Five years after its initial assessment of a former nuclear waste dump in Armstrong County, the Army Corps of Engineers has decided to pursue a $53 million plan to excavate and remove soil from the 40-acre site along the Kiskiminetas River.

Based on the decision announced by the corps yesterday, a contractor will dig out an estimated 40,000 cubic yards of radioactive waste material and soil from the property known as the "Shallow Land Disposal Area." It is a former disposal site for the Nuclear Materials and Equipment Co., or NUMEC, in Parks, 32 miles northeast of Pittsburgh.

The soil will be taken to a radioactive dump site in Clive, Utah.

Removal of the contaminated waste and soil was one of five alternatives considered, and according to the corps, "the most protective in the long term" of human health and the environment.

NUMEC, which began making nuclear fuel at its facility in nearby Apollo in 1957 and processed up to 450 metric tons a year, legally dumped an estimated 23,500 cubic yards of waste slag, sludge and solvents contaminated with radioactive uranium and thorium at the site from 1961 to 1970.

The thorium and uranium, some still considered "highly enriched," are buried in 10 trenches on 1.5 acres of the 40-acre site.

Radioactive americium and plutonium also have been found in soil samples from the site.

The corps' 2002 assessment of the site found "no substantial radiological exposure threat to human health."

But it also warned that subsidence in the heavily undermined area could cause the radioactive waste to enter the groundwater and endanger human health and the environment.

Citizens Action for a Safe Environment, a local group founded 18 years ago to push for cleanup of the Shallow Land property, had also expressed concern that subsidence could cause widespread contamination.

Karen Auer, a corps spokeswoman, said radioactivity has been measured in the groundwater on the property, but it has not migrated off site and has not been found in a small surface stream on the site.

The state Department of Environmental Protection has tested the Kiskiminetas River but found no radioactive contamination.

The corps' contractor for the project, Cabrera Services Inc. of Connecticut, will propose draft plans for the work early next month.

No excavation work will take place until after a natural gas pipeline is relocated off the vacant, fenced site, and a public meeting on the work plan is held sometime during the first three months of 2008.