2005-06-24_REVISION - M2000016 (13)

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~1FARG E NORTH AMERICA AGGREIiATES, CONCRETE !4 ASPHALT The results of the model consider the effects of the lined pits. It is our understanding that the DIvIG is concerned with the effects on the prevailing groundwater flow in the area from the silt poxtds which will act as barriers to the groundwater flow. Because the lined pits will have a negligible effect on the groundwater tattle, it follows that the silt ponds, which compared to the lina:d pits have a high rate of permeability, will also have a negligible effect (less than 0.5 feet, plus or minus) on the groundwater flow following reclamation. 10. Page 4 of the AMEC report states, `At she end of the mine life, 10 pits will remain opened and unlined. "The permit application indicates 12 pits will remain open and unlined. If the model did not adequately represent the applied for mining condition, analyses and conclusions based upon this model cannot be validated. The applicant must address this discrepancy, and if the applied- for conditions were not modeled, provia'e a reconstructed, reanalyzed hydrologic model. The: model represents the appropriate mining and reclamation conditions, 10 pits will remain open and unlined. Please see Exhibit D l Reclamation Plan. 11. Meino Items 9 and 11: From review of the AMEC report, there is no evidence that effects of the silt storage ponds were included in the hydrologic model. Therefore, the p. IO conclusions that "the aquifer system quickly returns to normal and there is little long-term influence by the mining operations" are based upon an incomplete picture. Additionally, the extent of mounding and, shadowing created by the silt storage ponds and the clay-lined pits was not quantified or mapped. Please resolve these deficiencifs by providing an accurate model that clearly depicts these impacts. See'comment 9 above. Assuming the silt ponds result in the same impacts as the lined storage vessels, an impact of less than 0.5 feet, plus or minus, is anticipated. In actuality, the impacts will', be even less due to the higher pexme:ability of silt in comparison to lined storage. Based upon our meeting with the Division, Lafrrge understands additional modeling of the silt ponds is not Necessary at this time. 12. Menlo Item 1 Q and AMEC, p. 9: The refarred -to AMEC report provides snapshots of mine dew-2tering impacts with output from the AMEC model reflecting ground water surface elevations at the end of years 1,10,20,30, and 40, for comparison with the "baseline model. "The Division needs to see the impacts to ground water and to surface water, as applicable, of each cell when it is dewatered. The applicant needs to provide a model and maps depicting these requested data_ See comment 9 above. 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 rea,!ity, it will probably be pumped into the South Platte River, but the flow will not affect the waG>r surface elevation in the South Platte River and then fore will not affect the model results. " The .groundwater model did not explicitly model the effects of discharge from the dewatered pits to the South Platte River, though it did model the effect of the decrease in head in the pits on the LAFARGE NORTH AMERICA INC. -Lafarge Construction Materials 10170 Church Ranch Way, Suite 200, Westminster, Colorado 80021 Telephone: (303) 657-4000 Facsimile: (303) 657037