A specialist team of civilian contractors began work last week on removing chemical and conventional warfare ordnance buried at the site at the end of World War II.

They are uncertain what they will find as the involvement in chemical warfare remained highly secretive even to military agencies until the Defence Department confirmed last year — reported exclusively in the Lithgow Mercury — that mustard gas and phosgene gas bombs had been stockpiled at Marrangaroo during the war and buried on the site at the end of hostilities.

The department announced plans to decontaminate the area in a major operation that got under way last week.

In preliminary test digs a number of bombs were found but all were empty.

That, however, could not be accepted as evidence that there was no danger from whatever else was buried.

Emergency plans put in place with residents and local services were put to the test on Thursday when the contractors unearthed what was identified as a 250 pound (113 kilogram) phosgene bomb.

The detonator was missing but it was believed the bomb still contained its deadly load.

Markings on the casing indicated the bomb was of 1944 vintage.

It was found in an excavation about 300 metres from Reserve Road in an area where numerous other bombs have already been unearthed.

Authorities notified residents of the find and police set up road blocks a short distance from the highway intersection while a delicate examination was made of the suspect find.

After less than an hour the bomb was declared safe with no harmful contents.

The examination took place within a containment tent designed to prevent any escape of toxic material into the atmosphere and it was not considered necessary to evacuate residents.

The decontamination program being carried out by specialist firm Milsearch is expected to continue well into the year.