Graduation Term

Summer 2025

Degree Name

Master of Science (MS)

Department

Department of Geography-Geology: Hydrogeology

Committee Chair

Eric Peterson

Committee Member

Lisa Tranel

Committee Member

Jonathan Thayn

Abstract

Increasing sulfate (SO42-) concentrations in the water environment, corresponding with increases in urbanization and industrialization, are a rising global concern. Over 250 mg/L, sulfate threatens human health and ecosystems. Elevated concentrations influence carbonate rock weathering, contributing to the evolution of the global carbon cycle. Knowledge of sulfate sources, whether natural or anthropogenic, is essential for understanding sulfate transport and fate in groundwater. This study investigates SO42- origin and transport in groundwater in an area dominated by agricultural land use in Mclean County, Illinois. Specifically, we explored these questions: 1) Do sulfate concentrations change with groundwater depth? And 2) Are there seasonal differences in sulfate concentrations in groundwater? Water samples collected over 9 years (2015-2024) from 37 observation wells were analyzed for major anions, including SO42-. Based on depths, wells screened at 4.6m (A) and 3.1m (B) were categorized as deep groundwater, while wells screened at 2.3m (C) and 1.5m (D) were categorized as shallow groundwater. Seasons were categorized following agricultural practices into spring/planting (April – June), summer/growing (July – September), fall/harvest (October – December), and winter/fallow (January – March). A cumulative probability plot and a one-way ANOVA revealed two SO42- populations, with deep groundwater statistically different from shallow groundwater, indicating depth-related changes in SO42-. A two-way ANOVA showed no seasonal differences in SO42- concentrations. Depth differences in SO42- are due to geogenic rock-water interactions, releasing more sulfate in deeper groundwater wells. In contrast, shallow groundwater wells (SW) have lower sulfate levels, due to infiltration and recharge. Groundwater flow dynamics also contribute, with deeper groundwater having a longer residence time, allowing more rock-water interactions than shallow groundwater. Seasonal changes involving precipitation, agricultural runoff, and temperature shifts may not have an impact on sulfate levels, as suggested by the lack of seasonal variation in SO₄²⁻ concentrations between the SW and DW groups.

Access Type

Thesis-Open Access

DOI

https://doi.org/10.30707/ETD.1763755358.906091

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