Modeling a Large-Scale Historic Aquifer Test: Insight into the Hydrogeology of a Regional Fault Zone.

Faults can act as flow barriers or conduits to groundwater flow by introducing heterogeneity in permeability. We examine the hydrogeology of the Sandwich Fault Zone, a 137 km long zone of high-angle faults in northern Illinois, using a large-scale historic aquifer test. The fault zone is poorly understood at depth due to the majority of the faults being buried by glacial deposits and its near-vertical orientation which limits geologic sampling across faults.

Developing Potentiometric Surfaces and Flow Fields with a Head-Specified MODFLOW Model.

Investigating changes in an aquifer system often involves comparison of observed heads from different synoptic measurements, generally with potentiometric surfaces developed by hand or a statistical approach. Alternatively, head-specified MODFLOW models, in which constant head cells simulate observed heads, generate gridded potentiometric surfaces that explicitly account for Darcy's Law and mass balance. We developed a transient head-specified MODFLOW model for the stratified Cambrian-Ordovician sandstone aquifer system of northeastern Illinois to analyze flow within its 275 m deep cone of depression.

A hybrid framework for improving recharge and discharge estimation for a three-dimensional groundwater flow model.

We employed the ArcGIS plug-in package PRO-GRADE (Lin et al. 2009), developed for zonation of recharge/discharge (R/D) for modeling two-dimensional aquifer systems, to develop alternative R/D zonations for an existing three-dimensional groundwater flow model of a complex hydrogeologic setting. Our process began by intersecting PRO-GRADE output with the existing model's 4-zone R/D representation to develop a model having 12 R/D zones (R12) and then calibrating the resulting model using PEST.

Extremely alkaline (pH > 12) ground water hosts diverse microbial community.

Chemically unusual ground water can provide an environment for novel communities of bacteria to develop. Here, we describe a diverse microbial community that inhabits extremely alkaline (pH > 12) ground water from the Lake Calumet area of Chicago, Illinois, where historic dumping of steel slag has filled in a wetland. Using microbial 16S ribosomal ribonucleic acid gene sequencing and microcosm experiments, we confirmed the presence and growth of a variety of alkaliphilic beta-Proteobacteria, Bacillus, and Clostridium species at pH up to 13.

Geochemistry of extremely alkaline (pH>12) ground water in slag-fill aquifers.

Extremely alkaline ground water has been found underneath many shuttered steel mills and slag dumps and has been an impediment to the cleanup and economic redevelopment of these sites because little is known about the geochemistry. A large number of these sites occur in the Lake Calumet region of Chicago, Illinois, where large-scale infilling of the wetlands with steel slag has created an aquifer with pH values as high as 12.8.

Arsenic in glacial aquifers: sources and geochemical controls.

A total of 176 wells in sand-and-gravel glacial aquifers in central Illinois were sampled for arsenic (As) and other chemical parameters. The results were combined with archived and published data from several hundred well samples to determine potential sources of As and the potential geochemical controls on its solubility and mobility. There was considerable spatial variability in the As concentrations.

Hydrostratigraphic modeling of a complex, glacial-drift aquifer system for importation into MODFLOW.

Deposition from at least three episodes of glaciation left a complex glacial-drift aquifer system in central Illinois. The deepest and largest of these aquifers, the Sankoty-Mahomet Aquifer, occupies the lower part of a buried bedrock valley and supplies water to communities throughout central Illinois. Thin, discontinuous aquifers are present within glacial drift overlying the Sankoty-Mahomet Aquifer.