New Mexico Geological Society Annual Spring Meeting — Abstracts

Deterioration of geothermal resources due to overexploitation often results from the lack of a comprehensive water management system. We have investigated the sustainability and water management practices of the Truth or Consequences, New Mexico, hot-spring system in the southern Rio Grande Rift. There are currently ten commercial spa resorts and an estimated 158 geothermal production wells utilizing the relatively hot (~ 41 °C) groundwater within the town’s 0.6 km² historic hot-springs district. Over the last seven decades there has been an estimated 285% increase in the number of geothermal wells in this area. Theis et al. (1941) provided measurements of borehole discharge temperature, water-table elevation, artesian pressure heads, water chemistry and natural hot-spring discharge. We replicated these measurements between October 1, 2012 and September 30, 2013 for comparison to gain insight into the system’s response to development. We also estimated current water consumption and characterized diurnal temperature and pressure patterns to guide resource management.

We found that there has been virtually no change in water chemistry between 1941 and 2013. However, silica and cation-based geothermometry indicates that deep reservoir temperatures may have increased by 10 to 14%; this might be a result of drawing water from greater depths due to increased pumping in the area. Spatial discharge and temperature patterns have shifted, while temperature magnitudes show little change (~ 1 °C decline). The temperature decline is most likely due to changes in well depth, as current wells are typically 40% shallower than those of 1941. The spatial pattern of water-table elevation has changed very little, while the magnitude of mean water-table elevation has declined by approximately 0.4 meters. Additionally, artesian pressures appear to have dropped, although data are very limited. The estimated amount of natural geothermal discharge has declined by approximately 13% to 7.14 x 10^-2 m³s^-1. Overall, the evidenced changes are marginal considering the aggressive development that has taken place since 1941; thereby suggesting the system is reasonably healthy. Our analysis of daily water-table elevations and discharge temperatures in the hot-springs district indicates that fluctuations of these parameters are largely controlled by human water demand. Measured values decline during periods of high demand and recover when demand diminishes. The periods of daily recovery are believed to play an important role in mitigating long-term adverse effects of development. Data on water consumption limit our ability to make inferences about future development, as only 6.3% of appropriated water is accounted for in the current reporting system regulated by the State. While evidence suggests that the system is currently not overexploited, it is imperative that a comprehensive monitoring program and water usage reporting system be emplaced before the resource is further developed.