A plan to clean up an asbestos-contaminated waste dump at Valley Forge National Historical Park has finally been approved following nearly a decade of negotiations.

Approximately 112 acres along County Line Road near the Welcome Center's lower parking lot are contaminated by asbestos and other toxic wastes, the legacy of a manufacturing operation from the late 19th century to the early 1970s.

The remediation plan, which was recently approved by state environmental officials and the U.S. Department of the Interior, calls for excavation and removal of the most heavily contaminated soils to a facility that is permitted to dispose of such wastes. The area will then be filled in with clean topsoil, graded, seeded with native grasses, and planted with trees and shrubs.

The $11.6 million project will be shared by the state and the federal government. Both are due to meet with a mediator next month to determine who will pay for what, said Andy Hartzell, an attorney with the state Department of Environmental Protection.

Hartzell said that $500,000 of the costs would be paid by the Keene Corp., according to a settlement agreement the company reached with the federal government.

Keene, which is now part of Reinhold Industries, operated an asbestos-manufacturing facility on private land that was surrounded by Valley Forge State Park, according to a statement from the National Park Service. The National Park Service took over the park in 1976.

Other contaminants have been detected, including arsenic, lead and PCBs. Contributing to the contamination was another former company, Baldwin Ehret Magnesia Co., which Keene acquired in the 1960s, Hartzell said.

Contamination also has been found at a number of old quarries and in a drainage ditch that runs under the Conrail tracks and empties into the Schuylkill.

"I'm glad that we have an agreement on the remedy," said Hartzell. "That was not an easy resolution."

Contact staff writer Nancy Petersen at 610-701-7602 or npetersen@phillynews.com.