Warkworth Mining Limited (WML) proposed to extend its Warkworth Mine, near Singleton in the Hunter Valley. Warkworth Mine was an existing open cut coal mine with an approved production rate of 18 million tonnes per annum of Run of Mine coal. An Environmental Assessment (EA) was prepared to accompany a Project Application for the proposal under New South Wales Planning Legislation. The proposal was to extend the approved mining area and continue mining operations for 21 years.

As part of the EA, a review of the water impacts was prepared by JP Environmental to identify and mitigate water impacts that may have arisen from the proposed development.

Catchment losses, impacts on local and regional watersheds and the performance of the clean and dirty water systems were assessed looking out 21 years. The adequacy of existing and proposed monitoring regimes for operational and compliance management were examined.

A computer based simulation model was used to assess the dynamics of the system under conditions of varying rainfall and groundwater seepage rather than a simple wet and dry year water balance. The adopted approach provided a probabilistic outcome addressing varying catchment areas, groundwater seepage or rainfall runoff accumulations attributed to increasing soil moisture. System modelling indicated that the site would experience both water shortfalls and surpluses. Testing of the mine water system against 115 years of daily rainfall records indicated surpluses could be easily managed by utilising HRSTS high and flood flow discharge opportunities, and that the supplementary water sources were adequate to meet any shortfalls.

The project received development approval in 2012.