Chemistry of Low-Temperature Geothermal Waters at Klamath Falls, Oregon

Abstract

Thermal water at Klamath Falls, Oregon, occurs in a heterogeneous aquifer at depths of 60 to 610 meters over an area of about 5 square kilometers. Waters measuring 70 to 100°C are utilized for district space heating. These thermal waters meter the shallow aquifer through a permeable fault zone on the northeast side of the city, and undergo mixing and cooling as they flow southwestward. Chemical and isotopic analyses of well discharges indicate that in the aquifer mixing occurs between shallow cold groundwater containing 2.0 TU tritium and a deeper tritium free thermal groundwater at 100 to 120°C. This deeper water apparently results from the mixing of old, tritium free cold groundwater and deep thermal groundwater at about 190°C and 120 mg/kg C1. The temperature and chlorinity of the deep thermal water are based on SO4 isotope and silica geothermometers an chloride and silica mixing models.