VISUALIZING THE MAHOMET AQUIFER FOR PLANNERS IN CENTRAL ILLINOIS

To demonstrate the areal extent of the Mahomet aquifer, a glacial deposit in a buried bedrock valley, for the non-scientists and planners of the Mahomet Aquifer Consortium and the Regional Water Supply planning group, geo-scientists proposed construction of a physical 3-dimensional model of the thickness and distribution of aquifer materials. The planners of the consortium requested base map information, such as county lines, major rivers and municipalities and interstate highways to help orient users. The resulting physical model, engraved with base map information, provides a versatile planning, communication, and educational tool.

To produce the physical model of the bedrock valley and the aquifer materials that lie within it, a laser cutting machine guided by digital contour data exported from ESRI ArcMAP format was used to cut elevation slices out of plexiglas and masonite. Raster data sets for aquifer thickness and elevation of the bedrock surface were acquired and clipped to the study area. The aquifer thickness data were added to the bedrock elevation data to produce elevation of the aquifer surface. These raster surfaces were converted to 40-foot interval vector contour lines, converted to AutoCAD format, and loaded into the laser cutting machine. Two layers were cut for each contour interval, one from masonite, the other from plexiglas. The positive space cut from the masonite layer formed the bedrock valley. The negative space cut from the plexiglas layer became the infilling aquifer materials. Base map data were etched into an additional plexiglas layer and a case was built to support the model layers.

The same vector contour layers used to construct the physical model were used to ‘build’ a transparent virtual model that addresses the analytical and educational needs of the planners. They can run the digital virtual model interactively, customizing views and data layers to suit specific needs. It can be ‘painted’ with geologic and other maps to show sequence and distribution of materials or hydrologic properties. Three dimensional shapes that represent water wells or boreholes can be symbolized with data and projected onto the model. An automated slide show of successive snapshots of the virtual layers allows a custom model to be distributed to or accessed by the public through an interactive WEB site.