Oxygen and nitrate enhanced in situ bioremediation of an oil -contaminated salt marsh

Salt marshes are among the most ecologically-sensitive areas to oil spills and remediation activities. Contaminated marshes may take years or decades to recover. Bioremediation is the process of enhancing naturally-occurring biodegradation by supplying limiting nutrients and terminal electron acceptors (TEAS). During this study, two TEAS (O2 and NO3 -) were evaluated for their ability to enhance natural in situ biodegradation of total petroleum hydrocarbons (TPH) in an oil-contaminated marsh. EPA (9071A) and ASTM (D5831) methods were evaluated for screening TPH in the contaminated marsh sediments. The ASTM Method was selected to evaluate TPH levels in candidate sites at the Fore River Creek salt marsh, Portland, ME impacted by the Julie N oil spill in 1996. Two plots in the marsh received air and NO3- , two served as controls. Subsurface horizontal wells were used to inject the amendments into the sediments. During 1998--1999, degradation of short chain (SC) and long chain (LC) aliphatics and aromatics, abundance of oil-degrading bacteria, nutrients and Spartina alterniora growth were monitored. Results indicated that natural attenuation (control) significantly reduced the TPH. The overall (1998--1999) degradation rates in the controls were 7.8 +/- 2.1 and 3.0 +/- 1.0 mg/kgdw/d for SC and LC aliphatics, respectively; and 6.9 +/- 4.8 mg/kgdw/d for aromatics. The NO3- amendment degradation rates for SC aliphatics and aromatics were 4.7 +/- 2.4 mg/kgdw/d and 4.5 +/- 3.3 mg/kgdw/d, respectively. These degradation rates were not significantly different than control rates. During the first season (Summer and Fall 1998), the air and NO3- amendments significantly degraded more SC aliphatics than the control, while NO 3- significantly degraded LC aliphatics. Porewater monitoring indicated more NO3- amendment was needed to promote denitrification. In addition, low degradation rates in the amendments plots may have been caused by problems with the well (distribution) system and mass transfer limitations. There was no significant change in the abundance of oil-degradees, probably because they were already established when the study began two years after the spill. Subsurface addition of air and NO3- has the potential to accelerate in situ biodegradation of Nos. 2 and 4 fuel oils in marsh sediments if problems with the supply of the amendments can be overcome