Temporal Changes in Manganèse Concentrations in Water from the Fredericton Aquifer, New Brunswick

A geochemical field study was conducted on the municipal aquifer in Fredericton, New Brunswick, Canada to determine the cause of increased manganese levels, from 0.02 mg/1 to about 1.0 mg/1 over a 34‐year period, in three of five production wells. The source of water for each of the five production wells has been determined to be infiltrated river water or precipitation, or a mixture of these sources. Wells that are predominately withdrawing infiltrated river water have corresponding high manganese concentrations, and redox potential data indicate that manganese tends to be in the aqueous form Mn 2+ . Geochemical modeling further suggests that the ground water is undersaturated with several common manganese minerals, while remaining supersaturated with iron oxide‐hydroxide minerals. The primary cause of the temporal increase in manganese concentrations is attributed to increased dissolved organic carbon introduced to the aquifer as a result of the escalating contribution of river water to the aquifer with time. Oxidation of organic matter proceeds in a ground‐water environment, as dissolved oxygen is depleted, by utilizing manganese oxides as electron acceptors.