THE CONTAINMENT OF TOXIC WASTES .2. METAL MOVEMENT IN LEACHATE AND DRAINAGE AT PARC LEAD-ZINC MINE, NORTH WALES

Nant Gwydyr, a tributary of the River Conwy in North Wales, has been a ffected by metal wastes, from a lead and zinc mine, Pare Mine, through contaminated mine drainage waters and episodal erosion of an unstable tailings heap. From 1954 when the mining operation was discontinued t o 1978 when a reclamation programme aimed to stabilise the tailings wa s accomplished, 13 000 tonnes of metalliferous spoil, containing 43 to nne Pb, 104 tonne Zn, and I tonne Cd was eroded from the main tailings dam. Dispersal and redeposition during flood events caused extensive pollution of the agricultural land of the flood plain. Analysis of the present wafer quality of the Nant Gwydyr, 14 years after the stabilis ation work, shows that although there has been a marked improvement an d no particulate matter is released, the Nant Gwydyr is still a pollut ed stream. Under normal discharge conditions, it contributes approxima tely I tonne of Zn, 0.2 tonne of Pb and 0.05 tonne of Cd per year to t he River Conwy. Most of this originates from water issuing from the mi ne adit which has been impossible to control. There is still, however, a major contribution by the leachate from the tailings heap, because the stabilisation method used does not prevent this. The control of po llution in mine drainage is discussed.