Will flooding or erosion of historic landfills result in a significant release of soluble contaminants to the coastal zone?

Abstract

Historically, solid wastes were commonly landfilled in the coastal zone in sites with limited engineering to isolate waste from adjacent coastal environments. Climate change is increasing the likelihood that these historic coastal landfills will be inundated or eroded resulting in the release of soluble contaminants to the coastal zone. Previously research has focussed on the environmental impacts of leaching from landfills in freshwater environments with little or no consideration being given to saline environments. This research investigated the magnitude, variability and potential environmental consequences of soluble metal release from solid wastes when historic coastal landfills are inundated, or wastes are eroded and released into fresh or saline waters. The proportions of the sites' total metal contents released to solution varied by up to an order of magnitude between different landfills due to the different physical and chemical characteristics of the solid wastes, but the proportions released were typically ≪1% in freshwater. Inundation by saline water significantly increases the proportions of the total metal contents released to solution, e.g. 5450% more Pb in one study site (median value), but again the proportions were typically ≪1%. The exception was Cd, where up to 9% of the total Cd load of one site was released in saline water. This puts into question the suitability of current landfill regulatory tests, e.g. the EU Waste Acceptance Criteria, and many risk assessment methods, which only consider freshwater inundation and leaching. However, the very low proportions of metals mobilised from the solid waste and the high dilution ratios in coastal waters, mean EQSs for the Protection of Surface Water are unlikely to be exceeded, and the release of solid wastes through coastal erosion poses a greater threat to coastal ecological health than leaching of soluble metals from contained solid wastes.