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Environmental Contamination Through Residual Trace Metal Dispersal from a Derelict Lead-Zinc Mine¹

ABSTRACT

Studies of historical and current environmental problems in the vicinity of a derelict Pb-Zn mine at Parc, near Llanwrst in North Wales, have shown that heavy metal dispersal occurs through contaminated mine drainage waters and episodal erosion of an unstable tailings dam.

Since the discontinuation of mining operations an estimated 13,000 metric tons of metalliferous spoil, equivalent to 43 metric tons Pb, 104 metric tons Zn, and 1 metric ton Cd, have been eroded from the main tailings dam. Dispersal by a tributary of the River Conwy and redeposition during flooding events has caused extensive contamination of lowland agricultural pastures. Streamwater pollution by tailings and dissolved metal salts in mine effluent continues to have a pronounced adverse effect on the flora and fauna of the tributary.

Under normal discharge conditions mean net transfer of metals into the main Conwy River approximates to 0.27 kg Pb, 15 kg Zn, and 0.1 kg Cd over 24 hours. However, because of the increased particulate load during surface drainage and flooding episodes, net dispersal increases unequally for the different metals, to a rate above that anticipated from discharge-concentration relationships.

With a remaining deposit of 250,000 metric tons of mine tailings, tip stabilization measures have been initiated as a safeguard against further degradation of natural resources in the locality.

Key Words: sheet and gulley erosion • pyrite oxidation • dissolved metals • suspended solids • mine drainage

¹ Contribution from the Botany Dep., Univ. of Liverpool, P.O. Box 147, Liverpool, United Kingdom.

² Lecturers in Botany, Univ. of Liverpool.

Received for publication March 12, 1979.