Using Heat as a Tracer to Estimate Deep Saline Groundwater Inputs to the Rio Grande in the Mesilla Basin, New Mexico, USA

Pepin, Jeff

Using Heat as a Tracer to Estimate Deep Saline Groundwater Inputs to the Rio Grande in the Mesilla Basin, New Mexico, USA

Tuesday, February 27, 2018: 3:00 p.m.

Jeff Pepin , New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Andrew Robertson , New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Christina Ferguson , New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Erick Burns , Oregon Water Science Center, U.S. Geological Survey, Portland, OR

Profiles of temperature with depth below ground surface are used to locate groundwater upflow zones and to estimate associated salinity fluxes from deep (greater than 1 km) parts of the Mesilla Basin regional aquifer to the Rio Grande. The Mesilla Basin in southern New Mexico, western Texas, and northern Chihuahua, Mexico, where it is known as the Conejos-Médanos Basin, was designated by the United States as a priority transboundary aquifer in part because of the presence of the Rio Grande within the basin. Declining water levels, deteriorating water quality, and increasing use of water resources on both sides of the international border raise concerns about the sustainability of regional water supplies. The Rio Grande wintertime chloride concentration more than doubles (120 ppm to 280 ppm) as the river flows through 70 miles of the Mesilla Basin. Previous researchers attributed this reduction in water quality to the upwelling of deep sedimentary brines and geothermal waters within the basin. However, the spatial distribution of these upflow zones and their groundwater flow rates are poorly understood. Temperature profiles from 373 existing boreholes within the basin are affected by the advection of heat, resulting in characteristic thermal signatures at upflow zones. At least three distinct upflow zones near regional faults have been identified. The Bredehoeft and Papadopulos (1965) one-dimensional heat-transport analytical solution is applied to upflow-zone profiles to estimate their corresponding vertical groundwater flow rates. Temperature, heat flow, and salinity maps are constructed to approximate the areal extents of identified upflow zones. These areal estimates are then combined with the vertical groundwater flow calculations and salinity data to quantify volumetric salinity fluxes to the shallow aquifer system and Rio Grande. The results of this study will inform understanding of the impact of deep saline groundwater on regional water supplies for the Mesilla Basin.

Jeff Pepin, New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Jeff is a hydrology Ph.D. Candidate at New Mexico Tech and student intern at the USGS New Mexico Water Science Center. He specializes in geothermal systems, electromagnetic geophysics (MT, AMT, and TEM), and applied geostatistics.

Andrew Robertson, New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Andrew Robertson is a hydrologist and a unit chief for the hydrogeology and geochemistry program area at the New Mexico Water Science Center. Andrew received a M.S. degree in Water Resources from the University of New Mexico. Since joining the USGS in in 2008, Andrew's work has been focused on using geochemical and isotopic tracers to answer questions relating to groundwater hydrology and contaminant fate and transport.

Christina Ferguson, New Mexico Water Science Center, U.S. Geological Survey, Albuquerque, NM

Christina is a M.S. student at the University of New Mexico and student intern at the USGS New Mexico Water Science Center.

Erick Burns, Oregon Water Science Center, U.S. Geological Survey, Portland, OR

Erick Burns has a diverse professional background, including house painter, sailor, bartender, nuclear power plant operator, teacher, barrista, and hydrogeologist. In 1992, he returned to early interests in geology and the natural world that arose from growing up in the desert. He obtained a Geology degree from Northern Arizona University in 1994 followed by a M.S. degree in Hydrologic Sciences from the University of Nevada – Reno in 1996, and a M.S. degree in Applied Mathematics and a PhD in Bioresource Engineering from Oregon State University in 2004. His research interests are diverse, including: study of coupled groundwater and heat flow, regional groundwater flow modeling, the use of geostatistical methods to understand trends and predictive uncertainty, the use of imperfect data to reduce uncertainty in water resource management, and the use of process thermodynamics to understand non-ideal behavior of fluids in soils. During his 15 years as a practicing hydrogeologist, Erick has worked as a consultant, a regulator, a university researcher and educator, and since 2006, he has served as a project hydrogeologist for the U.S. Geological Survey, conducting groundwater and heat flow studies across a variety of scales and terrains.