THE IMPACT OF SURFACE DRAINAGE ALTERATION ON SEDIMENT DISPERSAL AND CONTAMINANT RELEASE AT A DISUSED COPPER - ARSENIC MINE IN THE TAMAR VALLEY, DEVON

Development of Devon Great Consols former Cu/As mine for tourism has resulted in a number of alterations to surface drainage patterns. Since earlier research published in 2008 and 2011 a slope, previously described as ‘stable’ has failed leading to quantities of highly contaminated mine spoil dispersing through heathland and woodland towards the Tamar River. The current study investigates the impact of this development in terms of sediment transport and dissolved metal (Al, Cd, Cu, Ni, Pb and Zn) and metalloid (As) concentrations in stream and river waters. Stream and river water samples (ten sites and two sites respectively) were collected on six occasions during the period March – July (including the wettest June in over one hundred years). Concentrations of dissolved contaminants were determined following ICP-OES and ICP-MS analysis. Total suspended and dissolved solid concentrations were determined through mass balance following filtration. A number of surface drainage alterations are shown to be failing in containing spoil/ sediments and the impact upon the failed bund has led to substantial sediment dispersal and vegetation death. Comparisons with previous research showed a decrease in concentration of the metals Ni, Pb and Zn at various locations with no statistical difference evident in other contaminants although this may be due to dilution effects. All contaminants breached environmental quality standards in surface drains with Cu and Al also causing a failure in the Tamar on a number of occasions. Concentrations of dissolved copper were shown to have increased downstream of the bund failure (P = 0.000, = 9961 μg l-1) although the effects of this have yet to influence the final discharge to the Tamar