On June 24, 1989 at approximately 0500, the Uruguayan motor vessel
Presidente Rivera ran hard aground in the Delaware River
near Claymont, Delaware, south of Marcus Hook, Pennsylvania.
The grounding damaged four of the vessel's cargo tanks,
resulting in the release of approximately 7310 barrels of No. 6 Oil into the river.
The weather at the time was cloudy with occasional thunderstorms,
variable light winds, 71F, and 2-3 miles visibility.
The owners of the vessel assumed responsibility
and hired a contractor to deploy booms around the ship.
Another company was hired as prime contractor for the entire cleanup operation.
Cleanup operations began immediately.
By mid-morning of the first day, the vessel had been boomed and lightering operations had commenced.
A Multi Agency Local Response Team (MALRT) meeting was held at noon on the first day
at the Marine Safety Office (MSO) Philadelphia.
By the morning of June 25, the vessel had been refloated
and moved to the Sun Oil Co. terminal at Marcus Hook, Pennsylvania for final lightering and inspection.
By June 28, there was no significant free-floating oil observed in the river.
The vessel was in dry dock in Philadelphia by July 8.
Cleanup operations continued into the spring of 1990.
No. 6 fuel oil is a heavy product with an API gravity that ranges from 7 to 14.
The Presidente Rivera was carrying over 452,000 barrels of oil at the time of the incident.
The No. 6 Oil was heavy and its pour point was greater than the temperature of the water.
The spilled oil congealed into "pancake" like, tar globs which floated with the river current.
Only 10 percent of the oil was visible above the surface.
The vessel pilot reported to the USCG immediately after the grounding
that 1000 barrels had spilled.
An overflight made at first light on June 24 determined
that there was considerably more than this amount in the water.
At the time of the overflight, the cargo surveyor reported
that there were approximately 38,095 barrels of oil unaccounted for based upon tank soundings.
Further inspection of the vessel showed that some of the missing oil had drained
into previously empty cargo tanks due to internal damage to the bulkheads.
The amount spilled was not accurately determined until 1400 June 27,
by which time 21 miles of Pennsylvania and Delaware shoreline had been oiled.