The Okinawa Defense Bureau and the city of Okinawa uncovered seven more barrels Tuesday at a former U.S. military installation in the prefecture that may have been used to hold toxic chemicals during the Vietnam War, stoking concern among residents.

Prior to Tuesday’s findings, the city had dug up 19 barrels from the same site in mid-June.

The barrels found Tuesday had been buried about 1 meter deep in a soccer ground adjacent to the Kadena Air Base that had been part of the installation until 1987, the Defense Ministry said.

The barrels had white stripes around their rims and bore “Dow Chemical” markings, a city official said. The Dow Chemical Co. was one of the main developers of Agent White and other herbicides. Some decayed barrels were also marked “30 gallons,” the official added.

The ministry and the city plan by month’s end to complete a study of soil samples and the barrels, checking for any trace of toxic chemicals, a ministry official said. The ministry said it is also considering digging across a wider area to determine if more barrels are buried in the area.

Jon Mitchell, a contributor to The Japan Times who has been investigating the Agent Orange issue in Okinawa, said that although the position of the white stripes on the barrels seems to suggest they’re not Agent White, there is a strong possibility they could be other toxic chemicals.

“Usually, these herbicides’ stripes were around the middle of barrels. But, from the photographs, it seems to be at the top. So that does seem to suggest it’s not Agent White,” Mitchell said.

Agent White is commonly known to be contained in larger barrels than the 30-gallon (114-liter) drums found at the soccer ground, he said, adding, however, there is also evidence suggesting Dow may have used smaller barrels to send defoliant to Vietnam.

“Even if this is not Agent White, then there is a strong chance that it is another type of dangerous chemical,” Mitchell said. “So it’s important that the barrels are checked and also a wider area is checked. There might be more, much deeper around the area.”

The Defense Ministry has asked the U.S. military to confirm what the site was used for when it was part of the Kadena base, but had not received an answer as of Wednesday.

“(The U.S. military) said it doesn’t have detailed documents about it. So we haven’t received an answer. But we will continue to seek an answer,” the official said.

Mitchell urged the U.S. military to be forthright.

“This is an example of American military pollution,” Mitchell said. “This is a soccer ground. This is where children play. It’s time the American government took Okinawa residents’ worries seriously. They need to cooperate fully with the investigation and come clean about the issue.”

In January, a story by Mitchell in The Japan Times shed light on a September 1971 report produced by the U.S. Army’s Fort Detrick in Maryland, the Pentagon’s main center for biochemical weapons research.

It summarized the military’s usage of chemicals during the Vietnam War, and among the locations cited is a reference to “Herbicide stockpiles elsewhere in PACOM-U.S. (Pacific Command) government restricted materials Thailand and Okinawa (Kadena).”