Despite last week's last minute back flip of support from Wingecarribee Council, the  State Government's Planning Assessment Commission has given Boral approval to double production at the Medway Coal mine.

The approval means Boral will be able to lift production from the pit, which dates back to the 1800's, to around 460,000 tonnes a year.

The coal will be trucked to Berrima, where some will be used in the Boral Cement Works, while the remainder will road hauled to Port Kembla,  from where it will be exported overseas.

Council last week overturned its initial support for the expansion, after being told of allegations Boral's discharges into local waterways contained heavy metals.

The company says the claims are un-true, and all discharges are monitored, and have been found to be within regulatory limits.

Boral employee and Wingecarribee Councillor Graham Mc Laughlin had earlier expression concerns that if the mine expansion was rejected, it could lead to the closure of the cement works, and the loss of hundreds of jobs.

Cr Mc Laughlin says the approval is great news for Boral and the economy of the southern highlands.