Hydrochemistry of selected parameters at the Raft River KGRA, Cassia County, Idaho

Low to moderate temperature (< 150/sup 0/C) geothermal fluids are being developed in the southern Raft River Valley of Idaho. Five deep geothermal wells ranging in depth from 4911 feet to 6543 feet (1490 to 1980 meters) and two intermediate depth (3858 feet or 1170 meters) injection wells have been drilled within the Raft River KGRA. Several shallower (1423-500 feet or 430-150 meters) wells have also been constructed to monitor the environmental effects of geothermal development of the shallower aquifer systems. Sampling of water from wells within the KGRA has been conducted since the onset of the project in 1974. Five analytical laboratories have conducted analyses on waters from the KGRA. Charge-balance error calculations conducted on the data produced from these laboratories indicated that data from three laboratories were reliable while two were not. A method of equating all data was established by using linear regression analyses on sets of paired data from various laboratories. The chemical data collected from the deep geothermal wells indicates that a two reservoir system exists within the Raft River KGRA. Each reservoir is associated with a major structural feature. These features are known as the Bridge Fault System (BFS) and the Narrows Structure (NS).