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CCU0d3 ANALYSIS OF PROPOSED SALT PRODUCTION FROM THERMAL WATERS AT GLENWOOD SPRINGS, COLORADO ~ February 7, 1994 Q ~ Thermal springs at Glenwood, Colorado contribute 440,000 tons of salt each year to the flow of the Colorado River. It has been proposed that this addition of salt can be reduced significantly by producing saline water from wells, extraction of the salt for commercial use, and disposal of the desalinated water to the River. In particilar, the "Redstone 29-1 Well" is an existing well under con- sideration for salt production. An important economic consideration is determination of whether the amount of salt entering the River is reduced by an amount reasonably close to amount of salt ex- tracted from well water. The analysis presented here is based almost entirely on three reports, two by Eisenhauer (1983, 1986) and one by Geldon (1989). These reports contain much relevant informa- tion on the geochemistry and geology of the Glenwood Hot Psrings, on well tests that were carried out in the Redstone 29-1 Well, and on regional hydrogeology. The ground water regime in the vicinity of Glenwood Springs has been well studied over the past two decades as a consequence of interest in producing thermal waters for heat and energy production. Information about the saline thermal waters and the relevant geology and hydrogeology are easily available from recent reviews by Eisenhauer (1983) and by Geldon (1989). In addition to these sources, geophysical data on the Glenwood Springs thermal area are available from the Geo- physics Department, Colorado School of Mines. These three sources were the basis for the following analysis. 1. Geological Setting of the Glenwood Thermal Springs: Above and below Glenwood Springs, the Colorado River is deeply incised into a sequence of sedimentary rocks of Paleozoic age. The older rocks are largely carbonate in composition, while the younger are arenaceous in character, sandstone and shale. Total thickness in the vicinity of Glenwood Springs is about 5600 feet. At Glenwood Springs, the canyon of the Colorado River has cut about two thirds of the way through this sequence, with Leadville limestone (Mississippian age) being exposed in a keystone fault block beneath the city of Glenwood Springs (see Fig. 1). This structure is the reason for the existence of the thermal springs. 2. Regional Hydrogeology: Devonian-Mississippian carbonate rocks and Pennsylvanian- Permian sandstones form the two important regional aquifers over most of northwestern Colorado. At Glenwood Springs, where the Colorado River has cut through the upper regional aquifer, thermal springs are supplied by waters from the lower carbonate aquifer, and in particular, by the Leadville limestone. Geldon (1989) compiled maps (Figures 2, 3, and 4) showing the potentiometric head, hy- draulic conductivity and transmissivity in the carbonate regional aquifer over northwestern Colorado. While these maps are based on relatively sparse data, they show clearly the regional support for the Glenwood thermal springs. Regionally, except for a small area around Glenwood Springs, the hy- draulic conductivity (a measure of the ease with which fluid can be driven through a rock) is modest, falling in the range from 0.001 to 1 foot per day. The regional pattern shows a belt of high hydraulic conductivity, in the range from 1 to 10 feet per day, extending from northwest to southeast through Glenwood Springs. At Glenwood Springs, hydraulic conductivity is 10 to 100 times greater. The ,/ 8271.300 1