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Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Water Bearing Formations

Well Records

Well Logs

References

Plates

Ground Water, continued

Quality of Water

Figure 11--Analyses of waters from the Ogallala formation in Thomas County. Numbers refer to analyses in table 5. A large version of this figure is available.

Figure 12--Map of Thomas County showing areal distribution of iron and total dissolved solids in well waters in Thomas County. A large version of this figure is available.

Chemical Constituents in Relation to Use

Total dissolved solids--The residue left after a natural water has evaporated consists of rock materials, with which may be included some organic materials and a small amount of water of crystallization. Water containing less than 500 parts per million of dissolved solids generally is entirely satisfactory for domestic use, except for difficulties resulting from its hardness, and, in some areas, because of excessive iron corrosiveness. Water having more than 1,000 parts per million of dissolved solids is likely to contain enough of certain constituents to produce a noticeable taste or to make the water unsuitable in some other respects.

The total dissolved solids in samples of water collected from private wells in this area ranged from 225 parts per million in well 101 to 349 parts in well 114. As all of the samples collected contained less than 850 parts per million the water is suitable for most ordinary purposes. Thirteen of the samples contained less than 250 parts per million, eight samples contained between 250 and 300 parts, and only three samples contained more than 300 parts.

Hardness--The hardness of water, which is the property that generally receives the most attention, is most commonly recognized by its effect when soap is used with the water in washing. Calcium and magnesium cause almost all of the hardness of ordinary water. These constituents are also the active agents in the formation of the greater part of all the scale formed in steam boilers and in other vessels in which water is heated or evaporated.

In addition to total hardness, the table of analyses indicates the carbonate hardness and the non-carbonate hardness. The carbonate hardness is that due to the presence of calcium and magnesium bicarbonate, and it is largely removed by boiling. In some reports this type of hardness has been called temporary hardness. The non-carbonate hardness is due to the presence of sulphates or chlorides of calcium and magnesium, but it cannot be removed by boiling and has sometimes been called permanent hardness. With reference to use with soap, there is no difference between the carbonate and non-carbonate hardness. In general, the non-carbonate hardness forms harder scale in steam boilers.

Water having a hardness less than 50 parts per million is generally rated as soft, and its treatment for removal of hardness under ordinary circumstances is not necessary. Hardness between 50 and 150 parts per million does not seriously interfere with the use of water for most purposes, but it does slightly increase the consumption of soap; its removal by a softening process is profitable for laundries or other industries using large quantities of soap. Water in the upper part of this range of hardness will cause considerable scale in steam boilers. Hardness exceeding 150 parts per million can be noticed by anyone; if the hardness is 200 or 300 parts per million it is common practice to soften water for household use or to install a cistern to collect soft rainwater. Where municipal water supplies are softened, an attempt is generally made to reduce the hardness to 60 or 80 parts per million. The additional improvement from further softening of a whole public supply is not deemed worth the increase in cost.

The hardness of samples of water collected from wells in Thomas County ranged from 162 (well 89) to 270 (well 114) parts per million. Only two samples had more than 250 parts per million of hardness and 14 samples had less than 200 parts per million of hardness.

Iron--Next to hardness, iron is the constituent of natural waters that receives the most attention. The quantity of iron in ground waters may differ greatly from place to place, even though the waters are from the same formation. If a water contains much more than 0.1 part per million iron, the excess may separate out and settle as a reddish sediment. Iron, which may be present in sufficient quantity to give a disagreeable taste and to stain cooking utensils, may be removed from most waters by simple aeration and filtration, but a few waters require the addition of lime or some other substance.

Two of the samples collected in Thomas County (wells 33 and 92) contained less than 0.15 part per million of iron; 20 samples contained between 0.15 and 5.0 parts, and two samples (wells 64 and 21) contained more than 5.0 parts. The highest iron content was in the sample collected from well 21, which contained 10 parts per million.

Fluoride--Although determinable quantities of fluoride are not as common as fairly large quantities of other constituents of natural waters, it is desirable to know the amount of fluoride present in water that is likely to be used by children. Fluoride in water has been shown to be associated with the dental defect known as mottled enamel which may appear on the teeth of children who drink water containing excessive quantities of fluoride during the period of formation of the permanent teeth. It has been stated that waters containing 1 part per million or more of fluoride are likely to produce mottled enamel, although the effect of 1 part per million is not usually very serious (Dean, 1936). If the water contains as much as 4 parts per million of fluoride, 90 percent of the children exposed are likely to have mottled enamel and 35 percent or more of the cases will be classed as moderate or worse. Recent work has indicated a beneficial effect from the presence of a small amount of fluoride in drinking water in decreasing the incidence of dental caries. Discussions in the literature suggest that this beneficial effect may be produced by quantities of fluoride of less than 1 part per million which would not have any measurable effect upon the quality of tooth enamel (Dean, Jay, Arnold, and Elvove, 1941).

Two samples of water collected from wells 2 and 33 in Thomas County contained 2.0 parts per million of fluoride, 19 samples contained less than 2.0 parts but more than 1.0 part, and 3 samples contained less than 1.0 part. Well 101 had the lowest fluoride content--0.5 part per million.

Sanitary Considerations

The entire population of Thomas County and nearly all of the livestock are dependent on well-water supplies as there are no permanently flowing streams in the county. Although the county has three municipal water plants that are safeguarded against pollution, a large percentage of the population is dependent upon private wells, and every precaution should be taken to protect these supplies from pollution. Deep drilled wells on the uplands that penetrate relatively impervious silt above the water table are less subject to pollution than are shallow dug or driven wells in the valleys where pervious sandy material extends from the surface down to the shallow water table. A well should not be located close to or below possible sources of pollution, such as barnyards, privies, and cesspools, and every well should be tightly sealed down to a level somewhat below the water table. It is generally advisable to locate a well on a spot that is slightly higher than the surrounding ground, or bank earth around the top of the well so that surface drainage will run away from rather than into the well. If a well must be located near a source of possible pollution it should be up slope from it so that rain water will run from the location of the well toward the source of pollution rather than toward the well. Drilled wells are generally satisfactorily protected by the casing, although some are poorly sealed at the top.

Quality in Relation to Stratigraphy

With the exception of the sample of water from well 14 that encounters both alluvium and the Ogallala sediments, all of the analyses reported in table 5 and figure 11 are of water pumped from the Ogallala formation; therefore the general discussion of chemical constituents in relation to use applies specifically to water in the Ogallala formation.

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