Session: Undergraduate Research Posters: Environmental Chemistry:

Ingestion of soluble manganese (Mn) via drinking water can cause severe human health effects, with chronic low-level exposure of even just 100 ppb Mn linked to several health and developmental issues. A recent United States Geological Survey (USGS) study found ~17% of groundwater wells within the Shenandoah Valley, Virginia region have Mn concentrations exceeding 100 ppb. A substantial portion of the population in the region relies on groundwater wells for drinking water. Mn is particularly problematic in groundwater, as aqueous Mn is most stable under reducing conditions and its oxidative precipitation is kinetically slow in the absence of microbes. Using National Water Quality Assessment and National Uranium Resource Evaluation data from the USGS and data from the Virginia Household Water Quality Project (VAHWQP) containing spatially referenced groundwater geochemistry data, we determined the lithology and most likely aquifers for 9,032 well water samples in this region. Primary and secondary rock types associated with each aquifer were cross-referenced with well water geochemistry data to confirm aquifer assignments. Aqueous Mn concentrations average highest in groundwater from unconsolidated, shale, and sandstone aquifers. Groundwater from dolostone aquifers is consistently very low in Mn and standard deviation, indicating that wells drilled into dolostone aquifers are reliably unsusceptible to Mn contamination in the Shenandoah Valley region. Limestone aquifers also have low Mn average concentrations, though several outliers containing higher concentrations of Mn occur in limestone aquifers with sulfur-rich secondary rock types. These results suggest that the lithology of aquifers is a key controlling factor on Mn concentrations in well water in the Shenandoah Valley. The correlation between Mn and surface water and soil dissolved organic carbon using data from the Soil Survey Geographic Database, will also be explored.

Margaret Grace Roquemore

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