Water Supply Planning: Middle Illinois Assessment of Water Resources for Water Supply Final Report

Walton R. Kelly, Daniel B. Abrams, H. Vernon Knapp, Zhenxing Zhang, Benedykt Dziegielewski, Daniel R. Hadley, George S. Roadcap, Devin H. Mannix, Yanqing Lian, Scott C. Meyer, Jason F. Thomason

Research output: Book/Report/Conference proceedingTechnical report


This report examines the impacts of current and future demands on water supplies for the Middle Illinois Water Supply Planning Region (WSPR) in central Illinois, an area comprising seven counties: LaSalle, Livingston, Marshall, Peoria, Putnam, Stark, and Woodford.

Initial water demand scenarios were developed out to 2060 for the five major water sectors, including thermoelectric power generation, public supply, self-supplied domestic, self-supplied industrial and commercial (IC), and self-supplied irrigation, livestock, and environmental (ILE), and are described in a companion report (Meyer et al., In press). Thermoelectric power-generation facilities located adjacent to the Illinois River dominate present and future demand in the region. Current water usage is an estimated 588 Mgd, or 76 percent of the region’s use. Self-supplied IC accounts for the second largest demand, at 17 percent. Public supply accounts for 5 percent, ILE uses 1 percent, and the domestic sector uses less than 1 percent.

Significant water resources are available to meet demands in the Middle Illinois WSPR, including both groundwater and surface water. Most of the region can use groundwater resources from two major aquifer systems. There are substantial productive sand and gravel aquifers in the region, primarily in the Illinois River Valley, but also in western Woodford County, eastern and western Livingston County, and northwestern LaSalle County. The deeper Cambrian-Ordovician sandstone aquifer system is productive throughout the region, although its usefulness decreases farther south because of increasing depth and salinity.

Sand and gravel aquifers should be sufficient to meet their projected demands, at least on a regional scale. Local issues regarding the sand and gravel aquifers may still occur because of the tight clustering of well fields, the variable quality and saturated thickness of the sands and gravels along the Illinois River, variability of the Illinois River stage, and elevated chloride concentrations. There are 28 public water supply systems using sand and gravel aquifers that could be considered at risk, either from falling water levels, relatively unproductive aquifers, high demands, or vulnerability to contamination. LaSalle and Sparland were identified as being sensitive to both future water demand and water quality concerns.

In most of the region, the sandstone aquifers are projected to have enough water to satisfy demands to 2060. The area of greatest concern, however, is in east-central LaSalle County along the Illinois River where the sandstone is not hydrologically connected to the Illinois River. Increasing demands, such as from industrial growth, might cause head declines that could put the St. Peter Sandstone at risk of going dry locally and reduce the productivity of wells in the lower Ironton-Galesville aquifer.

Both aquifer systems have some water quality issues of concern. Nitrate and arsenic are the main concerns as to the sand and gravel aquifers. The main water quality concerns regarding the sandstone aquifers are radium, salinity, and fluoride.

The primary surface water sources in the Middle Illinois WSPR are the Illinois and Vermilion Rivers. The Illinois River generally provides a sufficient and reliable water supply for public water supply and industry. The supply is sufficient to meet Peoria’s surface water demands for public supply. However, water withdrawal for thermoelectric power generation could be restricted because of low flows set by permits and high water temperatures during drought conditions.

The Vermilion River provides an adequate water supply for Pontiac and Streator public water systems. The water supply in both cities is enhanced by off-stream reservoirs and ion exchange systems for both water quantity and quality purposes. The Pontiac public supply system is classified as at risk, but could be marginally adequate if an ion exchange system is installed. The Streator public supply system is considered adequate. However, Pontiac and Streator withdrawals may potentially cause adverse impacts on aquatic ecosystems in the Vermilion River.

Changes to the Lake Michigan diversion have altered the low flow conditions in the Illinois River. With the decreasing diversion from Lake Michigan, the lowest flow amounts along the Illinois River are expected to decrease again in the near future. Although these changes do not limit the availability of flow to meet most water supply needs, they can pose challenges for low flow and protected flow management of the river.

During low flow conditions, operation of the powerhouse at Lockport, which is upstream of the Middle Illinois WSPR, can create sizeable fluctuations in the amount of water released and available to downstream users. At each successive downstream lock and dam on the Des Plaines and Upper Illinois Rivers, operations by the U.S. Army Corps of Engineers appear to effectively pass these fluctuations downstream while attempting to maintain the target pool level behind each dam. An existing unsteady flow routing model for the Illinois River was used to replicate these operating conditions, focusing specifically on the Marseilles dam and pool within the WSPR. This model was also used to investigate the impacts related to selected alternative operation scenarios. These scenarios suggest that there is the potential to incrementally attenuate the low flow fluctuation at each successive downstream dam through modest changes in pool-level management. This study did not attempt to evaluate the possibility that modifications could also be made at Lockport to reduce the amplitude of the flow fluctuations.
Original languageEnglish (US)
PublisherIllinois State Water Survey
Number of pages124
StatePublished - Aug 2018

Publication series

NameISWS Contract Report


  • ISWS


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