CHAMPAIGN, Ill. - Deep sandstone aquifers that feed water supplies to parts of Northeastern Illinois are at risk of becoming partially or completely depleted in the next 35 years, a new study at the Illinois State Water Survey (ISWS) suggests.
Daniel Abrams, a groundwater flow modeler at the ISWS, University of Illinois, and colleagues conducted the largest measurement of deep sandstone groundwater levels in 34 years. Water levels in 576 wells were measured in 33 counties between July 2014 and February 2015.
Risk of desaturation of the deep aquifers
of northeastern Illinois, based on the 2014
mass measurement conducted by the ISWS.
In northeastern Illinois, the sandstone aquifers are hundreds of feet deep, meaning that water pumped from the aquifer is not readily replenished by precipitation. As a result, water levels are hundreds of feet lower than when deep pumping began in the Chicago region in the 1800s.
“Most of the first wells constructed in northeastern Illinois were flowing,” Abrams said.
Currently, water levels are hundreds of feet below land surface, often at or near the top of the sandstone. This creates a risk of depletion, also known as desaturation, of the sandstone aquifers. Desaturation has potential negative outcomes, including the fact that small-capacity wells penetrating the upper portion of the sandstone may go dry.
“Additional wells may need to be constructed to meet demand,” Abrams said. “Desaturated sandstone also becomes exposed to oxygen, which alters the water chemistry, with potentially negative effects. If the water level decreases enough, the entire aquifer can become unusable.”
Desaturation of sandstone is not a new phenomenon in northeastern Illinois. The uppermost sandstone aquifer was desaturated during the 1980s in Cook and DuPage Counties at the height of groundwater pumping. This desaturation was one impetus for these communities to switch to Lake Michigan water, which resulted in water levels partially recovering.
To date, the Lake Michigan distribution network does not extend completely into the westernmost counties of the Chicago metropolitan area. Many of the communities and industries outside of this service area still rely on sandstone aquifers. Consequently, partial desaturation is now observed at many wells in Will, Kendall, and Kane Counties.
“Complete desaturation of the uppermost sandstone in Will County is just now occurring,” Abrams said.
The researchers used a groundwater flow model in which several scenarios were run to speculate about the future risk for the deeper-level aquifers.
“The future extent of desaturation will depend on the rate of withdrawals from the deepest sandstone aquifers. Unconstrained groundwater pumping from these sandstones will result in further desaturation,” Abrams said.
Communities that switch to alternate water sources will help keep the aquifers viable for industries, residential well owners, and others who have few alternatives.
“It is our recommendation that communities collaborate in planning for water supply decisions,” he said.