A low-temperature geothermal system in central Mexico: Hydrogeochemistry and potential heat source

The groundwater of low-temperature geothermal systems located in the Mexican Highlands is used as an urban water supply owing to water scarcity in the area. In the Juventino Rosas (JR) area, central Mexico, the highest well temperature is 508 degrees C; most of the hot waters range from 248 degrees C to 488 degrees C. The aquifer systems are formed mainly by Oligocene-Pliocene rhyolite-ignimbrite rocks, basaltic-andesitic rocks of the Trans Mexican Volcanic Belt (TMVB), and Quaternary sediments that filled the valleys. The groundwater of these aquifers contains hazardous elements such as arsenic at 0.0026-0.045 mg/L, fluoride at 0.569-3.03 mg/L, and radon at 1,000-52,300 Bq/m(3). Tectonic and subsidence faults and fractures allow rapid ascension of geothermal flow. The presence of this flow was corroborated by the water geochemistry and the water table behavior. Hydrogeochemical modeling was used to define this system as low temperature rather than geothermal.