Assessment of groundwater quality in the Western aquifers of Mauritius using isotope techniques

This contribution reports the results obtained in the IAEA TC project MAR/8/007, initiated in 2007. Fourteen boreholes were sampled during three sampling campaigns (rainy season, winter and summer): analyses include major ions, trace elements, stable isotopes (δ2H, δ18O and δ13C) and a microbiological assessment (TC and E. coli). Results indicate that groundwater quality is generally good. Recharge mostly occurs in the central plateau area, but the increase in nitrates along the groundwater flow and the common presence of E. coli indicate that a minor recharge occurs all over the aquifer’s extension. Infiltration is rapid and favoured by the presence of vertical fractures in the basalts. Discharge occurs at a lower altitude and is marked by a different stable isotope content and lower nitrates. In addition to validating the general groundwater circulation model, these results show that aquifers are not adequately protected against a possible input of pollutants from the surface.