Today the caverns are filled with liquified propane and butane and are among the largest mechanically mined, underground storage caverns in the world. Sun spokesmen say the caverns are safer and better than traditional gas-storage tanks, either above ground or underground. Together, the five tanks store nearly 2 million barrels, or 84 million gallons, of liquified gas.
"The caverns today are an excellent way to store material," said Gary Rabik, environmental manager for Sun Co.
Few, if any, of their competitors have caverns, said Sun spokeswoman Shannon Breuer. The geological requirements and the tremendous construction cost keep most from having them. There are a few such caverns in the United States, she said, but most are elsewhere in the world.
Taking advantage of a 500-foot granite vein that runs about 25 feet below ground, Sun officials started planning the first storage cavern in the 1950s. It would be dug out of solid granite 300 feet underground. Located in the western end of the refinery just off Post Road, it was completed and filled with liquid butane in 1958.
From 1961 to 1976, four more caverns were dug, the largest and last with a capacity of more than a million barrels. Raver, at work on cavern No. Five, dealt mostly with the above-ground operations. He watched the heavy machinery being dismantled so that it could be lowered, piece by piece, down the shaft to the cavern.
First, he said, two men were sent down the narrow shaft to "start tinking away with chisels." Then came the dismantled heavy-earthmovers, drills and jackhammers that tore away the granite laterally. Two auxiliary shafts had been drilled to allow air into the cavern, Raver said.
The man called the "powder monkey" set all the dynamite charges and was the last to emerge from the cavern before blasting was done. "The ground would rumble, and people would go have lunch," Raver said. Workers had to wait for the dust to clear before they ventured back down to remove the blasted rock and dirt.
From his records, Raver noted that 850,000 pounds of dynamite was used and 110,000 blasting caps set in the 17-month project. Outside contractors were brought in for this and every other cavern. Fifty-two men alternated on three shifts, five days a week, and the container used to clear rocks, which held five cubic yards of material, made more than 80,000 trips into the cavern.
When it was nearly over, Raver stood on that container, which was turned upside-down, clutching the cable connected to it, and was lowered into the cavern. Inside, it was 40 feet high and about 25 feet wide, he said. The 7,000 feet of interconnecting, honeycomb tunnels take up 11 acres underground. Natural pressure from the groundwater above the cavern keeps the liquified gas
The engineering feats were pushed to the backs of people's minds in 1978, when a leak from Cavern No. 3 triggered explosions and fires in homes along Green Street, a block from the borough hall.
Five houses in the 1100 block of Green Street were heavily damaged, and nearly 60 others in the area had to be evacuated after the Jan. 28 incident. Tony Mazzocchi, a representative for the Oil, Chemical and Atomic Workers' Union, told reporters at the time that Sun Co. had been "playing roulette . . . with the people of Marcus Hook."
The leak occurred when faulty monitoring led to overflow of the cavern, Rabik told residents at a special environmental seminar about storage tanks and caverns last month.
There were no injuries in the accident, but 30 families were displaced for several months while the cleanup was carried out and butane and propane gas fume levels were reduced.
Scores of other residents fled the area when they heard the explosions. George Duffy was living on Delaware Avenue and told an Inquirer reporter in 1978 that the first explosion sent him falling down his stairs. He took his wife and three children, all in their nightclothes, to a relative's house outside of town.
"When you live in Marcus Hook and you hear an explosion, you know it is time to leave," he said at the time.
Sun paid for the hotel bills of several displaced families. Others, by choice, relied on friends and relatives for shelter during those months. They moved back gradually, afraid to trust the Sun representatives who told them there would be no more explosions.
The company agreed in March 1978 to install electronic gas monitors and alarm systems in the homes of families on Green Street who wanted them. They cost about $900 each and were to be monitored regularly by Sun Co. technicians.
Installed in about five homes, the alarm systems were eventually removed, Breuer said. They often were triggered falsely, and they became unnecessary as more monitoring systems were installed at the refinery.
Since 1978, Breuer and Rabik said, the company has added countless safety systems, and the caverns, previously untouched by regulatory agencies, are now heavily regulated. Rabik said the state Department of Labor and Industry, as well as the U.S. Occupational Safety and Health Administration, make sure there are "redundant" monitors and alarms for each cavern.
Rabik said that there are frequent inspections and testing of the equipment that monitors gas levels in the caverns, and that employees undergo much more training than before the accident. In addition, a computer automatically stops the filling of caverns at the 90 percent level.
At the storage tank and cavern seminar last month, at least one resident wondered what would happen if an earthquake shook the caverns. Rabik and Breuer answered that nothing would happen.
In a later interview, Breuer said there had been three minor earthquakes since the caverns were constructed. One occurred two years before the 1978 explosions. The caverns were built with thought to earthquakes, she said, and residents can feel comfortable that a quake would not rupture the enormous caverns.