A 14-month pilot-scale bioventing study, sponsored by the New Hampshire Department of Environmental Services, was conducted by the University of New Hampshire to determine the effects of the time between the contamination event and the onset of bioventing, as well as air flowrate, temperature, and nutrient amendments. Freshly contaminated soil was not readily amenable to bioventing. Bioventing was effective (82–92.5 percent removal) for acclimated soil amended with nutrients at 10 °C and 20 °C for the 275 cm3/min and 140 cm3/min air flowrates, respectively. First order degradation rates after nutrient addition were −6.11 ± 0.83 (×10−3)/day and −6.57 ± 1.71 (×10−3)/day, respectively. The results indicate that bioventing will be best applied when the contamination has occurred at least two years before the onset of treatment. © 2014 Wiley Periodicals, Inc.