Harnessing modelling of heat transport to delineate brine leakage through a karst system: The Dead Sea Works' evaporation ponds case study

The industrial evaporation ponds of the Dead Sea Works are located in the Dead Sea rift valley, Israel. To prevent brine leakage, the ponds were sealed by 40-m deep impermeable dikes, except in the Ye'elim alluvial fan, at the northwest corner, where the leakage continues. The average leakage at present is approximately 100 million cubic meters per year, a significant portion of which discharges via a spring located approximately 0.5 km north of the ponds' embankment; the rest flows into the Dead Sea underground. We hypothesized two main reasons for the increase in leakage over time: the dropping level of the Dead Sea, which increases the hydraulic gradient, and the diameter expansion of the subsurface karst network of fast-flowing conduits. The brine in the evaporation ponds is warmer than the ground in the summer, colder in the winter. Therefore, the brine leaking within the karst conduits warms and cools, respectively, the surrounding porous medium, as detected by field monitoring. One of the conduits was also detected through a geoelectrical survey. In addition, we identified an increased brine-leakage rate in the winter. We propose that this results from temporal changes in the diameter of the conduits due to the infiltration of low-salinity water entering the network. The diluted water dissolves the salt and causes the conduits to expand. Using a numerical model that solves the coupled groundwater flow and heat transport equations, we were able to reproduce all of these field observations and validate the suggested explanations.