RALEIGH — Another four pounds of mercury were found at a Camp Lejeune water plant that's expected to remain offline for at least two more weeks as a contractor continues to search for the toxic liquid metal.

Eight pounds of elemental mercury were found Sept. 15 at the Hadnot Point Water Treatment Plant, and a New Bern-based contractor hired to clean up and investigate the plant found another four pounds. Because mercury is so heavy, the total 12 pounds is equal to about 1.5 pints.

A possible source is water pressure meters containing elemental mercury that were removed from the plant in the 1980s and replaced with digital meters.

Base spokesman Nat Fahy said the contractor, Shamrock Environmental Corp., began Tuesday using cameras in non-accessible areas of the piping and reservoir to determine if mercury has settled in other places. Meanwhile, areas that normally get their water from Hadnot Point will instead be serviced by the Holcomb Boulevard plant.

Elemental mercury is found in items such as thermometers and fluorescent bulbs. The Environmental Protection Agency says it's generally not found in elevated levels in drinking water. Any impact on human health is remote since this form of mercury doesn't dissolve in water, Fahy said.

Camp Lejeune has a history of toxins in drinking water. Health officials estimate as many as 1 million people may have been exposed to tainted groundwater at the base over several decades. In August, President Barack Obama signed a bill into law providing health benefits to Marines and family members exposed to contaminated drinking water at Camp Lejeune from 1957 to 1987.

Documents show Marines leaders were slow to respond when tests in the early 1980s showed higher than normal levels of contaminates in groundwater at the base, likely caused by leaking fuel tanks and an off-base dry cleaner.