Quality of Water
The chemical character of the ground waters in Pawnee and Edwards counties is indicated by the analyses in Table 9 and Table 10. The analyses were made by H. A. Stoltenberg in the Water and Sewage Laboratory of the Kansas State Board of Health. Seventy-one samples of water were collected from representative wells distributed as uniformly as possible within the area and among the water-bearing formations. The constituents listed were determined by methods used by the U. S. Geological Survey.
The following discussion of the chemical constituents of ground water in relation to use has been adapted from publications of the U. S. Geological Survey.
When water is evaporated the residue consists mainly of the mineral constituents listed in the tables of analyses and generally includes a small quantity of organic material and a little water of crystallization. Waters containing less than 500 parts per million of dissolved solids generally are satisfactory for domestic use, except for difficulties resulting from their hardness or excessive content of iron. Waters containing more than 1,000 parts per million are likely to include enough of certain constituents to cause a noticeable taste or to make the water unsuitable in some other respects.
The dissolved solids in samples of water from Pawnee and Edwards counties ranged from 145 to 8,834 parts per million. Ten of the samples contained between 500 and 1,000 parts per million and seven samples contained more than 1,000 parts per million (Table 11). More than 75 percent of the samples of water contained less than 500 parts per million and, therefore, are suitable for most ordinary uses.
Table 11--Dissolved solids in samples of water from wells in Pawnee and Edwards counties.
(parts per million)
|Number of samples|
|More than 1,000||7||0||7|
The hardness of water, which is the property that generally receives the most attention, is most commonly recognized by its effects when soap is used with the water for washing. Calcium and magnesium cause almost all the hardness of ordinary water. These constituents also are the active agents in the formation of most of the scale in steam boilers and in other vessels in which water is heated or evaporated.
In addition to the total hardness, the tables of analyses show the carbonate hardness and the noncarbonate hardness. The carbonate hardness is that caused by calcium and magnesium bicarbonates and can be almost entirely removed by boiling. In some reports this type of hardness is called temporary hardness. The noncarbonate hardness is caused by sulfates and chlorides of calcium and magnesium, but it cannot be removed by boiling and has been called permanent hardness. With reference to use with soap, there is no difference between the carbonate and noncarbonate hardness. In general the noncarbonate hardness forms harder scale in steam boilers.
Water having a hardness of less than 50 parts per million generally is rated as soft, and its treatment for the 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; however, it does slightly increase the consumption of soap, and softening is profitable for laundries or other industries using large quantities of soap. Waters in the upper part of this range of hardness will cause scale on steam boilers. Hardness of more than 150 parts per million can be noticed by anyone, and if the hardness is 200 or 300 parts per million it is common practice in some parts of the country to soften water for household use or to install cisterns to collect soft rain water. Where municipal water supplies are softened, an attempt generally is made to reduce the hardness to 60 or 80 parts per million. The additional improvements from further softening of a whole public supply is not deemed worth the increase in cost.
Water samples collected in Pawnee and Edwards counties ranged in hardness from 96 to 2,734 parts per million; hence none of the samples of water would be rated as soft. Only 3 of the 71 samples had a hardness of less than 150 parts per million, whereas 61 of the 71 samples had a hardness between 150 and 400 parts per million (Table 12).
Table 12--Hardness of samples of water from wells in Pawnee and Edwards counties.
(parts per million)
|Number of samples|
|Less than 100||0||1||1|
|More than 1,000||2||0||2|
Next to hardness, iron is the constituent of natural waters that in general receives the most attention. The quantity of iron in ground waters may differ greatly from place to place, even though the waters are derived from the same formation. If a water contains much more than 0.1 part per million of iron, the excess may precipitate and settle as a reddish sediment. Iron, which may be present in sufficient quantity to give a disagreeable taste and to stain cooking utensils and porcelain fixtures, may be removed from most waters by simple aeration and filtration, but a few waters require the addition of lime or some other substance.
The iron content of samples of water from wells in Pawnee and Edwards counties ranged from less than 0.1 part to 34 parts per million, the greatest concentration being in water from the Dakota formation. Forty-six of the samples contained 1 part per million of iron or less and 14 samples contained more than 5 parts per million (Table 13).
Table 13--Iron content of samples of water from wells in Pawnee and Edwards counties.
(parts per million)
|Number of samples|
Although determinable quantities of fluoride are not as common as fairly large quantities of the other constituents of natural water, it is desirable to know the amount of fluoride in water that is likely to be used by children. Fluoride in drinking water has been shown to be associated with the dental defect known as mottled enamel, which may appear on the teeth of children during the period of formation of the permanent teeth. It has been stated that waters containing more than 1.5 parts per million of fluoride are likely to produce mottled enamel on the teeth of children (Dean, 1936 J. If the water contains as much as 4 parts per million of fluoride, 90 percent of the children drinking the water are likely to have mottled enamel, and 35 percent or more of the children will have moderately or badly mottled enamel. Contents of fluoride up to 1 part per million are believed to be beneficial in inhibiting tooth decay.
Fifteen of the 71 samples of water collected in Pawnee and Edwards counties contained 1 part per million or more of fluoride, the greatest concentrations being in waters from the Dakota formation. The fluoride content of the waters ranged from 0.1 part to 4.6 parts (Table 14).
Table 14--Fluoride content of samples of water from wells in Pawnee and Edwards counties.
(parts per million)
|Number of samples|
|Less than 0.5||17||2||19|
|More than 2.9||1||0||1|
Water for irrigation
The suitability of water for irrigation is commonly believed to depend mainly on the quantity of soluble salts and on the ratio of the quantity of sodium to the total quantity of sodium, calcium, and magnesium. The quantity of chloride may l)e large enough to affect the use of the water, and in some areas there may be other constituents, such as boron, in sufficient quantity to cause difficulty. In a discussion of the interpretation of analyses with reference to irrigation in southern California, Scofield (19331 states that if the concentration of dissolved salts is less than 700 parts per million there is not much probability of harmful effects in irrigation, but that if it exceeds 2,100 parts per million there is a strong probability of damage to the crops, to the land, or to both. Water containing less than 50 percent sodium (the percentage being calculated as 100 times the ratio of the sodium to all the bases, in equivalents) is not likely to be injurious, but if it contains more than 60 percent sodium its use is inadvisable. Similarly, less than about 150 parts per million of chloride is not objectionable, but more than about 350 parts per million of chloride is undesirable. It is recognized that the harmfulness of irrigation water is so dependent upon the type of land and crops, on the manner of use, and on the drainage that no definite limits can be adopted.
Most of the waters of Pawnee and Edwards counties can be used safely for irrigation. Eight samples of water contained between 700 and 2,100 parts per million of dissolved solids. Five of these samples were from the alluvium of the Arkansas Valley but three were from the Dakota formation, which would not yield sufficient water for extensive irrigation. Waters from two wells contained more than 2,100 parts per million of dissolved solids and probably would be harmful to crops. One of these samples was from the alluvium of the Arkansas Valley and the other was from the Permian redbeds.
The sodium content of only four samples of water exceeded the limit set by Scofield. These samples were from the Dakota formation and the Permian redbeds, two formations that do not yield water to irrigation wells in this area. Three samples of water contained between 150 and 350 parts per million of chloride and two samples contained more than 350 parts. Of these samples, only one was from a formation that yields water to irrigation wells in this area. The concentration of borate in six samples of water from wells in Pawnee County was determined but it was not sufficient to be harmful to crops.
The analyses of water given in Table 9 and Table 10 show only the amounts of dissolved mineral matter in the water and do not indicate the sanitary quality of the water. An abnormal amount of certain mineral matter, such as more than a few parts per million of nitrate, however, may indicate pollution of the water.
Most of the population of Pawnee and Edwards counties is dependent upon water supplies from wells, and every precaution should be taken to protect these supplies from pollution. A well should not be constructed near possible sources of pollution, such as barnyards, privies, and cesspools, and every well should be tightly sealed to a level somewhat below the water table. Dug wells are more likely to be contaminated from surface sources than are drilled wells, chiefly because dug wells generally are not effectively cased or sealed at the top. Drilled wells generally are well protected by the casing, although many are poorly sealed at the top.
The quality of water from the principal water-bearing formations in Pawnee and Edwards counties is shown in Figure 10 and is discussed below.
Figure 10--Typical analyses of waters from the principal water-bearing formations in Pawnee and Edwards counties.
The undifferentiated redbeds of Permian age yield little or no water to wells in this area, but the quality of the water from these beds is important because of the danger of pollution of the overlying beds that contain fresh water. Several deep wells and test holes in this area have encountered salt water under artesian pressure in these deposits. It is essential, therefore, that such wells and test holes be effectively sealed to prevent contamination of other waters. One well, near Frizell, was reported to have had a flow of nearly 700 gallons a minute. Test hole 28 encountered salt water under artesian pressure. The analysis of this water is shown in Figure 10. This hole was cemented to prevent contamination of other waters.
Water from the Dakota formation generally contains a large amount of dissolved solids (the average for 10 samples was 669 parts per million) but is only moderately hard, owing to natural softening (Figs. 10 and 11). The dissolved solids ranged from 361 to 1,475 parts per million, whereas the hardness ranged from 131 to 301 parts per million. Water from the Dakota formation generally contains a relatively high ratio of sodium to the total bases. This ratio exceeded 50 percent in 4 of the 10 samples, the highest being 86 percent. These relatively soft sodium bicarbonate waters may represent calcium bicarbonate waters in which the calcium and magnesium have been exchanged for sodium by reaction with base-exchange silicates in the rocks as the water percolated through the formation. The base-exchange silicates probably are the clay-forming minerals in the Dakota formation. The degree of softening depends upon the amount and softening capacity of base-exchange silicates in the clay and upon the length of time the hard water remains in contact with the silicates.
Figure 11--Map of Pawnee and Edwards counties showing the hardness of ground waters.
All but one of the samples of water from the Dakota formation contained sufficient fluoride to be harmful to children's teeth. The fluoride content of these samples ranged from 0.5 part to 4.6 parts per million and averaged 2.0 parts.
Two samples of water were collected from wells penetrating the Greenhorn limestone. They were calcium bicarbonate waters containing 354 and 409 parts per million of dissolved solids and having hardnesses of 204 and 334 parts per million, respectively (Fig. 10). The fluoride contents were 0.2 and 1 part per million, respectively.
The Fairport chalky shale member of the Carlile shale yields small quantities of water to a few wells in northern Pawnee County. The dissolved solids in samples of water from three of these wells averaged 506 parts per million and the hardness averaged 339 parts per million. The fluoride content ranged from 0.1 part to 1.1 parts per million.
These deposits, which underlie the dune-sand area south of Arkansas River, contain the softest ground water in Pawnee and Edwards counties. The amount of dissolved solids in 23 samples of water from these beds ranged from 145 to 439 parts per million and averaged 274. The hardness ranged from 96 to 282 and averaged 184. The fluoride content of these waters generally is low, as indicated by Figure 12. None of the samples contained enough fluoride to be harmful to children's teeth, the average fluoride content being 0.5 part per million.
Figure 12--Map of Pawnee and Edwards counties showing the fluoride content of ground waters.
Waters from these deposits are moderately uniform in chemical quality. The amount of dissolved solids in 14 samples ranged from 287 to 696 parts per million and averaged 390 parts. The hardness, which ranged from 218 to 432 parts per million, averaged 288 parts per million. The fluoride content of these waters generally is low (average 0.5 parts per million) and only one sample contained as much as 1.0 part per million.
Eighteen samples of water from the alluvium of the Pawnee and Arkansas Rivers were analyzed. The composition of the waters in the two valleys is not alike (Fig. 10).
Water from the alluvium of the Arkansas Valley generally is very hard but may be much softer on the south side of the valley (Fig. 11) near the sand dunes because of the movement of the softer water from the south into the valley. The amount of dissolved solids in eight samples of water from wells that were not close to the sand dunes ranged from 493 to 2,250 parts per million and averaged 1,176. The hardness, which ranged from 302 to 1,066 parts per million, averaged 612 parts. The amounts of dissolved solids in three samples of water from wells near the edge of the sand dunes were 246, 307, and 543 parts per million. The hardnesses were 175, 196, and 359 parts, respectively. The fluoride content of waters from the alluvium of the Arkansas Valley averaged 0.7 part per million.
Waters from the alluvium of the Pawnee Valley were softer than the average water from the alluvium of the Arkansas Valley (Figs. 10 and 11). The average amount of dissolved solids in these waters was 327 parts per million and the average hardness was 268 parts per million. The average fluoride content of these waters (0.5 part per million) was slightly lower than that of waters from the alluvium of the Arkansas Valley.
Kansas Geological Survey, Pawnee and Edwards Geology and Groundwater
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Web version June 2004. Original publication date March 1949.