An analytical solution is developed describing vertical steady flow of groundwater and heat through an isotropic, homogeneous, and fully saturated semiconfining layer. A typecurve method for estimating groundwater velocities from temperature data is presented.

A solution is presented for the change in water level in a well of finite diameter after g known volume of water is suddenly injected or withdrawn. A set of type curves computed from this solution permits a determination of the transmissibility of the aquifer. (

The water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by Earth tide dilatation of the aquifer. Because a finite amount of time is needed for water to flow into and out of the well, there exists a phase shift (or time lag) between the tidal dilatation of the aquifer and the water level response in the well. We derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity, storage coefficient, well radius, and the period of the harmonic disturbance. This solution is rather insensitive to the storage coefficient. Thus if the phase shift is known for a harmonic disturbance, the transmissivity can be calculated given a rough estimate of the storage coefficient. Theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying, as in the case of Earth tides. This opens the possibility of estimating aquifer transmissivity from water level records that show Earth tide fluctuations. A case study, using data from a site near Parkfield, California, is presented to illustrate application of the theory. Phase shifts of the O• (25.82hour period) and M 2 (12.42-hour period) tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure. A brief error analysis suggests that the computed O x phase shift is subject to large uncertainty, while the computed M 2 phase shift is substantially more accurate. Based on an assumed storage coefficient range of 10 -• to 10 -6, the estimated transmissivity range is 8 x 10 -6 to 2 x 10 -• m2/s. While hydraulic tests have not been performed to validate these estimates, the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake.

An experiment in an oil field at Rangely, Colorado, has demonstrated the feasibility of earthquake control. Variations in seismicity were produced by controlled variations in the fluid pressure in a seismically active zone. Precise earthquake locations revealed that the earthquakes clustered about a fault trending through a zone of high pore pressure produced by secondary recovery operations. Laboratory measurements of the frictional properties of the reservoir rocks and an in situ stress measurement made near the earthquake zone were used to predict the fluid pressure required to trigger earthquakes on preexisting fractures. Fluid pressure was controlled by alternately injecting and recovering water from wells that penetrated the seismic zone. Fluid pressure was monitored in observation wells, and a computer model of the reservoir was used to infer the fluid pressure distributions in the vicinity of the injection wells. The results of this experiment confirm the predicted effect of fluid pressure on earthquake activity and indicate that earthquakes can be controlled wherever we can control the fluid pressure in a fault zone.

The water level in a well open to an artesian aquifer responds to pressure‐head fluctuations caused by the dilatation of the aquifer. Based on hydrologic considerations, it is shown that (1) most well‐aquifer systems respond to disturbances with periods of less than several days as if the well were drilled into a medium of infinite or partially bounded extent, and (2) the representation of an aquifer as a finite cavity is unrealistic for most well‐aquifer systems. The amplitude of tidal water level fluctuations in well‐aquifer systems depends on the dilatation and the specific storage of the aquifer. Analysis of the dilatation caused by the earth tide is based on the assumptions that (1) the latitudinal and longitudinal strains caused by the earth tide are determined by the elastic properties of the earth as a whole and are largely independent of the elastic properties of a near surface aquifer, and (2) the vertical strain of a near surface aquifer depends on Poisson's ratio (or the Lamé constants) for the aquifer and the latitudinal and longitudinal strains. The tidal dilatation can be computed from equilibrium tide theory provided that Poisson's ratio is known. The amplitude of the tidal dilatation produced by the large semidiurnal wave, M2, is approximately 1 × 10−8. It is not unusual to have earth‐tide fluctuations in wells corresponding to M2 with an amplitude of 1 to 2 cm. The fact that tidal water‐level fluctuations depend upon the specific storage of the aquifer explains the variation in amplitude which troubled others. The specific storage and the porosity of the aquifer can be computed from an analyses of earth‐tide fluctuations if Poisson's ratio for the aquifer is known. Computations of specific storage and porosity are presented for three artesian wells for which tidal harmonic analysis of hydrograph data was published by Melchior. The results of these calculations appear to be better than one might reasonably expect.