Beginning October 15, the project will double the 3400 cubic metre facility that has been operating since the 1930s.

Much of its mechanisms were intended to have a 30-year maximum life, but the plant has functioned for nearly 60 years beyond that.

It is expected the entire overhaul will cost $9 million, with council to provide the funding shortfall.

Before the present, the last upgrade was completed in 1992, still a year before the jail was opened.

“The original structure needs to be demolished and rebuilt. When it is, it will include the latest modern technology too,” said the treatment facility’s project leader Nadeeka Mannage.

In the 26 years that have followed the last upgrade, the town itself has also grown from fewer than 5000 to 6555, not including the jail population.

“The existing capacity is not enough to treat all of Junee anymore, it hasn’t been for a while,” said Ms Mannage.

With another 480 inmates expected to arrive at the jail, it has become a primary focus to increase the town's sewerage capabilities.

The push to upgrade the facility began when the jail construction was announced last year.

Since the prison expansion is on track for completion by the end of next year, a greater necessity has been placed on the sewerage plantation.

“We’re at the initial stages, a contractor  has begun the work. We have to have it finished by August 2019,” said Ms Mannage.

If the jail is completed before the treatment centre, Ms Mannage is confident there will still be some flexibility.

“Even if [the jail] is completed and commissioned before the sewerage plant, they will not be utilising the full capacity straight away,” Ms Mannage said.

“There will be room for 500 residents, but they will not shift 500 in all at the same time. It will be done in stages,.”