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Surficial Geology And Groundwater Investigation Of The Garden Prairie, Il 7.5 Minute Quadrangle

Logan Seipel, Illinois State University

Imported from ProQuest Seipel_ilstu_0092N_10521.pdf

Abstract

Expansion and over pumping in the greater Chicago metropolitan area has raised concerns regarding groundwater resources. In McHenry County, municipal and domestic water supplies in the county are extracted exclusively from groundwater (Meyer, 1998) and largely from shallow sand and gravel aquifers. It is important to have an in depth understanding of the geology and processes affecting the surficial aquifer in order for best management practices to be implemented. Thus, the county has taken an aggressive approach to understanding these shallow aquifer systems though regional mapping and flow models.

This research focuses on understanding the characteristics and distribution of surficial geologic materials and impacts of heavy withdrawals on shallow aquifer systems in the Garden Prairie 7.5 Minute Quadrangle. This project is composed of two main chapters: 1) a surficial geologic map and 2) a groundwater flow model.

The geologic map was produced to delineate the surficial geologic materials at the 1:24,000 scale. Construction of this map was completed using multiple data-sets such as traditional field mapping techniques, interpretation of well logs, high resolution LiDAR data, and NRCS soils data. The Garden Prairie Quadrangle hosts geologic formations from both the Illinois and Wisconsin glacial episodes, and lies on the western extent of Wisconsin Glaciation. This former geologic setting has left much of the quadrangle overlain by outwash sediments that used to fill former outwash valleys.

A groundwater flow model was developed to understand local groundwater flow systems impacted by an irrigation well within a shallow unconfined aquifer in McHenry County, Illinois. Previous studies have look at regional effects of heavy groundwater withdrawals (Meyer, 2013), this study focuses on the local effects of unconfined aquifer pumping. These shallow unconfined aquifers, from which many high-capacity irrigation wells extract groundwater, are comprised of sand and gravel that fill former glacial outwash valleys. A local groundwater flow model was thus constructed to address the potential cumulative impacts of irrigation wells on groundwater drawdown and capture zones in the Kishwaukee River Valley.