ORIGIN AND DISCHARGE OF SALTWATER IN THE ROLLING PLAINS AND CONCHO RIVER WATERSHED, WEST TEXAS

Discharge of naturally occurring saltwater from the Permian Basin influences groundwater quality across much of the Texas Rolling Plains and the Concho River Valley. The eastward-directed movement of saltwaters in Guadalupian and older Paleozoic formations might have been active for only the past 5 to 10 Ma, if a topographically related drive is owing to Basin and Range Uplift and headward erosion of river systems. Broad mixing zones between modified-connate Ca-Cl and meteoric Na-Cl saltwaters occur on both sides of the Southern High Plains. The eastward-moving saltwater is modeled as mixtures of Permian evaporatively concentrated seawater and meteoric water recharged under steep vertical gradients on the eastern side of the Southern High Plains. Eastward flow of fluids from the Permian basin can account for oil fields and saltwater naturally occurring at shallow depths. Some Permian formations, for example, the Coleman Junction, have enough hydraulic head that upward-discharge of saltwater to near-surface aquifers through poorly plugged wells has been a documented problem. Comparison of ionic ratios and stable isotopic compositions between saltwaters and salinity-impacted local groundwater might help identify a saltwater source. Br/Cl, Cl/SO₄, Ca/Na and δD/δ¹⁸O ratios tend to differ between Permian and Pennsylvanian formation waters, at least in the Concho River watershed. Other sources of salinization include evaporative concentration of irrigation water, for example, in the Lipan aquifer, and deeply drilled water wells not being plugged after encountering saltwater.