2005-06-24_REVISION - M2000016 (13)

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~-FARG E NCIRTH AMERICA AGGREGATES, CONCRETE Ei ASPHALT determine the cause of the problem and. if necessary, implement measures to either restore the we] 1's output or provide a temporary alternate supply of water to the owner. 18. (Ah1EC, p.12J 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 speciftc criteria for establishing that "well yields cannot be met ana' 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. Lafarge has committed to specific measures to protect surrounding well owners for adverse effects from the mining operafion in the Groundwater Monitoring Program previously submitted to your office. The language in the Groundwater Monitoring Program simply suggests that there are alternate means of remedying any effects on surrounding wells, and, as confirmed at our recent meeting, Lafarge is not required to commit to one specific course of action. 1 R (AhfEC, p.14) The applicant must explain the statement, "Groundwater monitoring of existing monitoring and production well water IE vels 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. The primary purpose of the groundwater model is to predict the maximum extent of effects to the prevailing hydrologic balance from the Honing operaton in order to determine locations where monitoring wells should be located to protect sun-ounding property owners. The results of the groindwater model show that the proposed groundwater monitoring plan will be sufficient to identify adverse effects to surrounding wells or other structures in a proactive manner. If, for example, a surrounding well shows signs of adverse effects resulting from the mining operation, at that time the monitoring data can be used to determine if the adverse effects to the well are linked to the mining operation. The grorndwater model could then be used at such a time to help undclrstand how the mining operation may be influencing the effects on the well. The monitoring data' can at that time be used to refine the model to develop a better understanding of how the mining operation may be affecting the well. We are not aware of any instances where the DMG has required operators of gravel pits to model their operations on an ongoing basis. Only when the monitoring wells show that a surrounding strucaure could be affected by the mining operation may an update to the groundwater model be required, though this may not be necessary depending on the circumstances. 20. Menzo 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. o 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. LAFARGE NORTH AMERICA INC. -Lafarge Construction Materials 10170 Church Ranch Way, Suite 200, Westminster, Colorado 80021 Telephone: (303) 657-4000 Facsimile: (303) 657-4037