Influence of the Nature and the Weathering of Oil on Surfwashing Efficiency: Experimental Study with the Shoreline Bench

Following an oil spill on a sandy shoreline, an alternative technique to sediment excavation consists in relocating the contaminated sediment into the surf zone. The sediments are thus subjected to the natural cleaning action of the sea. Waves break down the piles of oily sand, separate the oil from the sediment, spread out the sediment over the beach and clean it by agitation and abrasion, while moving it back up to its original location. The efficiency of this technique depends on many environmental parameters such as the nature of the substrate (particle size), wave energy, and the nature and weathering stage of the oil. In order to assess the influence of these parameters on surfwashing efficiency, experimental studies were conducted using the “shoreline bench”, an automated tool developed at Cedre. Twelve replicate mesocosms, each consisting of a tank filled with a bed of medium grain sand (100 to 1000 μm) and seawater were fixed to an oscillating table (periodic movement : 30 s) to generate identical wave action in each tank. After one hour of agitation, samples of sediment were collected and the oil extracted using an automated solvent extraction system. The amount of oil remaining in the sediment was quantified by spectrophotometry. For the test involving weathered oil, the degree of degradation was assessed by gas chromatography coupled to a mass spectrometer (GC/MS). This paper describe the methodology and the results obtained with different oils and degrees of weathering, particle sizes and use (or not) of a cleaning agent.