The U.S. Geological Survey water quality file WATSTORE contains chemical analyses for several hundred thousand ground-water samples from the United States. Nearly 100,000 of these analyses are sufficiently complete to be of use in geothermal exploration. Through examination of about 500 analyses of samples from the Imperial Valley, California, supplemented by an additional 8,000 analyses from adjacent parts of the Basin and Range province, we have established normal ranges for the various chemical geothermal indicators and the criteria by which a geothermal water may be recognized. For the Imperial Valley, California, we propose the following values as signifying potential geothermal water: silica geotemperature, > 100 °C; Na-K-Ca geotemperature, > 125 °C; fluoride, >2.5 ppm; in situ temperature, >35 °C; heat flow, > 120 mW m−2.
We used these criteria to scan WATSTORE for potential geothermal prospects in the Imperial Valley. This scan outlined at least ten major anomalous areas, including all but one of the six Known Geothermal Resource Areas (KGRAs). The rediscovery of the KGRAs underscores the potential value of WATSTORE as a rapid reconnaissance tool in geothermal exploration. Anomalous areas that are not KGRAs are located east and west of the Salton Sea (Hot Mineral Well and Holly Hot Well), near Coyote Wells, near Camp Dunlap, and east of Brawley. Smaller anomalies are present throughout the study area, particularly along the Brawley fault and the southern extension of the San Andreas fault zone.