PROVIDENCE — A criminal trial against a Houston-based gas company for its role in a 2004 mercury spill in Pawtucket opened yesterday in U.S. District Court, with testimony from the maintenance worker who discovered the spill.

David Gendron testified that the former Southern Union facility on Tidewater Street had been used as a storage site for the company even though it was unmanned and had fallen into disrepair over the decades, with homeless people living in some buildings while many others were heavily vandalized.

Southern Union Co. is charged with two counts of illegally storing mercury, a highly toxic metal that attacks the central nervous system, and one count of failing to notify authorities when vandals apparently broke into the facility and dumped the toxin on the property and the nearby Lawn Terrace Apartments.

Discovery of the contamination at the apartment complex forced a temporary closure that displaced 147 residents while Southern Union undertook a massive clean-up, at the cost of $6.6 million.

On Oct. 19, 2004, Gendron, who now works for National Grid (the utilities company that took over Southern Union’s New England holdings in 2006), said that he was clearing brush at 91 Tidewater St., an expansive property described during the trial as larger than two football fields.

Gendron noticed that one of the doors on a building used for storing obsolete equipment had been kicked in and the lock shattered. He saw “quart-sized” droplets and puddles nearly 8 inches in diameter on the ground around the entrance. Elsewhere he found “nickel and dime-sized” silver droplets.

He recognized the silvery liquid as mercury, and immediately called a supervisor, who instructed him not to enter the building until department heads arrived. Gendron testified that in the hours after the spill was discovered, only employees of Southern Union and the environmental remediation company it hired, Clean Harbors, were on site.

Located along the Seekonk River, the Tidewater facility, until the late 1970s, had been a gas manufacturing plant. But by 2004, there was no longer any routine maintenance and no staff on site, according to Gendron.

As a result, there were large gaps in the barbed wire perimeter fence and the brush was heavily overgrown. There was graffiti on rusting, crumbling buildings, and evidence –– including tents and a makeshift fire pit –– that squatters were living on the site.

“There was quite a bit of vandalism. I was afraid to go down there at night,” Gendron said.

Defense lawyer Daniel Fetterman said in his opening statements that while conditions at the Tidewater facility were “regrettable,” the company “had never abandoned mercury” there.

He said that the company will argue it did not need a permit to store the mercury on site because it was a material that the company intended to recycle, not dispose of as a waste.

The key issue was the distinction between a “hazardous material,” which Southern Union was not required to have a permit to store, and a “hazardous waste,” which does require a permit, he said.

“This company spent hundreds of thousands of dollars to develop a program” to remove and recycle gas regulators containing mercury from residences, he said. “The intent, right from the beginning, was to treat the mercury as a material.”

Fetterman said that the defense will show that the company notified the National Response Center, in Washington, D.C., on the day the spill was discovered, which led to notification of local and national authorities, including the U.S. Environmental Protection Agency, the U.S. Coast Guard, the state Department of Environmental Management, and the Pawtucket Fire Department.

The defense will also prove that Southern Union, which has pleaded not guilty on all charges, had no obligation to notify authorities of the spill at the apartment complex because, at the time the spill was discovered, it was believed that the contamination was contained to company land.

Kevin M. Cassidy, a lawyer for the U.S. Department of Justice, said in his opening statements that the prosecution would show in the coming weeks that Southern Union had no use for the mercury it was storing at the site.

The prosecution’s key witness, former employee Marc Viera, will testify that he had tried on at least four occasions to notify his superiors of the need to dispose of the mercury accumulating at the site, said Cassidy.

Another company employee will testify that concerns about mercury on the site had been brought to a company safety committee in the months leading up to the spill.

The prosecution will also prove that in the days after the company had discovered the spill it had reached out to environmental remediation companies to clean the contamination, but not the city’s fire and police departments, as required by law.

In all, the prosecution intends to call approximately 15 witnesses to the stand, many of whom work for or worked for Southern Union or its successor, National Grid.

They will also call to the stand employees of the various consulting firms that the company hired to clean the spill, as well as one of the vandals that broke into the Tidewater site, according to Cassidy.

The defense will put another one of the vandals, who is currently serving a prison sentence at the Adult Correctional Institutions in Cranston, on the witness stand.

Southern Union faces over $67 million in fines if found guilty on all three counts, according to the U.S. Attorney’s office.

pmarcelo@projo.com