OILING OF LOUISIANA'S CENTRAL SANDY BEACHES

A 60-km long barrier island chain fronting Barataria Bay, LA, was oiled between May and late July 2010 due to the Macondo spill. Much of the oil came onshore during strong winds, elevated tides, and high wave energy associated with tropical cyclones in late July. Some of the oil was buried during the waning stages of the storms as sand moved onshore by constructional waves covering oil in berm areas, such as at the entrance to washover fans and at the base of foredunes. During the oiling event, mousse mixing with sand in the swash zone became grounded forming surface residue mats on sandy substrates and marsh platforms. The landward movement of sand bars, alongshore migration of beach cusps, and vertical accretion on the beachface served to bury oil as well.

An initial response focused on removal of emulsified oil covering the upper beachface and supratidal zone. During spring low tides, mats exposed in the lower intertidal and subtidal zones were also cleaned. In August and September approximately 2000 pits and 8000 auger holes located and delineated buried oil. Sixty-seven beach profiles along 40 km of barrier beaches helped to determine the dynamicism of the beach and depth of oil burial. Oil buried above the water table formed cohesive oiled layers as much as 20-cm thick covered by 10 to 80 cm of clean sand. Oil buried below the water table became diffused vertically by the rise and fall of the tides forming bands (10-50 cm thick) varying from pooled to stained sand.