Geochemical Assessment of San Bernardino Geothermal Well Waters after Ten Years of Production

Abstract

Hot water wells in the South San Bernardino Geothermal Area, California produce 54-58°C mixtures of geothermal and near surface waters from sedimentary aquifers at depths of <400 m. Wellhead temperatures have fluctuated slightly since two production wells have been used to supply the geothermal district heating project, but a decease of >3°C observed in Spring 1990 is uncommon. Well water samples collected in April 1990 yield the lowest geothermometry results and water compositions verify that the samples contain the most near surface water and of any collected to date. However, temperatures measured in deep sedimentary aquifers have not changed appreciable since 1984. Well production temperatures are evidently controlled more by local recharge, lithogies, pumping rates, and the condition of the wells than variations in reservoir temperatures. Utilization of the resources has not and is not anticipated to affect the temperatures of geothermal aquifers at depth in the sedimentary reservoir.