Contamination of a Chalk aquifer by mine drainage at Tilmanstone, East Kent, U.K.

Abstract

Summary Arising from the discharge at the surface of minewater drainage pumped from a mine in the Kent Coalfield, which underlies the Chalk of East Kent, U.K., an area of some 27 km 2 of the Chalk aquifer has become contaminated with saline water having concentrations of chloride between 200 and 5000 mg/l. Between 1907, when the first shaft was sunk, until 1974, when the discharge onto the Chalk ceased, it is estimated that 318 000 tonnes of chloride were discharged, and only about 15% has so far been dissipated by stream flows. An investigation has been carried out to determine the size and shape of the plume of contamination, and to examine possibilities for rehabilitation of the aquifer. The work has shown that the top 40-50 m of Chalk has become saturated with highly saline water, but at greater depths the contaminant is localized around well-developed fissures. The results of fifteen months pumping of a production borehole located near the centre of the pollution plume suggests that a long period would be required for the contamination to be cleared, and this has been supported by the results of a mathematical model.