Christiane Hoppe, PhD, candidate and Jorg E. Drewes, PhD, Colorado School of Mines
The interest in riverbank filtration (RBF) as a pretreatment process for public water supplies is increasing in the United States. Riverbank filtration has been shown to be effective in moderating the peak concentrations of various contaminants in the river and, in many cases, to remove these contaminants below detection levels. A RBF site at the South Platte River, Colorado, was selected to evaluate the removal of emerging organic contaminants, such as pharmaceutical residues, flame retardants, pesticides, and disinfection by-products (N-nitrosodimethylamine - NDMA). Both groundwater monitoring wells, with travel times representing 5 to 30 days, and river water were monitored for bulk parameter (TOC, pH, UV absorbance, nutrients, conductivity, iron, and manganese) and organic micropollutants. In addition, controlled column studies were conducted to better understand the removal mechanisms of organic micropollutants during riverbank filtration. Five columns in series were operated under saturated anoxic flow conditions and one column was operated under unsaturated, oxic flow conditions in order to study removal of contaminants predominantly through biodegradation. Furthermore, an abiotic control column was employed to account for removal through adsorption processes. All columns were fed with South Platte River water at a hydraulic loading rate of 0.26 ft/day. Results for the South Platte River and the wells have shown that bulk water quality parameters of the wells were not significantly impacted by variations of water quality in the river. Results both from field monitoring as well as controlled column studies support that biodegradable micropollutants were already removed below the detection limit within 5 to 7 days of residence time. Removal due to adsorption of the target compounds was not observed in the abiotic column. Persistent micropollutants, such as flame retardants and antiepileptic drugs, did not exhibit any removal under anoxic or abiotic conditions after a residence time of 30 days.
The 2007 Ground Water Summit
