DEFINING GROUNDWATER SYSTEM RECHARGE AND VULNERABILITY AREAS IN REGIONS OF SUBURBAN EXPANSION: OVERVIEW OF THE NORTHERN ILLINOIS EXAMPLE

The principal water resources in northern Illinois, deep bedrock aquifers and surface water, are now fully committed. Increased demands for water will focus on shallow sand-and-gravel aquifers and the upper bedrock dolomite, which belong to shallow groundwater flow systems closely linked to surface watersheds. The quantity, rates and quality of water recharging these systems are sensitive to physical and chemical changes occurring at the ground surface. However, the region is experiencing rapid suburban expansion, which is not only driving increased water demands but also changing the physical hydrology of the watersheds and introducing new potential contaminant sources to recharge entering the very aquifers on which these demands will be made. We do not generally have detailed knowledge of the relationship between particular shallow aquifers and their flow systems, watersheds, recharge rates, source areas, flow pathways, and contaminant travel times. For most areas we have only general map and well-record data bases, supplemented by a few engineering or hydrogeological case studies; we know little about the mechanisms and magnitudes of the impacts of development on individual aquifers, and cannot specify the areas of vulnerability, recharge quantities, watershed-aquifer linkages, and identifiable impacts. Therefore, communities and planning agencies are limited in their ability to restrict or guide suburban development over these systems. Analysis and delineation of groundwater systems properly involves field investigations coupled with the use of computer models (e.g. MODFLOW-MODPATH variants) which can simulate complex groundwater flow systems and travel pathways, and with the GIS database of hydrological and geological information which can be used to help construct maps and provide modeling data. However, communities and agencies are limited by personnel and budget considerations from conducting such complete hydrogeological studies, especially on the county scale. One way of dealing with this problem is a cooperative approach between communities and academic institutions so that research and educational goals can be combined with community planning and environmental needs.