FIELD INVESTIGATION OF NUTRIENT PULSE MIXING IN AN IN-SITU BIOSTIMULATION EXPERIMENT

A permeable wall was installed in a shallow, uncontaminated portion of the Borden aquifer, and periodically flushed with a solution of potas sium acetate. The acetate pulses were injected at intervals of 5-7 wee ks and were observed to merge within 5-10 m of the injection wall. The chief mechanism for the merging of these pulses was longitudinal disp ersion. Geochemical changes in the aquifer, manifested as the developm ent of a sustained reducing environment, indicated that the dispersive mixing occurred at the scale of the microorganisms and was not merely an artifact of the sampling method. This work indicates that large-pe riod pulsed injections of a substrate solution might be useful in bior emediation programs where the promotion of injected and ambient water mixing is desirable. It is also advantageous, from the standpoint of b iofouling prevention, that this mixing occur at some distance from the injection wells.