  Microbial migration towards a trichloroethene (TCE) dense non-aqueous phase
liquid (DNAPL) could facilitate the bioaugmentation of TCE DNAPL source zones.
This study characterized the motility of the Geobacter dechlorinators in a TCE
to cisdichloroethene dechlorinating KB-1TM subculture. No chemotaxis towards or
away from TCE was found using an agarose in-plug bridge method. A second
experiment placed an inoculated aqueous layer on top of a sterile sand layer
and showed that Geobacter migrated several centimeters in the sand layer in
just $7$ days. A random motility coefficient for Geobacter in water of $0.24
\pm 0.02$ cm$^2$ day$^{-1}$ was fitted. A third experiment used a
diffusion-cell setup with a $5.5$ cm central sand layer separating a DNAPL from
an aqueous top layer as a model source zone to examine the effect of random
motility on TCE DNAPL dissolution. With top layer inoculation, Geobacter
quickly colonized the sand layer, thereby enhancing the initial TCE DNAPL
dissolution flux. After $19$ days, the DNAPL dissolution enhancement was only
$24\%$ lower than with an homogenous inoculation of the sand layer. A
diffusion-motility model was developed to describe dechlorination and migration
in the diffusion-cells. This model suggested that the fast colonization of the
sand layer by Geobacter was due to the combination of random motility and
growth on TCE.
