Hydrogeologic, geophysical, water-quality, transient-tracer, and flow-model analysis of the ground-water flow system near Dillon, Montana

The purpose of the report is describe the groundwater flow system in the basin-fill aquifer in the lower Blacktail Deer Creek, lower Beaverhead River, and lower Rattlesnake Creek valleys near Dillon. Specific objectives of the study, conducted during 1993--1994, were to: (1) Describe the ground-water flow system in the basin-fill aquifer using water-level data; (2) Help to further define the hydrogeologic framework of the basin-fill aquifer using the geophysical technique, seismic refraction; (3) Differentiate sources of recharge to the aquifer based on water-quality data collected in the study area; (4) Determine the ages of groundwater in the aquifer from samples collected from wells throughout the study area using chlorofluorocarbon (CFC) and tritium and helium isotope (({sup 3}H)-({sup 3}He)) dating techniques; and (5) Develop a conceptual and numerical cross-sectional ground-water flow model of the flow system along a designated flow path in the aquifer.