Illinois State Library

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Title

• Leaky artesian aquifer conditions in Illinois

Description

• Most if not all of the so called artesian aquifers in Illinois are actually leaky artesian aquifers. If the permeability of the confining bed is very low, vertical leakage may be difficult to measure within the average period (8 to 24 hours) of pumping tests. However, since the cone of depression created by pumping a well tapping a leaky artesian aquifer continues to expand until discharge is balanced by the amount of induced leakage, it does not follow that vertical leakage is of small importance over extended periods of time. As the cone of depression grows in extent and depth, the area of leakage and the vertical hydraulic gradient become large. Accordingly then, with long periods of pumping, contribution by leakage through a confining bed may be appreciable even though the vertical permeability is very low. If a source is available to replenish continuously the confining bed, the cone of depression developed by a well pumping for long extended periods will be influenced by the vertical permeability of the confining bed in addition to the hydraulic properties and geohydrologic boundaries of the main aquifer. Any long-range forecast of well or aquifer yield must include the important effects of leakage through the confining bed. The vertical permeability of a confining bed often can be determined from the results of pumping tests as described in this publication.

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1. Leaky artesian aquifer conditions in Illinois (20061005222537_ISWSRI-39.pdf).
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