Mapping the Land Beneath Our Feet: A Field Demonstration of Data Collection Techniques
On August 15, 2007, the Bondville Road Station, a research facility maintained by the University of Illinois Department of Electrical Engineering and the Illinois State Water Survey, was the venue for a field demonstration given by the Illinois State Geological Survey (ISGS) to the Board of Natural Resources and Conservation, the Mahomet Aquifer Consortium Board and committee members, and other dignitaries. Forty-five guests attended.
The demonstration provided an opportunity for the Survey's guests to view many of the techniques and equipment used by Survey scientists to collect subsurface information. Chief William Shilts welcomed the guests and indicated that the purpose of the trip was to familiarize everyone with many of the field tools and techniques the Survey uses to reveal the geology beneath our feet. Donald Keefer, Director of the Geologic Mapping and Hydrogeology Center, presented an overview of ISGS mapping and hydrogeologic programs, including the Governor's Water Supply Initiative. William Dey, Hydrogeology Section, spoke about studies of the Mahomet aquifer and reasons for being at the Bondville Road Station. The speakers emphasized the value to Illinois' citizens of the information gathered using the techniques and equipment being demonstrated and the reports, maps, and analyses that present the information.
Using core obtained from a nearby borehole, Andrew Stumpf, Quaternary Geology Section, described the ISGS drilling program and the high value of direct observations from continuous cores for characterizing sediment properties and interpreting environments of deposition and the geologic history of Illinois. Jack Aud, ISGS driller, and his crew demonstrated the drilling and core retrieval technique using the Survey's CME drill rig.
David Larson, Hydrogeology Section Head, used a cut-away model of an observation well to describe how such wells are constructed. The observation well provides a means to measure properties such as hydraulic head and hydraulic conductivity and to collect groundwater samples for analysis. Larson gave an overview of the significance and value of information that can be obtained from observation wells.
Timothy Young, Geophysics Section, exhibited some of the ISGS borehole geophysical logging tools and demonstrated their capabilities. He explained that certain physical and chemical properties, such as density and natural emission of gamma radiation, vary with different types of earth materials. He described how those properties are measured with different tools to determine the type of geologic materials that are present in a borehole.
Two surficial geophysical techniques, one old and the other new, were described by Timothy Larson, Geophysics Section. Use of the old technique, electrical earth resistivity (EER), dates from 1931. The updated version of this technique, high resolution electrical earth resistivity (HREER), is used at the ISGS primarily to distinguish sand and gravel from silt and clay. The results of an HREER survey can help geologists map the location and extent of aquifers. Larson then demonstrated how ground penetrating radar (GPR) uses radio waves to detect changes in earth materials or buried objects in the shallow subsurface.
Seismic reflection was another surficial geophysical technique highlighted at the field demonstration. Timothy Larson explained the process as Steve Sargent, Geophysics Section, assisted by students from the University of Illinois and Illinois State University, demonstrated the operation of the ISGS landstreamer, the equipment used to collect the seismic data. The landstreamer, developed and built by researchers and staff at the ISGS, allows for the rapid collection of high-resolution reflection data.
Robert Scott, Illinois State Water Survey, discussed the range of research projects being conducted at the Bondville Road Station by a variety of state, national, and international governmental agencies as well as various academic institutions. His presentation included a highlight of the Water Survey's long-term monitoring program, the Weather and Atmospheric Resources Monitoring (WARM), which is also on site.