Marine Terminals Corporation (MTC) provides stevedoring, maintenance and terminal operating services to the Port of Portland, which owns Terminal 6. The spill occurred on the evening of May 2, 2003, when MTC employees were filling a mobile tanker truck on the property with diesel fuel. The employees received a call and left the area without turning off the diesel pump. (An employee is required to be present during all fueling operations, according to the Port’s spill plan.)

While fueling the tank, MTC was using a high-capacity nozzle that discharges fuel at a rate of 50 gallons a minute. The fuel discharge occurred over a 75-minute period. A total of about 3,750 gallons of diesel fuel was released. Fuel that overflowed from the tanker drained into an oil-water separator that discharged into the Columbia Slough. Approximately 2,700 gallons of fuel was released into the Slough. Only 300 gallons were recovered, with the rest spreading from the Slough into both the Willamette and Columbia rivers, resulting in an oily sheen.