Manganese in Private Drinking Water Systems: A Statewide Assessment of Virginia

Abstract

Approximately 20% of Virginians consume water from private systems and roughly 80% have never tested the water quality or have only tested it once. Manganese (Mn) is a contaminant gaining attention due to its health risks. The United States Environmental Protection Agency (EPA) regulates Mn in public water systems with a Secondary Maximum Contaminant Level (SMCL) of 0.05 mg/L for aesthetic concerns and a Health Advisory Limit (HAL) of 0.3 mg/L for lifetime exposure. Despite EPA standards for public systems, private systems remain unregulated—including for Mn. Chronic exposure to Mn, even at concentrations as low as 0.1-1.2 mg/L, has been associated with neurodevelopmental issues, behavioral disorders, and cognitive impairment, particularly among children. Vulnerable groups such as infants, pregnant women, and the elderly are also at heightened risk. This study examines Mn in private drinking water systems in Virginia by investigating which geogenic and related variables influence concentrations and identifying clusters of high Mn concentrations. Using 24,561 samples collected and analyzed by the Virginia Household Water Quality Program (VAHWQP) at Virginia Tech from 2008-2023, this study employs spatial and statistical methods utilizing Python 3.11.3 and ArcGIS Pro 3.4.2. Key variables analyzed include rock type and age, soil order and suborder, land cover, well depth, proximity to surface water bodies, and homeowner reported use of household water treatment devices. Results establish that approximately 10% of statewide private drinking water samples exceeded the EPA's SMCL, with the highest concentrations clustered in northern and southwestern Virginia. Almost 16% of samples exceeded the SMCL in Loudoun County, suggesting a presence of localized factors that warrant further attention. Metamorphic rocks such as gneiss and metabasalt as well as proximity to surface water were significantly associated with higher concentrations of Mn. Water softeners were shown to effectively reduce Mn concentrations: the mean Mn concentration in untreated samples was 0.032 mg/L, compared to 0.014 mg/L in samples from households using water softeners. This study contributes to a better understanding of Mn occurrence in private drinking water systems and provides insights that can help inform future outreach targeting Virginia residents. This study also informs policy and decision makers, public health professionals, and others conducting research on private systems, Mn, and methods for Mn abatement.