The limestone aquifers of Malta: their recharge conditions from isotope and chemical surveys

Abstract

The potable water supply in Malta is heavily dependent on groundwater. The two main aquifers, the Perched Aquifer and the Mean Sea Level Aquifer (MSLA), are vertically stacked and separated by impermeable formations. Groundwater is now being threatened by over-pumping and pollution. An isotope and chemical survey was undertaken on rain and groundwater to identify the recharge conditions and set new strategies for exploiting and protecting groundwater. The main results show that: (a) an elevation effect does not appear in rainwater 8, sO, so that groundwater cannot be distinguished in either of the aquifers by means of stable isotopes, and (b) groundwater tritium content shows an old recharge of MSLA and a very long residence time. Tritium results look inconsistent with other data, suggesting a present day recharge split into two components: a rapid portion through fractures, and a slow portion through rock porosity which is dominant.