PROVIDENCE, R.I. - The Southern Union gas company was ordered Friday to pay $18 million for illegally storing mercury waste, which was exposed to the public five years ago when vandals stole the hazardous liquid from a rundown building and spilled it at an apartment complex.

U.S. District Judge William Smith on Friday fined the Texas company $6 million and ordered an additional $12 million in payments to the community, saying the company had committed a "serious crime" by storing liquid mercury at a decrepit building in Pawtucket without the required permit.

"It must be enough to get the attention of other companies who might be doing the same thing," Smith said of his penalty.

Southern Union in 2001 began storing home gas regulators containing mercury at a facility in a densely populated section of Pawtucket. The mercury was initially removed from regulators and then shipped out of state, but that program lapsed in 2004, and soon liquid mercury began accumulating in plastic jugs, glass containers and other receptacles.

A group of vandals broke into the building in September 2004, stole several vials and dumped the liquid on the ground and at a nearby low-income apartment complex, displacing and endangering residents, prosecutors said. About 90 residents recently settled a lawsuit over the spill for undisclosed terms.

Southern Union lawyer John Tarantino asked for leniency, saying the case marked the first time in the company's 80-year history that it had faced criminal charges. He said Southern Union had already spent more than $6 million cleaning up the mess and had placed affected residents in a hotel and offered them food vouchers.

"Southern Union is not a chronic offender. It is not a company that has a reputation for being in trouble with regulators who is constantly being fined," Tarantino said.

Smith agreed to stay the fine pending an appeal. He ordered the company to spend $11 million on an endowed fund that would dispense grants related to childhood exposure to environmental toxins.

Southern Union faced a maximum fine of $38.1 million - or $500,000 for each day the mercury was stored without a permit.

Federal prosecutors sought a fine of more than $20 million, saying Southern Union attempted to keep the spill quiet by failing to alert the city fire department.

"This thing could have been avoided, this whole situation, if they had a mind to comply with the law. They just didn't care," said Assistant U.S. Attorney Terrence Donnelly.

The company was acquitted at a jury trial last year of two other charges of failing to report the spill and of illegally storing gas regulators that still contained the mercury.

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