ISSN:
1745-6584
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Energy, Environment Protection, Nuclear Power Engineering
,
Geosciences
Notes:
Water-bearing properties of crystalline rocks are dependent on the occurrence of joints and faults and the extent of weathering. Interstitial openings caused by weathering are mostly at depths of less than 100 feet. Joints are less abundant and openings along joint planes are smaller as depth increases. Openings along fault surfaces also tend to close with depth. These geological observations which indicate a decrease in rock permeability with depth are verified by a study of well yields and water-injection tests. Mean yields per foot of well are 0.23 to 0.30 gpm at 100 feet but only 0.013 to 0.04 gpm at 1000 feet. Mean injection rates per foot of drill hole under 100 psi pressure are 0.11 to 0.4 gpm at 100 feet but only 0.014 to 0.038 gpm at 1000 feet. Median values of both well yields and injection rates are from one-half to one-third of the mean values. Geologic structure is more important than rock type in determining yields and injection rates. The decrease in rock permeability with depth indicates an increase in the unit cost of water with depth. The optimum depth of a well is, therefore, determined largely by economic factors. Unless geologic factors are favorable, wells in crystalline rocks should be less than 600 feet deep. In general, domestic wells should be less than 150 to 250 feet deep.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1745-6584.1964.tb01750.x
