Roswell Basin Aquifer

The Roswell Artesian Basin consists of an eastward-dipping carbonate aquifer overlain by a leaky evaporitic confining unit, overlain in turn by an unconfined alluvial aquifer. The carbonate aquifer is artesian to the east but under water-table conditions in the western outcrop area.

Water-producing zones in the carbonate aquifer rise stratigraphically from north to south and from west to east. Some wells may penetrate as many as five water-producing zones. Secondary porosity is developed in vuggy and cavernous limestone, solution-collapse breccia, and solution-enlarged fractures. Recharge occurs by direct infiltration of precipitation and by runoff from intermittent losing streams flowing eastward across a broad area east of the Sacramento Mountains.

During the initial development of the artesian aquifer, many wells flowed to the surface and high volume springs fed the Pecos River. Decades of intensive pumping have caused substantial declines in hydraulic head in the aquifer, and by the mid-20th century it was estimated that withdrawals exceeded recharge. Most down-gradient flow is intercepted by irrigation wells in the Artesian Basin. Mineral content of the water rapidly increases in an eastward direction. Chloride concentrations range from about 15 mg/kg in the unconfined area to as much as 7,000 mg/kg in an artesian well east of Roswell, N.M. Chloride concentration also increases with depth. The freshwater-saltwater interface migrates westward during periods of low rainfall.

The carbonate aquifer provides habitat for several federally listed endangered invertebrate species: the Roswell springsnail (Pyrgulopsis roswellensis), Koster's springsnail (Juturnia kosteri), and Noel's amphipod (Gammarus desperatus) are listed as endangered and the Pecos assiminea (Assiminea pecos) is listed as endangered with critical habitat under the Endangered Species Act of 1973, as amended (Act). These four invertebrates occur at sinkholes, springs, and associated spring runs and wetland habitats. They are found at one site in Chaves County, New Mexico, and Pecos assiminea is also found at one site in Pecos County, Texas, and one site in Reeves County, Texas.