QUANTIFICATION AND ISOLATION OF THE BAROMETRIC INFLUENCE ON GROUND-WATER LEVELS IN THE PENNSYLVANIAN INGLEFIELD SANDSTONE, SOUTHWESTERN INDIANA

Ground-water levels measured in the Pennsylvanian Inglefield Sandstone of southwestern Indiana display responses to loading by atmospheric pressure changes. The remarkable inverse relation between barometric pressure change and water level change is recorded in both deep and shallow piezometers (each with ten foot screened intervals) in the Ground-Water Monitoring Laboratory on the University of Southern Indiana campus. The calculated barometric efficiency of this sandstone unit is between 0.85 and 0.93, suggesting a very rigid aquifer skeleton. Although barometric responses must be quantified and successfully removed to evaluate actual potential (water level) changes in an aquifer, the recognition and interpretation of barometric responses can aid in evaluating hydrostratigraphy and aquifer properties.

Continuous water level and barometric pressure measurements permitted the quantification, isolation, and removal of barometric responses from piezometer hydrographs. After removal of the barometric influence, additional, smaller scale sinusoidal fluctuations in water levels are observed that may represent Earth tide responses. Further analyses are required to interpret these fluctuations.

The rapid and constant barometric response functions in these piezometers are diagnostic of a confined system, suggesting that the Inglefield Sandstone is a confined aquifer in this area. Whereas the micritic West Franklin Limestone forms a basal confining layer, stratigraphic observations do not indicate the presence of an obvious upper confining layer. Heterogeneity within the Inglefield Sandstone, in particular a fine-grained facies with oriented mica grains likely serves as an upper confining layer.