GSA Connects 2021 in Portland, Oregon

Paper No. 120-10
Presentation Time: 2:30 PM-6:30 PM


CROY, Marina1, CULBERTSON, Haley1, GOLDMANN, Christopher2, WILLIS, Noah3, ROQUEMORE, Margaret Grace1, LYON, Eva C.1 and HINKLE, Margaret1, (1)Geology Department, Washington and Lee University, 204 W. Washington Street, Lexington, VA 24450, (2)Geosciences Department, Trinity University, San Antonio, TX 78212, (3)Geology Department, Whitman College, Walla Walla, WA 99362

A substantial fraction of the Shenandoah Valley, VA population relies on ground and spring water for domestic use. Manganese (Mn) is of particular concern in groundwater, as low-level chronic exposure to aqueous Mn concentrations >100 ppb in drinking water can result in developmental complications in children and, at 3 times those concentrations, have been linked to increased cancer mortality rates. Water quality measurements including pH, dissolved oxygen, specific conductivity, temperature, and both water and soil samples were collected from springs throughout the Shenandoah Valley to supplement pre-existing groundwater well data from the National Water-Quality Assessment (NAWQA) and the Virginia Household Water Quality Program (VAHWQP). Through ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), water samples were analyzed for cation, anion, and trace metal concentrations. Soil morphology, geochemical composition, and mineralogy were analyzed using scanning electron microscopy paired with electron dispersive X-ray spectroscopy (SEM/EDS), X-ray fluorescence (XRF), and X-ray diffraction (XRD). X-ray absorption fine structure spectroscopy data used to determine soil Mn redox state and speciation will also be discussed. Factors such as soil type, soil geochemistry, and aquifer lithology were linked with each location to determine if correlations exist with aqueous Mn concentrations. While carbonate aquifers appear to have a protective effect by decreasing soluble Mn, those with primary or secondary rock types bearing sulfur (such as black shales) increase soluble Mn in both groundwater wells and springs. Groundwater hosted in unconsolidated material has the highest risk of becoming contaminated with harmful Mn. Analyzing the distribution of Mn in Shenandoah Valley drinking water sources suggests that groundwater wells and springs within carbonate aquifers are preferable to those composed of unconsolidated materials or containing black shale in regards to avoiding low-level chronic Mn exposure.