DETECTING RECENT CHANGE IN THE SANDSTONE AQUIFER OF SOUTHWESTERN INDIANA WITH HIGH RESOLUTION, LONG-TERM MONITORING

Hourly groundwater levels have been recorded from a piezometer nest in the Pennsylvanian Inglefield Sandstone on the University of Southern Indiana campus since January 2010. The Inglefield Sandstone has long been used as a domestic water supply in developed and rural areas of SW Indiana. The aquifer is heterogeneous, but locally is dominated by a fine-grained and cross-bedded, micaceous quartz sandstone with a discontinuous basal conglomerate, and a saturated thickness of ~20 m. The purpose of this effort is to compile and interpret long-term water levels from the Inglefield Sandstone to characterize groundwater responses to stress and to detect environmental change. Facets of this ongoing investigation focus on barometric efficiency, earth tidal responses, potential seismic loading, and secular trends.

The aquifer consistently displays vertically downward flow (recharge conditions), shallow aquifer water levels range from 0.5 – 1 m above deep water levels. The shallow aquifer displays seasonal fluctuations of ~0.15 m. The deep aquifer has a seasonal variability of ~0.03 m. Notably, potential in the shallow aquifer has risen over 0.6 m since 2010, whereas potential in the deep aquifer has remained essentially constant. The change in shallow aquifer water levels coincides with expansion of the public water supply system in Evansville, IN. Nearly 150 connections to public water are documented for the 65 km2 surrounding the monitoring site since 2010. The majority of these new public water supply connections represent conversions of existing homes that were domestic groundwater users. We hypothesize that the rise in groundwater level is a response to the shift from domestic groundwater to use of surface water from the Ohio River as part of the public water supply. Implications of higher shallow aquifer water levels include the potential to increase the flux of shallow contaminants to the deep aquifer in response to increased vertical gradients.