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Request#3:Additional Detail of Hydrogeology in Plate 29— Section A-A' <br /> The cross-section submitted on December 9th as Plate 29 does not show enough detail <br /> beneath the ECOSA to illustrate the relationship between the ECOSA, ECOSA underdrains, <br /> Grassy Valley perched aquifer, Grassy Valley Creek, and the portion of the area identified on <br /> Plate 9 (Rev. 1) as the "area where drainage tunnels do not cause significant head change in <br /> diatreme"which underlies the ECOSA. The vertical scale of the figure is too small to show the <br /> requested details. The Division did not request the Carlton Tunnel elevation be shown on this <br /> cross-section, as it is displayed on other figures submitted. Please increase the vertical scale <br /> of the figure as necessary to show sufficient detail for the requested features. The features of <br /> interest occur from surface to approximately 9,500 foot elevation (below the surface). <br /> Additionally, please ensure all features are labeled on the figure, including Grassy Valley <br /> Creek and monitoring wells, if appropriate. <br /> Response: <br /> The requested additional section detail for Plate 29 is presented in Plate 29a, both of which <br /> are attached to this submission. The location of Section A-A' is shown on Plate 28, which has <br /> been revised to more clearly show the location of the Amendment 11 mining activities. <br /> Plate 29a shows the upper portion of the Cripple Creek mining district, and the zones of <br /> saturation that occur as a result of the infiltration of precipitation, followed with predominantly <br /> vertical flow down into the volcanic rockmass, ultimately in general flowing to the Carlton <br /> Tunnel. <br /> The piezometric strings that have been installed to identify the groundwater flow regime are <br /> shown on the section, along with the measured groundwater elevations at each location <br /> where a piezometer has been completed. Water tables —actually the upper limits of the zones <br /> of positive water pressure in the rockmass - have been inferred from all the data. As shown, in <br /> this section both the colluvium and the underlying rock is frequently saturated. <br /> The unconsolidated material above the bedrock in Grassy Valley has been studied in detail by <br /> CC&V as part of the materials developed in support of permitting mining development into <br /> Grassy Valley. This study involved the drilling of a total of 29 soil boreholes and four <br /> piezometers on four cross sections across Grassy Valley, and the results are shown in Plate <br /> 29b. These sections show an even greater level of detail of the shallow glacial till materials in <br /> the valley, and also provide additional insight into the infiltration behavior of the shallow <br /> colluvial soil in the valley: <br /> 1. In all locations tested, the water level in the installed wells was 20 feet below the <br /> wetland ground surface, which is in general saturated. This indicates that the materials <br /> in the valley have sufficiently low vertical permeability to prevent drainage of the <br /> wetland to the subsurface, but not so low permeability as to render the material <br /> underlying the water table to be unsaturated. <br /> 2. Surrounding deep wells in the bedrock all have water levels significantly below the <br /> base of the colluvium, indicating that there is unsaturated material underlying the valley <br /> fill colluvium. The presence of this unsaturated material ensures that any actions taken <br /> by mining will not impact the rate of groundwater flow from the colluvium to the <br /> bedrock. <br /> Page 4 of 8 <br />