Fluid Geochemistry at the Raft River Geothermal Field, Idaho: New Data and Hydrogeological Implications

Abstract

Following a period of exploration and development in the mid-late 1970’s, there was little activity at the Raft River geothermal field for the next ~20 years. US Geothermal Inc. acquired the project in 2002, and began commercial power generation in January 2008. From mid-2004 to present, US Geothermal Inc. has collected geochemical data from geothermal and monitoring wells in the field, as well as other shallow wells in the area. An additional sampling program was completed in July 2010 to measure a wider range of trace elements and key water isotopes (δ18O, δD, and 3H (Tritium)) in the field. The data indicate that the fluid geochemistry in the field is spatially variable and complex, with two distinct deep geothermal fluid types (high vs. low K, Na, Cl, Ca, Li, F concentrations) and two groundwater fluid types. These differences have been interpreted to reflect deep structural controls on fluid pathways in the field, which has compartmentalized the fluids and limited the degree of mixing between them.