Présentations Colloques

Oral Presentation
8.04
Session 8.04: Isotopic and residence time tracers
Yechieli Yoseph
Dating of saline groundwater from several Israeli aquifers, indication for paleo seawater intrusion
This study deals with dating of saline groundwater, with salinity closed to that of seawater (mostly >75% seawater), in order to estimate the timing of past events of seawater intrusion. Such dating was seldom conducted before since, in most cases, even the most saline water samples have a significant component of fresh water. **Dating of saline groundwater was conducted in two of the main aquifers in Israel (the Coastal Aquifer and the Mountain Aquifer). In the Coastal Aquifer, most of the saline water was found to be young (>50 years, tritium containing, ~60 PMC) indicating recent seawater intrusion. However, in some of the deeper sub-aquifers, older saline water was found (5-10 PMC, i.e. older than ~10,000 years), implying penetration of seawater at older time. Complementary age determinations were conducted on the fresh groundwater, some of which were found to be very old. **In the Mountain Aquifer, old saline water bodies were found in several locations. Estimation of the age of the different end members (fresh and saline) showed that the seawater component is older than 30,000 year, probably beyond radiocarbon dating. The isotopic values of this old seawater component is similar to that of the present seawater (e.g. δ+18O of ~1.5%0 and 1.8%0 in old and recent seawater) which implies that the intrusion took place in similar sea conditions to that of the present ones. An attempt to determine the age of this old seawater will be done with noble gases. **Numerical simulations were conducted with FEFLOW in order to examine the flow regime in the different parts of the coastal aquifer. **Due to the limitation of the radiocarbon methods, samples were taken for analysis of 81Kr and 39Ar in November 2005 and some results are planned to be given in this presentation.**
Israel