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8. On page G-5, the applicant states that in order to ensure that the proposed mining does not adversely impact the prevailing hydrologic balance in the vacinity of the Lyons site, Western Mobile will employ a slurry wall and compaction of backfilled slopes as mitigation techniques. Page G-2 of the application states that ground water recharge occurs from the south and west and that dischazge of ground water is into the St. Vrain and the South Branch. At times of low ground water conditions the St. Vrain may be recharging the ground water. Page G-l states that the site is characterized by flood plain features. Page G-2 also states that the ground water table is typically two to three feet below the ground surface on the average, but it may rise to the surface during the spring and early summer runoff periods or fall as low as six feet below the ground surface during the late fall and winter. Finally, the lanuary 28, 1997 RMC letter to Scott Gudahl states that surface and ground water features north of the valley will be protected by a slurry wall constructed parallel to St. Vrain Creek and the South Branch. With this information, it appears that there is a strong hydrologic connection between the St. Vrain (and South Branch) and the surrounding flood plain, ie: riparian, wetland, subirrigated meadow complex. The applicant will need to explain how the normal and essential hydrologic functions of recharge and dischazge for this alluvial-ground water system will occur following installation of the slurry wall and what long-tetm impacts or changes to the system might be expected. Tn particular, will the reclaimed floodplaln complex be able to resume a naturally occuring hydrologic interchange with the main stem and south branch of the St. Vrain for the 2200 linear feet of channel passing through or adjacent to the site? Also, the applicant should explain how the upgradient and downgradient ends of the slurry wall will be keyed or configured into the surrounding alluvium. 9. The applicant will need to clearly identify on an appropriate map the location of all proposed slurry walls. In addition, the applicant will need to provide specific information regarding the construction of the slurry walls including the depth, thickness, description of bedrock key cuts, construction materials, construction methods, and quality controUquality assurance procedures. The applicant will need to supply cross sectional engineering designs for the features noted above. The applicant will also need to indicate the linear footage of slurry wall to be constructed and provide a time schedule for when various portions of the slurry wall will be completed. l0. The applicant has referenced probable impacts to ground water relating to mine dewatering and final reclamation activities via the January 28, 1997 RMC letter to Scott Gudahl. These probable impacts are based on RMC's experience with other pits sealed with either liners or slurry walls. Tn order to accurately evaluate the impacts to surface and/or ground water at the Lyons Pit-Rockin' WP site and surrounding azea, the Division requests that the applicant provide a detailed hydrogeologic evaluation of the expected impacts to surface and/or groundwater during both mining and during final reclamation. This evaluation should include the depth and lateral extent of the cone(s) of depression expected during the various phases of the mine plan when dewatering is employed. The evaluation should also include an inventory of all wells (regardless of use) that occur within the cone(s) of depression and an assessment of the impact expected to each particular well. The well inventory should include the following information fer each well: owners name and address, location, use(s), depth, screened interval, yield, and construction details. The applicant will also need to provide a revised map showing the location of each of these wells. The hydrogeologic evaluation should also define the vertical and lateral