Northrop Grumman Corp. has reached an agreement with the U.S. Environmental Protection Agency to spend $21 million to build a groundwater cleanup system to cleanse a major contamination site in the San Gabriel Valley, the EPA announced Thursday.

The groundwater contamination site, underneath the cities of Industry, La Puente and Walnut, was declared a federal Superfund site in 1984. The EPA found that the groundwater was contaminated by over 60 facilities that used highly-polluting volatile organic compounds for degreasing and metal cleaning.

The biggest source of pollution was determined to be a rocket propulsion manufacturing facility operated by Aerojet Engineering Corp., which sold its rocket engineering division to Northrop Grumman Corp. in 2001. Northrop has represented all of the facility owners and operators within the Superfund site in lengthy and complex negotiations with the EPA.

Under terms of the settlement, Northrop Grumman will spend an estimated $21 million to build a series of wells to pump out the contaminated groundwater. The company will also install water pipelines and a treatment plant to remove the contaminants from the water.

“This settlement is an important step toward restoring this valuable source of drinking water,” said Keith Takata, director of the Superfund program for the EPA’s Pacific Southwest office.

According to the EPA announcement, Northrop Grumman has already spent $10 million on cleanup under a 2002 order from the agency. The current settlement also includes $555,000 in reimbursements from Northrop to the EPA and the California Department of Toxic Substances Control for past costs the agencies incurred.

Northrop Grumman spokesman Tom Henson said the company has a policy of not commenting on settlement discussions with regulatory agencies.