Contributions on the Presence of Arsenic IN Fissured Aquifers IN the Buntsandstein (LOWER TRIASSIC) of the Iberian Chain (AUTONOMOUS REGION OF VALENCIA, SPAIN)

A study of hydrogeological data from water samples taken from boreholes in the fissured aquifer of the Buntsandstein facies is presented. This sequence is characterized by river deposits and corresponds to the Lower Triassic of the Iberian Chain (sublithoarenites to quartzarenites and even subarkoses). The sampling points are situated in the Autonomous Region of Valencia (Spain).

The hydrochemical facies of the samples analyzed were calcium-magnesium bicarbonate sulfate or sulfate-bicarbonate, with significant concentrations of certain minor elements such as Li, Sr, Mn, Fe, Ba and As.

The hydrochemistry of this aquifer is determined largely by its lithology and mineralogy. Chlorite stands out as the main source of magnesium, and of certain mineralizations such as the hydrothermal veins of barite that date from the Alpine Phase, while As, Co, Cu, Pb and Zn are present as trace elements. All these features point to mineralization in the Paleozoic basement rocks and of lixiviation in hot solution over sediments rich in heavy metals. The presence of neoform pyrite is also recognized, in the anoxic levels, as well as quartz, siderite, calcite, dolomite and iron oxides (goethite, hematite and limonite).

Liberation of arsenic into the groundwater is related to the regime of borehole abstraction. Arsenic concentration increases with pumping time and also seems to be determined in part by whether the pumping is constant or intermittent.

The sulfate character of many of these waters indicates the influence of flushing of the evaporite layers (Mid to Upper Triassic), or the presence of ancient, sulfate-enriched seawater. In turn, these sulphated waters exercise a large influence on salinization of coastal detritic aquifers that lie adjacent, and which also suffer salinization linked to seawater intrusion.