Experts say it could cost more than $500 million to clean up the toxic plume that began in Bethpage and is now moving south.

State DEC officials want Northrop Grumman and the Navy to pay for the remediation and took a major step toward that goal Wednesday by notifying both entities that it will assess the damage and determine cleanup costs -- which the federal government and the aerospace company are responsible for.

Adrienne Esposito, an environmentalist, says the bill may ring up at around $600 million.

"Government can't walk away from pollution problems," she says. "They should be held to a standard where government cares about public health, and government does the right thing. If New York state has to make the federal government do that, than that's the way it should be."

Residents say that they avoid drinking water in the area and prefer bottled water due to the contamination.

The Navy did not immediately respond to News 12 requests for comment. Northrup Grumman says it is reviewing the claims made by the state DEC.