Thermal springs in the Payette River basin, west-central Idaho

The Payette River basin, characterized by steep, rugged mountains and narrow river valleys, occupies an area of about 3 ,300 square miles in west-central Idaho. Predominant rock types in the basin include granitic rocks of the Idaho batholith and basalt flows of the Columbia River Basalt Group. Waters from thermal springs in the basin, temperatures of which range from 34 to 86 degrees Celsius, are sodium bicarbonate types and are slightly alkaline. Dissolved-solids concentrations range from 173 to 470 milligrams per liter. Reservoir temperatures determined from the sodium-potassium-calcium and silicic acid-corrected silica geothermometers range from 53 to 143 degrees Celsius. Tritium, present in concentrations between 0 and 2 tritium units, indicate sampled thermal waters are at least 100 years old and possibly more than 1,000 years old. Stable isotope data indicate it is unlikely any of the nonthermal waters sampled are representative of precipitation that recharges the thermal springs in the basin. Thermal springs discharged about 5,700 acre-feet of water in 1979. Associated convective heat flux is 1.1x10 to the 7th power calories per second. (USGS)