Sources and Variability of Manganese in Well Water of the North Carolina Piedmont.

Manganese (Mn) is a naturally occurring groundwater contaminant of growing concern. Consumption of high quantities of Mn in well water may lead to severe neurological problems and increased infant and cancer-induced mortality rates. Approximately 50% of sampled wells in North Carolina have Mn concentrations that exceed the state drinking water standard of 0.05 mg L^-1. The sources of Mn to groundwater are generally unknown, and spatial patterns of concentrations, which range from below detection limits to greater than 2 mg L^-1, are variable, making it difficult to predict where high concentrations might occur and thereby minimize public exposure. The primary objective of this research is to identify the surface and subsurface properties that regulate dissolved Mn concentrations in groundwater of the NC Piedmont region. In particular, we are examining Mn spatial associations, characterizing potential solid-phase sources of Mn, and determining Mn retention capacities within different subsurface locations. Chemical analyses of Mn in soil, saprolite, and bedrock samples from ten NC Division of Water Quality (DWQ) groundwater research stations are being integrated with existing US Geological Survey and NC Department of Public Health well-water data, NC Geological Survey geology maps, and NC soil maps. Across the Piedmont, concentrations of Mn that exceed health limits are generally found in shallow wells. High concentrations are clustered within the Carolina Slate and Mesozoic geozones, which are overlain by the Carolina terrane and Triassic Basin soil systems. Initial results suggest that Mn may be drawn into groundwater from near-surface sources. Field data and ongoing laboratory studies of Mn release and transport will be used to develop groundwater susceptibility maps that identify locations at risk for high Mn concentrations in well water.