Since early this year a group of specialist contractors commissioned by the Defence Department has been working at Marrangaroo to identify and clear chemical warfare residue buried at various locations around the site at the owned of World War Two.

The decontamination program follows confirmation last year of the previously top secret wartime operation where Marrangaroo served as a storage and distribution depot for chemical weapons, including mustard gas.

The inspection team is from a United Nations monitoring organisation based in The Hague.

In an update to various players in the project including Lithgow Council and the local emergency services the Defence Department says the work at Marrangaroo is progressing well.

Since excavation works began on 19 February the contractors, Milsearch, have excavated approximately 20 of the burial areas.

They are processing the excavated material as they go. Excavated items include small arms, marine markers, detonators, practice bombs and even some asbestos material. Hundreds of thousands of items of small arms munitions have been excavated and demilitarised. Large quantities of metal that has been confirmed free from any explosive have been sent off for recycling.

The excavation of the main burial area uncovered 267 bomb casings of 250lb classification that may have once contained phosgene or mustard agent.

All have been confirmed to be free of any chemical agent and are being reported under the Chemical Weapons Convention.

The international body, the Organisation for the Prohibition of Chemical Weapons, is visiting Australia and is touring the Marrangaroo site today as part of their visit.

One of the burial areas also uncovered 30lb incendiary items containing traces of white phosphorous. This caused a delay to work while Milsearch and Defence worked with the key emergency services contacts to ensure appropriate work and response procedures were in place.

The pit has since been successfully completed, resulting in the removal of over 4000 items.

Due to the unexpected time to clear the two main pits it is now expected that excavations will be completed by the end of July and Milsearch will remain on site until September to complete the rehabilitation of the area.