Underground » Environment - Subsidence and Mine Water
Seepage of water from aquifers into the workings of coal mines often requires large amounts of water to be pumped to the surface. This water if often used for coal washing with or without augmentation from stormwater. The mixture contains elevated concentrations of dissolved salts and metals and can pose environmental risks to aquatic biota. While much is recycled, excess water may still be released into the environment. In times of low rainfall, such releases may be the only source of water for creeks, although at other times, the water is diluted by other sources of runoff to create a gradient of salinity in which the potential effects of the discharge decrease with increasing distance from the source.
Regulations aimed at reducing environmental effects currently stipulate the quality of water that can be released from mines. These are predominantly based on national generic guidelines derived from ecotoxicological studies (ANZECC 2000). These guidelines are conservative and were intended to be supplemented over time by site-specific guidelines tailored to local geological, hydrological and ecological conditions. Deriving site-specific water quality guidelines for the mining industry requires knowledge of the effects of specific mine discharges on local stream biota. However, the available information deals mainly with dry land salinity and much less is known about the effects of mine water on stream biota. With standardisation of methods, research on site-specific effects of mine water could contribute to a database of field and ecotoxicological information that would be valuable not only in setting meaningful targets, but also in predicting the potential effects of mine discharges in unique situations.
This project was funded by the Australian Coal Association Research Program, with significant in kind contributions from several coal mining companies, including BHP Billiton, Tahmoor Colliery and Ravensworth Colliery, and The Ecology Lab, The University of Technology, Sydney and Macquarie University, Sydney.
The study was undertaken in the Southern and Hunter coalfields of New South Wales. The former encompasses the Georges River and Hawkesbury-Nepean catchments, where the focus was on Brennans Creek and downstream of the confluence of the creek with the Georges River, hereafter referred to as Brennans Ck/GR, (West Cliff Colliery), Allens Creek on the Nepean River (West Pit Top Appin Colliery) and Tea Tree Hollow on the Bargo River (Tahmoor Colliery). Bowmans Creek (Ravensworth Colliery), in the Hunter catchment, was the study area for the Hunter Coalfield. The project, which is supported by literature reviews of the effects of elevated salinity on aquatic biota and of water quality management in mining areas in Australia, aimed to obtain information on, and develop an understanding of the effects of saline mine water discharge on aquatic biota and contribute to the development of site-specific water quality guidelines for the coal mining industry in New South Wales.