Authorities expect to identify in the next six weeks the source of tar balls and petroleum-coated garbage which has polluted long sections of beaches stretching from Hua Hin district in Prachuap Khiri Khan to neighbouring Cha-am district of Phetchaburi.
The findings are expected to point to whether the problem was caused by oil producers based in the Gulf of Thailand, said Veerasak Pungrassamee, acting chief of the Mineral Fuels Department (MFD).
The results will help narrow down the ongoing probe into the pollution which occurs only rarely at beaches in the two districts.
Visitors to the beaches have been put off by long stretches of black, sticky garbage washed ashore, which prompted the MFD to start the probe. At the same time, local authorities have begun the labour-intensive task of removing the slick from the beaches from Khao Takiap in Prachuap Khiri Khan to Cha-am, spanning over 10 kilometres.
Samples of the tar balls have been collected by experts from SGS (Thailand) Ltd for examination in a laboratory in Belgium. They will be compared with the "fingerprints" of crude oil dug in the Gulf of Thailand, Mr Veerasak said yesterday.
The fingerprints refer to the unique characteristics of crude oil obtained in certain areas.
Mr Veerasak said oil slicks have appeared in other areas along the Gulf of Thailand but checks of the tar balls washed up in those locations confirmed they did not come from crude oil.
But in the case of the oil slick washed up in Hua Hin and Cha-am, his department will wait for SGS (Thailand) to present its lab results before making a conclusion.
The company, a subsidiary of Switzerland-based SGS, has been hired to make a database of fingerprints of crude oil obtained in the Gulf of Thailand so they can be compared with the footprints of any tar balls found drifting in the sea or washed up on beaches.
The department has also asked the company to study the impact of tar balls on the coastal ecosystem in the Gulf.
The First Naval Area Command is also helping the department find the cause of the pollution by conducting an aerial inspection of the sea near the slick area. The navy yesterday flew over areas from the King's Klai Kangwon Palace to Suan Son Pradiphat in Prachuap Khiri Khan.
An initial inspection led to the belief the pollution might have come from cargo vessels, command chief Vice Adm Rangsarit Sattayanukul said yesterday.
Naval officers also found more oil in a long band drifting about one nautical mile off the Hua Hin beach. It will likely wash ashore soon, Vice Adm Rangsarit said.
Meanwhile, government workers, soldiers and residents yesterday helped clean beaches from Khao Takiap to Hua Hin.
They scooped up blackened sand and oil-coated debris and garbage and put it in large bags which were hauled away by garbage trucks, said Hua Hin mayor Nopporn Wuthikul.
The tar balls and garbage is expected to be removed within two days if there are no new oil slicks, said Prachuap Khiri Khan governor Thawi Naritsirikun.
Mr Nopporn warned people not to swim at Hua Hin beach until authorities have finished testing the water quality and given the all-clear.