Abstract Hydrogeological information is crucial to the development of a sound environmental impact assessment (EIA) for a proposed mine, as well as the management of potential environmental impacts during and after exploitation. However, the determination of hydrogeological parameters is not customarily included in mineral exploration surveys, with the result that many EIAs end up being rather light in hydrogeological content. Examples from the Tarkwa gold mining district of Ghana illustrate this point. Consequences of such an inadequate hydrogeological understanding are potentially serious, ranging from an inability to predict future problems in water quality after the cessation of mining, to a lack of understanding of hydrogeological controls on slope stability, which is arguably manifest in the catastrophic spill of cyanide-rich processing effluents from a breached tailings dam at Wassa West, near Tarkwa, on 16 October 2001. To redress this deficiency, we propose that a hydrogeological database be assembled during the mineral exploration phase, according to a specified protocol (‘check-list’). Using these data, a rational conceptual hydrogeological model for the mine site and its surrounding area can be developed, providing the basis for a thorough consideration of groundwater aspects within the statutory Environmental Impact Assessment, which is (as in most other countries) required by Ghanaian government statute before a mining lease is approved. The resources required to set-up such a database are small compared to the benefits.

Abstract On cessation of mining open pits or opencast workings that extend below the water table are likely to fill with water and thus develop a mine pit lake (MPL). This body of water remains as a permanent feature on the mine site and as such becomes a closure issue with respect to water quality and potential to degrade groundwater. Further, it may present a risk to the environment through the development of poor quality water with elevated concentrations of metals, metalloids, sulphate and depressed pH. The prediction of future pit lake water quality within a MPL is, therefore, essential in considering environmental impact on a closed or abandoned mine facility. The controls on a MPL will vary over time, and will involve chemical, biological and physical processes. Localized and regional-scale processes affect these in turn. Consequently, in order to predict pit lake water quality it is essential to understand the hydrogeological, geochemical and limnological processes that influence water quality.

Abstract Using data for 81 coal mine discharges in the UK, the influence of discharge hydrogeology on discharge chemistry is assessed and typical chemical parameters derived for five discharge types. A combination of modified and new classification schemes is used to differentiate between the various discharge sources. Drainage from spoil tips generally has a pH below 5 and net-alkalinity values as low as — 2500 mg l −1 CaCO 3 . Drainage from flooded workings and pumped discharges are net-alkaline, while drainage from flooded and free draining workings are either moderately net-alkaline or net-acidic. Iron is the major contaminant of concern, although many mine waters contain less than 30 mg l −1 and Fe/SO 4 ratios are less than unity. The classification schemes developed can be used to assess mine water treatment requirements and processes operating in passive treatment systems.