Master's Theses or Doctor of Nursing Practice

Department

Geosciences

Degree Name

Master of Science (MS)

Abstract

Fifty-one private domestic wells across western Kansas were sampled to quantify nitrate and arsenic occurrence, identify geochemical controls, and evaluate carcinogenic and non-carcinogenic health risks for adult and child receptors in a region where groundwater serves as the primary drinking water source with no routine regulatory oversight. Samples were analyzed for major ions, nutrients, and trace elements by ICP-MS, ion chromatography, and UV-Vis spectrophotometry. Shapiro-Wilk testing confirmed non-normal distributions for both contaminants; inter-county comparisons were therefore conducted using Kruskal-Wallis tests with Dunn's post-hoc correction. Health risk was quantified via chronic daily intake (CDI), hazard quotient (HQ), HQ-based Water Quality Index (HQ-WQI), and incremental lifetime cancer risk (ILCR) frameworks. Nitrate ranged from 0.09 to 25.2 mg/L (mean: 5.41 mg/L), exceeding the EPA MCL of 10 mg/L in five wells (9.8%). Arsenic ranged from below detection to 19.0 µg/L (mean: 3.88 µg/L), with a single well (2.0%) exceeding the EPA MCL of 10 µg/L. Kruskal-Wallis tests detected no statistically significant inter-county differences in nitrate (H = 2.17, p = 0.338) or arsenic (H = 3.19, p = 0.203), indicating contamination is organized at the well and land-use scale rather than the county scale. Arsenic correlations with major ions are consistent with geogenic redox driven mobilisation; nitrate correlations with sodium, chloride, and total dissolved solids reflect diffuse agricultural loading. Non-carcinogenic risk assessment identified nitrate as the primary driver of pediatric concern, with child HQ exceeding unity in multiple wells; adult HQ remained below 1 for both contaminants at all sites. The HQ-WQI framework classified 43 of 51 wells (84.3%) within moderate to high-risk categories for the child receptor. ILCR assessment using the USEPA IRIS oral slope factor for inorganic arsenic (SF = 1.5 mg·kg⁻¹·day⁻¹)⁻¹ identified 13 wells (25.5%) as exceeding the unacceptable carcinogenic risk threshold (ILCR > 1×10⁻⁴) for the adult receptor, NT-19 at 19.0 µg/L recording the highest value at 3.49×10⁻⁴, a factor of 3.49 above the threshold. For the child receptor, NT-19 alone exceeded the threshold (ILCR = 1.63×10⁻⁴), while 90.2% of wells fell within the cautionary range. Application of prospective lower thresholds (As = 5 µg/L; NO₃ = 5 mg/L) would substantially reclassify both datasets, underscoring the inadequacy of current MCL compliance as the sole protective mechanism for private well users in this agricultural corridor.

Keywords

Redox Reaction, Co-Contaminant, Hazard Quotient, Health Risk Assessment, Water Quality

Advisor

Dr. Thomas Schafer

Date of Award

Spring 2026

Document Type

Thesis

Rights

© The Author

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