Salinity Contributions from Geothermal Waters to the Rio Grande and Shallow Aquifer System in the Transboundary Mesilla (United States)/Conejos-Médanos (Mexico) Basin

Jeff D Pepin,Andrew J Robertson,Shari A Kelley

doi:10.3390/w14010033

Jeff D Pepin, Andrew J Robertson + Show 1 more

Open Access

https://doi.org/10.3390/w14010033

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Abstract

Freshwater scarcity has raised concerns about the long-term availability of the water supplies within the transboundary Mesilla (United States)/Conejos-Médanos (Mexico) Basin in Texas, New Mexico, and Chihuahua. Analysis of legacy temperature data and groundwater flux estimates indicates that the region’s known geothermal systems may contribute more than 45,000 tons of dissolved solids per year to the shallow aquifer system, with around 8500 tons of dissolved solids being delivered from localized groundwater upflow zones within those geothermal systems. If this salinity flux is steady and eventually flows into the Rio Grande, it could account for 22% of the typical average annual cumulative Rio Grande salinity that leaves the basin each year—this salinity proportion could be much greater in times of low streamflow. Regional water level mapping indicates upwelling brackish waters flow towards the Rio Grande and the southern part of the Mesilla portion of the basin with some water intercepted by wells in Las Cruces and northern Chihuahua. Upwelling waters ascend from depths greater than 1 km with focused flow along fault zones, uplifted bedrock, and/or fractured igneous intrusions. Overall, this work demonstrates the utility of using heat as a groundwater tracer to identify salinity sources and further informs stakeholders on the presence of several brackish upflow zones that could notably degrade the quality of international water supplies in this developed drought-stricken region.

Highlights

Natural and anthropogenic salinization of water supplies challenges sustainable water resource management, in drought-stricken regions such as the southwesternUnited States and northern Mexico [1]
Upflow in the east is associated with the East Mesa geothermal system and the upflow profiles are within the developed portion of this system near Tortugas Mountain
Southwestern upflow is associated with the undeveloped East Potrillo geothermal system, where two upflow zones were identified along the east side of the East Potrillo Mountains

Summary

Introduction

Natural and anthropogenic salinization of water supplies challenges sustainable water resource management, in drought-stricken regions such as the southwesternUnited States and northern Mexico [1]. States) and Chihuahua (Mexico) is one populated region facing these challenges in light of declining water levels, deteriorating water quality, and increased water use on both sides of the international border (Figure 1) [2]. Driscoll and Sherson (2016) later demonstrated that during periods of minimal upstream reservoir releases (i.e., non-release seasons) within the 2009 to 2013 time period, Rio Grande salinity (as approximated by total dissolved solids (TDS)) averaged about 1500 mg/L at the basin inlet (RG-LB, Figure 1) and increased to approximately 2200 mg/L at the outlet (RG-EP, Figure 1) [4].

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