Coupled 2-D Geophysics to Better Characterize Shallow Sand and Gravel Aquifers

Combining profiles of high-resolution seismic and electrical-resistivity data has provided detailed insights into the character of shallow, glacially-derived aquifers in McHenry County, Illinois. These shallow aquifers were deposited within meltwater outwash valleys during multiple glacial episodes. The unconfined aquifers in these valleys are easily accessible and are a primary source of domestic and agricultural water supplies. Thus, it is important to understand their detailed character and distribution.

Miles of seismic reflection profiles were coupled with electrical resistivity profiles to optimize interpretations of aquifer character. Thus, at the same locations, seismic-reflection profiles indicated aquifer boundaries and internal sediment structures, while electrical resistivity profiles indicated textural and facies changes within the aquifer. When combined, these data were complementary to one another and consistent with local and regional interpretations of the geologic framework. Furthermore, the new insights contribute greatly to better understanding how the geologic framework controls groundwater recharge and contamination potential.