Ferrographic tracking of bacterial transport in the field at the Narrow Channel focus area, Oyster, VA

The first results from an innovative bacterial tracking technique, ferrogra phic capture, applied to bacterial transport in groundwater are reported in this paper. Ferrographic capture was used to analyze samples during an Oct ober 1999 bacterial injection experiment at the Narrow Channel focus area o f the South Oyster site, VA. Data obtained using this method showed that th e timing of bacterial breakthrough was controlled by physical (hydraulic co nductivity) heterogeneity in the vertical dimension as opposed to variation in sediment surface or aqueous chemical properties. Ferrographic tracking yielded results that compared well with results from other tracking techniq ues over a concentration range of 8 orders of magnitude and provided a low detection limit relative to most other bacterial tracking techniques. The l ow quantitation limit of this method (similar to 20 cells/mL) allowed obser vation of transport of an adhesion-deficient bacterium over distances great er than 20 m in the fine sand aquifer underlying this site.