RECOVERY OF SUNKEN AND BURIED OIL IN COASTAL WATERDURING THE ERIKA SPILL

摘要

The Erika spilled a very high density, high PAHcontent persistent heavy fuel oil that impacted over 400 kms ofFrance's West Brittany coastline resulting in a protracted periodof shoreline cleanup. One of the sites oiled by the HFO was PenBron, located seaward of the Croisic salt marshes. This laargeand very environmentally sensitive area with extensive salt pansand bivalve production was polluted by a significant spill ofsunken oil buried in the sediment. In view of the risk to localresources and amenities, operations were undertaken to remedythe sunken oil spill: the pollution was mapped and cleanuptechniques studied to define the optimum technique for removingthe oil that sank and was buried in an area subject to strong tidalcurrents. Site restoration was conducted in two stages:1. Sediment in the most polluted area (700 m2) wasmobilized by a mechanical shovel dredge mounted on abarge and the sediment was sent to a refinery to bedisposed of along with waste from other locations.2. Sediment from the surrounding area (10 000 m2) wasremoved by a pump dredger; pumping the sediment- oil -water mixture ashore to a lagoon where the oil wasremoved from the sediment by floatation and skimmedwhile the water was filtered before being released. Theresidual oil concentration in the sand was monitored bychemical analysis to decide on how to dispose of it best:replacing it on site or treating it as a specific waste.This operation involved over 5,500 tonnes of sediment.Environmental impact was minimised as 85% of the sediment wasreinstated safely on site, thus avoiding the risk of shorelineerosion which could have happened in the event of excessivesediment removal.