235-13 Community-Engaged Assessment of Groundwater Suitability and Challenges in the Karst Aquifers of Rockbridge County, Virginia

Session: Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part I

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Abstract:

In rural regions where most households rely on private wells and springs for drinking and domestic needs, access to safe groundwater is a public health priority. Rockbridge County, Virginia, exemplifies such a context, with approximately 70% of households depending on private water sources. As these sources are typically not subject to routine monitoring, groundwater quality assessments remain limited—underscoring the need for community-engaged investigations to address this knowledge gap. This community-based study aims to characterize the hydrogeochemical signatures and assess contamination in the groundwater system of Rockbridge County. Geologically, the county spans the Blue Ridge Province along its eastern boundary and the ridges of the Valley and Ridge Province to the west, with the Great Valley forming a broad central lowland between these uplands. The Great Valley is underlain by a structurally complex sequence of folded and faulted limestones and dolostones, interbedded with shale, forming a highly productive karst aquifer system. This valley also contains most of the county’s farmland. The combination of intensive agricultural land use and aging infrastructure poses a heightened risk of anthropogenic contamination to this aquifer system.

In collaboration with local residents, this study analyzed water samples from 58 private wells and springs across Rockbridge County to assess water-quality indicators, including basic physical parameters, major and minor ions, dissolved carbon species, and microbial contaminants. Initial findings indicate an oxic groundwater environment (mean dissolved oxygen: 5.15 mg/L) with notable alkalinity (mean: 5139.83 µmol/L as CaCO₃). Strong correlations between alkalinity and both total dissolved solids (TDS; r² = 0.82) and dissolved inorganic carbon (r² = 0.91) suggest carbonate dissolution as a dominant geochemical process. Groundwater is prevalently hard, with a mean TDS of 381 mg/L, and 12% of samples exceed the U.S. EPA’s secondary maximum contaminant level for TDS. Microbial contamination is also common, with total coliforms detected in ~50% of samples, including 19% from depths exceeding 50 meters. Weak or insignificant correlations between depth and concentrations of dissolved organic carbon, chloride, and nitrate suggest substantial vertical permeability within the aquifer system, increasing the vulnerability of deeper groundwater to surface-derived contamination. While certain analyses remain ongoing, the findings from this study offer critical insights into groundwater potability and support evidence-based decision-making for public health protection and sustainable groundwater stewardship in the region.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11140

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