2008-08-25_REVISION - M1980244 - Laserfiche WebLink

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c) Under infiltration the operator states, "taken as an infiltration rate over the foot print of the diaterme, the average Carlton Tunnel Portal flow represents an infiltration rate of 6.99 inches per year or 37% of total precipitation of 19.58 inches. This is a high infiltration rate; the expected value could be no more than 25 % based on infiltration evaluations of mountain basins in Nevada". Do these mountain basins in Nevada have the same geologic conditions and under ground working developments as the ones encountered in the Cripple Creek Mining District? Please provide the appropriate data to support your conclusions. In lieu of the supporting data, the DRMS will require the operator to utilize the higher infiltration rate taken as the average as stated above unless the supporting dat for the mountain basins in Nevada is provided. d) The operator states, "The Carlton Tunnel today captures essentially all the ground water in the district. The flow from the Carlton Tunnel represents the collection of ground water infiltration to the diatremal materials as described". Under the infiltration section, the operator states," Evaluation of the data indicates that the infiltration rate is not in fact representative of the ground water system in the district. On an annual basis the infiltration rate has been computed in the same way and the results are presented in Figure 5. This figure shows that the ground water yield decreases with precipitation, indicating that some process other than precipitation and infiltration is influencing the flow rates at the Carlton Tunnel. Under "Impacts of Mining", the operator states, "The infiltration to the regional groundwater system is driven by precipitation". The Division is a bit confused by the conflicting statement. Is CC&V saying the discharge from the Carlton Tunnel could be impacted by other unknown contributors, other than the rate of infiltration from the mining district expressing itself as ground water flow at the tunnel? Please explain. E. CC&V'S consultants stated, "during development of the proposed MLE, project activities, the net effect of the WHEX portion of the East Cresson Mine and the ECOSA is expected to reduce flows to Grassy Creek. The current average annual flow rate is about 40 gpm. Modeling results, including sensitivity analyses, suggests that during development the average annual flow rate at GV-03 may range from 25 to 31 inches. Please provide a detailed flow rate measuring plan for Grassy Creek and piezometer water level measuring plan for the riparian areas for approval by the DRMS. Is the shallow alluvium aquifer that currently feeds the wetlands in these areas disconnected from the bed rock aquifer? Has CC&V conducted a well draw down pump test, to show these two aquifers are not connected? What about existing fracture zones in the bed rock, what impact will additional mining have on the transmissivity of water from the alluvial aquifer to the bed rock aquifer? With out well draw down pumping tests to show the disconnection of the alluvial aquifer from the deep bed rock aquifer, how can CC&V assure the Division that the wetlands will not be permanently affected when mining extends beyond the elevation of the alluvial aquifer? CC&V's hydrologic consultants recommended that the operator supplement additional water to the Grassy Valley Creek to maintain flow rates similar to those currently observed throughout the year due to the expected impact of mining in the Wild Horse East Cresson Mine Expansion area, which will lower the water shed feeding the creek & wetlands. The expected decrease based on the mass balance will range anywhere from 20 % to 30% of the total flow. Where would this supplemental water come from? Where is the warranty for the purchase of this water in Exhibit "L"? Worst case scenario, the Division would like to see analyzed would be that the proposed mining activities could cut of the flow in Grassy 9