Federal and state officials are investigating whether a chemical spill that flowed into the Potomac River was caused by illegal dumping.

Yesterday, the FBI began inquiries into the cause of the spill of 2,500 to 3,000 gallons of petroleum products that moved along a six-mile stretch from Long Branch near Fort Belvoir into Accotink Creek, Accotink Bay and finally the Potomac River.

Preliminary investigation found that the spill, which was reported Tuesday morning, was "a mixture of volatile petroleum products, including chlorinated hydrocarbons," said Albert Giles, technical services supervisor for the regional office of the State Water Control Board.

Although there was some risk of explosion, state officials are unsure whether there is any remaining health risk, said Giles, noting that samples had been taken for analysis. There was no evidence of a fish kill, he said.

In addition to the Water Control Board and the FBI, Virginia's Emergency Response Team, the Coast Guard and Fairfax County fire and rescue personnel have been involved with the case.

By yesterday afternoon, the Fairfax County hazardous material team had placed booms at Poe Road Bridge at Fort Belvoir and near Telegraph and Backlick roads to catch the remaining chemicals.

Giles said state and federal officials had identified a suspect in the spill who had agreed to contract with a firm to clean up the site. He declined to identify the suspect.

FBI spokesman James E. Mull confirmed that his agency was investigating possible violations of the Clean Water Act.

Mull said if it is determined that there was negligence or that the chemicals were dumped deliberately, his office would report its findings to the U.S. Attorney's Office, which would decide whether to prosecute.

A negligence violation in this case could carry a maximum penalty of a year in jail and a fine of $2,500 to $25,000 a day. Intentional dumping could carry a penalty of three years in prison and a fine of $5,000 to $50,000 a day.