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Alleviation of Chloride Contamination
Several control measures possibly could be utilized to alleviate the chloride contamination problem in the study area. These include desalinization, dilution, evaporation, and diversion.
Desalinization costs have decreased in recent years but are still prohibitively expensive. The cost of producing freshwater by desalinization, exclusive of collection and effluent disposal cost, is in the range of $0.50 to $1.00 per 1,000 gal (U.S. Army Engineer District, Tulsa, 1965). Other methods of controlling salt contamination would certainly be less expensive.
Dilution of contaminated water with good-quality water is another viable alternative and probably the most commonly used method of contamination abatement. Large storage areas are required so that dilution water can be available during periods of low flow. This method is currently being used in the Kansas River system whereby water is released from reservoirs during low-flow periods to improve water quality in the Kansas River at Topeka, Lawrence, and other municipalities where the water is used for public supply.
Implementation of lined evaporation basins is another alternative that should be considered. The mean annual precipitation in the study area is about 32 inches per year, and the average pan evaporation is 58 inches per year. In addition, salt evaporation operations were successfully undertaken in the late 1800s east of Salina. Evaporation may be a viable alternative in areas where the water introduced to the evaporation basins is highly saturated with respect to sodium chloride. Interception of highly saturated saline water by wells completed in the Wellington aquifer, followed by spreading of the water in basins, would be an example of this method. It should be noted, however, that the use of evaporation ponds also may provide a potential source of ground-water contamination.
Diversion of freshwater around a salt-source area or of saline water out of a system via injection wells or transportation from the area is not a control plan in itself but must be used with other brine collection and control systems.
Discussion of measures that possibly could be implemented to control pollution caused by flow of highly mineralized water from the Wellington aquifer into freshwater stream-aquifer systems will be limited to the southern emission area; i.e., the area between Belle Plaine and Geuda Springs.
Because the saline-water inflow area is fairly limited, alleviation of the inflow to the Ninnescah River alluvium possibly could be accomplished by installation of interception wells screened in the Wellington aquifer. The saline water could be injected into disposal wells completed in the Arbuckle Group, which in this area is a highly permeable unit and often used for disposal of brines produced with oil and gas. The Arbuckle is found at depths of about 3,900 feet in this area. Another possible method of disposal is implementation of evaporation ponds as mentioned earlier.
Alternatively, a series of wells could be screened in the contaminated part of the alluvium. These wells could be pumped during high-flow periods, and the saline water could be diluted with river water and removed from the area.
The saline-water emission area is more diverse in the Slate Creek basin than in the Ninnescah alluvium, and interception of saline water in the subsurface is infeasible. Thus, alleviation would require construction of a collection system whereby the saline water could be gathered at the surface and transported via pipeline to disposal wells completed in the Arbuckle Group. The Arbuckle in this area occurs at depths ranging from 3,100 to 3,600 feet.
Because of the small quantities of contaminated water involved, probably the most feasible method of chloride alleviation in Salt Creek would be by dilution. Possibly an inflatable dam could be constructed that would store the saline water until the occurrence of a high-flow event. Then, when the stage in the stream reaches a predetermined level, the dam could be deflated to allow the diluted water to flow into the Arkansas River.
Recommendations for Future Studies
The "Equus beds" aquifer northwest of Wichita is the principal source of water for public supply for the city and also yields large supplies of ground water for irrigation. Increased withdrawals and continued uncontrolled development could result in mining of ground water, reduced well yields, and possible deterioration of water quality as a result of saline-water inflow from the Wellington aquifer and that part of the "Equus beds" in the Burrton-Buhler area that is presently contaminated.
The study should include reevaluation of existing hydrologic and chemical-quality data using up-to-date techniques. Additional test drilling is needed to define the relation of the "Equus beds" aquifer to the Wellington aquifer. Solute transport digital models would then be used to simulate ground-water flow in the "Equus beds" as a result of stresses applied via increased pumpage and to determine the potential for movement of saline water from the Wellington aquifer into the 'Equus beds" aquifer and the Wichita well field.
Deterioration of the alluvial aquifer in a small area west of Belle Plaine has occurred as a result of saline-water inflow from the Wellington aquifer. In this area, the head in the Wellington aquifer is above the head in the unconsolidated deposits. A detailed study is needed to describe the geohydrologic relationships between the freshwater alluvial aquifer and the Wellington aquifer; to determine the extent, severity, and direction of movement of saline water in the aquifer; and to assess possible means of alleviation or control of the contamination.
The study should include installation of observation wells screened at the base of the alluvium and in the Wellington aquifer. Water-level measurements from these wells and radioactive logs could be used in conjunction with electrical logs from local oil tests to gain an understanding of the local geohydrologic relationships between the alluvial aquifer and the Wellington aquifer. The wells should be sampled periodically to determine water type and to monitor chemical changes that may occur, as well as to ascertain areas of saline-water inflow to the alluvial aquifer.
A variable-density digital flow model could be used to aid in determination of the quantity, source(s), and direction of movement of saline water that is entering the alluvial aquifer.
Summary
Degradation of chemical quality in freshwater streams and aquifers in central Kansas has adversely affected their suitability for public use. The degradation occurs as a result of natural discharge of saline water from the Wellington aquifer. The contaminating water is derived from differential solution of the eastern edge of the Hutchinson Salt Member and associated gypsum units of the Wellington Formation where they are in close proximity to freshwater systems.
The dissolution of salt and gypsum has resulted in formation of a discontinuous zone of solution cavities and collapsed beds (termed the Wellington aquifer) that trends from Salina southward toward the Oklahoma state line.
The generalized potentiometric surface of the Wellington aquifer was determined through measurements of water levels in wells completed in the Wellington aquifer and by results of a steady-state digital model of ground-water flow.
Comparison of maps of the potentiometric surface of the Wellington aquifer and the water table of the overlying freshwater deposits indicates that the ground water enters the Wellington aquifer from downward leakage of freshwater (pls. 1 and 4). Also indicated on the potentiometric maps is a ground-water divide east of Hutchinson. The potentiometric surface slopes north to the Smoky Hill River valley where, between New Cambria and Solomon, the head of the potentiometric surface of the Wellington aquifer is higher than the water table of the unconsolidated deposits. Saline-water inflow to the alluvium and stream occurs in this area.
Another major direction of flow from the potentiometric high is southeast toward the Belle Plaine-Adamsville-Geuda Springs area where the head in the Wellington aquifer is higher than the head in the freshwater deposits and where saline water is emitted to stream valleys and onto the land surface in the form of springs and seeps.
The potentiometric head in the Wellington aquifer is also higher than the head in the freshwater deposits in the area just east of Hutchinson. However, the confining layer between the Wellington aquifer and freshwater deposits is about 300 feet thick in this area, and it is doubtful that the head differential is great enough to overcome the flow-retardation effects of such a thick confining bed.
Another area of possible upward flow of saline water to the freshwater deposits is in the Arkansas River valley between Hutchinson and Mount Hope. In this area, the confining layer has been eroded by the ancestral Arkansas River so that there is less than 100 feet of shale between the Wellington aquifer and the freshwater deposits. Unknown quantities of saline water may be entering the freshwater system in this area.
Seepage and salinity measurements and regression-analysis methods were used to estimate the quantity of saline water that is entering the Arkansas River and its tributaries between Derby and Arkansas City as a result of ground-water inflow from the Wellington aquifer. These methods indicate that about 294 tons of chloride per day are entering the freshwater system in this area. J. B. Gillespie (U. S. Geological Survey, oral commun., 1978) reports that about 369 tons of chloride per day are entering the Smoky Hill River between New Cambria and Solomon. The concentrated saltwater discharge into the two systems is about 0.60 ft3/s and 0.76 ft3/s, respectively.
Possible methods of alleviation of the saline-water contamination include interception by wells of the saline water in the Wellington aquifer before it enters the freshwater systems, interception by wells at the base of the fresh-water deposits where they are present, and collection at land surface in areas of seeps and springs. Subsequent to interception, methods of disposal include injection to the Arbuckle Group, dilution with fresh stream water during high-flow events, and evaporation in ponds.
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Kansas Geological Survey, Geology
Placed on web Jan. 2006; originally published 1981.
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