When the Environmental Protection Agency discovered an old, abandoned hazardous chemical plant in surburban Boston last year, it couldn't just knock the building down or blow it up.

The highly contaminated plant, filled with dangerous, toxic materials, was located in a densely populated area. Residents living nearby feared that if the factory were demolished with normal explosives the health and safety of their neighborhoods would be threatened.

Instead, the entire plant had to be dismantled piece by piece and hauled away -- no easy task with 50 contaminated tanks, including a 24-foot-diameter, 40-foot-high container partially filled with poisonous sludge.

NUS Corp., a Gaithersburg environmental and energy consulting firm, was called to do the job.

*At a toxic wastewater lagoon in southern New Jersey, experts needed a way to collect and examine sediment and surface samples from the hazardous water that threatened to spread toxic chemicals to the air and public wells of the populous area.

Again, it was NUS that experts turned to for help. NUS technicians designed and built a special raft for the perilous task. Then, after donning fully protective gear, they ventured out over the deep lagoon in hazardous conditions to get core samples from the contaminated sludge.

*A sparsely populated 30-acre area of small farms, woods and coal mines in western Pennsylvania became a site for waste disposal in the early 1950s. Over a period of three decades, a body of liquid waste, dumped mainly by the steel industry, accumulated to form a lagoon more than 30 feet deep.

Pennsylvania authorities grew uneasy about the effects of the lagoon on the local environment, especially the possible contamination of nearby streams and community drinking water. So, the Pennsylvania Department of Environmental Resources ordered the site closed down. But first, the department needed advice on how to do it safely and economically.

An NUS hazardous waste team of experts was called in to cover the toxic waste and at the same time prevent the groundwater from coming into contact with the dangerous sludge.

NUS says it is involved in the cleanup of more than 100 hazardous waste sites. Its employes, dressed in astronaut-like suits and other elaborative protective gear, are working across the country processing and transporting toxic waste materials.

With nearly 800 hazardous waste sites still on the EPA national priority list, waste management is "one of the waves of the future," said Charles F. Jones, NUS president, who has been with the company for 23 years.

"There's no doubt that the hazardous waste management business is really booming," said Jon Holtzman, spokesman for the Chemical Manufacturers Association in Washington.

Along with building and operating hazardous waste facilities, NUS performs laboratory analyses and advises companies on site selection, costs, environmental liabilities and processes involved in toxic disposal.

NUS, now a wholly owned subsidiary of Halliburton Co., was founded in 1960 as Nuclear Utilities Services, providing consulting, engineering and radioactive waste management services to the nuclear industry. "Having been in this business for a quarter of a century, we grew up with the nuclear industry," said NUS spokeswoman Shelly Alfaro. With only four employes initially, the firm started as a group of "PhD types doing calculations on computers," according to one NUS official.

But the company has grown to a hands-on-site firm of more than 1,600 employes, including environmental and chemical engineers, air-quality scientists, health and safety experts and meteorologists who worked to help industry in less theoretical ways. "We've moved to a 'Let's be practical' company," Alfaro said.

It was a good strategy.

NUS is now a $100 million-a-year company with offices in 19 American cities as well as Brazil, England and Saudi Arabia. The firm also has two subsidiaries in West Germany and Japan.

The company's name was shortened to NUS in 1966 to reflect its diversification into areas other than nuclear utilities, such as water pollution control.

By the early 1980s, the nuclear design and engineering industry began to decline, with fewer new plants being built. So NUS shifted gears and started to transfer the majority of its resources to hazardous and nuclear waste management.

"It was a logical switch for us to make," said Jones of NUS. "And the transition was not difficult because we had been involved in water and air pollution work from the beginning."

In 1981, only 5 percent of the company's business involved handling hazardous waste. Now, more than one-third of its business is in toxic waste work.

"It's the biggest single growth area we've got right now," said Paul Goldstein, an NUS vice president who oversees the firm's hazardous waste projects. He said the company is in the forefront of hazardous waste technology and management in large part because of its central role in the federal government's Superfund cleanup efforts.

In 1982, the Environmental Protection Agency awarded NUS a two-year contract to conduct field investigations and cleanup planning at Superfund hazardous waste sites in 21 states east of the Mississippi and Ohio rivers. The 1982 contract was part of a $200 million award to NUS and another company.

The $1.6 billion Superfund, created by Congress in 1980, was to be used in cleaning up the nation's most dangerous toxic waste sites that posed imminent danger to human health and the environment. It was designated specifically to clean up "orphan sites," places where it was unclear who was responsible for the contamination.

The EPA has finished work on only six "national priority" sites. Nearly 800 of an estimated 14,000 potentially dangerous sites still remain singled out for quick action as "imminent hazards" to public health.

"The national priority list may ultimately grow to 2,200 sites," said Holtzman of the Chemical Manufacturers Association.

"The EPA can't take a site off the national priority list until they're sure that it's completely taken care of," Holtzman said. "Although a site may have been cleaned up, it may take years of monitoring to be sure it is safe enough to come off the EPA list.

Recently, NUS was awarded a two-year extension on the EPA Superfund contract. "The estimated value is $130 million for the full four-year contract," said Tom Centi, who manages the Superfund contract for NUS.

Besides its contract with the EPA, NUS handles contaminated waste projects for the Energy and Defense departments and several state and local governments.

Government and industry officials agree there is no "cookie-cutter" approach to cleaning up hazardous waste sites, because each area presents unique and often risky problems. To help prepare its staff to deal with problems they may encounter at waste sites, such as fires, explosions, caustic chemicals and toxic gases, NUS has set up a $1 million television studio that it uses to make video training films shot at on-site locations.

In the nuclear area, NUS says it is still involved with about 90 percent of the country's nuclear reactors. It handles low-level radioactive waste resulting from the routine operation of a nuclear power plant, such as contamination of water, hardware, filters and clothing.

"It's not generally the terribly hot stuff," explained Donald L. Couchman, NUS senior vice president.

After the Three Mile Island accident in Pennsylvania, NUS was one of many companies called in to help restore the contaminated plant. NUS transported waste from the cleanup activities.

One decontamination method NUS uses, called "liquid abrasive decontamination," blasts the contaminated object with water containing an abrasive. By using a special machine that controls water and air pressure, a technician scrubs the decontaminated equipment with the liquid abrasive, making it possible to remove surface contaminants often without taking off the surface paint.

To clean radioactively contaminated water, NUS uses a sophisticated filtration device called Transfix. The company does not bury contaminants directly but ships the hazardous particles to a burial site after it has separated them from the water.

"Nuclear waste gets all the publicity," said Couchman of NUS. "But low-level nuclear waste is a trivial problem for society compared to hazardous waste, and it's a relatively simple problem to deal with."