Prairie Research Institute

Illinois State Geological Survey

Prior understanding and knowledge of geologic conditions minimizes liabilities for siting, building, maintaining, and improving transportation infrastructure. This knowledge reduces road construction project delays and associated costs and contributes to mitigation plans to reduce or avoid potential problems and problem areas.

ISGS staff investigate natural and man-made hazards and conduct detailed mapping and modeling to inform decisions on transportation work at the local, state, and national levels. State transportation agencies rely on ISGS’ expertise, data, and tools for infrastructure development. At the same time, ISGS assessments help ensure that Illinois’ natural resources are protected from negative effects of planned roadway and bridge construction and maintenance.


Coal mines, especially underground mines, can be unseen hazards for transportation infrastructure. ISGS has been mapping both surface and underground coal mines for many years, and the results and maps from this work are available on the ISGS Resources site. The Coal Mines in Illinois Viewer (ILMINES) allows anyone to search for possible coal mine hazards by address or place. The ILMINES Wiki is a work in progress that displays Illinois mines and provides access to maps and other data known about each mine, information that can be used to make informed infrastructure decisions.

Sinkholes and landslides also pose significant safety and economic risks related to roads and bridges. ISGS geologists use Graphic Information System (GIS) databases to interpret the lidar-shaded imagery and distinguish sinkholes from other depressions. They also use Illinois Height Modernization Lidar Data and the statewide 1:500,000-scale bedrock geology map layer that defines generalized areas of underlying carbonate bedrock. The sinkhole inventory includes two GIS datasets: Illinois Sinkhole Points (n=21,799) and Illinois Sinkhole Areas (n=138).

In addition, ISGS geologists have compiled information about landslides for decades, including case histories and photographs, and have produced maps that are useful to developers, businesses, and local government agencies.

Environmental site assessments

Since 1989, ISGS staff have provided the Illinois Department of Transportation (IDOT) with information on environmental conditions throughout the state associated with highway projects as part of the Environmental Site Assessment program. Environmental conditions can include various natural and man-made hazards that may be present on existing IDOT rights-of-way or on sites proposed for acquisition.

ISGS site assessments for IDOT are referred to as Preliminary Environmental Site Assessments (PESAs) and are different from industry-standard Environmental Site Assessments (ESAs), which typically only apply to a single property. ISGS PESAs have historically been completed over the entire IDOT project, which can range in scope from a single property or parcel to entire towns.

ISGS PESAs provide IDOT with information on environmental conditions they use to protect worker and public safety, reduce IDOT’s liability, and minimize delays by operating efficiently and cost-effectively.

For more information about IDOT site assessments, view A Manual for Conducting Preliminary Environmental Site Assessments for Illinois Department of Transportation Infrastructure Projects.

Wetlands and water quality

Geologists in the ISGS Wetlands Geology section assist IDOT through the Statewide Hydrologic Survey Program by gathering data to assess and characterize hydrologic, geologic, and water quality conditions in wetlands throughout the state. The data gathered through these studies are used to screen potential wetland restoration sites, monitor progress of wetland restoration goals, and evaluate water quality in sensitive habitats associated with specific geologic settings. The scientific information produced under this partnership not only helps IDOT to comply with environmental regulations but also increases the understanding of wetlands in Illinois.

The Wetlands Geology Section works closely with the Wetland Science Program at the Illinois Natural History Survey to monitor wetland restoration sites, report on progress toward restoration objectives, and evaluate water quality in critical habitats for threatened and endangered species. Research collaboration using data collected with IDOT support has resulted in an increased understanding of the evolution of wetland restoration sites. Hydrologic and geologic data contribute to research on planted tree mortality due to flooding, sediment storage in floodplain wetlands, and tradeoffs among wetland functions at IDOT restoration sites.

Geologists also assist the Illinois Tollway through the Tollway Runoff Monitoring Program. Under this program, ISGS gathers data to evaluate the environmental impacts of roadway runoff and the treatment effectiveness of best management practices (BMPs) in reducing adverse effects of roadway construction and operations on wetlands and streams in the Chicago Area Waterways System (CAWS). The data gathered through these studies aid the Tollway in complying with various water quality regulations under the Clean Water Act as well as in meeting strategic environmental goals under the Tollway Stormwater Management program.

Under this partnership with the Tollway, ISGS staff establish and maintain water quality monitoring networks, sample surface and groundwater, and analyze these environmental data to:

  • evaluate treatment of road runoff contaminants by bioswales and other BMPs
  • detect trends in runoff pollutants relative to established water quality standards
  • evaluate effects of roadway deicing activities on surface and groundwater quality
  • provide data to mitigate impacts to sensitive habitats
  • evaluate the effects of roadway construction activities on waterways.

Geophysical data

ISGS geophysicists have periodically supported IDOT geotechnical engineers to help assess and mitigate landslide sites along Illinois roadways. Electrical geophysical surveys provide high-resolution, two-dimensional images of the shallow subsurface, which can then be used to interpret geologic layers and moisture conditions. IDOT engineers use these data to address the physical conditions that have contributed to active slope failures in Illinois.

Soil strength is an important parameter when addressing road and bridge construction and maintenance. ISGS supports IDOT geotechnical engineers by conducting research that addresses the failure strength of geologic soils in Illinois. This research uses state-of-the-art field techniques (cone-penetrometer testing and hydraulic-profiling tools) that concurrently measure both soil strength and moisture properties of geologic soils. These data and analyses help IDOT engineers plan roadway projects more effectively and economically, and they may help IDOT develop new construction and safety standards for future infrastructure development. 

Aggregate resources

ISGS has long been the primary objective source of information about the location and quality of the sand, gravel, and crushed stone resources in Illinois that are essential for transportation infrastructure projects. Geologists in the Aggregate Program inventory these resources and maintain a repository of data for present and future exploration. Data on aggregate quality are particularly important for IDOT, which uses stringent quality tests before aggregates may be used on state roads.