Three sites in Craigieburn and one in Campbellfield were uncovered on March 8 and 15, after information was received by WorkSafe and the Environment Protection Authority (EPA).
They contain large quantities of waste chemicals being stored in a similar way to those at eight sites discovered in Epping and Campbellfield in late December.
Under Victoria's Dangerous Goods Act, duty holders who breach regulations in relation to the storage and handling of dangerous goods are required to take action to ensure their sites comply with the law.
WorkSafe can step in to directly ensure sites are made safe if it believes this is necessary. It can also recover costs from the duty holder.
The occupier of these four sites was issued with directions to make them safe when they were uncovered.
WorkSafe has now exercised its powers under the Dangerous Goods Act to take action to safely remove the dangerous goods from the sites.
While the exact quantity of waste being stored is not known, the maximum capacity of the four sites, based on calculations of airspace, is 11 million litres.
The removal operation is expected to take a number of months.
Safety will remain the taskforce's first priority and the sites have 24-hour security, atmospheric monitoring and spill containment measures in place.
The taskforce, which includes EPA, fire services, Victoria Police and local councils, has also been liaising with government agencies to ensure nearby facilities have contingency plans in place for emergencies.
The taskforce first stepped in to directly control the clean-up of the eight sites discovered in Epping and Campbellfield in early January.
So far more than 1.7 million litres of waste chemicals have been removed from these sites, including flammable liquids such as paints, solvents and inks.
Of the eight sites, one in Epping has been completely cleared. Removal works are underway at two further sites, and preparation works are underway at others.