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M-2000-016, Lafarge West, Inc.: Riverbend Operation, AM-Ot Apri122, 2005 Adequacy Memo #2 Page 5 21. Memo Item 13: Regarding the potential effects of pit dewatering on the amounts of water conveyed by the Fort Lupton Bottom Ditch, the Brighton Ditch, and Big Dry Creek, the applicant refers to the AMEC report, which does not appear to address ditch losses or losses from Big Dry Creek as a result of pit dewatering and subsequent lowering of the ground water table. The applicant must project the amount of water that will be lost from these structures if these structures leak and the ground water level around the structures is lowered as a result of mining activities. The applicant needs to indicate whether this issue has been investigated and the results of that investigation. If this issue has not been addressed, please investigate the potential impacts to the water conveyed in these ditches and the creek, and submit the results to the Division for review. 22. Memo Item 14: Lafarge needs to commit to specific mitigation measures to remedy expected penmanent impacts to ground water flow in the area. This includes addressing permanent impacts to vegetation. Using a trigger point of a 2 feet change from historic ground water levels is acceptable, once adequate monitoring well sites are identified. However, this trigger point cannot be coupled with "physical injury to a structure." Please remove all references to requiring physical injury to a structure. The trigger point of 2 feet should result in the initiation of a study to determine potential impacts to vegetation and surface and ground water users, followed by permanent mitigation measures, if necessary. In the case of vegetation effects, especially the cottonwoods in the wildlife corridor, immediate interim mitigation measures must be specified to protect this vegetation. Since the applicant indicates that significant changes are expected from the silt ponds, mitigation measures should also address these impacts (e.g., French drains around silt ponds as well). Groundwater Monitoring Plan: 23. On the Monitoring Well Locations map, the cells shown do not entirely match those on the Reclamation Plan maps of Exhibit F. Please modify the Monitoring Well Locations map to correct all discrepancies. 24. Memo item 16: The applicant must provide the list or table requested in the previous adequacy review showing well permit numbers and constructed depths for all the monitoring wells. 25. Memo Item 16: In addition to providing a baseline monitoring well for Well Permit No. 7280 (see Item 17 on p. 4 of this memo), as requested by the previous Memo Item 16, additional monitoring wells will need to be selected and/or installed to monitor impacts not only to "potentially impacted wells," but the overall hydrologic balance, including silt storage and lined pond impacts. There needs to be a minimum of one monitoring well upgradient and one monitoring well downgradient of each cell. There must be monitoring wells both up- and downgradient of all of the silt storage ponds and lined ponds, as well as to monitor unlined pits during dewatering activities. In addition to the general guidelines just provided, there need to be two monitoring wells on each side of Phase 3, Cell 1 (48-acre silt storage pond). Ground water gradients must be clearly defined on associated maps. The applicant also needs adequate monitoring of potentially impacted wells and vegetation. 26. Memo Item 17: In considering the applicant's response, the Division will require month) monitoring of ground water levels in the monitoring wells associated with that phase for one vear prior to commencement of mining in that phase. Please also see above responses to Memo Item 16. Once proper idenfrfication of the cone of depression and the extent of mounding and shadowing has been made, consideration of monitoring frequency of other wells based on the cone of depression will be addressed.