Groundwater Flow Modeling of Inter-aquifer Water Exchange in Toledo northwest Ohio

The aquifer system within northwest Ohio have been thought to consist of a surficial sand aquifer, a glacial till aquitard, and a confined carbonate aquifer. However, the integrity of the confining unit has been a subject of debate. Some technical reports have described the carbonate aquifer to be totally confined whereas other research characterizing the glacial till in the region have suggested possible structures like joints or fractures within the unit which could result in inter-aquifer water exchange. The objective of this study is to use a groundwater flow model to investigate the hydraulic leakance of the glacial aquitard at the Stranahan Arboretum, Toledo, in Northwest Ohio for which a conceptual hydrogeological model, based on geophysical surveys and well logs data, was set up using a MODFLOW model. The conceptual model of the site consists of a 1 - 2 m surficial sand aquifer, a 3 - 10 m glacial lacustrine sediment, 2 - 5 m thick till both comprising the aquitard overlying a carbonate aquifer at a depth ranging 12 - 16.5 m. Two additional boreholes were drilled at the study site to estimate the hydraulic parameters of the carbonate aquifer and leakage through the aquitard by conducting pump tests. Pump test data was analyzed with AQTESOLVE using the Hantush-Jacob solution for leaky aquifer. Result of pump test in the carbonate aquifer shows transmissivity range of 2.48E-3 to 9.368E-3 m/s, storativity of 0.0007715 to 0.01192, hydraulic conductivity of 9.92E-5 to 3.75E-4 m/s, and leakage coefficient of 0.019 - 0.4223. The hydraulic conductivity of the aquitard was estimated within the range of 3.42E-6 - 2.38E-5 m/s. We plan to calibrate the groundwater model using PEST to predict the inter-aquifer water exchange and compare results with field measurements to test the plausibility of the model. Leakage through the confining unit will pose a contamination threat to the groundwater. Hence, model result will help to understand aquifer interaction while also providing local data for regional groundwater-surface water model and other water management initiatives around the region.