Questions pertaining to isotopic and hydrochemical evidence of fracture-controlled water flow and solute transport in a chalk aquitard

This study focused on water flow and solute transport processes through vadose and saturated Eocene chalk in the northern and central Negev desert, Israel. The chalk underlies a major industrial complex in the northern Negev, where groundwater contamination has been observed. Groundwater samples were collected from 23 boreholes, which were also monitored throughout one year for water levels, pH and electrical conductance. In addition, four dry-drilled holes were bored through the vadose zone. Core and auger samples, collected at 30 to 50 cm intervals, were used for chemical and isotopic analyses. On the basis of observed tritium and contamination in the deep groundwater, the similarity of stable isotopic composition between the groundwater and precipitation, and the heterogeneity of the groundwater isotopic and chemical composition, fractured controlled flow and transport in the saturated chalk aquitard was inferred. In the vadose zone, fractured controlled percolation and transport was suggested on the basis of the presence of tritium spikes below the tritium front, and the vertical gradual depletion and dilution of pore water stable isotopic composition and ion concentrations, respectively. However, many of the above observations could be viewed as indications for stagnant groundwater receiving no regional advective flow and transport via the vadose zone, except for focused recharge from the ephemeral streams intersecting the chalk. The competing interpretations were weighed and assessed. We concluded that the fractures do play a major role in water flow and solute transport in both the vadose and saturated zones of the chalk aquitard.