MODEL OF A GROUNDWATER/SURFACE WATER INTERACTION WITHIN THE TICONA CHANNEL NEAR LEONORE, ILLINOIS

The Ticona Channel, which is located in north-central Illinois, is an ancient river valley that has been partially filled with Illinoian sand and gravel and capped with Wisconsinan till. Increasing water supply demands prompted the investigation of the valley fill sand and gravel as a potential groundwater source. Recently collected field data from geophysical profiles, geologic mapping, and well logs indicated the possible occurrence of a groundwater/surface water interaction between the Vermilion River and the Ticona Channel sediments. From the field data, a working hypothesis of a hydrologic interaction was tested by building a groundwater model. The occurrence of such an interaction could amplify groundwater contamination concerns and limit aquifer potential.

A steady-state groundwater flow model was created in MODFLOW that simulated a groundwater/surface water interaction between the Vermilion River and the Ticona Channel sediments. Borehole data indicated that the aquifer material was not fully saturated; therefore the aquifer was modeled as unconfined. The aquifer material was assumed homogeneous and isotropic. The model demonstrated that the Vermilion River recharges the aquifer where the aquifer material (sand) is exposed at river level. Different scenarios were run in order to determine a best fit hydraulic conductivity and aerial recharge value. These values were calibrated with a monitoring well located in the center of the aquifer. Because the sand is covered by 40 m (130 ft) of glacial till, evapotranspiration was negligent and aerial recharge was a function of the glacial till hydraulic conductivity. Hydraulic conductivity of the sand was determined to be approximately 1.00E-3 m/s and aerial recharge was predicted as 1.00E-12 m/s.

The groundwater model supported the working hypothesis that a groundwater/surface water interaction occurs within the study area. However, the realization of this groundwater/surface water interaction must be examined more closely in order to better characterize the possibility of contamination, as it is possible that contaminates from the Vermilion River could infiltrate into the aquifer. The effects of pumping groundwater out of the aquifer must also be more closely evaluated, as the effects of over-pumping within in the aquifer on the river is not yet known.