A house in the Spring Valley neighborhood in D.C. is demolished as more munitions may be buried underneath. (Katherine Frey/The Washington Post)

The Army Corps of Engineers on Thursday began to demolish a stately brick home in the District’s Spring Valley neighborhood that might sit atop a cache of World War I-era chemical munitions that has included mustard gas and arsenic.

Army officials hope to determine whether any chemical agents or munitions remain at the vacant property, which was used for researching and testing chemical agents, equipment and munitions from 1917 to 1920.

A pit near the house’s back porch is expected to hold contaminated soil, glass and other debris, and munitions, said Dan Noble, a project manager. The site is in the 4800 block of Glenbrook Road NW.

“We also know we’re going to find more [munitions and contaminated soil] off the front of the house,” he said. “We saw it the first time” while digging in the area.

No public health hazards are anticipated, officials said. Army officials don’t expect to find contamination on adjacent properties, which have been cleaned.

At the property now being cleaned, “we do anticipate soil contamination . . . and will take the soil off-site to examine it,” said Brenda Barber, a project manager. “Groundwater will continue to be monitored.”

The area used by the Army during World War I — now designated as the Spring Valley Formerly Used Defense Site — covers more than 660 acres in Northwest Washington. About 1,600 private homes, American University’s main campus and the Wesley Theological Seminary are within that area.

More than 500 items related to munitions, such as bottles of arsenic trichloride and canister shells of liquid mustard, have been removed from the residential property on Glenbrook Road during two investigations between 2000 and 2010. The Army has also removed 400 pounds of laboratory glass and 100 tons of contaminated soil in that time. The Army has been removing buried munitions there since 1993.

Demolition of the house, vacant since 2001 and owned by American University, is expected to take two to three weeks, Barber said. The Army will first knock the five-bedroom home into its basement, then remove debris and any munitions to a federal dump site near Sibley Memorial Hospital for analysis and recycling or disposal.

The property is divided into two areas, according to the probability of finding more munitions, Barber said. Low-probability areas near the front of the house will undergo open-air excavation with environmental-safety monitoring. High-probability areas will be excavated under a tentlike structure, and air will be filtered to ensure safety for nearby residents.

Neighbors said they are glad excavation is underway, but they have differing opinions on the site’s safety.

“I’m sure they’re doing the best they can ... but there’s a lot of unknowns,” said Christine Dietrich, who lives across the street from the Glenbrook site. “I’m not willing to expose my 1- and 5-year-old children, playing in this front yard, to the things in that basement.”

Advisory Neighborhood Commission member Nan Wells said that she is “watchful” of the project but that the Army’s cleanup plan is appropriate and reasonable.

“It’s important that what they find is finally gotten rid of,” Wells said. “The Army will not be coming back here again.”

The project will take 18 months to complete, Barber said, after which the property will be free of contaminants and fit to build upon.