A cross-sectional ground-water flow model was constructed of the Palo Duro Basin to analyze available hydrogeologic data and better understand the causes of underpressuring below the Evaporite Aquitard and mechanisms of recharge and discharge to and from the Deep-Basin Brine Aquifer. Various effects of lithostratigraphy and topography on subhydrostatic conditions in the deep section were investigated in different simulations.
The model indicates that the subhydrostatic pressures beneath the Evaporite Aquitard are caused by segregation of deep and shallow flow systems by the low-permeable evaporite section and drainage of the deep system by relatively permeable granite wash deposits. The Pecos River, which allows underflow of some groundwater recharging in the New Mexico area to the west, enhances underpressuring beneath the western half of the High Plains by serving as a discharge area for water that would otherwise move downdip into the Deep-Basin Brine Aquifer. In addition to this recharge, about 26% of the groundwater in the Deep-Basin Brine Aquifer originates from leakage through the evaporite section, assuming K2 = 2.8 x 10-4 md, the upper limit of aquitard permeability suggested by the model.
The groundwater flow pattern within the Deep-Basin Brine Aquifer is governed by the spatial distribution of more permeable strata, particularly the granite wash deposits. In the cross-sectional model, most of the groundwater in the Deep-Basin Brine Aquifer discharges laterally through the eastern boundary and eventually by upward leakage in the easternmost part of the cross-section.
Ground-water travel times through the Deep-Basin Brine Aquifer from the westernmost recharge area in New Mexico to the eastern boundary of the model range between 1.2 and 4 million years, depending on the flow path depicted by the streamtubes and average porosities of the different units.Bureau of Economic Geolog
