Groundwater Resources, continued
Chemical Character of GroundwaterWater is commonly referred to as the universal solvent. Various gases and minerals are taken into solution by water as it is precipitated and as it percolates through the earth materials. The kind and amount of impurities in ground water may be determined by chemical analysis. The corrosiveness, encrusting tendency, palatability, and other objectionable or desirable properties also can be predicted from the results of a quantitative chemical analysis. Ordinarily, greater amounts of dissolved mineral constituents are found in groundwater than in surface water in eastern Kansas because groundwater has been in contact with soluble materials in the geologic strata for a longer time.
The chemical character of ground water in Johnson County is indicated by chemical analyses of 54 water samples from selected wells, test holes, and springs. The analyses are listed in table 4 and table 9. The mineral constituents are reported in milligrams per liter (mg/l). Factors for converting milligrams per liter to milliequivalents per liter are given in table 5. Even though the analyses were made several years ago, they should still be representative of the chemical quality of ground water in Johnson County.
Table 5--Factors for converting milligrams per liter to milliequivalents per liter.
Quality in Relation to Use
Water for domestic use should not contain excessive amounts of hardness, iron, magnesium, chloride, sulfate, nitrate, fluoride, or dissolved solids. The maximum concentrations of various constituents in drinking water recommended by the U.S. Public Health Service are summarized in table 6.
Table 6--Recommended maximum amounts of various constituents in drinking water (adapted from U.S. Public Health Service, 1962).
The suitability of ground water for irrigation depends upon the effects of the mineral constituents in the water on both the plants and the soils being irrigated. Water used for irrigation should not contain excessive amounts of dissolved solids, boron, or bicarbonate, and should not have a high calcium magnesium to sodium ratio.
Water-quality requirements for industrial processes vary widely. Some industrial uses require water of extremely high quality, whereas others satisfactorily use water of low quality. The concentrations of dissolved solids, hardness, iron, and hydrogen ion (pH), and the alkalinity and temperature of the ground water are some of the more important factors in determining the usability of the water.
The discussion of the various dissolved constituents that affect the chemical quality and use of ground water has been adopted from various sources including the American Public Health Association and others (1955), California State Water Pollution Control Board (1952), Hem (1959), Rainwater and Thatcher (1960), U.S. Salinity Laboratory Staff (1954), and U.S. Public Health Service (1962).
In this report, water is classified from fresh to briny according to its dissolved-solids content and specific conductance as given in table 7.
Table 7--Classification of water according to dissolved-solids content and specific conductance (from Winslow and Kister, 1956, p. 5; Robinove and others, 1958, p. 3).
Dissolved solids--When water is evaporated, the residue consists mainly of the mineral constituents listed in table 4, except bicarbonate. The residue may include a small quantity of organic material or water of crystallization. Water containing less than 500 mg/l dissolved solids generally is satisfactory for domestic use, except for difficulties resulting from its hardness or iron content. Water containing more than 1,000 mg/l dissolved solids may have certain constituents in sufficient quantity to produce a noticeable taste or to make it unsuitable in some other respect.
Smith and others (1942) and Heller (1933) have described experiments with livestock using known concentrations of salts in the animals' drinking water. They conclude that sheep have a greater tolerance than cattle and cattle have a greater tolerance than hogs to mineralized drinking water. In general, the experiments indicate that about 10,000 mg/l is the upper limit of dissolved solids that can be tolerated by livestock. Cattle on some farms in eastern Kansas are drinking water with 3,000 to 5,000 mg/l dissolved solids (chiefly sodium chloride and sodium bicarbonate) with no apparent ill effects.
The concentrations of dissolved solids in 42 samples of groundwater collected in Johnson County from wells, test holes, and springs are given in table 4. The dissolved-solids concentration ranged from 119 to 5,090 mg/b.
Specific conductance--The specific conductance is a measure of the ability of water to conduct an electric current and is an indication of the ionic strength of the solution. Because conductance is the reciprocal of resistance, the units in which specific conductance is reported are reciprocal ohms or "mhos." Natural waters have specific conductance values much less than 1 mho and, therefore, are reported in millionths of mhos or micromhos at a standard temperature of 25 deg. C (77 deg. F). For practical purposes the relation between specific conductance and concentration of dissolved solids is linear for dilute solutions, such as the water used for domestic and stock purposes in Johnson County. Specific conductance is conveniently determined with a Wheatstone bridge using a standardized conductivity cell, and the results are converted to the approximate value of the dissolved-solids concentration.
The relationship between specific conductance and dissolved solids is expressed as:
Specific conductance (micromhos at 25 deg. C) x A = Dissolved solids (mg/l).
The factor A has a value ranging from 0.5 to 1.0 but A commonly has a value between 0.55 and 0.75 (Hem, 1959, p. 40).
Hardness--Calcium and magnesium cause nearly all the hardness of water and are the active agents in the formation of most of the scale in steam boilers and other vessels in which water is heated or evaporated. Dissolved calcium and magnesium react with soap to form a sticky curd that is difficult to remove from containers and fabrics. Soap will not cleanse or lather until the hardness-causing constituents have been removed.
Total hardness (carbonate plus noncarbonate hardness) and noncarbonate hardness of water in Johnson County are given in table 4. Carbonate, or temporary, hardness can be removed almost entirely by boiling. Noncarbonate hardness is due to the presence of calcium and magnesium from salts of sulfate and chloride. It cannot be removed by boiling and, therefore, is sometimes reported as permanent hardness. The two types of hardness have the same reaction with soap.
The hardness of water is arbitrarily classified as follows: 60 mg/l or less, soft; 61-120 mg/l, moderately hard; 121-180 mg/l, hard; and 181 mg/l or more, very hard (Durfor and Becker, 1964). Soft water used for domestic or municipal purposes is seldom treated to remove hardness. Very hard water, when used for municipal or domestic supplies, commonly is softened. Municipalities decrease the hardness by the addition of lime and soda ash. Individual domestic water supplies are commonly softened with zeolite-type softeners. Cisterns may be installed to collect soft rainwater for laundry and washing purposes.
The tolerance to hardness of water used for industrial processes varies greatly, ranging from 2 mg/l or less for high pressure steam boilers to several hundred milligrams per liter for other process waters. Hard water is generally more suitable for irrigation than soft water due to a favorable calcium magnesium to sodium ratio.
The total hardness of 45 samples of groundwater collected in Johnson County ranged from 14 to 581 mg/b (table 4).
Iron and manganese--Iron, in the ferrous state, is generally present in small quantities in most natural ground water. If water containing more than 0.1 mg/l iron is exposed to the air, some of the iron may oxidize and precipitate as a reddish sediment. Iron in concentrations in excess of 0.3 mg/l is undesirable as it may stain cooking utensils, plumbing fixtures, and clothing being laundered, or give a disagreeable taste to the water. Dissolved manganese also causes objectionable staining and taste problems, but is less commonly present. In water treatment plants, iron and manganese are commonly removed by aeration or chlorination, or both followed by sedimentation and filtration.
The concentration of iron in 45 samples of groundwater collected in Johnson County ranged from 0.04 to 25 mg/l (table 4). Iron in concentrations of 0.3 mg/l or more was found in 26 of the samples.
Fluoride--Fluoride in concentrations of about 1 mg/l in drinking water used by children during the period of tooth calcification prevents or lessens the incidence of tooth decay; concentrations greater than 1.5 mg/l may cause mottling of the enamel (Dean, 1936, 1938). The U.S. Public Health Service (1962) recommends 1.2 mg/l as the maximum concentration of fluoride in drinking water used in Johnson County. The concentration of fluoride in 43 samples of ground water collected in Johnson County ranged from 0.0 to 14 mg/l. The fluoride concentration exceeded 1.5 mg/l in three samples.
Fluoride, unlike chloride, is only sparingly soluble in water and usually is present in only small amounts. It is often characteristic of waters from deep strata and of salt water from oil and gas wells. In Johnson County fluoride is commonly more abundant in water from sandstone and black shale aquifers than from aquifers of other rock types.
Nitrate--Nitrate is highly soluble, but groundwater in Kansas generally contains only small amounts, usually less than 10 mg/l (Metzler and Stoltenberg, 1950, table 3). Concentrations of 90 mg/l of nitrate in drinking water may cause cyanosis, or oxygen starvation, if used in the preparation of a baby's formula (Metzler and Stoltenberg, 1950), and some authorities (Comly, 1945) recommend that water containing more than 45 mg/l should not be used for preparation of infants' formulas. Drinking water standards established by the U.S. Public Health Service (1962) recommend 45 mg/l as the maximum concentration. Of the 45 samples of groundwater collected from Johnson County and analyzed for nitrate, three contained concentrations of more than 45 mg/l.
Nitrate from natural sources generally is attributed to the oxidation of nitrogen of the air by bacteria and to the decomposition of organic material in the soil. In general, shallow water-table aquifers having a significant range in fluctuation of the water table appear to have more nitrate attributable to natural sources than do other aquifers. Fertilizers and animal wastes may also contribute nitrates directly to water resources.
Sulfate--The concentration of sulfate is not very critical for domestic or irrigation uses or for many industrial processes. Sulfate in groundwater is derived chiefly from the solution of gypsum and the oxidization of pyrite. Most of the sulfate in the domestic and irrigation water supplies of Johnson County probably results from the oxidization of small amounts of pyrite disseminated through the limestones, shales, and sandstones through which the water percolates. Sulfate in ground water in concentrations in excess of about 500 mg/l may have a laxative effect on persons not accustomed to drinking such water. The concentration of sulfate in 45 samples analyzed ranged from 1.6 to 1,320 mg/l.
Chloride--Most naturally occurring chlorides are very soluble. Chloride concentrations in ground water are known to range from less than 1 mg/l in some shallow aquifers to many thousand milligrams per liter in some of the deep strata. Sodium and chloride are the chief dissolved constituents in the ground water in some of the deeper aquifers. A sodium chloride water with a chloride concentration of 150 to 200 mg/l can be detected by persons having a sensitive taste. Water with a high chloride content is corrosive to many metal surfaces, and many crops may be injured by waters containing excessive quantities of chloride.
Chloride in ground water may be derived from connate marine water in the sediments, from sewage and animal wastes, or from solution of minerals containing chloride. It has little effect on the suitability of water for ordinary use unless the quantity is enough to give the taste of salt.
The concentration of chloride in 47 water samples from Johnson County (table 4) ranged from 3.5 to 2,730 mg/l.
Sanitary considerations--The analyses of water (table 4) show only the amount of dissolved minerals and do not indicate the sanitary quality of the water. Well water may contain mineral matter that gives the water an objectionable taste, but still be free from harmful bacteria and, consequently, safe for drinking. Other well water, good-tasting and seemingly pure, may contain harmful bacteria. Water supplies obtained from wells that are properly constructed and located away from sources of pollution are almost always free of harmful bacteria. Because human and animal wastes are high in chloride and nitrogenous material, the presence of abnormal concentrations of both chloride and nitrate can be indicative of pollution from these sources.
Recommendations for well locations and for sanitary well construction and pump installation can be obtained from the Kansas State Department of Health. A bacteriological analysis of water from individual wells may be obtained at little or no cost to the well owner from the Division of Environmental Health of the Kansas State Department of Health. The County Health Officer can explain the procedure for obtaining this analysis.
Temperature--The temperature of the earth at a depth of 30 feet may be expected to vary less than 1 deg. F annually (Collins, 1925). Groundwater at depths of 30 to 60 feet, likewise, has only a small variation in temperature and generally exceeds the mean annual air temperature by 20 to 30 deg. F. Groundwater temperature in Johnson County, therefore, should range from about 57 deg. to 59 deg. F in aquifers at a depth of about 30 feet. At very shallow depths the ground water has a slightly greater temperature variation, as shown in table 4. Water samples from Wisconsinan and Recent alluvium ranged in temperature from 53 deg. to 60 deg. F (12 deg. to 16 deg. C). Wells pumping near a stream may induce recharge from the stream, and thus cause an increase or decrease in the groundwater temperature. The temperature of the Kansas River ranges from 32 deg. to about 80 deg. F (Fishel and others, 1953, p. 23).
Temperature of groundwater in deeper aquifers increases about 1 deg. C (1 4/5 deg. F) for each 100 feet of depth. Groundwater from Mississippian rocks at a depth of 1,100 feet below band surface would have a temperature of about 78 deg. F and water from Arbuckle rocks at a depth of 1,900 feet below band surface would have a temperature of about 92 deg. F.
Kansas Geological Survey, Johnson County Geohydrology|
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Web version April 2002. Original publication date Dec. 1971.