Biodegradation of BTEX in subsurface materials contaminated with gasoline: Granger, Indiana

The microbial ecology and potential for biodegradation of benzene, toluene, ethylbenzene, and o- and m-xylene (BTEX) in core materials contaminated with unleaded gasoline were investigated. The site studied was unique because a portion of the contaminated area was biostimulated in a demonstration of the use of hydrogen peroxide as an oxygen source in in situ biorestoration. Two years after termination of the field demonstration, core samples were collected from uncontaminated, contaminated, and biostimulated areas at the site and analyzed for inorganic nutrients, microbial numbers, mineralization potential of glucose, benzene, and toluene using liquid scintillation counting, and biotransformation of BTEX using gas chromatography. The results indicated that the subsurface microflora at the site was active and capable of degrading a variety of compounds. Microbial numbers and contaminant biodegradation potential in samples from the biostimulated area were greater than in uncontaminated and contaminated zones. Toluene, ethylbenzene, and m-xylene were removed in all core materials, whereas o-xylene was recalcitrant. Mineralization experiments indicated that toluene was mineralized to a greater extent than benzene. These data indicated that the biodegradation potential of the subsurface material from the biostimulated zone, which still contained residual hydrocarbon, remained enhanced for at least 2 yr after the in situ biorestoration process had been terminated.