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USGS1960

Borehole geophysical methods for analyzing specific capacity of multiaquifer wells : ground-water hydraulics

Conventional well-logging techniques, combined with measurements of flow velocity in the borehole, can provide information on the discharge-drawdown characteriBtic8 of the several aquifers penetrated by a well. The information is most conveniently presented in a graph showing aquifer discharges as functions of the water level in the well at a particular time. To determine the discharge-drawdown characteristics, a well is pumped at a steady rate for a certain length of time. While the well is being pumped, measurements are made of drawdown and of the discharge rates of the individual aquifers within the well. Discharge rates and drawdowns ,are usually recorded as functions of time, and their values for any given time during the test are obtained by interpolation. The procedure is repeated for several different rates of total well discharge. The well may be allowed to recover after each step, or discharge may be changed from one rate to another, and changes in discharge and drawdown may be measured by extrapolation. The flow measurements within the well may be made by use of a subsurface flowmeter or by one of several techniques involving the injection of electrolytic or radioactive tracers. The method was tested on a well in Mercer County, Pa., and provided much useful information on aquifer yields, 'thieving,' and hydrostatic heads of the individual zones.

Water Supply Paper↗
USGS1961

A Simple Method for Determining Specific Yield from Pumping Tests

A simpler solution which greatly reduces the time necessary to compute the specific yield by the pumping-test method of Remson and Lang (1955) is presented. The method consists of computing the volume of dewatered material in the cone of depression and comparing it with the total volume of discharged water. The original method entails the use of a slowly converging series to compute the volume of dewatered material. The solution given herein is derived directly from Darcy's law.

Water Supply Paper↗
USGS1962

Theory of aquifer tests

The development of water supplies from wells was placed on a rational basis with Darcy's development of the law governing the movement of fluids through sands and with Dupuit's application of that law to the problem of radial flow toward a pumped well. As field experience increased, confidence in the applicability of quantitative methods was gained and interest in developing solutions for more complex hydrologic problems was stimulated. An important milestone was Theis' development in 1935 of a solution for the nonsteady flow of ground water, which enabled hydrologists for the first time to predict future changes in ground-water levels resulting from pumping or recharging of wells. In the quarter century since, quantitative ground-water hydrology has been enlarging so rapidly as to discourage the preparation of comprehensive textbooks. This report surveys developments in fluid mechanics that apply to groundwater hydrology. It emphasizes concepts and principles, and the delineation of limits of applicability of mathematical models for analysis of flow systems in the field. It stresses the importance of the geologic variable and its role in governing the flow regimen. The report discusses the origin, occurrence, and motion of underground water in relation to the development of terminology and analytic expressions for selected flow systems. It describes the underlying assumptions necessary for mathematical treatment of these flow systems, with particular reference to the way in which the assumptions limit the validity of the treatment.

Water Supply Paper↗
USGS1962

A formula for computing transmissibility causing maximum possible drawdown due to pumping

By modifying the Theis nonequilibrium formula a relation is found in which the maximum possible drawdown is expressed in terms of a unique value for the aquifer coefficient of transmissibility. The relation is valid for any specified period and rate of pumping, for a given aquifer coefficient of storage, and for ,any desired radial distance from the center of pumping.

Water Supply Paper↗
USGS1962

Constant-head pumping test of a multiaquifer well to determine characteristics of individual aquifers

This report describes the theory and field procedures for determining the transmissibility and storage coefficients and the original hydrostatic head of each aquifer penetrated by a multiaquifer well. The procedure involves pumping the well in such a manner that the drawdown of water level is constant while the discharges of the different aquifers are measured by means of borehole flowmeters. The theory is developed by analogy to the heat-flow problem solved by Smith. The internal discharge between aquifers after the well is completed is analyzed as the first step. Pumping at constant, drawdown constitutes the second step. Transmissibility and storage coefficients are determined by a method described by Jacob and Lohman, after the original internal discharge to or from the aquifer has been compensated for in the calculations. The original hydrostatic head of each aquifer is then determined by resubstituting the transmissibility and storage coefficients into the first step of the analysis. The method was tested on a well in Chester County, Pa., but the results were not entirely satisfactory, owing to the lack of sufficiently accurate methods of flow measurement and, probably, to the effects of entrance losses in the well. The determinations of the transmissibility coefficient and static head can be accepted as having order-of-magnitude significance, but the determinations of the storage coefficient, which is highly sensitive to experimental error, must be rejected. It is felt that better results may be achieved in the future, as more reliable devices for metering the flow become available and as more is learned concerning the nature of entrance losses. If accurate data can be obtained, recently developed techniques of digital or analog computation may permit determination of the response of each aquifer in the well to any form of pumping.

Water Supply Paper↗
USGS1964

Methods of determining permeability, transmissibility and drawdown

If the Theis graphical method is used for determining the hydraulic constants of an aquifer under water-table conditions, the observed drawdowns should be corrected for the decrease in saturated thickness. This is especially true if the drawdown is a large fraction of the original saturated thickness, for then the computed coefficient of permeability is highly inaccurate if based on observed, rather than corrected, water levels. Wenzel's limiting formula, a modification of the Theis graphical method, is useful where u=r2s/4Tt is less than about 0.01. However, a shorter procedure for determination of the coefficient of transmissibility, as well as the coefficient of storage, consists of plotting the values of the corrected drawdowns against the values of the logarithm of r. Wenzel (1942) suggested that observation wells be situated on lines that extend upgradient and downgradient from the pumped well. However, a detailed analysis of aquifer-test results indicates that such a restriction is unnecessary. The gradient method for determining permeability should yield the same results as the Thies method. The former, when applied for a distance within the range of applicability of the latter, is merely a duplication of effort or, at best, a crude check. Because of the limitations of accuracy in plotting, the gradient method is much less satisfactory. That Wenzel (1942) obtained identical results from the two methods is regarded as a coincidence. Failure to take into consideration the fact that the pumped well does not tap the full thickness of the aquifer leads to an apparent coefficient of permeability that is much too low, especially if the aquifer consists of stratified sediments. The average coefficient of permeability computed from uncorrected drawdowns may be only a little more than half of the true value.

Water Supply Paper↗
USGS1961

Exploratory drilling for ground water in the Mountain Iron-Virginia area, St. Louis County, Minnesota

The Mountain Iron-Virginia area is a broad, southwest-trending valley in the central part of the Mesabi Range. The valley, which heads in the Laurentian Divide, and covers about 120 square miles, coincides approximately with a bedrock valley filled with as much as 150 feet of glacial deposits. A complex sequence of glacioaqueous sediments made up of clay, silt, sand, and gravel was delineated from test holes drilled at 238 sites. These sediments range in thickness from 0 to 125 feet and can be considered a hydrologic unit, bounded below by sandy till or bedrock and above by as much as 60 feet of clayey till. The piezometric surface ranges from 0 to about 70 feet below land surface, thus, the glacioaqueous deposits are not everywhere completely saturated. In places, however, the water is under artesian pressure. Within the Mountain Iron-Virginia area about 50 square miles are underlain by deposits 20 feet or more in thickness of silt, sand, or gravel that constitute an aquifer that is a large potential source for additional water supplies. Except for iron and manganese, which are present in excessive amounts in some wells, the water meets U.S. Public Health Service standards for municipal supplies. Pumping tests of wells in the permeable sand or gravel deposits at five sites indicate that yields of several hundred gallons per minute and possibly as much as 2,000 gpm (gallons per minute) can be expected.

Minnesota↗
USGS1961

Aquifers in melt-water channels along the southwest flank of the Des Moines Lobe, Lyon County, Minnesota

During the Gary and Mankato substages of Wisconsin glaciation the Des Moines lobe advanced southeastward through the broad lowland of the Minnesota River valley of southwestern Minnesota, and thence southward to central Iowa. Among the most prominent topographic features in Lyon County, Minn., are five southeastward-trending end moraines, two of which are associated with and parallel to belts of surficial outwash that are approximately half a mile to a mile wide. Test drilling indicated that one of the belts of outwash is underlain by a complex system of buried melt-water channels. The other is the upper part of a series of deposits in an incised channel. The channels are filled with till, glaciolacustrine deposits, and outwash, which includes permeable deposits of water-bearing sand and gravel. Associated with the surficial melt-water channels is a pronounced southeastward-trending linear drainage pattern. By studying the lineation of streams and lakes, analyzing the available water-well data, and drilling test holes, several elongate deposits of buried outwash having little or no topographic expression were located. The long axes of the deposits are generally parallel to the lineation of the drainage and the end moraines. The melt-water channels in Lyon County trend southeastward because the flank of the ice sheet was confined by a landmass that sloped to the northeast. Similar buried channels may be present elsewhere along the southwest flank of the Des Moines lobe. If so, they probably can be located by the methods described.

Minnesota↗
USGS1963

Ground-water geology of Karnes County, Texas

The exposed rocks and those underlying Karnes County dip toward the Gulf of Mexico at average rates ranging from 20 to more than 200 feet per mile. The oil fields are on structures associated with faulting; the effect of faulting on the occurrence of ground water has not been determined. The principal water-bearing formations, from oldest to youngest, underlying the county are the Carrizo sand, Yegua formation, Jackson group, Catahoula tuff, Oakville sandstone, and Lagarto clay. They range in age from Eocene to Miocene and all are of sedimentary origin. About 40 million acre-feet of usable water (water containing less than 3,000 ppm) is stored more then 2,500 feet below land surface in the Carrizo sand; 30 million acre-feet is stored in the younger formations at depths less than 1,000 feet. Ground-water withdrawals for municipal, industrial, and domestic use averaged about 1.7 million gpd in 1957. Irrigation and stock supplies were derived from both ground- and surface-water sources. In general, water levels from 1936 through 1957 were not affected appreciably by withdrawals. Recharge to the ground-water reservoir from precipitation, although only a small percentage of total precipitation, exceeded withdrawals of ground water by wells in 1957. Most of the usable ground water in Karnes County is of substandard quality; whereas water from the San Antonio River, although hard, is of excellent quality. Wells tapping the Carrizo may yield as much as 1,000 gpm in the northwestern part of the county; wells in the shallower formations may yield as much as 600 gpm in the most favorable areas, but in some places may yield only a few gallons per minute of water suitable only for stock.

Water Supply Paper↗