Transient Groundwater Flow Model of the American Bottoms Aquifer, East St. Louis, IL

Krasowski, Michael P.; Jones, Allan E.; Pierson, Tyler M.

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https://hdl.handle.net/2142/130896 Copy

Description

Title

Transient Groundwater Flow Model of the American Bottoms Aquifer, East St. Louis, IL

Author(s)

• Krasowski, Michael P.
• Jones, Allan E.
• Pierson, Tyler M.

Issue Date

2025-12

Keyword(s)

• llinois Department of Transportation
• Groundwater
• American Bottoms Aquifer
• East St. Louis
• Aquifers
• Mississippi River
• Infrastructure
• Dewatering wells
• Monitoring
• Hydrogeology
• MODFLOW
• Python
• Parameter-elevations Regression on Independent Slopes Model (PRISM)
• Nash-Sutcliffe Efficiency (NSE)
• Groundwater flow

Date of Ingest

2025-12-22T12:52:18-06:00

Geographic Coverage

Illinois

Abstract

In collaboration with the Illinois Department of Transportation, researchers at the Illinois State Water Survey’s Groundwater Science section developed a transient groundwater flow model of the American Bottoms Aquifer near East St. Louis, IL. This work built on prior steady-state modeling analyses from this same intergovernmental collaboration (Jones et al. 2020). The study area was the American Bottoms region within Madison and St. Clair counties. The aquifer is bounded by the Mississippi River to the west and by limestone bedrock bluffs to the north, east, and southeast. Major groundwater withdrawals started in the region in the early 1900s and peaked at around 110 million gallons per day in the mid-1960s, producing significant drawdown in observed water levels at major pumping centers. During this time, many infrastructure improvements were made in the region, including the construction of major highway projects considering the then-current low water table elevations. However, as industrial withdrawals began to decrease starting in the 1960s, groundwater levels rose, threatening infrastructure and endangering traffic on these vital thoroughfares. In response to the rising groundwater levels, the Illinois Department of Transportation (IDOT) installed dewatering wells along important stretches of interstate to protect infrastructure in the area by removing excess groundwater. To improve understanding of the region’s hydrogeology and the impact of the dewatering wells on the regional groundwater flow regime, groundwater flow modeling was completed using MODFLOW via the Python programming language. Hydrologic conditions, such as river stage, recharge from precipitation, and evapotranspiration, were temporally varied to reflect empirical records of conditions. Mississippi River stage was based on historic U.S. Geological Survey gaging station measurements, while precipitation and recharge estimates were incorporated from the Parameter-elevations Regression on Independent Slopes Model (PRISM) from the PRISM Climate Group. Estimates of anthropogenic groundwater withdrawals were derived from analog records of regional pumpage (pre-1980) and from Illinois Water Inventory Program (Wessman 2021) records of withdrawals (post-1980). Estimated pumping rates for the IDOT dewatering system were determined from communication with IDOT technical staff, but detailed observations of exact pumpage are not, as of this report, being actively recorded. Regional synoptic measurements of groundwater elevations were performed in the American Bottoms in 1966, 1971, 1977, 1980, 1985, 1990, and 1995. The transient model was calibrated manually to observations during these years. Overall, the model performed well with R2 values that ranged from 0.64 to 0.89, root-mean-square error values ranging from 3.78 ft to 6.25 ft, mean absolute error ranging from 2.78 ft to 4.23 ft, mean error ranging from -1.87 ft to 0.69 ft, and percent bias ranging from -0.48 to 0.17 % (typical water levels range from 375 to 420 ft amsl). There is also strong agreement between the monthly model results and a long-term groundwater monitoring site’s monthly data, with a calculated Nash-Sutcliffe Efficiency (NSE) of 0.57. These model results convey that the model structure accurately reproduces typical hydrogeologic processes present in the American Bottoms Aquifer. Model results suggest groundwater generally flows from east and northeast to west and southwest in the American Bottoms Aquifer (including in the vicinity of the IDOT dewatering system). Important deviations from this regional trend include areas where the aquifer is impacted by transient influences such as groundwater pumping or high stages on the Mississippi River. The model displayed responsive behavior to empirically observed changes in precipitation, stage of the Mississippi River, and groundwater pumpage.

Publisher

Illinois State Water Survey

Series/Report Name or Number

ISWS Contract Report 2025-03

Type of Resource

text

Genre of Resource

technical report

Language

eng

Sponsor(s)/Grant Number(s)

Illinois Department of Transportation (IDOT); Project 2096

Copyright and License Information

University of Illinois Board of Trustee

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