At last year’s Palisades Day Parade, a Spring Valley resident demanded a health study.

The U.S. Army Corps of Engineers has spent the past two decades trying to clean up the remnants of a World War I-era weapons-testing range located in what is today the upscale Northwest D.C. neighborhood of Spring Valley. And, according to a report in The New York Times yesterday, cleanup teams might finally be zeroing in on one of the nexuses of the damage by demolishing a stately brick house that might be on top of a chemical burial pit nicknamed “Hades.”

By figuratively unleashing Hell, Corps of Engineers teams working on Spring Valley’s decontamination might find a major stockpile of early-20th-century mustard gas canisters that many believe damaged the soil and made residents susceptible to respiratory and endocrine diseases that can be traced to arsenic.

The pit in question got its underworld-borne name from Army Sgt. Charles William Maurer, who worked at the chemical weapons facility associated with nearby American University and photographed a large quantity of mustard gas canisters in a hole he labeled “Hades.” The Army Corps of Engineers’ cleanup of Spring Valley, which began in 1993, has dug up other pits of old chemical weapons beneath houses, including that of the South Korean ambassador, but not “Hades”:

In 1993, workers uncovered mortars at one home, setting off an evacuation. The corps and the Environmental Protection Agency conducted a two-year investigation and some cleanup efforts, and then declared the inquiry complete.

But a dogged city employee generated a report indicating that disposal pits remained. Separately, evidence supporting that conclusion came from a trove of photos that an Army sergeant, Charles William Maurer, had left to his daughter.

One photo showed Maurer standing over canisters lined up at the edge of a pit. On the back, he wrote: “The most feared and respected place in the grounds. The bottles are full of mustard, to be destroyed here. In Death Valley. The hole called Hades.” Late in life, he would not go near the spot, said his daughter, Addie Ruth Maurer Olson, 89.

The Times reports that the corps plans to raze the house, which is owned by American University, later this spring. Finding Hades might bring a quicker end to a two-decade project that may wind up costing more than $230 million, but after so much time, some Spring Valley residents are tired of the corps’ many promises that don’t always pan out.

“We keep finding out one thing after another where the Army corps says one thing and it turns out not to be true, and the situation turns out to be much worse than what they told us,” Kirk Slowinski, a landscaper who grew up in the neighborhood and is a leading critic of the corps, told the Times.