GROUNDWATER MODEL DESIGN OF NORTHEASTERN ILLINOIS: A CASE STUDY FOR BUILDING GROUNDWATER MODELS AND INFORMATION DATABASES

The population of the Chicago metropolitan area is predicted to grow to 9 million residents by the year 2020, an increase of almost 15 percent over the present-day population. This projected growth may be limited by the availability of water from shallow aquifers in the region, currently a poorly understood groundwater resource. The aquifers in northeastern Illinois present several challenges to hydrogeologists. The deep aquifers are extensive and influenced by pumping centers that are widely separated, while the shallow aquifers consist of discontinuous, unconsolidated glacial aquifers and the weathered upper surface of the shallow bedrock. The multiple layers of this system interact with each other and with surface water bodies. The data and information of hydrogeologic investigations in the region are dispersed over several states and many agencies in a range of formats.

A study of the regional hydrogeology in northeastern Illinois has been jointly conducted by the Illinois State Water Survey and the Illinois State Geological Survey in order to extend the knowledge of the regional groundwater resources and establish a framework for follow-on analyses and updating of models to address physical, social and economic changes. In addition to numerical modeling, this study advances the organization, quantification, and interpretation of large quantities of geohydrological data in a format that is widely accessible and adaptable to future modeling studies. GIS (Geographic Information System) has been useful for building such a knowledge base, since it includes utilities for cataloging, analysis, transfer and documentation of the data and information, complemented by programming and scripting tools for translating geohydrological data into model-ready formats. We have developed several procedures to efficiently manage, interpolate, and reformat MODFLOW data using ArcGIS 8.2. Although one of the end products of this study is an analysis using a set of nested groundwater flow models based on MODFLOW, the project will also establish a series of GIS coverages and databases that provide a baseline analysis of groundwater in the region as well as a framework for future studies.