Roman mining landscapes in the Murcia Region, SE Spain: Risk assessment of mine ponds

The Mining District of Cartagena-La Unión (SE Spain), mined since the Roman period, exhibits high levels of metal contamination and this poses a great risk to the surrounding environment. This chapter presents the results of the application of geophysical, geochemical and hydrological techniques in two mine ponds located in this area. Its aim is to determine their degree of contamination by heavy metal, to evaluate risks of mobility and dispersion of heavy metals, to study the erosive capacity of the runoff, and to discuss geotechnical stability of the ponds. Metal contents found in the ponds show that although the Descargador pond is more vulnerable to oxidation and leaching processes than Encontrada, they both could be considered polluted due to their high metal concentrations. When materials from the Descargador pond are exposed to adverse weather conditions they can be eroded, while in the Encontrada pond most of the surface is covered by a natural soil layer and vegetation which protects it against erosion. In the former, it is recommended to apply some conservation measures, including the addition of alkaline materials, natural soil and organic matter. In the latter, it is recommended to improve the present conditions in order to control acidification and to minimize risks of landslides and transport of highly contaminated materials.