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-7- ADDITIONAL COMMENTS ON PROBABLE HYDROLOGIC CONSEQUENCES 1. There 1s some concern within the Division as to the potential impacts of the Mine No. 3 and Middle Creek detention basins on the water quality of the alluvial aquifer system within the permit and adjacent areas. Both detention basins are located adjacent to alluvial deposits and are projected by the applicant to be in hydrologic communication with the alluvial ground water system. Therefore, the "Probable Hydrologic Consequences" section of the permit application should be expanded to include a discussion of potential water quality effects of the detention basins on the alluvial ground water system. The discussion should include detailed geologic cross-sections extending at least 500 feet adjacent to the basins, clearly identifying the relationship between the basins and adjacent undisturbed bedrock, backfilled overburden material, and alluvial deposits. Additionally, the discussion should include an estimation of contribution from water percolating through reclaimed spoils Into the basins, an estimation of seepage rates out of the basins, and a predicted "worst case" value of total dissolved solids of water contained within the detention basins. 2. As part of the applicant's proposed reclamation plan, the Middle Creek pit will be backfilled and graded to approximate original contour. This reclaimed pit will eventually fill with water to some undetermined elevation due to discharge from the undisturbed bedrock aquifer, seepage from adjacent backfilled spoils, and downward infiltration of precipitation. A projection of the maximum anticipated water level elevation wtthtn the reclaimed pit should be made, based on data and observations from the site, and this information should be included in the permit application. 3. Due to the potential for hydrologic communication between the reclaimed pit, the adjacent Middle Creek detention basin, and the alluvial aquifer system, the applicant should install a monitor well in the backfilled and regraded Middle Creek pit. Monitoring of water levels and water quality within this spoils aquifer will be very important in evaluating long-term impacts to the hydrologic balance of the area. For similar reasons to those stated above, the Division also requests that a spoils aquifer monitor well be Installed at the Mine No. 3 site, near the Mine No. 3 detention basin. Sample analysis and monitoring frequency for both spoils aquifer wells should be conducted as discussed earlier in this memo under the "Hydrologic Monitoring Plan". VII. Alluvial Valley Floors - Rules 2.06.8 and 4.24 Unconsolidated streamlaid deposits holding streams have been identified wtthtn the proposed permit and adjacent areas and are shown on Map 4, Mine No. 3 Hydrology. As shown on the map, three areas are acknowledged by the applicant as meeting the geomorphic criteria of alluvial valley floors. These areas are: 1) the flood plain of Fish Creek; 2) the flood plain of Foidel Creek downstream from USGS Gaging Station 09243900; and 3) the flood plain of Middle Creek downstream from USGS Gaging Station 09243700.