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

Abstract

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 Mn2+. 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.

Mobilization and retardation of reduced manganese in sandy aquifers: Column experiments, modeling and implications

“…Groundwater contamination with Mn is a well know phenomenon (Silvey and Johnston, 1977;Thomas et al, 1994;Bourg and Bertin, 1994;Klinchuch and Delfino, 2000;Buschmann et al, 2007). High Mn concentrations appear in wells long time after the onset of water production from the aquifer.…”

“…The Fredericton aquifer is recharged by direct precipitation and by the Saint John River water (Thomas et al, 1994). Enhanced groundwater production during the 1960s increased the recharge by river water and, hence, the supply of dissolved organic carbon into the aquifer.…”

“…Such environments may serve as "natural" laboratories for the study of Mn mobilization and re-deposition in the sedimentary record under variable environmental conditions. Mobilization of manganese in aquifers due to recharge of organic-rich water and microbial activity has been the focus of several field and laboratory studies (Jacobs et al, 1988;Von Gunten et al, 1991;Matsunaga et al, 1993;Bertin, 1993, 1994;Thomas et al, 1994;Ludvigsen et al, 1998;Petrunice et al, 2005, Oren et al, 2007. Precipitation of Mn-oxides due to oxidation of Mn 2+ by dissolved oxygen was suggested in several studies as the process responsible for the down flow decrease of dissolved Mn 2+ in aquifers (Bourg and Bertin, 1994;Klinchuch and Delfino, 2000;Scott et al, 2002).…”

“…High concentrations of Mn 2+ are common in anthropogenically disturbed aquatic environments such as acid mine drainage, landfill leachate, soil aquifer treatment (SAT) of effluents, and river-bank filtration systems (Fllipek et al, 1987;Von Gunten et al, 1991;Thomas et al, 1994;Ludvigsen et al, 1998;Woo and Choi, 2001;Scott et al, 2002;Oren et al, 2007;Buschmann et al, 2007). Such environments may serve as "natural" laboratories for the study of Mn mobilization and re-deposition in the sedimentary record under variable environmental conditions.…”

“…Thomas et al, 1994;Petrunice et al, 2005;Oren et al, 2007) and in packed column experiments (Petrunice et al, 2005). Adsorption of Mn 2+ was also described as an intermediate process, followed by particle surface oxidation of Mn 2+ and precipitation of solid Mn-oxides, for Mn retardation in an alluvial aquifer (Bourg and Bertin, 1993).…”