Joint inversion of marine LOTEM and DED data from the Bat Yam coastal aquifer, offshore Israel

Groundwater aquifers are important for the freshwater supply all over the world, especially in dry regions. It occurs that the water bearing rock matrix extends offshore below the sea floor, and as a consequence fresh water is embedded within good conducting seawater-saturated sediments. Whether an aquifer is open to seawater intrusion or closed, depends on the local hydrogeological setting. Prior studies showed that for high demand on fresh water and high exploitation rates, it is necessary to understand the interaction between sea and fresh water to prevent deterioration of the aquifer. Several geophysical surveys have been carried out in the past to investigate a coastal aquifer in the Palmahim region of Israel, which serves as one of the main reservoirs of the national water supply system. Time domain marine LOTEM and DED data have thereby been recorded on similarprofiles. Both results show a resistor at an assumed aquifer depth of roughly 100 m with a comparable offshore extension of 3.5 km from the coastline. However, until now the LOTEM and DED data have only been interpreted separately using 1D inversion and extensive 2D forward modeling. This study presents the first joint 1D and 2D inverse modeling studies of marine LOTEM and DED techniques using synthetic and field data. The synthetic results indicate large benefits of using a joint inversion of both appliedsurvey techniques. However, a joint inversion of the field data is still in progress. Yet, a 2D inversion of the DED data is promising and indicates a brackish transition zone at the expected lateral aquifer boundary. This finding seems consistent with prior studies and suggests an open aquifer scenario with seawater intrusion. This outcome is essential for the groundwater management and supply in Israel.