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• Kane County water resources investigations: interim report on shallow aquifer potentiometric surface mapping.

Description

• Prompted by concerns for their county's water resources, Kane County officials funded a multifaceted project to be conducted by the Illinois State Water Survey (ISWS) and Illinois State Geological Survey (ISGS). The project, initiated in May 2002 and scheduled to conclude in May 2007, will provide baseline water-resources data, analyses, and tools for future analyses of water resources available to the county. This report presents and discusses groundwater data and analyses performed as a part of the ongoing investigations in Kane County. Shallow aquifers considered include the unconsolidated sand-and-gravel aquifers and the uppermost bedrock (i.e., the shallow bedrock aquifer). Deeper bedrock aquifers, including the productive Ancell Group and Ironton-Galesville sandstones, are not within the scope of this study, but are discussed in other ISWS reports. The study area includes Kane County and adjacent townships covering a total area of 1260 square miles. A network of 1010 private, public, industrial, and commercial wells was assembled during the inventory phase (May 2002 -August 2003). During the synoptic phase (September -October 2003), water-level measurements were collected from those wells. Waterlevel data were used to construct potentiometric maps for four shallow aquifers: the unnamed tongue below the Batestown Member, the Ashmore Tongue, the aggregated Glasford Formation sands, and the shallow bedrock. Using only groundwater data to constrain the potentiometric surfaces of individual aquifers, the potentiometric surfaces still closely correlated with perennial stream configurations and land-surface topography. The Fox River and Marengo Ridge are the most influential features that determine regional groundwater flow patterns in the county. Groundwater flow west of the Fox River is predominantly to the south and east. East of the Fox River, flow is to the south and west. The interim potentiometric maps can be used to characterize regional groundwater flow, identify areas of groundwater recharge and discharge, determine regional effects of groundwater withdrawals, and provide a baseline for comparison with future groundwater conditions. The maps will be useful in developing a conceptual model of groundwater flow and mathematical groundwater flow models for a wide range of analyses, including aquifer development scenarios. In 2003, 46 high-capacity wells accounted for 6.3 billion gallons or 97 percent of the total reported groundwater withdrawals of 6.5 billion gallons from the shallow aquifers in Kane County. If unreported withdrawals also are estimated, total withdrawals in 2003 may have been as much as 6.9 billion gallons. Groundwater withdrawals appear to have locally influenced the head surfaces, particularly in east-central and southeastern Kane County. Areas of relatively low head in the shallow bedrock aquifer may reflect large withdrawals from the aquifer, hydraulically connected units, and/or areas of significant discharge to the Fox River. A preliminary analysis of aquifer connections was based on potentiometric surfaces. Areas of potential aquifer connection were identified solely on similarity of measured heads. However, to refine this analysis, aquifer connections need to be evaluated further, taking into account aquifer concurrence and predicted thicknesses of intervening clay-rich geologic deposits. Nomenclature previously used to describe the aquifers of Kane County needs to be reevaluated to address vertical and horizontal aquifer continuity. That reevaluation will require additional geological modeling to more fully characterize and differentiate hydrostratigraphic units of importance such as sands in the Tiskilwa and Glasford Formations. Interim potentiometric maps presented in this report are subject to change as the conceptual hydrostratigraphy evolves. If the interim maps require changes, final versions will be released in the final report on groundwater investigations in 2007.

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1. Kane County water resources investigations: interim report on shallow aquifer potentiometric surface mapping. (20061003184617_ISWSCR2005-04.pdf).
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