The Influence of underground coal mining on Ground water (1984)

Morton K L, Connelly R J, Carr, P A

Abstract
Due to a combination of geologic and economic factors, bord and pillar mining was, until comparatively recently, employed almost exclusively in South African coalfields. Even today, at shallow depths and moderate seam thickness, it is difficult to improve on for productivity, cost effectiveness and percentage extraction. An advantage of this method, in which coal pillars are left unmined to support the overlying strata, is that the ground surface and sub-surface strata, and hence the ground water regime, remain largely undisturbed.
However, in 1964 the scarcity of coking coal and the rapid decrease in percentage extraction with increasing depth and seam thickness using bord and pillar mining methods prompted trials with caving or total extraction mining methods. Application of these methods gained additional impetus following publication of the Petrick Commission Report in 1975 which recommended a substantial increase in the controlled price of coal and which consequently resulted in an improvement in the economic viability of total extraction mining methods. ‘These methods, notably longwall, pillar extraction and rib pillar extraction, allow the overlying strata to collapse into the excavation formed by the removal of the coal and thus result in considerable disturbance of the overlying strata. This has a disruptive effect on the surface run off and the sub-surface ground water regime.
The object of this paper therefore is to examine the mechanism and consequences of disturbance of the ground water regime by total extraction mining methods.

Morton, K.L., Connelly, R.J. & Carr, P.A., 1984. The influence of underground coal mining on groundwater. International Symposium on Groundwater, Johannesburg: NWWA of USA.