Greg Nielson pushed a joystick, and a video camera zoomed in on three men in moon suits and gas masks as they prepared to blow up a weapon of mass destruction less than five miles from the White House.

Later, the crew slid the rusting World War I artillery shell into a small steel vault and sealed the door. They detonated a shaped explosive charge to cut the projectile open, and pumped in reagent to neutralize its contents: liquid mustard, an infamous chemical warfare agent.

The process is “as safe as sliced bread,” said Nielson, the operation leader, at a control panel in a nearby trailer. “Maybe safer.”

The destruction of five poison-filled shells and 20 other suspect items ended last week. But the strange saga of America’s most unusual hazardous waste site is far from over.

Since 1993, the Army Corps of Engineers has removed 84 chemical-filled shells and more than 1,000 conventional munitions, plus at least 44,000 tons of contaminated dirt and debris, from the verdant campus of American University and the manicured lawns of Spring Valley, one of Washington’s most prestigious neighborhoods.

The toxic trash dates from 1917 and 1918, when the military leased the then-rural campus and nearby farms to test gruesome gases. After the war, soldiers and scientists buried lethal leftovers in unmarked pits, calling the area Death Valley.

A developer renamed it Spring Valley, and mansions sprouted. Presidents Lyndon B. Johnson, Richard Nixon and George H.W. Bush lived here before they entered the White House. U.S. Atty. Gen. Eric H. Holder Jr. and Sen. Dianne Feinstein (D-Calif.), among other top officials and foreign diplomats, reside here now.

The Pentagon says 5,000 old arsenals and other former defense sites may hold hazardous waste. But the bomb hunt here “is the No. 1 priority,” said Col. David Anderson, the Army Corps district commander. “This is the nation’s capital.”

The Army has spent $180 million and expects to spend $15 million more to finish the job, Anderson said.

So far, government agencies and independent studies have not found adverse health effects on American University students or the 4,000 or so residents of Spring Valley.

“Overall, community health is very good,” said Beth Resnick, coauthor of a 2007 study by the Johns Hopkins Bloomberg School of Public Health. “Cancer rates overall are low. Mortality rates are low.”

She said a new study may focus on several people who lived near the burial pits and reportedly suffered rare cancers, blood disorders and other ailments. It’s not known if military waste played a role.

For now at least, the oak-shaded streets buzz with lawn mowers, not public outcry. Property values are stable, and activists acknowledge that few residents share their suspicion that the Army Corps has downplayed dangers and concealed data, a charge the Army denies.

“They’re deliberately misleading people,” said Nan Wells, who represents part of Spring Valley in local government. “They just want to leave.”

Tom Smith, another Army Corps critic, said many residents have become complacent. “We’ve grown a little too accustomed to having the Army in our backyards, literally in our backyards, for the last 17 years,” he said.

The yard that causes the most concern is between the official residence of South Korea’s ambassador, Han Duk-soo, and the white-columned house of American University’s president, Cornelius Kerwin. Previous digs unearthed more than 300 munitions and chemical weapons debris on the South Korean property and toxic chemicals beside the AU house.

A high fence with barbed wire guards the current excavation, known as Pit 3. A two-story, tent-like structure covers the hole to prevent leaks. It also hides the men in hazmat suits and breathing apparatus on a winding street of stately homes and purple azaleas.

Engineers believed the digging was almost finished until they uncovered more than 500 pounds of jugs, beakers and other laboratory glassware this spring. On March 29, a broken bottle spewed smoke inside the containment tent.

Tests show the fumes came from arsenic trichloride, which is poisonous by inhalation, skin contact or ingestion. Known as “arsenic butter,” the compound was used to boost the lethality of mustard, a blister agent that reportedly caused more than 1 million casualties in World War I, and to produce lewisite, dubbed the “dew of death,” and other chemical warfare agents.

The find was deemed so perilous that work has been halted until Army engineers can determine how to safely proceed.

“The concern is they may find a lot more, and there’s a real question whether the air pollution controls are adequate,” said Paul Chrostowski, an environmental scientist who monitors the cleanup for the university.

Kerwin, the university president, was forced to abandon his home for two years when his yard was dug up. He and his wife moved back last fall after tests showed the hazard was gone.

“We may have to change our analysis now,” Chrostowski said. “He may have to move again.”

The long-forgotten ordnance first made news in 1993 when workers digging a utility line unearthed an arsenal. Two years later, after removing 141 munitions, the Army Corps declared the danger over.

But local historians and amateur sleuths found old photos, logbooks and other records that suggested hazardous waste and explosives were scattered over 661 acres. Excavations, evacuations and lawsuits have ebbed and flowed ever since.

Crews have dug up arsenic-laced lawns and spread clean soil at about 140 homes so far, and more are planned. They recently began searching for debris by the reservoir that supplies drinking water to Washington after rusting artillery and mortar shells were found in the weeds.

“It’s taken years to understand the magnitude and scope” of the pollution, said Steve Hirsh, the Spring Valley project manager at the Environmental Protection Agency. “This is really a unique problem.”

The long cleanup has put the university in an uncomfortable spotlight. School officials must balance public safety with public relations, taking pains not to spark undue alarm among the 11,000 students and their parents, as well as prospective students.

In 2001, the university evacuated its campus day-care center and closed nearby athletic fields after dangerous levels of arsenic were found in the soil.

Medical tests of the toddlers and others proved normal. But the day-care center stayed shut until last year, long after the contaminated dirt was scooped up and hauled away. Artificial turf was laid on the sports fields, and a girls lacrosse team practiced there on a recent morning.

Not far away, a backhoe clawed at the soil behind a former fraternity house. Now used by campus police, the building overlooks a ravine that was once a dump. The Army will drill under the building this summer to look for more pollution.

David Taylor, assistant to the university president, said he was eager to see the Army complete the cleanup. “We told them: ‘Do it right. Do it thoroughly. And then wrap it up.’ ”

The work draws little apparent interest among students. Only a dozen people showed up when six experts gathered recently to give presentations on the cleanup. A senior, Michael Ginsberg, had organized the panel as part of his honors project.

“Most students don’t even know there were chemical weapons here,” Ginsberg, 21, said in frustration.

Kent Slowinski, a landscaper, leads informal tours of waste sites on campus and in Spring Valley. He starts at the school’s McKinley Building, where a plaque by the door reads “Birthplace of Army Chemical Corps.”

“You’ll notice it doesn’t say anything about developing or testing chemical weapons on dogs, goats and other animals,” he said grimly.

Five chemical rounds have been rendered harmless since April 16. All were destroyed on a patch of federal property behind Sibley Memorial Hospital, about a mile from campus. Three held the poisonous gas arsine, one had liquid mustard and one carried lewisite. Another 60 to 80 conventional munitions will be turned to scrap this summer.

“We considered transporting off-site,” said Dan Noble, the Army Corps’ project manager. “But you risk traffic accidents. This is by far the safest way to do it. Here we have complete control.”

The fenced compound looks like a construction site. Front-end loaders rumble by stacks of blue barrels, filled with arsenic-laced dirt, that will be hauled to a hazardous waste dump. More fences, cameras and an infrared laser help protect chemical rounds and other unsafe materials destined for destruction.

“Some soldier was probably walking out here 90 years ago and a sergeant comes up to him and says, ‘Hey you, the war’s over. Dig a hole. Get rid of all this!’ ” said Anderson, the Army Corps district commander. “Could they ever imagine it would come to this?”

bob.drogin@latimes.com