Fate and Persistence of Crude Oil Stranded on a Sheltered Beach

Abstract

Detailed observations, mapping and sampling were conducted following an experimental spill of 15 m3 ofc rude oil adjacent to the coast at Cape Hatt, Baffi Island, N.W.T. The beach could not retain all of the oil that reached the shoreline, and as a result, one-third of the spilled oil was recovered in cleanup activities on the water, approximately one-third was lost to the atmosphere and to the Ocean and one-thrd remained stranded on the intertidal zone. The stranded oil was subject to natural cleaning processes during approximately 6 months ofo pen-water periods from 1981to 1983. Over this period the surface area of oil cover was reduced by approximately half, whereas estimates indicate that 80% of the oil initially stranded (5.3 m3) was removed. This natural removal of stranded oil occurred in a very sheltered environment. The reduction of the surface area and of the volume of oil resulted primarily from the physical processes associated with wave activity and ground-water leaching. By 1983 an asphalt pavement had developed in the upper intertidal zone on the beach-face slope. Total hydrocarbon concentrations of samples collected from the asphalt pavement indicated a significant increase in oil-in-sediment values in this zone to concentrations in the order of 2-5%. Oil removed from the beach was transported into the adjacent nearshore bottom sediments, where oil concentrations increased sixfold between 1981 and 1983. Physio-chemical weathering rates were relatively rapid immediately following the release of the oil, as the lower molecular weight (Cl to CIO) hydrocarbons evaporated. Subsequent physio-chemical changes were heterogeneous: weathering and biodegradation progressing slowly where oil-in-sediment concentrations exceeded 1%. The primary conclusion from the investigations undertaken to date is that oil isr emoved in substantial quantities from the intertidal zone even in such a sheltered, low-energy arctic environment. Similar changes should also be expected from comparable environments in lower latitudes.