A pipeline ruptured while oil was being pumped from a tanker at a jetty off Si Racha, in Chon Buri province, on Sunday night, but the spill had been confined and the slick mapped, and the clean up started, officials said.
The Pollution Control Department and the Marine Department set up a prevention and mitigation centre to deal with the drifting slick. The spill occurred out at sea at a jetty run by Thai Oil Public Co Ltd.
According to a Thai Oil announcement, while Arab light crude was being transferred from a tanker at Single Buoy Mooring-2 (SBM-2), a pipeline ruptured about 9pm, causing oil to leak out into the sea.
The pipeline valve was closed and buoys laid around the spot to contain the spill, in line with international standards. The leak had been stopped. There were no injuries, the statement said.
Thai Oil had chemical dispersants and necessary equipment at hand to cope with any such incident, the company said.
On Monday morning, a drone was flown over the scene and detected an oil slick about 5 kilometres long. The disaster prevention and mitigation office of Chon Buri was informed.
The Pollution Control Department said an estimated 50-70 cubic metres of crude oil had leaked into the sea. The company had been given permission to use 6,000 litres of dispersant to break up the slick.
Officials using Oilmap, an oil spill modelling system, said the slick was expected to reach Koh Thai and Khang Khao islands in Ao Udom area, and probably also Won Napha beach in Chon Buri, from Sept 8-10, the department said in its announcement.
Water samples would be collected for an analysis and evaluation of the environmental impact.