REFINING OUR UNDERSTANDING OF HETEROGENEITY IN THE INGLEFIELD SANDSTONE AQUIFER, SOUTHWESTERN INDIANA: OUTCROPS, CORES, AND GAMMA LOGS

In order to more fully understand groundwater flow conditions in the local domestic aquifer of southwestern Indiana, the three-dimensional heterogeneity of the Pennsylvanian Inglefield Sandstone was characterized through outcrop, core, and geophysical observations. This facet of research was part of a larger project that included the development of a real-time groundwater level data-stream and educational website to inform the community about the local groundwater resource and hydrogeologic processes. Field observations of local Inglefield Sandstone outcrops provided a broad view of the range of heterogeneities in the aquifer. At five sites, samples were collected, evaluated, and compared in the lab using thin section petrography and grain size analyses. Detailed gamma logging of the established groundwater monitoring site on the University of Southern Indiana campus provided site-specific data on aquifer heterogeneity. Our data indicate that the Inglefield Sandstone contains approximately 20% matrix and framework grains comprise nearly 70% quartz with varying amounts of feldspar and lithics. The sandstone is moderately sorted with a mean grain size that ranges from fine- to coarse-grained. Outcrops display horizontal bedding, low to high angle cross bedding, lenticular bedding, and channel forms. One local outcrop displays stratigraphic variability that includes discontinuous lenses of gray shale. Gamma logging corroborates mesoscale (outcrop) observations and identifies heterogeneities within the Inglefield Sandstone including coarse, medium, and fine grained sands with interbedded fine-grained mudrocks. The field and lab data indicate the potential for spatial variability in the aquifer due to stratigraphic heterogeneity and varying grain sizes and clay content. Characterizing the spatial heterogeneity of the Inglefield Sandstone is prerequisite to developing a conceptual model of groundwater flow within this locally important domestic aquifer and understanding its vulnerability to contamination.