Middle Illinois
ISWS, with assistance from colleagues at the Illinois State Geological Survey, finished its initial assessment of water supply in the Middle Illinois region in 2018. Significant water resources, including both groundwater and surface water, are available to meet demands in the Middle Illinois region. Most of the region — encompassing LaSalle, Livingston, Marshall, Peoria, Putnam, Stark, and Woodford counties — can use groundwater resources from two major aquifer systems: (1) sands and gravels, primarily in the Illinois River Valley; and (2) the deeper Cambrian-Ordovician sandstone aquifer system, although its usefulness decreases farther south because of increasing depth and salinity.
Sand and Gravel Analysis
While sand and gravel aquifers should be sufficient on a regional level to meet projected demands, local issues may limit their use, and almost 30 public water supply systems could be considered at risk.
This map contains information on demands and available water supply in the shallow aquifers of the Middle Illinois region. The results in this map are provisional and under review by the Middle Illinois water supply planning committee. For more information, contact Daniel Abrams at 217-244-1520 or dbabrams@illinois.edu.
Sandstone Analysis
The sandstone aquifers are projected to have enough water to meet demand through 2060, except possibly in east-central LaSalle County along the Illinois River, where the sandstone is not hydrologically connected to the Illinois River. As a result, relatively limited withdrawals can have a comparatively large drawdown.
This map contains information regarding demands and available water supply in the Cambrian-Ordovician sandstone aquifers of the Middle Illinois region. The results in this map are provisional and under review by the Middle Illinois water supply planning committee. For more information, contact Daniel Abrams at 217-244-1520 or dbabrams@illinois.edu.
Surface Water Analysis
The Illinois River generally provides a sufficient and reliable water supply for industries and the city of Peoria, which is the only public water supply withdrawing from it. However, water withdrawal for thermoelectric power generation could be restricted due to low flows set by permits and elevated water temperatures during drought. The Vermilion River, augmented by off-channel storage, provides an adequate water supply for Pontiac and Streator. However, their withdrawals may have adverse impacts on the river’s aquatic ecosystems.
Low flow in the Illinois River has decreased significantly in recent decades due to declining water diversions from Lake Michigan by Chicago, and this decrease is expected to continue. During low-flow conditions, the Illinois River between Marseilles and Kingston Mines appears to be losing water even though the drainage area increases dramatically downstream. Understanding these changes in low flow is critical for effective protected flow management; therefore, it is vital to accurately monitor low flow in the river.
Report
Middle Illinois Assessment of Water Resources for Water Supply Final Report