More than 20 years after federal legislation added a Parks Township nuclear waste dump to a list of sites in need of remediation, excavation work is finally underway on what’s expected to be a years-long cleanup process.

The U.S. Army Corps of Engineers began its excavation at the site — formally known as the Shallow Land Disposal Area — on April 7, according to an announcement the Corps sent Tuesday.

The 44-acre property was operated by Nuclear Materials and Equipment Corp. (NUMEC) in the 1960s and early ’70s, leaving behind enriched uranium and other harmful substances from the production of materials primarily for nuclear-powered submarines and power plant fuel. It was later sold to BWX Technologies Inc. (formerly Babcock and Wilcox).

In total, there are about 33,000 cubic yards of materials in 10 trenches at the site.

Excavated materials will be shipped by truck to a Lawrence County facility then sent via railroad to commercial disposal sites in Utah or Texas, officials previously said during a public meeting. Materials that cannot be commercially disposed of will be sent to the Nevada National Security Site in the Mojave Desert north of Las Vegas.

The Corps held numerous public meetings to share information with local residents, some of whom have expressed concerns about further contamination from the site.

Remediation is expected to take about six years and cost more than $500 million dollars.

The corps said in a statement that excavation work would begin at Trench 8 and “may vary as conditions change.”

“During each stage of excavation, the Corps of Engineers and its contractors will continuously monitor the site and adjust operations as needed while prioritizing worker and public safety, complying with regulatory requirements, and following best practices,” statement said.

Work was previously expected to begin last winter. It’s unclear what caused the delay.

Army Corps spokesman Andrew Byrne said project leadership would answer media questions at a press conference scheduled Thursday at the site.

The Parks Township property is among those listed in the Formerly Utilized Sites Remedial Action Program (FUSRAP).

The program cleans up sites contaminated by atomic weapons and nuclear energy production in the mid-20th century.

The Corps previously remediated sites in Aliquippa and Springdale.