2005-07-13_REVISION - M2000016 (27)

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FEB-II-05 IT:05 FROM-Colorado Division of Minerals b 6¢olo¢y +130386635Ei T-855 P 038lOIIr-52E At-2000-016, Lafarge Wesl. Ina: Riverbend Operaran, Ah1-01 February 71, 2005 Adequacy Memo Page 3 t2. The applicant needs to describe how the drawdown of the pits and any shadowing mounding effects will impact the structural integrity of the surrounding wells, surface water drainages, activities which rely on groundwater in the vicinity of the site, and vegetation on or near the site (including the cottonwood trees in the riparian area near the South Platte River and the wetlands located adjacent to the pits}. The applicant must also describe any mitigation measures to be implemented and trigger points that would put mitigation measures into effect. 13. The Division has concerns that there may be effects on the amount of water conveyed in the Fort Lupton Bottom Ditch, the Brighton Ditch, and Big Dry Creek due to dewatedng of the pit. The applicant must project the amount of water that will be lost from these structures if these structures Teak 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 im~estigaticn. If this issue has not been addressed, they must investigate the potential impacts to the water conveyed in these ditches and submit the results to the Division for review. t4. Due to the potential for permanent impacts to ground water, the applicant may need to take permanent mitigation measures such as installing French drains. The applicant should consider this eventuality and respond to this concern. Groundwater Monitoring Plan: 16. Page 24 of 81 of Exhibit G and Table 1 by AMEC (following p. 27 of 81 -Gravel Well Permit Application} indicate that 13 wells are within 600 feet of the site, with 2 potentially impacted, and the "Groundwater Monitoring Plan" states 20 wells are within 600 feet with 6 potentially impacted. Please investigate and correct these values, well listings, and associated maps so that the permit application is consistent. 76. Based upon the strong potential for ground water impacts from dewatering 12 large open pits and lining three pits, additional monitoring wells will need to be selected and/or installed to ensure compliance with Rute 3.'1.6(1) of the Construction Material Rules and Regulations, which requires that "tlisturbances to the prevailing hydrologic balance of the affected land and to the surounding area and to the quantity and quality of water in surface and groundwater systems both during and after the mining operation and during reclamation shall be minimized....' The applicant must also provide a list or table showing Well Permit numbers and constructed depths for all the monitoring wells. 17. Once the monitoring well quantities and positions are deemed adequate by the Division, to establish baseline ground water levels, monitoring frequency for ground water levels in the monitoring wells will need to be increased to monthly. One full year of monthly data will need to be collected and reported prior to beginning mining. The data submitted with the application is inadequate in frequency and extent of monitoring ~ryells. A technical revision will be required to reduce monitoring frequency. t8. Section 32 of the "Groundwater Monitoring Plan" proposes mitigation measures for alleviating offsite ground water impacts which include delivering water by "pumping and piping or by a drain system," -delivering replacement water by pumping dewatering water to the affected party(s), pumping from the onsite wells, and delivery from the Brighton Ditch shares controlled by the operator-' II appears that changes of water rights may be necessary for implementation of these mitigation measures. For water sources to be legally available when needed for mitigation, they likely need to be included in the Substitute Water Supply Plan ('SWSP') submitted to the Office of the Stato Engineer ("OSE"). The applicant must ensure this mitigation water is approved for those uses