TRIALS conducted last week will help determine if a multi-million dollar aerial water bomber will remain part of Victoria's fire fighting armoury.

A massive, converted DC-10 passenger plane, on trial in Victoria from the US, dropped 42,000 litres of retardant in Enfield State Forest, south-west of Ballarat last week.

A second test was conducted at a private farm near Shelford, in which the water bomber dropped two half loads of retardant on a paddock of stubble.

Department of Sustainability and Environment chief fire office Ewan Waller said planned burns were conducted in both trials, to intersect with the retardant to see how it performed.

The aerial water bomber, also known as "Vicki", has only been used once for fire fighting this season - on a bushfire in the Murray Sunset National Park, about 50km south of Mildura.

The Californian aircraft is being housed at Avalon Airport as part of a $10 million trial.

It will remain in Victoria until later this month when the DSE and CFA will prepare a report for the government on its effectiveness.

Mr Waller said Vicki would continue to be tested until its departure.

"Thankfully, we've had only one fire this season that required the use of the DC-10, which has been great news for Victorian communities and our fire agencies," Mr Waller said.

"But our testing program depends on the right weather conditions, which we have no control over, so we'll continue to take every opportunity to do more testing."