104-1 Assessing Groundwater Chemistry and Quality in Private Wells and Springs in Rockbridge County, Virginia

Session: A Showcase of Undergraduate Research in Hydrogeology (Posters)

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In Rockbridge County, Virginia — a rural region predominantly characterized by agricultural land use — where 70% of the population relies on private wells and springs for their primary water supply, ensuring groundwater safety is critical for protecting public health. However, these private water sources are seldom monitored, and thus, comprehensive data on groundwater quality remains limited. This community-based study investigates the hydrogeochemical signatures of groundwater in Rockbridge County, aiming to evaluate its potability and identify the major geochemical processes influencing the water chemistry. A total of 58 water samples were collected from sources in the county and analyzed for physical parameters [total dissolved solids (TDS), dissolved oxygen (DO), pH], major and minor ion chemistry, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and microbial indicators including Escherichia coli (E.coli) and total coliforms. Geologically, the region is complex, underlain primarily by carbonate formations along with some siliciclastic sedimentary rocks, and various igneous and metamorphic rocks. Preliminary results indicate that the groundwater system is predominantly oxic [median dissolved oxygen (DO): 5.41 mg/L], with high alkalinity (median 5223.9 μmol/L as CaCO₃) that shows strong positive correlations with TDS (r² = 0.8241) and DIC (r² = 0.9135). The water is relatively hard, with 12% of samples exceeding the Environmental Protection Agency’s secondary maximum contaminant level (SMCL) for TDS. These results suggest carbonate mineral dissolution as a primary geochemical process. Most waters exhibited near-neutral pH (median: 7.25), which is inversely related to alkalinity, indicating increased carbonate dissolution at slightly lower pH levels, enhancing the system’s buffering capacity. While Spearman’s rank correlation analysis reveals a weak decline in chloride (ρ = –0.300, p = 0.011) and DOC (ρ = –0.249, p = 0.030) concentrations with increasing depth, nitrate shows no significant depth trend. This suggests high permeability and vertical connectivity within the carbonate aquifer system. Coliform bacteria were detected in 48% of samples, of which 55% came from sources less than 50 meters deep. E. coli was detected only in spring samples, suggesting potential vulnerability to surficial contamination. These findings are critical for understanding the suitability of this groundwater system as a drinking water source. Moreover, this work aims to fuel data-driven decision-making in the public health sector and support groundwater resource management across Rockbridge County. 

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

doi: 10.1130/abs/2025AM-9057

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