Abstract

Parc mine in north Wales was abandoned after closure in 1963 and spoil heaps were left to erode into the Nant Gwydyr and Conwy River. A storm event in 1964 caused the west slope of the tailings dam to collapse into the river, polluting 11 ha of farmland with lead and zinc. Reclamation work commenced in 1978 and involved reshaping the tailings pile and capping the north and central sections of the site with limestone quarry waste. The north section was also sown with metal-tolerant vegetation (Festuca rubra, Argostis tenuis and Trifolium repens). The aim of the study was to understand how different reclamation surfaces affected soil chemistry using GIS.

The uncapped south section, whilst having the most heavily polluted soil (74 mg/kg As, 24,000 mg/kg Pb, and 19,000 mg/kg Zn), supported the establishment of patchy but diverse metal-tolerant vegetation (Alnus incana, Fagus sylvatica, Ulex, Sorbus aucuparia). The capped north section had the least polluted soil (19 mg/kg As, 478 mg/kg Pb, and 1400 mg/kg Zn), densely vegetated with a nitrogen-fixing legume (Trifolium repens), and was able to support grazing animals, but remained visually incongruous and failed to support the re-establishment of native vegetation. The central section, which combined capping with native vegetation (Betula pubescens and Quercus petraea), was considered moderately polluted (26 mg/kg As, 3908 mg/kg Pb, and 9000 mg/kg Zn). Zinc was found to be the limiting contaminant for vegetation growth with soil concentrations exceeding 12 000 mg/kg corresponding to areas of bare ground in the south and central sections. Barium was the only element to increase in the capped sections, indicating the limestone quarry waste used to cap the tailings was most likely barium-rich.

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