The Navy detected high levels of mercury in an indoor sink at Pearl Harbor Kai Elementary School from a water sample collected on March 16, according to a Navy press release.

The sample detected mercury at 3.9 parts per billion, nearly double the acceptable level of 2 ppb set by the U.S. Environmental Protection Agency.

The sink is located in an administrative building and not regularly used by students, according to the Navy, which said the faucet, and not the drinking water system, is the likely source of the mercury.

The detection is part of comprehensive water testing that the Navy has been conducting since jet fuel contaminated its water system in November as a result of a leak at its Red Hill fuel facility. While the Hawaii Department of Health has lifted the “do not drink” advisory for all affected neighborhoods around Joint Base Pearl Harbor-Hickam, the Navy continues to take water samples as part of a long-term monitoring plan.

The Navy said that mercury was not detected in five other samples taken at the elementary school.

The school’s principal was notified of the mercury detection on March 28, the same day that validated sampling results were received. The Navy says it replaced the faucet on March 30 and is taking new water samples.

High exposure to mercury, particularly over a prolonged period, can cause damage to the gastrointestinal tract, nervous system and kidneys, according to the EPA. Symptoms of high exposure can include skin rashes, mood swings, muscle weakness, memory loss and other mental disturbances.