News 12 has learned most of the contaminants have been cleaned from a groundwater plume in North Hempstead, but officials say it is going to take another 20 or more years to finish the job.

Lockheed Martin says it has cleaned up 70% of the plume, that spans 900 acres in North Hempstead, but added that remediation will continue through at least 2044.

Project officials say the public has no risk of exposure to the contaminated groundwater that's 100 to 400 feet underground, but environmentalists disagree.

"It's actually disturbing that there are plumes across Long Island that are going to take so long to remediate. We're going to be pretty old, some of us in 2050. For residents it's important to stay vigilant and make sure they get cleaned up," says Adrienne Esposito, of Citizens Campaign for Environment.

The groundwater plume originated from a 94-acre Lake Success facility on Marcus Avenue where chemicals used for manufacturing were dumped in dry wells for decades.

Lockheed Martin would not give an exact cost, but estimates the overall cleanup costs to be several hundred million dollars.