Bioremediation is an emerging in situ treatment technology for soil an
d groundwater cleanup. Research in the past decade has made significan
t progress toward understanding how to stimulate microbial growth in t
he subsurface by optimizing the physical/chemical conditions. Recent l
aboratory observations and field demonstrations indicate that bioremed
iation can also be limited by mass transfer processes. In this paper,
factors restricting microbial growth are reviewed, and the importance
of bioavailability on the performance of in situ bioremediation is dis
cussed by using aromatic hydrocarbons as model contaminants. Successfu
l application of bioremediation relies upon an understanding of intera
ctions among microorganisms, organic contaminants and soil/aquifer mat
erials. Applications of biofilm kinetics toward this goal are addresse
d. Model simulations and laboratory studies suggest that both low temp
erature and slow desorption rate could greatly lengthen the time requi
red for effective in situ bioremediation of aromatic hydrocarbons.