BAYOU PEROT AND THE UNUSUAL SITUATION OF STRANDED OIL ADHERED TO MUD FLATS

Abstract

ABSTRACT The Environmental Sensitivity Index ranks Sheltered Mud Flats as a 9 on a scale of 1 to 10 (with 10 being the most sensitive of habitats). Mud flats are very soft substrates that will not support even the lightest of foot traffic by cleanup workers. Conventional wisdom suggests that oil that strands on a mud flat during low water will lift and float free during the next high water event. Afterwards, the flat will generally appear free of oil. It is very unusual for stranded oil to form a strong adhesive bond to the wet substrate such that during high water events, water flows over the oil, and the oil doesn't resurface and float away. When the water level drops, the oil remains. This unusual process was one of the problems facing responders during the Bayou Perot Oil Spill in Southern Louisiana in January, 2007. The spill was reportedly caused by a vessel striking a small platform and wellhead. The incident resulted in an uncontrolled, wild well release that lasted for nearly five days. During that time, more than 7000 bbls of crude oil and production water emulsion were thought to have been released into the environment. Several thousand of those barrels became stranded in an adjacent wetland with most of the oil stranded on mud flats and in shallow canals with little to no water. The water levels were very low at the time of the event. Subsequent tidal and wind-driven water level changes failed to significantly free the oil. Most of the emulsified oil remained adhered to the mud flats. The question and response challenge became, “How do you clean mud flats adjacent to sensitive marsh habitat without causing unacceptable collateral damage?” Field tests were conducted using several types of sorbents (snare, sweeps, and bagasse), a solidifier, squeegees, and burning. The outcome, based on these tests, was to use “Airboat-deployed Vacuum Recovery Systems. This paper provides a case study of an unusual, and challenging, oiling event that required a series of field experiments to develop a practical cleanup strategy.