Water resources of Teton County, Wyoming, exclusive of Yellowstone National Park

Nolan, Bernard; Miller, Kirk

Surface- and ground-water data were compiled and analyzed to summarize the water resources of Teton County, exclusive of Yellowstone National Park. This study, prepared in cooperation with the Wyoming State Engineer, is one in a series describing the water resources of Wyoming counties. The wells and springs inventoried in the Teton County study area most commonly were completed in or issued from unconsolidated deposits of Quaternary age, and rocks of Tertiary, Mesozoic, and Paleozoic age. The largest discharges measured, reported, or estimated were from Quaternary unconsolidated deposits (3,000 gallons per minute), the Bacon Ridge Sandstone of Cretaceous age (800 gallons per minute), and the Madison Limestone of Mississippian age (800 gallons per minute). Discharges from all other geologic units differed but most wells and springs yielded 25 gallons per minute or less. A time-domain electromagnetic survey of Jackson Hole indicated that the depth of the Quaternary unconsolidated deposits ranged from about 380 feet in the northern part of Antelope Flats to about 2,400 feet near the Potholes area in Grand Teton National Park. Electrical resistivity, a general indicator of grain size in subsurface rock, ranged from 2 to 380 ohm-meters. The low values are assumed to represent less permeable (fine-grained) materials such as claystones, shales, siltstones, or fine-grained sandstones, and the higher values are assumed to represent coarse-grained materials such as sand and gravel. Streamflow in the study area is both perennial and intermittent. Most streams originate in the mountains and are perennial, although some streams are intermittent along a particular reach in some years. The Gros Ventre River at Zenich flowed intermittently for brief periods in 1988 and 1992. Ground water is recharged by infiltration of precipitation, streamflow leakage, irrigation water, and inflow from other aquifers. Ground water is discharged through pumped wells and is naturally discharged by springs and seeps, by evapotranspiration, and by discharge to streams and other geologic units. In a gain-and-loss study of the Snake River, the estimated ground-water discharge for a stream reach between streamflow-gaging stations near Moran and south of the Flat Creek confluence was 395 cubic feet per second. Geostatistical methods were used to generate water-level contours from 137 water-level measurements in selected Quaternary unconsolidated deposits and 118 stream altitudes. The waterlevel contours indicate that ground water flows from topographically high areas toward the Snake River and southwest through the valley in the general direction of the river. Water levels were deeper in October than July 1993, in all but 1 of 27 wells completed in Quaternary unconsolidated deposits and remeasured in October 1993. The median change was -1.76 feet. Dissolved-solids concentrations in water samples from Quaternary unconsolidated deposits and rocks of Tertiary, Mesozoic, and Paleozoic age ranged from 80 to 1,060 milligrams per liter. A water sample collected from a rhyolite flow of Quaternary age had the lowest dissolved-solids concentration (22 milligrams per liter) in the study area. The largest nitrite-plus-nitrate concentrations were found in water samples collected from Quaternary landslide deposits (7.50 milligrams per liter) and the Bear River Formation of Cretaceous age (9.70 milligrams per liter). Water type varied between lithologic groupings.

Water resources of Teton County, Wyoming, exclusive of Yellowstone National Park

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