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In recent years the Village of Antioch in Lake County has grown so rapidly that the population sign on the road into town might as well be fitted with rolling numbers, like an odometer. Aware that such growth might overtax the shallow sand and gravel aquifer Antioch currently relies on for its water supply, village leaders undertook a serious investigation of their options in 2008. The question they sought to answer was whether the Village could continue to rely on its system of wells for water, or it should apply for a share of the state’s allocation of water from Lake Michigan.
To answer this question, Antioch’s leaders needed to understand how much water the aquifer holds, and for that they needed information about its depth, shape and horizontal extent. Conveniently for them, scientists with the Illinois State Geological Survey (ISGS) were able to provide that information, since Antioch’s aquifer fell within the boundaries of a larger project, already underway, to create three-dimensional geologic maps of the Great Lakes region.
As you might imagine, developing a three dimensional picture that begins at land surface and extends down to bedrock is a complex task just about anywhere. But it is especially so in northeastern Illinois, where the advance and retreat of glaciers repeatedly added to and reshuffled the geologic materials that constitute the earth’s surface there.
Scientists from the ISGS employ data from a variety of sources to create such a picture. Their best data comes from continuous, three-inch diameter core samples they obtain by boring down to bedrock themselves. [Photo: ISGS scientists with a newly extracted core sample in Lake County. By Joel Dexter.] These samples provide an actual record of the types and order of materials present below the surface. Constraints on time and budgets limit the number of core samples scientists can obtain, however, so they learn what they can from other sources, too. From the data they gather, ISGS scientists produce various depictions of geological features, including two-dimensional cross sections, three-dimensional block models, and even more complex visualizations.
Thanks to the information that the ISGS was able to provide them, village leaders in Antioch were able to see clearly that their aquifer was not as extensive as they had hoped, and that only obtaining a share of water from Lake Michigan would enable the village to grow without worries about the limits of its water supply.
Although I’ve given Antioch’s concern about its aquifer as an example of how three-dimensional geologic mapping is useful, I should emphasize that the information such mapping provides is important in numerous other ways, too. From zoning decisions that protect wetlands, to siting requirements for landfills, to understanding the potential impact an earthquake might have in a given area, it is valuable to know what’s down below our feet.
The University of Illinois Institute for Natural Resource Sustainability, of which the ISGS is part, will hold its second annual “Naturally Illinois” expo on March 12-13. Among the things to see and do there will be baby Illinois turtles, a 30-ft. wind turbine powering scientific instruments, fossils to dig, and biodiesel made from waste. This is a super event for introducing young people to the world of science and a great reminder to all of how Illinois benefits from the work of its state scientific surveys. Details at http://www.inrs.illinois.edu/expo/
