Modeling regional salinization of the Ogallala aquifer, Southern High Plains, TX, USA

Two extensive plumes (combined area >1000 km(2)) have been delineated withi n the Ogallala aquifer in the Southern High Plains, TX, USA. Salinity varie s within the plumes spatially and increases with depth; Cl ranges from 50 t o >500 mg l(-1) Variable-density flow modeling using SUTRA has identified t hree broad regions of upward cross-formational flow from the underlying eva porite units. The upward discharge within the modeled plume area is in the range of 10(-4)-10(-5) m(3) day(-1), and the TDS concentrations are typical ly >3000 mg l(-1). Regions of increased salinity, identified within the Whi tehorse Group (evaporite unit) underlying the Ogallala aquifer, are control led by the structure and thickness variations relative to the recharge area s. Distinct flow paths, on the order of tens of km to >100 km in length, an d varying flow velocities indicate that the salinization of the Ogallala aq uifer has been a slow, ongoing process and may represent circulation of wat ers recharged during Pleistocene or earlier times. On-going pumping has had negligible impact on the salinity distribution in the Ogallala aquifer, al though simulations indicate that the velocity distribution in the underlyin g units may have been affected to depths of 150 m after 30 years of pumping . Because the distribution of saline ground water in this region of the Oga llala aquifer is heterogeneous, careful areal and vertical characterization is warranted prior to any well-field development. (C) 2000 Elsevier Scienc e B.V. All rights reserved.