Geological Features Central to Landfill Expansion Plans

Geological characteristics that were formed thousands of years ago make Prairie View an ideal location for landfill operations, according to the geologist leading expansion plans for the facility.

During Wednesday’s landfill committee meeting, Marty Fallon of Geologic Associates provided committee members with a detailed explanation of the site’s geological advantages, highlighting how glacial history created favorable conditions for waste management.

“As recent as 13,000 years ago, right where we’re sitting here today was covered by about 2,000 feet of ice during the last glacial period,” Fallon explained. “That clay is very dense, and the reason it’s so dense is because there was 2,000 feet of ice, and all that weight of that ice compacted that clay.”

This compacted glacial clay creates a natural barrier that helps protect groundwater from potential contamination. Fallon displayed microscopic images showing how the flat, platey particles of clay stack upon one another to inhibit water movement.

According to maps from the Illinois State Geological Survey presented during the meeting, the landfill sits on an area with low potential for aquifer contamination due to these thick clay deposits in what geologists call the Rockdale Moraine.

Beneath the clay, the region rests on Silurian dolomite bedrock, similar to limestone, which Fallon noted is the same foundation supporting Chicago’s skyscrapers.

The upcoming site investigation will extend the testing grid established in the 1990s when the original landfill was developed. Nine new boring locations will be drilled, with samples collected for laboratory analysis.

Engineers will also install devices called piezometers that allow monitoring of groundwater levels and flow. These installations will help verify that geological conditions in the proposed expansion area match expectations based on regional data and previous site investigations.

“We want to verify that the geology that we see in that horizontal expansion area is consistent with regional publications. We want to verify that it’s consistent with the information that was documented at the existing facility,” Fallon said.

The uppermost aquifer at the site is located at the top portion of the bedrock, according to Fallon. The investigation will include monitoring of water movement both horizontally and vertically through the various geological layers.

Drilling is scheduled to begin on April 21 and continue for two to three weeks, followed by aquifer testing and installation of monitoring equipment. Laboratory analysis and data compilation will take several additional months.

“I love geology,” Fallon told the committee, “and that nice compacted clay makes a nice spot for landfilling.”