Date of Award

5-2022

Document Type

Thesis open access

Department

Geology

First Advisor

Brady Ziegler

Abstract

Aqueous manganese (Mn2+) in groundwater used for drinking water has adverse aesthetic effects at concentrations ≥ 50 ppb and adverse human health effects at concentrations ≥ 100 ppb. Mn2+ in groundwater may have anthropogenic (mines, pesticide, gasoline) or geogenic (rocks and minerals) sources. Private drinking water wells are vulnerable to Mn2+ contamination because their water quality is not routinely monitored. This study uses groundwater data from 1587 private wells in the Shenandoah Valley, VA to assess the spatial distribution of Mn2+ in groundwater and identify possible Mn2+ contamination mechanisms. Using geospatial and statistical analyses I found that samples collected near the valley center predominantly in shale host lithologies contained Mn2+ ≥ 50 ppb more frequently (26%) than sandstone (25%), metamorphic (13%), limestone (3%), dolostone (2%), igneous (0%), and black shale (0%) lithologies. Additionally, samples collected in closer proximity to surface water had higher Mn2+ concentrations. Groundwater samples with elevated Mn2+ (≥ 100 ppb) occurred on average 206 m from surface water as opposed to 304 m on average for low Mn2+ samples (≤ 100 ppb). Our data suggest that elevated Mn2+ in groundwater occurs near rivers at the valley center where old, anoxic groundwater upwells and reductively dissolves Mn oxides in soils and sediment. Overall, those who source drinking water from wells in the Shenandoah Valley should be cautious of consuming untreated water within shale lithologies.

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