Geological Survey Water-Supply Paper 1475-F Ground Water at Grant Village Site Yellowstone National Park, Wyoming

Ground water, in moving through rock strata from recharge areas toward points of discharge, dissolves some of the rock materials with which it comes in contact. All ground water therefore contains mineral matter in solution. The significance of the chemical and physical characteristics of water have been discussed in detail by Hem (1959), the California Water Pollution Control Board (1952, 1954), and many others. The above publications may be consulted for more detailed discussions of the chemical quality of water. Maximum limits of concentration for some of the chemical constituents commonly found in water have been specified by the U.S. Public Health Service (1946) for water used on common carriers in interstate traffic. These drinking-water standards have been accepted by the American Water Works Association as criteria of quality for all public water supplies in the United States.

During the present investigation, 11 samples of ground water were collected from the test wells in the Grant Village area. The analyses of the ground-water samples, together with the analyses of 4 samples of surface water collected from different points in Yellowstone Lake, are shown in table 2. All analyses were made at the Geological Survey laboratory, Lincoln, Nebr.

The analyses show only the dissolved mineral content of the waters, not their sanitary condition. The dissolved mineral constituents are reported in parts per million (ppm). A part per million is a unit weight of a constituent in a million unit weights of water. Results given in parts per million may be converted to grains per U.S. gallon by dividing by 17.12.

Silica (SiO₂) may occur in water as finely divided or colloidal suspended matter. In concentrations commonly found in natural or treated water, silica seems to cause no adverse physiological effects to man, livestock, or fish. It is industrially important, however, because it contributes to the formation of boiler scale, or may help to cement other substances into a hard scale, and may be carried over in the steam of high-pressure boilers to form deposits on turbine blades. Very large concentrations of silica were found in all the samples of ground water from wells in the Grant Village area. Silica concentrations ranged from 172 ppm in test well 1 to 43 ppm in test well 5. The silica content was lowest in water from test wells, 4, 5, and 6, but silica concentrations in all the ground water analyzed were above the recommended limit of 20 ppm for use as feedwater in boilers at pressures of 250 pounds per square inch or less. The silica content of the surface-water samples ranged from 5.6 to 7.4 ppm.

Iron (Fe) is present in small quantities in most natural water. Surface water, unless it is acidic, rarely contains more than a few tenths of a part per million. Much ground water, however, may contain several parts per million of iron. Iron in solution may impart an unpleasant taste to water, and upon precipitating from solution it may cause reddish-brown stains on enamelware and porcelain fixtures and on fabrics washed in the water. Iron in small quantities can be removed from water by aeration and settling or filtration, but water having large concentrations of iron may require other treatment. A considerable amount of iron was present in most of the ground-water samples. The iron content ranged from 0.17 to 1.5 ppm. Only one sample, that from the upper zone in test well 6, contained less than the recommended upper limit of 0.3 ppm for drinking water. The iron content of the surface-water samples ranged from 0.01 to 0.03 ppm.

Fluoride (F) occurs in sedimentary, igneous, and metamorphic rocks in minerals such as fluorite and apatite. Volcanic ash may contain fluoride-bearing minerals, and fluoride is often associated with volcanic or fumarolic gases. In most natural surface water fluoride is present in only small concentrations, whereas in ground water it is present in somewhat larger concentrations—in some water as high as several parts per million. Fluoride in small quantities apparently is beneficial in normal development of teeth, but more than about 1.0 ppm in drinking water may cause permanent mottling of the tooth enamel of children (California Water Pollution Control Board, 1952, p. 257). Ground-water samples high in fluoride were obtained from test well 2 (5.3, 4.6, and 5.1 ppm) and test well 3 (12 ppm). In the water samples from the other test wells, the fluoride concentration was less than the recommended upper limit of 1.5 ppm for drinking water.

Hydrogen-ion concentration generally is expressed in terms of pH units. The pH range is from 0 to 14; water having a pH of 7.0 is said to be neutral. Progressive values of pH below 7.0 denote increasing acidity, and progressive values above 7.0 denote increasing alkalinity. The pH of all except one of the ground-water samples ranged from 6.8 to 7.6. Water from a depth of 55 to 71 feet in test well 6 had a pH of 9.3; however, the pH may have increased greatly in this sample during the interval before analysis, as a preliminary analysis made with a field kit on the day following collection of the sample indicated a pH of only 6.8. The increase in pH may have occurred as a result of precipitation of silica in the water sample before the laboratory analysis was made.

The hardness of water is commonly recognized by the quantity of soap needed for washing purposes and by the formation of an undesirable curd when soap is used with the water. Calcium and magnesium cause nearly all the hardness of ordinary water. These constituents, together with silica, also are active agents in the formation of scale in steam boilers and other containers in which water is heated or evaporated. Carbonate hardness refers to the hardness expressed in terms of calcium carbonate equivalent to the carbonate and bicarbonate. Any hardness in excess of this amount is reported as noncarbonate hardness. Water that has a hardness of less than about 50 ppm generally is considered to be soft, and treatment for reduction of the hardness is unnecessary. Hardness between 50 and 150 ppm requires increased use of soap but does not otherwise seriously affect the use of water for most purposes. The carbonate hardness of water from test well 1 was 169 ppm, but that of the other ground-water samples ranged from 9 to 53 ppm. Thus, most of the ground-water samples were moderately soft. Noncarbonate hardness was not present in any of the ground-water samples. Carbonate hardness of the 4 surface-water samples from Yellowstone Lake ranged from 21 to 23 ppm; noncarbonate hardness was not present.

TABLE 2.—Chemical analyses of ground and
[Chemical constituents in parts per million]

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In summary, water from test well 1 is of poor quality because of the very high concentration of silica (172 ppm) and an objectionable amount of iron (1.5 ppm). Water from the other test wells, except for a generally high silica and iron content and high fluoride concentration as indicated in the foregoing discussion, is generally satisfactory for most uses. Surface water from Yellowstone Lake is excellent in quality and is chemically satisfactory for most uses.