The “El Descargador” area is located in the Sierra Minera, southeastern Spain, in the former mining district of Cartagena-La Union. More than 2500 years of mining has occurred in this area, generating large quantities of ore processing waste with high concentrations of heavy metals. The dispersal of heavy metal pollutants originated from the affected area, through the "rambla" (ephemeral river) to Mar Menor, was investigated. The total study area is roughly 0.32 km2, with five silt ponds of various size and depth. Soils from the total affected area, silt ponds, and the rambla were studied to indicate the pathways of hydric transport and the spatial distribution of heavy metals, including Cd, Cu, Pb, Zn, and Fe.
Soil samples were collected according to a regular sampling grid, created using Geographic Information Systems (GIS), of 100 m2 in the entire affected area, and a 50 m2 grid in the silt ponds. Samples were also taken every 300 m from the confluence of the rambla with Mar Menor, upstream to the affected area. Samples were collected at two sampling depth levels, 0-0.10 m for surface soils and below 0.30 m for sub-surface soils. pH, electrical conductivity, Redox potential, total and soluble heavy metals, and soluble salts were analyzed in each sample.
Results indicate that pH in surface soils ranges from 1.99 to 7.56, while sub-surface pH ranged from 2.15 to 7.35. Concentrations of metals decreased in sub-surface soils of the total affected area. Following completion of analysis, GIS maps were created representing the spatial distribution of the heavy metals and the environmental impact. A risk assessment will be developed for reclamation recommendations. These results will also be used to select representative sampling points for leaching tests in undisturbed soil columns.
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