amount of discharge is so low in relation to the stream flow that there will be no cumulative effects to the hydrologic balance outside the permit area.