In the late 1980s, the United States military discovered levels of toxic polychlorinated biphenyls (PCBs) at land on Kadena Air Base that exceeded safe standards by many orders of magnitude, suggests an in-house report obtained by The Japan Times. Despite the possible risks to service members and local Okinawans, it appears the U.S Air Force failed to alert Japanese authorities and has been concealing information about the contamination — which potentially remains dangerous today — for more than 25 years.

According to the documents, base officials discovered the pollution following a November 1986 accident in which 20 gallons (76 liters) of oil spilled from an electrical transformer at an open storage area within Kadena. Subsequent environmental tests conducted by a military laboratory in the U.S. revealed in March 1987 that the spilled oil contained PCBs at a concentration of 214 parts per million (ppm) — but the soil was contaminated at 2,290 ppm. A second round of tests, returned in October 1987, showed soil contamination of 5,535 ppm.

The report — written on Dec. 1, 1987 — concluded that the pollution must have predated the accident: "It appears that the incident [the November 1986 spill] merely 'opened a can of worms.' Soil sampling in the open storage yard would have yielded high PCB levels whether the spill had occurred or not."