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C> tv i-" co cipitation and snowmelt infiltrating outcrops or seeping down through overlying aquifers and confin- ing layers. Streams incised into the Devonian and Mississippian carbonate. rocks unit in recharge areas drain some of the water in circulation. Near Meredith, for example, a spring flowing into a tributary of the Frying Pan River discharges at a rate of about 1,200 gal/min (Boettcher, 1972, p. 8). However, most of the discharge south and east of Glenwood Springs is to the Colorado River. According to. URS Corporation (1983, p. 3-25), 22 springs and diffuse seepage entering the Colorado River be- tween Dotsero and Glenwood Springs have a combined discharge of 13,500 gallmin (30.2 cu ft/s). Some of the water discharging to the Colorado River at Glenwood Springs is intercepted by the Redstone 21-9 well, which has a flowing discharge of 1,400 to 2,300 gal/min. Water not discharged to wells, springs, or streams enters the Piceance basin as subsurface flow. In the White River Plateau, water in the Devonian and Mississippian carbonate rocks unit flows radially towards the Colorado River, South Fork White River, North Fork White River, Rifle Creek and other small streams, and to the Burns basin. Recharge occurs by infiltration of precipita- tion, mainly snowmelt, over broad areas of outcrop or sub crop. However, much of this recharge is intercepted by springs within the area and either evaporates or flows into surface drainages. Seventy of these springs in Garfield and Rio Blanco Counties have a combined discharge of 2,600 gal/min (Teller and Welder, 1983, p. 13-16). Streams draining the plateau gain substantially from springs. For example, the streamflow in Rifle Creek upstream from the Rifle Falls Fish Hatchery increases by 12,600 gallmin (28 cu ft/s) from springs entering within a 4-mi reach (Teller and Welder, 1983, p. 12). In the Burns basin, water enters the hydrostratigraphic unit from outcrop areas on the flanks of the Park Range, Gore Range, and White River Plateau. A well near McCoy tapping this water supply discharges at a rate of 3,200 gal/min, with a head of 300 ft above land surface (Hampton, 1974, p. 60). In the center of the basin, water slowly percolates into overlying hydro-stratigraphic units. A divide extending along the Uinta Mountains, Axial Basin arch, and Park Range directs ground- water movement north to the Sand Wash basin or south to the Piceance basin. Additional recharge areas south of the divide include the White River Plateau and Uncompahgre Plateau. Water in the Sand Wash basin percolates into overlying hydrostratigraphic units or leaves the area by subsurface flow into the Washakie basin of Wyoming. Water in the Piceance basin either percolates into overly- ing hydrostratigraphic units or, mixing with water from the Uinta basin of Utah and the Uinta Moun- tains, discharges to springs and streams in the vicinity of the confluence of the Green and Yampa Rivers. The largest spring in this area, Split Mountain Warm Spring, discharges at a rate of 2,700 gall min (Sumsion, 1976, p. 45). 3. Hydrogeological Setting of the springs at Glenwood Springs From Eisenhauer Origin of Springs Thermal saline springs occur along the Colorado River about 3.2 km (2 mi- southwest of the Colorado-Eagle River confluence (Dotsero) near Glenwood Springs. These springs and associated ground-water systems contribute approximately 400,000 t (440,000 tons) of dissolved solids to the Colorado River per year. Measured spring flows account for about 50 percent of this amount. Most of the remainder is attributable to unseen saline groundwater seepage through river alluvium. Springs in both areas exhibit high rates of flow and issue from solution- widened joints, bedding planes, and fractures in Mississippian Leadville Limestone. Springs occur in areas where the Leadville Limestone outcrops at the level of the river. Specific springs locations are probably fault or fracture controlled. A-6