PNNL

Abstract

Extended tailing of low bacterial concentrations following breakthrough at the Narrow Channel focus area was observed for four months. Bacterial attachment and detachment kinetics associated with breakthrough and extended tailing were determined by fitting a 1-D transport model to the field breakthrough-tailing data. Spatial variations in attachment rate constant (kf) were observed under forced gradient conditions (i.e., kf decreased as travel distance increased), possibly due to decreased bacterial adhesion with increased transport distance. When pore water velocity decreased by an order of magnitude at 9 days following injection, apparent bacterial attachment rates did not decrease with velocity as expected from filtration theory, but instead increased greatly for most of the wells. The coincidence of the increase in apparent attachment rate with the occurrence of protist blooms suggested that the loss of bacteria from the aqueous phase during the protist blooms was not governed by filtration, but rather by predation. Simulations were performed to examine the transport distances achieved with and without detachment, using attachment and detachment rates similar to those obtained in this field study. Simulations that included detachment showed that transport distances of bacteria may significantly increase due to detachment under the conditions examined.