Continuous flow column experiments were used at different temperatures to study the importance of motility on advective transport of bacteria through repacked, but otherwise unaltered, natural aquifer sediment. The bacterium used was A0500, a flagellated, spore-forming rod isolated from the deep subsurface (180 m). At 4¿C, A0500 was nonmotile because there was no flagellar metabolism. Bacteria removal was greater at 4¿C than at 18¿C. Similar experiments with microspheres showed an opposite effect, with greater removal at 18¿ than 4¿C, which was consistent with colloid filtration theory. The sticking efficiency (&agr;) for nonmotile A0500 (4¿C), estimated using a steady state colloid filtration model, was over 3 times that of the motile A0500 (18¿C), 0.073 versus 0.022.

Analysis of complete breakthrough curves using a nonsteady, kinetically limited, transport model suggested that motile A0500 bacteria traveled twice as far as nonmotile A0500 bacteria before becoming attached to the sediment grains. Once attached, nonmotile bacteria detached on a timescale of 9--17 days versus 4--5 days for the motile bacteria. Bacterial motility facilitates advective transport through sediments by changing the attachment-detachment kinectics to effectively reduce retardation and increase the fraction of time bacteria spend in a detached versus an attached state. Consequently, travel times to deep aquifers from recharge waters could be significantly affected by bacterial motility. ¿ American Geophysical Union 1995