THREE-DIMENSIONAL GROUNDWATER FLOW MODELING USING A GEOLOGIC FRAMEWORK MODEL OF NEAR-SURFACE GLACIAL SEQUENCES: NORTHEASTERN INDIANA
This project focuses on the Huntertown aquifer system in Allen County, Indiana, which is located within the northwestern flank of Erie Lobe moraines. The main aquifer is contained within the Pleistocene Huntertown Formation, which is composed of glaciofluvial and glaciolacustrine facies interbedded with loamy till. A previously constructed 3-D GFM of the Huntertown Formation was built by constructing georeferenced raster data sets representing the morphology of each major bounding surface. The upper boundary of the model is the ground surface and the bottom of the model is the overconsolidated till of the Trafalgar Formation (Pleistocene). Because we are working in depths less than 200 feet (60 meters), we were able to employ new information from detailed borehole data and seismic-reflection surveys to refine our depiction of the hydrogeologically important Lagro Formation, a mud-rich till that caps the aquifer sequence. Refinements to the upper part of the GFM that represents the Lagro Formation (Pleistocene) include numerous sand and gravel units within and below the till.
Transient flow simulations were undertaken for the study area using the GFM. Soil and land-cover data provided spatially distributed bases for parameterizing the top surface of the model. Model outputs were processed to map areas of upward and downward near-surface flow, allowing us to identify areas of potential groundwater recharge and discharge. Locations of potential recharge and discharge are controlled by a combination of geologic materials and topographic variables. We review our methods of gleaning important information from numerical models to inform decision makers about aquifer sensitivity and vulnerability to contamination.