INVESTIGATIONS OF WATER AVAILABILITY IN NORTHEASTERN ILLINOIS

By the year 2020, the population of the greater Chicago metropolitan area is predicted to increase by almost 15 percent over the present-day population. Prompted by concerns over the adequacy of the water supply to support such growth, the Illinois State Water Survey and Illinois State Geological Survey have conducted a study of the water resources in this region with the specific objective of providing a scientific basis for the formulation of policy and management strategy. The investigations have included geologic and hydrologic field studies, records searches, database construction and management, and computer-assisted mapping and modeling of the geology, groundwater and surface water systems.

Groundwater flow models on two scales are a central deliverable because they constitute tools for future evaluation of the consequences of groundwater development schemes and management scenarios. These include (1) a high-resolution model of shallow aquifers in the chief county of concern that is nested within (2) a lower-resolution, regional-scale model covering parts of Illinois, Wisconsin, Michigan and Indiana. Streamflow within the area of concern was assessed using a flow accounting model that also provided groundwater discharge targets for calibrating the groundwater models. Studies using these models have emphasized quantifying the impacts of alternative pumping scenarios (e.g., drawdown, changes to the hydrologic budget, and the associated uncertainties), rather than an estimate of the safe yield.