A s part of development of a regional source water protection plan, in 2015–2016, the New Mexico Bureau of Geology and Mineral Resources performed a technical review of existing hydrogeology studies in Curry and Roosevelt counties in east-central New Mexico. Additionally, groundwater quality was tested in several wells, and groundwater levels were examined to provide up-to-date information on the availability of groundwater in the region. This report describes the results of the hydrogeologic review and findings from the groundwater study.

The agricultural economy of Union County in northeastern New Mexico is highly dependent on groundwater. Ongoing drought, large new groundwater appropriations both within the county and in adjacent parts of Texas, and large water level declines in wells have led to concern amongst county residents over groundwater supplies. This report documents the finding of a hydrogeology study begun in 2010 to better understand the aquifers utilized in east-central Union County. The study covers 650 square miles and extends from north of Clayton to south of Sedan, and east to the state line. The study was jointly sponsored by Northeastern Soil and Water Conservation District (NESWCD) and the Aquifer Mapping Program of the New Mexico Bureau of Geology and Mineral Resources. The goals of the study were to refine the existing geologic map of the area, describe the geologic framework of the aquifers that are utilized, describe present and historic water levels and trends over time, and utilize these data with geochemistry and age-dating techniques to understand the occurrence, age, and flowpaths of groundwater, and to identify the locations and processes of groundwater recharge.

Between August 2006 and April 2007, the New Mexico Bureau of Geology and Mineral Resources conducted a spring inventory and preliminary geochemical sampling as a first step in evaluating the hydrogeologic connections between the ground water and the Rio Grande in Taos County. The objective and principal task was to locate, inventory, describe, and selectively sample the springs of the Rio Grande gorge. The springs in the Rio Grande gorge appear to naturally fall into zones or clusters that coincide with either a hydrologically important geologic feature, such as a fault or a volcano, or one of the perennial tributaries of the Rio Grande. Spring data are evaluated in the context of the regional geologic and hydrologic framework. Basic data are presented for springs surveyed in the following locations: • the Sunshine Valley in the Ute Mountain reach, • the Cerro Chiflo area, above the Cerro gaging station, • the west side of the gorge near Bear Crossing, • the Arroyo Hondo area, • Taos Junction Bridge, • Pilar, and • The Racecourse reach of the Rio Grande, between the BLM quartzite site and the county line. Water samples were collected from 31 springs and analyzed for general chemistry, trace metals, stable isotopes, and for several relative age-dating analyses, including tritium, chlorofluorocarbons (CFCs), and carbon-14. The report contains maps of the locations of inventoried springs, data tables that characterize the springs, the results of geochemical sampling and laboratory analysis of spring water chemistry and a variety of tracers, and a brief summary of the location and field parameters of each major cluster of springs.