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Mr. Ralph Lopez June 9, 1994 Page 2 with either the water bearing zones in the overburden or the water bearing zones, including, possibly the Trinidad sandstone, in the underburden. Finally, the fact that there are mine inflows at all suggests that there is communication of the mine workings with water bearing zones. Depending on the relative hydraulic heads of water in the mine workings, in water bearing zones in the overburden and in water bearing zones in the underburden, the coal slurry mine water could flow outside the mine workings and affect the groundwater regime. Therefore, please provide either 1) evidence that the slurry water will not migrate into overburden or underburden aquifers or to surface waters or 2) calculations demonstrating that the effect of the migrating slurry water will not adversely affect the present or future use of groundwater or surface water. 2. In the May 11, 1994 adequacy response submittal from Basin Resources, in section A.1., it is stated that the mine seal will be modified in order to allow mine water discharge, if discharge should occur. With this possibility of mine water reaching the surface, compliance with surface water standards needs to be addressed. will the possible discharge of mine water be in compliance with NPDES effluent limitations and will the downstream water quality be in compliance with receiving stream standards, or will water treatment be necessary? Will the NPDES permit need to be modified? Please quantify your conclusions. Also, it must be noted that the need for any water treatment may hold up phase 3 bond release. Rule 3.06.1 requires that the performance bond liability include the construction of treatment facilities for mine drainage. Further, the rule states that bond liability is in effect until the treatment facilities are removed. 3. In the May 11, 1994 adequacy response to the Division's second adequacy letter, Basin states that the long term quality of the mine water will be slightly worse than the thickener water quality. However, due to long term continued dissolution of chemical constituents from the coal slurry solids into the mine water, the quality of the mine water may start becoming worse than what the current slurry water analysis suggests. But, by then, enough coal slurry solids may be in the mine that nothing could be done to protect the hydrologic regime. Please quantify your predictions concerning the effects of the chemistry of the slurry solids on the long teen water quality within the mine.