Pilot-scale evaluation of bioaugmentation for in-situ remediation of a carbon tetrachloride contaminated aquifer

An experiment was performed in a carbon tetrachloride (CT)- and nitrate-contaminated aquifer at Schoolcraft, MI, to evaluate bioaugmentation with Pseudomonas stutzeri KC, a denitrifying bacterium that degrades CT without producing chloroform (CF). A test section of the aquifer was treated to create pH conditions favorable for KC and then inoculated with culture grown aerobically on site. Activity was sustained with pulses of acetate-amended groundwater, followed by "chase" pulses of acetate-free water. In regions with effective substrate delivery, KC was detected, nitrate levels fell by 85%, pH levels increased, and CT levels decreased by similar to 65%, with no significant increase in CF. After 3 weeks, denitrification and CT transformation activity decreased, and KC was no longer detected in groundwater from four wells. Loss of denitrification was attributed to the acetate-free chase. Upon eliminating the chase, CT transformation resumed, and KC was detected, but CF production was also observed, implicating indigenous organisms as agents of transformation. Final sediment analyses indicated 60-88% CT removal, little CF, and persistent KC. This work demonstrates subsurface pH adjustment, subsurface transport of KC, assimilation of KC into the aquifer community, CT removal without CF production after inoculation, and CF formation when KC activity declined.