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Publication Abstract

Groundwater Studies for Water Supply Planning in Kendall County, IL Roadcap, George S., Scott C. Meyer, Walton R. Kelly, H. Allen Wehrmann, Yu-Feng Lin, 2013  Illinois State Water Survey, Champaign, IL,  ISWS CR 2013-05    Full Text Available

Kendall County is currently dependent on groundwater to supply all of its communities, industries, and rural residents. With a county population estimated to grow from nearly 100,000 in 2007 to 190,000 by 2030 and 280,000 by 2050, a path to sustainable growth needs to incorporate sound planning and management decisions regarding groundwater availability and use within the county. To assist the county with planning, the Illinois State Water Survey conducted a series of investigations that included: a) measurement of water levels in the different aquifers, b) assessment of the groundwater quality in shallow wells, and c) assessment of the impacts of growing water demands on the groundwater resources using digital groundwater flow models. The groundwater resources of Kendall County can be divided into three units: 1) the sand and gravel aquifer in the northwestern corner of the county that is used by Plano, 2) the shallow bedrock aquifers in the southwest and northeast corners of the county that are used by Newark and several smaller supplies, and 3) the deep sandstone aquifers that occur throughout the county (and the northeastern Illinois region) and account for 75 percent of the county’s water use and serve Oswego, Yorkville, Montgomery, and Joliet.

Water levels from the deep sandstone aquifers appear to be split by the Sandwich Fault Zone which cuts across the center of the county from northwest to southeast. The deepest water levels, often going below sea level, occur north and east of the fault near the large cones of depressions centered in the Aurora and Joliet areas. South of the fault, water levels in the sandstones are several hundred feet higher than north of the fault, suggesting that any northward flow towards the pumping centers is being cut off by the fault acting as a flow barrier.

Groundwater quality in the Shallow Bedrock Aquifer and sand and gravel aquifers in Kendall County is generally very good. With the exception of some elevated chloride values possibly due to road salt runoff, human activities have not caused significant contamination of these aquifers. Contaminants associated with agricultural activities (nitrate and atrazine) were generally below analytical detection limits. Water quality was found to be a function of both well depth and overlying till thickness, with generally better quality in deeper wells underlying thicker till deposits that protect aquifers from potentially contaminating activities.

For the Kendall County groundwater assessment, the authors significantly modified and recalibrated the previous regional groundwater flow model developed to include the hydraulic effects of the Sandwich Fault and the interconnections between the deep aquifers caused by the wells themselves. To estimate the effects of the increased water demand, a baseline, a high, and a low pumping scenario were simulated using the groundwater flow model out to the year 2050. Model results from all three scenarios indicate that water levels in the deep aquifers will continue to decline and potentially reach levels that adversely affect water supplies. A significant model result is that areas of the Ancell sandstone become completely dewatered, exacerbating drawdowns even further and potentially reducing well yields. A modified baseline scenario was created with additional future wells that were able to mitigate much of the adverse impacts. An area of concern for dewatering in all of the scenarios is the industrial corridor along the Des Plaines River in Will County. Because the Ancell sandstone is near the surface in southern Kendall County, any groundwater development should include an assessment of the impact of high-capacity and multi-aquifer wells on the surrounding private wells.



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