Factors determining the long-term persistence of Exxon Valdez oil in gravel beaches

The largest amounts of, and the least weathered, oil found eight years after the Exxon Valdez oil spill occurred at depths of 25-50+ cm under the protective cover of a well-sorted cobble/boulder armor on intermittently exposed, coarse-grained gravel beaches within Prince William Sound, Alaska. In addition to the armoring, other factors enhancing the retention of the oil include Bat slopes of the middle beach and a thick sediment veneer over a bedrock platform, Natural cleaning of the subsurface sediments was accomplished within three years on the finer-grained gravel beaches that have steeper slopes, a thin sediment veneer over the rock platform, and no surface armoring. Minor berm relocation was an effective technique for removing subsurface oil from the finer-grained gravel berms at the high-tide line. Extensive storm berm relocation caused disruptions to beach morphology and sediment distribution which lasted for up to six years. (C) 1999 Elsevier Science Ltd. All rights reserved.