University of California Water Resources Center

Widespread contamination of groundwater by MTBE has triggered the exploration of different technologies for in situ removal of the pollutant. After laboratory studies revealed that bacterial strain PMl is capable of rapid and complete MTBE biodegradation, the organism was tested in an in-situ bioaugmentation field study at Port Hueneme Naval Base, Oxnard, CA. Two small pilot test plots (A and B) located down gradient from an MTBE source were injected with pure oxygen at two depths. One plot (B) was also inoculated with Strain PMl. MTBE concentrations upstream from plots A and B initially varied temporally from 1.5 to 6 mg per L. By six months after treatment began, MTBE concentrations wells downstream from the injection bed substantially decreased in the shallow zone of the groundwater in both plots, even in the absence of Strain PM 1. In the deeper zone, downstream MTBE concentrations also decreased substantially in Plot A and to lesser extent in Plot B. Difficulties in delivery of oxygen to the deep zone of Plot B, evidenced by low dissolved oxygen concentrations, are likely responsible for low rates of MTBE removal at that location. We measured the survival and movement of PMl in groundwater using three different methods for detection of PMl rDNA sequences: TaqMan quantitative peR, Denaturing Gradient Gel Electrophoresis (DGGE), and Intergenic Spacer Region (ITS) analysis. A naturally occurring organism with >99% rDNA sequence similarity to Strain PMl was detected in groundwater collected outside the test plots. Changes in the groundwater microbial community were also monitored over time using ITS, a PCR-based DNA fingerprinting method. The largest differences in the microbial community profiles were observed between the shallow and deep groundwater samples, regardless of whether they were from plot A or B.