RECHARGE ANALYSES INTO SHALLOW GLACIAL AND DEEP BEDROCK AQUIFERS RELATED TO THE TROY BEDROCK VALLEY SYSTEM, DEKALB COUNTY, ILLINOIS

A variety of methods have been employed to both measure and estimate recharge into near-surface aquifer systems, including “rule-of-thumb” precipitation percentages, stream discharge loss calculations, tensiometer and piezometer measurements, isotope analyses, and GIS and digital modeling. Subsequent recharge rates and pathways to deeper aquifer systems are more difficult to directly measure and require more comprehensive efforts to digitally model entire systems, in conjunction with direct measurements to calibrate the model results. As DeKalb County is on the verge of expansion from the Chicago metropolitan area and serves as a recharge area for the regional aquifer system, a combined application of modeling-GIS-field-lab approaches to this ideal critical setting will assist researchers and agencies involved with these problems across the nation.

The primary goals of this study are to 1) critically evaluate the results of various methods previously employed in DeKalb County (which produced recharge estimates between 0.2 and 13 inches per year to the local glacial aquifer system) along with proposed isotopic groundwater dating techniques and 2) these results are also being evaluated as inputs into a county-scale model to provide a rare comparison of a wide variety of recharge quantification methods applied within a single large area. The groundwater flow model will track recharge through the surficial deposits to the shallow glacial groundwater system and ultimately to the deeper regional bedrock aquifer systems associated with the Troy Bedrock Valley. A background goal is to benefit water planning within the rapidly urbanizing, 11-county greater Chicago region of northeastern Illinois, comparing this higher-resolution local model’s discharge into the regional bedrock aquifer system to that of the Illinois State Water Survey’s regional model.