Both mining the Lithgow seam, Springvale and Angus Place lie adjacent to one another, approximately 15 kilometres north west of Lithgow in New South Wales. Together the mines supply five million tonnes of thermal coal to the local power stations.

Angus Place currently mines a block 250m wide, 3300m long and a working thickness of 3.2m. Springvale has similar conditions with blocks 255m wide, 1900m long and a working thickness of 3.25m.

Two confined aquifers lay in the mine overburden. There is no hydraulic connection between the two aquifers, the dominating aquifer being immediately above the Lithgow-Lidsdale seam.

Flow rate measurements conducted in the workings show an increasing trend as headings approach within 200 metres of the flooded workings of the abandoned Lithgow State Mine, which is believed to be recharging the lower of the dominant aquifer mainly through porous rock.

Water inflow and a model to predict water flow on mine workings has been developed through the use of piezometric monitoring, underground inflow measurements from both development roadway and formed goafs and surface drill hole permeability/conductivity tests.

“It has been essential to gain an understanding of the interaction between strata permeability mining induced stress, fractures and pore pressure so that the effect of mining on groundwater flow around roadways and longwall can be assessed and options as to controlling water can be evaluated,” mine general manager Bob Miller said.

This has been achieved to some degree where accurate predictions of groundwater flows from various areas of the mine can be made.

Strata water drainage and mine dewatering systems are now being designed and installed to manage future water make at Springvale. This model will also be applied at Angus Place where rate of inflow is expected to be less than Springvale.

Springvale currently discharges 15 megalitres per day and Angus Place five megalitres per day under EPA licence conditions. The mines discharge to tributaries of the Wolgan and Cox’s Rivers, with no impact or downstream water quality.

Groundwater is captured by inseam pumps and pipelines and submersible borehole pumps connected to boreholes delivering direct to the mine surface. Nuisance water from development faces and outbye areas is contained in the inpit system and discharged via drift entries to the surface for treatment.

Angus Place enjoys the benefit of an extensive underground water storage facility in the abandoned workings north of the operation.

Both mines’ longwall retreat is generally up dip and extensive floor heave experienced in roadways adjacent to the goaf renders it difficult to capture water generated from the roof and floor in the area. Consequently water gravitates to the lowest point of the mine.

To combat this Springvale has employed a series of submersible borehole pumps in the dip workings of the mine. Petroleum industry technology was used for the multi-stage turbine pumps which deliver water at 70l/sec from a depth of 430m through a steel cased borehole 450mm diameter. Each pump is powered by two 225Kw electric motors operating at 3.3KV at 50Hz.

“The pumps have proven completely reliable and similar units will be employed to handle the projected increase in discharge volumes in the future,” Miller said.

A study has just been completed into the feasibility of supplying water to the Delta Electricity Power Stations.

Recently a memorandum of understanding was signed between Springvale and Delta Electricity covering the treatment and transfer of Springvale’s discharge water to Wallerawang Power Station. Efficient reuse of the discharge water of Wallerawang Power Station will reduce the amount of water drawn from the Cox’s River catchment.

The transfer scheme is designed to deliver up to 30 megalitres of water per day and is scheduled for completion in the second quarter of 2005.