T121 Arsenic, Fluoride, and Other Geogenic Contaminants in Groundwater Systems: Advances in Data Science for Monitoring Long-Term Risks and Mitigation

Monday, 10 October 2022
1:30 PM - 5:30 PM
405

ASSESSING MANGANESE CONCENTRATIONS IN GROUNDWATER ACROSS THE SHENANDOAH VALLEY, VA

Paper number: T121-9
Program: Technical Sessions
Time: 3:25 PM – 3:40 PM

Authors

Abstract

Elevated concentrations of aqueous manganese (Mn) in drinking water cause adverse human health effects and undesirable aesthetic consequences. Chronic exposure to aqueous Mn ≥ 100 parts per billion (ppb) may cause increased cancer mortality rates, Parkinson’s disease, and developmental complications in children. Private drinking water sources are particularly vulnerable to Mn contamination because their water quality is not routinely monitored. Mn2+ can be mobilized into anoxic groundwater during reductive dissolution of Mn oxides This study uses groundwater data collected by the Virginia Household Water Quality Program (VAHWQP) from 915 private wells in the Shenandoah Valley, VA to assess the spatial distribution and mechanisms of aqueous Mn contamination. Samples were collected from the tap inside residences and analyzed for cations and major anions. The reported type of water treatment system present (if applicable) was recorded; Wilcoxon signed-rank tests determined that UV light and water softener treatments decreased Mn concentrations in a statistically significant way. Geospatial and statistical analyses including concentration mapping, regression analysis, hierarchical cluster analysis, and principal component analysis identified spatial and geochemical characteristics most inclined to contribute to elevated Mn2+. Results show that 63% of samples with Mn ≥ 100 ppb occur in shale lithologies near the valley center. This is consistent with groundwater flow modeling that evinces upwelling of old groundwater (≥ 20 years) in the same region. To evaluate mineralogic origins of Mn in groundwater, we performed a ternary analysis of Fe2+, Mg2+, and Si to link Mn mobilization to reduction of oxides, dissolution of carbonates, and weathering of silicates, respectively. Elevated Mn2+ in groundwater is predominantly controlled by redox conditions and is associated with elevated Fe2+. When Fe > 1 mole% of the Fe/Mg/Si sum, average Mn concentration was 214 ppb; when Fe < 1 mole%, the average Mn concentration was 17.9 ppb. Consideration of these factors may help reduce risk of Mn exposure among the Shenandoah Valley’s population, ≥ 36% of which utilize private wells for drinking water.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382881

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.