CHAMPAIGN, Ill. - Groundwater resources in McHenry County may be strained in 35 to 40 years, potentially causing local water shortages and detrimental effects to the ecology of local streams, according to Scott Meyer, hydrogeologist at the Illinois State Water Survey (ISWS), a division of the Prairie Research Institute at the University of Illinois.

Meyer and colleagues at ISWS mapped water levels from 329 McHenry County wells in 1994 and again in 2011. They also constructed a computer model to simulate groundwater flow from over 8,700 wells, showing the impacts of water supply usage based on various scenarios of pumping to the year 2050.

Findings showed that water levels in shallow wells actually increased about 2 feet from 1994 to 2011, suggesting that changes in pumping rates, climate, land use, and other factors have not resulted in a county-wide decline of water levels during that period.  The results suggest that the more important influence on shallow groundwater levels in the county was precipitation, which was significantly greater in McHenry County in 2011 than in 1994.

Simulation of groundwater flow in the deep aquifers underlying McHenry County suggests that by 2030 there may be enough drawdown in deep wells, particularly in the southeastern part of the county, that well production capacity could be affected. If well pumps are not set sufficiently deep, drawdown can cause failure of wells to provide expected amounts of water.

“Our models also suggest that there could be significant additional drawdown in the vicinities of shallow well fields supplying public water systems of Woodstock and several other communities in southeastern McHenry County,” Meyer said.

The largest drawdown in shallow aquifers occurs in the vicinities of public water system wells and commercial wells in and near Woodstock, Algonquin, Carpentersville, Cary, and Crystal Lake.

With a growing population and need for an increased water supply, withdrawals from shallow wells can reduce natural groundwater discharge to surface water, in turn reducing base flow in streams.  The study showed that the natural groundwater discharge in the McHenry County area has been reduced by 11.5 percent.

“In addition to causing reduced rates of base flow in streams and lowering of water levels in lakes and wetlands, loss of groundwater discharge is likely to affect surface water temperature and chemistry, but we don’t have a good understanding of how these losses affect the ecology of surface waters and associated environments,” Meyer said.  “This is an excellent subject for further research.”

In the most extreme pumping scenario to 2050, modeling showed a 39 percent reduction in groundwater discharge within and near Crystal Creek and a 37 percent reduction in the city of Woodstock.

This information and future studies can be used to inform stakeholders’ decisions regarding water supply development in McHenry County in order to minimize the undesirable impacts from pumping in light of a growing population and increased need for water supplies.

A report on the study, “Groundwater Simulation Modeling and Potentiometric Surface Mapping, McHenry County, IL,” is available on the ISWS website, http://isws.illinois.edu/pubdoc/CR/ISWSCR2013-06.pdf.