The level of a cancer-causing chemical found in tap water at a military base in North Carolina was intentionally not reported, an AP review finds.

An environmental contractor deliberately did not report the level of the dangerously high levels of benzene at Camp Lejeune for a federal health review.

Benzene has been traced to massive leaks from fuel tanks at the base, according to recently disclosed studies.

For years, Marines who served at Camp Lejeune on the North Carolina coast have blamed their families' cancers and other ailments on tap water tainted by dry cleaning solvents, and many accuse the military of covering it up.

A July 1984 report said benzene was found 380 parts per billion in the water supply. In 1991 another contractor warned the Navy of the health hazards posed by such levels of benzene.

By 1992 a third contractor, the Michael Baker Corp., released a draft report on the feasibility of fixing the overall problem. The citing of the 1984 level of 380 parts per billion changed to 38 parts per billion.

One sample from a series of tests conducted from June 2007 to August 2009 registered 3,490 parts per billion, according to a report from a fourth contractor.

Kyla Bennett, who spent 10 years as an enforcement officer for the Environmental Protection Agency before becoming an ecologist and environmental attorney, reviewed the different reports and said it was difficult to conclude innocent mistakes were made in the Baker Corp. documents.

"It is weird that it went from 380 to 38 and then it disappeared entirely," she said. "It does support the contention that they did do it deliberately."

David Higie, a spokesman for Baker Corp., declined to discuss the company's reports or why its employees might have revised the benzene levels. He has referred questions to the military