New Mexico Geological Society Annual Spring Meeting — Abstracts

The Salt Basin is a closed drainage basin located in southeastern New Mexico and northwestern Texas. Since the 1950s, extensive groundwater withdrawals have been associated with agricultural irrigation in the Dell City, Texas region, just south of the New Mexico-Texas border. The Salt Basin groundwater system was declared by the New Mexico State Engineer during 2000 in an attempt to regulate and control growing interest in the groundwater resources of the basin. In order to help guide long-term management strategies, the hydrogeologic framework of the Salt Basin was developed by reconstructing the tectonic forcings that have affected the basin during its formation, identifying the depositional environments that formed and the resultant distribution of facies, and compiling information on the surface and subsurface extent of the various hydrogeologic units. The hydrogeologic framework provided insight on the distribution of permeability within the basin and allowed the groundwater flow system to be conceptualized.

The hydrogeologic framework was also used to aid in the development of a threedimensional groundwater flow model using MODFLOW-2000. The MODFLOW model was used to test the conceptualization of the groundwater flow system. Additional objectives included quantifying the distribution of permeability, and corroborating the radiocarbon groundwater ages calculated by a contemporaneous study using inverse geochemical modeling in NETPATH. MODPATH was used to compute travel times for comparison with radiocarbon groundwater ages. Initial results indicated that the model was able to produce a good match to observed groundwater levels and regional groundwater flow, but was unable to adequately reproduce the radiocarbon groundwater ages. This was believed to be due to the recharge boundary condition applied to the model domain, which was derived from an independent water-balancebased recharge study of the Salt Basin. As a result, an elevation-dependent recharge distribution was investigated. The elevation-dependent recharge model was able to produce a good match to radiocarbon groundwater ages, in addition to observed groundwater levels and regional groundwater flow.