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Ground-water Resources
Source, Occurrence, and Movement of Ground Water
The discussion of the occurrence of ground water in Douglas County is based partly on a detailed treatment by Meinzer (1923, 1923a). A general discussion of the principles of ground-water occurrence with special reference to Kansas has been given by Moore and others (1940).
Ground water is the part of the water below the surface of the land that is in the zone of saturation and supplies wells and springs. It is derived mainly from precipitation, falling as rain or snow, some of which reaches the zone of saturation by percolation downward through the soil and subsoil.
The rocks in the outer crust of the earth are not solid but contain many openings, or voids, that hold air, water, or other fluids. Generally, the rock formations below a certain level are saturated with water. The upper surface of the zone of saturation is not a level surface nor a static surface, but one that has many irregularities, which on a modified scale are generally similar to the irregularities of the surface topography. Under natural conditions, the small part of the precipitation that reaches the zone of saturation moves slowly toward the streams and discharges into them or is lost by transpiration and evaporation in the valley areas.
Water in the zone of saturation, available to wells, may be unconfined or confined. Unconfined or free ground water is water that does not have a confining or impermeable body restricting its upper surface. The upper surface of unconfined ground water is called the water table. Shallow wells constructed in the near-surface weathered limestone, sandstone, and shale, the alluvial deposits in stream valleys, and the colluvial slope deposits generally tap unconfined ground water. Ground water is said to be confined if it occurs in permeable zones between relatively impermeable beds that confine the water under pressure. Most of the wells constructed in the unweathered Pennsylvanian bedrock tap confined ground water.
Ground-water Recharge and Discharge
The addition of water to the underground reservoir is called recharge and may be effected in several ways. The most important source of recharge is local precipitation; for shallow upland wells local precipitation is the only source of recharge. Lesser amounts are contributed elsewhere by influent seepage from streams and ponds and by subsurface inflow from adjacent areas. Locally, however, influent seepage from streams may contribute an important amount of recharge to adjacent alluvial deposits and to the bedrock where streams cut across permeable zones in bedrock.
Recharge is seasonal in the Midwest, including Douglas County. Generally the water levels of wells have been lowered by natural drainage into streams during the winter, when the soil is frozen and precipitation is slight. During the spring months precipitation is fairly abundant, temperature is moderately cool, and transpiration and evaporation demands are low, resulting in considerable recharge. Recharge may occur in other seasons, also, whenever precipitation is sufficient to overcome soil-moisture deficiency built up during a preceding dry period.
Ground water moves downward through the permeable rocks in accordance with the character and structure of the rocks, to points of lower elevation. It may discharge directly into a stream as a spring or seep or may discharge by evaporation or transpiration where the water table is near the surface. A part of the ground water is discharged from wells, but, with the exception of the municipal, industrial, and irrigation pumpage in the Kansas River valley in the vicinity of Lawrence, the amount discharged by wells in Douglas County is small compared with that discharged by other means.
Under natural conditions, over a long period of time, approximate equilibrium exists between the amount of water that it added annually to ground-water storage and the amount that is discharged annually.
Chemical Character of Ground Water
Water is often 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 can be predicted from the results of a quantitative analysis.
The analyses of 112 samples of water from wells, test holes, and springs in Douglas County are given in Table 4 in parts per million (ppm). Factors for converting parts per million of mineral constituents to equivalents per million are given in Table 5.
Table 5.--Factors for converting parts per million of mineral constituents to equivalents per million.
| Cation | Conversion factor |
Anion | Conversion factor |
|---|---|---|---|
| Ca++ | 0.0499 | HCO3- | 0.0164 |
| Mg++ | 0.0822 | SO4-- | 0.0208 |
| Na+ | 0.0435 | Cl- | 0.0282 |
| NO3- | 0.0161 | ||
| F- | 0.0526 |
Quality in relation to use
Ground water from properly constructed wells characteristically has good bacterial and sanitary quality, but the chemical character of the water is of importance also. Water to be used for drinking should not contain excessive amounts of iron, magnesium, chloride, sulfate, nitrate, and certain other constituents. Water used for cooking and washing has these and other limitations, chiefly of hardness and bicarbonate. Water used for irrigation should not contain excessive mineral matter nor excessive amounts of chloride or of sodium in relation to other cations.
Ground water used in industrial processes generally must meet certain standards. These standards for some processes may be much more critical than standards for drinking water. The total dissolved solids, hardness, hydrogen-ion concentration (pH), alkalinity, and iron are some of the more important factors. Temperature also is an important factor in many industrial uses of ground water.
Dissolved solids
When water is evaporated the residue consists mainly of the mineral constituents listed in Table 4 and may include a small quantity of organic material and water of crystallization. Water containing less than 500 ppm of dissolved solids generally is satisfactory for domestic use, except for difficulties resulting from its hardness, or an excessive content of iron. Water containing more than 1,000 ppm of dissolved solids may include enough of certain constituents to produce a noticeable taste or to make it unsuitable in some other respect.
The amount of dissolved solids in 66 samples of ground water collected in Douglas County from wells, test holes, and springs is indicated in Table 4. The dissolved solids content ranged from 135 to 21,400 ppm. Twenty-two samples, all from Pennsylvanian sandstone and limestone aquifers, contained more than 1,000 ppm.
Hardness
Hardness of water is commonly recognized by its effect when soap is used with the water. Calcium and magnesium cause nearly all the hardness of water and are the active agents in the formation of the greater part of scale in steam boilers and other vessels in which water is heated or evaporated.
In addition to the total hardness, the table of analyses gives the carbonate and noncarbonate hardness of water in Douglas County. Carbonate, or temporary, hardness can be removed almost entirely by boiling. The noncarbonate hardness is due to the presence of sulfates or chlorides of calcium and magnesium; it cannot be removed by boiling and, therefore, is sometimes called permanent hardness. The two types of hardness have the same reaction when the water is used with soap.
Water having a hardness of less than 60 ppm is rated as soft and is seldom treated to remove hardness. Hardness of 60 to 120 ppm increases the consumption of soap but does not seriously interfere with the use of the water for most purposes. Hardness of more than 120 ppm can be noticed by anyone; if the amount is about 200 ppm or more the water is sometimes softened for household use, or cisterns may be installed to collect soft rainwater. Where municipal supplies are softened, the hardness is generally reduced to between 80 and 100 ppm.
The hardness of 97 samples of ground water collected in Douglas County ranged from 19 to 2,590 ppm (Table 4). The hardest and softest waters were from Pennsylvanian sandstones, but more than half of the samples collected from Pennsylvanian rocks had a hardness of less than 200 ppm. Almost all the water samples collected from Quaternary deposits have a hardness range from 200 to 800 ppm, and in general they are appreciably harder than water from the Pennsylvanian sandstones.
Iron
Iron (Fe) generally is present in small quantities in most natural ground water. If water contains much more than 0.1 ppm, some of the iron may precipitate as a reddish sediment. Iron in excess of 0.3 ppm is undesirable, as it may stain cooking utensils, plumbing fixtures, and clothing being laundered, or give a disagreeable taste to the water.
The iron content of 96 samples of ground water collected in Douglas County ranged from 0.03 to 49 ppm (Table 4). Of the 96 samples, 69 contained 0.3 ppm or more of iron.
Fluoride
Fluoride (F) in concentrations of about 1 ppm in drinking water used by children during the period of calcification of the teeth prevents or lessens the incidence of tooth decay; concentrations greater than 1.5 ppm may cause mottling of the enamel (Dean, 1936, 1938; U. S. Public Health Service, 1946).
The fluoride content of 97 samples of ground water collected in Douglas County ranged from 0.0 to 12 ppm. Fifteen samples, all from Pennsylvanian sandstone aquifers, contained fluoride in amounts greater than 1.5 ppm.
Nitrate
A concentration of 90 ppm of nitrate (NO3) in drinking water may cause cyanosis and hence is judged by the Kansas State Board of Health to be dangerous to infants (Metzler and Stoltenberg, 1950), and some authorities (Comly, 1945) recommend that water containing more than 45 ppm should not be used for preparation of infants' formulas. Concentrations of nitrate found in ground water generally do not cause cyanosis in older children or adults but may have other adverse effects.
Of the 64 samples analyzed for nitrate (NO3), only 4 contained more than 90 ppm. Of these, 3 samples were from shallow dug wells, which as a rule are more susceptible to contamination from the surface than are deeper, drilled wells. The nitrate content of the 64 samples ranged from 0.0 to 257 ppm.
Sulfate
Sulfate (SO4) in ground water is derived chiefly from solution of gypsum and the oxidization of iron sulfides, Sulfate occurring in ground water as magnesium sulfate (Epsom salt) and sodium sulfate (Glauber's salt) in excess of about 500 ppm may have a laxative effect on persons not accustomed to drinking such water.
Chloride
Chloride (Cl) in ground water may be derived from connate marine water in the sediments, from sewage, or, in small quantities, from solution of minerals containing chloride. Chloride has little effect on the suitability of water for ordinary use unless the quantity is enough to give the taste of salt. A chloride content of about 250 or 300 ppm can be detected by persons having a sensitive taste. Water strong in chloride is corrosive to many metal surfaces.
Sodium chloride is the chief dissolved constituent of the ground water in some of the deeper Pennsylvanian sandstone aquifers, which prevents use of otherwise adequate supplies of ground water in some parts of the county.
The chloride content of 112 samples analyzed ranged from 1.5 to 12,800 ppm.
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 may be free from harmful bacteria and consequently may be safe for drinking. Other well water, good tasting and seemingly pure, may contain harmful bacteria. Excessive amounts of certain dissolved minerals, such as chloride or nitrate, may indicate pollution.
Recommended sanitary types of construction and suggestions for locations and pump installations for different types of wells can be obtained from the Kansas State Board of Health.
Changes in temperature and quality of water--The temperature of ground water tapped by wells is uniformly about 57°F to 59°F in this area but may be a few degrees colder or warmer in very shallow or very deep aquifers. In most aquifers, except very shallow ones, the annual temperature fluctuation is small. The pumping of wells located near a stream may induce recharge from the stream, and thus cause an increase or decrease in the temperature of ground water being pumped. The temperature of Kansas River ranges from about 32°F to 80°F, and if a significant proportion of ground water being pumped from a well is indirect recharge of appreciably colder or warmer river water, the well-water temperature may be noticeably affected. According to temperature records kept by Westvaco Mineral Products Division of Food Machinery & Chemical Corp. at its Lawrence plant, ground water pumped from its well field, 0.6 to 0.7 mile from Kansas River, has a nearly constant temperature of 58°F throughout the year, the maximum variation reportedly being about half a degree. Wells therefore must be much closer to the river to be noticeably affected by fluctuations in the temperature of the river water.
The chemical quality of water in an aquifer may be modified by ground-water development and use. Return flow from irrigation, waste water from industry, or waste water from municipalities generally contains a greater proportion of dissolved matter than it had prior to use. If all or a part of this water is returned to the aquifer it may result in a ground-water supply of lower quality. If development of ground-water supplies results in additional recharge of ,letter or poorer water to the aquifer, it may produce ground water of respectively better or poorer quality.
Aquifer Properties
An aquifer is a geologic formation, a part of a formation, or a group of formations that will yield water. The quantity of ground water that an aquifer will yield to wells depends partly on its thickness, extent, continuity, and homogeneity, and partly on its physical properties of permeability and porosity.
The field coefficient of permeability (P) is defined as the number of gallons of water that will move in 1 day, at the prevailing water temperature, through a vertical section of the aquifer I foot square under a hydraulic gradient of 100 percent or 1 foot per foot. Coefficients of permeability of less than 100 gallons a day per square foot are considered low, coefficients of 100 to 1,000 are medium, and those of more than 1,000 are considered high. The coefficient of transmissibility (T) is equal to the field coefficient of permeability multiplied by the thickness (m) of the aquifer.
The coefficient of storage (S) is defined as the volume of water, measured in cubic feet, released from storage in each column of the aquifer having a base I foot square and a height equal to the thickness of the aquifer, when the water table or other piezometric surface is lowered 1 foot. In water-table aquifers the coefficient of storage for long periods of pumping is approximately the specific yield and has a range from about 0.1 to 0.3. The specific yield is defined as the ratio of the volume of water a saturated material will yield by gravity to its own volume. For artesian aquifers the coefficient of storage generally is very small, ranging from about 10-5 to 10-3.
The coefficients of transmissibility and of storage are used in making quantitative estimates of water available in an aquifer, and of the water-level decline that will result from pumping. Controlled aquifer (or pumping) tests can be made to obtain the data required to determine these coefficients.
Drawdown in a well is the lowering of the water table or piezometric surface caused by pumping or artesian flow. The specific capacity of a well is the discharge expressed as rate of yield per unit of drawdown, generally gallons per minute per foot of draw-down.
Hydrologic data on the principal aquifers, obtained by pumping and laboratory tests, and information supplied by well owners are summarized in Table 6.
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Kansas Geological Survey, Geohydrology of Douglas County
Web version Aug. 1999. Original publication date Dec. 1960.
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