The Permian Basin (fig. 1) comprises a large area in the southern midcontinent region and includes major portions of Texas, New Mexico, Oklahoma, and Kansas. Within this basin brine springs and seeps discharge more than 20,000 tons per day of sodium chloride (common table salt). This brine contaminates many streams greatly impairing the utility of their waters. The water in some streams is of such poor quality it cannot be used for municipal and industrial purposes and for irrigation. Nor is the problem limited to the Permian Basin. The contaminated streams leaving the Permian Basin bring salty water to downstream areas of Arkansas and Louisiana, as well as to other parts of Texas, New Mexico, Oklahoma, and Kansas. In no comparable area of the interior United States are natural sources of salt water so widespread or deleterious to the fresh water supply of so large a segment of the nation's population and industry.

The Brazos River traverses the eastern part of the Permian Basin, and is potentially one of the principal sources of water in Texas. It carries an average daily load of 1,650 tons of sodium chloride (common table salt) into Possum Kingdom Reservoir, about 110 miles west of Dallas. More than 85 percent of this salt is contributed by the Salt Fork Brazos River, and more than one-half originates from Springs and seeps in Croton and Salt Croton Creeks, tributaries to the Salt Fork Brazos River. The undesirably high chloride content of the water impounded in Possum Kingdom Reservoir limits the utility of this water, although it is used for irrigation and by some industries.

Understanding of the origin and hydrology of the natural brine is fundamental to consideration of engineering measures to control the flow of salt water to streams, or to general plans to alleviate the situation in any way that includes altering the brine-discharge system.

Previous investigations of natural brine features have been directed toward describing the local details of individual problem areas. Thus the occurrence of brine features has been described strictly in terms of the local environment. The origin and discharge of brine have been ascribed invariably to local sources and to local hydraulic controls. The case for local origin of the brine has been stated by Ward and Leonard (1961). According to their hypothesis brines evolve in the circulation of ground water in local hydraulic systems which feature the following conditions: (a) halite deposits or halite-bearing rocks at relatively shallow depth; (b) ground water that circulates to the halite-bearing zones; and (c) a local topographically low area where the water can emerge as a mineral spring.

An alternate hypothesis (Greenman and Stevens, 1963) is that the salt springs originate as outcrops of a regional body of brine and that the primary factors determining their distribution are regional hydrologic controls, such as physiography, geology, and climate. The precise location of springs, the nature and amount of discharge, as well as their salinity, depend on secondary hydrologic factors, such as local geologic conditions, local topography that governs the movement of the overlying fresh water, and the hydrologic environment in the vicinity of the springs, which determines the amount of mixing of the brine and the fresh water at each locality. In general, the brine is a water body separate and distinct from the overlying fresh water. The salinity of individual springs is determined by the amount of mixing of the brine with the fresh water not by solution of salt-bearing materials in local hydraulic systems. The geographic zone in which all of the brine springs and seeps occur is determined by regional topographic and perhaps climatic conditions. If the regional hypothesis is true, remedial measures must take into account a set of hydraulic and hydrologic circumstances that is fundamentally different from that postulated previously.