INVESTIGATING MANGANESE REMOVAL AND MOBILIZATION MECHANISMS DURING MANAGED AQUIFER RECHARGE

Managed aquifer recharge (MAR) can benefit communities by increasing groundwater yields, preventing land subsidence, and reducing saltwater intrusion in coastal areas. One method of MAR is injecting treated wastewater into aquifers. However, injecting water with a different chemical composition than native groundwater may result in unintentional releases of geogenic contaminants, including arsenic (As), manganese (Mn), and others. Our study focuses on the removal and mobilization of Mn in the Potomac Aquifer System, Virginia resulting from the Sustainable Water Initiative for Tomorrow (SWIFT), an MAR project implemented in 2018 by the Hampton Roads Sanitation District to address the overuse of groundwater in the Potomac Aquifer and reduce the nutrient load to the Chesapeake Bay. Mn is a geogenic contaminant of interest due to adverse health effects, including intellectual impairments in children. Mn levels in drinking water are guided by a secondary maximum contaminant level set by the Environmental Protection Agency.

In this study, we will utilize batch experiments, laboratory columns, and large-scale columns with Potomac Aquifer sediments and various water chemistries to test biogeochemical conditions which can promote the removal or release of Mn into groundwater of the Potomac Aquifer. We will evaluate microbially-mediated reactions, including Mn reduction driven by oxidation of dissolved organic carbon, and abiotic chemical Mn removal and mobilization processes, such as adsorption, desorption, and complexation with organics. Unveiling the Mn removal and mobilization mechanisms acting in a large-scale MAR operation will inform operational conditions to minimize release of geogenic contaminants at the SWIFT and other MAR efforts worldwide.