Groundwater contamination by nitrates and chlorides washed out from phosphorite ores in the Negev Desert, Israel

A sharp rise in the nitrate-content (up to 7200 mg L^-1) and in the chlorinity (up to 92000 mg L^-1) was observed during the 1980's in the water of the Aqrabim spring outflowing in the Negev desert, Israel. The source of pollutants was traced to a resevoir of wastewater derived from the dressing of phosphorite ores mined in the area. These ores and the overlying gravels are characterized by high concentrations of soluble nitrates, chlorides and sulphates. Groundwater flow-paths were delineated by using chemical changes observed in the wastewater reservoir. During the last 6 years, the continuous percolation of wastewater enhanced the flushing of chalk and clay particles from the fractured chert aquifer causing a sharp increase in groundwater flow-rates from the reservoir to the springs from 7.5 m day^-1 (in 1980) to 53 m day^-1 (in 1986). This change suggests the development of new flow paths. The resulting rapid propagation of the contamination plume may have disastrous consequences on the limited water resources in the northern Arava-Dead Sea area.