The blowout of Ixtoc I on June 3, 1979, released at least 476,000 tons of oil into the Gulf of Mexico until the well was capped on March 24, 1980. The predicted northward drift of the oil caused the U.S. government to sponsor a pre-spill coastline mapping project (called the Environmental Sensitivity Index), which was used in developing the response strategy of the U.S. Coast Guard Strike Team and accurately predicted the reaction and persistence of Ixtoc I oil along Gulf Coast beaches when major impacts occurred during August and September 1979. In total, approximately 3,900 tons of Ixtoc I oil washed onto exposed beaches of fine-grained sand and mixed sand and shell in south Texas. Little oil passed into the productive back-barrier lagoons. A tropical storm on September 13, 1979, removed more than 90 percent of the beached oil. By spring 1980, oil remained only as scattered tar mats (8 percent oil, 180 tons total) at the toe of the beach. The quantity of tar balls on the beach could not be differentiated from chronic accumulations.

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