2008-09-17_REVISION - M1980244 (28)

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is presently no observable flow from the Moffat Tunnel portal and no flow has been observed • in decades from the Moffat Tunnel portal. b) Roosevelt Tunnel 1. Again the operator states "flow from the tunnel largely ceased when the Carlton Tunnel was installed at a lower elevation ". Flows from the Roosevelt tunnel have never ceased and continue to flow to Cripple Creek. The argument used by CC&V, when requested by the Colorado Department of Public Health and Environment (CDPHE), to permit the discharge from the tunnel was, to prove there was no connection from the areas being impacted by CC&V'S current activities up gradient of the tunnel discharge. A flow rate from the portal has been measured by both the DRMS and CC&V and data should be available. Please explain. Response: The statement made by CC&V is correct. The flow from the Roosevelt Tunnel was historically as high as 12,000 gpm, and dropped to a few gallons per minute after the installation of the Carlton Tunnel in 1941 (Figure 3 included as Attachment 8). The last measurements taken by CC&V showed the flow to be variable, averaging 16 gpm (CC&V, Amendment No. 8). This flow is insignificant, and does not derive from the diatreme, as shown by repeated inspections of the tunnel. For the purposes of the water balance evaluation, the diatremal flow is considered, so any current flow from the Roosevelt Tunnel is not • included. c) Under infiltration the operator states, "taken as an infiltration rate over the foot print of the diatreme, 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 data for the mountain basins in Nevada is provided. Response: The statement in the report is that "the expected value would be no more than 25%, based on infiltration in mountain basins in Nevada." CC&V stands by this statement as a reasonable expectation, based on this study, which remains the most accepted evaluation of infiltration in mountain terrains. The Nevada mountain basins have similar geoltydrologic conditions to the conditions at the Cripple Creek diatreme: • The (vertical) hydraulic conductivity of the rockmass is in general higher than the infiltration rate, allowing infiltrating water to enter the deep ground water regime. • The presence or absence of underground wvorkings in the hydrogeologic conditions occurring at both the Nevada mountain basins and in the Cripple Creek diatreme are 26