2005-04-22_REVISION - M2000016 - Laserfiche WebLink

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M-2000-016, Lafarge West, Inc.: Riverbend Operation, AM-01 Adequacy Memo #2 April 22, 2005 Page 4 water, as applicable, of each cell when it is dewatered. The applicant needs to provide a model and maps depicting these requested data. 13. (AMEC, p. 9) Please provide the basis for and explain the statements, "Ground water flows into the pit and then leaves the system. In reality, it will probably be pumped into the South Platte River, but the flow will not affect the water surface elevation in the South Platte River and therefore will not affect the model results " 14. (AMEC, p. 11) Page 11 of the AMEC report indicates that registered alluvial wells within 600 feet were identified based on SEO records. Were field inspections conducted to identify ALL wells within 600 feet? Will any wells beyond the 600-foot-radius be affected by the mine operations? 15. (AMEC, pp.11-12) Regarding Well Permit No. 2216, the report concludes, "The estimated drop in groundwater level at this well should have a minimal impact to the historic use of the well." Table 5 shows that the modeled water level change at this well during mining is -3.0 feet. What is the basis for this conclusion? 16. (AMEC, p. 12) The necessary agreement with the owner of Well Permit No. 13697, which is expected to be unusable during the life of Phase 6 Cell 1, must be obtained prior to approval of this amendment. 17. (AMEC p. 12) Well Permit No. 7280 was identified as within 600 feet, but opposite the South Platte River from the mining activities, so not expected to be sign~cantly affected. The Division agrees that impacts are not likely. However, to verify this assumption, the applicant must install or identify a monitoring well in the vicinity of this well suitable for establishing a baseline and monitoring for potential impacts. See also the Groundwater Monitoring Plan section of this memo. 18. (AMEC p. 12) What were the criteria and how was it determined that "only one of these wells [of the 4non-Lafarge wells within 600 feet] should not have the ability to pump at historic rates?" The applicant must commit to specific criteria for establishing that "well yields cannot be met and mining dewatering is determined to be the cause of reduced well yield." The applicant must also state what measures will be taken to mitigate well impacts, rather than provide a list of possibilities. 19. (AMEC, p. 14) The applicant must explain the statement, "Groundwater monitoring of existing monitoring and production well water levels should be completed as mine operations proceed." Additionally, the applicant must provide a plan to check calibration of the ground water model by comparing predicted to actual drawdown in the monitoring wells, and recalibrating the model as necessary. 20. Memo Item 12: Please provide documentation as to whether onsite wetlands and potentially impacted wetlands offsite are considered jurisdictional wetlands by the US Army Corps of Engineers. Absent of this documentation, all of these wetlands will be assumed to be jurisdictional. • For all jurisdictional wetlands that will need to be replaced on site, the applicant must submit a plan for replacing these wetlands so the Division can calculate the bond necessary to implement the plan. • For any offsite wetlands, please describe how any impacts to wetlands will be identified and the mitigation measures the applicant will take to minimize disturbances to the hydrologic balance in relation to these wetlands.