Bacterial Transport in NAPL-Contaminated Porous Media

To understand the effect of a non-aqueous-phase liquid (NAPL) on bacterial transport, column experiments in the presence and absence of a NAPL were conducted using two bacterial strains and two different porous media. The presence of a NAPL (tetrachloroethene) decreased the retention of Pseudomonas fluorescens P17 in quartz and soil columns (factor of 2 for quartz and 1.6 for the soil). In contrast, there was little change in the overall transport of P. putida KT2442 in soil columns in the presence of a NAPL. To understand how a NAPL phase might affect bacterial transport, several different mechanisms of particle removal by a NAPL were hypothesized, and a filtration model was modified to test each hypothesis. Only one of the five models was consistent with the increased transport of P17 in the presence of the NAPL suggesting that the NAPL produced large, immobile zones of water. The presence of immobile water zones would decrease overall porosity, reduce the number of packing grains available for particle filtration, and increase water velocity, resulting in increased bacterial transport in the presence of a NAPL.