Behavior and Persistence of Spilled Oil on Shoreline

MICHEL, JACQUELINE, Research Planning, Inc., Columbia, SC

Recent oil spills have re-demonstrated the range of shoreline impacts that are possible from medium to large spills in the United States, i.e., the Exxon Valdez spill which significantly contaminated over 1000 km of shoreline in Alaska and the Mega Borg, which resulted in widely scattered tar balls over a small area. Immediate and total removal of stranded oil should not always be the primary objective. Instead, shoreline cleanup strategies developed for oil spills need to consider the persistence and short- to long-term persistence of stranded oil. There are environmental impact considerations other than intertidal communities that need to be incorporated into the decision-making process, e.g., the potential for contact by organisms prior to natural removal or the transfer of oil int more sensitive areas.

There are several general guidelines on the persistence of stranded oil. High-energy shorelines are rapidly and effectively cleaned by natural processes, although there are micro-environments where oil tends to persist (wave shadows, supratidal zone, rock crevices, etc.). On sand and mixed sand and gravel beaches, oil tends to be buried below

clean layers of sediment, but erosional/depositional cycles will result in oil removal, usually within one year. In sheltered environments (wetlands, tidal flats) oil will persist for long periods; therefore, oil removal is frequently required, though it is usually poorly implemented.

Cobble/boulder beaches, while usually very complex, present a special problem. They can be found in a range of energy settings, with years between periods of storm activity. These beaches can hold large volumes of oil; they can be a source of long-term (one year) leaching and sheening; subsurface oil is very difficult to remove by surface treatment methods; and they have poorly understood sedimentation patterns, so it is difficult to predict rates of sediment reworking. Studies of recent oil spills have shown a need for shoreline-specific technologies for these types of beaches.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)