Impact of sand mining upon the Groundwater Chemistry, Piranema Sand Mining District, Itaguaí and Seropédica region, Rio de Janeiro

Abstract:

The Seropédica-Itaguaí Sand Mining district supplies about 70% of sand for civil construction of Rio de Janeiro Metropolitan Region. The sand extraction process is fact by the remove of the surface sedimentary layers; make water table fills the produced hole. The sand extraction activities cause the oxidation of reduced sediments (ancient coast lines lithologies - mangrove environment), providing low pH values (reaching values < 4) and high SO₄ contents (reaching more than 90 mg L^-1). The relatively high acidity of these waters, similar to ore pit lakes environment and associated acid mine drainage, contributes to accelerated weathering rate, especially the silicates minerals, which produces high concentrations of Al (> 10 mg.L^-1).

Keywords:
hydrogeochemistry; acidification; sand pit lakes; groundwater