PROVIDENCE — Gary C. Sunday quickly surveyed the puddles of silvery mercury scattered around the ramshackle buildings of the Southern Union-owned facility before he made the call to his superior.

“I told him that I thought it was a bad situation,” he said.

On the other end of the phone call, John Jackson, his boss, instructed him not to contact the police until more company officials arrived. Sunday, then a facilities manager for the gas company, waited at 91 Tidewater St., in Pawtucket.

It was Oct. 19, 2004, the day that a maintenance worker, David Gendron, reported a break-in and possible mercury spill to the company at the long-neglected, former gas manufacturing plant along the Seekonk River.

Sunday had not even stepped into the buildings where more of the mercury lay. That job rested with Robert Shurtleff.

A worker for the environmental consulting firm Clean Harbors, Shurtleff was on scene within an hour of Sunday’s arrival.

Dressed in a full-body chemical suit and wearing a respirator, he entered the buildings, finding liquid mercury floating in children’s swimming pools and inside discontinued gas regulators.

He found a pint-sized plastic bottle of the highly toxic liquid in a paint can in a small wooden cabinet with a broken lock. He relayed a report to his supervisor: “I said it was bigger than we expected and we needed assistance,” he said.

Sunday and Shurtleff were two of the main witnesses to testify in U.S. District Court in Providence yesterday, the second day of the criminal trial against the Southern Union gas company for its role in a 2004 mercury spill that would eventually lead authorities to further contamination of a nearby apartment complex.

The Houston-based company is charged with two counts of illegally storing mercury and one count of failing to notify authorities when it learned that vandals had apparently broken into the facility and dumped the toxin on the property.

The same mercury was later traced to the Lawn Terrace Apartments, and resulted in the displacement of hundreds of city residents.

Federal prosecutors introduced Sunday and Shurtleff into the trial yesterday to demonstrate that the company, rather than reaching out to local authorities, as required by law when a hazardous waste is released, attempted to quietly clean up the mess.

According to Sunday’s testimony, his boss, Jackson, instructed him not to allow persons unaffiliated with the company — including police and fire officials — onto the site.

Sunday said even before the spill, the company considered the facility “a closed site, unless there was a fire or threat of emergency.”

As it grew dark on Oct. 19, Sunday said he arranged for a security guard to watch the site — which had been cordoned off with yellow tape and a protective covering — overnight.

Police did not arrive on scene until the afternoon of Oct. 20; by then, Shurtleff said that cleanup crews disposed of the gas regulators containing mercury, the paint can of mercury, and the mercury in the kiddie pools.

They had vacuumed up most of the mercury outside, and were in the process of tearing up and disposing of asphalt as a precaution.

Meanwhile Sunday mentioned to his boss, Jackson, that he had taken some photographs of the spill and its surroundings. He was advised not to share them with the police.

Sunday said he complied, although he testified that he felt “uncomfortable” with the request.

Under cross examination from defense attorney John A. Tarantino, Sunday said that at no time did the police ask him to hand over any photos.

The trial recessed for the day after 1:30 p.m. yesterday, and continues in Judge William E. Smith’s courtroom this morning.

pmarcelo@projo.com