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<br />Page 5 <br /> <br /><::> <br />l\J <br />W <br />w <br /> <br />to have very low hydraulic conductivity. <br /> <br />Another consideration in defining the recharge area is the relatively rapid seasonal response of <br />the Leadville Limestone. There are numerous observations of increased water levels in wells <br />and increased spring discharge after particularly wet winter periods (Galloway, 1985). The <br />resolution of existing water level data is not sufficient to see responses to major precipitation <br />events, but rather generally wet or dry periods. This suggests that most of the groundwater flow <br />path is within the highly permeable Leadville and very little restriction exists in the recharge <br />area, either because of faulting/fracturing, limited thicknesses of low permeability material, or <br />the Leadville is exposed at the surface. <br /> <br />The general conclusion of all investigators regarding the source of the thermal water is deep <br />circulation within an enhanced geothermal gradient. There is no evidence for a specific heat <br />source. Groundwater would have to circulate to depths of 4,000 to 6,000 feet within a gradient <br />of 30 degrees C per kilometer (Repplier and Fargo, 1981) to obtain the maximum observed <br />groundwater temperatures. It is reasonable to assume that the geologic structures in this area <br />permit water circulation to these depths. <br /> <br />Summary of Conceptual Model <br /> <br />1. Runoff due to precipitation infiltrates over a relatively large area underlain by Eagle <br />Valley Evaporites. The recharge area(s) are located at elevations greater than Glenwood <br />Springs (Figure 2). <br /> <br />la. Alternately, infiltration occurs where the Leadville Limestone is at the surface and does <br />not come in contact with salt units until much deeper within the structure (Figure 4). <br /> <br />2. As the infiltrating water percolates downward, salt deposits are dissolved, increasing <br />groundwater salinity. <br /> <br />3. Either because of faulting or limited thickness of Belden Shale, groundwater moves <br />rapidly into the Leadville Limestone. <br /> <br />Michael J. Galloway <br />ConsuIJlng [[ydrogeologlst <br /> <br />ProjecllOI6 <br />