EVALUATION OF GROUND-WATER CHEMISTRY IN CURLEW VALLEY, UTAH AND IDAHO

Curlew Valley is a Y-shaped valley located in northern Utah and southern Idaho. Three ground-water flow systems (Kelton, Juniper-Black Pine, and Holbrook-Snowville) exist in the valley. A group of six springs, called the Locomotive Springs, discharges near the shore of Great Salt Lake, and provides water for a waterfowl management area. Discharge from the springs has significantly declined in recent years, accompanied by ground-water level decline in wells throughout Curlew Valley. The Utah Geological Survey collected water samples from wells and one of the Locomotive Springs and analyzed them for general chemistry, oxygen-18, deuterium, tritium, carbon-14, and carbon-13 to determine the source, movement, and age of ground water in Curlew Valley.

Temporal water chemistry data obtained from the Utah Department of Agriculture and Food indicate that ground-water quality has deteriorated in the central part of the valley, which is evident by a large plume of high electrical-conductivity ground water. The major ions in the high electrical-conductivity ground water are sodium and chloride. Agriculture is the dominant land use in the valley and relies primarily on ground water for crop irrigation. The salination of ground water is likely a result of application of irrigation water to the agriculture fields. Chemical and isotopic data suggest that transpiration is causing the build up of salts in the soil, not evaporation.

Oxygen-18 and deuterium isotopic data from the three flow systems each plot together indicating similar sources. All data plots below the global meteoric water line suggesting evaporation of recharge water. Bar M spring data, from the Locomotive Springs, plot between the Holbrook-Snowville and the Juniper-Black Pine flow-system data, suggesting ground water discharged from Bar M spring is derived from both flow systems. Tritium and carbon-14 data indicate that ground water from the Holbrook-Snowville and Kelton flow systems consists mainly of modern ground water. The age of ground water in the Juniper-Black Pine flow system is between 3500 and 12,000 years old; ground water from this flow system may have been recharged during cooler climatic conditions. Bar M spring was dated at 1400 years old, which also suggests mixing between the Juniper-Black Pine and Holbrook-Snowville flow systems.