Trends in Natural Removal of the Exxon Valdez Oil Spill in Prince William Sound from September 1989 to May 1990

Abstract

ABSTRACT As part of NOAA's scientific support of the federal on-scene coordinator, a program was conducted to monitor the changes in the distribution and character of oil spilled by the Exxon Valdez along the various shoreline types of Prince William Sound between September 1989 (when treatment was terminated) and May 1990 (when treatment was to be resumed). The primary objective of the program was to determine the extent of natural removal over the winter and identify the types of treatment problems to be addressed in 1990. Eighteen stations were established in Prince William Sound, including four set-aside sites, where no treatment was conducted. At monthly intervals, the stations were surveyed for changes in the topographic profile, sediment distribution patterns, surface oil coverage, and the concentration and distribution of subsurface oil. Weatherstations were installed at three locations in Prince William Sound to record localized patterns in wind speed and direction for correlation with shoreline changes. Natural processes during the storm season removed up to 90 percent of the surface oil from exposed and intermittently-exposed shorelines. Even sheltered shorelines showed up to 50 percent surface oil removal. Subsurface oil, the deepest of which occurred on exposed cobble/boulder beaches, was removed by sediment reworking of the top 20 cm on most beaches and deeper at the high-tide berm. However, oil below these depths showed an average 40 percent reduction for the period September 1989 to March 1990. The persistence of this subsurface oil continued to be a major issue during the 1990 treatment activities.